Method for continuously crystallizing lithium hexafluorophosphate and lithium hexafluorophosphate crystal

Abstract

The invention provides a lithium hexafluorophosphate continuous crystallization method and a lithium hexafluorophosphate crystal, and the lithium hexafluorophosphate continuous crystallization method comprises the following steps: mixing a hydrogen fluoride solution containing lithium hexafluorophosphate with an auxiliary agent gas, and carrying out continuous crystallization on the mixed material, carrying out multi-stage cooling on the mixed material in the continuous crystallization process; the auxiliary agent gas comprises one or more of boron trifluoride, silicon tetrafluoride and arsenic pentafluoride. By introducing auxiliary agent gas and combining gradient cooling, crystal ordered growth of lithium hexafluorophosphate can be promoted, and stable production of controllable continuous crystal of lithium hexafluorophosphate can be realized; and meanwhile, the adopted assistant gas does not influence the purity of the product, so that high-quality lithium hexafluorophosphate crystals can be continuously obtained, and the method is suitable for industrial production.

Description

Technical Field

[0001] This application relates to the field of lithium hexafluorophosphate crystal preparation technology, and in particular to a method for continuous crystallization of lithium hexafluorophosphate and lithium hexafluorophosphate crystals. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) is a key electrolyte material in lithium-ion battery electrolytes and is currently the most widely used electrolyte material in lithium-ion batteries. With the large-scale development of the new energy electric vehicle market and applications such as mobile devices and energy storage, the market demand for lithium-ion batteries will increase year by year, and consequently, the future market prospects for LiPF6 will be even broader.

[0003] The crystal morphology of lithium hexafluorophosphate (LiPF6) has a significant impact on the electrolyte preparation process. Currently, the preparation process of LiPF6 suffers from the problem of uncontrollable crystal morphology, which urgently needs to be addressed. Summary of the Invention

[0004] Based on this, this application provides a method for continuous crystallization of lithium hexafluorophosphate with controllable crystal morphology and lithium hexafluorophosphate crystals.

[0005] The first aspect of this application provides a method for the continuous crystallization of lithium hexafluorophosphate, comprising the following steps:

[0006] A hydrogen fluoride solution containing lithium hexafluorophosphate is mixed with an additive gas, and the mixture is continuously crystallized. During the continuous crystallization process, the mixture is subjected to multi-stage cooling. The additive gas includes one or more of boron trifluoride, silicon tetrafluoride, and arsenic pentafluoride.

[0007] In some embodiments, multi-stage cooling includes a first stage of cooling and a second stage of cooling performed sequentially.

[0008] In some embodiments, the temperature of the hydrogen fluoride solution after the first stage of cooling is -15°C to -25°C.

[0009] In some embodiments, the temperature of the hydrogen fluoride solution after the second-stage cooling is -26°C to -40°C.

[0010] In some embodiments, the residence time after the first stage of cooling is 20 min to 60 min.

[0011] In some embodiments, the residence time after the second-stage cooling is 30 min to 90 min.

[0012] In some embodiments, the mass percentage of the auxiliary gas relative to the mass of lithium hexafluorophosphate contained in the hydrogen fluoride solution is 0.1% to 1%.

[0013] In some embodiments, the temperature of the hydrogen fluoride solution is -10°C to 10°C.

[0014] In some embodiments, the lithium hexafluorophosphate accounts for 17%-23% of the mass of the hydrogen fluoride solution.

[0015] In some embodiments, the method further includes: solid-liquid separation and drying of the material obtained after continuous crystallization.

[0016] In some embodiments, the drying temperature is 50°C to 80°C.

[0017] In some embodiments, the drying time is 3 to 6 hours.

[0018] In some embodiments, the drying pressure is 10 kPa to 30 kPa.

[0019] The second aspect of this application provides a lithium hexafluorophosphate crystal, which is prepared by the continuous crystallization method of lithium hexafluorophosphate according to the first aspect of this application, wherein the particle size variation coefficient of the lithium hexafluorophosphate crystal is ≤0.65.

