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

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 (Cu2+) 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 CuF2 additive accelerates Li+ transport kinetics and enables uniform Li+ deposition during Li plating/stripping. As a result, the Cu2+‐coordinated PEO electrolytes deliver a high critical current density of 1.5 mA cm−2 at 30 °C. An all‐solid‐state Li‐LiNi0.83Co0.12Mn0.05O2 (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. [ABSTRACT FROM AUTHOR]