Rational design heterostructured bimetallic selenides for high capacity and durability sodium/potassium-ion storage

Abstract

• The synergistic effects effectively improve the electrochemical performance. • DFT calculation was performed to unveil the interaction between CoSe 2 and Cu 2 Se. • The reaction mechanism was investigated via in-situ / ex-situ XRD and HRTEM. Transition metal selenides are regarded as a type of promising candidate anode material for sodium/potassium ion batteries owing to their high theoretical specific capacity. However, it is still a challenge to design and construct appropriate nanostructures to address the fatal issue of vast volume variation stemmed from repeated ion intercalation/deintercalation. Herein, simple solvothermal method combined with calcination treatment was applied to synthesis CoSe 2 -Cu 2 Se nanospheres encapsulated in nitrogen-doped carbon shells (CoSe 2 -Cu 2 Se@NC) as high-performance anode material for sodium/potassium ion batteries. The as obtained CoSe 2 -Cu 2 Se@NC electrode features unique heterogeneous structure, uniform carbon coating, large specific surface area and synergistic effects, which ultimately accelerate charge/electron transfer, restrain volume expansion, and thus improve electrochemical performance. Density functional theory results disclose the heterojunctions existed in the CoSe 2 -Cu 2 Se interface contribute to the prominent rate capability for the composite. As a result, CoSe 2 -Cu 2 Se@NC nanospheres displays good rate performance and improved durability in cycling for sodium/potassium ion batteries. In additional, the depth reaction mechanism of CoSe 2 -Cu 2 Se@NC were explored by in-situ and ex-situ XRD analyses.