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

Abstract

Localized high-concentration electrolytes (LHCEs) are prevalent in high-voltage Li-metal batteries featuring their high specific energy and long cycle life. However, the most used component 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) for LHCEs is very expensive and limited supply due to the explosive nature of the tetrafluoroethylene feedstock and the very dangerous synthesis process, which precludes it from 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-(2,2,2-trifluoro-ethoxy) propane solvent (HFTEP), which is much cheaper, more eco-friendly, and more scalable than the TTE. Stronger dipole-dipole and weaker Li+–solvent interactions are discovered in the electrolyte with HFTEP compared to the TTE-based electrolyte. The HFTEP-based electrolyte exhibits excellent Li-metal plating-stripping Coulombic efficiency of ~99.28% and longer cycling stability than the TTE-based electrolyte. When the HFTEP-based electrolyte is matched with 4.5~4.6 V high-Ni cathodes, impressively, the cathode itself shows a high capacity retention of 91% after 200 cycles, and an anode-free pouch cell can retain 85% of its original capacity after 100 cycles. This work greatly supports the practical application of the LHCEs in high-energy Li-metal batteries.