A Synergistic Triphase Electrolyte Design Enables 4.6 V LiCoO ₂ Quasi‐Solid‐State Batteries with Ultra‐Long Cycling

Abstract

ABSTRACT Pushing LiCoO 2 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, LiCoO 2 ‐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||LiCoO 2 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.