[0020] In some embodiments, the coefficient of variation of the particle size of the lithium hexafluorophosphate crystal is ≤0.60.

[0021] In some embodiments, the D50 of the lithium hexafluorophosphate crystal is 100μm-300μm.

[0022] The aforementioned method for continuous crystallization of lithium hexafluorophosphate (LiPF6) promotes the orderly growth of LiPF6 crystals by introducing an auxiliary gas and combining it with multi-stage cooling, achieving stable and controllable continuous crystallization production of LiPF6. Simultaneously, the auxiliary gas used does not affect the purity of the product, facilitating the continuous production of high-quality LiPF6 crystals, making it suitable for industrial production. Furthermore, the LiPF6 crystals obtained using this method do not require crushing, and the yield of qualified products is close to the theoretical yield. Therefore, compared with batch crystallization processes, the continuous crystallization method for LiPF6 of this application significantly improves both production efficiency and product yield. Detailed Implementation

[0023] To facilitate understanding of the present invention, a more complete description of this application will be provided below with reference to relevant embodiments. Preferred embodiments of the present application are given below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the disclosure of this application will be achieved.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0025] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0026] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0027] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0028] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0029] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0030] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0031] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0032] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0033] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, but sequentially is preferred.

[0036] The crystal morphology of lithium hexafluorophosphate (LiPF6) significantly impacts the subsequent electrolyte preparation process. Both excessively large and small LiPF6 crystal sizes can lead to problems in electrolyte preparation. Currently, the mainstream preparation process for LiPF6 still predominantly employs intermittent crystallization, which suffers from uncontrollable crystal morphology and urgently needs a solution. Some crystallization processes also require post-crystallization crushing and sieving, resulting in low production efficiency and relatively poor crystal morphology and particle size. Particle size sieving is necessary to obtain products with acceptable particle sizes; excessively large or small crystals can only be used as substandard products or require recrystallization, easily leading to low product yield.

[0037] To address the aforementioned issues, this application proposes a method that involves introducing an auxiliary gas into a hydrogen fluoride solution containing lithium hexafluorophosphate and continuously crystallizing it. During this continuous crystallization process, multi-stage cooling is performed to obtain lithium hexafluorophosphate crystals with controllable morphology. This method offers advantages such as a safe and environmentally friendly process, high product quality, and suitability for industrial production.

[0038] One or more embodiments of this application provide a method for continuous crystallization of lithium hexafluorophosphate, comprising the following steps: mixing a hydrogen fluoride solution containing lithium hexafluorophosphate with an additive gas and continuously crystallizing the mixed material, wherein the mixed material is subjected to multi-stage cooling during the continuous crystallization process; the additive gas includes one or more of boron trifluoride, silicon tetrafluoride and arsenic pentafluoride.

[0039] It should be noted that continuous crystallization refers to a crystallization process in which materials are continuously fed in and out, and the concentration, temperature, slurry density, and crystal particle size distribution of all liquid materials remain unchanged.

[0040] The introduced auxiliary gas dissolves in the hydrogen fluoride solution. The auxiliary gas can affect the aggregation dynamics of molecules in the solution, change the induction period of lithium hexafluorophosphate crystallization, and enable lithium hexafluorophosphate to crystallize in a more uniform manner.

[0041] Gradient cooling of a hydrogen fluoride solution containing lithium hexafluorophosphate can better release the supersaturation of lithium hexafluorophosphate in the solution, resulting in more orderly crystallization of lithium hexafluorophosphate and optimizing the uniformity of crystal particle size.

