Method for manufacturing positive electrode active material for lithium-ion secondary batteries

Abstract

The present invention relates to a method for manufacturing a lithium ion secondary battery that can effectively improve the cycle characteristics of a thium ion secondary battery. 【Solution means】Formula: Li a Mn b Fe c M x A method for manufacturing a positive electrode active material for a lithium ion secondary battery represented by PO4 and carrying carbon, comprising the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water i (II) A step of subjecting the obtained slurry water i to a hydrothermal reaction and then spray-drying to obtain granulated bodies (III) A step of firing the obtained granulated bodies in an inert gas atmosphere The method for manufacturing a positive electrode active material for a lithium ion secondary battery includes a step of adding a conductive carbon material in step (I) and / or step (II), and in step (III), the flow rate of the inert gas is 250 mL / min or more, and the firing temperature is 700 °C to 1200 °C.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a positive electrode active material for lithium-ion secondary batteries that can effectively improve the cycle characteristics of lithium-ion secondary batteries by reducing the unwanted leaching of carbon supported on the positive electrode active material for lithium-ion secondary batteries. [Background technology]

[0002] Lithium-ion batteries and other secondary batteries are used in a wide range of fields, including mobile phones, digital cameras, notebook PCs, hybrid vehicles, and electric vehicles. Due to their high safety and large capacity, LiMn is used as the cathode material for these lithium-ion batteries. x Fe 1-x Positive electrode active materials such as PO4 are considered promising. However, these positive electrode active materials also have the characteristic of low conductivity, so in order to ensure battery characteristics such as cycle characteristics in lithium-ion secondary batteries, various improvements are being made, such as trying to identify the physical properties and shape of positive electrode active material particles, and adding and supporting carbon materials.

[0003] For example, Patent Document 1 describes an attempt to improve the cycle characteristics of a secondary battery by controlling the crystallite size and porosity of the positive electrode active material. Also, Patent Document 2 describes... An ionic organic substance is used as the carbon source, and the electrode active material (Li) is coated with a specific carbonaceous film. a A x M y The electrode material, which is an aggregate of PO4, etc., is used to improve the cycle characteristics. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-133173 [Patent Document 2] Japanese Patent Publication No. 2020-053291 [Overview of the Initiative]

Problems to be Solved by the Invention

[0005] However, in recent years, as lithium ion secondary batteries that exhibit even higher cycle characteristics are demanded, controlling the properties such as the crystallite size of the positive electrode active material, as in Patent Document 1 above, still only yields insufficient results, and even the technology described in Patent Document 2 above is in a situation where further improvement is desired.

[0006] Therefore, the present invention relates to a method for manufacturing a lithium ion secondary battery that can effectively improve the cycle characteristics of the lithium ion secondary battery.

Means for Solving the Problems

[0007] Therefore, as a result of intensive studies to solve the above problems, the present inventors newly noted that as the lithium ion secondary battery is repeatedly used, there is a risk that the carbon supported on the positive electrode active material constituting the positive electrode may be eluted unnecessarily, and such carbon can also be a source of organic acids that impair battery characteristics. And the present inventors found that if a positive electrode active material capable of effectively reducing the elution of such carbon can be produced, the cycle characteristics of the lithium ion secondary battery can be effectively improved, and thus arrived at the present invention.

[0008] That is, the present invention provides the following formula (A): Li a Mn b Fe c M x PO4···(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 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, which is represented by and has carbon supported, comprising the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain slurry water i. (II) The obtained slurry water i is subjected to a hydrothermal reaction and then spray-dried to obtain granules. (III) A process of calcining the obtained granules under an inert gas atmosphere. Equipped with, Step (I) and / or step (II) include a step of adding a conductive carbon material, The present invention provides a method for producing a positive electrode active material for lithium-ion secondary batteries, wherein in step (III), the flow rate of the inert gas is 250 mL / min or more, and the firing temperature is 700°C to 1200°C. [Effects of the Invention]

[0009] The positive electrode active material for lithium-ion secondary batteries obtained by the manufacturing method of the present invention allows for robust carbon support and effectively prevents unwanted carbon leaching. Therefore, the cycle characteristics of a lithium-ion secondary battery constructed using such a positive electrode active material can be improved very effectively. [Modes for carrying out the invention]

[0010] The present invention will be described in detail below. The present invention provides a method for producing a positive electrode active material for lithium-ion secondary batteries, which is represented by the following formula (A) and has carbon supported on it (hereinafter also referred to as "active material (A)"). Li a Mn b Fe c M x PO4···(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.)

