A Li + Preparation method of -NH2 / mesoporous carbon adsorbent and liquid lithium hexafluorophosphate

Abstract

The application discloses a Li + A preparation method of Li + Amino-functionalized mesoporous carbon adsorbent and liquid lithium hexafluorophosphate, which is suitable for an amino-functionalized impurity removal adsorbent in a hydrogen fluoride-containing system. A liquid lithium hexafluorophosphate solution is obtained by reacting a carbonate suspension of LiF with phosphorus pentafluoride, and then the solution is functionalized by an amino group, wherein the amino-functionalized agent is 3-aminopropyl dimethyl fluorosilane, which can exist stably in the impurity removal system containing hydrogen fluoride. In a conventional preparation method of the liquid lithium hexafluorophosphate, a silazane / phosphate or lithiumized molecular sieve is usually added to remove water, acid or metal ions, however, the addition of the additive will affect the performance of a battery, and the preparation process of the lithiumized molecular sieve is complex, and it is difficult to realize industrialization. The Li + The amino-functionalized mesoporous carbon adsorbent can realize deep removal of impurities in a liquid lithium hexafluorophosphate system.

Description

Technical Field

[0001] This invention belongs to the field of preparation of liquid lithium hexafluorophosphate, specifically relating to an adsorbent suitable for hydrogen fluoride-containing systems and a method for preparing liquid lithium hexafluorophosphate. Background Technology

[0002] Lithium hexafluorophosphate is the most watched material in the electrolyte industry chain. It has high solubility, good oxidation resistance, strong electrochemical stability, and high compatibility with positive and negative electrode materials. It is known as the best lithium battery electrolyte in terms of comprehensive performance.

[0003] LiF + PF5 → LiPF6

[0004] Currently, there are two industrial production routes for lithium hexafluorophosphate (LiPF6). The first is the solid-state LiPF6 route, where gaseous phosphorus pentafluoride reacts with lithium fluoride dissolved in anhydrous hydrogen fluoride solution in an HF system to synthesize a LiPF6 solution, which is then crystallized at a lower temperature to obtain a high-purity crystalline product. However, the solid-state crystallization method suffers from several drawbacks. The crystallization process is difficult to control, resulting in large crystal particles. Furthermore, the LiPF6·HF adduct, along with small amounts of metal ions and moisture, are easily trapped within the crystal particles, making them difficult to remove and affecting the product's applicability. Additionally, the long cooling crystallization time leads to low production efficiency and a low overall product yield. The second method is the carbonate solvent method for synthesizing LiPF6. Since carbonates are important solvents for electrolyte preparation, the synthesized LiPF6 carbonate solution does not require additional separation of the solvent and LiPF6, eliminating the need for complex crystallization processes and equipment. This significantly improves production efficiency, reduces production costs, and enhances the product's competitiveness.

[0005] Compared to solid lithium hexafluorophosphate preparation methods, liquid lithium hexafluorophosphate, due to the lack of crystallization and purification, has significantly higher levels of HF, moisture, and Fe metal ions in the system than the control targets, resulting in a low product qualification rate. This issue has become a major challenge that urgently needs to be addressed in the preparation of liquid lithium hexafluorophosphate.

[0006] In traditional methods, silazane / phosphate ester additives are usually added to remove acid and water. However, these additives are difficult to remove once introduced, which affects battery performance. Alternatively, lithium molecular sieves are added to remove impurities, but lithium molecular sieves are expensive and complex to prepare, making them difficult to industrialize.

[0007] Patent CN102107093A mentions using lithium-ion molecular sieves to remove water from the carbonate solution of lithium hexafluorophosphate, reducing the water content from 104 ppm to below 10 ppm. However, this method has a long impurity removal time, and the preparation of lithium-ion molecular sieves is complex. Patent CN1148829C mentions adding oxides (MgO, Al2O3) to the carbonate solution of lithium hexafluorophosphate to control free acid below 30 ppm, but this method introduces metallic impurities, limiting its industrial application. Patent CN111525192A reports that adding aminosilane additives to lithium-ion electrolytes can remove water and acid, but nitrogen-containing substances have poor stability during battery charging and discharging, affecting battery life. Summary of the Invention

[0008] This invention provides a Li + A method for preparing -NH2 / mesoporous carbon adsorbents is provided, along with a method for preparing liquid lithium hexafluorophosphate. The Li used... + -NH2 / mesoporous carbon adsorbents can achieve deep removal of impurities from liquid lithium hexafluorophosphate systems, improving product quality and being easy to recycle and economical.

