Design towards recyclable micron-sized Na2S cathode with self-refinement mechanism.

Sodium sulfide (Na₂S) as an initial cathode material in room-temperature sodium-sulfur batteries is conducive to get rid of the dependence on Na-metal anode. However, the micron-sized Na₂S that accords with the practical requirements is obstructed due to poor kinetics and severe shuttle effect. Herein, a subtle strategy is proposed via regulating Na₂S redeposition behaviours. By the synergistic effect from both conductive structure and cuprous sulfide (Cu₂S) catalysis, the micron-sized Na₂S particles are broken down and redeposited to nano-size during the initial cycle which can be fully utilized in subsequent cycles. Consequently, the Na₂S/CPVP@Cu₂S||Na cell delivers excellent cyclability (670 mAh g_S^-1 after 500 cycles) with a remarkable average Coulombic efficiency over 99.7% and rate capability (480 mAh g_S^-1 at 4 A g_S^-1). Besides, the Na-free anodes are used to prove the application prospects. This work provides an innovative idea for utilizing micron-sized Na₂S and offers insights into its conversion pathway.