JP2011091010A - Method for manufacturing for reformed fine-powder positive electrode material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a reformed fine-powder positive electrode material, capable of being formed into particulates in which an average particle size is ≤1 μm and can reduce the content of impurities at a detection limit or below, and capable of being made as an electrode of a lithium ion battery suitable for the lithium ion battery with power of high electron conductivity by improving electron transfer characteristics. <P>SOLUTION: The method for manufacturing for a reformed fine-powder positive electrode material includes the steps of: heating and pressurizing the positive electrode material including impurities, a polar solvent, and a supercritical fluid in a pressure-resistant container so as to make the supercritical fluid at a supercritical state or a subcritical state; gasifying the supercritical fluid by reducing pressure in the pressure-resistant container; separating the positive electrode material which becomes fine powder; polymerizing monomer by heating and pressurizing the positive electrode material which becomes fine powder, monomer which becomes as conductive monomer by polymerization, an oxidizer for polymerizing the monomer, and the supercritical fluid in the pressure-resistant container so as to make the supercritical fluid at a supercritical state or a subcritical state; and gasifying the supercritical fluid by reducing pressure in the pressure-resistant container. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a modified finely powdered positive electrode material. More specifically, impurities in the positive electrode material raw material can be removed to have a high purity, and the fine powdery material is further improved in conductivity. The present invention relates to a method for producing a modified finely divided positive electrode material.

  In recent years, research on secondary batteries for use in portable electronic devices and hybrid vehicles has been underway. As typical secondary batteries, lead storage batteries, alkaline storage batteries, lithium ion batteries, and the like are known. Among various secondary batteries, the lithium ion battery has advantages such as high output and high energy density.

  A lithium ion battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte having an active material capable of reversibly inserting and removing lithium ions.

As the positive electrode material of the lithium ion battery, metal oxide, metal sulfide, polymer, or the like is used. For example, a lithium-free compound such as TiS ₂ , MoS ₂ , NbSe ₂ , V ₂ O ₅ , LiMO ₂ ( M = Co, Ni, Mn, Fe, etc.), lithium composite oxides such as LiMn ₂ O ₄ are known.

  Metal-containing compounds such as the above metal oxides, metal sulfides, lithium-free compounds, and lithium composite oxides are industrially produced from natural minerals.

  For example, titanium is naturally produced in various forms as titanium dioxide, such as gold beryl (rutile), anorthite (anatase), brookite, ilmenite, perovskite, titanite. Titanium disulfide is produced from these minerals through several synthetic steps.

  Molybdenum is produced as molybdenite (molybdenite), molybdenite (wolfenite), water lead sha (molybdite), etc. Molybdenum disulfide is produced by refining the molybdenite ore and other minerals as starting materials.

  Manganese is the heavy metal most widely present on the earth after iron, and is produced as minerals such as soft manganese ore, hard manganese ore and limonite. Lithium manganate can be produced by eutectic melting of manganese dioxide produced from a manganese mineral and an alkali metal oxide.

  Iron, cobalt, and nickel are also produced from minerals and refined to produce metallic iron, metallic cobalt, and metallic nickel. Using these as raw materials, various iron compounds, cobalt compounds, and nickel compounds are synthesized.

  By the way, the material forming the positive electrode in the lithium ion battery must be of high purity in order to realize discharge over a long period of time, and as much as possible to increase the mounting density of the positive electrode in the lithium ion battery. In order to improve the charge transfer reaction of the lithium ion battery, it is required to have high conductivity.

  However, industrially available cathode materials for lithium ion batteries contain mineral-derived impurities, impurities derived from various chemicals used to synthesize the final cathode material, and the like. .

  Various positive electrode materials can be cleaned using pure water and chemicals before being processed into positive electrodes, or various purification operations can be applied to increase their purity, but they can be discharged for a long time. In order to realize a lithium ion battery, development of a positive electrode material having high conductivity has been promoted by further increasing the purity of the current positive electrode material.

For example, the invention described in Patent Document 1 relates to a method for producing a positive electrode material for a lithium ion battery and a lithium ion battery. The invention described in this Patent Document 1 is “general formula Li _x A _y PO ₄ (0.8 <x <2, 0 <y <1.5, where A is Co, Ni, Mn, Fe, Cu, A method for producing a positive electrode material for a lithium ion battery represented by: one selected from Cr, wherein Li (lithium) component, P (phosphorus) component and A component (where A is Co, Ni, Mn, Li _x A _y PO ₄ is synthesized by reacting one type selected from Fe, Cu, and Cr in a fluid in a subcritical state, a critical state, or a supercritical state. a method for producing a positive electrode material "(see claim 1 of Patent Document 1)," the general formula _{Li x a y B z C w} PO 4 (B and C Mg, Ca, Zn, Ge, Ti, Sr, Ba , Sc, Y, Al, Ga, In, Si, B, rare earth element? It is one kind selected from each other, 0.8 <x <2, 0 <y <1.5, 0 ≦ z <1.5, 0 ≦ w <1.5, z and w are 0 at the same time A Li (lithium) component, a P (phosphorus) component, and an A component (where A is Co, Ni, Mn, Fe, Cu, Cr). In addition to one selected from Mg, Ca, Zn, Ge, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, and rare earth elements. A method for producing a positive electrode material for a lithium ion battery, comprising reacting components in a fluid in a subcritical state, a critical state, or a supercritical state to synthesize the Li _x A _y B _z C _w PO ₄ ”( (See claim 2 of Patent Document 1).

