WO2024125338A1

WO2024125338A1 - Preparation method for liquid lithium hexafluorophosphate, and electrolyte and lithium-ion battery

Info

Publication number: WO2024125338A1
Application number: PCT/CN2023/136110
Authority: WO
Inventors: 向书槐; 贾超洋; 韦松
Original assignee: 深圳新宙邦科技股份有限公司
Priority date: 2022-12-12
Filing date: 2023-12-04
Publication date: 2024-06-20

Abstract

In order to solve the problem of hydrogen chloride residues in the existing preparation process of lithium hexafluorophosphate, the present invention provides a preparation method for liquid lithium hexafluorophosphate. The preparation method comprises the following operation steps: obtaining primary phosphorus pentafluoride; bringing the primary phosphorus pentafluoride to be in sufficient contact with an adsorption material, such that hydrogen chloride in the primary phosphorus pentafluoride is adsorbed on a chlorine modified carbon material to obtain a purified phosphorus pentafluoride gas, wherein the adsorption material comprises at least one of the chlorine modified carbon material, chlorinated aromatic hydrocarbon, a chlorinated aromatic hydrocarbon polymer, and aryl ether; and synthesis reaction: dissolving lithium fluoride in a solvent, and introducing the purified phosphorus pentafluoride gas to prepare liquid lithium hexafluorophosphate. In addition, further disclosed in the present invention are an electrolyte prepared by using the preparation method, and a lithium-ion battery. The preparation method provided by the present invention can effectively reduce hydrogen chloride residues in the electrolyte and improve the performance of the lithium-ion battery.

Description

A preparation method of liquid lithium hexafluorophosphate, electrolyte and lithium ion battery

Technical Field

The invention belongs to the technical field of secondary battery manufacturing, and specifically relates to a preparation method of liquid lithium hexafluorophosphate, an electrolyte and a lithium ion battery.

Background technique

Entering the new century, high-performance lithium-ion batteries have increasingly become an important area of development for the new energy industry. As a key raw material for the production of lithium-ion secondary batteries, lithium hexafluorophosphate (LiPF ₆ ) has a very mature preparation process. The general preparation method is to introduce phosphorus pentafluoride (PF ₅ ) gas into an anhydrous hydrogen fluoride solution containing lithium fluoride to react and obtain a liquid lithium hexafluorophosphate product. Among them, the method for industrial production of phosphorus pentafluoride is to generate it through the reaction of phosphorus pentachloride and anhydrous hydrogen fluoride, or to generate it through the mixed reaction of phosphorus trichloride, anhydrous hydrogen fluoride and liquid chlorine. The specific reaction process is as follows:
PCl ₅ +HF PF ₅ +HCl;
PCl ₃ +Cl ₂ +HF PF ₅ +HCl;

The above process produces a mixed gas of phosphorus pentafluoride, hydrogen chloride and unreacted hydrogen fluoride. Due to the strong Lewis acidity of phosphorus pentafluoride, it is very easy to react with alkali or nucleophilic reagents, and compete with hydrogen chloride and hydrogen fluoride, so pure phosphorus pentafluoride cannot be obtained by general deacidification methods. Hydrogen fluoride gas can be removed by condensation. However, the byproduct hydrogen chloride cannot be completely separated by simple distillation, which is not conducive to the concept of process production and green environmental protection. At the same time, the residual hydrogen chloride will affect the purity of the subsequent production of lithium hexafluorophosphate products. Therefore, it is necessary to develop a separation and purification process that is simple to operate, has high separation efficiency, and produces less three wastes.

Summary of the invention

Aiming at the problem of residual hydrogen chloride in the existing preparation process of lithium hexafluorophosphate, the present invention provides a preparation method of liquid lithium hexafluorophosphate, an electrolyte and a lithium ion battery.

The technical solution adopted by the present invention to solve the above technical problems is as follows:

In one aspect, the present invention provides a method for preparing liquid lithium hexafluorophosphate, comprising the following steps:

Obtaining primary phosphorus pentafluoride;

Then the primary phosphorus pentafluoride is fully contacted with the adsorption material to adsorb the hydrogen chloride in the primary phosphorus pentafluoride. on a chlorine-modified carbon material to obtain purified phosphorus pentafluoride gas, wherein the adsorbent material comprises at least one of a chlorine-modified carbon material, a chlorinated aromatic hydrocarbon, a chlorinated aromatic hydrocarbon polymer, and an aromatic ether;

Synthesis reaction: Lithium fluoride is dissolved in a solvent and purified phosphorus pentafluoride gas is introduced to prepare liquid lithium hexafluorophosphate.

Optionally, the adsorbent material is selected from at least one of a chlorine-modified carbon material, or a chlorinated aromatic hydrocarbon, a chlorinated aromatic hydrocarbon polymer, and an aromatic ether.

Optionally, the preparation method of the primary phosphorus pentafluoride is:

Preparation of phosphorus pentafluoride: Phosphorus trichloride, hydrogen fluoride and chlorine are introduced into a reactor, the temperature of the reactor is controlled to be -50°C to 30°C, the pressure in the reactor is controlled to be 0.1 to 1.0 MPa, and a mixed gas containing phosphorus pentafluoride is obtained after a reaction time of 2 to 6 hours;

Distillation: The mixed gas is passed into a distillation tower, the feed temperature is controlled at 5-35°C, and the tower top pressure is 0.06-0.5MPa, phosphorus pentafluoride is separated to obtain primary phosphorus pentafluoride.

Optionally, the chlorine-modified carbon material is selected from at least one of chlorine-modified carbon nanotubes, chlorine-modified graphite and chlorine-modified graphene.

Optionally, the chlorine-modified carbon nanotubes are prepared by the following method:

In a closed reactor, Fe-Co/CaCO ₃ is used as a catalyst, nitrogen and ethylene are introduced, and the temperature is gradually increased to 650° C. to 900° C., dichlorobenzene is introduced, and the introduction of ethylene is stopped after the reaction for 1-2 hours to obtain chlorine-modified carbon nanotubes. The synthesized chlorine-modified carbon nanotubes are acid-washed, filtered, washed with water, and then dried to obtain chlorine-modified carbon nanotubes;

Alternatively, the carbon nanotubes are added to a sodium hypochlorite solution, adjusted to neutrality with hydrochloric acid, filtered after sufficient reaction, washed with water, and dried to obtain chlorine-modified carbon nanotubes.

