JP2020011892A - Lithium metal composite oxide powder, positive electrode active substance for lithium secondary battery, positive electrode, and lithium secondary battery - Google Patents

Abstract

To provide a positive electrode active substance for a lithium secondary battery, which generates little gas and prevents the battery from swelling; to provide a positive electrode using the active substance; and to provide a lithium secondary battery using the positive electrode.SOLUTION: This invention relates to a positive electrode active substance for a lithium secondary battery, comprising a lithium metal composite oxide powder constituted from: primary particles; secondary particles which are aggregates of the primary particles; and single particles that are present independently from the primary particles or the secondary particles, wherein the positive electrode active substance is expressed by the following formula (I): Li[Li(NiCoMnM)]O(provided that M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, La, and V; and -0.1≤x≤0.2, 0≤y≤0.4, 0≤z≤0.4, and 0≤w≤0.1 are satisfied). The single particles have an average compression strength of more than 80 MPa.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to a lithium metal composite oxide powder, a positive electrode active material for a lithium secondary battery, a positive electrode, and a lithium secondary battery.

  As a positive electrode active material for a lithium secondary battery, a lithium metal composite oxide powder is used. Lithium secondary batteries have already been put to practical use not only in small power sources for mobile phones and notebook computers, but also in medium or large power sources for automobiles and power storage.

  The lithium metal composite oxide powder may be composed of primary particles and secondary particles formed by agglomeration of the primary particles. When the lithium metal composite oxide powder is used as a positive electrode active material for a lithium secondary battery, the lithium metal composite oxide powder comes into contact with the electrolyte on the surface of the primary particles and the surface and inside of the secondary particles, and from the inside of the particles during charging. Desorption of lithium ions occurs, and at the time of discharge, insertion of lithium ions into the particles occurs. Since the surface state of the particles affects the desorption and insertion of lithium ions, controlling the surface state of the primary particles or secondary particles of the lithium metal composite oxide powder can improve cycle characteristics and improve battery energy density. It is important for improving battery characteristics such as improvement.

  For example, Patent Literature 1 discloses a lithium composite oxide composed of monodispersed primary particles (corresponding to single particles of the present invention) containing lithium as a main component and one element selected from the group consisting of cobalt, nickel, and manganese. Product powder is described. The lithium composite oxide described in Patent Literature 1 has a specific average particle diameter, a specific surface area, and a bulk density, and has no aggregated particles. Patent Literature 1 describes that the use of a lithium composite oxide composed of monodispersed primary particles does not have a grain boundary, and is less likely to crack or break during molding of a positive electrode material.

JP 2004-355824 A

As described in Patent Literature 1, a lithium composite oxide composed of monodispersed primary particles is less likely to crack or break than secondary particles.
On the other hand, when a secondary battery is used, a new surface may be generated due to a slight crack generated at the particle interface. The surface of the particle generated as a new surface becomes a reaction site with the electrolytic solution. At this reaction site, a decomposition reaction of the electrolytic solution occurs, and gas may be generated. The generated gas causes battery swelling.
The present invention has been made in view of the above circumstances, and a lithium metal composite oxide powder that generates a small amount of gas and suppresses battery swelling, and a positive electrode active material for a lithium secondary battery containing the lithium metal composite oxide powder. It is an object to provide a substance, a positive electrode using the same, and a lithium secondary battery using the same.

