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A novel high-performance 3D polymer binder for silicon anode in lithium-ion batteries
Journal of Physics and Chemistry of Solids 135 (2019) 109113
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A novel high-performance 3D polymer binder for silicon anode in lithiumion batteries
T
Lubing Yua, Jian Liua,b,c,*, Shuaishuai Hea, Chaofan Huanga, Lihui Gana,b,c,**, Zhengliang Gonga,***, Minnan Longa,b,c a
College of Energy, Xiamen University, Xiamen, 361005, China Xiamen Key Laboratory of Clean and High-valued Applications of Biomass, Xiamen University, Xiamen, 361102, China c Fujian Engineering and Research Center of Clean and High-valued Technologies for Biomass, Xiamen University, Xiamen, 361102, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: 3D polymer binder Carboxymethylcellulose Lithium-ion batteries Silicon anode
For high-capacity silicon (Si) anodes, the design of new binder is a feasible way to overcome the rapid capacity decay attributed to the large volume change of silicon (Si) anode in the repeated charging/discharging process. Here a newly designed binder with 3D structure was developed using CMC as the backbone, and acrylamide (AM), acrylic acid (AA) as the branch. The molecular structure was characterized by Fourier transform infrared (FTIR), and ethanol washing was applied for getting rid of unreacted monomers. The multifunctional binder with 3D structure and rich polar groups was prepared by cross-linking grafting. Polyacrylamide provides a strong adhesion and contributes to the formation of the solid electrolyte intermediate phase (SEI) layers on the surface of electrodes. The results show that CMC and polyacrylic acid with carboxyl groups not only strengthened the bonding force between the current collectors and the silicon nanoparticles (SiNPs), also improved the linkage among SiNPs. Therefore, the loading weight of commercial Si was about 0.75 mg cm−2, even after 150 deep cycles, and a high capacity of 1210.7 mAh g−1 was resulted in the Si anode. The prepared novel high-performance binder shows a potential application on the silicon anode in lithium-ion batteries.
1. Introduction For the past few years, with the rapid development of portable electronic devices and energy storage devices [1], the demand of lithium ion battery (LIB) has increased sharply due to its advantages such as high energy density, good rate performance, low price, safety and durability [2–4]. As the most popular anode material for commercial LIBs, graphite has only a theoretical specific capacity of 372 mAh g−1, which makes it difficult to meet the market demand [5]. Silicon (Si) is deemed to the most promising next-generation negative electrode material because it is an abundant element in the earth and its theoretical specific capacity is recorded as about 4200 mAh g−1, more than ten times as much as that of traditional graphite materials [2,6,7]. However, in order to realize the commercialization of Si anodes, there are still two problems to be solved. One is that the volume of Si particles vigorously expands (~400%) during repeated lithiation/delithiation. It resulted in rapid capacity decay and severe pulverization of the electrode, thus the cycle life is shortened [6,8–11]. The other is the
formation of an unstable SEI film on the surface of the SiNPs during charge/discharge, which results in an increase in impedance and coulomb efficiency goes down [8,12]. In order to solve the above problems, a series of strategies have been proposed, including changing the morphology of Si particles, using nanosized Si and nano-Si composite materials, such as Si nanoparticles [13], nanowires [14,15], nanotubes [16,17], porous silicon [18,19], carbon-coated materials [20,21]. All of the above related literatures suggest that the introduction of coatings and nanostructures can mitigate the damage of large volume change to the electrode effectively, reserving better cycle performance and higher capacity, but these processes are relatively complicated and not conducive to industrialization [22]. Therefore, it is meaningful to maintain the structural stability of electrodes for further boost the electrochemical performance of the negative electrode materials. A more convenient and practical idea is the development of a structurally stable polymer binder to adapt to the reciprocating volume change in the repeated cycles. The related researches in this area have also increased in recent years [6,23].
*
Corresponding author. College of Energy, Xiamen University, Xiamen, 361005, China. Corresponding author. Xiamen Key Laboratory of Clean and High-valued Applications of Biomass, Xiamen University, Xiamen, 361102, China. *** Corresponding author. E-mail addresses: [email protected] (J. Liu), [email protected] (L. Gan), [email protected] (Z. Gong). **
https://doi.org/10.1016/j.jpcs.2019.109113 Received 18 May 2019; Received in revised form 15 July 2019; Accepted 21 July 2019 Available online 22 July 2019 0022-3697/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Physics and Chemistry of Solids 135 (2019) 109113
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2.3. Electrochemical measurements
Serving as one of the important battery components, the binders have the function of attaching the active material and the conductive agent to the copper foil. Although the binder is not the active component of the battery electrodes, it has great influence on the electrochemical properties and the integrity of the electrode [24]. Although poly(vinylidene fluoride) (PVDF) is a widely used LIBs binder, there are also difficulties to adapt to future development trends due to its environmentally unfriendly nature and the weak interaction force between PVDF binder and nano-Si particles. Recently, many studies have confirmed that functional binders with carboxyl group and amine group, such as sodium carboxymethyl cellulose (CMC) [25], sodium alginate (SA) [26], xanthan gum [27], guar gum (GG) [28], poly(acrylic acid) (PAA) [29], poly(acrylamide) (PAM) [4] and polyamide imide (PAI), etc., show better properties, lower cost, more environmentallyfriendly than PVDF in Si-based anodes. These functional binders form covalent bonds with the Si particles, which improves the performance of the battery significantly. In addition, grafting a polyfunctional group such as polyvinyl alcohol or dopamine onto the PAA to form a conductive polymer can improve the electrochemical properties of Si anode [9,10]. Despite that, there is no multipoint contact between the onedimensional (1D) polymer binder and Si particles, resulting in the tendency for Si to slip during repeated cycles [30]. Therefore, there is a need to develop functional polymers with a three-dimensional (3D) network structure, such as crosslinked PAM [4], PAA grafted CMC [31], SA grafted PAA [1] and CMC grafted PAN [6], which has been successfully applied on Si-based anodes. Although these functional binders have significantly improved electrochemical performances, the high capacity Si-based LIBs for industrialization still requires the exploration of new binder systems. In this work, we report a functionalized 3D structure binder with a linear CMC skeleton for Si-based LIBs, which successfully grafts carboxyl-rich AA and AM with a large amount of amine groups by free radical polymerization. Unlike the simple linear polymers as CMC, sodium poly (acrylic acid) (NaPAA) and PAM, the newly developed composite binder has a 3D network structure with more contact points for Si particles, and contains high-density carboxyl groups for strengthening the binding force between the slurry and the Cu current collectors. The enhanced binding forces contribute to the structural integrity of electrode, and a large amount of amine-based PAM can increase the conductivity. Therefore, the electrochemical performance of Si anode improves effectively.
SiNPs, acetylene black and the prepared binder were ground into a uniform paste in the weight ratio of 6:2:2.The slurry was coated on the pure copper foil, dried at 50 °C for 12 h in a vacuum oven. The load of commercial Si on the copper foil is approximately 0.75 mg cm−2. The electrolyte is a mixture of diethyl carbonate (DEC), dimethyl carbonate (DMC) and ethyl carbonate (EC) (volume ratio 1:1:1) dissolved in 1.0 mol of LiPF6, containing 2% vinyl carbonate (VC) and 10 wt % ethyl fluoride carbonate (FEC) as additives. The CR2025 button battery is assembled in a glove box under argon atmosphere with no more than 10 ppm of oxygen and water. The membrane and cathode materials are Celgard 2400 film and Li sheet, respectively. The electrochemical performance was investigated in the LAND battery test system (CT2001A, made in wuhan, China) at 30 °C in the voltage window of 0.005–1.500 V, relative to the Li/Li +. 2.4. Material characterization The prepared samples were investigated by Fourier transform infrared (FTIR, Nicoleti S5, Thermo Fisher, USA, scanning electron microscopy (SEM, Zeiss Sigma) and X-ray diffraction (XRD, Ultima IV, Rigaku, Japan, at the scan rate of 10°min−1 within 2θ = 10–90°. The 180° peel test was performed on a Universal Material Evaluation Tester (UTM-4000, SUNS, Shenzhen, China). First, the different binders were uniformly formulated into a 2% homogeneous sol, and then the binder was coated on a Cu foil in a thickness of 200 μm and subjected to vacuum drying at 50 °C for 12 h. Prior to the peel test, the Cu foil was cut into long strips of 4 cm*1 cm and then joined to a 1 cm wide tape. The speed of peeling was 1 cm min-1, and the force versus displacement diagram was online recorded. The viscosity of the binder was tested using an LVDVC230 viscosity characterization tester (Brookfiedl, USA) at a test temperature of 25 °C and the binder solution concentration of 15 g L−1. Prior to the viscosity test, the binder was stirred overnight to ensure uniform dispersion. 3. Results and discussion 3.1. Design concept and characterizations of CMC-NaPAA-PAM 3.1.1. Design concept and FTIR spectra of CMC-NaPAA-PAM In the presence of CMC, ammonium persulfate was used as the initiator, N,N-Methylenebisacrylamide (MBAA) acting as the crosslinker, and the acrylic acid and acrylamide monomers were polymerized and covalently crosslinked to obtain a 3D hyperbranched polymeric binder. The design concept of the CMC-NaPAA-PAM is shown in Fig. 1. The binders were characterized by FTIR spectra. (Fig. 2). After grafting polymerization and covalently cross-linking, the absorption peaks at 1260 cm−1 (-OH) and 894 cm−1 (C–O) completely disappeared [32]. This indicates that by heating, the initiator ammonium persulfate successfully extracts H from the CMC to form a large amount of free radicals [33,34]. A few new absorption peaks at 1653 cm−1 (C]O, NA, amide Ⅰ), 1616 cm−1 (N–H, NA, amide Ⅱ), 1420 cm−1 (C–N, NA, amide Ⅲ) [30], 1563 cm−1(Back stretching vibration) and −1 1451 cm (stretching vibration) appeared, which can be ascribed to the –COO− groups from NaPAA [6]. In addition, The peak at 1113 cm−1 is caused by an increase in the –NH– stretching due to the crosslinking of MBAA [35]. The results evidenced the successful synthesis of 3D polymer binder.
