Electrochemical Performance Of Si Anodes Research Articles

An easy-to-prepare flexible 3D network aqueous binder with gradient hydrogen bonding for high-performance silicon anodes

Although silicon (Si) anode has extremely high specific capacity, the damage to the electrode caused by the huge volume expansion greatly hinders its practical application in lithium-ion batteries. Aiming to alleviate this problem, a high-performance aqueous binder (AMNG) with gradient hydrogen bonding and flexible three-dimensional network structure is prepared by a one-pot method. Compared to the conventional linear polyacrylic acid (PAA) binder, the AMNG binder exhibits enhanced ionic conductivity and stress dissipation for Si nanoparticles, which is able to greatly reduce the side reactions caused by volume changes and considerably improve the electrochemical performance of Si anodes. As a result, the Si nanoparticles using the AMNG binder exhibit an initial discharge capacity as high as 3101 mAh g−1 with a Coulombic efficiency of 89.95%, and a capacity retention of 71.6% for 120 cycles, which are superior to the electrode using PAA, corresponding to 2832 mAh g−1, 88.37% and 28.1%, respectively. More prominently, the practical application of the AMNG binder is evaluated in high-mass-loading Si-based electrodes and even in full cells with LiFePO4, all showing satisfied performance. Therefore, this design approach is valuable as a reference for the preparation of commercial aqueous binders.

Plasma Surface Treatment of Cu Current Collectors for Improving the Electrochemical Performance of Si Anodes.

The practical utilization of Si electrodes is hindered by their substantial volume expansion during alloying and dealloying processes, which causes mechanical damage and separation from Cu current collectors. To alleviate the problem of Si composite detachment from Cu current collectors, the surface of the Cu current collectors is modified using atmospheric oxygen plasma. Plasma treatment improves the wetting ability of the Cu current collectors and, consequently, the coating quality of the Si electrodes. The uniform distribution of the Si electrode components reduces the sheet resistance and improves the adhesion properties of the Si electrodes containing surface-modified Cu current collectors. As a result, the volume expansion of Si during alloying and dealloying is reduced; this results in an excellent rate capability of 1584 mA h g-1 at a current density of 3.6 A g-1 (135% that of bare Cu) and excellent cycle performance of 1545 mA h g-1 after 300 cycles (Si electrodes with bare Cu exhibit 930 mA h g-1). Therefore, the developed plasma treatment method for Cu current collectors is expected to be an economical and efficient approach for improving the Li-ion battery performance.

Insights into the SiO2 Stress Effect on the Electrochemical Performance of Si anode.

Silicon (Si) is regarded as the most potential anode material for next-generation lithium-ion batteries (LIBs). However, huge volume expansion hinders its commercial application. Here, a yolk-shell structural nitrogen-doped carbon coated Si@SiO2 is prepared by SiO2 template and HF etching method. The as-prepared composite exhibits superior cycling stability with a high reversible capacity of 577mA h g-1 at 1 A g-1 after 1000 cycles. The stress effect of SiO2 on stabilizing the electrochemical performance of Si anode is systematically investigated for the first time. In situ thickness measurement reveals that the volume expansion thickness of Si@SiO2 upon charge-discharge is obviously smaller than Si, demonstrating the electrode expansion can be effectively inhibited to improve the cyclability. The density functional theory (DFT) calculation further demonstrates the moderate young's modulus and enhanced hardness after SiO2 coating contribute significantly to the mechanical reinforcement of overall Si@SiO2@void@NC composite. Various post-cycling electrode analyses also address the positive effects of inner stress from the Si core on effectively relieving the damage to electrode structure, facilitating the formation of a more stable inorganic-rich solid electrolyte interphase (SEI) layer. This study provides new insights for mechanical stability and excellent electrochemical performance of Si-based anode materials.