That is, the present invention includes the following inventions [1] to [6].
[1] A lithium metal composite oxide powder composed of secondary particles formed by agglomeration of primary particles and single particles existing independently of the secondary particles, and has the following composition formula ( A lithium metal composite oxide powder represented by I), wherein the average crushing strength of the single particles exceeds 80 MPa.
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(Where M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, La and V; −0.1 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, and 0 ≦ w ≦ 0.1.)
[2] The lithium metal composite oxide powder according to [1], wherein in the composition formula (I), 0 <x ≦ 0.1 and 0 <y ≦ 0.4.
[3] The ratio (D ₉₀ −) of a value obtained by subtracting 10% cumulative volume particle size D ₁₀ from 90% cumulative volume particle size D _{90 of the} positive electrode active material for a non-aqueous electrolyte secondary battery to 50% cumulative volume particle size D _{50. D 10} / D ₅₀₎ is less than 2.0, [1] or [2] lithium metal composite oxide powder according to. [4] The lithium metal composite oxide powder according to any one of [1] to [3], wherein the average particle diameter of the single particles is 0.5 μm or more and 7 μm or less.
[5] A positive electrode active material for a lithium secondary battery, comprising the lithium metal composite oxide powder according to any one of [1] to [4].
[6] A positive electrode comprising the positive electrode active material for a lithium secondary battery according to [5].
[7] A lithium secondary battery having the positive electrode according to [6].

  ADVANTAGE OF THE INVENTION According to this invention, the generation | occurence | production of a gas is small and the lithium metal composite oxide powder which suppressed battery swelling, the positive electrode active material for lithium secondary batteries, the positive electrode using the same, and the lithium secondary battery using the same are provided. can do.

FIG. 1 is a schematic configuration diagram illustrating an example of a lithium ion secondary battery. FIG. 1 is a schematic configuration diagram illustrating an example of a lithium ion secondary battery.

In the present invention, “primary particles” are particles having no grain boundary on the appearance, and mean particles constituting secondary particles.
In the present invention, “secondary particles” are particles formed by agglomeration of the primary particles.
In the present invention, the term “single particles” refers to particles that exist independently of the secondary particles and have no grain boundary in appearance, for example, particles having a particle diameter of 0.5 μm or more.

<Positive electrode active material for lithium secondary batteries>
The present embodiment relates to a lithium secondary battery including a lithium metal composite oxide powder composed of secondary particles formed by agglomeration of primary particles, and single particles present independently of the secondary particles. Positive electrode active material for use (hereinafter, may be referred to as “positive electrode active material”).
The positive electrode active material of the present embodiment contains independently present single particles. The positive electrode active material of the present embodiment is represented by the following composition formula (I). Moreover, in the positive electrode active material of the present embodiment, the average crushing strength of the independently existing single particles exceeds 80 MPa.
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(Where M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, La and V; −0.1 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, and 0 ≦ w ≦ 0.1.)

  The positive electrode active material of the present embodiment contains independently present single particles, and the average crushing strength of the single particles exceeds 80 MPa. That is, the single particles contained in the positive electrode active material of the present embodiment have a structure with high particle strength. Such a single particle has no grain boundary in the particle and does not easily cause particle cracking. For this reason, a new surface due to particle cracking is unlikely to occur. In other words, the decomposition reaction of the electrolytic solution that may occur on the new surface is less likely to occur. That is, according to the present embodiment, it is possible to provide a positive electrode active material that hardly generates gas in the battery and can suppress the battery from swelling.

As a correlation value indicating that gas generation in the battery is suppressed, there is an amount of decomposed electricity.
According to the present embodiment, it is possible to reduce the generation of the amount of decomposition electricity (sometimes referred to as “float electricity”) observed when an irreversible reaction occurs with the electrolyte at the particle interface.

<Measurement of the amount of electrolysis>
In the present embodiment, the amount of decomposition electricity is a value measured by the following method.
A lithium secondary battery (coin cell) is manufactured using the positive electrode active material of the present embodiment. The positive electrode comprises the positive electrode active material of the present embodiment, a conductive material (acetylene black), and a binder (PVdF) in a composition of positive electrode active material for lithium secondary battery: conductive material: binder = 92: 5: 3 (mass ratio). Then, the mixture is kneaded and kneaded so as to prepare a paste-like positive electrode mixture.