2. Experimental section 2.1. Materials Commercial Si nanoparticles (Si NPs) in the diameters about 100 nm were from Naiou Co., China. Other reagents were purchased from Aladdin. The electrolyte and lithium-plate were obtained from Suzhou Fosai new material Co.
2.2. 3D binder preparation CMC (1.0 g) was dissolved in 100 mL deionized water. Nitrogen was injected for 3 h to remove oxygen, and then 0.2 g of acrylamide (AM), 0.1 g of N,N′-methylenebis(acrylamide) (MBAA), 3 mL of acrylic acid, 0.10 g of (NH4)2S2O8 and 0.03 g of NaHSO3 were added. The mixed liquor was then heated to 55 °C in a water bath and stirred for 3 h to produce the binder in a nitrogen atmosphere, named as CMC-NaPAAPAM. The obtained sample was adjusted to pH = 6 with sodium hydroxide solution to get the raw CMC-NaPAA-PAM. Finally, the neutralized gel was washed for three times with absolute ethanol, and then vacuum dried to obtain the powdery CMC-NaPAA-PAM.
3.1.2. XRD analysis of CMC-NaPAA-PAM X-ray diffraction (XRD) analysis is an effect method to investigate the crystal structure of the binders. For comparison, the XRD of CMC, NaPAA and CMC-NaPAA-PAM were measured. As shown in Fig. 3. CMC showed a characteristic diffraction peak at 20.74°, and NaPAA showed three characteristic diffraction peaks at 18.94°, 24.24°, and 33.62°, 2
Journal of Physics and Chemistry of Solids 135 (2019) 109113
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Fig. 1. Scheme for synthesis of CMC-NaPAA-PAM.
24.00°, almost same to one of those of NaPPA, indicating that part of the original structure also affects in the new structure of CMC-NaPAAPAM. 3.1.3. 180° peeling and viscosity test of CMC-NaPAA-PAM In order to evaluate the adhesion between the binder and the Cu foil, we conducted a peel test at 180° The force-displacement curve (Fig. 4a) clearly shows that the average peel force of CMC-NaPAA-PAM (1.18 N) is greater than that of NaPAA (1.08 N) and CMC (0.52 N), indicating that the CMC-NaPAA-PAM rich in amine groups and carboxyl groups increases the adhesion of polymeric binder to the surface of Si, so the mechanical stability of Si electrode is enhanced. This conclusion is consistent with the results of PAA grafted CMC [28], and its strong peel force is considered to be one of the reasons for the enhanced electrode cycle stability. The rheological properties of the binders were evaluated through a viscosity test, as shown in Fig. 4b. The viscosity of CMC, NaPAA and CMC-NaPAA-PAM are 879 mPa s, 3956 mPa s and 1026 mPa s, respectively. Since the tight winding reduced its apparent viscosity in the aqueous dispersion, the viscosity of the CMC-NaPAA-PAM is not so high as expected. It is assumed that compared to the 1D linear structure of NaPAA and CMC, CMC-NaPAA-PAM with 3D network structure has a complex branched structure with a certain steric hindrance, so that the branches can extend without destroying the bonds between each other.
Fig. 2. FTIR spectra of CMC-NaPAA-PAM, CMC and Na PAA.
3.2. Electrochemical performances 3.2.1. Cycling performance of the ethanol washed CMC-NaPAA-PAM at 420 mA g−1 Since the conversion rate cannot reach 100% in any polymerization process, a certain amount of monomers must be remained. In order to eliminate the potential negative impacts, an ethanol washing step was introduced in the research. The effect of ethanol washing on the electrochemical properties was explored (Fig. 5). The control sample free of ethanol washing is named as raw CMC-NaPAA-PAM. For the long-term cycle stability, the average coulombic efficiency of CMC-NaPAA-PAM was 98.80%(2–150 cycle), and after 150 cycles, a relatively high specific capacity of 1210.7 mAh g−1 was still kept. On the contrary, the average coulomb efficiency of the raw CMC-NaPAA-PAM from the 2nd to the 150th cycle was 98.06%. After 150 cycles, the specific capacity only retained 793.1 mAh g−1. Both average coulomb efficiency and capacity retention rate were improved to different degrees after ethanol washing. Through qualitative analysis of ethanol washing solution by gas chromatography (Agilent Technologies, USA), unpolymerized AM monomer was detected in the alcohol washing solution, which may be one of the facts affecting the electrochemical properties. The specific mechanism is still not clear, and further research is needed. Therefore, the innovative ethanol washing step in this research is meaningful.
Fig. 3. XRD patterns of CMC, NaPAA and CMC-NaPAA-PAM.
which are identified as the different lattice planes. In the curve of 3D binder, the characteristic diffraction peaks of both NaPAA and CMC vanished. The newly generated peak does not match those of the crystal structure of NaPAA or CMC, which indicates that the molecular structure of CMC-NaPAA-PAM is reconstituted and recrystallized in the reaction. The obtained XRD pattern displayed a diffraction peaks at 3
Journal of Physics and Chemistry of Solids 135 (2019) 109113
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Fig. 4. (a)The results on 180° peeling test of the binders. (b) The results on viscosity test of the binders.
512.0 and 610.3 mAh g−1, and the retention rates were 19.2% and 32.2%, respectively, obviously lower than that of 3D adhesive electrodes. The significant improvement in lithium storage performance of the Si anode with CMC-NaPAA-PAM is mainly ascribed to its 3D network structure, which offer a good channel for ion transport and has hydrogen bonding on the surface of Si particles and CMC-NaPAA-PAM. The CMC-NaPAA-PAM provides multi-point attachments with Si NPs, which contributes to the improved binding properties with both Si NPs and Cu current collect, facilitating the formation of a steady SEI film on the surface of electrodes.
3.2.3. Cyclic voltammetry spectra of Si anodes with CMC-NaPAA-PAM Fig. 6c shows the cyclic voltammetrye (CV) curves for initial 3 cycles between the CMC-NaPAA-PAM electrode at a sweep speed of 0.20 mV s−1 and a voltage range of 0.01 and 1.50 V. Obviously, the CV curve of first cycle in the discharge process (cathode scanning) is quite different from those of the following periods. A broad peak of about 0.80 V can be observed, which is ascribed to the formation of a stable SEI film on the SiNPs surface and the irreversible reduction of electrolytes. After the first scanning, the reduction peak of 0.80 V disappeared, suggesting the generation of a SEI film on the surface of electrode. [36] In the subsequent CV curve, it is observed that the discharge curve shows a reduction peak at 0.20 V, and the charge curve has two oxidation peaks at 0.37 and 0.54 V, corresponding to the formation of LixSi alloy in the lithiation of Si NPs and LixSi delithiation, respectively [37,38]. The peak current gradually increased in the second and third scans, which was mainly ascribed from the gradual activation of the electrodes [39].
Fig. 5. Cycling performance of the ethanol washed CMC-NaPAA-PAM and the control at 420 mAg−1.
