Enabling All‐Solid‐State Li Metal Batteries Operated at 30 °C by Molecular Regulation of Polymer Electrolyte

Abstract The low ionic conductivity of poly(ethylene oxide) (PEO)‐based polymer electrolytes at room temperature and the undesired lithium‐dendrite growth at Li|PEO interface impede their further application. Herein, a PEO polymer is regulated at the molecular level through a copper ion (Cu 2+ ) coordination effect with both PEO and Li salts to achieve a high Li + conductivity of 0.2 mS cm −1 and a transference number of 0.42 at 30 °C. Moreover, the Cu‐coordinated PEO electrolyte is neither sticky nor hygroscopic because the hydrophilic oxygen groups in PEO are terminated by Cu ions. Furthermore, the in situ formed F/Li‐rich inorganic layer induced by CuF 2 additive accelerates Li + transport kinetics and enables uniform Li + deposition during Li plating/stripping. As a result, the Cu 2+ ‐coordinated PEO electrolytes deliver a high critical current density of 1.5 mA cm −2 at 30 °C. An all‐solid‐state Li‐LiNi 0.83 Co 0.12 Mn 0.05 O 2 (NCM83) battery with such a copper coordinated PEO electrolyte exhibits a long cycle life over 500 cycles with a capacity retention of 71% under 0.6 C at 30 °C. When the mass loading increases to a record high of 7 mg cm −2 , the Li‐NCM83 cell delivers a high areal capacity of 1.07 mAh cm −2 under 0.1 C at 30 °C.