Wide-temperature range and high safety electrolytes for high-voltage Li-metal batteries

Along with the keeping growing demand for high-energy-density energy storage system, high-voltage Li-metal batteries (LMBs) have attracted many attentions. In view of many defects of the commercial electrolytes, such as flammability, limited operation temperature range, and severe Li dendrite growth, non-flammable phosphate-based localized highly concentrated electrolytes (LHCE) have been explored as one of the safe electrolytes for LMBs. But until now there is rare report on wide-temperature range LMBs using phosphate-based electrolytes. Here, we prepare a wide-temperature LHCE, which is composed of lithium difluoro(oxalato)borate (LiDFOB), triethyl phosphate (TEP), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and explore the applicability in wide-temperature LMBs from −40 to 70 °C. In the LHCE, both TEP and HFE are non-flammable, and Li⁺ is highly coordinated with TEP and DFOB⁻, which can effectively inhibit the TEP decomposition on anode, and facilitate the preferential reduction of DFOB⁻, thus obtain a robust solid electrolyte interphase (SEI) to suppress Li dendrite growth and side reactions. Therefore, this LHCE can not only endow Li/Cu and Li/Li cells with high Coulombic efficiency (CE) and long cycling lifespan, but also be applied to LiFePO₄ (LFP)/Li and LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523)/Li LMBs. Most importantly, the NCM523/Li LMBs with LHCE can deliver stable cycling performance at 4.5 V high-voltage and high-temperature (70 °C), as well as excellent low-temperature capacity retention even though both charging and discharging process were carried out at −40 °C.