Optionally, the chlorine-modified graphite is prepared by the following method:

After the graphite is dried, chlorine gas with a purity of 99.999% is introduced at 300-400° C. for reaction at a ventilation rate of 30-70 L/h; the reaction time is 3-8 hours. After the reaction is completed, the residual chlorine gas is replaced with nitrogen to obtain chlorine-modified graphite.

Optionally, the chlorine-modified graphene is prepared by the following method:

After the graphene is heated and vacuumed to remove water, it is placed in a chlorine atmosphere and heated to 150-260° C., the weight ratio of chlorine to graphene is 1-1.6:1, and the reaction time is 1-2 hours to obtain chlorine-modified graphene.

Optionally, the chlorine-modified carbon material is fixed in a fixed bed reactor, and the mixed gas is continuously passed through the fixed bed reactor, the temperature of the fixed bed reactor is 5°C to 35°C, the pressure is 0.1 to 0.8 MPa, and the ventilation flow rate is 200 to 6300 L/h.

Optionally, in the "synthesis reaction" operation, the temperature is controlled at -20°C to 10°C, and the solvent is selected from linear carbonates.

Optionally, when the chlorine-modified carbon material is saturated with hydrogen chloride, the hydrogen chloride on the chlorine-modified carbon material is removed by liquid dissolution or high-temperature gas purging, the temperature of the high-temperature gas is 150°C to 240°C, and the chlorine-modified carbon material from which the hydrogen chloride is removed is reused.

Optionally, the chlorinated aromatic hydrocarbon is selected from the compound shown in structural formula 1:

R ₁ to R ₆ are each independently selected from H, a C1-C4 hydrocarbon group, a C1-C4 halogenated hydrocarbon group or a halogen atom, and at least one chlorine atom is contained in R ₁ to R ₆ .

Optionally, the compound represented by structural formula 1 is selected from one or more of the following compounds:

Optionally, the chlorinated aromatic polymer is selected from the compound shown in Structural Formula 2:

Among them, R is selected from chlorine atoms, Y is selected from hydrogen, methyl or polybutadiene groups, and n is 500-1000.

Optionally, the compound represented by structural formula 2 is selected from one or more of the following compounds:

Among them, n is 500~1000, and m is 500~1000.

Optionally, the aryl ether is selected from the compound shown in structural formula 3:

Wherein, R ₁₁ to R ₂₀ are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl or halogen.

Optionally, the compound represented by structural formula 3 is selected from one or more of the following compounds:

Optionally, the adsorbent material is liquid, and the adsorbent material is introduced into a spray tower, and a circulating pump is used for circulating spraying. Primary phosphorus pentafluoride gas is introduced from the bottom of the spray tower, and the gas introduction flow rate is 200 to 300 L/h. Purified phosphorus pentafluoride gas is exported from the top of the spray tower.

Optionally, the adsorbent material is solid, and the adsorbent material is prepared into particles and filled in a packed tower, primary phosphorus pentafluoride gas is introduced from the feed port of the packed tower and discharged from the discharge port of the packed tower, and the gas introduction flow rate is 100 to 200 L/h to obtain purified phosphorus pentafluoride gas; when the adsorbent material is saturated with hydrogen chloride, the hydrogen chloride on the adsorbent material is dissolved and removed by an organic solvent, and the adsorbent material with the hydrogen chloride removed is reused.

On the other hand, the present invention provides an electrolyte comprising liquid lithium hexafluorophosphate, wherein the liquid lithium hexafluorophosphate is prepared by the above-mentioned preparation method.

In another aspect, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode and the electrolyte as described above.

According to the preparation method of liquid lithium hexafluorophosphate provided by the present invention, most of the hydrogen chloride and almost all of the hydrogen fluoride in the mixed gas are first removed by distillation to obtain primary phosphorus pentafluoride containing a small amount of hydrogen chloride, and then the primary phosphorus pentafluoride is adsorbed by an adsorption material.

Among them, the carbon material of the chlorine-modified carbon material itself has the ability to adsorb and enrich gas, wherein the chlorine element on the surface of the carbon material can serve as a halogen covalent bond receptor, and can also serve as a halogen-hydrogen covalent bond receptor, and its binding force with the chlorine element is much greater than its binding force with the fluorine element. Therefore, compared with phosphorus pentafluoride, the chlorine-modified carbon material has a stronger affinity for adsorption of hydrogen chloride, and can remove hydrogen chloride in primary phosphorus pentafluoride by adsorption to purify phosphorus pentafluoride. The adsorption method using chlorine-modified carbon materials has low energy consumption, is suitable for continuous production, and improves production efficiency. The chlorine-modified carbon material can be recycled after desorption, and has the characteristics of environmental protection, sustainability and economic benefits.

At least one of chlorinated aromatic hydrocarbons, chlorinated aromatic hydrocarbon polymers and aromatic ethers is used as the primary phosphorus pentafluoride gas adsorption material. The adsorption material has a benzene ring, which has a "p-π" interaction force with the chlorine atom, so that the distance between the chlorine atom and the carbon atom is basically the same as the van der Waals radius of the two, thereby playing a role in adsorbing hydrogen chloride. The benzene ring can also form an "anion-π" interaction force with the chloride ion, further increasing its adsorption effect on hydrogen chloride. At the same time, the halogen atoms in the compound can form a Cl-H...Cl halogen bond similar to the hydrogen bond structure with the hydrogen atoms of hydrogen chloride, which can further adsorb hydrogen chloride molecules. At the same time, the adsorption capacity of the adsorption material for phosphorus pentafluoride is relatively weak, so that phosphorus pentafluoride and hydrogen chloride mixed gas can be effectively separated, effectively improving the purity of phosphorus pentafluoride, and ultimately improving the purity of the obtained liquid lithium hexafluorophosphate. degree, so that it can be directly used in the electrolyte to improve the electrochemical performance of lithium-ion batteries.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

The present invention provides a method for preparing liquid lithium hexafluorophosphate, comprising the following steps:

Preparation of phosphorus pentafluoride: phosphorus trichloride, hydrogen fluoride and chlorine are mixed and reacted and introduced into a reactor, the temperature of the reactor is controlled to be -50°C to 30°C, the pressure in the reactor is controlled to be 0.1 to 0.3 MPa, and the reaction time is 2 to 6 hours to obtain a mixed gas containing phosphorus pentafluoride;

Distillation: The mixed gas is passed into a distillation tower, the feed temperature is controlled at 5-35°C, the tower top pressure is 0.06-0.5MPa, phosphorus pentafluoride is separated to obtain primary phosphorus pentafluoride;