Rational Electrolyte Design for Interfacial Chemistry Modulation to Enable Long‐Term Cycling Si Anode

AbstractThe silicon anode is promising for high‐energy density lithium‐ion batteries owing to its ultrahigh theoretical capacity. However, the practical deployment of Si anodes is significantly hindered by its large volume change and unstable electrode/electrolyte interphase associated with routine electrolytes. Herein, a cyclic ether‐based electrolyte is designed and shows high compatibility with Si anodes. By simply decreasing the prevalence of ethereal oxygen groups and increasing the degree of molecule unsaturation of 1,2‐dimethoxyethane simultaneously, the resulting cyclic tetrahydrofuran (THF) presents a weak solvation capability and strong polymerization. Experimental and computational evidence demonstrates this rational design leads to a remarkable improvement in electrochemical performance of Si anodes. By forming a thin, elastic, and LiF‐rich inorganic‐polymeric solid‐electrolyte interphase film, the Si electrode cycled in THF‐based electrolyte exhibits long‐term cycling stability with a high reversible capacity of 1995.7 mAh g−1 after 400 cycles. The full‐cells with Si/graphite anodes and LiFePO4 cathodes maintain over 80% capacity retention after 600 cycles.

Design of multifunctional polymeric binders in silicon anodes for lithium‐ion batteries

AbstractSilicon (Si) is a promising anode material for lithium‐ion batteries (LIBs) owing to its tremendously high theoretical storage capacity (4200 mAh g−1), which has the potential to elevate the energy of LIBs. However, Si anodes exhibit severe volume change during lithiation/delithiation processes, resulting in anode pulverization and delamination with detrimental growth of solid electrolyte interface layers. As a result, the cycling stability of Si anodes is insufficient for commercialization in LIBs. Polymeric binders can play critical roles in Si anodes by affecting their cycling stability, although they occupy a small portion of the electrodes. This review introduces crucial factors influencing polymeric binders' properties and the electrochemical performance of Si anodes. In particular, we emphasize the structure–property relationships of binders in the context of molecular design strategy, functional groups, types of interactions, and functionalities of binders. Furthermore, binders with additional functionalities, such as electrical conductivity and self‐healability, are extensively discussed, with an emphasis on the binder design principle.

S doped CNTs scaffolded Si@C spheres anode toward splendid High-Temperature performance in Lithium-ion Battery

The poor electronical conductivity and large volume change of nano-silicon anode has seriously hindered its further application. To overcome these drawbacks, we employed the S-doped multiwalled carbon nanotubes (SCNTs) as the conductive additive to fabricating a scaffolded framework for the first time. The as-assembled Si anode with 5 wt% SCNTs (Si@C-5SCNTs) shows a large specific capacity of 939 mA h g−1 at 2 A g−1 within 0–1 V, significantly higher than that of Si@C (466 mA h g−1) and Si@C-5CNTs (720 mA h g−1), showing a superior rate performance. Besides, it shows higher initial coulombic efficiency, Li-ion diffusion coefficient, cycling performance, and smaller volume change than that of Si@C and Si@C-CNTs at room temperature. Even at 40 ℃, the Si@C-5SCNTs anode still show a superior rate performance (1842 and 819 mAh g−1 at 0.05 and 2 A g−1, respectively) and cycling stability (83.6% capacity retention) than that of Si@C and Si@C-5CNTs. To better explain the significantly enhanced electrochemical performance of Si anode both room and high temperature conditions, both the chemo-mechanical coupling and internal temperature distribution models have been rational constructed, and further demonstrated that the SCNTs can effectively buffer the volume expansion and reduce the internal local temperature rise.

Dendrimer Based Binders Enable Stable Operation of Silicon Microparticle Anodes in Lithium-Ion Batteries.

High-capacity anode materials (e.g., Si) are highly needed for high energy density battery systems, but they usually suffer from low initial coulombic efficiency (CE), short cycle life, and low-rate capability caused by large volume changes during the charge and discharge process. Here, a novel dendrimer-based binder for boosting the electrochemical performance of Si anodes is developed. The polyamidoamine (PMM) dendrimer not only can be used as binder, but also can be utilized as a crosslinker to construct 3D polyacrylic acid (PAA)-PMM composite binder for high-performance Si microparticles anodes. Benefiting from maximum interface interaction, strong average peeling force, and high elastic recovery rate of PAA-PMM composite, theSi electrode based on PAA-PMM achieves a high specific capacity of 3590 mAh g-1 with an initial CE of 91.12%, long-term cycle stability with 69.80% retention over 200 cycles, and outstanding rate capability (1534.8 mAh g-1 at 3000mA g-1 ). This work opens a new avenue to use dendrimer chemistry for the development of high-performance binders for high-capacity anode materials.

