First-principles study of high-entropy sulfides and their alkali metal-doped modification as cathode material for sodium-ion batteries.

High-entropy materials (HEMs) have been explored as high-capacity cathode materials for sodium-ion batteries (SIBs) due to their excellent structural stability and abundant metal redox sites. Among them, high-entropy sulfides (HESs) have greater potential and more extensive research than high-entropy oxides, as they exhibit higher charging voltage and theoretical capacity as cathodes. Furthermore, alkali metal doping of HESs can further enhance their performance and broaden their application fields. Inspired by the cocktail effect of HEMs, we performed the first theoretical calculation of the properties of Na(MnFeCoNi)1/2S and its Li-doped derivative, Na7/8Li1/8(MnFeCoNi)1/2S, to understand their potential as SIB cathode materials. Using density functional theory based on first principles, we investigated the structure and electronic characteristics of Na(MnFeCoNi)1/2S and Na7/8Li1/8(MnFeCoNi)1/2S, and calculated their theoretical voltage and capacity, respectively. Compared with Na(MnFeCoNi)1/2S, Na7/8Li1/8(MnFeCoNi)1/2S showed better electronic performance in reducing the band gap and increasing the density of states, ultimately providing a specific capacity of 160.3 mAh·g-1 and a charging voltage of 4.85 V in sodium-ion storage. Moreover, Na7/8Li1/8(MnFeCoNi)1/2S exhibited remarkable structural stability throughout the sodium-ion deintercalation process, thus it can be reasonably concluded that Na7/8Li1/8(MnFeCoNi)1/2S can serve as an excellent cathode material for future SIB applications.