[0042] Understandably, the continuous crystallization method for lithium hexafluorophosphate of this application, by introducing an auxiliary gas and combining it with gradient cooling, can promote the orderly growth of lithium hexafluorophosphate crystals, achieving stable and controllable continuous crystallization production of lithium hexafluorophosphate. Simultaneously, the auxiliary gas used does not affect the purity of the product, which is beneficial for the continuous production of high-quality lithium hexafluorophosphate crystals and is suitable for industrial production. Furthermore, the lithium hexafluorophosphate crystals obtained by this method do not require crushing, and the yield of qualified products is close to the theoretical yield. Therefore, compared with batch crystallization processes, the continuous crystallization method for lithium hexafluorophosphate of this application significantly improves both production efficiency and product yield.

[0043] It should be noted that the mother liquor generated during the crystallization process can be reused in the lithium hexafluorophosphate synthesis unit to improve the overall yield of lithium hexafluorophosphate preparation and crystallization.

[0044] In some implementations, multi-stage cooling includes a first-stage cooling and a second-stage cooling performed sequentially.

[0045] It should be noted that in this article, the terms "first-stage cooling," "second-stage cooling," etc., are used for descriptive purposes only and should not be interpreted as indicating or implying relative importance or quantity, nor should they be interpreted as implicitly specifying the importance or quantity of the indicated technical features. Moreover, "first-stage cooling," "second-stage cooling," etc., only serve the purpose of non-exhaustive enumeration and should be understood as not constituting a closed limitation on quantity.

[0046] As a non-limiting example, the continuous crystallization method of lithium hexafluorophosphate of this application can be implemented using a two-stage cooling continuous crystallization apparatus.

[0047] In some optional embodiments, the temperature of the hydrogen fluoride solution after the first-stage cooling is -15°C to -25°C; for example, it can be, but is not limited to, -15°C, -16°C, -17°C, -18°C, -19°C, -20°C, -21°C, -22°C, -23°C, -24°C, -25°C, or any range between two of the above temperatures. When the temperature of the hydrogen fluoride solution after the first-stage cooling is within this range, sufficient seed crystals can be obtained for lithium hexafluorophosphate to crystallize at a specific temperature. Optionally, the temperature of the hydrogen fluoride solution after the first-stage cooling is -15°C to -20°C.

[0048] In some exemplary embodiments, the temperature of the hydrogen fluoride solution after the second-stage cooling is -26°C to -40°C; for example, it can be, but is not limited to, -26°C, -27°C, -28°C, -29°C, -30°C, -31°C, -32°C, -33°C, -34°C, -35°C, -36°C, -37°C, -38°C, -39°C, -40°C, or any two of the above temperatures. When the temperature of the hydrogen fluoride solution after the second-stage cooling is within this range, the supersaturation of lithium hexafluorophosphate in the hydrogen fluoride solution can be better released, allowing the seed crystals that crystallized after the first-stage cooling to continue to grow uniformly, resulting in lithium hexafluorophosphate crystals that meet the requirements.

[0049] As one possible implementation, the residence time after the first-stage cooling is 20 min to 60 min; for example, it can be, but is not limited to, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or any range between two of the above times. Thus, the lithium hexafluorophosphate solution has sufficient time to generate crystal nuclei during the crystallization process after the first-stage cooling.

[0050] In some exemplary embodiments, the residence time after the second-stage cooling is 30 to 90 minutes; for example, it can be, but is not limited to, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, 90 minutes, or any range between two of the above times. Thus, the lithium hexafluorophosphate nuclei obtained from the crystallization after the first-stage cooling have sufficient time to grow to the required particle size.

[0051] In some embodiments, the mass percentage of the additive gas relative to the mass of lithium hexafluorophosphate contained in the hydrogen fluoride solution is 0.1% to 1%; for example, it can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any range between two of the above values. When the amount of additive gas is within the above range, it is beneficial to control the particle size of the obtained lithium hexafluorophosphate crystals within a suitable range without affecting the quality of the lithium hexafluorophosphate crystals.

