High-performance lithium metal batteries enabled by fluorinated aromatic diluent assisted nonflammable localized high-concentration electrolytes

Localized high concentration electrolytes (LHCEs) possess low viscosity, good wettability, sufficient ionic conductivity and good compatibility with lithium metal anodes. However, diluents of LHCEs suffer from high density, high-cost and low activity in the formation of robust SEIs. Herein, we developed a trimethyl phosphate (TMP)-based nonflammable LHCE diluted by 1,2-difluorobenzene (DFB), which lower density, lower cost, lower LUMO and better fluorine-donating property. With the addition of DFB, 3.2 M LiFSI/TMP/DFB (LiFSI/TMP/DFB 0.75:1:0.5) exhibits reduced viscosity (49.2 mPa s) and improved ionic conductivity (1.27 mS cm−1), while the local high-concentration solvation structure of TMP-Li+-FSI− is retained. DFB can fabricate LiF-rich SEI on lithium metal anodes owing to its low LUMO and fluorine donor properties, and efficiently inhibits lithium dendrites. Remarkably, the battery performance of the LHCE is significantly improved by DFB. 3.2 M LiFSI/TMP/DFB endows LiNi0.8Co0.1Mn0.1O2/Li cells with excellent long-term cycle performance (capacity retention of 80.1% after 500 cycles). LiFePO4/Li cells with 3.2 M LiFSI/TMP/DFB demonstrate high rate capability (discharge capacity of 112.7 mAh g−1 at 5 C rate) and outstanding long-term cycle performance (capacity retention of 80.9% after 850 cycles).