Insight into the potential of M-NbS (M = Pd, Ti and V) monolayers as anode materials for alkali ion (Li/Na/K) batteries.

Doping engineering significantly improves the electrochemical characteristics of electrode materials in alkali ion batteries. Herein, first-principles calculations were performed to systematically explore the effects of metal atom doping in NbS monolayers by substituting the Nb atoms with metal M atoms (M = Pd, Ti and V) on the structural stability and electrochemical performances. The results demonstrate that M-NbS monolayers can exhibit superior characteristics, including outstanding mechanical flexibility, excellent electronic conductivity, fast charge-discharge rate, low open circuit voltage and high theoretical capacity for alkali ion (Li, Na, and K) storage. Additionally, when alkali ions approach the doping sites of M-NbS monolayers, the diffusion energy barriers for Li ions and Na ions can decrease significantly. More importantly, NbS monolayers with metal doping can obtain the maximum theoretical capacity of 1470.87 mA h g and the lowest open circuit voltage of 0.17 V. The results of our research can provide a valuable theoretical foundation for the advancement of doped-engineering transition metal chalcogenide monolayers as anode materials in alkali ion battery applications.