What is the electrolyte of a lithium ion battery?
Lithium-ion battery electrolyte includes two parts: electrolyte and solvent.
Lithium ion batteries generally use lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6) and lithium trifluoromethanesulfonate (LiCF3SO3).
Because lithium perchlorate has strong oxidizing properties, which may cause safety problems and limit its practical application, arsenic is highly toxic and expensive, so it is not suitable for practical applications. The ionic conductivity of lithium tetrafluoroborate and lithium trifluoromethanesulfonate is very low, and lithium trifluoromethanesulfonate is highly corrosive to aluminum foil, which affects its use. Lithium hexafluorophosphate is the most widely used electrolyte at present, but its shortcomings such as high cost, poor thermal stability, and decomposition when exposed to water cannot meet the needs of future lithium battery development.
Because carbonate-based solvents have very good electrochemical stability under a wide window, they have been widely used. Including propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC). Ether organic solvents are also widely used in lithium ion batteries. Including tetrahydrofuran (THF), 1,3-dioxolane (DOL) and 2-methyltetrahydrofuran (2-MeTHF) and so on. Carboxylic acid esters are also an effective solvent. Including γ-butyrolactone (γ-BL), methyl propionate (MP), ethyl acetate (EA), etc. These solvents can easily form a mixed solvent to improve the electrochemical performance of the lithium ion battery.
The thermal stability of the electrolyte has a great influence on the performance of the lithium ion battery, because the actual use environment temperature of the battery varies greatly (-40~80℃), and the interior of the battery is affected by the Joule heating effect, and sometimes it can exceed 200℃. , And organic solvents are also very easy to burn, so it is easy to cause fire. Another problem is that this type of electrolyte has a low voltage window, and the current electrolyte voltage window is generally lower than 4.5V. Ionic liquid is a kind of salt that is in liquid state at room temperature or lower temperature. Ionic liquid has many advantages over other solvents: non-flammable, non-volatile, strong solubility, high ionic conductivity, electrochemical and thermal stability Good and wide voltage window, it is an ideal lithium-ion battery electrolyte. The main problem of current ionic liquids is the high viscosity, which inhibits the high-current discharge performance of the battery. Gel polymer electrolyte is a solid electrolyte that can prevent the leakage of lithium-ion battery electrolyte, improve battery safety performance, increase the specific capacity of the full battery, and has very high ionic conductivity, which has very good application prospects.
The current research direction is to increase the voltage window and further improve the lithium ion conductivity. Solid ceramic electrolyte has very good mechanical strength, high lithium ion transport performance and non-flammable properties, and has become a current research hotspot. The use of this type of electrolyte can effectively improve the safety performance of lithium-ion batteries. Because of its strong mechanical strength, it can effectively avoid the short circuit problem caused by lithium dendrites. At the same time, it is not combustible, so the battery using ceramic solid electrolyte is difficult to burn. The current main problem is that lithium ion conductivity needs to be improved.
Can learn more about lithium-ion batteries.