[0009] To achieve the above-mentioned objectives, the technical solution provided by this invention is as follows:

[0010] A method for preparing high-purity liquid lithium hexafluorophosphate includes the following steps:

[0011] (a) A liquid lithium hexafluorophosphate solution was obtained by reacting a suspension of LiF in a carbonate solvent with phosphorus pentafluoride.

[0012] (b) Lithium-functionalized amino groups in lithium + In the presence of -NH2 / mesoporous carbon adsorbent, the reaction solution is subjected to deep deacidification, dehydration and removal of Fe metal ions.

[0013] Furthermore, in the LiF carbonate solvent suspension, the mass of LiF is 1-5% of the mass of carbonate, preferably 3-4%.

[0014] The carbonate is one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, preferably dimethyl carbonate.

[0015] Furthermore, the molar ratio of PF5 to LiF is 1.01-1.05:1, preferably 1.02-1.03:1.

[0016] Furthermore, the reaction temperature is 5-40℃, preferably 10-20℃.

[0017] Furthermore, the reaction pressure is 0.1-1.0 MPa, preferably 0.4-0.6 MPa.

[0018] Furthermore, the reaction time is 1-6 hours, preferably 3-4 hours.

[0019] The Li described in this invention + The preparation method of -NH2 / mesoporous carbon adsorbent includes the following steps:

[0020] (1) Disperse mesoporous carbon in toluene solution, stir and add 3-aminopropyldimethylfluorosilane, and then react under heating conditions to carry out amination. After the reaction is completed, wash with ethanol and filter to separate solid NH2 / mesoporous carbon.

[0021] (2) Add NH2 / mesoporous carbon to a quantitative amount of water, add dilute hydrofluoric acid to adjust the pH of the system to weak acidity, and then add solid LiF under stirring and heating conditions to lithiate NH2 / mesoporous carbon. After the process is completed, filter the solid and dry it.

[0022] Further, in step (1), the mesoporous carbon and 3-aminopropyldimethylfluorosilane are added to toluene to prepare a suspension. Based on the total mass of toluene as 100%, the mesoporous carbon content is 1-5 wt%, preferably 2-3 wt%; the 3-aminopropyldimethylfluorosilane content is 0.3-1.0 wt%, preferably 0.6-0.8 wt%; and the amount of ethanol used for washing is 5-10 times the amount of toluene used, preferably 6-8 times.

[0023] Further, in step (2), based on the mass of water, the NH2 / mesoporous carbon content is 3-7 wt%, preferably 4-5 wt%; the lithium fluoride content is 0.1-0.6 wt%, preferably 0.2-0.4 wt%.

[0024] Furthermore, in step (1), the reaction temperature is 70-100℃, preferably 80-90℃; the reaction time is 2-5h, preferably 3-4h.

[0025] Furthermore, in step (2), the pH of the system is adjusted to 4-6, preferably 5-6, using dilute hydrofluoric acid.

[0026] Further, in step (2), the heating temperature is 20-40℃, preferably 25-30℃; the lithiation time is 5-9h, preferably 7-8h.

[0027] This invention provides a method for removing impurities from liquid lithium hexafluorophosphate, comprising the following steps: adding Li to a synthesized LiPF6 carbonate solution under ambient temperature and pressure conditions. + -NH2 / mesoporous carbon adsorbent, after stirring to remove impurities for a certain period of time, the solution is filtered to obtain high-purity liquid lithium hexafluorophosphate product.

[0028] Furthermore, the Li +The amount of -NH2 / mesoporous carbon adsorbent is 0.5-2.0% of the LiPF6 carbonate solution, preferably 1.0-1.5 wt%; the impurity removal temperature is 10-30℃, preferably 15-20℃; the impurity removal time is 0.5-4h, preferably 2-3h; and the pressure is atmospheric pressure.

[0029] The LiPF6 carbonate solution synthesized in this invention has the following composition: LiPF6 5.5-22.6%, water: 200-450 ppm, acidity (as HF): 490-760 ppm, Fe metal ions: 45-90 ppm, and the remainder is carbonate.

