Aqueous Binder with Self‐Emulsifying Characteristics for Practical Si/C Anode in Lithium‐Ion Batteries

Silicon/carbon (Si/C) materials have achieved commercial applications as a solution to the problems of large volume expansion and short lifespan of silicon-based anodes in lithium-ion batteries. However, the potential risk of structural fracture and localized differences in surface adsorption properties lead to difficulties in maintaining the structural integrity of Si/C anodes using conventional binders during repeated lithiation/delithiation. Herein, an aqueous binder (PVA-g-M) based on polyvinyl alcohol (PVA) grafted methacrylic acid (MAA) obtained by self-emulsifying emulsion polymerization is reported. The introduction of carboxyl groups of MAA enables PVA-g-M to form more hydrogen bonds, thereby enhancing both the cohesion of the binder film and its adhesion to silicon-based surface. Simultaneously, the methyl-containing segments of MAA can wet the carbon-based surface, thereby enhancing the adhesion of PVA-g-M to carbonaceous materials. In addition, the hydroxyl groups on both the PVA segments and the silicon surface can be esterified with the carboxyl groups during the heat treatment, thus further improving the bonding strength. As-prepared Si/C anodes with PVA-g-M binder can significantly inhibit the electrode volume expansion and maintain high structural integrity during cycling as well as form SEIs with high lithium fluoride content, showing excellent cycling stability (81.1 % capacity retention after 300 cycles).