Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite-free plating of a lithium-metal anode and a Li+ extraction from an oxide host cathode without electrolyte oxidation in a high-voltage cell during the charge process. Therefore, a double-layer polymer electrolyte is investigated, in which one polymer provides dendrite-free plating of a Li-metal anode and the other allows a Li+ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium-metal anode and a poly(N-methyl-malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li+ conductivity on crossing the polymer/polymer interface.