However, referring to paragraph number 0021 of Patent Document 1, “the synthesized product is then collected by filtration by suction filtration or the like, washed with water, and then dried to obtain a general formula Li _x A _y B _z C. _w PO ₄ (A is one selected from Co, Ni, Mn, Fe, Cu, Cr, B and C are Mg, Ca, Zn, Ge, Ti, Sr, Ba, Sc, Y, Al, Ga, It is one kind selected from In, Si, B and rare earth elements, 0.8 <x <2, 0 <Y <1.5, 0 ≦ z <1.5, 0 ≦ w <1.5. ”Is obtained, and the purity of the obtained positive electrode material for a lithium ion battery is not described. Referring to the example of Patent Document 1, in Example 1, “... after the reaction was performed, the reaction tube was taken out and quenched with cooling water to stop the reaction. Thereafter, the reaction product was suction filtered. later recovered by filtration, shows a X-ray diffraction pattern of the reaction product to dry. FIG. Thereby, the reaction product there is a description that was identified as LiFePO _4. ", the purity of the reaction product There is no description about. Even if other examples disclosed in Patent Document 1 are referred to, there is no description about the purity of the reaction product.

  Patent Document 2 discloses a lithium-based composite metal oxide capable of inserting and extracting lithium ions, wherein at least a part of the crystal structure has a single crystal structure. (Refer to claim 1 of patent document 2). This lithium-based composite metal oxide is “a method for producing a lithium-based composite metal oxide capable of inserting and extracting lithium ions, in which at least lithium ions and other metal ions are placed in supercritical or subcritical water. And a hydrothermal reaction to produce a lithium-based composite metal oxide at least partially having a single crystal structure ”(Patent Document 2). (See claim 4).

  According to the description of Patent Document 2, “.... Further, oxides synthesized by hydrothermal reaction at about 200 to 300 ° C. generally contain crystal water or hydroxyl groups in the crystal surface or on the crystal surface. However, by synthesizing or processing by hydrothermal reaction in subcritical or supercritical water near the critical point, lithium-based composite metal oxides that do not contain crystal water or hydroxyl groups and have high crystallinity can be obtained. There is no description about the purity of the synthesized lithium-based composite metal oxide. Moreover, there is no disclosure of a technique for further improving the conductivity of the obtained lithium-based composite metal oxide.

The invention described in Patent Document 3 states that “a raw material aqueous solution in which a lithium salt aqueous solution, a manganese salt aqueous solution, and an alkali concentration adjusting solution are mixed so that the molar ratio of Li to Mn (Li / Mn) is between 1 and 10. A method for producing a powder material for a positive electrode of a secondary battery, wherein the powder is obtained by drying the reaction product after reacting in a supercritical state or subcritical state of water, wherein the raw material aqueous solution is used as the alkali concentration adjusting liquid. ^{Is a} method for producing a powder material for a positive electrode of a secondary battery, wherein the hydrogen ion concentration is adjusted to 1.5 × 10 ⁻¹³ or less (see claim 1 of Patent Document 3).

  According to the example disclosed in Patent Document 3, “the recovered slurry-like reaction product is filtered through a glass filter (not shown), and then the solid content is dried in a desiccator containing anhydrous phosphoric acid for 24 hours. “Powder material was obtained” (paragraph number 0024 of Patent Document 3, Example 1), “Positive electrode powder material was obtained in the same manner as Example 1” (Patent Document 3) Paragraph Nos. 0025, 0026, 0027, 0028 and Examples 2 to 4), and there is no description of how to refine the positive electrode powder to increase its purity. Moreover, although the positive electrode is produced using the obtained positive electrode powder material as it is, in the present situation where further improvement of the discharge characteristics of the lithium ion electrode is desired, Patent Document 3 discloses the discharge characteristics of the lithium ion electrode. It does not disclose useful information about improvement.

  The invention described in Patent Document 4 relates to a supercritical fluid composition comprising carbon dioxide and a cyclopentadienyl compound having a specific chemical structure (claims of Patent Document 4). This patent document 4 discloses that the disclosed supercritical fluid composition is “a precious metal that is difficult to remove with an aqueous cleaning solution can be complexed and eluted into the supercritical fluid, and a strong oxidizing agent or acid can be dissolved. Since it is not used in a large amount, it does not damage the substrate or the device. ”(Patent Document 4, paragraph number 0008). Furthermore, according to the description of Patent Document 4, “in order to remove precious metals more efficiently and to remove contaminating metals such as Na, K, and Fe other than precious metals contained on the substrate surface, water, ammonia, KOH Basic substances such as amines, or acidic substances such as formic acid, acetic acid, HCl, HF, HI, fluorine or sulfuric acid surfactants, pyridine, 2,2′-bipyridine, ethylenediamine, ethylenediaminetetraacetic acid, etc. Pyridine or amine-based chelating agents may be added, and these compounds may be mixed alone or in combination of two or more, although the mixing ratio is not particularly limited. In addition, each single element is preferably less than 10 mol% in the supercritical composition, and noble metals suitable for cleaning with the supercritical fluid of the present invention include Au, Ag, Ru, Rh, Pd, Os, Ir, Pt is mentioned, and it is particularly suitable for Ru.

However, in Patent Document 4, “... a Ru-contaminated 2-inch silicon substrate was placed in the cleaning tank. Then, the fluid 1 container was filled with ethylenecyclopentadienyl, and so on. The inside of the tank was completely carbon dioxide atmosphere, returned to normal pressure, the silicon substrate in the cleaning tank was taken out, and surface analysis was performed.As a result, the Ru contamination amount before cleaning was 1E + 14 atom / cm ² . The only empirical data that “Ru contamination amount decreased to 1E + 08 atom / cm ² after cleaning” indicates that only Ru has been removed from the contaminated substrate surface of the silicon substrate. This is reported as an effect (see paragraph No. 0018 of Patent Document 4).