[0052] In some embodiments, the temperature of the hydrogen fluoride solution is -10°C to 10°C; for example, it can be, but is not limited to, -10°C, -9°C, -8°C, -7°C, -6°C, -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, or any range between two of the above temperatures. When the temperature of the hydrogen fluoride solution is within the above range, premature crystallization of lithium hexafluorophosphate before entering the crystallization stage can be avoided, which would affect the stability of the subsequent crystallization stage operation.

[0053] In some embodiments, the mass percentage of lithium hexafluorophosphate in the hydrogen fluoride solution is 17%-23%; for example, it can be, but is not limited to, 17%, 18%, 19%, 20%, 21%, 22%, 23%, or any range between two of the above mass percentages. Therefore, when the concentration of the crystallization solution is within the above range, it is beneficial to achieve stable nucleation and growth of lithium hexafluorophosphate crystals. Optionally, the mass percentage of lithium hexafluorophosphate in the hydrogen fluoride solution is 17%-22%.

[0054] As one possible implementation method, the continuous crystallization method of lithium hexafluorophosphate further includes: solid-liquid separation and drying of the material obtained after continuous crystallization.

[0055] In some alternative embodiments, the drying temperature is 50°C to 80°C; for example, it can be, but is not limited to, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or any range between two of the above temperatures.

[0056] In some embodiments, the drying pressure is 10 kPa to 30 kPa; for example, it can be, but is not limited to, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa or any range between two of the above pressures.

[0057] In some exemplary embodiments, the drying time is 3 to 6 hours; for example, it can be, but is not limited to, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or any range between two of the above times.

[0058] It should be noted that the drying temperature, pressure, and time can be combined in any suitable way, and each of the three can be selected from any drying temperature, pressure, and time described in this article.

[0059] One or more embodiments of this application provide a lithium hexafluorophosphate crystal, which is prepared by the above-described continuous crystallization method of lithium hexafluorophosphate, and the particle size variation coefficient of the lithium hexafluorophosphate crystal is ≤0.65.

[0060] It should be noted that the particle size variation coefficient is used to reflect the particle size dispersion. The smaller the particle size variation coefficient, the more concentrated the particle size distribution.

[0061] In some alternative implementations, the coefficient of variation of the particle size of lithium hexafluorophosphate crystals is ≤0.60.

[0062] In some embodiments, the D50 of the lithium hexafluorophosphate crystal is 100μm-300μm; for example, it can be, but is not limited to, 100μm, 120μm, 140μm, 160μm, 180μm, 200μm, 220μm, 240μm, 260μm, 280μm, 300μm, or any range between two of the above D50 values.

[0063] The technical solutions of this application will be described in detail below with reference to specific embodiments. It should be understood that these embodiments are only for illustrating this application and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application first, or follow experimental manuals or conventional conditions in the field, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the field.

[0064] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0065] Unless otherwise specified, all raw materials in the following examples and comparative examples are commercially available or prepared using conventional methods.

[0066] It should be noted that the analytical methods for the lithium hexafluorophosphate crystals in the following embodiments and comparative examples refer to the industry standard for lithium hexafluorophosphate (HG / T 4066-2015).

[0067] Unless otherwise specified, all the embodiments and comparative examples below use a continuous crystallization apparatus with two-stage cooling.

[0068] The effective yield of lithium hexafluorophosphate crystals mentioned in the following examples and comparative examples refers to the yield of lithium hexafluorophosphate crystals with a particle size D50 in the range of 100-300 μm. The calculation formula is: Effective yield of lithium hexafluorophosphate crystals = Mass of lithium hexafluorophosphate crystals with a particle size D50 in the range of 100-300 μm / Total mass of lithium hexafluorophosphate contained in the hydrogen fluoride clear solution introduced during crystallization.

