Colloidal CuInS₂@CNT Electrode Enabling High-Rate Sodium Storage and Durable Aqueous Copper-Ion Batteries

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 CuInS₂@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, CuInS₂@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, CuInS₂@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.