Process for the continuous production of electrolyte comprising alkali metal hexafluorophosphate

Abstract

A process for continuously producing an electrolyte comprising an alkali metal hexafluorophosphate is provided. The process comprises a mother liquor production step of producing a mother liquor in the form of a slurry comprising an organic solvent, an alkali metal hexafluorophosphate dissolved therein, and unreacted alkali metal fluoride particles, in a reactor; a filtration step of introducing a portion of the mother liquor into a first cross-flow filter to obtain a filtrate and a retentate, the filtrate being obtained by filtering the unreacted alkali metal fluoride particles from the mother liquor and comprising the organic solvent and the alkali metal hexafluorophosphate; a reflux step of refluxing the retentate obtained in the filtration step into the reactor; a transport step of transporting the filtrate obtained in the filtration step to a subsequent process; and a reaction progress step comprising backflushing a second cross-flow filter with a make-up organic solvent at a molar flow rate equal to the molar flow rate of the organic solvent comprised in the filtrate of the transport step to obtain a backflush effluent and supplying the backflush effluent into the reactor.

Description

[0001] This application claims priority to Korean Patent Application No. 10-2025-0050160, filed with the Ministry of Intellectual Property (MOIP) on April 17, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The exemplary embodiments of the present invention relate to electrolytes containing alkali metal hexafluorophosphates, and more specifically, to electrolytes containing alkali metal hexafluorophosphates that can be used in secondary batteries and the like. Background Technology

[0003] Recently, rechargeable batteries have become a key component in a wide range of applications, from portable electronic products (such as mobile phones and laptops) and cordless electronic devices (such as vacuum cleaners) to electric vehicles, and demand for them is expected to continue to increase.

[0004] As an example of a secondary battery, a lithium secondary battery operates based on the following principle: lithium ions in the positive electrode active material move through the electrolyte to the negative electrode and are intercalated into the layered structure of the negative electrode active material (charging), and then the lithium ions intercalated into the layered structure of the negative electrode active material return to the positive electrode through the electrolyte (discharging). The electrolyte is a lithium salt dissolved in an organic solvent, and lithium hexafluorophosphate, which has high stability and excellent electrical performance, is mainly used as the lithium salt.

[0005] Although lithium hexafluorophosphate is prepared using various methods, there is a need for a preparation method that can reduce costs. Summary of the Invention

[0006] Lithium hexafluorophosphate is primarily produced using batch processes; however, batch processes are inefficient for large-scale production because each batch requires reaction and filtration time. Furthermore, since reaction conditions may vary slightly from batch to batch, there is a possibility of reduced product uniformity. Additionally, the high-concentration slurry generated during the manufacturing process frequently causes filter clogging, potentially leading to maintenance costs and time losses.

[0007] Therefore, exemplary embodiments of the present invention provide a method for preparing an electrolyte containing an alkali metal hexafluorophosphate with excellent performance at low cost.

[0008] The technical objectives of this invention are not limited to those described above, and other technical objectives not mentioned will be clearly understood by those skilled in the art from the following description.

[0009] In some example embodiments, a method for continuously preparing an electrolyte comprising alkali metal hexafluorophosphate is provided. The method includes: a mother liquor preparation step, preparing a mother liquor in slurry form within a reactor, the mother liquor comprising an organic solvent, alkali metal hexafluorophosphate dissolved in the organic solvent, and unreacted alkali metal fluoride particles; a filtration step, introducing a portion of the mother liquor into a first cross-flow filter to obtain filtrate and residue, the filtrate being obtained by filtering unreacted alkali metal fluoride particles from the mother liquor and comprising the organic solvent and alkali metal hexafluorophosphate; a reflux step and a conveying step, in which the residue obtained in the filtration step is refluxed back into the reactor, and in the conveying step, the filtrate obtained in the filtration step is conveyed to a subsequent process; and a reaction proceeding step, including backwashing a second cross-flow filter with supplemented organic solvent at a molar flow rate equal to the molar flow rate of the organic solvent contained in the filtrate of the conveying step to obtain backwash effluent, and supplying the backwash effluent to the reactor.

[0010] The second cross-flow filter may include unreacted alkali metal fluoride particles located on the filter surface of the second cross-flow filter. The backwash effluent may be an alkali metal fluoride dispersion in which the unreacted alkali metal fluoride particles located on the filter surface of the second cross-flow filter are dispersed in a supplemental organic solvent.

[0011] The reaction proceeding step may further include supplying supplemental alkali metal fluoride and supplemental phosphorus pentafluoride into the reactor at a molar flow rate equal to that of the alkali metal hexafluorophosphate contained in the filtrate of the delivery step, to generate additional mother liquor.

[0012] The mother liquor may contain alkali metal hexafluorophosphate, which can be obtained by reacting the initial alkali metal fluoride and initial phosphorus pentafluoride in the initial organic solvent after the initial organic solvent, initial alkali metal fluoride, and initial phosphorus pentafluoride are supplied to the reactor. The initial phosphorus pentafluoride may be supplied in its stoichiometric amount, and the initial alkali metal fluoride may be supplied in excess relative to its stoichiometric amount. The molar ratio of the initial alkali metal fluoride to the initial phosphorus pentafluoride may be from 1.05 to 1.3.

[0013] The mother liquor may contain alkali metal hexafluorophosphate, which can be obtained by reacting the initial alkali metal fluoride and initial phosphorus pentafluoride in the initial organic solvent after the initial organic solvent, initial alkali metal fluoride, and initial phosphorus pentafluoride are supplied to the reactor. The initial organic solvent may be the backwash effluent obtained by backwashing the second cross-flow filter.

[0014] When the flow rate of the filtrate in the delivery step is greater than or equal to the reference value, the reaction proceeding step, filtration step, reflux step, and delivery step can be executed continuously.

[0015] The filtration step, reflux step, conveying step, and reaction proceeding step are respectively the first filtration step, the first reflux step, the first conveying step, and the first reaction proceeding step. In this case, when the flow rate of the filtrate in the first conveying step is less than a reference value, the method may further include: a second filtration step, in which a portion of the mother liquor is introduced into a second cross-flow filter to filter unreacted alkali metal fluoride particles from the mother liquor, thereby obtaining filtrate and residue, the filtrate obtained from the second cross-flow filter containing an organic solvent and alkali metal hexafluorophosphate; a second reflux step and a second conveying step, in which the residue obtained in the second filtration step is refluxed back into the reactor in the second reflux step, and the filtrate obtained in the second filtration step is conveyed to a subsequent process in the second conveying step; and a second reaction proceeding step, including the step of backwashing the first cross-flow filter with supplemented organic solvent at a molar flow rate equal to the molar flow rate of the organic solvent contained in the filtrate of the second conveying step to obtain backwash effluent, and the step of supplying the backwash effluent obtained by backwashing the first cross-flow filter to the reactor.

