Enhanced Sodium Polysulfide Adsorption by In Situ Construction of NiS 2 /Cu 2 S Heterointerfaces and Sulfur Vacancies Enabling High‐Performance Sodium Storage

Nickel disulfides have been actively investigated as sodium-ion battery anode materials because of their relatively high capacity and relatively low cost. However, their practical application is severely hindered by overcharge failure in ether-based electrolytes induced by the dissolution of sodium polysulfides. Herein, sulfur vacancy-rich NiS₂/Cu₂S heterojunction nanoclusters anchored on Ti₃C₂T_x MXene nanosheets (NCMX) are synthesized through a facile solvothermal method. Density functional theory calculation combined with ex situ characterizations illustrates that sulfur vacancies significantly enhance the adsorption of sodium polysulfides, while the heterointerface-induced built-in electric field facilitates rapid Na⁺ adsorption and accordingly accelerates their efficient conversion to Na₂S. The synergistic effects endow the NCMX anode with exceptional sodium-ion storage performances. It delivers remarkable reversible capacity (668 mAh g^-1 at 0.1 A g^-1), superb rate capability (482 mAh g^-1 at 5 A g^-1), and impressive cycling stability (543 mAh g^-1 after 1000 cycles at 1 A g^-1 with a negligible capacity decay of 0.0034% per cycle). Such a strategy of simultaneous construction of heterojunction and sulfur vacancies paves a new avenue to tackle the polysulfide shuttling to design advanced high-performance transition metal disulfide anodes for sodium-ion storage.