JP2022090425A - Method for manufacturing cathode active material used for lithium ion secondary battery - Google Patents

Abstract

To provide a method for manufacturing a cathode active material, enabling suppression of bonding of particles included in a raw material powder of the cathode active material caused by sintering of the particles.SOLUTION: A method for manufacturing a cathode active material disclosed here comprises: a cathode active material raw material fine particle preparation step of preparing a transition metal hydroxide having an average particle size in a laser diffraction and light scattering method of less than 4 μm; a mixing step of mixing a transition metal hydroxide with a lithium compound; and a sintering step of sintering a mixture obtained by the mixing step. In the sintering step, the sintering is performed by scattering the mixture into gas having temperature reached to a burning temperature.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for producing a positive electrode active material used in a lithium ion secondary battery.

In recent years, secondary batteries such as lithium-ion secondary batteries have been used as portable power supplies for personal computers, mobile terminals, etc., and vehicle drive power supplies for electric vehicles (EV), hybrid vehicles (HV), plug-in hybrid vehicles (PHV), etc. It is suitably used for.

The positive electrode of a lithium ion secondary battery is generally provided with a positive electrode active material capable of storing and releasing lithium ions. For example, Patent Document 1 discloses lithium transition metal-containing composite oxide particles having a narrow particle size distribution and a hollow structure as a positive electrode active material in order to obtain a lithium ion secondary battery having excellent cycle characteristics and output characteristics. Has been done. Since the difference in voltage applied to the particles is small due to the narrow particle size distribution, it is possible to prevent selective deterioration of the particles and realize excellent cycle characteristics. Further, since the hollow structure through which the electrolyte can penetrate increases the reaction area with the electrolyte, excellent output characteristics can be realized.

However, with a positive electrode active material having a hollow structure, it is difficult to improve the tap density (g / cm ³ ), so that there is a problem in improving the cell capacity. Therefore, in order to improve the cell capacity while ensuring the reaction area with the electrolyte, for example, it is considered to use a positive electrode active material having a structure having a small particle size and few internal voids (typically a solid structure). There is.

Japanese Unexamined Patent Publication No. 2018-104276

However, according to the study of the present inventor, if the average particle size of the positive electrode active material raw material powder (positive electrode active material precursor) is reduced (for example, less than 4 μm) in order to produce a positive electrode active material having a small particle size, conventional methods are used. It has been found that severe sintering can occur in the commonly used batch firing method. By such sintering, the particles constituting the raw material powder are bonded to each other, the particle size of the positive electrode active material becomes much larger than the particle size of the raw material powder, and the particle size of the produced positive electrode active material is large. The variation in particle size also increases. Therefore, there is a demand for a technique for suppressing bonding of such raw material powder particles to each other by sintering.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a positive electrode active material capable of suppressing bonding due to sintering of particles contained in a positive electrode active material raw material powder. do.

In order to solve the above problems, the present inventor fired a mixture of a positive electrode active material raw material powder having a small average particle size and a lithium compound under various conditions. As a result of diligent studies, it was found that the positive electrode active material can be produced while suppressing sintering by dispersing the mixture in a gas having reached the firing temperature and firing, and the present invention has been completed. ..
That is, the positive electrode active material manufacturing method disclosed here includes a positive electrode active material raw material powder preparation step for preparing a transition metal hydroxide having an average particle diameter of less than 4 μm in a laser diffraction / light scattering method, and the transition metal water. It includes a mixing step of mixing an oxide and a lithium compound, and a firing step of firing the mixture obtained in the mixing step. The firing step is characterized in that the mixture is dispersed in a gas that has reached the firing temperature to be fired.
According to this configuration, since the mixture of the positive electrode active material raw material powder and the lithium compound can be fired in a state of being dispersed in the gas, the particles contained in the raw material powder can be bonded to each other by sintering. It can be suppressed.

Further, in a preferred embodiment of the method for producing a positive electrode active material disclosed herein, in the firing step, a slurry in which the mixture is dispersed in a non-polar solvent is sprayed into a gas that has reached the firing temperature to obtain the mixture. To bake. Also, in another preferred embodiment, the alkoxide is included as such a non-polar solvent.
According to such a configuration, since the mixture can be fired in a state of being more dispersed in the gas, bonding due to sintering can be further suppressed.

Further, in a preferred embodiment of the method for producing a positive electrode active material disclosed herein, in the firing step, the mixture is fired using a fluidized bed heat treatment apparatus provided with a medium for crushing the mixture. In another preferred embodiment, zirconia balls are used as such media.
According to such a configuration, since the mixture can be fired while being crushed by the media in the fluidized bed, it is possible to suppress an increase in the particle size of the positive electrode active material due to sintering.

