Harmful treatment methods of lithium battery electrolyte
electrolyte is the 'blood' of lithium-ion batteries. It conducts electrons between the positive and negative electrodes in the battery. It is a guarantee for lithium-ion batteries to obtain the advantages of high voltage and high specific energy. Electrolyte is generally prepared from high-purity organic solvents, electrolyte lithium salt (lithium hexafluorophosphate, LiFL6), necessary additives and other raw materials under certain conditions in a certain proportion.
Invasion route: inhalation, ingestion, transdermal absorption.
Health hazards: This product is a mild irritant and anesthetic. It may cause headache, dizziness, weakness, nausea, dyspnea, etc. after inhalation. Liquid or high-concentration vapor is irritating. Oral irritation of the gastrointestinal tract. Long-term repeated contact with the skin is irritating.
②Toxicological data and environmental behavior
Toxicity: It is estimated that it can enter the body through the gastrointestinal tract, skin and respiratory tract and show moderate toxicity. It is more irritating than dimethyl carbonate.
Acute toxicity: LD501570mg/kg (rat oral); human inhalation 20mg/L (vapor) u0026 TImes; 10 minutes, tearing and nasal mucosal irritation.
Reproductive toxicity: 11.4mg/kg (pregnant mice) in the abdominal cavity of hamsters, which has obvious teratogenic effects.
Hazard characteristics: flammable, and may cause burning when exposed to open flames and high heat. Its vapor is heavier than air and can spread to a considerable distance in a lower place, and it will cause back-combustion when it encounters an open flame.
Combustion (decomposition) products: carbon monoxide and carbon dioxide.
Electrolyte treatment technology
1. Recovery of electrolyte under liquid nitrogen conditions
Tong Dongge uses propylene carbonate to treat electrolyte in the process of lithium battery pack recovery ( PC) Recycle the electrolyte; PC has the highest rate of extraction, and the electrolyte can be completely extracted after 2 hours. In order to avoid fire and explosion, under the protection of liquid nitrogen, the waste battery is cut open and the active material is taken out. The active material is soaked in an electrolyte solvent such as PC for a period of time to leach out the electrolyte, and then filtered in an inert atmosphere. PC can be recycled and reused many times. The recovered electrolyte is purified according to the situation, and LiPF6 is recovered.
2. High-temperature pyrolysis and volatilization to generate hydrolysate
At this stage, most of the experimental studies do not pay enough attention to the electrolyte, and high-temperature pyrolysis or roasting lithium batteries are used. Low (around 180C), allowing the electrolyte to decompose and volatilize freely. During the pyrolysis process, the electrolyte generates toxic gases such as HF and LiF. In the large-scale lithium battery recovery process, it is necessary to increase the secondary treatment of the exhaust gas.
3. Alkaline solution treatment
Zhao Dongjiang and others use dilute alkaline water to soak the single cell, the HF generated by the electrolyte will react as follows: HF
+ NaOH→NaF+H20, and then crush the battery. This treatment method can effectively reduce the generation of HF, but it cannot realize the recovery of fluorine-containing electrolyte.
4. NMP treatment electrolyte
The liquid electrolyte is dispersed and adsorbed in the gap between the electrode and the diaphragm. Therefore, you can choose an appropriate solvent [acetonitrile, N-methylpyrrolidone ( NMP)] is leached at 50C. After separating the solid from the solvent, the solvent is recovered and recycled by vacuum distillation, and the rest is pure electrolyte. The solvent for vacuum distillation should have a boiling point lower than the decomposition temperature of the electrolyte lithium salt (about 80C), and it should be anhydrous operation. According to this method, the maximum recovery value of the electrolyte can be obtained by economical and environmentally friendly means.
Organic solvents are the main part of the electrolyte and are closely related to the performance of the electrolyte. Generally, high-dielectric constant solvents and low-viscosity solvents are used in combination; commonly used electrolyte lithium salts include lithium perchlorate, lithium hexafluorophosphate, Lithium tetrafluoroborate, etc., but in terms of cost and safety, lithium hexafluorophosphate is the main electrolyte used in commercial lithium-ion batteries; the use of additives has not been commercialized, but it has always been one of the research hotspots of organic electrolytes.
Since the successful development of lithium-ion battery electrolyte in 1991, lithium-ion batteries have quickly entered the market of electronic information products such as notebook computers and mobile phones, and have gradually occupied a dominant position. At present, the technology of lithium-ion battery electrolyte products is also in further development. In terms of the research and production of lithium battery pack electrolyte, the international companies engaged in the research and development of lithium-ion battery electrolyte are mainly concentrated in Japan, Germany, South Korea, the United States, Canada and other countries. Japan’s electrolyte is the fastest growing. The largest market share.
The commonly used electrolyte systems in China include EC+DMC, EC+DEC, EC+DMC+EMC, EC+DMC+DEC, etc. Different electrolytes use different conditions, have different compatibility with the positive and negative electrodes of the battery, and have different decomposition voltages. The electrolyte composition is 1mol/L LiPF/EC+DMC+DEC+EMC, which has better cycle life, low-temperature performance and safety performance than ordinary electrolytes, which can effectively reduce gas generation and prevent battery swelling. The decomposition voltages of EC/DEC and EC/DMC electrolyte systems are 4.25V and 5.10V, respectively.
According to Bellcore research, LiPF/EC+DMC has good compatibility with carbon anodes. For example, in LixC6/LiMnO4 batteries, using LiPF/EC+DMC as the electrolyte, it can be stable to 4.9 at room temperature. V, 55℃ can be stabilized to 4.8V, and its liquid phase range is -20℃~130℃. The outstanding advantages are a wide temperature range, good compatibility with carbon anode, high safety index, good cycle life and discharge characteristic.
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