A Synergistic Triphase Electrolyte Design Enables 4.6 V LiCoO₂ Quasi-Solid-State Batteries with Ultra-Long Cycling

Pushing LiCoO₂ to ≥4.5 V causes coupled degradation: electrolyte oxidation and cathode structural collapse, especially at high rates. Here, we propose a triphase synergistic gel-electrolyte to tackle both failure modes. The system, constructed by in situ thermal polymerization, integrates an ether-rich crosslinked polymer network, surface-activated AlN fillers with Lewis acid-base sites, and a fluorinated electrolyte. This design regulates Li⁺ transport, confines free solvent molecules, and reconstructs the solvation sheath. More importantly, it induces a uniform, inorganic-rich cathode-electrolyte interphase at an early stage. Consequently, LiCoO₂-based quasi-solid-state cells deliver exceptional stability: over 1000 cycles at 4.6 V and 5 C with an average decay of only ∼0.03% per cycle, and 85.98% capacity retention after 500 cycles in practical Si-C||LiCoO₂ pouch cells. Operando EIS-DRT analysis reveals that the triphase electrolyte substantially suppresses the growth and fluctuation of interphase-related polarization at high voltage, making the remaining impedance evolution more governed by transport/contact processes. This work demonstrates that decoupling interfacial and structural degradation through a synergistic electrolyte design is key to realizing high-voltage, high-power, long-life quasi-solid-state batteries.