Further, in a preferred embodiment of the method for producing a positive electrode active material disclosed herein, the transition metal hydroxide comprises at least one metal element selected from the group consisting of Ni, Mn, and Co.
According to such a configuration, it is possible to produce a positive electrode active material suitable for a lithium ion secondary battery in which an increase in the average particle size due to sintering is suppressed.

It is sectional drawing which shows typically the structure of the lithium ion secondary battery which comprises the positive electrode active material produced by the manufacturing method of the positive electrode active material which concerns on one Embodiment. It is a schematic exploded view which shows the structure of the winding electrode body which comprises the positive electrode active material produced by the manufacturing method of the positive electrode active material which concerns on one Embodiment. It is a rough flowchart for demonstrating the manufacturing process of the positive electrode active material which concerns on one Embodiment. It is a schematic diagram of the firing apparatus used in the manufacturing method of the positive electrode active material which concerns on one Embodiment. It is a schematic diagram of the fluidized bed heat treatment apparatus used in the manufacturing method of the positive electrode active material which concerns on one Embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Since the positive electrode active material produced by the method disclosed here can be suitably used as the positive electrode active material of the lithium ion secondary battery, first, a configuration example of the lithium ion secondary battery 100 will be described. Matters other than those specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art. Further, in the following drawings, members / parts having the same function are designated by the same reference numerals, and duplicate explanations may be omitted or simplified. Further, the dimensional relations (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relations.
Further, when the numerical range is described as A to B (where A and B are arbitrary numerical values) in the present specification, it is the same as the general interpretation and means A or more and B or less. ..

As used herein, the term "secondary battery" generally refers to a battery that can be repeatedly charged and discharged, and includes a so-called storage battery (that is, a chemical battery) such as a lithium ion secondary battery and a capacitor (that is, a physical battery) such as an electric double layer capacitor. ) Is included. Further, in the present specification, the "lithium ion secondary battery" is a secondary battery that uses lithium ions as a charge carrier and charges and discharges between a positive electrode and a negative electrode by the transfer of electric charges associated with the lithium ions. Further, in the present specification, the “active material” refers to a material that reversibly stores and releases charge carriers.

The lithium ion secondary battery 100 shown in FIG. 1 is a square type formed by accommodating a flat wound electrode body 20 and a non-aqueous electrolyte (not shown) inside a battery case 30. It is a sealed battery. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection. Further, a thin-walled safety valve 36 set to release the internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or higher is provided. Further, the battery case 30 is provided with a liquid injection port (not shown) for injecting a non-aqueous electrolyte. The material of the battery case 30 is preferably a metal material having high strength, light weight, and good thermal conductivity, and examples of such a metal material include aluminum and steel.

As shown in FIGS. 1 and 2, the wound electrode body 20 has a long sheet-shaped positive electrode 50 and a long sheet-shaped negative electrode 60 via two long sheet-shaped separators 70. It is an electrode body that is laminated and wound around a winding axis. The positive electrode 50 includes a positive electrode current collector 52 and a positive electrode active material layer 54 formed in the longitudinal direction on one or both sides of the positive electrode current collector 52. On one edge of the positive electrode current collector 52 in the winding axis direction (that is, the sheet width direction orthogonal to the longitudinal direction), the positive electrode active material layer 54 is not formed in a band shape along the edge. A portion where the positive electrode current collector 52 is exposed (that is, a positive electrode current collector exposed portion 52a) is provided. Further, the negative electrode 60 includes a negative electrode current collector 62 and a negative electrode active material layer 64 formed in the longitudinal direction of one side or both sides of the negative electrode current collector 62. At the edge of the negative electrode current collector 62 on one side opposite to the winding axis direction, the negative electrode active material layer 64 is not formed in a band shape along the edge, and the negative electrode current collector 62 is exposed ( That is, the negative electrode current collector exposed portion 62a) is provided. A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are bonded to the positive electrode current collector exposed portion 52a and the negative electrode current collector exposed portion 62a, respectively. The positive electrode current collector plate 42a is electrically connected to the positive electrode terminal 42 for external connection, and realizes conduction between the inside and the outside of the battery case 30. Similarly, the negative electrode current collector plate 44a is electrically connected to the negative electrode terminal 44 for external connection, and realizes conduction between the inside and the outside of the battery case 30.

