Reaction-Ball-Milling-Driven Surface Coating Strategy to Suppress Pulverization of Microparticle Si Anodes

In this work, we report a novel reaction-ball-milling surface coating strategy to suppress the pulverization of microparticle Si anodes upon lithiation/delithiation. By energetically milling the partially prelithiated microparticle Si in a CO2 atmosphere, a multicomponent amorphous layer composed of SiOx, C, SiC, and Li2SiO3 is successfully coated on the surface of Si microparticles. The coating level strongly depends on the milling reaction duration, and the 12 h milled prelithiated Si microparticles (BM12h) under a pressure of 3 bar of CO2 exhibit a good conformal coating with 1.006 g cm–3 of tap density. The presence of SiC remarkably enhances the mechanical properties of the SiOx/C coating matrix with an approximately 4-fold increase in the elastic modulus and the hardness values, which effectively alleviates the global volume expansion of the Si microparticles upon lithiation. Simultaneously, the existence of Li2SiO3 insures the Li-ion conductivity of the coating layer. Moreover, the SEI film formed on the electrode surface maintains relatively stable upon cycling due to the remarkably suppressed crack and pulverization of particles. These processes work together to allow the BM12h sample to offer much better cycling stability, as its reversible capacity remains at 1439 mAh g–1 at 100 mA g–1 after 100 cycles, which is nearly 4 times that of the pristine Si microparticles (381 mAh g–1). This work opens up new opportunities for the practical applications of micrometer-scale Si anodes.