Manufacturing method of cathode active material for lithium ion secondary batteries

Abstract

To provide a method of manufacturing a cathode active material for lithium ion secondary batteries capable of obtaining a lithium ion secondary battery improved in battery characteristics with simple means while using cellulose which is a relatively inexpensive carbon material.SOLUTION: Provided is a manufacturing method of a cathode active material for lithium ion secondary batteries configured by carrying a carbon by a particle A represented by the formula (A): LiaMnbFecMxPO4. The manufacturing method of the cathode active material for lithium ion secondary batteries includes the following steps (I)-(III) of: (I) preparing slurry water (i) containing preliminary particles A' of the particles A, cellulose and water; (II) applying the obtained slurry water (i) to mechanical strong stirring and obtaining slurry water (ii) by fibrillating the cellulose; and (III) spraying, drying and then calcinating the obtained slurry water (ii).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 a simple means using cellulose.

Background Art

[0002] Development of secondary batteries used in portable electronic devices, hybrid vehicles, electric vehicles, etc. has been carried out, and in particular, lithium ion secondary batteries are widely known. Among these, a positive electrode active material composed of a compound such as Li(Fe,Mn)PO having an olivine type structure is not greatly affected by resource constraints and can exhibit high safety, so it is an optimal positive electrode material for obtaining a high-output and large-capacity lithium ion secondary battery. On the other hand, in order to impart sufficient conductivity, it is desirable to support carbon on such a positive electrode active material, and various manufacturing methods have been developed. 4 For example, Patent Document 1 discloses a method of coating a surface of positive electrode active material particles with a carbon nanostructure such as carbon nanotubes or nanographene by plasma decomposition of an organic compound. Further, Patent Document 2 discloses a method for producing a positive electrode forming material in which carbon nanofibers whose surfaces are hydrophilized by an oxidation treatment are dispersed in a dispersion medium and adhered to the particle surfaces of a positive electrode active material.

[0003]

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] ​However, in the manufacturing method using plasma decomposition as in Patent Document 1, special equipment and technology are required, and the complication of the manufacturing process is inevitable. Further, even in the technology described in Patent Document 2, it is necessary to obtain an expensive carbon material such as carbon nanofibers, and detailed studies for realizing simple means have not been sufficiently made.

[0006] Therefore, the present invention relates to a method for manufacturing a positive electrode active material for a lithium ion secondary battery, which can obtain a lithium ion secondary battery having excellent battery characteristics while using cellulose, which is a relatively inexpensive carbon material, by simple means.

Means for Solving the Problems

[0007] Therefore, as a result of intensive studies to solve the above problems, the present inventor prepared a slurry water containing preliminary particles, cellulose, and water for forming a positive electrode active material for a lithium ion secondary battery, and then subjected it to mechanical strong stirring to obtain a slurry water in which cellulose is defibrated, and by subjecting this to spray drying and firing, a method for manufacturing a positive electrode active material that realizes a lithium ion secondary battery that exhibits excellent battery physical properties by simple means while using inexpensive cellulose was found.

[0008] That is, the present invention provides 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 manufacturing a positive electrode active material for a lithium ion secondary battery in which carbon is supported on particles A represented by the following, the following steps (I) to (III): (I) Step of preparing slurry water i containing preliminary particle A' of particle A, cellulose, and water (II) Step of subjecting the obtained slurry water i to mechanical strong stirring to obtain slurry water ii in which cellulose is defibrated (III) Step of spray-drying the obtained slurry water ii and then firing it Provided is a method for manufacturing a positive electrode active material for a lithium-ion secondary battery, which comprises the above steps.

Effect of the Invention

[0009] According to the manufacturing method of the present invention, as a carbon material, by using inexpensive cellulose without using expensive nanofibers such as carbon nanofibers and cellulose nanofibers, a positive electrode active material for manufacturing a lithium-ion secondary battery having excellent battery physical properties can be produced by a simple means. Moreover, the lithium-ion secondary battery thus obtained exhibits battery physical properties equivalent to those of a battery obtained from a positive electrode active material using cellulose nanofibers.

Embodiment for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail. The manufacturing method of the positive electrode active material for a lithium-ion secondary battery of the present invention is a manufacturing method for obtaining a positive electrode active material for a lithium-ion secondary battery in which carbon is supported on particle A 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.)

[0011] In the above formula (A), for a, it is preferably 0.6 ≦ a ≦ 1.2, more preferably 0.65 ≦ a ≦ 1.15, and even more preferably 0.7 ≦ a ≦ 1.1. For b, it is preferably 0.4 ≦ b ≦ 0.8. For c, it is preferably 0.2 ≦ c ≦ 0.6. For x, it may be 0 ≦ x ≦ 0.2, or even 0 ≦ x ≦ 0.15, or 0 ≦ x ≦ 0.1. Further, from the viewpoint of further increasing the discharge capacity, M may further be Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd.

