Design and synthesis of Janus-structured mutually doped SnO₂-Co₃O₄ hollow nanostructures as superior anode materials for lithium-ion batteries

Janus-structured materials composed of mutually doped SnO₂-Co₃O₄ hollow nanostructures were designed and synthesized for use as an efficient anode material for lithium-ion batteries. The Janus-structured powder consisting of Co-doped SnSe nanoplates and Sn-doped CoSe_x polyhedral structures was synthesized by a one-pot spray pyrolysis process. Similarly, the structured SnO₂-Co₃O₄ powder consisting of Co-doped SnO₂ hollow nanoplates and Sn-doped Co₃O₄ hollow polyhedral structures was prepared by a nanoscale Kirkendall diffusion process. The doping of both materials in the hollow SnO₂ nanoplates and Co₃O₄ polyhedral structures improved the reversible capacities and cycling performances of the Janus-structured SnO₂-Co₃O₄ composite powder. This was achieved by minimizing the growth of metallic Sn and Co nanocrystals during cycling, improving the decomposition of Li₂O, and facilitating the conversion of Sn to SnO₂ during the delithiation process through a catalytic effect of metallic Co. The discharge capacity of the Janus-structured SnO₂-Co₃O₄ hollow powder with a Sn:Co ratio of 1:2 at a current density of 1 A g^-1 for the 1000^th cycle was 1058.7 mA h g^-1. This Janus-structured mutually doped SnO₂-Co₃O₄ composite powder showed extraordinary cycling and rate performances for lithium ion storage.