The important role of the filter washing and drying machine in the safe production of lithium hexafluorophosphate

2023/03/26


Lithium hexafluorophosphate is one of the core materials of lithium-ion batteries. The quality of the product determines the charging and discharging performance, service life and safety of lithium-ion batteries. The performance of the electrolyte prepared by lithium hexafluorophosphate and organic carbonate solvents directly affects the charge and discharge capacity, cycle life and safety of the lithium-ion secondary battery; due to its strong hygroscopicity, it is easily decomposed in the air , its preparation conditions are very strict, and the packaging and storage environment also have strict requirements. It decomposes into acid when it encounters water, which has a corrosive effect on human tissue and cannot be directly contacted. It must be stored in an airtight container. When using must be in humidity<Operate in a dry environment of 10ppm to prevent decomposition.

The commonly used purification methods of LiPF6 are mainly thermal vacuum drying method and dissolution recrystallization method. The dissolution recrystallization method is to dissolve LiPF6 in ether, dimethyl carbonate or diethyl carbonate at a certain temperature, centrifuge to remove insoluble matter, and then lower the temperature. , so that LiPF6 will recrystallize from the organic solvent, and the LiPF6 crystal obtained by filtration will be vacuum-dried to obtain the final product, as disclosed in CN1884046. This purification method, but this method is relatively complicated to operate and cannot be produced continuously. And when LiPF6 is purified, the recrystallization product will entrain certain organic solvents, which affects the purity of the product, and the use of a large amount of organic solvents in the purification leads to increased production costs, so it is difficult to apply LiPF6 to large-scale production. In addition, CN1462722 discloses a A method of using acid gas to remove moisture in LIPF6. On the one hand, this method cannot remove hydrogen fluoride in LiPF6 crude product, and introduces acid gas impurities.

Compared with the above methods, the thermal vacuum drying method is to directly heat and purify the LiPF6 crude product in a vacuum state, which is a purification method suitable for the large-scale production of LiPF6, and can avoid the secondary pollution of LiPF6 in the dissolution recrystallization method The main problem of the thermal vacuum drying method is how to avoid the decomposition of LiPF6 during the heating process and each particle of the LiPF6 crude product is fully exposed to the vacuum environment, so that there is no inclusion of hydrogen fluoride in the final LiPF6 product , so that the content of hydrogen fluoride in the LiPF6 product is less than 80ppm.


However, due to the toxicity of lithium hexafluorophosphate, it must be strictly managed during the production and management of lithium hexafluorophosphate, and more importantly, choose the most suitable lithium hexafluorophosphate production equipment.

In order to overcome the various problems encountered in the traditional lithium hexafluorophosphate crystallization filtration and drying, and at the same time meet the transformation of the chemical industry to high quality, high value-added, multi-variety, and small batches. Wuxi ZhangHua Machinery Co., Ltd. successfully developed and produced lithium hexafluorophosphate filtration washing and drying All-in-one machine (patent number: 202122464595.4).

The new technology relates to the field of separation and purification of lithium battery electrolytes. It uses nitrogen pressure filtration and pulse vacuum low-temperature drying to remove HF and impurities in crude lithium hexafluorophosphate products. It provides a high-efficiency, safe and continuous production of six A special device for lithium oxyphosphate purification and drying.

Lithium hexaoxophosphate purification conical filter washing and drying machine working principle

Lithium hexafluorophosphate purified conical filter washing and drying machine has a barrel-cone structure, and a heating jacket is installed on the circular body and the lower cone to heat or cool the material. A hollow shaft and a variable-angle variable-conductor are installed inside the multi-function machine. The hollow spiral stirring device is used for mold mixing, which stirs and lifts the material, and pushes out the material when it is discharged. A conical filtering device with a relatively complex structure is installed in the lower cone, and a specially designed non-dead angle quick-opening discharge device or a non-dead angle pneumatic discharge ball valve is installed at the bottom of the equipment.

In the reaction stage, the reaction materials are added from the top. The unique stirring structure can make the materials evenly stirred in the machine, and the materials are heated or cooled simultaneously through the cylinder jacket, cone jacket, hollow shaft and hollow ribbon, so that The material fully reacts in the machine. In the filtration stage, the machine can filter and dry the material in the machine by pressurizing or vacuuming, and add washing liquid, so that the material can be automatically repulped and washed several times in the machine, and then pressed dry after meeting the washing requirements. In the drying stage, the cylinder jacket, cone jacket, hollow shaft, and hollow ribbon heat the material at the same time and vacuumize the top, vacuum-tightly dry the material at low temperature, and automatically seal and discharge the material after drying.