[0016] In the first filtration step, unreacted alkali metal fluoride particles may accumulate on the filter surface of the first cross-flow filter, and the backwash effluent obtained by backwashing the first cross-flow filter is an alkali metal fluoride dispersion in which the unreacted alkali metal fluoride particles accumulated on the filter surface of the first cross-flow filter are dispersed in a supplemented organic solvent.

[0017] The second reaction step may further include supplying supplemental alkali metal fluoride and supplemental phosphorus pentafluoride into the reactor at a molar flow rate equal to the molar flow rate of alkali metal hexafluorophosphate contained in the filtrate of the second delivery step, to generate additional mother liquor.

[0018] When the flow rate of the filtrate in the second delivery step is greater than or equal to the reference value, the second reaction proceeding step, the second filtration step, the second reflux step, and the second delivery step can be executed continuously.

[0019] When the flow rate of the filtrate in the second conveying step is less than a reference value, the first filtration step, the first reflux step, the first conveying step, and the first reaction proceeding step can be performed. In the first reaction proceeding step, the backwash effluent obtained by backwashing the second cross-flow filter can be an alkali metal fluoride dispersion, in which unreacted alkali metal fluoride particles accumulated in the second cross-flow filter during the second filtration step are dispersed in a supplemented organic solvent.

[0020] When the flow rate of the filtrate in the first delivery step is greater than or equal to the reference value, the first reaction proceeding step, the first filtration step, the first reflux step, and the first delivery step can be executed consecutively. When the flow rate of the filtrate in the first delivery step is less than the reference value, the second filtration step, the second reflux step, the second delivery step, and the second reaction proceeding step can be executed.

[0021] The organic solvent can be a chain or cyclic carbonate, lactone, chain or cyclic ether, or a mixture thereof. An example organic solvent is ethyl methyl carbonate (EMC).

[0022] Alkali metal fluorides can be LiF, and alkali metal hexafluorophosphates can be LiPF6. Attached Figure Description

[0023] The exemplary embodiments of the present invention will become more apparent from the detailed description of the accompanying drawings, in which: Figure 1 This is a schematic diagram illustrating a preparation system for preparing a concentrated electrolyte containing alkali metal hexafluorophosphate (MPF6) according to an embodiment of the present invention, and also showing that a first cross-flow filter in the preparation system performs filtration of the mother liquor, while a second cross-flow filter supplies additional organic solvent to the reactor through backwashing. Figure 2 It is shown Figure 1 An enlarged schematic diagram of the cross-flow filter in the preparation system; Figure 3 This is a flowchart illustrating the preparation of a concentrated electrolyte containing alkali metal hexafluorophosphate (MPF6) according to an embodiment of the present invention; Figure 4 This is a schematic diagram showing the supply of additional organic solvent to the reactor through backwashing of the first cross-flow filter while the mother liquor is being filtered by the second cross-flow filter; and Figure 5 yes Figure 4 An enlarged schematic diagram of the cross-flow filter in the preparation system. Detailed Implementation

[0024] In the following description, preferred embodiments of the invention will be presented in more detail with reference to the accompanying drawings to explain the invention more specifically. However, the invention is not limited to the embodiments described herein and may be implemented in other forms. In the drawings, when a layer is referred to as being "on" another layer or substrate, the layer may be formed directly on said other layer or substrate, or a third layer may be interposed between them. In this embodiment, "first," "second," or "third" is not intended to impose any limitation on the components, but should be understood as terms used to distinguish components.

[0025] Methods for preparing alkali metal hexafluorophosphates Alkali metal hexafluorophosphates can be prepared by the following reaction: [Reaction Formula] MF+PF5→MPF6 In the above reaction formula, M is an alkali metal, and can be Li, Na, or K. MF is an alkali metal fluoride, and can be, for example, lithium fluoride (LiF), sodium fluoride (NaF), or potassium fluoride (KF). MPF6 is an alkali metal hexafluorophosphate, and can be LiPF6, NaPF6, or KPF6.

[0026] The reaction described above can be carried out in an organic solvent in which alkali metal fluorides (MF) are insoluble but alkali metal hexafluorophosphates (MPF6) are soluble. Specifically, the organic solvent can be a chain or cyclic carbonate, lactone, chain or cyclic ether, or a mixture thereof.

[0027] The chain carbonates can be dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (EMC), and the cyclic carbonates can be ethylene carbonate, propylene carbonate, or butyl carbonate. The lactones can be γ-butyrolactone or γ-valerolactone. The ethers can be chain ethers (such as dimethoxyethane or diethyl ether) or cyclic ethers (such as tetrahydrofuran, methyltetrahydrofuran, or dioxane).

[0028] In one example, the organic solvent may be a chain or cyclic carbonate (specifically, a chain carbonate, more specifically, ethyl methyl carbonate (EMC)).

[0029] For the reaction described above, phosphorus pentafluoride (PF5) can be introduced into the organic solvent in a gaseous state, and alkali metal fluoride (MF) can be introduced into the organic solvent in a solid state (i.e., in particulate state) or in a slurry state dispersed in the organic solvent. The alkali metal hexafluorophosphate (MPF6) obtained by reacting phosphorus pentafluoride (PF5) with alkali metal fluoride (MF) in an organic solvent can be dissolved in the organic solvent. In other words, an organic solvent solution of alkali metal hexafluorophosphate (MPF6) can be obtained through the reaction.

[0030] Phosphorus pentafluoride (PF5) can be introduced in stoichiometric amounts as shown in the reaction formula, and an excess of alkali metal fluoride (MF) can be introduced relative to the stoichiometric amounts. Specifically, the molar ratio of MF / PF5 can be from 1.05 to 1.3, more specifically, from 1.15 to 1.25. In this case, the introduced PF5 reacts rapidly and completely with MF to prepare MPF6 without acidic impurities caused by side reactions with the organic solvent. However, due to the excess introduction of MF, MF will remain as solid particles in the organic solvent solution of MPF6 prepared by the reaction. Therefore, the organic solvent solution of MPF6 (hereinafter referred to as the "mother liquor") can have a slurry form containing unreacted MF.

[0031] The reaction can be carried out in a moisture-free atmosphere at a pressure below atmospheric pressure and a temperature of about 5°C to 15°C (specifically, 7°C to 12°C).

[0032] System for preparing alkali metal hexafluorophosphates Figure 1 This is a schematic diagram illustrating a preparation system for preparing a concentrated electrolyte containing alkali metal hexafluorophosphate (MPF6) according to an embodiment of the present invention. It also shows that a first cross-flow filter in the preparation system performs filtration of the mother liquor, while a second cross-flow filter supplies additional organic solvent to the reactor through backwashing. Figure 2 It is shown Figure 1 An enlarged schematic diagram of the cross-flow filter in the preparation system.

[0033] Reference Figure 1 and Figure 2 The preparation system may include a reactor 100 in which the above-described reaction occurs. The reactor 100 may include a stirrer, and an alkali metal fluoride supply line L20 may be connected to the reactor 100 to supply solid alkali metal fluoride (MF).

