- Email: [email protected]
Free-standing polymer electrolyte for all-solid-state lithium batteries operated at room temperature
Journal of Power Sources xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour
Free-standing polymer electrolyte for all-solid-state lithium batteries operated at room temperature Shih-Ting Hsu a, Binh T. Tran a, Ramesh Subramani a, Hanh T.T. Nguyen a, Arunkumar Rajamani a, Ming-Yu Lee a, Sheng-Shu Hou a, b, Yuh-Lang Lee a, b, Hsisheng Teng a, b, c, * a b c
Department of Chemical Engineering, National Cheng Kung University, Tainan, 70101, Taiwan Hierarchical Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung University, Tainan, 70101, Taiwan Center of Applied Nanomedicine, National Cheng Kung University, Tainan, 70101, Taiwan
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� Solid polymer electrolyte with no sol vent, ionic liquid, oligomer, or semisolid additives. � Free-standing feature for roll-to-roll as sembly of lithium ion batteries. � Polymer chains networked by hubs for high segmental mobility. � A high Liþ transference number for minimized polarization and large voltage range.
A R T I C L E I N F O
A B S T R A C T
Keywords: Solid lithium battery Solid polymer electrolyte Free-standing polymer electrolyte Room-temperature solid battery
This study reports a networked solid polymer electrolyte (N-SPE) containing no solvent, ionic liquid, oligomer, or semisolid additives for lithium-ion batteries (LIBs). The N-SPE comprises a lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt as well as a polymer framework constructed using cage-like polyhedral oligomeric silses quioxane (POSS) and serving as hubs to network poly(ethylene oxide-co-polypropylene oxide) (P(EO-co-PO)) chains. The networking prevents polymer chain twisting that hinders ion transport. Raman analysis indicates that the POSS hubs improve the dissociation of LiTFSI and localize TFSI anions. The N-SPE exhibits a low glass transition temperature of 43 � C, a high 25 � C ionic conductivity of 1.1 � 10 4 S cm 1, and a small activation energy of 3.5 kJ mol 1 for ion conduction. The localization of TFSI results in a high lithium transference number of 0.62, which is determined to be beneficial to Liþ transport. By incorporating the N-SPE into the LiFePO4 cathode and using a free-standing N-SPE membrane, this study assembles a Li|N-SPE|LiFePO4 battery, which delivers a high capacity of 160 mAh g 1 at 25 � C and exhibits excellent charge discharge cycling stability. The free-standing feature of the N-SPE makes roll-to-roll assembly of LIBs readily scalable for industrial applications.
* Corresponding author. Department of Chemical Engineering, National Cheng Kung University, Tainan, 70101, Taiwan. E-mail address: [email protected] (H. Teng). https://doi.org/10.1016/j.jpowsour.2019.227518 Received 24 August 2019; Received in revised form 10 November 2019; Accepted 26 November 2019 0378-7753/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Shih-Ting Hsu, Journal of Power Sources, https://doi.org/10.1016/j.jpowsour.2019.227518
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
1. Introduction
Table 1 Polymeric structure and ionic conductivity of SPEs and electrochemical per formance of the resulting Li|SPE|LiFePO4 batteries reported in literature.
Lithium-ion batteries (LIBs), which have high energy density, have become integral to modern life [1]. Most LIBs are assembled using liquid electrolytes, and this raises concerns regarding battery safety and sta bility in extended applications of such batteries [2]. Developing solid-state electrolytes to replace liquid electrolytes is an effective so lution to the aforementioned concerns for LIBs [1,3–5]. When solid-state electrolytes are used, dendrite growth can be reduced, thus preventing battery from short circuit; moreover, the risk of explosion can be elim inated because of the solvent-free feature of such electrolytes. Solid-state electrolytes also exhibit excellent mechanical, thermal, and dimensional stability [6,7]. Among solid-state electrolytes, solid polymer electrolytes (SPEs) exhibit the advantages of high structural flexibility and work ability, which enable roll-to-roll assembly of batteries. However, LIBs that are assembled using SPEs are generally operated at temperatures higher than room temperature (25 � C), and this thus restricts the application of SPE-based LIBs. Room-temperature SPEs containing no solvent, ionic liquid [8], oligomer [9], or semisolid (e.g., succinonitrile) [10] have yet to be extensively explored for use in LIBs. Only a few studies have researched SPEs for LIBs operated at temperatures of 25–30 � C (Table 1) and the capacities of the resulting all-solid-state LIBs were not high [9,11–17]. Poly(ethylene oxide) (PEO) has been widely used as the polymeric matrix of SPEs because of its high dielectric constant, which facilitates salt dissociation [12,14]. The ether oxygen atoms in the PEO backbone coordinate with cations in the amorphous regions of the polymer to promote ion motion. Despite their strength in inducing salt dissociation and cation coordination, PEO-based SPEs has poor ionic conductivity at room temperature because of their strong crystallization tendency and poor mechanical strength [18]. Numerous methods have been developed to suppress the crystalli zation of PEO and improve its mechanical strength. A study reported that the addition of inert fillers effectively reduced the crystalinity of the PEO host and increased the ionic conductivity and mechanical property of the resulting SPEs [19]. However, some fillers aggregated in the composite SPEs, thereby reducing the cycle life of the resulting batteries [19,20]. Moreover, the addition of ionic liquids or oligomers to the PEO host substantially promoted the performance of the resulting batteries at room temperature; nevertheless, these additives would deteriorate the mechanical stability of SPEs at high temperatures and would thus not constitute an ideal component of SPEs [19,21,22]. Other studies have revealed that modifying PEO by using ionic liquid molecules to form single lithium-ion copolymers increased the Liþ transference number of the resulting SPEs; however, this synthesis method is expensive and complex, and it is thus not feasible for practical applications [23,24]. A comprehensive design that involves copolymerizing PEO with polypropylene oxide (PPO), which has a structural feature similar to that of PEO, effectively suppresses the crystallization of PEO with the methyl side chains of PPO and provides a hydrophobic property that is com plementary to hydrophilic PEO [25–28]. Copolymerized PPO improves both the ionic conductivity of PEO and has good affinity with electrodes. Regarding mechanical strength, using inorganic linkers to crosslink PEO chains and forming three-dimensional (3D) frameworks for SPEs constitute an ideal strategy for strengthening SPEs [20,29–32]. The aforementioned structural designs suggest that a 3D P(EO-co-PO) framework is promising for use in room-temperature solid-state LIBs. In this study, we used a linear P(EO-co-PO) with amino ends as the host polymer (Scheme 1a). The presence of PPO typically suppresses the crystallization tendency of PEO and improves the mobility of the poly mer chains [25–27]. Inorganic polyhedral oligomeric silsesquioxane (POSS), which comprises a Si–O framed cage and eight tentacles with epoxy ends (Scheme 1a), was used to interconnect the P(EO-co-PO) polymer chains. Scheme 1b displays a 3D radial network formed through this interconnection. The networked P(EO-co-PO) was incorporated with a lithium bis(trifluoromethanesulfonyl)imide to form a networked
No.
Polymeric structure of SPEs
Conductivity (S cm 1)
1
Cross-linked PEGDAa
8.9 � 10
5
2
Sandwich-like PPCb
2.2 � 10
4
3
PCL -SN with PAN
4.0 � 10
4
4
Organic/inorganic hybrid of PEGMAf MOFg-PEOh composite
1.1 � 10
4
4.3 � 10
5
Cross-linked PEAi and PEdAj blend Si-doped PEGk
1.2 � 10
4
1.2 � 10
4
8
Cellulose-supported PEO and PCAl
1.3 � 10
5
9
Networked P(EO-coPO)m
1.1 � 10
4
5
6 7
c
d
e
Capacity (mA h g 1)
Ref.
115 @ 0.1C (RT) 80 @ 0.2C (RT) 140 @ 0.1C (RT) 116 @ 0.5C (RT) 101 @ 1C (RT) 137 @ 0.5C (25 � C) 140 @ 0.2C (28 � C) 80 @ 1C (28 � C) 110 @ 0.2C (30 � C) 102 @ 0.5C (30 � C) 78 @ 1C (30 � C) 104 @ 0.03C (25 � C) 49 @ 0.1C (25 � C) 160 @ 0.1C (25 � C) 159 @ 0.2C (25 � C) 157 @ 0.3C (25 � C) 153 @ 0.5C (25 � C) 137 @ 1C (25 � C)
[15] [17] [16] [14] [13]
[12] [9]
[11]
This work
RT - Room Temperature. a poly(ethylene glycol) diglycidyl ether. b Poly(propylene carbonate). c Poly(ε-caprolactone). d Succinonitrile. e Poly(acrylonitrile). f Poly(ethylene glycol) methyl ether methacrylate. g Metal-organic framework. h Poly(ethylene oxide). i Polyetheramine. j Polyetherdiamine. k Poly(ethylene glycol). l Poly(cyano acrylate). m Poly(ethylene oxide-co-polypropylene oxide).
SPE (N-SPE). In the N-SPE, the ether groups formed continuous path ways for Liþ transport [20,24,29–31]. Scheme 1b presents that the Liþ ions traveled (through polymeric segmental motions) in the straightened radial polymer chains of the N-SPE [19,28,33]. The POSS hubs were evenly distributed in the N-SPE because of the small POSS size (approximately 1.5 nm). By contrast, a linear SPE (L-SPE, i.e., the as-received P(EO-co-PO) incorporated with LiTFSI without 3D networking (Scheme 1c) comprised intertwined polymer chains that tended to impede the transport of Liþ ions. The all-solid-state N-SPE exhibited high thermal stability and a wide electrochemical window of 5.4 V (vs. Li/Liþ). A battery was assembled using a free-standing N-SPE film, which was inserted between a Li-metal anode and a LiFePO4 cathode; the assembled battery delivered capacity levels of 160 and 137 mAh g 1 at 0.1 and 1 C-rates, respectively, at room temperature and exhibited high charge–discharge cycling stability. This battery was determined to outperform reported SPE LIBs containing no solvent, oligomers, or semisolids (e.g., succinonitrile) [8–10]. The pre sent study provides the foundation for designing all-solid-state 2
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
Scheme 1. (a) Schematic illustration of the chemical configurations of the P(EO-co-PO) polymer chain with amino ends and a POSS cage exhibiting eight tentacles with epoxy ends. (b) Conceptual illustration of Liþ ion transport in N-SPE, in which the P(EO-co-PO) chains are straightened by the POSS hubs. (c) Liþ ion transport in L-SPE that comprises intertwined polymer chains.
PEO-based polymer electrolytes that can be used for high-rate LIBs at room temperature. The free-standing feature of the N-SPE enables the achievement of scalable LIB assembly for industrial application.
which were roll-pressed to improve the contact between materials. The loading of LiFePO4 was ~2 mg cm 2 and the thickness of the electrode material was approximately 60 μm. The Li|N-SPE|LiFePO4 battery was assembled by sandwiching the free-standing N-SPE membrane between the Li-metal foil and LiFePO4 cathode and then sealed in a coin cell. All batteries were stored in an oven at 60 � C for 24 h to enhance the adhesion between the electrodes and electrolyte.
2. Experimental section 2.1. Materials The POSS with an average molecular weight of 1337 g mol 1 (EP0409, Hybrid, USA), P(EO-co-PO) (O,O0 -bis(2-aminopropyl) poly propylene glycol-block-polyethylene glycol-block-polypropylene glycol, with an average molecular weight of 2000 g mol 1, Aldrich, USA), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; Aldrich, USA), polyvinylidene fluoride with an average molecular weight of 534 000 g mol 1 (PVdF; Aldrich, USA), tetrahydrofuran (Aldrich, USA), 1-methyl2-pyrrolidinone (Alfa Aesar, USA), carbon black (Taiwan Maxwave Co., Taiwan), KS4 (Taiwan Maxwave Co., Taiwan) and Lithium iron phos phate (BTR New Energy Material, China) were used.
2.4. Analysis and measurements The surface of the N-SPE was analyzed using scanning electron mi croscopy (SEM; JOEL JSM-6700F, Japan), accompanied by an energy dispersive X-ray spectrometer (Oxford INCA400, Japan) for elemental analysis. Raman spectra of the membranes were recorded using a Bay spec Raman spectrometer (USA) with a laser line of 780 nm and reso lution of 4 cm 1 at room temperature. The Gaussian function was used to deconvolute bands of the Raman spectra into constituent peaks. The melting points (Tm) and glass transition temperature (Tg) of the polymer electrolytes were analyzed by Differential scanning calorimetry (DSC; Shimadzu, DSC-60, Japan) at a heating rate of 10 � C min 1. Thermog ravimetric analysis (TGA; PerkinElmer, TGA-7, USA) of the N-SPE was performed from room temperature to 800 � C at a ramp of 10 � C min 1. The ionic conductivity of the N-SPE was analyzed using AC impedance spectroscopy (Zahner-Elecktrik IM6e, Germany) at various temperatures (25–60 � C). The N-SPE membrane was sandwiched between the two stainless-steel (SS) electrodes for the impedance measurements operated at 5 mV within a frequency range of 0.1 Hz–100 kHz. Linear potential scans on SS|N-SPE|Li at 1 mV s 1 were used to analyze the electro chemical stability of the N-SPE. Galvanostatic charge discharge of the Li|N-SPE|LiFePO4 battery was performed between 2.5 and 4.0 V using a battery test equipment (Acutech System BAT-750, Taiwan). All elec trochemical measurements were operated at 25 � C.