  The invention described in Patent Document 5 states that “lithium ions and metal ions of other metals are hydrothermally reacted using water under supercritical or subcritical conditions as a solvent to obtain a lithium-based metal composite oxide. The method for producing a lithium-based metal composite oxide characterized by the above (claim 1 of Patent Document 5).

The invention described in Patent Document 5 states that “LiCoO ₂ fine particles can be obtained by various methods as described above. However, these methods have the following drawbacks.

First, in the solid phase method, LiCO ₃ that is an unreacted residue is contained in the product, and it is difficult to remove this. There are also problems that the reaction time is long and the reaction temperature is high. In the spray pyrolysis method, the crystallinity of LiCoO ₂ is better as the temperature is higher. Accordingly, in order to obtain a good quality LiCoO ₂ , a treatment at a considerably high temperature is required. Further, it is considered difficult to make the particle diameter 0.56 μm or less. Further, the sol-gel method requires a very long treatment, and there is a problem that the cost increases when considering industrialization. (See paragraph numbers 0009 and 0010 of Patent Document 5),
“... To obtain a method for producing a lithium-based metal composite oxide capable of obtaining a good quality lithium metal oxide compound such as LiCoO ₂ in a relatively low temperature and in a short time” is an object of the invention (Patent Documents) 5 paragraph number 0011).

  According to the description of Patent Document 5, there is an evaluation that “the diameter of the generated particles is 400 nm to 1 μm, which is quite fine particles” (paragraph number 0057 of Patent Document 5).

  On the other hand, in the technical field of lithium ion batteries, there is a demand for high performance positive electrode materials having finer particle diameters and improved electron transfer characteristics for the purpose of improving lithium ion battery characteristics.

JP 2004-95386 A JP 2001-163700 A JP 2001-202947 A JP 2004-59837 A JP 2000-72445 A

  The present invention aims to eliminate some of the problems of conventional lithium ion batteries, and more specifically, it can be formed into fine particles that can be evaluated as having an average particle size of 1 μm or less, Impurity content can be reduced to below the detection limit, and further, electron transfer characteristics can be further improved to provide a lithium ion battery electrode suitable for a lithium ion battery having high electron conductivity. It is an object of the present invention to provide a method for producing a modified finely powdered positive electrode material.

Means for solving the problems are as follows:
(1) A cathode material material containing a cathode material and a material other than the cathode material, a polar solvent, and a supercritical fluid, and the supercritical fluid is in a supercritical state or a subcritical state in a pressure vessel. So as to heat and pressurize, then gasify the supercritical fluid by lowering the pressure in the pressure vessel, and separate the positive electrode material that became fine powder,
The finely divided positive electrode material, a monomer that becomes a conductive polymer by polymerization, an oxidant for polymerizing the monomer, and a supercritical fluid, wherein the supercritical fluid is in a supercritical state or A method for producing a modified fine powder cathode material, characterized in that the monomer is polymerized by heating and pressurizing so as to be in a subcritical state, and then the pressure in the pressure vessel is lowered to gasify the supercritical fluid. And
(2) In the method for producing a modified finely divided positive electrode material according to (1), the polar solvent is water and / or a water-soluble polar organic solvent, and the supercritical fluid is carbon dioxide,
(3) In the method for producing a modified finely powdered positive electrode material according to (1) or (2), the positive electrode material is LiMn ₂ O ₄ , LiFeO ₂ , LiCoO ₂ , LiNiO ₂ , a general formula Li _x A _y. Phosphate represented by PO ₄ (where 0.8 <x <2, 0 <y <1.5, A is one selected from Co, Ni, Mn, Fe, Cu, and Cr), and general wherein _{Li x A y B z C w} PO 4 ( provided that, B and C is Mg, Ca, Zn, Ge, Ti, Sr, Ba, Sc, Y, Al, Ga, in, Si, B, and rare earth elements Selected different types, 0.8 <x <2, 0 <y <1.5, 0 ≦ z <1.5, 0 ≦ w <1.5, z and w are not 0 at the same time ) At least one selected from the group consisting of phosphates,
(4) In the method for producing a modified finely powdered positive electrode material according to any one of (1) to (3), the positive electrode material raw material contains at least 0.5% by mass of a substance other than the positive electrode material as an impurity. Contains,
(5) In the method for producing a modified finely divided cathode material according to any one of (1) to (3), the monomer is selected from the group consisting of 3,4-ethylenedioxythiophene, pyrrole, and aniline. At least one monomer selected.

  According to the present invention, fine particles having a uniform particle size with an average particle size of 1 μm or less, the purity is so high that the impurity content is below the detection limit, and the amount of electron transfer can be improved. A modified finely divided positive electrode material suitable for a positive electrode material of a lithium ion battery with improved electrical conductivity can be easily produced by a simple operation.

FIG. 1 is a schematic explanatory view showing a modified fine powdery cathode material production apparatus as an example for carrying out the method of the present invention. FIG. 2 is an SEM image of a commercially available product called “LiMn ₂ O ₄ ”. FIG. 3 is an SEM image of the high purity LiMn ₂ O ₄ powder obtained through the second step. FIG. 4 is an image obtained by EDS analysis of the high purity LiMn ₂ O ₄ powder obtained through the second step. FIG. 5 is an image obtained by EDS analysis of the high purity LiMn ₂ O ₄ powder obtained through the second step. FIG. 6 is an image obtained by EDS analysis of the high purity LiMn ₂ O ₄ powder obtained through the second step. FIG. 7 is an image obtained by EDS analysis of the high purity LiMn ₂ O ₄ powder obtained through the second step. FIG. 8 is an image obtained by EDS analysis of the high purity LiMn ₂ O ₄ powder obtained through the second step.

