JP5845955B2 - Method for producing lithium hexafluorophosphate concentrate - Google Patents

Description

  The present invention relates to a method for producing a lithium hexafluorophosphate concentrate and an electrolyte for a lithium ion battery using the same and containing lithium hexafluorophosphate as an electrolyte.

  Various methods for producing lithium hexafluorophosphate which is an electrolyte useful for lithium ion batteries and the like have been proposed. In the method for producing lithium hexafluorophosphate using a solvent, anhydrous hydrogen fluoride is dissolved as a solvent. There is a method (Non-patent Document 1) in which gaseous lithium pentafluoride is reacted with lithium fluoride, and the produced lithium hexafluorophosphate is crystallized and taken out.

  In this method, the reaction yield of lithium hexafluorophosphate is high, but a large amount of anhydrous hydrogen fluoride having high vapor pressure and toxicity and corrosiveness must be used as a solvent, and handling is not easy. . Furthermore, there are many factors that lead to an increase in costs, such as the need to produce phosphorus pentafluoride, which is one of the raw materials, in a separate process, and the need for a crystallization process of lithium hexafluorophosphate.

  In general electrolyte production, lithium hexafluorophosphate is first produced and dissolved in a predetermined lithium battery solvent to obtain an electrolyte solution. As a method for producing lithium hexafluorophosphate, for example, there is a method of reacting solid lithium fluoride and gaseous phosphorus pentafluoride without solvent (Patent Document 1). In this method, a film of a reaction product is formed on the surface of lithium fluoride, and the reaction does not proceed completely, so that unreacted lithium fluoride may remain.

  Similarly, there is a method (Patent Document 2) in which anhydrous hydrogen fluoride is added to phosphorus pentachloride and lithium fluoride and reacted without solvent. In this method, the reaction is not easily controlled, and cooling to several tens of degrees Celsius is necessary.

  There is also a method of reacting lithium fluoride and phosphorus pentafluoride in an organic solvent (Patent Document 3). Although this method has great advantages in terms of reaction control and reaction product purity, as described above, it is necessary to produce and handle phosphorus pentafluoride gas, which is one of the raw materials, in a separate process. Remain.

Further, anhydrous hydrogen fluoride or polar organic solvent CH ₃ CN is used as a solvent, and phosphorus trichloride is reacted with chlorine and hydrogen fluoride to obtain phosphorus pentafluoride. Further, lithium fluoride is added to the same reactor. There is also a method of producing lithium hexafluorophosphate by reacting with phosphorus pentafluoride (Patent Document 4). This method is efficient because phosphorous pentafluoride is produced in the same reactor. However, since it produces phosphorus pentafluoride with a high vapor pressure, expensive equipment such as a pressurized reactor and complicated Many problems remain, such as the need for operation, and basically the need for a crystallization process, which makes it difficult to fundamentally reduce the cost of electrolyte production.

On the other hand, in a non-aqueous organic solvent, phosphorous trichloride, chlorine and lithium chloride are reacted, and then the reaction product produced in the solvent is reacted with hydrogen fluoride to produce an electrolyte for a lithium ion battery. There is a method (Patent Document 5). In this method, a high-purity electrolyte solution for lithium ion batteries containing lithium hexafluorophosphate as an electrolyte can be obtained. In this method, a part of lithium hexafluorophosphate is decomposed by the decomposition reaction shown below, so that solid lithium fluoride is deposited. Therefore, it is necessary to remove it by a filtration operation in a subsequent step.
_{LiPF 6 → LiF ↓ + PF 5} ↑

JP-A 64-72901 JP-A-10-72207 JP-A-9-165210 JP-A-10-81505 JP 2007-184246 A

J. et al. Chem. Soc. Part 4, 4408 (1963)

  When the solid precipitate (lithium fluoride) is removed in the subsequent step as in the method of Patent Document 5, it is necessary to treat the precipitate generated as a by-product for each synthesis batch as waste.

  In the present invention, phosphorus trichloride, chlorine, lithium chloride and / or lithium fluoride are reacted in a non-aqueous organic solvent, and then the reaction product generated in the solvent is reacted with hydrogen fluoride. Then, after removing hydrogen chloride from the reaction solution by degassing treatment, filtration is performed, and in the method of degassing and concentrating the filtrate to obtain a lithium hexafluorophosphate concentrated solution, the precipitation generated as a by-product for each synthesis batch For producing a lithium hexafluorophosphate concentrate with high purity more efficiently without treating the waste as waste, and an electrolytic solution for lithium ion batteries containing lithium hexafluorophosphate as an electrolyte using the same The manufacturing method of this is provided.

  As a result of earnest research in view of such problems, the present inventors have reacted phosphorus trichloride, chlorine, lithium chloride and / or lithium fluoride in a non-aqueous organic solvent, and then in the solvent. The produced reaction product is reacted with hydrogen fluoride, and then hydrogen chloride is removed from the reaction solution by degassing, followed by filtration. The filtrate is degassed and concentrated to obtain a lithium hexafluorophosphate concentrate. In the method, the filtration is carried out in an inert atmosphere substantially free of moisture, and the filtrate containing lithium fluoride solids separated from the filtrate by the filtration is subjected to the reaction steps (I) and (II). By using it as a raw material for the reaction in at least one of the steps, the high-purity lithium hexafluorophosphate is more efficiently produced without treating the precipitate generated as a by-product for each synthesis batch as waste. It found to be able to produce a reduced solution, which was led to the present invention.