Then, the primary phosphorus pentafluoride is fully contacted with an adsorption material, so that the hydrogen chloride in the primary phosphorus pentafluoride is adsorbed on the chlorine-modified carbon material to obtain purified phosphorus pentafluoride gas, and the adsorption material is selected from the chlorine-modified carbon material;

The preparation method of the liquid lithium hexafluorophosphate first removes most of the hydrogen chloride and almost all of the hydrogen fluoride in the mixed gas by distillation to obtain primary phosphorus pentafluoride containing a small amount of hydrogen chloride, and then the primary phosphorus pentafluoride is adsorbed by a chlorine-modified carbon material. The carbon material itself has the ability to adsorb and enrich gas, wherein the chlorine element on the surface of the carbon material can be used as a halogen bond covalent bond receptor, and can also be used as a halogen-hydrogen covalent bond receptor, and its binding force with the chlorine element is much greater than its binding force with the fluorine element. Therefore, compared with phosphorus pentafluoride, the chlorine-modified carbon material has a stronger affinity for adsorption of hydrogen chloride, and can remove hydrogen chloride in the primary phosphorus pentafluoride by adsorption, and purify the phosphorus pentafluoride. Compared with the existing multi-stage distillation method, the method of combining distillation with chlorine-modified carbon material adsorption is adopted, and the phosphorus pentafluoride obtained has higher purity and relatively lower energy consumption, is suitable for continuous production, and improves production efficiency. The chlorine-modified carbon material can be recycled after desorption, and has the characteristics of environmental protection, sustainability and economic benefits.

In some embodiments, the chlorine-modified carbon material is selected from at least one of chlorine-modified carbon nanotubes, chlorine-modified graphite, and chlorine-modified graphene.

Carbon nanotubes are mainly composed of several to dozens of layers of coaxial circular tubes with hexagonal carbon atoms. The advantage of large specific surface area makes them often used as adsorption materials. At the same time, the abundant p orbitals overlap with each other outside the carbon nanotube sheets to form highly delocalized large π bonds. The mutual attraction can adsorb hydrogen chloride. By chlorine-modifying the carbon nanotubes, the π bonds formed on the surface of the carbon nanotubes are more electron-deficient, making it easier to attract anions in hydrogen chloride. At the same time, there will be weak hydrogen bonds between the chloride ions in the chlorine-modified carbon nanotubes and the hydrogen chloride, which is more conducive to adsorption in the filler of the chlorine-modified carbon nanotubes.

Specifically, the chlorine-modified carbon nanotubes are prepared by the following method:

Graphite is a transitional crystal between atomic crystal, metal crystal and molecular crystal. In the crystal, carbon atoms in the same layer form covalent bonds by sp2 hybridization. Each carbon atom is connected to three other carbon atoms. Six carbon atoms form regular hexagonal π bonds on the same plane and stretch to form a lamellar structure. The adsorption of hydrogen chloride by chlorine-modified graphite is similar to that of chlorine-modified carbon nanotubes.

Specifically, the chlorine-modified graphite is prepared by the following method:

Graphene is a new material with carbon atoms connected by sp2 hybridization tightly stacked into a single-layer two-dimensional honeycomb lattice structure. The arrangement of carbon atoms inside is the same as that of graphite single atomic layer, with sp2 hybrid orbitals forming bonds. In addition to the σ bond linking other carbon atoms to form a hexagonal ring honeycomb layered structure, the pz orbital of each carbon atom perpendicular to the layer plane can form a large multi-atomic π bond that runs through the entire layer. The adsorption of hydrogen chloride by chlorine-modified graphene is similar to that of chlorine-modified carbon nanotubes.

Specifically, the chlorine-modified graphene is prepared by the following method:

In some embodiments, the chlorine-modified carbon material is fixed in a fixed bed reactor, and the mixed gas is continuously passed through the fixed bed reactor. The temperature of the fixed bed reactor is 5°C to 35°C, the pressure is 0.1 to 0.8 MPa, and the ventilation flow rate is 200 to 6300 L/h.

By preparing the chlorinated modified carbon material into a fixed bed reactor, when hydrogen chloride is adsorbed, Primary phosphorus pentafluoride gas is introduced into one end of the fixed bed reactor, and purified phosphorus pentafluoride is extracted from the other end of the fixed bed reactor to achieve continuous production. In some embodiments, in order to achieve better purification effect, multiple fixed bed reactors can be connected in series to achieve multi-stage filtration purification.

In some embodiments, during the "synthesis reaction" operation, the temperature is controlled at -20°C to 10°C.

When the reaction temperature is too low, on the one hand, the reaction rate is affected, and on the other hand, there is also the problem of high energy consumption; and when the reaction temperature exceeds 10°C, the reaction rate of lithium fluoride and phosphorus pentafluoride is likely to be too fast, thereby generating a large amount of heat and inducing side reactions with the organic solvent.

In some embodiments, in the "synthesis reaction" operation, the solvent is selected from linear carbonates, and the linear carbonates include one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

By using a straight-chain carbonate as a reaction solvent, a straight-chain carbonate solution containing lithium hexafluorophosphate can be directly obtained by reaction, and the straight-chain carbonate itself can be used as a solvent for the electrolyte. Therefore, the liquid lithium hexafluorophosphate obtained by the "synthesis reaction" can be directly applied to the electrolyte after filtering and purification and/or after impurity detection, and there is no need to prepare solid lithium hexafluorophosphate through crystallization and drying methods in the traditional organic solvent method, which effectively reduces energy consumption.

In other embodiments, when solid lithium hexafluorophosphate needs to be prepared, the liquid lithium hexafluorophosphate can be crystallized, filtered and dried to obtain solid lithium hexafluorophosphate.

In some embodiments, when the chlorine-modified carbon material is saturated with hydrogen chloride, the hydrogen chloride on the chlorine-modified carbon material is removed by liquid dissolution or high-temperature gas purging, the temperature of the high-temperature gas is 150°C to 240°C, and the chlorine-modified carbon material with hydrogen chloride removed is reused.

Specifically, the liquid used for removing hydrogen chloride is selected from an inert solvent that does not react with phosphorus pentafluoride or hydrogen chloride, and the inert solvent includes diethyl ether, tetrahydrofuran, petroleum ether, etc. Specifically, the fixed bed reactor is cleaned and the hydrogen chloride is dissolved by an inert solvent. After cleaning, the inert solvent is removed by vacuum drying to obtain a chlorine-modified carbon material from which hydrogen chloride is removed.

