JP4479223B2 - Method for producing fluorine-containing lithium compound - Google Patents

Description

The present invention is represented by the general formula LiMF _X (M represents an element selected from the group consisting of B, P, As, Sb, Bi, V, Nb, and Ta, and x is a number from 4 to 6). More particularly, the present invention relates to a method for easily producing LiMF _X that does not include impurities such as HF and other by-products that adversely affect battery performance.

LiMF _X produced according to the present invention is useful as an electrolyte, particularly as an electrolyte for lithium batteries and lithium ion batteries.

  In recent years, the demand for energy storage devices such as lithium ion batteries has increased rapidly due to the rapid spread of digital portable electronic devices such as mobile phones, personal digital assistants, and notebook computers. In addition, these energy storage devices are attracting attention as power sources for electric vehicles and hybrid vehicles from the viewpoint of global environmental problems and energy saving.

  These energy storage devices require an electrolyte as a constituent material, and an organic electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent is often used as the electrolyte for the purpose of operating at a high operating voltage.

For example, in a lithium ion secondary battery using a lithium metal or a compound of lithium and carbon or a metal other than lithium as a negative electrode and a positive electrode mainly composed of a lithium transition metal oxide, a cyclic structure such as ethylene carbonate or propylene carbonate is used. An electrolyte solution in which LiPF ₆ , LiBF ₄ or the like is dissolved as an electrolyte in a mixed solvent of a carbonate ester and a chain carbonate ester such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate is used exclusively (for example, see Non-Patent Document 1). ).

  Such an electrolyte for a lithium ion battery using a non-aqueous solvent can be used at a high voltage because of the high electrochemical stability of the non-aqueous solvent and the electrolyte. Designed to maximize stability, when impurities are included in the electrolyte, almost all of these impurities are electrochemically stable compared to the non-aqueous solvent and electrolyte. Therefore, it is easy to react inside the battery, which causes deterioration of battery performance.

  For this reason, it is requested | required that the nonaqueous solvent and electrolyte which comprise such electrolyte solution should not contain an impurity.

By the way, as a method for producing LiPF ₆ exclusively used as an electrolyte for a lithium ion battery, a method for producing LiPF, LiOR (R: alkyl group) and the like by reaction with HPF ₆ is also known in the same manner as ordinary salts. However, in this method, since it is mixed as an impurity in LiPF _{6 from} which a hydrolysis product is obtained, a method of producing by reaction of LiF and PF ₅ is generally used (for example, Patent Documents 1 to 4). reference).

The PF ₅ used in this reaction is generally obtained by reacting another pentavalent phosphorus compound such as PCl ₅ with HF and exchanging the ligand, or oxidizing a trivalent phosphorus compound such as PCl _3. It is often produced by performing ligand exchange with HF, and the PF ₅ production reaction and the reaction between the produced PF ₅ and LiF are carried out as a series of reactions (for example, Patent Documents 5 to 5). 10).

However, in these methods using HF for the reaction, there is a high possibility that HF remains attached to LiPF ₆ to be produced. Also, any by-products derived from the original ligand, such as HCl produced as a by-product, remain as impurities in the same manner as HF. And since these impurities have a bad influence on battery performance, the process removed enough after reaction is needed.

In recent years, a new manufacturing method has been proposed to solve the problem of impurities caused by HF. For example, a method for producing LiF and P from other inorganic fluorides has been proposed (see, for example, Patent Document 11). In this method, although there is an advantage of not using HF, the inorganic fluoride used for the reaction is used. fluorine after compound or reaction problems removal of inorganic matter generated by detachment newly generated, also, a method of reacting the LiCl, and PCl ₅ in the presence of F ₂ (for example, see Patent Document 12) are also proposed In this method, unlike HF, F ₂ that can be easily removed is used, but there is still a problem of HCl by-production.
U.S. Pat.No. 3,070,020 JP-A-9-165210 International Publication WO2000-010917 Japanese Patent Laid-Open No. 2001-122604 Japanese Unexamined Patent Publication No. 4-175216 JP-A-5-279003 JP-A-6-056413 International Publication No. WO98-06666 European Published Patent No. 846657 Japanese Patent Laid-Open No. 11-171518 Japanese Patent Laid-Open No. 2001-122605 German patent 10027211 Makoto Ue et al., “Development and Market of Lithium Ion Battery Materials” (CMC) Chapter 6 (1997)

The present invention solves the above-mentioned conventional problems, and general formula LiMF _X (M represents an element selected from the group consisting of B, P, As, Sb, Bi, V, Nb, and Ta, and x is 4 to 4). 6 is a method of producing a fluorine-containing lithium compound represented by the following formula, which can easily produce LiMF _X that does not include impurities such as HF and its by-products that adversely affect battery performance. It aims to provide a possible method.