Controlled surface oxidation of mesoporous silicon microparticles to achieve a stable Si/SiOx anode for lithium-ion batteries

Silicon (Si) is the most promising next-generation anode material for lithium-ion batteries. However, it often suffers from a fast capacity fading due to the large volume changes during the lithiation/delithiation resulting in electrical contact loss between different components of the anode and eventually in battery fading. Mesoporous structure of silicon is a potential material to overcome the issue as the pores could accommodate the volume change during the battery cycling. However, its high surface area can cause continuous parasitic electrolyte decomposition reactions, causing low initial coulombic efficiency (ICE), capacity fading, and battery safety issue. In this study, the surface passivation of mesoporous Si microparticles produced with electrochemical etching and milling was realized through thermal oxidation. The silicon oxide (SiOx) layer generated acted as a protective layer to stabilize the Si surface, thus improving Si electrode performance. Electrochemical characterization showed that the electrode performance of Si/SiOx was strongly correlated with the oxygen content. The Si/SiOx anode delivered a discharge capacity of over 2000 mAh g−1 when the oxygen content was less than 34 wt%, but a much lower capacity when there was higher oxygen content. The best sample (oxidation at 700 °C) showed ICE of 78% and a stable cycling performance for over 180 cycles with a limited capacity of 800 mAh g−1. The results indicate that the appropriate oxidation of mesoporous Si surface to get optimized surface/oxygen content enhances the electrochemical performance of Si anodes essentially.

A Comparative Investigation of Various Binders for Silicon Anodes: Interactions with Other Components, Rheological Property, and Behavior in Operando Dilatometry

AbstractBenefitting from its outstanding advantages, silicon (Si) has been considered as one of the best candidates of anode materials for next‐generation lithium ion batteries (LIBs). Among various influencing factors on the electrochemical performance of Si anodes, binder attracts more and more attention though occupying only a small portion. Well‐designed binders play a critical role in improving cycling performance of Si anodes. Herein, sodium carboxymethyl cellulose (CMC), poly (acrylic acid) (PAA), sodium alginate (SA), polyvinylidene difluoride (PVDF), and polyacrylonitrile (PAN) are selected as binders, and their effects on the electrochemical performance are investigated. PAA, CMC, and SA form both dynamic hydrogen bonds and covalent bonds with Si while PAN and PVDF form monotonous hydrogen bonds with Si. Defects of PAA and CMC in slurry mixing and subsequent drying process originated from high modulus and poor liquidity are exposed. The binder influence on expansion/contraction behavior of silicon anodes is innovatively investigated in real time. Electrodes with PAA binder exhibit the greatest expansion but the highest reversibility, which contributes to superior electrochemical performance. This article aims to provide useful information for failure mechanism analysis of binders as well as design of advanced binders for high energy LIBs.

In Situ Construction of a Multifunctional Interface Regulator with Amino-Modified Conjugated Diene toward High-Rate and Long-Cycle Silicon Anodes.

Silicon (Si) is deemed to be the next-generation lithium-ion battery anode. However, on account of the poor electronic conductivity of Si materials and the instability of the solid electrolyte interphase layer, the electrochemical performance of Si anodes is far from reaching the application level. In this work, a multifunctional poly(propargylamine) (PPA) interlayer is constructed on the Si surface via a simple in situ polymerization method. Benefiting from the electronic conductivity, ionic conductivity, robust interphase interactions for hydrogen bonding, and stability of multifunctional PPA, the optimized Si@PPA-7% electrode shows improved lithium storage capability. A high capacity of 1316.3 mAh g-1 is retained after 500 cycles at 2.1 A g-1, and 2370.3 mAh g-1 can be delivered at 42 A g-1, which are in stark contrast to the unmodified Si electrode. Furthermore, the rate and cycle capabilities of the LiFePO4//Si@PPA-7% full cell are also obviously better than those of LiFePO4//Si.

