Method of producing positive electrode active material for lithium ion secondary battery

Abstract

To provide a production method with which a positive electrode active material for a lithium ion secondary battery effectively increasing discharge capacity in a lithium ion secondary battery can be obtained efficiently, while the method is simple means.SOLUTION: A method for producing a positive electrode active material for a lithium ion secondary battery which is represented by a formula (A): LiaMnbFecMxPO4 includes the following steps (I)-(III): (I) a step of, after mixing a lithium compound, a metal compound including at least a manganese compound and / or an iron compound, a phosphate compound, a pH adjuster, and water to obtain slurry water i, heating and stirring the slurry water under an atmospheric pressure equal to or lower than an ambient pressure at a temperature of lower than 100°C, thereby obtaining particles A; (II) a step of mixing the obtained particles A, a specific dispersant, water and specific water-insoluble carbon powder while adjusting a mass ratio (dispersant:water) of dispersant to water is to be 10:90 to 70:30, thereby obtaining slurry water ii; and (III) a step of spray-drying the obtained slurry water ii. The method does not require a firing step.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a positive electrode active material for a lithium ion secondary battery by simple and efficient means. [Background technology]

[0002] Secondary batteries for use in portable electronic devices, hybrid cars, electric cars, etc. are being developed, and lithium-ion secondary batteries in particular are widely known. Among these, Li(Fe,Mn)PO 4 Positive electrode active materials made of compounds such as these are not greatly affected by resource limitations and can exhibit high safety, making them optimal positive electrode materials for obtaining high-output, large-capacity lithium-ion secondary batteries. In order to produce these useful positive electrode active materials, various developments have been carried out in the past.

[0003] For example, Patent Documents 1 and 2 disclose a production method using a so-called solid-state reaction method in which a mixture obtained from raw material compounds such as lithium phosphate and metal compounds, and a conductive carbon material is fired, while Patent Document 3 discloses a production method that does not rely on the solid-state reaction method, in which a slurry obtained by subjecting raw material compounds to a hydrothermal reaction is granulated.

[0004] Usually, in order to impart sufficient electrical conductivity to the positive electrode active material thus obtained, various carbon sources are further added and then the material is calcined to support carbon on the surface of the positive electrode active material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-047751 A [Patent Document 2] JP 2005-050684 A [Patent Document 3] JP 2013-149602 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the production methods using the solid-state reaction method as described in Patent Documents 1 and 2 require calcination and pulverization in an inert gas atmosphere, which inevitably complicates the production process. On the other hand, even the production method using a hydrothermal reaction described in Patent Document 3 requires pressure treatment under heating conditions of 100°C or higher, which necessitates the development of dedicated equipment, and also requires a calcination treatment to add and support a carbon source. As described above, none of the conventional techniques has yet succeeded in sufficiently simplifying and streamlining the manufacturing method.

[0007] Therefore, the present invention relates to a production method that can efficiently obtain a positive electrode active material for a lithium ion secondary battery that effectively increases the discharge capacity of the lithium ion secondary battery, despite being a simple method. [Means for solving the problem]

[0008] Therefore, the present inventors conducted intensive research to solve the above-mentioned problems, and as a result, they discovered a method for producing a positive electrode active material that realizes a lithium ion secondary battery with a high discharge capacity, without the need for excessive pressurization or heating, and without going through a firing step, by mixing particles A obtained by heating and stirring a lithium compound, a metal compound, a phosphate compound, a pH adjuster, and water with a specific dispersant and water in a specific mass ratio, together with a water-insoluble carbon powder to obtain slurry water, and then spray-drying the slurry water.

[0009] That is, the present invention relates to a compound represented by the following formula (A): Li a Mn b Fe c M x PO 4 (A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and represent numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3.) A method for producing a positive electrode active material for a lithium ion secondary battery represented by the following steps (I) to (III): (I) After mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, a pH adjuster, and water to obtain slurry water i, heating and stirring are performed at a temperature below 100°C under an atmospheric pressure below atmospheric pressure to obtain particles A. (II) The obtained particles A, a dispersant, water, and water-insoluble carbon powder are adjusted and mixed so that the mass ratio of the dispersant to water (dispersant: water) is 10:90 to 70:30 to obtain slurry water ii, where the dispersant is one or more selected from ethanol, acetone, isopropyl alcohol, acetonitrile, and t-butyl alcohol, and the water-insoluble carbon powder is one or more selected from ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, and graphite. (III) A step of spray-drying the obtained slurry water ii is provided, and a method for producing a positive electrode active material for a lithium ion secondary battery that does not undergo a firing step is provided.