[0030] The amino-functionalizing agent of the mesoporous carbon is 3-aminopropyldimethylfluorosilane. Compared with the conventional amino-functionalizing agent 3-aminopropyldimethylsiloxane, 3-aminopropyldimethylfluorosilane can exist stably in a purification system containing hydrogen fluoride, while 3-aminopropyldimethylsiloxane will be acidified into methanol and alkanes due to the presence of silicon-oxygen structure, and silicon will be converted into silicon tetrafluoride.

[0031] The Li used in this invention + -NH2 / mesoporous carbon adsorbents exhibit highly efficient impurity removal. Mesoporous carbon itself possesses abundant mesoporous channels, providing ample space for impurity adsorption. By modifying the mesoporous carbon with functional groups to load amino groups, the adsorption and removal capabilities of mesoporous carbon for HF, H2O, and metal ions are enhanced. Furthermore, lithiation of NH2 / mesoporous carbon removes potential impurity ions from the adsorbent and, on the other hand, the loaded Lithium... + Li ions can replace Fe metal ions in liquid lithium hexafluorophosphate solution. In summary, Li + -NH2 / mesoporous carbon adsorbent can efficiently remove water, HF and Fe metal ions from liquid lithium hexafluorophosphate solution.

[0032] The positive effects of this invention are as follows:

[0033] The method of this invention has the advantages of mild process conditions (low temperature, normal pressure) and high product purity. Under optimal conditions, the yield of liquid lithium hexafluorophosphate prepared in carbonate solvents by this method can reach 99%, with Fe metal ion content <3ppm, water content <5ppm, and acidity <10ppm in the product. Specific implementation methods

[0034] The following embodiments are not intended to limit the scope of the present invention. Any modifications or equivalent substitutions made to the present invention without departing from the spirit and scope thereof should be covered within the protection scope of the claims of the present invention.

[0035] All raw materials used in the examples are conventional raw materials in the art, and the purity specifications used are analytical grade or chemically pure.

[0036] I. Information on the source of raw materials in the following examples:

[0037] Phosphorus pentafluoride (99.97%) was purchased from Tianjin Saimet Company; battery-grade lithium fluoride was purchased from Taixing Yinxin Chemical Technology Co., Ltd.; battery-grade dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate were purchased from Inokai Technology Co., Ltd.; hydrofluoric acid and mesoporous carbon (pore size: 3.7 nm, specific surface area: 1201 m²) were also purchased. 2 / g, pore volume: 1.36cm 3 (g), toluene, and anhydrous ethanol were purchased from Aladdin Reagent Co., Ltd., and 3-aminopropyldimethylfluorosilane was purchased from Maclean Reagent Co., Ltd.

[0038] II. The following test methods are used in the various examples of the present invention:

[0039] Acidity analysis of lithium hexafluorophosphate crystal products: Using bromothymol blue as an indicator, the free acid (calculated as HF) in a 0.1 g / mL lithium hexafluorophosphate crystal sample was titrated with a 0.01 mol / L sodium hydroxide standard solution. The calculation formula is as follows:

[0040] w=(V-V0)cM / (m×10-3)

[0041] In the formula:

[0042] V—The amount of standard sodium hydroxide titration solution consumed in the titration test solution, in ml;

[0043] V0—The volume of sodium hydroxide standard solution consumed in the titration of the blank test solution, in ml;

[0044] c—The accurate concentration of the sodium hydroxide standard solution, in mol / L;

[0045] m—mass of solids in the sample, in grams;

[0046] M — Molar mass of hydrogen fluoride, in g / mol

[0047] Moisture content was determined using a Leder LSDKS-RLJ2 automatic rapid Karl Fischer moisture analyzer, with a testing range of 1 ppm to 100% water. The measurement voltage was constant current polarization detection, and the electrolysis current was an automatic pulse current of 400 mA.

[0048] Metal ion determination was performed using an ICAP7200 inductively coupled plasma optical emission spectrometer (ICP-OES) from Thermo Fisher Scientific, USA, and according to the standard GB-T19282-2014 method. The content of the corresponding cations (Fe / K / Na / Ni / Zn / Cu, etc.) was determined by comparing the standard concentration curves of each cation.

[0049] The purity of liquid lithium hexafluorophosphate was analyzed using a DIONX ICS-1500 ion chromatograph (USA), equipped with an AG14 anion guard column, an AS14 anion separator column, an ULTRA II anion regeneration suppressor, and a DS6 heated conductivity cell. The eluent consisted of a mixture of 3.5 mmol / L Na₂CO₃ and 1.0 mmol / L NaHCO₃, at a flow rate of 1.2 mL / min, a column temperature of 30 °C, and a conductivity cell temperature of 30 °C.

