Fire-retardant lithium hexafluorophosphate organic solution preparation method, lithium hexafluorophosphate and lithium battery

Abstract

The application discloses a preparation method of a flame-retardant lithium hexafluorophosphate organic solution, lithium hexafluorophosphate and a lithium battery. The preparation method comprises the following steps: mixing and reacting a lithium hexafluorophosphate salt and a benign flame-retardant solvent solution containing a lithium compound to obtain a lithium hexafluorophosphate solution with a flame-retardant effect, wherein the benign flame-retardant solvent comprises at least one of a phosphate ester and a phosphite ester; removing part of the solvent in the lithium hexafluorophosphate solution with the flame-retardant effect to obtain a concentrated solution; adding a carbonate to the concentrated solution to remove impurities; and then removing the carbonate to obtain the flame-retardant lithium hexafluorophosphate organic solution. The preparation method of the flame-retardant lithium hexafluorophosphate organic solution provided by the application does not require a strict anhydrous and anaerobic reaction environment, and the reaction speed is fast. The obtained flame-retardant lithium hexafluorophosphate organic solution does not need to go through processes such as drying, crystallization and dissolution, and can be directly used in a battery and has a certain flame-retardant property. The performance of the flame-retardant lithium hexafluorophosphate organic solution is similar to that of a commercial electrolyte.

Description

Technical Field

[0001] This invention relates to the field of lithium hexafluorophosphate preparation technology, and particularly to a method for preparing flame-retardant lithium hexafluorophosphate organic solution, lithium hexafluorophosphate, and lithium batteries. Background Technology

[0002] Driven by the rapid growth of electric vehicles, the lithium battery industry continues its rapid growth momentum. Industry innovation is accelerating, with new products and technologies constantly emerging, and various new battery technologies being introduced one after another. The lithium battery industry is also moving forward with the new opportunities of the times. Lithium-ion batteries have advantages such as high energy density, high voltage, long lifespan, and low self-discharge rate, and are currently widely used in mobile devices, electric vehicles, energy storage systems, and other fields.

[0003] Electrolyte is one of the four key raw materials for lithium batteries. It serves as the carrier for ion transport within the battery, acting as a conductor between the positive and negative electrodes to provide an environment for lithium ions to freely intercalate and deintercalate. It plays a crucial role in the battery's energy density, power density, cycle life, safety performance, and wide-temperature operation. Among the three main components of the electrolyte, the solvent remains relatively constant; the key to improving performance lies in the lithium salt and additives. The lithium salt determines the basic physicochemical properties of the electrolyte and is the most important component affecting the characteristics of lithium batteries. Currently, considering factors such as battery cost and safety performance, the mainstream lithium salt is lithium hexafluorophosphate, which offers high electrochemical reliability, room temperature operating range, and price advantages due to industrial-scale production.

[0004] Currently, the main synthesis processes for lithium hexafluorophosphate include gas-solid reaction, hydrofluoric acid solvent method, organic solvent method, and ion exchange method. Large-scale industrial production primarily uses the hydrofluoric acid solvent method, where lithium halides are dissolved in anhydrous hydrogen fluoride, and then high-purity PF5 gas is introduced to react and generate lithium hexafluorophosphate crystals. These crystals are then separated and dried to obtain the final lithium hexafluorophosphate product. This reaction occurs in the liquid phase, is uniform and easily controlled, facilitating continuous production, and boasts a fast reaction rate and high conversion rate. However, this process requires the addition of an inert gas such as nitrogen for protection, resulting in relatively high energy consumption and cost. Furthermore, the crystallization process after the reaction is a significant challenge. In addition, the lithium hexafluorophosphate prepared by these methods is always a solid after crystallization and drying, requiring dissolution in an electrolyte solvent for subsequent use. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention directly obtains a lithium hexafluorophosphate electrolyte with flame-retardant properties without the need for crystallization followed by dissolution, and applies it to batteries; in addition, lithium hexafluorophosphate can be crystallized from the lithium hexafluorophosphate electrolyte for further application in lithium-ion batteries.