[0034] The screw feeder SF-400, electronic scale WI, screw feeder motor inverter SIC-1, alkali metal fluoride switching valve V20, and motor M driving the screw feeder SF-400 can be installed in the alkali metal fluoride supply line L20. The screw feeder SF-400 can be used to introduce alkali metal fluoride into reactor 100 through the alkali metal fluoride supply line L20, and the supply of alkali metal fluoride can be controlled by receiving signals from the electronic scale WI and adjusting the revolutions per minute (RPM) of the screw feeder motor inverter SIC-1.

[0035] A phosphorus pentafluoride supply line L10 can be connected to reactor 100, supplying gas containing phosphorus pentafluoride (PF5) through the phosphorus pentafluoride supply line L10. A phosphorus pentafluoride flow meter FE-10, a phosphorus pentafluoride flow control valve FV-10, and a phosphorus pentafluoride on / off valve V10 can be installed in the phosphorus pentafluoride supply line L10. The phosphorus pentafluoride flow meter FE-10 measures the flow rate of phosphorus pentafluoride and transmits the phosphorus pentafluoride to the phosphorus pentafluoride flow controller FIC-10, which in turn controls the phosphorus pentafluoride flow control valve FV-10 to regulate the supply amount of phosphorus pentafluoride-containing gas to reactor 100 through the phosphorus pentafluoride supply line L10.

[0036] In addition to phosphorus pentafluoride gas, the gas containing phosphorus pentafluoride may also contain hydrochloric acid gas. The hydrochloric acid gas may also be included in the filtrate obtained in the first and second filtration steps, which will be described later, and is then fed to a subsequent process, which may be a process for removing acids including hydrochloric acid. Hereinafter, the gas containing phosphorus pentafluoride may be referred to as phosphorus pentafluoride.

[0037] A first organic solvent supply or reflux line L31 and a second organic solvent supply or reflux line L32 can be connected to reactor 100 to supply organic solvent or residue containing organic solvent discharged from the cross-flow filter (described later). Furthermore, a mother liquor discharge line L40 can be connected to reactor 100 to discharge mother liquor in slurry form containing unreacted alkali metal fluoride (MF) particles, wherein the mother liquor is an organic solvent solution containing alkali metal hexafluorophosphate as a reaction product.

[0038] The viscosity of the mother liquor prepared in reactor 100 can be from 0.8 mPa·s to 60 mPa·s, for example, from 5 mPa·s to 40 mPa·s. In this case, a suitable production rate of alkali metal hexafluorophosphate can be obtained while appropriately maintaining the filter replacement cycle. For this purpose, the concentration of alkali metal hexafluorophosphate in the mother liquor can be adjusted.

[0039] Specifically, the mother liquor may contain 8 to 12 moles of alkali metal hexafluorophosphate per 50 moles of organic solvent, and the molar ratio of unreacted alkali metal fluoride (MF) particles to alkali metal hexafluorophosphate (MPF6) may be 0.05 to 0.3, more specifically, 0.15 to 1.25.

[0040] The preparation system may also include at least two cross-flow filters, such as a first cross-flow filter 210 and a second cross-flow filter 220. Each of the cross-flow filters 210 and 220 may include a feed solution compartment 215 or 225 therein, a filtrate compartment 219 or 229 surrounding the outside of the feed solution compartment 215 or 225, and a filter 217 or 227 as a porous membrane located therebetween.

[0041] Each feed solution compartment 215 or 225 can be a space where the mother liquor flows between the mother liquor inlet 212 or 222 and the outlet 211 or 221. The mother liquor inlet 212 or 222 is connected to the mother liquor discharge line L40 of the reactor 100 and the mother liquor in slurry form is introduced into the mother liquor inlet 212 or 222. The treated mother liquor (i.e., residue) is discharged through the outlet 211 or 221.

[0042] Filter 217 or 227 filters out unreacted alkali metal fluoride (MF) particles larger than the filter pore size from the mother liquor, and filtrate compartment 219 or 229 can be a space for introducing filtrate (i.e., an organic solvent solution of alkali metal hexafluorophosphate from which unreacted alkali metal fluoride (MF) particles have been removed by filter 217 or 227).

[0043] The residue is the remaining solution of the mother liquor discharged from the mother liquor inlet 212 or 222 and the unreacted alkali metal fluoride (MF) particles accumulated on the surface of the filter 217 or 227. However, since neither the unreacted alkali metal fluoride (MF) particles nor the organic solvent solution of alkali metal hexafluorophosphate is completely removed from the residue and they remain therein, the residue can maintain the slurry state in which the alkali metal fluoride (MF) particles are dispersed in the organic solvent solution of alkali metal hexafluorophosphate.

[0044] In each of the cross-flow filters 210 and 220, the flow of the mother liquor as the feed solution between the mother liquor inlet 212 or 222 and the outlet 211 or 221, and the flow of the filtrate through the filter 217 or 227, are not parallel but can intersect each other. Compared to conventional filters where the flow of the feed solution and the flow of the filtrate are in the same direction (i.e., the flow of the feed solution is perpendicular to the filter surface), these cross-flow filters 210 and 220 take a relatively long time for the filter pores to become clogged with solid particles, resulting in a reduction in manufacturing costs.

[0045] The diameter (φ) of the feed solution compartment 215 or 225 of each cross-flow filter 210 or 220 can be 2 mm to 5 mm, for example, 3 mm to 4 mm, to prevent clogging of the feed solution compartment 215 or 225 and to obtain the desired filtrate flow rate.

[0046] Each cross-flow filter 210 or 220 may have a porous polyolefin layer, such as a porous polyethylene layer, as its filter 217 or 227. Alternatively, filter 217 or 227 may be composed of a single layer of porous polyethylene. In this case, compared to ceramic filters that react with HF to produce water, filter 217 or 227 does not react with HF, thereby improving filter life and the purity of the organic solvent solution of alkali metal hexafluorophosphate. Furthermore, the pore size of filter 217 or 227 may be from 0.1 μm to 10 μm. Simultaneously, the average particle size of the alkali metal fluoride supplied via alkali metal fluoride supply line L20 may be from 50 μm to 100 μm, for example, from 60 μm to 80 μm; however, as mentioned above, the particle size may decrease because excess alkali metal fluoride reacts with phosphorus pentafluoride gas in reactor 100 while circulating through the preparation system. Therefore, in order to properly filter alkali metal fluoride particles, the pore size of filter 217 or 227 can be in the range of 0.1 μm to 10 μm, and within this pore size range, the lifespan of the cross-flow filter can be properly ensured.

[0047] A mother liquor discharge valve V40 and a mother liquor pump P40, used to allow or prevent the discharge of mother liquor, can be installed in a mother liquor discharge line L40 connected downstream of reactor 100. A mother liquor flow meter FE-40 can be further installed in the mother liquor discharge line L40. The mother liquor discharge line L40 branches downstream of the mother liquor pump P40 into a first mother liquor supply line L41 and a second mother liquor supply line L42, and mother liquor supply lines L41 and L42 can be connected to the mother liquor inlets 212 and 222 of cross-flow filters 210 and 220, respectively. The first mother liquor inlet valve V41 and the second mother liquor inlet valve V42 can be installed in the first mother liquor supply line L41 and the second mother liquor supply line L42, respectively, to allow or prevent the flow of mother liquor according to commands from controller 500.

