Oxygen-modulated metal nitride clusters with moderate binding ability to insoluble Li2Sx for reversible polysulfide electrocatalysis

Multiphase sulfur redox reactions with advanced homogeneous and heterogeneous electrochemical processes in lithium-sulfur (Li-S) batteries possess sluggish kinetics. The slow kinetics leads to significant capacity decay during charge/discharge processes. Therefore, electrocatalysts with adequate sulfur-redox properties are required to accelerate reversible polysulfide conversion in cathodes. In this study, we have fabricated an oxygen-modulated metal nitride cluster (C-MoNx-O) that has a moderate binding ability to the insoluble Li2Sx for reversible polysulfide electrocatalysis. A Li-S battery equipped with C-MoNx-O electrocatalyst displayed a high discharge capacity of 875 mAh g(-1) at 0.5 C. The capacity decay rate of each cycle was only 0.10% after 280 cycles, which is much lower than the control groups (C-MoOx: 0.16%; C-MoNx: 0.21%). Kinetic studies and theoretical calculations suggest that C-MoNx-O electrocatalyst presents a moderate binding ability to the insoluble Li2S2 and Li2S when compared to the C-MoOx and C-MoNx surfaces. Thus, the C-MoNx-O can effectively immobilize and reversibly catalyze the solid-solid conversion of Li2S2-Li2S during charge-discharge cycling, thus promoting reaction kinetics and eliminating the shuttle effect. This study to design oxygen-doped metal nitrides provides innovative structures and reversible solid-solid conversions to overcome the sluggish redox chemistry of polysulfides.