[0006] To achieve the above objectives, the present invention provides a method for preparing a flame-retardant lithium hexafluorophosphate organic solution, comprising,

[0007] A lithium hexafluorophosphate solution is obtained by mixing and reacting a solution of a benign flame-retardant solvent containing lithium compounds, wherein the benign flame-retardant solvent includes at least one of phosphate esters and phosphites.

[0008] A concentrated solution is obtained by removing some of the solvent from a lithium hexafluorophosphate solution that has a flame-retardant effect. Carbonate is added to the concentrated solution to remove impurities, and then the carbonate is removed to obtain a flame-retardant lithium hexafluorophosphate organic solution.

[0009] Furthermore, the benign flame-retardant solvent solutions of hexafluorophosphate and lithium-containing compounds are prepared by dissolving dried hexafluorophosphate and lithium-containing compounds in benign flame-retardant solvents, respectively.

[0010] Further, the molar ratio of the hexafluorophosphate to the lithium-containing compound is 1:(1-2), and exemplary ratios can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, and other ratios within the range. If the ratio is too low, potassium hexafluorophosphate will not be completely converted into lithium hexafluorophosphate, affecting the yield; if the ratio is too high, too much lithium compound will remain, affecting subsequent impurity removal steps and ultimately affecting product purity. The amount of undesirable solvents such as halogenated hydrocarbons will also increase. It should be noted that the molar concentration of the solution formed by the hexafluorophosphate and the lithium-containing compound is not limited; it is only necessary to ensure that the molar ratio of hexafluorophosphate to the lithium-containing compound in the two solutions is 1:(1-2).

[0011] Furthermore, the hexafluorophosphate includes at least one of ammonium hexafluorophosphate, sodium hexafluorophosphate, and potassium hexafluorophosphate;

[0012] The lithium-containing compound includes at least one of lithium nitrate, lithium chloride, lithium carbonate, lithium oxalate, and lithium hydroxide.

[0013] Furthermore, the phosphate ester includes at least one of trimethyl phosphate and triethyl phosphate;

[0014] The phosphite includes at least one of tripropyl phosphite, tributyl phosphite, and triphenyl phosphite.

[0015] Furthermore, the reaction between hexafluorophosphate and the benign flame-retardant solvent solution containing lithium compounds is carried out at room temperature for 12 to 24 hours, exemplarily 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, and 24 hours; the reaction temperature is 80 to 90 degrees Celsius, exemplarily 80 degrees Celsius, 85 degrees Celsius, and 90 degrees Celsius.

[0016] Furthermore, vacuum distillation is used to remove some of the solvent from the flame-retardant lithium hexafluorophosphate solution, and vacuum distillation is continued until the beneficial flame-retardant solvent can no longer be distilled off to obtain a concentrated solution.

[0017] Further, the carbonate includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate;

[0018] The volume of the carbonate is 3 to 5 times the volume of the concentrate.

[0019] Furthermore, the benign flame-retardant solvent and the carbonate are also recycled.

[0020] The present invention also provides a flame-retardant lithium hexafluorophosphate organic solution, which is obtained by the above-described method for preparing the flame-retardant lithium hexafluorophosphate organic solution.

[0021] The present invention also provides lithium hexafluorophosphate, which is obtained by adding a halogenated hydrocarbon to the above-mentioned flame-retardant lithium hexafluorophosphate organic solution and then crystallizing it, wherein the halogenated hydrocarbon includes at least one of dichloromethane, trichloromethane, carbon tetrachloride, and trichloroethane.

[0022] The present invention also provides a lithium battery in which the electrolyte includes the above-mentioned flame-retardant lithium hexafluorophosphate organic solution; or, the electrolyte includes the above-mentioned lithium hexafluorophosphate.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The flame-retardant lithium hexafluorophosphate organic solution preparation method provided by the present invention does not require a harsh anhydrous and oxygen-free reaction environment. The reaction speed is fast, precipitation occurs upon contact, and the reaction process is transparent and controllable. The obtained flame-retardant lithium hexafluorophosphate organic solution does not require drying, crystallization, and re-dissolution processes and can be used directly in batteries. It is also compatible with graphite, has certain flame retardancy, and the assembled secondary battery has good electrochemical performance, similar to that of commercial electrolytes.