[0048] The outlets 211 and 221 of the cross-flow filters 210 and 220 can be connected to the first organic solvent supply or return line L31 and the second organic solvent supply or return line L32, respectively. The first organic solvent discharge valve V31a and the second organic solvent discharge valve V32a can be installed in the organic solvent supply or return lines L31 and L32, respectively, to allow or prevent the flow of residual material through one of the organic solvent supply or return lines L31 and L32 and the flow of organic solvent through the other, according to a command from the controller 500. Furthermore, organic solvent flow meters FE-31 and FE-32 and organic solvent valves V31b and V32b can be installed in the first organic solvent supply or return line L31 and the second organic solvent supply or return line L32.

[0049] Fresh solvent supply lines L50, L51, and L52 can be connected to the filtrate compartments 219 and 229 of the corresponding cross-flow filters 210 and 220, through which fresh organic solvent is supplied from solvent reservoir 300. A fresh solvent pump P50, a fresh solvent flow meter FE-50, and a fresh solvent flow control valve FV-50 can be installed in the integrated fresh solvent supply line L50 connected to solvent reservoir 300. The fresh solvent flow meter FE-50 measures the flow rate of the supplied fresh solvent and transmits this information to a fresh solvent flow controller FIC-50, which in turn controls the fresh solvent flow control valve FV-50 to regulate the amount of fresh solvent supplied through the fresh solvent supply lines L50. The integrated fresh solvent supply line L50 can branch into a first fresh solvent supply line L51 and a second fresh solvent supply line L52 downstream of the fresh solvent pump P50, the fresh solvent flow meter FE-50, and the fresh solvent flow control valve FV-50. The first fresh solvent supply line L51 and the second fresh solvent supply line L52 can be connected to the filtrate compartments 219 and 229 of the cross-flow filters 210 and 220, respectively. The first fresh solvent supply valve V51 and the second fresh solvent supply valve V52 can be installed in the first fresh solvent supply line L51 and the second fresh solvent supply line L52, respectively, to allow or stop the flow of fresh solvent according to commands from the controller 500.

[0050] In one embodiment of the present invention, a fresh solvent or a fresh organic solvent refers to a solvent that does not contain a solute (specifically, a gas containing phosphorus pentafluoride (PF5), an alkali metal fluoride (MF), or an alkali metal hexafluorophosphate (MPF6)), and may be one of the above-mentioned organic solvents or a mixture of two or more organic solvents.

[0051] Filtrate discharge lines L60, L61, and L62 for discharging filtrate can be connected to filtrate compartments 219 and 229 of cross-flow filters 210 and 220. Specifically, the first filtrate discharge line L61 and the second filtrate discharge line L62 can be connected to filtrate compartments 219 and 229 of cross-flow filters 210 and 220, respectively, and the first filtrate discharge valve V61 and the second filtrate discharge valve V62 can be installed in the first filtrate discharge line L61 and the second filtrate discharge line L62, respectively, to allow or stop the flow of filtrate according to commands from controller 500. The first filtrate discharge line L61 and the second filtrate discharge line L62 can be integrated downstream of the first filtrate discharge valve V61 and the second filtrate discharge valve V62 to form an integrated filtrate discharge line L60, which can be connected to equipment 400 for performing subsequent processes. Equipment 400 can be equipment for removing acids including hydrochloric acid. The filtrate discharge flow meter FE-60 and the filtrate flow control valve FV-60 can be installed in the integrated filtrate discharge line L60. The filtrate discharge flow meter FE-60 measures the flow rate of the discharged filtrate and transmits it to the filtrate flow controller FIC-60, which in turn controls the filtrate flow control valve FV-60 to regulate the discharge volume of filtrate through the integrated filtrate discharge line L60.

[0052] All devices within the preparation system can be controlled via controller 500. Specifically, controller 500 can open or close valves, operate pumps, operate flow controllers, adjust electronic scales, adjust flow control valves, operate agitators in the reactor, and control the temperature in the reactor and the temperature of the cross-flow filter.

[0053] Figure 3 This is a flowchart illustrating the preparation of a concentrated electrolyte containing alkali metal hexafluorophosphate (MPF6) according to an embodiment of the present invention.

[0054] Figure 4 This is a schematic diagram showing that while the mother liquor is being filtered by the second cross-flow filter, supplemental organic solvent is supplied to the reactor through backwashing of the first cross-flow filter. Figure 5 yes Figure 4 An enlarged schematic diagram of the cross-flow filter in the preparation system.

[0055] Reference Figure 1 , Figure 2 , Figure 4 and Figure 5During the preparation of a concentrated electrolyte containing alkali metal hexafluorophosphate (MPF6) according to an embodiment of the present invention, the controller 500 can control the phosphorus pentafluoride switching valve V10, the alkali metal fluoride switching valve V20, the mother liquor discharge valve V40, the first organic solvent discharge valve V31a and the second organic solvent discharge valve V32a respectively installed in the first organic solvent supply or return line L31 and the second organic solvent supply or return line L32, and the organic solvent valves V31b and V32b respectively installed in the first organic solvent supply or return line L31 and the second organic solvent supply or return line L32 to be in the open state.

[0056] Reference Figure 3 , Figure 1 and Figure 2 The mother liquor preparation step S10 can be performed to prepare a mother liquor in the reactor 100 as an organic solvent solution of alkali metal hexafluorophosphate in the form of a slurry containing unreacted alkali metal fluoride particles. Subsequently, step S21, including a first filtration step, a first reflux step, and a first conveying step, can be performed. The first filtration step can be performed to introduce a portion of the mother liquor in the reactor 100 into a first cross-flow filter 210, thereby obtaining filtrate D from which alkali metal fluoride particles are filtered out and residual material E remaining after filtering out the mother liquor. Furthermore, a first reflux step can be performed to reflux the residual material E obtained in the first filtration step back into the reactor 100, and a first conveying step can be performed to convey the filtrate D obtained in the first filtration step to a subsequent process. In this embodiment, filtrate may refer to an organic solvent solution of alkali metal hexafluorophosphate containing unreacted alkali metal fluoride particles that has been filtered out. For ease of description, the first filtration step, the first reflux step, and the first conveying step may all be given the same reference numeral "S21" below.

[0057] In the mother liquor preparation step S10, the mother liquor (i.e., the initial mother liquor) may contain an alkali metal hexafluorophosphate, which is obtained by reacting the initial alkali metal fluoride and the initial phosphorus pentafluoride in the initial organic solvent after the initial organic solvent, the initial alkali metal fluoride and the initial phosphorus pentafluoride are supplied to the reactor 100.

