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Enhanced electrolyte performance by adopting Zwitterionic lithium-silica sulfobetaine silane as electrolyte additive for lithium-ion batteries
Materials Chemistry and Physics 243 (2020) 122577
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Enhanced electrolyte performance by adopting Zwitterionic lithium-silica sulfobetaine silane as electrolyte additive for lithium-ion batteries Isheunesu Phiri a, Chris Yeajoon Bon a, Manasi Mwemezi a, Louis Hamenu b, Alfred Madzvamuse c, Jeong Ho Park a, Kwang Se Lee d, Jang Myoun Ko a, *, Yunfeng Lu e a
Department of Applied Chemistry & Biotechnology, Hanbat National University, 125 Dongseo-daero, Deokmyeong-dong, Yuseong-gu, Daejeon, South Korea Department of Chemistry School of Physical and Mathematical Sciences, College of Basic and Applied Sciences University of Ghana, Legon, Ghana Department of Chemistry, University of Zimbabwe, PO Box MP167, Mount Pleasant, Harare, Zimbabwe d Kyungnam College of Information & Technology, Department of Advanced Materials & Chemical Engineering, 45 Jurye-ro, Sasang-gu, Busan, South Korea e UCLA-ENN Center for Nanomedicines and Energy Conversion, UCLA-HK Center for Graphene Technology and Energy Storage, UCLA-Dynavolt Research Center, University of California, Los Angeles, 90095, CA, USA b c
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
� Zwitterion sulfobetaine silane is syn thesized and grafted onto silica nanoparticles. � The additive enhances ionic conductiv ity and electrochemical stability. � Full cells have a stable cycle perfor mance at 1C over 200 cycles.
A R T I C L E I N F O
A B S T R A C T
Keywords: Silica Zwitterion Ionic conductivity Solid electrolyte interface
Zwitterionic lithium-silica sulfobetaine silane is fabricated by first synthesizing zwitterion sulfobetaine silane, grafting it onto hydrophilic silica to form silica sulfobetaine silane, and then lithiating the silica sulfobetaine silane. The resultant lithium-silica sulfobetaine silane additive is used as a liquid electrolyte additive in lithiumion batteries with varying weight percentages in 1 M LiPF6 (ethylene carbonate/dimethyl carbonate ¼ 1:1). The electrolytes with the lithium-silica sulfobetaine silane shows higher ionic conductivities (1.92 � 10 2 S cm 1 at RT and 1.62 � 10 3 S cm 1 at 20 � C) and greater electrochemical stability (anodic limit at ~5.5 V vs. Li/Liþ ) than the pure electrolyte (anodic limit at ~4.6 V vs. Li/Liþ ). The discharge capacity of the lithium nickel cobalt manganese oxide/graphite cell is improved at higher C-rates with the addition of lithium-silica sulfobetaine silane due to increased ionic conductivity. The lithium nickel cobalt manganese oxide/graphite cells with the lithium-silica sulfobetaine silane additive also show stable cycling performance. These findings warrant the use of lithium-silica sulfobetaine silane as an electrolyte additive in lithium-ion batteries.
* Corresponding author. E-mail addresses: [email protected] (K.S. Lee), [email protected] (J.M. Ko). https://doi.org/10.1016/j.matchemphys.2019.122577 Received 3 September 2019; Received in revised form 14 December 2019; Accepted 23 December 2019 Available online 25 December 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
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Fig. 1. Schematic representation of the synthesis of the zwitterion SB, grafting SB onto OX50, and lithiation to form Li–SiSB.
1. Introduction
capability and formation of a stable solid electrolyte interface (SEI) [36] that promotes (i) intercalation and deintercalation of Liþ ions at extreme potentials, (ii) a more stable cycle life, and (iii) improved power and energy density and also improved battery safety [37–39]. A thinner but stable SEI would be ideal for good battery performance and Bryne and coworkers showed that the use of zwitterion promoted to formation of such in an ionic liquid (IL) based electrolyte because the zwitterions improved the migration of Liþ ions to the graphite electrode which reduced the co-intercalation of organic species [40]. Therefore, zwit terions can be used electrolyte additives because they enable the dissociation of salts, formation of a stable SEI formation and enhanced migration of dissociated ions [23]. In this study, lithium nickel manganese cobalt oxide (NCM) was used as the cathode due to its high capacity, but the major drawback of using NCM is its subsequent capacity fading over many cycles [41]. There are many reports on the application of zwitterions in LIBs; however, most of the reports are concentrated on the ionic conductivity of zwitterion s/lithium salt mixtures or ion–conductive polyzwitterions or zwitterions as additives in SPEs [23,32]. The additive effect of zwitterions in car bonate–based liquid electrolyte systems for LIBs is far less studied. Therefore, in this work, we fabricated a zwitterionic salt with high ionic conductivity, wide electrochemical window, and cycling stability as an additive for carbonate–based liquid electrolytes in LIBs. Herein, we grafted the sulfobetaine zwitterion onto silica nanoparticle and then lithiated it. The zwitterionic salt obtained was investigated as an elec trolyte additive to enhance the electrochemical performance of a LiPF6 based electrolyte with the hope of improving the rate performance and thermal stability of NCM/graphite cells.
The demand for lithium-ion batteries (LIBs) has been on the rise due to the ever increasing demand for various electronic devices e.g. electric vehicles and other portable electronic devices [1–3]. The three main components of a LIB are cathode, anode and an electrolyte [4]. In order to improve the performance of LIBs, studies have been done to improve the electrode materials, separator material and well as electrolytes [5–7]. Of particular interest is the use of additives to suppress dendrite formation [8–12] and also improve electrolyte performance e.g. ceramic materials such as silica nanoparticles have been used in carbonate based electrolytes, and other additives include zwitterions which have been used in ionic liquid, gel and solid electrolytes [13–22]. Zwitterions are interesting because of their chemistry where a cation end and an anion end (ion pairs) are covalently bound together in one molecule [23,24]. This isoionic characteristic results in zwitterions having a large molec ular dipole moment [25,26] which enables zwitterions to disassociate salts in electrolytes resulting in an increased ionic conductivity in these electrolyte systems [21,27,28]. Them being isoionic also makes zwit terions immobile in solutions when a potential is applied hence they cannot be charge carries but this in turn promotes target–ion migration as observed and reported by Ohno et al. [23,29–33], however a pure zwitterion has a very low ionic conductivity [29]. The zwitterions mainly used as electrolyte additives have the sulfonate group (SO3 Þ and it has been previously reported that SO3 are good exchange sites for Liþ ions because of the easiness to associate and dissociate between the SO3 group and Liþ ions [27,34,35]. Zwitterionic additives have also been shown to increase rate 2
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Fig. 2. Characterization of OX50 and Li–SiSB: (a) XPS analysis, (b) FT-IR analysis, and (c) TGA analysis. SEM and digital image (insert) for (d) OX50 and (e) Li–SiSB.
2. Experimental
The white precipitate was filtered off and repeatedly washed with anhydrous acetone. The product was dried at 70 � C under vacuum for 24 h and stored under argon. Fig. 1 shows the scheme for the synthesis process.
2.1. Synthesis of zwitterion sulfobetaine silane N,N-Dimethylaminopropyl) trimethoxysilane (�98.0%, Sigma Aldrich) (5 g, 24 mmol) was added to 1,3-propanesultone (98%, Sigma Aldrich) (3 g, 25 mmol) in anhydrous acetone (�99.5%, Sigma Aldrich) (25 mL) under argon and stirred vigorously for 6 h at room temperature.
2.2. Grafting of zwitterion to silica nanoparticles SB was dissolved in a small amount of H2O and added dropwise with 3
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vigorous stirring to a 10 wt% silica nanoparticle solution previously heated to 60 � C (�5 � C). The solution pH was adjusted to 3.5, using dilute HCl (35.0–37.0%, Duksan reagents). The reaction mixture was then stirred under reflux for 2 h. The solution was then centrifuged at 7000 rpm (Avant J-25, Beckman Coulter centrifuge) for 20 min. The centrifugate was washed twice by dispersing again in water and centrifuging again. The final centrifugate was collected and dried under vacuum at 60 � C for 48 h.
anode electrodes were composed of LiNi0.4Co0.2Mn0.4O2 (NCM-424, Ecopro, Korea) and graphite (Kokam Co.) (93 wt%) as active materials, respectively, 4 wt% Super P (Imerys, Switzerland) as a conductive ad ditive, and 3 wt% polyvinylidene fluoride (Kreha, Japan, Mw � 350,000) as a polymeric binder in N-methyl-2-pyrrolidone (NMP, Sigma Aldrich) as a dispersing agent. The viscous slurry was cast onto an aluminum foil (15 μm, Aluminum, Korea) using a doctor blade apparatus, dried at 120 � C for 24 h, and then pressed with a roll pressing machine (WV-60, Samyang 60, Korea). The electrodes were punched into spherical discs with a diameter of 14 mm and 16 mm for the cathode and anode, respectively. The loadings of the electroactive materials were calculated to be 20.66 � 0.5 mg and 13.33 � 0.5 mg for NCM and graphite, respectively. The coin cells were prepared by sandwiching a PE sepa rator (18 mm, 20 μm, Celgard) between the fabricated cathode and anode, and filling the cell with the prepared electrolyte in an argon-filled glove box. The prepared cells were aged for 12 h and then charged and discharged at constant current (CC) mode at 0.1C in a voltage range of 2.8–4.4 V using a battery cycler (Toscot 3000, Toyo, systems). Subse quently, the cells were charged at 0.1 C at constant current/constant voltage (CC/CV) mode and then discharged at 0.1, 0.2, 0.5, 1, 2, and 4C within the same voltage range. As a reference, the C-rate was calculated using 160 mAhg 1 as the experimental specific capacitance of NCM. Cycling was performed by charging-discharging at 1C. The electro chemical impedance spectra were also obtained after the 1st and 100th cycle in a frequency range of 10 2–105 Hz. The surface image of the cathode and anode electrodes was observed after the initial discharge using FE-SEM (Hitachi S-4800), which was equipped with an energy dispersive X-ray spectroscope (EDX) to determine the chemical composition of the SEI.
2.3. Lithiation of zwitterion grafted silica nanoparticles (SiSB) SiSB (0.32 g) was added into the solution of lithium chloride (2.4 g in 100 mL of DI water) and ultrasonicated for 15 min and left to react at room temperature for 48 h. Product was collected after centrifugation, washed with copious amounts of acetone, and dried under vacuum at 120 � C for 4 days to obtain lithium-silica sulfobetaine silane (Li–SiSB). 2.4. Characterization of lithiated zwitterion grafted silica nanoparticles Chemical analyses of the Li–SiSB and the bare OX50 was conducted using X-ray photoelectron spectroscopy (XPS) (VersaProbe II Scanning XPS Microprobe, Physical Electronics), Fourier transform infrared spectroscopy (FT-IR, Nicolet iS5, USA) and thermal was analyzed using a thermogravimetric analyzer (TGA, N1000, SCINCO). 2.5. Electrolyte preparation and electrochemical characterization Five electrolyte solutions were prepared. The electrolyte denoted as “pure electrolyte” is 1 M LiPF6 dissolved in EC/DMC (1:1 V/V) (PanaX eTec). The other four electrolyte samples were made by dissolving different weight percentages of the Li–SiSB additive in the pure elec trolyte and stirring for 7 days in an argon-filled glove box. The Li–SiSB was completely dissolved in the baseline electrolyte to give a clear so lution. The pure electrolyte was used as a reference. Ionic conductivity tests for the electrolytes were done using two stainless steel (0.5 � 1 cm) electrodes in an glass cuvette (Aldrich, pathlength ¼ 10 mm) at various temperatures ranging from 20 to 60 � C. Complex impedance spec troscopy tests were carried out using an Autolab (ECO CHEMIE PGSTAT 100) in a frequency range of 10 2–10 5 Hz. Linear sweep voltammetry (LSV) was conducted on coin-type (2032) half cells composed of stain less steel plates as working electrodes, lithium metal foil as counter and reference electrodes, liquid electrolytes with and without additives, and a polyethylene (PE) separator on an Autolab instrument (ECO CHEMIE PGSTAT 100) in a potential window of 2–7 V at a scan rate of 1 mV s 1. Cyclic voltammetry (CV) measurements were carried out in the potential range of 0–3 V and a scan rate of 0.5 mV s 1, with lithium foils as the reference and counter electrodes and graphite as the working electrode.