[0011] 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 acceptable, and further 0 ≤ x ≤ 0.15 may be acceptable, and 0 ≤ x ≤ 0.1 may be acceptable. Also, from the perspective of further increasing the discharge capacity, M may further be Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd.)

[0012] Specific examples of such active material (A) include, for example, LiMnPO4, LiFePO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.9 Fe 0.1 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.75 Fe 0.15 Mg 0.1 PO4, LiMn 0.75 Fe 0.19 Zr 0.03 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4, Li 0.6 Mn[[ID=6而已。1]]<0000已。0>Fe 0.36Examples include PO4, among others, LiFePO4 and LiMn. 0.8 Fe 0.2 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4 is preferred, LiMn 0.4 Fe 0.6 PO4, LiMn 0.7 Fe 0.3 PO 4、 Li 1.2 Mn 0.63 Fe 0.27 PO4 is preferable.

[0013] The active material (A) obtained by the present invention has carbon supported on it. This carbon is carbon obtained by carbonizing the conductive carbon material used in the manufacturing process, and is equivalent to the amount of carbon atoms in the conductive carbon material. The amount of carbon supported in 100% by mass of the total amount of active material (A) is preferably 0.5% to 3% by mass, more preferably 0.9% to 2% by mass, and even more preferably 1.0% to 1.3% by mass.

[0014] The amount of carbon supported in 100% by mass of the active material (A) may be calculated from the carbon-carbon equivalent of the total amount of carbon material used. Alternatively, the total carbon content can be determined by measurement using a carbon-sulfur analyzer, and the obtained value can be considered as the amount of carbon supported in 100% by mass of the active material (A).

[0015] The present invention relates to a method for producing a positive electrode active material for a lithium-ion secondary battery, which is represented by the above formula (A) and has carbon supported on it, and comprises the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain slurry water i. (II) The obtained slurry water i is subjected to a hydrothermal reaction and then spray-dried to obtain granules. (III) A process of calcining the obtained granules under an inert gas atmosphere. Equipped with, Step (I) and / or step (II) include a step of adding a conductive carbon material, In step (III), the flow rate of the inert gas is 250 mL / min or more, and the firing temperature is 700°C to 1200°C.

[0016] With this manufacturing method of the present invention, an active material (A) in which the added conductive carbon material is firmly supported as carbon can be obtained effectively and efficiently. Therefore, a lithium-ion secondary battery obtained using such active material (A) can effectively suppress the unnecessary leaching of carbon from such active material (A) during repeated use, and can also effectively reduce the generation of organic acids.

[0017] Step (I) 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, and water to obtain slurry water i.

[0018] Examples of lithium compounds that can be used include hydroxides (e.g., LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Among these, hydroxides are preferred.

[0019] Examples of manganese compounds that can be used include one or more of the following: metal oxalate salts, metal sulfate salts, metal chlorides, and hydrates thereof. Among these, metal sulfate salts and their hydrates are preferred.

[0020] Examples of iron compounds that can be used include one or more of the following: metal oxalate salts, metal sulfate salts, metal chlorides, and hydrates thereof. Among these, metal sulfate salts and their hydrates are preferred. In addition, metal compounds other than these manganese and iron compounds (M: M is synonymous with M in formula (A)) may also be used.

[0021] Examples of usable phosphoric acid compounds include orthophosphoric acid (H3PO4, phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Among these, phosphoric acid is preferred, and it is preferable to use it as an aqueous solution with a concentration of 70% to 90% by mass.

[0022] The slurry water i obtained by mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water preferably contains 2.0 to 4.0 moles of lithium, more preferably 2.0 to 3.1 moles, per mole of phosphate, and each raw material may be added as appropriate to achieve these amounts.