Examples of the positive electrode current collector 52 constituting the positive electrode 50 include aluminum foil. The positive electrode active material layer 54 can include a positive electrode active material produced by the method disclosed herein. Further, the positive electrode active material layer 54 may contain a conductive material, a binder, or the like. As the conductive material, for example, carbon black such as acetylene black (AB) or other carbon material (graphite or the like) can be preferably used. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.
In the positive electrode active material layer 54, the positive electrode active material and a material (conductive material, binder, etc.) used as needed are dispersed in an appropriate solvent (for example, N-methyl-2-pyrrolidone: NMP) to form a paste (or It can be formed by preparing a composition (in the form of a slurry), applying an appropriate amount of the composition to the surface of the positive electrode current collector 52, and drying the composition.

Examples of the negative electrode current collector 62 constituting the negative electrode 60 include copper foil and the like. The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, a carbon material such as graphite, hard carbon, or soft carbon can be used. Further, the negative electrode active material layer 64 may further contain a binder, a thickener and the like. As the binder, for example, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.
In the negative electrode active material layer 64, a negative electrode active material and a material (binder or the like) used as needed are dispersed in an appropriate solvent (for example, ion-exchanged water) to prepare a paste-like (or slurry-like) composition. , An appropriate amount of the composition can be applied to the surface of the negative electrode current collector 62 and dried.

As the separator 70, various microporous sheets similar to those conventionally used for lithium ion secondary batteries can be used, and for example, a microporous resin made of a resin such as polyethylene (PE) or polypropylene (PP). The sheet is mentioned. The microporous resin sheet may have a single-layer structure or a multi-layer structure having two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). Further, the surface of the separator 70 may be provided with a heat resistant layer (HRL).

As the non-aqueous electrolyte, the same one as that of the conventional lithium ion secondary battery can be used, and typically, an organic solvent (non-aqueous solvent) containing a supporting salt can be used. As the non-aqueous solvent, an aprotic solvent such as carbonates, esters, ethers and the like can be used. Among them, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like can be preferably adopted. Alternatively, a fluorinated solvent such as a fluorinated carbonate such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC) and trifluorodimethylcarbonate (TFDMC) is preferably used. be able to. As such a non-aqueous solvent, one kind may be used alone, or two or more kinds may be used in combination as appropriate. As the supporting salt, for example, lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ can be preferably used. The concentration of the supporting salt is not particularly limited, but is preferably about 0.7 mol / L or more and 1.3 mol / L or less.
The non-aqueous electrolyte may contain components other than the above-mentioned non-aqueous solvent and supporting salt as long as the effects of the present invention are not significantly impaired. It may contain various additives such as thickeners.

The positive electrode active material produced by the production method according to one embodiment is produced by using a positive electrode active material raw material powder having a small average particle size in a laser diffraction / light scattering method (for example, an average particle size of less than 4 μm). In the production method disclosed here, it is possible to suppress the bonding between particles by sintering the raw material powder and perform firing. Therefore, the average particle size of the produced positive electrode active material in the laser diffraction / light scattering method is typically less than 4 μm because the difference from the average particle size of the raw material powder is small, for example, 3.5 μm. It can be less than or equal to or less than 3 μm. Further, typically, such an average particle size is, for example, 0.1 μm or more, and may be 1 μm or more, 2 μm or more, or 2.5 μm or more.
In the present specification, the "average particle size" is the particle size D50 ("median size" corresponding to the cumulative frequency of 50% by volume from the side with the smaller particle size in the volume-based particle size distribution based on the laser diffraction / light scattering method. It is also called.). Further, the positive electrode active material may be in the form of secondary particles in which primary particles are aggregated.

The positive electrode active material produced by the production method according to one embodiment contains lithium transition metal oxide particles and has a crystal structure similar to that of known lithium transition metal oxide particles used as a positive electrode active material for a lithium ion secondary battery. And may have a similar composition. For example, the lithium transition metal oxide particles may have a crystal structure such as a layered structure or a spinel structure.

As the lithium transition metal oxide particles, a lithium transition metal oxide containing at least one of Ni, Co, and Mn is preferable as the transition metal element, and specific examples thereof are lithium nickel-based composite oxides (eg, a lithium nickel-based composite oxide). LiNiO ₂ ), Lithium-cobalt-based composite oxide (eg, LiCoO ₂ ), Lithium-manganese-based composite oxide (eg, LiMn _{2O 4} ), Lithium-nickel-manganese-based composite oxide (eg, LiNi _0.5 Mn _1.5 ) O ₄ ), lithium nickel cobalt manganese-based composite oxide (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and the like can be mentioned.

