Synergistically promoting the catalytic conversion of polysulfides via in-situ construction of Ni-MnO2 heterostructure on N-doped hollow carbon spheres towards high-performance sodium-sulfur batteries

Abstract

The room-temperature sodium-sulfur (RT Na-S) battery is considered to be a highly promising electrochemical energy storage device, attributed to its high energy density, rich sulfur reserve, and nontoxicity. However, it is constrained by the polysulfide shuttling and the low intrinsic conductivity of active sulfur. A sacrificial template method has been used to develop hetero-structured Ni-MnO2 embedded in micro/mesoporous hollow carbon spheres (HCS@Ni-MnO2) to overcome these challenges. As evidenced by electrochemical properties and computational results, the construction of hetero-structured Ni-MnO2 provides a strong affinity to polysulfides. Meanwhile, the highly conductive in-situ constructing Ni-MnO2 structure has strong adsorption to soluble sodium polysulfides and effectively improves the catalytic conversion. The micro- and mesoporous hollow carbon sphere improves the reactivity of the sulfur cathodes and physically suppresses polysulfides shuttling. Befitting from the physical and chemical confinement and the fast redox reaction of polysulfides, the as-prepared S/HCS@Ni-MnO2 cathode exhibits a high capacity of 1031.7 mAh g−1 at 0.2 A g−1 after 100 cycles, surpassing the capacities of S/HCS@Ni (820.3 mAh g−1), S/HCS@MnO2 (942.4 mAh g−1) and S/HCS (866.7 mAh g−1). Moreover, the battery with S/HCS@Ni-MnO2 cathode also exhibits excellent cycle life (586.8 mAh g−1 at 5 A g−1 after 1000 cycles) and a high rate performance (553.8 mAh g−1 at 10 A g−1). This study provides an efficient strategy for synthesizing multiple compound hetero-structured materials to facilitate the development of energy storage applications.