Dual weakly solvated electrolytes with enhanced interfacial stability for ultrastable alloying-type Bi anodes in potassium-ion batteries.

Weakly solvated electrolytes (WSE) have been proposed for potassium-ion batteries (PIBs) to address the interfacial stability issue of K-storage via weakening the cation-solvent interaction to achieve anion-rich solvation sheath for constructing anion-derived stable solid electrolyte interface (SEI) film. However, the insufficient salt dissociation capacity of the employed solvents with low solvation ability significantly limited the wide manipulation of solvation structures for realizing satisfactory K-storage performance. Herein, a dual weakly solvated electrolytes (DWSE) was developed for alloy-type Bi-based K-storage anode. The dual weakly solvated structures with abundant contact ion pair (CIP) and aggregate (AGG) were manipulated via employing a cyclic ether of tetrahydrofuran (THF) with monovalent coordination with K as the bulk solvent, and increased salt concentrations simultaneously. The prepared carbon confined Bi anode (Bi@C) in the optimized DWSE delivered a distinct three-step alloying mechanism with high reversible capacity (468 mAh/g at 50 mA/g), cycling stability (381 mAh/g after 100 cycles at 50 mA/g) and rate properties (336 mAh/g even at 400 mA/g). The fast ion transfer kinetics and anion-derived KF-rich SEI were revealed to be responsible for the excellent K-storage performance of Bi@C anode. These results provide a new thought for the electrolyte development of advanced energy storage devices.