Effect of the Invention

[0010] According to the production method of the present invention, without requiring excessive pressurization, heating, etc. as in the case of using a hydrothermal reaction, the reaction can be effectively advanced by heating and stirring under an atmospheric pressure below atmospheric pressure, and only by spray-drying a predetermined slurry water without requiring a firing step for supporting carbon, a positive electrode active material capable of exhibiting excellent battery physical properties can be obtained, and a simple and efficient production method can be realized.

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, the present invention will be described in detail. The method for producing a positive electrode active material for a lithium ion secondary battery according to the present invention is a production method for obtaining a positive electrode active material for a lithium ion secondary battery represented by the following formula (A). Li a Mn b Fe c M x PO 4 ···(A) (In the formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. )

[0012] In the above formula (A), for a, 0.6 ≤ a ≤ 1.2 is preferable, 0.65 ≤ a ≤ 1.15 is more preferable, and 0.7 ≤ a ≤ 1.1 is even more preferable. For b, 0.4 ≤ b ≤ 0.8 is preferable. For c, 0.2 ≤ c ≤ 0.6 is preferable. For x, 0 ≤ x ≤ 0.2 may be sufficient, further 0 ≤ x ≤ 0.15 may be sufficient, and 0 ≤ x ≤ 0.1 may be sufficient. Also, from the viewpoint of further increasing the discharge capacity, M may further be Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd.

[0013] Specifically, for example, LiMnPO 4 , LiFePO 4 , LiMn 0.3 Fe 0.7 PO 4 , LiMn 0.4 Fe 0.6 PO 4 , LiMn 0.45 Fe 0.55 PO 4 , LiMn 0.7 Fe 0.3 PO 4 , LiMn0.9 Fe 0.1 PO 4 , LiMn 0.8 Fe 0.2 PO 4 , LiMn 0.75 Fe 0.15 Mg 0.1 PO 4 , LiMn 0.75 Fe 0.19 Zr 0.03 PO 4 , LiMn 0.6 Fe 0.4 PO 4 , LiMn 0.5 Fe 0.5 PO 4 , Li 1.2 Mn 0.63 Fe 0.27 PO 4 , Li 0.6 Mn 0.84 Fe 0.36 PO 4 Among them, LiMn 0.8 Fe 0.2 PO 4 , LiMn 0.4 Fe 0.6 PO 4 , LiMn 0.45 Fe 0.55 PO 4 , LiMn 0.7 Fe 0.3 PO 4 , LiMn 0.6 Fe 0.4 PO 4 , Li 1.2 Mn 0.63 Fe 0.27 PO 4 is preferred.

[0014] The method for producing a positive electrode active material for a lithium ion secondary battery of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery represented by the above formula (A), comprising the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound including at least a manganese compound and / or an iron compound, a phosphate compound, a pH adjuster, and water to obtain slurry water i, and then heating and stirring the mixture at a temperature of less than 100° C. under an atmospheric pressure equal to or lower than atmospheric pressure to obtain particles A. (II) a step of mixing the obtained particles A, a dispersant, water, and a water-insoluble carbon powder while adjusting the mass ratio of the dispersant to the water (dispersant:water) to be 10:90 to 70:30 to obtain a slurry water ii; The dispersant is one or more selected from ethanol, acetone, isopropyl alcohol, acetonitrile, and t-butyl alcohol; and The water-insoluble carbon powder is one or more selected from the group consisting of Ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, and graphite. (III) A step of spray-drying the obtained slurry water ii This manufacturing method does not require a firing step.

