3D Network Binder via In Situ Cross‐Linking on Silicon Anodes with Improved Stability for Lithium‐Ion Batteries

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.

Body Armor-Inspired Double-Wrapped Binder with High Energy Dispersion for a Stable SiOx Anode

The high specific capacity and relatively low volume expansion of silicon suboxide (SiO_x) highlight its potential as one of the most promising anode materials for lithium-ion batteries. Nevertheless, the traditional binder of polyacrylic acid (PAA) still cannot adapt to enormous stress during the repeated volume expansion/contraction owing to its intrinsic rigid backbone. Inspired by the "soft and hard composite body armor", we herein design a double-wrapped binder consisting of PAA with a high internal Young's modulus (hard part) and polyurethane (DOU) with a low external Young's modulus (soft part). When the SiO_x particle expands during lithiation, the rigid PAA firstly accommodates the volume change to dissipate most of the inner stress, and the elastic DOU with triple dynamic bonds serves as a buffer layer to absorb the residual stress via the breakage/formation of dynamic bonds. By optimizing the PAA/DOU ratio, the SiO_x anode can maintain the integrity during long-term cycling and deliver a relatively high reversible capacity of 1064.1 mAh g^-1 with a preeminent capacity retention of 83.7% at 0.5C after 300 cycles. Such a double-wrapped binder can provide a novel design strategy for multicomponent functional polymer binders toward high-performance SiO_x anodes.

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, the Si 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 3000 mA g^-1 ). This work opens a new avenue to use dendrimer chemistry for the development of high-performance binders for high-capacity anode materials.

Multiscale Polymeric Materials for Advanced Lithium Battery Applications

Riding on the rapid growth in electric vehicles and the stationary energy storage market, high-energy-density lithium-ion batteries and next-generation rechargeable batteries (i.e., advanced batteries) have been long-accepted as essential building blocks for future technology reaching the specific energy density of 400 Wh kg^-1 at the cell-level. Such progress, mainly driven by the emerging electrode materials or electrolytes, necessitates the development of polymeric materials with advanced functionalities in the battery to address new challenges. Therefore, it is urgently required to understand the basic chemistry and essential research directions in polymeric materials and establish a library for the polymeric materials that enables the development of advanced batteries. Herein, based on indispensable polymeric materials in advanced high-energy-density lithium-ion, lithium-sulfur, lithium-metal, and dual-ion battery chemistry, the key research directions of polymeric materials for achieving high-energy-density and safety are summarized and design strategies for further improving performance are examined. Furthermore, the challenges of polymeric materials for advanced battery technologies are discussed.

Random Copolymer Hydrogel as Elastic Binder for the SiOx Microparticle Anode in Lithium-Ion Batteries

Silicon suboxides (SiO_x) have been widely concerned as a practical anode material for the next-generation lithium-ion batteries due to their relatively high theoretical capacity and lower volume change compared to silicon (Si). Nevertheless, traditional binder poly(vinylidene difluoride) (PVDF) still cannot hold the integrity of the SiO_x particle due to its weak van der Waals force. Herein, a copolymer binder for SiO_x microparticles is synthesized through a facile method of free radical polymerization between acrylamide (AM) and acrylic acid (AA). By adjusting the mass ratio of the AM/AA monomer, the copolymer binder can generate a covalent-noncovalent network with superior elastic properties from the synergistic effect. During electrochemical testing, the SiO_x anode with the optimal copolymer binder (AM/AA = 3:1) delivered a reversible capacity of 734 mAh g^-1 (two times that of commercial graphite) at 0.5C after 300 cycles. Thus, this work developed a green and effective strategy for synthesizing a water-soluble binder for Si-based anodes.

A Review on Recent Advances for Boosting Initial Coulombic Efficiency of Silicon Anodic Lithium Ion batteries

Rechargeable silicon anode lithium ion batteries (SLIBs) have attracted tremendous attention because of their merits, including a high theoretical capacity, low working potential, and abundant natural sources. The past decade has witnessed significant developments in terms of extending the lifespan and maintaining high capacities of SLIBs. However, the detrimental issue of low initial Coulombic efficiency (ICE) toward SLIBs is causing more and more attention in recent years because ICE value is a core index in full battery design that profoundly determines the utilization of active materials and the weight of an assembled battery. Herein, a comprehensive review is presented of recent advances in solutions for improving ICE of SLIBs. From design perspectives, the strategies for boosting ICE of silicon anodes are systematically categorized into several aspects covering structure regulation, prelithiation, interfacial design, binder design, and electrolyte additives. The merits and challenges of various approaches are highlighted and discussed in detail, which provides valuable insights into the rational design and development of state-of-the-art techniques to deal with the deteriorative issue of low ICE of SLIBs. Furthermore, conclusions and future promising research prospects for lifting ICE of SLIBs are proposed at the end of the review.