That is, the present invention provides a reaction step (I) in which phosphorus trichloride, chlorine, lithium chloride and / or lithium fluoride are reacted in a non-aqueous organic solvent.
Reacting the reaction product produced in the solvent in the reaction step (I) with hydrogen fluoride, reaction step (II),
After the reaction step (II), after removing hydrogen chloride from the reaction solution by deaeration treatment, filtration is performed, and the filtrate is deaerated and concentrated to obtain a lithium hexafluorophosphate concentrate.
The filtration is performed in an inert atmosphere substantially free of moisture, and the filtrate containing the lithium fluoride solid content separated from the filtrate by the filtration is treated with at least one of the reaction steps (I) and (II). A method for producing a lithium hexafluorophosphate concentrate, characterized by being used as a raw material for a reaction in one step.

  The filtration is performed using a filter cloth or a cartridge filter, a pressure filter, a vacuum filter, a filter press machine, a sedimentation separator by centrifugation, a filter separator, or a cloth using an ultrafiltration membrane. Use a flow filter or the like. The filtration is performed in an inert atmosphere substantially free of moisture. When filtration is performed in an atmosphere containing moisture in an open system such as the air, the concentration of impurities such as hydrogen fluoride and difluorophosphoric acid, which are impurities, increases due to the hydrolysis reaction of lithium hexafluorophosphate, which causes quality problems. In the case where the filtrate is used as a raw material for the next batch, the concentration of chloride ions in the lithium hexafluorophosphate concentrate or coloration may occur mainly due to adhering moisture. Further, the filtering operation in the atmosphere is an acid gas, and there is a concern about the corrosion of equipment and the toxic effect on the human body, which is not preferable in the manufacturing operation. In addition, the inert atmosphere which does not contain water | moisture content is inert gas atmosphere, such as nitrogen and argon, and generally means an atmosphere with a dew point of -50 degrees C or less, Preferably it is -60 degrees C or less.

  Moreover, the said filtrate needs to contain lithium fluoride solid content. The filtrate containing the recovered lithium fluoride solid content is consumed as a lithium source and a fluorine source in the next batch reaction, so it is basically not a waste, and in particular, the lithium recovery rate is close to 100%. It is also useful in terms of raw material costs.

  Moreover, it is preferable that the said filtration thing is a slurry which consists of lithium fluoride solid content and the non-aqueous organic solvent solution of lithium hexafluorophosphate. If it is in a slurry state, it can be taken out and transferred in a sealed state using a pump and piping, and can be handled safely.

  The filtration is preferably cross flow filtration. Filtration methods other than cross-flow filtration require solid handling such as separation, collection, and movement of the filtrate from the filter cloth, etc. in a closed system after filtration, which is cumbersome and dangerous and troublesome. If it is a filtration system, the filtrate can be handled as a slurry containing lithium fluoride solids and a non-aqueous organic solvent, and operations such as liquid transfer are easy in a closed system. Further, cross flow filtration is a method of continuous filtration in a sealed state, and this filtration method is particularly preferable because filtration can be performed in an inert atmosphere substantially free of moisture.

  Moreover, it is preferable that the said filtration thing is a slurry whose solid content concentration is 0.1-10 mass%. If the solid content concentration of the filtrate is less than 0.1% by mass, filtration concentration by cross flow filtration is not sufficient and is not efficient. On the other hand, a slurry of more than 10% by mass is not preferable because not only the cross flow filtration operation becomes difficult due to the increase in viscosity but also the slurry transfer itself becomes difficult. Therefore, in order to transfer a slurry having a solid content concentration exceeding 10% by mass, a non-aqueous organic solvent is added to the slurry in advance before the transfer to adjust the solid content concentration to 0.1 to 10% by mass. There is a need. In addition, a filtration method other than cross flow filtration generally yields a slurry of 10% by mass or more. However, if the operation is performed in an inert atmosphere substantially free of moisture, it is a quality problem even if used as a raw material for the next batch. There is no.

  In the present invention, the lithium hexafluorophosphate concentrate obtained by the above production method is further subjected to at least one treatment selected from filtration, concentration, dilution with a non-aqueous organic solvent, and addition of an additive. This is a method for producing an electrolytic solution for a lithium ion battery containing lithium hexafluorophosphate as an electrolyte.

  Degassing concentration is a method of increasing the concentration of a solute by discharging the gas phase part contained in the solvent by volatilization out of the system by reducing the pressure or by circulating a carrier gas such as nitrogen gas or dry air. It is. In the present invention, it is found that by using degassing concentration, the concentration of the solute is increased and acidic impurities are discharged together with the solvent, whereby a highly purified lithium hexafluorophosphate concentrate can be produced. .

  The acidic impurity concentration contained in the lithium hexafluorophosphate concentrate is preferably as low as possible, and the acidic impurity concentration contained in the concentrate obtained in the present invention is 500 mass ppm or less, more preferably 150 mass ppm or less. It is desirable to be. If the acidic impurity concentration exceeds the above range, it is not preferable because it may adversely affect the lithium battery characteristics. Furthermore, the lower the chloride ion concentration contained in the lithium hexafluorophosphate concentrate, the better. The chloride ion concentration contained in the concentrate obtained in the present invention is 20 ppm by mass or less, more preferably 5 ppm by mass or less. It is desirable that If the chloride ion concentration exceeds the above range, the lithium battery characteristics may be adversely affected.

  According to the present invention, after reacting phosphorus trichloride, chlorine, lithium chloride and / or lithium fluoride, the reaction product produced in the solvent is reacted with hydrogen fluoride, and then degassed. In the method of removing hydrogen chloride from the reaction solution and then filtering and degassing and concentrating the filtrate to obtain a lithium hexafluorophosphate concentrate, the precipitate generated as a by-product for each synthesis batch is treated as waste. Therefore, a highly purified lithium hexafluorophosphate concentrate can be produced more efficiently.

