DE10027211A1 - Production of lithium hexafluorophosphate, useful as battery electrolyte, involves reacting phosphorus pentachloride with fluorine-dehydrated hydrofluoric acid and reacting the product with lithium chloride - Google Patents

Abstract

Production of lithium hexafluorophosphate (LiPF6) by (a) reacting phosphorus pentachloride (PCl5) with hydrofluoric acid (HF) and (b) reacting the resulting phosphorus pentafluoride with lithium chloride (LiCl) in HF comprises: (i) carrying out steps (a) and (b) using anhydrous HF from which moisture has been removed by treatment with fluorine (F2) gas; and (ii) contacting the reaction mixture in step (b) with F2 gas.

Description

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a process for the production of lithium hexafluorophosphate (LiPF ₆ ) with high yield and purity, which is one of the wesent union elements that make up a lithium ion secondary battery cell and a lithium polymer battery cell.

Description of the prior art

A lithium ion battery cell or a lithium polymer battery cell is composed essentially of an anode made of a lithium oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or the like, a cathode made of a carbon material such as graphite and an electrolytic solution composed of a solvent in an organic solvent dissolved electrolyte. Examples of the organic solvent include non-aqueous solvents such as a mixed solvent of ethylene carbonate (hereinafter referred to as "EC") and dimethyl carbonate (hereinafter referred to as "DMC"), a mixed solvent of EC and diethyl carbonate (hereinafter referred to as "DEC") and the like. Furthermore, lithium hexafluorophosphate is typically used as an electrolyte.

When the battery cell is charged electrically, the Li-Ion gets into one Cavity in the cathode and is attached to this, whereas that at the Li-ion adheres when the battery cell is electrically discharged to the cathode Anode returns. In this case, the Li-Ion moves through the electrolyte solution solution. As a result, the performance of the battery cell as its Le lithium hexafluorophosphate, which is used in the elec  The electrolyte used in the trolyt solution is very strict with regard to the requirements like purity etc. limited.

In general, lithium hexafluorophosphate is prepared by reacting lithium fluoride (LiF) with phosphorus pentafluoride (PF ₅ ), which is obtained by reacting phosphorus pentachloride (PCl ₅ ) and hydrofluoric acid (HF), in a concentrated hydrofluoric acid solution. In this reaction, when the reaction system for producing lithium hexafluorophosphate contains moisture, lithium oxyfluorophosphate (LiPO _x F _y ) is produced as a by-product, and the lithium hexafluorophosphate is also partially dissolved in the LiF, which then remains as an impurity in the lithium hexafluorophosphate. Accordingly, it is preferred that the moisture content in the reaction system for producing lithium hexafluorophosphate be as low as possible.

A metal component contained in the raw material used in the manufacturing process drive from lithium hexafluorophosphate is used, is included, or a me tall component, which is introduced by corrosion of the equipment, differ the ionization potential of a Li metal. Hence life duration of a battery cell if the metal component contained in the electrolyte is to be shortened.

Furthermore, lithium hexafluorophosphate dissolves in LiF, HF and PF ₃ , which are then converted into the gas state when moisture is contained in the end product, as a result of which an internal pressure forms in the battery cell. In particular, since HF reacts with the organic solvent and also has an effect on corrosion in a case where the battery cell is closed, it adversely affects the stability of the battery cell. For these reasons, the lithium hexafluorophosphate (LiPF ₆ ) used as the electrolyte is subject to strict requirements with regard to purity, moisture content, metal component, the proportion of free hydrofluoric acid and the like.

SUMMARY OF THE INVENTION

The present invention is characterized in that HF, completely dried by means of F _{2, is} used as one of the starting materials for the production of lithium hexafluorophosphate, in order essentially to prevent the formation of lithium oxyfluorophosphate (LiPO _x F _y ) as a by-product and also to use lithium hexafluorophosphate ( Protect LiPF ₆ ) from moisture dissolution, thereby making it possible to produce lithium hexafluorophosphate (LiPF ₆ ) in high purity without reducing the yield.

