Multiscale Engineering of PEO Electrolytes for High‐Voltage and Ultrastable Solid‐State Lithium Batteries With Exceptional Room‐Temperature Performance

Poly(ethylene oxide) (PEO) electrolytes show significant promise for flexible solid-state batteries, yet face insufficient ion transport kinetics and interfacial stability. Herein, we propose a multiscale engineering that synergistically modulates both macro-mesoscopic polymer architectures and microscopic solvation configurations by incorporating poly(ethylene oxide)-poly(2-dimethylaminoethyl methacrylate) nitrate (PEG-PDMAEMAH⁺·NO₃ ^-) additives. The introduced polycationic chains effectively disrupt PEO crystallinity, promote segmental motion and enhance the solubility of NO₃ ^-. Importantly, NO₃ ^- with high donor number can competitively coordinate with Li⁺, weakening the ethylene oxide-Li⁺ chelation and thereby boosting bulk Li⁺ mobility. The resulting anion-rich solvation structure lowers the desolvation energy barrier and fosters the formation of robust, highly conductive inorganic-rich solid electrolyte interlayers at both the cathode and anode, which enhances the interfacial kinetics and high-voltage tolerance. Consequently, the engineered PEO electrolyte enables lithium metal batteries to operate stably at near-room temperature (30°C) without liquid plasticizers. Correspondingly, the 4.3 V LiNi_0.8Co_0.1Mn_0.1O₂ cell achieves stable cycling over 500 cycles at 0.2 C with a high capacity retention (82.7%), while the LiFePO₄ cell maintains stable operation for 1200 cycles at 0.5 C (30°C). The proposed strategy creates an avenue to accelerate the eventual commercialization of the polymer electrolytes for solid-state lithium batteries.