[0012] 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 0.5 Fe 0.5 PO 4 , LiMn 0.6 Fe 0.4 PO 4 , LiMn 0.7 Fe 0.3 PO 4 , LiMn 0.75 Fe 0.25 PO 4 , LiMn 0.8 Fe 0.2 PO 4 , LiMn 0.9 Fe 0.1 PO 4 , LiMn 0.75 Fe 0.15 Mg 0.1 PO 4 , LiMn 0.75 Fe 0.19 Zr 0.03 PO 4 , Li 1.2 Mn 0.63 Fe 0.27 PO 4 , Li 0.6 Mn 0.84 Fe 0.36 PO 4include, etc. Among them, LiMn 0.75 Fe 0.25 PO 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 、Li 1.2 Mn 0.63 Fe 0.27 PO 4 are preferred.

[0013] 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 in which carbon is supported on particle A represented by the above formula (A), and the following steps (I) to (III): (I) A step of preparing slurry water i containing preliminary particle A' of particle A, cellulose, and water (II) A step of subjecting the obtained slurry water i to mechanical strong stirring to obtain slurry water ii in which cellulose is defibrated (III) A step of spray-drying the obtained slurry water ii and then firing it is a manufacturing method comprising.

[0014] Step (I) included in the manufacturing method of the present invention is a step of preparing slurry water i containing preliminary particle A' of particle A, cellulose, and water. Here, the preliminary particle A' of particle A used in step (I) is a particulate compound using a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, and a phosphoric acid compound as raw material compounds. As will be described later, regardless of whether it is before or after being subjected to a hydrothermal reaction, it means all the particles that will form particle A as the present invention progresses through the steps.

[0015] In step (I) of the present invention, as the preliminary particles A' of particles A, a compound obtained by subjecting the above raw material compound to a hydrothermal reaction may be used, and then slurry water i containing cellulose and water may be prepared. Such step (I) is hereinafter referred to as "step (I)-a". In this case, the preliminary particles A' of particles A mean the primary particles of particles A formed by undergoing a hydrothermal reaction. Further, in step (I), slurry water i may be prepared by subjecting slurry water containing the above raw material compound, cellulose, and water to a hydrothermal reaction. Such step (I) is hereinafter referred to as "step (I)-b". In this case, the preliminary particles A' of particles A mean all the particles of the above raw material compound mixed in the slurry water before being subjected to the hydrothermal reaction. That is, in the production method of the present invention, as step (I), after passing through either step (I)-a or step (I)-b, as described later, it is only necessary to shift to step (II) using the thus obtained slurry water i.

[0016] Examples of the lithium compound that can be used as the raw material compound for the preliminary particles A' of particles A include hydroxides (such as LiOH·H 2 O, LiOH), carbonates, sulfates, and acetates. Among them, hydroxides are preferred.

[0017] The metal compound that can be used as the raw material compound for the preliminary particles A' of particles A only needs to contain at least a manganese compound and / or an iron compound. Examples of the manganese compound that can be used as the raw material compound for the preliminary particles A' of particles A include manganese acetate, manganese nitrate, manganese sulfate, etc. These may be used alone or in combination of two or more. Among them, from the viewpoint of enhancing battery characteristics, manganese sulfate is preferred. Examples of the iron compound that can be used as the raw material compound for the preliminary particles A' of particles A include iron acetate, iron nitrate, iron sulfate, etc. These may be used alone or in combination of two or more. Among them, from the viewpoint of enhancing battery characteristics, iron sulfate is preferred. In addition to these manganese compounds and iron compounds, metal (M: M has the same meaning as M in formula (A)) compounds other than the manganese compounds and iron compounds may also be used.

[0018] Examples of the phosphate compound that can be used as the raw material compound of the preliminary particle A' of particle A include orthophosphoric acid (H 3 PO 4 , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, and the like. Among them, it is preferable to use phosphoric acid, and it is preferably used as an aqueous solution with a concentration of 70% by mass to 90% by mass.

[0019] First, as step (I), the case of adopting step (I)-a will be described. In step (I)-a, as the preliminary particle A' of particle A, the primary particles of particle A formed by undergoing a hydrothermal reaction are used. In obtaining such a preliminary particle A' of particle A, for example, after mixing a phosphate compound into the slurry water a' containing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound is added to obtain slurry water A' containing the preliminary particle A' of particle A, and then such slurry water A' may be subjected to a hydrothermal reaction.

