Double-salt electrolyte for Li-ion batteries operated at elevated temperatures

Lithium ion batteries (LIBs) have swept the whole energy storage field. However, the current mainstream lithium batteries are difficult to operate stably at high temperature (>60°C) due to the decomposition of electrolyte and solid electrolyte interphase (SEI), the cathode metal elements dissolution behavior, and potential thermal runaway. Here, We report a double-salt electrolyte with lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluoro(oxalato)borate (LiDFOB) as electrolyte salt, fluoroethylene carbonate (FEC), and tetra(ethylene glycol) dimethyl ether (TEGDME) as cosolvent, which delivers excellent ionic conductivity, high electrochemical stability and satisfactory ability to impede the dissolution of Fe element under elevated temperature (70°C). In addition, the electrolyte is benefited to form a robust and thermal-resistance solid-electrolyte interface (SEI) layer on the surface of graphite (Gr) anode, which shows improved decomposition temperature (86°C). The assembled thermally stable and high-safety 1300 mAh 18650-type LiFePO4|Gr cell shows high Coulombic efficiency (∼99.7%), improved cycling stability with discharge capacity 871.1 mAh after 200 cycles at 0.5 C and 70°C. This work affords a splendid strategy for address the unstable interface at both cathode and anode for safe high-temperature LIBs.