The method for producing a fluorine-containing lithium compound of the present invention (Claim 1) shows a general formula LiMF _X (M is an element selected from the group consisting of P , As, Sb, Bi, V, Nb, and Ta, and x is the number of 4-6 in a method for producing a fluorine-containing lithium compound represented by.), and LiF, and M element, was premixed, a method of contacting the fluorine gas presence, M The charging molar ratio of LiF to the element is more than 1.0 and 1.5 or less .

Method for producing a fluorine-containing lithium compound of the present invention (claim 2) has the general formula LiMF _X (M represents P, As, Sb, Bi, V, Nb, and an element selected from the group consisting of Ta, x Is a number of 4 to 6.) In the method for producing a fluorine-containing lithium compound represented by the following formula, LiF and M element fluoride or M element fluoride and M element mixture are mixed in advance. The method is a contact method in the presence of fluorine gas, characterized in that the charged molar ratio of LiF to element M and / or its fluoride exceeds 1.0 and is 1.5 or less .

That is, as a result of intensive studies, the present inventors preferably used LiF and M element, or LiF and M element fluoride or a mixture of M element fluoride and M element in the presence of fluorine gas. Is contacted in a single reaction vessel at a temperature of 100 ° C. or higher, that is, reaction of M element and F ₂ in the presence of LiF, reaction of fluoride of M element and F _{2 in the} presence of LiF, Alternatively, it has been found that LiMF _X containing no impurities such as HF and HCl that adversely affect the battery performance of a lithium ion battery can be produced by the reaction of M element and fluoride of M element with F ₂ in the presence of LiF. The present invention has been completed.

According to the method for producing a fluorine-containing lithium compound of the present invention, LiMF _X that does not contain impurities such as HF and its byproducts, which adversely affect battery performance, can be easily produced.

  Hereinafter, embodiments of the method for producing a fluorine-containing lithium compound of the present invention will be described in detail.

In the present invention, the M element to be brought into contact with LiF includes those selected from the group consisting of B, P, As, Sb, Bi, V, Nb, and Ta, and the fluorides thereof are AsF ₃ and SbF _3. , SbF ₅ , BiF ₃ , VF ₂ , VF ₄ , VF ₅ , NbF ₄ , NbF ₅ , TaF _{5 and the} like. In addition, M element can also use 2 or more types together.

  Since LiF and M element and / or fluoride thereof theoretically react at 1: 1 (molar ratio), the charged molar ratio is ideally 1: 1 and is preferably close to this. However, it is difficult to accurately measure the amount by adjusting it to 1: 1, and as an industrial production method, the element of M and / or its element can be easily removed in a small excess of LiF that can be easily removed in the subsequent steps. Compared to the case where the fluoride is excessive, it is preferable. Therefore, the charged molar ratio of LiF to M element and / or its fluoride is usually 1.0 or more and 2.0 or less, preferably more than 1.0 and 1.5 or less.

  Since LiF, M element and / or fluoride thereof are solid, from the viewpoint of reactivity, it is preferable that the crystal is finer and the average particle size is preferably 100 μm or less, more preferably 10 μm or less. A fine powder is preferable. However, if it is too fine, there is a problem such as powder scattering, so that the average particle diameter is preferably 0.01 μm or more, and the average particle diameter is particularly preferably 0.1 to 10 μm. LiF and M element, or LiF and M element fluoride or a mixture of M element fluoride and M element may be mixed in advance and adjusted to a predetermined particle size, or pulverized while mixing. And you may adjust to such an average particle diameter.

  LiF and M element may be separately charged in the reaction vessel to start the reaction, but it is preferable to start the reaction after mixing them in advance. As a mixing method of LiF and M element, or a mixing method of LiF and fluoride of M element or a mixture of fluoride of M element and mixture of M element, they may be mixed in a single apparatus, but convection Using a mixer suitable for each mixing region of shearing and diffusion, mixing may be performed in a plurality of stages.

