The Application Of Ionic Liquid Electrolyte For Lithium Ion Batteries

Lithium ion battery is the green energy batteriesthe since 1990 s,it is widely used for its excellent performance such as high energy density,long life in charge and discharge,high voltage and no memory effect.Electrolyte is an important component of lithium-ion batteries,determining the battery performance largely.Currently,the market commercialized lithium-ion battery is mainly composed of the lithium salt LiPF6 and carbonate-based organic solvent,LiPF6 is very sensitive to water,decomposition can occur in case of traces of water,HF is corrosive,which can shorten battery's life.The carbonate-based organic solvent is flammable,explosive and volatile,there is a serious security risk at high power density,therefore,we need to develop a new system to replace the electrolyte.Since ionic liquid has many excellent properties such as no volatile,non-flammable,high conductivity and wide electrochemical window,so ionic liquid is widely applied to the lithium-ion battery electrolyte.The ionic liquid1-ethyl-1-methyl-piperidine bis(trifluoromethylsulfonyl)imide salt(EMP-TFSI)and lithium salt electrolyte(LiTFSI)are added into the conventional carbonate-based organic systems in order to improve its performances.In addition,the sulfone(SL)solvent has high anode stability,a new high-pressure electrolyte system is prepared.Both electrolyte systems are studied for electrochemical properties.1.The lithium salt concentration is constant,a series of tests are carried to study the impact of ionic liquids content to both systems in the electrochemical properties,such as combustion performance,thermal stability and conductivity,the results show that when the ionic liquid content is 50wt%,the hybrid electrolyte system shows good physical and chemical properties and electrochemical properties.2.Then,according to the above experimental results,ionic liquid of 50wt% content and the organic solvent are mixed to prepare a mixed electrolyte system with different lithium salt concentration,the conductivity,electrochemical stability and other tests of electrolyte system are carried.For EC/DEC system,adding ionic liquids improves the anodic oxidation potential of the electrolyte,the electrolyte is possibly applied to highvoltage cathode material.For EC/DEC and SL/DEC both systems,after adding ionic liquid,the conductivity value is higher than the electrolyte system containing no ionic liquid at low temperature,so the low-temperature properties of the electrolyte is improved.3.LiPF6 is sensitive to water,and is easy to break down,the electrochemical properties of LiPF6,LiTFSI and LiBOB three kinds of lithium salts added to the organic carbonate solvent are studied,but also the content of the ionic liquid as a variable for comparison.For LiPF6,the electrochemical window is the widest,for LiBOB,the conductivityis the highest,for LiTFSI,thermal stability is the best and the transference number is the highest.