[0023] Furthermore, step (I) may include a step of adding a conductive carbon material. That is, in step (I), a conductive carbon material may be further added to the slurry water i. The conductive carbon material is a material used to effectively enhance the electronic conductivity of the resulting positive electrode active material for lithium-ion secondary batteries. Through the manufacturing method of the present invention, it is carbonized and becomes carbon, which is firmly supported on the positive electrode active material for lithium-ion secondary batteries. If step (I) does not include the step of adding a conductive carbon material, then the step of adding a conductive carbon material may be included in step (II) described later, or the step of adding a conductive carbon material may be included in both step (I) and step (II).

[0024] Examples of conductive carbon materials that can be used include, specifically, monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch, dextrin, and cellulose; nanofibers of polysaccharides such as cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, and chitosan nanofibers; polyols and polyethers such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butanediol, propanediol, polyvinyl alcohol, and glycerin; and one or more organic acids such as citric acid, tartaric acid, and ascorbic acid. In particular, from the viewpoint of enhancing solubility and dispersibility in solvents to enable effective function as a carbon material, firmly supporting it on the positive electrode active material for lithium-ion secondary batteries, and effectively suppressing the elution of carbon from the positive electrode active material for lithium-ion secondary batteries, one or more selected from monosaccharides, polysaccharides, and polysaccharide nanofibers are preferred, one or more selected from glucose, cellulose, and cellulose nanofibers are more preferred, and it is even more preferable to include cellulose nanofibers as at least one conductive carbon material.

[0025] The amount of conductive carbon material added can be adjusted as appropriate so that the amount of carbon supported in the resulting active material (A) is the desired amount. For example, when added only in step (I), the amount is preferably 1 to 8 parts by mass, more preferably 2 to 7 parts by mass, and even more preferably 3 to 6 parts by mass, per 1 part by mass of the solid content of slurry water i.

[0026] Furthermore, nitrogen gas may be purged from the slurry water i after the addition of each of the above raw materials. When nitrogen gas is purged, the reaction can proceed with a reduced dissolved oxygen concentration in the slurry water i, effectively suppressing the oxidation of the metal compound while forming trilithium phosphate (Li3PO4) as a precursor of the active material (A).

[0027] Furthermore, it is preferable to pre-mix the obtained slurry water i before proceeding to step (II). The mixing time is preferably 0.25 hours to 24 hours, and more preferably 0.5 hours to 15 hours. In addition, it is preferable to use ultrasonic mixing for such mixing.

[0028] Step (II) is a step in which the slurry water i obtained in step (I) is subjected to a hydrothermal reaction and then spray-dried to obtain granules.

[0029] The hydrothermal reaction can take place at temperatures above 100°C, with 130°C to 200°C being preferred. The hydrothermal reaction is preferably carried out in a pressure vessel. When the reaction is carried out at 130°C to 200°C, the pressure is preferably 0.3 MPa to 1.6 MPa, and when the reaction is carried out at 140°C to 160°C, the pressure is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 hours to 48 hours, and more preferably 0.2 hours to 24 hours.

[0030] It is preferable to subject the material to a hydrothermal reaction, then filter it, wash it with water, and obtain a washed material. The obtained washed material is then appropriately mixed with water to make slurry water II, and this slurry water II is spray-dried to obtain granules. The solid content concentration in slurry water ii is preferably 5% to 30% by mass, more preferably 5% to 20% by mass, and even more preferably 5% to 15% by mass.

[0031] Step (II) may also include a step of adding a conductive carbon material, in which case the conductive carbon material should be further added to the slurry water ii. The conductive carbon material that can be used is the same as described above. Specifically, the content of conductive carbon material in 100% by mass of the solid content of slurry water II is preferably 0.04% to 2.0% by mass, more preferably 0.05% to 1.7% by mass, and even more preferably 0.06% to 1.5% by mass. Conductive carbon material should be added in such amounts. It is preferable to pre-stir the slurry water ii after adding water and before spray drying. The stirring time for the slurry water ii is preferably 3 to 60 minutes, more preferably 5 to 30 minutes. The temperature of the slurry water ii is preferably 10°C to 60°C, more preferably 20°C to 40°C.

[0032] Next, the slurry water II obtained after the hydrothermal reaction is spray-dried to obtain granules. In this spray-drying process, the operating conditions can be set appropriately depending on the equipment used. For example, when using a micro-mist dryer equipped with four fluid nozzles (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.), the processing conditions are preferably such that the hot air temperature is 110°C to 300°C, and more preferably 150°C to 250°C. Furthermore, the volume ratio of the hot air supply amount to the slurry water supply amount (hot air supply amount / slurry water supply amount) is preferably 500 to 10000, and more preferably 1000 to 9000.