[0020] The content of the lithium compound in the slurry water a' is preferably 5 parts by mass to 50 parts by mass, more preferably 7 parts by mass to 45 parts by mass, based on 100 parts by mass of water. Before adding the phosphate compound to the slurry water a', it is preferable to stir the slurry water a' in advance. The stirring time of such slurry water a' is preferably 1 minute to 15 minutes, more preferably 3 minutes to 10 minutes. Also, the temperature of the slurry water a' is preferably 20°C to 90°C, more preferably 20°C to 70°C.

[0021] When mixing phosphoric acid with the slurry water a', it is preferable to dropwise add the phosphoric acid while stirring the slurry water a'. The dropping time of the phosphoric acid into the slurry water a' is preferably 5 seconds to 10 minutes, more preferably 5 seconds to 5 minutes. Also, the stirring time of the slurry water i' while dropping the phosphoric acid is preferably 0.5 hours to 24 hours, more preferably 3 hours to 12 hours. Further, the stirring speed of the slurry water a' while dropping the phosphoric acid is preferably 200 rpm to 700 rpm, more preferably 250 rpm to 600 rpm, and even more preferably 300 rpm to 500 rpm. When stirring the slurry water a', it is further preferable to cool it to a temperature below the boiling point temperature of the slurry water a'. Specifically, it is preferably cooled to 80°C or lower, and more preferably cooled to 20°C to 60°C.

[0022] After mixing the phosphoric acid compound, the slurry water a' preferably contains 2.0 moles to 4.0 moles of lithium per 1 mole of phosphoric acid, more preferably 2.0 moles to 3.1 moles. The above lithium compound and phosphoric acid compound may be used so as to obtain such an amount. More specifically, after mixing the phosphoric acid compound, the slurry water a' preferably contains 2.7 moles to 3.3 moles of lithium per 1 mole of phosphoric acid, and more preferably 2.8 moles to 3.1 moles.

[0023] After mixing the phosphoric acid compound, it is advisable to reduce the dissolved oxygen in the slurry water a' by nitrogen bubbling. By reducing the dissolved oxygen, the oxidation of the metal compound added in the next step can be effectively suppressed.

[0024] From the viewpoint of more effectively suppressing the oxidation on the surface of the preliminary particles A' of the particles A, it is preferable to set the dissolved oxygen concentration in the slurry water a' to 1.5 mg / L or less, and more preferably 0.5 mg / L or less. Next, a metal compound containing at least a manganese compound and / or an iron compound is added to the slurry water a' to obtain a slurry water A' containing the preliminary particles A' of the particles A.

[0025] When using both a manganese compound and an iron compound, the molar ratio of their use (manganese compound: iron compound) is preferably from 99:1 to 30:70, more preferably from 90:10 to 40:60, and even more preferably from 85:15 to 45:55. Further, the total addition amount of these metal compounds is preferably from 0.98 mol to 1.01 mol, more preferably from 0.99 mol to 1.005 mol, per 1 mol of phosphate ions contained in the slurry water a'. In addition, when using a metal (M: M has the same meaning as M in formula (A)) compound other than the manganese compound and the iron compound together with these manganese compounds or iron compounds, the total addition amount of the manganese compound, the iron compound, and the metal compound other than the manganese compound and the iron compound is preferably from 0.95 to 1.01 mol, more preferably from 0.98 to 1.005 mol, per 1 mol of phosphate ions contained in the slurry water a'.

[0026] Next, in step (I)-a, the obtained slurry water A' is subjected to a hydrothermal reaction. The amount of water used when subjecting to such a hydrothermal reaction is preferably from 10 mol to 50 mol, more preferably from 12.5 mol to 45 mol, per 1 mol of phosphate ions contained in the slurry water A', from the viewpoints of the solubility of the metal compound, the ease of stirring, and the efficiency of synthesis, etc. Further, the temperature during the hydrothermal reaction may be 100°C or higher, and preferably 130°C to 180°C. The hydrothermal reaction is preferably carried out in a pressure-resistant container. When the reaction is carried out at 130°C to 180°C, the pressure at this time is preferably from 0.3 MPa to 1.1 MPa, and when the reaction is carried out at 140°C to 160°C, the pressure is preferably from 0.3 MPa to 0.8 MPa. The hydrothermal reaction time is preferably from 0.1 hour to 48 hours, and more preferably from 0.2 hour to 24 hours.