In Situ Room-Temperature Cross-Linked Highly Branched Biopolymeric Binder Based on the Diels-Alder Reaction for High-Performance Silicon Anodes in Lithium-Ion Batteries

Silicon (Si) is an auspicious anode material in next-generation lithium-ion batteries due to its exceptional theoretical gravimetric capacity, environmental friendliness, and high natural abundance. However, the practical application of Si anodes remains a "must-solve" challenge because of its drastic capacity fading that results from the inherent property of drastic volume expansion of Si during repeated lithiation and delithiation. Developing binders employed in robust electrodes has been considered an economical and practical method to affect the electrochemical performance of Si-based electrodes. Some natural polymers have demonstrated good adhesive properties with Si-active materials. However, they have limited capacity to keep the structural integrity of electrodes because the network structures solely based on weak hydrogen bonds are susceptible to deformation during cycling. Herein, we develop an in situ covalently cross-linked three-dimensional (3D) supramolecular network and apply it to the Si electrode to improve cycling performance. This network architecture is constructed using furan-modified branched arabinoxylan of corn fiber gum (CFG) and an ionically conductive cross-linker of maleimido-poly(ethylene glycol) (PEG) through the Diels-Alder reaction. The maleimide groups in PEG can react spontaneously with the furan groups in CFG at room temperature without any other stimulation, thus forming strong covalent bonds in the network. The cross-linked CFG-PEG binder has demonstrated robust adhesive properties with Si-active materials and the current collector. The branching of CFG and functional groups of PEG are conducive to improving the lithium-ion conductivity in the silicon anode, resulting in excellent rate performances. The Si anode with a cross-linked CFG-PEG binder exhibits superior cycling stability. As a result, an in situ cross-linking 3D network as a novel binder has a great potential for fabricating an advanced Si anode in next-generation Li-ion batteries.

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.

Uncovering the Chemistry of Cross-Linked Polymer Binders via Chemical Bonds for Silicon-Based Electrodes

Great efforts have been devoted to the development of high-energy-density lithium-ion batteries (LIBs) to meet the requirements of emerging technologies such as electric cars, large-scale energy storage, and portable electronic devices. To this end, silicon-based electrodes have been increasingly regarded as promising electrode materials by virtue of their high theoretical capacity, low costs, environmental friendliness, and high natural abundance. It has been noted that during repeated cycling, severe challenges such as huge volume change remain to be solved prior to practical application, which boosts the development of advanced cross-linked binders via chemical bonds (CBCBs) beyond traditional PVDF binder. This is because CBCBs can effectively fix the electrode particles, inhibit the volume expansion of Si particles, and stabilize the solid electrolyte interface and thus can enable good cycling stability of silicon anode-based batteries. In light of these merits, CBCBs hence arouse much attention from both industry and academia. In this review, we present chemical/mechanical characteristics of CBCBs and systematically discuss the recent advancements of cross-linked binders via chemical bonding for silicon-based electrodes. Focus is placed on the cross-linking chemistries, construction methods and structure-performance relationships of CBCBs. Finally, the future development and performance optimization of CBCBs are proposed. This discussion will provide good insight into the structural design of CBCBs for silicon-based electrodes.

Covalently Bonded Si-Polymer Nanocomposites Enabled by Mechanochemical Synthesis as Durable Anode Materials

Silicon is one of the most promising anode materials for lithium-ion batteries due to its high theoretical capacity and low cost. However, significant capacity fading caused by severe structural degradation during cycling limits its practical implication. To overcome this barrier, we design a covalently bonded nanocomposite of silicon and poly(vinyl alcohol) (Si-PVA) by high-energy ball-milling of a mixture of micron-sized Si and PVA. The obtained Si nanoparticles are wrapped by resilient PVA coatings that covalently bond to the Si particles. In such nanostructures, the soft PVA coatings can accommodate the volume change of the Si particles during repeated lithiation and delithiation. Simultaneously, as formed covalent bonds enhance the mechanical strength of the coatings. Due to the significantly improved structural stability, the Si-PVA composite delivers a lifespan of 100 cycles with a high capacity of 1526 mAh g^-1. In addition, a high initial Coulombic efficiency of over 86% and an average value of 99.2% in subsequent cycles can be achieved. This reactive ball-milling strategy provides a low-cost and scalable route to fabricate high-performance anode materials.