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

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