3.2.2. Cycling performance of the CMC, NaPAA and CMC-NaPAA-PAM at 420 mA g−1 To evaluate the different binders, the electrochemical cycling performance of the prepared Si anodes was tested under the voltage window of 0.005–1.500 V for constant current charging/discharging. The current density in the first cycle was 100 mA g−1, and that of the subsequent cycles was 420 mA g−1Fig. 6a shows the voltage profile of Si electrodes with different binders for the first charge and discharge. The electrodes of the three binders all have a long flat discharge platform less than 0.1 V, which is derived from lithium ions inserted into Si to form LixSi alloy. The voltage window of 0.25–0.70 V presents an inclined long charging platform, corresponding to the extraction of lithium ions. This result is consistent with the CV curve in Fig. 6c. As shown in Fig. 6b that in the initial several cycles, the reversible Liextraction capacity of all the samples were higher than 2000 mAh g−1. The initial discharge/charge capacities of the CMC-NaPAA-PAM binder electrode in the first cycle were 2395.3/2026.7 mAh g−1. The initial coulombic efficiency (ICE) reached up to 84%, and the average CE from the second cycle to the 150th cycle was 98.8%. After 150 cycles, a high capacity of 1210.7 mAh g−1 was maintained. In contrast, the initial discharge/charge capacities of the CMC and NaPAA electrodes were 3374.3/2264.5 and 2375.8/1437.4 mAh g−1, and the initial coulombic efficiencies were only 79% and 60.5%, respectively. The average CE reduced to 97.9% and 98.1% in the rest of cycles. During the 100 cycles, the capacity of CMC and NaPAA electrodes rapidly decreased to
3.2.4. Rate performance of CMC-NaPAA-PAM electrode Fig. 6d shows the rate capability of CMC-NaPAA-PAM electrode. The first cycle was activated with a current of 0.03 C, the current density gradually increased from 0.1, 0.2 and 0.5–1.0 C, and the discharge capacities were 2024, 1544, 1174 and 714 mAh g−1, corresponding to 80.5, 61.4, 46.7 and 28.4% of the capacity at 100 mA g-1 (2512.9 mAh g−1), respectively. When the current density returned back to 420 mA g−1 after 20 cycles at high current cycles, the reversible capacity recovered to about 1790 mAh g−1, The results show that the CMC-NaPAA-PAM electrode is highly reversible. The satisfied rate performance of 3D binder electrode can be attributed to two aspects: firstly, a good conductive network encapsulating Si NPs; secondly, the high resistance to deformation attributed to multi-point interaction of CMC-NaPAA-PAM and Si electrodes. 4
Journal of Physics and Chemistry of Solids 135 (2019) 109113
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Fig. 6. Electrochemical measurement of CMC, NaPAA and CMC-NaPAA-PAM anode: (a)First charge and discharge voltage profile of silicon anode with different binder; (b) cycling performance of the CMC, NaPAA and CMC-NaPAA-PAM at 420 m A g−1; (c) the cyclic voltammetry spectra of CMC-NaPAA-PAM electroed; (d) rate performance of CMC-NaPAA-PAM electrode; (e) Nyquist plots of Si electrode with the prepared binders (CMC, NaPAA and CMC-NaPAA-PAM) after the 100 charging/discharging cycles at room temperature.
Fig. 7. SEM images on the electrodes of fresh of CMC(a), NaPAA (b) and CMC-NaPAA-PAM (c), and after cycling of CMC (d), NaPAA(e) and CMC-NaPAA-PAM (f).
RSEI/RCT of the CMC electrode led to the fastest decay of capacity. On the contrary, the CMC-NaPAA-PAM electrode showed the smallest RSEI/ RCT, which proves that the cross-linked and grafted binder with 3D network structure is more favorable for the building of the stable SEI layer. Thus, the CMC-NaPAA-PAM electrode has more stable cycle performance.
3.2.5. Nyquist plots To further investigate the effect of different binders on the electrochemical performance, the impedance spectra of electrodes with CMC, NaPAA and CMC-NaPAA-PAM were measured at the frequency between 0.01 and 10000Hz for a specific cycle. As shown in Fig. 6e, all the curves are composed of two parts. One is a concave semicircle showing the frequency range of high to intermediate, the diameter corresponding to the specific value of SEI resistance (RSEI) to charge transfer resistance (RCT) at the electrode/electrolyte interface, and the other is the oblique line of the low frequency region, representing the diffusion resistance of Li+ in the electrode materials (Warburg impedance, Zw) [2,10]. The RSEI/RCT of the CMC, NaPAA and CMCNaPAA-PAM electrodes were 82 Ω, 50.9 Ω and 35.7 Ω. The maximum
3.3. SEM analysis In order to further research the influence of binder mechanical strength on cyclic stability, the surface of the electrode before and after 100 cycles were characterized with a scanning electron microscope (SEM). As shown in Fig. 6a–f, the CMC and NaPAA electrodes (Fig. 7a 5
Journal of Physics and Chemistry of Solids 135 (2019) 109113
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Fig. 8. Proposed working mechanism on the contribution of CMC-NaPAA-PAM to the solution for the volume change of Si particles during cycling.
after 150 cycles. Therefore, the CMC-NaPAA-PAM shows promising potential for LIB from an industrial application point of view.
and b) exhibited a rougher surface, while the CMC-NaPAA-PAM electrode (7c) shows a smooth surface. The electrodes were subjected to SEM analysis after 100 cycles of charge/discharge at the current density of 420 mA g−1, and their surface morphologies are shown in Fig. 6d, e and f. It can be seen in Fig. 7d and e that the CMC and NaPAA electrodes were severely damaged, with multiple large cracks and a light appearance suggesting the thick SEI film. On the contrary, after 100 cycles, the surface of CMC-NaPAA-PAM electrode shows better integrity with very small cracks. The thinner SEI film and smaller cracks indicates that the higher binding ability of CMC-NaPAA-PAM can maintain the electrode stability even after long-term cycling, thus greatly improve the electrochemical performance.
Funding information This research was financially supported by Energy Development Foundation of College of Energy, Xiamen University (No. 2018NYFZ03 &No. 2017NYFZ02). References [1] B. Gendensuren, E.-S. Oh, Dual-crosslinked network binder of alginate with polyacrylamide for silicon/graphite anodes of lithium ion battery, J. Power Sources 384 (2018) 379–386. [2] D. Shen, C. Huang, L. Gan, J. Liu, M. Long, Rational design of Si@SiO2/C composite using sustainable cellulose as carbon resource for anode in lithium-ion batteries, ACS Appl. Mater. Interfaces 10 (2018) 7946–7954. [3] T. Ikonen, T. Nissinen, E. Pohjalainen, O. Sorsa, T. Kallio, V.P. Lehto, Electrochemically anodized porous silicon: towards simple and affordable anode material for Li-ion batteries, Sci. Rep. 7 (2017) 7880. [4] X. Zhu, Z. Fei, Z. Li, L. Zhang, Y. Song, J. Tao, S. Sayed, L. Chen, X. Wang, J. Sun, A highly stretchable cross-linked polyacrylamide hydrogel as an effective binder for silicon and sulfur electrodes toward durable lithium-ion storage, Adv. Funct. Mater. 28 (2018) 1705015. [5] L. Wei, Z. Hou, L. Wei, Z. Hou, High performance polymer binders inspired by chemical finishing of textiles for silicon anodes in lithium ion batteries, J. Mater. Chem. 5 (2017) 42. [6] S. Tong, X. Dong, W. Tang, D. Wang, X. Zhang, X. Xia, X. Wang, J. Tu, Biomassderived carbon/silicon three-dimensional hierarchical nanostructure as anode material for lithium ion batteries, Mater. Res. Bull. 96 (2017) S0025540817312497. [7] J. Dae Soo, H. Tae Hoon, P. Seung Bin, C. Jang Wook, Spray drying method for large-scale and high-performance silicon negative electrodes in Li-ion batteries, Nano Lett. 13 (2013) 2092–2097. [8] K. Lee, S. Lim, T.-H. Kim, Dopamine-conjugated poly(acrylic acid) blended with an electrically conductive polyaniline binder for silicon anode, Bull. Korean Chem. Soc. 39 (2018) 873–878. [9] J. He, L. Zhang, Polyvinyl alcohol grafted poly (acrylic acid) as water-soluble binder with enhanced adhesion capability and electrochemical performances for Si anode, J. Alloy. Comp. 763 (2018) 228–240. [10] S. Chen, M.L. Gordin, R. Yi, G. Howlett, H. Sohn, D. Wang, Silicon core-hollow carbon shell nanocomposites with tunable buffer voids for high capacity anodes of lithium-ion batteries, Phys. Chem. Chem. Phys. 14 (2012) 12741–12745. [11] Z.-Y. Wu, L. Deng, J.-T. Li, Q.-S. Huang, Y.-Q. Lu, J. Liu, T. Zhang, L. Huang, S.G. Sun, Multiple hydrogel alginate binders for Si anodes of lithium-ion battery, Electrochim. Acta 245 (2017) 363–370. [12] J. Qin, M. Wu, T. Feng, C. Chen, C. Tu, X. Li, C. Duan, D. Xia, D. Wang, High rate capability and long cycling life of graphene-coated silicon composite anodes for lithium ion batteries, Electrochim. Acta 256 (2017) 259–266. [13] Z. Jia, G. Christopher, L. Nian, C. Yi, Z. Xiang, Nanoporous silicon networks as anodes for lithium ion batteries, Phys. Chem. Chem. Phys. 15 (2012) 440–443. [14] H. Wu, G. Chan, J.W. Choi, I. Ryu, Y. Yao, M.T. Mcdowell, S.W. Lee, A. Jackson, Y. Yang, L. Hu, Stable cycling of double-walled silicon nanotube battery anodes through solid-electrolyte interphase control, Nat. Nanotechnol. 7 (2012) 310–315. [15] J. Chen, L. Bie, S. Jing, F. Xu, Enhanced electrochemical performances of silicon nanotube bundles anode coated with graphene layers, Mater. Res. Bull. 73 (2016) 394–400. [16] K. Wang, S. Pei, Z. He, L.-a. Huang, S. Zhu, J. Guo, H. Shao, J. Wang, Synthesis of a novel porous silicon microsphere@carbon core-shell composite via in situ MOF coating for lithium ion battery anodes, Chem. Eng. J. 356 (2019) 272–281. [17] Y. Liu, Z. Tai, T. Zhou, V. Sencadas, J. Zhang, L. Zhang, K. Konstantinov, Z. Guo, H.K. Liu, An all-integrated anode via interlinked chemical bonding between double-