3. Results and discussion 3.1. Silica nanoparticle modification 0.5 g of the Li–SiSB was dissolved in HF acid and the Li content was determined using ICP-AES. The amount of Lithium was determined to be 0.178 g Liþ.g 1 of Li–SiSB. The chemical analysis of the synthesized nanosalt is shown in Fig. 2. The XPS analysis of OX50 analysis shows no presence of N, S, and C but that for Li–SiSB shows a peak at a binding energy of 284.1 eV which is attributed to the C1s in the hydrocarbon chains [42–44]. The peak at 168.1 eV is attributed to Sulphur S2p in the sulfonate C SO3 in the zwitterion and the peak at 400.5 eV is attributed to the N1s peak of the quaternary ammonium cations in the zwitterion ( Nþ(CH3)2R ) [45–47]. The IR spectra of the bare OX50 in Fig. 2(b) shows a stretch at 3523 cm 1 which is attributed to the O–H stretching in the Si–OH groups. The stretch at 1068 cm 1 is attributed to the Si–O–Si bonding in the OX50. The Li–SiSB, shows stretches at 2944 and 809 cm 1 which are attributed to the stretching vibrations of the C–H bonds [48,49]. The stretch at 1184 cm 1 is attributed to the Si–O–C asymmetric stretch and the stretch at 1074 cm 1 is due to the stretching vibrations in the sulfonate group, SO3 [50,51]. The stretch at 1496 cm 1 is attributed to the C–H and N–H stretches in the quaternary ammonium group ( Nþ(CH3)2R ) and peak at 1039 cm 1 is due to the Si–O–Si bonding in the zwitterionic grafted silica nanoparticles [50,51]. Fig. 2 (c) shows TGA curves for the OX50, SB and Li–SiSB from 100 to 800 � C. The initial mass decrease for OX50 observed below 120 � C is due to the evaporation of adsorbed water which was determined to be <1% and the total weight loss of 3.4 wt% at 800 � C, which was due to loss of both adsorbed water and the one formed by condensation of silanol groups on the surface of the silica nanoparticles [43]. For SB, decrease in mass was accredited to decomposition of the SB zwitterion and for Li–SiSB, the initial decrease in mass below 170 � C was due loss of water from condensation of silanol groups on the surface of the silica nano particles and above 170 � C, the weight loss was due to decomposition of the grafted SB on the surface of silica nanoparticles which was then used
2.6. Cell preparation and electrochemical characterization Coin-type (2032) full cells (NCMkelectrolytekgraphite) were assem bled in an argon-filled glove box to investigate the effect of the additives on the performance of LIBs at room temperature. The cathode and anode electrodes were composed of LiNi0.4Co0.2Mn0.4O2 (NCM-424, Ecopro, Korea) and graphite (80 wt%) as active materials, respectively, 10 wt% Super P (Imerys, Switzerland) as a conducting agent, and 10 wt% pol yvinylidene fluoride (Kreha, Japan, Mw � 350,000) as a binder in Nmethyl-2-pyrrolidone (NMP, Sigma Aldrich) as a dispersing agent. The prepared cells were charged at 0.1 C at constant current/constant voltage (CC/CV) mode and then discharged at different C-rates ranging from 0.1C to 4C within the same voltage range. Cycling was performed by charging-discharging at 1C. Complex impedance spectroscopy tests were carried out after cell formation and after cycling. Coin-type (2032) full cells (NCMkelectrolytekgraphite) were fabri cated in an argon-filled glove box to investigate the effect of the addi tives on the performance of LIBs at room temperature. The cathode and 4
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Fig. 3. (a) Arrhenius plots of the ionic conductivities and (b) electrochemical stability of the electrolyte samples. Nyquist plots of NCM/graphite cells for electrolyte samples (c) after formation and (d) after 100 cycles. Table 1 Summary of ionic conductivities of the pure electrolyte and the Li–SiSB added electrolytes. Ionic conductivity (S cm 1) 20� C Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
0.0006831 0.0009343 0.0009987 0.0016206 0.0013385
10� C 0.0028179 0.0037554 0.0049479 0.0066148 0.0053426
0� C
25� C
60� C
0.0071635 0.0082463 0.0091425 0.0112880 0.0094747
0.0109380 0.0134520 0.0142020 0.0192020 0.0163859
0.0191165 0.0195270 0.0259798 0.0315800 0.0274390
probably due to the fact that the fabrication involves grafting of the zwitterion on silanol groups which does not affect the lattice position of the Si and O atoms thereby maintaining the morphological structure of the silica nanoparticles.
to determine the degree of particle functionalization [43]. The Li–SiSB had a weight loss of 37.2 wt% at 800 � C due to the loss of the grafted zwitterion thus about 37.2 wt% of the surface was functionalized. The SEM images in Fig. 2 (d and e) of the silica nanoparticles and the as-prepared Li–SiSB respectively show no morphological differences
3.2. Electrochemical performance 3.2.1. Ionic conductivity Fig. 3 (a) shows the Arrhenius plots of the ionic conductivities of the pure electrolyte and Li–SiSB containing electrolytes. The temperature dependence of ionic conductivity can be explained using the Vogel–Fulcher–Tammann (VFT) equation (Equation (1)) [52]. � � B (1) σ ¼ σ0 exp T T0 where σ is the ionic conductivity, T is the temperature in Kelvin, and σ0 , B, and T0 are constants. The plots show that the ionic conductivities exhibit the VFT behavior, which shows a steep decrease of ionic con ductivity at low temperatures due to increased viscosity and lower ionic mobility caused by the freezing of the electrolyte [53]. Table 1 shows the ionic conductivities of the pure electrolyte and the Li–SiSB added
Fig. 4. Proposed model for the dissociation of the LiPF6 salt by the zwitterionic Li–SiSB additive in the electrolyte. 5
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Fig. 5. Cyclic voltammograms (a1 and b1) and Charge/discharge of graphite vs Li/Liþ (a2 and b2) for (a) pure electrolyte, (b) 1 wt% Li–SiSB.
electrolytes. The ionic conductivities were calculated from the Nyquist plots. C ¼
l RA
conductivity [17]. At low temperatures, as the electrolyte components lose their kinetic energy and become less mobile, the zwitterion mole cules self–assemble [59] creating ionic channels [26] that enhance Liþ migration which explains why the Li–SiSB containing electrolytes had better conductivity at low temperature.
(2)
Where R is the resistance on the Z ́ axis, A is the area of the electrode, and l is the separation of the electrodes [54]. The ionic conductivities of the Li–SiSB-based electrolytes were much higher compared to previous re ports of the electrolytes with the lithium-silica salts of corresponding concentrations [5,6,55]. This behavior was also observed when zwit terions containing an ether group were added to a carbonate-based electrolyte [16,56]. Zwitterions have a large dipole moment that en hances ion dissociation by the immobilization of the PF6 on the Nþ of the SB (Fig. 4) [32,56,57]. The lithium ion concentration is also enhanced by the extra lithium ions from the zwitterionic salt which also improves ionic conductivity [5]. Although the SO3 group of the zwit terion can also immobilize Liþ ions, it has been reported that SO3 are good exchange sites for Liþ ions because the SO3 group and Liþ ions can easily associate and dissociate resulting in formation of Liþ ionic chan nels [26,27,34,35]. Also, the fact that Liþ ions are being competed for by PF6 and SO3 anions, the Liþ ion solvation sheath (ionic sphere) is affected leading to easy migration of Liþ ions [57]. However there is a decrease in ionic conductivity as the concentration of zwitterion in creases because (i) there would be more SO3 groups per Liþ ion which creates another ionic sphere reducing mobility of Liþ ions [58] and (ii) there would be an increase in viscosity, which in turn reduces ionic
3.2.2. Electrochemical stability Fig. 3(b) shows the LSVs of the different electrolyte samples. The pure electrolyte exhibits an anodic limit at ~4.6 V (vs. Li/Liþ). All the electrolyte samples with the Li–SiSB additive show anodic limit at ~5.5 V (vs. Li/Liþ). This shows that the electrochemical windows are improved by adding the Li–SiSB. The increase in electrochemical win dow was due to the fact that zwitterions can immobilize the PF6 anions (Fig. 4) thereby reducing the amount of PF6 anions that reach the electrode [19] thus protecting the electrolyte. Zwitterions also enable the formation of a stable SEI layer on the surface of the electrodes [60] thereby protecting the electrolyte from decomposition at higher volt ages. Silica nanoparticles also help in reducing the corrosion of current collectors at higher voltages [61,62] which also help in electrochemical stability. 3.2.3. Cyclic voltammetry CV measurements were done using graphitekelectrolytekLi cells. Fig. 5 shows the cyclic voltammograms for the cells containing pure electrolyte and Li–SiSB electrolytes with graphite as the working elec trode. Electrolyte additives are used to facilitate early and stable SEI 6
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Fig. 6. Charge/discharge curves of (a) pure electrolyte, (b) 1 wt% Li–SiSB, (c) 2 wt% Li–SiSB, (d) 3 wt% Li–SiSB, (e) 4 wt% Li–SiSB, and (f) discharge capacities as a function of C-rate of the electrolyte samples at a potential range of 2.8–4.4 V.
formation on the graphite anode surface and to obviate exfoliation of the graphite layers during the lithium intercalation and deintercalation [63–66]. A good carbonate–based electrolyte additive would form an SEI layer before intercalation of Liþ ions and also before the decompo sition of ethylene carbonate (EC) which usually happens around 0.60 V vs. Li/Liþ, thereby reducing electrolyte decomposition [63,67]. Some of the additives used have major draw backs such as (i) co–intercalation with the Liþ ions into the graphite layers e.g. propylene carbonate (PC) which leads to exfoliation of the graphite layers, (ii) the additive co–intercalated with the Liþ ions will decompose to form gases there by making the battery less safe and (iii) some have a high viscosity e.g. EC, which therefore requires them to be used with other solvents to reduce the viscosity but this in turn leads the electrolyte to be flammable [13, 63–66]. In our study, cells with the Li–SiSB additive showed a peak at 1.86 V which did not appear in the CV for the pure electrolyte which is attributed to the formation of the passivation layer by the zwitterion [13]. Cells with pure electrolyte and Li–SiSB additive both showed irreversible peaks at 0.51 V which are attributed to the decomposition of EC [54,68]. The Liþ ion intercalation and deintercalation peaks appear
in the potential range of 0–0.20 V, and around 0.40 V vs. Li/Liþ respectively [68–74] for both cells with the pure electrolyte and Li–SiSB additive. This shows that the zwitterionic Li–SiSB forms the SEI layer earlier before decomposition of EC and lithium intercalation. Fig. 5 also shows the charge and discharge curves of graphitekelectrolytekLi cells in the cut-off voltage range of 0.005–3 V. The cell with 1 wt% Li–SiSB had a discharge capacity of 332 mAh g 1 during the 1st cycle. After the 2nd cycle, the discharge capacity was constant at 327 mAh g 1 which shows that the Liþ ions intercalation and deintercalation was stable [75–79]. 3.2.4. Cell performances Fig. 6 shows the charge/discharge profiles at different C-rates of the various electrolyte samples. Fig. 6(f) shows discharge capacity as a function of C-rate. The pure electrolyte shows lower discharge capacities at both lower and higher C-rates compared to the Li–SiSB containing electrolytes. This improved performance is attributed to the higher ionic conductivities of the electrolytes with the Li–SiSB and formation of a stable SEI which allows for effective transport of lithium ions across the interface [5,6]. The increased gap in charge and discharge voltage
Fig. 7. (a) Cycling performance of the NCM/graphite cells (b) coulombic efficiency of the NCM/graphite cells. 7
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plateaus with increasing C-rate shows that cell is controlled by Liþ ion diffusion rate within the electrolyte and electrode/electrolyte interfaces at high current densities [75]. Fig. 7(a) shows the cycling performance of the NCM/graphite cells using different electrolyte samples. The electrolyte with 1 wt% showed the best cycling performance with a high capacitance retention of 74.5% compared to the pure electrolyte with a capacitance retention of 17.7% after 200 cycles. This shows the effec tiveness of Li–SiSB as an additive in lowering the rate of capacity fading in NCM cells at a high cut-off voltage. From these observations, it can be stated that Li–SiSB has great compatibility with the graphite anode and NCM cathode. The coulombic efficiency (CE) [76] which is defined as:
Table 2 Impedance characteristics after cell formation and 100 charge-discharge cycles. Electrolyte
RS (Ω)
RSEI ðΩÞ
Rct ðΩÞ
RW ðΩÞ
(After cell formation) Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
3.1 2.5 1.7 1.5 1.4
20.0 11.3 12.3 13.4 14.9
13.7 5.8 7.9 9.9 11.4
0.9 0.4 0.4 0.3 0.3
(After 100 cycles) Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
4.4 2.7 2.6 2.4 2.4
22.6 10.1 12.0 13.0 14.2
14.2 6.9 8.7 10.3 12.6
0.9 0.4 0.3 0.3 0.2
η¼
Cd : Cc
(3)
where Cd is the discharge capacity of a cell at a particular cycle, and Cc is the charge capacity of the cell in the same cycle also showed stable
Fig. 8. The reduction mechanism of EC to EC– by electron transfer from the graphite edge and the interaction of EC and EC– with the zwitterion.
Fig. 9. Cross sectional view and surface morphologies of the (a) unused graphite anode and after the initial discharge at for (b) pure electrolyte, (c) 1 wt% Li–SiSB and the corresponding EDX elemental analysis of the SEI surface. 8
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Table 3 Elemental compositions of the SEI layer on graphite surfaces after cycling.
Liþ þ EC þ e → ROCO2 Li þ ROH
A higher percentage of fluorine in the SEI layer would indicate greater decomposition of the LiPF6 electrolyte salt. Due to the reduced fluorine atomic percentages on the SEI surface from EDX elemental analysis, the zwitterion could have interfered with the decomposition reactions (Equations (4) and (5)) of LiPF6. We postulate that the zwit terions immobilize the PF6 thereby isolating them hence subduing their reductive decomposition also reducing the number of PF6 that are co–intercalated into the graphite.
