Regulating ion-solvent chemistry enables fast conversion reaction of tellurium electrode for potassium-ion storage

Tellurium (Te) has attracted wide interests as the electrode material of potassium-ion batteries (KIBs) due to its high theoretical capacity and good electronic conductivity, but still faces the issues of polytelluride dissolution in electrolyte and the loss of active Te species. Herein, we propose an ion–solvent complex tunning strategy to allow reversible and fast conversion reaction of Te electrode for K+ storage. The electrolyte of potassium hexafluorophosphate (KPF6) dissolved in dimethoxyethane (DME) enables rapid electrochemically-driven conversion of Te in electrode to in-situ construct amorphous CuxTe upon cycling, which benefits from strong oxidation tendency of K+–PF6−–2DME complex to lose electrons. Moreover, the weak solvation facilitates the formation of a thin solid/electrolyte interphase with the KF-rich inner layer on Te electrode, further enhancing K+ diffusion. In addition, the weak interaction between the potassium polytelluride and K+–PF6−–2DME complex largely inhibits the solubility of polytelluride intermediates. Consequently, the Te-based electrode exhibits a high reversible capacity of 272 mAh/g at 0.05 A/g, excellent rate capability (168 mAh/g at 2.0 A/g), and superior cycling stability. This approach could be extended to other alkali metal–chalcogen batteries (Li–S, Li–Se, Na–S, Na–Se, etc.).