  In the method of the present invention, (1) a positive electrode material, a polar solvent, and a supercritical fluid are heated and pressurized in a pressure vessel so that the supercritical fluid is in a supercritical state or a subcritical state, Next, the inside of the pressure vessel is returned to, for example, normal pressure, and a first step of separating the finely divided positive electrode material, (2) the finely divided positive electrode material, a monomer that becomes a conductive polymer by polymerization, An oxidant for polymerizing the monomer and a supercritical fluid are heated and pressurized in a pressure resistant container so that the supercritical fluid is in a supercritical state or a subcritical state, and then the monomer is polymerized. A second step of returning the inside of the pressure vessel to, for example, normal pressure.

  The positive electrode material raw material in the first step contains a positive electrode material and a material other than the positive electrode material. The positive electrode material is also referred to as a positive electrode active material. The substance used as the positive electrode material can be used as the positive electrode material in the present invention.

As a positive electrode material, a general formula Li _1-x M _{1 + x} O ₂ (where M is at least one element selected from Fe, Co, Ni, Cr, V, Mn, Ti, Sc, and Y. x is , 0.1 or more and 0.9 or less), a general formula LiMn _2−x M _x O ₄ (where M is a kind selected from Fe, Co, Ni, Mg, and Nb) Element, and x is 0 or more and 1.5 or less.), And phosphate compounds such as transition metals such as Fe, Mn, Co, and Ni having an olivine structure.

Preferable examples of the positive electrode material represented by the general formula LiMn _2−x M _x O ₄ include LiMn ₂ O ₄ . Preferable examples of the phosphate compound such as transition metal having the olivine structure include, for example, the general formula Li _x A _y PO ₄ (where 0.8 <x <2, 0 <y <1.5, , Mn, Co, Ni, Cu and Cr), and a general formula Li _x A _y B _z C _w PO ₄ (where B and C are Mg, Ca, Zn, It is a different kind selected from Ge, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, and rare earth elements, and 0.8 <x <2, 0 <y <1.5. , 0 ≦ z <1.5, 0 ≦ w <1.5, and z and w are not 0 at the same time) at least one selected from the group consisting of phosphates.

As the positive electrode material, LiFeO ₂ , LiCoO ₂ , LiNiO _{2 and the} like can also be suitably employed.

  The positive electrode material used in the method of the present invention contains the positive electrode material and a material that does not form the positive electrode material. Substances that do not form positive electrode materials are usually referred to as impurities. In addition, the positive electrode material contains various substances as impurities depending on the raw material of manufacture. Whatever the impurities are, according to the method of the present invention, the impurities can be removed.

Commercial products called positive electrode materials often contain impurities. For example, commercially available products referred to as "LiMn ₂ O _4", 0.07% of Ca as LiMn ₂ O ₄ and impurities serving as a positive electrode material, 0.01% to Fe, 0.04% of K, the Na 0. There is an example containing 18%, Ni 0.001%, and Mg 0.04%. Although not all commercial products have been investigated, commercial products that are considered to be positive electrode materials or positive electrode active materials include minerals that are raw materials for producing positive electrode materials, and various chemicals used as raw materials obtained from these minerals. In some cases, a substance that is mixed when the positive electrode material is produced by reacting the above is included as an impurity.

  In the method of the present invention, a commercial product containing the impurities in a proportion of at most 0.1 to 0.5% by mass with respect to the weight of the commercial product can be used as a positive electrode material, and an alkaline earth metal compound For example, a commercial product containing an alkaline earth metal oxide as an impurity can be used as the positive electrode material.

  Examples of the polar solvent in the method of the present invention include water and a water-soluble polar organic solvent.

  As said water, ion-exchange water, ultrapure water, etc. can be used.

  Examples of the water-soluble polar organic solvent include lower alcohols that dissolve in water such as methyl alcohol, ethyl alcohol, and propyl alcohol, or are miscible with water, particularly lower alcohols having 1 to 3 carbon atoms, formaldehyde, acetaldehyde, and ethylaldehyde. Water-soluble aldehydes, water-soluble ketones such as acetone, methyl ethyl ketone and diethyl ketone, water-soluble ethers such as dimethyl ether and methyl ethyl ether, acetonitrile, tetrahydrofuran, and dimethyl sulfoxide can be mentioned. Mixing two or more of the above polar solvents May be used.

  Among these, the water-soluble polar organic solvent suitable for the method of the present invention is preferably the lower alcohol, for example, a lower alcohol having 1 to 3 carbon atoms, the water-soluble ether, the water-soluble aldehyde, or the water-soluble ketone.

  In the method of the present invention, the polar solvent has an action of extracting impurities contained in the positive electrode material. The amount of the polar solvent used can be appropriately determined according to the mode of carrying out the method of the present invention as long as the extraction effect can be exhibited, and specifically 10 to 1000 mass with respect to the positive electrode material raw material. %, Preferably 100 to 200% by mass. If the amount of the polar solvent used is smaller than the lower limit, the positive electrode material may have less effect of removing impurities, and if the amount used is larger than the upper limit, the impurities removed to the extent that the amount of the polar solvent is increased. The effect may not be seen.

  Examples of the supercritical fluid include a substance that is a gas at normal temperature and normal pressure, becomes a supercritical state or a subcritical state under the conditions of a heating temperature of 40 to 500 ° C. and a pressure of 7 to 50 MPa. Preferred examples of such supercritical fluids include carbon dioxide and saturated or unsaturated lower hydrocarbons such as methane, ethane, propane, ethylene, and propylene. A particularly preferred supercritical fluid in the process of this invention is carbon dioxide.

  The amount of supercritical fluid such as carbon dioxide used in the pressure vessel is usually 80 to 1000 g, preferably 95 to 800 g, with respect to 5 g of the positive electrode material.

