A method for purifying crude lithium difluorophosphate solid

Abstract

The present application relates to the field of chemical industry, and discloses a method for purifying crude lithium difluorophosphate solid, comprising the following steps: (1) adding a solvent to the crude lithium difluorophosphate to fully dissolve it, thereby obtaining a crude lithium difluorophosphate solution; (2) adding a dehydrating agent to the crude lithium difluorophosphate solution, heating and stirring, and fully dehydrating it; (3) passing the dehydrated solution through a reactor containing a metal adsorbent for cyclic reaction, concentrating and drying to obtain a high-purity lithium difluorophosphate solid. The metal adsorbent described in step (3) comprises a chelating agent A and a chelating agent B. The purification method of the present invention can obtain a low-water, low-metal-ion, high-purity lithium difluorophosphate solid. The high-purity lithium difluorophosphate solid is applied to the field of lithium-ion batteries, and can enhance the low-temperature resistance, chemical stability, cycle characteristics, electrical conductivity, and high-temperature storage performance of the battery.

Description

Technical Field

[0001] The invention relates to the technical field of chemical engineering, in particular to a method for purifying crude lithium difluorophosphate solid. Background Art

[0002] The proper use of a small amount of certain substances as functional additives in lithium-ion battery electrolytes is one of the most effective and economical ways to improve the performance of lithium-ion batteries. Generally, without significantly increasing the cost of the electrolyte, the use of a small amount of additives (usually less than 5% by mass fraction or volume fraction) can significantly improve certain properties of lithium-ion batteries, such as the battery's initial charge and discharge efficiency, cycle life, reversible capacity, electrolyte ion conductivity and electronic conductivity, thermal stability, low temperature performance, compatibility of positive and negative electrode materials, etc.

[0003] Lithium difluorophosphate is an excellent lithium-ion battery additive. Whether used alone or as a combined additive, lithium difluorophosphate can significantly increase the cycle life of the battery. In high energy density and silicon-carbon negative electrode batteries, lithium difluorophosphate also has a very obvious effect.

[0004] In batteries, high-purity lithium difluorophosphate can provide stable ion transport, reduce the resistance of the electrolyte, and improve the energy density and cycle life of the battery; at the same time, low-water lithium difluorophosphate can reduce battery durability issues such as self-discharge of lithium batteries and decomposition of the electrolyte; and low metal ions can improve the stability of the electrolyte and extend the service life of the battery.

[0005] Therefore, it is urgently needed in the art to propose a lithium difluorophosphate solid that can purify low moisture, low metal ions and high purity. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for purifying crude lithium difluorophosphate solid. The purified lithium difluorophosphate solid has the advantages of low moisture, low metal ions and high purity.

[0007] To achieve the above object, the present invention is implemented by the following technical scheme: a method for purifying crude lithium difluorophosphate solid, comprising the following steps:

[0008] (1) adding a solvent to the crude lithium difluorophosphate to fully dissolve it, thereby obtaining a crude lithium difluorophosphate solution;

[0009] (2) adding a dehydrating agent to the crude lithium difluorophosphate solution, heating and stirring to fully dehydrate;

[0010] (3) The dehydrated solution is passed through a reactor containing a metal adsorbent for a cyclic reaction, and high-purity lithium difluorophosphate solid is obtained after concentration and drying.

[0011] Preferably, the solvent in step (1) is acetonitrile or ethylene glycol dimethyl ether.

[0012] Preferably, the dissolution temperature in step (1) is 10-70°C and the pressure is 0-100 kPa.

[0013] Preferably, the dehydrating agent in step (2) is bismuth trichloride or antimony trichloride.

[0014] Preferably, the amount of the dehydrating agent added in step (2) is 0.5% to 1% of the total weight of the solution.

[0015] Preferably, the dehydration conditions in step (2) are: temperature of 20-50° C., pressure of 0-50 kPa, and stirring time of 1-2 h.

[0016] Preferably, the metal adsorbent in step (3) comprises chelating agent A and chelating agent B, and the amount of metal ion adsorbent is 0.5% to 1% of the total weight of the solution.

[0017] Preferably, the chelating agent A is a metal adsorbent having a carrier with a glucosamine-type functional group.