[0015] In this manner, the manufacturing method of the present invention is a method capable of obtaining particles A corresponding to the preliminary particles of the positive electrode active material for lithium ion secondary batteries represented by the above formula (A) simply by heating and stirring the specified raw material compounds, without going through a hydrothermal reaction, and capable of producing a highly useful positive electrode active material for lithium ion secondary batteries simply by spray-drying a slurry water obtained by mixing water-insoluble carbon powder together with the particles A while adjusting a specific mass ratio between the particles A and water, i.e., without going through a calcination step.

[0016] The step (I) of the production method of the present invention is a step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, a pH adjuster, and water to obtain slurry water i, and then heating and stirring the mixture at an ambient pressure equal to or lower than atmospheric pressure at a temperature of less than 100°C to obtain particles A.

[0017] The lithium compounds that can be used include hydroxides (e.g., LiOH·H 2 O, LiOH), carbonates, sulfates, and acetates. Among them, carbonates are preferred from the viewpoint of easily promoting the reaction without going through a hydrothermal reaction and effectively producing particles A.

[0018] The metal compound that can be used may contain at least a manganese compound and / or an iron compound. The manganese compound and the iron compound may be one or more of metal oxalates, metal sulfates, metal chlorides, and hydrates thereof. Among them, metal oxalates, metal chlorides, and hydrates thereof are preferred from the viewpoint of easily promoting the reaction without going through a hydrothermal reaction and effectively producing particles A. In addition to these manganese compounds and iron compounds, compounds of metals other than manganese compounds and iron compounds (M: M has the same meaning as M in formula (A)) may be used.

[0019] The phosphoric acid compounds that can be used include orthophosphoric acid (H 3 PO 4 Examples of suitable phosphoric acid include phosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Among these, phosphoric acid is preferably used.

[0020] The pH adjuster that can be used includes one or two hydroxides selected from NaOH and KOH. By using such a pH adjuster, it is considered that the reaction of the above components is favorably promoted without the need for excessive heating or pressurization in the presence of water in the slurry water i, and without necessarily using a metal sulfate. Among them, NaOH is preferable from the viewpoint of further increasing the discharge capacity of the obtained battery.

[0021] The contents of the lithium compound, metal compound, and phosphate compound in the slurry water i are, for example, as follows: 0.2 Mn 0.8 PO 4In the case of (a), the molar ratio of the total content of the iron compound and the manganese compound to the content of the lithium compound is preferably 1:1 to 1:2.5 in terms of the conversion ratio of metal ions (total of manganese ions and iron ions) to lithium ions (metal ions:lithium ions). Also, the molar ratio of the content of the lithium compound to the content of the phosphate compound is preferably 1:1 to 2.5:1 in terms of the conversion ratio of lithium ions to phosphate ions (lithium ions:phosphate ions).

[0022] The content of water in the slurry water i is preferably 10 to 50 mol, more preferably 13 to 30 mol, per mol of phosphorus ion of the phosphate compound, from the viewpoints of solubility of the raw material compounds, ease of stirring, synthesis efficiency, and the like.

[0023] The molar ratio of the lithium compound content to the pH adjuster content in the slurry water i is preferably 2.5:0.5 to 1:2, and more preferably 2:1 to 1:1.5, calculated as the ratio of lithium ions to hydroxide ions (lithium ions:hydroxide ions).

[0024] In obtaining the slurry water i, the order of addition of the above components is not particularly limited, but from the viewpoint of preventing side reactions and allowing the reaction to proceed easily, it is preferable to prepare a precursor slurry by mixing at least a phosphoric acid compound, a lithium compound, water, and a pH adjuster, and then add a metal compound to obtain the slurry water i. That is, when the raw materials are added in this order, no condensation occurs, stirring is easy, and the reaction can proceed well without the need for excessive heating or pressure.

