Synergistic realization of superior potassium storage in group VB metal sulfoselenides via complex-assisted interlayer expansion and augmented charge transfer effect

Transition metal sulfoselenides inherit the 2D structure, large interlayer spacing, and high reactivity of their binary sulfide counterparts while tuning interlayer spacing and electronic structure via Se substitution for S, enhancing reaction kinetics and showing promise for potassium storage. Herein, a series of Group VB metal sulfoselenides (VSSe, NbSSe, and TaSSe) were successfully synthesized via chemical vapor transport and systematically evaluated their electrochemical properties as anodes for potassium-ion batteries. A combination of analytical techniques was employed to elucidate the underlying potassium storage mechanism, with findings confirming all three materials operate via intercalation. Both experimental findings and theoretical calculations reveal that NbSSe stands out among the three materials, showcasing exceptional electrochemical performance, the swiftest kinetics, the highest degree of metallicity, and the lowest reaction polarization. The essence of its enhanced performance lies in the unique ability of NbSSe to establish an interlayer expansion skeleton through complexes formed between the current collector Cu and electrolyte solvent molecules, which substantially widens the ion transport pathways - a feature absent in VSSe and TaSSe. Additionally, the pronounced charge transfer effect of Nb creates a synergistic interaction, and it is the combination of these two factors that propels NbSSe to ultimately attain superior electrochemical properties.