2.2. Preparation of N-SPE We dissolved POSS and P(EO-co-PO) (at a molar ratio of 1:10, an optimized value for fast ion transport) in THF and then thermally treated the solution at 60 � C for 4 h to link the POSS and P(EO-co-PO) chains for forming networked P(EO-co-PO). With this dissolution-and-linking process, POSS can be uniformly distributed in the N-SPE. The LiTFSI salt was added to the solution at a Liþ:EO molar ratio of 1:15 with continuous stirring for 24 h. The resultant solution was spread on a Teflon dish for evacuation at 90 � C for THF removal. A free-standing NSPE of approximately 70 μm thick was obtained after the solvent removal. 2.3. Electrode synthesis and battery assembly
3. Results and discussion
The electrode slurry is prepared using 70 wt% of active material (LiFePO4), 15 wt% of binder (N-SPE and PVdF at 2:1), 15 wt% of con ducting agent (super-P and KS4 at 2:1), and NMP used as solvent. The prepared homogenous slurry was casted on aluminum foil using doctor blade technique and the coated foil was vacuumed at 90 � C for 12 h to remove NMP. The coated foil was then punched into 1.327-cm2 discs,
3.1. Physical and chemical properties of SPE Fig. S1a displays the X-ray diffraction (XRD) patterns of the net worked and as-received P(EO-co-PO) polymer films that served as the polymer hosts of the N-SPE and L-SPE, respectively. Without 3
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
Fig. 1. Photograph of the free-standing N-SPE membrane.
Fig. 3. Raman spectra for TFSI anion vibration in the regime of 725–760 cm 1 for different electrolytes at 25 � C: (a) N-SPE and (b) L-SPE. The inset of panels (a) and (b) depict the configurations of cis- and trans-TFSI anions, respectively.
assembled batteries. Networking through POSS reinforced the me chanical strength of the P(EO-co-PO). Fig. 1 depicts the photograph of the N-SPE membrane, which comprised the networked polymer and LiTFSI. The membrane was determined to be flexible, transparent, and homogeneous and exhibited dimensional stability. The flexible feature of the N-SPE membrane can enable its use in batteries of diverse shapes and configurations. Fig. S1b presents the SEM analysis of the N-SPE membrane. The image reveals the rugged surface of the membrane; the accompanying elemental Si mapping indicates a homogeneous distri bution of POSS in the membrane. Fig. 2a illustrates the DSC profiles of the as-received P(EO-co-PO) polymer, L-SPE, and N-SPE; the DSC process was performed over the temperature range of 100 to 200 � C. The as-received polymer exhibi ted a strong endothermic peak for melting at a temperature (i.e., Tm) of approximately 39 � C, indicating a high crystallization tendency of P(EOco-PO). The Tg occurred at approximately 61 � C, revealing the pres ence of amorphous zones in the as-received P(EO-co-PO). After the asreceived polymer was incorporated with LiTFSI, the resulting L-SPE did not present a Tm in the DSC profile because the lithium salt deteri orated the ordering of the polymer chains. The L-SPE exhibited a Tg of 25 � C, which is similar to the value reported for PEO–LiTFSI solid electrolyte systems [37]. The added lithium salt coordinated with the polymer to retard the motion of the polymer chains, thereby resulting in a high Tg. When networked using the POSS hubs, the N-SPE exhibited a considerably lower Tg of 43 � C than did the L-SPE (Fig. 2a). The network configuration of the N-SPE reduced the attractive interaction between chains, thereby increasing the segmental mobility of the polymer chains and lowering the Tg. Fig. 2b illustrates the TGA profile of the N-SPE. The profile of the LSPE was similar to that of the N-SPE. According to the profile in Fig. 2b, the N-SPE exhibited an abrupt loss in weight at ~350 � C due to the thermal decomposition of the ether linkages [38,39]. Compared with the thermal stability of PEO-based SPEs that have a decomposition temperature of ~300 � C [12,40], the superior thermal stability of the P (EO-co-PO)-based SPEs (i.e., N-SPE and L-SPE) suggests that the PO units strengthen the polymer chains. The inset of Fig. 2b displays the focused
Fig. 2. Thermal analysis of the polymer and SPEs. (a) DSC profiles of the asreceived P(EO-co-PO), L-SPE, and N-SPE. (b) TGA profile of the N-SPE; the inset shows the focused profile in the temperature range of 30–95 � C.
networking, the as-received P(EO-co-PO) exhibited diffraction peaks of crystallized PEO in the 2θ range of 15� –30� [34,35]. After being sub jected to crosslinking with POSS, the networked P(EO-co-PO) did not exhibit any diffraction peaks in the XRD pattern. This result indicates that POSS networked the P(EO-co-PO) chains to suppress the crystalli zation of PEO. Amorphous characteristics are beneficial for ion transport in an SPE [36]. The N-SPE and L-SPE were produced by introducing the LiTFSI salt into the networked and as-received P(EO-co-PO) at an ethylene oxide (EO)/Li ratio of 15/1. The as-received P(EO-co-PO) was soft and did not exhibit sufficient mechanical strength to ensure the dimensional integrity of the 4
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
3.2. Electrochemical properties of SPE The temperature dependence of Liþ-ion transport in SPEs can be simulated using two models: the Arrhenius model and Vogel–Tammann–Fulcher (VTF) model [43,44]. The Arrhenius model predicts the ion transport through hopping in a polymer matrix, whereas the VTF model predicts the transport associated with segmental motions of a polymer. Fig. 4a shows the temperature (T; in K) dependence of N-SPE conductivity (σ) according to the Arrhenius model. The σ values were determined from the AC impedance spectra of the N-SPE that was inserted between two stainless-steel foils (Fig. S2). The N-SPE had a room-temperature (25 � C) conductivity of 1.1 � 10 4 S cm 1, which is higher than those of reported PEO-based SPEs (~10 5 S cm 1 or lower) [13,45–48]. The high conductivity of the N-SPE can be attributed to the less restricted polymer chain motion (according the DSC analysis) and the higher degree of salt dissociation (according to the Raman analysis). Fig. 4 reveals that the Arrhenius model did not accurately simulate the temperature dependence of the conductivities of the N-SPE. Fig. S3 shows the temperature dependence of N-SPE conductivity according to the VTF model, � � Ea 1 σ ¼ A0 T 2 exp (1) RðT T0 Þ where A0 is a constant proportional to the number of carrier ions, Ea is the pseudo-activation energy related to the motion of the polymer segmental mobility, T0 is the ideal glass transition temperature, and R is the gas constant. The linear fit displayed in Fig. S2 indicates that the segmental motions of the polymer chains govern ion mobility [28,49]. The Ea value calculated for the ionic conductivity of the N-SPE was 3.5 kJ mol 1 (or 0.037 eV), which is lower than that of PEO-based SPEs (~0.5 eV) [46]. The low Ea value of the N-SPE indicates that the established POSS networking effectively facilitated the thermal motion of the polymer chains to expedite ion transport [50,51]. We focus on the performance of the N-SPE in the following discussions because the N-SPE exhibited superior properties to the L-SPE and other reported SPEs in LIB applications [29,36,52,53]. The Liþ ion transference number (tLiþ) of the N-SPE was determined through polarization of a Li|N-SPE|Li cell. The tLiþ value was calculated according to the following Bruce–Vincent equation [54]:
Fig. 4. (a) Temperature (T) dependence of N-SPE conductivity (σ) in the temperature of 25–60 � C according to the Arrhenius model. (b) Linear sweep voltammogram of a cell assembled by inserting the N-SPE film between a working stainless steel electrode and a Li-metal counter electrode at 25 � C with a scan rate of 5 mV s 1.
TGA profile of the N-SPE in the range of 30–95 � C. The solvent used in the N-SPE synthesis was tetrahydrofuran, which has a boiling point of 66 � C and has a low dielectric constant of 7.6. The TGA weight loss within 30–95 � C was approximately 0.7%, indicating an extremely low solvent content and thus a negligible contribution of solvent molecules to the ion transport in the N-SPE. The minimal weight loss at tempera tures within 100–351 � C might result from volatilization of organic impurities contained in the raw materials for the N-SPE. Fig. 3 shows a comparison of the Raman spectra of the N-SPE and LSPE in the wavenumber range of 725–760 cm 1, which corresponds to the expansion–contraction mode of TFSI anions [24]. The signal in this range comprises peaks of three TFSI conformational states: two free TFSI states in cis (738 cm 1) and trans (742 cm 1) conformations and one Liþ-associated TFSI (748 cm 1) state. The Gaussian function was used to deconvolute the Raman spectra into their constituent peaks. The fractions of Liþ-associated TFSI in the entire TFSI population were 7.6% and 18% for the N-SPE and L-SPE, respectively, indicating that the degree of Liþ association with TFSI anions was lower in the N-SPE than it was in the L-SPE. This result signifies that the POSS hubs in the N-SPE may have provided Lewis acid–base interaction sites to facilitate lithium salt dissociation [41]. We anticipate that the Si4þ sites on the POSS served as the Lewis acid to attract TFSI anions and that the ether groups in the polymer chains attracted Liþ ions and facilitated the transport of Liþ along the polymer chain through segmental motion. Moreover, as revealed in Fig. 3, the content of the free TFSI of the N-SPE was high in the cis conformation (the inset of Fig. 3a), which has a smaller size than that of the trans conformation (the inset of Fig. 3b) and has been a favored conformation for immobilization in a crystalline framework [42]. The high cis-TFSI content of the N-SPE indicates that the free TFSI anions were immobilized in proximity to the POSS hubs, possibly due to the attraction by the Si4þ sites. The 3D networking along with anion immobilization caused by the POSS hubs in the N-SPE was determined to be advantageous for the transport of Liþ cations.
tLiþ ¼
ISS ðΔVDC I0 Rint;0 Þ I0 ðΔVDC ISS Rint;ss Þ
(2)
where I0 and Iss are the initial and steady-state currents respectively, under polarization at a low DC voltage (VDC) of 5 mV (Fig. S4a). The Iss value was determined when the current variation rate was lower than 0.1 μA min 1. Rint,0 and Rint,ss are the initial and steady-state resistances respectively, that are associated with charge transfer at the Li-metal interfaces and were determined by conducting AC impedance analysis (Fig. S4b). The tLiþ value of the N-SPE was determined to be 0.62, which is considerably higher than those of Liþ–SPE systems (generally within 0.15–0.3) [55,56]. The low tLiþ values of Liþ–SPEs can be attributed to the severe tangling of polymer chains; the segmental motion of polymer chains constitutes the primary mechanism for transporting Liþ ions in SPEs [57]. In the present study, the high tLiþ value of the N-SPE can be attributed to the presence of the POSS hubs and hydrophobic methyl side chains that straightened the intertwined polymer chains to facilitate Liþ ion transport in the networked framework (Scheme 1). Moreover, the Raman analysis (Fig. 3) indicated that the TFSI anions might be attracted by the Si4þ sites on the POSS hubs to impede anion transport. Previous studies have reported that Lewis acid sites not only help lithium salt dissociation but also provide additional Liþ transport channels to improve the tLiþ value [58]. High electrochemical stability is an essential feature of high-energy LIBs. However, studies have reported that PEO-based SPEs ruptured at potentials higher than 4.3 V (vs. Liþ/Li) and that the contained salt 5
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
value), thereby suppressing the decomposition of the ether linkages in the polymer and TFSI anions at high voltages. 3.3. Performance of the all-solid-state battery We used a free-standing N-SPE film (70 μm), LiFePO4 cathode, and Li-metal anode to assemble a Li|N-SPE|LiFePO4 battery. In the battery, a mixture of polyvinylidene fluoride and the N-SPE (at a mass ratio of 1:2) was used as the binder for casting the LiFePO4 cathode. Using the N-SPEcontaining binder improved the connection between the solid electro lyte and LiFePO4 powder. Scheme 2 presents the configuration of the Li| N-SPE|LiFePO4 battery that was assembled using the free-standing NSPE film. With this battery design, the external region of the freestanding film was well connected to the cathode film through the NSPE embedded in the cathode and the center zone of the free-standing film maintained its mechanical integrity and firmly partitioned the cathode and anode. The excellent affinity between the N-SPE species in the cathode and free-standing film ensured the swift transport of Liþ ions across the electrolyte–cathode interface. Scheme 2 demonstrates the feasibility of the roll-to-roll assembly of the Li|N-SPE|LiFePO4 battery by using the proposed free-standing N-SPE. Fig. 5a presents the room-temperature (25 � C) galvanostatic char ge discharge profiles of the Li|N-SPE|LiFePO4 battery at various Crates, which was charged to 4.0 V at 0.1 C-rate (at a current density of approximately 30 μA cm 2) and subsequently discharged to 2.5 V at various C-rates. We determined the battery C-rates according to the capacity of the LiFePO4 cathode, under the assumption that the maximum achievable capacity of this battery system was 170 mAh g 1 (theoretical capacity of LiFePO4). As shown in Fig. 5a, the Li|N-SPE| LiFePO4 battery delivered discharge capacities of 160, 159, 157, 153, and 137 mAh g 1 at 0.1, 0.2, 0.3, 0.5 and 1 C-rates, respectively. The capacities achieved at room temperature were high and superior to those reported for LIBs assembled using all-solid-state SPEs without any solvent, oligomer, or semisolid additives [12,15,61]. The cyclic vol tammogram of the Li|N-SPE|LiFePO4 battery was presented in Fig. S5, showing the capability of the N-SPE in facilitating Liþ-ion transport. Fig. 5b illustrates the charge discharge cycling capacities of the Li| N-SPE|LiFePO4 battery at 0.1 and 0.2 C-rates for 50 cycles. The battery exhibited high capacity retentions of 95% and 92% at 0.1 and 0.2 Crates, respectively, with a Coulombic efficiency of approximately 100%. The admirable performance of this battery can be attributed to the intimate contact between the N-SPE and electrodes through the PPO methyl side chain as well as to the efficient Liþ pathways created in the 3D SPE network that exhibited high polymer chain mobility, a high degree of salt dissociation, and TFSI anion immobilization [12,29,36]. Fig. S6 presents the result of cycling at 0.3C, revealing a high capacity retention of 75% after 100 cycles with approximately 100% of Coulombic efficiency throughout the cycling. In addition to the superior performance, the simplicity of electrolyte synthesis and battery assem bly demonstrates the high readiness of the N-SPE for use in industrial-scale production processes [29,30,62]. The rate capability of the Li|N-SPE|LiFePO4 battery was demon strated by subjecting it to a repeated galvanostatic charge discharge test between 2.5 and 4.0 V (vs. Liþ/Li) at varying C-rates, as presented in Fig. S7. The charge discharge test was conducted from 0.1 to 1 C-rate and then back to 0.1 C-rate. Similar to the results shown in Fig. 5a, the capacity of the battery decreased with the C-rate. The Coulombic effi ciency was maintained at approximately 100% in the entire test. The capacity was returned to its original value when the battery operation was back to the lowest C-rate (i.e., back to 160 mAh g 1 at 0.1 C-rate), indicating excellent reversibility and stability of the battery under conditions of varying storage rates. We conducted lithium stripping–plating tests on the N-SPE by using cells comprising two Li-metal electrodes that sandwiched the N-SPE. Fig. 6 displays the voltage–time curves obtained from the test. In the curve, each half-wave represents the voltage response to the applied
Scheme 2. Schematic for the roll-to-roll assembly of a Li|N-SPE|LiFePO4 bat tery using the free-standing N-SPE film. The focused configuration of the resulting battery depicts POSS-networked polymer framework in the N-SPE and excellent connection between the N-SPE species in the cathode and freestanding film.