[0027] The content of the preliminary particles A' of the particles A in the obtained slurry water A' is preferably from 10 to 50% by mass, more preferably from 15 to 45% by mass, and even more preferably from 20 to 40% by mass. In addition, in step (I)-a, the slurry water A' after the hydrothermal reaction may be used as it is (step (I)-a'), or the slurry water A' after the hydrothermal reaction may be filtered, washed with water, and dried to isolate the preliminary particles A' of the particles A once, and then the slurry water A'' obtained by repulping may be used instead of such slurry water A' (step (I)-a''). Among them, from the viewpoint of obtaining a highly useful positive electrode active material while simplifying the manufacturing method of the present invention, it is more preferable to adopt step (I)-a' than to adopt step (I)-a''.

[0028] In step (I)-a, after obtaining the slurry water A' or the slurry water A'' after the hydrothermal reaction, cellulose is added thereto to prepare a slurry water i containing the preliminary particles A' of the particles A, cellulose, and water. Here, the cellulose is used as a carbon source, is defibrated by being subjected to mechanical strong stirring in the subsequent step (II), and is then carbonized through the subsequent step (III) to form a periodic structure, and is thus favorably and uniformly supported on the particles A represented by the above formula (A) as carbon, and the battery characteristics can be effectively enhanced.

[0029] Cellulose usually has a powder form, and the particle size of such cellulose is preferably 1 μm to 1000 μm, more preferably 3 μm to 1000 μm, still more preferably 3 μm to 500 μm, and even more preferably 5 μm to 200 μm from the viewpoint of facilitating uniform mixing with the preliminary particles A' of the particles A and effectively promoting the defibration of the powdered cellulose by subjecting it to mechanical strong stirring in the subsequent step (II). Note that the particle size of cellulose is the value of the largest mesh opening among the mesh openings through which 90% by mass or more of the total mass passes.

[0030] The amount of cellulose added in step (I)-a' or step (I)-a'' may be appropriately adjusted so that the amount of carbon supported on particle A based on the total mass of the positive electrode active material for a lithium ion secondary battery obtained by the production method of the present invention corresponds to the amount of carbon derived from the defibrated cellulose, to be a desired amount in terms of the amount of carbon atoms of cellulose based on the total mass of the positive electrode active material for a lithium ion secondary battery. Specifically, the amount of carbon atoms of cellulose in 100% by mass of the obtained positive electrode active material for a lithium ion secondary battery is the amount of carbon supported on particle A, preferably 0.3% by mass to 6% by mass, more preferably 0.4% by mass to 3.1% by mass, and still more preferably 0.5% by mass to 1.5% by mass. Cellulose may be added to slurry water A' or slurry water A'' to prepare slurry water i so as to be such an amount. Note that the amount of carbon atoms of cellulose derived from the defibrated cellulose present in the positive electrode active material for a lithium ion secondary battery can be determined by measurement using a carbon-sulfur analyzer.

[0031] When adding cellulose here, in the case of step (I)-a' where slurry water A' after being subjected to a hydrothermal reaction is used as it is, after adding cellulose, dehydration is performed, and then repulping is carried out to prepare slurry water i. At this time, it is preferable to stir slurry water i in advance before dehydration after adding cellulose. The stirring time of such slurry water i is preferably 3 minutes to 60 minutes, more preferably 10 minutes to 60 minutes. Also, the temperature of slurry water i is preferably 5°C to 80°C, more preferably 20°C to 60°C. Also, in the case of step (I)-a'' where slurry water A' after being subjected to a hydrothermal reaction is filtered, washed with water, and dried to isolate preliminary particle A' of particle A once, and then repulped, and slurry water A'' containing preliminary particle A' of particle A is used, the slurry water after adding cellulose may be used as it is as slurry water i.

[0032] On the other hand, the case of adopting step (I)-b as step (I) will be described. In step (I)-b, the slurry water B' containing the raw material compound, cellulose, and water used as the preliminary particle A' of particle A is subjected to a hydrothermal reaction. The content of each raw material compound in the slurry water B' is the same as the content of each raw material compound in the slurry water a' in step (I)-a. Also, the addition amount of cellulose may be an amount such that the content of cellulose falls within the above range based on the mass of particle A constituting the positive electrode active material for a lithium ion secondary battery obtained by the production method of the present invention. When subjecting the slurry water B' to a hydrothermal reaction, each of the various conditions is the same as in the case of the hydrothermal reaction in step (I)-a. Next, in step (I)-b, the obtained slurry water after the hydrothermal reaction is dehydrated and then repulped to prepare slurry water i.