Atomic percentage compositions Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
C
O
F
P
Si
80.25 85.38 85.09 86.12 86.69
10.01 3.92 4.30 3.29 2.73
8.36 7.51 6.97 7.09 6.84
1.38 0.77 0.61 0.59 0.58
~ 2.42 3.03 2.91 3.16
values above 98% throughout 200 cycles (Fig. 7(b)) indicating decom position of electrolyte components in forming the SEI during the initial cycle and subduing of side reactions thereby preventing further decomposition of electrolyte during cycling [76,77]. Nyquist plots for the NCM/graphite cells are shown in Fig. 3(c and d) and corresponding values are summarized in Table 2. The solution resistance (Rs) increases from the 1st cycle to the 100th cycle as expected due to electrolyte decomposition [6]. It is observed that electrolyte samples with the Li–SiSB additive have lower Warburg impedance (RW) during cycling, which entails faster lithium-ion diffusion into the graphite [6]. It was observed that the SEI resistance (RSEI) of a pure electrolyte increased with cycling but that of the electrolytes with the Li–SiSB additive becomes stabilized due to stabilization of the electro lyte which prevents further decomposition [78,79]. Its known that EC undergoes a ring-opening reaction to form a stable radical anion (EC–) [59] which can be further reduced to carbonate (CO23 ) and ethylene (C2H2) or self-coupling to form ethylene dicarbonate (EDC2 ) near the electrode [80]. Since we observed that the RSEI becomes stabilized in electrolytes with the Li–SiSB additive, we postulate that (i) the zwit terion molecules near the electrode surface are able to suppress the migration of EC– into the bulk solution by immobilizing the EC– on the Nþ (Fig. 8) [13]. (ii) Furthermore, the EC molecules is the bulk form Van der Waals interactions with the zwitterions hence their movement to wards the electrodes is minimized thereby reducing further decompo sition of the electrolyte resulting in a stable SEI. The silica nanoparticles also help in SEI formation and consequently better cycling performance [5,62,81]. The electrolyte samples with the Li–SiSB additive exhibited lower values of Rct compared to the pure electrolyte which shows that addition of the zwitterion reduces the Rct between the electrolyte and cathode [19] due to formation of a stable SEI hence higher discharge capacity observed even at lower C-rates [5]. The surface morphologies of the graphite electrodes after cell formation are shown in Fig. 9 and the elemental analysis using EDX is summarized in Table 3. An SEI film formed can be observed for used electrodes compared to the unused electrode. It can be seen that the SEI layer is formed and distributed across the surface of the electrode. The SEI layer of the electrode where the pure electrolyte was used is shown to be thicker (e3μmÞ than that formed when using Li–SiSB (e1:5μmÞ which is further confirmed by the elemental analysis. The atomic percentages (Table 3) which were determined after 100 cycles also show that the fluorine percentage on the electrode surface decreases with the use of the Li–SiSB additive. This is due the zwitterion enabling (i) the forma tion of SEI before the decomposition and (ii) reduced migration of EC and PF6 towards the electrode resulting in a thinner SEI. The decom position of LiPF6 leads to the production of LiF which forms part of the SEI and also PF5 and PF3 [82,83] and also Liþ ion react with EC mole cules in a single electron ring opening reaction leading to formation of Lithium carbonate that also forms part of the SEI as shown in Equations (4)–(6). The formation of LiF causes a reduction in the Liþ concentration in the electrolyte thereby reducing battery capacity [84–87]. PF6 þ 3Liþ þ 2e → 3LiF↓ þ PF3 ↑
(4)
LiPF6 → LiF↓ þ PF5 ↑
(5)
(6)
4. Conclusion Zwitterionic Li–SiSB was synthesized and used as a liquid electrolyte additive for LIBs. Electrolyte samples with the Li–SiSB additive showed an increased ionic conductivity and enhanced electrochemical stability. The NCM/graphite cells with the electrolyte samples with the Li–SiSB showed greater discharge capacities at higher C-rates and a stable cycling performance due to increased ionic conductivity and stable SEI formation. The high performance electrolyte additive can greatly in crease energy density due to its high voltage window and increase power density due to its high ionic conductivity. The Li–SiSB additive is therefore a strong candidate for use as a liquid electrolyte additive for high voltage LIBs. 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. Acknowledgements This research was supported by a grant (10047758) from the Tech nology Development Program for Strategic Core Materials funded by the Korean Ministry of Trade, Industry & Energy. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.matchemphys.2019.122577. References [1] S. Yang, Y. Gong, Z. Liu, L. Zhan, D.P. Hashim, L. Ma, R. Vajtai, P.M. Ajayan, Bottom-up approach toward single-crystalline VO2-graphene ribbons as cathodes for ultrafast lithium storage, Nano Lett. 13 (2013) 1596–1601. [2] B. Ji, F. Zhang, M. Sheng, X. Tong, Y. Tang, A novel and generalized lithium-ionbattery configuration utilizing Al foil as both anode and current collector for enhanced energy density, Adv. Mater. 29 (1–7) (2017). [3] G. Ma, S. Li, W. Zhang, Z. Yang, S. Liu, X. Fan, F. Chen, Y. Tian, W. Zhang, S. Yang, M. Li, A general and mild approach to controllable preparation of manganese-based micro- and nanostructured bars for high performance lithium-ion batteries, Angew. Chem. Int. Ed. 55 (2016) 3667–3671. [4] S.S. Zhang, A review on the separators of liquid electrolyte Li-ion batteries, J. Power Sources 164 (2007) 351–364. [5] L. Hamenu, H.S. Lee, M. Latifatu, K.M. Kim, J.W. Park, Y.G. Baek, J.M. Ko, R. B. Kaneret, Lithium-silica nanosalt as a low-temperature electrolyte additive for lithium-ion batteries, Curr. Appl. Phys. 16 (2016) 611–617. [6] M. Latifatu, M. Hu, S. Jun, C. Yeajoon, C. Kang, W.I. Cho, J.M. Ko, Lithium modified silica as electrolyte additive for lithium secondary batteries, Solid State Ion. 319 (7–12) (2018). [7] J. Ha, H.S. Lee, L. Hamenu, M. Latifatu, Y.M. Lee, K.M. Kim, J. Oh, W.I. Cho, J. M. Ko, Improvement of low-temperature performance by adopting polydimethylsiloxane- g -polyacrylate and lithium-modified silica nanosalt as electrolyte additives in lithium-ion batteries, J. Ind. Eng. Chem. 37 (2016) 325–329. [8] J. Meng, F. Chu, J. Hu, C. Li, Liquid polydimethylsiloxane grafting to enable dendrite-free Li plating for highly reversible Li-metal batteries, Adv. Funct. Mater. 29 (1–13) (2019).
9
I. Phiri et al.
Materials Chemistry and Physics 243 (2020) 122577
[9] F. Chu, et al., Metal-organic frameworks as electrolyte additives to enable ultrastable plating/stripping of Li anode with dendrite inhibition, ACS Appl. Mater. Interfaces 11 (2019) 3869–3879. [10] J. Hu, K. Chen, C. Li, Nanostructured Li-rich fluoride coated by ionic liquid as high ion-conductivity solid electrolyte additive to suppress dendrite growth at Li metal anode, ACS Appl. Mater. Interfaces 10 (2018) 34322–34331. [11] F. Chu, J. Hu, J. Tian, X. Zhou, Z. Li, C. Li, In situ plating of porous Mg network layer to reinforce anode dendrite suppression in Li-metal batteries, ACS Appl. Mater. Interfaces 10 (2018) 12678–12689. [12] J. Hu, J. Tian, C. Li, Nanostructured carbon nitride polymer-reinforced electrolyte to enable dendrite-suppressed lithium metal batteries, ACS Appl. Mater. Interfaces 9 (2017) 11615–11625. [13] I. Phiri, C.Y. Bon, S. Kim, M. Manasi, L. Hamenu, A. Madzvamuse, S.H. Kim, J. M. Ko, Effects of novel benzotriazole based zwitterionic salt as electrolyte additive for lithium ion batteries, Curr. Appl. Phys. 20 (122–131) (2020). [14] N.S. Choi, Y.M. Lee, B.H. Lee, J.A. Lee, J.K. Park, Nanocomposite single ion conductor based on organic-inorganic hybrid, Solid State Ion. 167 (2004) 293–299. [15] J. Sun, P. Bayley, D.R. Macfarlane, M. Forsyth, Gel electrolytes based on lithium modified silica nano-particles, Electrochim. Acta 52 (2007) 7083–7090. [16] H. Kim, D.Q. Nguyen, H.W. Bae, J.S. Lee, B.W. Cho, H.S. Kim, M. Cheong, H. Lee, Effect of ether group on the electrochemical stability of zwitterionic imidazolium compounds, Electrochem. Commun. 10 (2008) 1761–1764. [17] D.Q. Nguyen, J. Hwang, J.S. Lee, H. Kim, H. Lee, M. Cheong, B. Lee, H.S. Kim, Multi-functional zwitterionic compounds as additives for lithium battery electrolytes, Electrochem. Commun. 9 (2007) 109–114. [18] D.Q. Nguyen, H.W. Bae, E.H. Jeon, J.S. Lee, M. Cheong, H. Kim, H.S. Kima, H. Lee, Zwitterionic imidazolium compounds with high cathodic stability as additives for lithium battery electrolytes, J. Power Sources 183 (2008) 303–309. [19] S. Yamaguchi, M. Yoshizawa-fujita, H. Zhu, M. Forsyth, Y. Takeoka, M. Rikukawa, Improvement of charge/discharge properties of oligoether electrolytes by zwitterions with an attached cyano group for use in lithium-ion secondary batteries, Electrochim. Acta 186 (2015) 471–477. [20] F. Wohde, R. Bhandary, J.M. Moldrickx, J. Sundermeyer, M. Sch€ onhoff, B. Roling, Liþ ion transport in ionic liquid-based electrolytes and the influence of sulfonatebased zwitterion additives, Solid State Ion. 284 (2016) 37–44. [21] F. Lind, L. Rebollar, P. Bengani-Lutz, A. Asatekin, M.J. Panzer, Zwitterioncontaining ionogel electrolytes, Chem. Mater. 28 (2016) 8480–8483. [22] T. Mizumo, T. Watanabe, H. Ohno, Thermally stable and proton conductive ionogel based on brønsted acidic ionic liquid with the support of silicate network, Polym. J. 40 (2008) 1099–1104. [23] H. Ohno, M. Yoshizawa-Fujita, Y. Kohno, Design and properties of functional zwitterions derived from ionic liquids, Phys. Chem. Chem. Phys. 20 (2018) 10978–10991. [24] Q. Shao, L. Mi, X. Han, T. Bai, S. Liu, Y. Li, S. Jiang, Differences in cationic and anionic charge densities dictate zwitterionic associations and stimuli responses, J. Phys. Chem. B 118 (2014) 6956–6962. [25] Z. Chen, W.Q. Lu, J. Liu, K. Amine, LiPF6/LiBOB blend salt electrolyte for highpower lithium-ion batteries, Electrochim. Acta 51 (2006) 3322–3326. [26] R. Rondla, J.C.Y. Lin, C.T. Yang, I.J.B. Lin, Strong tendency of homeotropic alignment and anisotropic lithium ion conductivity of sulfonate functionalized zwitterionic imidazolium ionic liquid crystals, Langmuir 29 (2013) 11779–11785. [27] C. Tiyapiboonchaiya, J.M. Pringle, J. Sun, N. Byrne, P.C. Howlett, D.R. Macfarlane, M. Forsyth, The zwitterion effect in high-conductivity polyelectrolyte materials, Nat. Mater. 3 (29–32) (2004). [28] Q. Shao, Y. He, S. Jiang, Molecular Dynamics simulation study of ion interactions with zwitterions, J. Phys. Chem. B 115 (2011) 8358–8363. [29] M. Yoshizawa, A. Narita, H. Ohno, Design of ionic liquids for electrochemical applications, Aust. J. Chem. 57 (2004) 139–144. [30] H. Lee, D.B. Kim, S.H. Kim, H.S. Kim, S.J. Kim, D.K. Choi, Y.S. Kang, J. Won, Zwitterionic silver complexes as carriers for facilitated-transport composite membranes, Angew. Chem. Int. Ed. 43 (2004) 3053–3056. [31] H. Ohno, M. Yoshizawa, W. Ogihara, A new type of polymer gel electrolyte: zwitterionic liquid/polar polymer mixture, Electrochim. Acta 48 (2003) 2079–2083. [32] M. Yoshizawa, M. Hirao, K. Ito-Akita, H. Ohno, Ion conduction in zwitterionic-type molten salts and their polymers, J. Mater. Chem. 11 (2001) 1057–1062. [33] M. Yoshizawa-Fujita, N. Byrne, M. Forsyth, D.R. MacFarlane, H. Ohno, Proton transport properties in zwitterion blends with Brønsted acids, J. Phys. Chem. B 114 (2010) 16373–16380. [34] K. Ito, N. Nishina, H. Ohno, High lithium ionic conductivity of poly(ethylene oxide) s having sulfonate groups on their chain ends, J. Mater. Chem. 7 (1997) 1357–1362. [35] A. Narita, W. Shibayama, H. Ohno, Structural factors to improve physico-chemical properties of zwitterions as ion conductive matrices, J. Mater. Chem. 16 (2006) 1475–1482. [36] N. Byrne, P.C. Howlett, D.R. MacFarlane, M.E. Smith, A. Howes, A.F. Hollenkamp, T. Bastow, P. Hale, M. Forsyth, Effect of zwitterion on the lithium solid electrolyte interphase in ionic liquid electrolytes, J. Power Sources 184 (2008) 288–296. [37] K. Xu, Nonaqueous liquid electrolytes for lithium-based rechargeable batteries, Chem. Rev. 104 (2004) 4303–4417. [38] N.S. Choi, Z. Chen, S.A. Freunberger, X. Ji, Y.K. Sun, K. Amine, G. Yushin, L. F. Nazar, J. Cho, P.G. Bruce, Challenges facing lithium batteries and electrical double-layer capacitors, Angew. Chem. Int. Ed. 51 (2012) 9994–10024. [39] K. Xu, Electrolytes and interphases in Li-ion batteries and beyond, Chem. Rev. 114 (2014) 11503–11618.
