Synergetic Sn Incorporation‐Zn Substitution in Copper‐Based Sulfides Enabling Superior Na‐Ion Storage

Transition-metal sulfides have been regarded as perspective anode candidates for high-energy Na-ion batteries. Their application, however, is precluded severely by either low charge storage or huge volumetric change along with sluggish reaction kinetics. Herein, an effective synergetic Sn incorporation-Zn substitution strategy is proposed based on copper-based sulfides. First, Na-ion storage capability of copper sulfide is significantly improved via incorporating an alloy-based Sn element. However, this process is accompanied by sacrifice of structural stability due to the high Na-ion uptake. Subsequently, to maintain the high Na-ion storage capacity, and concurrently improve cycling and rate capabilities, a Zn substitution strategy (taking partial Sn sites) is carried out, which could significantly promote Na-ion diffusion/reaction kinetics and relieve mechanical strain-stress within the crystal framework. The synergetic Sn incorporation and Zn substitution endow copper-based sulfides with high specific capacity (≈560 mAh g