In the present specification, the "lithium-nickel-cobalt-manganese-based composite oxide" is an oxide containing Li, Ni, Co, Mn, and O as constituent elements, and one or more of the other oxides. It is a term that also includes oxides containing typical elements. Examples of such additive elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn and the like. Examples include metal elements. Further, the additive element may be a metalloid element such as B, C, Si, P or a non-metal element such as S, F, Cl, Br, I. This also applies to the above-mentioned lithium nickel-based composite oxide, lithium cobalt-based composite oxide, lithium manganese-based composite oxide, lithium nickel-manganese-based composite oxide, and the like.

Next, a method for producing the positive electrode active material disclosed here will be described. As shown in the flowchart of FIG. 3, the method for producing positive positive active material particles disclosed here is a positive positive active material raw material powder for preparing a transition metal-containing compound having an average particle diameter of less than 4 μm in a laser diffraction / light scattering method. The preparation step S11, the mixing step S12 for mixing the transition metal-containing compound and the lithium compound, and the firing step S13 for firing the mixture obtained in the mixing step are included.

First, the positive electrode active material raw material powder preparation step S11 will be described. The positive electrode active material raw material powder preparation step S11 may be the same as a normal method for producing a positive electrode active material raw material powder.
As the raw material powder for the positive electrode active material prepared here, a conventionally used transition metal hydroxide can be used, and among them, at least one kind of metal element selected from the group consisting of Ni, Mn, and Co. It is preferable to contain a transition metal hydroxide comprising. Specific examples include nickel-based composite hydroxides, cobalt-based composite hydroxides, manganese-based composite hydroxides, nickel-manganese-based composite hydroxides, nickel-cobalt-manganese-based composite hydroxides, and iron-nickel-manganese-based composite hydroxides. Things etc. can be mentioned.

In the present specification, the term "nickel-cobalt-manganese-based composite hydroxide" refers to one or more of other hydroxides having Ni, Co, Mn, O, and H as constituent elements. It is a term that also includes hydroxides containing additive elements. Examples of such additive elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn and the like. Examples include metal elements. This also applies to the above-mentioned nickel-based composite hydroxide, cobalt-based composite hydroxide, manganese-based composite hydroxide, nickel-manganese-based composite hydroxide, and the like.

The average particle size of the positive electrode active material raw material powder is typically less than 4 μm, and can be, for example, 3.5 μm or less or 3 μm or less. Further, typically, such an average particle size is, for example, 0.1 μm or more, and may be 1 μm or more, 2 μm or more, or 2.5 μm or more.
Hereinafter, a suitable example of the positive electrode active material raw material powder preparation step S11 will be described.

First, an aqueous solution of the transition metal compound is prepared. As the transition metal compound, for example, a water-soluble compound such as a sulfate of a transition metal, a nitrate of a transition metal, or a halide of a transition metal can be used. As the element of the transition metal, it is preferable to use at least one selected from the group consisting of Ni, Mn and Co. Also, prepare an aqueous solution of the alkaline compound. As the alkaline compound, for example, lithium hydroxide, sodium hydroxide, potassium hydroxide and the like can be used, and sodium hydroxide is preferable. Also, prepare ammonia water.

On the other hand, water (typically ion-exchanged water) is added to the reaction vessel, and the atmosphere is replaced with an inert gas (for example, _N2 gas, Ar gas, etc.) while stirring the inside of the reaction vessel. Next, an aqueous solution of the alkaline compound is added to the reaction vessel to adjust the pH (for example, pH 11 to 13).

While stirring the inside of the reaction vessel, the aqueous solution of the transition metal compound and the aqueous ammonia are added dropwise to the reaction vessel. At this time, since the pH in the reaction vessel is lowered, the pH in the reaction vessel is adjusted within the range of 11 to 13 by appropriately adding an aqueous solution of the alkaline compound. Further, at this time, the ammonia concentration of the aqueous solution in the reaction vessel is adjusted to be maintained at 10 g / L to 30 g / L.

After dropping the aqueous solution of the transition metal compound and the aqueous ammonia, the reaction vessel is allowed to stand for a predetermined time (for example, 1 hour to 3 hours). This sufficiently precipitates the transition metal hydroxide particles. Then, the transition metal hydroxide particles are collected by suction filtration or the like, washed with water, and then dried. Thereby, a transition metal hydroxide powder (positive electrode active material raw material powder) can be obtained.

