Conformal Polymer Electrolyte Enabled by Nitrile Coordination for Long‐Cycle Solid‐State Lithium Metal Batteries

Abstract Lithium metal is a highly promising anode for next‐generation high‐energy‐density batteries due to its high theoretical capacity, yet its practical application remains hindered by poor interfacial compatibility with polymer solid‐state electrolytes (PSEs). Herein, an in situ solidification PSE that utilizes poly(ethyleneglycol)methyletheracrylate (PEGMEA) and methylated pivalonitrile (PN) is developed (PNF), which forms an conformal and mechanically robust solid electrolyte interphase (SEI) on the lithium metal surface. The coordination between the nitrile group (–C≡N) and Li⁺ regulates interfacial ion transport, while the formed organic–inorganic (hybrid) SEI effectively combines mechanical flexibility and interfacial rigidity to buffer lithium volume fluctuations and inhibit dendrite growth. Benefiting from the enhanced Li + hopping sites and improved ionic mobility, the PNF electrolyte exhibits high ionic conductivity, i.e., 3.47 × 10 −4 S cm −1 at 30°C. Li|PNF|Li symmetric cells show exceptional cycling stability, surpassing 1000 h at 0.5 mA cm −2 . Notably, Li|PNF|LiFePO 4 cells achieve a capacity retention of 92.8% after 1000 cycles at 0.5C and 78.9% after 2000 cycles at 1C rate, both at 30°C, highlighting the exceptional conformal properties of the electrolyte resulting in the superior cycling performance. This study establishes a design framework for constructing long‐term cycling, solid‐state lithium‐metal batteries through tailored interfacial engineering of PSEs.