In Situ Polymerized Composite Polymer Electrolyte and Atomic Layer Deposition Enable Dual-Interface Engineering for High-Voltage Solid-State Lithium Batteries

Abstract Although high-nickel ternary cathode (NCM811) delivers a high specific capacity, it suffers from interfacial adverse reactions, transition metal dissolution, and structural deterioration during cycling. To stabilize the cathode surface, a uniform Li3PO4 coating layer (∼2.5 nm) is deposited on NCM811 via powder atomic layer deposition. This coating effectively suppresses high-voltage phase transitions and mitigates electrolyte oxidation. Furthermore, a poly(ethylene glycol) dimethyl ether (PEGDME)-based composite polymer electrolyte is fabricated via in situ polymerization. In this system, the poly(methyl methacrylate) network serves as a mechanical backbone, while low-molecular-weight PEGDME provides ionic conduction channels. The incorporation of 7.5 wt % Li6.4La3Zr1.4Ta0.6O12 (LLZTO) enhances the ionic conductivity to 3.47 × 10–4 S cm–1 and the Li+ transference number to 0.665 at 60 °C, primarily attributed to the additional Li+ pathways constructed by the LLZTO filler within the polymer matrix. By integrating the Li3PO4-coated cathode with the optimized electrolyte, the solid-state battery delivers a discharge capacity of 152.0 mAh g–1 at 0.5C (4.3 V, 60 °C) and retains 77.88% of its capacity after 170 cycles. This "dual-interface" modification strategy effectively improves the compatibility between high-voltage cathodes and polymer electrolytes, offering new insights for the development of practical solid-state batteries.