[0033] Step (III) is a step in which the granules obtained in step (II) are calcined in an inert gas atmosphere, wherein the flow rate of the inert gas is 250 mL / min or more and the calcination temperature is 700°C to 1200°C. By going through this step of calcination at a temperature of 700°C to 1200°C in an inert gas atmosphere with an excessive flow rate, an active material (A) is obtained in which carbon derived from the conductive carbon material is firmly supported. This effectively suppresses the unwanted leaching of carbon when used in lithium-ion secondary batteries and also greatly contributes to reducing the generation of organic acids.

[0034] An inert gas atmosphere specifically refers to an atmosphere consisting of one or more gases selected from nitrogen gas, argon gas, hydrogen gas, and mixtures thereof. Among these, nitrogen gas is preferred from the viewpoint of effectively reducing the amount of unwanted carbon leaching.

[0035] Furthermore, the inert gas flow rate refers to the amount of inert gas supplied per unit time (volume flow rate) to the firing apparatus, such as a tubular electric furnace. From the viewpoint of effectively reducing the amount of carbon leaching when using lithium-ion secondary batteries, the inert gas flow rate is 250 mL / min or more, preferably 500 mL / min to 2000 mL / min, and more preferably 600 mL / min to 1000 mL / min. Furthermore, the flow rate of the inert gas is typically 15 m / sec to 500 m / sec, but from the viewpoint of effectively reducing the amount of carbon leaching when using lithium-ion secondary batteries, it is preferably 30 m / sec to 200 m / sec, and more preferably 40 m / sec to 160 m / sec.

[0036] The firing temperature is 700°C to 1200°C, preferably 700°C to 1000°C, and more preferably 720°C to 900°C, from the viewpoint of effectively reducing the amount of carbon leached when lithium-ion secondary batteries are used. The heating rate to reach the above firing temperature is preferably 5°C / min to 100°C / min, more preferably 7°C / min to 75°C / min, and even more preferably 8°C / min to 50°C / min.

[0037] The firing time is the time from the point when the desired firing temperature is raised (firing start time) to the point when the maintenance of the raised temperature is released and cooling begins (firing end time), and is preferably 60 to 900 minutes, more preferably 80 to 750 minutes, and even more preferably 200 to 390 minutes.

[0038] The active material (A) obtained by the manufacturing method of the present invention is a material used as a positive electrode active material for lithium-ion secondary batteries, and in the resulting lithium-ion secondary battery, it can fully exhibit the effect of suppressing the unwanted leaching of carbon. As one indicator of this effect, a measurement test of the amount of eluted carbon (TOC, unit: mg / L) can be performed, and the ratio of the obtained value to the amount of carbon loaded in the active material (A) (TOC / amount of carbon loaded) (unit: mg / (L·mass%)) can be used. Specifically, in the active material (A) obtained by the manufacturing method of the present invention, the ratio of the amount of eluted carbon to the amount of carbon supported (TOC / amount of carbon supported) is preferably 3.5 mg / (L·mass%) or less, more preferably 3.0 mg / (L·mass%) or less, and even more preferably 2.0 mg / (L·mass%) or less, or the amount of eluted carbon is preferably 0 mg / L, in which case the ratio of the amount of eluted carbon to the amount of carbon supported (TOC / amount of carbon supported) is 0 mg / (L·mass%). Specifically, the measurement test for eluted carbon (TOC) is the test performed using the method described in the examples.

[0039] The active material (A) obtained by the manufacturing method of the present invention can be used to construct a lithium-ion secondary battery according to conventional methods. Specifically, for example, the active material (A) is kneaded with acetylene black, Ketjenblack, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. to prepare a positive electrode slurry, which is then coated onto a current collector and subsequently press-molded to produce a positive electrode. A lithium-ion secondary battery to which a positive electrode obtained using the active material (A) can be applied is not particularly limited as long as it has a positive electrode, a negative electrode, an electrolyte, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte as essential components.

