Boosting Polysulfide Redox Kinetics by Graphene- Supported Ni Nanoparticles with Carbon Coating

摘要

Lithium-sulfur batteries have attracted extensive attention because of their high energy density. However, their application is still impeded by the inherent sluggish kinetics and solubility of intermediate products (i.e., polysulfides) of the sulfur cathode. Herein, graphene-supported Ni nanoparticles with a carbon coating are fabricated by directly carbonizing a metal-organic framework/graphene oxide composite, which is then dispersed on a commercial glass fiber membrane to form a separator with electrocatalytic activity. In situ analysis and electrochemical investigation demonstrate that this modified separator can effectively suppress the shuttle effect and regulate the catalytic conversion of intercepted polysulfides, which is also confirmed by density functional theory calculations. It is found that Ni-C sites can chemically interact with polysulfides and stabilize the radical S-3(center dot-) through Ni-S bonds to enable fast dynamic equilibrium with S-6(2-), while Ni nanoparticles reduce the oxidation barrier of Li2S and accelerate ion/electron transport. As a result, the corresponding lithium-sulfur battery shows a high cycle stability (88% capacity retention over 100 cycles) even with a high sulfur mass loading of 8 mg cm(-2) and lean electrolyte (6.25 mu L mg(-1)). Surprisingly, benefitting from the improved kinetics, the battery can work well at -50 degrees C, which is rarely achieved by conventional Li-S batteries.