3.4. Proposed working mechanism of CMC-NaPAA-PAM The proposed working mechanism on the action of different binders to Si particles is shown in Fig. 8. After repeated lithiation/delithiation, the Si particles expand and shrink repeatedly, and the 1D linear CMC and NaPAA binders cannot withstand the corresponding stresses. The huge stress generates cracks within Si particles, and the cracks propagation finally results in the pulverization of Si particles, leading to lose contact with conductive matrix and rapid capacity fading. Non-linear CMC-NaPAA-PAM molecules with branching, which have multiple points of contact with Si particles, can significantly increase the adhesion of polymeric binder to Si surface, thus mitigate the stress and suppress the pulverization of Si particles. This also explains why 3D binder shows better performance than CMC and NaPAA in Si anode. 4. Conclusion In summary, a novel CMC-NaPAA-PAM was successfully developed by grafting and crosslinking in this study. It has the advantages of mild reaction conditions, wide source of raw materials and simple preparation process. A step of ethanol washing was developed to get rid of the negative impact by the unpolymerized AM monomers. The product was further purified and tested in the Si anode of LIB as a binder. The 3D network structure of the binder and the multi-point interaction contributes to maintaining the integrity of the Si electrode. It is found that more polar groups such as carboxyl groups and amino groups contributes to the formation of hydrogen bonds with SiNPs, resulting in a forceful interaction between the Si surface and the polymeric binder. The CMC-NaPAA-PAM provides multi-point interaction with the surface of Si NPs, which greatly enhances the binding properties with both Si NPs and Cu current collect, and promotes the generation of a stable SEI layer on the surface of Si NPs. Therefore, the Si anode with the CMCNaPAA-PAM show good cycle performance, high initial coulombic efficiency and satisfied rate capability. At a current density of 420 mA g−1 and a loading density of pure Si about 0.75 mg cm−2, a relatively high specific capacity of 1210.7 mAh g−1 can be obtained 6
Journal of Physics and Chemistry of Solids 135 (2019) 109113
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[18]
[19]
[20]
[21] [22]
[23]
[24]
[25]
[26]
[27]
[28]
[29] L. Wei, C. Chen, Z. Hou, H. Wei, Poly (acrylic acid sodium) grafted carboxymethyl cellulose as a high performance polymer binder for silicon anode in lithium ion batteries, Sci. Rep. 6 (2016) 19583. [30] M.D. Kurkuri, S.G. Kumbar, T.M. Aminabhavi, Synthesis and characterization of polyacrylamide-grafted sodium alginate copolymeric membranes and their use in pervaporation separation of water and tetrahydrofuran mixtures, J. Appl. Polym. Sci. 86 (2002) 272–281. [31] Y. Liu, W.B. Wang, A.G. Wang, Adsorption of lead ions from aqueous solution by using carboxymethyl cellulose-g-poly (acrylic acid)/attapulgite hydrogel composites, Desalination 259 (2010) 258–264. [32] J.J. Li, L. Zhang, J. Gu, Y.P. Sun, X.S. Ji, Cross-linking of poly(vinyl alcohol) with N,N '-methylene bisacrylamide via a radical reaction to prepare pervaporation membranes, RSC Adv. 5 (2015) 19859–19864. [33] E.S. Mohamed, A. Amr, D. Knittel, E. Schollmeyer, Synthesis and application of new sizing and finishing additives based on carboxymethyl cellulose, Carbohydr. Polym. 81 (2010) 769–774. [34] S. Thayyath ANIRUDHAN, R. Sylaja REJEENA, Thorium(IV) removal and recovery from aqueous solutions using tannin-modified poly(glycidylmethacrylate)-grafted zirconium oxide densified cellulose, Ind. Eng. Chem. Res. 50 (2011) 1–3. [35] X. Ji, J. Li, L. Zhang, J. Gu, Y.P. Sun, Cross-linking of Poly(vinyl alcohol) with N,N’methylene bisacrylamide via a radical reaction to prepare pervaporation membranes, RSC Adv. 5 (2015) 19859–19864. [36] D.A. Agyeman, K. Song, G.H. Lee, M. Park, Y.M. Kang, Carbon-coated Si nanoparticles anchored between reduced graphene oxides as an extremely reversible anode material for high energy-density Li-ion battery, Advanced Energy Materials 6 (2016) 1600904. [37] B. Liu, P. Soares, C. Checkles, Y. Zhao, G. Yu, Three-dimensional hierarchical ternary nanostructures for high-performance Li-ion battery anodes, Nano Lett. 13 (2013) 3414–3419. [38] J.H. Zhu, J. Yang, Z.X. Xu, J.L. Wang, Y.N. Nuli, X.D. Zhuang, X.L. Feng, Silicon anodes protected by a nitrogen-doped porous carbon shell for high-performance lithium-ion batteries, Nanoscale 9 (2017) 8871–8878. [39] Z. Min, Y. Jie, Z. Yu, H. Chen, P. Feng, Novel hybrid Si nanocrystals embedded in a conductive SiOx@C matrix from one single precursor as a high performance anode material for Lithium-ion batteries, J. Mater. Chem. 5 (2017) 7026–7034.
shelled–yolk-structured silicon and binder for lithium-ion batteries, Adv. Mater. 29 (2017) 1703028. C. Luo, L.L. Du, W. Wu, H.L. Xu, G.Z. Zhang, S. Li, C.Y. Wang, Z.G. Lu, Y.H. Deng, Novel lignin-derived water-soluble binder for micro silicon anode in lithium-ion batteries, ACS Sustain. Chem. Eng. 6 (2018) 12621–12629. S.H. Lee, J.H. Lee, D.H. Nam, M. Cho, J. Kim, C. Chanthad, Y. Lee, Epoxidized natural rubber/chitosan network binder for silicon anode in lithium-ion battery, ACS Appl. Mater. Interfaces 10 (2018) 16449–16457. D. Shin, H. Park, U. Paik, Cross-linked poly(acrylic acid)-carboxymethyl cellulose and styrene-butadiene rubber as an efficient binder system and its physicochemical effects on a high energy density graphite anode for Li-ion batteries, Electrochem. Commun. 77 (2017) 103–106. J. Zhu, C. Gladden, N. Liu, Y. Cui, X. Zhang, Nanoporous silicon networks as anodes for lithium ion batteries, Phys. Chem. Chem. Phys. 15 (2012) 440–443. J. Yoon, D.X. Oh, C. Jo, J. Lee, D.S. Hwang, Improvement of desolvation and resilience of alginate binders for Si-based anodes in a lithium ion battery by calciummediated cross-linking, Phys. Chem. Chem. Phys. 16 (2014) 25628–25635. Y.K. Jeong, T.W. Kwon, I. Lee, T.S. Kim, A. Coskun, J.W. Choi, Millipede-inspired structural design principle for high performance polysaccharide binders in silicon anodes, Energy Environ. Sci. 8 (2015) 1224–1230. J. Liu, Q. Zhang, T. Zhang, J.T. Li, L. Huang, S.G. Sun, A robust ion-conductive biopolymer as a binder for Si anodes of lithium-ion batteries, Adv. Funct. Mater. 25 (2015) 3599–3605. S. Komaba, N. Yabuuchi, T. Ozeki, Z.J. Han, K. Shimomura, H. Yui, Y. Katayama, T. Miura, Comparative study of sodium polyacrylate and poly(vinylidene fluoride) as binders for high capacity Si-graphite composite negative electrodes in Li-ion batteries, J. Phys. Chem. C 116 (2012) 1380–1389. Y.K. Jeong, T.W. Kwon, I. Lee, T.S. Kim, A. Coskun, J.W. Choi, Hyperbranched βcyclodextrin polymer as an effective multidimensional binder for silicon anodes in lithium rechargeable batteries, Nano Lett. 14 (2014) 864–870. Y.K. Jeong, T.W. Kwon, I. Lee, T.S. Kim, A. Coskun, J.W. Choi, Millipede-inspired structural design principle for high performance polysaccharide binders in silicon anodes, Energy Environ. Sci. 8 (2015) 1224–1230. L. Yi, W. Wang, A. Wang, Adsorption of lead ions from aqueous solution by using carboxymethyl cellulose- g-poly (acrylic acid)/attapulgite hydrogel composites, Desalination 259 (2010) 258–264.