[0025] The order of addition of the lithium compound, the phosphate compound, the water, and the pH adjuster is not particularly limited, but from the viewpoint of increasing the dispersibility of the resulting slurry water i and from the viewpoint of smoothly proceeding with the reaction, it is preferable to mix the lithium compound, the pH adjuster, and the water in advance to obtain a preliminary slurry water. Such a preliminary slurry water preferably contains 20 to 50 parts by mass of the lithium compound, more preferably 25 to 45 parts by mass of the lithium compound, and even more preferably 30 to 40 parts by mass of the lithium compound, relative to 100 parts by mass of water. Next, it is preferable to drop the phosphate compound into the obtained preliminary slurry water while stirring to obtain the above-mentioned precursor slurry. By dropping the phosphate compound and stirring while adding it little by little, the reaction in the obtained precursor slurry proceeds well, the precursor particles to be generated are generated while being uniformly dispersed, and the unnecessary aggregation of such particles can be effectively suppressed. In addition, orthophosphoric acid (H 3 PO 4 When (b) is used, it is preferably used as an aqueous solution having a concentration of 70 to 90% by mass. The dropping speed of the (b) phosphoric acid compound into the preliminary slurry water is preferably 15 to 50 mL / min, more preferably 20 to 45 mL / min, and further preferably 28 to 40 mL / min. The stirring time of the preliminary slurry water is preferably 1 to 24 hours, and more preferably 5 to 15 hours.

[0026] The temperature of the preliminary slurry water when being stirred is preferably 20 to 90°C, and more preferably 20 to 70°C. When the preliminary slurry water is stirred, it is preferable to cool it to a temperature equal to or lower than the boiling point of the preliminary slurry water, specifically, it is preferable to cool it to 80°C or lower, and more preferably to 20 to 60°C.

[0027] The precursor slurry preferably contains 1 to 2.5 moles of lithium per mole of phosphorus, more preferably 1.5 to 2.5 moles. If the molar amount of lithium is less than the lower limit, the pH will be lowered more than necessary due to an increase in unreacted phosphoric acid, and unnecessary metal hydrates will be generated in the subsequent steps, increasing the viscosity of the mixture, which may prevent the reaction from proceeding well. On the other hand, if the molar amount of lithium exceeds the upper limit, particles A that provide good performance may not be obtained. In addition, it is preferable to reduce the dissolved oxygen content of the precursor slurry by bubbling nitrogen therethrough, which can effectively prevent oxidation of the metal compound to be added in the subsequent step.

[0028] Next, the metal compounds are added to the precursor slurry prepared above, and the order of adding the metal compounds is not particularly limited. In addition to adding these compounds, an antioxidant may be added as necessary. Examples of such antioxidants include sodium sulfite (Na 2 SO 3 ), Sodium hydrosulfite (Na 2 S 2 O 4 ), aqueous ammonia, etc. The amount of the antioxidant added is preferably 0.01 to 1 mol, and more preferably 0.03 to 0.5 mol, per mol of the metal compound, from the viewpoint of preventing inhibition of the production of particles A due to excessive addition of the antioxidant.

[0029] The pH of the resulting slurry water i at 25° C. is preferably 3.5 to 9.0, more preferably 4.0 to 8.0, and even more preferably 4.5 to 7.5, from the viewpoints of preventing side reactions and allowing the reaction to proceed smoothly.

[0030] The slurry water i can be heated and stirred at atmospheric pressure or less to allow the reaction for producing particles A to proceed. Specifically, the pressure less than atmospheric pressure may be 0.1 MPa or less. That is, the production method of the present invention can easily obtain particles A by allowing the reaction to proceed well without the need for special pressure application or large-scale equipment. The stirring time is preferably 6 to 48 hours, more preferably 12 to 24 hours. The temperature during the reaction is less than 100° C., preferably 65° C. to 95° C., and more preferably 70° C. to 90° C. Therefore, excessive heating or pressure is not required, and the reaction can proceed smoothly. The apparatus used for heating and stirring the slurry water i is not particularly limited, and may be either a batch type or a continuous type, and may also be one that uses a heating method (indirect or direct).

