A method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate

Abstract

This invention provides a method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, comprising the following steps: under vacuum conditions, heating LiH2PO4 to 200-300℃ for dehydration polymerization to obtain Li2H2P2O7; dispersing Li2H2P2O7 in an electronic-grade carbonate organic solvent, introducing PF5 gas for fluorination reaction, and then purifying the solution to obtain liquid lithium hexafluorophosphate. This invention directly generates dissolved LiPF6 by converting LiH2PO4 to lithium dihydrogen pyrophosphate through high-temperature dehydration, followed by fluorination reaction with PF5 in an electronic-grade organic solvent. This method completely eliminates the HF solvent system, avoiding the risk of strong corrosion from the source, and also eliminates the multi-step process of "solid synthesis-crystallization-drying-redissolution," achieving a short-process, low-cost, and highly safe preparation from inexpensive lithium source to liquid electrolyte.

Description

Technical Field

[0001] This invention relates to the field of electronic chemical preparation technology, and specifically to a method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate. Background Technology

[0002] LiPF6, as a core solute in lithium-ion battery electrolytes, has long dominated the commercial lithium salt market due to its high ionic conductivity, wide electrochemical window, and excellent film-forming properties among carbonate solvents. However, its inherent thermal instability and strong hygroscopicity (easily decomposes in water to produce HF) place extremely high demands on the anhydrous control of the production environment and product purity, which are key factors restricting electrolyte quality.

[0003] Currently, mainstream processes, such as the hydrogen fluoride solvent method in patent CN1850592A, have high conversion rates, but rely on large amounts of highly toxic and corrosive anhydrous HF. The equipment requires special materials such as Hastelloy, resulting in high investment and maintenance costs. Furthermore, the subsequent solid crystallization, drying, and redissolution processes are complex and energy-intensive. Patent CN103265002B uses the ion exchange method, which improves safety. However, this method generally suffers from problems such as incomplete raw material conversion, high impurity content, and difficulty in industrial scale-up, making it difficult to meet the stringent standards for low moisture and low metal impurities required for battery-grade applications.

[0004] Therefore, developing a method for preparing liquid lithium hexafluorophosphate that has higher process safety, higher purity, simpler process, and meets the needs of existing electrolyte production has become an urgent problem to be solved in this field. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, aiming to solve the technical problems in the prior art of preparing liquid lithium hexafluorophosphate that rely on highly corrosive hydrogen fluoride, have high equipment costs, and have incomplete raw material conversion and high impurity content, which makes it difficult to meet the requirements of battery-grade applications.

[0006] In a first aspect, the present invention provides a method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, comprising the following steps: S1. Under vacuum conditions, LiH2PO4 is heated to 200~300℃ for dehydration polymerization to obtain Li2H2P2O7; S2. Disperse Li2H2P2O7 in an electronic-grade carbonate organic solvent, introduce PF5 gas to carry out a fluorination reaction, and obtain liquid lithium hexafluorophosphate after purification.

[0007] Preferably, in step S1, the vacuum degree is ≤200 Pa; the dehydration polymerization time is 2~4h.

[0008] Preferably, in step S2, the electronic-grade carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, methyl ethyl carbonate, and propylene carbonate.

[0009] Preferably, in step S2, the moisture content of the electronic-grade carbonate organic solvent is ≤10 ppm.

[0010] Preferably, in step S2, the mass ratio of Li2H2P2O7 to electronic-grade carbonate organic solvent is (10~20):(80~90).

[0011] Preferably, in step S2, the molar ratio of PF5 to Li2H2P2O7 is (2.8~4.0):1.

[0012] Preferably, in step S2, the PF5 gas introduction rate satisfies the requirement of maintaining a gauge pressure of 0.15~0.25 MPa.

[0013] Preferably, in step S2, the temperature of the fluorination reaction is -10℃ to 0℃, and the time of the fluorination reaction is 8 to 12 hours.

[0014] Preferably, in step S2, the post-purification treatment includes: solid-liquid separation of the reaction solution, degassing under reduced pressure, and adsorption to remove impurities.

