Heterogeneous Mediator Enabling Three-Dimensional Growth of Lithium Sulfide for High-Performance Lithium–Sulfur Batteries

[摘要] Two-dimensional (2D) deposition regime of insulating lithium sulfide (Li 2 S) is a major obstacle to achieve high reversible capacity in the conventional glyme-based lithium–sulfur (Li–S) batteries as it leads to rapid loss of active electrode surface and low sulfur utilization. Achieving three-dimensional (3D) growth of Li 2 S is therefore considered to be necessary, but the available strategies are mainly based on the electrolyte manipulations, which inevitably lead to added complexity of the electrode–electrolyte compatibility and, in particular, instability of the lithium anode. In this work, we have developed a heterogeneous polysulfide mediator composed of discrete Mo 5 N 6 anchored on graphene, which functions on the cathode side, to regulate the deposition mode of Li 2 S. Mo 5 N 6 can efficiently boost the formation of Li 2 S as demonstrated by a series of experimental and computational results. More importantly, the discrete distribution of Mo 5 N 6 nucleants on graphene postpones the merging of adjacent Li 2 S nuclei to promote their isotropic growth. Thus, 3D deposits of Li 2 S is guided by the heterogeneous mediator. Benefiting from these unique superiorities, Li–S cells with high rate capability of 954 mAh g −1 at 2 C and long cycle life exceeding 1000 cycles are realized without advanced lithium anode protection.

[关键词] electrocatalysis;lithium sulfide nucleation;lithium–sulfur batteries;polysulfide redox reaction;shuttle effect