Enhanced Performance of Silicon Anodes through Hybrid Surface Engineering

Silicon (Si) is a promising anode material for next-generation lithium-ion batteries (LIBs) due to its high theoretical capacity. However, Si-containing anodes typically suffer from unacceptably short lives because of the unrestricted growth of the solid electrolyte interphase (SEI). In this study, hybrid surface coatings are developed to stabilize the SEI in high loading pure Si anodes using atomic and molecular layer deposition. The coatings, consisting of LiF paired with lithicone, create an ionically conductive surface that enhances the capacity retention, rate performance, and longevity. Careful binder selection helps demonstrate the full utility of the coatings by enabling high loading electrodes to cycle continuously at current densities of 1200 mA/gSi. Uncoated controls, in comparison, fail within just 10 cycles at lower loadings. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy are used to provide supporting evidence of the coating composition and efficacy. The data indicate that our lithicone coating is converted to Li2CO3 upon cycling contributing to favorable LiF/Li2CO3 interfaces that enhance the space-charge effect at the active material’s surface. When applied to electrodes made with thermally stable binders and increasingly higher loadings (approaching 5 mAh/cm2), ion transport through the bulk electrode, rather than SEI growth, is shown to be the limiting factor. Furthermore, data suggests a favorable interaction between lithicone precursors and poly(acrylic acid) binders mitigates thermal decomposition at higher temperatures. The work presented here represents the successful realization of composite coatings containing LiF/Li2CO3 components to stabilize high-loading Si anodes. This work helps inform advanced surface engineering strategies to achieve highly reversible, high-capacity Si anodes capable of fast charging for high-performance LIBs.