Research Advances on Chemical Crosslinked Gel Polymer Electrolytes for Lithium Ion Batteries

In recent years, there are many explosion accidents of portable electronic devices, which are mainly due to the electrolyte leakage of the separator/electrolyte system of traditional lithium-ion batteries and severe heat shrinkage of the separator resulting in short-circuiting between positive and negative electrodes. The appearance of polymer electrolytes has greatly improved the safety of traditional lithium-ion batteries. Polymer electrolytes mainly include all-solid polymer electrolytes (SPEs) and gel polymer electrolytes (GPEs). For all-solid polymer electrolytes, it still needs a long way for their industrial application because they have low ionic conductivity (10^-6-10^-8 S/cm) at ambient temperature, which does not meet the basic requirements for practical use. GPEs are a hybrid system formed by trapping liquid electrolyte in a polymer matrix, combining the advantages of high safety of solid electrolyte and high ion conductivity of liquid electrolyte. Among them, cross-linked GPEs have received extensive attention. The cross-linking networks prevent the leakage of electrolyte and improve the mechanical properties and dimensional stability of polymer matrix, so the battery safety performance can be greatly improved. Cross-linked GPEs prepared by thermal initiation, photoinitiation, radiation initiation, epoxy ring-opening addition, and sol-gel methods are reviewed according to their initiating and preparing methods, meanwhile their mechanical and electrochemical properties are also introduced.