The present invention provides a reaction step (I) in which phosphorus trichloride, chlorine, lithium chloride and / or lithium fluoride are reacted in a non-aqueous organic solvent.
Reacting the reaction product produced in the solvent in the reaction step (I) with hydrogen fluoride, reaction step (II),
After the reaction step (II), after removing hydrogen chloride from the reaction solution by deaeration treatment, filtration is performed, and the filtrate is deaerated and concentrated to obtain a lithium hexafluorophosphate concentrate.
The filtration is performed in an inert atmosphere substantially free of moisture, and the filtrate containing the lithium fluoride solid content separated from the filtrate by the filtration is treated with at least one of the reaction steps (I) and (II). The present invention provides a method for producing a lithium hexafluorophosphate concentrate, characterized by being used as a raw material for the reaction in one step.

  Hereinafter, the present invention will be described in detail.

1. Method for producing lithium hexafluorophosphate concentrate and electrolytic solution using the same (1) Solvent The non-aqueous organic solvent used has a high chemical stability and has a high chain solubility or a high solubility of lithium hexafluorophosphate. A cyclic carbonate compound or an ether compound having two or more oxygen atoms is desirable. Examples of such solvents include chain carbonate compounds such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, cyclic carbonate compounds such as ethylene carbonate, propylene carbonate, and butylene carbonate, γ-butyrolactone, γ-valerolactone, Examples include chain ether compounds such as 1,2-dimethoxyethane and diethyl ether, and cyclic ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran and dioxane. For reasons of high dielectric constant and high acid resistance, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and 1,2-dimethoxyethane are preferred.

  The said non-aqueous organic solvent can be used 1 type or in mixture of several types.

(2) Regarding the reaction step (I) The production method of the present invention is prepared by first charging raw materials phosphorus trichloride and lithium chloride and / or lithium fluoride into a non-aqueous organic solvent, and blowing chlorine gas into this. The reaction is carried out in the non-aqueous organic solvent, and then hydrogen fluoride is introduced into the solvent containing the reaction product and reacted with the reaction product.

  In the present invention, the molar ratios of the lithium component (lithium chloride and lithium fluoride), chlorine, and phosphorus trichloride are 1 to 1.1: 1: 1 to 2, and the amount of phosphorus trichloride is chlorine gas. It is necessary to charge the same amount or more than chlorine gas. This is because if the amount of chlorine gas is larger than phosphorus trichloride, excess chlorine gas reacts with the solvent to generate impurities. For this reason, it is necessary to prepare the amount of phosphorus trichloride in a range of 1 to 2 times mol of chlorine gas. Further, the amount of the lithium component is preferably 1 to 1.1 times mol of chlorine in terms of raw material cost. More preferably, it is 1.0 times mol.

  As a feature of the present invention, since the lithium component in the filtrate can be reused almost 100%, for example, lithium fluoride in the filtrate, which is a residue of the previous synthesis batch, can be used as a raw material for the next batch. If the filtrate containing 0.1 times the molar amount of lithium fluoride produced in the synthesis of the previous batch is used as the raw material for the next batch, the amount of lithium chloride charged into the next batch is in the range from the above lithium component range. The amount is 0.9 to 1.0 times the molar amount obtained by subtracting the lithium chloride amount, and the amount of lithium chloride charged can be reduced.

  The amount of the raw material charged in the non-aqueous organic solvent needs to be 300 g or less, preferably 200 g or less, of lithium components (lithium chloride and lithium fluoride) with respect to 1 liter of the non-aqueous organic solvent. When the amount of the lithium component exceeds 300 g with respect to 1 liter of the non-aqueous organic solvent, the solid content concentration during the reaction increases, and a uniform and efficient reaction becomes difficult.

  The lower limit of the temperature at which this reaction is carried out is −40 ° C., preferably 5 ° C., and the upper limit is 100 ° C., preferably 50 ° C. If reaction temperature is less than -40 degreeC, since a non-aqueous organic solvent will coagulate | solidify, reaction does not advance. Moreover, when higher than 100 degreeC, since it causes coloring and a side reaction, it is unpreferable.

  The pressure during the reaction is not particularly limited, but there is no gas component to be generated, and the reaction proceeds rapidly 100% at atmospheric pressure. Therefore, a special pressure-resistant reactor is not required, and the reaction is basically performed near atmospheric pressure.

  Further, if light is irradiated during the reaction, the reaction between the non-aqueous organic solvent and chlorine may proceed, so it is desirable to carry out the reaction under light-shielded conditions.

After completion of the blowing of chlorine gas, the lithium chloride powder charged into the reactor is dissolved in whole or in part by the following reaction formula [1] to become an intermediate compound presumed to be lithium hexachlorophosphate.
_{LiCl + PCl 3 + Cl 2 →} LiPCl 6 [1]

When a filtrate containing lithium fluoride is used as a raw material for the reaction step (I), the lithium fluoride is dissolved in whole or in part according to the following reaction formula [2], and LiPCl _x F _y It becomes the presumed intermediate compound.
aLiF + bLiCl + cPCl ₃ + dCl ₂ → eLiPCl _x F _y [2]
(X is an arbitrary number of chlorine elements, y is an arbitrary number of fluorine elements, and the sum of x and y is 6. a to e are arbitrary numbers.)

