Highly reversible conversion reaction in Sn2Fe@SiOx nanocomposite: A high initial Coulombic efficiency and long lifetime anode for lithium storage

Abstract SiOx based Li-ion anode materials have attracted great attention in both research and industrial areas. To achieve high Coulombic efficiencies in SiOx-based anodes, a new class of Sn2Fe@SiOx composites have been fabricated by ball milling, to greatly enhance the reversibility of conversion reactions in lithiated SiOx. In this multiple-phase composite, the in-situ formed nanosized Sn2Fe are firmly attached on the SiOx surfaces to build up insulated/metallic interfaces, which can promote the Li extracting from Li-Si-O glass and regenerating of SiOx during de-lithiation. The Sn2Fe@SiOx composites contribute high ICE values up to 78%, among the highest values reported so far for SiOx-based powder anodes. In addition, the Sn2Fe@SiOx composites demonstrate large stable capacities of 700 mAh/g at 200 mA/g with Coulombic efficiencies beyond 99%, and superlong lifetime of more than 1000 cycles at high rate of 1000 mA/g. All these data indicate the promising potential of Sn2Fe@SiOx as an interface material for high-performance anodes. Furthermore, both the material design strategy and fabrication method are simple, cost effective, and scalable, we hope this work can be beneficial in paving the way towards the solution of the reversibility issue of other conversion-type anode materials for high energy Li-ion batteries.