[0050] Example 1

[0051] 1) Preparation of liquid lithium hexafluorophosphate solution:

[0052] 300g of dimethyl carbonate was weighed and placed in a 500mL 316L reactor. 9.0g of lithium fluoride (3.0%) was added, and the mixture was stirred at 500rpm until homogeneous. Nitrogen gas was then introduced to 0.5MPa. After stabilization, 44.9g of PF5 (PF5:LiF molar ratio 1.03:1) was slowly introduced into the reactor. The reactor pressure was kept constant, the reaction temperature was 15℃, and the reaction was carried out for 3 hours. After the experiment, nitrogen gas was introduced to purge the reactor 5 times. After releasing the pressure, the reactor was disassembled to obtain liquid lithium hexafluorophosphate, which was then sampled for analysis.

[0053] Lithium hexafluorophosphate yield / % Moisture / ppm Acidity / ppm Fe ions / ppm 99.9 224 534 53

[0054] 2) Preparation of Li + -NH2 / mesoporous carbon adsorbent:

[0055] 6g of mesoporous carbon was dispersed in 300g of toluene in a three-necked flask (2%). 2.1g of 3-aminopropyldimethylfluorosilane (0.7%) was added with stirring. The mixture was then heated to 85°C and reacted under normal pressure for 3 hours. After the reaction was completed, the mixture was filtered, washed with 1800g of ethanol (6 times the volume), and then filtered again to obtain NH2 / mesoporous carbon.

[0056] 4g of NH2 / mesoporous carbon was added to 100g of water (4%) and placed in a three-necked flask. Then, 0.3g of LiF (0.3%) was added, and a small amount of 5% hydrofluoric acid was added dropwise to adjust the pH of the system to 5. The reaction temperature was controlled at 25℃, and the reaction time was 7h. After filtration, the mixture was dried at 50℃ for more than 10h to obtain Li. + -NH2 / mesoporous carbon adsorbent.

[0057] 3) Liquid lithium hexafluorophosphate for impurity removal:

[0058] Take 200g of the liquid lithium hexafluorophosphate solution from (1) into a tetrafluoroethylene flask, and add 2.0g of Li +-NH2 / mesoporous carbon adsorbent (1.0%), the reaction solution temperature was controlled at 15℃, stirred for 2h, and then the adsorbent was removed by filtration to obtain high-purity liquid lithium hexafluorophosphate, which was then sent for analysis.

[0059] Moisture / ppm Acidity / ppm Fe ions / ppm 3 5 <1

[0060] Example 2

[0061] 300g of methyl ethyl carbonate was weighed and placed in a 500mL 316L reactor. 3.0g of lithium fluoride (1.0%) was added, and the mixture was stirred at 500rpm until homogeneous. Nitrogen gas was then introduced to 0.6MPa. After stabilization, 15.3g of PF5 (PF5:LiF molar ratio 1.05:1) was slowly introduced into the reactor. The reactor pressure was kept constant, the reaction temperature was 35℃, and the reaction was carried out for 6 hours. After the experiment, nitrogen gas was introduced to purge the reactor 5 times. After releasing the pressure, the reactor was disassembled to obtain liquid lithium hexafluorophosphate, which was then sampled for analysis.

[0062] Lithium hexafluorophosphate yield / % Moisture / ppm Acidity / ppm Fe ions / ppm 99.8 313 495 88

[0063] 2) Preparation of Li + -NH2 / mesoporous carbon adsorbent:

[0064] 15g of mesoporous carbon was dispersed in 300g of toluene in a three-necked flask (5%). 1.5g of 3-aminopropyldimethylfluorosilane (0.5%) was added with stirring. The mixture was then heated to 95°C and reacted under normal pressure for 2 hours. After the reaction was completed, the mixture was filtered, washed with 2700g of ethanol (9 times the volume), and then filtered again to obtain NH2 / mesoporous carbon.

[0065] Add 5g of NH2 / mesoporous carbon to 100g of water (5%) and place the mixture in a three-necked flask. Then add 0.1g of LiF (0.1%), and adjust the pH of the system to 4 by adding a small amount of 5% hydrofluoric acid. Control the reaction temperature at 40℃ and the reaction time at 5h. Then filter and dry at 50℃ for more than 10h to obtain Li. + -NH2 / mesoporous carbon adsorbent.

