阅读说明：本技术 一种二氟磷酸锂的纯化方法 (Method for purifying lithium difluorophosphate ) 是由 徐辑亮 毛冲 戴晓兵 于 2019-09-17 设计创作，主要内容包括：本发明提供了一种二氟磷酸锂的纯化方法,包括以下步骤：S1：在惰性气体保护气氛下,用有机溶剂溶解二氟磷酸锂粗品,经过分子筛脱除水、精密过滤器过滤后得到水份小于5ppm、不溶物含量小于200ppm的二氟磷酸锂溶液；S2：向S1步骤得到的二氟磷酸锂溶液中加入脱酸剂,得到酸值(以HF计)低于10ppm的二氟磷酸锂溶液；S3：将S2步骤二氟磷酸锂溶液进行重结晶,得到杂质金属离子含量低于1ppm的二氟磷酸锂固体颗粒；S4：将S3步骤二氟磷酸锂干燥、破碎,得到水份、游离酸、不溶物、金属离子含量极低的二氟磷酸锂颗粒产品。该方法可以有效的将品质较差的二氟磷酸锂的水份、酸和金属杂质脱除,降低不溶物含量,提高二氟磷酸锂的产品品质。(The invention provides a purification method of lithium difluorophosphate, which comprises the following steps: s1: under the protection atmosphere of inert gas, dissolving a lithium difluorophosphate crude product by using an organic solvent, removing water by using a molecular sieve, and filtering by using a precision filter to obtain a lithium difluorophosphate solution with the water content of less than 5ppm and the insoluble content of less than 200 ppm; s2: adding a deacidification agent into the lithium difluorophosphate solution obtained in the step S1 to obtain a lithium difluorophosphate solution with an acid value (calculated by HF) of less than 10 ppm; s3: recrystallizing the lithium difluorophosphate solution obtained in the step S2 to obtain lithium difluorophosphate solid particles with impurity metal ion content lower than 1 ppm; s4: and (4) drying and crushing the lithium difluorophosphate obtained in the step S3 to obtain a lithium difluorophosphate granular product with extremely low water content, free acid content, insoluble content and metal ion content. The method can effectively remove moisture, acid and metal impurities of lithium difluorophosphate with poor quality, reduce the content of insoluble substances and improve the product quality of the lithium difluorophosphate.)

1. A method for purifying lithium difluorophosphate is characterized by comprising the following steps:

the method comprises the following steps:

S1: under the protection atmosphere of inert gas, dissolving a lithium difluorophosphate crude product by using an organic solvent, removing water by using a molecular sieve, and filtering by using a precision filter to obtain a lithium difluorophosphate solution with the water content of less than 5ppm and the insoluble content of less than 200 ppm;

S2: adding a deacidification agent into the lithium difluorophosphate solution obtained in the step S1 to obtain a lithium difluorophosphate solution with an acid value lower than 10 ppm;

S3: recrystallizing the lithium difluorophosphate solution obtained in the step S2 to obtain lithium difluorophosphate solid particles with impurity metal ion content lower than 1 ppm;

S4: and (4) drying and crushing the lithium difluorophosphate solid particles obtained in the step S3 to obtain lithium difluorophosphate particle products with extremely low water content, free acid content, insoluble content and metal ion content.

2. The method for purifying lithium difluorophosphate according to claim 1, wherein the organic solvent in step S1 is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or acetonitrile; the water content of the solvent is less than 15 ppm; the dissolving temperature is controlled at 10-60 ℃; the ratio of the solvent to the lithium difluorophosphate is 1:2-1: 5.

3. The method for purifying lithium difluorophosphate of claim 1, wherein the molecular sieve in step S1 is a lithiated 3A, 4A or 5A molecular sieve; precision filter core precision is at 0.1um-1 um.

4. the method of purifying lithium difluorophosphate of claim 1, wherein the deacidification agent in step S2 is hexamethyldisilazane, dicyclohexylcarbodiimide, N- (trimethylsilyl) ethylenediamine or nonamethyltrisilazane; the addition amount of the deacidification agent is 3-9 per mill; the deacidification temperature is controlled within 40-45 deg.C, and the deacidification time is not less than 30 min.

5. The method for purifying lithium difluorophosphate of claim 1, wherein the recrystallization in step S3 comprises vacuum distillation concentration, freeze crystallization, washing and centrifugal filtration.

6. The method for purifying lithium difluorophosphate as claimed in claim 5, wherein the vacuum degree of the vacuum distillation concentration is controlled to be-0.1 to-0.9 bar, and the concentration temperature is controlled to be 40 to 70 ℃.

7. The method for purifying lithium difluorophosphate of claim 5, wherein the freezing temperature of the frozen crystals is-10 to 40 ℃ and the cooling rate is 1 to 10 ℃/min.

8. The method for purifying lithium difluorophosphate as claimed in claim 5, wherein the washing solvent used in the washing centrifugal filtration process is one of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, and the water content is less than 5 ppm; the rotating speed of the centrifuge is 100-2000 r/min.

9. the method of purifying lithium difluorophosphate of claim 1, wherein the impurity metal ions include sodium ions, iron ions, nickel ions, chromium ions, potassium ions, calcium ions, lead ions, magnesium ions, cadmium ions, copper ions, aluminum ions, zinc ions, and arsenic ions.

10. The method for purifying lithium difluorophosphate as claimed in claim 1, wherein the drying vacuum degree in step S4 is controlled to be-0.1 to-0.9 bar, the drying temperature is controlled to be 40 to 90 ℃, and the drying time is 6 to 8 hours.

[ technical field ]

The invention relates to a purification method of lithium difluorophosphate, belonging to the technical field of lithium ion batteries.