(3) Reaction step (II) Next, anhydrous hydrogen fluoride is introduced into the reactor in order to fluorinate the intermediate compound produced in the reaction formulas [1] and [2]. At this time, anhydrous hydrogen fluoride may be gaseous or liquid. The intermediate compounds produced by the above reaction formulas [1] and [2] are reacted by the following reaction formulas [3] and [4], respectively, to obtain the target product lithium hexafluorophosphate.
LiPCl ₆ + 6HF → LiPF ₆ + 6HCl [3]
LiPCl _x F _y + xHF → LiPF ₆ + xHCl [4]

Moreover, when the filtrate containing lithium fluoride is used as the raw material of the reaction step (II), the target product lithium hexafluorophosphate is obtained by the following reaction formula [5].
LiF + PCl ₅ + 5HF → LiPF ₆ + 5HCl [5]
(PCl ₅ is produced by the reaction of PCl ₃ and Cl ₂ )

  The amount of anhydrous hydrogen fluoride introduced is 6.01 times mol or more in molar ratio with respect to the total amount of lithium hexachlorophosphate, phosphorus pentachloride as an intermediate product, and excess phosphorus trichloride in the previous reaction. is necessary. If the amount of anhydrous hydrogen fluoride is less than 6.01 mol in molar ratio, the fluorination of lithium hexachlorophosphate and phosphorus pentachloride does not proceed sufficiently, and partially fluorinated lithium chlorinated phosphate and phosphorus trichloride As a result, the chlorine concentration in the liquid becomes high, resulting in a high concentration of acidic impurities, which may adversely affect the lithium battery characteristics. When the amount of anhydrous hydrogen fluoride is 6.01 times mol or more in molar ratio with respect to the total amount of lithium hexachlorophosphate, phosphorus pentachloride and excess phosphorus trichloride, lithium hexachlorophosphate is completely reacted. In addition to changing to lithium hexafluorophosphate, phosphorus pentachloride is consumed and converted to lithium hexafluorophosphate, and excess phosphorus trichloride also reacts with phosphorus trifluoride with a high vapor pressure. It can be easily removed by a subsequent decompression process or the like. For this reason, it is necessary to introduce the anhydrous hydrogen fluoride in an amount equal to or more than the total amount of lithium hexachlorophosphate, phosphorus pentachloride, and excess phosphorus trichloride. The introduction amount of anhydrous hydrogen fluoride is preferably in the range of 6.01 to 7.20 times mol of the total amount of lithium hexachlorophosphate, phosphorus pentachloride and excess phosphorus trichloride from the viewpoint of raw material cost.

  The lower limit of the temperature at which this reaction is carried out is −40 ° C., preferably 5 ° C., and the upper limit is 100 ° C., preferably 50 ° C. If reaction temperature is less than -40 degreeC, since a non-aqueous organic solvent will coagulate | solidify, reaction does not advance. Moreover, when higher than 100 degreeC, it becomes a cause of coloring and a side reaction, and since there exists a possibility that the fall of a yield and the acidic impurity concentration contained in a concentrate may become 500 mass ppm or more, it is unpreferable.

  Although the pressure during this reaction is not particularly limited, it is generally carried out near atmospheric pressure in order to remove by-product hydrogen chloride.

(4) Removal of hydrogen chloride from the reaction solution by degassing treatment Since the lithium hexafluorophosphate solution containing the solids synthesized as described above is a hydrogen chloride saturated solution, it is a subsequent filtration operation. If the majority of the hydrogen chloride is discharged out of the system in advance by vacuum degassing or inert gas circulation, foaming and pressure rise are unlikely to occur and the filtration operation can be performed easily and safely. Can do. Hydrogen chloride is removed from the system by reducing the pressure or supplying a carrier gas substantially free of moisture such as inert gas such as nitrogen and argon or dry air, and dissolving dissolved hydrogen chloride in the gaseous state. This is done by discharging. The removal of hydrogen chloride in this step is a crude purification performed for the purpose of improving the efficiency of the filtration step and improving work safety, and does not aim for 100% removal. In the subsequent degassing and concentration step, hydrogen fluoride and the like can be sufficiently removed in addition to hydrogen chloride. For this reason, the concentration of hydrogen chloride after removal in this step is not particularly limited, but is generally 0.2% by mass or less.

  A vacuum pump, an aspirator, etc. can be used for pressure reduction. The pressure reduction is performed by keeping the reactor in a sealed state and then maintaining the system at a pressure lower than atmospheric pressure. The lower the pressure in the system and the higher the temperature in the system, the more efficiently hydrogen chloride can be removed. However, if the temperature is too high, the resulting concentrated solution may become colored or decompose lithium lithium hexafluorophosphate. There is a possibility that the yield decreases due to the concentration of the non-aqueous organic solvent and the concentration increases due to the scattering of the non-aqueous organic solvent, and the viscosity increases to adversely affect the subsequent filtration step. For this reason, the upper limit of the temperature is 90 ° C., preferably 60 ° C. Further, if the temperature is too low, the removal rate of hydrogen chloride decreases, and further, the lithium hexafluorophosphate solution may solidify. Therefore, the lower limit of the temperature is −20 ° C., preferably 10 ° C. Since the pressure in the system varies depending on the hydrogen chloride concentration and the temperature and vapor pressure of the liquid, it cannot be said unconditionally. However, the reduced pressure can maintain the degree of vacuum in the tank at 10 kPa or less in absolute pressure. preferable. When the holding pressure exceeds 10 kPa, it is not preferable because hydrogen chloride cannot be eliminated until the concentration is lower than the desired concentration or it takes a long time to eliminate hydrogen chloride below the desired concentration. When the carrier gas is circulated, it may be circulated only in the gas phase portion, but it is more efficient if it is circulated in the liquid by bubbling or the like.

(5) Filtration After the removal of the hydrogen chloride, the reaction solution obtained is filtered to separate the filtrate from the filtrate containing lithium fluoride solids. For filtration, pressure filters, vacuum filters, filter presses using filter cloths and cartridge filters, sedimentation separators by filtration, filtration separators, and cross-flow filters using ultrafiltration membranes However, it is desirable to use the cross flow filtration method as described above in terms of handling and cost. In the cross-flow filtration, an ultrafiltration membrane such as ceramic or resin is used, and a lithium hexafluorophosphate solution containing a synthesized solid content is pressurized and circulated through the filtration membrane.

