JP5151121B2 - Method for producing electrolytic solution for lithium ion battery and lithium ion battery using the same - Google Patents

Description

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

  Various methods for producing lithium hexafluorophosphate which is an electrolyte useful for lithium ion batteries and the like have been proposed. In general, an electrolytic solution is produced by first producing lithium hexafluorophosphate, and a predetermined solvent for lithium batteries. The method of making it melt | dissolve in and making it an electrolyte solution is performed. 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. There is also a method (Patent Document 2) in which anhydrous hydrogen fluoride is added to phosphorus pentachloride and lithium fluoride and reacted without solvent. This is not easy to control the reaction and requires cooling to several tens of degrees Celsius below freezing point.

  On the other hand, in the method for producing lithium hexafluorophosphate using a solvent, gaseous phosphorus pentafluoride is reacted with lithium fluoride in which anhydrous hydrogen fluoride is dissolved as a solvent, and the produced lithium hexafluorophosphate is crystallized. There is a method (Non-patent Document 1) in which the data is converted into an image and taken out.

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

  There is also a method (Patent Document 3) in which lithium fluoride and phosphorus pentafluoride are reacted in an organic solvent. This method has great advantages in terms of reaction control and purity. However, as described above, since it is necessary to manufacture and handle phosphorus pentafluoride gas, which is one of the raw materials, in another process, there remains a problem of cost.

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.
JP-A 64-72901 JP-A-10-72207 JP-A-9-165210 JP-A-10-81505 J. et al. Chem. Soc. Part 4, 4408 (1963)

  The object of the present invention is to produce an electrolyte solution for lithium ion batteries using lithium hexafluorophosphate as an electrolyte, as described above, without using an anhydrous hydrogen fluoride solvent that is not easy to handle and expensive equipment In addition, an electrolyte solution using lithium hexafluorophosphate as an electrolyte is manufactured at low cost without using a complicated operation and without performing a crystallization process, and is used for a lithium ion battery.

  As a result of intensive research in view of such problems, the present inventors have not used an anhydrous hydrogen fluoride solvent that is not easy to handle in the production of an electrolyte for lithium ion batteries using lithium hexafluorophosphate as an electrolyte. In addition, the present inventors have found a method that does not require expensive equipment and complicated operations, and that can obtain an electrolytic solution using lithium hexafluorophosphate as an electrolyte at low cost without performing a crystallization process, and has reached the present invention.

That is, in the production of an electrolytic solution for a lithium ion battery using lithium hexafluorophosphate as an electrolyte, the present invention reacts phosphorus trichloride with chlorine and lithium chloride in a non-aqueous organic solvent, and then in the solvent. It is a method for producing an electrolytic solution for a lithium ion battery, characterized by reacting the produced reaction product with hydrogen fluoride, and further reacting with lithium chloride. In particular, the non-aqueous organic solvent is a chain or A cyclic carbonate, or an ether compound having two or more oxygen atoms, and the carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, or propylene carbonate only. Or at least one of the ether compounds is 1, - there is provided a manufacturing method which is a dimethoxyethane, respectively.

  The method for producing an electrolytic solution for a lithium ion battery containing lithium hexafluorophosphate according to the present invention has a high reaction yield and can basically perform a reaction at atmospheric pressure. By using a non-aqueous organic solvent for a lithium battery as a solvent, there is an advantage that the reaction solution can be directly used as an electrolyte for a lithium ion battery without crystallization and taking out lithium hexafluorophosphate powder.

  The manufacturing method of the electrolyte solution for lithium ion batteries of this invention is implemented in any one type in the said nonaqueous organic solvent for lithium batteries, or several types of mixed solvents.

  The non-aqueous organic solvent used is preferably a chain or cyclic carbonate compound having high chemical stability and high solubility of lithium hexafluorophosphate, or an ether compound having two or more oxygen atoms. Examples of such a solvent include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane and the like.