When high-temperature gas purging is used to remove hydrogen chloride, a protective gas that does not react with phosphorus pentafluoride or hydrogen chloride, such as nitrogen, argon, etc., is used. Through heat conduction and airflow, the hydrogen chloride on the surface of the chlorine-modified carbon material is made more active, and then carried away from the chlorine-modified carbon material by the high-temperature gas.

Another embodiment of the present invention provides a method for preparing liquid lithium hexafluorophosphate, comprising the following steps:

Preparation of phosphorus pentafluoride: adding phosphorus pentachloride and hydrogen fluoride to a reactor respectively, controlling the reaction temperature to be -50 to 30°C, the reaction time to be 6 to 12 hours, and the reaction pressure to be 0.1 to 1.0 MPa, to obtain a mixed gas containing phosphorus pentafluoride;

Then, the primary phosphorus pentafluoride gas is passed into an absorption tower provided with an adsorption material to remove impurities in the primary phosphorus pentafluoride gas, thereby obtaining a purified phosphorus pentafluoride gas; the adsorption material comprises at least one of chlorinated aromatic hydrocarbons, chlorinated aromatic hydrocarbon polymers and aromatic ethers;

Synthesis reaction: Lithium fluoride is dissolved in a solvent and phosphorus pentafluoride gas is introduced to prepare liquid lithium hexafluorophosphate.

The preparation method of the liquid lithium hexafluorophosphate adopts phosphorus pentachloride and hydrogen fluoride to react to generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, removes most of the hydrogen chloride and almost all of the hydrogen fluoride in the mixed gas by distillation, and obtains a primary phosphorus pentafluoride gas containing a small amount of hydrogen chloride, and adopts at least one of chlorinated aromatic hydrocarbons, chlorinated aromatic hydrocarbon polymers and aromatic ethers as the adsorption material of the primary phosphorus pentafluoride gas, and the adsorption material has a benzene ring, which has a "p-π" interaction force with the chlorine atom, so that the distance between the chlorine atom and the carbon atom is basically the same as the van der Waals radius of the two, thereby playing a role in adsorbing hydrogen chloride. The benzene ring can also form an "anion-π" interaction force with the chloride ion, further increasing its adsorption effect on hydrogen chloride. At the same time, the halogen atoms in the compound can form a Cl-H...Cl halogen bond similar to the hydrogen bond structure with the hydrogen atoms of hydrogen chloride, which can further adsorb hydrogen chloride molecules. At the same time, the adsorption capacity of the adsorption material for phosphorus pentafluoride is relatively weak, so that phosphorus pentafluoride and hydrogen chloride mixed gas can be effectively separated, the purity of phosphorus pentafluoride is effectively improved, and finally the purity of the obtained liquid lithium hexafluorophosphate is improved, so that it can be directly used in the electrolyte to improve the electrochemical performance of lithium-ion batteries.

In some embodiments, the adsorption material does not contain nitrogen element, because it is easy to coordinate with phosphorus pentafluoride, resulting in the adsorption of non-fluorinated phosphorus while adsorbing hydrogen chloride, thus affecting the purification effect.

In some embodiments, the chlorinated aromatic hydrocarbon is selected from the compound shown in Structural Formula 1:

Chlorine atoms have better affinity with hydrogen chloride, which is more conducive to improving the adsorption of hydrogen chloride.

In some preferred embodiments, in the compound represented by structural formula 1, the C1-C4 hydrocarbon group is selected from methyl, ethyl, isopropyl or tert-butyl, and the C1-C4 halogenated hydrocarbon group is selected from trifluoromethyl or trichloromethyl.

In a preferred embodiment, the compound represented by structural formula 1 is selected from one or more of the following compounds:

In some embodiments, the chlorinated aromatic polymer is selected from the compound shown in Structural Formula 2:

In a preferred embodiment, the compound represented by structural formula 2 is selected from one or more of the following compounds:

Among them, n is 500~1000, and m is 500~1000.

In some embodiments, the aryl ether is selected from the compound shown in structural formula 3:

The benzene ring contained in the compound shown in structural formula 3 has an adsorption effect on hydrogen chloride. At the same time, the compound has large steric hindrance substituents on both sides of the ether bond, which makes it impossible for the phosphorus pentafluoride molecule to approach the oxygen atom to form a complex. Therefore, the oxygen atom preferentially forms a hydrogen bond with the hydrogen atom in the hydrogen chloride, promoting the separation of hydrogen chloride and phosphorus pentafluoride, and then obtaining pure phosphorus pentafluoride gas.

In a preferred embodiment, the compound represented by structural formula 3 is selected from one or more of the following compounds:

In some embodiments, the absorption tower is a spray tower or a packed tower.

In some embodiments, the adsorbent material is a liquid, which is introduced into a spray tower and circulated and sprayed using a circulating pump. Primary phosphorus pentafluoride gas is introduced from the bottom of the spray tower at a gas introduction rate of 200 to 300 L/h, and purified phosphorus pentafluoride gas is extracted from the top of the spray tower.

The hydrogen chloride in the primary phosphorus pentafluoride gas is adsorbed by the adsorption material and is enriched in the adsorption material to form a hydrogen chloride solution.

In some embodiments, after the liquid adsorption material adsorbs a certain amount of hydrogen chloride, a solution of hydrogen chloride can be extracted, and an extractant is added to extract the hydrogen chloride. After extraction, the layers are separated and the adsorption material can be reused.

In some embodiments, the adsorbent material is solid, and the adsorbent material is prepared into particles and filled in a packed tower. Primary phosphorus pentafluoride gas is introduced from the feed port of the packed tower and discharged from the discharge port of the packed tower. The gas introduction flow rate is 100 to 200 L/h to obtain purified phosphorus pentafluoride gas.

The use of a packed tower is conducive to continuous production.

In some embodiments, in order to achieve better purification effects, multiple spray towers or multiple packed towers may be connected in series or used in combination to achieve multi-stage adsorption purification.

In some embodiments, when the adsorbent material is saturated with hydrogen chloride, an organic solvent is used to dissolve and remove the hydrogen chloride on the adsorbent material, and the adsorbent material from which the hydrogen chloride is removed is reused.

Specifically, the organic solvent used for removing hydrogen chloride is selected from an inert solvent that does not react with phosphorus pentafluoride or hydrogen chloride, and the inert solvent includes diethyl ether, tetrahydrofuran, petroleum ether, etc. Specifically, the packed tower is cleaned and hydrogen chloride is dissolved by an inert solvent. After cleaning, the inert solvent is removed by vacuum drying to obtain an adsorption material for removing hydrogen chloride.