Next, the mixing step S12 will be described. As the lithium compound used here, for example, a compound that is converted into an oxide by firing such as lithium carbonate, lithium nitrate, and lithium hydroxide can be used.
A mixture is obtained by mixing the above-mentioned positive electrode active material raw material powder and a lithium compound according to a known method using a known mixing device (eg, shaker mixer, V blender, ribbon mixer, juriamixer, ladygemixer, etc.). Can be done.
The mixing amount of the positive electrode active material raw material powder and the lithium compound may be appropriately changed according to the elemental ratio of lithium and the transition metal contained in the desired positive electrode active material.

Next, the firing step S13 will be described. In the firing step S13, it is preferable to perform firing by dispersing the mixture obtained in the mixing step S12 in a gas (typically in air) that has reached a firing temperature (for example, 900 ° C. to 1000 ° C.). By dispersing the mixture in the gas, it is possible to prevent the particles of the raw material powder contained in the mixture from joining each other by sintering.

By dispersing the mixture in the gas that has reached the firing temperature, heat is easily transferred to the mixture, so that the firing time can be, for example, 1 hour or less (typically 30 minutes or less).
Hereinafter, embodiments (I) and (II) will be described as preferred examples of the firing step S13 with reference to the drawings. FIG. 4 is a schematic view of a firing device for explaining the firing method of the embodiment (I). FIG. 5 is a schematic view of a fluidized bed heat treatment apparatus for explaining the firing method of the embodiment (II). The arrows shown in FIGS. 4 and 5 indicate the direction of the flow (supply and exhaust) of the gas that has reached the firing temperature.

<Embodiment (I)>
As shown in FIG. 4, a nozzle 84 for supplying the mixture M obtained in the mixing step S12 to the firing container 82 and a cyclone (powder separator) 86 for separating the fired product (positive electrode active material). Prepare a firing device connected to and. First, a high-temperature gas (for example, 900 ° C. to 1000 ° C.) is supplied to the firing container 82. Such a gas may be supplied according to a known method, and for example, air heated by an electric heater can be supplied as hot air.

Next, the mixture M is supplied from the nozzle 84 to the firing container 82. At this time, it is preferable that the mixture is a slurry dispersed in a solvent, and the slurry is sprayed and supplied. As a result, the dispersibility of the mixture in the firing container 82 is increased, and the particles contained in the mixture M are separated from each other, so that the bonding of the particles due to sintering can be further suppressed. The spraying method is not particularly limited, and spraying can be performed using a known sprayer.

As the solvent used for the slurry, it is preferable to use a non-polar solvent. If it is a non-polar solvent, the positive electrode active material raw material powder and the lithium compound can be mixed more uniformly in the solvent. As the non-polar solvent, for example, alkoxide, acetone and the like can be used, and among them, alkoxide is preferably used. As the alkoxide, for example, lithium alkoxide (eg, lithium methoxyd, lithium ethoxyde, etc.), nickel 2-methoxyethoxydo, or the like can be used.

The mixture M supplied from the nozzle 84 is fired by the high temperature gas previously supplied to the firing container 82. The firing time can be, for example, 10 minutes or less (typically 1 minute or less).

The calcined mixture (positive electrode active material) can be recovered by the cyclone 86. The air discharged by the cyclone can recover particles that were not recovered by the cyclone, for example, by passing through a device equipped with a bag filter. A known cyclone may be used.

<Embodiment (2)>
As shown in FIG. 5, a fluidized bed heat treatment apparatus 90 including a media 92, a mesh (rectifying plate) 94, a nozzle 96 for supplying the mixture M obtained in the mixing step S12, and a bag filter 98 is prepared. Then, by continuously supplying hot air of a high-temperature gas (for example, 900 ° C. to 1000 ° C.) that has reached the firing temperature into the fluidized bed heat treatment apparatus 90, the media 92 is dispersed in the fluidized bed heat treatment apparatus 90 and flows. Form a layer. After forming the fluidized bed, the mixture M is supplied to the fluidized bed from the nozzle 96. Thereby, the mixture is calcined by the hot air of the high temperature gas and the heat conduction from the media 92. Further, when the media 92 come into contact with each other in the fluidized bed, the mixture can be calcined while crushing the mixture. The firing time can be, for example, 1 hour or less (typically 30 minutes or less). After firing, the fired mixture (positive electrode active material) is recovered. The recovery method may be a known method, and for example, the positive electrode active material can be recovered by using a cyclone, a filter, or the like.

The mixture M supplied from the nozzle 96 may be in the form of powder or in the form of slurry. When in the form of powder, the mixture M can be supplied from the nozzle 96 by a preheat-compressed gas (typically air having a temperature of 900 ° C. or lower). Further, when the mixture M is made into a slurry, the same procedure as in the above-mentioned embodiment (I) may be used.

