In Situ Cross-linked Carboxymethyl Cellulose-Polyethylene Glycol Binder for Improving the Long-Term Cycle Life of Silicon Anodes in Li Ion Batteries

Advances and future perspectives on silicon-based anodes for lithium-ion batteries

Silicon (Si)-based anode has emerged as the most promising anode material for next-generation lithium-ion batteries (LIBs) due to its high specific capacity, suitable operating potential and abundant natural reserves. Nevertheless, the drastic volume effect of Si particles during lithiation/delithiation leads to particle pulverization, electrode structure collapse, and solid electrolyte interfacial (SEI) film instability, which results in a rapid reversible capacity degradation of Si-based anodes. It is essential to deeply analyze the failure mechanism of silicon-based electrodes and explore suitable improvement methods to achieve higher capacity retention. Herein, we systematically summarize the improvement strategies for Si-based anodes, including regulating material particle size, optimizing structure and composition, and exploring new binders, along with their enhancement mechanisms. In addition, the preparation of high-performance Si-based electrodes based on newly developed 3D printing technology in recent years is discussed. Lastly, several possible directions and emerging challenges for Si anode are presented to facilitate further improvement in practical applications. Overall, this review is expected to provide basic understanding and insights into the practical application of Si-based materials in next-generation LIBs negative electrodes.

Cross-linked multifunctional binder in situ tuning solid electrolyte interface for silicon anodes in lithium ion batteries

Silicon is considered as the most promising anode material for high performance lithium-ion batteries due to its high theoretical specific capacity and low working potential. However, severe volume expansion problems existing during the process of (de)intercalation which seriously hinders its commercial progress. Binder can firmly adhere silicon and conductive agent to the current collector to maintain the integrity of the electrode structure, thereby effectively alleviating the silicon volume expansion and realizing lithium-ion batteries with high electrochemical performance. In this paper, citric acid (CA) and carboxymethyl cellulose (CMC) are adopted to construct a covalently crosslinked CA@CMC binder by an easy-to-scale-up esterification treatment. The Si@CA@CMC-1 electrode material shows an impressive initial coulombic efficiency (ICE) at 82.1% and after 510 cycles at 0.5 A/g, its specific capacity is still higher than commercial graphite. The excellent electrochemical performance of Si@CA@CMC-1 can be attributed to the ester bonds formed among CA@CMC binder and silicon particles. Importantly, by decoupling in situ EIS combining XPS at different cycles, it can be further proved that the CA@CMC binder can tune the component of SEI which provide a new-route to optimize the performance of silicon.

Application and Development of Silicon Anode Binders for Lithium-Ion Batteries

The use of silicon (Si) as a lithium-ion battery's (LIBs) anode active material has been a popular subject of research, due to its high theoretical specific capacity (4200 mAh g^-1). However, the volume of Si undergoes a huge expansion (300%) during the charging and discharging process of the battery, resulting in the destruction of the anode's structure and the rapid decay of the battery's energy density, which limits the practical application of Si as the anode active material. Lithium-ion batteries' capacity, lifespan, and safety can be increased through the efficient mitigation of Si volume expansion and the maintenance of the stability of the electrode's structure with the employment of polymer binders. The main degradation mechanism of Si-based anodes and the methods that have been reported to effectively solve the Si volume expansion problem firstly are introduced. Then, the review demonstrates the representative research work on the design and development of new Si-based anode binders to improve the cycling stability of Si-based anode structure from the perspective of binders, and finally concludes by summarizing and outlining the progress of this research direction.

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.

Zn2+-Imidazole Coordination Crosslinks for Elastic Polymeric Binders in High-Capacity Silicon Electrodes

Recent research has built a consensus that the binder plays a key role in the performance of high-capacity silicon anodes in lithium-ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn2+-imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn2+-imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long-term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full-cells paired with LiNi0.8Co0.15Al0.05O2 cathodes. The present study underlines the importance of highly reversible metal ion-ligand coordination chemistries for binders intended for high capacity alloying-based electrodes.

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.

Sulfonation of alginate grafted with polyacrylamide as a potential binder for high-capacity Si/C anodes

A systematic approach for how to find an appropriate polymer binder for high-capacity LIB anodes is presented in this study. As an example, a newly-developed SAlg-g-PAAm binder, alginate functionalized with sulfo groups and subsequently grafted with polyacrylamide, is used for the Si/C electrode. Various characteristics of the binder polymer itself, two basic characteristics of the electrode with respect to the binder, and the effect of the binder on cell performance are subsequently investigated. In all respects, the SAlg-g-PAAm polymer is a very promising binder for high-capacity anodes. The sulfo groups in the binder improve the ionic conductivities in both the binder and the electrode, leading to reduced charge transfer resistance. In addition, the sulfonation of the alginate grafted with polyacrylamide significantly enhances the mechanical and adhesion properties of the binder and consequently decreases the volume change generated during cycles. These advantages of the SAlg-g-PAAm binder ultimately lead to a considerable enhancement in the electrochemical performance of the high-capacity Si/C electrodes.

A systematic approach for how to find an appropriate polymer binder for high-capacity LIB anodes is presented in this study.