Fig. 5. Electrochemical performance of the Li|N-SPE|LiFePO4 battery at 25 � C. (a) Galvanostatic charge–discharge profiles of the battery at different current densities. (b) Variations of the capacity and Coulombic efficiency in the char ge discharge cycling at 0.1 and 0.2 C-rates. The charge-discharge was operated between 2.5 and 4.0 V and the C rates were defined on the basis of the theo ritical capacity of LiFePO4 (170 mAh g 1).
(LiTFSI) decomposed at 5.1 V (vs. Liþ/Li) [59,60]. These electro chemical instabilities are detrimental to the high-energy demand of LIBs. Fig. 4b displays the linear sweep voltammogram of a cell assem bled by inserting the N-SPE film between an SS electrode and a Li-metal counter at 25 � C. As revealed in the voltammogram, the current profile did not abruptly rise until the applied voltage sweep reached approxi mately 5.4 V (vs. Liþ/Li). The high electrochemical stability of the N-SPE can be attributed to the affinity of the methyl side chains of PPO to the electrode and the immobilization of TFSI (reflected by the high tLiþ 6
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment The authors acknowledge the support of Ministry of Science and Technology in Taiwan through grant numbers 107-2221-E-006-111MY3, 107-2221-E-006-110-MY3, 108-3116-F-006-012-CC1, and 1082622-8-006-014. Authors also acknowledge the support from the Hier archical Green-Energy Materials (Hi-GEM) Research Center and the Center of Applied Nanomedicine at National Cheng Kung University from The Featured Areas Research Center Program within the frame work of the Higher Education Sprout Project by the Ministry of Educa tion and the Ministry of Science and Technology (107-3017-E-006-003). Fig. 6. Voltage-time profile for lithium stripping-plating of a Li|N-SPE|Li cell, where each half-wave is the voltage response to the applied current of 0.1 mA cm 2 in 1 h stripping or plating.
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.jpowsour.2019.227518.
current of 0.1 mA cm 2 during 1-h stripping–plating tests conducted to analyze the dendrite formation dynamics. The cell lifetime was deter mined by the sudden drop in the voltage profile when dendrites bridged the two electrodes to short circuit the cell. As illustrated in Fig. 6, the Li| N-SPE|Li cell had not shown the failure sign of short-circuit for over 500 h and the voltage–time profile remained stable during the entire cycling (the inset of Fig. 6). The result indicates that the strengthened 3D polymer network suppressed the piercing growth of Li dendrites, which are caused by the uneven formation of the solid electrolyte interface (SEI) layer on the Li-metal surface [63]. The SEI layer was produced during the chemical interaction between the solvent molecules and Li-metal surface [64]. In the absence of solvent molecules, the N-SPE enabled smooth plating of Li metal on the electrode surface. However, the polarization voltage was high (~0.25 V), indicating the contact between the N-SPE and Li-metal electrode needs to be improved [65, 66].
References [1] R. Chen, W. Qu, X. Guo, L. Li, F. Wu, The pursuit of solid-state electrolytes for lithium batteries: from comprehensive insight to emerging horizons, Mater. Horiz. 3 (2016) 487–516, https://doi.org/10.1039/C6MH00218H. [2] S. Chen, K. Wen, J. Fan, Y. Bando, D. Golberg, Progress and future prospects of high-voltage and high-safety electrolytes in advanced lithium batteries: from liquid to solid electrolytes, J. Mater. Chem. 6 (2018) 11631–11663, https://doi.org/ 10.1039/c8ta03358g. [3] L. Fan, S. Wei, S. Li, Q. Li, Y. Lu, Recent progress of the solid-state electrolytes for high-energy metal-based batteries, Adv. Energy Mater. 8 (2018), https://doi.org/ 10.1002/aenm.201702657, 1702657. [4] P. Hu, J. Chai, Y. Duan, Z. Liu, G. Cui, L. Chen, Progress in nitrile-based polymer electrolytes for high performance lithium batteries, J. Mater. Chem. 4 (2016) 10070–10083, https://doi.org/10.1039/c6ta02907h. [5] A.B. Puthirath, S. Patra, S. Pal, M. Manoj, A. Puthirath Balan, S. Jayalekshmi, N. N. Tharangattu, Transparent flexible lithium ion conducting solid polymer electrolyte, J. Mater. Chem. 5 (2017) 11152–11162, https://doi.org/10.1039/ c7ta02182h. [6] R. Yu, J.J. Bao, T.T. Chen, B.K. Zou, Z.Y. Wen, X.X. Guo, C.H. Chen, Solid polymer electrolyte based on thermoplastic polyurethane and its application in all-solidstate lithium ion batteries, Solid State Ion. 309 (2017) 15–21, https://doi.org/ 10.1016/j.ssi.2017.06.013. [7] A. Arya, A.L. Sharma, Polymer electrolytes for lithium ion batteries: a critical study, Ionics 23 (2017) 497–540, https://doi.org/10.1007/s11581-016-1908-6. [8] L.T.M. Le, T.D. Vo, K.H.P. Ngo, S. Okada, F. Alloin, A. Garg, P.M.L. Le, Mixing ionic liquids and ethylene carbonate as safe electrolytes for lithium-ion batteries, J. Mol. Liq. 271 (2018) 769–777, https://doi.org/10.1016/j.molliq.2018.09.068. [9] X. Ji, H. Zeng, X. Gong, F. Tsai, T. Jiang, R.K.Y. Li, H. Shi, S. Luan, D. Shi, A Sidoped flexible self-supporting comb-like polyethylene glycol copolymer (Si-PEG) film as a polymer electrolyte for an all solid-state lithium-ion battery, J. Mater. Chem. 5 (2017) 24444–24452, https://doi.org/10.1039/c7ta07741f. [10] Q. Zhang, K. Liu, F. Ding, W. Li, X. Liu, J. Zhang, Safety-reinforced succinonitrilebased electrolyte with interfacial stability for high-performance lithium batteries, ACS Appl. Mater. Interfaces 9 (2017) 29820–29828, https://doi.org/10.1021/ acsami.7b09119. [11] J. Zhang, L. Yue, P. Hu, Z. Liu, B. Qin, B. Zhang, Q. Wang, G. Ding, C. Zhang, X. Zhou, J. Yao, G. Cui, L. Chen, Taichi-inspired rigid-flexible coupling cellulosesupported solid polymer electrolyte for high-performance lithium batteries, Sci. Rep. 4 (2014) 6272, https://doi.org/10.1038/srep06272. [12] T.M. Liu, D. Saikia, S.Y. Ho, M.C. Chen, H.M. Kao, High ion-conducting solid polymer electrolytes based on blending hybrids derived from monoamine and diamine polyethers for lithium solid-state batteries, RSC Adv. 7 (2017) 20373–20383, https://doi.org/10.1039/c7ra01542a. [13] S. Suriyakumar, M. Kanagaraj, N. Angulakshmi, M. Kathiresan, K.S. Nahm, M. Walkowiak, K. Wasi� nski, P. P� ołrolniczak, A.M. Stephan, Charge-discharge studies of all-solid-state Li/LiFePO4cells with PEO-based composite electrolytes encompassing metal organic frameworks, RSC Adv. 6 (2016) 97180–97186, https://doi.org/10.1039/c6ra17962b. [14] J. Zhang, C. Ma, J. Liu, L. Chen, A. Pan, W. Wei, Solid polymer electrolyte membranes based on organic/inorganic nanocomposites with star-shaped structure for high performance lithium ion battery, J. Member. Sci. 509 (2016) 138–148, https://doi.org/10.1016/j.memsci.2016.02.049. [15] Y. Cui, X. Liang, J. Chai, Z. Cui, Q. Wang, W. He, X. Liu, Z. Liu, G. Cui, J. Feng, High performance solid polymer electrolytes for rechargeable batteries: a self-catalyzed
4. Conclusions This study demonstrated the high performance of POSS-networked P (EO-co-PO) in conveying Liþ ions in an N-SPE for LIBs. The methyl chain of PPO in the polymer suppressed polymer crystallization and improved the affinity to the electrodes, thereby promoting the mobility of Liþ ions in the electrolyte bulk and at the electrolyte-electrode interface. The cage-like POSS molecules served as hubs to incorporate the straightened P(EO-co-PO) chains, thus forming a 3D polymer network in the N-SPE. The 3D network exhibited a low Tg of 43 � C, indicating the high segmental mobility of the polymer chains. The pseudo-activation energy related to the ionic conductivity in the N-SPE was 3.5 kJ mol 1 (or 0.037 eV), confirming the low restriction of the mobility of the polymer chains. The POSS hubs not only minimized the tangling of the polymer chains to facilitate Liþ ion transport but also localized TFSI anions, likely through interaction with the contained Si4þ sites. Thus, the N-SPE exhibited an ionic conductivity of 1.1 � 10 4 S cm 1 at 25 � C and a high tLiþ of 0.62. The unique feature of our electrolyte design enabled the assembly of an all-solid-state Li|N-SPE|LiFePO4 battery by using a freestanding N-SPE membrane where the N-SPE was mixed with a binder to form the cathode film. The resulting all-solid-state battery delivered capacities of 160 and 137 mAh g 1 at 0.1 and 1 C-rates, respectively, at 25 � C along with excellent charge–discharge cycling stability. The use of the free-standing N-SPE provides the foundation to realize roll-to-roll assembly of all-solid-state LIBs in an industrial scale.
7
S.-T. Hsu et al.