[40] B.N. Byrne, P.C. Howlett, D.R. Macfarlane, M. Forsyth, The zwitterion effect in ionic Liquids : towards practical rechargeable lithium-metal batteries, Adv. Mater. 17 (2005) 2497–2501. [41] F. Schipper, E.M. Erickson, C. Erk, J. Shin, F.F. Chesneau, D. Aurbach, Review — recent advances and remaining challenges for lithium I . Nickel-rich, LiNiCoyMnzO2, J. Electrochem. Soc. 164 (2017) 6220–6228. [42] M. Xu, L. Zhou, L. Hao, L. Xing, W. Li, B.L. Lucht, Investigation and application of lithium difluoro(oxalate)borate (LiDFOB) as additive to improve the thermal stability of electrolyte for lithium-ion batteries, J. Power Sources 196 (2011) 6794–6801. [43] H. Zhao, Z. Jia, Yuan Wen, H. Hu, Y. Fu, G.L. Baker, G. Liu, Fumed silica-based single-ion nanocomposite electrolyte for lithium batteries, ACS Appl. Mater. Interfaces 7 (2015) 19335–19341. [44] Y. Zhu, W. Xie, F. Zhang, T. Xing, J. Jin, Superhydrophilic in-situ-cross-linked zwitterionic polyelectrolyte/PVDF-blend membrane for highly efficient oil/water emulsion separation, ACS Appl. Mater. Interfaces 9 (2017) 9603–9613. [45] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-Ray Photoelectron Spectroscopy, Perkin-Elmer, Boca Raton, FL, 1992. [46] S. Yeh, C. Chen, W. Chen, C. Huang, Modification of silicone elastomer with zwitterionic silane for durable antifouling properties, Langmuir 30 (2014) 11386–11393. [47] S.H. Ye, C.A. Johnson Jr., J.R. Woolley, H. Murata, L.J. Gamble, K. Ishihara, W. R. Wagner, Simple surface modification of a titanium alloy with silanated zwitterionic phosphorylcholine or sulfobetaine modifiers to reduce thrombogenicity, Colloids Surf., B 79 (2010) 357–364. [48] B. Liu, L. Zhang, H. Wang, Z. Bian, Preparation of MCC/MC silica sponge and its oil/water separation apparatus application, Ind. Eng. Chem. Res. 56 (2017) 5795–5801. [49] G. Socrates, Infrared and Raman Characteristics Group Frequencies: Tables and Charts, third ed., JohnWiley and Sons, 2001. [50] Y. Song, Y. Sun, X. Zhang, J. Zhou, a L. Zhang, Homogeneous quaternization of cellulose in NaOH/urea aqueous solutions as gene carriers, Biomacromolecules 9 (2008) 2259–2264. [51] B.R. Knowles, P. Wagner, S. McLaughlin, M.J. Higgins, P.J. Molino, Silica nanoparticles functionalized with zwitterionic sulfobetaine siloxane for application as a versatile antifouling coating system, ACS Appl. Mater. Interfaces 9 (2017) 18584–18594. [52] M.G. McLin, C.A. Angell, Ion-pairing effects on viscosity/conductance relations in Raman-characterized polymer electrolytes: lithium perchlorate and sodium triflate in PPG(4000), J. Phys. Chem. 95 (1991) 9464–9469. [53] K.M. Kim, N. Vu Ly, J.H. Won, Y.G. Lee, W.I. Cho, J.M. Ko, R.B. Kaner, Improvement of lithium-ion battery performance at low temperature by adopting polydimethylsiloxane-based electrolyte additives, Electrochim. Acta 136 (2014) 182–188. [54] L. Hamenu, Alfred Madzvamuse, Latifatu Mohammed, Yong Min Lee, Jang Myoun Ko, Chris Yeajoon Bon, Sang Jun Kim, Won Il Cho, Yong Gu Baek, Jongwook Park, Benzotriazole as an electrolyte additive on lithium-ion batteries performance, J. Ind. Eng. Chem. 53 (2017) 241–246. [55] J. Cardoso, D. Nava, P. Garc, F. Herna, Synthesis, characterization and theoretical insights of green chitosan derivatives presenting enhanced Li þ ionic conductivity, J. Phys. Chem. C 119 (2015) 4655–4665. [56] J.N. Krishnan, H.S. Kim, J.K. Lee, B. Cho, E.J. Roh, S. Lee, Organic solvents containing zwitterion as electrolyte for Li ion cells, Bull. Korean Chem. Soc. 29 (2010) 1705–1710. [57] J. Sun, D.R. Macfarlane, N. Byrne, M. Forsyth, Zwitterion effect in polyelectrolyte gels based on lithium methacrylate- N,N-dimethyl acrylamide copolymer, Electrochim. Acta 51 (2006) 4033–4038. [58] Z.H. Li, Q.L. Xia, L.L. Liu, G.T. Lei, Q.Z. Xiao, D.S. Gao, X.D. Zhou, Effect of zwitterionic salt on the electrochemical properties of a solid polymer electrolyte with high temperature stability for lithium ion batteries, Electrochim. Acta 56 (2010) 804–809. [59] P. Bengani-Lutz, E. Converse, P. Cebe, A. Asatekin, Self-assembling zwitterionic copolymers as membrane selective layers with excellent fouling resistance: effect of zwitterion chemistry, ACS Appl. Mater. Interfaces 9 (2017) 20859–20872. [60] M. Suematsu, M. Yoshizawa-fujita, H. Zhu, M. Forsyth, Y. Takeoka, M. Rikukawa, Effect of zwitterions on electrochemical properties of oligoether-based electrolytes, Electrochim. Acta 175 (2015) 209–213. [61] H. Louis, Y.G. Lee, K.M. Kim, W. Il Cho, J.M. Ko, Suppression of aluminum corrosion in lithium bis(trifluoromethanesulfonyl) imide based electrolytes by the addition of fumed silica, Bull. Korean Chem. Soc. 34 (2013) 1795–1799. [62] Y. Li, P.S. Fedkiw, Effect of gel electrolytes containing silica nanoparticles on aluminum corrosion, Electrochim. Acta 52 (2007) 2471–2477. [63] S.J. An, J. Li, C. Daniel, D. Mohanty, S. Nagpure, D.L. Wood, The state of understanding of the lithium-ion-battery graphite solid electrolyte interphase (SEI) and its relationship to formation cycling, Carbon N. Y. 105 (2016) 52–76. [64] V. Etacheri, R. Marom, R. Elazari, G. Salitra, D. Aurbach, Challenges in the development of advanced Li-ion batteries: a review, Energy Environ. Sci. 4 (2011) 3243–3262. [65] K. Tasaki, K. Kanda, T. Kobayashi, S. Nakamura, M. Ue, Theoretical studies on the reductive decompositions of solvents and additives for lithium-ion batteries near lithium anodes, J. Electrochem. Soc. 153 (2006) A2192. [66] S. Flandrois, B. Simon, Carbon materials for lithium-ion rechargeable batteries, Carbon N. Y. 37 (1999) 165–180. [67] S.H. Lee, H.G. You, K.S. Han, J. Kim, I.H. Jung, J.H. Song, A new approach to surface properties of solid electrolyte interphase on a graphite negative electrode, J. Power Sources 247 (2014) 307–313.
10
I. Phiri et al.
Materials Chemistry and Physics 243 (2020) 122577
[68] P. Nov� ak, F. Joho, R. Imhof, J.C. Panitz, O. Haas, In situ investigation of the interaction between graphite and electrolyte solutions, J. Power Sources 81–82 (1999) 212–216. [69] L. Hamenu, Alfred Madzvamuse, Latifatu Mohammed, Yong Min Lee, Jang Myoun Ko, Chris Yeajoon Bon, Sang Jun Kim, Won Il Cho, Yong Gu Baek, Jongwook Park, Benzotriazole as an electrolyte additive on lithium-ion batteries performance, J. Ind. Eng. Chem. 53 (2017) 241–246. [70] M. Yamagata, N. Nishigaki, S. Nishishita, Y. Matsui, T. Sugimoto, M. Kikuta, T. Higashizaki, M. Kono, M. Ishikawa, Charge–discharge behavior of graphite negative electrodes in bis(fluorosulfonyl)imide-based ionic liquid and structural aspects of their electrode/electrolyte interfaces, Electrochim. Acta 110 (2013) 181–190. [71] S. Seki, Y. Kobayashi, H. Miyashiro, Y. Ohno, Y. Mita, N. Terada, P. Charest, A. Guerfi, K. Zaghib, Compatibility of N-methyl-N-propylpyrrolidinium cation room-temperature ionic liquid electrolytes and graphite electrodes, J. Phys. Chem. C 112 (2008) 16708–16713. [72] J. Reiter, M. N� adhern� a, R. Dominko, Graphite and LiCo1/3Mn1/3Ni1/3O2 electrodes with piperidinium ionic liquid and lithium bis(fluorosulfonyl)imide for Li-ion batteries, J. Power Sources 205 (2012) 402–407. [73] J. Towada, T. Karouji, H. Sato, Y. Kadoma, K. Shimada, K. Ui, Charge–discharge characteristics of natural graphite electrode in N, N-diethyl-N-methyl-N-(2methoxyethyl)ammonium bis(trifluoromethylsulfonyl)amide containing lithium ion for lithium-ion secondary batteries, J. Power Sources 275 (2015) 50–54. [74] S. Horiuchi, H. Zhu, M. Forsyth, Y. Takeoka, M. Rikukawa, M. Yoshizawa-Fujita, Synthesis and evaluation of a novel pyrrolidinium-based zwitterionic additive with an ether side chain for ionic liquid electrolytes in high-voltage lithium-ion batteries, Electrochim. Acta 241 (2017) 272–280. [75] M. Liu, B. Jin, Q. Zhang, X. Zhan, F. Chen, High-performance solid polymer electrolytes for lithium ion batteries based on sulfobetaine zwitterion and poly (ethylene oxide) modified polysiloxane, J. Alloy. Comp. 742 (2018) 619–628. [76] A.J. Smith, J.C. Burns, J.R. Dahn, A high precision study of the coulombic efficiency of Li-ion batteries, Electrochem. Solid State Lett. 13 (2010) A177.
[77] F. Yang, D. Wang, Y. Zhao, K.L. Tsui, S.J. Bae, A study of the relationship between coulombic efficiency and capacity degradation of commercial lithium-ion batteries, Energy 145 (2018) 486–495. [78] I.A. Profatilova, S.S. Kim, N.S. Choi, Enhanced thermal properties of the solid electrolyte interphase formed on graphite in an electrolyte with fluoroethylene carbonate, Electrochim. Acta 54 (2009) 4445–4450. [79] X. Zuo, C. Fan, X. Xiao, J. Liu, J. Nan, High-voltage performance of LiCoO2/ graphite batteries with methylene methane disulfonate as electrolyte additive, J. Power Sources 219 (2012) 94–99. [80] M.J. Boyer, G.S. Hwang, Theoretical evaluation of ethylene carbonate anion transport and its impact on solid electrolyte interphase formation, Electrochim. Acta 266 (2018) 326–331. [81] Y. Li, P.S. Fedkiw, Nanocomposite gel electrolytes based on fumed silica for lithium-ion batteries, J. Electrochem. Soc. 12 (2007) 1140–1145. [82] T. Kawaguchi, K. Shimada, T. Ichitsubo, S. Yagi, E. Matsubara, Surface-layer formation by reductive decomposition of LiPF6 at relatively high potentials on negative electrodes in lithium ion batteries and its suppression, J. Power Sources 271 (2014) 431–436. [83] L. Xing, X. Zheng, M. Schroeder, J. Alvarado, A. von Wald Cresce, K. Xu, Q. Li, W. Li, Deciphering the ethylene carbonate-propylene carbonate mystery in Li-ion batteries, Acc. Chem. Res. 51 (2018) 282–289. [84] X. Cui, F. Tang, Y. Zhang, C. Li, D. Zhao, F. Zhou, S. Li, H. Feng, Influences of trace water on electrochemical performances for lithium hexafluoro phosphate- and lithium Bis(oxalato)borate-based electrolytes, Electrochim. Acta 273 (2018) 191–199. [85] C. Li, Z. Li, P. Wang, H. Liu, D. Zhao, S.X. Wang, S. Li, Studies of air-exposure effects and remediation measures on lithium bis(oxalato)borate, New J. Chem. 43 (2019) 14238–14245. [86] S. Li, D. Zhao, P. Wang, X. Cui, F. Tang, Electrochemical effect and mechanism of adiponitrile additive for high-voltage electrolyte, Electrochim. Acta 222 (2016) 668–677. [87] J.G. Han, K. Kim, Y. Lee, N.S. Choi, Scavenging materials to stabilize LiPF6 -containing carbonate-based electrolytes for Li-ion batteries, Adv. Mater. 31 (2019) 1–12.