  In the method of the present invention, as the first step, the positive electrode material raw material, the polar solvent, and the supercritical fluid are accommodated in a pressure resistant container so that the supercritical fluid is in a subcritical state or a supercritical state in the pressure resistant container. Then, the inside of the pressure vessel is pressurized and heated. The pressure and temperature realized in the pressure vessel can be appropriately determined according to the type of the supercritical fluid. The time for maintaining the supercritical fluid in the subcritical state or the supercritical state in the pressure vessel is appropriately determined according to the type of the positive electrode material, and usually 30 minutes to 20 hours is sufficient. However, a longer time may be required depending on the type of the positive electrode material.

  When carbon dioxide is employed as the supercritical fluid, the pressure in the pressure vessel is 7-25 MPa, preferably 9-15 MPa, and the temperature in the pressure vessel is maintained at 85-110 ° C, preferably 95-105 ° C. Examples of the time for maintaining the pressure and temperature include 0.5 to 3 hours, preferably 1 to 2 hours.

  When the supercritical fluid is maintained in the subcritical state or the supercritical state in the pressure vessel, the inside of the pressure vessel is preferably stirred by an appropriate stirring means.

  After maintaining the inside of the pressure vessel in a subcritical state or a supercritical state for a predetermined time, the pressure is lowered to such an extent that the supercritical fluid in the pressure vessel is gasified.

  When carbon dioxide is employed as the supercritical fluid, carbon dioxide that has been in a supercritical state or a subcritical state is gasified only by setting the inside of the pressure resistant vessel to normal pressure.

  By gasifying the supercritical fluid, there is a gaseous supercritical fluid, a liquid polar solvent and fine powder in the pressure vessel, so that the gaseous supercritical fluid is discharged outside the pressure vessel, Separate polar solvent and fine powder. The separation operation can be performed, for example, as an operation for discharging the polar solvent in the pressure vessel through the filtering means to the outside of the pressure vessel.

  In the method of the present invention, the positive electrode material in powder form is produced by the first step. The positive electrode material obtained in the first step can be used as it is for a lithium ion secondary battery as a positive electrode material. However, the present invention aims to produce a positive electrode material with further improved conductivity. The positive electrode material obtained in the step is subjected to the second step.

  In the method of the present invention, in the second step, the fine powdered positive electrode material obtained in the first step, a monomer that becomes a conductive polymer by polymerization, an oxidant for polymerizing the monomer, a supercriticality In the pressure vessel, the monomer is polymerized by heating and pressurizing so that the supercritical fluid is in a supercritical state or a subcritical state, and then the pressure in the pressure vessel is lowered to supercritical fluid. Gasify.

  The pressure vessel used in the second step can be used again as it is in the first step, and is separate from the pressure vessel used in the first step. A pressure vessel having the same or different shape and structure as the pressure vessel used may be employed.

  Examples of the supercritical fluid used in the second step include the same type of supercritical fluid used in the first step. Further, a supercritical fluid different from the supercritical fluid used in the first step may be used, and any one of the supercritical fluids exemplified as the supercritical fluid used in the first step. Seeds may be used. Moreover, the supercritical fluid obtained by recovering the supercritical fluid used in the first step after the completion of the first step can also be used in the second step.

  The amount of supercritical fluid such as carbon dioxide used in the pressure vessel is usually 80 to 1000 g, preferably 95 to 800 g, with respect to 1 g of finely divided positive electrode material.

  The monomer that becomes a conductive polymer by polymerization may be a conductive polymer exemplified below by polymerization. Examples of the conductive polymer include poly (3,4-ethylenedioxythiophene), polyacetylene, polyparaphenylene, Examples thereof include polyphenylene vinylene, polypyrrole, poly (3-methylthiophene), polyaniline, polythiophene, polythienylene vinylene, polyfluorene, polyacene and the like. Preferable conductive polymers include at least one polymer selected from the group consisting of poly (3,4-ethylenedioxythiophene), polypyrrole, and polyaniline.

  Examples of the monomer that becomes the conductive polymer by polymerization include, for example, 3,4-ethylenedioxythiophene, acetylene, paraphenylene, phenylene vinylene, pyrrole, 3-methylthiophene, aniline, thiophene, thienylene vinylene, fluorene, acene, and the like. These derivatives can be mentioned.

  The usage-amount of the said monomer in a 2nd process is 10-20 mass% normally with respect to the fine powder-form positive electrode material obtained at the 1st process. When the amount of the monomer used is less than the above range, the conductivity of the positive electrode material obtained through the second step may not be improved so much. May decrease.

Examples of the oxidizing agent used when the monomer is made into a conductive polymer by oxidative polymerization include FeCl ₃ , Fe (ClO ₄ ) ₃ , iron such as an iron (III) salt of an organic acid and an inorganic acid having an organic group ( III) salts, dichromates such as _{H 2 O 2, K 2 Cr} 2 O 7, alkali metal persulfates, ammonium persulfate, alkali metal perborates, copper such as potassium permanganate and copper tetrafluoroborate Salt, peroxodisulfate and the like.

  Examples of the iron (III) salt of an inorganic acid having an organic group include a monoester iron (III) salt of sulfuric acid with an alkanol having 1 to 20 carbon atoms such as an Fe (III) salt of lauryl sulfate.

  Examples of the iron (III) salt of an inorganic acid having an organic acid include Fe (III) salts of alkyl sulfonic acids having 1 to 20 carbon atoms such as methane and dodecane-sulfonic acid, and 2-ethylhexylcarboxylic acid. Fe (III) salts of aliphatic carboxylic acids having 1 to 20 carbon atoms, Fe (III) salts of aliphatic perfluorocarboxylic acids such as trifluoroacetic acid and perfluorooctanoic acid, aliphatic dicarboxylic acids such as oxalic acid Fe (III) salts of aromatic sulfonic acids optionally substituted with alkyl groups of 1 to 20 carbon atoms, such as Fe (III) salts, benzenesulfonic acid, paratoluenesulfonic acid, dodecylbenzenesulfonic acid Etc.

