As the transmission medium of ion movement, electrolyte is generally composed of solvent and lithium salt. Molten salt electrolyte is also a viable electrolyte system. The liquid electrolyte is made of organic solvents, the solid electrolyte is made of inorganic compounds or polymers, and the polymer electrolyte is made of polymers and lithium salts. Polyelectrolytes (Polyelectrolytes) are also considered polymer electrolytes. Generally speaking, the electrolyte solution usually refers to a liquid electrolyte.
The electrodes of lithium ion batteries use materials with lithium ion intercalation/deintercalation capabilities, which are separated by a separator before they are immersed in the liquid electrolyte. During the charging process, the liquid electrolyte transports lithium ions from the positive electrode to the negative electrode, and the discharge process is the opposite. Porous electrodes using transition metal oxides and carbon as active materials, respectively, are used as the positive and negative electrodes of lithium rechargeable batteries. Because of this, the electrolyte not only provides lithium ions by penetrating the micropores, but also exchanges lithium ions on the surface of the active material. The working voltage and energy density of lithium rechargeable batteries are determined by the positive and negative materials. The choice of electrolyte is also very important. It is very necessary for a high-performance battery to obtain excellent ionic conductivity between the electrodes.
Table 1 shows the characteristics of lithium rechargeable battery electrolyte.
1) Since lithium primary batteries were first developed in the 1970s, liquid electrolytes made by dissolving lithium salts in organic solvents have been widely used. Most lithium rechargeable batteries in use now also use organic electrolytes.
2) Ionic liquid electrolyte is composed of molten salt whose melting point is below room temperature, and is used together with lithium salt. Because they do not contain flammable and combustible organic solvents, they are considered to be used to make safer batteries.
3) The solid polymer electrolyte is prepared by dissolving lithium salt into a highly polar polymer, but because the conductivity of this electrolyte is too low, it has not been used in actual battery production.
4) The gel polymer electrolyte is composed of a polymer matrix and a liquid electrolyte, and its performance is between the polymer electrolyte and the liquid electrolyte. Lithium ion batteries using gel polymer electrolytes are called polymer lithium ion batteries. The characteristics of liquid electrolyte, ionic liquid electrolyte, polymer electrolyte, and gel polymer electrolyte are discussed above. We will also pay attention to other components that have an important impact on the electrochemical performance and safety of the battery, such as separators, binders, conductive agents, and current collectors.
|Liquid electrolyte||Ionic liquid electrolyte||Solid polymer electrolyte||Gel polymer electrolyte|
|composition||Organic solvent + lithium salt||Room temperature ionic liquid + lithium salt||Polymer + lithium salt||Organic solvent + polymer + lithium salt|
|Ion conductivity||high||high||Low||Relatively high|
|Low temperature performance||Relatively good||Difference||Difference||Relatively good|
|Thermal stability||Difference||good||very good||Relatively good|