[0018] Preferably, the chelating agent B is a metal adsorbent having a carrier having one or a combination of thiol, thiourea, amino, a group derived from triazabicyclodecene, thiourea, imidazole, sulfonic acid, hydroxyl, aminoacetate, amide oxime, and aminophosphoric acid groups.

[0019] Preferably, the cyclic reaction conditions in step (3) are: temperature of 20-70°C, pressure of 0-100 kPa, and reaction time of 1 h.

[0020] Preferably, the crude lithium difluorophosphate in step (1) is prepared by dissolving lithium hexafluorophosphate in a lipid solvent, adding hexamethyldisiloxane to the lithium hexafluorophosphate solution, and then concentrating and drying to obtain a crude lithium difluorophosphate solid.

[0021] The present invention provides a device for purifying crude lithium difluorophosphate solid, comprising:

[0022] A lithium difluorophosphate dissolving kettle, used to dissolve crude lithium difluorophosphate to obtain a crude lithium difluorophosphate solution;

[0023] A dehydrating agent silo is used to store the dehydrating agent and add the dehydrating agent to the lithium difluorophosphate solution, and is connected to the lithium difluorophosphate dissolving kettle;

[0024] The metal ion removal reactor is used to receive the solution pumped from the dissolving kettle and remove metal ions from the solution in a circulation reaction;

[0025] The three-in-one kettle B is used to receive the lithium difluorophosphate solution after the metal ions are removed, and to concentrate and dry the solution to obtain high-purity lithium difluorophosphate solid.

[0026] Preferably, the device further comprises:

[0027] Lithium hexafluorophosphate silo, used to store lithium hexafluorophosphate;

[0028] A lithium hexafluorophosphate dissolving kettle, used for dissolving lithium hexafluorophosphate, connected to the outlet of the lithium hexafluorophosphate silo;

[0029] A lithium difluorophosphate synthesis kettle, used for synthesizing crude lithium difluorophosphate, which is connected to the outlet of the lithium hexafluorophosphate dissolution kettle;

[0030] A hexamethyldisiloxane storage tank is used to store hexamethyldisiloxane and to drop hexamethyldisiloxane into the lithium difluorophosphate synthesis reactor;

[0031] The three-in-one reactor A is used to receive the crude lithium difluorophosphate synthesized in the lithium difluorophosphate synthesis reactor, and obtain the crude lithium difluorophosphate solid after concentration and drying.

[0032] The present invention provides a method for purifying crude lithium difluorophosphate solid. It has the following beneficial effects:

[0033] 1. The present invention adds a certain amount of dehydrating agent (bismuth trichloride or antimony trichloride) from a dehydrating agent silo into a lithium difluorophosphate dissolving kettle for heating and stirring for dehydration. The dehydrating agent itself is insoluble in organic solvents and will not react with substances in the solvent; the dehydrating agent can react chemically with water to generate a precipitate to achieve the dehydration effect. Compared with molecular sieve dehydration, this method requires lower cost, lower temperature, lower pressure, and the moisture content can be reduced to less than 50ppm; in addition, the dehydrating agent does not require a separate dehydration container for dehydration, and can be directly added to the lithium difluorophosphate dissolving kettle for stirring and dehydration.

[0034] 2. The present invention adds an appropriate amount of chelating agent to the demetallization ion reactor, and the lithium difluorophosphate solution is continuously circulated through the demetallization ion reactor, which is beneficial to the removal of metal ions. The chelating agent can not only adsorb multiple metal ions at the same time but also does not produce other substances to pollute the product. The total content of metal ions in the product of this method can be reduced to less than 10ppm.

[0035] 3. The present invention directly adds a dehydrating agent into a lithium difluorophosphate dissolving kettle to remove water contained in the solution, and does not need to perform a separate molecular sieve dehydration treatment; then the lithium difluorophosphate solution is continuously circulated through a metal ion removal reactor to remove metal ions; finally, the lithium difluorophosphate is concentrated and dried through a three-in-one kettle (B) to remove the organic solvent, thereby obtaining lithium difluorophosphate with a purity of more than 99.95%, a water content of less than 50 ppm, and a total metal ion content of less than 10 ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the method flow of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The combined preparation device of liquid ammonia and ammonia water provided by the present invention is as follows: Figure 1 As shown, it includes a lithium hexafluorophosphate silo, a lithium hexafluorophosphate dissolving kettle, a lithium difluorophosphate synthesis kettle, a hexamethyldisiloxane storage tank, a dissolving kettle filter, a synthesis kettle filter, a dehydrating agent silo, a demetallization ion reactor, a demetallization ion filter, a three-in-one kettle (A), a three-in-one kettle (B), a dissolving kettle pump, and a product tank.