  The amount of the oxidizing agent used is larger than the amount theoretically necessary for oxidative polymerization of the monomer, and is preferably 0.1 to 2 equivalents per mole of the monomer.

  In the second step, it is preferable that any one or a mixture of two or more of the polar solvents described above as a polar solvent that can be used in Step 1 together with the monomer is charged in a pressure resistant container.

  When ethanol is used as the polar solvent in the second step, the mixing ratio of ethanol and the monomer in the pressure-resistant container is usually 1 to 200 parts by mass of ethanol, preferably 50% of ethanol with respect to 1 part by mass of the monomer. -150 parts by mass. If the mixing ratio of the ethanol is less than the above range, moisture is lost during drying / dispersion operation and drying occurs, which may cause inconvenience that the conductive polymer formed by polymerization of the monomer shrinks. If the blending ratio is exceeded, the water dispersion concentration of the processed product becomes thin and cannot be used as it is, and there may be a disadvantage that the concentration must be adjusted for use.

  In this second step, there is no restriction on the order in which the supercritical fluid, the fine powdered positive electrode material, the monomer, the oxidant, and the optionally added ethanol are charged into the pressure vessel. In addition, the monomer and the fine powdered positive electrode material may be mixed before being put into the pressure vessel, and the resulting mixture may be put into the pressure vessel.

  In the second step, it is preferable to add a surfactant in addition to the polar solvent charged into the pressure vessel together with the monomer.

  Examples of the surfactant include a nonionic surfactant, and examples thereof include a product name of DYNOL 604 acetylenic dialcohol made by Air Products and Chemicals.

  The amount of the surfactant used is preferably 0.01 to 0.1 mol with respect to 1 mol of the monomer. Within the above range, the dispersibility of the monomer in the polar solvent is stabilized.

  In the second step, when carbon dioxide is employed as the supercritical fluid, the pressure in the pressure vessel is 7 to 25 MPa, preferably 9 to 15 MPa, and the temperature in the pressure vessel is 85 to 110 ° C, preferably 95 to 105 ° C. The time for maintaining the inside of the pressure vessel in the subcritical state or supercritical state is usually 0.5 to 3 hours, preferably 1 to 2 hours.

  When the supercritical fluid is maintained in the subcritical state or the supercritical state in the pressure vessel, the inside of the pressure vessel is preferably stirred by an appropriate stirring means.

  After maintaining the inside of the pressure vessel in a subcritical state or a supercritical state for a predetermined time, the pressure is lowered to such an extent that the supercritical fluid in the pressure vessel is gasified.

  When carbon dioxide is employed as the supercritical fluid, carbon dioxide that has been in a supercritical state or a subcritical state is gasified only by setting the inside of the pressure resistant vessel to normal pressure.

  Carbon dioxide gasified in the pressure vessel may be released as it is outside the pressure vessel, or the carbon dioxide gas may be recovered and reused.

  When gaseous carbon dioxide is released from the pressure vessel, fine powder can be obtained. This fine powder is a composite of a positive electrode material and a conductive polymer. Here, the term “composite” indicates a form in which fine particles of a conductive polymer are attached to the surface of a fine powdery positive electrode material, a form in which the positive electrode material and the conductive polymer are integrated with each other, and the like. However, at present, it has been confirmed that the conductive polymer is attached to the particle surface of the fine powdered positive electrode material obtained in the second step.

  An example of an apparatus for producing the method according to the present invention will be described with reference to FIG.

  FIG. 1 shows a schematic view of a modified fine powdery cathode material production apparatus which is an example suitable for carrying out the present invention. As shown in FIG. 1, the modified finely powdered positive electrode material manufacturing apparatus 1 includes a pressure vessel 2, a carbon dioxide cylinder 3, a polar solvent storage tank 4, a manual valve 5, a monomer supply device 6, an oxidizing agent. And a supply device 7. The modified pulverized positive electrode material manufacturing apparatus 1 shown in FIG. 1 can realize the first step and the second step in the present invention by using one pressure-resistant vessel 2.

  The pressure vessel 2 accommodates a positive electrode material raw material, a polar solvent, and carbon dioxide, which are objects, as long as the carbon dioxide can be brought into a supercritical state while the pressure vessel 2 is kept airtight. It may be a scale and may have various structures with various materials. It is preferable that the pressure vessel 2 includes a stirrer 2A for stirring the inside of the pressure vessel 2. A manual valve 5 is connected to the subsequent stage of the pressure vessel 2.

  The carbon dioxide cylinder 3 stores carbon dioxide, which is an example of a supercritical fluid in the present invention, and supplies carbon dioxide gas to the pressure vessel 2. The carbon dioxide cylinder 3 is connected to the front stage of the pressure vessel 2. A pump 3A and a manual valve 3B are connected between the carbon dioxide cylinder 3 and the pressure vessel 2 in this order.

  The polar solvent storage tank 4 stores pure water, which is a preferred example of a polar solvent, and supplies the pure water to the pressure vessel. The polar solvent storage tank 4 is connected to the front stage of the pressure vessel 2. Between the polar solvent storage tank 4 and the pressure vessel 2, a pump 4 </ b> A and a manual valve 4 </ b> B are connected in this order.

  The pressure vessel 2 is formed so that the monomer can be charged into the pressure vessel 2 from the monomer supply device 6 via a pipe. This pipe is provided with a valve (not shown), which is closed when the carbon dioxide in the pressure vessel 2 is maintained in the subcritical state or the supercritical state.