  The filtrate of the lithium hexafluorophosphate solution that has passed through the filtration membrane is transferred to a tank for concentration in the next step, and a concentration operation is performed.

  On the other hand, since the solid content concentration in the slurry of the circulating slurry containing the solid content increases with the progress of filtration, it is preferable to manage the filtration operation in the range of the slurry having the solid content concentration of 0.1 to 10% by mass. . After completion of the filtration operation, the slurry is transferred to a tank in which the next batch reaction is performed, or if the next batch reaction is performed in the tank in which the filtration operation is performed, the slurry is kept waiting.

(4) Degassing concentration Hydrogen chloride, phosphorus trifluoride, and excessively introduced hydrogen fluoride present in the filtrate obtained by the filtration are removed by degassing concentration.

  In degassing concentration, the gas phase part containing volatile components from the solution is evacuated, or a carrier gas substantially free of moisture such as inert gas such as nitrogen and argon or dry air is circulated to remove the volatile components. This is done by discharging out of the system. Further, the concentration of lithium hexafluorophosphate is increased by the degassing concentration operation, and it becomes possible to produce an electrolytic solution for a lithium ion battery using the concentrated solution.

  A vacuum pump, an aspirator, etc. can be used for pressure reduction. The pressure reduction is performed by keeping the reactor in a sealed state and then maintaining the system at a pressure lower than atmospheric pressure. The lower the pressure in the system and the higher the temperature in the system, the more efficient the concentration can be. However, if the temperature is too high, the resulting concentrated solution may be colored or the concentration of lithium hexafluorophosphate Since the yield is reduced due to decomposition, the upper limit of the temperature is 90 ° C, preferably 60 ° C. On the other hand, if the temperature is too low, the concentration rate decreases and becomes inefficient, and further, the lithium hexafluorophosphate solution may coagulate, and if coagulated, it becomes difficult to concentrate, so the lower limit of the temperature is −20 ° C, preferably 10 ° C. Since the pressure in the system varies depending on the temperature and vapor pressure of the liquid to be concentrated, it cannot be generally stated, but the reduced pressure preferably maintains the vacuum in the tank at 10 kPa or less in absolute pressure. When the holding pressure exceeds 10 kPa, impurities such as hydrogen chloride and hydrogen fluoride cannot be excluded until the concentration is lower than the desired concentration, or the impurities are excluded until the concentration is lower than the desired concentration. Since it takes a long time, it is not preferable. Further, it is more preferable that the holding pressure is 1 kPa or less because the impurities can be eliminated to a low concentration. When the carrier gas is circulated, it may be circulated only in the gas phase portion, but it is more efficient if it is circulated in the liquid by bubbling or the like.

  The lower limit of the temperature during deaeration and concentration is -20 ° C, preferably 10 ° C, and the upper limit is 90 ° C, preferably 60 ° C. When the temperature during deaeration and concentration is less than −20 ° C., not only is the concentration efficiency low, but the lithium hexafluorophosphate solution may be solidified, so that acidic impurities are difficult to remove. Moreover, when higher than 90 degreeC, it becomes a cause of coloring and decomposition | disassembly, and as a result, it becomes difficult to make acidic impurity concentration contained in a concentrate into 500 mass ppm or less, and it is unpreferable.

  Although the concentration depends on the initial concentration of lithium hexafluorophosphate, the concentration of lithium hexafluorophosphate after concentration is preferably as high as possible, and it is removed until the concentration of lithium hexafluorophosphate is at least 25% by mass. It is necessary to air-concentrate, and it is preferably about 35 to 45% by mass. Concentration to a concentration exceeding 45% by mass is not preferred because it may cause precipitation of lithium hexafluorophosphate solids. Furthermore, in the case of concentration at a concentration of less than 25% by mass, it becomes difficult to reduce the concentration of acidic impurities contained in the concentrated solution to 500 ppm by mass or less, and it will be described later using the lithium hexafluorophosphate concentrated solution. Since it is difficult to produce the electrolyte solution, it is not preferable. Therefore, the concentrated concentration is preferably about 35 to 45% by mass.

The high-purity lithium hexafluorophosphate concentrate obtained by the degassing concentration can be used as a raw material for the electrolyte solution of a lithium ion battery. When used in a lithium ion battery, the concentrated solution is further subjected to at least one treatment selected from filtration, concentration, dilution with a non-aqueous organic solvent, and addition of an additive, so that an electrolytic solution having a desired concentration and configuration is obtained. A lithium ion battery electrolyte solution is obtained. The filtration uses a filter cloth or a cartridge filter, a pressure filter, a vacuum filter, a filter press machine, a sedimentation separator by centrifugation, a filter separator, and a cross flow filter using an ultrafiltration membrane Remove lithium fluoride, etc. In addition, acidic impurities such as hydrogen fluoride can be removed by passing the concentrated solution through an ion exchange resin. The temperature at that time is preferably 15 to 50 ° C. in order to prevent decomposition of lithium hexafluorophosphate, a non-aqueous organic solvent, and an ion exchange resin. Moreover, 16-34 degreeC is more preferable from a viewpoint of the viscosity of the said concentrate which passes through an ion exchange resin. The base structure of the ion exchange resin is a styrene divinylbenzene copolymer, styrene, acrylic, or the like, and the functional groups are —SO ₃ H, —N (CH ₃ ) ₂ , —N (X) (CH ₃ ) _3. , —N (X) (C ₂ H ₄ OH) (CH ₃ ) _{2 and the} like. X is a halide. The concentration is performed by distilling off the solvent and the like by vacuum degassing in a sealed state to adjust to a desired concentration. Moreover, you may remove an acidic impurity with a solvent in the said concentration. The dilution with the non-aqueous organic solvent is performed by diluting with a non-aqueous organic solvent such as ethyl methyl carbonate to adjust to a desired concentration. Further, an additive may be contained in the electrolyte solution of the lithium ion battery.