[0039] Wherein, the lithium hexafluorophosphate silo outlet is connected to the lithium hexafluorophosphate dissolving kettle inlet. The material outlet of the lithium hexafluorophosphate dissolving kettle is connected to the dissolving kettle filter inlet, and the dissolving kettle filter outlet is connected to the lithium difluorophosphate synthesis kettle inlet. The outlet of the hexamethyldisiloxane storage tank is connected to the lithium difluorophosphate synthesis kettle inlet. The outlet of the lithium difluorophosphate synthesis kettle is connected to the synthesis kettle filter inlet, the synthesis kettle filter outlet is connected to the three-in-one kettle (A) inlet, and the three-in-one kettle (A) outlet is connected to the lithium difluorophosphate dissolving kettle inlet. The dehydrating agent silo outlet is connected to the lithium difluorophosphate dissolving kettle inlet. The lithium difluorophosphate dissolving kettle outlet is connected to the demetallization ion reactor inlet through the dissolving kettle pump, and the demetallization ion reactor outlet is connected to the lithium difluorophosphate dissolving kettle inlet. The dissolving kettle pump outlet is connected to the demetallization ion filter inlet, the demetallization ion filter outlet is connected to the three-in-one kettle (B) inlet, and the three-in-one kettle (B) outlet is connected to the product tank.

[0040] The purification method steps of the present invention will be further described below in conjunction with embodiments.

[0041] Embodiment 1:

[0042] (1) Dissolving crude lithium difluorophosphate solid: Use 2000kg of electronic grade dimethyl carbonate solvent to dissolve 500kg of lithium hexafluorophosphate. Add 865kg of hexamethyldisiloxane to the lithium hexafluorophosphate solution to react and generate crude lithium difluorophosphate, and then obtain crude lithium difluorophosphate solid through three-in-one kettle (A). Add crude lithium difluorophosphate to the lithium difluorophosphate dissolving kettle, add 1300kg of ethylene glycol dimethyl ether to the dissolving kettle, and fully dissolve it to obtain crude lithium difluorophosphate solution. The temperature of the lithium difluorophosphate dissolving kettle is 10°C and the pressure is 0kPa.

[0043] (2) Dehydration treatment: 8 kg of dehydrating agent (bismuth trichloride) was added from the dehydrating agent silo into the lithium difluorophosphate dissolving kettle and heated and stirred for 2 hours to fully dehydrate the lithium difluorophosphate dissolving kettle. During dehydration, the temperature of the lithium difluorophosphate dissolving kettle was 20° C. and the pressure was 0 kPa.

[0044] (3) Metal ion removal treatment: The solution in the lithium difluorophosphate dissolving kettle enters the metal ion removal reactor (8kg metal adsorbent is ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid) through the dissolving kettle pump and circulates continuously for 1 hour to fully adsorb metal ions. After the cycle is completed, the lithium difluorophosphate solution enters the three-in-one kettle (B), where it is concentrated and dried to obtain high-purity lithium difluorophosphate solid. The temperature of the metal ion removal reactor is 20°C and the pressure is 0kPa.

[0045] The crude lithium difluorophosphate solid was dissolved, dehydrated, and demetallated to obtain a water content of <50ppm and metal ions (Fe 3+ Mg 2+ , Ca 2+ , Cu 2+ High-purity lithium difluorophosphate solid with a total content of <8ppm.