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Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
A novel high-performance 3D polymer binder for silicon anode in lithiumion batteries
T
Lubing Yua, Jian Liua,b,c,*, Shuaishuai Hea, Chaofan Huanga, Lihui Gana,b,c,**, Zhengliang Gonga,***, Minnan Longa,b,c a
College of Energy, Xiamen University, Xiamen, 361005, China Xiamen Key Laboratory of Clean and High-valued Applications of Biomass, Xiamen University, Xiamen, 361102, China c Fujian Engineering and Research Center of Clean and High-valued Technologies for Biomass, Xiamen University, Xiamen, 361102, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: 3D polymer binder Carboxymethylcellulose Lithium-ion batteries Silicon anode
For high-capacity silicon (Si) anodes, the design of new binder is a feasible way to overcome the rapid capacity decay attributed to the large volume change of silicon (Si) anode in the repeated charging/discharging process. Here a newly designed binder with 3D structure was developed using CMC as the backbone, and acrylamide (AM), acrylic acid (AA) as the branch. The molecular structure was characterized by Fourier transform infrared (FTIR), and ethanol washing was applied for getting rid of unreacted monomers. The multifunctional binder with 3D structure and rich polar groups was prepared by cross-linking grafting. Polyacrylamide provides a strong adhesion and contributes to the formation of the solid electrolyte intermediate phase (SEI) layers on the surface of electrodes. The results show that CMC and polyacrylic acid with carboxyl groups not only strengthened the bonding force between the current collectors and the silicon nanoparticles (SiNPs), also improved the linkage among SiNPs. Therefore, the loading weight of commercial Si was about 0.75 mg cm−2, even after 150 deep cycles, and a high capacity of 1210.7 mAh g−1 was resulted in the Si anode. The prepared novel high-performance binder shows a potential application on the silicon anode in lithium-ion batteries.
1. Introduction For the past few years, with the rapid development of portable electronic devices and energy storage devices [1], the demand of lithium ion battery (LIB) has increased sharply due to its advantages such as high energy density, good rate performance, low price, safety and durability [2–4]. As the most popular anode material for commercial LIBs, graphite has only a theoretical specific capacity of 372 mAh g−1, which makes it difficult to meet the market demand [5]. Silicon (Si) is deemed to the most promising next-generation negative electrode material because it is an abundant element in the earth and its theoretical specific capacity is recorded as about 4200 mAh g−1, more than ten times as much as that of traditional graphite materials [2,6,7]. However, in order to realize the commercialization of Si anodes, there are still two problems to be solved. One is that the volume of Si particles vigorously expands (~400%) during repeated lithiation/delithiation. It resulted in rapid capacity decay and severe pulverization of the electrode, thus the cycle life is shortened [6,8–11]. The other is the
formation of an unstable SEI film on the surface of the SiNPs during charge/discharge, which results in an increase in impedance and coulomb efficiency goes down [8,12]. In order to solve the above problems, a series of strategies have been proposed, including changing the morphology of Si particles, using nanosized Si and nano-Si composite materials, such as Si nanoparticles [13], nanowires [14,15], nanotubes [16,17], porous silicon [18,19], carbon-coated materials [20,21]. All of the above related literatures suggest that the introduction of coatings and nanostructures can mitigate the damage of large volume change to the electrode effectively, reserving better cycle performance and higher capacity, but these processes are relatively complicated and not conducive to industrialization [22]. Therefore, it is meaningful to maintain the structural stability of electrodes for further boost the electrochemical performance of the negative electrode materials. A more convenient and practical idea is the development of a structurally stable polymer binder to adapt to the reciprocating volume change in the repeated cycles. The related researches in this area have also increased in recent years [6,23].
*
Corresponding author. College of Energy, Xiamen University, Xiamen, 361005, China. Corresponding author. Xiamen Key Laboratory of Clean and High-valued Applications of Biomass, Xiamen University, Xiamen, 361102, China. *** Corresponding author. E-mail addresses: [email protected] (J. Liu), [email protected] (L. Gan), [email protected] (Z. Gong). **
https://doi.org/10.1016/j.jpcs.2019.109113 Received 18 May 2019; Received in revised form 15 July 2019; Accepted 21 July 2019 Available online 22 July 2019 0022-3697/ © 2019 Elsevier Ltd. All rights reserved.
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2.3. Electrochemical measurements
Serving as one of the important battery components, the binders have the function of attaching the active material and the conductive agent to the copper foil. Although the binder is not the active component of the battery electrodes, it has great influence on the electrochemical properties and the integrity of the electrode [24]. Although poly(vinylidene fluoride) (PVDF) is a widely used LIBs binder, there are also difficulties to adapt to future development trends due to its environmentally unfriendly nature and the weak interaction force between PVDF binder and nano-Si particles. Recently, many studies have confirmed that functional binders with carboxyl group and amine group, such as sodium carboxymethyl cellulose (CMC) [25], sodium alginate (SA) [26], xanthan gum [27], guar gum (GG) [28], poly(acrylic acid) (PAA) [29], poly(acrylamide) (PAM) [4] and polyamide imide (PAI), etc., show better properties, lower cost, more environmentallyfriendly than PVDF in Si-based anodes. These functional binders form covalent bonds with the Si particles, which improves the performance of the battery significantly. In addition, grafting a polyfunctional group such as polyvinyl alcohol or dopamine onto the PAA to form a conductive polymer can improve the electrochemical properties of Si anode [9,10]. Despite that, there is no multipoint contact between the onedimensional (1D) polymer binder and Si particles, resulting in the tendency for Si to slip during repeated cycles [30]. Therefore, there is a need to develop functional polymers with a three-dimensional (3D) network structure, such as crosslinked PAM [4], PAA grafted CMC [31], SA grafted PAA [1] and CMC grafted PAN [6], which has been successfully applied on Si-based anodes. Although these functional binders have significantly improved electrochemical performances, the high capacity Si-based LIBs for industrialization still requires the exploration of new binder systems. In this work, we report a functionalized 3D structure binder with a linear CMC skeleton for Si-based LIBs, which successfully grafts carboxyl-rich AA and AM with a large amount of amine groups by free radical polymerization. Unlike the simple linear polymers as CMC, sodium poly (acrylic acid) (NaPAA) and PAM, the newly developed composite binder has a 3D network structure with more contact points for Si particles, and contains high-density carboxyl groups for strengthening the binding force between the slurry and the Cu current collectors. The enhanced binding forces contribute to the structural integrity of electrode, and a large amount of amine-based PAM can increase the conductivity. Therefore, the electrochemical performance of Si anode improves effectively.
SiNPs, acetylene black and the prepared binder were ground into a uniform paste in the weight ratio of 6:2:2.The slurry was coated on the pure copper foil, dried at 50 °C for 12 h in a vacuum oven. The load of commercial Si on the copper foil is approximately 0.75 mg cm−2. The electrolyte is a mixture of diethyl carbonate (DEC), dimethyl carbonate (DMC) and ethyl carbonate (EC) (volume ratio 1:1:1) dissolved in 1.0 mol of LiPF6, containing 2% vinyl carbonate (VC) and 10 wt % ethyl fluoride carbonate (FEC) as additives. The CR2025 button battery is assembled in a glove box under argon atmosphere with no more than 10 ppm of oxygen and water. The membrane and cathode materials are Celgard 2400 film and Li sheet, respectively. The electrochemical performance was investigated in the LAND battery test system (CT2001A, made in wuhan, China) at 30 °C in the voltage window of 0.005–1.500 V, relative to the Li/Li +. 2.4. Material characterization The prepared samples were investigated by Fourier transform infrared (FTIR, Nicoleti S5, Thermo Fisher, USA, scanning electron microscopy (SEM, Zeiss Sigma) and X-ray diffraction (XRD, Ultima IV, Rigaku, Japan, at the scan rate of 10°min−1 within 2θ = 10–90°. The 180° peel test was performed on a Universal Material Evaluation Tester (UTM-4000, SUNS, Shenzhen, China). First, the different binders were uniformly formulated into a 2% homogeneous sol, and then the binder was coated on a Cu foil in a thickness of 200 μm and subjected to vacuum drying at 50 °C for 12 h. Prior to the peel test, the Cu foil was cut into long strips of 4 cm*1 cm and then joined to a 1 cm wide tape. The speed of peeling was 1 cm min-1, and the force versus displacement diagram was online recorded. The viscosity of the binder was tested using an LVDVC230 viscosity characterization tester (Brookfiedl, USA) at a test temperature of 25 °C and the binder solution concentration of 15 g L−1. Prior to the viscosity test, the binder was stirred overnight to ensure uniform dispersion. 3. Results and discussion 3.1. Design concept and characterizations of CMC-NaPAA-PAM 3.1.1. Design concept and FTIR spectra of CMC-NaPAA-PAM In the presence of CMC, ammonium persulfate was used as the initiator, N,N-Methylenebisacrylamide (MBAA) acting as the crosslinker, and the acrylic acid and acrylamide monomers were polymerized and covalently crosslinked to obtain a 3D hyperbranched polymeric binder. The design concept of the CMC-NaPAA-PAM is shown in Fig. 1. The binders were characterized by FTIR spectra. (Fig. 2). After grafting polymerization and covalently cross-linking, the absorption peaks at 1260 cm−1 (-OH) and 894 cm−1 (C–O) completely disappeared [32]. This indicates that by heating, the initiator ammonium persulfate successfully extracts H from the CMC to form a large amount of free radicals [33,34]. A few new absorption peaks at 1653 cm−1 (C]O, NA, amide Ⅰ), 1616 cm−1 (N–H, NA, amide Ⅱ), 1420 cm−1 (C–N, NA, amide Ⅲ) [30], 1563 cm−1(Back stretching vibration) and −1 1451 cm (stretching vibration) appeared, which can be ascribed to the –COO− groups from NaPAA [6]. In addition, The peak at 1113 cm−1 is caused by an increase in the –NH– stretching due to the crosslinking of MBAA [35]. The results evidenced the successful synthesis of 3D polymer binder.