[0025] 2. The preparation method provided by this invention has mild reaction conditions, simple steps, low raw material cost, does not require the use of toxic or highly corrosive substances, and does not have high requirements for production equipment, which is conducive to realizing industrial production. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The equation for the reaction of preparing lithium hexafluorophosphate in Example 1 of the present invention is shown;

[0028] Figure 2 The combustion performance of the flame-retardant lithium hexafluorophosphate organic solution of Example 1 of the present invention is shown in the diagrams under open flame and after the open flame is removed.

[0029] Figure 3 The electrochemical performance diagram of Application Example 1 of the present invention is shown;

[0030] Figure 4 The electrochemical performance diagram of application example 2 of the present invention is shown. Detailed Implementation

[0031] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The source of the experimental materials used in the following embodiments of the present invention is not particularly limited; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0033] Example 1

[0034] A method for preparing a flame-retardant lithium hexafluorophosphate organic solution includes the following steps:

[0035] S1. Weigh out 36.82 g of dry white crystalline potassium hexafluorophosphate and 27.58 g of dry white crystalline lithium nitrate in a glove box, and dissolve them in 300 mL and 200 mL of trimethyl phosphate, respectively, to obtain two solutions. Mix the two solutions and stir the mixture at room temperature for 24 h. Figure 1 The reaction equation is also shown. After the reaction is completed, the mixture is filtered to obtain a lithium hexafluorophosphate solution with flame retardant effect.

[0036] S2. The flame-retardant lithium hexafluorophosphate solution is distilled under reduced pressure at 85°C until trimethyl phosphate can no longer be distilled off to obtain a concentrated solution. The concentrated solution is then transferred to a glove box, and three times the volume of dimethyl carbonate is added and allowed to stand for 12 hours. The precipitate is filtered off, and then dimethyl carbonate is removed and recovered by rotary evaporation. Finally, a trimethyl phosphate solution of lithium hexafluorophosphate with a concentration of about 2.5 mol / L is obtained, which is the flame-retardant lithium hexafluorophosphate organic solution. Figure 2 The combustion performance of the flame-retardant lithium hexafluorophosphate organic solution prepared in this embodiment under open flame and after the open flame is removed is shown. It can be seen that there is no flame after the open flame is removed, which indicates that the flame-retardant lithium hexafluorophosphate organic solution prepared in this embodiment has good flame-retardant properties.

[0037] In this embodiment, the molar ratio of potassium hexafluorophosphate to lithium nitrate is 1:2; trimethyl phosphate and dimethyl carbonate can be recovered and recycled.

[0038] Example 2

[0039] A method for preparing a flame-retardant lithium hexafluorophosphate organic solution includes the following steps:

[0040] S1. Weigh 36.82g of dry white crystalline potassium hexafluorophosphate and 16.95g of dry white crystalline lithium chloride in a glove box and dissolve them in 300mL and 200mL of trimethyl phosphate respectively to obtain two solutions. Mix the two solutions and stir at room temperature for 24h. After the reaction is completed, filter to obtain a lithium hexafluorophosphate solution with flame retardant effect.

[0041] S2. The flame-retardant lithium hexafluorophosphate solution is distilled under reduced pressure at 85°C until trimethyl phosphate can no longer be distilled off to obtain a concentrated solution. The concentrated solution is then transferred to a glove box, and diethyl carbonate with a volume of 4 times that of the concentrated solution is added and allowed to stand for 12 hours. The precipitate is filtered off, and then diethyl carbonate is removed and recovered by rotary evaporation. Finally, a trimethyl phosphate solution of lithium hexafluorophosphate with a concentration of about 2 mol / L is obtained, which is the flame-retardant lithium hexafluorophosphate organic solution.

[0042] In this embodiment, the molar ratio of potassium hexafluorophosphate to lithium chloride is 1:2; trimethyl phosphate and diethyl carbonate can be recovered and recycled.

[0043] Example 3

[0044] A method for preparing a flame-retardant lithium hexafluorophosphate organic solution includes the following steps:

[0045] S1. Weigh 36.82g of dry white crystalline potassium hexafluorophosphate and 27.58g of dry white crystalline lithium nitrate in a glove box and dissolve them in 300mL and 200mL of triethyl phosphate respectively to obtain two solutions. Mix the two solutions and stir at room temperature for 12h. After the reaction is completed, filter to obtain a lithium hexafluorophosphate solution with flame retardant effect.