[16]
[17]
[18] [19] [20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29] [30]
[31]
[32] [33] [34]
[35]
[36]
[37]
Journal of Power Sources xxx (xxxx) xxx
strategy toward facile synthesis, Adv. Sci. 4 (2017), https://doi.org/10.1002/ advs.201700174. D. Zhang, L. Zhang, K. Yang, H. Wang, C. Yu, D. Xu, B. Xu, L.M. Wang, Superior blends solid polymer electrolyte with integrated hierarchical architectures for allsolid-state lithium-ion batteries, ACS Appl. Mater. Interfaces 9 (2017) 36886–36896, https://doi.org/10.1021/acsami.7b12186. H. Yue, J. Li, Q. Wang, C. Li, J. Zhang, Q. Li, X. Li, H. Zhang, S. Yang, Sandwich-like poly(propylene carbonate)-based electrolyte for ambient-temperature solid-state lithium ion batteries, ACS Sustain. Chem. Eng. 6 (2018) 268–274, https://doi.org/ 10.1021/acssuschemeng.7b02401. M. Yang, J. Hou, Membranes in lithium ion batteries, Membranes 2 (2012) 367–383, https://doi.org/10.3390/membranes2030367. H. Choi, H.W. Kim, J.K. Ki, Y.J. Lim, Y. Kim, J.H. Ahn, Nanocomposite quasi-solidstate electrolyte for high-safety lithium batteries, Nano Res. 10 (2017) 3092–3102, https://doi.org/10.1007/s12274-017-1526-2. J. Shim, D.G. Kim, H.J. Kim, J.H. Lee, J.C. Lee, Polymer composite electrolytes having core-shell silica fillers with anion-trapping boron moiety in the shell layer for all-solid-state lithium-ion batteries, ACS Appl. Mater. Interfaces 7 (2015) 7690–7701, https://doi.org/10.1021/acsami.5b00618. J. Suk, Y.H. Lee, D.Y. Kim, D.W. Kim, S.Y. Cho, J.M. Kim, Y. Kang, Semiinterpenetrating solid polymer electrolyte based on thiol-ene cross-linker for allsolid-state lithium batteries, J. Power Sources 334 (2016) 154–161, https://doi. org/10.1016/j.jpowsour.2016.10.008. M. Nakayama, S. Wada, S. Kuroki, M. Nogami, Factors affecting cyclic durability of all-solid-state lithium polymer batteries using poly(ethylene oxide)-based solid polymer electrolytes, Energy Environ. Sci. 3 (2010) 1995–2002, https://doi.org/ 10.1039/c0ee00266f. L. Porcarelli, A.S. Shaplov, M. Salsamendi, J.R. Nair, Y.S. Vygodskii, D. Mecerreyes, C. Gerbaldi, Single-ion block copoly(ionic liquid)s as electrolytes for all-solid state lithium batteries, ACS Appl. Mater. Interfaces 8 (2016) 10350–10359, https://doi. org/10.1021/acsami.6b01973. G. Yang, C. Chanthad, H. Oh, I.A. Ayhan, Q. Wang, Organic-inorganic hybrid electrolytes from ionic liquid-functionalized octasilsesquioxane for lithium metal batteries, J. Mater. Chem. 5 (2017) 18012–18019, https://doi.org/10.1039/ c7ta04599a. D. Sygkridou, A. Rapsomanikis, E. Stathatos, Functional transparent quasi-solid state dye-sensitized solar cells made with different oligomer organic/inorganic hybrid electrolytes, Sol. Energy Mater. Sol. Cells 159 (2017) 600–607, https://doi. org/10.1016/j.solmat.2016.01.019. D. Saikia, H.Y. Wu, Y.C. Pan, C.P. Lin, K.P. Huang, K.N. Chen, G.T.K. Fey, H. M. Kao, Highly conductive and electrochemically stable plasticized blend polymer electrolytes based on PVdF-HFP and triblock copolymer PPG-PEG-PPG diamine for Li-ion batteries, J. Power Sources 196 (2011) 2826–2834, https://doi.org/ 10.1016/j.jpowsour.2010.10.096. Q. Lu, Y.B. He, Q. Yu, B. Li, Y.V. Kaneti, Y. Yao, F. Kang, Q.H. Yang, Dendrite-free, high-rate, long-life lithium metal batteries with a 3D cross-linked network polymer electrolyte, Adv. Mater. 29 (2017), https://doi.org/10.1002/adma.201604460, 1604460. S.H. Wang, Y.Y. Lin, C.Y. Teng, Y.M. Chen, P.L. Kuo, Y.L. Lee, C. Te Hsieh, H. Teng, Immobilization of anions on polymer matrices for gel electrolytes with high conductivity and stability in lithium ion batteries, ACS Appl. Mater. Interfaces 8 (2016) 14776–14787, https://doi.org/10.1021/acsami.6b01753. Q. Pan, D.M. Smith, H. Qi, S. Wang, C.Y. Li, Hybrid electrolytes with controlled network structures for lithium metal batteries, Adv. Mater. 27 (2015) 5995–6001, https://doi.org/10.1002/adma.201502059. Q. Pan, D. Barbash, D.M. Smith, H. Qi, S.E. Gleeson, C.Y. Li, Correlating electrode–electrolyte interface and battery performance in hybrid solid polymer electrolyte-based lithium metal batteries, Adv. Energy Mater. 7 (2017), https://doi. org/10.1002/aenm.201701231, 1701231. J. Shim, D.G. Kim, J.H. Lee, J.H. Baik, J.C. Lee, Synthesis and properties of organic/inorganic hybrid branched-graft copolymers and their application to solidstate electrolytes for high-temperature lithium-ion batteries, Polym. Chem. 5 (2014) 3432–3442, https://doi.org/10.1039/c4py00123k. Ji Hu, Wanhui Wang, Haiyan Peng, Mengke Guo, Yuezhan Feng, Zhigang Xue, Yunsheng Ye, Flexible Organic Inorganic hybrid solid electrolytes formed via thiol acrylate photopolymerization, Macromolecules 50 (2017) 1970–1980. Y.Y. Lin, Y.M. Chen, S.S. Hou, J.S. Jan, Y.L. Lee, H. Teng, Diode-like gel polymer electrolytes for full-cell lithium ion batteries, J. Mater. Chem. 5 (2017) 17476–17481, https://doi.org/10.1039/c7ta04886f. R. Blanga, M. Goor, L. Burstein, Y. Rosenberg, A. Gladkich, D. Logvinuk, I. Shechtman, D. Golodnitsky, The search for a solid electrolyte, as a polysulfide barrier, for lithium/sulfur batteries, J. Solid State Electrochem. 20 (2016) 3393–3404, https://doi.org/10.1007/s10008-016-3303-7. A.R. Polu, H.W. Rhee, Nanocomposite solid polymer electrolytes based on poly (ethylene oxide)/POSS-PEG (n¼13.3) hybrid nanoparticles for lithium ion batteries, J. Ind. Eng. Chem. 31 (2015) 323–329, https://doi.org/10.1016/j. jiec.2015.07.005. D. Lin, W. Liu, Y. Liu, H.R. Lee, P.C. Hsu, K. Liu, Y. Cui, High ionic conductivity of composite solid polymer electrolyte via in situ synthesis of monodispersed SiO2 nanospheres in poly(ethylene oxide), Nano Lett. 16 (2016) 459–465, https://doi. org/10.1021/acs.nanolett.5b04117. B. Cong, Y. Song, N. Ren, G. Xie, C. Tao, Y. Huang, G. Xu, J. Bao, Polyethylene glycol-based waterborne polyurethane as solid polymer electrolyte for all-solidstate lithium ion batteries, Mater. Des. 142 (2018) 221–228, https://doi.org/ 10.1016/j.matdes.2018.01.039.
[38] E. Calahorra, M. Cortazar, Thermal decomposition of poly(ethy1ene oxide), poly (methy1 methacrylate), and their mixtures by thermogravimetric method, J. Polym. Sci. Polym. Lett. Ed. 23 (1985) 257–260, https://doi.org/10.1002/ pol.1985.130230509. [39] T. Degradation, P. Oxide, P. Oxide, Thermal degradation of polyethylene oxide and polypropylene oxide, J. Polym. Sci. 36 (1959) 183–194, https://doi.org/10.1002/ pol.1959.1203613015. [40] T. Shodai, B.B. Owens, H. Ohtsuka, J.-I. Yamaki, Thermal stability of the polymer electrolyte (PEO)8LiCF3SO3, J. Electrochem. Soc. 141 (1994) 2978–2981, https:// doi.org/10.1149/1.2059268. [41] B. Chen, Q. Xu, Z. Huang, Y. Zhao, S. Chen, X. Xu, One-pot preparation of new copolymer electrolytes with tunable network structure for all-solid-state lithium battery, J. Power Sources 331 (2016) 322–331, https://doi.org/10.1016/j. jpowsour.2016.09.063. [42] F. Capitani, F. Trequattrini, O. Palumbo, A. Paolone, P. Postorino, Phase transitions of PYR14-TFSI as a function of pressure and temperature: the competition between smaller volume and lower energy conformer, J. Phys. Chem. B 120 (2016) 2921–2928, https://doi.org/10.1021/acs.jpcb.5b12667. [43] J. Souquet, Salt-polymer complexes: strong or weak electrolytes? Solid State Ion. 85 (1996) 149–157, https://doi.org/10.1016/0167-2738(96)00052-5. [44] Q. Xiao, X. Wang, W. Li, Z. Li, T. Zhang, H. Zhang, Macroporous polymer electrolytes based on PVDF/PEO- b -PMMA block copolymer blends for rechargeable lithium ion battery, J. Member. Sci. 334 (2009) 117–122, https://doi. org/10.1016/j.memsci.2009.02.018. [45] W. Wieczorek, D. Raducha, A. Zalewska, J.R. Stevens, Effect of salt concentration on the conductivity of PEO-based composite polymeric electrolytes, J. Phys. Chem. B 102 (1998) 8725–8731, https://doi.org/10.1021/jp982403f. [46] J. Gurusiddappa, W. Madhuri, R. Padma Suvarna, K. Priya Dasan, Studies on the morphology and conductivity of PEO/LiClO4, Mater. Today: SAVE Proc. 3 (2016) 1451–1459, https://doi.org/10.1016/j.matpr.2016.04.028. [47] X. Fu, D. Yu, J. Zhou, S. Li, X. Gao, Y. Han, P. Qi, X. Feng, B. Wang, Inorganic and organic hybrid solid electrolytes for lithium-ion batteries, CrystEngComm 18 (2016) 4236–4258, https://doi.org/10.1039/c6ce00171h. [48] L. Chen, Y. Li, S.P. Li, L.Z. Fan, C.W. Nan, J.B. Goodenough, PEO/garnet composite electrolytes for solid-state lithium batteries: from “ceramic-in-polymer” to “polymer-in-ceramic”, Nano Energy 46 (2018) 176–184, https://doi.org/10.1016/ j.nanoen.2017.12.037. [49] M.H. Cohen, D. Turnbull, Molecular transport in liquids and glasses, J. Chem. Phys. 31 (1959) 1164–1169, https://doi.org/10.1063/1.1730566. [50] K. Xu, Nonaqueous liquid electrolytes for lithium-based rechargeable batteries, Chem. Rev. 104 (2004) 4303–4417, https://doi.org/10.1021/cr030203g. [51] M. Klett, M. Giesecke, A. Nyman, F. Hallberg, R.W. Lindstr€ om, G. Lindbergh, I. Fur� o, Quantifying mass transport during polarization in a Li Ion battery electrolyte by in situ 7Li NMR imaging, J. Am. Chem. Soc. 134 (2012) 14654–14657, https://doi.org/10.1021/ja305461j. [52] S. Choudhury, R. Mangal, A. Agrawal, L.A. Archer, A highly reversible roomtemperature lithium metal battery based on crosslinked hairy nanoparticles, Nat. Commun. 6 (2015) 10101, https://doi.org/10.1038/ncomms10101. [53] Z. Wang, S. Wang, A. Wang, X. Liu, J. Chen, Q. Zeng, L. Zhang, W. Liu, L. Zhang, Covalently linked metal-organic framework (MOF)-polymer all-solid-state electrolyte membranes for room temperature high performance lithium batteries, J. Mater. Chem. 6 (2018) 17227–17234, https://doi.org/10.1039/c8ta05642k. [54] J. Evans, C.A. Vincent, P.G. Bruce, Electrochemical measurement of transference numbers in polymer electrolytes, Polymer 28 (1987) 2324–2328, https://doi.org/ 10.1016/0032-3861(87)90394-6. [55] M.M. Hiller, M. Joost, H.J. Gores, S. Passerini, H.D. Wiemh€ ofer, The influence of interface polarization on the determination of lithium transference numbers of salt in polyethylene oxide electrolytes, Electrochim. Acta 114 (2013) 21–29, https:// doi.org/10.1016/j.electacta.2013.09.138. [56] P.G. Bruce, M.T. Hardgrave, C.A. Vincent, The determination of transference numbers in solid polymer electrolytes using the Hittorf method, Solid State Ion. 53–56 (1992) 1087–1094, https://doi.org/10.1016/0167-2738(92)90295-Z. [57] S. Srivastava, J.L. Schaefer, Z. Yang, Z. Tu, L.A. Archer, 25th Anniversary article: polymer-particle composites: phase stability and applications in electrochemical energy storage, Adv. Mater. 26 (2014) 201–234, https://doi.org/10.1002/ adma.201303070. [58] M. Grzelczak, J. Vermant, E.M. Furst, L.M. Liz-marza, Directed self-assembly of nanoparticles, ACS Nano 4 (2010) 3591–3605, https://doi.org/10.1021/ nn100869j. [59] Y. Zhao, Z. Huang, S. Chen, B. Chen, J. Yang, Q. Zhang, F. Ding, Y. Chen, X. Xu, A promising PEO/LAGP hybrid electrolyte prepared by a simple method for allsolid-state lithium batteries, Solid State Ion. 295 (2016) 65–71, https://doi.org/ 10.1016/j.ssi.2016.07.013. [60] A. ling Zhang, F. yu Cao, G. zhou Na, S. Wang, S. xi Li, J. chi Liu, A novel PEObased blends solid polymer electrolytes doping liquid crystalline ionomers, Ionics 22 (2016) 2103–2112, https://doi.org/10.1007/s11581-016-1732-z. [61] K. Xu, Electrolytes and interphases in Li-ion batteries and beyond, Chem. Rev. 114 (2014) 11503–11618, https://doi.org/10.1021/cr500003w. [62] Y.C. Jung, M.S. Park, D.H. Kim, M. Ue, A. Eftekhari, D.W. Kim, Room-temperature performance of poly(ethylene ether carbonate)-based solid polymer electrolytes for all-solid-state lithium batteries, Sci. Rep. 7 (2017), https://doi.org/10.1038/ s41598-017-17697-0, 17482. [63] Y.M. Chen, S.T. Hsu, Y.H. Tseng, T.F. Yeh, S.S. Hou, J.S. Jan, Y.L. Lee, H. Teng, Minimization of ion–solvent clusters in gel electrolytes containing graphene oxide quantum dots for lithium-ion batteries, Small 14 (2018), https://doi.org/10.1002/ smll.201703571, 1703571.
8
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
[64] D. Lin, Y. Liu, Y. Cui, Reviving the lithium metal anode for high-energy batteries, Nat. Nanotechnol. 12 (2017) 194–206, https://doi.org/10.1038/nnano.2017.16. [65] Z. Wang, M. Zhu, Z. Peia, Q. Xue, H. Li, Y. Huang, C. Zhi, Polymers for supercapacitors: boosting the development of the flexible and wearable energy storage, Mater. Sci. Eng. R. in press. doi:10.1016/j.mser.2019.100520.
[66] F. Mo, G. Liang, Z. Huang, H. Li, D. Wang, C. Zhi, Adv. Mater. 31 (2019), https:// doi.org/10.1002/adma.201902151, 1902151.