  Specifically, as the mixer, a mortar can be used in a small amount. Air jet type, shear / diffusion mixing as a preferred device for early convection mixing areas, such as ribbon blender, V blender, conical blender, etc. As a device suitable for the region, a device having a blade, a roll or the like on each of the rotation shafts of the vertical axis rotation type and the horizontal axis rotation type can be exemplified.

Fluorine gas (F ₂ ) used for the reaction is a gas at normal temperature and has extremely high reactivity. Therefore, in the reaction, it is preferable to use without dilution, but it may be diluted with a gas inert to F ₂ . As such an inert gas, a rare gas such as helium or argon, nitrogen, or a perfluoroalkane having 4 or less carbon atoms is used. The concentration of fluorine gas in these inert gases is usually 1% by volume or more, preferably 50% by volume or more. If this concentration is too low, the productivity will deteriorate.

Further, the amount of F ₂ charged with respect to the element M and / or its fluoride must be at least the theoretical amount necessary to form LiMF _X, and is preferably twice or more the theoretical amount. When the amount of F ₂ charged is large, there is no problem on the reaction surface, but there are problems such as the pressure in the apparatus and the recovery of unreacted F ₂ , and therefore, the theoretical amount is preferably 100 times or less, preferably 20 times or less.

The reaction of M element and F ₂ in the presence of LiF, the reaction of M element fluoride and F ₂ in the presence of LiF, or the reaction of M element and M element fluoride and F _{2 in the} presence of LiF, Preferably, the reaction is carried out under heating at 100 ° C. or higher, but this reaction is performed as a raw material supply and reaction form, such as LiF and M element which are solid raw materials, fluoride of LiF and M element, or LiF and M element and M. The reaction tank charged with elemental fluoride may be filled with F ₂ and then heated, or F ₂ may be filled or distributed after heating the reaction tank charged with a solid raw material. Also, within the reaction vessel, it may be supplied solid material while circulating F _2. Also, once F ₂ is filled in the reaction vessel charged with the solid raw material, it is heated for a predetermined time, once cooled, F ₂ is removed with reduced pressure or inert gas, and then F ₂ is filled again and heated. The operation may be repeated. The reaction efficiency can be increased by adjusting the reaction such that the reaction raw materials such as F ₂ are divided and supplied as appropriate.

  The reaction apparatus may be either a batch type or a flow type. In addition, when using a solid raw material that has been sufficiently mixed, stirring in the reaction tank is not essential, but if a reaction tank provided with a vertical or horizontal rotation shaft having blades, rolls, etc. is used, This is preferable because the reaction can proceed smoothly.

From the viewpoint of improving reactivity and safety, before introducing the F ₂ gas into the reaction tank and after completion of the reaction, the reaction tank is evacuated or filled with an inert gas. it is preferably kept, also in the reaction in addition to the intermediate reaction atmosphere (gas phase) is generated in the reaction, substantially only the F ₂ gas or F ₂ is desirably only gas and an inert gas.

  As a method for taking out the product from the reaction apparatus, in the case of a batch method, a method of extracting from the lower part of the apparatus, scooping from the upper part of the apparatus, or extracting the apparatus by overturning the apparatus can be adopted. In the case of carrying out the process, it is possible to adopt a method such as withdrawing as it is while continuously carrying out the reaction with a conveyor or a screw feeder. It is preferable that In addition, when the obtained product is reactive with a compound mixed from the outside environment such as water or oxygen, and when it is necessary to maintain its purity, it is taken out from the apparatus under an inert gas environment. It is necessary to keep it.

  The method of the present invention employs so-called One pot synthesis, in which the target fluorine-containing lithium compound is obtained without supplying a reaction intermediate and the like after supplying reaction raw materials to the reaction system. This is also industrially advantageous in that it can be performed. When one pot synthesis is performed in a batch system, for example, the reaction may be performed in a single reaction tank.

Incidentally, the reaction vessel from the filling or flowing a F ₂ gas, sealing property is high, also, it is required to be able to withstand the pressure and temperature in the reaction conditions described later. However, it is not preferable from the viewpoint of equipment to design so as to withstand conditions that are much stricter than the conditions actually used for the reaction, and any design that is appropriately designed for the selected reaction conditions may be used.