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Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Enhanced electrolyte performance by adopting Zwitterionic lithium-silica sulfobetaine silane as electrolyte additive for lithium-ion batteries Isheunesu Phiri a, Chris Yeajoon Bon a, Manasi Mwemezi a, Louis Hamenu b, Alfred Madzvamuse c, Jeong Ho Park a, Kwang Se Lee d, Jang Myoun Ko a, *, Yunfeng Lu e a
Department of Applied Chemistry & Biotechnology, Hanbat National University, 125 Dongseo-daero, Deokmyeong-dong, Yuseong-gu, Daejeon, South Korea Department of Chemistry School of Physical and Mathematical Sciences, College of Basic and Applied Sciences University of Ghana, Legon, Ghana Department of Chemistry, University of Zimbabwe, PO Box MP167, Mount Pleasant, Harare, Zimbabwe d Kyungnam College of Information & Technology, Department of Advanced Materials & Chemical Engineering, 45 Jurye-ro, Sasang-gu, Busan, South Korea e UCLA-ENN Center for Nanomedicines and Energy Conversion, UCLA-HK Center for Graphene Technology and Energy Storage, UCLA-Dynavolt Research Center, University of California, Los Angeles, 90095, CA, USA b c
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
� Zwitterion sulfobetaine silane is syn thesized and grafted onto silica nanoparticles. � The additive enhances ionic conductiv ity and electrochemical stability. � Full cells have a stable cycle perfor mance at 1C over 200 cycles.
A R T I C L E I N F O
A B S T R A C T
Keywords: Silica Zwitterion Ionic conductivity Solid electrolyte interface
Zwitterionic lithium-silica sulfobetaine silane is fabricated by first synthesizing zwitterion sulfobetaine silane, grafting it onto hydrophilic silica to form silica sulfobetaine silane, and then lithiating the silica sulfobetaine silane. The resultant lithium-silica sulfobetaine silane additive is used as a liquid electrolyte additive in lithiumion batteries with varying weight percentages in 1 M LiPF6 (ethylene carbonate/dimethyl carbonate ¼ 1:1). The electrolytes with the lithium-silica sulfobetaine silane shows higher ionic conductivities (1.92 � 10 2 S cm 1 at RT and 1.62 � 10 3 S cm 1 at 20 � C) and greater electrochemical stability (anodic limit at ~5.5 V vs. Li/Liþ ) than the pure electrolyte (anodic limit at ~4.6 V vs. Li/Liþ ). The discharge capacity of the lithium nickel cobalt manganese oxide/graphite cell is improved at higher C-rates with the addition of lithium-silica sulfobetaine silane due to increased ionic conductivity. The lithium nickel cobalt manganese oxide/graphite cells with the lithium-silica sulfobetaine silane additive also show stable cycling performance. These findings warrant the use of lithium-silica sulfobetaine silane as an electrolyte additive in lithium-ion batteries.
* Corresponding author. E-mail addresses: [email protected] (K.S. Lee), [email protected] (J.M. Ko). https://doi.org/10.1016/j.matchemphys.2019.122577 Received 3 September 2019; Received in revised form 14 December 2019; Accepted 23 December 2019 Available online 25 December 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.
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Fig. 1. Schematic representation of the synthesis of the zwitterion SB, grafting SB onto OX50, and lithiation to form Li–SiSB.
1. Introduction
capability and formation of a stable solid electrolyte interface (SEI) [36] that promotes (i) intercalation and deintercalation of Liþ ions at extreme potentials, (ii) a more stable cycle life, and (iii) improved power and energy density and also improved battery safety [37–39]. A thinner but stable SEI would be ideal for good battery performance and Bryne and coworkers showed that the use of zwitterion promoted to formation of such in an ionic liquid (IL) based electrolyte because the zwitterions improved the migration of Liþ ions to the graphite electrode which reduced the co-intercalation of organic species [40]. Therefore, zwit terions can be used electrolyte additives because they enable the dissociation of salts, formation of a stable SEI formation and enhanced migration of dissociated ions [23]. In this study, lithium nickel manganese cobalt oxide (NCM) was used as the cathode due to its high capacity, but the major drawback of using NCM is its subsequent capacity fading over many cycles [41]. There are many reports on the application of zwitterions in LIBs; however, most of the reports are concentrated on the ionic conductivity of zwitterion s/lithium salt mixtures or ion–conductive polyzwitterions or zwitterions as additives in SPEs [23,32]. The additive effect of zwitterions in car bonate–based liquid electrolyte systems for LIBs is far less studied. Therefore, in this work, we fabricated a zwitterionic salt with high ionic conductivity, wide electrochemical window, and cycling stability as an additive for carbonate–based liquid electrolytes in LIBs. Herein, we grafted the sulfobetaine zwitterion onto silica nanoparticle and then lithiated it. The zwitterionic salt obtained was investigated as an elec trolyte additive to enhance the electrochemical performance of a LiPF6 based electrolyte with the hope of improving the rate performance and thermal stability of NCM/graphite cells.
The demand for lithium-ion batteries (LIBs) has been on the rise due to the ever increasing demand for various electronic devices e.g. electric vehicles and other portable electronic devices [1–3]. The three main components of a LIB are cathode, anode and an electrolyte [4]. In order to improve the performance of LIBs, studies have been done to improve the electrode materials, separator material and well as electrolytes [5–7]. Of particular interest is the use of additives to suppress dendrite formation [8–12] and also improve electrolyte performance e.g. ceramic materials such as silica nanoparticles have been used in carbonate based electrolytes, and other additives include zwitterions which have been used in ionic liquid, gel and solid electrolytes [13–22]. Zwitterions are interesting because of their chemistry where a cation end and an anion end (ion pairs) are covalently bound together in one molecule [23,24]. This isoionic characteristic results in zwitterions having a large molec ular dipole moment [25,26] which enables zwitterions to disassociate salts in electrolytes resulting in an increased ionic conductivity in these electrolyte systems [21,27,28]. Them being isoionic also makes zwit terions immobile in solutions when a potential is applied hence they cannot be charge carries but this in turn promotes target–ion migration as observed and reported by Ohno et al. [23,29–33], however a pure zwitterion has a very low ionic conductivity [29]. The zwitterions mainly used as electrolyte additives have the sulfonate group (SO3 Þ and it has been previously reported that SO3 are good exchange sites for Liþ ions because of the easiness to associate and dissociate between the SO3 group and Liþ ions [27,34,35]. Zwitterionic additives have also been shown to increase rate 2
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Fig. 2. Characterization of OX50 and Li–SiSB: (a) XPS analysis, (b) FT-IR analysis, and (c) TGA analysis. SEM and digital image (insert) for (d) OX50 and (e) Li–SiSB.
2. Experimental
The white precipitate was filtered off and repeatedly washed with anhydrous acetone. The product was dried at 70 � C under vacuum for 24 h and stored under argon. Fig. 1 shows the scheme for the synthesis process.
2.1. Synthesis of zwitterion sulfobetaine silane N,N-Dimethylaminopropyl) trimethoxysilane (�98.0%, Sigma Aldrich) (5 g, 24 mmol) was added to 1,3-propanesultone (98%, Sigma Aldrich) (3 g, 25 mmol) in anhydrous acetone (�99.5%, Sigma Aldrich) (25 mL) under argon and stirred vigorously for 6 h at room temperature.
2.2. Grafting of zwitterion to silica nanoparticles SB was dissolved in a small amount of H2O and added dropwise with 3
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vigorous stirring to a 10 wt% silica nanoparticle solution previously heated to 60 � C (�5 � C). The solution pH was adjusted to 3.5, using dilute HCl (35.0–37.0%, Duksan reagents). The reaction mixture was then stirred under reflux for 2 h. The solution was then centrifuged at 7000 rpm (Avant J-25, Beckman Coulter centrifuge) for 20 min. The centrifugate was washed twice by dispersing again in water and centrifuging again. The final centrifugate was collected and dried under vacuum at 60 � C for 48 h.
anode electrodes were composed of LiNi0.4Co0.2Mn0.4O2 (NCM-424, Ecopro, Korea) and graphite (Kokam Co.) (93 wt%) as active materials, respectively, 4 wt% Super P (Imerys, Switzerland) as a conductive ad ditive, and 3 wt% polyvinylidene fluoride (Kreha, Japan, Mw � 350,000) as a polymeric binder in N-methyl-2-pyrrolidone (NMP, Sigma Aldrich) as a dispersing agent. The viscous slurry was cast onto an aluminum foil (15 μm, Aluminum, Korea) using a doctor blade apparatus, dried at 120 � C for 24 h, and then pressed with a roll pressing machine (WV-60, Samyang 60, Korea). The electrodes were punched into spherical discs with a diameter of 14 mm and 16 mm for the cathode and anode, respectively. The loadings of the electroactive materials were calculated to be 20.66 � 0.5 mg and 13.33 � 0.5 mg for NCM and graphite, respectively. The coin cells were prepared by sandwiching a PE sepa rator (18 mm, 20 μm, Celgard) between the fabricated cathode and anode, and filling the cell with the prepared electrolyte in an argon-filled glove box. The prepared cells were aged for 12 h and then charged and discharged at constant current (CC) mode at 0.1C in a voltage range of 2.8–4.4 V using a battery cycler (Toscot 3000, Toyo, systems). Subse quently, the cells were charged at 0.1 C at constant current/constant voltage (CC/CV) mode and then discharged at 0.1, 0.2, 0.5, 1, 2, and 4C within the same voltage range. As a reference, the C-rate was calculated using 160 mAhg 1 as the experimental specific capacitance of NCM. Cycling was performed by charging-discharging at 1C. The electro chemical impedance spectra were also obtained after the 1st and 100th cycle in a frequency range of 10 2–105 Hz. The surface image of the cathode and anode electrodes was observed after the initial discharge using FE-SEM (Hitachi S-4800), which was equipped with an energy dispersive X-ray spectroscope (EDX) to determine the chemical composition of the SEI.
2.3. Lithiation of zwitterion grafted silica nanoparticles (SiSB) SiSB (0.32 g) was added into the solution of lithium chloride (2.4 g in 100 mL of DI water) and ultrasonicated for 15 min and left to react at room temperature for 48 h. Product was collected after centrifugation, washed with copious amounts of acetone, and dried under vacuum at 120 � C for 4 days to obtain lithium-silica sulfobetaine silane (Li–SiSB). 2.4. Characterization of lithiated zwitterion grafted silica nanoparticles Chemical analyses of the Li–SiSB and the bare OX50 was conducted using X-ray photoelectron spectroscopy (XPS) (VersaProbe II Scanning XPS Microprobe, Physical Electronics), Fourier transform infrared spectroscopy (FT-IR, Nicolet iS5, USA) and thermal was analyzed using a thermogravimetric analyzer (TGA, N1000, SCINCO). 2.5. Electrolyte preparation and electrochemical characterization Five electrolyte solutions were prepared. The electrolyte denoted as “pure electrolyte” is 1 M LiPF6 dissolved in EC/DMC (1:1 V/V) (PanaX eTec). The other four electrolyte samples were made by dissolving different weight percentages of the Li–SiSB additive in the pure elec trolyte and stirring for 7 days in an argon-filled glove box. The Li–SiSB was completely dissolved in the baseline electrolyte to give a clear so lution. The pure electrolyte was used as a reference. Ionic conductivity tests for the electrolytes were done using two stainless steel (0.5 � 1 cm) electrodes in an glass cuvette (Aldrich, pathlength ¼ 10 mm) at various temperatures ranging from 20 to 60 � C. Complex impedance spec troscopy tests were carried out using an Autolab (ECO CHEMIE PGSTAT 100) in a frequency range of 10 2–10 5 Hz. Linear sweep voltammetry (LSV) was conducted on coin-type (2032) half cells composed of stain less steel plates as working electrodes, lithium metal foil as counter and reference electrodes, liquid electrolytes with and without additives, and a polyethylene (PE) separator on an Autolab instrument (ECO CHEMIE PGSTAT 100) in a potential window of 2–7 V at a scan rate of 1 mV s 1. Cyclic voltammetry (CV) measurements were carried out in the potential range of 0–3 V and a scan rate of 0.5 mV s 1, with lithium foils as the reference and counter electrodes and graphite as the working electrode.