When the reaction temperature is too low, on the one hand, the reaction rate is affected, and on the other hand, there is also the problem of high energy consumption; and when the reaction temperature exceeds 10°C, the reaction rate of lithium fluoride and phosphorus pentafluoride is likely to be too fast, thereby generating a large amount of heat and inducing side reactions with the solvent.

By using a straight-chain carbonate as a reaction solvent, a straight-chain carbonate solution containing lithium hexafluorophosphate can be directly obtained by reaction, and the straight-chain carbonate itself can be used as a solvent for the electrolyte. Therefore, the liquid lithium hexafluorophosphate obtained by the "synthesis reaction" can be directly applied to the electrolyte after filtering, purification and impurity detection. There is no need to prepare solid lithium hexafluorophosphate through crystallization and drying in the traditional organic solvent method, which effectively reduces energy consumption.

In other embodiments, when solid lithium hexafluorophosphate needs to be prepared, the liquid hexafluorophosphate may be prepared by The lithium fluorophosphate is crystallized, filtered and dried to obtain lithium hexafluorophosphate solid.

Another embodiment of the present invention provides an electrolyte comprising liquid lithium hexafluorophosphate, wherein the liquid lithium hexafluorophosphate is prepared by the above-mentioned preparation method.

By directly applying the liquid lithium hexafluorophosphate prepared by the above preparation method to the electrolyte, the co-production of lithium hexafluorophosphate and the electrolyte is achieved, which can effectively prevent the lithium hexafluorophosphate from mixing with water or other deterioration during the crystallization and drying process, thereby shortening the process flow and ensuring the quality of the electrolyte.

In some embodiments, in order to adjust the concentration of lithium hexafluorophosphate in the electrolyte, a solvent may be additionally added to the electrolyte to reduce the concentration of lithium hexafluorophosphate or lithium hexafluorophosphate solid dispersion may be added to dissolve to increase the concentration of lithium hexafluorophosphate.

In some embodiments, in the electrolyte, the concentration of the lithium hexafluorophosphate is 0.1 mol/L to 8 mol/L. In a preferred embodiment, in the electrolyte, the concentration of the lithium hexafluorophosphate is 0.5 mol/L to 2.5 mol/L. In most cases, the concentration of the lithium hexafluorophosphate prepared by the above preparation method is relatively high, so an additional solvent needs to be added, and the solvent can be EMC (ethyl methyl carbonate) or DMC (dimethyl carbonate) which is the same as the organic solvent, or a cyclic carbonate, an ether solvent, a nitrile solvent, and a carboxylic acid ester solvent.

In some embodiments, the ether solvent includes a cyclic ether or a chain ether, preferably a chain ether with 3 to 10 carbon atoms and a cyclic ether with 3 to 6 carbon atoms. The cyclic ether may be, but not limited to, one or more of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH ₃ -THF), and 2-trifluoromethyltetrahydrofuran (2-CF ₃ -THF); the chain ether may be, but not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Since the chain ether has a high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred.

In some embodiments, the nitrile solvent may specifically be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile.

In some embodiments, the cyclic carbonate may specifically be, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

In some embodiments, the carboxylate solvent includes cyclic carboxylate and/or linear carbonate. Examples of cyclic carboxylate include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of linear carbonate include one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

In some embodiments, the sulfone solvent includes cyclic sulfone and chain sulfone. Preferably, in the case of cyclic sulfone, In the case of a sulfone, it is usually a compound having 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms. In the case of a chain sulfone, it is usually a compound having 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms.

In some embodiments, additives are further added to the electrolyte, and the additives include one or more of cyclic sulfate compounds, sultone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds and nitrile compounds.

Another embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and the electrolyte as described above.

In some embodiments, the positive electrode includes a positive electrode material layer containing a positive electrode active material. The type of the positive electrode active material is not particularly limited and can be selected according to actual needs, as long as it is a positive electrode active material or a conversion positive electrode material that can reversibly embed/de-embed lithium ions.

In a preferred embodiment, the positive electrode active material can be selected from one or more of LiFe1 _-x'M'x'PO4 _, _LiMn2 _-y'M _y'O4 _and _{LiNixCoyMnzM1} _-xyzO2 _, wherein M' is selected from one or more of Mn, Mg, Co, _Ni , _Cu , Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, M is selected from one or more of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, and 0≤x'＜1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1, and the positive electrode active material can also be selected from one or more of sulfides, selenides and halides. _More _preferably _, _the positive electrode active material can be selected _from _one or _more of _LiCoO2 , _LiNiO2 _, _LiMnO2 _, _LiFePO4 _, _{LiFe0.7Mn0.3PO4} _, _{LiFe0.8Mn0.2PO4} _, _LiNi1 _/ _3Co1 _/ _3Mn1 _/ _3O2 _, _{LiNi0.5Co0.2Mn0.3O2} _, _{LiNi0.6Co0.2Mn0.2O2} _, _{LiNi0.8Co0.1Mn0.1O2} _, _{LiNi0.8Co0.15Mn0.05O2} _, _{LiNi0.5Co0.2Mn0.2Al0.1O2} _, _LiMn2O4 _, _and _{LiNi0.5Co0.2Al0.3O2} _.

In some embodiments, the negative electrode includes a negative electrode material layer including a negative electrode active material.

In a preferred embodiment, the negative electrode active material includes at least one of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the tin-based negative electrode may include tin, tin carbon, tin oxygen, and tin metal compounds; the lithium negative electrode may include metallic lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium silicon alloy, a lithium sodium alloy, a lithium potassium alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.

In some embodiments, the lithium-ion battery further includes a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet.

The diaphragm may be an existing conventional diaphragm, a polymer diaphragm, a non-woven fabric, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP and triple-layer PP/PE/PP and other diaphragms.

The present invention is further described below by way of examples.

Example 1

This example is used to illustrate the preparation method of lithium hexafluorophosphate disclosed in the present invention, which includes the following steps:

(1) Preparation of chlorine-modified carbon nanotubes: 1.0 g of Fe-Co/CaCO ₃ catalyst was placed in a quartz boat and placed in the center of a quartz tube in a horizontal furnace. Under nitrogen (240 mL/min) and ethylene (90 mL/min) gas flow, the mixture was heated to 700°C in a gradient manner, dichlorobenzene was introduced, and the introduction of ethylene was stopped after 2 hours of reaction, and the mixture was cooled to room temperature under nitrogen protection. The quartz boat was then taken out of the reactor to obtain chlorine-modified carbon nanotubes. The synthesized chlorine-modified carbon nanotubes were stirred in 30% HNO ₃ at room temperature for 2 hours, filtered, and the remaining black solid was washed with distilled water until the pH value of the filtrate reached about 6.5. The chlorine-modified carbon nanotubes were then dried in an oven at 120°C for 12 hours, prepared into adsorption columns, and 5 of them were connected in series.