As the media 92, known media (for example, ceramic balls or the like) can be used, but it is particularly preferable to use zirconia balls. Since zirconia balls have high heat resistance, they are suitable for use in air that has reached the firing temperature. The particle size of the media 92 may be, for example, 0.05 mm to 25 mm (typically 0.5 mm to 3 mm), and may be, for example, 1 mm.

As the mesh (rectifying plate) 94 and the bag filter 98, those conventionally used in the fluidized bed heat treatment apparatus may be used. In FIG. 5, the bug filter 98 is installed in a container in which a fluidized bed is formed, but the location of the bug filter is not limited to this. For example, a cyclone is attached to the exhaust port of the container. A bug filter may be installed at the exhaust port after passing through the cyclone.

The lithium ion secondary battery 100 can be used for various purposes. For example, it can be suitably used as a high-output power source (driving power source) for a motor mounted on a vehicle. The type of vehicle is not particularly limited, but typically examples thereof include automobiles, for example, plug-in hybrid automobiles (PHVs), hybrid automobiles (HVs), electric vehicles (EVs), and the like. The lithium ion secondary battery 100 can also be used in the form of an assembled battery in which a plurality of lithium ion secondary batteries 100 are electrically connected.

As described above, as an example, a square non-aqueous electrolytic solution lithium ion secondary battery provided with a flat-shaped wound electrode body provided with a positive electrode active material manufactured by the manufacturing method according to the embodiment has been described. However, this is only an example and is not limited. For example, instead of the wound electrode body, a non-aqueous electrolyte secondary battery may be provided in which a laminated electrode body in which a sheet-shaped positive electrode and a sheet-shaped negative electrode are alternately laminated via a separator is provided. Further, a polymer battery using a polymer electrolyte as the electrolyte may be used. Further, a cylindrical battery case, a coin-shaped battery case, or the like may be used instead of the square battery case, or a laminated secondary battery using a laminated film instead of the battery case may be used.

Hereinafter, examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Preparation of positive electrode active material raw material powder and mixture of the powder and lithium compound>
A raw material solution was prepared by dissolving nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), and manganese sulfate (MnSO ₄ ) in ion-exchanged water so as to have a molar ratio of 1: 1: 1. In addition, aqueous ammonia and aqueous sodium hydroxide solution were prepared.
Ion-exchanged water was added to the reaction vessel, and the atmosphere inside the reaction vessel was replaced with an inert gas while stirring to create an inert atmosphere. Next, an aqueous NaOH solution was added into the reaction vessel to adjust the pH to be in the range of 11-13. Then, a certain amount of the above raw material solution and aqueous ammonia were added dropwise to the reaction vessel. At this time, in order to keep the pH within the above range, an aqueous NaOH solution was appropriately added. At the same time, the ammonia concentration of the aqueous solution in the reaction vessel was adjusted to be maintained at 10 g / L to 30 g / L. After dropping the above raw material solution and aqueous ammonia, the mixture was allowed to stand for 1 to 3 hours to obtain a precipitate. The precipitate is collected by suction filtration, washed with ion-exchanged water, and then dried under reduced pressure at 40 ° C to 80 ° C for 6 to 8 hours to obtain a positive electrode active material raw material powder made of nickel-cobalt-manganese composite hydroxide. Obtained.

The obtained raw material powder and lithium carbonate (Li ₂ CO ₃ ) are mixed in a dairy pot so that the total molar ratio of nickel, cobalt and manganese contained in the raw material powder to lithium is 1: 1. Mixing gave a mixture.
Hereinafter, the firing method will be described. In the following firing, in the reference example, a mixture in which the positive electrode active material raw material powder having an average particle size of 4 μm is mixed, and in Examples 1 to 4, the positive particle active material having an average particle size of 2.8 μm. A mixture of raw material powder was used.

<Baking>
(Reference example, Example 1)
The above mixture was transferred to an alumina crucible and fired in a muffle furnace at 400 ° C. to 1000 ° C. for 5 to 10 hours. As a result, lithium composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ : NCM) particles, which are the fired products (positive electrode active material) of Reference Example and Example 1, were obtained.