Technical Improvement of Lithium Hexafluorophosphate Purification Conical Filter Washing and Drying Machine
(1) Crystallization mother liquor and lithium hexafluorophosphate crystals are sealed and filtered for efficient separation, effectively reducing the content of impurity metal ions.
Conventional thermal drying method is widely used, but this method takes a long time to dry crystals, and has defects such as incomplete drying, and HF in the product cannot be removed effectively and quickly, thereby affecting product quality. The purity of the lithium hexafluorophosphate product obtained through filtration and purification is greater than 99.9%, and the process has high safety, the mother liquor can be recycled, and the cost is low.

(2) Fully enclosed operation, operated under the protection of positive oxygen pressure.
Lithium hexafluorophosphate is easy to decompose when it meets water. Because of its strong hygroscopicity, it is easy to decompose in the air, and its preparation conditions are also very strict. This requires that the production process of lithium hexafluorophosphate involves high purity, low temperature, no water and dust. , therefore, all processes in the system are carried out under the protection of inert gas. The preferred inert gas is nitrogen, and the system is filled with nitrogen to ensure positive pressure in the system, which can effectively prevent air from contacting the product.


(3) In the drying process, multi-interval and multi-temperature heating is adopted: in the early stage of drying, low temperature and slow heating are adopted to remove residual acid on the surface of the crystal; the time of the high-heat drying section in the later stage is reduced to effectively separate free sulfur, and the degree of decomposition of LPF6 is reduced to lowest


(4) The nitrogen pulse vacuum drying method is adopted in the later stage of drying, which shortens the dry explosion time of LiPF6 crystals, makes the drying uniform, improves the drying efficiency and quality, and does not accumulate or block materials in the drying chamber after drying.
The material is forced to be heated in the cone-shaped body, so that the heat exchange between the material and the heating ribbon and the wall is completed when the material moves irregularly in all directions, and the purpose of mixing and drying is achieved in a short time under vacuum. The new pulse mixing design uses high-pressure nitrogen to impact the materials and mix them quickly. The mixing of the materials is more rapid and uniform, and the acid inside the product crystal and a small amount of residual acid on the surface can be quickly removed. Compared with the traditional thermal drying method, nitrogen pulses Direct air drying can greatly shorten the drying time, and at the same time reduce the content of free ions in the product, effectively remove the HF inclusions, improve product quality, and be more conducive to production operations.


(5) The thermal stability of lithium hexafluorophosphate is worse than that of other lithium salts. It can be decomposed into LiF and PF5 in a small amount at 60°C. After the free acid index meets the requirements, perform rapid cooling to reduce the influence of the high temperature zone on the insoluble matter.

(6) Both the heat source and the cold source use a heat conduction oil mold temperature machine with precise temperature control
The hot oil mold temperature machine obtains low-pressure and high-temperature heat medium, which is easy to adjust, uniform heating, and can meet the precise process temperature; when the temperature of the heat transfer oil is higher than 80 ℃, it must be isolated from the air, otherwise the heat transfer oil will be rapidly vaporized and deteriorated. Heat transfer oil is flammable, and effective fire prevention measures should be set.

(7) Air-dry double-end mechanical seal is adopted.
Replace the traditional "liquid blocking" principle with "gas blocking", that is, replace the sealing liquid with pressure with sealing gas to ensure "zero escape" of the process medium; the whole set of seals operates without contact, and its power consumption is only that of traditional double-end faces 5% of the seal, the service life is more than 5 times longer than the traditional seal: the auxiliary system with simple structure ensures that the process medium is not polluted and the process medium does not leak to the atmosphere, completely getting rid of the traditional double-end mechanical seal on the cooling water and oil system Dependence, the sealing gas adopts industrial nitrogen or industrial instrument air, and its pressure is 0.15~0.2MPa higher than that of the medium.
(8) Automatic control system, intelligently able to check the operating status of the equipment and the dryness of the material; no manual operation is required to frequently connect the equipment pipeline, reduce labor intensity, use hot nitrogen to isolate the material from the air, and keep the acidity of the product stable, due to the whole process Airtight transportation, so the product quality is more stable and the operation is safer and more convenient.



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