[0040] Here, the negative electrode is not particularly limited in its material composition as long as it can absorb lithium ions during charging and release them during discharge; known material compositions can be used. For example, lithium metal, graphite, silicon-based materials (Si, SiOx), lithium titanate, or amorphous carbon materials can be used. It is preferable to use an electrode formed of an intercalate material capable of electrochemically absorbing and releasing lithium ions, especially a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination; for example, a combination of graphite and silicon-based materials can be used.

[0041] The electrolyte is prepared by dissolving a support salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent commonly used in the electrolyte of lithium-ion secondary batteries. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds, etc., can be used.

[0042] The supporting salt is not particularly limited in type, but is preferably at least one of the following: an inorganic salt selected from LiPF6, LiBF4, LiClO4, and LiAsF6; a derivative of the inorganic salt; an organic salt selected from LiSO3CF3, LiC(SO3CF3)2, LiN(SO3CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9); and a derivative of the organic salt.

[0043] The separator serves to electrically insulate the positive and negative electrodes and to hold the electrolyte. For example, a porous synthetic resin membrane, particularly a porous membrane made of polyolefin polymers (polyethylene, polypropylene), can be used.

[0044] Solid electrolytes electrically insulate the positive and negative electrodes and exhibit high lithium-ion conductivity. For example, La 0.51 Li 0.34 TiO 2.94 Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75S4, 30Li2S 26B2S3 44LiI, 63Li2S 36SiS2 1Li3PO4, 57Li2S 38SiS2 5Li4SiO4, 70Li2S 30P2S5, 50Li2S 50GeS2, Li7P3S 11 Li 3.25 P 0.95 Use S4.

[0045] The shape of the lithium-ion secondary battery having the above configuration is not particularly limited and may be various shapes such as coin-type, cylindrical, or prismatic, or it may be an irregular shape enclosed in a laminate casing. [Examples]

[0046] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. The measurements and evaluations were carried out according to the following methods. The results are shown in Table 1.

[0047] [Example 1] Slurry ia was obtained by mixing 1272 g of LiOH·H2O with 4 L of water. Then, while stirring the obtained slurry ia for 3 minutes at a temperature of 25°C, 1153 g of 85% aqueous phosphoric acid solution was added dropwise at a rate of 35 mL / min, and the mixture was stirred at a speed of 400 rpm for 12 hours to obtain slurry ib containing Li3PO4. The obtained slurry ib was purged with nitrogen to adjust the dissolved oxygen concentration of slurry ib to 0.5 mg / L. Then, 964 g of MnSO4·5H2O and 1668 g of FeSO4·7H2O were added to the total amount of slurry ib to obtain slurry ic. The molar ratio (manganese compound:iron compound) of the added MnSO4 and FeSO4 was 40:60.

[0048] Next, the obtained slurry ic was placed in an autoclave and subjected to a hydrothermal reaction at 170°C for 1 hour. The pressure inside the autoclave was 0.8 MPa. After the hydrothermal reaction, the resulting crystals were filtered, and then washed with 12 parts by mass of water per 1 part by mass of crystals to obtain washed product a. 768 g of the obtained washed product a was taken, 0.8 L of water and 982 g of cellulose nanofiber I-1 (Wma-10002, manufactured by Sugino Machine, fiber diameter 4 to 20 nm) were added thereto to obtain slurry ii. The obtained slurry ii was dispersed for 1 minute with an ultrasonic stirrer (T25, manufactured by IKA) to uniformly color the whole, and then spray-dried using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd., nozzle air flow rate 75 L / min, supply air temperature 120 °C) to obtain granule z.

[0049] 20.000 g of the obtained granule z was collected and placed in a combustion boat, and then the combustion boat was placed at the center of the cylinder of a small tubular furnace. Next, the flow rate of N2 gas (room temperature: 25 °C) in the small tubular furnace was set to 1000 mL / min (flow velocity: 79.6 m / s), and it was held at 25 °C for 10 minutes as it was. Then, the heating rate of the heater was set to 10 °C / min and heated up to 800 °C, and the temperature of 800 °C was held and fired for 360 minutes. Then, the heater was stopped and allowed to cool to 25 °C, and active material A1 (LiMn 0.4 Fe 0.6 PO4) supported with carbon was obtained.