9
Contents lists available at ScienceDirect
Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour
Free-standing polymer electrolyte for all-solid-state lithium batteries operated at room temperature Shih-Ting Hsu a, Binh T. Tran a, Ramesh Subramani a, Hanh T.T. Nguyen a, Arunkumar Rajamani a, Ming-Yu Lee a, Sheng-Shu Hou a, b, Yuh-Lang Lee a, b, Hsisheng Teng a, b, c, * a b c
Department of Chemical Engineering, National Cheng Kung University, Tainan, 70101, Taiwan Hierarchical Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung University, Tainan, 70101, Taiwan Center of Applied Nanomedicine, National Cheng Kung University, Tainan, 70101, Taiwan
H I G H L I G H T S
G R A P H I C A L A B S T R A C T
� Solid polymer electrolyte with no sol vent, ionic liquid, oligomer, or semisolid additives. � Free-standing feature for roll-to-roll as sembly of lithium ion batteries. � Polymer chains networked by hubs for high segmental mobility. � A high Liþ transference number for minimized polarization and large voltage range.
A R T I C L E I N F O
A B S T R A C T
Keywords: Solid lithium battery Solid polymer electrolyte Free-standing polymer electrolyte Room-temperature solid battery
This study reports a networked solid polymer electrolyte (N-SPE) containing no solvent, ionic liquid, oligomer, or semisolid additives for lithium-ion batteries (LIBs). The N-SPE comprises a lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt as well as a polymer framework constructed using cage-like polyhedral oligomeric silses quioxane (POSS) and serving as hubs to network poly(ethylene oxide-co-polypropylene oxide) (P(EO-co-PO)) chains. The networking prevents polymer chain twisting that hinders ion transport. Raman analysis indicates that the POSS hubs improve the dissociation of LiTFSI and localize TFSI anions. The N-SPE exhibits a low glass transition temperature of 43 � C, a high 25 � C ionic conductivity of 1.1 � 10 4 S cm 1, and a small activation energy of 3.5 kJ mol 1 for ion conduction. The localization of TFSI results in a high lithium transference number of 0.62, which is determined to be beneficial to Liþ transport. By incorporating the N-SPE into the LiFePO4 cathode and using a free-standing N-SPE membrane, this study assembles a Li|N-SPE|LiFePO4 battery, which delivers a high capacity of 160 mAh g 1 at 25 � C and exhibits excellent charge discharge cycling stability. The free-standing feature of the N-SPE makes roll-to-roll assembly of LIBs readily scalable for industrial applications.
* Corresponding author. Department of Chemical Engineering, National Cheng Kung University, Tainan, 70101, Taiwan. E-mail address: [email protected] (H. Teng). https://doi.org/10.1016/j.jpowsour.2019.227518 Received 24 August 2019; Received in revised form 10 November 2019; Accepted 26 November 2019 0378-7753/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Shih-Ting Hsu, Journal of Power Sources, https://doi.org/10.1016/j.jpowsour.2019.227518
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
1. Introduction
Table 1 Polymeric structure and ionic conductivity of SPEs and electrochemical per formance of the resulting Li|SPE|LiFePO4 batteries reported in literature.
Lithium-ion batteries (LIBs), which have high energy density, have become integral to modern life [1]. Most LIBs are assembled using liquid electrolytes, and this raises concerns regarding battery safety and sta bility in extended applications of such batteries [2]. Developing solid-state electrolytes to replace liquid electrolytes is an effective so lution to the aforementioned concerns for LIBs [1,3–5]. When solid-state electrolytes are used, dendrite growth can be reduced, thus preventing battery from short circuit; moreover, the risk of explosion can be elim inated because of the solvent-free feature of such electrolytes. Solid-state electrolytes also exhibit excellent mechanical, thermal, and dimensional stability [6,7]. Among solid-state electrolytes, solid polymer electrolytes (SPEs) exhibit the advantages of high structural flexibility and work ability, which enable roll-to-roll assembly of batteries. However, LIBs that are assembled using SPEs are generally operated at temperatures higher than room temperature (25 � C), and this thus restricts the application of SPE-based LIBs. Room-temperature SPEs containing no solvent, ionic liquid [8], oligomer [9], or semisolid (e.g., succinonitrile) [10] have yet to be extensively explored for use in LIBs. Only a few studies have researched SPEs for LIBs operated at temperatures of 25–30 � C (Table 1) and the capacities of the resulting all-solid-state LIBs were not high [9,11–17]. Poly(ethylene oxide) (PEO) has been widely used as the polymeric matrix of SPEs because of its high dielectric constant, which facilitates salt dissociation [12,14]. The ether oxygen atoms in the PEO backbone coordinate with cations in the amorphous regions of the polymer to promote ion motion. Despite their strength in inducing salt dissociation and cation coordination, PEO-based SPEs has poor ionic conductivity at room temperature because of their strong crystallization tendency and poor mechanical strength [18]. Numerous methods have been developed to suppress the crystalli zation of PEO and improve its mechanical strength. A study reported that the addition of inert fillers effectively reduced the crystalinity of the PEO host and increased the ionic conductivity and mechanical property of the resulting SPEs [19]. However, some fillers aggregated in the composite SPEs, thereby reducing the cycle life of the resulting batteries [19,20]. Moreover, the addition of ionic liquids or oligomers to the PEO host substantially promoted the performance of the resulting batteries at room temperature; nevertheless, these additives would deteriorate the mechanical stability of SPEs at high temperatures and would thus not constitute an ideal component of SPEs [19,21,22]. Other studies have revealed that modifying PEO by using ionic liquid molecules to form single lithium-ion copolymers increased the Liþ transference number of the resulting SPEs; however, this synthesis method is expensive and complex, and it is thus not feasible for practical applications [23,24]. A comprehensive design that involves copolymerizing PEO with polypropylene oxide (PPO), which has a structural feature similar to that of PEO, effectively suppresses the crystallization of PEO with the methyl side chains of PPO and provides a hydrophobic property that is com plementary to hydrophilic PEO [25–28]. Copolymerized PPO improves both the ionic conductivity of PEO and has good affinity with electrodes. Regarding mechanical strength, using inorganic linkers to crosslink PEO chains and forming three-dimensional (3D) frameworks for SPEs constitute an ideal strategy for strengthening SPEs [20,29–32]. The aforementioned structural designs suggest that a 3D P(EO-co-PO) framework is promising for use in room-temperature solid-state LIBs. In this study, we used a linear P(EO-co-PO) with amino ends as the host polymer (Scheme 1a). The presence of PPO typically suppresses the crystallization tendency of PEO and improves the mobility of the poly mer chains [25–27]. Inorganic polyhedral oligomeric silsesquioxane (POSS), which comprises a Si–O framed cage and eight tentacles with epoxy ends (Scheme 1a), was used to interconnect the P(EO-co-PO) polymer chains. Scheme 1b displays a 3D radial network formed through this interconnection. The networked P(EO-co-PO) was incorporated with a lithium bis(trifluoromethanesulfonyl)imide to form a networked
No.
Polymeric structure of SPEs
Conductivity (S cm 1)
1
Cross-linked PEGDAa
8.9 � 10
5
2
Sandwich-like PPCb
2.2 � 10
4
3
PCL -SN with PAN
4.0 � 10
4
4
Organic/inorganic hybrid of PEGMAf MOFg-PEOh composite
1.1 � 10
4
4.3 � 10
5
Cross-linked PEAi and PEdAj blend Si-doped PEGk
1.2 � 10
4
1.2 � 10
4
8
Cellulose-supported PEO and PCAl
1.3 � 10
5
9
Networked P(EO-coPO)m
1.1 � 10
4
5
6 7
c
d
e
Capacity (mA h g 1)
Ref.
115 @ 0.1C (RT) 80 @ 0.2C (RT) 140 @ 0.1C (RT) 116 @ 0.5C (RT) 101 @ 1C (RT) 137 @ 0.5C (25 � C) 140 @ 0.2C (28 � C) 80 @ 1C (28 � C) 110 @ 0.2C (30 � C) 102 @ 0.5C (30 � C) 78 @ 1C (30 � C) 104 @ 0.03C (25 � C) 49 @ 0.1C (25 � C) 160 @ 0.1C (25 � C) 159 @ 0.2C (25 � C) 157 @ 0.3C (25 � C) 153 @ 0.5C (25 � C) 137 @ 1C (25 � C)
[15] [17] [16] [14] [13]
[12] [9]
[11]
This work
RT - Room Temperature. a poly(ethylene glycol) diglycidyl ether. b Poly(propylene carbonate). c Poly(ε-caprolactone). d Succinonitrile. e Poly(acrylonitrile). f Poly(ethylene glycol) methyl ether methacrylate. g Metal-organic framework. h Poly(ethylene oxide). i Polyetheramine. j Polyetherdiamine. k Poly(ethylene glycol). l Poly(cyano acrylate). m Poly(ethylene oxide-co-polypropylene oxide).
SPE (N-SPE). In the N-SPE, the ether groups formed continuous path ways for Liþ transport [20,24,29–31]. Scheme 1b presents that the Liþ ions traveled (through polymeric segmental motions) in the straightened radial polymer chains of the N-SPE [19,28,33]. The POSS hubs were evenly distributed in the N-SPE because of the small POSS size (approximately 1.5 nm). By contrast, a linear SPE (L-SPE, i.e., the as-received P(EO-co-PO) incorporated with LiTFSI without 3D networking (Scheme 1c) comprised intertwined polymer chains that tended to impede the transport of Liþ ions. The all-solid-state N-SPE exhibited high thermal stability and a wide electrochemical window of 5.4 V (vs. Li/Liþ). A battery was assembled using a free-standing N-SPE film, which was inserted between a Li-metal anode and a LiFePO4 cathode; the assembled battery delivered capacity levels of 160 and 137 mAh g 1 at 0.1 and 1 C-rates, respectively, at room temperature and exhibited high charge–discharge cycling stability. This battery was determined to outperform reported SPE LIBs containing no solvent, oligomers, or semisolids (e.g., succinonitrile) [8–10]. The pre sent study provides the foundation for designing all-solid-state 2
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
Scheme 1. (a) Schematic illustration of the chemical configurations of the P(EO-co-PO) polymer chain with amino ends and a POSS cage exhibiting eight tentacles with epoxy ends. (b) Conceptual illustration of Liþ ion transport in N-SPE, in which the P(EO-co-PO) chains are straightened by the POSS hubs. (c) Liþ ion transport in L-SPE that comprises intertwined polymer chains.
PEO-based polymer electrolytes that can be used for high-rate LIBs at room temperature. The free-standing feature of the N-SPE enables the achievement of scalable LIB assembly for industrial application.
which were roll-pressed to improve the contact between materials. The loading of LiFePO4 was ~2 mg cm 2 and the thickness of the electrode material was approximately 60 μm. The Li|N-SPE|LiFePO4 battery was assembled by sandwiching the free-standing N-SPE membrane between the Li-metal foil and LiFePO4 cathode and then sealed in a coin cell. All batteries were stored in an oven at 60 � C for 24 h to enhance the adhesion between the electrodes and electrolyte.
2. Experimental section 2.1. Materials The POSS with an average molecular weight of 1337 g mol 1 (EP0409, Hybrid, USA), P(EO-co-PO) (O,O0 -bis(2-aminopropyl) poly propylene glycol-block-polyethylene glycol-block-polypropylene glycol, with an average molecular weight of 2000 g mol 1, Aldrich, USA), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; Aldrich, USA), polyvinylidene fluoride with an average molecular weight of 534 000 g mol 1 (PVdF; Aldrich, USA), tetrahydrofuran (Aldrich, USA), 1-methyl2-pyrrolidinone (Alfa Aesar, USA), carbon black (Taiwan Maxwave Co., Taiwan), KS4 (Taiwan Maxwave Co., Taiwan) and Lithium iron phos phate (BTR New Energy Material, China) were used.
2.4. Analysis and measurements The surface of the N-SPE was analyzed using scanning electron mi croscopy (SEM; JOEL JSM-6700F, Japan), accompanied by an energy dispersive X-ray spectrometer (Oxford INCA400, Japan) for elemental analysis. Raman spectra of the membranes were recorded using a Bay spec Raman spectrometer (USA) with a laser line of 780 nm and reso lution of 4 cm 1 at room temperature. The Gaussian function was used to deconvolute bands of the Raman spectra into constituent peaks. The melting points (Tm) and glass transition temperature (Tg) of the polymer electrolytes were analyzed by Differential scanning calorimetry (DSC; Shimadzu, DSC-60, Japan) at a heating rate of 10 � C min 1. Thermog ravimetric analysis (TGA; PerkinElmer, TGA-7, USA) of the N-SPE was performed from room temperature to 800 � C at a ramp of 10 � C min 1. The ionic conductivity of the N-SPE was analyzed using AC impedance spectroscopy (Zahner-Elecktrik IM6e, Germany) at various temperatures (25–60 � C). The N-SPE membrane was sandwiched between the two stainless-steel (SS) electrodes for the impedance measurements operated at 5 mV within a frequency range of 0.1 Hz–100 kHz. Linear potential scans on SS|N-SPE|Li at 1 mV s 1 were used to analyze the electro chemical stability of the N-SPE. Galvanostatic charge discharge of the Li|N-SPE|LiFePO4 battery was performed between 2.5 and 4.0 V using a battery test equipment (Acutech System BAT-750, Taiwan). All elec trochemical measurements were operated at 25 � C.
