Solvent molecular design enables high graphite compatibility and good oxidation stability in low-concentration K-ion battery electrolytes

Abstract

Traditional low-concentration ether-based electrolytes have attracted considerable attention due to their low cost, high ionic conductivity, and low viscosity. However, they face critical challenges, including poor oxidative stability at the cathode side and severe [K⁺-solvent] co-intercalation into the graphite anode at the anode side for potassium-ion batteries (PIBs). To address these issues, we present a novel approach using a weakly coordinating solvent—1,2-dimethoxypropane (DMP). Unlike the linear ether molecule 1,2-dimethoxyethane (DME), DMP features an additional methyl group that induces strong steric hindrance. This structural modification reduces the interaction between K⁺ ions and the solvent, forming an anion-rich solvation structure (ARSS) in the low-concentration electrolyte. The ARSS triggers the formation of an inorganic-rich solid electrolyte interphase (SEI) and enables high compatibility with the graphite anode. This results in a high initial Coulombic efficiency (CE) of 80.9% and remarkable capacity retention of 92.4% after 10 months of deep cycling. Furthermore, the ARSS substantially enhances the electrolyte oxidative stability, allowing the K₂Mn[Fe(CN)₆]₂ (KMHCF) cathode to deliver reliable cycling performance over 500 cycles at a high cut-off voltage of 4.3 V. These findings provide valuable insights into the design of low-concentration electrolytes, paving the way for the development of high-voltage and long-life PIBs.