  As described above, after reacting phosphorus trichloride, chlorine, lithium chloride and / or lithium fluoride, the reaction product produced in the solvent is reacted with hydrogen fluoride, and then filtered. And degassing and concentrating the filtrate to obtain a lithium hexafluorophosphate concentrate, and the high-purity hexafluorophosphorus can be obtained more efficiently without treating the precipitate generated as a by-product for each synthesis batch as waste. A lithium acid concentrate can be produced. Further, lithium hexafluorophosphate crystals can be obtained from a solution containing lithium hexafluorophosphate obtained as described above as an electrolyte by a crystallization process of cooling or concentration. Since the lithium ion battery solvent is used as the non-aqueous organic solvent used in the reaction, lithium lithium hexafluorophosphate is directly removed from the solution obtained by the reaction as a solid in the crystallization process. It can be used as a raw material for an electrolytic solution.

2. Next, the configuration of the lithium ion battery of the present invention will be described. The lithium ion battery of the present invention is a lithium hexafluorophosphate concentrate obtained by the production method of the present invention or a lithium containing lithium hexafluorophosphate as an electrolyte using the lithium hexafluorophosphate concentrate. It is characterized by using an electrolytic solution for an ion battery, and the other components used in general lithium ion batteries are used. That is, it consists of positive and negative electrodes capable of inserting and extracting lithium, a separator, a container and the like.

  The negative electrode includes at least a negative electrode material and a current collector, and the positive electrode includes at least a positive electrode material and a current collector.

  The current collector is a conductive sheet that exchanges electrons with the positive electrode material or the negative electrode material, and a metal, a carbon material, or a conductive polymer can be used. For example, an aluminum foil is used for the positive electrode and a copper foil is used for the negative electrode.

  Although it does not specifically limit as a negative electrode material, The lithium metal which can occlude / release lithium, the alloy and intermetallic compound of lithium and another metal, various carbon materials, artificial graphite, natural graphite, metal oxide, metal nitride , Activated carbon, or a conductive polymer is used.

The positive electrode material is not particularly limited. For example, a lithium-containing transition metal composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , or LiMn ₂ O ₄ , and a plurality of transition metals of these lithium-containing transition metal composite oxides are used. Mixtures, those in which some of the transition metals of the lithium-containing transition metal composite oxides are substituted with other metals, lithium-containing transition metal phosphates such as LiFePO ₄ or LiMnPO ₄ , those lithium-containing transition metals A mixture of a plurality of phosphate transition metals, a lithium-containing transition metal phosphate transition metal partially substituted with another metal, TiO ₂ , V ₂ O ₅ , MoO _3, etc. Oxides, sulfides such as TiS ₂ or FeS, or polyacetylene, polyparaphenylene, polyaniline, and poly A conductive polymer such as pyrrole, activated carbon, a polymer that generates radicals, or a carbon material is used.

  By adding acetylene black, ketjen black, carbon fiber, or graphite as a conductive material to a positive electrode material or a negative electrode material, and polytetrafluoroethylene, polyvinylidene fluoride, or SBR resin as a binder, it is easily formed into a sheet shape Can be molded.

  As a separator for preventing contact between the positive electrode and the negative electrode, a nonwoven fabric or a porous sheet made of polypropylene, polyethylene, paper, glass fiber or the like is used.

  A lithium-ion battery having a coin shape, cylindrical shape, square shape, aluminum laminate sheet shape, or the like is assembled from the above elements.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by this Example.

[Example 1]
(First batch)
A jacketed SUS reactor coated with a polytetrafluoroethylene resin (hereinafter referred to as “PFA resin”) on a wetted portion was charged with 80 kg of ethyl methyl carbonate (hereinafter referred to as “EMC”), phosphorus trichloride (hereinafter referred to as “EMC”). 23.1 kg (described as “PCl ₃ ”) and 6.8 kg of lithium chloride (hereinafter referred to as “LiCl”) were charged. Next, while stirring with a stirrer, 11.4 kg of chlorine gas (hereinafter referred to as “Cl ₂ ”) was blown in to perform chlorination reaction. At this time, cooling water was passed through the jacket to maintain the liquid temperature at 20 to 30 ° C. Next, with the same stirring, the liquid temperature was maintained at 20 to 30 ° C., and 19.9 kg of anhydrous hydrogen fluoride (hereinafter referred to as “HF”) was blown to perform a fluorination reaction. A reaction solution was obtained. At this time, by-product hydrogen chloride gas was discharged out of the system and neutralized with an alkali scrubber. The obtained reaction solution was degassed by depressurizing the reactor using a dry vacuum pump to remove most of the hydrogen chloride dissolved in the solution. Thereafter, when sampling was performed, the solution was slightly cloudy, and when analyzed, lithium fluoride (hereinafter referred to as “LiF”) and lithium hexafluorophosphate (hereinafter referred to as “LiPF ₆ ”) were described. ) Was confirmed. The concentration of LiPF _{6 in} the solution was 23% by mass, and the reaction yield was about 93%. Furthermore, the acidic impurity concentration was 4500 mass ppm, and other impurities were hardly recognized.

  Next, the reaction solution obtained after removing hydrogen chloride was introduced into a cross flow filter (ultrafiltration membrane; ceramic membrane) while circulating with a slurry pump, and filtration operation was performed. The filtrate was transparent and transferred to a jacketed SUS reaction vessel coated with PFA for the next step. The solid content concentration of the slurry was 0.2% by mass as a result of mass spectrometry.