2.2. Preparation of N-SPE We dissolved POSS and P(EO-co-PO) (at a molar ratio of 1:10, an optimized value for fast ion transport) in THF and then thermally treated the solution at 60 � C for 4 h to link the POSS and P(EO-co-PO) chains for forming networked P(EO-co-PO). With this dissolution-and-linking process, POSS can be uniformly distributed in the N-SPE. The LiTFSI salt was added to the solution at a Liþ:EO molar ratio of 1:15 with continuous stirring for 24 h. The resultant solution was spread on a Teflon dish for evacuation at 90 � C for THF removal. A free-standing NSPE of approximately 70 μm thick was obtained after the solvent removal. 2.3. Electrode synthesis and battery assembly
3. Results and discussion
The electrode slurry is prepared using 70 wt% of active material (LiFePO4), 15 wt% of binder (N-SPE and PVdF at 2:1), 15 wt% of con ducting agent (super-P and KS4 at 2:1), and NMP used as solvent. The prepared homogenous slurry was casted on aluminum foil using doctor blade technique and the coated foil was vacuumed at 90 � C for 12 h to remove NMP. The coated foil was then punched into 1.327-cm2 discs,
3.1. Physical and chemical properties of SPE Fig. S1a displays the X-ray diffraction (XRD) patterns of the net worked and as-received P(EO-co-PO) polymer films that served as the polymer hosts of the N-SPE and L-SPE, respectively. Without 3
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
Fig. 1. Photograph of the free-standing N-SPE membrane.
Fig. 3. Raman spectra for TFSI anion vibration in the regime of 725–760 cm 1 for different electrolytes at 25 � C: (a) N-SPE and (b) L-SPE. The inset of panels (a) and (b) depict the configurations of cis- and trans-TFSI anions, respectively.
assembled batteries. Networking through POSS reinforced the me chanical strength of the P(EO-co-PO). Fig. 1 depicts the photograph of the N-SPE membrane, which comprised the networked polymer and LiTFSI. The membrane was determined to be flexible, transparent, and homogeneous and exhibited dimensional stability. The flexible feature of the N-SPE membrane can enable its use in batteries of diverse shapes and configurations. Fig. S1b presents the SEM analysis of the N-SPE membrane. The image reveals the rugged surface of the membrane; the accompanying elemental Si mapping indicates a homogeneous distri bution of POSS in the membrane. Fig. 2a illustrates the DSC profiles of the as-received P(EO-co-PO) polymer, L-SPE, and N-SPE; the DSC process was performed over the temperature range of 100 to 200 � C. The as-received polymer exhibi ted a strong endothermic peak for melting at a temperature (i.e., Tm) of approximately 39 � C, indicating a high crystallization tendency of P(EOco-PO). The Tg occurred at approximately 61 � C, revealing the pres ence of amorphous zones in the as-received P(EO-co-PO). After the asreceived polymer was incorporated with LiTFSI, the resulting L-SPE did not present a Tm in the DSC profile because the lithium salt deteri orated the ordering of the polymer chains. The L-SPE exhibited a Tg of 25 � C, which is similar to the value reported for PEO–LiTFSI solid electrolyte systems [37]. The added lithium salt coordinated with the polymer to retard the motion of the polymer chains, thereby resulting in a high Tg. When networked using the POSS hubs, the N-SPE exhibited a considerably lower Tg of 43 � C than did the L-SPE (Fig. 2a). The network configuration of the N-SPE reduced the attractive interaction between chains, thereby increasing the segmental mobility of the polymer chains and lowering the Tg. Fig. 2b illustrates the TGA profile of the N-SPE. The profile of the LSPE was similar to that of the N-SPE. According to the profile in Fig. 2b, the N-SPE exhibited an abrupt loss in weight at ~350 � C due to the thermal decomposition of the ether linkages [38,39]. Compared with the thermal stability of PEO-based SPEs that have a decomposition temperature of ~300 � C [12,40], the superior thermal stability of the P (EO-co-PO)-based SPEs (i.e., N-SPE and L-SPE) suggests that the PO units strengthen the polymer chains. The inset of Fig. 2b displays the focused
Fig. 2. Thermal analysis of the polymer and SPEs. (a) DSC profiles of the asreceived P(EO-co-PO), L-SPE, and N-SPE. (b) TGA profile of the N-SPE; the inset shows the focused profile in the temperature range of 30–95 � C.
networking, the as-received P(EO-co-PO) exhibited diffraction peaks of crystallized PEO in the 2θ range of 15� –30� [34,35]. After being sub jected to crosslinking with POSS, the networked P(EO-co-PO) did not exhibit any diffraction peaks in the XRD pattern. This result indicates that POSS networked the P(EO-co-PO) chains to suppress the crystalli zation of PEO. Amorphous characteristics are beneficial for ion transport in an SPE [36]. The N-SPE and L-SPE were produced by introducing the LiTFSI salt into the networked and as-received P(EO-co-PO) at an ethylene oxide (EO)/Li ratio of 15/1. The as-received P(EO-co-PO) was soft and did not exhibit sufficient mechanical strength to ensure the dimensional integrity of the 4
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
3.2. Electrochemical properties of SPE The temperature dependence of Liþ-ion transport in SPEs can be simulated using two models: the Arrhenius model and Vogel–Tammann–Fulcher (VTF) model [43,44]. The Arrhenius model predicts the ion transport through hopping in a polymer matrix, whereas the VTF model predicts the transport associated with segmental motions of a polymer. Fig. 4a shows the temperature (T; in K) dependence of N-SPE conductivity (σ) according to the Arrhenius model. The σ values were determined from the AC impedance spectra of the N-SPE that was inserted between two stainless-steel foils (Fig. S2). The N-SPE had a room-temperature (25 � C) conductivity of 1.1 � 10 4 S cm 1, which is higher than those of reported PEO-based SPEs (~10 5 S cm 1 or lower) [13,45–48]. The high conductivity of the N-SPE can be attributed to the less restricted polymer chain motion (according the DSC analysis) and the higher degree of salt dissociation (according to the Raman analysis). Fig. 4 reveals that the Arrhenius model did not accurately simulate the temperature dependence of the conductivities of the N-SPE. Fig. S3 shows the temperature dependence of N-SPE conductivity according to the VTF model, � � Ea 1 σ ¼ A0 T 2 exp (1) RðT T0 Þ where A0 is a constant proportional to the number of carrier ions, Ea is the pseudo-activation energy related to the motion of the polymer segmental mobility, T0 is the ideal glass transition temperature, and R is the gas constant. The linear fit displayed in Fig. S2 indicates that the segmental motions of the polymer chains govern ion mobility [28,49]. The Ea value calculated for the ionic conductivity of the N-SPE was 3.5 kJ mol 1 (or 0.037 eV), which is lower than that of PEO-based SPEs (~0.5 eV) [46]. The low Ea value of the N-SPE indicates that the established POSS networking effectively facilitated the thermal motion of the polymer chains to expedite ion transport [50,51]. We focus on the performance of the N-SPE in the following discussions because the N-SPE exhibited superior properties to the L-SPE and other reported SPEs in LIB applications [29,36,52,53]. The Liþ ion transference number (tLiþ) of the N-SPE was determined through polarization of a Li|N-SPE|Li cell. The tLiþ value was calculated according to the following Bruce–Vincent equation [54]:
Fig. 4. (a) Temperature (T) dependence of N-SPE conductivity (σ) in the temperature of 25–60 � C according to the Arrhenius model. (b) Linear sweep voltammogram of a cell assembled by inserting the N-SPE film between a working stainless steel electrode and a Li-metal counter electrode at 25 � C with a scan rate of 5 mV s 1.
TGA profile of the N-SPE in the range of 30–95 � C. The solvent used in the N-SPE synthesis was tetrahydrofuran, which has a boiling point of 66 � C and has a low dielectric constant of 7.6. The TGA weight loss within 30–95 � C was approximately 0.7%, indicating an extremely low solvent content and thus a negligible contribution of solvent molecules to the ion transport in the N-SPE. The minimal weight loss at tempera tures within 100–351 � C might result from volatilization of organic impurities contained in the raw materials for the N-SPE. Fig. 3 shows a comparison of the Raman spectra of the N-SPE and LSPE in the wavenumber range of 725–760 cm 1, which corresponds to the expansion–contraction mode of TFSI anions [24]. The signal in this range comprises peaks of three TFSI conformational states: two free TFSI states in cis (738 cm 1) and trans (742 cm 1) conformations and one Liþ-associated TFSI (748 cm 1) state. The Gaussian function was used to deconvolute the Raman spectra into their constituent peaks. The fractions of Liþ-associated TFSI in the entire TFSI population were 7.6% and 18% for the N-SPE and L-SPE, respectively, indicating that the degree of Liþ association with TFSI anions was lower in the N-SPE than it was in the L-SPE. This result signifies that the POSS hubs in the N-SPE may have provided Lewis acid–base interaction sites to facilitate lithium salt dissociation [41]. We anticipate that the Si4þ sites on the POSS served as the Lewis acid to attract TFSI anions and that the ether groups in the polymer chains attracted Liþ ions and facilitated the transport of Liþ along the polymer chain through segmental motion. Moreover, as revealed in Fig. 3, the content of the free TFSI of the N-SPE was high in the cis conformation (the inset of Fig. 3a), which has a smaller size than that of the trans conformation (the inset of Fig. 3b) and has been a favored conformation for immobilization in a crystalline framework [42]. The high cis-TFSI content of the N-SPE indicates that the free TFSI anions were immobilized in proximity to the POSS hubs, possibly due to the attraction by the Si4þ sites. The 3D networking along with anion immobilization caused by the POSS hubs in the N-SPE was determined to be advantageous for the transport of Liþ cations.
tLiþ ¼
ISS ðΔVDC I0 Rint;0 Þ I0 ðΔVDC ISS Rint;ss Þ
(2)
where I0 and Iss are the initial and steady-state currents respectively, under polarization at a low DC voltage (VDC) of 5 mV (Fig. S4a). The Iss value was determined when the current variation rate was lower than 0.1 μA min 1. Rint,0 and Rint,ss are the initial and steady-state resistances respectively, that are associated with charge transfer at the Li-metal interfaces and were determined by conducting AC impedance analysis (Fig. S4b). The tLiþ value of the N-SPE was determined to be 0.62, which is considerably higher than those of Liþ–SPE systems (generally within 0.15–0.3) [55,56]. The low tLiþ values of Liþ–SPEs can be attributed to the severe tangling of polymer chains; the segmental motion of polymer chains constitutes the primary mechanism for transporting Liþ ions in SPEs [57]. In the present study, the high tLiþ value of the N-SPE can be attributed to the presence of the POSS hubs and hydrophobic methyl side chains that straightened the intertwined polymer chains to facilitate Liþ ion transport in the networked framework (Scheme 1). Moreover, the Raman analysis (Fig. 3) indicated that the TFSI anions might be attracted by the Si4þ sites on the POSS hubs to impede anion transport. Previous studies have reported that Lewis acid sites not only help lithium salt dissociation but also provide additional Liþ transport channels to improve the tLiþ value [58]. High electrochemical stability is an essential feature of high-energy LIBs. However, studies have reported that PEO-based SPEs ruptured at potentials higher than 4.3 V (vs. Liþ/Li) and that the contained salt 5
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
value), thereby suppressing the decomposition of the ether linkages in the polymer and TFSI anions at high voltages. 3.3. Performance of the all-solid-state battery We used a free-standing N-SPE film (70 μm), LiFePO4 cathode, and Li-metal anode to assemble a Li|N-SPE|LiFePO4 battery. In the battery, a mixture of polyvinylidene fluoride and the N-SPE (at a mass ratio of 1:2) was used as the binder for casting the LiFePO4 cathode. Using the N-SPEcontaining binder improved the connection between the solid electro lyte and LiFePO4 powder. Scheme 2 presents the configuration of the Li| N-SPE|LiFePO4 battery that was assembled using the free-standing NSPE film. With this battery design, the external region of the freestanding film was well connected to the cathode film through the NSPE embedded in the cathode and the center zone of the free-standing film maintained its mechanical integrity and firmly partitioned the cathode and anode. The excellent affinity between the N-SPE species in the cathode and free-standing film ensured the swift transport of Liþ ions across the electrolyte–cathode interface. Scheme 2 demonstrates the feasibility of the roll-to-roll assembly of the Li|N-SPE|LiFePO4 battery by using the proposed free-standing N-SPE. Fig. 5a presents the room-temperature (25 � C) galvanostatic char ge discharge profiles of the Li|N-SPE|LiFePO4 battery at various Crates, which was charged to 4.0 V at 0.1 C-rate (at a current density of approximately 30 μA cm 2) and subsequently discharged to 2.5 V at various C-rates. We determined the battery C-rates according to the capacity of the LiFePO4 cathode, under the assumption that the maximum achievable capacity of this battery system was 170 mAh g 1 (theoretical capacity of LiFePO4). As shown in Fig. 5a, the Li|N-SPE| LiFePO4 battery delivered discharge capacities of 160, 159, 157, 153, and 137 mAh g 1 at 0.1, 0.2, 0.3, 0.5 and 1 C-rates, respectively. The capacities achieved at room temperature were high and superior to those reported for LIBs assembled using all-solid-state SPEs without any solvent, oligomer, or semisolid additives [12,15,61]. The cyclic vol tammogram of the Li|N-SPE|LiFePO4 battery was presented in Fig. S5, showing the capability of the N-SPE in facilitating Liþ-ion transport. Fig. 5b illustrates the charge discharge cycling capacities of the Li| N-SPE|LiFePO4 battery at 0.1 and 0.2 C-rates for 50 cycles. The battery exhibited high capacity retentions of 95% and 92% at 0.1 and 0.2 Crates, respectively, with a Coulombic efficiency of approximately 100%. The admirable performance of this battery can be attributed to the intimate contact between the N-SPE and electrodes through the PPO methyl side chain as well as to the efficient Liþ pathways created in the 3D SPE network that exhibited high polymer chain mobility, a high degree of salt dissociation, and TFSI anion immobilization [12,29,36]. Fig. S6 presents the result of cycling at 0.3C, revealing a high capacity retention of 75% after 100 cycles with approximately 100% of Coulombic efficiency throughout the cycling. In addition to the superior performance, the simplicity of electrolyte synthesis and battery assem bly demonstrates the high readiness of the N-SPE for use in industrial-scale production processes [29,30,62]. The rate capability of the Li|N-SPE|LiFePO4 battery was demon strated by subjecting it to a repeated galvanostatic charge discharge test between 2.5 and 4.0 V (vs. Liþ/Li) at varying C-rates, as presented in Fig. S7. The charge discharge test was conducted from 0.1 to 1 C-rate and then back to 0.1 C-rate. Similar to the results shown in Fig. 5a, the capacity of the battery decreased with the C-rate. The Coulombic effi ciency was maintained at approximately 100% in the entire test. The capacity was returned to its original value when the battery operation was back to the lowest C-rate (i.e., back to 160 mAh g 1 at 0.1 C-rate), indicating excellent reversibility and stability of the battery under conditions of varying storage rates. We conducted lithium stripping–plating tests on the N-SPE by using cells comprising two Li-metal electrodes that sandwiched the N-SPE. Fig. 6 displays the voltage–time curves obtained from the test. In the curve, each half-wave represents the voltage response to the applied
Scheme 2. Schematic for the roll-to-roll assembly of a Li|N-SPE|LiFePO4 bat tery using the free-standing N-SPE film. The focused configuration of the resulting battery depicts POSS-networked polymer framework in the N-SPE and excellent connection between the N-SPE species in the cathode and freestanding film.