[0046] Embodiment 2:

[0047] (1) Dissolving crude lithium difluorophosphate: 500 kg of lithium hexafluorophosphate was dissolved in 2000 kg of electronic grade dimethyl carbonate solvent. 865 kg of hexamethyldisiloxane was added dropwise to the lithium hexafluorophosphate solution to react and generate crude lithium difluorophosphate, which was then obtained through a three-in-one kettle (A) to obtain a crude lithium difluorophosphate solid. The crude lithium difluorophosphate was added to a lithium difluorophosphate dissolving kettle, and 1300 kg of ethylene glycol dimethyl ether was added to the dissolving kettle to fully dissolve it to obtain a crude lithium difluorophosphate solution. The temperature of the lithium difluorophosphate dissolving kettle was 40°C and the pressure was 50 kPa.

[0048] (2) Dehydration treatment: 12 kg of dehydrating agent (antimony trichloride) was added from the dehydrating agent silo to the lithium difluorophosphate dissolving kettle and heated and stirred for 2 hours to fully dehydrate the lithium difluorophosphate dissolving kettle. During dehydration, the temperature of the lithium difluorophosphate dissolving kettle was 35° C. and the pressure was 25 kPa.

[0049] (3) Metal ion removal treatment: The solution in the lithium difluorophosphate dissolving kettle enters the metal ion removal reactor (12kg metal adsorbent is hydroxyethylidene diphosphonic acid, ethylenediamine tetramethylenephosphonic acid, diethylenetriamine penta (methylenephosphonic acid)) through the dissolving kettle pump and circulates continuously for 1 hour to fully adsorb metal ions. After the cycle is completed, the lithium difluorophosphate solution enters the three-in-one kettle (B), where it is concentrated and dried to obtain high-purity lithium difluorophosphate solid. The temperature of the metal ion removal reactor is 45°C and the pressure is 50kPa.

[0050] The crude lithium difluorophosphate was dissolved, dehydrated, and demetallated to obtain a water content of <30ppm and metal ions (Fe 3+ Mg 2+ , Ca 2+ , Cu 2+ High-purity lithium difluorophosphate solid with a total content of <5ppm.

[0051] Embodiment 3:

[0052] (1) Dissolving crude lithium difluorophosphate: 500 kg of lithium hexafluorophosphate was dissolved in 2000 kg of electronic grade dimethyl carbonate solvent. 865 kg of hexamethyldisiloxane was added dropwise to the lithium hexafluorophosphate solution to react and generate crude lithium difluorophosphate, which was then obtained through a three-in-one kettle (A) to obtain a crude lithium difluorophosphate solid. The crude lithium difluorophosphate was added to a lithium difluorophosphate dissolving kettle, and 1300 kg of ethylene glycol dimethyl ether was added to the dissolving kettle to fully dissolve the crude lithium difluorophosphate solution. The temperature of the lithium difluorophosphate dissolving kettle was 70°C and the pressure was 100 kPa.

[0053] (2) Dehydration treatment: 16 kg of dehydrating agent (antimony trichloride) was added from the dehydrating agent silo into the lithium difluorophosphate dissolving kettle and heated and stirred for 2 hours to fully dehydrate the lithium difluorophosphate dissolving kettle. During dehydration, the temperature of the lithium difluorophosphate dissolving kettle was 50° C. and the pressure was 50 kPa.

[0054] (3) Metal ion removal treatment: The solution in the lithium difluorophosphate dissolving kettle enters the metal ion removal reactor (16kg metal adsorbent is hydroxyethylidene diphosphonic acid, ethylenediamine tetramethylenephosphonic acid, diethylenetriamine penta (methylenephosphonic acid)) through the dissolving kettle pump and circulates continuously for 1 hour to fully adsorb metal ions. After the cycle is completed, the lithium difluorophosphate solution enters the three-in-one kettle (B), where it is concentrated and dried to obtain high-purity lithium difluorophosphate solid. The temperature of the metal ion removal reactor is 70°C and the pressure is 100kPa.

[0055] The crude lithium difluorophosphate was dissolved, dehydrated, and demetallated to obtain a water content of <50ppm and metal ions (Fe 3+ Mg 2+ , Ca 2+ , Cu2+ High-purity lithium difluorophosphate solid with a total content of <8ppm.

[0056] Experimental example:

[0057] The product lithium difluorophosphate solid obtained in Example 1-3 was measured, and the results are shown in the following table:

[0058]

[0059] Example 1-3: Test data of lithium difluorophosphate solid prepared by conventional method

[0060] It can be seen from the test data table that the purification method of the present invention can obtain low-water, low-metal ion, high-purity lithium difluorophosphate solid. High-purity lithium difluorophosphate solid is applied to the field of lithium-ion batteries and can enhance the low-temperature resistance, chemical stability, cycle characteristics, conductivity and high-temperature storage performance of the battery.