[0058] The initial organic solvent can be the organic solvent obtained by backwashing the second cross-flow filter 220, i.e., the backwash effluent B. In this embodiment, backwashing can refer to the organic solvent flowing from the filtrate compartments 219 or 229 of the respective cross-flow filters 210 and 220 into the feed solution compartments 215 or 225 via filters 217 or 227. Specifically, with the second mother liquor inlet valve V42, the second filtrate discharge valve V62, and the first fresh solvent supply valve V51 closed by the controller 500, the second fresh solvent supply valve V52 can be opened, and the fresh solvent pump P50 can be operated to supply fresh organic solvent A from the organic solvent reservoir 300 to the filtrate compartment 229 of the second cross-flow filter 220 through the integrated fresh solvent supply line L50 and the second fresh solvent supply line L52. The organic solvent introduced into the filtrate compartment 229 of the second cross-flow filter 220 can pass through the filter 227 and be sent to the feed solution compartment 225. The organic solvent (i.e., backwash effluent B) fed to the feed solution compartment 225 can be discharged through the second outlet 221 and supplied to the reactor 100 through the second organic solvent supply or return line L32.

[0059] Initial alkali metal fluoride (MF) can be introduced in solid particulate form into reactor 100, which is already supplied with initial organic solvent, via alkali metal fluoride supply line L20. After or during the introduction of the initial alkali metal fluoride (MF), the stirrer in reactor 100 can be operated, and the reactor temperature can be lowered to room temperature or lower, specifically, 5°C to 15°C, for example, 10°C. Subsequently, initial phosphorus pentafluoride (PF5) can be slowly introduced in gaseous form via phosphorus pentafluoride supply line L10, which is immersed in the organic solvent within reactor 100. As a result, as described in the above reaction formula, phosphorus pentafluoride (PF5) and alkali metal fluoride (MF) can react in the organic solvent to prepare alkali metal hexafluorophosphate.

[0060] As described above, initial phosphorus pentafluoride (PF5) can be introduced according to the stoichiometric amount shown in the reaction formula, and an excess of initial alkali metal fluoride (MF) can be introduced relative to the stoichiometric amount. In this case, the introduced initial phosphorus pentafluoride (PF5) can react rapidly with all the initial alkali metal fluoride (MF) to prepare alkali metal hexafluorophosphate (MPF6) without acidic impurities caused by side reactions with organic solvents. However, due to the excess introduction of initial alkali metal fluoride (MF), it may remain as solid particles in the initial mother liquor, which is an organic solvent solution of the alkali metal hexafluorophosphate prepared by the reaction. Therefore, the initial mother liquor may have a slurry form containing unreacted alkali metal fluoride (MF) particles.

[0061] The introduction rate of phosphorus pentafluoride (PF5) can be adjusted by operating the phosphorus pentafluoride flow controller FIC-10 and the phosphorus pentafluoride flow control valve FV-10 according to commands from the controller 500. The introduction rate of alkali metal fluoride (MF) can be adjusted by controlling the screw feeder motor inverter SIC-1. The introduction rate of organic solvents can be adjusted by operating the fresh solvent flow controller FIC-50 and the fresh solvent flow control valve FV-50 according to commands from the controller 500.

[0062] The concentration of alkali metal hexafluorophosphate in the initial mother liquor (specifically, the molar ratio of alkali metal hexafluorophosphate to organic solvent in the initial mother liquor) can be from 8 to 12 moles of alkali metal hexafluorophosphate per 50 moles of organic solvent, but is not limited thereto. Furthermore, the molar ratio of unreacted alkali metal fluoride (MF) particles to alkali metal hexafluorophosphate (MPF6) in the initial mother liquor can be from 0.05 to 0.3, more specifically, from 0.15 to 0.25, but is not limited thereto. In the continuous preparation method of the electrolyte, which will be described later, the concentration of alkali metal hexafluorophosphate in the mother liquor and the molar ratio of unreacted alkali metal fluoride (MF) particles to alkali metal hexafluorophosphate (MPF6) can be kept substantially the same as those in the initial mother liquor.

[0063] In step S21, which includes the first filtration step, the first reflux step, and the first delivery step, the controller 500 may close the second mother liquor inlet valve V42, the first fresh solvent supply valve V51, and the second filtrate discharge valve V62, and open the first mother liquor inlet valve V41, the second fresh solvent supply valve V52, and the first filtrate discharge valve V61. This state may also be maintained in the first reaction proceeding step S41, which will be described later.

[0064] In the first filtration step, the controller 500 can operate the mother liquor pump P40 to introduce a portion C of the mother liquor in the reactor 100 into the feed solution compartment 215 through the mother liquor discharge line L40, the first mother liquor supply line L41, and the mother liquor inlet 212 of the first cross-flow filter 210, all located downstream of the reactor 100. The filtrate D obtained by removing alkali metal fluoride particles from the mother liquor C via the filter 217 can be introduced into the filtrate compartment 219, and the residue E, consisting of filtrate D discharged from the mother liquor C and unreacted alkali metal fluoride (MF) particles remaining on the filter 217, can be discharged through the outlet 211. In the first filtration step, unreacted alkali metal fluoride (MF) particles can accumulate on the surface of the filter 217 that contacts the feed solution compartment 215.

[0065] In the first reflux step, the permeate E can be refluxed back to reactor 100 via the first organic solvent supply or reflux line L31.

[0066] In the first conveying step, the filtrate D introduced into the filtrate compartment 219 can be introduced into the equipment 400 for performing subsequent processes through the first filtrate discharge line L61 and the integrated filtrate discharge line L60.

[0067] The controller 500 can perform a first evaluation step S31 to evaluate whether the flow rate of filtrate D in the first delivery step is equal to or greater than a reference value. Specifically, the filtrate flow meter FE-60 installed in the integrated filtrate discharge line L60 can measure the flow rate of filtrate D delivered to subsequent processes and transmit the measured flow rate value to the controller 500. The controller 500 can allow different steps to be performed based on whether the measured flow rate value is equal to or greater than a predetermined reference value. The reference value can be a value corresponding to 90% of the initial flow rate of filtrate D. Furthermore, the controller 500 can calculate the molar flow rate of the organic solvent and the molar flow rate of the alkali metal hexafluorophosphate in the filtrate D in the first delivery step by using the molar ratio of alkali metal hexafluorophosphate to organic solvent in the mother liquor and the measured flow rate of filtrate D in the first delivery step.

[0068] When the flow rate of filtrate D in the first delivery step is equal to or greater than a reference value, the first reaction proceeding step S41 can be performed. The first reaction proceeding step S41 may include backwashing the second cross-flow filter 220 with fresh organic solvent or supplemented organic solvent A at a molar flow rate equal to the molar flow rate of the organic solvent contained in the filtrate D of the first delivery step to obtain backwash effluent B, and supplying backwash effluent B to reactor 100. The first reaction proceeding step S41 may also include supplying supplemented alkali metal fluoride and supplemented phosphorus pentafluoride to reactor 100 at a molar flow rate equal to the molar flow rate of alkali metal hexafluorophosphate contained in the filtrate D of the first delivery step to additionally generate mother liquor. Therefore, the amount of mother liquor in reactor 100 and the molar ratio of alkali metal hexafluorophosphate to organic solvent in the mother liquor can be kept constant.

