Abstract
Lithium-ion batteries with conventional LiPF6 carbonate electrolytes are prone to failure at high temperature. In this work, the thermal stability of a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiODFB) in carbonate solvents was analyzed by accelerated rate calorimetry (ARC) and differential scanning calorimetry (DSC). LiTFSI-LiODFB dual-salt carbonate electrolyte decomposed when the temperature exceeded 138.5 °C in the DSC test and decomposed at 271.0 °C in the ARC test. The former is the onset decomposition temperature of the solvents in the electrolyte, and the latter is the LiTFSI-LiODFB dual salts. Flynn-Wall-Ozawa, Starink, and autocatalytic models were applied to determine pyrolysis kinetic parameters. The average apparent activation energy of the dual-salt electrolyte was 53.25 kJ/mol. According to the various model fitting, the thermal decomposition process of the dual-salt electrolyte followed the autocatalytic model. The results showed that the LiTFSI-LiODFB dual-salt electrolyte is significantly better than the LiPF6 electrolyte in terms of thermal stability.
Highlights
The development of high-energy-density, long-cycle-life, and high-safety secondary lithium-based batteries is essential to meet the emerging needs of the electronics and automotive industry, and various energy storage systems [1,2]
LiPF6 is sensitive to moisture and will react with trace moisture impurities in the electrolyte to generate a small amount of hydrofluoric acid (HF), which will be more severe at high temperatures
To meet the requirements of high energy density and high safety in lithium-ion batteries, it is desirable to improve the stability of the electrolyte under high pressure and high temperature
Summary
The development of high-energy-density, long-cycle-life, and high-safety secondary lithium-based batteries is essential to meet the emerging needs of the electronics and automotive industry, and various energy storage systems [1,2]. The study found that compared with high-voltage (5 V vs Li+/Li) Li/LiNi0.5Mn1.5O4 cells using LiPF6 electrolytes, the cells with LiTFSI0.5-LiODFB0.5 dual-salt electrolyte had excellent cycling stability and rate performance [21]. When the cathode was LiFePO4 or LiCoO2, the cells with the best ratio of LiTFSI0.6-LiODFB0.4 (25 ◦C) and LiTFSI0.4-LiODFB0.6 (60 ◦C) dual-salt electrolytes in solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and both had excellent cycling stability and rate performance compared with using LiPF6 electrolyte [19,20]. Studies have shown that whether used in lithium-ion batteries or lithium metal batteries, the LiTFSI-LiODFB dual-salt electrolyte is superior to LiPF6-based electrolytes in cycling stability and rate capability under specific proportions and specific conditions. The findings of the current study could provide reference information on the thermal stability of dual-salt electrolytes
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