A General Atomic Surface Modification Strategy for Improving Anchoring and Electrocatalysis Behavior of Ti₃C₂T₂ MXene in Lithium-Sulfur Batteries.

Abstract

Multiple negative factors, including the poor electronic conductivity of sulfur, dissolution and shuttling of lithium polysulfides (Li₂S_<i>n</i>), and sluggish decomposition of solid Li₂S, seriously hinder practical applications of lithium-sulfur (Li-S) batteries. To solve these problems, a general strategy was proposed for enhancing the electrochemical performance of Li-S batteries using surface-functionalized Ti₃C₂ MXenes. Functionalized Ti₃C₂T₂ (T = N, O, F, S, and Cl) showed metallic conductivity, as bare Ti₃C₂. Among all Ti₃C₂T₂ investigated, Ti₃C₂S₂, Ti₃C₂O₂, and Ti₃C₂N₂ offered moderate adsorption strength, which effectively suppressed Li₂S_<i>n</i> dissolution and shuttling. This Ti₃C₂T₂ exhibited effective electrocatalytic ability for Li₂S decomposition. The Li₂S decomposition barrier was significantly decreased from 3.390 eV to ∼0.4 eV using Ti₃C₂S₂ and Ti₃C₂O₂, with fast Li⁺ diffusivity. Based on these results, O- and S-terminated Ti₃C₂ were suggested as promising host materials for S cathodes. In addition, appropriate functional group vacancies could further promote anchoring and catalytic abilities of Ti₃C₂T₂ to boost the electrochemical performance of Li-S batteries. Moreover, the advantages of a Ti₃C₂T₂ host material could be well retained even at high S loading, suggesting the potential of surface-modified MXene for confining sulfur in Li-S battery cathodes.