[0069] Specifically, when the measured flow rate value of the filtrate D obtained in the first filtration step and conveyed to the subsequent process in the first conveying step is equal to or greater than a predetermined reference value, the controller 500 can keep the second mother liquor inlet valve V42, the first fresh solvent supply valve V51, and the second filtrate discharge valve V62 closed, and the first mother liquor inlet valve V41, the second fresh solvent supply valve V52, and the first filtrate discharge valve V61 open. Furthermore, the controller 500 can operate the fresh solvent pump P50, the fresh solvent flow controller FIC-50, and the fresh solvent flow control valve FV-50, such that fresh organic solvent or supplementary organic solvent A (having the same molar flow rate as the organic solvent contained in filtrate D) is supplied from the organic solvent reservoir 300 to the filtrate compartment 229 of the second cross-flow filter 220 through the integrated fresh solvent supply line L50 and the second fresh solvent supply line L52. The organic solvent introduced into the filtrate compartment 229 can pass through the filter 227 and be sent to the feed solution compartment 225. The organic solvent (i.e., backwash effluent B) fed to the feed solution compartment 225 can be discharged through the second outlet 221 and then supplied to the reactor 100 through the second organic solvent supply or return line L32.

[0070] Furthermore, when the measured flow rate of the filtrate D obtained in the first filtration step and conveyed to the subsequent process in the first conveying step is equal to or greater than a predetermined reference value, the controller 500 can operate the screw feeder motor inverter SIC-1 to supply supplementary alkali metal fluoride to the reactor 100 at the same molar flow rate as the alkali metal hexafluorophosphate contained in the filtrate D, and can operate the phosphorus pentafluoride flow controller FIC-10 and the phosphorus pentafluoride flow control valve FV-10 to supply supplementary phosphorus pentafluoride to the reactor 100 at the same molar flow rate as the alkali metal hexafluorophosphate contained in the filtrate D. As a result, within the reactor 100, the newly supplied equal amounts of supplementary phosphorus pentafluoride (PF5) and supplementary alkali metal fluoride (MF) react in an organic solvent to further prepare the mother liquor. Simultaneously, since the initially excessive alkali metal fluoride (MF) remains within the preparation system, the further prepared mother liquor can be maintained in a slurry state.

[0071] In the first evaluation step S31, if the flow rate of the filtrate in the first delivery step is equal to or greater than the reference value, the first reaction proceeding step S41, the first filtration step S21, the first reflux step S21, and the first delivery step S21 can be executed consecutively. Furthermore, the first filtration step S21, the first reflux step S21, the first delivery step S21, the first evaluation step S31, and the first reaction proceeding step S41 can be performed simultaneously.

[0072] Meanwhile, if the flow rate of the filtrate D obtained in the first filtration step S21 and conveyed to the subsequent process in the first conveying step S21 is less than a reference value, it may mean that a large amount of unreacted alkali metal fluoride (MF) particles have accumulated on the surface of the filter 217 of the first cross-flow filter 210 that is in contact with the feed solution compartment 215. Therefore, the controller 500 can stop feeding the mother liquor to the first cross-flow filter 210 and instead feed the mother liquor to the second cross-flow filter 220. At the same time, the supply of fresh organic solvent to the second cross-flow filter 220 can be stopped, and fresh organic solvent can be fed to the first cross-flow filter 210.

[0073] Specifically, refer to Figure 3 , Figure 4 and Figure 5 Step S22 includes a second filtration step, a second reflux step, and a second conveying step. For ease of description, the second filtration step, the second reflux step, and the second conveying step can all be given the same reference numeral "S22". When the flow rate of the filtrate D obtained in the first filtration step S21 and conveyed to the subsequent process in the first conveying step S21 is less than a reference value, the second filtration step S22 can be performed by introducing a portion of the mother liquor in the reactor 100 into the second cross-flow filter 220 to obtain filtrate D from which unreacted alkali metal fluoride particles are filtered out and the residual residue E remaining after filtering the mother liquor. In addition, the second reflux step S22, which recirculates the residual residue E obtained in the second filtration step back to the reactor 100, and the second conveying step S22, which conveys the filtrate D obtained in the second filtration step to the subsequent process, can be performed.

[0074] Specifically, the controller 500 can close the first mother liquor inlet valve V41, the second fresh solvent supply valve V52, and the first filtrate discharge valve V61, and can also open the second mother liquor inlet valve V42, the second filtrate discharge valve V62, and the first fresh solvent supply valve V51. This state can also be maintained in step S42 of the second reaction, which will be described later.

[0075] In the second filtration step, the mother liquor pump P40 is operated to introduce a portion C of the mother liquor in reactor 100 into feed solution compartment 225 through the mother liquor discharge line L40, the second mother liquor supply line L42, and the mother liquor inlet 222 of the second cross-flow filter 220, all located downstream of reactor 100. Filtrate D, obtained by removing alkali metal fluoride particles from mother liquor C via filter 227, is introduced into filtrate compartment 229, and residue E, consisting of filtrate D discharged from mother liquor C and unreacted alkali metal fluoride (MF) particles remaining on filter 227, is discharged through the second outlet 221. In the second filtration step, unreacted alkali metal fluoride (MF) particles may accumulate on the surface of filter 227 that contacts feed solution compartment 225.

[0076] In the second reflux step, the permeate E can be refluxed back to reactor 100 via the second organic solvent supply or reflux line L32.

[0077] In the second conveying step, the filtrate D introduced into the filtrate compartment 229 can be introduced into the equipment 400 for performing subsequent processes through the second filtrate discharge line L62 and the integrated filtrate discharge line L60.

[0078] The controller 500 can perform a second evaluation step S32 to evaluate whether the flow rate of filtrate D in the second delivery step is equal to or greater than a reference value. Specifically, the filtrate flow meter FE-60 installed in the integrated filtrate discharge line L60 can measure the flow rate of filtrate D delivered to the subsequent process and transmit the measured flow rate value to the controller 500. The controller 500 can allow different steps to be performed based on whether the measured flow rate value is equal to or greater than a predetermined reference value. Here, the reference value can be a value corresponding to 90% of the initial flow rate of filtrate D. Furthermore, the controller 500 can calculate the molar flow rate of the organic solvent and the molar flow rate of the alkali metal hexafluorophosphate in the filtrate D in the second delivery step by using the molar ratio of alkali metal hexafluorophosphate to organic solvent in the mother liquor and the measured flow rate of filtrate D in the second delivery step.