(Example 2)
It was fired using a fluidized bed heat treatment device. A zirconia ball having a diameter of 1 mm was installed in the fluidized bed heat treatment apparatus. Next, hot air of air at 900 ° C. to 1000 ° C. was continuously introduced into the fluidized bed heat treatment apparatus to disperse the zirconia balls to form a fluidized bed. Next, the mixture was supplied to the fluidized bed using air whose temperature was 800 ° C. to 900 ° C. by preheat compression, and firing was performed for 1 minute to 30 minutes. Then, the zirconia ball and the fired mixture (positive electrode active material) were separated by a filter to obtain lithium composite oxide (NCM) particles which are the positive electrode active material of Example 2.

(Example 3)
The above mixture was dispersed in 2-methoxyethanol containing nickel 2-methoxyethoxydo to prepare a slurry. On the other hand, air at 900 ° C. to 1000 ° C. was continuously blown into the firing container. The slurry was fired by spraying it into the firing machine with a sprayer. After firing, the fired product was recovered by a cyclone. In this way, lithium composite oxide particles (NCM), which is the positive electrode active material of Example 3, were obtained.

(Example 4)
The above mixture was put into an electric furnace equipped with a stirring blade and fired at 900 ° C. to 1000 ° C. for 1 to 2 hours while rotating the stirring blade. As a result, lithium composite oxide (NCM) particles, which are the positive electrode active material of Example 4, were obtained.

<Manufacturing of lithium-ion secondary battery for evaluation>
Using the positive electrode active materials of Examples 2 to 4 and Reference Examples, lithium ion secondary batteries for evaluation were prepared. On the other hand, in the fired product of Example 1, the bonding between the particles due to sintering was severe and the positive electrode sheet could not be coated, so that the lithium ion secondary battery for evaluation could not be manufactured.
As the lithium ion secondary battery for evaluation, the positive electrode active material produced above, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are used as a positive electrode active material: AB: PVDF = 87 :. A paste for forming a positive electrode active material layer was prepared by mixing in N-methyl-2-pyrrolidone so as to have a mass ratio of 10: 3. This paste was applied to both sides of an aluminum foil current collector using a film applicator manufactured by Allgood, and dried at 80 ° C. for 5 minutes to prepare a positive electrode sheet.

Natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are used in a mass ratio of C: SBR: CMC = 96: 2: 2. A paste for forming a negative electrode active material layer was prepared by mixing in ion-exchanged water so as to be. This paste was applied to both sides of a copper foil current collector using a film applicator manufactured by Allgood, and dried at 80 ° C. for 5 minutes to prepare a negative electrode sheet.

Further, as a separator sheet, a porous polyolefin sheet having a three-layer structure of PP / PE / PP was prepared.

The prepared positive electrode sheet, the negative electrode sheet, and the prepared separator sheet were superposed and wound to prepare a cylindrical wound electrode body. Electrode terminals were attached to the positive electrode sheet and the negative electrode sheet of the manufactured wound electrode body by welding, respectively, and housed in a battery case having a liquid injection port.

Next, the non-aqueous electrolytic solution was sealed from the injection port of the battery case, and the injection port was hermetically sealed. As a non-aqueous electrolytic solution, LiPF ₆ as a supporting salt was added to a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 4: 3. The one dissolved at a concentration of 0.0 mol / L was used. As described above, the evaluation lithium ion secondary batteries of each example were obtained.

<Measurement of average particle size>
The median diameter (D50) was measured for each of the positive electrode active material raw material powders of each of the above-mentioned prepared examples (excluding Example 1) using a laser diffraction type particle size distribution measuring device. The results are shown in Table 1 as "raw material powder average particle size (μm)". In addition, the median diameter (D50) was measured in the same manner for each of the fired products (positive electrode active materials) of each example. The results are shown in Table 1 as "average particle size of fired product (μm)". The fired product of Example 1 was observed with a scanning electron microscope (SEM), and the results of comparison with the scale bar were shown.

<Activation treatment and measurement of initial discharge capacity>
A constant current-constant voltage method is used, and after constant current charging of each evaluation lithium ion secondary battery manufactured above to 4.1 V with a current value of 1 / 3C, a constant voltage is applied until the current value becomes 1 / 50C. It was charged and fully charged. Then, each evaluation lithium ion secondary battery was constantly discharged to 3.0 V at a current value of 1 / 3C. The discharge capacity at this time was taken as the initial discharge capacity. The charge / discharge operation was performed at 25 ° C. Further, “1C” here means the magnitude of the current that can charge the SOC (state of charge) from 0% to 100% in one hour.

<Initial resistance measurement>
Each of the activated lithium ion secondary batteries for evaluation was adjusted to an open circuit voltage of 3.70 V. This was placed in a temperature environment of 25 ° C. Discharging was performed for 10 seconds at a current value of 1C, and the amount of voltage change ΔV was determined. Battery resistance was calculated using the current value and ΔV. The ratio of the initial resistance of the evaluation lithium ion secondary battery of each example was obtained when the initial resistance of the evaluation lithium ion secondary battery of Example 4 was 1.00. The results are shown in Table 1.