[0033] From the viewpoint of effectively performing a mechanical strong stirring treatment and effectively advancing the fibrillation of cellulose in the subsequent step (II), the solid content concentration of the slurry water i obtained in step (I) is preferably 10% by mass to 50% by mass, more preferably 15% by mass to 45% by mass, and still more preferably 20% by mass to 40% by mass. Also, from the same viewpoint, the viscosity of the slurry water i at 20°C is preferably 1 mPa·sec to 300 mPa·sec, more preferably 10 mPa·sec to 250 mPa·sec, and still more preferably 10 mPa·sec to 200 mPa·sec. Note that the viscosity of the slurry water i means a value measured by a Brookfield B-type viscometer.

[0034] Step (II) in the manufacturing method of the present invention is a step of subjecting the slurry water i obtained in step (I) to mechanical strong stirring to obtain slurry water ii in which cellulose is defibrated. As a result, while applying a strong impact force such as a shearing force to the slurry water i and stirring, it is possible to appropriately defibrate the cellulose contained in the slurry water i and obtain slurry water ii in which the cellulose defibrated together with the preliminary particles A' is well dispersed. Therefore, by using such slurry water i and passing through the subsequent step (III), it is possible to uniformly and firmly support the carbon derived from the refined cellulose on the particles A.

[0035] In subjecting to mechanical strong stirring, an apparatus capable of stirring while applying a strong impact force such as a shearing force to the solid content in the slurry water i may be used, and it can be appropriately selected and used, such as a planetary apparatus, a rotor-stator type apparatus, a blade rotation type apparatus, etc. Examples of the stirring method of the apparatus include a circulation type, a batch type, and a pass type. From the viewpoint of effectively defibrating cellulose, the stirring method is preferably a circulation type. Specific examples of such an apparatus include a media stirring mill, a wet jet mill, a homogenizer, a ball mill, and a planetary mill. More specifically, an attritor, a bead mill, a wet jet mill, a high-speed dissolver, a Henschel mixer, etc. may be mentioned. Among them, from the viewpoint of simply and effectively performing mechanical strong stirring, it is preferable to use a media stirring mill or a wet jet mill.

[0036] In step (II), when performing mechanical strong stirring, the operating conditions such as the treatment time and the number of treatments may be appropriately set according to the apparatus used. In addition, the temperature of the slurry water i when subjecting to mechanical strong stirring does not particularly require heating or warming, and for example, it may be usually 5°C to 40°C, preferably 10°C to 30°C.

[0037] More specifically, for example, when using an attritor which is a media agitation mill, the processing time of mechanical strong agitation is preferably 12 hours to 72 hours, more preferably 24 hours to 72 hours, and even more preferably 36 hours to 72 hours. As the media, it is preferably made of ceramic, and it is more preferable to select zirconia balls. The media diameter is preferably 0.5 mm to 30 mm, more preferably 1 mm to 10 mm, from the viewpoint of allowing good fibrillation of cellulose. Also, for example, when using a bead mill which is a media agitation mill, the number of times of mechanical strong agitation is preferably 1 time to 15 times, more preferably 5 times to 10 times. As the media, it is preferably made of ceramic, and it is more preferable to select zirconia balls. The media diameter is preferably 0.1 mm to 3 mm, more preferably 0.5 mm to 3 mm. In addition, when using a star mill which is a media agitation mill or a starburst which is a wet jet mill, the number of times of mechanical strong agitation is preferably 5 times to 30 times, and even more preferably 10 times to 30 times. When using a high-speed dissolver (manufactured by Makino), the processing time of mechanical strong agitation is preferably 5 minutes to 60 minutes.

[0038] In step (II), from the viewpoint of reliably performing the fibrillation of cellulose, after subjecting to mechanical strong agitation and before shifting to step (III), it is preferable that the slurry water passed through a mesh with an opening of 250 μm or less in advance is used as slurry water ii. If the cellulose is in an unfibrillated state, it will remain on the mesh without passing through a mesh with such an opening, so it can be removed, and it is possible to ensure the collection of slurry water containing only fibrillated cellulose. The opening of the mesh to be used may be 250 μm or less, preferably 75 μm to 250 μm, and more preferably 75 μm to 150 μm.

[0039] Step (III) included in the production method of the present invention is a step of spray-drying the slurry water ii obtained in step (II) and then firing it. In step (III), when performing spray drying, the operating conditions may be appropriately set according to the equipment used. For example, as the processing conditions in a micro mist dryer (MDL-050M, manufactured by GF Co., Ltd.) equipped with a four-fluid nozzle, the hot air temperature is preferably 110°C to 300°C, and more preferably 150°C to 250°C. Also, the ratio of the supply amount of hot air to the supply amount of slurry water (supply amount of hot air / supply amount of slurry water) is preferably 500 to 10,000, and more preferably 1,000 to 9,000.