[0079] When the flow rate of filtrate D in the second delivery step is equal to or greater than a reference value, the second reaction proceeding step S42 can be performed. The second reaction proceeding step S42 may include backwashing the first cross-flow filter 210 with fresh organic solvent or supplemented organic solvent A at a molar flow rate equal to the molar flow rate of the organic solvent contained in the filtrate D of the second delivery step to obtain backwash effluent B, and supplying backwash effluent B to reactor 100. The second reaction proceeding step S42 may also include supplying supplemented alkali metal fluoride and supplemented phosphorus pentafluoride to reactor 100 at a molar flow rate equal to the molar flow rate of alkali metal hexafluorophosphate contained in the filtrate D of the second delivery step to additionally generate mother liquor. Therefore, the amount of mother liquor in reactor 100 and the molar ratio of organic solvent to alkali metal hexafluorophosphate in the mother liquor can be kept constant.

[0080] Specifically, when the measured flow rate of the filtrate D obtained in the second filtration step and conveyed to the subsequent process in the second conveying step is equal to or greater than a predetermined reference value, the controller 500 can keep the first mother liquor inlet valve V41, the first filtrate discharge valve V61, and the second fresh solvent supply valve V52 closed, and the first fresh solvent supply valve V51, the second mother liquor inlet valve V42, and the second filtrate discharge valve V62 open. Furthermore, the controller 500 can operate the fresh solvent pump P50, the fresh solvent flow controller FIC-50, and the fresh solvent flow control valve FV-50, so that fresh organic solvent or supplementary organic solvent A (having the same molar flow rate as the organic solvent contained in filtrate D) is supplied from the organic solvent reservoir 300 to the filtrate compartment 219 of the first cross-flow filter 210 through the integrated fresh solvent supply line L50 and the first fresh solvent supply line L51. The organic solvent introduced into the filtrate compartment 219 can pass through the filter 217 and be sent to the feed solution compartment 215. In this process, during the first filtration step S21, unreacted alkali metal fluoride (MF) particles accumulated on the surface of the filter 217 of the first cross-flow filter 210 in contact with the feed solution compartment 215 are washed and dispersed in the organic solvent supplied to the feed solution compartment 215 (i.e., backwash effluent B). The backwash effluent B containing the unreacted alkali metal fluoride (MF) particles can be discharged through the outlet 211 and supplied to the reactor 100 through the first organic solvent supply or return line L31. Thus, washing of the unreacted alkali metal fluoride (MF) particles accumulated on the surface of the filter 217 in the first filtration step S21 can also be performed by supplying the backwash effluent B containing organic solvent A and unreacted alkali metal fluoride particles obtained by backwashing the first cross-flow filter 210 with organic solvent A to the reactor 100. Therefore, a separate particle washing process or a separate washing solution is not required, which significantly reduces maintenance time.

[0081] Furthermore, when the measured flow rate of filtrate D obtained in the second filtration step and conveyed to the subsequent process in the second conveying step is equal to or greater than a predetermined reference value, controller 500 can operate screw feeder motor inverter SIC-1 to supply supplementary alkali metal fluoride to reactor 100 at a molar flow rate identical to that of alkali metal hexafluorophosphate contained in filtrate D. It can also operate phosphorus pentafluoride flow controller FIC-10 and phosphorus pentafluoride flow control valve FV-10 to supply supplementary phosphorus pentafluoride to reactor 100 at a molar flow rate identical to that of alkali metal hexafluorophosphate contained in filtrate D. As a result, within reactor 100, the newly supplied equivalent of phosphorus pentafluoride (PF5) and alkali metal fluoride (MF) react in an organic solvent to further prepare mother liquor. Simultaneously, since the initial excess of alkali metal fluoride (MF) remains within the preparation system, the further prepared mother liquor can be maintained in a slurry state.

[0082] In the second evaluation step S32, if the flow rate of the filtrate in the second delivery step is equal to or greater than the reference value, the second reaction proceeding step S42, the second filtration step S22, the second reflux step S22, and the second delivery step S22 can be executed consecutively. Furthermore, the second filtration step S22, the second reflux step S22, the second delivery step S22, the second evaluation step S32, and the second reaction proceeding step S42 can be performed simultaneously.

[0083] Meanwhile, if the measured flow rate of the filtrate D obtained in the second filtration step S22 and conveyed to the subsequent process in the second conveying step S22 is less than the reference value, it may mean that a large amount of unreacted alkali metal fluoride (MF) particles have accumulated on the surface of the filter 227 of the second cross-flow filter 220 that is in contact with the feed solution compartment 225. Therefore, the controller 500 can stop feeding the mother liquor to the second cross-flow filter 220 and instead feed the mother liquor to the first cross-flow filter 210. At the same time, the supply of fresh organic solvent to the first cross-flow filter 210 can be stopped, and fresh organic solvent can be fed to the second cross-flow filter 220.

[0084] As a result, it is possible to proceed with the referenced steps. Figure 1 , Figure 2 and Figure 3 The first filtration step S21, the first reflux step S21, the first transport step S21, the first evaluation step S31, and the first reaction proceeding step S41 are described.

[0085] In addition, refer to Figure 1 and Figure 2In the first reaction step S41, fresh organic solvent or replenished organic solvent A, at a molar flow rate equal to that of the organic solvent contained in filtrate D, is supplied from the organic solvent reservoir 300 to the filtrate compartment 229 of the second cross-flow filter 220 via integrated fresh solvent supply line L50 and second fresh solvent supply line L52. The organic solvent supplied to the filtrate compartment 229 is then conveyed to the feed solution compartment 225 via filter 227. In this process, unreacted alkali metal fluoride (MF) particles accumulated on the surface of filter 227 of the second cross-flow filter 220 in contact with the feed solution compartment 225 in the second filtration step S22 can be washed and dispersed in the organic solvent conveyed to the feed solution compartment 225 by fresh organic solvent A (i.e., backwash effluent B). The backwash effluent B containing unreacted alkali metal fluoride (MF) particles can be discharged through the second outlet 221 and supplied to reactor 100 through the second organic solvent supply or reflux line L32.

[0086] As described above, by supplying the backwash effluent B obtained by backwashing the second crossflow filter 220 with organic solvent A to the reactor 100, the washing of unreacted alkali metal fluoride (MF) particles accumulated on the surface of filter 227 in the second filtration step S22 can also be performed. Therefore, there is no need to perform a separate particle washing process or use a separate washing solution for this purpose, which significantly reduces maintenance time.

[0087] When the molar flow rate of alkali metal hexafluorophosphate in the filtrate D obtained in the first filtration step S21 or the second filtration step S22 and delivered to the subsequent process is X mol / hr, the molar flow rate of the organic solvent can be approximately 3X mol / hr to 6X mol / hr. Therefore, the molar flow rate of fresh or replenished organic solvent supplied to the first cross-flow filter 210 or the second cross-flow filter 220 in the first reaction step S41 or the second reaction step S42 can be approximately 3X mol / hr to 6X mol / hr, and the molar flow rates of replenished alkali metal fluoride and replenished phosphorus pentafluoride supplied to reactor 100 in the first reaction step S41 or the second reaction step S42 can both be X mol / hr.