Likewise, the present invention is characterized in that F ₂ gas of high purity is introduced in a desired amount during the reaction for the production of lithium hexafluorophosphate (LiPF ₆ ) to essentially cause the formation of lithium oxyfluorophosphate (LiPO _x F _y ) as a by-product to prevent the moisture contained in a solid raw material such as PCl ₅ , LiX (X = F, Br, Cl or I) or the like, or other moisture, during which the reaction can be introduced, thereby enabling lithium hexafluorophosphate (LiPF ₆ ) in high purity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT GENE

In a general process for the production of hydrofluoric acid The production of hydrofluoric acid becomes full after the raw materials are constantly dried to control moisture. In egg In the last process, hydrofluoric acid is replaced by anhydrous sulfur acid to remove the moisture contained therein. After you subjected to this drying process contains hydrofluoric acid typically about 100 ppm moisture and also about 50 ppm sulfuric acid, a high-boiling substance due to the passage through water-free sulfur acid.

As described above, the proportion of the metal component in the electrolyte very critical with sufficient quality for battery cells. Because, however  all equipment used in the manufacture of HF is made of steel, hydrofluoric acid itself becomes a large number of metal components contain. The anhydrous hydrofluoric acid resulting from this process re is for direct use as a starting material for the production of an elec trolyts of unsuitable quality for battery cells because they are high Shares in moisture, sulfuric acid, metal components and the like has. Therefore, drying and cleaning is necessary.

The prior art did not yet know the way to fully dry anhydrous hydrofluoric acid using F ₂ gas as in the present invention, in which it could be used in battery cell quality.

In the present invention, the reaction formula according to which the remaining moisture is dried in the anhydrous hydrofluoric acid is as follows:

H ₂ O (in HF) + 2F ₂ → 2HF + OF ₂ (↑)

This drying is carried out under the following conditions:
Blow-through time: 1 to 3 hours
Temperature: -10 to 30 ° C
Flow rate: 1 to 1000 g / h

As shown in the reaction formula, when the moisture in the hydrofluoric acid reacts with F ₂ gas for conversion to hydrofluoric acid, oxyfluoride (OF ₂ ), which has a very low boiling point of -145 ° C, is removed and easily after the reaction evaporated.

In a further characteristic, the present invention relates to the purification of PCl ₅ and LiCl, which are solid starting materials. Commercially available compounds generally have corresponding product specifications in terms of purity, moisture content, metal component and the like. Even if it is well known that the use of a high purity raw material leads to an increase in the quality level of the final product, it causes an increased manufacturing cost, thereby reducing competitiveness. Accordingly, the present invention uses PCl ₅ and LiCl, which are relatively cheap raw materials containing impurities such as moisture, etc.

As described above, when the raw material contains moisture, lithium oxyfluorophosphate (LiPO _x F _y ) can be produced, which is very difficult to isolate by recrystallization.

The present invention is characterized in that F ₂ gas is introduced into a reaction vessel in order to completely remove the moisture contained in the solid starting materials, thereby essentially preventing the formation of lithium oxyfluorophosphate (LiPO _x F _y ).

Moreover, even if lithium oxyfluorophosphate (LiPO _x F _y ) is generated during the reaction, it is converted into lithium hexafluorophosphate (LiPF ₆ ) and oxyfluoride (OF ₂ ) by the F ₂ gas according to the present invention, thereby increasing the yield.

It is also another feature of the present invention that Control of metal components equipment that is covered with a fluororesin such as poly tetrafluoroethylene (hereinafter referred to as "PTFE") is coated for all ver drive are used, and that pipes made of a PFA resin such as Te trafluoroethylene / perfluoroalkyl vinyl ether copolymer can be used as well if two reactors.

The reasons why all the equipment is coated with the fluororesin and the piping made of PFA resin are as follows.

In the prior art, a reactor made of a material was used anhydrous hydrofluoric acid, like a monel metal, can withstand one Ni-based alloy, Cr-based alloy, or the like. On however, such material is very expensive and therefore disadvantageous with regard to one commercial factor. When this material is exposed to air, it comes out also in contact with moisture so that it can corrode.  

Where the equipment used in the reaction is corroded, it will Product is inevitably contaminated with the corroded materials. The Like contaminants act as a factor affecting the metal content in the product elevated.

Where the equipment is contaminated, it must be used throughout the process be repaired. This causes a huge increase in entertainment and entertainment Repair costs and therefore leads to process inefficiency.

