Fabrication of CoSe2/FeSe2 heterostructures with a stable solid-electrode interphase film and low surface activation energy for Na-ion batteries†

Abstract

The abundant availability and potential cost benefits of sodium-ion batteries (SIBs) have generated increasing interest as viable alternatives to lithium-ion batteries (LIBs). However, the development of SIBs is considerably hindered by their inferior cycling stability and limited rate capability, which stem from the larger ionic size of Na⁺ compared to Li⁺. Despite their potential, the adoption of SIBs is significantly limited by their low rate capability and cycling stability. This issue primarily arises from the larger ionic size of Na⁺, which can diminish the structural stability of electrode materials and lead to sluggish reaction kinetics. Herein, a novel cubic yolk–shell CoSe₂/FeSe₂@N-doped carbon heterostructure (YS-CoSe₂/FeSe₂@NC) was successfully developed by combining polydopamine (PDA) coating with a simple selenation method. Based on the advantages of the structure, the YS-CoSe₂/FeSe₂@NC electrode exhibits exceptional cycling stability, maintaining a capacity of 366.6 mA h g⁻¹ at 5 A g⁻¹ after 5000 cycles in a half-cell, while also demonstrating a notable reversible capacity of 363.6 mA h g⁻¹ at 1 A g⁻¹ after 500 cycles in a full-cell. Ex situ XRD, HRTEM, SAED and XPS analyses suggest that the enhanced sodium storage properties of YS-CoSe₂/FeSe₂@NC can be ascribed to improved electrode kinetics and the stability of the solid-electrode interphase film, which result from the YS structure and the presence of the CoSe₂/FeSe₂ heterojunction and NC layer.