Electron-repulsion effect of anti-solvent strategy for long-cycle nickel sulfide-containing potassium-ion batteries

Abstract

Transition metal dichalcogenides experience severe structural degradation when used as anodes in potassium-ion batteries, resulting in undesirable electrochemical behaviors. To tackle this challenge, a novel approach involving "anti-solvent-enhanced local high-concentration electrolytes" was proposed to enhance the electrochemical stability of transition metal dichalcogenides for potassium-ion storage. This improvement is attributed to the facilitation of the aggregation of local solvation structures within the ether-based electrolyte. We demonstrate the effectiveness of this method by utilizing nickel sulfide composite materials. By diluting the ether-based high-concentration electrolyte with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) anti-solvent, the nickel sulfide containing anode achieved an ultra-high specific capacity of 382 mAh g−1 after 1500 cycles at 1 A g−1. We found that the HFE anti-solvent, with its high concentration of negatively charged fluorine atoms, exerts a strong electron-repulsion effect on the bis(fluorosulfonyl)imide anions, promoting the aggregation of local solvation structures. It not only lowers the desolvation energy but also exhibits high stability during interactions with the interface, thereby improving and keeping the K-ion’s migration ability. This, in turn, improves the cycling stability of the electrode during the potassiation-depotassiation process. We believe that this new strategy of improving potassium-ion storage performance will drive advancements in related fields.