[0066] 3) Liquid lithium hexafluorophosphate for impurity removal:

[0067] Take 200g of the liquid lithium hexafluorophosphate solution from (1) into a tetrafluoroethylene flask, and add 1.0g of Li + -NH2 / mesoporous carbon adsorbent (0.5%), the reaction solution temperature was controlled at 10℃, stirred for 0.5h, and then filtered to remove the adsorbent to obtain high-purity liquid lithium hexafluorophosphate, which was then sent for analysis.

[0068] Moisture / ppm Acidity / ppm Fe ions / ppm 7 6 3

[0069] Example 3

[0070] 300g of diethyl carbonate was weighed and placed in a 500mL 316L reactor. 15.0g of lithium fluoride (5.0%) was added, and the mixture was stirred at 500rpm until homogeneous. Nitrogen gas was then introduced to 0.1MPa. After stabilization, 75.6g of PF5 (PF5:LiF molar ratio 1.04:1) was slowly introduced into the reactor. The reactor pressure was kept constant, the reaction temperature was 5℃, and the reaction was carried out for 1h. After the experiment, nitrogen gas was introduced to purge the reactor 5 times. After releasing the pressure, the reactor was disassembled to obtain liquid lithium hexafluorophosphate, and a sample was taken for analysis.

[0071] Lithium hexafluorophosphate yield / % Moisture / ppm Acidity / ppm Fe ions / ppm 99.9 437 751 48

[0072] 2) Preparation of Li + -NH2 / mesoporous carbon adsorbent:

[0073] 9g of mesoporous carbon was dispersed in 300g of toluene in a three-necked flask (3%). 0.9g of 3-aminopropyldimethylfluorosilane (0.3%) was added with stirring. The mixture was then heated to 70°C and reacted under normal pressure for 4 hours. After the reaction was completed, the mixture was filtered, washed with 2100g of ethanol (7 times the amount), and then filtered again to obtain NH2 / mesoporous carbon.

[0074] 7g of NH2 / mesoporous carbon was added to 100g of water (7%) and placed in a three-necked flask. Then, 0.5g of LiF (0.5%) was added, and a small amount of 5% hydrofluoric acid was added dropwise to adjust the pH of the system to 6. The reaction temperature was controlled at 30℃, and the reaction time was 9h. After filtration, the mixture was dried at 50℃ for more than 10h to obtain Li. + -NH2 / mesoporous carbon adsorbent.

[0075] 3) Liquid lithium hexafluorophosphate for impurity removal:

[0076] Take 200g of the liquid lithium hexafluorophosphate solution from (1) into a tetrafluoroethylene flask, and add 3.0g of Li + -NH2 / mesoporous carbon adsorbent (1.5%), the reaction solution temperature was controlled at 20℃, stirred for 1.0h, and then the adsorbent was removed by filtration to obtain high-purity liquid lithium hexafluorophosphate, which was then sent for analysis.

[0077] Moisture / ppm Acidity / ppm Fe ions / ppm 11 15 6

[0078] Example 4

[0079] 1) Preparation of liquid lithium hexafluorophosphate solution:

[0080] 300g of dimethyl carbonate was weighed and placed in a 500mL 316L reactor. 6.0g of lithium fluoride (2.0%) was added, and the mixture was stirred at 500rpm until homogeneous. Nitrogen gas was then introduced to 0.8MPa. After stabilization, 29.7g of PF5 (PF5:LiF molar ratio 1.02:1) was slowly introduced into the reactor. The reactor pressure was kept constant, the reaction temperature was 20℃, and the reaction was carried out for 5 hours. After the experiment, nitrogen gas was introduced to purge the reactor 5 times. After releasing the pressure, the reactor was disassembled to obtain liquid lithium hexafluorophosphate, which was then sampled for analysis.

[0081] Lithium hexafluorophosphate yield / % Moisture / ppm Acidity / ppm Fe ions / ppm 99.8 398 672 61

[0082] 2) Preparation of Li + -NH2 / mesoporous carbon adsorbent:

[0083] 3g of mesoporous carbon was dispersed in 300g of toluene in a three-necked flask (1%). 2.4g of 3-aminopropyldimethylfluorosilane (0.8%) was added with stirring. The mixture was then heated to 100℃ and reacted under normal pressure for 5 hours. After the reaction was completed, the mixture was filtered, washed with 1500g of ethanol (5 times the amount), and then filtered again to obtain NH2 / mesoporous carbon.

