Designing Bidirectionally Functional Polymer Electrolytes for Stable Solid Lithium Metal Batteries

Abstract The development of high energy density lithium metal batteries has been retarded by the uncontrolled lithium dendrite formation and unstable Ni‐rich cathode–electrolyte interface (CEI). Herein, the bidirectionally functional polymer electrolytes (BDFPE) are designed via direct UV solidification of functional polymer species on electrode surfaces to simultaneously handle the interface issues faced by anodes and cathodes. By constructing the BDFPE, a smooth and dendrite‐free lithium deposition is enabled for Li||Li symmetry cells after 1800 h ultralong cycling at 1 mA cm −2 and 1 mAh cm −2 , which are attributed to the fast ion conductivity (5.84 × 10 −4 S cm −1 ), high Li + transfer number (0.69) of BDFPE and low interfacial resistance between electrode and solid electrolytes. Furthermore, Li||LiNi 0.6 Co 0.2 Mn 0.2 O 2 batteries demonstrate a favorable cycling and rate capability, and a stable and phosphate‐based CEI layer is constructed in situ. DFT studies reveal that the functional additives FEC and TEP participate in the interface formation. The finding provides a promising design strategy to accommodate the anode and cathode interfaces for high energy density lithium metal batteries.