Regulating Lithium Transfer Pathway to Avoid Capacity Fading of Nano Si Through Sub-Nano Scale Interfused SiO_x /C Coating.

Abstract

Si nanoparticles (NPs) are considered as a promising high-capacity anode material owing to their ability to prevent mechanical failure from drastic volume change during (de)lithiation. However, upon cycling, a quick capacity fading is still observed for Si NPs, and the underlying mechanism remains elusive. In this contribution, it is demonstrated that the quick capacity fading is mainly caused by the generation of dead (electrochemically inert) Si with blocked electron conductivity in a densely composited Si/SEI (solid electrolyte interface) hybrid. This is due to the combined influence of electrolyte-related side reactions and the accompanied agglomeration of Si NPs. A compact, sub-nano scale interfused SiO_x /C composite coating onto the Si NPs is constructed, and a highly stabilized electrochemistry is achieved upon long cycling. The SiO_x /C coating with electron/ion dual transport paths and robust mechanical flexibility enables a fast and stable lithium ion/electron dual diffusion pathway towards the encapsulated Si. With fast reaction kinetics, stable SEI, and an antiagglomeration feature, the obtained Si@SiO_x /C composite demonstrates a stable high capacity. This work unravels new perspectives on the capacity fading of Si NPs and provides an effective encapsulating method to remedy the structure degradation and capacity fading of nano Si.