More specifically, the aluminum foil surface is placed on the lower lid of a coin cell (manufactured by Hosen Co., Ltd.) for the coin-type battery R2032, and a laminated film separator (on a porous film made of polypropylene, A heat resistant porous layer is laminated (thickness: 25 μm). Here, 300 μL of the electrolyte is injected. The electrolytic solution to be used is prepared by dissolving LiPF ₆ in a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate so as to have a concentration of 1.0 mol / L.
Next, using metallic lithium as the negative electrode, the negative electrode was placed on the upper side of the laminated film separator, covered with a gasket, covered with a cover, and caulked with a caulking machine to form a lithium secondary battery (coin-type battery R2032; Battery ").

Further, a test is performed as follows using the obtained coin-shaped cell.
That is, constant-current constant-voltage charging is performed at a test temperature of 60 ° C., a maximum charging voltage of 4.3 V, a charging time of 60 hours, and a charging current of 0.05 CA.
In the constant-current constant-voltage charging, the integrated amount of electricity for 30 hours after the shift to the constant voltage mode of 4.3 V is calculated as the float amount of electricity (mAh / g).

≪Average crush strength≫
In the present embodiment, the “average crush strength” of the single particles contained in the positive electrode active material refers to a value measured by the following method.

First, a test pressure (load) is applied to one arbitrarily selected single particle using a “micro compression tester MCT-510” manufactured by Shimadzu Corporation for the positive electrode active material powder, and the displacement amount of the single particle is measured. Measure. When the test pressure is gradually increased, the pressure value at which the displacement becomes maximum while the test pressure is almost constant is defined as the test force (P) and is shown in the following equation (A) (Journal of the Japan Mining Association, Vol. 81, (1965)), the crushing strength (St) is calculated. This operation is performed five times in total, and the average crushing strength is calculated from the average value of the five crushing strengths.
St = 2.8 × P / (π × d × d) (d: single particle diameter) (A)

In the present embodiment, the average crushing strength of independently present single particles exceeds 80 MPa, is preferably 100 MPa or more, more preferably 110 MPa or more, and particularly preferably 120 MPa or more.
When the average crushing strength of the single particles is equal to or more than the lower limit value, for example, it is difficult for particle cracks to occur in a press step during molding or a positive electrode molding where the volume has changed when charge and discharge are repeated, and a single particle having a high particle strength. Become.

<< Composition formula (I) >>
The positive electrode active material of the present embodiment is represented by the following composition formula (I).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(Where M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, La and V; −0.1 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, and 0 ≦ w ≦ 0.1.)

From the viewpoint of obtaining a lithium secondary battery having good cycle characteristics, x in the composition formula (I) preferably exceeds 0, more preferably 0.01 or more, and further preferably 0.02 or more. . In addition, from the viewpoint of obtaining a lithium secondary battery having higher initial coulomb efficiency, x in the composition formula (I) is preferably 0.1 or less, more preferably 0.08 or less, and 0.06 or less. It is more preferred that:
The upper limit and the lower limit of x can be arbitrarily combined.
In the present embodiment, it is preferable that 0 <x ≦ 0.1.
In the present specification, the “cycle characteristic” means a characteristic in which the battery capacity is reduced due to repetition of charge and discharge, and means a capacity ratio at the time of re-measurement to the initial capacity.

From the viewpoint of obtaining a lithium secondary battery having a low internal resistance of the battery, y in the composition formula (I) preferably exceeds 0, more preferably 0.005 or more, and is 0.01 or more. More preferably, it is particularly preferably 0.05 or more. Further, from the viewpoint of obtaining a lithium secondary battery having high thermal stability, y in the composition formula (I) is more preferably 0.35 or less, and further preferably 0.33 or less.
The upper limit and the lower limit of y can be arbitrarily combined.
In the present embodiment, it is preferable that 0 <y ≦ 0.4.

  In the present embodiment, in the composition formula (I), 0 <x ≦ 0.1, and more preferably 0 <y ≦ 0.4.

