Synthesis Of Phosphonate-functionalized Ionic Liquids And Its Application In Lithium-ion Batteries

With the development of society and the reduction of non-renewable energy reserves,the concept of sustainable development has gained popular support,and people have begun to pursue a more green and environment-friendly lifestyle.Among them,the rapid development of the electric vehicle industry is in line with this trend,and the construction of various small or large energy storage equipment is also a"recipe"for energy issues and environmental protection issues.Lithium-ion batteries have the advantages of high specific energy,high voltage,long charge-discharge life,low self-discharge rate,no memory effect,and wide operating temperature.Compared with fuel cells,solar cells,and hydrogen batteries,it is a more mature battery technology,and the market demand and share are increasing year by year.The electrolyte in lithium-ion batteries is an important part of it,and is known as the"blood"of lithium-ion batteries.The research on the electrolyte is endless,and the cycle performance,rate performance,low temperature performance and safety performance of the battery have been optimized to a certain extent,which has promoted the rapid development of lithium ion battery technology.Ionic liquids have become research hotspots in the field of lithium ion battery electrolytes due to their non-volatile,non-flammable,high electrical conductivity,and wide electrochemical stability windows.In this paper,a method using a functionalized ionic liquid as an electrolyte additive is used to improve battery performance.Aiming at the application of phosphine-functionalized ionic liquids in lithium-ion batteries,the following three parts of work have been completed:First,the synthesis,purification,and characterization of phosphine-functionalized ionic liquids;Second,the effect of changes in phosphine-functionalized ionic liquid functional groups on battery performance.Third,the inhibition of the corrosion of aluminum current collectors by phosphine-functionalized ionic liquids.（1）Three phosphine-functionalized ionic liquids were designed and synthesized in this paper and purified.Nuclear magnetic characterization proved that high-purity ionic liquids were synthesized.（2）The improvement of Li/LiCoO₂ performance of PFIL-1 and PFIL-2 ionic liquids was studied,and the differences in battery performance caused by functionalized ionic liquids with different groups were discussed.It was found that the addition of OEt group ionic liquids can make the battery performance better.The mechanism of PFIL-2 was studied by electrochemical experiments,TEM and XPS.（3）The addition of PFIL-3 can improve the cycling performance of Li/NCM811 in electrolytes with Li TFSI as the lithium salt.After comparative experiments,it can be found that PFIL-3 can reduce the occurrence of electrolyte side reactions by inhibiting the corrosion of aluminum current collector by LiTFSI.