Lithium Difluorophosphate-Based Dual-Salt Low Concentration Electrolytes for Lithium Metal Batteries

The safety hazards and low Coulombic efficiency originating from the growth of lithium dendrites and decomposition of the electrolyte restrict the practical application of Li metal batteries (LMBs). Inspired by the low cost of low concentration electrolytes (LCEs) in industrial applications, dual-salt LCEs employing 0.1mLi difluorophosphate (LiDFP) and 0.4mLiBOB/LiFSI/LiTFSI are proposed to construct a robust and conductive interphase on a Li metal anode. Compared with the conventional electrolyte using 1mLiPF(6), the ionic conductivity of LCEs is reduced but the conductivity decrement of the separator immersed in LCEs is moderate, especially for the LiDFP-LiFSI and LiDFP-LiTFSI electrolytes. The accurate Coulombic efficiency (CE) of the Li||Cu cells increases from 83.3% (electrolyte using 1mLiPF(6)) to 97.6%, 94.5%, and 93.6% for LiDFP-LiBOB, LiDFP-LiFSI, and LiDFP-LiTFSI electrolytes, respectively. The capacity retention of Li||LiFePO(4)cells using the LiDFP-LiBOB electrolyte reaches 95.4% along with a CE over 99.8% after 300 cycles at a current density of 2.0 mA cm(-2)and the capacity reaches 103.7 mAh g(-1)at a current density of up to 16.0 mA cm(-2). This work provides a dual-salt LCE for practical LMBs and presents a new perspective for the design of electrolytes for LMBs.