From the viewpoint of obtaining a lithium secondary battery having high cycle characteristics, z in the composition formula (I) is preferably 0.01 or more, more preferably 0.02 or more, and 0.1 or more. It is more preferred that there be. Further, from the viewpoint of obtaining a lithium secondary battery having high storage stability at a high temperature (for example, in a 60 ° C. environment), z in the composition formula (I) is preferably 0.39 or less, and is 0.38 or less. More preferably, it is still more preferably 0.35 or less.
The upper limit and the lower limit of z can be arbitrarily combined.

In addition, from the viewpoint of obtaining a lithium secondary battery having a low internal resistance of the battery, w in the composition formula (I) preferably exceeds 0, more preferably 0.0005 or more, and 0.001 or more. Is more preferable. From the viewpoint of obtaining a lithium secondary battery having a large discharge capacity at a high current rate, w in the composition formula (I) is preferably 0.09 or less, more preferably 0.08 or less, and 0 or less. 0.07 or less.
The upper limit and the lower limit of w can be arbitrarily combined.

  In the present embodiment, y + z + w in the composition formula (I) is preferably less than 0.5, and more preferably 0.3 or less.

  M in the composition formula (I) is at least one metal selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, La and V. Represents

  Further, from the viewpoint of obtaining a lithium secondary battery having high cycle characteristics, M in the composition formula (I) is at least one metal selected from the group consisting of Ti, Mg, Al, W, B, and Zr. And from the viewpoint of obtaining a lithium secondary battery having high thermal stability, it is preferable that the metal is at least one metal selected from the group consisting of Ti, Al, W, B and Zr.

In the present embodiment, the ratio (D ₉₀ −D) of the value obtained by subtracting the 10% cumulative volume particle size D ₁₀ from the 90% cumulative volume particle size D _{90 of the} positive electrode active material for a lithium secondary battery to the 50% cumulative volume particle size D _{50. 10} / D ₅₀ ) is preferably less than 2.0.

Cumulative volume particle size is measured by the laser diffraction scattering method.
First, 0.1 g of lithium metal composite oxide powder is put into 50 ml of a 0.2 mass% aqueous sodium hexametaphosphate solution to obtain a dispersion in which the powder is dispersed.
Next, the particle size distribution of the obtained dispersion is measured using Microtrack MT3300EXII (laser diffraction scattering particle size distribution measuring device) manufactured by Microtrac Bell Co., Ltd. to obtain a volume-based cumulative particle size distribution curve.
In the obtained cumulative particle size distribution curve, when the whole is taken as 100%, the value of the particle diameter at the point where the cumulative volume from the fine particle side becomes 10% is 10% cumulative volume particle size D ₁₀ (μm), The value of the particle diameter at the point of 50% is 50% cumulative volume particle size D ₅₀ (μm), and the value of the particle diameter at the point of 90% is 90% cumulative volume particle size D ₉₀ (μm).

In the present embodiment, (D ₉₀ −D ₁₀ ) / D ₅₀ is preferably 1.9 or less, more preferably 1.8 or less.

In the present embodiment, the average particle size of the single particles is preferably 0.5 μm or more, more preferably 0.75 μm or more, and particularly preferably 1.0 μm or more. The average particle size of the single particles is preferably 7 μm or less, more preferably 6 μm or less, and particularly preferably 5 μm or less.
The above upper limit and lower limit can be arbitrarily combined. In the present embodiment, the average particle diameter of the single particles is preferably 0.5 μm or more and 7 μm or less.

  Since the primary particles are aggregated to form secondary particles, the particles do not grow greatly, and the particle diameter is about 0.1 μm or more and less than 0.5 μm.

In the present embodiment, the average particle size of the particles was determined by the following method.
First, the positive electrode active material powder is placed on a conductive sheet stuck on a sample stage, and is irradiated with an electron beam having an accelerating voltage of 20 kV using JSM-5510 manufactured by JEOL Ltd. to perform SEM observation. 50 single particles were arbitrarily extracted from an image (SEM photograph) obtained by the SEM observation, and for each single particle, the distance between parallel lines separated by a parallel line obtained by drawing a projected image of the single particle from a certain direction ( Is measured as the particle diameter of a single particle. The arithmetic average of the particle diameters of the obtained single particles is defined as the average single particle diameter of the positive electrode active material powder.