2. Experimental section 2.1. Materials Commercial Si nanoparticles (Si NPs) in the diameters about 100 nm were from Naiou Co., China. Other reagents were purchased from Aladdin. The electrolyte and lithium-plate were obtained from Suzhou Fosai new material Co.
2.2. 3D binder preparation CMC (1.0 g) was dissolved in 100 mL deionized water. Nitrogen was injected for 3 h to remove oxygen, and then 0.2 g of acrylamide (AM), 0.1 g of N,N′-methylenebis(acrylamide) (MBAA), 3 mL of acrylic acid, 0.10 g of (NH4)2S2O8 and 0.03 g of NaHSO3 were added. The mixed liquor was then heated to 55 °C in a water bath and stirred for 3 h to produce the binder in a nitrogen atmosphere, named as CMC-NaPAAPAM. The obtained sample was adjusted to pH = 6 with sodium hydroxide solution to get the raw CMC-NaPAA-PAM. Finally, the neutralized gel was washed for three times with absolute ethanol, and then vacuum dried to obtain the powdery CMC-NaPAA-PAM.
3.1.2. XRD analysis of CMC-NaPAA-PAM X-ray diffraction (XRD) analysis is an effect method to investigate the crystal structure of the binders. For comparison, the XRD of CMC, NaPAA and CMC-NaPAA-PAM were measured. As shown in Fig. 3. CMC showed a characteristic diffraction peak at 20.74°, and NaPAA showed three characteristic diffraction peaks at 18.94°, 24.24°, and 33.62°, 2
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Fig. 1. Scheme for synthesis of CMC-NaPAA-PAM.
24.00°, almost same to one of those of NaPPA, indicating that part of the original structure also affects in the new structure of CMC-NaPAAPAM. 3.1.3. 180° peeling and viscosity test of CMC-NaPAA-PAM In order to evaluate the adhesion between the binder and the Cu foil, we conducted a peel test at 180° The force-displacement curve (Fig. 4a) clearly shows that the average peel force of CMC-NaPAA-PAM (1.18 N) is greater than that of NaPAA (1.08 N) and CMC (0.52 N), indicating that the CMC-NaPAA-PAM rich in amine groups and carboxyl groups increases the adhesion of polymeric binder to the surface of Si, so the mechanical stability of Si electrode is enhanced. This conclusion is consistent with the results of PAA grafted CMC [28], and its strong peel force is considered to be one of the reasons for the enhanced electrode cycle stability. The rheological properties of the binders were evaluated through a viscosity test, as shown in Fig. 4b. The viscosity of CMC, NaPAA and CMC-NaPAA-PAM are 879 mPa s, 3956 mPa s and 1026 mPa s, respectively. Since the tight winding reduced its apparent viscosity in the aqueous dispersion, the viscosity of the CMC-NaPAA-PAM is not so high as expected. It is assumed that compared to the 1D linear structure of NaPAA and CMC, CMC-NaPAA-PAM with 3D network structure has a complex branched structure with a certain steric hindrance, so that the branches can extend without destroying the bonds between each other.
Fig. 2. FTIR spectra of CMC-NaPAA-PAM, CMC and Na PAA.
3.2. Electrochemical performances 3.2.1. Cycling performance of the ethanol washed CMC-NaPAA-PAM at 420 mA g−1 Since the conversion rate cannot reach 100% in any polymerization process, a certain amount of monomers must be remained. In order to eliminate the potential negative impacts, an ethanol washing step was introduced in the research. The effect of ethanol washing on the electrochemical properties was explored (Fig. 5). The control sample free of ethanol washing is named as raw CMC-NaPAA-PAM. For the long-term cycle stability, the average coulombic efficiency of CMC-NaPAA-PAM was 98.80%(2–150 cycle), and after 150 cycles, a relatively high specific capacity of 1210.7 mAh g−1 was still kept. On the contrary, the average coulomb efficiency of the raw CMC-NaPAA-PAM from the 2nd to the 150th cycle was 98.06%. After 150 cycles, the specific capacity only retained 793.1 mAh g−1. Both average coulomb efficiency and capacity retention rate were improved to different degrees after ethanol washing. Through qualitative analysis of ethanol washing solution by gas chromatography (Agilent Technologies, USA), unpolymerized AM monomer was detected in the alcohol washing solution, which may be one of the facts affecting the electrochemical properties. The specific mechanism is still not clear, and further research is needed. Therefore, the innovative ethanol washing step in this research is meaningful.
Fig. 3. XRD patterns of CMC, NaPAA and CMC-NaPAA-PAM.
which are identified as the different lattice planes. In the curve of 3D binder, the characteristic diffraction peaks of both NaPAA and CMC vanished. The newly generated peak does not match those of the crystal structure of NaPAA or CMC, which indicates that the molecular structure of CMC-NaPAA-PAM is reconstituted and recrystallized in the reaction. The obtained XRD pattern displayed a diffraction peaks at 3
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Fig. 4. (a)The results on 180° peeling test of the binders. (b) The results on viscosity test of the binders.
512.0 and 610.3 mAh g−1, and the retention rates were 19.2% and 32.2%, respectively, obviously lower than that of 3D adhesive electrodes. The significant improvement in lithium storage performance of the Si anode with CMC-NaPAA-PAM is mainly ascribed to its 3D network structure, which offer a good channel for ion transport and has hydrogen bonding on the surface of Si particles and CMC-NaPAA-PAM. The CMC-NaPAA-PAM provides multi-point attachments with Si NPs, which contributes to the improved binding properties with both Si NPs and Cu current collect, facilitating the formation of a steady SEI film on the surface of electrodes.
3.2.3. Cyclic voltammetry spectra of Si anodes with CMC-NaPAA-PAM Fig. 6c shows the cyclic voltammetrye (CV) curves for initial 3 cycles between the CMC-NaPAA-PAM electrode at a sweep speed of 0.20 mV s−1 and a voltage range of 0.01 and 1.50 V. Obviously, the CV curve of first cycle in the discharge process (cathode scanning) is quite different from those of the following periods. A broad peak of about 0.80 V can be observed, which is ascribed to the formation of a stable SEI film on the SiNPs surface and the irreversible reduction of electrolytes. After the first scanning, the reduction peak of 0.80 V disappeared, suggesting the generation of a SEI film on the surface of electrode. [36] In the subsequent CV curve, it is observed that the discharge curve shows a reduction peak at 0.20 V, and the charge curve has two oxidation peaks at 0.37 and 0.54 V, corresponding to the formation of LixSi alloy in the lithiation of Si NPs and LixSi delithiation, respectively [37,38]. The peak current gradually increased in the second and third scans, which was mainly ascribed from the gradual activation of the electrodes [39].
Fig. 5. Cycling performance of the ethanol washed CMC-NaPAA-PAM and the control at 420 mAg−1.