[0015] Preferably, the solid-liquid separation temperature is -10 to -5℃; the degassing conditions are: temperature -20 to -10℃, absolute pressure 1 to 2 kPa; the adsorbent used for adsorption and impurity removal includes lithium molecular sieve and / or activated alumina.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate (LiH2PO4). Lithium dihydrogen phosphate is used as the lithium source. After high-temperature dehydration to generate lithium dihydrogen pyrophosphate (Li2H2P2O7), it undergoes a low-temperature fluorination reaction with phosphorus pentafluoride (PF5) in a carbonate organic solvent to produce crude lithium hexafluorophosphate (LiPF6). Insoluble matter is removed by filtration, and impurities such as byproduct hydrogen fluoride (HF) and phosphorus trifluoride oxyfluoride (POF3) are removed by vacuum degassing. Finally, battery-grade liquid lithium hexafluorophosphate is obtained. This method avoids the highly corrosive environment of the traditional hydrofluoric acid method, reduces the risk of equipment corrosion and the amount of highly toxic HF used, reduces equipment investment costs, and improves production safety.

[0017] The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate provided by this invention synthesizes the liquid product in a one-step process in the battery electrolyte solvent, eliminating high-energy-consuming steps such as solid crystallization, drying, and re-dissolution. In addition, the main byproducts (HF, POF3) are volatile gases that can be efficiently removed by low-temperature vacuum degassing without the need for complex purification steps. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate in Example 1 of the present invention. Detailed Implementation

[0019] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0020] To address the technical problems in existing technologies for preparing liquid lithium hexafluorophosphate, such as reliance on highly corrosive hydrogen fluoride, high equipment costs, and incomplete raw material conversion with high impurity content that fails to meet battery-grade application requirements, this invention provides a method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate. This method involves using LiH₂PO₄ as a raw material, undergoing deep dehydration polymerization to form anhydrous Li₂H₂P₂O₇, and then performing a low-temperature fluorination reaction with PF₅ in a battery-grade organic solvent to directly generate dissolved LiPF₆. This avoids the highly corrosive nature of the traditional HF solvent method and the complex process of re-dissolving solid LiPF₆.

[0021] In a first aspect, embodiments of the present invention provide a method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, comprising the following steps: S1. Under vacuum conditions, LiH2PO4 is heated to 200~300℃ for dehydration polymerization to obtain Li2H2P2O7; S2. Disperse Li2H2P2O7 in an electronic-grade carbonate organic solvent, introduce PF5 gas to carry out a fluorination reaction, and obtain liquid lithium hexafluorophosphate after purification.

[0022] In the technical solution of this invention embodiment, LiH2PO4 is used as a raw material, which is deeply dehydrated and polymerized to form anhydrous Li2H2P2O7. Then, it undergoes a low-temperature fluorination reaction with PF5 in an electronic-grade organic solvent to directly generate dissolved LiPF6. This invention utilizes PF5 as both a fluorinating agent and a phosphorus source, breaking the POP bonds in the dihydrogen pyrophosphate ion in the organic solvent, and ultimately converting all phosphorus centers into PF6. - The anion is released, yielding an organic solution of LiPF6. The mechanism of this reaction is the dissociation of Li₂H₂P₂O₇ in the solvent to release Li₂. + and H2P2O7 2 PF5 is a strong Lewis acid and fluorinating agent. It attacks the oxygen atom in the dihydrogen pyrophosphate group, especially the bridging oxygen in the POP bond, causing bond breaking and fluorination substitution.

[0023] Furthermore, in some embodiments, in step S1, the vacuum degree of the vacuum condition is ≤200 Pa; the dehydration polymerization time is 2~4h.

[0024] Furthermore, in some embodiments, in step S1, LiH2PO4 is heated to 240~260℃ to dehydrate and polymerize to obtain Li2H2P2O7.

[0025] In the technical solution of this embodiment of the invention, the reaction equation for this step is as follows: 2LiH2PO4→Li2H2P2O7+H2O↑; Dehydration is incomplete at too low a temperature, and glassy lithium metaphosphate is easily formed at too high a temperature.

[0026] Furthermore, in some embodiments, in step S2, the electronic-grade carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, methyl ethyl carbonate, and propylene carbonate.

[0027] Furthermore, in some embodiments, in step S2, the moisture content of the electronic-grade carbonate organic solvent is ≤10ppm.

[0028] In the technical solution of this invention embodiment, electronic-grade carbonate organic solvents are selected as reaction solvents, which can be directly used as solvent components of the subsequent electrolyte, avoiding the subsequent separation and impurity removal process and solid lithium hexafluorophosphate re-dissolution process, and directly obtaining liquid lithium hexafluorophosphate products that meet the requirements of electrolyte production. Strict control of solvent moisture can prevent lithium hexafluorophosphate from decomposing in water and generating impurities, thus ensuring product purity.

