Non-Negligible Role of Multifunctional MXene Hosts for Li–S Batteries: Anchoring and Electrocatalysis
Chunlei Wei, Timing Fang, Xiao Tang, Pan Wang, Xiaomin Liu
Abstract
Lithium–sulfur (Li–S) batteries have attracted great enthusiasm in recent years. Nevertheless, the serious shuttle effect of lithium polysulfides (Li2Sn), poor conductivity of S and intermediate products, and relatively slow dynamics make its commercial application face severe challenges. Here, functionalized M2CT2 MXenes (M = Ti, Nb, Cr; T = bare, O, F, OH) were used as the sulfur host to build multifunctional cathodes, in which the inhibition of the shuttle effect by the anchoring effect and accelerating discharging/charging kinetics by electrocatalysis were studied via first-principles. The strong anchoring strength of M2CO2/M2CF2 to Li2Sn could effectively suppress the shuttle behavior. The anchoring ability of MXenes is a double-edged sword, and moderate anchoring strength should be considered. Compared comprehensively, Nb2CO2 has a better electrocatalysis performance for the sulfur reduction reaction during discharging. It also accelerates the decomposition of Li2S and migration of Li+ on the cathode which increases charging kinetics. The improvement in kinetics is related to the enhancement of electronic conductivities of Nb2CO2–Li2Sn composites. In short, Nb2CO2-based multifunctional sulfur cathodes effectively suppress the shuttle effect and improve reaction kinetics. This work expands the application of the MXene family, especially providing guidelines for the utilization of Nb-based MXene in energy storage.