  In the production method of the present invention, first, phosphorus trichloride and lithium chloride as raw materials are charged into a non-aqueous organic solvent, and chlorine gas is blown into the non-aqueous organic solvent, whereby the reaction is carried out in the non-aqueous organic solvent, and then the reaction product is produced. Hydrogen fluoride is introduced into the solvent containing the product and reacted with the reaction product.

  In the present invention, each molar ratio of lithium chloride, chlorine, and phosphorus trichloride is 1 to 1.1: 1: 1 to 2, and the amount of phosphorus trichloride is the same as chlorine gas or more than chlorine gas. It is necessary to prepare a lot. 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 charge more phosphorus trichloride in the range of 1 to 2 times mol than chlorine gas. The amount of lithium chloride is preferably 1 to 1.1 times mol of chlorine gas in terms of raw material cost. More preferably, it is 1.05-1.1 times mol.

  Next, the amount of the raw material charged into the non-aqueous organic solvent needs to be 400 g or less, preferably 100 g or less of lithium chloride with respect to 1 liter of the non-aqueous organic solvent. When the amount of lithium chloride exceeds 400 g with respect to 1 liter of non-aqueous organic solvent, the product becomes saturated, unreacted lithium chloride is generated, and the reaction cannot proceed.

  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.

  In addition, when light is irradiated during the reaction, there is a possibility that a reaction between the non-aqueous organic solvent and chlorine occurs.

  On the other hand, after completion of the blowing of chlorine gas, the lithium chloride powder charged into the reactor is completely or partially dissolved by the reaction formula (1) to become an intermediate compound presumed to be lithium hexachlorophosphate.

LiCl + PCl ₃ + Cl ₂ → LiPCl ₆ (1)
Next, in order to fluorinate the produced lithium hexachlorophosphate, anhydrous hydrogen fluoride is introduced into the reactor. At this time, anhydrous hydrogen fluoride may be gaseous or liquid. The target product lithium hexafluorophosphate is obtained by the following reaction formula (2).
LiPCl ₆ + 6HF → LiPF ₆ + 6HCl (2)
The amount of anhydrous hydrogen fluoride introduced is required to be 6.01 times mol or more in molar ratio with respect to the total amount of lithium hexachlorophosphate as an intermediate product and excess phosphorus trichloride in the previous reaction. If the amount of anhydrous hydrogen fluoride is the same or less than the combined amount of lithium hexachlorophosphate and excess phosphorus trichloride, the fluorination of lithium hexachlorophosphate does not proceed sufficiently and partially fluorinated chlorinated phosphoric acid Since lithium and phosphorus trichloride remain, the chlorine concentration in the liquid increases, which may adversely affect 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 and excess phosphorus trichloride, the lithium hexachlorophosphate is completely lithium hexafluorophosphate. In addition to the reaction, excess phosphorus trichloride also reacts with phosphorus trifluoride having a high vapor pressure and can be easily removed by a subsequent decompression process or the like. For this reason, the amount of anhydrous hydrogen fluoride needs to be introduced more than the total amount of lithium hexachlorophosphate 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 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, since it causes coloring and a side reaction, 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.

In the obtained non-aqueous lithium hexafluorophosphate organic solution, by-product hydrogen chloride, phosphorus trifluoride, and excess hydrogen fluoride present in the liquid can be removed by decompression, bubbling, distillation, etc. In addition, hydrogen fluoride can be removed, for example, by re-addition of lithium chloride, converted into hydrogen chloride having a high vapor pressure by the reaction formula (3), and reduced pressure treatment, bubbling treatment, distillation or the like. An electrolytic solution in which high purity lithium hexafluorophosphate is dissolved, which can be used for a lithium ion battery, is obtained.
HF + LiCl → LiF + HCl (3)
Although it is possible to obtain lithium hexafluorophosphate crystals from the lithium hexafluorophosphate solution obtained as described above by a crystallization process such as cooling or concentration, in the present invention, the non-aqueous organic solvent used in the reaction is used. As a lithium ion battery solvent, it can be used directly as an electrolyte raw material for lithium ion batteries without taking out lithium hexafluorophosphate as a solid in the crystallization process from the solution obtained by the reaction. Is possible.