Next, the filtrate was sealed by heating 45 ° C. warm water through the reactor jacket, and then degassed and concentrated using a dry vacuum pump. From the start of deaeration and concentration, the pressure in the vessel decreased, and distillation of EMC as a non-aqueous organic solvent was confirmed, and continued until the concentration of LiPF ₆ in the synthesis solution reached 40% by mass. The pressure in the reaction vessel at the end of degassing concentration was about 3 hPa. After completion of the deaeration and concentration, nitrogen gas was introduced into the container, the pressure was returned to atmospheric pressure, sampling and analysis were performed. As a result, the product was LiPF ₆ and almost no other product was observed. The acidic impurity concentration was reduced to 290 mass ppm. The chloride ion concentration (hereinafter referred to as “Cl concentration”) was less than 3 ppm by mass, and no coloring was observed. The results are shown in Table 1.

(2nd batch)
Into the jacketed SUS reactor coated with the same PFA resin as in the first batch, the filtered material collected in the first batch (slurry composed of LiF solids and the LiPF ₆ EMC solution) is used as a raw material. About 20 kg was used, and EMC: 65 kg, PCl ₃ : 18.8 kg, and LiCl: 5.0 kg were charged. Next, chlorination reaction was performed by blowing 9.2 kg of Cl ₂ while stirring with a stirrer. At this time, cooling water was passed through the jacket to maintain the liquid temperature at 20 to 30 ° C. Next, the liquid temperature was kept cooled to 20 to 30 ° C. while stirring similarly, and fluorination reaction was performed by blowing HF: 16.0 kg to obtain a reaction solution. At this time, by-product hydrogen chloride gas was discharged out of the system and neutralized with an alkali scrubber. The obtained reaction solution was degassed by depressurizing the reactor using a dry vacuum pump to remove most of the hydrogen chloride dissolved in the solution. Thereafter, when sampling was performed, the solution was slightly cloudy, and when analyzed, generation of LiF and LiPF ₆ was confirmed. The concentration of LiPF _{6 in} the solution was 22% by mass, and the reaction yield was about 92%. Furthermore, the acidic impurity concentration was 1500 mass ppm, and other impurities were hardly recognized.

  Next, the reaction solution obtained after removing hydrogen chloride was introduced into a cross flow filter while circulating with a slurry pump, and a filtration operation was performed. Cross flow filtration was performed under the same conditions as in the first batch. The filtrate was transparent, and the solid content concentration of the slurry was 0.2% by mass as a result of mass spectrometry.

Next, the filtrate was degassed and concentrated under the same conditions as in the first batch. When sampling and analysis were performed after completion of degassing concentration, the product was LiPF ₆ and other products were hardly observed. The acidic impurity concentration was reduced to 60 mass ppm. Further, the Cl concentration was less than 3 ppm by mass, and no coloring was observed. The results are shown in Table 1.

[Examples 2 to 6]
Used in Example 1, the solvent type and _amount, PCl 3, LiCl, the amount of Cl _2, and HF, except for changing the filtered product and the addition step using the same procedure as in Example 1 LiPF ₆ A concentrated solution was prepared. In any of the above Examples, the product after concentration was only LiPF ₆ , and there was no quality problem in the obtained solution. The results are shown in Table 1. In the table, “DEC” means diethyl carbonate and “DMC” means dimethyl carbonate.

  In Example 4, the filtrate obtained in Example 3 was used. However, because the solid content concentration of the filtrate was too high, EMC was added to the filtrate to obtain a solid content concentration of 5.0. What was adjusted to the mass% was transferred and used.

[Comparative Example 1]
(First batch)
To a jacketed SUS reactor coated with the same PFA resin as in Example 1 on the wetted part, about 20 kg of the filtrate collected in Example 4 (slurry composed of LiF solid content and EMC solution of LiPF ₆ ) EMC: 65 kg, PCl ₃ : 18.8 kg, LiCl: 5.0 kg were charged. Next, chlorination reaction was performed by blowing 9.2 kg of Cl ₂ while stirring with a stirrer. At this time, cooling water was passed through the jacket to maintain the liquid temperature at 20 to 30 ° C. Next, the liquid temperature was kept cooled to 20 to 30 ° C. while stirring similarly, and fluorination reaction was performed by blowing HF: 16.0 kg to obtain a reaction solution. At this time, by-product hydrogen chloride gas was discharged out of the system and neutralized with an alkali scrubber. The obtained reaction solution was degassed by depressurizing the reactor using a dry vacuum pump to remove most of the hydrogen chloride dissolved in the solution. Thereafter, when sampling was performed, the solution was slightly cloudy, and when analyzed, generation of LiF and LiPF ₆ was confirmed. The concentration of LiPF _{6 in} the solution was 23% by mass, and the reaction yield was about 92%. Furthermore, the acidic impurity concentration was 5500 ppm by mass, and other impurities were hardly recognized.

  Next, filtration operation was performed using a pressure filter coated with PFA on the reaction solution obtained after removing hydrogen chloride. In addition, filtration operation was divided into several times and scraped solid content in air | atmosphere. As a result of mass analysis, the solid content concentration of the filtrate was 45% by mass.

Next, the filtrate was degassed and concentrated under the same conditions as in Example 1. After sampling and analysis after completion of degassing concentration, the product was LiPF ₆ , and several thousand mass ppm of lithium difluorophosphate (hereinafter referred to as “LiPO ₂ F ₂ ”) was recognized as the other product. It was. The acidic impurity concentration was as high as 620 mass ppm, and reddish brown coloring was observed. The results are shown in Table 2.