[0084] 3g of NH2 / mesoporous carbon was added to 100g of water (3%) and placed in a three-necked flask. Then, 0.6g of LiF (0.6%) was added, and a small amount of 5% hydrofluoric acid was added dropwise to adjust the pH of the system to 5. The reaction temperature was controlled at 35℃, and the reaction time was 7h. After filtration, the mixture was dried at 50℃ for more than 10h to obtain Li. + -NH2 / mesoporous carbon adsorbent.

[0085] 3) Liquid lithium hexafluorophosphate for impurity removal:

[0086] Take 200g of the liquid lithium hexafluorophosphate solution from (1) into a tetrafluoroethylene flask, and add 4.0g of Li + -NH2 / mesoporous carbon adsorbent (2.0%), the reaction solution temperature was controlled at 25℃, stirred for 3.0h, and then the adsorbent was removed by filtration to obtain high-purity liquid lithium hexafluorophosphate, which was then sent for analysis.

[0087] Moisture / ppm Acidity / ppm Fe ions / ppm 14 10 5

[0088] Example 5

[0089] 1) Preparation of liquid lithium hexafluorophosphate solution:

[0090] 300g of methyl ethyl carbonate was weighed and placed in a 500mL 316L reactor. 12.0g of lithium fluoride (4.0%) was added, and the mixture was stirred at 500rpm until homogeneous. Nitrogen gas was then introduced to 1.0MPa. After stabilization, 58.7g of PF5 (PF5:LiF molar ratio 1.01:1) was slowly introduced into the reactor. The reactor pressure was kept constant, the reaction temperature was 40℃, and the reaction was carried out for 2 hours. After the experiment, nitrogen gas was introduced to purge the reactor 5 times. After releasing the pressure, the reactor was disassembled to obtain liquid lithium hexafluorophosphate, which was then sampled for analysis.

[0091] Lithium hexafluorophosphate yield / % Moisture / ppm Acidity / ppm Fe ions / ppm 99.8 350 583 72

[0092] 2) Preparation of Li + -NH2 / mesoporous carbon adsorbent:

[0093] 12g of mesoporous carbon was dispersed in 300g of toluene in a three-necked flask (4%). 3.0g of 3-aminopropyldimethylfluorosilane (1.0%) was added with stirring. The mixture was then heated to 75°C and reacted under normal pressure for 3 hours. After the reaction was completed, the mixture was filtered, washed with 3000g of ethanol (10 times the volume), and then filtered again to obtain NH2 / mesoporous carbon.

[0094] 6 g of NH₂ / mesoporous carbon was added to 100 g of water (6%) and placed in a three-necked flask. Then, 0.4 g of LiF (0.4%) was added, and a small amount of 5% hydrofluoric acid was added dropwise to adjust the pH of the system to 4. The reaction temperature was controlled at 20 °C, and the reaction time was 6 h. After filtration, the mixture was dried at 50 °C for more than 10 h to obtain Li. + -NH2 / mesoporous carbon adsorbent.

[0095] 3) Liquid lithium hexafluorophosphate for impurity removal:

[0096] Take 200g of the liquid lithium hexafluorophosphate solution from (1) into a tetrafluoroethylene flask, and add 2.0g of Li + -NH2 / mesoporous carbon adsorbent (1.0%), the reaction solution temperature was controlled at 30℃, stirred for 4.0h, and then the adsorbent was removed by filtration to obtain high-purity liquid lithium hexafluorophosphate, which was then sent for analysis.

[0097] Moisture / ppm Acidity / ppm Fe ions / ppm 9 13 11

[0098] Comparative Example 1

[0099] The synthesis of liquid lithium hexafluorophosphate and the preparation of the adsorbent were carried out in essentially the same manner as in Example 1, except that 3-aminopropyldimethylfluorosilane in the adsorbent preparation process was replaced with 3-aminopropyltrimethylsilane. The impurity content of the product after purification by the adsorbent is as follows:

[0100] Moisture / ppm Acidity / ppm Fe ions / ppm 98 364 31

Claims

1. A Li + A method of preparing a -NH2 / mesoporous carbon adsorbent, comprising the steps of: (1) mesoporous carbon is dispersed in toluene solution, 3-aminopropyl dimethyl fluorosilane is added by stirring, then amination is carried out under heating condition, after the end, washing is carried out with ethanol, and solid NH2 / mesoporous carbon is separated by filtration; (2) NH2 / mesoporous carbon is added into quantitative water, dilute hydrofluoric acid is added to adjust the pH of the system to weak acidity, then lithiumation is carried out on NH2 / mesoporous carbon by adding solid LiF under stirring and heating condition, after the end, the solid is filtered and dried.

