Study On High Temperature And High Pressure Double-bonded Piperidine Ionic Liquid Lithium Ion Electrolyte

Lithium-ion batteries with higher energy density and wider application have more requirements for safety performance.Especially in the field of new energy vehicles,due to the high working capacity and working voltage of the battery cells,the battery is prone to short circuit and the local temperature is overheat.At the same time,the commercial electrolyte is generally LiPF₆ and carbonate organic solvent,wherein the carbonate organic solvent is flammable at high temperature.This is the main reason for the burning accidents of new energy vehicles in recent years.In addition,LiPF₆ easily decomposes with a trace of water or in a high temperature environment to generate HF and destroy the structure of the positive electrode material.Therefore,it is important to develop a safe and stable electrolyte.Based on the research of lithium ion electrolyte safety in recent years,a new ionic liquid PP₁₃*DFOB was used to design an electrolyte that can protect the cathode material at high temperature,and the mechanism of electrolyte formation was studied.The research content of this paper is as follows:?1?Preparation of an ionic liquid electrolyte using a novel ionic liquid PP₁₃*TFSI.0.4 M LiDFOB:PP13*TFSI/EMC/FEC electrolyte was prepared by mixing ionic liquid and organic solvent.In order to find the best ratio,three different electrolytes were prepared.The performance of the electrolyte system was optimized when a 50%volume concentration of PP₁₃*TFSI was applied.The lithium-rich half-cell assembled using this electrolyte was subjected to a high-temperature cycle test at 40? for 100cycles,and the battery had a discharge specific capacity of 157.1 mAh g^-1 and a capacity retention ratio of 91%.After 100 cycles of the high temperature cycle test at55?,the discharge specific capacity was 172.7 mAh g^-1,and the capacity retention rate was 97.2%.SEI film on the surface of the lithium-rich positive electrode formed with this electrolyte was found by a field emission electron scanning microscope test.?2?Transmission electron microscopy showed that the SEI film structure was a two-layer film structure and the thermal stability of the double-layer SEI film was discussed.To analyze and disscuss the effects of LiDFOB and PP₁₃*TFSI in the formation of SEI film,electrolytes of three different compositions were prepared It was found that the SEI film formed when both LiDFOB and PP₁₃*TFSI were present was a two-layer film structure.A two-layered SEI film was synthesized by combining with theoretical calculations.The inner layer was mainly composed of LiDFOB,which was porous and non-uniform,and its thickness ranged from 18.63 nm to 43.18nm.The outer layer is mainly composed of PP₁₃*TFSI,which is a layer of dark and dense film with a thickness of about 11.15 nm.The lithium-rich half-cell assembled with the electrolyte of LiDFOB and PP₁₃*TFSI simultaneously had a discharge specific capacity of 165.2 mAh g^-1 and a capacity retention rate of 90.9%after 150cycles of high-temperature cycle test at 55?.?3?The mechanism of inhibition of aluminum corrosion was investigated by using film-forming ionic liquids.By comparing PP₁₃TFSI,PP₁₃*TFSI,PP₁₃DFOB and PP₁₃*DFOB,it was found that PP₁₃*DFOB formed SEI film on the aluminum current collector.The presence of Al can be found by EDX spectrum analysis of Al surface.It is found that the electrolyte containing PP₁3*DFOB can form an SEI film to cover the Al surface to inhibit the occurrence of aluminum corrosion.In addition,by TG test analysis,it was found that the electrolyte containing PP₁₃*DFOB can be stably present at high temperatures.The above results indicate that PP₁₃*DFOB ionic liquid is a safe electrolyte component with great potential application value.