[ background art ]

The lithium difluorophosphate used as the lithium ion battery electrolyte additive obviously improves the electrochemical performance. Research results show that the addition of lithium difluorophosphate into a lithium hexafluorophosphate electrolyte system can reduce electrode polarization, and simultaneously, the cycling stability and high-temperature storage performance of the battery at normal temperature and high temperature are obviously improved. In addition, the lithium difluorophosphate additive is beneficial to the diffusion and charge transfer of lithium ions on the positive and negative electrode interfaces. Therefore, the lithium difluorophosphate used as the lithium ion battery electrolyte additive has high industrial value.

Lithium difluorophosphate products inevitably have certain amounts of HF, H20 and other metal impurity ions and insoluble impurities introduced by undesirable or improper control of the operating environment during the actual production process.

wherein, HF catalyzes the hydrolysis of lithium hexafluorophosphate to accelerate the deterioration of the electrolyte of the lithium ion battery; meanwhile, the polymerization of the organic solvent is catalyzed, so that the viscosity of the electrolyte is increased, and the conductivity is reduced. LiF generated by hydrolysis increases the interface impedance of the electrode, so that the specific capacity, the cycle efficiency and the like of the battery are continuously reduced until the whole battery is damaged.

Wherein H₂o has bad influence on the performance of the lithium ion battery electrolyte, the higher the water content in the lithium ion battery electrolyte is, the performance of the battery such as charge and discharge, cycle efficiency and the like is rapidly reduced, and when the water content exceeds 0.1%, the lithium ion battery is completely damaged.

In the charging process, metal impurity ions are firstly inserted into the carbon negative electrode, so that the positions where lithium ions are inserted are reduced, and the reversible capacity of the lithium ion battery is reduced. The high concentration of metal impurity ions may also result in failure to form an effective passivation layer on the surface of the graphite electrode, causing the entire battery to fail.

in conclusion, the lithium difluorophosphate used as an additive obviously improves the electrochemical performance of the battery, but the lithium difluorophosphate with low quality cannot improve the electrochemical performance of the battery, but is caused by HF and H₂0 and the introduction of metal impurity ions lead to the failure of the battery performance. The invention discloses a purification method of lithium difluorophosphate, which can effectively remove water, acid and metal impurities in lithium difluorophosphate with poor quality, reduce the content of insoluble substances and improve the product quality of lithium difluorophosphate.

[ summary of the invention ]

Exists for the lithium difluorophosphate production processHF, H of₂o and metal ion impurities are removed in sequence according to the sequence of removing water, removing acid and removing metal ions, and a refined lithium difluorophosphate product with the water content of less than 5ppm, the acid value (calculated by HF) of less than 50ppm, the metal ions of less than 1ppm and the insoluble substances of less than 200ppm is obtained. The lithium difluorophosphate purification method specifically comprises the following steps:

S1: under an inert atmosphere, dissolving lithium difluorophosphate by using an organic solvent, removing water by using a molecular sieve, and filtering by using a precision filter to obtain a lithium difluorophosphate solution with the water content of less than 5ppm and the insoluble content of less than 200 ppm;

S2: adding the lithium difluorophosphate solution obtained in the step S1 into a deacidification agent to obtain a lithium difluorophosphate solution with an acid value (calculated by HF) of less than 10 ppm;

s3: recrystallizing the lithium difluorophosphate solution obtained in the step S2 to obtain lithium difluorophosphate solid particles with the impurity metal ion content lower than 1 ppm;

S4: and (4) drying and crushing the lithium difluorophosphate obtained in the step S3 to obtain a lithium difluorophosphate granular product with extremely low water content, free acid content, insoluble content and metal ion content.

In the invention, the organic solvent in step S1 is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or acetonitrile; the water content of the solvent is less than 15 ppm; the dissolving temperature is controlled at 10-60 ℃; the ratio of the solvent to the lithium difluorophosphate is 1:2-1: 5.

in the invention, the molecular sieve in the step S1 is a lithiated 3A, 4A or 5A molecular sieve; precision filter core precision is at 0.1um-1 um.

In the invention, the deacidification agent in the step S2 is hexamethyldisilazane, dicyclohexylcarbodiimide, N- (trimethylsilyl) ethylenediamine or nonamethyltrisilazane; the addition amount of the deacidification agent is 3-9 per mill; the deacidification temperature is controlled within 40-45 deg.C, and the deacidification time is not less than 30 min.

In the present invention, the recrystallization in step S3 includes vacuum distillation concentration, freeze crystallization, washing and centrifugal filtration.

In the invention, the vacuum degree of vacuum distillation concentration is controlled to be-0.1-0.9 bar, and the concentration temperature is 40-70 ℃;

In the invention, the freezing temperature of the frozen crystal is-10-40 ℃, and the cooling speed is 1-10 ℃/min.

in the invention, the washing solvent in the washing centrifugal filtration process is one of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, and the water content is less than 5 ppm; the rotating speed of the centrifuge is 100-2000 r/min.

In the invention, the impurity metal ions comprise sodium ions, iron ions, nickel ions, chromium ions, potassium ions, calcium ions, lead ions, magnesium ions, cadmium ions, copper ions, aluminum ions, zinc ions and arsenic ions.

In the invention, the vacuum degree of the drying in the step S4 is controlled to be-0.1-0.9 bar, the drying temperature is controlled to be 40-90 ℃, and the drying time is 6-8 h.

The method can effectively remove moisture, acid and metal impurities of lithium difluorophosphate with poor quality, reduce the content of insoluble substances and improve the product quality of the lithium difluorophosphate.

[ detailed description of the invention ]