[0069] Example 1

[0070] Continuous crystallization experiments were conducted using a device with a two-stage cooling crystallizer. A hydrogen fluoride solution containing lithium hexafluorophosphate (17% by mass) at -10℃ was introduced into the first-stage crystallizer at a rate of 50 kg / h, along with boron trifluoride gas at a rate of 0.0255 kg / h. The temperature of the first-stage crystallizer was controlled at -20℃, and the residence time was maintained at 30 min by adjusting the liquid level. After crystallization in the first-stage crystallizer, the solution was transferred to the second-stage crystallizer, where the temperature was controlled at -40℃, and the residence time was maintained at 90 min by adjusting the liquid level. After crystallization, the solution was filtered to obtain wet lithium hexafluorophosphate crystals. These wet crystals were then dried at 10 kPa and 60℃ for 4 h. The resulting lithium hexafluorophosphate crystals had a particle size D50 of 232 μm, a particle size variation coefficient of 0.52, and a purity of 99.97%, meeting the industry standard HG / T. 4066-2015, and then after sieving, lithium hexafluorophosphate crystals in the range of 100-300μm were obtained. The effective yield of lithium hexafluorophosphate crystals was calculated to be 29.4%.

[0071] Example 2

[0072] Continuous crystallization experiments were conducted using a device with a two-stage cooling crystallizer. A hydrogen fluoride solution containing lithium hexafluorophosphate (lithium hexafluorophosphate at a mass ratio of 19%), at -5℃, was introduced into the first-stage crystallizer at a rate of 50 kg / h, along with silicon tetrafluoride gas at a rate of 0.095 kg / h. The temperature of the first-stage crystallizer was controlled at -19℃, and the residence time was controlled to 20 min by adjusting the liquid level. After crystallization in the first-stage crystallizer, the solution was transferred to the second-stage crystallizer, where the temperature was controlled at -35℃, and the residence time was controlled to 60 min by adjusting the liquid level. After crystallization, the solution was filtered to obtain wet lithium hexafluorophosphate crystals. The wet product was then dried at 20 kPa and 70℃ for 5 h. The resulting lithium hexafluorophosphate crystals had a particle size D50 of 189 μm, a particle size variation coefficient of 0.47, and a purity of 99.98%, meeting the industry standard HG / T. 4066-2015, and then after sieving, lithium hexafluorophosphate crystals in the range of 100-300μm were obtained. The effective yield of lithium hexafluorophosphate crystals was calculated to be 31.5%.

[0073] Example 3

[0074] Continuous crystallization experiments were conducted using a device with a two-stage cooling crystallizer. A hydrogen fluoride solution containing lithium hexafluorophosphate (LiPF6) at 10°C (LiPF6 mass percentage in the hydrogen fluoride solution was 21%) was introduced into the first-stage crystallizer at a rate of 50 kg / h, along with arsenic pentafluoride gas at a rate of 0.0105 kg / h. The temperature of the first-stage crystallizer was controlled at -15°C, and the residence time was controlled to 40 min by adjusting the liquid level. After crystallization in the first-stage crystallizer, the solution was transferred to the second-stage crystallizer, where the temperature was controlled at -28°C, and the residence time was controlled to 30 min by adjusting the liquid level. After crystallization, the solution was filtered to obtain wet LiPF6 crystals. The wet product was then dried at 10 kPa and 50°C for 3 h. The resulting LiPF6 crystals had a particle size D50 of 268 μm, a particle size variation coefficient of 0.50, and a purity of 99.98%, meeting the industry standard HG / T. 4066-2015, and then after sieving, lithium hexafluorophosphate crystals in the range of 100-300μm were obtained. The effective yield of lithium hexafluorophosphate crystals was calculated to be 38%.