Fig. 5. Electrochemical performance of the Li|N-SPE|LiFePO4 battery at 25 � C. (a) Galvanostatic charge–discharge profiles of the battery at different current densities. (b) Variations of the capacity and Coulombic efficiency in the char ge discharge cycling at 0.1 and 0.2 C-rates. The charge-discharge was operated between 2.5 and 4.0 V and the C rates were defined on the basis of the theo ritical capacity of LiFePO4 (170 mAh g 1).
(LiTFSI) decomposed at 5.1 V (vs. Liþ/Li) [59,60]. These electro chemical instabilities are detrimental to the high-energy demand of LIBs. Fig. 4b displays the linear sweep voltammogram of a cell assem bled by inserting the N-SPE film between an SS electrode and a Li-metal counter at 25 � C. As revealed in the voltammogram, the current profile did not abruptly rise until the applied voltage sweep reached approxi mately 5.4 V (vs. Liþ/Li). The high electrochemical stability of the N-SPE can be attributed to the affinity of the methyl side chains of PPO to the electrode and the immobilization of TFSI (reflected by the high tLiþ 6
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment The authors acknowledge the support of Ministry of Science and Technology in Taiwan through grant numbers 107-2221-E-006-111MY3, 107-2221-E-006-110-MY3, 108-3116-F-006-012-CC1, and 1082622-8-006-014. Authors also acknowledge the support from the Hier archical Green-Energy Materials (Hi-GEM) Research Center and the Center of Applied Nanomedicine at National Cheng Kung University from The Featured Areas Research Center Program within the frame work of the Higher Education Sprout Project by the Ministry of Educa tion and the Ministry of Science and Technology (107-3017-E-006-003). Fig. 6. Voltage-time profile for lithium stripping-plating of a Li|N-SPE|Li cell, where each half-wave is the voltage response to the applied current of 0.1 mA cm 2 in 1 h stripping or plating.
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.jpowsour.2019.227518.
current of 0.1 mA cm 2 during 1-h stripping–plating tests conducted to analyze the dendrite formation dynamics. The cell lifetime was deter mined by the sudden drop in the voltage profile when dendrites bridged the two electrodes to short circuit the cell. As illustrated in Fig. 6, the Li| N-SPE|Li cell had not shown the failure sign of short-circuit for over 500 h and the voltage–time profile remained stable during the entire cycling (the inset of Fig. 6). The result indicates that the strengthened 3D polymer network suppressed the piercing growth of Li dendrites, which are caused by the uneven formation of the solid electrolyte interface (SEI) layer on the Li-metal surface [63]. The SEI layer was produced during the chemical interaction between the solvent molecules and Li-metal surface [64]. In the absence of solvent molecules, the N-SPE enabled smooth plating of Li metal on the electrode surface. However, the polarization voltage was high (~0.25 V), indicating the contact between the N-SPE and Li-metal electrode needs to be improved [65, 66].
References [1] R. Chen, W. Qu, X. Guo, L. Li, F. Wu, The pursuit of solid-state electrolytes for lithium batteries: from comprehensive insight to emerging horizons, Mater. Horiz. 3 (2016) 487–516, https://doi.org/10.1039/C6MH00218H. [2] S. Chen, K. Wen, J. Fan, Y. Bando, D. Golberg, Progress and future prospects of high-voltage and high-safety electrolytes in advanced lithium batteries: from liquid to solid electrolytes, J. Mater. Chem. 6 (2018) 11631–11663, https://doi.org/ 10.1039/c8ta03358g. [3] L. Fan, S. Wei, S. Li, Q. Li, Y. Lu, Recent progress of the solid-state electrolytes for high-energy metal-based batteries, Adv. Energy Mater. 8 (2018), https://doi.org/ 10.1002/aenm.201702657, 1702657. [4] P. Hu, J. Chai, Y. Duan, Z. Liu, G. Cui, L. Chen, Progress in nitrile-based polymer electrolytes for high performance lithium batteries, J. Mater. Chem. 4 (2016) 10070–10083, https://doi.org/10.1039/c6ta02907h. [5] A.B. Puthirath, S. Patra, S. Pal, M. Manoj, A. Puthirath Balan, S. Jayalekshmi, N. N. Tharangattu, Transparent flexible lithium ion conducting solid polymer electrolyte, J. Mater. Chem. 5 (2017) 11152–11162, https://doi.org/10.1039/ c7ta02182h. [6] R. Yu, J.J. Bao, T.T. Chen, B.K. Zou, Z.Y. Wen, X.X. Guo, C.H. Chen, Solid polymer electrolyte based on thermoplastic polyurethane and its application in all-solidstate lithium ion batteries, Solid State Ion. 309 (2017) 15–21, https://doi.org/ 10.1016/j.ssi.2017.06.013. [7] A. Arya, A.L. Sharma, Polymer electrolytes for lithium ion batteries: a critical study, Ionics 23 (2017) 497–540, https://doi.org/10.1007/s11581-016-1908-6. [8] L.T.M. Le, T.D. Vo, K.H.P. Ngo, S. Okada, F. Alloin, A. Garg, P.M.L. Le, Mixing ionic liquids and ethylene carbonate as safe electrolytes for lithium-ion batteries, J. Mol. Liq. 271 (2018) 769–777, https://doi.org/10.1016/j.molliq.2018.09.068. [9] X. Ji, H. Zeng, X. Gong, F. Tsai, T. Jiang, R.K.Y. Li, H. Shi, S. Luan, D. Shi, A Sidoped flexible self-supporting comb-like polyethylene glycol copolymer (Si-PEG) film as a polymer electrolyte for an all solid-state lithium-ion battery, J. Mater. Chem. 5 (2017) 24444–24452, https://doi.org/10.1039/c7ta07741f. [10] Q. Zhang, K. Liu, F. Ding, W. Li, X. Liu, J. Zhang, Safety-reinforced succinonitrilebased electrolyte with interfacial stability for high-performance lithium batteries, ACS Appl. Mater. Interfaces 9 (2017) 29820–29828, https://doi.org/10.1021/ acsami.7b09119. [11] J. Zhang, L. Yue, P. Hu, Z. Liu, B. Qin, B. Zhang, Q. Wang, G. Ding, C. Zhang, X. Zhou, J. Yao, G. Cui, L. Chen, Taichi-inspired rigid-flexible coupling cellulosesupported solid polymer electrolyte for high-performance lithium batteries, Sci. Rep. 4 (2014) 6272, https://doi.org/10.1038/srep06272. [12] T.M. Liu, D. Saikia, S.Y. Ho, M.C. Chen, H.M. Kao, High ion-conducting solid polymer electrolytes based on blending hybrids derived from monoamine and diamine polyethers for lithium solid-state batteries, RSC Adv. 7 (2017) 20373–20383, https://doi.org/10.1039/c7ra01542a. [13] S. Suriyakumar, M. Kanagaraj, N. Angulakshmi, M. Kathiresan, K.S. Nahm, M. Walkowiak, K. Wasi� nski, P. P� ołrolniczak, A.M. Stephan, Charge-discharge studies of all-solid-state Li/LiFePO4cells with PEO-based composite electrolytes encompassing metal organic frameworks, RSC Adv. 6 (2016) 97180–97186, https://doi.org/10.1039/c6ra17962b. [14] J. Zhang, C. Ma, J. Liu, L. Chen, A. Pan, W. Wei, Solid polymer electrolyte membranes based on organic/inorganic nanocomposites with star-shaped structure for high performance lithium ion battery, J. Member. Sci. 509 (2016) 138–148, https://doi.org/10.1016/j.memsci.2016.02.049. [15] Y. Cui, X. Liang, J. Chai, Z. Cui, Q. Wang, W. He, X. Liu, Z. Liu, G. Cui, J. Feng, High performance solid polymer electrolytes for rechargeable batteries: a self-catalyzed
4. Conclusions This study demonstrated the high performance of POSS-networked P (EO-co-PO) in conveying Liþ ions in an N-SPE for LIBs. The methyl chain of PPO in the polymer suppressed polymer crystallization and improved the affinity to the electrodes, thereby promoting the mobility of Liþ ions in the electrolyte bulk and at the electrolyte-electrode interface. The cage-like POSS molecules served as hubs to incorporate the straightened P(EO-co-PO) chains, thus forming a 3D polymer network in the N-SPE. The 3D network exhibited a low Tg of 43 � C, indicating the high segmental mobility of the polymer chains. The pseudo-activation energy related to the ionic conductivity in the N-SPE was 3.5 kJ mol 1 (or 0.037 eV), confirming the low restriction of the mobility of the polymer chains. The POSS hubs not only minimized the tangling of the polymer chains to facilitate Liþ ion transport but also localized TFSI anions, likely through interaction with the contained Si4þ sites. Thus, the N-SPE exhibited an ionic conductivity of 1.1 � 10 4 S cm 1 at 25 � C and a high tLiþ of 0.62. The unique feature of our electrolyte design enabled the assembly of an all-solid-state Li|N-SPE|LiFePO4 battery by using a freestanding N-SPE membrane where the N-SPE was mixed with a binder to form the cathode film. The resulting all-solid-state battery delivered capacities of 160 and 137 mAh g 1 at 0.1 and 1 C-rates, respectively, at 25 � C along with excellent charge–discharge cycling stability. The use of the free-standing N-SPE provides the foundation to realize roll-to-roll assembly of all-solid-state LIBs in an industrial scale.
7
S.-T. Hsu et al.