3. Results and discussion 3.1. Silica nanoparticle modification 0.5 g of the Li–SiSB was dissolved in HF acid and the Li content was determined using ICP-AES. The amount of Lithium was determined to be 0.178 g Liþ.g 1 of Li–SiSB. The chemical analysis of the synthesized nanosalt is shown in Fig. 2. The XPS analysis of OX50 analysis shows no presence of N, S, and C but that for Li–SiSB shows a peak at a binding energy of 284.1 eV which is attributed to the C1s in the hydrocarbon chains [42–44]. The peak at 168.1 eV is attributed to Sulphur S2p in the sulfonate C SO3 in the zwitterion and the peak at 400.5 eV is attributed to the N1s peak of the quaternary ammonium cations in the zwitterion ( Nþ(CH3)2R ) [45–47]. The IR spectra of the bare OX50 in Fig. 2(b) shows a stretch at 3523 cm 1 which is attributed to the O–H stretching in the Si–OH groups. The stretch at 1068 cm 1 is attributed to the Si–O–Si bonding in the OX50. The Li–SiSB, shows stretches at 2944 and 809 cm 1 which are attributed to the stretching vibrations of the C–H bonds [48,49]. The stretch at 1184 cm 1 is attributed to the Si–O–C asymmetric stretch and the stretch at 1074 cm 1 is due to the stretching vibrations in the sulfonate group, SO3 [50,51]. The stretch at 1496 cm 1 is attributed to the C–H and N–H stretches in the quaternary ammonium group ( Nþ(CH3)2R ) and peak at 1039 cm 1 is due to the Si–O–Si bonding in the zwitterionic grafted silica nanoparticles [50,51]. Fig. 2 (c) shows TGA curves for the OX50, SB and Li–SiSB from 100 to 800 � C. The initial mass decrease for OX50 observed below 120 � C is due to the evaporation of adsorbed water which was determined to be <1% and the total weight loss of 3.4 wt% at 800 � C, which was due to loss of both adsorbed water and the one formed by condensation of silanol groups on the surface of the silica nanoparticles [43]. For SB, decrease in mass was accredited to decomposition of the SB zwitterion and for Li–SiSB, the initial decrease in mass below 170 � C was due loss of water from condensation of silanol groups on the surface of the silica nano particles and above 170 � C, the weight loss was due to decomposition of the grafted SB on the surface of silica nanoparticles which was then used
2.6. Cell preparation and electrochemical characterization Coin-type (2032) full cells (NCMkelectrolytekgraphite) were assem bled in an argon-filled glove box to investigate the effect of the additives on the performance of LIBs at room temperature. The cathode and anode electrodes were composed of LiNi0.4Co0.2Mn0.4O2 (NCM-424, Ecopro, Korea) and graphite (80 wt%) as active materials, respectively, 10 wt% Super P (Imerys, Switzerland) as a conducting agent, and 10 wt% pol yvinylidene fluoride (Kreha, Japan, Mw � 350,000) as a binder in Nmethyl-2-pyrrolidone (NMP, Sigma Aldrich) as a dispersing agent. The prepared cells were charged at 0.1 C at constant current/constant voltage (CC/CV) mode and then discharged at different C-rates ranging from 0.1C to 4C within the same voltage range. Cycling was performed by charging-discharging at 1C. Complex impedance spectroscopy tests were carried out after cell formation and after cycling. Coin-type (2032) full cells (NCMkelectrolytekgraphite) were fabri cated in an argon-filled glove box to investigate the effect of the addi tives on the performance of LIBs at room temperature. The cathode and 4
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Fig. 3. (a) Arrhenius plots of the ionic conductivities and (b) electrochemical stability of the electrolyte samples. Nyquist plots of NCM/graphite cells for electrolyte samples (c) after formation and (d) after 100 cycles. Table 1 Summary of ionic conductivities of the pure electrolyte and the Li–SiSB added electrolytes. Ionic conductivity (S cm 1) 20� C Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
0.0006831 0.0009343 0.0009987 0.0016206 0.0013385
10� C 0.0028179 0.0037554 0.0049479 0.0066148 0.0053426
0� C
25� C
60� C
0.0071635 0.0082463 0.0091425 0.0112880 0.0094747
0.0109380 0.0134520 0.0142020 0.0192020 0.0163859
0.0191165 0.0195270 0.0259798 0.0315800 0.0274390
probably due to the fact that the fabrication involves grafting of the zwitterion on silanol groups which does not affect the lattice position of the Si and O atoms thereby maintaining the morphological structure of the silica nanoparticles.
to determine the degree of particle functionalization [43]. The Li–SiSB had a weight loss of 37.2 wt% at 800 � C due to the loss of the grafted zwitterion thus about 37.2 wt% of the surface was functionalized. The SEM images in Fig. 2 (d and e) of the silica nanoparticles and the as-prepared Li–SiSB respectively show no morphological differences
3.2. Electrochemical performance 3.2.1. Ionic conductivity Fig. 3 (a) shows the Arrhenius plots of the ionic conductivities of the pure electrolyte and Li–SiSB containing electrolytes. The temperature dependence of ionic conductivity can be explained using the Vogel–Fulcher–Tammann (VFT) equation (Equation (1)) [52]. � � B (1) σ ¼ σ0 exp T T0 where σ is the ionic conductivity, T is the temperature in Kelvin, and σ0 , B, and T0 are constants. The plots show that the ionic conductivities exhibit the VFT behavior, which shows a steep decrease of ionic con ductivity at low temperatures due to increased viscosity and lower ionic mobility caused by the freezing of the electrolyte [53]. Table 1 shows the ionic conductivities of the pure electrolyte and the Li–SiSB added
Fig. 4. Proposed model for the dissociation of the LiPF6 salt by the zwitterionic Li–SiSB additive in the electrolyte. 5
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Fig. 5. Cyclic voltammograms (a1 and b1) and Charge/discharge of graphite vs Li/Liþ (a2 and b2) for (a) pure electrolyte, (b) 1 wt% Li–SiSB.
electrolytes. The ionic conductivities were calculated from the Nyquist plots. C ¼
l RA
conductivity [17]. At low temperatures, as the electrolyte components lose their kinetic energy and become less mobile, the zwitterion mole cules self–assemble [59] creating ionic channels [26] that enhance Liþ migration which explains why the Li–SiSB containing electrolytes had better conductivity at low temperature.
(2)
Where R is the resistance on the Z ́ axis, A is the area of the electrode, and l is the separation of the electrodes [54]. The ionic conductivities of the Li–SiSB-based electrolytes were much higher compared to previous re ports of the electrolytes with the lithium-silica salts of corresponding concentrations [5,6,55]. This behavior was also observed when zwit terions containing an ether group were added to a carbonate-based electrolyte [16,56]. Zwitterions have a large dipole moment that en hances ion dissociation by the immobilization of the PF6 on the Nþ of the SB (Fig. 4) [32,56,57]. The lithium ion concentration is also enhanced by the extra lithium ions from the zwitterionic salt which also improves ionic conductivity [5]. Although the SO3 group of the zwit terion can also immobilize Liþ ions, it has been reported that SO3 are good exchange sites for Liþ ions because the SO3 group and Liþ ions can easily associate and dissociate resulting in formation of Liþ ionic chan nels [26,27,34,35]. Also, the fact that Liþ ions are being competed for by PF6 and SO3 anions, the Liþ ion solvation sheath (ionic sphere) is affected leading to easy migration of Liþ ions [57]. However there is a decrease in ionic conductivity as the concentration of zwitterion in creases because (i) there would be more SO3 groups per Liþ ion which creates another ionic sphere reducing mobility of Liþ ions [58] and (ii) there would be an increase in viscosity, which in turn reduces ionic
3.2.2. Electrochemical stability Fig. 3(b) shows the LSVs of the different electrolyte samples. The pure electrolyte exhibits an anodic limit at ~4.6 V (vs. Li/Liþ). All the electrolyte samples with the Li–SiSB additive show anodic limit at ~5.5 V (vs. Li/Liþ). This shows that the electrochemical windows are improved by adding the Li–SiSB. The increase in electrochemical win dow was due to the fact that zwitterions can immobilize the PF6 anions (Fig. 4) thereby reducing the amount of PF6 anions that reach the electrode [19] thus protecting the electrolyte. Zwitterions also enable the formation of a stable SEI layer on the surface of the electrodes [60] thereby protecting the electrolyte from decomposition at higher volt ages. Silica nanoparticles also help in reducing the corrosion of current collectors at higher voltages [61,62] which also help in electrochemical stability. 3.2.3. Cyclic voltammetry CV measurements were done using graphitekelectrolytekLi cells. Fig. 5 shows the cyclic voltammograms for the cells containing pure electrolyte and Li–SiSB electrolytes with graphite as the working elec trode. Electrolyte additives are used to facilitate early and stable SEI 6
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Fig. 6. Charge/discharge curves of (a) pure electrolyte, (b) 1 wt% Li–SiSB, (c) 2 wt% Li–SiSB, (d) 3 wt% Li–SiSB, (e) 4 wt% Li–SiSB, and (f) discharge capacities as a function of C-rate of the electrolyte samples at a potential range of 2.8–4.4 V.
formation on the graphite anode surface and to obviate exfoliation of the graphite layers during the lithium intercalation and deintercalation [63–66]. A good carbonate–based electrolyte additive would form an SEI layer before intercalation of Liþ ions and also before the decompo sition of ethylene carbonate (EC) which usually happens around 0.60 V vs. Li/Liþ, thereby reducing electrolyte decomposition [63,67]. Some of the additives used have major draw backs such as (i) co–intercalation with the Liþ ions into the graphite layers e.g. propylene carbonate (PC) which leads to exfoliation of the graphite layers, (ii) the additive co–intercalated with the Liþ ions will decompose to form gases there by making the battery less safe and (iii) some have a high viscosity e.g. EC, which therefore requires them to be used with other solvents to reduce the viscosity but this in turn leads the electrolyte to be flammable [13, 63–66]. In our study, cells with the Li–SiSB additive showed a peak at 1.86 V which did not appear in the CV for the pure electrolyte which is attributed to the formation of the passivation layer by the zwitterion [13]. Cells with pure electrolyte and Li–SiSB additive both showed irreversible peaks at 0.51 V which are attributed to the decomposition of EC [54,68]. The Liþ ion intercalation and deintercalation peaks appear
in the potential range of 0–0.20 V, and around 0.40 V vs. Li/Liþ respectively [68–74] for both cells with the pure electrolyte and Li–SiSB additive. This shows that the zwitterionic Li–SiSB forms the SEI layer earlier before decomposition of EC and lithium intercalation. Fig. 5 also shows the charge and discharge curves of graphitekelectrolytekLi cells in the cut-off voltage range of 0.005–3 V. The cell with 1 wt% Li–SiSB had a discharge capacity of 332 mAh g 1 during the 1st cycle. After the 2nd cycle, the discharge capacity was constant at 327 mAh g 1 which shows that the Liþ ions intercalation and deintercalation was stable [75–79]. 3.2.4. Cell performances Fig. 6 shows the charge/discharge profiles at different C-rates of the various electrolyte samples. Fig. 6(f) shows discharge capacity as a function of C-rate. The pure electrolyte shows lower discharge capacities at both lower and higher C-rates compared to the Li–SiSB containing electrolytes. This improved performance is attributed to the higher ionic conductivities of the electrolytes with the Li–SiSB and formation of a stable SEI which allows for effective transport of lithium ions across the interface [5,6]. The increased gap in charge and discharge voltage
Fig. 7. (a) Cycling performance of the NCM/graphite cells (b) coulombic efficiency of the NCM/graphite cells. 7
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plateaus with increasing C-rate shows that cell is controlled by Liþ ion diffusion rate within the electrolyte and electrode/electrolyte interfaces at high current densities [75]. Fig. 7(a) shows the cycling performance of the NCM/graphite cells using different electrolyte samples. The electrolyte with 1 wt% showed the best cycling performance with a high capacitance retention of 74.5% compared to the pure electrolyte with a capacitance retention of 17.7% after 200 cycles. This shows the effec tiveness of Li–SiSB as an additive in lowering the rate of capacity fading in NCM cells at a high cut-off voltage. From these observations, it can be stated that Li–SiSB has great compatibility with the graphite anode and NCM cathode. The coulombic efficiency (CE) [76] which is defined as:
Table 2 Impedance characteristics after cell formation and 100 charge-discharge cycles. Electrolyte
RS (Ω)
RSEI ðΩÞ
Rct ðΩÞ
RW ðΩÞ
(After cell formation) Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
3.1 2.5 1.7 1.5 1.4
20.0 11.3 12.3 13.4 14.9
13.7 5.8 7.9 9.9 11.4
0.9 0.4 0.4 0.3 0.3
(After 100 cycles) Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
4.4 2.7 2.6 2.4 2.4
22.6 10.1 12.0 13.0 14.2
14.2 6.9 8.7 10.3 12.6
0.9 0.4 0.3 0.3 0.2
η¼
Cd : Cc
(3)
where Cd is the discharge capacity of a cell at a particular cycle, and Cc is the charge capacity of the cell in the same cycle also showed stable
Fig. 8. The reduction mechanism of EC to EC– by electron transfer from the graphite edge and the interaction of EC and EC– with the zwitterion.
Fig. 9. Cross sectional view and surface morphologies of the (a) unused graphite anode and after the initial discharge at for (b) pure electrolyte, (c) 1 wt% Li–SiSB and the corresponding EDX elemental analysis of the SEI surface. 8
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Table 3 Elemental compositions of the SEI layer on graphite surfaces after cycling.
Liþ þ EC þ e → ROCO2 Li þ ROH
A higher percentage of fluorine in the SEI layer would indicate greater decomposition of the LiPF6 electrolyte salt. Due to the reduced fluorine atomic percentages on the SEI surface from EDX elemental analysis, the zwitterion could have interfered with the decomposition reactions (Equations (4) and (5)) of LiPF6. We postulate that the zwit terions immobilize the PF6 thereby isolating them hence subduing their reductive decomposition also reducing the number of PF6 that are co–intercalated into the graphite.