[0046] S2. The flame-retardant lithium hexafluorophosphate solution is distilled under reduced pressure at 90°C until triethyl phosphate can no longer be distilled off to obtain a concentrated solution. The concentrated solution is then transferred to a glove box, and dimethyl carbonate is added in a volume of 5 times that of the concentrated solution and allowed to stand for 12 hours. The precipitate is filtered off, and dimethyl carbonate is removed and recovered by rotary evaporation. Finally, a triethyl phosphate solution of lithium hexafluorophosphate with a concentration of about 2.5 mol / L is obtained, which is the flame-retardant lithium hexafluorophosphate organic solution.

[0047] In this embodiment, the molar ratio of potassium hexafluorophosphate to lithium nitrate is 1:2; triethyl phosphate and dimethyl carbonate can be recovered and recycled.

[0048] Example 4

[0049] A method for preparing a flame-retardant lithium hexafluorophosphate organic solution includes the following steps:

[0050] S1. Weigh 36.82g of dry white crystalline potassium hexafluorophosphate and 27.58g of dry white crystalline lithium nitrate in a glove box and dissolve them in 300mL and 200mL of tripropyl phosphite respectively to obtain two solutions. Mix the two solutions and stir at room temperature for 24h. After the reaction is completed, filter to obtain a lithium hexafluorophosphate solution with flame retardant effect.

[0051] S2. The flame-retardant lithium hexafluorophosphate solution is distilled under reduced pressure at 85°C until tripropyl phosphite can no longer be distilled off to obtain a concentrated solution. The concentrated solution is then transferred to a glove box, and dimethyl carbonate is added in a volume of 4 times that of the concentrated solution and allowed to stand for 12 hours. The precipitate is filtered off, and dimethyl carbonate is removed and recovered by rotary evaporation. Finally, a lithium hexafluorophosphate tripropyl phosphite solution with a concentration of approximately 2.5 mol / L is obtained, which is the flame-retardant lithium hexafluorophosphate organic solution.

[0052] In this embodiment, the molar ratio of potassium hexafluorophosphate to lithium nitrate is 1:2; tripropyl phosphite and dimethyl carbonate can be recovered and recycled.

[0053] Comparative Example 1

[0054] A method for preparing a flame-retardant lithium hexafluorophosphate organic solution includes the following steps:

[0055] S1. Weigh 36.82g of dry white crystalline potassium hexafluorophosphate and 27.58g of dry white crystalline lithium nitrate in a glove box and dissolve them in 300mL and 200mL of tripropyl phosphite respectively to obtain two solutions. Mix the two solutions and stir at room temperature for 24h. After the reaction is completed, filter to obtain a lithium hexafluorophosphate solution with flame retardant effect.

[0056] S2. Distill the flame-retardant lithium hexafluorophosphate solution under reduced pressure at 85°C until tripropyl phosphite can no longer be distilled off to obtain a concentrated solution, which is the flame-retardant lithium hexafluorophosphate organic solution.

[0057] In this comparative example, the molar ratio of potassium hexafluorophosphate to lithium nitrate is 1:2; tripropyl phosphite can be recovered and recycled.

[0058] Comparative Example 2

[0059] S1. Weigh 55.23g of dry white crystalline potassium hexafluorophosphate and 27.58g of dry white crystalline lithium nitrate in a glove box and dissolve them in 400mL and 200mL of trimethyl phosphate respectively to obtain two solutions. Mix the two solutions and stir at room temperature for 24h. After the reaction is completed, filter to obtain a lithium hexafluorophosphate solution with flame retardant effect.

[0060] S2. The flame-retardant lithium hexafluorophosphate solution is distilled under reduced pressure at 85°C until trimethyl phosphate can no longer be distilled off to obtain a concentrated solution. The concentrated solution is then transferred to a glove box, and three times the volume of dimethyl carbonate is added and allowed to stand for 12 hours. The precipitate is filtered off, and then dimethyl carbonate is removed and recovered by rotary evaporation. Finally, a trimethyl phosphate solution of lithium hexafluorophosphate with a concentration of about 2.5 mol / L is obtained, which is the flame-retardant lithium hexafluorophosphate organic solution.

