Dual crosslinked binders based on poly(2-hydroxyethyl methacrylate) and polyacrylic acid for silicon anode in lithium-ion battery

Research Progress of Polyacrylate Binders for Silicon-Based Anodes in Lithium-Ion Batteries

Silicon (Si) has emerged as a preeminent candidate for next-generation lithium-ion batteries (LIBs) anodes, primarily attributed to its exceptionally high specific capacity. Nevertheless, the substantial volumetric expansion accompanying lithium alloying reactions has long posed a critical challenge to the commercial viability of silicon-based anodes. Binders as connectors between the active Si particles, conductive agents, and current collectors, playing a crucial role in stabilizing the structure of silicon anodes in LIBs. Polyacrylic acid (PAA) water-based binders contain abundant carboxyl groups (─COOH) that can enhance adhesive strength. However, simple linear PAA does not adequately accommodate the significant volume expansion of silicon anodes. To address this issue, various structural optimization strategies have been applied to modify PAA binders. In this context, a comprehensive review is conducted on the recently developed PAA-based binders, which cover linear, branched, and 3D network configurations. A meticulous comparison is carried out regarding their initial coulombic efficiency, areal capacity, and material costs. Moreover, in-depth insights are offered to elucidate the mechanisms by which these structural modifications augment the properties of the binders and the performance of the cells. Ultimately, the prospective directions for the evolution of PAA-based binders designed for Si-based anodes in high-energy-density LIBs are deliberated.

Dual Cross-Linked Poly(ether imide)/Poly(vinyl alcohol) Network Binder with Improved Stability for Silicon Based Anodes in Lithium-Ion Batteries

The abundance and exceptional theoretical capacity of silicon make it a leading contender for next-generation lithium-ion battery anodes. However, its practical application is significantly hindered by rapid capacity degradation arising from substantial volume fluctuations during cycling. To address this limitation, an subtly dual cross-linked binder system was developed by incorporating soft poly(vinyl alcohol) (PVA) macromolecules into a poly(ether imide) (PEI) matrix. This innovative design leverages the rigid PEI framework, fortified through chemical ester cross-linking, to effectively suppress the expansion for silicon nanoparticles. Concurrently, the reversible hydrogen bonding within PVA could dissipate the stress to inhibit the volume changes, thereby preserving the materials' mechanical stability and structural integrity. This synergistic interplay ensures a stabilized electrode interface and enhanced durability with outstanding cycling stability, that of a high specific capacity of 2126 mAh/g and 92.1% retention over 200 cycles at 0.84 A/g. Further refinement of the anode formulation enabled an impressive areal capacity of 9.3 mAh/cm2 with submicron silicon, underscoring the transformative potential of this dual cross-linked system for next-generation energy storage solutions.

An Advanced 3D Crosslinked Conductive Binder for Silicon Anodes: Leveraging Glycerol Chemistry for Superior Lithium-Ion Battery Performance

Silicon (Si) anodes hold great promise for high-capacity lithium-ion batteries (LIBs), yet their practical application is hindered by severe volume expansion and mechanical degradation. To tackle these challenges, we present an innovative 3D crosslinked conductive polyoxadiazole (POD) binder engineered with glycerol (GL) to form a robust network of covalent and hydrogen bonds. This unique chemical architecture not only enhances adhesion and mechanical resilience to effectively dissipate the stresses induced by Si's volumetric changes but also constructs a robust conductive framework to facilitate electron transfer. The dynamic interplay between strong covalent and flexible hydrogen bonds in the POD-c-GL binder enables superior structural integrity and stable solid-electrolyte interphase (SEI) during cycling. The Si@POD-c-GL anode exhibits remarkable electrochemical performance, including a high initial Coulombic efficiency, impressive rate capability, and outstanding cycling stability. This work highlights the potential of harnessing in situ crosslinking chemistry to develop advanced binders, paving the way for the next generation of high-performance Si anodes in LIBs.

Poly(Acrylic Acid)-Based Polymer Binders for High-Performance Lithium-Ion Batteries: From Structure to Properties

Poly(acrylic acid) (PAA) and its derivatives have emerged as promising candidates for enhancing the electrochemical performance of lithium-ion batteries (LIBs) as binder materials. Recent research has focused on evaluating their ability to improve adhesion with silicon (Si) particles and facilitate ion transport while maintaining electrode integrity. Various strategies, including mixing modifications and copolymerization methods, are highlighted and the structural and physicochemical properties of these binders are examined. Additionally, the interaction mechanisms between PAA-based binders and active materials and their impact on key electrochemical properties such as initial Coulombic efficiency (ICE) and cycle stability are discussed. The findings underscore the efficacy of tailored PAA-based binders in enhancing the electrochemical properties of LIBs, offering insights into the design principles and practical implications for advanced battery materials. These advancements hold promise for developing high-performance lithium batteries capable of meeting future energy storage demands.

