Investigating on physical and electrochemical properties of high concentrated electrolytes based on LiBF4 salt for 5 V Li-ion rechargeable batteries

In this work, highly concentrated electrolytes were prepared by dissolving tetrafluoroborate (LiBF4) salt in the two solvents including tetramethylene sulfone (TMS) and trimethyl phosphate (TMP) with different mole ratios. The results indicated that the electrolyte LiBF4/TMS (1:3) (~3.4 M) possessed the highest oxidation stability of 6.2 V (vs. Li+/Li) and high ionic conductivity of 1.0 mS/cm that could be promising for high voltage Li-ion batteries operated in the voltage range of 3.5-4.9 V. The electrolyte compatibility with high voltage cathode Li || LiNi0.5Mn1.5O4 (LNMO) was evaluated in coin-cell configuration, which displayed high reversible discharge capacity of 113 mAh/g in the first cycle and high initial Coulombic efficiency >91% and remained >80% of the initial capacity at the 100th cycle. By using the cyclic voltammetry (CV) method, the diffusion coefficient was also calculated as about 4.51×10-11 cm2/s.