Regulating the Solvation Structure in Polymer Electrolytes for High-Voltage Lithium Metal Batteries

Solid polymer electrolytes are promising electrolytes for safe and high-energy-density lithium metal batteries. However, traditional ether-based polymer electrolytes are limited by their low lithium-ion conductivity and narrow electrochemical window because of the well-defined and intimated Li⁺-oxygen binding topologies in the solvation structure. Herein, we proposed a new strategy to reduce the Li⁺-polymer interaction and strengthen the anion-polymer interaction by combining strong Li⁺-O (ether) interactions, weak Li⁺-O (ester) interactions with steric hindrance in polymer electrolytes. In this way, a polymer electrolyte with a high lithium ion transference number (0.80) and anion-rich solvation structure is obtained. This polymer electrolyte possesses a wide electrochemical window (5.5 V versus Li/Li⁺) and compatibility with both Li metal anode and high-voltage NCM cathode. Li||LiNi_0.5Co_0.2Mn_0.3O₂ full cells with middle-high active material areal loading (~7.5 mg cm^-2) can stably cycle at 4.5 V. This work provides new insight into the design of polymer electrolytes for high-energy-density lithium metal batteries through the regulation of ion-dipole interactions.