Fabrication of CoSe2/FeSe2 heterostructures with stable solid electrolyte interface 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 mAh g-1 at 5 A g-1 after 5000 cycles in half-cell, while also demonstrating a notable reversible capacity of 363.6 mAh g-1 at 1 A g-1 after 500 cycles in full-cell. The 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 electrolyte interface film, which result from the YS structure and the presence of the CoSe2/FeSe2 heterojunction and NC layer.