3.2.2. Cycling performance of the CMC, NaPAA and CMC-NaPAA-PAM at 420 mA g−1 To evaluate the different binders, the electrochemical cycling performance of the prepared Si anodes was tested under the voltage window of 0.005–1.500 V for constant current charging/discharging. The current density in the first cycle was 100 mA g−1, and that of the subsequent cycles was 420 mA g−1Fig. 6a shows the voltage profile of Si electrodes with different binders for the first charge and discharge. The electrodes of the three binders all have a long flat discharge platform less than 0.1 V, which is derived from lithium ions inserted into Si to form LixSi alloy. The voltage window of 0.25–0.70 V presents an inclined long charging platform, corresponding to the extraction of lithium ions. This result is consistent with the CV curve in Fig. 6c. As shown in Fig. 6b that in the initial several cycles, the reversible Liextraction capacity of all the samples were higher than 2000 mAh g−1. The initial discharge/charge capacities of the CMC-NaPAA-PAM binder electrode in the first cycle were 2395.3/2026.7 mAh g−1. The initial coulombic efficiency (ICE) reached up to 84%, and the average CE from the second cycle to the 150th cycle was 98.8%. After 150 cycles, a high capacity of 1210.7 mAh g−1 was maintained. In contrast, the initial discharge/charge capacities of the CMC and NaPAA electrodes were 3374.3/2264.5 and 2375.8/1437.4 mAh g−1, and the initial coulombic efficiencies were only 79% and 60.5%, respectively. The average CE reduced to 97.9% and 98.1% in the rest of cycles. During the 100 cycles, the capacity of CMC and NaPAA electrodes rapidly decreased to
3.2.4. Rate performance of CMC-NaPAA-PAM electrode Fig. 6d shows the rate capability of CMC-NaPAA-PAM electrode. The first cycle was activated with a current of 0.03 C, the current density gradually increased from 0.1, 0.2 and 0.5–1.0 C, and the discharge capacities were 2024, 1544, 1174 and 714 mAh g−1, corresponding to 80.5, 61.4, 46.7 and 28.4% of the capacity at 100 mA g-1 (2512.9 mAh g−1), respectively. When the current density returned back to 420 mA g−1 after 20 cycles at high current cycles, the reversible capacity recovered to about 1790 mAh g−1, The results show that the CMC-NaPAA-PAM electrode is highly reversible. The satisfied rate performance of 3D binder electrode can be attributed to two aspects: firstly, a good conductive network encapsulating Si NPs; secondly, the high resistance to deformation attributed to multi-point interaction of CMC-NaPAA-PAM and Si electrodes. 4
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Fig. 6. Electrochemical measurement of CMC, NaPAA and CMC-NaPAA-PAM anode: (a)First charge and discharge voltage profile of silicon anode with different binder; (b) cycling performance of the CMC, NaPAA and CMC-NaPAA-PAM at 420 m A g−1; (c) the cyclic voltammetry spectra of CMC-NaPAA-PAM electroed; (d) rate performance of CMC-NaPAA-PAM electrode; (e) Nyquist plots of Si electrode with the prepared binders (CMC, NaPAA and CMC-NaPAA-PAM) after the 100 charging/discharging cycles at room temperature.
Fig. 7. SEM images on the electrodes of fresh of CMC(a), NaPAA (b) and CMC-NaPAA-PAM (c), and after cycling of CMC (d), NaPAA(e) and CMC-NaPAA-PAM (f).
RSEI/RCT of the CMC electrode led to the fastest decay of capacity. On the contrary, the CMC-NaPAA-PAM electrode showed the smallest RSEI/ RCT, which proves that the cross-linked and grafted binder with 3D network structure is more favorable for the building of the stable SEI layer. Thus, the CMC-NaPAA-PAM electrode has more stable cycle performance.
3.2.5. Nyquist plots To further investigate the effect of different binders on the electrochemical performance, the impedance spectra of electrodes with CMC, NaPAA and CMC-NaPAA-PAM were measured at the frequency between 0.01 and 10000Hz for a specific cycle. As shown in Fig. 6e, all the curves are composed of two parts. One is a concave semicircle showing the frequency range of high to intermediate, the diameter corresponding to the specific value of SEI resistance (RSEI) to charge transfer resistance (RCT) at the electrode/electrolyte interface, and the other is the oblique line of the low frequency region, representing the diffusion resistance of Li+ in the electrode materials (Warburg impedance, Zw) [2,10]. The RSEI/RCT of the CMC, NaPAA and CMCNaPAA-PAM electrodes were 82 Ω, 50.9 Ω and 35.7 Ω. The maximum
3.3. SEM analysis In order to further research the influence of binder mechanical strength on cyclic stability, the surface of the electrode before and after 100 cycles were characterized with a scanning electron microscope (SEM). As shown in Fig. 6a–f, the CMC and NaPAA electrodes (Fig. 7a 5
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Fig. 8. Proposed working mechanism on the contribution of CMC-NaPAA-PAM to the solution for the volume change of Si particles during cycling.
after 150 cycles. Therefore, the CMC-NaPAA-PAM shows promising potential for LIB from an industrial application point of view.
and b) exhibited a rougher surface, while the CMC-NaPAA-PAM electrode (7c) shows a smooth surface. The electrodes were subjected to SEM analysis after 100 cycles of charge/discharge at the current density of 420 mA g−1, and their surface morphologies are shown in Fig. 6d, e and f. It can be seen in Fig. 7d and e that the CMC and NaPAA electrodes were severely damaged, with multiple large cracks and a light appearance suggesting the thick SEI film. On the contrary, after 100 cycles, the surface of CMC-NaPAA-PAM electrode shows better integrity with very small cracks. The thinner SEI film and smaller cracks indicates that the higher binding ability of CMC-NaPAA-PAM can maintain the electrode stability even after long-term cycling, thus greatly improve the electrochemical performance.
Funding information This research was financially supported by Energy Development Foundation of College of Energy, Xiamen University (No. 2018NYFZ03 &No. 2017NYFZ02). References [1] B. Gendensuren, E.-S. Oh, Dual-crosslinked network binder of alginate with polyacrylamide for silicon/graphite anodes of lithium ion battery, J. Power Sources 384 (2018) 379–386. [2] D. Shen, C. Huang, L. Gan, J. Liu, M. Long, Rational design of Si@SiO2/C composite using sustainable cellulose as carbon resource for anode in lithium-ion batteries, ACS Appl. Mater. Interfaces 10 (2018) 7946–7954. [3] T. Ikonen, T. Nissinen, E. Pohjalainen, O. Sorsa, T. Kallio, V.P. Lehto, Electrochemically anodized porous silicon: towards simple and affordable anode material for Li-ion batteries, Sci. Rep. 7 (2017) 7880. [4] X. Zhu, Z. Fei, Z. Li, L. Zhang, Y. Song, J. Tao, S. Sayed, L. Chen, X. Wang, J. Sun, A highly stretchable cross-linked polyacrylamide hydrogel as an effective binder for silicon and sulfur electrodes toward durable lithium-ion storage, Adv. Funct. Mater. 28 (2018) 1705015. [5] L. Wei, Z. Hou, L. Wei, Z. Hou, High performance polymer binders inspired by chemical finishing of textiles for silicon anodes in lithium ion batteries, J. Mater. Chem. 5 (2017) 42. [6] S. Tong, X. Dong, W. Tang, D. Wang, X. Zhang, X. Xia, X. Wang, J. Tu, Biomassderived carbon/silicon three-dimensional hierarchical nanostructure as anode material for lithium ion batteries, Mater. Res. Bull. 96 (2017) S0025540817312497. [7] J. Dae Soo, H. Tae Hoon, P. Seung Bin, C. Jang Wook, Spray drying method for large-scale and high-performance silicon negative electrodes in Li-ion batteries, Nano Lett. 13 (2013) 2092–2097. [8] K. Lee, S. Lim, T.-H. Kim, Dopamine-conjugated poly(acrylic acid) blended with an electrically conductive polyaniline binder for silicon anode, Bull. Korean Chem. Soc. 39 (2018) 873–878. [9] J. He, L. Zhang, Polyvinyl alcohol grafted poly (acrylic acid) as water-soluble binder with enhanced adhesion capability and electrochemical performances for Si anode, J. Alloy. Comp. 763 (2018) 228–240. [10] S. Chen, M.L. Gordin, R. Yi, G. Howlett, H. Sohn, D. Wang, Silicon core-hollow carbon shell nanocomposites with tunable buffer voids for high capacity anodes of lithium-ion batteries, Phys. Chem. Chem. Phys. 14 (2012) 12741–12745. [11] Z.-Y. Wu, L. Deng, J.-T. Li, Q.-S. Huang, Y.-Q. Lu, J. Liu, T. Zhang, L. Huang, S.G. Sun, Multiple hydrogel alginate binders for Si anodes of lithium-ion battery, Electrochim. Acta 245 (2017) 363–370. [12] J. Qin, M. Wu, T. Feng, C. Chen, C. Tu, X. Li, C. Duan, D. Xia, D. Wang, High rate capability and long cycling life of graphene-coated silicon composite anodes for lithium ion batteries, Electrochim. Acta 256 (2017) 259–266. [13] Z. Jia, G. Christopher, L. Nian, C. Yi, Z. Xiang, Nanoporous silicon networks as anodes for lithium ion batteries, Phys. Chem. Chem. Phys. 15 (2012) 440–443. [14] H. Wu, G. Chan, J.W. Choi, I. Ryu, Y. Yao, M.T. Mcdowell, S.W. Lee, A. Jackson, Y. Yang, L. Hu, Stable cycling of double-walled silicon nanotube battery anodes through solid-electrolyte interphase control, Nat. Nanotechnol. 7 (2012) 310–315. [15] J. Chen, L. Bie, S. Jing, F. Xu, Enhanced electrochemical performances of silicon nanotube bundles anode coated with graphene layers, Mater. Res. Bull. 73 (2016) 394–400. [16] K. Wang, S. Pei, Z. He, L.-a. Huang, S. Zhu, J. Guo, H. Shao, J. Wang, Synthesis of a novel porous silicon microsphere@carbon core-shell composite via in situ MOF coating for lithium ion battery anodes, Chem. Eng. J. 356 (2019) 272–281. [17] Y. Liu, Z. Tai, T. Zhou, V. Sencadas, J. Zhang, L. Zhang, K. Konstantinov, Z. Guo, H.K. Liu, An all-integrated anode via interlinked chemical bonding between double-
3.4. Proposed working mechanism of CMC-NaPAA-PAM The proposed working mechanism on the action of different binders to Si particles is shown in Fig. 8. After repeated lithiation/delithiation, the Si particles expand and shrink repeatedly, and the 1D linear CMC and NaPAA binders cannot withstand the corresponding stresses. The huge stress generates cracks within Si particles, and the cracks propagation finally results in the pulverization of Si particles, leading to lose contact with conductive matrix and rapid capacity fading. Non-linear CMC-NaPAA-PAM molecules with branching, which have multiple points of contact with Si particles, can significantly increase the adhesion of polymeric binder to Si surface, thus mitigate the stress and suppress the pulverization of Si particles. This also explains why 3D binder shows better performance than CMC and NaPAA in Si anode. 4. Conclusion In summary, a novel CMC-NaPAA-PAM was successfully developed by grafting and crosslinking in this study. It has the advantages of mild reaction conditions, wide source of raw materials and simple preparation process. A step of ethanol washing was developed to get rid of the negative impact by the unpolymerized AM monomers. The product was further purified and tested in the Si anode of LIB as a binder. The 3D network structure of the binder and the multi-point interaction contributes to maintaining the integrity of the Si electrode. It is found that more polar groups such as carboxyl groups and amino groups contributes to the formation of hydrogen bonds with SiNPs, resulting in a forceful interaction between the Si surface and the polymeric binder. The CMC-NaPAA-PAM provides multi-point interaction with the surface of Si NPs, which greatly enhances the binding properties with both Si NPs and Cu current collect, and promotes the generation of a stable SEI layer on the surface of Si NPs. Therefore, the Si anode with the CMCNaPAA-PAM show good cycle performance, high initial coulombic efficiency and satisfied rate capability. At a current density of 420 mA g−1 and a loading density of pure Si about 0.75 mg cm−2, a relatively high specific capacity of 1210.7 mAh g−1 can be obtained 6