[0029] Furthermore, in some embodiments, in step S2, the mass ratio of Li2H2P2O7 to electronic-grade carbonate organic solvent is (10~20):(80~90).

[0030] Furthermore, in some embodiments, in step S2, the molar ratio of PF5 to Li2H2P2O7 is (2.8~4.0):1.

[0031] In the technical solution of this invention embodiment, PF5 is used in excess to drive the reaction and capture trace amounts of water.

[0032] Furthermore, in some embodiments, in step S2, the PF5 gas introduction rate satisfies the requirement of maintaining a gauge pressure of 0.15~0.25 MPa.

[0033] Furthermore, in some embodiments, in step S2, the temperature of the fluorination reaction is -10℃ to 0℃; and the time of the fluorination reaction is 8 to 12 hours.

[0034] Furthermore, in some embodiments, in step S2, the post-purification treatment includes: solid-liquid separation of the reaction solution, degassing under reduced pressure, and adsorption to remove impurities.

[0035] In the technical solution of this invention embodiment, the equation for the fluorination reaction is as follows: 5Li2H2P2O7 + 14PF5 → 10LiPF6 + 7P2O5 + 10HF; the generated P2O5 will continue to react with excess PF5 to form POF3. Unreacted solids Li2H2P2O7 and P2O5 can be removed by solid-liquid separation; HF, POF3 and excess PF5 can be removed by degassing under reduced pressure; residual acidic impurities can be adsorbed to remove impurities.

[0036] Furthermore, in some embodiments, the solid-liquid separation temperature is -10 to -5°C.

[0037] Furthermore, in some embodiments, the conditions for degassing under reduced pressure are: temperature -20~-10℃, absolute pressure 1~2kPa.

[0038] Furthermore, in some embodiments, the adsorbent used for adsorption and impurity removal includes activated alumina.

[0039] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0040] Example 1 A schematic diagram of the process for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate is shown below. Figure 1 As shown, see Figure 1 A method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, the specific steps of which are as follows: (1) Weigh 93.6 g of lithium dihydrogen phosphate (LiH2PO4) raw material and place it in a dry glove box. Under the conditions of 250±5℃ and dynamic vacuum degree ≤200 Pa, high-purity nitrogen is introduced as the carrier gas and the material is heated to remove water for 2.5 hours. After the weight loss rate of the material stabilizes at about 17.3% (about 16.2 g), heating is stopped, and about 77.4 g of white powdered anhydrous Li2H2P2O7 is obtained.

[0041] (2) The obtained 77.4 g of anhydrous Li2H2P2O7 was rapidly transferred to a jacketed fluorination reactor. 620 g of battery-grade dimethyl carbonate (DMC) solvent, which had been deeply dehydrated to ≤10 ppm water content by 4A molecular sieves, was added to the reactor. The mass ratio of solvent to solid was approximately 89:11. Under nitrogen protection, the mixture was mechanically stirred at room temperature for 30 minutes to form a homogeneous solid-liquid suspension system.

[0042] (3) Turn on the low-temperature circulation device of the reactor jacket to cool the suspension system and maintain it at -8±2℃, and control the pressure of the reactor gauge at 0.20±0.05 MPa. Slowly introduce deeply dried PF5 gas into the system at a rate of 10 g / h, with a total PF5 introduction amount of 164.3 g (molar ratio n(PF5):n(Li2H2P2O7)≈3.2:1). During the reaction, as the solid gradually dissolves, the system becomes clear, and the total reaction time is 10 hours.

[0043] (4) After the reaction, the material was kept at -5℃ for 1 hour, and then pressurized with 0.4 MPa high-purity nitrogen to a filter press pre-cooled to -10℃ to remove residual trace insoluble matter. The filtrate was transferred to a distillation apparatus and degassed under low temperature and reduced pressure at -15℃ and 1.5 kPa absolute pressure to remove volatile impurities. 5.0 g of γ-alumina powder activated at 300℃ was added to the distillate and stirred and adsorbed at room temperature for 1 hour to remove residual trace acidic impurities. Then, it was precisely filtered through a 0.1 μm PTFE filter. The concentration of LiPF6 was sampled and analyzed, and the calculated amount of anhydrous DMC solvent was added to precisely adjust its concentration to 1.10 mol / L. The final product was filtered through a 0.22 μm terminal filter and then filled with nitrogen in a glove box to obtain battery-grade liquid LiPF6 (DMC solution).

