“Electronic Sponge” Strategy Enables Polyether Electrolytes for High-Voltage and Fast-Charging Quasi-Solid-State Batteries

Abstract Polyether electrolytes are promising for lithium (Li) metal batteries yet suffer from insufficient Li+ conductivity, low oxidative thresholds, and unstable electrolyte–electrode interphases under high-voltage and fast-charging conditions. Herein, inspired by a natural sponge’s water absorption and release, we develop a unique “electronic sponge” (ES) strategy for bidirectional electron-transfer regulation. The ES withdraws electron density from ether oxygens to weaken Li+–oxygen coordination and stabilize lone-pair electrons while donating electrons to Li-salt anions to promote anion-derived decomposition toward robust LiF-rich solid electrolyte interphase (SEI)/cathode electrolyte interphase (CEI). This straightforward strategy synergistically improves Li+ transport, oxidative stability, and interphase stability. The resulting electrolyte achieves an ionic conductivity of 1.61 mS cm–1 at 25 °C, a Li+ transference number of 0.84, and an extended electrochemical stability window of 5.2 V. Li∥Li symmetric cells cycle stably for over 1000 h at 0.5 mA cm–2. Notably, Li∥LiNi0.8Co0.1Mn0.1O2 cells retain 82.5% capacity after 300 cycles at 4.6 V and sustain 500 cycles with ∼100% Coulombic efficiency and 82.6% capacity retention at 4.5 V and 5C. This work pioneers a universal electron regulation paradigm for designing advanced polyether electrolytes and stable interphases toward high-voltage, fast-charging quasi-solid-state batteries.