Atomic percentage compositions Pure electrolyte 1 wt% Li–SiSB 2 wt% Li–SiSB 3 wt% Li–SiSB 4 wt% Li–SiSB
C
O
F
P
Si
80.25 85.38 85.09 86.12 86.69
10.01 3.92 4.30 3.29 2.73
8.36 7.51 6.97 7.09 6.84
1.38 0.77 0.61 0.59 0.58
~ 2.42 3.03 2.91 3.16
values above 98% throughout 200 cycles (Fig. 7(b)) indicating decom position of electrolyte components in forming the SEI during the initial cycle and subduing of side reactions thereby preventing further decomposition of electrolyte during cycling [76,77]. Nyquist plots for the NCM/graphite cells are shown in Fig. 3(c and d) and corresponding values are summarized in Table 2. The solution resistance (Rs) increases from the 1st cycle to the 100th cycle as expected due to electrolyte decomposition [6]. It is observed that electrolyte samples with the Li–SiSB additive have lower Warburg impedance (RW) during cycling, which entails faster lithium-ion diffusion into the graphite [6]. It was observed that the SEI resistance (RSEI) of a pure electrolyte increased with cycling but that of the electrolytes with the Li–SiSB additive becomes stabilized due to stabilization of the electro lyte which prevents further decomposition [78,79]. Its known that EC undergoes a ring-opening reaction to form a stable radical anion (EC–) [59] which can be further reduced to carbonate (CO23 ) and ethylene (C2H2) or self-coupling to form ethylene dicarbonate (EDC2 ) near the electrode [80]. Since we observed that the RSEI becomes stabilized in electrolytes with the Li–SiSB additive, we postulate that (i) the zwit terion molecules near the electrode surface are able to suppress the migration of EC– into the bulk solution by immobilizing the EC– on the Nþ (Fig. 8) [13]. (ii) Furthermore, the EC molecules is the bulk form Van der Waals interactions with the zwitterions hence their movement to wards the electrodes is minimized thereby reducing further decompo sition of the electrolyte resulting in a stable SEI. The silica nanoparticles also help in SEI formation and consequently better cycling performance [5,62,81]. The electrolyte samples with the Li–SiSB additive exhibited lower values of Rct compared to the pure electrolyte which shows that addition of the zwitterion reduces the Rct between the electrolyte and cathode [19] due to formation of a stable SEI hence higher discharge capacity observed even at lower C-rates [5]. The surface morphologies of the graphite electrodes after cell formation are shown in Fig. 9 and the elemental analysis using EDX is summarized in Table 3. An SEI film formed can be observed for used electrodes compared to the unused electrode. It can be seen that the SEI layer is formed and distributed across the surface of the electrode. The SEI layer of the electrode where the pure electrolyte was used is shown to be thicker (e3μmÞ than that formed when using Li–SiSB (e1:5μmÞ which is further confirmed by the elemental analysis. The atomic percentages (Table 3) which were determined after 100 cycles also show that the fluorine percentage on the electrode surface decreases with the use of the Li–SiSB additive. This is due the zwitterion enabling (i) the forma tion of SEI before the decomposition and (ii) reduced migration of EC and PF6 towards the electrode resulting in a thinner SEI. The decom position of LiPF6 leads to the production of LiF which forms part of the SEI and also PF5 and PF3 [82,83] and also Liþ ion react with EC mole cules in a single electron ring opening reaction leading to formation of Lithium carbonate that also forms part of the SEI as shown in Equations (4)–(6). The formation of LiF causes a reduction in the Liþ concentration in the electrolyte thereby reducing battery capacity [84–87]. PF6 þ 3Liþ þ 2e → 3LiF↓ þ PF3 ↑
(4)
LiPF6 → LiF↓ þ PF5 ↑
(5)
(6)
4. Conclusion Zwitterionic Li–SiSB was synthesized and used as a liquid electrolyte additive for LIBs. Electrolyte samples with the Li–SiSB additive showed an increased ionic conductivity and enhanced electrochemical stability. The NCM/graphite cells with the electrolyte samples with the Li–SiSB showed greater discharge capacities at higher C-rates and a stable cycling performance due to increased ionic conductivity and stable SEI formation. The high performance electrolyte additive can greatly in crease energy density due to its high voltage window and increase power density due to its high ionic conductivity. The Li–SiSB additive is therefore a strong candidate for use as a liquid electrolyte additive for high voltage LIBs. 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. Acknowledgements This research was supported by a grant (10047758) from the Tech nology Development Program for Strategic Core Materials funded by the Korean Ministry of Trade, Industry & Energy. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.matchemphys.2019.122577. References [1] S. Yang, Y. Gong, Z. Liu, L. Zhan, D.P. Hashim, L. Ma, R. Vajtai, P.M. Ajayan, Bottom-up approach toward single-crystalline VO2-graphene ribbons as cathodes for ultrafast lithium storage, Nano Lett. 13 (2013) 1596–1601. [2] B. Ji, F. Zhang, M. Sheng, X. Tong, Y. Tang, A novel and generalized lithium-ionbattery configuration utilizing Al foil as both anode and current collector for enhanced energy density, Adv. Mater. 29 (1–7) (2017). [3] G. Ma, S. Li, W. Zhang, Z. Yang, S. Liu, X. Fan, F. Chen, Y. Tian, W. Zhang, S. Yang, M. Li, A general and mild approach to controllable preparation of manganese-based micro- and nanostructured bars for high performance lithium-ion batteries, Angew. Chem. Int. Ed. 55 (2016) 3667–3671. [4] S.S. Zhang, A review on the separators of liquid electrolyte Li-ion batteries, J. Power Sources 164 (2007) 351–364. [5] L. Hamenu, H.S. Lee, M. Latifatu, K.M. Kim, J.W. Park, Y.G. Baek, J.M. Ko, R. B. Kaneret, Lithium-silica nanosalt as a low-temperature electrolyte additive for lithium-ion batteries, Curr. Appl. Phys. 16 (2016) 611–617. [6] M. Latifatu, M. Hu, S. Jun, C. Yeajoon, C. Kang, W.I. Cho, J.M. Ko, Lithium modified silica as electrolyte additive for lithium secondary batteries, Solid State Ion. 319 (7–12) (2018). [7] J. Ha, H.S. Lee, L. Hamenu, M. Latifatu, Y.M. Lee, K.M. Kim, J. Oh, W.I. Cho, J. M. Ko, Improvement of low-temperature performance by adopting polydimethylsiloxane- g -polyacrylate and lithium-modified silica nanosalt as electrolyte additives in lithium-ion batteries, J. Ind. Eng. Chem. 37 (2016) 325–329. [8] J. Meng, F. Chu, J. Hu, C. Li, Liquid polydimethylsiloxane grafting to enable dendrite-free Li plating for highly reversible Li-metal batteries, Adv. Funct. Mater. 29 (1–13) (2019).
9
I. Phiri et al.
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[9] F. Chu, et al., Metal-organic frameworks as electrolyte additives to enable ultrastable plating/stripping of Li anode with dendrite inhibition, ACS Appl. Mater. Interfaces 11 (2019) 3869–3879. [10] J. Hu, K. Chen, C. Li, Nanostructured Li-rich fluoride coated by ionic liquid as high ion-conductivity solid electrolyte additive to suppress dendrite growth at Li metal anode, ACS Appl. Mater. Interfaces 10 (2018) 34322–34331. [11] F. Chu, J. Hu, J. Tian, X. Zhou, Z. Li, C. Li, In situ plating of porous Mg network layer to reinforce anode dendrite suppression in Li-metal batteries, ACS Appl. Mater. Interfaces 10 (2018) 12678–12689. [12] J. Hu, J. Tian, C. Li, Nanostructured carbon nitride polymer-reinforced electrolyte to enable dendrite-suppressed lithium metal batteries, ACS Appl. Mater. Interfaces 9 (2017) 11615–11625. [13] I. Phiri, C.Y. Bon, S. Kim, M. Manasi, L. Hamenu, A. Madzvamuse, S.H. Kim, J. M. Ko, Effects of novel benzotriazole based zwitterionic salt as electrolyte additive for lithium ion batteries, Curr. Appl. Phys. 20 (122–131) (2020). [14] N.S. Choi, Y.M. Lee, B.H. Lee, J.A. Lee, J.K. Park, Nanocomposite single ion conductor based on organic-inorganic hybrid, Solid State Ion. 167 (2004) 293–299. [15] J. Sun, P. Bayley, D.R. Macfarlane, M. Forsyth, Gel electrolytes based on lithium modified silica nano-particles, Electrochim. Acta 52 (2007) 7083–7090. [16] H. Kim, D.Q. Nguyen, H.W. Bae, J.S. Lee, B.W. Cho, H.S. Kim, M. Cheong, H. Lee, Effect of ether group on the electrochemical stability of zwitterionic imidazolium compounds, Electrochem. Commun. 10 (2008) 1761–1764. [17] D.Q. Nguyen, J. Hwang, J.S. Lee, H. Kim, H. Lee, M. Cheong, B. Lee, H.S. Kim, Multi-functional zwitterionic compounds as additives for lithium battery electrolytes, Electrochem. Commun. 9 (2007) 109–114. [18] D.Q. Nguyen, H.W. Bae, E.H. Jeon, J.S. Lee, M. Cheong, H. Kim, H.S. Kima, H. Lee, Zwitterionic imidazolium compounds with high cathodic stability as additives for lithium battery electrolytes, J. Power Sources 183 (2008) 303–309. [19] S. Yamaguchi, M. Yoshizawa-fujita, H. Zhu, M. Forsyth, Y. Takeoka, M. Rikukawa, Improvement of charge/discharge properties of oligoether electrolytes by zwitterions with an attached cyano group for use in lithium-ion secondary batteries, Electrochim. Acta 186 (2015) 471–477. [20] F. Wohde, R. Bhandary, J.M. Moldrickx, J. Sundermeyer, M. Sch€ onhoff, B. Roling, Liþ ion transport in ionic liquid-based electrolytes and the influence of sulfonatebased zwitterion additives, Solid State Ion. 284 (2016) 37–44. [21] F. Lind, L. Rebollar, P. Bengani-Lutz, A. Asatekin, M.J. Panzer, Zwitterioncontaining ionogel electrolytes, Chem. Mater. 28 (2016) 8480–8483. [22] T. Mizumo, T. Watanabe, H. Ohno, Thermally stable and proton conductive ionogel based on brønsted acidic ionic liquid with the support of silicate network, Polym. J. 40 (2008) 1099–1104. [23] H. Ohno, M. Yoshizawa-Fujita, Y. Kohno, Design and properties of functional zwitterions derived from ionic liquids, Phys. Chem. Chem. Phys. 20 (2018) 10978–10991. [24] Q. Shao, L. Mi, X. Han, T. Bai, S. Liu, Y. Li, S. Jiang, Differences in cationic and anionic charge densities dictate zwitterionic associations and stimuli responses, J. Phys. Chem. B 118 (2014) 6956–6962. [25] Z. Chen, W.Q. Lu, J. Liu, K. Amine, LiPF6/LiBOB blend salt electrolyte for highpower lithium-ion batteries, Electrochim. Acta 51 (2006) 3322–3326. [26] R. Rondla, J.C.Y. Lin, C.T. Yang, I.J.B. Lin, Strong tendency of homeotropic alignment and anisotropic lithium ion conductivity of sulfonate functionalized zwitterionic imidazolium ionic liquid crystals, Langmuir 29 (2013) 11779–11785. [27] C. Tiyapiboonchaiya, J.M. Pringle, J. Sun, N. Byrne, P.C. Howlett, D.R. Macfarlane, M. Forsyth, The zwitterion effect in high-conductivity polyelectrolyte materials, Nat. Mater. 3 (29–32) (2004). [28] Q. Shao, Y. He, S. Jiang, Molecular Dynamics simulation study of ion interactions with zwitterions, J. Phys. Chem. B 115 (2011) 8358–8363. [29] M. Yoshizawa, A. Narita, H. Ohno, Design of ionic liquids for electrochemical applications, Aust. J. Chem. 57 (2004) 139–144. [30] H. Lee, D.B. Kim, S.H. Kim, H.S. Kim, S.J. Kim, D.K. Choi, Y.S. Kang, J. Won, Zwitterionic silver complexes as carriers for facilitated-transport composite membranes, Angew. Chem. Int. Ed. 43 (2004) 3053–3056. [31] H. Ohno, M. Yoshizawa, W. Ogihara, A new type of polymer gel electrolyte: zwitterionic liquid/polar polymer mixture, Electrochim. Acta 48 (2003) 2079–2083. [32] M. Yoshizawa, M. Hirao, K. Ito-Akita, H. Ohno, Ion conduction in zwitterionic-type molten salts and their polymers, J. Mater. Chem. 11 (2001) 1057–1062. [33] M. Yoshizawa-Fujita, N. Byrne, M. Forsyth, D.R. MacFarlane, H. Ohno, Proton transport properties in zwitterion blends with Brønsted acids, J. Phys. Chem. B 114 (2010) 16373–16380. [34] K. Ito, N. Nishina, H. Ohno, High lithium ionic conductivity of poly(ethylene oxide) s having sulfonate groups on their chain ends, J. Mater. Chem. 7 (1997) 1357–1362. [35] A. Narita, W. Shibayama, H. Ohno, Structural factors to improve physico-chemical properties of zwitterions as ion conductive matrices, J. Mater. Chem. 16 (2006) 1475–1482. [36] N. Byrne, P.C. Howlett, D.R. MacFarlane, M.E. Smith, A. Howes, A.F. Hollenkamp, T. Bastow, P. Hale, M. Forsyth, Effect of zwitterion on the lithium solid electrolyte interphase in ionic liquid electrolytes, J. Power Sources 184 (2008) 288–296. [37] K. Xu, Nonaqueous liquid electrolytes for lithium-based rechargeable batteries, Chem. Rev. 104 (2004) 4303–4417. [38] N.S. Choi, Z. Chen, S.A. Freunberger, X. Ji, Y.K. Sun, K. Amine, G. Yushin, L. F. Nazar, J. Cho, P.G. Bruce, Challenges facing lithium batteries and electrical double-layer capacitors, Angew. Chem. Int. Ed. 51 (2012) 9994–10024. [39] K. Xu, Electrolytes and interphases in Li-ion batteries and beyond, Chem. Rev. 114 (2014) 11503–11618.
