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 gS−1 after 500 cycles) with a remarkable average Coulombic efficiency over 99.7% and rate capability (480 mAh gS−1 at 4 A gS−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. Authors report that micron-sized Na2S particles can be self-refinement into nanoparticles during the initial cycle under rapid solid-liquid-solid conversion, which facilitates the development of Na-free anode systems in room-temperature sodium-sulfur batteries.