<Measurement of capacity retention rate after cycle>
Each of the activated lithium ion secondary batteries for evaluation was placed in an environment of 60 ° C. Each evaluation lithium-ion secondary battery was charged at a constant current of 4.2 V at 2C, and then discharged at a constant current of 3.0 V at 2C, which was repeated for 200 cycles. Then, the discharge capacity after 200 cycles was measured by the same method as the above-mentioned initial discharge capacity. Then, the cycle capacity retention rate (%) is calculated by the following equation 1:
(Discharge capacity after 200 cycles) / (Initial discharge capacity) x 100 ... Equation 1
Calculated by The results are shown in Table 1.

<Measurement of volume / volume ratio>
Using the measured initial discharge capacity, the ratio of the volume capacity of each example to the volume capacity (mAh / cm ³ ) of Example 4 was calculated. The results are shown in Table 1.

As shown in Table 1, in the reference example in which the average particle size of the raw material powder is 4 μm or more, there is no significant change in the average particle size of the positive electrode active material which is the fired product even in the batch type firing in the muffle furnace. rice field. On the other hand, as shown in Example 1, when the average particle size of the raw material powder is less than 4 μm (here, 2.8 μm), the particles of the raw material powder are violently sintered by batch firing in a muffle furnace. Bonding occurred, resulting in a fired product having a particle size of more than 10 μm.

On the other hand, in Examples 2 and 3 in which firing was performed in a state of being dispersed in a gas having reached the firing temperature, the difference between the average particle size of the raw material powder and the average particle size of the fired product (positive electrode active material) was large. Since it was small, it can be seen that the bonding between the particles due to sintering was suppressed and the particles were fired. Further, as in Example 4, when firing in an electric furnace while stirring with a stirring blade, the average particle size of the fired product (positive electrode active material) was smaller than that of the raw material powder, so that the stirring blade excessively used the firing blade. It is considered that the fired product was made finer.

Further, when the volume capacity ratio, initial resistance, and cycle capacity retention rate of Examples 2 to 4 shown in Table 1 are compared, it can be seen that Examples 2 and 3 are superior to Example 4 in all respects.
Therefore, by firing the positive electrode active material raw material powder in a state of being dispersed in a gas that has reached the firing temperature, it is difficult to suppress the bonding of the raw material powder particles by sintering in the past. Raw material powder of less than 4 μm can be calcined. As a result, it can be seen that a positive electrode active material having more excellent battery performance (specifically, volume-capacity ratio, battery resistance reducing effect, and cycle capacity retention rate) can be produced.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

20 Winding electrode body 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode 52 Positive electrode collector 52a Positive electrode current collector exposed part 54 Positive electrode active material layer 60 Negative electrode 62 Negative electrode collection Electrode 62a Negative electrode collector Exposed part 64 Negative electrode active material layer 70 Separator 82 Firing container 84, 96 Nozzle 86 Cyclone 90 Flow layer heat treatment device 92 Media 94 Mesh 98 Bug filter 100 Lithium ion secondary battery

Claims (6)

A method for producing a positive electrode active material for a lithium ion secondary battery.
A positive electrode active material raw material powder preparation step for preparing a transition metal hydroxide having an average particle diameter of less than 4 μm in a laser diffraction / light scattering method, and
A mixing step of mixing the transition metal hydroxide and a lithium compound,
A firing step of firing the mixture obtained in the mixing step, and a firing step.
Including
Here, a method for producing a positive electrode active material, which comprises firing the mixture by dispersing it in a gas that has reached a firing temperature in the firing step. The method for producing a positive electrode active material according to claim 1, wherein in the firing step, the mixture is fired by spraying a slurry in which the mixture is dispersed in a non-polar solvent into a gas that has reached the firing temperature. The method for producing a positive electrode active material according to claim 2, which comprises an alkoxide as the non-polar solvent. The method for producing a positive electrode active material according to claim 1, wherein in the firing step, the mixture is fired using a fluidized bed heat treatment apparatus provided with a medium for crushing the mixture. The method for producing a positive electrode active material according to claim 4, wherein zirconia balls are used as the medium. The method for producing a positive electrode active material according to any one of claims 1 to 5, wherein the transition metal hydroxide comprises at least one metal element selected from the group consisting of Ni, Mn, and Co.

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