Rational Design of Bimetallic Cobalt‐Copper Sulfides with Enhanced Reaction Kinetics and Suppressed Shuttle for High‐Performance Sodium‐Ion Batteries

ABSTRACT Development of advanced anodes for sodium‐ion batteries (SIBs) remains challenging due to the sluggish kinetics and severe volume expansion. Here, we report the rational design of bimetallic Co/Cu sulfides embedded in N/S‐doped carbon matrices, via chemical vapor sulfurization of MOF precursor. The optimized CuCo ₂ S ₄ electrode achieves exceptional sodium storage performance, delivering a high capacity of 573.3 mA h g ⁻¹ at 0.2 A g ⁻¹ and maintaining 504.2 mA h g ⁻¹ at 5 A g ⁻¹ after 3000 cycles with 85.6% capacity retention. Interestingly, the CuCo ₂ S ₄ and the other Cu/Co mixed sulfides obtained after Cu incorporation show greatly enhanced sodium storage capacity, cycling stability, and rate capability, as compared with the single metal sulfides (CoS _x or CuS _x ). DFT calculations reveal that CuCo ₂ S ₄ displays smaller energy barriers for Na ⁺ migration and higher polysulfide adsorption capability than those for CoS _1.035 . The synergistic interaction of bimetallic Co/Cu sulfides greatly enhances the redox reactivity with fast Na ⁺ transport kinetics, lower charge transfer resistance, and suppressed polysulfide shuttle effect during cycling, which corroboratively contributes to the superior cycling performance of CoCuS‐2. Moreover, the CoCuS‐2||Na ₃ V ₂ (PO ₄ ) ₃ full cell demonstrates good cycling performance, delivering 255.9 mA h g ⁻¹ at 1 A g ⁻¹ after 700 cycles with 80.9% capacity retention.