Effect of lithium salt type on silicon anode for lithium-ion batteries

Silicon (Si) is one of the most promising anode materials in the next generation of Li-ion batteries. However, the application of Si is restricted by its unsatisfactory electrochemical performance. This work investigates the influence of lithium salt type on the electrochemical performance of Si anode, and shows that lithium salt type plays an importing role in determining the electrochemical performance of Si anode. Through investigation and optimization, lithium hexafluorophosphate (LiPF6)-lithium bis(fluorosulfonyl)imide (LiFSI)-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) ternary composite lithium salt with a mole ratio of 7:1:2 exhibits the best cycling stability and rate capability. It retains a high capacity of 1879.8 mAh g−1 after 400 cycles at 0.5 C charge and discharge, and still maintains 1851.4 mAh g−1 at 30 C; which are significantly higher than the 583.3 and 316.4 mAh g−1 of the LiPF6-based electrolyte under the same conditions. The underlying mechanism is investigated, and the results indicate that the lithium type has an effect on both the Si anode and the lithium counter electrode, and the synergistic effect of LiPF6-LiFSI-LiTFSI enables high-rate and long-cycle Si anodes.

Crosslinked poly(acrylic acid) enhances adhesion and electrochemical performance of Si anodes in Li-ion batteries

Water-soluble binders such as poly (acrylic acid) (PAA) possess many advantages in the slurry and electrode preparation due to their low-cost and environmental friendliness. However, due to the linear nature of these binders, they are susceptible to slide under the continuous volume variation of Si-containing anodes during cycling. Therefore, a three-dimensional (3D) interconnected polymeric network is required to provide robust mechanical adhesion with the Si particles to maintain the electrode integrity for excellent cycle stability. Here, pentaerythritol (PER) is used as a crosslinking agent to connect the linear PAA binder to enhance its adhesion strength for Si anodes, which is systematically confirmed using Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric (TG) measurements. Si electrodes with crosslinked PAA-PER binder show enhanced adhesion and elasticity, exhibiting a more robust electrode integrity than purely PAA-based Si electrodes. Galvanostatic cycling shows that Si-PAA-5%PER electrodes maintain a higher discharge capacity of 514.3 mAh g-1 (after 10 cycles) for micro-sized and 1502.1 mAh g-1 (after 105 cycles) for nano-sized Si particles compared to 257.6 mAh g-1 and 1413.9 mAh g-1 for micro- and nano-sized Si in Si-PAA electrodes, respectively. XPS analyses on cycled electrodes confirmed that crosslinked PAA-PER binder has no negative effects on the SEI formation and its functionality in Si electrodes. SEM cross-sections reveal that Si-PAA-5%PER electrodes show reduced electrode thickness variation (micro-/nano-: 114.2%/182.2%) than that of Si-PAA electrodes (micro-/nano-: 134.1%/212.0%) after cycling, which indicates that crosslinked PAA-PER binder can enhance the electrode integrity due to its 3D interconnected network. This work provides meaningful insight into the exploration of novel binders and their impact on the SEI formation and functionality, especially for high-capacity alloy-type anode materials.

A Strategic Approach to Use Upcycled Si Nanomaterials for Stable Operation of Lithium-Ion Batteries.

Silicon, as a promising next-generation anode material, has drawn special attention from industries due to its high theoretical capacity (around 3600 mAh g−1) in comparison with conventional electrodes, e.g., graphite. However, the fast capacity fading resulted by a large volume change hinders the pragmatic use of Si anodes for lithium ion batteries. In this work, we propose an efficient strategy to improve the cyclability of upcycled Si nanomaterials through a simple battery operation protocol. When the utilization degree of Si electrodes was decreased, the electrode deformation was significantly alleviated. This directly led to an excellent electrochemical performance over 100 cycles. In addition, the average charge (delithation) voltage was shifted to a lower voltage, when the utilization degree of electrodes was controlled. These results demonstrated that our strategic approach would be an effective way to enhance the electrochemical performance of Si anodes and improve the cost-effectiveness of scaling-up the decent nanostructured Si material.

Improving the electrochemical performance of Si anode by using N-doped carbon materials in lithium-ion batteries

Improving the electrochemical performance of Si anode by using N-doped carbon materials in lithium-ion batteries

A novel covalently grafted binder through in-situ polymerization for high-performance Si-based lithium-ion batteries

Binder modification is an effective method to restrain the volume effect of Si anodes in high energy density lithium-ion batteries. In this work, a novel binder grafting strategy is proposed to prepare urea formaldehyde resin (UFR) grafted polyvinyl alcohol (PVA) binder to overall enhance the electrochemical performance of Si anodes. The advanced binder solves the problems of poor dispersibility, mechanical stability, and chemical stability of PVA binder. Benefit from the lithium conductivity and flexibility of the UFR modified PVA binder, the Si anode delivers over 2000 mAh/g after 200 cycles at a current density of 2.1 A/g, and retains 1837 mAh/g at 42 A/g. Furthermore, the PVA-UFR binder also exhibits obvious advantages in full cells, and the cycle stability of Si//LiFePO4 is significantly improved.