[0050] [Example 2] Active material A2 (LiMn 0.4 Fe 0.6 PO4) supported with carbon was obtained in the same manner as in Example 1, except that the flow rate of N2 gas in the small tubular furnace where granule z was placed was set to 2000 mL / min (flow velocity: 159.2 m / s).

[0051] [Example 3] Active material A3 (LiMn 0.4 Fe 0.6 PO4) supported with carbon was obtained in the same manner as in Example 1, except that the flow rate of N2 gas in the small tubular furnace where granule z was placed was set to 500 mL / min (flow velocity: 39.8 m / s).

[0052] [Example 4] The flow rate of N2 gas in a small tubular furnace where granule z was stationary was set to 500 mL / min (flow velocity: 39.8 m / s), and after holding it as it was for 10 minutes, the heating rate of the heater was set to 10 °C / min and heated to 800 °C. Except for holding the temperature of 800 °C for 90 minutes for firing, in the same manner as in Example 1, an active material A4 (LiMn 0.4 Fe 0.6 PO4) in which carbon was supported was obtained.

[0053] [Example 5] The flow rate of N2 gas in a small tubular furnace where granule z was stationary was set to 2000 mL / min (flow velocity: 159.2 m / s), and after holding it as it was for 10 minutes, the heating rate of the heater was set to 10 °C / min and heated to 720 °C. After that, except for holding the temperature of 720 °C for 720 minutes for firing, in the same manner as in Example 1, an active material A5 (LiMn 0.4 Fe 0.6 PO4) in which carbon was supported was obtained.

[0054] [Example 6] The flow rate of N2 gas in a small tubular furnace where granule z was stationary was set to 700 mL / min (flow velocity: 55.7 m / s), and after holding it as it was for 10 minutes, the heating rate of the heater was set to 10 °C / min and heated to 950 °C. After that, except for holding the temperature of 950 °C for 120 minutes for firing, in the same manner as in Example 1, an active material A6 (LiMn 0.4 Fe 0.6 PO4) in which carbon was supported was obtained.

[0055] [Example 7] Using Ar gas instead of N2 gas, the flow rate of Ar gas in a small tubular furnace where granule z was stationary was set to 1000 mL / min (flow velocity: 79.6 m / s), and after holding it as it was for 10 minutes, the heating rate of the heater was set to 10 °C / min and heated to 750 °C. After that, except for holding the temperature of 750 °C for 180 minutes for firing, in the same manner as in Example 1, an active material A7 (LiMn 0.4 Fe 0.6 PO4) in which carbon was supported was obtained.

[0056] [Comparative Example 1] In the small tubular furnace in which the granulated material z was placed, the flow rate of N2 gas was set to 100 mL / min (flow velocity: 8.0 m / s), and it was maintained at this rate for 10 minutes. Then, the heating rate of the heater was set to 10°C / min to raise the temperature to 600°C, and this temperature of 600°C was maintained for 30 minutes for firing. Except for this, the active material C1 (LiMn), in which carbon is supported, was fired in the same manner as in Example 1. 0.4 Fe 0.6 PO4) was obtained.

[0057] [Comparative Example 2] In a small tubular furnace in which granulated material z was placed, the flow rate of N2 gas was set to 50 mL / min (flow velocity: 4.0 m / s), and this was maintained for 10 minutes. Then, the heating rate of the heater was set to 10 °C / min to raise the temperature to 650 °C. After that, the heater was immediately stopped without maintaining the temperature of 650 °C and allowed to cool to 25 °C. Except for this, the process was carried out in the same manner as in Example 1, with the active material C2 (LiMn) having carbon supported on it. 0.4 Fe 0.6 PO4) was obtained.

[0058] [Comparative Example 3] Except for using Ar gas instead of N2 gas, setting the flow rate of Ar gas in a small tubular furnace containing the granulated material z to 1000 mL / min (flow velocity: 79.6 m / s), maintaining this for 10 minutes, then setting the heater's heating rate to 10°C / min to raise the temperature to 650°C, and maintaining this temperature for 30 minutes for firing, the process was carried out in the same manner as in Example 1, except that the active material C3 (LiMn) on which carbon is supported was used. 0.4 Fe 0.6 PO4) was obtained.

[0059] Carbon load (total carbon content) The total carbon content of the obtained active material was measured using a carbon-sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.) and determined as the carbon loading amount.