[0044] The LiPF6 was tested and found to have a purity of 99.97%, a moisture content of 8 ppm, a Cl content of 3 ppm, a sulfate content of 2 ppm, a HF content of 29 ppm, and an insoluble matter content of 63 ppm.

[0045] Example 2 A method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, the specific steps of which are as follows: (1) Weigh 93.6 g of lithium dihydrogen phosphate (LiH2PO4) raw material and place it in a dry glove box. Under the conditions of 250±5℃ and dynamic vacuum degree ≤200 Pa, high-purity nitrogen is introduced as the carrier gas and the material is heated to remove water for 2.5 hours. After the weight loss rate of the material stabilizes at about 17.0% (about 15.9 g), heating is stopped, and about 77.7 g of white powdered anhydrous Li2H2P2O7 is obtained.

[0046] (2) The obtained 77.7 g of anhydrous Li2H2P2O7 was rapidly transferred to a jacketed fluorination reactor. 730 g of battery-grade diethyl carbonate (DEC) solvent, which had been deeply dehydrated to ≤10 ppm water content by 4A molecular sieves, was added to the reactor. The mass ratio of solvent to solid was approximately 90:10. Under nitrogen protection, the mixture was mechanically stirred at room temperature for 30 minutes to form a homogeneous solid-liquid suspension system.

[0047] (3) Turn on the low-temperature circulation device of the reactor jacket to cool the suspension system and maintain it at -5±2℃, and control the pressure of the reactor gauge at 0.20±0.05 MPa. Slowly introduce deeply dried PF5 gas into the system at a rate of 8 g / h, with a total PF5 introduction of 165.0 g (molar ratio n(PF5):n(Li2H2P2O7)≈3.2:1). During the reaction, as the solid gradually dissolves, the system becomes clear, and the total reaction time is 11 hours.

[0048] (4) After the reaction, the material was kept at -5℃ for 1 hour, and then pressurized with 0.4 MPa high-purity nitrogen to a filter press pre-cooled to -5℃ to remove residual trace insoluble matter. The filtrate was transferred to a distillation apparatus and degassed under low temperature and reduced pressure at -10℃ and 2 kPa absolute pressure to remove volatile impurities. 5 g of 4A lithium molecular sieve dried at 200℃ for 10 h was added to the distillate and stirred and adsorbed at room temperature for 1.5 hours to remove residual trace acidic impurities. Then, it was precisely filtered through a 0.1 μm PTFE filter. The concentration of LiPF6 was sampled and analyzed, and the calculated amount of anhydrous DEC solvent was added to precisely adjust its concentration to 1.10 mol / L. The final product was filtered through a 0.22 μm terminal filter and then filled with nitrogen in a glove box to obtain battery-grade liquid LiPF6 (DEC solution).

[0049] The LiPF6 was tested and found to have a purity of 99.91%, a moisture content of 17 ppm, a Cl content of 6 ppm, a sulfate content of 9 ppm, a HF content of 43 ppm, and an insoluble matter content of 144 ppm.

[0050] Example 3 A method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, the specific steps of which are as follows: (1) Weigh 93.6 g of lithium dihydrogen phosphate (LiH2PO4) raw material and place it in a dry glove box. Under the conditions of 250±5℃ and dynamic vacuum degree ≤200 Pa, high-purity nitrogen is introduced as the carrier gas and the material is heated to remove water for 2.5 hours. After the weight loss rate of the material stabilizes at about 17.4% (about 16.3 g), heating is stopped, and about 77.3 g of white powdered anhydrous Li2H2P2O7 is obtained.

[0051] (2) The obtained 77.3 g of anhydrous Li2H2P2O7 was rapidly transferred to a jacketed fluorination reactor. A mixed solvent of 310 g of dehydrated DMC and 310 g of dehydrated EC (ethylene carbonate) was added to the reactor, with a solvent-to-solid mass ratio of approximately 89:11. Under nitrogen protection, the mixture was mechanically stirred at room temperature for 30 minutes to form a homogeneous solid-liquid suspension system.

[0052] (3) Turn on the low-temperature circulation device of the reactor jacket to cool the suspension system and maintain it at -8±2℃, and control the pressure of the reactor gauge at 0.20±0.05 MPa. Slowly introduce deeply dried PF5 gas into the system at a rate of 10 g / h, with a total PF5 introduction amount of 179.7 g (molar ratio n(PF5):n(Li2H2P2O7)≈3.5:1). During the reaction, as the solid gradually dissolves, the system becomes clear, and the total reaction time is 10 hours.