In addition, the main reason why two reactors are used is that they allow the manufacturing costs to be reduced by using a relatively cheap one To reduce the starting material and also to ver the content of metal components wrestle.

For lithium hexafluorophosphate (LiPF ₆ ) according to the present invention, either PF ₅ or PCl ₅ can be used as the base raw material. However, it is preferred to use PCl ₅ because PF ₅ is expensive compared to PCl ₅ . When HF ₂ treated and dried with F ₂ gas is added to PCl ₅ , which is in the solid state, in a first reactor, HF and PCl _{5 are} immediately converted into gaseous PF ₅ and HCl (first reaction step).

Therefore, impurities contained in the PCl ₅ , which is in the solid state, remain in the first reactor, and only PF ₅ and HCl, each of which is high in purity, are introduced into a second reactor. As a result, it is possible to produce a high purity lithium hexafluorophosphate (LiPF ₆ ) while using relatively inexpensive PCl ₅ .

In the second reactor there are the following second and third reaction steps performed according to the present invention.

The reaction formulas and conditions for producing lithium hexafluorophosphate (LiPF ₆ ) according to the present invention are as follows:

1. Reaction formulas

• a) First reaction step: PCl ₅ + 5 HF PF ₅ + 5 HCl
• b) second reaction step: PF ₅ + LiCl / HF solution LiPF ₆ / HF solution
• c) third reaction step: LiPF ₆ solution + F ₂ gas

2. Reaction conditions

• a) first reaction step: reaction temperature from -80 ° C to room temperature, reaction pressure from 6 to 28 kg / cm ² .g and reaction time from 10 minutes to 3 hours.
• b) second reaction step: reaction temperature from -30 ° C to room temperature, reaction pressure from 1 to 20 kg / cm ² .g and reaction time from 1 to 3 hours.
• c) third reaction step: F ₂ gas flow rate from 1 to 1,000 g / h, reaction temperature from -10 ° C to 0 ° and contact time from 10 to 30 minutes.

3. Cleaning conditions Recrystallization at a temperature of -80 ° C to 0 ° C.

The present invention, having a number of the features mentioned above, is a process for producing lithium hexafluorophosphate (LiPF ₆ ) with a high yield of 90% or more, a high purity of 99.8% or more, a low moisture content of 20 ppm or less and a low free HF content of 150 ppm or less.

Meanwhile, Japanese Patent Laid-Open Publication No. 4-175,216 discloses a method in which PCl ₅ and HF are reacted to synthesize PF ₅ gas and a solution of HF and LiF is prepared in a separate vessel in which the synthesized PF ₅ gas is introduced to synthesize LiPF ₆ . Such a manufacturing process is carried out under the following conditions: a molar ratio of HF to LiF between 10 and 20, a reaction temperature of -30 to 0 ° C, a feed flow rate of PF ₅ of 5 to 30 liters / h and a particle size of the LiPF _{6 produced} from 1 to 6 mm. A disadvantage of this process is that expensive LiF is used as the starting material. Another disadvantage of this process is that lithium hexafluorophosphate (LiPF ₆ ) is obtained in a yield of less than 70%. The reason for the latter disadvantage is that PF ₅ gas, which has a boiling point similar to HCl, which is generated together with PF ₅ in the reaction of PCl ₅ and HF, largely during the removal of HCl to reduce the pressure reaction get lost.

The above-mentioned Japanese patent publication says that the moisture content in LiPF ₆ , the final product, is not more than 10 ppm, but there is no mention showing that dried HF is used as a raw material. Consequently, it can be assumed that a product which is produced in accordance with the method of the panicky patent publication clearly contains an impurity in LiPO _x F _y . It also shows that in the method of Japanese patent publication, vacuum drying would be carried out over an extended period of time to obtain a final product containing a moisture content of 10 ppm or less. Meanwhile, Japanese Patent Laid-Open No. Sho 60-251109 discloses a method in which PCl ₅ reacts with HF + LiX (X = Cl, F, I, Br), etc. in a single reactor. In this reaction, the ratio of HF to LiX is 20 to 50 weight / weight.