In addition, as a material of the reaction tank, it is necessary to withstand F ₂ gas at a predetermined reaction temperature and pressure under the condition that water, oxygen, and other substances other than raw materials do not exist. Special steels that are generally said to have F ₂ resistance, such as steel, Monel, Inconel, etc., can be mentioned.

  The reaction pressure is preferably 0.1 to 100 atmospheres (0.01 to 10 MPa), and more preferably 0.5 to 10 atmospheres (0.05 to 1 MPa). The reaction temperature is preferably 100 ° C. or higher, particularly 200 ° C. or higher, preferably 1000 ° C. or lower, particularly preferably 500 ° C. or lower.

The reaction time varies depending on the temperature, pressure, the amount of raw material charged, the F ₂ concentration, the number of repetitions in the case of the F ₂ filling method, the F ₂ flow rate per unit time in the case of the F ₂ flow method, Usually, it is 1 to 500 hours.

Examples of the fluorine-containing lithium compound produced by the present invention, preferably LiPF _6, LiBF _4, and the like.

  Hereinafter, the method of the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

Example 1
28.69 mg (1.106 mmol) of LiF and 34.23 mg (1.105 mmol) of red phosphorus were mixed using an agate mortar under a nitrogen atmosphere, and this mixture was charged into a stainless steel pressure vessel having an internal volume of 21 ml. After reducing the pressure to a vacuum state, the atmosphere was replaced with Ar, and the pressure was reduced again to remove oxygen from the atmosphere.

Then, after reducing the pressure again, the container was filled with F ₂ gas until the pressure became 4 atm (0.4 MPa) and sealed, then heated to 300 ° C. and held for 10.5 hours. Then, after allowing to cool to room temperature, the unreacted F ₂ was removed under reduced pressure and replaced with Ar, and then F ₂ gas was filled again to 4 atm, and heated and held in the same manner. After performing this operation four times, the container was released under an Ar atmosphere to obtain 100.86 mg of LiPF ₆ (yield 96.08%).

Examples 2-5
A starting material shown in Table 1 was used in place of red phosphorus (however, the amount used was equimolar with red phosphorus in Example 1), and the reaction conditions were changed as shown in Table 1. When the reaction was carried out in the same manner as in Example 1, the reaction products shown in Table 1 could be obtained in the yields shown in Table 1.

  In any of Examples 1 to 5, the obtained reaction product was identified by X-ray diffraction, and it was confirmed that all were target compounds and there were no peaks of other compounds.

The method of the present invention can easily produce an electrolyte that does not contain impurities such as HF and its by-products that adversely affect battery performance in producing LiPF ₆ as an electrolyte used in an electrolyte for a lithium ion battery. It is a method and its industrial utility is extremely large.

Claims (6)

Fluorine-containing lithium represented by the general formula LiMF _X (M represents an element selected from the group consisting of P , As, Sb, Bi, V, Nb, and Ta, and x is a number from 4 to 6). In a method for producing a compound,
LiF and M element are mixed in advance and then contacted in the presence of fluorine gas ,
A method for producing a fluorine-containing lithium compound, wherein the molar ratio of LiF to M element is more than 1.0 and 1.5 or less . Fluorine-containing lithium represented by the general formula LiMF _X (M represents an element selected from the group consisting of P , As, Sb, Bi, V, Nb, and Ta, and x is a number from 4 to 6). In a method for producing a compound,
LiF and M element fluoride or a mixture of M element fluoride and M element are mixed in advance , and then contacted in the presence of fluorine gas ,
A method for producing a fluorine-containing lithium compound, wherein a charged molar ratio of LiF to M element and / or fluoride thereof exceeds 1.0 and is 1.5 or less . According to claim 1, method for producing a fluorine-containing lithium compound M element and said red phosphorus der Rukoto.   The temperature at which LiF is brought into contact with M element and / or a fluoride of M element in the presence of fluorine gas is 100 ° C or higher and 1000 ° C or lower. A method for producing a fluorine-containing lithium compound.   5. The fluorine according to claim 1, wherein the reaction time for contacting LiF with M element and / or a fluoride of M element in the presence of fluorine gas is 1 to 500 hours. A method for producing a lithium compound. In any one of claims 1 to 5, the production method of the fluorine-containing lithium compound, and a fluorine-containing lithium compound, which is a LiP F _6.