An esterified cross-linked polymer binder for high-rate stabilised silicon anodes in lithium-ion batteries

Silicon is renowned for its high theoretical capacity as an anode material in lithium-ion batteries, yet its extensive volume changes during charge and discharge cycles pose significant challenges to its commercial viability. This study addresses these issues by developing composite binders that mitigate mechanical stresses and restrict silicon expansion. We utilize guar gum, a natural polysaccharide, and polyacrylic acid, a linear polymer, to create a cross-linked binder through condensation reactions between hydroxyl and carboxyl groups. This cross-linked structure enhances the mechanical properties of the binder, effectively suppresses the volume expansion of silicon particles, and greatly improves the cycling performance of the silicon electrode. At the same time, the electrodes obtain excellent high-rate performance profit from their high lithium ion diffusion coefficient. Samples with different degrees of cross-linking are obtained by treating the electrodes at different temperatures. The results prove and highlight the critical role of cross-linking in binder performances. Notably, the half-cell retains a specific capacity of 1500 mAh/g after 500 cycles at a high current density of 6 A/g (1 C=4.2 A/g) and 1709.8 mAh/g at a very high current density of 21 A/g (corresponding to 5 C). The full cell using Ni_0.8Co_0.1Mn_0.1O₂ (NCM811) has a specific capacity of 113.3 mAh/g at 5 C, demonstrating significant potential for practical applications.