As previously described, this process has the disadvantage that metal components contained in PCl ₅ , LiX and the like can be contained in LiPF ₆ , the final product, due to the use of a single reactor. Furthermore, there is another disadvantage that recrystallizations are inevitably necessary several times to remove the metal components, and it is difficult to use the product as a battery cell quality because its yield is not more than 82% and its purity is only 99%.

Furthermore, the document has no information regarding moisture levels and Metal components, which is counter evidence of low purity.

Japanese Patent Laid-Open Publication No. Heisei 5-279003 discloses a method which is characterized in that PCl ₅ reacts with HF gas to produce PF ₅ and HCl gas, the PF ₅ / HCl gas produced by a Cooling tower flows at a temperature of -40 to -80 ° C and the PF ₅ / HCl gas passed therethrough is introduced into a reactor containing LiF that is dissolved in HF to produce LiPF ₆ .

A disadvantage of this process is that the reaction yield is no longer than 65%.

EP 0643433 A1 relates to a process for the direct production of LiPF ₆ (EC / DEC) by dissolving the starting material NH ₄ PF ₆ in a battery-cell quality solvent such as EC, DEC or the like and allowing the resulting solution to react with LiH. This reaction produces NH ₃ and H ₂ gases, and the former must be removed because it remains dissolved in the solvent.

In this process, the EC or EC solvent used decreases with the progress of the reaction and, consequently, the solvent must be compensated to correspond to the desired concentration. The reaction is also based on the assumption that the conversion is 100%. However, it apparently cannot be used as an electrolytic solution because the unreacted material (NH ₄ PF ₆ , LiH) is likely to exist and because there is no process for removing metal components associated with NH ₄ PF ₆ and LiH gives, etc. Comparisons between the present invention and the above-mentioned prior art are summarized in Table 1 below.

Table 1

Comparison between the invention and the prior art

The following examples are for illustration only and limit in in no way the scope of this invention.

example 1 Drying anhydrous hydrofluoric acid

A gas bubble tube made of PFA resin was placed in a carbon steel container has a capacity of 20 kg, installed, and 18 kg of hydrofluoric acid (you Depoint: 19.2 ° C, moisture content: 100 ppm were placed in this container leads).

This container was immersed in a water bath and at a temperature of Maintained 0 ° C to 10 ° C.

F ₂ gas with a purity of over 99% and a concentration of over 99%, which was generated by operating an F ₂ electrolysis reactor, was introduced into the container, bubbled and contacted with the hydrofluoric acid, the F ₂ gas flow rate and the contact time as reaction conditions were about 61 g / h and 30 min, respectively.

Distillation of anhydrous hydrofluoric acid

A container containing HF dried with F _{2 was} heated to a temperature of 60 ° C to 130 ° C.

HF was distilled by evaporation and condensation while the pressure in the container was maintained at 1 kg / cm ² .G. The distilled HF was analyzed for the moisture content by a turbidity method. The result showed that the distilled HF contained 1 ppm of moisture or less and very small amounts of 1 ppm or less of metal components (Fe, Mn, Ca, Na, K, Pb, Zn, Cd, Ni, Mg, Al) . The dried and distilled HF of this process was used to synthesize LiPF ₆ through the first and second reaction steps mentioned above.

Generation of lithium hexafluorophosphate (LiPF ₆ )

A magnetic stir bar was placed in a PTFE-coated pressure reactor (the first reactor) with a 1.5 liter capacity, 52.93 g of PCl ₅ were introduced into the reactor, the reaction atmosphere was replaced by nitrogen gas (N ₂ ) and the reactor was then replaced with connected to an RF supply line.

Separately, 6.53 g of LiCl was introduced into a PTFE-coated pressure reactor (the second reactor) with a 1.5 liter capacity, the inside of the reactor was replaced with nitrogen gas (N ₂ ), and 300 g of dry HF was then introduced into the reactor.

The first and second reactors were connected together and together men cooled down.

When 100 g rose from there to 13 kg / cm ² .G over time, anhydrous hydrofluoric acid was supplied to the first reactor using a quantitative pump while maintaining the temperature of the reactor at -30 ° C Pressure in the reactor increased to 28 kg / cm ² .G by a simultaneous exothermic reaction.