(2nd batch)
A jacketed SUS reactor in which the wetted part was coated with the same PFA resin as in the first batch of Comparative Example 1 was charged with EMC: 65 kg, PCl ₃ : 18.8 kg, LiCl: 5.0 kg, and the above comparison About 0.6 kg of the filtrate (cake) collected in the first batch of Example 1 was charged. Next, chlorination reaction was performed by blowing 9.2 kg of Cl ₂ while stirring with a stirrer. At this time, cooling water was passed through the jacket to maintain the liquid temperature at 20 to 30 ° C. Next, the liquid temperature was kept cooled to 20 to 30 ° C. while stirring similarly, and fluorination reaction was performed by blowing HF: 16.0 kg to obtain a reaction solution. At this time, by-product hydrogen chloride gas was discharged out of the system and neutralized with an alkali scrubber. The obtained reaction solution was degassed by depressurizing the reactor using a dry vacuum pump to remove most of the hydrogen chloride dissolved in the solution. Thereafter, when sampling was performed, the solution was slightly cloudy, and when analyzed, generation of LiPO ₂ F ₂ was confirmed in addition to LiF and LiPF ₆ . The concentration of LiPF _{6 in} the solution was 20% by mass, and the reaction yield was a low value of about 82%. Furthermore, the acidic impurity concentration was as high as 12000 mass ppm.

  Next, the reaction solution obtained after removing hydrogen chloride was filtered in the same manner as in the first batch of Comparative Example 1 above. The solid content concentration of the filtrate was 44% by mass as a result of mass spectrometry.

Next, the filtrate was degassed and concentrated under the same conditions as in Example 1. When sampling and analysis were performed after completion of degassing concentration, the product was LiPF ₆ and LiPO ₂ F ₂ was found to be several thousand mass ppm as other products. The acidic impurity concentration was as high as 2500 mass ppm, and the Cl concentration was as high as 30 mass ppm. Further, reddish brown coloration was observed in the concentrate. The results are shown in Table 2.

[Example 7]
The concentrate obtained in the second batch of Example 1 was filtered using a cartridge filter, a test cell was prepared using the obtained filtrate, and the performance as an electrolyte was evaluated by a charge / discharge test. First, the LiPF ₆ / EMC solution, which is the filtrate obtained by filtration, is concentrated about twice, and then ethylene carbonate (hereinafter referred to as “EC”) becomes EMC: EC = 2: 1 by volume. Thus, an electrolyte solution of 1 mol / L LiPF ₆ (EMC, EC mixed solvent) was prepared.

  Using this electrolytic solution, a test cell using graphite as a negative electrode and lithium cobaltate as a positive electrode was assembled. Specifically, 95 parts by mass of natural graphite powder was mixed with 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder, and N, N-dimethylformamide was further added to form a slurry. This slurry was applied on a nickel mesh and dried at 150 ° C. for 12 hours to obtain a test negative electrode body. Further, 85 parts by mass of lithium cobaltate was mixed with 10 parts by mass of graphite powder and 5 parts by mass of PVDF, and N, N-dimethylformamide was further added to form a slurry. This slurry was applied on an aluminum foil and dried at 150 ° C. for 12 hours to obtain a test positive electrode body.

Using a polypropylene nonwoven fabric as a separator, a test cell was assembled using the electrolytic solution, the negative electrode body, and the positive electrode body. Subsequently, a constant current charge / discharge test was repeated at 0.35 mA / cm ² for both charging and discharging, and the cycle of charging to 4.2 V and discharging to 2.5 V was repeated to observe the change in capacity retention rate.

  As a result, the charge / discharge efficiency was almost 100%, and the capacity retention rate after the end of 100 cycles did not change at all.

[Example 8]
The concentrated solution obtained in Example 3 was filtered off using a cartridge filter, and the obtained filtrate was passed through an ion exchange resin column to reduce the acidic impurity concentration to 10 ppm by mass. Using this concentrate, a test cell was prepared in the same manner as in Example 7, and the performance as an electrolytic solution was evaluated by a charge / discharge test.

  As a result, the charge / discharge efficiency was almost 100%, and the capacity retention rate after the end of 100 cycles did not change at all.

Claims (5)

Reaction step (I) in which phosphorus trichloride, chlorine, lithium chloride and / or lithium fluoride are reacted in a non-aqueous organic solvent;
Reacting the reaction product produced in the solvent in the reaction step (I) with hydrogen fluoride, reaction step (II),
After the reaction step (II), after removing hydrogen chloride from the reaction solution by deaeration treatment, filtration is performed, and the filtrate is deaerated and concentrated to obtain a lithium hexafluorophosphate concentrate.
The filtration is performed in an inert atmosphere substantially free of moisture, and the filtrate containing the lithium fluoride solid content separated from the filtrate by the filtration is treated with at least one of the reaction steps (I) and (II). A method for producing a concentrated solution of lithium hexafluorophosphate, which is used as a raw material for a reaction in one step. 2. The production of a lithium hexafluorophosphate concentrate according to claim 1, wherein the filtrate is a slurry composed of a solid content of lithium fluoride and a non-aqueous organic solvent solution of lithium hexafluorophosphate. Method. The method for producing a lithium hexafluorophosphate concentrate according to claim 1 or 2, wherein the filtration is cross flow filtration. The method for producing a lithium hexafluorophosphate concentrate according to any one of claims 1 to 3, wherein the filtrate is a slurry having a solid concentration of 0.1 to 10% by mass. The lithium hexafluorophosphate concentrate obtained by the production method according to any one of claims 1 to 4 is further filtered, concentrated, diluted with a non-aqueous organic solvent, and added with an additive. A method for producing an electrolytic solution for a lithium ion battery containing lithium hexafluorophosphate as an electrolyte, wherein at least one selected treatment is performed.