Bifunctional hydrogen-bonding cross-linked polymeric binders for silicon anodes of lithium-ion batteries

The optimization of polymeric binders has been considered as an effective strategy to accommodate the huge volume change of Si anodes during lithiation and delithiation processes. In this work, three dimensional polymeric binders (CMC/TU) with multiple hydrogen bonds were designed and fabricated through the copolymerization reaction between carboxymethylcellulose sodium (CMC) and thiourea (TU), which possess bifunctional effects on Cu current collectors and Si active materials. On the one hand, similar to the interaction mechanism at rubber-metal boundary in tire industry, the formation of dendritic Cu_xS layers results in physical interlocked forces to strengthen the binding forces of CMC/TU binders with Cu current collectors. On the other hand, the generation of hydrogen bonds between polymeric binders and Si oxide layers can enhance the binding forces of CMC/TU binders with Si active materials and stabilize the electrode/electrolyte interface. When served as binders to Si microparticles (1–5 μm), they exhibited initial coulomb efficiency of 89.9% and reached 1059 mAh g⁻¹ after 150 cycles, which results from the bifunctional roles of CMC/TU binders for maintaining electrode integrity during the discharge and charge processes. The developed synthetic method provides a strategy to enhance the electrochemical properties of Si-based materials, and can be widely applied to other electrode materials.