[0075] Example 4

[0076] Continuous crystallization experiments were conducted using a device with a two-stage cooling crystallizer. A hydrogen fluoride solution containing lithium hexafluorophosphate (22% by mass) at 5°C was introduced into the first-stage crystallizer at a rate of 50 kg / h, along with silicon tetrafluoride gas at a rate of 0.066 kg / h. The temperature of the first-stage crystallizer was controlled at -17°C, and the residence time was maintained at 60 min by adjusting the liquid level. After crystallization in the first-stage crystallizer, the solution was transferred to the second-stage crystallizer, where the temperature was controlled at -26°C, and the residence time was maintained at 30 min by adjusting the liquid level. After crystallization, the solution was filtered to obtain wet lithium hexafluorophosphate crystals. These wet crystals were then dried at 30 kPa and 80°C for 6 h. The resulting lithium hexafluorophosphate crystals had a D50 of 248 μm, a coefficient of variation of 0.45, and a purity of 99.97%, meeting the industry standard HG / T. 4066-2015, and then after sieving, lithium hexafluorophosphate crystals in the range of 100-300μm were obtained. The effective yield of lithium hexafluorophosphate crystals was calculated to be 36.3%.

[0077] Example 5

[0078] The methods in Example 5 and Example 2 are similar, except that in Example 5, silicon tetrafluoride gas is introduced into the first-stage crystallization vessel at a rate of 0.0285 Kg / h; all other aspects are the same.

[0079] The dried lithium hexafluorophosphate crystals have a particle size D50 of 206 μm, a particle size variation coefficient of 0.65, and a purity of 99.98%, which meets the industry standard HG / T 4066-2015. After sieving, lithium hexafluorophosphate products in the range of 100-300 μm are obtained. The effective yield of lithium hexafluorophosphate crystals is calculated to be 31.4%.

[0080] Example 6

[0081] The methods in Example 6 and Example 2 are similar, except that in Example 6, silicon tetrafluoride gas is introduced into the first-stage crystallization vessel at a rate of 0.0095 Kg / h; all other aspects are the same.

[0082] The dried lithium hexafluorophosphate crystals have a particle size D50 of 189 μm, a particle size variation coefficient of 0.62, and a purity of 99.97%, which meets the industry standard HG / T 4066-2015. After sieving, lithium hexafluorophosphate products in the range of 100-300 μm are obtained. The effective yield of lithium hexafluorophosphate crystals is calculated to be 31.4%.

[0083] Example 7

[0084] The methods in Example 7 and Example 2 are similar, except that in Example 7, silicon tetrafluoride gas is introduced into the first-stage crystallization vessel at a rate of 0.0076 Kg / h; all other aspects are the same.

[0085] The dried lithium hexafluorophosphate crystals have a particle size D50 of 256 μm, a particle size variation coefficient of 0.70, and a purity of 99.97%, which meets the industry standard HG / T 4066-2015. After sieving, lithium hexafluorophosphate products in the range of 100-300 μm are obtained. The effective yield of lithium hexafluorophosphate crystals is calculated to be 30.8%.

[0086] Example 8

[0087] The methods in Example 8 and Example 2 are similar, except that in Example 8, silicon tetrafluoride gas is introduced into the first-stage crystallization vessel at a rate of 0.1045 Kg / h; all other aspects are the same.

[0088] The dried lithium hexafluorophosphate crystals have a particle size D50 of 136 μm, a particle size variation coefficient of 0.67, and a purity of 99.98%, which meets the industry standard HG / T 4066-2015. After sieving, lithium hexafluorophosphate products in the range of 100-300 μm are obtained. The effective yield of lithium hexafluorophosphate crystals is calculated to be 31%.

[0089] Comparative Example 1

[0090] In Comparative Example 1, no auxiliary gas was introduced during crystallization, and multi-stage cooling was not employed. Specifically:

[0091] 100 kg of a hydrogen fluoride solution containing lithium hexafluorophosphate (lithium hexafluorophosphate accounts for 19% of the mass of the hydrogen fluoride solution) was added to a crystallization vessel. The temperature of the solution was controlled at -5℃ and gradually cooled to -35℃ at a cooling rate of 0.1℃ / min. The solution was then aged at -35℃ for 30 min. After crystallization, the solution was filtered to obtain wet lithium hexafluorophosphate crystals. The wet product was then dried at 20 kPa and 70℃ for 5 h. After drying, the particle size D50 of the lithium hexafluorophosphate crystals was 262 μm, the particle size variation coefficient was 0.78, and the purity was 99.96%. The product was then sieved to obtain lithium hexafluorophosphate products in the range of 100-300 μm. The effective yield of lithium hexafluorophosphate crystals was calculated to be 25%.

