What are the components of polymer solid electrolyte?

Polymer solid electrolyte is one of the common solid electrolytes, and usually refers to an electrolyte containing polymer materials and capable of ion migration. The polymer solid electrolyte has the advantages of good thermal stability, high stability to lithium, good cycle performance, and can be prepared into flexible thin film batteries. It is currently the most promising solution to fundamentally solve the safety problems of commercial lithium batteries.

The polymer solid electrolyte is composed of polymer matrix, lithium salt and additives.

The polymer matrix provides a supporting framework and an ion transfer medium, and requires good solubility for the lithium salt, in which the lithium salt is easy to dissociate and the dissociated ions are easy to diffuse. Generally, organic polymers with high dielectric constant, polarizing groups, and low glass transition temperature are used.

Lithium salts can provide lithium ions, in order to increase the concentration and mobility of lithium ions in the polymer system, lithium salts are usually selected with low lattice energy, high degree of anion charge delocalization, high dispersion constant, and good stability. Commonly used lithium salts are LiPF₆, LiClO₄, LiBF₄, LiBOB, LiTFSI and so on.

Additives can be organic liquids and organic small molecular substances, electrolytes, inorganic fillers or ionic liquids, etc., in order to improve the overall performance of the polymer solid electrolyte. Organic liquids, organic small molecular substances (such as oligomers) and electrolytes are also called plasticizers, which usually swell the polymer matrix into a gel state, which can greatly increase the ionic conductivity. Commonly used organic liquids include carbonates such as DMC, DEC, PC, EC, etc., and small organic molecules include PEG (polyethylene glycol), PEGDMA (polyethylene glycol dimethacrylate), and so on.

Inorganic fillers as additives can improve the interface performance between the electrolyte and the electrode, reduce the crystallinity and glass transition temperature of the polymer, and increase the conductivity of the electrolyte. Inorganic fillers can be divided into two categories: one is inert filler, which does not have the ability to conduct ions and does not directly participate in ion conduction, such as Al₂O₃, SiO₂, TiO₂, BaTiO₃, zeolite, clay, etc.; the other is active filler, usually Inorganic solid electrolytes, which have the ability to conduct ions, play a role in conducting ions and inducing electrochemical reactions, such as γ-LiAlO₂, Li₃N, LAGP, LATP, LLTO, LLZO, etc.

In summary, polymer solid electrolytes for lithium batteries refer to the addition of various lithium salts to polymers. The electrolyte system that uses additives to improve electrolyte performance can effectively avoid security issues , as the like lithium battery leakage, internal short-circuits, and flammability and explosion .