The most important components in a secondary battery are electrode materials, separators, and electrolytes. The main function of the electrolyte is to conduct ions to ensure that the ions move between the anode and cathode at a certain rate during the charging and discharging process of the battery to form the entire electrical circuit to generate current. As an important medium for ion conduction in secondary batteries, electrolyte has an important impact on improving the performance of secondary batteries such as cycle stability and safety. Battery electrolytes come in many forms, such as non-aqueous liquids (organic solvents and ionic liquids), colloids, organic solids, and inorganic solids. At present, secondary battery products mainly use non-aqueous liquid electrolytes. The non-aqueous liquid electrolyte usually adopts organic solvent electrolyte, that is, it is prepared from high-purity organic solvent, electrolyte salt, necessary additives and other raw materials according to a certain proportion. However, with the development of secondary battery applications, new functional electrolyte materials (gel polymer electrolytes, solid electrolytes) have gradually occupied important fields, and many functionalized batteries have been applied.
Figure 1. Electrolyte in battery
- Lithium-ion battery: Lithium-ion battery has the advantages of high energy density, high output voltage, long cycle life, and low environmental pollution, and has important applications in electronic products and automobiles. In lithium-ion batteries, the electrolyte mainly plays the role of conducting lithium ions. Lithium-ion battery electrolyte is mainly composed of conductive lithium salt with high non-localized charge, organic solvent with high dielectric constant, and electrolyte additive with good compatibility. This kind of non-aqueous electrolyte prepared by dissolving lithium salt as a solute in an organic solvent can significantly affect the voltage and conductivity of the battery.
- Secondary flexible batteries: Colloidal or solid electrolytes can be used as flexible materials in the field of secondary flexible batteries. Such batteries have stronger conductivity, better material fusion and improved safety. For rechargeable secondary flexible batteries, the advantages of gel polymer electrolytes, such as mechanical stability, flexibility, and resistance to leakage, endow this type of electrolyte materials with broader applications.
- Functional secondary battery: According to the requirements of different application fields, secondary batteries can be divided into flame-retardant batteries, high-voltage batteries, low-temperature batteries, etc. According to different application requirements, by changing the electrolyte to adjust the performance of the battery, a multifunctional secondary battery can be obtained. For example, the local high-concentration electrolyte will enhance the inter-ionic force with the increase of salt concentration, and has the advantages of wide electrochemical window, high rate capability, high ion migration number, good wettability to the electrode, and low viscosity. Such electrolytes can be used to prepare high-performance functionalized secondary batteries.
- Anh Le Mong, Qing Xuan Shi, Hyungjoon Jeon, Yun Sheng Ye, Xiao Lin Xie, Dukjoon Kim. Tough and Flexible, Super Ion-Conductive Electrolyte Membranes for Lithium-Based Secondary Battery Applications [J]. Adv. Funct. Mater., 2020, 31(12), 2008586.