Currently, Li-ion battery has been widely used in 3C device, electric vehicles, with environmentally friendly, no memory effect and so on. However, the narrow application temperature range limits its application in some areas and fields. At present, commercial Li-ion battery electrolytes have application temperature range of -20 °C ~ 60 °C and show a significantly lower capacity outside these temperatures. Researchers try to broaden their operating temperature by improving the solvent system and the use of lithium salts.

Recently, Zhang et al. [1] studied the effect of different ratios of LiBF4 and LiODFB mixtures on electrochemical performance with EC, PC and EMC as co-solvents, and LiCoO2 was used as cathode at 25 °C, -20 °C, and 60 °C. The results show LiCoO2 / Li cells in pure LiBF4-based electrolyte exhibited a significant fade and relatively low capacity after cycling at 25 °C and 60 °C. With the increase of the concentration of LiODFB, the capacity and cycling performance of the cell have been significantly improved. At -20 ° C, LiBF4 and mixed salt systems both showed good cycling performance. Among the different ratios of LiBF4/LiODFB mixture, the LiBF4 / LiODFB (8: 2) electrolyte shows good cycling performance over a wide-temperature range. The experiments about internal resistance show that the increase of LiODFB concentration does not cause a significant increase in the resistance at 25 °C. However, the increase of LiODFB concentration obviously caused the increase of cell resistance at -20 °C. At 60 °C, the cell resistance decreased significantly. The researchers also analyzed the morphology and composition of the LiCoO2 cathode surface. The above experimental results show that LiCoO2/Li cells using LiBF4/ LiODFB (8: 2) -based electrolytes exhibits high discharge capacity and excellent cycling stability.

Although the mixture of different lithium salt improves cycling performance and discharge capacity, it fails to effectively improve the rate performance of the Li-ion battery. This may be a problem to be solved in the future for mixed lithium salts electrolyte. In addition, the electrochemical mechanism of the synergistic effect of mixed lithium salts at high and low temperatures needs further study.

References:

[1] Zhang, L., Sun, Y., Zhou, Y. et al. Ionics (2018). DOI: 10.1007 / s11581-018-2470-1

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