Molecular Structure Optimization of Fluorinated Ether Electrolyte for All Temperature Fast Charging Lithium-Ion Battery

New electrolytes are needed to replace commercial carbonate electrolytes to enable a wider working temperature range, higher energy density, and faster charging of lithium-ion batteries (LIBs). Fluorinated diluents and solvents have shown promise in LIB electrolyte design, but most of them are considered per- and polyfluoroalkyl substances (PFAS) with significant environmental and health concerns. In this work, we design a family of non-PFAS, partially fluorinated ether solvents for LIB electrolytes. Through rational molecular design, an optimized rate capability is achieved by low viscosity, weak lithium-ion solvation, and high ion diffusivity. The optimized electrolytes enable a longer cycle life and better rate capability (up to 6 C) than previously reported fluorinated ethers or commercial carbonate electrolyte in graphite/LiNi_0.8Mn_0.1Co_0.1O₂ (Gr/NMC811) full cells. In addition, they also show an extended working temperature window with stable long-term cycling from 60 to −40 °C. This work shows a promising path to next generation batteries capable of extreme conditions without introducing PFAS concerns.