Optimal Blend between Carbonate Solvents and Fluoroethylene Carbonate for High-Voltage and High-Safety Li(Ni0.8Mn0.1Co0.1)O2 Lithium-Ion Cells

The current work performs a comprehensive investigation to determine the best blend between fluoroethylene carbonate and common carbonate solvents, that is, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), for high-voltage and high-safety lithium-ion cells. These three kinds of electrolytes denoted FEMC, FDEC, and FDMC, respectively, are researched herein. The cells containing FDMC exhibit more superior performance in long-term cycling and high-temperature storage at high voltages. This may be ascribed to the thin but reliable passivation layer constructed on the cathode surface, which improves the electrode/electrolyte interface and restrains the severe side reactions such that the degradation of cells at high voltages and the self-discharge of cells at elevated temperatures are successfully inhibited. Moreover, the FDMC electrolyte illustrates better flame retardancy than FEMC and FDEC electrolytes, and the thermal reactivity between FDMC electrolytes and delithiated cathode materials is suppressed as well, which further improves cells’ inherent safety under abusive conditions. The thermal runaway behavior of FDMC cells at accelerating rate calorimetry tests and nail tests is comparatively gentle; additionally, the thermal runaway induced by overcharge for FDMC cells occurs 35 s later than the other two kinds of cells.