[40] B.N. Byrne, P.C. Howlett, D.R. Macfarlane, M. Forsyth, The zwitterion effect in ionic Liquids : towards practical rechargeable lithium-metal batteries, Adv. Mater. 17 (2005) 2497–2501. [41] F. Schipper, E.M. Erickson, C. Erk, J. Shin, F.F. Chesneau, D. Aurbach, Review — recent advances and remaining challenges for lithium I . Nickel-rich, LiNiCoyMnzO2, J. Electrochem. Soc. 164 (2017) 6220–6228. [42] M. Xu, L. Zhou, L. Hao, L. Xing, W. Li, B.L. Lucht, Investigation and application of lithium difluoro(oxalate)borate (LiDFOB) as additive to improve the thermal stability of electrolyte for lithium-ion batteries, J. Power Sources 196 (2011) 6794–6801. [43] H. Zhao, Z. Jia, Yuan Wen, H. Hu, Y. Fu, G.L. Baker, G. Liu, Fumed silica-based single-ion nanocomposite electrolyte for lithium batteries, ACS Appl. Mater. Interfaces 7 (2015) 19335–19341. [44] Y. Zhu, W. Xie, F. Zhang, T. Xing, J. Jin, Superhydrophilic in-situ-cross-linked zwitterionic polyelectrolyte/PVDF-blend membrane for highly efficient oil/water emulsion separation, ACS Appl. Mater. Interfaces 9 (2017) 9603–9613. [45] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-Ray Photoelectron Spectroscopy, Perkin-Elmer, Boca Raton, FL, 1992. [46] S. Yeh, C. Chen, W. Chen, C. Huang, Modification of silicone elastomer with zwitterionic silane for durable antifouling properties, Langmuir 30 (2014) 11386–11393. [47] S.H. Ye, C.A. Johnson Jr., J.R. Woolley, H. Murata, L.J. Gamble, K. Ishihara, W. R. Wagner, Simple surface modification of a titanium alloy with silanated zwitterionic phosphorylcholine or sulfobetaine modifiers to reduce thrombogenicity, Colloids Surf., B 79 (2010) 357–364. [48] B. Liu, L. Zhang, H. Wang, Z. Bian, Preparation of MCC/MC silica sponge and its oil/water separation apparatus application, Ind. Eng. Chem. Res. 56 (2017) 5795–5801. [49] G. Socrates, Infrared and Raman Characteristics Group Frequencies: Tables and Charts, third ed., JohnWiley and Sons, 2001. [50] Y. Song, Y. Sun, X. Zhang, J. Zhou, a L. Zhang, Homogeneous quaternization of cellulose in NaOH/urea aqueous solutions as gene carriers, Biomacromolecules 9 (2008) 2259–2264. [51] B.R. Knowles, P. Wagner, S. McLaughlin, M.J. Higgins, P.J. Molino, Silica nanoparticles functionalized with zwitterionic sulfobetaine siloxane for application as a versatile antifouling coating system, ACS Appl. Mater. Interfaces 9 (2017) 18584–18594. [52] M.G. McLin, C.A. Angell, Ion-pairing effects on viscosity/conductance relations in Raman-characterized polymer electrolytes: lithium perchlorate and sodium triflate in PPG(4000), J. Phys. Chem. 95 (1991) 9464–9469. [53] K.M. Kim, N. Vu Ly, J.H. Won, Y.G. Lee, W.I. Cho, J.M. Ko, R.B. Kaner, Improvement of lithium-ion battery performance at low temperature by adopting polydimethylsiloxane-based electrolyte additives, Electrochim. Acta 136 (2014) 182–188. [54] L. Hamenu, Alfred Madzvamuse, Latifatu Mohammed, Yong Min Lee, Jang Myoun Ko, Chris Yeajoon Bon, Sang Jun Kim, Won Il Cho, Yong Gu Baek, Jongwook Park, Benzotriazole as an electrolyte additive on lithium-ion batteries performance, J. Ind. Eng. Chem. 53 (2017) 241–246. [55] J. Cardoso, D. Nava, P. Garc, F. Herna, Synthesis, characterization and theoretical insights of green chitosan derivatives presenting enhanced Li þ ionic conductivity, J. Phys. Chem. C 119 (2015) 4655–4665. [56] J.N. Krishnan, H.S. Kim, J.K. Lee, B. Cho, E.J. Roh, S. Lee, Organic solvents containing zwitterion as electrolyte for Li ion cells, Bull. Korean Chem. Soc. 29 (2010) 1705–1710. [57] J. Sun, D.R. Macfarlane, N. Byrne, M. Forsyth, Zwitterion effect in polyelectrolyte gels based on lithium methacrylate- N,N-dimethyl acrylamide copolymer, Electrochim. Acta 51 (2006) 4033–4038. [58] Z.H. Li, Q.L. Xia, L.L. Liu, G.T. Lei, Q.Z. Xiao, D.S. Gao, X.D. Zhou, Effect of zwitterionic salt on the electrochemical properties of a solid polymer electrolyte with high temperature stability for lithium ion batteries, Electrochim. Acta 56 (2010) 804–809. [59] P. Bengani-Lutz, E. Converse, P. Cebe, A. Asatekin, Self-assembling zwitterionic copolymers as membrane selective layers with excellent fouling resistance: effect of zwitterion chemistry, ACS Appl. Mater. Interfaces 9 (2017) 20859–20872. [60] M. Suematsu, M. Yoshizawa-fujita, H. Zhu, M. Forsyth, Y. Takeoka, M. Rikukawa, Effect of zwitterions on electrochemical properties of oligoether-based electrolytes, Electrochim. Acta 175 (2015) 209–213. [61] H. Louis, Y.G. Lee, K.M. Kim, W. Il Cho, J.M. Ko, Suppression of aluminum corrosion in lithium bis(trifluoromethanesulfonyl) imide based electrolytes by the addition of fumed silica, Bull. Korean Chem. Soc. 34 (2013) 1795–1799. [62] Y. Li, P.S. Fedkiw, Effect of gel electrolytes containing silica nanoparticles on aluminum corrosion, Electrochim. Acta 52 (2007) 2471–2477. [63] S.J. An, J. Li, C. Daniel, D. Mohanty, S. Nagpure, D.L. Wood, The state of understanding of the lithium-ion-battery graphite solid electrolyte interphase (SEI) and its relationship to formation cycling, Carbon N. Y. 105 (2016) 52–76. [64] V. Etacheri, R. Marom, R. Elazari, G. Salitra, D. Aurbach, Challenges in the development of advanced Li-ion batteries: a review, Energy Environ. Sci. 4 (2011) 3243–3262. [65] K. Tasaki, K. Kanda, T. Kobayashi, S. Nakamura, M. Ue, Theoretical studies on the reductive decompositions of solvents and additives for lithium-ion batteries near lithium anodes, J. Electrochem. Soc. 153 (2006) A2192. [66] S. Flandrois, B. Simon, Carbon materials for lithium-ion rechargeable batteries, Carbon N. Y. 37 (1999) 165–180. [67] S.H. Lee, H.G. You, K.S. Han, J. Kim, I.H. Jung, J.H. Song, A new approach to surface properties of solid electrolyte interphase on a graphite negative electrode, J. Power Sources 247 (2014) 307–313.
10
I. Phiri et al.
Materials Chemistry and Physics 243 (2020) 122577
[68] P. Nov� ak, F. Joho, R. Imhof, J.C. Panitz, O. Haas, In situ investigation of the interaction between graphite and electrolyte solutions, J. Power Sources 81–82 (1999) 212–216. [69] L. Hamenu, Alfred Madzvamuse, Latifatu Mohammed, Yong Min Lee, Jang Myoun Ko, Chris Yeajoon Bon, Sang Jun Kim, Won Il Cho, Yong Gu Baek, Jongwook Park, Benzotriazole as an electrolyte additive on lithium-ion batteries performance, J. Ind. Eng. Chem. 53 (2017) 241–246. [70] M. Yamagata, N. Nishigaki, S. Nishishita, Y. Matsui, T. Sugimoto, M. Kikuta, T. Higashizaki, M. Kono, M. Ishikawa, Charge–discharge behavior of graphite negative electrodes in bis(fluorosulfonyl)imide-based ionic liquid and structural aspects of their electrode/electrolyte interfaces, Electrochim. Acta 110 (2013) 181–190. [71] S. Seki, Y. Kobayashi, H. Miyashiro, Y. Ohno, Y. Mita, N. Terada, P. Charest, A. Guerfi, K. Zaghib, Compatibility of N-methyl-N-propylpyrrolidinium cation room-temperature ionic liquid electrolytes and graphite electrodes, J. Phys. Chem. C 112 (2008) 16708–16713. [72] J. Reiter, M. N� adhern� a, R. Dominko, Graphite and LiCo1/3Mn1/3Ni1/3O2 electrodes with piperidinium ionic liquid and lithium bis(fluorosulfonyl)imide for Li-ion batteries, J. Power Sources 205 (2012) 402–407. [73] J. Towada, T. Karouji, H. Sato, Y. Kadoma, K. Shimada, K. Ui, Charge–discharge characteristics of natural graphite electrode in N, N-diethyl-N-methyl-N-(2methoxyethyl)ammonium bis(trifluoromethylsulfonyl)amide containing lithium ion for lithium-ion secondary batteries, J. Power Sources 275 (2015) 50–54. [74] S. Horiuchi, H. Zhu, M. Forsyth, Y. Takeoka, M. Rikukawa, M. Yoshizawa-Fujita, Synthesis and evaluation of a novel pyrrolidinium-based zwitterionic additive with an ether side chain for ionic liquid electrolytes in high-voltage lithium-ion batteries, Electrochim. Acta 241 (2017) 272–280. [75] M. Liu, B. Jin, Q. Zhang, X. Zhan, F. Chen, High-performance solid polymer electrolytes for lithium ion batteries based on sulfobetaine zwitterion and poly (ethylene oxide) modified polysiloxane, J. Alloy. Comp. 742 (2018) 619–628. [76] A.J. Smith, J.C. Burns, J.R. Dahn, A high precision study of the coulombic efficiency of Li-ion batteries, Electrochem. Solid State Lett. 13 (2010) A177.
[77] F. Yang, D. Wang, Y. Zhao, K.L. Tsui, S.J. Bae, A study of the relationship between coulombic efficiency and capacity degradation of commercial lithium-ion batteries, Energy 145 (2018) 486–495. [78] I.A. Profatilova, S.S. Kim, N.S. Choi, Enhanced thermal properties of the solid electrolyte interphase formed on graphite in an electrolyte with fluoroethylene carbonate, Electrochim. Acta 54 (2009) 4445–4450. [79] X. Zuo, C. Fan, X. Xiao, J. Liu, J. Nan, High-voltage performance of LiCoO2/ graphite batteries with methylene methane disulfonate as electrolyte additive, J. Power Sources 219 (2012) 94–99. [80] M.J. Boyer, G.S. Hwang, Theoretical evaluation of ethylene carbonate anion transport and its impact on solid electrolyte interphase formation, Electrochim. Acta 266 (2018) 326–331. [81] Y. Li, P.S. Fedkiw, Nanocomposite gel electrolytes based on fumed silica for lithium-ion batteries, J. Electrochem. Soc. 12 (2007) 1140–1145. [82] T. Kawaguchi, K. Shimada, T. Ichitsubo, S. Yagi, E. Matsubara, Surface-layer formation by reductive decomposition of LiPF6 at relatively high potentials on negative electrodes in lithium ion batteries and its suppression, J. Power Sources 271 (2014) 431–436. [83] L. Xing, X. Zheng, M. Schroeder, J. Alvarado, A. von Wald Cresce, K. Xu, Q. Li, W. Li, Deciphering the ethylene carbonate-propylene carbonate mystery in Li-ion batteries, Acc. Chem. Res. 51 (2018) 282–289. [84] X. Cui, F. Tang, Y. Zhang, C. Li, D. Zhao, F. Zhou, S. Li, H. Feng, Influences of trace water on electrochemical performances for lithium hexafluoro phosphate- and lithium Bis(oxalato)borate-based electrolytes, Electrochim. Acta 273 (2018) 191–199. [85] C. Li, Z. Li, P. Wang, H. Liu, D. Zhao, S.X. Wang, S. Li, Studies of air-exposure effects and remediation measures on lithium bis(oxalato)borate, New J. Chem. 43 (2019) 14238–14245. [86] S. Li, D. Zhao, P. Wang, X. Cui, F. Tang, Electrochemical effect and mechanism of adiponitrile additive for high-voltage electrolyte, Electrochim. Acta 222 (2016) 668–677. [87] J.G. Han, K. Kim, Y. Lee, N.S. Choi, Scavenging materials to stabilize LiPF6 -containing carbonate-based electrolytes for Li-ion batteries, Adv. Mater. 31 (2019) 1–12.
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