Rational Design of Bimetallic Cobalt-Copper Sulfides with Enhanced Reaction Kinetics and Suppressed Shuttle for...

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 CuCo₂S₄ 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 CuCo₂S₄ 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 CuCo₂S₄ 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||Na₃V₂(PO₄)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.