<i>In\nSitu</i> Fabrication of Solvent-Free\nSolid Polymer Electrolytes for Wide-Temperature All-Solid-State Lithium\nMetal Batteries

All-solid-state lithium metal batteries (ASSLMBs) have\nbeen regarded\nas promising candidates to settle the safety issues of liquid electrolytes\nfor rechargeable lithium batteries. However, the currently reported\ngel polymer electrolytes still have flammable liquid solvents, thus\nleading to the potential safety hazard. Here, solvent-free deep eutectic\nsolid polymer electrolytes (SPEs) are designed and fabricated via\nan <i>in situ</i> polymerization, which are composed of\na poly(vinylidene fluoride–hexafluoropropylene) (PVDF–HFP)\nelectrospun membrane, succinonitrile (SN), poly(ethylene glycol) diacrylate\n(PEGDA200, <i>M</i><sub>n</sub> = 200 g mol<sup>–1</sup>), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium\ndifluoro(oxalato)borate (LiDFOB). The deep eutectic solvent (DES)\nwith SN/LiTFSI provides a superior room-temperature ionic conductivity,\nwhile the PEGDA200 precursor acts as cross-linking network to form\nSPEs under thermal initiation for free radical polymerization, and\nLiDFOB can form a stable solid electrolyte interface (SEI) layer.\nThe PVDF–HFP electrospun membrane with a three-dimensional\nnanofibrous network structure for SN/PEGDA200/LiTFSI/LiDFOB SPEs exhibits\na wide electrochemical stability window, high lithium-ion transference\nnumber, and good compatibility with the lithium metal anode. Furthermore,\nthe obtained SPEs assembled with Li//LiMn<sub>0.6</sub>Fe<sub>0.4</sub>PO<sub>4</sub>, Li//LiFePO<sub>4</sub>, and Li//LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub> asymmetric cells show\nexcellent cycling performance and rate capability at a wide temperature.\nThis strategy provides a promising path in designing high-energy-density\nASSLMBs for practical application.