[0061] In this embodiment, the molar ratio of potassium hexafluorophosphate to lithium nitrate is 1.5:2; trimethyl phosphate and dimethyl carbonate can be recovered and recycled.

[0062] Comparative Example 3

[0063] S1. Weigh 36.82g of dry white crystalline potassium hexafluorophosphate and 55.16g of dry white crystalline lithium nitrate in a glove box and dissolve them in 300mL and 400mL of trimethyl phosphate respectively to obtain two solutions. Mix the two solutions and stir at room temperature for 24h. After the reaction is completed, filter to obtain a lithium hexafluorophosphate solution with flame retardant effect.

[0064] S2. The flame-retardant lithium hexafluorophosphate solution is distilled under reduced pressure at 85°C until trimethyl phosphate can no longer be distilled off to obtain a concentrated solution. The concentrated solution is then transferred to a glove box, and four times the volume of dimethyl carbonate is added and allowed to stand for 12 hours. The precipitate is filtered off, and then dimethyl carbonate is removed and recovered by rotary evaporation. Finally, a lithium hexafluorophosphate trimethyl phosphate solution with a concentration of about 2.5 mol / L is obtained, which is the flame-retardant lithium hexafluorophosphate organic solution.

[0065] In this embodiment, the molar ratio of potassium hexafluorophosphate to lithium nitrate is 1:4; trimethyl phosphate and dimethyl carbonate can be recovered and recycled.

[0066] Example 5

[0067] A method for preparing lithium hexafluorophosphate involves adding dichloromethane to a flame-retardant lithium hexafluorophosphate organic solution prepared according to Example 1, precipitating crystals, and allowing it to stand for 6 hours. The clear liquid is then poured out, and the crystals are washed three times with dichloromethane. The liquid adhering to the surface is then vacuum-dried in a glove box vacuum chamber to obtain lithium hexafluorophosphate. The collected clear liquid is then concentrated and crystallized to recover dichloromethane, trimethyl phosphate, and excess raw material salts.

[0068] Example 6

[0069] A method for preparing lithium hexafluorophosphate involves adding chloroform to a flame-retardant lithium hexafluorophosphate organic solution prepared according to Example 2, allowing it to precipitate crystals, standing for 6 hours, pouring out the clear liquid, washing the crystals three times with chloroform, and vacuum drying the liquid adhering to the surface in a glove box vacuum chamber to obtain lithium hexafluorophosphate. The collected clear liquid is then concentrated, crystallized, and chloroform, trimethyl phosphate, and excess raw material salts are recovered.

[0070] Example 7

[0071] A method for preparing lithium hexafluorophosphate involves adding carbon tetrachloride to a flame-retardant lithium hexafluorophosphate organic solution prepared according to Example 3, allowing it to precipitate crystals, standing for 6 hours, pouring out the clear liquid, washing the crystals three times with dichloromethane, and vacuum drying the liquid adhering to the surface in a glove box vacuum chamber to obtain lithium hexafluorophosphate. The collected clear liquid is then concentrated, crystallized, and the dichloromethane, triethyl phosphate, and excess raw material salt are recovered.

[0072] Example 8

[0073] A method for preparing lithium hexafluorophosphate involves adding carbon tetrachloride to a flame-retardant lithium hexafluorophosphate organic solution prepared according to Example 4, allowing it to precipitate crystals, standing for 6 hours, pouring out the clear liquid, washing the crystals three times with dichloromethane, and vacuum drying the liquid adhering to the surface in a glove box vacuum chamber to obtain lithium hexafluorophosphate. The collected clear liquid is then concentrated, crystallized, and the dichloromethane, tripropyl phosphite, and excess raw material salt are recovered.

