High‐Mobility Cu⁺‐Induced Multi‐Dimensional Structured Copper‐Based Sulfide Anode for Advanced Sodium Ion Batteries

Abstract The pursuit of advanced anode materials to address inferior conductivity and slow ion diffusion has driven the development of fast‐charging sodium‐ion batteries (SIBs). Herein, a promising anode material of KCu 7 S 4 nanowires with a tunnel structure is proposed for SIBs. The Na + (de)insertion mechanisms of the KCu 7 S 4 anode are comprehensively elucidated through a combination of in situ TEM/SAED/XRD analyses and theoretical calculations. The detailed intermediates (Na 3 Cu 4 S 4 , NaCuS) and final products (CuS, Cu) during (de)sodiation processes are identified, revealing that the highly mobile Cu + ion can facilitate the formation of tunnel‐structured Na 3 Cu 4 S 4 and layer‐structured NaCuS during the electrochemical reaction process. The reaction dynamics indicate that the formation of Na 3 Cu 4 S 4 and NaCuS intermediates facilitates electron transfer and ion diffusion during Na + (de)insertion. Moreover, the KCu 7 S 4 anode exhibits a high discharge capacity of 337 mAh g −1 at 10 A g −1 , and the corresponding Na 3 V 2 (PO 4 ) 3 //KCu 7 S 4 full cell delivers a high energy density of 303 Wh kg −1 at 375 W kg −1 , demonstrating its excellent application prospect. This work opens a new avenue for fast‐charging electrode materials for advanced SIBs.