Cross-Linking Network of Soft-Rigid Dual Chains to Effectively Suppress Volume Change of Silicon Anode

Polyacrylic acid (PAA) is a promising binder for the high-capacity Si anode. However, the one-dimensional structure of PAA could cause the linear molecular chains to slide from the Si surface during the charge-discharge processes, leading to insufficient suppression of the massive volume expansion of the Si anode. Herein, a soft-rigid dual chains' network of PAA-sodium silicate (PAA-SS) was successfully constructed by cross-linking PAA and SS in situ at room temperature. The soft chains of PAA and the rigid chains of polysilicic acid synergistically ensure the enhanced adhesion property and mechanical strength. Therefore, the Si electrode with PAA-SS binder delivers a discharge capacity of 1559 mAh/g after 150 cycles at 4.2 A/g (1C) with an initial Coulombic efficiency of 93.2%. Moreover, the PAA-SS based SiC-500 electrode exhibits a discharge capacity of 441 mAh/g with the capacity retention of 88.2% after 500 cycles at 0.5 A/g, implying the PAA-SS binder's great industrial prospect in Si based electrodes.

Synergistic Double Cross-Linked Dynamic Network of Epoxidized Natural Rubber/Glycinamide Modified Polyacrylic Acid for Silicon Anode in Lithium Ion Battery: High Peel Strength and Super Cycle Stability

Silicon (Si), a high-capacity lithium-ion battery anode material, has aroused wide attention. Its further practical application has been limited by its huge volume change during the cycle. To reduce this defect, the double cross-linked product of glycinamide hydrochloride modified poly(acrylic acid) (PAG) and epoxidized natural rubber (ENR) was developed as a water-based binder to obtain sufficient elasticity and a sufficiently strong adhesive force. Due to the double cross-linked structures in the system, the binder was enabled to effectively disperse and transfer the stress generated by the volume expansion of the Si particles and keep the integrity of the electrode during the cycle, thus obtaining excellent cycle performance. When the current density was 1 A g-1, PE55 (PAG: ENR = 1:1 cross-linked polymer) electrode still achieved a specific capacity of 2322.2 mAh g-1 after 100 cycles of constant current charge and discharge, and PE55 binder exhibited excellent bonding properties (4.45 N) and mechanical properties (stress: 5.51 MPa, strain: 87.4%). The comparison of poly(acrylic acid) (PAA) electrodes suggests that the introduction of elastic polymer and the construction of double cross-linked structures can increase the stability of Si anodes.

Key Factors for Binders to Enhance the Electrochemical Performance of Silicon Anodes through Molecular Design

Silicon is considered the most promising candidate for anode material in lithium-ion batteries due to the high theoretical capacity. Unfortunately, the vast volume change and low electric conductivity have limited the application of silicon anodes. In the silicon anode system, the binders are essential for mechanical and conductive integrity. However, there are few reviews to comprehensively introduce binders from the perspective of factors affecting performance and modification methods, which are crucial to the development of binders. In this review, several key factors that have great impact on binders' performance are summarized, including molecular weight, interfacial bonding, and molecular structure. Moreover, some commonly used modification methods for binders are also provided to control these influencing factors and obtain the binders with better performance. Finally, to overcome the existing problems and challenges about binders, several possible development directions of binders are suggested.

Epoxy Cross-Linking Enhanced the Toughness of Polysaccharides as a Silicon Anode Binder for Lithium-Ion Batteries

The large volume expansion of a silicon anode induces serious mechanical failure and limits its applications. Owing to the intrinsic weak van der Waals force and poor toughness, it is unable to solve this issue with the current commercial poly(vinylidene difluoride) (PVDF) binder. The development of a binder with strong binding strength with silicon (Si) is urgent. Herein, a hydroxyl-rich three-dimensional (3D) network binder is synthesized by chemical cross-linking reactions between epichlorohydrin (ECH) and sodium hyaluronate (SH), which exhibits dramatically enhanced toughness and cohesive properties. The Si anode with the novel SH-ECH as the binder delivers excellent electrochemical performance, especially cycling stability. The discharge capacity could maintain 800.4 mAh g^-1 after 1000 cycles at a current of 0.2 C with the average capacity decay rate per cycle of 0.015%. Our results pave a new way for the tailoring of the chemical structures of natural polymers to realize lithium-ion batteries (LIBs) with superior electrochemical performance.

Dynamically Cross-Linked Polymeric Binder-Made Durable Silicon Anode of a Wide Operating Temperature Li-Ion Battery

The colossal volumetric expansion (up to 300%) of the silicon (Si) anode during repeated charge-discharge cycles destabilizes the electrode structure and causes a drastic drop in capacity. Here in this work, commercial poly(acrylic acid) (PAA) is cross-linked by hydroxypropyl polyrotaxane (HPR) via reversible boronic ester bonds to achieve a water-soluble polymeric binder (PAA-B-HPR) for making the Si anode of the Li-ion battery. Slidable α-cyclodextrins of modified polyrotaxane are allowed to move around when the unwanted volume variation occurs in the course of lithiation and delithiation so that the accumulated internal stress can be equalized throughout the system, while the reversible boronic ester bonds are capable of healing the damages created during manufacturing and service to maintain the electrode integrity. As a result, the Li-ion battery assembled with the Si anode comprised of the PAA-B-HPR binder possesses outstanding specific capacity and cycle stability within a wide temperature range from 25 to 55 °C. Especially, the Si@PAA-B-HPR anode exhibits a discharge specific capacity of 1056 mA h/g at 1.4 A/g after 500 cycles under a higher temperature of 55 °C, and the corresponding capacity fading rate per cycle is only 0.10%. The present work opens an avenue toward the practical application of the Si anode for Li-ion batteries.