Insights into the interfacial instability between carbon-coated SiO anode and electrolyte in lithium-ion batteries

Carbon-coated SiO is the most promising alternative to the graphite anode for improving the energy density of currently commercialized lithium-ion batteries but exhibits poor cyclic stability that leaves an unclear mechanism. To address this issue, the surface properties of commercial carbon-coated silicon monoxide are investigated in a 1.0 M LiPF₆–dimethyl carbonate electrolyte with and without ethylene carbonate (EC), with a comparison of graphite. Unlike graphite that can work well in the electrolytes with and without EC during initial 30 cycles, carbon-coated SiO suffers a serious capacity decay, especially in the electrolyte without EC. By identifying the samples after various cycles, it is found that a relatively stable interphase that makes graphite work well cannot be built on carbon-coated SiO. The chemical analyses demonstrate that there is a strong interaction between SiO with hydrofluoric acid in the electrolyte, which leads to destruction of the carbon-coating layer and prevents the formation of a protective interphase.