Designing on solvent composition of dual-salt low concentration electrolyte for inhibiting lithium dendrite growth at −20 ℃

Lithium metal batteries (LMBs) are expected to become a new generation of energy storage technology based on the high theoretical specific capacity and low potential of lithium metal anode. In order to promote the commercial application of LMBs, lithium dendrite has become an urgent issue to be resolved to improve the battery safety. Since temperature is a key factor on dendrite growth kinetics, it is of great significance to design novel electrolytes for LMBs to inhibit lithium dendrite growth at low temperature conditions. In this work, γ-butyrolactone (GBL) with low melting point, ethyl propanoate (EP) with high wettability and low viscosity, and fluoroethylene carbonate (FEC) with excellent film-forming performance are chosen as the electrolyte components (GBL/EP/FEC, 7:3:1 w/w/w). Lithium tetrafluoroborate (LiBF4) and lithium difluorophosphate (LiDFP) are used as dual salts to reformulate a low-concentration electrolyte (LCE) of 0.5 mol L−1 (M), i.e., 0.4 M LiBF4 + 0.1 M LiDFP. The solvent compositions of the LCE electrolyte are optimally designed for Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cells, resulting in good low-temperature cycling performance without affecting the room-temperature performance. The electrolyte enables the Li||NCM811 cells to maintain both 97% capacity after 100 cycles at room temperature and obviously suppress lithium dendrite growth at −20 °C.