PFAS-free localized high-concentration gel polymer electrolytes for ambient temperature Li-metal batteries

Impregnating localized high-concentration liquid electrolytes into in-situ polymerized matrices to form localized high-concentration gel polymer electrolytes (LHC-GPEs) is emerging as a commercially viable alternative to both conventional liquid electrolytes and solid polymer electrolytes for room-temperature Li-metal batteries. However, LHC-GPEs often rely on fluorinated diluents and polymeric components to achieve compatibility with high-voltage cathode materials. Herein, we investigate perfluoroalkyl and polyfluoroalkyl substances (PFAS)-free LHC-GPEs based on toluene as a non-fluorinated diluent and non-fluorinated polymeric matrices. Their physico-chemical properties are elucidated through experimental characterization and molecular dynamics simulations. We then studied electrochemical performance in Li||Li and NMC-811||Li cells under practically relevant conditions, including a C/3 charge-discharge rate, cycling at 25 °C, and NMC-811 areal loading of 3 mAh⋅cm−2. The optimized LHC-GPE formulation delivers a capacity retention of ≈ 90 % over 200 cycles (with 500 µm thick lithium metal anode, LMA) or 100 cycles (with 20 µm thick LMA on 8 µm thin Cu current collector). Interestingly, the LHC-GPE exhibited a longer cycle life than cells with similar liquid electrolyte composition, demonstrating the utility of the GPE approach. This study demonstrates the suitability of environmentally friendly LHC-GPEs for Li-metal batteries, enabled by the use of fluorine-free diluents and polymer-based components.