Discrete card-shaped bimetallic selenides as anode materials for sodium ion batteries with excellent long cycle stability

Abstract

With hollow cubic CoSn(OH)6 as the precursor and flake ZIFs as the skeleton, a bimetallic selenide SCS consisting of CoSe2 and SnSe was prepared by selenidation, which showed excellent sodium storage performance. The high capacity and excellent cycle stability of SCS are closely related to its structure. The SCS prepared in this work is composed of isolated nanosheets, on which cubic nanoparticles are evenly distributed. The nanosheets composed of CoSe2 and MOF-derived carbon is assembled into a grid structure that acts as a support and separator, ensuring the electrical contact of active materials during the cycle, and reducing the agglomeration of active sodium storage nanoparticles. Cubic nanoparticles also inhibit the collapse and disordered accumulation of nanosheets during the middle temperature selenidation process. The isolated card-shaped structure helps to maintain the stability of electrode structure, and the composition of bimetallic selenides provides high sodium storage capacity. At high current density of 5 ​A ​g−1, the discharge capacity of SCS can maintain 335 mAh·g−1 after 500 cycles.