  As described above, according to the present invention, in the manufacture of an electrolyte solution for lithium ion batteries using lithium hexafluorophosphate as an electrolyte, an anhydrous hydrogen fluoride solvent that is difficult to handle is not used, and expensive equipment and complicated Therefore, it is possible to obtain a high-purity electrolyte solution for a lithium ion battery at a low cost without requiring a simple operation and without performing a crystallization process. In addition, a lithium ion battery using the electrolytic solution can be provided.

  EXAMPLES Hereinafter, although this invention is further demonstrated based on an Example, it is not limited by this Example.

Example 1
In a polytetrafluoroethylene reactor, 500 g of dimethyl carbonate, 72 g of phosphorus trichloride, and 21 g of lithium chloride were charged and dispersed. At this time, a reactor made of light-shielded polytetrafluoroethylene reactor was used. While maintaining this dispersion at 10 ° C., 35.5 g of chlorine gas was introduced. The liquid after the introduction was completed became a pale yellow solution with the solid content dissolved, and the reaction proceeded to produce lithium hexachlorophosphate. 66 g of anhydrous hydrogen fluoride was introduced into the resulting solution while maintaining it at 10 ° C. The liquid after the introduction was changed from pale yellow to colorless, and lithium hexafluorophosphate was produced.

  Next, the excess hydrogen fluoride in the obtained solution is converted into hydrogen chloride and lithium fluoride by re-addition of lithium chloride, and by a reduced pressure treatment with hydrogen chloride and phosphorus trifluoride which are by-products during the reaction. Removed.

  When the obtained solution was analyzed by NMR, decomposition of dimethyl carbonate and the like were not observed, and the product was only lithium hexafluorophosphate. The amount of lithium hexafluorophosphate in the solution determined by NMR was 75 g, and the yield was confirmed to be almost 100%. Further, with respect to this solution, the acidic impurity concentration that adversely affects the lithium battery characteristics was 10 ppm, and was 70 ppm in terms of lithium hexafluorophosphate solid.

Example 2
In a polytetrafluoroethylene reactor, 500 g of diethyl carbonate, 72 g of phosphorus trichloride and 21 g of lithium chloride were charged and dispersed with stirring. At this time, a reactor made of light-shielded polytetrafluoroethylene reactor was used. While maintaining this dispersion at 10 ° C., 35.5 g of chlorine gas was introduced. The liquid after the introduction was completed became a pale yellow solution with the solid content dissolved, and the reaction proceeded to produce lithium hexachlorophosphate. 66 g of anhydrous hydrogen fluoride was introduced into the resulting solution while maintaining it at 10 ° C. The liquid after the introduction was changed from pale yellow to colorless, and lithium hexafluorophosphate was produced.

  Next, the excess hydrogen fluoride in the obtained solution is converted into hydrogen chloride and lithium fluoride by re-addition of lithium chloride, and by a reduced pressure treatment with hydrogen chloride and phosphorus trifluoride which are by-products during the reaction. Removed.

  When the obtained solution was analyzed by NMR, no decomposition or the like of diethyl carbonate was observed, and the product was only lithium hexafluorophosphate. The amount of lithium hexafluorophosphate in the solution determined by NMR was 75 g, and the yield was confirmed to be almost 100%. Further, with respect to this solution, the acidic impurity concentration that adversely affects the lithium battery characteristics was 14 ppm, and 98 ppm in terms of lithium hexafluorophosphate solids.