(2) Preparation of phosphorus pentafluoride: Phosphorus trichloride, anhydrous hydrogen fluoride and chlorine are placed in a PF ₅ reactor, nitrogen is passed through for protection, and the reaction temperature is controlled at about 10° C. to obtain a mixed gas of industrial-grade phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, and the mixed gas is passed through a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower are: feed temperature of 20° C., tower top pressure of 0.2 MPa, reflux ratio of 2:1, and tower top temperature of about -75° C.; primary phosphorus pentafluoride is obtained, and the primary phosphorus pentafluoride gas is then sent to an adsorption column to remove hydrogen chloride to obtain high-purity phosphorus pentafluoride. The treatment temperature is 25° C., the pressure is 0.5 MPa, and the ventilation flow rate is 350 L/h;

(3) Preparation of lithium fluoride: continuously adding an aqueous solution of hydrogen fluoride to an aqueous solution of lithium bicarbonate, stirring the reaction until the pH value is weakly acidic, filtering the generated lithium fluoride, and drying to obtain lithium fluoride;

(4) Synthesis reaction: In a synthesis reactor, lithium fluoride is dispersed in EMC (ethyl methyl carbonate), the temperature of the synthesis reactor is controlled at about -10°C, high-purity phosphorus pentafluoride is introduced, and nitrogen is passed for protection to prepare a primary lithium hexafluorophosphate solution;

(5) Purification: The primary lithium hexafluorophosphate solution produced in the synthesis reactor of step (4) is filtered to separate and obtain liquid lithium hexafluorophosphate.

Example 2

This example is used to illustrate the preparation method of lithium hexafluorophosphate disclosed in the present invention, and includes most of the operating steps in Example 1, except that:

In step (1), 100 g of carbon nanotubes were added to 10 L of sodium hypochlorite solution containing 5% effective chlorine, the pH was adjusted to neutral with hydrochloric acid, sealed and placed in a constant temperature water bath, stirred at 20° C. for 60 hours, filtered with a cellulose acetate filter membrane, repeatedly washed with distilled water, and placed in an oven at 50° C. for 72 hours to obtain Chlorine-modified carbon nanotubes were prepared into adsorption columns and 5 of them were connected in series.

Example 3

In step (1), 1 kg of 400-mesh graphite with a purity of 99.99% is added to a reaction kettle, and the temperature is first raised to 130° C. at -0.1 MPa and stirred for 2 h to remove moisture attached to the surface of the graphite, and then chlorine with a purity of 99.999% is introduced at 300-400° C. at a ventilation rate of 50 L/h; after ventilation for 6 h, the residual chlorine is replaced with nitrogen; and chlorine-modified graphite is obtained, which is prepared into an adsorption column and 5 columns are connected in series.

Example 4

In step (1), the graphene is heated and vacuumed to remove water, and then placed in a chlorine atmosphere and heated to 200°C, with a weight ratio of chlorine to graphene of 1.3:1 and a reaction time of 2h to obtain chlorine-modified graphene, which is prepared into an adsorption column and 5 of them are connected in series.

Comparative Example 1

This comparative example is used to compare and illustrate the preparation method of lithium hexafluorophosphate disclosed in the present invention, and includes most of the operating steps in Example 1, except that:

Do not perform step (1);

In step (2), a distillation tower is used to separate the hydrogen chloride in the mixed gas.

Comparative Example 2

In step (1), dried carbon nanotubes are used to directly prepare an adsorption column and five of them are connected in series.

Comparative Example 3

In step (1), dry graphite is used to directly prepare an adsorption column and five of them are connected in series.

Comparative Example 4

In step (1), dry graphene is used to directly prepare an adsorption column and five of them are connected in series.

Performance Testing

The free acid and chloride ion contents of the liquid lithium hexafluorophosphate prepared in the above examples and comparative examples were tested, and the test results were filled in Table 1.

Table 1

It can be seen from the test results in Table 1 that the preparation method provided by the present invention can effectively remove the hydrogen chloride gas in the mixed gas of phosphorus pentafluoride and hydrogen chloride generated by the reaction, thereby effectively reducing the content of chlorine in the finally synthesized liquid lithium hexafluorophosphate, improving the purity of lithium hexafluorophosphate, and being beneficial to improving the electrochemical performance of the prepared lithium ion battery.

Example 5

(1) Preparation of phosphorus pentafluoride: 250 g of phosphorus pentachloride was added to a reactor, and 20 g of anhydrous hydrogen fluoride was slowly introduced within 30 min. The reaction was carried out at 40° C. to continuously generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride. The mixed gas was introduced into a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower were: the feed temperature was controlled at 20° C. and the tower top pressure was 0.2 MPa. Primary phosphorus pentafluoride gas was obtained, and the primary phosphorus pentafluoride gas was then introduced into a three-stage spray tower. The three-stage spray tower used commercially available compound 1 (chlorobenzene) as a spray solvent. The gas introduction flow rate was 160 L/h. Purified phosphorus pentafluoride gas was obtained by spray absorption.

(2) Preparation of lithium fluoride: continuously adding an aqueous solution of hydrogen fluoride to an aqueous solution of lithium bicarbonate, stirring the reaction until the pH value is weakly acidic, filtering the generated lithium fluoride, and drying to obtain lithium fluoride;

(3) Synthesis reaction: In a synthesis reactor, lithium fluoride is dispersed into EMC (ethyl methyl carbonate), the temperature of the synthesis reactor is controlled at about -10°C, purified phosphorus pentafluoride gas is introduced, and nitrogen is passed for protection. A primary lithium hexafluorophosphate solution is prepared;

(4) Purification: After filtering the primary lithium hexafluorophosphate solution produced in the synthesis reactor in step (3), the filtered primary lithium hexafluorophosphate solution is pumped into a distillation tower to separate and obtain liquid lithium hexafluorophosphate.