[0040] The average particle size of the granulated product obtained by spray drying is the D value in the particle size distribution based on the laser diffraction / scattering method. 50 Preferably, it is 1 to 20 μm, and more preferably 3 to 15 μm. Here, the D value in the particle size distribution measurement 50 is a value obtained from the volume-based particle size distribution based on the laser diffraction / scattering method, and the D value 50 means the particle size (median diameter) at 50% cumulative. Therefore, the particle size of such granulated products may be adjusted by appropriately optimizing the operating conditions of the equipment used.

[0041] The obtained granulated product is then fired to obtain a positive electrode active material in which carbon derived from cellulose is supported on the particles A represented by the above formula (A). The firing conditions of the granulated product are preferably in a reducing atmosphere or an inert atmosphere. The firing temperature is preferably 400°C or higher, more preferably 600 to 800°C, the firing time is preferably 10 minutes to 3 hours, and more preferably 30 minutes to 1.5 hours.

[0042] Thus, the positive electrode active material for a lithium ion secondary battery obtained by the production method of the present invention is such that the carbon derived from cellulose that has been defibrated is uniformly supported with high uniformity so as to fill the gaps between the particles A without unnecessary uneven distribution in the particles A represented by the above formula (A). In this way, since the carbon derived from cellulose effectively fills the interparticle voids of the packing structure formed by the particles A, a conductive path is formed between the particles A in a state where the packing density of the positive electrode active material is increased, and thus excellent battery characteristics are exhibited.

[0043] The obtained positive electrode active material for a lithium ion secondary battery is a material that can be used as a positive electrode active material for a lithium ion secondary battery. Specifically, for example, after kneading the obtained positive electrode active material for a lithium ion secondary battery with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. to prepare a positive electrode slurry, it is coated on a current collector and then press-molded to produce a positive electrode. The lithium ion secondary battery to which the positive electrode obtained by using such a positive electrode active material for a lithium ion secondary battery can be applied is not particularly limited as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte as essential components.

[0044] Here, regarding the negative electrode, as long as it can occlude lithium ions during charging and release them during discharging, its material composition is not particularly limited, and a known material composition can be used. For example, lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, or a carbon material such as amorphous carbon can be used. And it is particularly preferable to use an electrode formed of an intercalation material that can electrochemically occlude and release 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 can be used.

[0045] The electrolyte is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent usually used in the electrolyte of a lithium-ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds, etc. can be used.

[0046] The type of the supporting salt is not particularly limited, but LiPF 6 , LiBF 4 , LiClO 4 and LiAsF 6 inorganic salts selected from, derivatives of the inorganic salts, 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 it is preferable that it is at least one of organic salts selected from and derivatives of the organic salts.

[0047] The separator electrically insulates the positive electrode and the negative electrode and serves to hold the electrolyte. For example, a porous synthetic resin film, particularly a porous film of a polyolefin-based polymer (polyethylene, polypropylene) may be used.

[0048] The solid electrolyte electrically insulates the positive electrode and the negative electrode and exhibits high lithium-ion conductivity. For example, La 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 Si 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 may be used.

[0049] 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 type, square type, etc., or an irregular shape enclosed in a laminated exterior body.

Examples

[0050] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0051] [Example 1] LiOH·H 2 O 4.05 kg and 120 L of water were mixed to obtain slurry water x1. Next, while maintaining the obtained slurry x1 at a temperature of 25°C, 3.75 kg of an 83% phosphoric acid aqueous solution was dropped at 1 L / min and stirred for 10 minutes to obtain slurry water x2 containing Li 3 PO 4 After nitrogen bubbling was performed on the obtained slurry water x2 to make the dissolved oxygen concentration of the slurry water x2 0.5 mg / L, 5.75 kg of MnSO 4 ·5H 2 O and 2.20 kg of FeSO 4 ·7H 2 O were added to the entire amount of the slurry water x2 to obtain slurry water x3. The molar ratio (manganese compound: iron compound) of the added MnSO 4 and FeSO 4 was 75:25. Next, the obtained slurry water x3 was put into an autoclave and subjected to a hydrothermal reaction at 180°C for 1 hour to obtain slurry water x4 containing preliminary particles A' of particle A. The pressure in the autoclave was 1.0 MPa.