[0061] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for purifying crude lithium difluorophosphate solid, characterized in that: The following steps are involved: (1) adding a solvent to the crude lithium difluorophosphate to fully dissolve it, thereby obtaining a crude lithium difluorophosphate solution; (2) adding a dehydrating agent to the crude lithium difluorophosphate solution, heating and stirring to fully dehydrate; (3) passing the dehydrated solution through a reactor containing a metal adsorbent for a cyclic reaction, and obtaining a high-purity lithium difluorophosphate solid after concentration and drying; The solvent in step (1) is acetonitrile or ethylene glycol dimethyl ether; The dehydrating agent in step (2) is bismuth trichloride or antimony trichloride, and the amount of the dehydrating agent added is 0.5% to 1% of the total weight of the solution; The metal adsorbent in step (3) comprises a chelating agent A and a chelating agent B, wherein the chelating agent A is a metal adsorbent having a carrier with a glucosamine-type functional group; the chelating agent B is a metal adsorbent having a carrier with one or a combination of a thiol group, a thiourea group, an amino group, a group derived from triazabicyclodecene, a thiourea group, an imidazole group, a sulfonic acid group, a hydroxyl group, an aminoacetate group, an amide oxime group, and an aminophosphoric acid group; the amount of the metal ion adsorbent is 0.5% to 1% of the total weight of the solution; The cyclic reaction conditions of step (3) are: temperature of 20-70° C., pressure of 0-100 kPa, and reaction time of 1 h.

2. A method for purifying a crude lithium difluorophosphate solid according to claim 1, characterized in that: The dissolving temperature in step (1) is 10-70° C. and the pressure is 0-100 kPa.

3. A method for purifying a crude lithium difluorophosphate solid according to claim 1, characterized in that: The dehydration conditions in step (2) are: temperature of 20-50° C., pressure of 0-50 kPa, and stirring time of 1-2 h.

4. A method for purifying a crude lithium difluorophosphate solid according to claim 1, characterized in that: The crude lithium difluorophosphate in step (1) is prepared by dissolving lithium hexafluorophosphate in a lipid solvent, adding hexamethyldisiloxane to the lithium hexafluorophosphate solution, and then concentrating and drying to obtain a crude lithium difluorophosphate solid.

5. A device for purifying crude lithium difluorophosphate solid, used for implementing a method for purifying crude lithium difluorophosphate solid as claimed in any one of claims 1 to 4, characterized in that: include: A lithium difluorophosphate dissolving kettle, used to dissolve crude lithium difluorophosphate to obtain a crude lithium difluorophosphate solution; A dehydrating agent silo is used to store the dehydrating agent and add the dehydrating agent to the lithium difluorophosphate solution, and is connected to the lithium difluorophosphate dissolving kettle; The metal ion removal reactor is used to receive the solution pumped from the dissolving kettle and remove metal ions from the solution in a circulation reaction; The three-in-one kettle B is used to receive the lithium difluorophosphate solution after the metal ions are removed, and to concentrate and dry the solution to obtain high-purity lithium difluorophosphate solid.

6. The device for purifying crude lithium difluorophosphate solid according to claim 5, characterized in that: The device also includes: Lithium hexafluorophosphate silo, used to store lithium hexafluorophosphate; A lithium hexafluorophosphate dissolving kettle, used for dissolving lithium hexafluorophosphate, connected to the outlet of the lithium hexafluorophosphate silo; A lithium difluorophosphate synthesis kettle, used for synthesizing crude lithium difluorophosphate, which is connected to the outlet of the lithium hexafluorophosphate dissolution kettle; A hexamethyldisiloxane storage tank is used to store hexamethyldisiloxane and to drop hexamethyldisiloxane into the lithium difluorophosphate synthesis reactor; The three-in-one reactor A is used to receive the crude lithium difluorophosphate synthesized in the lithium difluorophosphate synthesis reactor, and obtain the crude lithium difluorophosphate solid after concentration and drying.

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