Dimensional Gradient Structure of CoSe₂@CNTs-MXene Anode Assisted by Ether for High-Capacity, Stable Sodium Storage

Recently, abundant resources, low-cost sodium-ion batteries are deemed to the new-generation battery in the field of large-scale energy storage. Nevertheless, poor active reaction dynamics, dissolution of intermediates and electrolyte matching problems are significant challenges that need to be solved. Herein, dimensional gradient structure of sheet-tube-dots is constructed with CoSe₂@CNTs-MXene. Gradient structure is conducive to fast migration of electrons and ions with the association of ether electrolyte. For half-cell, CoSe₂@CNTs-MXene exhibits high initial coulomb efficiency (81.7%) and excellent cycling performance (400 mAh g^-1 cycling for 200 times in 2 A g^-1). Phase transformation pathway from crystalline CoSe₂-Na₂Se with Co and then amorphous CoSe₂ in the discharge/charge process is also explored by in situ X-ray diffraction. Density functional theory study discloses the CoSe₂@CNTs-MXene in ether electrolyte system which contributes to stable sodium storage performance owing to the strong adsorption force from hierarchical structure and weak interaction between electrolyte and electrode interface. For full cell, CoSe₂@CNTs-MXene//Na₃V₂ (PO₄)₃/C full battery can also afford a competitively reversible capacity of 280 mAh g^-1 over 50 cycles. Concisely, profiting from dimensional gradient structure and matched electrolyte of CoSe₂@CNTs-MXene hold great application potential for stable sodium storage.