[0088] The linear velocity of the liquid passing through the cross-flow filter can be from 1 m / sec to 10 m / sec, and in one example, it can be from 1 m / sec to 5 m / sec. Within this range, clogging of the cross-flow filter due to the viscosity of the alkali metal hexafluorophosphate organic solvent solution can be reduced, the filter life can be extended by reducing the wear rate of the filter, and the rise in reaction temperature can be suppressed by reducing frictional heat.

[0089] As described above, according to the present invention, electrolytes containing alkali metal hexafluorophosphates can be continuously prepared using at least two cross-flow filters, thereby significantly reducing the preparation cost of electrolytes containing alkali metal hexafluorophosphates. However, the effects of the present invention are not limited to those described above, and other effects not mentioned will be clearly understood by those skilled in the art from the appended description.

[0090] Although the present invention has been described in detail with reference to preferred embodiments, the present invention is not limited to the above embodiments, and those skilled in the art can make various modifications and changes within the technical spirit and scope of the present invention.

Claims

1. A method for continuously preparing an electrolyte containing an alkali metal hexafluorophosphate, the method comprising the following steps: The mother liquor preparation step involves preparing a mother liquor in slurry form within a reactor. The mother liquor contains an organic solvent, an alkali metal hexafluorophosphate dissolved in the organic solvent, and unreacted alkali metal fluoride particles. The filtration step involves introducing a portion of the mother liquor into a first cross-flow filter to obtain filtrate and residue. The filtrate is obtained by filtering unreacted alkali metal fluoride particles from the mother liquor, and the filtrate comprises the organic solvent and the alkali metal hexafluorophosphate. The process includes a reflux step and a conveying step, wherein in the reflux step, the residue obtained in the filtration step is refluxed back into the reactor, and in the conveying step, the filtrate obtained in the filtration step is conveyed to a subsequent process; and The reaction proceeding steps include backwashing the second crossflow filter with a supplemented organic solvent at a molar flow rate equal to the molar flow rate of the organic solvent contained in the filtrate of the delivery step to obtain a backwash effluent, and supplying the backwash effluent to the reactor.

2. The method according to claim 1, wherein, The second cross-flow filter includes unreacted alkali metal fluoride particles located on the filter surface of the second cross-flow filter, and The backwash effluent is an alkali metal fluoride dispersion in which the unreacted alkali metal fluoride particles on the filter surface of the second crossflow filter are dispersed in the supplemented organic solvent.

3. The method according to claim 1, wherein, The reaction process further includes supplying supplemental alkali metal fluoride and supplemental phosphorus pentafluoride into the reactor at a molar flow rate equal to the molar flow rate of the alkali metal hexafluorophosphate contained in the filtrate of the delivery step, to additionally generate the mother liquor.

4. The method according to claim 1, wherein, The mother liquor contains the alkali metal hexafluorophosphate, which is obtained by reacting the initial alkali metal fluoride and the initial phosphorus pentafluoride in the initial organic solvent after supplying the initial organic solvent, the initial alkali metal fluoride, and the initial phosphorus pentafluoride to the reactor. The initial phosphorus pentafluoride is supplied in its stoichiometric amount, and the initial alkali metal fluoride is supplied in excess relative to its stoichiometric amount.

5. The method according to claim 4, wherein, The molar ratio of the initial alkali metal fluoride to the initial phosphorus pentafluoride is 1.05 to 1.

3.

6. The method according to claim 1, wherein, The mother liquor contains the alkali metal hexafluorophosphate, which is obtained by reacting the initial alkali metal fluoride and the initial phosphorus pentafluoride in the initial organic solvent after supplying the initial organic solvent, the initial alkali metal fluoride, and the initial phosphorus pentafluoride to the reactor. The initial organic solvent is obtained by backwashing the second cross-flow filter.

7. The method according to claim 1, wherein, When the flow rate of the filtrate in the delivery step is greater than or equal to a reference value, the reaction proceeding step, the filtration step, the reflux step, and the delivery step are executed continuously.

8. The method according to claim 1, wherein, The filtration step, the reflux step, the conveying step, and the reaction proceeding step are respectively the first filtration step, the first reflux step, the first conveying step, and the first reaction proceeding step. Furthermore, when the flow rate of the filtrate in the first delivery step is less than a reference value, the method further includes: In the second filtration step, a portion of the mother liquor is introduced into the second cross-flow filter to filter the unreacted alkali metal fluoride particles from the mother liquor, thereby obtaining a filtrate and a residue. The filtrate obtained from the second cross-flow filter contains the organic solvent and the alkali metal hexafluorophosphate. A second reflux step and a second conveying step, wherein in the second reflux step, the residue obtained in the second filtration step is refluxed back into the reactor, and in the second conveying step, the filtrate obtained in the second filtration step is conveyed to subsequent processes; and The second reaction proceeding step includes backwashing the first cross-flow filter with a supplemented organic solvent at a molar flow rate equal to the molar flow rate of the organic solvent contained in the filtrate of the second delivery step to obtain a backwash effluent, and supplying the backwash effluent obtained by backwashing the first cross-flow filter to the reactor.

9. The method according to claim 8, wherein, In the first filtration step, the unreacted alkali metal fluoride particles accumulate on the filter surface of the first cross-flow filter, and The backwash effluent obtained by backwashing the first cross-flow filter is an alkali metal fluoride dispersion in which the unreacted alkali metal fluoride particles accumulated on the filter surface of the first cross-flow filter are dispersed in the supplemented organic solvent.

10. The method according to claim 8, wherein, The second reaction step further includes supplying supplemental alkali metal fluoride and supplemental phosphorus pentafluoride into the reactor at a molar flow rate equal to the molar flow rate of the alkali metal hexafluorophosphate contained in the filtrate of the second delivery step, to additionally generate the mother liquor.

11. The method according to claim 8, wherein, When the flow rate of the filtrate in the second delivery step is greater than or equal to the reference value, the second reaction proceeding step, the second filtration step, the second reflux step, and the second delivery step are executed consecutively.

12. The method according to claim 8, wherein, When the flow rate of the filtrate in the second delivery step is less than a reference value, the first filtration step, the first reflux step, the first delivery step, and the first reaction proceeding step are executed. In the first reaction step, the backwash effluent obtained by backwashing the second cross-flow filter is an alkali metal fluoride dispersion, in which the unreacted alkali metal fluoride particles accumulated in the second cross-flow filter during the second filtration step are dispersed in the supplemented organic solvent.

13. The method according to claim 12, wherein, When the flow rate of the filtrate in the first delivery step is greater than or equal to the reference value, the first reaction proceeding step, the first filtration step, the first reflux step, and the first delivery step are executed consecutively. When the flow rate of the filtrate in the first delivery step is less than the reference value, the second filtration step, the second reflux step, the second delivery step, and the second reaction proceeding step are executed.

14. The method according to claim 1, wherein, The organic solvent is a chain or cyclic carbonate, lactone, chain or cyclic ether, or a mixture thereof.

15. The method according to claim 14, wherein, The organic solvent is ethyl methyl carbonate.

16. The method according to claim 1, wherein, The alkali metal fluoride is LiF, and the alkali metal hexafluorophosphate is LiPF6.

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