Regulating In-MOF derivatives for bidirectionally boosting redox kinetics of sulfur cathodes

Abstract

Lithium sulfur (Li–S) batteries are regarded as a promising application device due to their high theoretical capacity and energy density. However, the commercialization of Li–S batteries is restricted due to their fast capacity fading caused by the shuttle effect of lithium polysulfide (LiPSs) and slow redox reaction of sulfur cathodes. Designing highly-active bidirectional electrocatalysts is an effective strategy to address the problems caused by complex multi-step reactions. Herein, the phase of In-metal-organic framework (In-MOF) derivatives are regulated by controlling the carbonization temperature, and In–In2O3@C heterostructure composite can be obtained at 800 °C. The results show that the polar In2O3 can not only effectively adsorb LiPSs but also accelerate the conversion from Li2S8 to Li2S4, and In can promote the conversion from Li2S4 to Li2S and simultaneously lower the dissociation energy barrier of Li2S. Due to the different catalytic functions of In and In2O3 for different reaction stages of Li–S batteries, In–In2O3@C shows bidirectionally catalytic effect, and renders the corresponding batteries achieve the best electrochemical properties. The specific discharge capacity of In–In2O3@C/S can reach 1298.5 mAh g−1 at 0.2 C after three cycles of activation, and it keeps 620.9 mAh g−1 after 80 cycles with Coulombic efficiency of approximate 100 %. Regulating the products of MOF derivatives provides a reference for the regulation of catalysts for Li–S batteries.