First-principles explorations of Li2S@V2CTx hybrid structure as cathode material for lithium-sulfur battery

Li2S-based cathodes have emerged as alternative cathode materials for lithium-sulfur batteries, which could overcome many of technical challenges. Here, we fully investigate loading content of Li2S on the V2CTx hybrid structure as a cathode, the open circuit voltage profile during the charge/discharge process, and the Li+ transfer energy barrier on the V2CTx surface using first-principles method. Our results indicate that V2CO2 would be one of the most suitable candidates for lithium-sulfur battery cathode. In Li2S@V2CO2 case, the lithium-oxygen bonding prevents sulfur from retaining its stable cyclical structure before lithiation yielding a distribution of sulfur chains tightly bonded to MXenes surface. Analysis of electron localization function indicates that the Li2S@V2CO2 composite include not only the covalent bonds of S-O, but also the ionic bonds of Li-O, which make the strong binding for this configuration. Also, nudged elastic band calculations indicate that the migration of Li ion on the both V2CO2 and V2C is very fast with energy barrier of 0.24 eV for V2CO2, 0.34 eV for V2C, which also can insure a good charge/discharge rate performance of the lithium-sulfur batteries. Finally, it might pave a way for the search of high-performance materials of energy storage devices.