Journal of Physics and Chemistry of Solids 135 (2019) 109113
L. Yu, et al.
[18]
[19]
[20]
[21] [22]
[23]
[24]
[25]
[26]
[27]
[28]
[29] L. Wei, C. Chen, Z. Hou, H. Wei, Poly (acrylic acid sodium) grafted carboxymethyl cellulose as a high performance polymer binder for silicon anode in lithium ion batteries, Sci. Rep. 6 (2016) 19583. [30] M.D. Kurkuri, S.G. Kumbar, T.M. Aminabhavi, Synthesis and characterization of polyacrylamide-grafted sodium alginate copolymeric membranes and their use in pervaporation separation of water and tetrahydrofuran mixtures, J. Appl. Polym. Sci. 86 (2002) 272–281. [31] Y. Liu, W.B. Wang, A.G. Wang, Adsorption of lead ions from aqueous solution by using carboxymethyl cellulose-g-poly (acrylic acid)/attapulgite hydrogel composites, Desalination 259 (2010) 258–264. [32] J.J. Li, L. Zhang, J. Gu, Y.P. Sun, X.S. Ji, Cross-linking of poly(vinyl alcohol) with N,N '-methylene bisacrylamide via a radical reaction to prepare pervaporation membranes, RSC Adv. 5 (2015) 19859–19864. [33] E.S. Mohamed, A. Amr, D. Knittel, E. Schollmeyer, Synthesis and application of new sizing and finishing additives based on carboxymethyl cellulose, Carbohydr. Polym. 81 (2010) 769–774. [34] S. Thayyath ANIRUDHAN, R. Sylaja REJEENA, Thorium(IV) removal and recovery from aqueous solutions using tannin-modified poly(glycidylmethacrylate)-grafted zirconium oxide densified cellulose, Ind. Eng. Chem. Res. 50 (2011) 1–3. [35] X. Ji, J. Li, L. Zhang, J. Gu, Y.P. Sun, Cross-linking of Poly(vinyl alcohol) with N,N’methylene bisacrylamide via a radical reaction to prepare pervaporation membranes, RSC Adv. 5 (2015) 19859–19864. [36] D.A. Agyeman, K. Song, G.H. Lee, M. Park, Y.M. Kang, Carbon-coated Si nanoparticles anchored between reduced graphene oxides as an extremely reversible anode material for high energy-density Li-ion battery, Advanced Energy Materials 6 (2016) 1600904. [37] B. Liu, P. Soares, C. Checkles, Y. Zhao, G. Yu, Three-dimensional hierarchical ternary nanostructures for high-performance Li-ion battery anodes, Nano Lett. 13 (2013) 3414–3419. [38] J.H. Zhu, J. Yang, Z.X. Xu, J.L. Wang, Y.N. Nuli, X.D. Zhuang, X.L. Feng, Silicon anodes protected by a nitrogen-doped porous carbon shell for high-performance lithium-ion batteries, Nanoscale 9 (2017) 8871–8878. [39] Z. Min, Y. Jie, Z. Yu, H. Chen, P. Feng, Novel hybrid Si nanocrystals embedded in a conductive SiOx@C matrix from one single precursor as a high performance anode material for Lithium-ion batteries, J. Mater. Chem. 5 (2017) 7026–7034.
shelled–yolk-structured silicon and binder for lithium-ion batteries, Adv. Mater. 29 (2017) 1703028. C. Luo, L.L. Du, W. Wu, H.L. Xu, G.Z. Zhang, S. Li, C.Y. Wang, Z.G. Lu, Y.H. Deng, Novel lignin-derived water-soluble binder for micro silicon anode in lithium-ion batteries, ACS Sustain. Chem. Eng. 6 (2018) 12621–12629. S.H. Lee, J.H. Lee, D.H. Nam, M. Cho, J. Kim, C. Chanthad, Y. Lee, Epoxidized natural rubber/chitosan network binder for silicon anode in lithium-ion battery, ACS Appl. Mater. Interfaces 10 (2018) 16449–16457. D. Shin, H. Park, U. Paik, Cross-linked poly(acrylic acid)-carboxymethyl cellulose and styrene-butadiene rubber as an efficient binder system and its physicochemical effects on a high energy density graphite anode for Li-ion batteries, Electrochem. Commun. 77 (2017) 103–106. J. Zhu, C. Gladden, N. Liu, Y. Cui, X. Zhang, Nanoporous silicon networks as anodes for lithium ion batteries, Phys. Chem. Chem. Phys. 15 (2012) 440–443. J. Yoon, D.X. Oh, C. Jo, J. Lee, D.S. Hwang, Improvement of desolvation and resilience of alginate binders for Si-based anodes in a lithium ion battery by calciummediated cross-linking, Phys. Chem. Chem. Phys. 16 (2014) 25628–25635. Y.K. Jeong, T.W. Kwon, I. Lee, T.S. Kim, A. Coskun, J.W. Choi, Millipede-inspired structural design principle for high performance polysaccharide binders in silicon anodes, Energy Environ. Sci. 8 (2015) 1224–1230. J. Liu, Q. Zhang, T. Zhang, J.T. Li, L. Huang, S.G. Sun, A robust ion-conductive biopolymer as a binder for Si anodes of lithium-ion batteries, Adv. Funct. Mater. 25 (2015) 3599–3605. S. Komaba, N. Yabuuchi, T. Ozeki, Z.J. Han, K. Shimomura, H. Yui, Y. Katayama, T. Miura, Comparative study of sodium polyacrylate and poly(vinylidene fluoride) as binders for high capacity Si-graphite composite negative electrodes in Li-ion batteries, J. Phys. Chem. C 116 (2012) 1380–1389. Y.K. Jeong, T.W. Kwon, I. Lee, T.S. Kim, A. Coskun, J.W. Choi, Hyperbranched βcyclodextrin polymer as an effective multidimensional binder for silicon anodes in lithium rechargeable batteries, Nano Lett. 14 (2014) 864–870. Y.K. Jeong, T.W. Kwon, I. Lee, T.S. Kim, A. Coskun, J.W. Choi, Millipede-inspired structural design principle for high performance polysaccharide binders in silicon anodes, Energy Environ. Sci. 8 (2015) 1224–1230. L. Yi, W. Wang, A. Wang, Adsorption of lead ions from aqueous solution by using carboxymethyl cellulose- g-poly (acrylic acid)/attapulgite hydrogel composites, Desalination 259 (2010) 258–264.
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