[0031] The slurry water i is reacted by heating and stirring, and then filtered, whereby particles A are obtained in high yield and have a high degree of crystallinity. The obtained particles A can be isolated by washing, filtering, and then drying. By isolating the particles A in this manner, the content of only the particles A in the slurry water can be grasped more accurately. The amount of water used during washing is preferably 5 to 100 parts by mass, more preferably 5 to 50 parts by mass, per 1 part by mass of particles A. Examples of drying methods include freeze drying, vacuum drying, spray drying, box drying, fluidized bed drying, and external heat drying. Of these, freeze drying is preferred. Furthermore, during drying, it is preferable to use a slurry prepared in advance using particles A. The content (solid content) of particles A in such a slurry is preferably 20 to 60% by mass, more preferably 30 to 50% by mass, and even more preferably 35 to 45% by mass, from the viewpoint of improving battery characteristics. Furthermore, during or after drying, the mixture may be classified using a separator, a cyclone, a sieve, or the like, or may be pulverized using a mortar pin mill, a roll mill, a crusher, or the like.

[0032] In addition, if the particles A are not isolated at this stage, in the subsequent step (II), the amount of water used can be appropriately adjusted, taking into account the amount of water adhering to the particles A, so that the mass ratio of the dispersant to water becomes a predetermined value, as described below.

[0033] The average particle size of the particles A obtained in step (I) is preferably 3 μm to 150 μm, more preferably 3 μm to 100 μm, and further preferably 5 μm to 50 μm, from the viewpoint of improving battery characteristics. The average particle size of the particles A refers to a value measured by the method described in the Examples.

[0034] The step (II) of the manufacturing method of the present invention is a step of obtaining slurry water ii by mixing the particles A obtained in the above step (I), a dispersant, water, and a water-insoluble carbon powder, adjusting the mass ratio of the dispersant to the water (dispersant:water) to 10:90 to 70:30. The slurry water ii thus obtained contains the particles A and the water-insoluble carbon powder well dispersed therein, and by spray drying in the step (III) described below, the particles A can be well supported with carbon without a firing step.

[0035] The dispersant used in step (II) is one or more selected from ethanol, acetone, isopropyl alcohol, acetonitrile, and t-butyl alcohol. Among them, ethanol and acetone are preferred from the viewpoint of uniformly dispersing the particles A and the water-insoluble carbon powder in the slurry water ii.

[0036] The water-insoluble carbon powder used in step (II) is one or more selected from Ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, and graphite. Among them, Ketjen black is preferred from the viewpoint of uniformly dispersing the particles A and the water-insoluble carbon powder in the slurry water ii.

[0037] The average particle size of the water-insoluble carbon powder is preferably 5 nm to 1000 nm, more preferably 5 nm to 300 nm, and even more preferably 10 nm to 100 nm, from the viewpoint of uniformly dispersing the water-insoluble carbon powder together with the particles A and allowing the particles A to effectively and efficiently support carbon. The average particle size of the water-insoluble carbon powder refers to a value measured by the method described in the Examples.

[0038] Average particle size of particle A (particle A 粒径 ) and the average particle size of the water-insoluble carbon powder ( 粒径 ) and the ratio (particle A 粒径 / Water insoluble carbon powder 粒径 ) is preferably 3 to 30,000, more preferably 10 to 20,000, and even more preferably 50 to 5,000, from the viewpoint of effectively supporting carbon without a calcination step while increasing dispersibility.

[0039] When mixing the particles A, the dispersant, water, and the water-insoluble carbon powder, the mass ratio of the dispersant to water (dispersant:water) is adjusted to 10:90 to 70:30, preferably 10:90 to 60:40, more preferably 15:85 to 50:50, and even more preferably 20:80 to 40:60.

[0040] The total amount of water and dispersant mixed in step (II) is preferably 50 parts by mass to 150 parts by mass, more preferably 54 parts by mass to 122 parts by mass, and even more preferably 67 parts by mass to 115 parts by mass, per 100 parts by mass of particles A.

[0041] The amount of the water-insoluble carbon powder to be mixed in step (II) is, in terms of carbon atom, preferably 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass, per 100 parts by mass of particles A.

[0042] In addition, it is preferable to adjust the above components so that the solid content concentration of the obtained slurry water ii is preferably 20% by mass to 70% by mass, more preferably 40% by mass to 65% by mass, and even more preferably 45% by mass to 60% by mass.

