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

ABSTRACT 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 + ·NO 3 − ) additives. The introduced polycationic chains effectively disrupt PEO crystallinity, promote segmental motion and enhance the solubility of NO 3 − . Importantly, NO 3 − 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 0.8 Co 0.1 Mn 0.1 O 2 cell achieves stable cycling over 500 cycles at 0.2 C with a high capacity retention (82.7%), while the LiFePO 4 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.