Main Components of Lithium Battery Electrolyte
2021-11-06
Lithium battery electrolyte is the carrier of ion transport in the battery, which is generally composed of lithium salt and organic solvent. Electrolyte plays the role of conducting ions between the positive and negative electrodes of lithium-ion battery, which is the guarantee for lithium-ion battery to obtain the advantages of high voltage and high specific energy. Electrolyte is generally made up of high-purity organic solvent, electrolyte lithium salt, necessary additives and other raw materials in a certain proportion under certain conditions.
1. Vinyl carbonate (molecular formula: C3H4O3)
Transparent colorless liquid (>35℃), crystalline solid at room temperature. Boiling point: 248℃/760mmHg, 243-244 ℃/740mmHg; Flash point: 160℃; Density: 1.3218; Refractive index: 1.4158 (50℃); Melting point: 35-38℃; This product is a good solvent for Polyacrylonitrile and polyvinyl chloride. It can be used as drawing liquid on textile; It can also be directly used as a solvent for removing acid gas and an additive for concrete; It can be used as pharmaceutical components and raw materials in medicine; It can also be used as plastic foaming agent and stabilizer of synthetic lubricating oil; In the battery industry, it can be used as an excellent solvent for lithium battery electrolyte.
2. Propylene carbonate (molecular formula: C4H6O3)
Colorless, odorless, or light yellow transparent liquid, soluble in water and carbon tetrachloride, miscible with ether, acetone, benzene, etc. it is an excellent polar solvent. It is mainly used in polymer operation, gas separation process and electrochemistry. In particular, it is used to absorb carbon dioxide from natural gas and synthetic ammonia raw materials in petrochemical plants. It can also be used as plasticizer, spinning solvent, olefin and aromatic extractant, etc.
3. Diethyl carbonate (molecular formula: C5H10O3)
Colorless liquid with slight smell; Steam pressure 1.33kPa/23.8℃; Flash point 25℃ (combustible liquid can volatilize into vapor and run into the air. With the increase of temperature, volatilization accelerates. When the mixture of volatile vapor and air can flash sparks in contact with the fire source, this short combustion process is called flash combustion, and the lowest temperature at which flash combustion occurs is called flash point. The lower the flash point, the greater the risk of fire.); Melting point -43℃; Boiling point 125.8℃; Solubility: insoluble in water, miscible in alcohol, ketone, ester and other organic solvents; Density: relative density (water=1)1.0; Relative density (air=1) 4.07; Stability: stable; Hazard marking 7 (flammable liquid); Main uses: used as solvent and organic synthesis.
4. Dimethyl carbonate (molecular formula: C3H6O3)
(dimethyl carbon, DMC) is a chemical raw material with non-toxic, excellent environmental protection performance and wide application. It is an important organic synthesis intermediate. Its molecular structure contains carbonyl, methyl and methoxy functional groups. It has a variety of reaction properties. It has the characteristics of safe, convenient, less pollution and easy transportation in production. Dimethyl carbonate is a promising "green" chemical product due to its low toxicity.
DMC has excellent solubility, narrow melting and boiling point range, large surface tension, low viscosity, small dielectric constant, high evaporation temperature and fast evaporation speed. Therefore, it can be used as a low toxic solvent in coating industry and pharmaceutical industry. It can be seen from table 1 that DMC is not only less toxic, but also has the characteristics of high flash point, low vapor pressure and high lower explosion limit in air. Therefore, DMC is a green solvent integrating cleanliness and safety.
5. Methyl ethyl carbonate
Molecular weight: 104.1, density 1.00g/cm3, colorless transparent liquid, boiling point 107 ℃, melting point -14℃. It is a high-tech and high value-added chemical product rising in recent years. It is an excellent solvent for lithium-ion battery electrolyte. It is the latest product extended with the increase of dimethyl carbonate and lithium-ion battery production. Because it has methyl and ethyl at the same time, it also has dimethyl carbonate Diethyl carbonate is also a solvent for special spices and intermediates. Due to the imbalance of methyl ethyl, the product is unstable and not suitable for long-term storage.
6. Lithium hexafluorophosphate
White crystal or powder, relative density 1.50. Deliquescence is strong; It is easily soluble in water and also soluble in organic solvents such as low concentration methanol, ethanol, acetone and carbonate. Decompose when exposed to air or heated. When exposed to the air or heated, lithium hexafluorophosphate decomposes rapidly in the air due to the action of water vapor, releasing PF5 and producing white smoke.
7. Phosphorus pentafluoride
Phosphorus pentafluoride (chemical formula: PF5) is a phosphorus halogen compound. The oxidation number of phosphorus atom is +5 and contains a three center four electron bond. Phosphorus pentafluoride is a colorless odor gas at normal temperature and pressure, which has strong irritation to skin, eyes and mucous membrane. It is a highly active compound, which will violently produce toxic and corrosive hydrogen fluoride white smoke in humid air. Phosphorus pentafluoride is used as a catalyst for polymerization.
8. Hydrofluoric acid
Colorless transparent fuming liquid. It is an aqueous solution of hydrogen fluoride gas. Weakly acidic. Pungent smell. It reacts with silicon and silicon compounds to form gaseous silicon tetrafluoride, but it does not corrode plastics, paraffin, lead, gold and platinum. It is miscible with water and ethanol. The relative density is 1.298. 38.2% hydrofluoric acid is an azeotropic mixture with an azeotropic point of 112.2℃. Toxic, minimum lethal dose (rat, abdominal cavity) 25mG/kg. It is corrosive and can strongly corrode metals, glass and silicon containing objects. Such as inhalation of steam or contact with the skin can form ulcers that are difficult to heal.
The main electrolytes used in lithium batteries are lithium perchlorate, lithium hexafluorophosphate, etc. However, the battery made of lithium perchlorate has poor low-temperature effect and explosion risk, while the battery made of lithium fluoride salt has good performance, no explosion risk and strong applicability, especially the battery made of lithium hexafluorophosphate, In addition to the above advantages, the disposal of waste batteries in the future is relatively simple and friendly to the ecological environment.
Issued by Alex, R&D, Nov. 6, 2021.
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