[0043] The time for mixing the above components is preferably 3 to 60 minutes, more preferably 3 to 45 minutes, and even more preferably 5 to 30 minutes, from the viewpoint of effectively obtaining the slurry water ii in which the particles A and the water-insoluble carbon powder are uniformly dispersed. The mixing temperature is preferably 5°C to 45°C, and more preferably 10°C to 30°C.

[0044] The manufacturing method of the present invention includes a step (III) of spray-drying the slurry water II obtained in the above step (II). By only going through the step (III), it is possible to obtain a positive electrode active material in which carbon is effectively supported without going through a calcination step.

[0045] In the spray drying, an apparatus capable of setting various operating conditions may be appropriately used. For example, when a micro mist dryer (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) equipped with a four-fluid nozzle is used, the hot air temperature is preferably set to 110°C to 300°C, more preferably set to 140°C to 250°C, and even more preferably set to 160°C to 200°C as a processing condition. In addition, the ratio of the supply amount of hot air to the supply amount of slurry water ii (supply amount of hot air / supply amount of slurry water ii) is preferably set to 500 to 10,000, and more preferably set to 1,000 to 9,000. The residence time for spray drying is preferably 0.01 to 0.25 minutes, more preferably 0.01 to 0.2 minutes, and further preferably 0.03 to 0.15 minutes.

[0046] Carbon is effectively supported on the obtained positive electrode active material. The average particle size of such a positive electrode active material is preferably 3 μm to 50 μm, more preferably 5 μm to 30 μm, and further preferably 7 μm to 20 μm. The average particle size of the positive electrode active material refers to a value measured by the method described in the Examples.

[0047] The amount of carbon supported on the obtained positive electrode active material is preferably 0.1 mass% to 5 mass%, more preferably 0.2 mass% to 3 mass%, and even more preferably 0.5 mass% to 2 mass%, based on 100 mass% of the total amount of the positive electrode active material including the supported carbon. The amount of carbon supported on the positive electrode active material (carbon support amount) can be measured using a carbon / sulfur analyzer.

[0048] The positive electrode active material obtained by the manufacturing method of the present invention can be used as it is as a positive electrode material without undergoing a sintering process, and a lithium ion secondary battery can be constructed according to a conventional method. Specifically, for example, the obtained lithium-based polyanion particles are kneaded with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. to prepare a positive electrode slurry, which is then applied to a current collector and press-molded to produce a positive electrode.

[0049] The lithium ion secondary battery to which such a positive electrode can be applied is not particularly limited as long as it essentially comprises a positive electrode, a negative electrode, an electrolyte, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte.

[0050] Here, the negative electrode is not particularly limited in terms of its material composition, and any known material composition can be used, as long as it can absorb lithium ions during charging and release them during discharging. For example, lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, or carbon materials such as amorphous carbon can be used. It is preferable to use an electrode formed of an intercalation material capable of electrochemically absorbing and releasing lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, and for example, a combination of graphite and silicon-based materials can be used.

[0051] The electrolyte solution is prepared by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is usually used in electrolytes for lithium ion secondary batteries, and examples of the organic solvent that can be used include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, and oxolane compounds.

[0052] The supporting salt is not particularly limited in type, but is preferably LiPF 6 , LiBF 4 , LiClO 4 and LiAsF 6 an inorganic salt selected from the group consisting of a derivative of said inorganic salt, LiSO 3 CF 3 , LiC(SO 3 CF 3 ) 2 and LiN(SO 3 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 and LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ) and at least one of the derivatives of said organic salts.

[0053] The separator serves to electrically insulate the positive and negative electrodes and to retain the electrolyte, and may be, for example, a porous synthetic resin film, particularly a porous film of a polyolefin polymer (polyethylene, polypropylene).

[0054] The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. 0.51 Li 0.34 TiO 2.94 , Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , Li 7 La 3 Zr2 O 12 , 50Li 4 SiO 4 50Li 3 BO 3 , Li 2.9 PO 3.3 N 0.46 , Li 3.6 S 0.6 P 0.4 O 4 , Li 1.07 Al 0.69 Ti 1.46 (PO 4 ) 3 , Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 , Li 10 GeP 2 S 12 , Li 3.25 Ge 0.25 P 0.75 S 4 , 30Li 2 S·26B 2 S 3 44LiI, 63Li 2 S·36SiS 2 1Li 3 PO 4 , 57Li 2 S·38SiS 2 5Li 4 SiO 4 , 70Li 2 S·30P 2 S 5 , 50Li 2 S·50GeS 2 , Li 7 P 3 S 11 , Li 3.25 P 0.95 S 4 can be used.