2. The method of claim 1, wherein, In the step (1), the mesoporous carbon and 3-aminopropyl dimethyl fluorosilane are added into toluene to prepare a suspension, wherein the content of mesoporous carbon is 1-5wt% and the content of 3-aminopropyl dimethyl fluorosilane is 0.3-1.0wt% based on the total mass of toluene being 100%; the amount of ethanol used for washing is 5-10 times the amount of toluene.

3. The method of claim 1, wherein, In the step (2), the content of NH2 / mesoporous carbon is 3-7wt% and the content of LiF is 0.1-0.6wt% based on the mass of water.

4. The method of claim 1, wherein, In the step (1), the reaction temperature is 70-100℃ and the reaction time is 2-5h; in the step (2), the pH of the system adjusted by dilute hydrofluoric acid is 4-6; the heating temperature is 20-40℃ and the lithiumation time is 5-9h.

5. The method of claim 1, wherein, In the step (1), the mesoporous carbon and 3-aminopropyl dimethyl fluorosilane are added into toluene to prepare a suspension, wherein the content of mesoporous carbon is 2-3wt% and the content of 3-aminopropyl dimethyl fluorosilane is 0.6-0.8wt% based on the total mass of toluene being 100%; the amount of ethanol used for washing is 6-8 times the amount of toluene.

6. The method of claim 1, wherein, In the step (2), the content of NH2 / mesoporous carbon is 4-5wt% and the content of LiF is 0.2-0.4wt% based on the mass of water.

7. The method of claim 1, wherein, In the step (1), the reaction temperature is 80-90℃ and the reaction time is 3-4h; in the step (2), the pH of the system adjusted by dilute hydrofluoric acid is 5-6; the heating temperature is 25-30℃ and the lithiumation time is 7-8h.

8. A preparation method of liquid lithium hexafluorophosphate, comprising the following steps: (a) obtaining a liquid lithium hexafluorophosphate solution by reacting a carbonate solvent suspension of LiF with PF5, (b) LiF prepared by the method of claim 1 + deacidifying, dehydrating and removing Fe metal ions from the liquid lithium hexafluorophosphate solution of step (a) in the presence of a mesoporous carbon adsorbent.

9. The method of claim 8, wherein, The mass of LiF in the carbonate solvent suspension of LiF is 1-5% of the mass of carbonate.

10. The method of claim 8, wherein, The carbonate is one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

11. The method of claim 8, wherein, The molar ratio of PF5 to LiF is 1.01-1.05:1, the reaction temperature is 5-40℃, the reaction pressure is 0.1-1.0Mpa and the reaction time is 1-6h.

12. The method of claim 8, wherein, The mass of LiF in the carbonate solvent suspension of LiF is 3-4% of the mass of carbonate.

13. The method of claim 8, wherein, The molar ratio of PF5 to LiF is 1.02-1.03:1, the reaction temperature is 10-20℃, the reaction pressure is 0.4-0.6Mpa and the reaction time is 3-4h.

14. The method of claim 8, wherein, The composition of the liquid lithium hexafluorophosphate solution in the step (a) is: LiPF6 5.5-22.6%, moisture 200-450ppm, acidity (calculated as HF) 490-760ppm, Fe metal ion 45-90ppm, and the rest is carbonate.

15. The method of claim 8, wherein, In step (b), Li + The amount of -NH2 / mesoporous carbon adsorbent is 0.5-2.0% of the amount of the liquid lithium hexafluorophosphate solution in step (a); the temperature for deacidification, dehydration and removal of Fe metal ions is 10-30°C, the time is 0.5-4h, and the pressure is normal pressure.

16. The method of claim 8, wherein, In step (b), Li + The amount of -NH2 / mesoporous carbon adsorbent is 1.0-1.5 wt% of the liquid lithium hexafluorophosphate solution in step (a); the temperature for deacidification, dehydration and removal of Fe metal ions is 15-20℃, the time is 2-3h, and the pressure is normal pressure.