The first reactor was raised to a temperature of 0 ° C, generated PF ₅ and HCl gas were fed to the second reactor by opening a valve and then left both reactors until their pressure was the same.

After the introduction of PF ₅ gas was completed, the second reactor was warmed to room temperature and the reaction was carried out at this temperature for 2 to 4 hours.

The second reactor was kept at a final pressure of 9 kg / cm ² .G at room temperature.

When the reaction ended, the pressure in the second reactor was released, the reactor cooled to 0 ° C and F ₂ gas then introduced into the reactor (35 liters / h, 30 min). The interior of the reactor was replaced with N ₂ to remove residual F ₂ gas, reaction products were conveyed to and filtered with a filter, and HF gas used as a filtering solvent was then dried under vacuum to 32 To obtain 7 g of LiPF ₆ (93%).

Raw LiPF ₆ was conveyed to a recrystallizer, 100 g of HF was added, and then recrystallized at -40 ° C to obtain pure LiPF ₆ . LiPF ₆ remaining in the stock solution was recovered up to 85% by concentration and recrystallization of the stock solution.

The recrystallized LiPF ₆ was vacuum dried. Analysis results of the dried product showed a purity of 99.8% or more (according to the substrate method), a moisture content of 13 to 18 ppm (according to the Karl Fischer Coulometer method) and a free HF content of 130 ppm (according to the Alkalimetry method). The analysis result of an electrolyte solution (EC / DEC, 1: 1 weight / weight, 1 M), which was produced using the LiPF ₆ obtained, shows an electrical conductivity of 7.6 to 7.9 mS / cm. In addition, a structural analysis of the LiPF ₆ obtained by NMR showed ¹⁹ F-NMR, ³¹ P-NMR and ⁷ Li-NMR. Such an NMR result confirmed that the LiPF _{6 obtained is} almost identical to the standard material.

Meanwhile, even when HCl is introduced into the second reactor together with PF ₅ , HCl does not adversely affect the production of LiPF ₆ because the reactivity of chlorine (Cl) is low compared to that of fluorine (F).

As can be seen from the above description, the present invention provides a process for producing lithium hexafluorophosphate (LiPF ₆ ) in which relatively cheap starting materials such as PCl ₅ , LiCl and the like are used, while a high-purity F ₂ obtained by electrolysis is used in the reaction system. Therefore, the present invention has the part before that it allows the production of lithium hexafluorophosphate (LiPF ₆ ) with high prey and purity.

Although the preferred embodiments of the invention are illustrative for the purposes of those disclosed, those skilled in the art will appreciate that various Changes, additions and exchanges are possible without the protective cover scope and spirit of the invention disclosed in the appended claims to soften.

Claims (4)

1. A process for the preparation of lithium hexafluorophosphate (LiPF ₆ ) using phosphorus pentachloride (PCl ₅ ), lithium chloride (LiCl) and hydrofluoric acid (HF) as starting materials, the process following the steps

• a) reacting the phosphorus pentachloride with the hydrofluoric acid to produce phosphorus pentafluoride (PF ₅ ), and
• b) allowing the phosphorus pentafluoride to react with the lithium chloride in a hydrofluoric acid solution to produce lithium hexafluorophosphate, wherein anhydrous hydrofluoric acid from which moisture has been removed by treatment with F ₂ gas is used in steps (a) and (b), and wherein Step (b) further comprises contacting the reaction system of step (b) with F ₂ gas.

2. The method according to claim 1, characterized in that the anhydrous hydrofluoric acid by treating the anhydrous hydrofluoric acid with F ₂ gas at an F ₂ flow rate of 1 to 1,000 kg / h and a temperature of -10 ° C to 30 ° C is obtained for a contact time of 1 to 3 hours. 3. The method according to claim 1, characterized in that the contact of the reaction system with the F ₂ gas in step (b) by introducing the F ₂ gas into the reaction system of step (b) at a temperature from room temperature to -30 ° C and an F ₂ flow rate of 1 to 1,000 g / h under a pressure of 1 to 20 kg / cm ² g is carried out in order to remove lithium oxyfluorophosphate from the reaction system of step (b). 4. The method according to claim 1, characterized in that the step te (a) and (b) are carried out in the respective reactors.