The exothermic reaction of lithium ion battery containing organic electrolyte in the initial stage of thermal runaway includes the decomposition of electrolyte and the reaction between electrolyte and electrode. These exothermic reactions accelerate the increase of heat. Because the organic electrolyte contains volatile solvents, such as propylene carbonate, dimethyl carbonate and ethylene glycol dimethyl ether, these solvents can dramatically increase the internal pressure of the battery, causing the battery to explode. Therefore, it is particularly important to use new systems to replace volatile and flammable electrolytes. Solid electrolyte can finally meet this requirement, but there is still a big technical barrier in the production of solid battery, mainly because it is extremely difficult to keep the electrode and solid electrolyte in full contact throughout the charge discharge process, and its conductivity cannot meet the requirements. Ionic liquid can be used as the ideal electrolyte of battery, and its nonvolatility and non combustion will make the battery safer.
Application in lithium ion battery
A variety of ionic liquids have been studied in order to be used as alternative electrolytes for lithium ion batteries. The reported application technologies of ionic liquids can be roughly divided into the following three categories: ionic liquids+supporting electrolytes+additives; Ionic liquid+supporting electrolyte+high potential alternating negative electrode; Ionic liquid+supporting electrolyte.
1. AlCl3 ionic liquid
The application of AlCl3 ionic liquid has a long history, and there are many examples about its application in batteries. The corrosivity of such ionic liquids limits their applications and cannot be used in traditional batteries. New battery systems, including AlCl3 acid base concentration cell, Al chloride cell, Cd bromide cell, Al polyaniline cell and Mg metal vanadate cell, overcome these shortcomings. However, there are still problems in the application of ionic liquids in lithium ion batteries, mainly because the cathode containing AlCl3 electrolyte is still not stable compared with lithium. At present, the potential of AlCl3 ionic liquid can be improved by using new negative electrodes (such as Li Al alloy layer oxide battery, Li Sn alloy negative electrode) or additives (such as SOCl2, H2O).
2. Ionic liquids formed by fluoride containing anions and non imidazole cations
It is difficult to find that the effect of pure ionic liquids in lithium batteries can be as good as that described previously. Here, "pure" means that ionic liquids only contain supporting electrolytes without additives.
Non imidazole system, asymmetric quaternary ammonium salt system and pyrazoline system can be used as pure ionic liquids matching lithium batteries.