  The pressure vessel 2 is formed so that the oxidant can be introduced into the pressure vessel 2 from the oxidant supply device 6 via a pipe. This pipe is provided with a valve (not shown), which is closed when the carbon dioxide in the pressure vessel 2 is maintained in the subcritical state or the supercritical state.

  The operation of the modified finely powdered positive electrode material manufacturing apparatus 1 will be described as follows.

  First, the positive electrode material is put into the pressure vessel 2.

  Next, the pump 3 </ b> A and the manual valve 3 </ b> B are operated to supply carbon dioxide in a supercritical state from the carbon dioxide cylinder 3 to the pressure vessel 2.

  Further, the pump 4A and the manual valve 4B are operated to supply pure water from the polar solvent storage tank 4 to the pressure resistant container 2. Note that the pure water and carbon dioxide supplied into the pressure vessel 2 may be either first, later, or simultaneously.

  Next, the pressure inside the pressure vessel 2 is raised and / or raised, so that the carbon dioxide supplied into the pressure vessel 2 is brought into a supercritical state. If necessary, carbon dioxide is further injected into the pressure vessel 2. At this time, the stirrer 2A is appropriately operated to mix carbon dioxide and pure water in a supercritical state. Thereafter, carbon dioxide is kept in a supercritical state for a predetermined time.

  After the elapse of a predetermined time, the manual valve 5 is operated to make carbon dioxide in the pressure resistant container 2 into a gaseous state and release it to the outside of the pressure resistant container 2 and return the inside of the pressure resistant container 2 to normal pressure. In the pressure vessel 2, water containing impurities contained in the positive electrode material (hereinafter, this water may be referred to as impurity-containing water) and the positive electrode material remain. The positive electrode material is recovered from the mixture of the impurity-containing water and the positive electrode material in the pressure vessel 2 by separation means, for example, filtration, and is left in the pressure vessel 2.

  The positive electrode material present in the pressure-resistant vessel 2 at this stage, that is, at the stage where the first step is completed, is finely divided, and the average particle size is usually 5 μm or less, and in some cases 1 μm or less.

  Next, the finely divided positive electrode material is left as it is in the pressure vessel 2, and the monomer, the oxidizing agent, and carbon dioxide are introduced into the pressure vessel, and lower aqueous alcohols such as methanol and ethanol are introduced into the pressure vessel. After the introduction, the pressure vessel 2 is hermetically closed.

  Next, the pressure inside the pressure vessel 2 is raised and / or raised, so that the carbon dioxide supplied into the pressure vessel 2 is brought into a supercritical state. If necessary, carbon dioxide is further injected into the pressure vessel 2. At this time, the stirrer 2A is actuated as appropriate to mix carbon dioxide and a lower aqueous alcohol such as ethanol that are in a supercritical state. Thereafter, carbon dioxide is kept in a supercritical state for a predetermined time.

  After the elapse of a predetermined time, the manual valve 5 is operated to make carbon dioxide in the pressure resistant container 2 into a gaseous state and release it to the outside of the pressure resistant container 2 and return the inside of the pressure resistant container 2 to normal pressure. In the pressure vessel 2, a lower aqueous alcohol such as ethanol and a composite of the positive electrode material and the conductive polymer remain. The lower aqueous alcohol such as ethanol remaining in the pressure vessel 2 after the end of the second step may contain residual impurities and conductive polymer contained in the positive electrode material obtained after the first step. is there. From the mixture of the lower aqueous alcohol such as ethanol and the composite of the positive electrode material and the conductive polymer in the pressure vessel 2, the composite of the positive electrode material and the conductive polymer is recovered by separation means such as filtration.

  A conductive polymer adheres to the surface of the particles of the positive electrode material thus obtained, and a composite of the positive electrode material and the conductive polymer is formed. The average particle size is often finely divided to 1 μm or less.

Example 1
A commercial product (product name: “LiMn ₂ O ₄ ”) (manufactured by Yunnan Yuxi River Dragon Technology Co., Ltd.) was used as the cathode material. As a result of elemental analysis using an elemental analyzer (product name: SEMTRAC mini EDS), this positive electrode material is 0.07% by mass of Ca, 0.01% by mass of Fe, and K as impurities. It contained 0.04% by mass, 0.18% by mass of Na, and 0.04% by mass of Mg. Lithium ion batteries manufactured by adopting commercial products containing impurities at such a ratio as a positive electrode material may cause phenomena such as heat generation, ignition and combustion during use. Can not do it.

  When the average particle diameter of this commercial product was measured with a particle size analyzer (trade name: Microtrack, manufactured by Nikkiso Co., Ltd.), the average particle diameter was 20 μm. The SEM image (1000 times) of this commercially available product is shown in FIG.

Moreover, the pellet of diameter 13mm was produced from this commercial item using the tablet preparation apparatus for IR. When the resistivity of this commercially available pellet was measured according to the resistivity test method by the four probe method (JIS K7194 conductive plastic four probe method), the surface resistivity was 0.295 × 10 ⁷ Ω / □. there were.

  1 part by mass of the commercial product was loaded into a pressure vessel. Next, 1 to 100 parts by weight of pure water and 600 parts by mass of carbon dioxide were charged in the pressure vessel. While heating the inside of a pressure vessel to 40-100 degreeC and pressurizing to 7-25 Mpa, the carbon dioxide in a pressure vessel was made into the supercritical state, and the supercritical state was maintained for 2 hours as it was.

  After the time had elapsed, the airtight state of the pressure vessel was released to return the inside of the pressure vessel to normal pressure, and carbon dioxide that had returned to a gaseous state in the pressure vessel was released out of the pressure vessel.