[0092] Comparative Example 2

[0093] The methods of Comparative Example 2 and Example 2 are similar, except that no auxiliary gas was added during crystallization in Comparative Example 2; all other aspects are the same. Comparative Example 2 is detailed below:

[0094] A continuous crystallization experiment was conducted using a device containing a two-stage cooling crystallizer. A hydrogen fluoride solution containing lithium hexafluorophosphate (LiPF6) at -5℃ (LiPF6 mass percentage in the hydrogen fluoride solution was 19%) was fed into the first-stage crystallizer at a rate of 50 kg / h. The temperature of the first-stage crystallizer was controlled at -19℃, and the residence time was controlled at 20 min by adjusting the liquid level in the first-stage crystallizer. After crystallization was completed in the first-stage crystallizer, the solution was fed into the second-stage crystallizer. The temperature of the second-stage crystallizer was controlled at -35℃, and the residence time was controlled at 60 min by adjusting the liquid level in the second-stage crystallizer. After crystallization, the solution was filtered to obtain wet LiPF6 crystals. The obtained wet product was then dried at 20 kPa and 70℃ for 5 h. After drying, the particle size D50 of the LiPF6 crystals was 276 μm, the particle size variation coefficient was 0.88, and the purity was 99.97%. After sieving, LiPF6 crystals in the range of 100-300 μm were obtained. The effective yield of LiPF6 crystals was calculated to be 27%.

[0095] Comparative Example 3

[0096] The method of Comparative Example 3 is similar to that of Example 2, except that multi-stage cooling was not used in Comparative Example 3; all other aspects are the same. Comparative Example 3 is detailed below:

[0097] 100 kg of a hydrogen fluoride solution containing lithium hexafluorophosphate (lithium hexafluorophosphate accounts for 19% of the mass of the hydrogen fluoride solution) was added to a crystallization vessel, and 0.19 kg of silicon tetrafluoride gas was introduced. The temperature of the solution was controlled at -5℃ and gradually cooled to -35℃ at a cooling rate of 0.1℃ / min. The solution was then aged at -35℃ for 30 min. After crystallization, the solution was filtered to obtain wet lithium hexafluorophosphate crystals. The wet product was then dried at 20 kPa and 70℃ for 5 h. After drying, the particle size D50 of the lithium hexafluorophosphate crystals was 289 μm, the particle size variation coefficient was 0.75, and the purity was 99.96%. The product was then sieved to obtain lithium hexafluorophosphate products in the range of 100-300 μm. The effective yield of lithium hexafluorophosphate crystals was calculated to be 27.2%.

[0098] Comparative Example 4

[0099] The methods of Comparative Example 4 and Example 2 are similar, except that the same amount of sulfur hexafluoride is used instead of silicon tetrafluoride gas in Comparative Example 4; everything else is the same.

[0100] The dried lithium hexafluorophosphate crystals had a particle size D50 of 277 μm, a particle size variation coefficient of 0.86, and a purity of 99.97%. After sieving, lithium hexafluorophosphate products in the range of 100-300 μm were obtained. The effective yield of lithium hexafluorophosphate crystals was calculated to be 27%.

[0101] The main parameter settings for the crystallization process in the above embodiments and comparative examples are shown in Table 1.