[0055] The shape of the lithium ion secondary battery having the above-mentioned configuration is not particularly limited, and may be various shapes such as a coin type, a cylindrical type, a square type, or an irregular shape enclosed in a laminate exterior body. EXAMPLES

[0056] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. The physical properties were measured by the following methods.

[0057] <Measurement of the average particle size of particle A, water-insoluble carbon powder, and positive electrode active material> Each measurement object was observed with a SEM (JSM-7001F, manufactured by JEOL Ltd.) to obtain 10 images of different fields of view. Next, 100 particles were randomly selected from the particles visible in the images, and the longest diameter was measured. The average value was calculated to obtain the average particle size.

[0058] <<Carbon Loading in Positive Electrode Active Material>> The measurements were made using a carbon / sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.).

[0059] [Example 1] 1) Production of Particle A LiOH H 2 2.518g (60mmol) O, 4.8g (120mmol) NaOH, and 90mL water were mixed to obtain a slurry water. Next, 11.068g of 85% phosphoric acid aqueous solution was added dropwise at 35mL / min to the obtained slurry water while stirring for 10 minutes while maintaining the temperature at 25°C, and then stirred for 12 hours to obtain a precursor slurry. The precursor slurry had a dissolved oxygen concentration of 0.5mg / L by nitrogen gas purging, and contained 1.6mol of lithium per mol of phosphorus.

[0060] Next, MnCl 2 4H 2 O 15.83g, FeCL 2 4H 2 Add 3.98 g of O to make a slurry with a pH of 6.0. 1 At this time, the added MnCl 2 and FeCL 2 The molar ratio of manganese compound to iron compound was 4:1.1 The molar ratio of the lithium compound content to the NaOH content (lithium ion:hydroxide ion) in the solution was 0.5:1. Subsequently, the obtained slurry i 1 The mixture was stirred at 80° C. for 12 hours under an atmospheric pressure of 0.1 MPa with nitrogen gas purging to allow the reaction to proceed. The resulting crystals were filtered and then washed with 12 parts by mass of water per part by mass of the crystals. The washed crystals were freeze-dried at −60° C. for 12 hours to obtain particles A (LiMn 0.8 Fe 0.2 PO 4 , average particle size 7.2 μm) was obtained.

[0061] 2) Manufacturing of positive electrode active material 1000 g of the obtained particles A, 12 g of Ketjen Black (average particle size 43 nm), 304 g of ethanol, and 708 mL of water (ethanol:water = 30:70) were ground and mixed in a planetary ball mill (media 1 mmΦ) for 1 hour, and filtered to obtain slurry water II. 1 (solid content concentration 50% by mass) was obtained. Then, the obtained slurry water II 1 The mixture was dispersed for 1 minute using an ultrasonic agitator (T25, manufactured by IKA Corporation) and then spray-dried (nozzle air flow rate 35 L / min, supply air temperature 160° C.) using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain a positive electrode active material (E1, carbon loading 1.2% by mass).

[0062] [Example 2] A positive electrode active material (E2, carbon supported amount 1.2 mass %) was obtained in the same manner as in Example 1, except that in 2) above, acetone was used instead of ethanol.

[0063] [Example 3] A positive electrode active material (E3, carbon supported amount 1.2 mass %) was obtained in the same manner as in Example 1, except that in the above 2), 152 g of ethanol and 860 mL of water (ethanol:water=15:85) were used.

[0064] [Example 4] A positive electrode active material (E4, carbon supported amount 1.2 mass %) was obtained in the same manner as in Example 1, except that in the above 2), 455 g of ethanol and 557 mL of water (ethanol:water=45:55) were used.

[0065] [Example 5] A positive electrode active material (E5, carbon supported amount 1.1 mass %) was obtained in the same manner as in Example 1, except that in the above 2), 557 g of ethanol and 455 mL of water (ethanol:water=60:40) were used.

