A facile in situ synthesis of nanocrystal-FeSi-embedded Si/SiOx anode for long-cycle-life lithium ion batteries

A cost-effective, environmentally friendly and industrialized method of using low-grade sources to prepare high-performance anode material for lithium ion batteries (LIBs) with high energy density and long cycle life is both appealing and challenging. Herein, we present a low-cost, scalable and controllable approach for preparing unique sub-micrometer core-shell structure nanocrystal-FeSi-embedded Si/SiOx (FSO) anode material directly from a low-grade Fe-Si alloy. The sub-micrometer FSO anode materials are controlled by in-situ reaction of the Fe-Si-O in the Fe-Si alloy according to the phase diagram. The XRD and Rietveld refinement results indicate that when the treatment temperature increase, (i) FeSi phase appears together with Si and FeSi2, and then (ii) Fe3Si phase appears together with Si and FeSi. Most importantly, benefited from the formation of the amorphous SiOx as buffer layer and self-conductive nanocrystal-FeSi as a robust skeleton to mechanically support the large volume change of Si during cycling, the sub-micrometer core-shell structure FSO anode exhibits a high capacity (931.3 mA h g−1) at 50 mA g−1 and a prolonged cycle performance with 86% capacity retention over 1000 cycles at 1 A g−1. The full cell with prelithiated FSO as the anode and commercial LiCoO2 as the cathode delivers a high energy density of 467.5 W h kg−1 at the 0.05 C. This work provides a promising route for commercial production of high-performance Si/SiOx-based anode materials in LIBs.