[0074] Comparative Example 4

[0075] A method for preparing lithium hexafluorophosphate involves adding dichloromethane to a flame-retardant lithium hexafluorophosphate organic solution prepared according to Comparative Example 1, precipitating crystals, and allowing it to stand for 6 hours. The clear liquid is then poured out, and the crystals are washed three times with dichloromethane. The liquid adhering to the surface is then vacuum-dried in a glove box vacuum chamber to obtain lithium hexafluorophosphate. The collected clear liquid is then concentrated, crystallized, and the dichloromethane, trimethyl phosphate, and excess raw material salt are recovered.

[0076] Comparative Example 5

[0077] A method for preparing lithium hexafluorophosphate involves adding dichloromethane to a flame-retardant lithium hexafluorophosphate organic solution prepared according to Comparative Example 2, precipitating crystals, and allowing it to stand for 6 hours. The clear liquid is then poured out, and the crystals are washed three times with dichloromethane. The liquid adhering to the surface is then vacuum-dried in a glove box vacuum chamber to obtain lithium hexafluorophosphate. The collected clear liquid is then concentrated, crystallized, and the dichloromethane, trimethyl phosphate, and excess raw material salt are recovered.

[0078] Comparative Example 6

[0079] A method for preparing lithium hexafluorophosphate involves adding dichloromethane to a flame-retardant lithium hexafluorophosphate organic solution prepared according to Comparative Example 3, precipitating crystals, and allowing it to stand for 6 hours. The clear liquid is then poured out, and the crystals are washed three times with dichloromethane. The liquid adhering to the surface is then vacuum-dried in a glove box vacuum chamber to obtain lithium hexafluorophosphate. The collected clear liquid is then concentrated, crystallized, and the dichloromethane, trimethyl phosphate, and excess raw material salt are recovered.

[0080] Test case

[0081] The main components of lithium hexafluorophosphate in Examples 5 to 8 and Comparative Example 2 of this invention were tested using inductively coupled plasma atomic emission spectrometry (ICP), elemental analysis, and moisture analyzer. The results are shown in Figure 1.

[0082] Table 1 Main Components of Lithium Hexafluorophosphate Products

[0083] Example <![CDATA[Li + (ppm)]]> <![CDATA[K + (ppm)]]> N content Moisture content (ppm) Commercial lithium hexafluorophosphate 772.47 0.04 0.00％ 0.4 Example 5 732.82 0.08 0.00％ 0.4 Example 6 681.00 0.17 0.03％ 0.5 Example 7 710.75 1.21 0.18％ 0.5 Example 8 697.00 1.73 0.25％ 0.4 Comparative Example 4 104.31 10.3 11.00％ 0.7 Comparative Example 5 307.3 187.01 0.07％ 0.6 Comparative Example 6 264.11 207.7 23％ 0.4

[0084] As can be seen from the results in Table 1, the lithium hexafluorophosphate prepared in the embodiments of this invention has a composition similar to that of commercially available lithium hexafluorophosphate. This is attributed to the good solubility of phosphate esters or phosphites in lithium salts and potassium hexafluorophosphate, which facilitates the reaction. Furthermore, the product exists in ionic form in organic solvents, so the properties of easily degraded lithium hexafluorophosphate are not affected by heating or exposure to air in the early stages of the process. Subsequent use of carbonates further removed impurities, resulting in a high-purity flame-retardant lithium hexafluorophosphate organic solution. Further precipitation of lithium hexafluorophosphate using unsuitable solvents such as dichloromethane, trichloromethane, or carbon tetrachloride solved the problems of difficult preparation and demanding environmental requirements for lithium hexafluorophosphate. In addition, the lithium hexafluorophosphate prepared in the embodiments is significantly superior to that in comparative examples 5-6, indicating the need for strict control of the molar ratio of hexafluorophosphate to lithium-containing compounds.

