Electrolytes are compounds that conduct electricity when dissolved in aqueous solution or a molten state. They are substances that are bonded by ionic bonds or polar covalent bonds. Ionic compounds can conduct electricity in aqueous solution or a molten state. Some covalent compounds can also conduct electricity in aqueous solution, but there are also solid electrolytes, whose conductivity comes from the migration of ions in the lattice.
- Electrolytic cell: The device that converts electrical energy into chemical energy is called electrolytic cell. The direct current is passed through the electrolyte solution, so that the electrolyte has a chemical reaction on the electrode, and the desired product can be prepared. The electrolysis process must have electrolyte, electrolytic cell, DC power supply system, analysis and control system, and product separation and recovery equipment. The electrolysis process should use low-cost raw materials as far as possible, improve the selectivity of the reaction, reduce the formation of by-products, shorten the production process, and facilitate the recovery and purification of the products. At present, the electrolysis process has been widely used in non-ferrous metal smelting, Chlor-alkali and inorganic salt production, organic chemistry, and other industries.
- Electrolyte battery:
(1) Lithium-ion organic liquid battery: The organic liquid electrolyte used in a lithium-ion battery is an electrolyte solution formed by dissolving an appropriate lithium salt in the organic non-proton mixed solvent. At present, the electrolyte used in lithium-ion battery generally chooses LiPF6 as lithium salt, and the solvent is a mixed solvent composed of vinyl carbonate (EC) and dimethyl carbonate (DMC) or diethyl carbonate (DEC).
Figure 1. Organic lithium ionic liquid battery
(2) Solid electrolyte battery: Solid electrolyte solves the problem of solid electrolyte interface film formed by liquid electrolyte in the process of charge and discharge, and greatly improves the cyclability and service life of the battery.
Figure 2. Solid-state lithium battery
(3) Alkaline electrolyte fuel cell: Alkaline electrolyte fuel cell is a kind of electrochemical energy storage device which can convert chemical energy stored in fuel and oxygen into electric energy directly. Due to the use of the alkaline system, the electrocatalytic performance of cathode and anode is greatly improved, and many non-platinum metals and oxides which can not be used in strong acid medium become optional catalysts, and the change of electroosmosis direction also inhibits the penetration of methanol from anode to cathode.
Figure 3. Alkaline fuel cell
According to the degree of ionization, strong electrolytes can be divided into strong electrolytes and weak electrolytes. Strong electrolytes can all be ionized, while weak electrolytes can only be partially ionized.
- Strong electrolyte: It is an electrolyte that is almost completely ionized in aqueous solution or a molten state. It is completely ionized and there is no ionization equilibrium. The general strong electrolytes are strong acids, strong bases, active metal oxides, and most salts, such as sulfuric acid, hydrochloric acid, calcium carbonate, copper sulfate and so on.
- Weak electrolyte: It is an electrolyte that is not completely ionized in an aqueous solution or a molten state. The conductive properties of strong and weak electrolytes have nothing to do with the solubility of the substance. General weak electrolytes have weak acids, weak bases and a small number of salts, such as acetic acid, ammonia monohydrate, lead acetate, mercuric chloride. Besides, water is a very weak electrolyte.
- Xu, K. (2004), "Nonaqueous liquid electrolytes for lithium-based rechargeable batteries." Chem. Rev 104, 4303-4418.
- Gauthier, M. et al. (2015), "Electrode–electrolyte interface in Li-ion batteries: current understanding and new insights." J. Phys. Chem. Lett. 6, 4653-4672.