Example 3
In a polytetrafluoroethylene reactor, 500 g of methyl ethyl carbonate, 72 g of phosphorus trichloride and 21 g of lithium chloride were charged and dispersed with stirring. At this time, a reactor made of light-shielded polytetrafluoroethylene reactor was used. While maintaining this dispersion at 10 ° C., 35.5 g of chlorine gas was introduced. The liquid after the introduction was completed became a pale yellow solution with the solid content dissolved, and the reaction proceeded to produce lithium hexachlorophosphate. 66 g of anhydrous hydrogen fluoride was introduced into the resulting solution while maintaining it at 10 ° C. The liquid after the introduction was changed from pale yellow to colorless, and lithium hexafluorophosphate was produced.

  Next, the excess hydrogen fluoride in the obtained solution is converted into hydrogen chloride and lithium fluoride by re-addition of lithium chloride, and by a reduced pressure treatment with hydrogen chloride and phosphorus trifluoride which are by-products during the reaction. Removed.

  When the obtained solution was analyzed by NMR, decomposition of methyl ethyl carbonate and the like were not observed, and the product was only lithium hexafluorophosphate. The amount of lithium hexafluorophosphate in the solution determined by NMR was 75 g, and the yield was confirmed to be almost 100%. Further, with respect to this solution, the acidic impurity concentration that adversely affects the lithium battery characteristics was 12 ppm, and 84 ppm in terms of lithium hexafluorophosphate solids.

  Next, a test cell was produced using this solution, and the performance as an electrolytic solution was evaluated by a charge / discharge test. First, the synthesized lithium hexafluorophosphate / methyl ethyl carbonate solution is concentrated about twice, and ethylene carbonate is added to the mixture so that methyl ethyl carbonate: ethylene carbonate = 2: 1 by volume ratio. A lithium fluorophosphate / (methyl ethyl carbonate / ethylene carbonate mixed solvent) electrolyte solution 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 weight of natural graphite powder was mixed with 5 parts by weight 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 weight of lithium cobaltate was mixed with 10 parts by weight of black smoke powder and 5 parts by weight 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. A test cell was assembled using a polypropylene nonwoven fabric as a separator, the reaction solution of this example as an electrolytic solution, and 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.

Comparative Example 1
In a polytetrafluoroethylene reactor, 500 g of anhydrous hydrogen fluoride was charged, and 32 g of lithium fluoride was dissolved. Moreover, phosphorus pentafluoride and anhydrous hydrogen fluoride were reacted in a separate reactor to obtain phosphorus pentafluoride gas, and 155 g of this was blown into the above-mentioned lithium fluoride solution for reaction. The resulting reaction solution was slowly cooled to −20 ° C. overnight to precipitate lithium hexafluorophosphate crystals. The crystals were separated by filtration and treated with reduced pressure at room temperature to remove the attached hydrogen fluoride. By the above operation, 65 g of lithium hexafluorophosphate crystals having a uniform particle size of about 1 mm were obtained. The concentration of acidic impurities in the crystal was 300 ppm.

Claims (5)

In the production of an electrolytic solution for a lithium ion battery using lithium hexafluorophosphate as an electrolyte, a reaction product produced in a nonaqueous organic solvent is reacted with phosphorus trichloride, chlorine, and lithium chloride, and then generated in the solvent. A method for producing an electrolytic solution for a lithium ion battery, comprising reacting hydrogen fluoride with hydrogen fluoride. In the production of an electrolytic solution for a lithium ion battery using lithium hexafluorophosphate as an electrolyte, a reaction product produced in a nonaqueous organic solvent is reacted with phosphorus trichloride, chlorine, and lithium chloride, and then generated in the solvent. A method for producing an electrolytic solution for a lithium ion battery, comprising reacting hydrogen fluoride with hydrogen chloride and then reacting with lithium chloride. The non-aqueous organic solvent according to any one of claims 1 and 2 is a chain or cyclic carbonate or an ether compound having two or more oxygen atoms. A method for producing an electrolytic solution for a lithium ion battery. The lithium ion according to claim 3, wherein the carbonate ester according to claim 3 is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. Manufacturing method of battery electrolyte. The method for producing an electrolytic solution for a lithium ion battery according to claim 3, wherein the ether compound according to claim 3 is 1,2-dimethoxyethane.