[0066] [Example 6] A positive electrode active material (E6, carbon supported amount 1.2 mass %) was obtained in the same manner as in Example 1, except that in the above 2), 708 g of ethanol and 304 mL of water (ethanol:water=70:30) were used.

[0067] [Comparative Example 1] A positive electrode active material (C1, carbon supported amount 1.1% by mass) was obtained in the same manner as in Example 1, except that in the above 2), 51 g of ethanol and 961 mL of water (ethanol:water=5:95) were used.

[0068] [Comparative Example 2] A positive electrode active material (C2, carbon supported amount 1.2 mass %) was obtained in the same manner as in Example 1, except that in the above 2), 810 g of ethanol and 202 mL of water (ethanol:water=80:20) were used.

[0069] [Comparative Example 3] A positive electrode active material (C3, carbon supported amount 1.1 mass %) was obtained in the same manner as in Example 1, except that in 2) above, glucose was used instead of Ketjen black.

[0070] Evaluation of charge / discharge characteristics Using each of the obtained positive electrode active materials, a positive electrode of a lithium ion secondary battery was prepared. Specifically, the obtained positive electrode active material, Ketjen black, and polyvinylidene fluoride were mixed in a weight ratio of 75:15:10, and N-methyl-2-pyrrolidone was added to this and thoroughly kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of aluminum foil with a thickness of 20 μm using a coater, and vacuum dried at 80 ° C for 12 hours. Thereafter, it was punched into a disk shape of φ 14 mm and pressed with a hand press at 16 MPa for 2 minutes to form a positive electrode. Next, a coin-type lithium ion secondary battery was constructed using the above positive electrode. A lithium foil punched to a diameter of 15 mm was used as the negative electrode. The electrolyte was a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1, with LiPF 6 The battery was dissolved at a concentration of 1 mol / L. A known separator, such as a polymer porous film of polypropylene, was used. These battery components were assembled and housed in an atmosphere with a dew point of -50°C or lower in a conventional manner to produce a coin-type lithium secondary battery (CR-2032).

[0071] The manufactured coin-type lithium secondary battery was used to perform three cycles of charge and discharge at 0.2 C in a 30° C. environment using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation), and the discharge capacity (mAh / g) was determined. The results are shown in Table 1.

[0072] [Table 1]

Claims

1. The following formula (A): Li ａ Mn ｂ Fe ｃ M ｘ 2O ４ ・・・(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x represent numbers that satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0, and that satisfy a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.) A method for producing a positive electrode active material for a lithium ion secondary battery, comprising the steps of (I) to (III): (I) A step of mixing a lithium compound, a metal compound including at least a manganese compound and / or an iron compound, a phosphate compound, a pH adjuster, and water to obtain slurry water i, and then heating and stirring the mixture at an atmospheric pressure or lower at a temperature of less than 100° C. to obtain particles A. (II) a step of mixing the obtained particles A, a dispersant, water, and a water-insoluble carbon powder in such a manner that the mass ratio of the dispersant to the water (dispersant:water) is adjusted to 10:90 to 70:30, thereby obtaining a slurry water ii; The dispersant is one or more selected from ethanol, acetone, isopropyl alcohol, acetonitrile, and t-butyl alcohol; and The water-insoluble carbon powder is one or more selected from the group consisting of Ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, and graphite. (III) A step of spray-drying the obtained slurry water ii The method for producing a positive electrode active material for a lithium ion secondary battery includes the steps of:

2. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the total amount of water and dispersant mixed in the step (II) is 50 parts by mass to 150 parts by mass per 100 parts by mass of particles A.

3. 3. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the water-insoluble carbon powder used in step (II) has an average particle size of 5 nm to 1000 nm.

4. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the mixing time in step (II) is 3 minutes to 60 minutes.

5. 3. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the solid content of the slurry water II obtained in step (II) is 20% by mass to 70% by mass.

6. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the temperature of heating and stirring in step (I) is 65°C or higher.

7. 3. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the hot air temperature in the spray drying in the step (III) is 110° C. to 300° C.

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