[0102] Table 1

[0103]

[0104] In Table 1, w represents the percentage of the mass of the auxiliary gas relative to the mass of lithium hexafluorophosphate contained in the hydrogen fluoride solution; T1 represents the temperature of the first-stage crystallizer, i.e., the temperature of the hydrogen fluoride solution after the first-stage cooling; t1 represents the residence time in the first-stage crystallizer, i.e., the residence time after the first-stage cooling; T2 represents the temperature of the second-stage crystallizer, i.e., the temperature of the hydrogen fluoride solution after the second-stage cooling; t2 represents the residence time in the second-stage crystallizer, i.e., the residence time after the second-stage cooling; T3 represents the temperature of the hydrogen fluoride solution; and mass percentage represents the mass percentage of lithium hexafluorophosphate in the hydrogen fluoride solution.

[0105] The particle size D50, particle size variation coefficient, purity, and effective yield of lithium hexafluorophosphate crystals obtained in the above embodiments and comparative examples are shown in Table 2.

[0106] Table 2

[0107]

[0108] As shown in Table 2, the continuous crystallization method of lithium hexafluorophosphate proposed in this application can promote the orderly growth of lithium hexafluorophosphate crystals by introducing auxiliary gas and combining it with multi-stage cooling, resulting in high-quality lithium hexafluorophosphate crystals with controllable crystal morphology and relatively concentrated particle size distribution; and the method has a high product yield.

[0109] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for continuous crystallization of lithium hexafluorophosphate, characterized in that, Includes the following steps: A hydrogen fluoride solution containing lithium hexafluorophosphate is mixed with an additive gas, and the mixture is continuously crystallized. During the continuous crystallization process, the mixture is subjected to multi-stage cooling. The additive gas includes one or more of boron trifluoride, silicon tetrafluoride, and arsenic pentafluoride.

2. The method for continuous crystallization of lithium hexafluorophosphate as described in claim 1, characterized in that, Multi-stage cooling includes a first-stage cooling and a second-stage cooling performed sequentially; Optionally, the temperature of the hydrogen fluoride solution after the first stage of cooling is -15℃ to -25℃; Optionally, the temperature of the hydrogen fluoride solution after the second-stage cooling is -26℃ to -40℃.

3. The method for continuous crystallization of lithium hexafluorophosphate as described in claim 2, characterized in that, The residence time after the first stage of cooling is 20 min to 60 min; and / or, The dwell time after the second stage of cooling is 30 to 90 minutes.

4. The method for continuous crystallization of lithium hexafluorophosphate as described in claim 1, characterized in that, The mass percentage of the auxiliary gas relative to the mass of lithium hexafluorophosphate contained in the hydrogen fluoride solution is 0.1% to 1%.

5. The method for continuous crystallization of lithium hexafluorophosphate as described in claim 1, characterized in that, The temperature of the hydrogen fluoride solution is -10℃ to 10℃.

6. The method for continuous crystallization of lithium hexafluorophosphate as described in claim 1, characterized in that, The lithium hexafluorophosphate in the hydrogen fluoride solution accounts for 17%-23% by mass.

7. The method for continuous crystallization of lithium hexafluorophosphate as described in any one of claims 1 to 6, characterized in that, Also includes: Solid-liquid separation and drying are performed on the material obtained after continuous crystallization; Optionally, the drying temperature is 50℃~80℃; Optionally, the drying time is 3 to 6 hours; Optionally, the drying pressure is 10 kPa to 30 kPa.

8. A lithium hexafluorophosphate crystal, characterized in that, The lithium hexafluorophosphate crystals are prepared by the continuous crystallization method according to any one of claims 1 to 7, wherein the particle size variation coefficient of the lithium hexafluorophosphate crystals is ≤0.

65.

9. The lithium hexafluorophosphate crystal as described in claim 8, characterized in that, The coefficient of variation of the particle size of the lithium hexafluorophosphate crystal is ≤0.

60.

10. The lithium hexafluorophosphate crystal as described in claim 8 or 9, characterized in that, The D50 of the lithium hexafluorophosphate crystal is 100μm-300μm.

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