[16]
[17]
[18] [19] [20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29] [30]
[31]
[32] [33] [34]
[35]
[36]
[37]
Journal of Power Sources xxx (xxxx) xxx
strategy toward facile synthesis, Adv. Sci. 4 (2017), https://doi.org/10.1002/ advs.201700174. D. Zhang, L. Zhang, K. Yang, H. Wang, C. Yu, D. Xu, B. Xu, L.M. Wang, Superior blends solid polymer electrolyte with integrated hierarchical architectures for allsolid-state lithium-ion batteries, ACS Appl. Mater. Interfaces 9 (2017) 36886–36896, https://doi.org/10.1021/acsami.7b12186. H. Yue, J. Li, Q. Wang, C. Li, J. Zhang, Q. Li, X. Li, H. Zhang, S. Yang, Sandwich-like poly(propylene carbonate)-based electrolyte for ambient-temperature solid-state lithium ion batteries, ACS Sustain. Chem. Eng. 6 (2018) 268–274, https://doi.org/ 10.1021/acssuschemeng.7b02401. M. Yang, J. Hou, Membranes in lithium ion batteries, Membranes 2 (2012) 367–383, https://doi.org/10.3390/membranes2030367. H. Choi, H.W. Kim, J.K. Ki, Y.J. Lim, Y. Kim, J.H. Ahn, Nanocomposite quasi-solidstate electrolyte for high-safety lithium batteries, Nano Res. 10 (2017) 3092–3102, https://doi.org/10.1007/s12274-017-1526-2. J. Shim, D.G. Kim, H.J. Kim, J.H. Lee, J.C. Lee, Polymer composite electrolytes having core-shell silica fillers with anion-trapping boron moiety in the shell layer for all-solid-state lithium-ion batteries, ACS Appl. Mater. Interfaces 7 (2015) 7690–7701, https://doi.org/10.1021/acsami.5b00618. J. Suk, Y.H. Lee, D.Y. Kim, D.W. Kim, S.Y. Cho, J.M. Kim, Y. Kang, Semiinterpenetrating solid polymer electrolyte based on thiol-ene cross-linker for allsolid-state lithium batteries, J. Power Sources 334 (2016) 154–161, https://doi. org/10.1016/j.jpowsour.2016.10.008. M. Nakayama, S. Wada, S. Kuroki, M. Nogami, Factors affecting cyclic durability of all-solid-state lithium polymer batteries using poly(ethylene oxide)-based solid polymer electrolytes, Energy Environ. Sci. 3 (2010) 1995–2002, https://doi.org/ 10.1039/c0ee00266f. L. Porcarelli, A.S. Shaplov, M. Salsamendi, J.R. Nair, Y.S. Vygodskii, D. Mecerreyes, C. Gerbaldi, Single-ion block copoly(ionic liquid)s as electrolytes for all-solid state lithium batteries, ACS Appl. Mater. Interfaces 8 (2016) 10350–10359, https://doi. org/10.1021/acsami.6b01973. G. Yang, C. Chanthad, H. Oh, I.A. Ayhan, Q. Wang, Organic-inorganic hybrid electrolytes from ionic liquid-functionalized octasilsesquioxane for lithium metal batteries, J. Mater. Chem. 5 (2017) 18012–18019, https://doi.org/10.1039/ c7ta04599a. D. Sygkridou, A. Rapsomanikis, E. Stathatos, Functional transparent quasi-solid state dye-sensitized solar cells made with different oligomer organic/inorganic hybrid electrolytes, Sol. Energy Mater. Sol. Cells 159 (2017) 600–607, https://doi. org/10.1016/j.solmat.2016.01.019. D. Saikia, H.Y. Wu, Y.C. Pan, C.P. Lin, K.P. Huang, K.N. Chen, G.T.K. Fey, H. M. Kao, Highly conductive and electrochemically stable plasticized blend polymer electrolytes based on PVdF-HFP and triblock copolymer PPG-PEG-PPG diamine for Li-ion batteries, J. Power Sources 196 (2011) 2826–2834, https://doi.org/ 10.1016/j.jpowsour.2010.10.096. Q. Lu, Y.B. He, Q. Yu, B. Li, Y.V. Kaneti, Y. Yao, F. Kang, Q.H. Yang, Dendrite-free, high-rate, long-life lithium metal batteries with a 3D cross-linked network polymer electrolyte, Adv. Mater. 29 (2017), https://doi.org/10.1002/adma.201604460, 1604460. S.H. Wang, Y.Y. Lin, C.Y. Teng, Y.M. Chen, P.L. Kuo, Y.L. Lee, C. Te Hsieh, H. Teng, Immobilization of anions on polymer matrices for gel electrolytes with high conductivity and stability in lithium ion batteries, ACS Appl. Mater. Interfaces 8 (2016) 14776–14787, https://doi.org/10.1021/acsami.6b01753. Q. Pan, D.M. Smith, H. Qi, S. Wang, C.Y. Li, Hybrid electrolytes with controlled network structures for lithium metal batteries, Adv. Mater. 27 (2015) 5995–6001, https://doi.org/10.1002/adma.201502059. Q. Pan, D. Barbash, D.M. Smith, H. Qi, S.E. Gleeson, C.Y. Li, Correlating electrode–electrolyte interface and battery performance in hybrid solid polymer electrolyte-based lithium metal batteries, Adv. Energy Mater. 7 (2017), https://doi. org/10.1002/aenm.201701231, 1701231. J. Shim, D.G. Kim, J.H. Lee, J.H. Baik, J.C. Lee, Synthesis and properties of organic/inorganic hybrid branched-graft copolymers and their application to solidstate electrolytes for high-temperature lithium-ion batteries, Polym. Chem. 5 (2014) 3432–3442, https://doi.org/10.1039/c4py00123k. Ji Hu, Wanhui Wang, Haiyan Peng, Mengke Guo, Yuezhan Feng, Zhigang Xue, Yunsheng Ye, Flexible Organic Inorganic hybrid solid electrolytes formed via thiol acrylate photopolymerization, Macromolecules 50 (2017) 1970–1980. Y.Y. Lin, Y.M. Chen, S.S. Hou, J.S. Jan, Y.L. Lee, H. Teng, Diode-like gel polymer electrolytes for full-cell lithium ion batteries, J. Mater. Chem. 5 (2017) 17476–17481, https://doi.org/10.1039/c7ta04886f. R. Blanga, M. Goor, L. Burstein, Y. Rosenberg, A. Gladkich, D. Logvinuk, I. Shechtman, D. Golodnitsky, The search for a solid electrolyte, as a polysulfide barrier, for lithium/sulfur batteries, J. Solid State Electrochem. 20 (2016) 3393–3404, https://doi.org/10.1007/s10008-016-3303-7. A.R. Polu, H.W. Rhee, Nanocomposite solid polymer electrolytes based on poly (ethylene oxide)/POSS-PEG (n¼13.3) hybrid nanoparticles for lithium ion batteries, J. Ind. Eng. Chem. 31 (2015) 323–329, https://doi.org/10.1016/j. jiec.2015.07.005. D. Lin, W. Liu, Y. Liu, H.R. Lee, P.C. Hsu, K. Liu, Y. Cui, High ionic conductivity of composite solid polymer electrolyte via in situ synthesis of monodispersed SiO2 nanospheres in poly(ethylene oxide), Nano Lett. 16 (2016) 459–465, https://doi. org/10.1021/acs.nanolett.5b04117. B. Cong, Y. Song, N. Ren, G. Xie, C. Tao, Y. Huang, G. Xu, J. Bao, Polyethylene glycol-based waterborne polyurethane as solid polymer electrolyte for all-solidstate lithium ion batteries, Mater. Des. 142 (2018) 221–228, https://doi.org/ 10.1016/j.matdes.2018.01.039.
[38] E. Calahorra, M. Cortazar, Thermal decomposition of poly(ethy1ene oxide), poly (methy1 methacrylate), and their mixtures by thermogravimetric method, J. Polym. Sci. Polym. Lett. Ed. 23 (1985) 257–260, https://doi.org/10.1002/ pol.1985.130230509. [39] T. Degradation, P. Oxide, P. Oxide, Thermal degradation of polyethylene oxide and polypropylene oxide, J. Polym. Sci. 36 (1959) 183–194, https://doi.org/10.1002/ pol.1959.1203613015. [40] T. Shodai, B.B. Owens, H. Ohtsuka, J.-I. Yamaki, Thermal stability of the polymer electrolyte (PEO)8LiCF3SO3, J. Electrochem. Soc. 141 (1994) 2978–2981, https:// doi.org/10.1149/1.2059268. [41] B. Chen, Q. Xu, Z. Huang, Y. Zhao, S. Chen, X. Xu, One-pot preparation of new copolymer electrolytes with tunable network structure for all-solid-state lithium battery, J. Power Sources 331 (2016) 322–331, https://doi.org/10.1016/j. jpowsour.2016.09.063. [42] F. Capitani, F. Trequattrini, O. Palumbo, A. Paolone, P. Postorino, Phase transitions of PYR14-TFSI as a function of pressure and temperature: the competition between smaller volume and lower energy conformer, J. Phys. Chem. B 120 (2016) 2921–2928, https://doi.org/10.1021/acs.jpcb.5b12667. [43] J. Souquet, Salt-polymer complexes: strong or weak electrolytes? Solid State Ion. 85 (1996) 149–157, https://doi.org/10.1016/0167-2738(96)00052-5. [44] Q. Xiao, X. Wang, W. Li, Z. Li, T. Zhang, H. Zhang, Macroporous polymer electrolytes based on PVDF/PEO- b -PMMA block copolymer blends for rechargeable lithium ion battery, J. Member. Sci. 334 (2009) 117–122, https://doi. org/10.1016/j.memsci.2009.02.018. [45] W. Wieczorek, D. Raducha, A. Zalewska, J.R. Stevens, Effect of salt concentration on the conductivity of PEO-based composite polymeric electrolytes, J. Phys. Chem. B 102 (1998) 8725–8731, https://doi.org/10.1021/jp982403f. [46] J. Gurusiddappa, W. Madhuri, R. Padma Suvarna, K. Priya Dasan, Studies on the morphology and conductivity of PEO/LiClO4, Mater. Today: SAVE Proc. 3 (2016) 1451–1459, https://doi.org/10.1016/j.matpr.2016.04.028. [47] X. Fu, D. Yu, J. Zhou, S. Li, X. Gao, Y. Han, P. Qi, X. Feng, B. Wang, Inorganic and organic hybrid solid electrolytes for lithium-ion batteries, CrystEngComm 18 (2016) 4236–4258, https://doi.org/10.1039/c6ce00171h. [48] L. Chen, Y. Li, S.P. Li, L.Z. Fan, C.W. Nan, J.B. Goodenough, PEO/garnet composite electrolytes for solid-state lithium batteries: from “ceramic-in-polymer” to “polymer-in-ceramic”, Nano Energy 46 (2018) 176–184, https://doi.org/10.1016/ j.nanoen.2017.12.037. [49] M.H. Cohen, D. Turnbull, Molecular transport in liquids and glasses, J. Chem. Phys. 31 (1959) 1164–1169, https://doi.org/10.1063/1.1730566. [50] K. Xu, Nonaqueous liquid electrolytes for lithium-based rechargeable batteries, Chem. Rev. 104 (2004) 4303–4417, https://doi.org/10.1021/cr030203g. [51] M. Klett, M. Giesecke, A. Nyman, F. Hallberg, R.W. Lindstr€ om, G. Lindbergh, I. Fur� o, Quantifying mass transport during polarization in a Li Ion battery electrolyte by in situ 7Li NMR imaging, J. Am. Chem. Soc. 134 (2012) 14654–14657, https://doi.org/10.1021/ja305461j. [52] S. Choudhury, R. Mangal, A. Agrawal, L.A. Archer, A highly reversible roomtemperature lithium metal battery based on crosslinked hairy nanoparticles, Nat. Commun. 6 (2015) 10101, https://doi.org/10.1038/ncomms10101. [53] Z. Wang, S. Wang, A. Wang, X. Liu, J. Chen, Q. Zeng, L. Zhang, W. Liu, L. Zhang, Covalently linked metal-organic framework (MOF)-polymer all-solid-state electrolyte membranes for room temperature high performance lithium batteries, J. Mater. Chem. 6 (2018) 17227–17234, https://doi.org/10.1039/c8ta05642k. [54] J. Evans, C.A. Vincent, P.G. Bruce, Electrochemical measurement of transference numbers in polymer electrolytes, Polymer 28 (1987) 2324–2328, https://doi.org/ 10.1016/0032-3861(87)90394-6. [55] M.M. Hiller, M. Joost, H.J. Gores, S. Passerini, H.D. Wiemh€ ofer, The influence of interface polarization on the determination of lithium transference numbers of salt in polyethylene oxide electrolytes, Electrochim. Acta 114 (2013) 21–29, https:// doi.org/10.1016/j.electacta.2013.09.138. [56] P.G. Bruce, M.T. Hardgrave, C.A. Vincent, The determination of transference numbers in solid polymer electrolytes using the Hittorf method, Solid State Ion. 53–56 (1992) 1087–1094, https://doi.org/10.1016/0167-2738(92)90295-Z. [57] S. Srivastava, J.L. Schaefer, Z. Yang, Z. Tu, L.A. Archer, 25th Anniversary article: polymer-particle composites: phase stability and applications in electrochemical energy storage, Adv. Mater. 26 (2014) 201–234, https://doi.org/10.1002/ adma.201303070. [58] M. Grzelczak, J. Vermant, E.M. Furst, L.M. Liz-marza, Directed self-assembly of nanoparticles, ACS Nano 4 (2010) 3591–3605, https://doi.org/10.1021/ nn100869j. [59] Y. Zhao, Z. Huang, S. Chen, B. Chen, J. Yang, Q. Zhang, F. Ding, Y. Chen, X. Xu, A promising PEO/LAGP hybrid electrolyte prepared by a simple method for allsolid-state lithium batteries, Solid State Ion. 295 (2016) 65–71, https://doi.org/ 10.1016/j.ssi.2016.07.013. [60] A. ling Zhang, F. yu Cao, G. zhou Na, S. Wang, S. xi Li, J. chi Liu, A novel PEObased blends solid polymer electrolytes doping liquid crystalline ionomers, Ionics 22 (2016) 2103–2112, https://doi.org/10.1007/s11581-016-1732-z. [61] K. Xu, Electrolytes and interphases in Li-ion batteries and beyond, Chem. Rev. 114 (2014) 11503–11618, https://doi.org/10.1021/cr500003w. [62] Y.C. Jung, M.S. Park, D.H. Kim, M. Ue, A. Eftekhari, D.W. Kim, Room-temperature performance of poly(ethylene ether carbonate)-based solid polymer electrolytes for all-solid-state lithium batteries, Sci. Rep. 7 (2017), https://doi.org/10.1038/ s41598-017-17697-0, 17482. [63] Y.M. Chen, S.T. Hsu, Y.H. Tseng, T.F. Yeh, S.S. Hou, J.S. Jan, Y.L. Lee, H. Teng, Minimization of ion–solvent clusters in gel electrolytes containing graphene oxide quantum dots for lithium-ion batteries, Small 14 (2018), https://doi.org/10.1002/ smll.201703571, 1703571.
8
S.-T. Hsu et al.
Journal of Power Sources xxx (xxxx) xxx
[64] D. Lin, Y. Liu, Y. Cui, Reviving the lithium metal anode for high-energy batteries, Nat. Nanotechnol. 12 (2017) 194–206, https://doi.org/10.1038/nnano.2017.16. [65] Z. Wang, M. Zhu, Z. Peia, Q. Xue, H. Li, Y. Huang, C. Zhi, Polymers for supercapacitors: boosting the development of the flexible and wearable energy storage, Mater. Sci. Eng. R. in press. doi:10.1016/j.mser.2019.100520.
[66] F. Mo, G. Liang, Z. Huang, H. Li, D. Wang, C. Zhi, Adv. Mater. 31 (2019), https:// doi.org/10.1002/adma.201902151, 1902151.
9