Ether-Based Gel Polymer Electrolyte for High-Voltage Potassium Ion Batteries

Low-concentration ether electrolytes cannot efficiently achieve oxidation resistance and excellent interface behavior, resulting in severe electrolyte decomposition at a high voltage and ineffective electrode–electrolyte interphase. Herein, we utilize sandwich structure-like gel polymer electrolyte (GPE) to enhance the high voltage stability of potassium-ion batteries (PIBs). The GPE contact layer facilitates stable electrode–electrolyte interphase formation, and the GPE transport layer maintains good ionic transport, which enabled GPE to exhibit a wide electrochemical window and excellent electrochemical performance. In addition, Al corrosion under a high voltage is suppressed through the restriction of solvent molecules. Consequently, when using the designed GPE (based on 1 m), the K||graphite cell exhibits excellent cycling stability of 450 cycles with a capacity retention of 91%, and the K||FeFe-Prussian blue cell (2–4.2 V) delivers a high average Coulombic efficiency of 99.9% over 2200 cycles at 100 mA g^–1. This study provides a promising path in the application of ether-based electrolytes in high-voltage and long-lasting PIBs.