Deep eutectic solvent-immobilized PVDF-HFP eutectogel as solid electrolyte for safe lithium metal battery

Highlights: • Fabrication of eutectogel with deep eutectic solvent. • Flexible and non-flammable electrolyte for LIBs. • Deep eutectic solvent immobilized PVDF-HFP. A novel cheap eutectogel (ETG) membrane based on the deep eutectic solvent (DES) immobilized poly (vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) is proposed as a solid electrolyte for safe lithium metal batteries in this study. The composition of DES is optimized, which is prepared by mixing the N-methylacetamide (NMAC) and the lithium bis [(trifluoromethyl)sulfonyl]imid (LiTFSI) with a molar ratio of 4:1. The eutectogel is formed by incorporating 70 wt% DES into the PVDF-HFP, which is non-flammable and shows excellent mechanical properties. This ETG membrane electrolyte with a thickness about 25 μm possess a high ionic conductivity (3.05 × 10⁻⁴ S cm⁻¹) at room temperature and a wide electrochemical stability window (~5 V). The Li//ETG//LiFePO₄ full cells deliver an acceptable discharge capacity of ~133.9 mAh g⁻¹ at 0.1C and room temperature after 100 charge-discharge cycles. The ETG membrane electrolyte can also endow the Li//ETG//LiFePO₄ pouch cell with flexibility and withstanding abuse operations, like nail penetration and cutting. We expect that the flexible and non-flammable eutectogel membrane will have implications for the use of DES based ionic liquids in the synthesis of advanced solid-state electrolytes for safer lithium batteries.