[0053] (4) After the reaction, the material was kept at -5℃ for 1 hour, and then pressurized with 0.4 MPa high-purity nitrogen to a filter press pre-cooled to -10℃ to remove residual trace insoluble matter. The filtrate was transferred to a distillation apparatus and degassed under low temperature and reduced pressure at -10℃ and 1.8 kPa absolute pressure to remove volatile impurities. 5 g of 4A lithium molecular sieve dried at 200℃ for 10 h was added to the distillate and stirred and adsorbed at room temperature for 1.5 hours to remove residual trace acidic impurities. Then, it was precisely filtered through a 0.1 μm PTFE filter. The concentration of LiPF6 was sampled and analyzed, and the calculated amount of anhydrous DMC / EC (1:1) mixed solvent was added to precisely adjust its concentration to 1.10 mol / L. The final product was filtered through a 0.22 μm terminal filter and then filled with nitrogen in a glove box to obtain battery-grade liquid LiPF6 (DMC / EC solution).

[0054] The LiPF6 was tested and found to have a purity of 99.95%, a moisture content of 12 ppm, a Cl content of 5 ppm, a sulfate content of 7 ppm, a HF content of 33 ppm, and an insoluble matter content of 126 ppm.

[0055] Example 4 A method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, the specific steps of which are as follows: (1) Weigh 93.6 g of lithium dihydrogen phosphate (LiH2PO4) raw material and place it in a dry glove box. Under the conditions of 250±5℃ and dynamic vacuum degree ≤200 Pa, high-purity nitrogen is introduced as the carrier gas and the material is heated to remove water for 2.5 hours. After the weight loss rate of the material stabilizes at about 17.3% (about 16.2 g), heating is stopped, and about 77.4 g of white powdered anhydrous Li2H2P2O7 is obtained.

[0056] (2) The obtained 77.4 g of anhydrous Li2H2P2O7 was rapidly transferred to a jacketed fluorination reactor. A mixed solvent of 186 g of dehydrated DMC and 434 g of dehydrated EMC (ethyl methyl carbonate) was added to the reactor, with a solvent-to-solid mass ratio of approximately 89:11. Under nitrogen protection, the mixture was mechanically stirred at room temperature for 30 minutes to form a homogeneous solid-liquid suspension.

[0057] (3) Turn on the low-temperature circulation device of the reactor jacket to cool the suspension system and maintain it at -8±2℃, and control the pressure of the reactor gauge at 0.20±0.05 MPa. Slowly introduce deeply dried PF5 gas into the system at a rate of 10 g / h, with a total PF5 introduction amount of 179.7 g (molar ratio n(PF5):n(Li2H2P2O7)≈3.5:1). During the reaction, as the solid gradually dissolves, the system becomes clear, and the total reaction time is 10 hours.

[0058] (4) After the reaction, the material was kept at -5℃ for 1 hour, and then pressurized with 0.4 MPa high-purity nitrogen to a filter press pre-cooled to -8℃ to remove residual trace insoluble matter. The filtrate was transferred to a distillation apparatus and degassed under low temperature and reduced pressure at -15℃ and 1.5 kPa absolute pressure to remove volatile impurities. 3 g of 4A lithium molecular sieve dried at 200℃ for 10 h was added to the distillate and stirred and adsorbed at room temperature for 1.5 hours to remove residual trace acidic impurities. Then, it was precisely filtered through a 0.1 μm PTFE filter. The concentration of LiPF6 was sampled and analyzed, and the calculated amount of anhydrous DMC / EMC (3:7) mixed solvent was added to precisely adjust its concentration to 1.10 mol / L. The final product was filtered through a 0.22 μm terminal filter and then filled with nitrogen in a glove box to obtain battery-grade liquid LiPF6 (DMC / EMC solution).

[0059] The LiPF6 was tested and found to have a purity of 99.94%, a moisture content of 11 ppm, a Cl content of 3 ppm, a sulfate content of 2 ppm, a HF content of 21 ppm, and an insoluble matter content of 72 ppm.

