Rational design of a cost-efficient and eco-friendly fluorinated ether for high-energy and long-lived Li-metal batteries

Localized high-concentration electrolytes (LHCEs) are widely used in high-voltage Li-metal batteries. However, the most used component in LHCEs—1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE)—is expensive and has a limited supply due to the explosive nature of its tetrafluoroethylene feedstock and the hazardous synthesis process, which hinders its practical application. To overcome these challenges, we designed and successfully synthesized another type of partially fluorinated ether, 1,1,1,2,3,3-hexafluoro-3-(2,2,3,3-tetrafluoro-propoxy)propane (HFTEP) solvent, which is inexpensive, eco-friendly, and scalable compared to TTE. The electrolyte with HFTEP displays stronger dipole-dipole and weaker Li⁺-solvent interactions compared to the TTE-based electrolyte. The HFTEP-based electrolyte exhibits a high average Coulombic efficiency of approximately 99.28% for Li-metal plating-stripping, and higher cycling stability than the TTE-based electrolyte. When paired with 4.5-4.6 V nickel-rich cathodes, the HFTEP-based electrolyte enables impressive performance: the cathode retained 91% of its capacity after 200 cycles, while an anode-free pouch cell retained 85% of its original capacity after 100 cycles. This work greatly supports the practical application of LHCEs in high-energy Li-metal batteries.