Colloidal CuInS 2 @CNT Electrode Enabling High‐Rate Sodium Storage and Durable Aqueous Copper‐Ion Batteries

ABSTRACT Transition metal sulfides are promising electrode materials for next‐generation rechargeable batteries owing to their high theoretical capacities and multiple redox‐active sites. However, their electrochemical performance is often limited by sluggish ion diffusion and severe structural degradation during cycling. Herein, we report a colloidal‐synthesized CuInS 2 @CNT as a structurally resilient and kinetically favorable electrode for both sodium‐ion and aqueous copper‐ion batteries. When used as anode materials for SIBs, CuInS 2 @CNT delivered a high reversible capacity of 339.1 mAhg −1 at a current density of 10.0 Ag −1 after 1000 cycle. Comprehensive electrochemical tests, including cyclic voltammetry, the galvanostatic intermittent titration technique, and in‐situ electrochemical impedance spectroscopy combined with the distribution of relaxation times, revealed fast kinetics during sodiation and desodiation. Moreover, when evaluated as cathode materials for aqueous copper‐ion batteries, CuInS 2 @CNT maintained 243.1 mAhg −1 at 5.0 Ag −1 after 2000 cycles. This dual‐system investigation provides design principles for ternary metal sulfide/carbon composites capable of maintaining reversible redox kinetics across different ion‐storage environments.