Example 6

This example is used to illustrate the preparation method of lithium hexafluorophosphate disclosed in the present invention, and includes most of the operating steps in Example 5, except that:

In step (1), phosphorus pentafluoride is prepared by adding 250 g of phosphorus pentachloride into a reactor, slowly introducing 20 g of anhydrous hydrogen fluoride within 30 minutes, reacting at 40° C. to continuously generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, and introducing the mixed gas into a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower are as follows: controlling the feed temperature to be 20° C. and the tower top pressure to be 0.2 MPa; obtaining primary phosphorus pentafluoride gas, and then feeding the primary phosphorus pentafluoride gas into a three-stage packed tower. The three-stage packed tower uses commercially available compound 6 (hexachlorobenzene) as a filter filler. The gas introduction flow rate is 160 L/h. Purified phosphorus pentafluoride gas is obtained by filtration and absorption.

Example 7

In step (1), phosphorus pentafluoride is prepared by adding 250 g of phosphorus pentachloride into a reactor, slowly introducing 20 g of anhydrous hydrogen fluoride within 30 minutes, reacting at 40° C. to continuously generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, and introducing the mixed gas into a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower are as follows: controlling the feed temperature to be 20° C. and the tower top pressure to be 0.2 MPa; obtaining primary phosphorus pentafluoride gas, and then feeding the primary phosphorus pentafluoride gas into a three-stage packed tower. The three-stage packed tower uses commercially available compound 7 (poly(4-chlorostyrene)) as a filter filler. The gas introduction flow rate is 160 L/h. Purified phosphorus pentafluoride gas is obtained by filtration and absorption.

Example 8

In step (1), phosphorus pentafluoride is prepared by adding 250 g of phosphorus pentachloride into a reactor, slowly introducing 20 g of anhydrous hydrogen fluoride within 30 min, reacting at 40° C. to continuously generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, and introducing the mixed gas into a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower are: controlling the feed temperature to 20° C. and the tower top pressure to 0.2 MPa; obtaining primary phosphorus pentafluoride gas, and then The primary phosphorus pentafluoride gas is fed into a three-stage packed tower, which uses homemade compound 9 (polystyrene-butadiene block copolymer) as a filter filler. The gas introduction flow rate is 160 L/h, and purified phosphorus pentafluoride gas is obtained by filtration and absorption.

The preparation method of compound 9 is as follows: 500g of polystyrene-butadiene block copolymer (MW.100000) is dissolved in 2L 1,2-dichloroethane, a catalyst of ferric chloride is added, 1 equivalent of chlorine is slowly introduced at 60°C, and the reaction is stirred for 24h to obtain a crude product solution, wherein the purity of 4-chlorostyrene-butadiene block copolymer is 85%, and the remaining impurities are monosubstituted ortho-, meta- and disubstituted products and unreacted raw materials. The reaction solution is filtered, and the filtrate is concentrated to remove the solvent to obtain a crude product of compound 9. The crude product is washed with tetrahydrofuran to remove the hydrogen chloride adsorbed therein, and then rinsed with petroleum ether and dried to obtain compound 9 that can be used for adsorption.

Example 9

In step (1), phosphorus pentafluoride is prepared by adding 250 g of phosphorus pentachloride into a reactor, slowly introducing 20 g of anhydrous hydrogen fluoride within 30 minutes, reacting at 40° C. to continuously generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, and introducing the mixed gas into a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower are as follows: controlling the feed temperature to 20° C. and the tower top pressure to 0.2 MPa; obtaining primary phosphorus pentafluoride gas, and then feeding the primary phosphorus pentafluoride gas into a three-stage spray tower. The three-stage spray tower uses commercially available compound 11 (diphenyl ether) as a spray solvent. The gas introduction flow rate is 160 L/h. Purified phosphorus pentafluoride gas is obtained by spray absorption.

Example 10

In step (1), phosphorus pentafluoride is prepared by adding 250 g of phosphorus pentachloride into a reactor, slowly introducing 20 g of anhydrous hydrogen fluoride within 30 minutes, reacting at 40° C. to continuously generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, and introducing the mixed gas into a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower are as follows: controlling the feed temperature to 20° C. and the tower top pressure to 0.2 MPa; obtaining primary phosphorus pentafluoride gas, and then feeding the primary phosphorus pentafluoride gas into a three-stage packed tower. The three-stage packed tower uses homemade graphite balls loaded with compound 13 as filter fillers. The gas introduction flow rate is 160 L/h, and purified phosphorus pentafluoride gas is obtained by filtration and absorption.

The preparation method of compound 13 is as follows: 500 g of propofol and 5 g of concentrated sulfuric acid are added to a reaction bottle and heated at 120 °C. The reaction was carried out for 12 hours to obtain a crude product of compound 13. An equivalent amount of sodium bicarbonate was added to neutralize the concentrated sulfuric acid, filtered, and the filtrate was distilled under reduced pressure to remove the generated water and unreacted propofol to obtain a refined product of compound 13 with an HPLC purity of 98% and a yield of 81%. Compound 13 was mixed with graphite spheres to obtain graphite spheres loaded with compound 13.

Comparative Example 5

This comparative example is used to compare and illustrate the preparation method of lithium hexafluorophosphate disclosed in the present invention, and includes most of the operating steps in Example 5, except that:

In step (1), phosphorus pentafluoride is prepared by adding 250 g of phosphorus pentachloride into a reactor, slowly introducing 20 g of anhydrous hydrogen fluoride within 30 min, reacting at 40° C. to continuously generate a mixed gas of phosphorus pentafluoride, hydrogen chloride and hydrogen fluoride, and introducing the mixed gas into a distillation tower to separate the phosphorus pentafluoride. The operating parameters of the distillation tower are as follows: controlling the feed temperature to 20° C. and the tower top pressure to 0.2 MPa; obtaining primary phosphorus pentafluoride gas;

Primary phosphorus pentafluoride gas is used as the reactant in step (3).

Comparative Example 6

In step (1), benzene is used as the spraying solvent.

Comparative Example 7

This comparative example is used to compare and illustrate the preparation method of lithium hexafluorophosphate disclosed in the present invention, and includes most of the operating steps in Example 7, except that:

In step (1), polystyrene is used as the filter filler.

Performance Testing

The free acid and chloride ion contents of the liquid lithium hexafluorophosphate prepared in the above examples and comparative examples were tested, and the test results were filled in Table 2.

