Introduction of lithium ion battery electrolyte classification

The electrolyte is used to transfer charge between the positive and negative electrodes, and should be conductive to ions and insulated from electrons. It has an extremely important impact on battery cycle performance, operating temperature range, and battery durability. Regarding lithium-ion batteries, the composition of the electrolyte involves at least two aspects: solvent and lithium salt. A. The choice of solvent for liquid electrolyte is mainly based on three aspects of property requirements. That is, dielectric constant, viscosity, and electron donor properties of the solvent. Generally speaking, a high dielectric constant is conducive to the dissociation of the lithium salt, while a strong electron donor ability is conducive to the dissolution of the electrolyte salt. The so-called electron donor property of the solvent is the inherent electron loss ability of the solvent molecule, and its ability determines the solvation ability of the cation of the electrolyte. Low viscosity can increase the mobility of ions and help improve conductivity. Currently, binary and multi-component mixed solvents which are a mixture of two or more solvents are usually used. Common organic solvents include ether, alkylcarbonate, lactone, ketal and so on. Lithium salt is mainly used to supply effective carriers. The choice of lithium salt generally follows the following principles: good stability (compatibility) with the positive and negative materials, that is, during storage, the electrochemical reaction speed at the interface between the electrolyte and the active material is small, which makes the battery self-discharge The capacity loss is minimized; the specific conductivity is high, and the ohmic pressure drop of the solution is small; the safety performance is high, non-toxic, and non-polluting. Commonly used lithium salts are as follows: lithium hexafluoroarsenate (LiPF6), LIAsF6 will release toxic arsenic during charge and discharge, and the price is relatively expensive. Lithium hexafluorophosphate (LiPF6), which has been widely used in commercial batteries, has high conductivity and good compatibility with carbon materials. The disadvantage is that it is relatively expensive, has poor stability in solid state, and is very sensitive to water. Lithium trifluoromethanesulfonate LiCF3SO2 has good stability, but its conductivity is only half of the liquid electrolyte based on LiPF6. Lithium tetrafluoroborate (LiBF4) and lithium perchlorate (LiCl04) are both widely used salts. However, lithium perchlorate-based imide lithium salts, typically lithium bisfluorosulfonphthalimide (LiN(CF3SO2)2), have electrical conductivity comparable to very dry LiPF6 electrolyte, and are more stable than FLiCF3SO2. .Solid Electrolyte Solid electrolyte, also known as super ion conductor or fast ion conductor. It refers to a type of solid ion conductive material whose ionic conductivity is close to (or in some cases exceeds) melting and electrolyte solution. It is a type of solid electrolyte. The peculiar solid material between solid and liquid is an abnormal state of matter, in which some atoms (ions) have a mobility close to that of liquid, while other atoms maintain their spatial structure (arrangement). This liquid One-solid two-phase, and its broad application prospects in various fields such as energy (including emergence, storage and energy saving), metallurgy, environmental protection, electrochemical devices, etc., have attracted physicists, chemists and materials. The wide attention of scientists. The polymer solid electrolyte is a solid electrolyte material formed by complexing a polymer containing solvable polar groups with a salt. In addition to showing the properties of common conductivity systems such as semiconductors and ionic solutions , It also has the plasticity that inorganic solid electrolyte can't reach. This feature makes polymer solid electrolyte show three advantages in application: film of any shape and thickness. So although the room temperature conductivity of polymer electrolyte is not high , Which is 2 to 3 orders of magnitude lower than inorganic ones. The internal resistance of the battery is greatly reduced due to the processing into a very thin film, so that the low conductance can be compensated by increasing the area/thickness ratio; tightness-complete contact with the electrode, Increase the charge and discharge current; Responsiveness-can withstand pressure changes well during the charge and discharge process and adapt to changes in electrode volume. The polymer solid electrolyte is light in weight, pressure resistant, shock resistant, fatigue resistant, non-toxic and non-corrosive. The electrochemical stability exhibited when forming a battery with electrodes has created a broader prospect for its application. At present, scientists at home and abroad are working on making it applicable to energy storage, electrochemical components, sensors, and many other researches. , Has become the strongest competitor in the development of high specific energy lithium-ion batteries. 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