(Invited) Tuning the Formation and Structure of the Silicon Electrode/Electrolyte Interphase in Superconcentrated Ionic Liquids

In order to push further the development of next generation Li-ion batteries (LiBs), high energy density, good capacity retention and increased safety are key features that need to be taken into account when designing energy storage devices. To this date, commercial batteries for portable devices mainly use graphite as anode. However, with the advent of electric vehicles and intelligent power grids, there is an increasing demand for high capacity materials to meet the energy and power requirement of these applications. More recently, Si anode has received considerable attention because of its natural abundance and its ability to deliver high energy density, with a gravimetric capacity of 3579 mAhg-1 which is almost 10 times that of graphite (372 mAhg-1) [1-2].Bearing in mind that commercial LiBS use carbonate electrolytes which are recognized to pose safety issues and have been identified to suffer from degradation during charge-discharge cycles, we explored in this study the performance of Si anode in ionic liquid electrolytes based on phosphonium and pyrrolidinium cations, systems that are currently the most studied in the field of Li batteries [3-4]. Ionic liquid electrolytes are an appealing alternative to carbonates mainly because of their low volatility and better stability.In the recent years, good electrochemical behavior has been observed in ionic liquids with high salt concentration [3-5]. In this work, we were able to demonstrate better electrochemical performance of Si anode in ionic liquid electrolytes with 3.2 M LiFSI compared to conventional carbonate electrolytes in terms of capacity and capacity retention at 50°C. Our recent study using superconcentrated electrolytes revealed the superior electrochemical behaviour of triethyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1222FSI) in a half-cell investigation of Si negative electrodes (Fig. 1). This result was linked to the stability of the electrolyte upon cycling and to improved lithium ion transport which is facilitated at high Li salt content [6]. Moreover, initial investigation of the SEI using NMR and XPS spectroscopy revealed that less degradation products are formed upon cycling in ionic liquid electrolytes compared to usual carbonates electrolytes. In the present work, we report the importance of tuning the Si/IL electrolyte interface as a function of IL cation nature and salt concentration. Experimental techniques such as 7Li, 19F MAS-NMR, SEM, and STEM-EDX were used to determine the SEI composition and morphology in order to further investigate its influence on the electrochemical performance as well as the relationship of the electrolyte chemistry (P1222FSI, N-methyl-N-propylpyrrolidinium (C3mpyr) FSI-based electrolytes and carbonate-based electrolyte) to the SEI properties. In addition, computational methods and differential capacitance (DC) experiments using AC impedance were applied to gain a better understanding of the SEI formation by examining the structuring at the electrode/electrolyte interphase.

Dopamine-modified carboxymethyl cellulose as an improved aqueous binder for silicon anodes in lithium-ion batteries

The intractable issues of silicon anodes hinder its wide application in high-capacity Li-ion batteries. Binders are proven to be one of the effective ways to enhance the electrochemical performance of Si anodes. Inspired by mussels, the water soluble binder carboxymethyl cellulose (CMC) is modified through amidation reaction, and the dopamine moieties are successfully introduced into the polymer backbone of CMC. The dopamine-modified CMC (CMC-DOP) is confirmed by liquid 1H nuclear magnetic resonance (1H NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The CMC-DOP with polar catechol groups and affluent anchoring points exhibits higher adhesive force and superior electrochemical performance. The Si @ CMC-DOP electrode delivers a high initial specific capacity of 3418.2 mAh g−1 and maintains satisfactory capacity of 1650.6 mAh g−1 after 200 cycles. Furthermore, the tight wrapping/coating effect of CMC-DOP binder can effectively protect the active material from exposure to electrolyte, and reduce the decomposition of electrolyte as well as the massive formation of solid electrolyte interface (SEI) layers. The Si electrode with CMC-DOP binder shows slight polarization and intact structure in long-term cycling.