[0060] Measurement of Total Carbon Extraction (TOC) 5g of each obtained active material was taken and placed in an open container (glass beaker) filled with 100mL of distilled water. Then, after stirring for 5 minutes, it was left to stand for 3 days. After standing, the mixture was stirred for 1 minute, filtered, and the filtrate was collected. 50 mL of the obtained filtrate was taken, and the amount of eluted carbon (mg / L) was measured using a total organic carbon analyzer (TOC-L, Shimadzu Corporation).

[0061] Calculation of the ratio of eluted carbon to supported carbon (TOC / supported carbon) The measured amount of eluted carbon (TOC) obtained above was divided by the amount of carbon loaded (total carbon content) to calculate the ratio (TOC / amount of carbon loaded) (mg / (L·mass%)), which was used as an indicator for evaluating the carbon elution reduction effect.

[0062] 《Confirmation test for organic acid elution》 Aluminum foil (3 x 3 cm) was immersed in the filtrate obtained from measuring the amount of eluted carbon and left to stand for 7 days. Then, the aluminum foil was collected and dried at room temperature, and the color change of the aluminum foil surface was visually inspected to check for the presence or absence of discoloration (brownish-red). If discoloration is present, it can be determined that organic acids have leached out.

[0063] Evaluation of battery characteristics (cycle characteristics) Each of the obtained active materials was used as a positive electrode material to fabricate a positive electrode for a lithium-ion secondary battery. Specifically, each of the obtained active materials, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added and thoroughly kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of 20 μm thick aluminum foil using a coating machine and vacuum dried at 80°C for 12 hours. After that, it was punched out into a φ14 mm disc shape and pressed with a hand press at 20 kN for 2 minutes to form the positive electrode.

[0064] Next, a coin-type secondary battery was constructed using the above-mentioned positive electrode. A lithium foil stamped to a diameter of φ15 mm was used as the negative electrode. For the electrolyte, a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 was used, in which LiPF6 was dissolved at a concentration of 1 mol / L. A porous polymer film was used as the separator. These battery components were assembled and housed in an atmosphere with a dew point of -50°C or lower using a conventional method to obtain a coin-type secondary battery (CR-2032).

[0065] Next, using the obtained coin-type secondary battery, the charge and discharge cycles were repeated 1000 times at 1C in a 45°C environment using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Co., Ltd.) to determine the discharge capacity (mAh / g) and the cycle characteristic value (capacity retention rate (%)) was calculated using the following formula (x). Cycle characteristics (%) = (Discharge capacity after 1000 cycles) / (Discharge capacity after 1 cycle) × 100 ...(x)

[0066] [Table 1]

Claims

1. Formula (A) below: 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 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, which is represented by and has carbon supported, comprising the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain slurry water i. (II) The obtained slurry water i is subjected to a hydrothermal reaction and then spray-dried to obtain granules. (III) A process of calcining the obtained granules under an inert gas atmosphere. Equipped with, Step (I) and / or step (II) include a step of adding a conductive carbon material, A method for producing a positive electrode active material for a lithium-ion secondary battery, wherein in step (III), the flow rate of the inert gas is 250 mL / min or more, and the firing temperature is 700°C to 1200°C.

2. A method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 1, wherein the firing time in step (III) is 90 minutes to 720 minutes.

3. A method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 1 or 2, wherein the amount of carbon supported in 100% by mass of the total positive electrode active material for a lithium-ion secondary battery is 0.5% by mass to 5.0% by mass.

4. A method for producing a positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 3, wherein the conductive carbon material added in step (I) and / or step (II) includes cellulose nanofibers.

5. Formula (A) below: 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 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, which is represented by and has carbon supported, comprising the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain slurry water i. (II) The obtained slurry water i is subjected to a hydrothermal reaction and then spray-dried to obtain granules. (III) A step of calcining the obtained granules under an inert gas atmosphere with a flow rate of 250 mL / min or more. Equipped with, Step (I) and / or step (II) include a step of adding a conductive carbon material, A method for reducing carbon elution from positive electrode active material for lithium-ion secondary batteries, wherein in step (III), the flow rate of the inert gas is 250 mL / min or more, and the firing temperature is 700°C to 1200°C.

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