[0085] Application Example 1

[0086] The flame-retardant lithium hexafluorophosphate organic solution from Example 1 was formulated into a lithium battery electrolyte with film-forming additives and assembled into graphite / lithium coin cells to test its electrochemical performance, thereby characterizing the performance of the flame-retardant lithium hexafluorophosphate organic solution of the example. In the lithium battery electrolyte formulation, the film-forming additives were fluoroethylene carbonate, vinylene carbonate, and lithium difluorooxalate borate. The amount of fluoroethylene carbonate added was 3% of the total electrolyte volume, the amount of vinylene carbonate added was 2% of the total electrolyte volume, and the amount of lithium difluorooxalate borate was 0.05 mol / L. During assembly, a glass fiber separator (Whatman WF / F) was used. Charge-discharge performance and cycle performance are as follows: Figure 3 As shown in the figure, the assembled graphite / lithium coin cell battery was charged and discharged at 0.25C in the first week, followed by cycling at a current density of 0.5C. The specific capacity at the start of the first week was 293.4 mAh / g, and the coulombic efficiency at the start of the first week was 82.2%. The average coulombic efficiency over 200 weeks was 99.6%, and the specific capacity at the start of the 200th week was 217.4 mAh / g, with a capacity retention of 74.1%. These results demonstrate that the electrolyte prepared using the flame-retardant lithium hexafluorophosphate organic solution of Example 1 of this invention has excellent battery cycling performance.

[0087] Application Example 2

[0088] The lithium hexafluorophosphate from Example 5 was used to prepare a lithium battery electrolyte, with the salt solvent being ethylene carbonate and dimethyl carbonate in a 1:1 volume ratio. A graphite / lithium coin cell was assembled using a glass fiber separator (Whatman WF / F) and its electrochemical performance was tested. The results are as follows: Figure 4As shown in the figure, the first week involved a 0.25C charge-discharge cycle, followed by a 0.5C current density cycle. The average coulombic efficiency over 200 cycles was 99.8%, and the charge specific capacity at the 200th week was 358.83 mAh / g, with a capacity retention of 99%. The coulombic efficiency is similar to that of commercial lithium hexafluorophosphate electrolytes, demonstrating good long-cycle performance.

[0089] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a fire-retardant lithium hexafluorophosphate organic solution, characterized in that, The application relates to a method for preparing a lithium hexafluorophosphate solution with a fire-retardant effect. The method comprises the following steps: mixing and reacting a benign fire-retardant solvent solution of a lithium hexafluorophosphate and a lithium-containing compound to obtain a lithium hexafluorophosphate solution with a fire-retardant effect, wherein the benign fire-retardant solvent comprises at least one of a phosphate and a phosphite; The method further comprises the following steps: removing part of the solvent in the lithium hexafluorophosphate solution with a fire-retardant effect to obtain a concentrated solution, adding a carbonate to the concentrated solution to remove impurities, and then removing the carbonate to obtain a fire-retardant lithium hexafluorophosphate organic solution.

2. The method for preparing flame-retardant lithium hexafluorophosphate organic solution according to claim 1, characterized in that, The molar ratio of the lithium hexafluorophosphate to the lithium-containing compound is 1: (1-2).

3. The method for preparing flame-retardant lithium hexafluorophosphate organic solution according to claim 1, characterized in that, The lithium hexafluorophosphate comprises at least one of ammonium hexafluorophosphate, sodium hexafluorophosphate and potassium hexafluorophosphate. The lithium-containing compound comprises at least one of lithium nitrate, lithium chloride, lithium carbonate, lithium oxalate and lithium hydroxide.

4. The method for preparing flame-retardant lithium hexafluorophosphate organic solution according to claim 1, characterized in that, The phosphate comprises at least one of trimethyl phosphate and triethyl phosphate. The phosphite comprises at least one of tripropyl phosphite, tributyl phosphite and triphenyl phosphite.

5. The method for preparing flame-retardant lithium hexafluorophosphate organic solution according to claim 1, characterized in that, The method further comprises the following step: removing part of the solvent in the lithium hexafluorophosphate solution with a fire-retardant effect by using reduced-pressure distillation, and performing the reduced-pressure distillation until the benign fire-retardant solvent cannot be distilled out to obtain the concentrated solution.

6. The method for preparing flame-retardant lithium hexafluorophosphate organic solution according to claim 1, characterized in that, The carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate and propylene carbonate. The volume of the carbonate is 3-5 times the volume of the concentrated solution.

7. The process for preparing a flame-resistant solution of lithium hexafluorophosphate according to any one of claims 1 to 6, characterized in that, The benign fire-retardant solvent and the carbonate can be recycled.

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