  A mixture of the powdery substance in the pressure vessel and a liquid containing water as a main component was taken out and filtered, and the filtrated substance was washed with pure water and dried to separate the powdery substance.

As a result of elemental analysis of this powdery substance with an elemental analyzer (manufactured by Nikkiso Co., Ltd., product name: SEMTRAC mini EDS), Ca, Fe, K, Na, Ni and Mg were not detected. As a result, the powder was high-purity LiMn ₂ O ₄ in which no impurities were detected.

When measured with a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Microtrac), the average particle size of the powder was 0.522 μm. In addition, pellets having a diameter of 13 mm were produced from this powder using an IR tablet production apparatus. When the resistivity of this pellet was measured according to a resistivity test method by a four-probe method (JIS K7194 conductive plastic four-probe method), the surface resistivity was 0.87 × 10 ⁵ Ω / □.

  While charging 1 part by mass of this powdery substance into the pressure vessel, 0.1 part by mass of monomer (3,4 ethylenedioxythiophene), 0.6 part by mass of oxidizing agent (iron paratoluenesulfonate), 0.1 parts by mass of ethanol and 600 parts by mass of carbon dioxide were charged in a pressure resistant container.

  While heating the inside of a pressure vessel to 70 degreeC and pressurizing to 10 Mpa, the carbon dioxide in a pressure vessel was made into the supercritical state, and the supercritical state was maintained as it was for 1 to 2 hours.

  After the time had elapsed, the airtight state of the pressure vessel was released to return the inside of the pressure vessel to normal pressure, and carbon dioxide that had returned to a gaseous state in the pressure vessel was released out of the pressure vessel.

  A mixture of the powdery substance in the pressure vessel and the liquid mainly composed of ethanol was taken out and filtered, and the filtrated substance was washed with pure water and dried to separate the powdery substance.

  When measured with a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Microtrac), the average particle size of this powder was 0.574 μm.

FIG. 3 shows an SEM image (1000 times) of the powdery product obtained through the second step, that is, high-purity LiMn ₂ O ₄ powder.

Images obtained by EDS analysis (manufactured by Nikkiso Co., Ltd., product name: SEMTRAC mini EDS) of the high-purity LiMn ₂ O ₄ powder obtained through the second step are shown in FIGS.

According to FIGS. 4-8, since it is observed that the oxygen molecule and sulfur molecule peculiar to the structure of the conductive polymer have a shape that matches the contour of the powder, the surface of the LiMn ₂ O ₄ powder is electrically conductive. It is recognized that the adhesive polymer is attached.

From the high-purity LiMn ₂ O ₄ powder obtained through the second step, pellets having a diameter of 13 mm were produced using an IR tablet production apparatus. When the resistivity of this pellet was measured according to a resistivity test method according to the four-probe method (JIS K7194 conductive plastic four-probe method), the surface resistivity was 0.747 × 10 ³ Ω / □. From this result, it was confirmed that the conductivity of the positive electrode material formed by attaching the conductive polymer to the surface is larger than the conductivity of the positive electrode material having no conductive polymer attached to the surface.

  In consideration of the above results, it has been concluded that according to the method of the present invention, it is possible to achieve high purity of the positive electrode material, fine particle formation of the positive electrode material, and achievement of high electrical conductivity.

DESCRIPTION OF SYMBOLS 1 Modified fine powdery positive electrode substance manufacturing apparatus 2 Pressure-resistant container 2A Stirrer 3 Carbon dioxide cylinder 3A Pump 3B Manual valve 4 Polar solvent storage tank 4A Pump 4B Manual valve 5 Manual valve 6 Monomer supply apparatus 7 Oxidant supply apparatus

Claims (5)

A positive electrode material raw material containing a positive electrode material and a substance other than this positive electrode material, a polar solvent, and a supercritical fluid, so that the supercritical fluid is in a supercritical state or a subcritical state in a pressure vessel, Heating and pressurizing, then lowering the pressure in the pressure vessel and gasifying the supercritical fluid, separating the positive electrode material that became fine powder,
The finely divided positive electrode material, a monomer that becomes a conductive polymer by polymerization, an oxidant for polymerizing the monomer, and a supercritical fluid, wherein the supercritical fluid is in a supercritical state or A method for producing a modified fine powder cathode material, characterized in that the monomer is polymerized by heating and pressurizing so as to be in a subcritical state, and then the pressure in the pressure vessel is lowered to gasify the supercritical fluid. .   The method for producing a modified finely divided positive electrode material according to claim 1, wherein the polar solvent is water and / or a water-soluble polar organic solvent, and the supercritical fluid is carbon dioxide. The positive electrode material is LiMn ₂ O ₄ , LiFeO ₂ , LiCoO ₂ , LiNiO ₂ , general formula Li _x A _y PO ₄ (where 0.8 <x <2, 0 <y <1.5, A is Co, Ni, Mn, Fe, Cu, and phosphate represented by one) selected from Cr, and the general formula _{Li x A y B z C w} PO 4 ( provided that, B and C is Mg, Ca, Zn, Ge , Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B and different rare earth elements, 0.8 <x <2, 0 <y <1.5, The above-mentioned claim 1 or 2 is at least one selected from the group consisting of phosphates represented by: 0 ≦ z <1.5, 0 ≦ w <1.5, z and w are not 0 at the same time A method for producing the modified finely divided positive electrode material as described.   The method for producing a modified finely divided positive electrode forming material according to any one of claims 1 to 3, wherein the positive electrode material raw material contains at most 0.5 mass% of a substance other than the positive electrode material as an impurity.   The modified finely divided positive electrode material according to any one of claims 1 to 4, wherein the monomer is at least one monomer selected from the group consisting of 3,4-ethylenedioxythiophene, pyrrole, and aniline. Production method.

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