Enhanced adhesion and electrochemical performance of Si anodes with gum arabic grafted poly(acrylic acid) as a water‐soluble binder

AbstractGum arabic grafted poly(acrylic acid) (GA‐g‐PAA) is synthesized as a mechanically robust water‐soluble binder for silicon (Si) anodes in lithium‐ion batteries by graft polymerization of acrylic acid onto GA backbone via a free radical reaction. 1H NMR and Fourier transform infrared spectroscopies and thermogravimetric analysis are systematically conducted to confirm the grafting polymerization process. GA‐g‐PAA with different grafting length of PAA shows enhanced adhesion strength and excellent flexibility after grafting. Optimal Si‐GA‐g‐8PAA electrode displays better cyclic stability, higher Coulombic efficiency and superior rate properties compared with a Si electrode with linear PAA binder. The Si‐GA‐g‐8PAA electrode exhibits a high electrical conductivity, low interfacial/charge transfer resistance and high lithium‐ion diffusion coefficient. GA‐g‐8PAA binder with grafted structure not only can maintain the mechanical and electrical integrity of the electrode, facilitating favorable electrochemical kinetics, but also assists in preserving a stable solid electrolyte interphase on Si surface upon long‐term cycling. Such a facile strategy for designing a novel grafted binder shows potential for practical application on high‐capacity anode materials with large volume change. © 2021 Society of Industrial Chemistry.

Constructing cycle-stable Si/TiSi2 composites as anode materials for lithium ion batteries through direct utilization of low-purity Si and Ti-bearing blast furnace slag

The large volume expansion and poor conductivity leading to the deterioration of electrochemical performance, is a significant challenge for Si-anode materials for practical applications. Previous researches have indicated that introducing a TiSi2 buffer with high conductivity to form Si/TiSi2 composites can effectively improve the electrochemical performance of Si anode. However, the facile and low-cost synthesis of Si/TiSi2 composites remains challenging. In this study, we propose a novel approach to preparing Si/TiSi2 composites as anode materials for lithium-ion batteries by coupling photovoltaic (PV) silicon waste (simulated using inexpensive low-purity Si (98.8%) in experiments) and metallurgical waste (Ti-bearing blast furnace slag, TBBFS) via a new method combining induction melting and mechanical ball milling. A series of Si/TiSi2 materials were obtained using different ratios of raw materials and investigated using SEM, TEM, XRD, XPS and electrochemical performance tests. The results show that TiSi2 not only acts as a buffer for the bulk expansion of Si, but also improves the electrical conductivity; therefore, the Si/TiSi2 materials exhibit enhanced cycling stability when more TiSi2 is introduced. The sample prepared using a low-purity Si and TBBFS with a mass ratio of 1:3 delivered a reversible capacity of 530 mAh g−1 after 200 cycles at a charge-discharge current density of 800 mA g−1. This work not only provides a new strategy and technology for introducing TiSi2 into Si-based anode materials, but also provides a green and sustainable technical route for the high value-added recycling of Ti-bearing blast furnace slag.

Influence of Binder Crystallinity on the Performance of Si Electrodes with Poly(vinyl alcohol) Binders

Silicon is a highly promising electrode material for Li-ion batteries because of its high theoretical capacity, but severe volume changes during cycling leads to pulverization and rapid capacity fading. The use of alternative and water-soluble polymer binders such as poly(vinyl alcohol) (PVA) or poly(acrylic acid) (PAA) can improve the cycling performance of Si-based Li-ion batteries. Here, we investigate the effect of the substitution of the hydroxyl groups of PVA chains by carboxylic acid and acetate groups on the electrochemical performance of Si anodes in Li-ion batteries. Using modified PVAs, a model system is created spanning the chemical space between PVA and PAA, and the role of different Si-adhering functionalities is investigated. When comparing the electrochemical performance of Li-ion battery cells using Si anodes and the investigated binder systems, PVA with the highest degree of hydrolysis exhibits a superior performance (100 cycles with 1019 mAh g–1) compared to modified PVAs and PAA as a binder for Si anodes. An increased degree of hydrolysis of PVA is also seen to be beneficial for high capacity retention. These effects can be largely explained by the crystallinity of the binder system, which renders an improved electrode integrity during cycling and less swelling of the Si particles.