[0052] To 137.75 kg of slurry water x4, 0.4 kg of powdered cellulose (KC flock, moisture content 2%, manufactured by Nippon Paper Industries Co., Ltd.) (3.5 parts by mass with respect to 100 parts by mass of the preliminary particles A' of particle A) was added, and then stirred with a stirrer for 10 minutes for dehydration to obtain an aggregate B of the preliminary particles A' and the powdered cellulose. To 1 part by mass of the obtained aggregate B, 4 parts by mass of water was added, and after stirring for 10 minutes and then dehydrating, this treatment was repeated 3 times, and finally water was added so that the content of the aggregate B became 40% by mass to obtain slurry water i-1 (solid content concentration: 41.4% by mass, viscosity at 25°C: 100 mPa·sec or less). The powder obtained by drying the slurry water i-1 was evaluated using a powder X-ray diffractometer, and the crystalline material was found to be only particles represented by LiMn 0.75 Fe 0.25 PO 4 .

[0053] 12 kg of the slurry water i-1 was placed in an attritor mill (MA15SE, tank capacity 100 L, 40 L of φ3 zirconia balls, temperature 10 °C, manufactured by Nippon Coke Co., Ltd.), and after stirring for 24 hours while circulating the slurry water i-1 inside the apparatus, it was passed through a mesh with an opening of 150 μm to obtain slurry water ii-1 (viscosity at 25 °C: 100 mPa·sec or less). Note that only an amount of cellulose less than 0.01 g remained on the mesh.

[0054] The obtained slurry water ii-1 was spray-dried using a spray dryer (MDL-050M, nozzle air flow rate 40 L / min, air supply temperature 190 °C, manufactured by GF Co., Ltd.) to obtain granulated particles (average particle size (D 50 value): 12 μm). Next, the obtained granulated particles were calcined at 700 °C for 1 hour in a nitrogen atmosphere (purity 99.9%), and then passed through a mesh with an opening of 75 μm to obtain a positive electrode active material (LiMn 0.75 Fe 0.25 PO 4 ), with a carbon loading of 2.0 mass%).

[0055] [Example 2] Using the same attritor mill as in Example 1, 12 kg of the slurry water i-1 obtained in Example 1 was stirred for 48 hours while circulating it inside the apparatus, and then passed through a mesh with an opening of 75 μm to obtain slurry water ii-2 (viscosity at 25 °C: approximately 150 mPa·sec). Note that only an amount of cellulose less than 0.01 g remained on the mesh. Next, except for using the obtained slurry water ii-2 instead of the slurry water ii-1, in the same manner as in Example 1, a positive electrode active material (LiMn 0.75 Fe 0.25 PO 4, a carbon content of 2.0% by mass was obtained.

[0056] [Example 3] 12 kg of the slurry water i-1 obtained in Example 1 was put into a wet jet mill (Starburst Turbo, processing pressure 200 MPa, manufactured by Sugino Machine Limited) and processed 5 times, and then passed through a mesh with an opening size of 150 μm to obtain slurry water ii-3 (viscosity at 25°C: 100 mPa·sec). Note that only an amount of cellulose less than 0.01 g remained on the mesh. Next, except that the obtained slurry water ii-3 was used instead of slurry water ii-1, in the same manner as in Example 1, a positive electrode active material (LiMn 0.75 Fe 0.25 PO 4 , a carbon content of 2.0% by mass was obtained.

[0057] [Example 4] 12 kg of the slurry water i-1 obtained in Example 1 was put into a wet jet mill (Starburst Turbo, processing pressure 200 MPa, manufactured by Sugino Machine Limited) and processed 30 times, and then passed through a mesh with an opening size of 75 μm to obtain slurry water ii-4 (viscosity at 25°C: about 150 mPa·sec). Note that only an amount of cellulose less than 0.01 g remained on the mesh. Next, except that the obtained slurry water ii-4 was used instead of slurry water ii-1, in the same manner as in Example 1, a positive electrode active material (LiMn 0.75 Fe 0.25 PO 4 , a carbon content of 2.0% by mass was obtained.

[0058] [Reference Example 1] To 4135.75 kg of the slurry water x obtained in Example 1, 4 kg of cellulose nanofibers (KY100G, water content 90%, manufactured by Daicel Chemical Industries, Ltd.) were added, and the mixture was stirred for 1 hour with a stirrer and dehydrated to obtain preliminary particles C'. To 1 part by mass of the obtained preliminary particles C', 4 parts by mass of water were added, and after stirring for 10 minutes, dehydration was performed, and this process was repeated 3 times. Finally, water was added so that the content of the preliminary particles C' was 40% by mass to obtain slurry water i-c (viscosity at 25°C: 400 mPa·sec or less). In addition, when the powder obtained by drying the slurry water i-c was evaluated with a powder X-ray diffractometer, the crystalline substance was LiMn 0.75 Fe 0.25 PO 4 and it was only composed of particles represented by Next, the obtained slurry water i-c was subjected to the same procedure as in Example 1 except that the slurry water i-c was used instead of the slurry water ii-1 without being subjected to mechanical strong stirring, and a positive electrode active material (LiMn 0.75 Fe 0.25 PO 4 , carbon loading: 2.0% by mass) in which carbon derived from cellulose nanofibers was supported was obtained.