Table 2

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

A method for preparing liquid lithium hexafluorophosphate, characterized in that it comprises the following steps:

Obtaining primary phosphorus pentafluoride;

The primary phosphorus pentafluoride is then fully contacted with an adsorption material, so that hydrogen chloride in the primary phosphorus pentafluoride is adsorbed on a chlorine-modified carbon material to obtain purified phosphorus pentafluoride gas, wherein the adsorption material comprises at least one of a chlorine-modified carbon material, a chlorinated aromatic hydrocarbon, a chlorinated aromatic hydrocarbon polymer, and an aromatic ether;

Synthesis reaction: Lithium fluoride is dissolved in a solvent and purified phosphorus pentafluoride gas is introduced to prepare liquid lithium hexafluorophosphate.
The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that the preparation method of the primary phosphorus pentafluoride is:

Preparation of phosphorus pentafluoride: Phosphorus trichloride, hydrogen fluoride and chlorine are introduced into a reactor, the temperature of the reactor is controlled to be -50°C to 30°C, the pressure in the reactor is controlled to be 0.1 to 1.0 MPa, and a mixed gas containing phosphorus pentafluoride is obtained after a reaction time of 2 to 6 hours;

Distillation: The mixed gas is passed into a distillation tower, the feed temperature is controlled at 5-35°C, and the tower top pressure is 0.06-0.5MPa, phosphorus pentafluoride is separated to obtain primary phosphorus pentafluoride.
The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that the adsorbent material is selected from at least one of a chlorine-modified carbon material, or a chlorinated aromatic hydrocarbon, a chlorinated aromatic hydrocarbon polymer, and an aromatic ether.
The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that the chlorine-modified carbon material is selected from at least one of chlorine-modified carbon nanotubes, chlorine-modified graphite and chlorine-modified graphene.
The method for preparing lithium hexafluorophosphate according to claim 4, characterized in that the chlorine-modified carbon nanotubes are prepared by the following method:

In a closed reactor, Fe-Co/CaCO 3 is used as a catalyst, nitrogen and ethylene are introduced, and the temperature is gradually increased to 650° C. to 900° C., dichlorobenzene is introduced, and the introduction of ethylene is stopped after the reaction for 1-2 hours to obtain chlorine-modified carbon nanotubes. The synthesized chlorine-modified carbon nanotubes are acid-washed, filtered, washed with water, and then dried to obtain chlorine-modified carbon nanotubes;

Alternatively, the carbon nanotubes are added to a sodium hypochlorite solution, adjusted to neutrality with hydrochloric acid, filtered after sufficient reaction, washed with water, and dried to obtain chlorine-modified carbon nanotubes.
The method for preparing lithium hexafluorophosphate according to claim 4, characterized in that the chlorine-modified graphite is prepared by the following method:

After the graphite is dried, chlorine gas with a purity of 99.999% is introduced at 300-400° C. for reaction at a ventilation rate of 30-70 L/h; the reaction time is 3-8 hours. After the reaction is completed, the residual chlorine gas is replaced with nitrogen to obtain chlorine-modified graphite.
The method for preparing lithium hexafluorophosphate according to claim 4, characterized in that the chlorine-modified graphene is prepared by the following method:

After the graphene is heated and vacuumed to remove water, it is placed in a chlorine atmosphere and heated to 150-260° C., the weight ratio of chlorine to graphene is 1-1.6:1, and the reaction time is 1-2 hours to obtain chlorine-modified graphene.
The method for preparing liquid lithium hexafluorophosphate according to claim 1 is characterized in that the chlorine-modified carbon material is fixed in a fixed bed reactor, and the mixed gas is continuously passed through the fixed bed reactor, the temperature of the fixed bed reactor is 5°C to 35°C, the pressure is 0.1 to 0.8 MPa, and the ventilation flow rate is 200 to 6300 L/h.
The method for preparing liquid lithium hexafluorophosphate according to claim 1 is characterized in that in the "synthesis reaction" operation, the temperature is controlled at -20°C to 10°C, and the solvent is selected from linear carbonates.
The method for preparing liquid lithium hexafluorophosphate according to claim 1 is characterized in that, when the chlorine-modified carbon material is saturated with hydrogen chloride, the hydrogen chloride on the chlorine-modified carbon material is removed by liquid dissolution or high-temperature gas purging, the temperature of the high-temperature gas is 150°C to 240°C, and the chlorine-modified carbon material from which the hydrogen chloride is removed is reused.
The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that the chlorinated aromatic hydrocarbon is selected from the compound shown in structural formula 1:

R 1 to R 6 are each independently selected from H, a C1-C4 hydrocarbon group, a C1-C4 halogenated hydrocarbon group or a halogen atom, and at least one chlorine atom is contained in R 1 to R 6 .
The method for preparing liquid lithium hexafluorophosphate according to claim 11, characterized in that the compound represented by structural formula 1 is selected from one or more of the following compounds:
The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that the chlorinated aromatic hydrocarbon polymer is selected from the compound shown in structural formula 2:

Among them, R is selected from chlorine atoms, Y is selected from hydrogen, methyl or polybutadiene groups, and n is 500-1000.
The method for preparing liquid lithium hexafluorophosphate according to claim 13, characterized in that the compound represented by structural formula 2 is selected from one or more of the following compounds:

Among them, n is 500~1000, and m is 500~1000.
The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that the aryl ether is selected from the compound shown in structural formula 3:

Wherein, R 11 to R 20 are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl or halogen.
The method for preparing liquid lithium hexafluorophosphate according to claim 15, characterized in that the compound represented by structural formula 3 is selected from one or more of the following compounds:
The method for preparing liquid lithium hexafluorophosphate according to claim 1 is characterized in that the adsorbent material is a liquid, the adsorbent material is introduced into a spray tower, a circulating pump is used for circulating spraying, primary phosphorus pentafluoride gas is introduced from the bottom of the spray tower, the gas introduction flow rate is 200 to 300 L/h, and purified phosphorus pentafluoride gas is extracted from the top of the spray tower.
The method for preparing liquid lithium hexafluorophosphate according to claim 1 is characterized in that the adsorbent material is solid, the adsorbent material is prepared into particles and filled in a packed tower, primary phosphorus pentafluoride gas is introduced from the feed port of the packed tower, and discharged from the discharge port of the packed tower, the gas introduction flow rate is 100 to 200 L/h, and purified phosphorus pentafluoride gas is obtained; when the adsorbent material is saturated with hydrogen chloride, the hydrogen chloride on the adsorbent material is dissolved and removed by an organic solvent, and the adsorbent material from which the hydrogen chloride is removed is reused.
An electrolyte, characterized in that it comprises liquid lithium hexafluorophosphate, wherein the liquid lithium hexafluorophosphate is prepared by the preparation method according to any one of claims 1 to 18.
A lithium-ion battery, comprising a positive electrode, a negative electrode and the electrolyte as claimed in claim 19.