[0060] Example 5 A method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, the specific steps of which are as follows: (1) Weigh 93.6 g of lithium dihydrogen phosphate (LiH2PO4) raw material and place it in a dry glove box. Under the conditions of 250±5℃ and dynamic vacuum degree ≤200 Pa, high-purity nitrogen is introduced as the carrier gas and the material is heated to remove water for 2.5 hours. After the weight loss rate of the material stabilizes at about 17.3% (about 16.2 g), heating is stopped, and about 77.4 g of white powdered anhydrous Li2H2P2O7 is obtained.

[0061] (2) The obtained 77.4 g of anhydrous Li2H2P2O7 was rapidly transferred to a jacketed fluorination reactor. 700 g of battery-grade propylene carbonate (PC) solvent, dehydrated to ≤10 ppm, was added to the reactor, with a solvent-to-solid mass ratio of approximately 90:10. Under nitrogen protection, the mixture was mechanically stirred at room temperature for 30 minutes to form a homogeneous solid-liquid suspension system.

[0062] (3) Turn on the low-temperature circulation device of the reactor jacket to cool the suspension system and maintain it at -8±2℃, and control the pressure of the reactor gauge at 0.10±0.05 MPa. Slowly introduce deeply dried PF5 gas into the system at a rate of 15 g / h, with a total PF5 introduction amount of 174.6 g (molar ratio n(PF5):n(Li2H2P2O7)≈3.4:1). During the reaction, as the solid gradually dissolves, the system becomes clear, and the total reaction time is 6 hours.

[0063] (4) After the reaction, the material was kept at -5℃ for 1 hour, and then pressurized with 0.4 MPa high-purity nitrogen to a filter press pre-cooled to -10℃ to remove residual trace insoluble matter. The filtrate was transferred to a distillation apparatus and degassed under low temperature and reduced pressure at -15℃ and 2.0 kPa absolute pressure to remove volatile impurities. 1.5 g of γ-alumina powder activated at 300℃ and 1.5 g of 4A lithium molecular sieve dried at 200℃ for 10 h were added to the distillate and stirred for 1.5 hours at room temperature to remove residual trace acidic impurities. Then, it was precisely filtered through a 0.1 μm PTFE filter. The concentration of LiPF6 was sampled and analyzed, and the calculated amount of anhydrous PC solvent was added to precisely adjust the concentration to 1.10 mol / L. The final product was filtered through a 0.22 μm terminal filter and then filled in a glove box with nitrogen to obtain battery-grade liquid LiPF6 (PC solution).

[0064] The LiPF6 was tested and found to have a purity of 99.96%, a moisture content of 14 ppm, a Cl content of 8 ppm, a sulfate content of 5 ppm, a HF content of 19 ppm, and an insoluble matter content of 51 ppm.

[0065] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate, characterized by, Includes the following steps: S1. Under vacuum conditions, LiH2PO4 is heated to 200~300℃ for dehydration polymerization to obtain Li2H2P2O7; S2. The Li2H2P2O7 is dispersed in an electronic-grade carbonate organic solvent, and PF5 gas is introduced to carry out a fluorination reaction. After purification, liquid lithium hexafluorophosphate is obtained.

2. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized in that, In step S1, the vacuum degree of the vacuum condition is ≤200 Pa; the dehydration polymerization time is 2~4h.

3. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized in that, In step S2, the electronic-grade carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, methyl ethyl carbonate, and propylene carbonate.

4. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized in that, In step S2, the moisture content of the electronic-grade carbonate organic solvent is ≤10 ppm.

5. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized in that, In step S2, the mass ratio of Li2H2P2O7 to the electronic grade carbonate organic solvent is (10~20):(80~90).

6. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized in that, In step S2, the molar ratio of PF5 to Li2H2P2O7 is (2.8~4.0):

1.

7. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized in that, In step S2, the PF5 gas is introduced at a rate that maintains a gauge pressure of 0.15~0.25 MPa. 8.The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized in that, In step S2, the temperature of the fluorination reaction is -10℃ to 0℃; the time of the fluorination reaction is 8 to 12 hours.

9. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 1, characterized by, In step S2, the post-purification treatment includes: solid-liquid separation of the reaction solution, degassing under reduced pressure, and adsorption to remove impurities.

10. The method for preparing liquid lithium hexafluorophosphate using lithium dihydrogen phosphate according to claim 9, characterized by, The temperature for solid-liquid separation is -10~-5℃; And / or, the conditions for degassing under reduced pressure are: temperature -20~-10℃, absolute pressure 1~2 kPa; And / or, the adsorbent used for adsorption and impurity removal includes lithium molecular sieves and / or activated alumina.

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