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

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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 (retaining 182.1 mA h g -1 after 200 cycles at 0.5 A g -1 and exhibiting a rate capability of 127 mA h g -1 at 1 A g -1 ), 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. NbSSe hosts Cu x (DME) n complexes from the Cu current collector and electrolyte solvent molecules, forming a stable framework that widens the ion transport channels and enhances the reaction kinetics, thereby yielding superior electrochemical performance over VSSe and TaSSe. Supported by DFT calculations, NbSSe's pronounced charge transfer effect is shown to promote the concurrent diffusion of electrons and ions. • S/Se coexistence regulates interlayer spacing and electronic structure in MSSe. • NbSSe exhibits superior electrochemical performance compared to VSSe and TaSSe. • The K + diffusion rate in NbSSe is faster than that in VSSe and TaSSe. • NbSSe promotes electron/ion diffusion kinetics via its strong charge transfer effect. • Cu x (DME) n complexes reversibly intercalate into NbSSe to form a supporting framework.