Poly(ethylene-<i>alt</i>-maleic acid)-Based Binders for Silicon Anodes

The development of high-energy-density lithium-ion batteries (LIBs) is essential for the advancement of electric vehicles and portable electronics. Silicon-rich anodes, with their exceptional theoretical capacity, hold promise for revolutionizing energy storage. However, challenges such as volumetric expansion during cycling hinder their practical use. Ionically conductive binders have been shown to enhance the mechanical stability and cyclability of silicon-based electrodes. Herein, water-soluble binders for silicon anodes were prepared by functionalization of poly(ethylene-<i>alt</i>-maleic anhydride) (PEaMAn) with ion-conducting polyether side chains and hydrolyzation of maleic anhydride at different ratios. Six binders were synthesized and characterized, and their electrochemical performance was evaluated in half-cells. Our results indicate that polyether-functionalized binders significantly reduced the slurry viscosity and thus enhanced electrodes' processability, compared to that of the fully hydrolyzed poly(ethylene-<i>alt</i>-maleic acid) (PEaMAc) binder. However, they also led to poor adhesion to the current collector, faster impedance increase, and capacity decay during cycling as compared to PEaMAc. On the contrary, electrodes with the fully hydrolyzed PEaMAc binder showed strong adhesion to the current collector and superior electrochemical performance, with an initial Coulombic efficiency of 71.3% and delithiation capacities of 2230 mAh g^-1 at C/10 and 1190 mAh g^-1 at 1C. Moreover, PEaMAc demonstrated significantly better rate performance compared to that of the conventional LiPAA binder, highlighting its potential as a highly effective binder for silicon anodes in lithium-ion batteries.