Tailoring polymer electrolyte solvation for 600 Wh kg^-1 lithium batteries

Polymer electrolytes paired with lithium-rich manganese-based layered oxide (LRMO) cathodes and anode-free cell design are considered one of the most promising high-energy-density and high-safety systems^1-4. However, the unstable anode morphological changes and the irreversible anionic reactions at the electrolyte-cathode interfaces induce oxygen escape and catalytic decomposition of polymer electrolytes, resulting in severe interfacial degradation and poor cycling stability. Here we design an in-built fluoropolyether-based polymer electrolyte composed of strongly solvating polyether and weakly solvating fluorohydrocarbon pendants, creating an anion-rich solvation structure and thus anion-derived fluorine-rich interfacial layers on the cathode and anode to resist interfacial issues. The LRMO cathode exhibits improved oxygen redox reversibility with substantially reduced oxygen-involving interfacial side reactions. This quasi-solid-state polymer electrolyte with 30 wt% trimethyl phosphate enables an LRMO cathode with a reversible high-areal-capacity cycling (>8 mAh cm^-2) in pouch cells and long-term stability (>500 cycles at 25 °C) in coin cells, respectively. The pouch cells exhibit an energy density of 604 Wh kg^-1 (1,027 Wh l^-1) and excellent safety under a nail penetration at a fully charged condition. Our work, therefore, provides a promising direction for creating practical high-energy-density and high-safety lithium batteries.