Design Of Ionic Liquid Functional Electrolyte And Its Application In Lithium Ion Batteries

With the widespread use of small mobile charging power sources and powered cars,lithium-ion batteries are considered to be the most promising battery technology.Currently,lithium-ion batteries are facing safety issues that urgently need to be resolved,which has become one of the factors that limit their rapid development.In lithium-ion batteries,the role of electrolyte is very important,equivalent to the"blood"of the battery,and has a profound impact on the battery’s energy density,capacity,safety performance,and cycle performance.Commercial electrolytes are prone to decomposition under high temperature and voltage and have poor temperature adaptability.Therefore,the development of an electrolyte system with high safety,high temperature resistance,high voltage resistance,wide temperature range and high lithium ion transmission rate has become the current top priority.Ionic liquids have the characteristics of wide electrochemical window,high flash point,wide operating temperature range and green pollution-free.In this paper,the stability of the interface is controlled under the combined action of ionic liquid and different co-solvents to improve electrochemical performance.（1）Mixed system of ionic liquid and fluorinated solvent.Fluorine atoms have high electronegativity and weak polarity.Fluorinated solvents have more fluorine atom substituents,so they exhibit excellent characteristics of high flash point and high oxidative decomposition voltage,and at the same time have good wettability with electrodes and separators.The presence of fluorine atoms is beneficial to promote the formation of Li F.Subsequently,the new ionic liquid-based mixed electrolyte system was matched with NCM622 and Li Fe PO₄ cathode materials for electrochemical testing and characterization.Through scanning electron microscopy and X-ray photoelectron spectroscopy analysis,the performance of the battery assembled by this mixed electrolyte system under high voltage and high temperature is studied.The experimental results show that the cathode and anode sides of the electrolyte can form a stable SEI film,and can circulate stably under high temperature and high voltage.（2）Mixed system of ionic liquid and sulfone solvent.Sulfone solvents are expected to improve the solubility,ionic conductivity and electrode compatibility of lithium salts as cosolvents.Sulfone solvents have a wider electrochemical window and a higher dielectric constant.More importantly,the participation of sulfone solvents will not reduce a series of excellent properties of ionic liquids.The mixed electrolyte system was matched with Li Fe PO₄ cathode material for electrochemical testing and characterization in the temperature range of-10℃ to 60℃.Through scanning electron microscopy and X-ray photoelectron spectroscopy and other methods,the influence of the mixed electrolyte system assembled into a battery on the electrochemical performance at different temperatures was explored.The experimental results show that the electrolyte can form a stable SEI film,which can circulate stably in the range of low temperature-10℃ to high temperature 60℃.