High-conductivity and elasticity interface consisting of Li-Mg alloy and Li3N on silicon for robust Li-ion storage

Abstract

Silicon (Si) materials are one of the industry's preferred choices for lithium-ion batteries (LIBs) anode in the near and mid-term due to their high theoretical capacity, abundance in earth and safety. However, the weak and low conductivity of the solid electrolyte interface (SEI) leads to poor cycling stability, limited Coulombic efficiency, and poor rate performance, consequently hampering practical applications. Herein, the MgSiN2 functional coating is prepared by in-situ evolution of Mg2Si on porous micro-Si (pMSi@MgSiN2) via a scalable one-step low-temperature nitriding strategy. Interestingly, MgSiN2 is converted into the robust multi-functional interface composed of highly conductive Li3N and elastic Li-Mg alloy during subsequent lithium intercalation, which is studied by in-situ/ex-situ methods. The multi-functional interface takes over the role of improving interfacial stability and ionic/electronic conductivity. As expected, the pMSi@MgSiN2 anode shows a high gravimetric capacity of 1981.5 mAh g−1 at 1.0 A g−1 after 150 cycles, together with a high initial Coulombic efficiency of over 88.4 %. Furthermore, a consider capacity of 894 mAh g−1 can be retained after 500 cycles at 5.0 A g−1. The results and strategy reveal a new route for the integrated design of Si interface or other alloy-type anode materials to the fast lithium storage performance.