Lithium difluoro(bisoxalato) phosphate-based multi-salt low concentration electrolytes for wide-temperature lithium metal batteries: Experiments and theoretical calculations

Current knowledge and works on high-energy-density Li metal batteries (LMBs) mainly focus on their room-temperature performances. However, the wide-temperature properties of LMBs manifesting greater significance in their large-scale applications are rarely explored. In this work, two LiDFBOP-based multi-salt low-concentration electrolytes (LCEs) are proposed and further explored by experiments and theoretical calculations for wide-temperature LMBs. Molecular dynamics (MD) simulations reveal the weaker attractive interactions between solvent molecules in LCEs, thus resulting in the lower viscosity and freezing point. Specially, the Li+ in representative solvation structures of LCEs possesses accelerated desolvation behavior with low charge-transfer impedance in Li||Li symmetric cells. Furthermore, the thermally stable Li salts in LCEs manifest obvious effect in stabilizing Li metal anode, which contributes to forming a compact solid electrolyte interphase (SEI) layer with good mechanical properties and high ionic conductivity. Ultimately, the Li||LiNi0.7Co0.1Mn0.2O2 battery exhibits extraordinary electrochemical performances over a wide temperature range (−25 °C to 70 °C). This work provides a facile and practical design strategy for the wide-temperature LMBs.