[0059] [Comparative Example 1] To the slurry water i-1 obtained in Example 1, without performing stirring using an attritor mill and without passing it through a mesh, it was used instead of the slurry water ii-1, and in the same manner as in Example 1, a positive electrode active material (LiMn 0.75 Fe 0.25 PO 4 , carbon loading: 2.0% by mass) in which carbon derived from cellulose was supported was obtained. In addition, when the slurry water i-1 used instead of the slurry water ii-1 was passed through a mesh with an opening of 150 μm, about 10 g of only cellulose remained on the mesh.

[0060] 《Evaluation of Charge and Discharge Characteristics》 Using each of the obtained positive electrode active materials, a positive electrode of a lithium-ion secondary battery was fabricated. Specifically, the obtained positive electrode active material, Ketjen black, and polyvinylidene fluoride were mixed at a blending ratio of 75:15:10 by weight, and N-methyl-2-pyrrolidone was added thereto and kneaded well to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of an aluminum foil with a thickness of 20 μm using a coater, and vacuum dried at 80 °C for 12 hours. Then, it was punched into a disk shape with a diameter of 14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode. Next, a coin-type lithium-ion secondary battery was constructed using the above positive electrode. A lithium foil punched into a diameter of 15 mm was used for the negative electrode. As the electrolytic solution, a solution in which LiPF 6 was dissolved at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1:1 was used. As the separator, a known one such as a polymer porous film made of polypropylene was used. These battery components were incorporated and housed by a conventional method in an atmosphere with a dew point of -50 °C or lower to manufacture a coin-type lithium secondary battery (CR-2032).

[0061] Charge and discharge tests were conducted at a constant current density using the manufactured secondary battery. The charging conditions at this time were constant current charging with a current of 0.1 CA (17 mAh / g) and a voltage of 4.5 V, and the discharging conditions were constant current discharging with a current of 3 CA and a cut-off voltage of 2.0 V. All temperatures were set at 30 °C. The results are shown in Table 1.

[0062]

Table 1

[0063] According to Table 1 above, it can be seen that for the positive electrode active materials of Examples 1 to 4 obtained by the manufacturing method of the present invention, despite using cellulose, it is possible to exhibit battery characteristics equivalent to those of Reference Example 1 using cellulose nanofibers. Also, it can be seen that for the positive electrode active material of Comparative Example 1, which uses cellulose but is obtained without mechanical strong stirring, the battery characteristics cannot be sufficiently improved.

Claims

1. A lithium-ion secondary battery positive electrode active material manufacturing method in which carbon is supported on particles A 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.) The method includes the following steps (I) to (III): (I) A step of preparing slurry water i containing preliminary particles A' of particles A, cellulose, and water (II) A step of subjecting the obtained slurry water i to mechanical strong stirring to obtain slurry water ii in which cellulose is defibrated (III) A step of spray-drying the obtained slurry water ii and then firing it A manufacturing method of a positive electrode active material for a lithium-ion secondary battery, comprising the above steps.

2. The manufacturing method of a positive electrode active material for a lithium-ion secondary battery according to Claim 1, wherein the solid content concentration of slurry water i in step (I) is 10% by mass to 50% by mass.

3. The manufacturing method of a positive electrode active material for a lithium-ion secondary battery according to Claim 1 or 2, wherein in step (I), after obtaining preliminary particles A' of particles A through a step of subjecting them to a hydrothermal reaction in advance, slurry water i is prepared using cellulose and water.

4. The manufacturing method of a positive electrode active material for a lithium-ion secondary battery according to Claim 1 or 2, wherein in step (II), after subjecting it to mechanical strong stirring, the slurry water that has passed through a mesh with an opening of 250 μm or less is obtained as slurry water ii.

5. The manufacturing method of a positive electrode active material for a lithium-ion secondary battery according to Claim 1 or 2, wherein the amount of carbon supported on particles A in the total mass of the positive electrode active material for a lithium-ion secondary battery is 0.3% by mass to 6% by mass.

6. The manufacturing method of a positive electrode active material for a lithium-ion secondary battery according to Claim 1 or 2, wherein cellulose is in powder form and has a particle size of 1 μm to 1000 μm.

Images