(Layered structure)
In the present embodiment, the crystal structure of the positive electrode active material is a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure.

The crystal structure of hexagonal _{type, P3, P3 1, P3 2} , R3, P3, R3, P312, P321, P3 1 12, P3 1 21, P3 2 12, P3 2 21, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P31m, P31c, P-3m1, P3c1, R3m, R3c, P6, P6 1, P6 5, P6 2, P6 4, P6 3 _{, P6, P6 / m, P6} 3 / m, P622, P6 1 22, P6 5 22, P6 2 22, P6 4 22, P6 3 22, P6mm, P6cc, P6 3 cm, P6 3 mc, P- 6m2, P-6c2, P- 62m, attributed to _{P-62c, P6 / mmm,} P6 / mcc, P6 3 / mcm, P6 3 / any one space group selected from the group consisting of mmc.

The crystal structure of monoclinic _{type, P2, P2 1, C2,} Pm, Pc, Cm, Cc, P2 / m, P2 1 / m, C2 / m, P2 / c, P2 1 / c, C2 / It belongs to any one space group selected from the group consisting of c.

  Among them, in order to obtain a lithium secondary battery having a high discharge capacity, the crystal structure is a hexagonal crystal structure belonging to space group R-3m or a monoclinic crystal structure belonging to C2 / m. Particularly preferred is a structure.

<Production method of lithium metal composite oxide powder>
In manufacturing the lithium metal composite oxide powder contained in the positive electrode active material of the present embodiment, first, a metal other than lithium, that is, at least Ni, is contained, and Co, Mn, Fe, Cu, Ti, Mg, Al, W , B, Mo, Nb, Zn, Sn, Zr, Ga, La and V to prepare a metal composite compound containing any one or more of the above metals, and convert the metal composite compound to a suitable lithium salt with an inert lithium salt. It is preferable to bake with a melting agent. As the metal composite compound, a metal composite hydroxide or a metal composite oxide is preferable. Hereinafter, an example of a method for producing a lithium metal composite oxide powder will be described separately for a production process for a metal composite compound and a production process for a lithium metal composite oxide.

(Manufacturing process of metal composite compound)
The metal composite compound can be produced by a generally known batch coprecipitation method or continuous coprecipitation method. Hereinafter, a method for producing the metal composite hydroxide containing nickel, cobalt, and manganese will be described in detail.

First co-precipitation method, in particular by a continuous method described in 2002-201028 JP-nickel salt solution, cobalt salt solution, is reacted manganese salt solution and a complexing _{agent, Ni a Co b Mn c (} OH) ₂ (where a + b + c = 1) is produced.

The nickel salt that is a solute of the nickel salt solution is not particularly limited, and for example, any one or more of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used. As the solute of the cobalt salt solution, for example, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used. As a manganese salt that is a solute of the manganese salt solution, for example, one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate can be used. More metal salts are used in proportions corresponding to the composition ratio of the _{Ni a Co b Mn c (OH} ) 2. Water is used as a solvent.

  The complexing agent is a complexing agent capable of forming a complex with nickel, cobalt, and manganese ions in an aqueous solution. For example, an ammonium ion donor (ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.) Ammonium salts), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

  At the time of precipitation, an alkali metal hydroxide (for example, sodium hydroxide or potassium hydroxide) is added, if necessary, to adjust the pH value of the aqueous solution.

The nickel salt solution, cobalt salt solution, and other manganese salt solution and is supplied continuously complexing agent to the reaction vessel, nickel, cobalt, and manganese to _{react, Ni a Co b Mn c (} OH) 2 Is manufactured. During the reaction, the temperature of the reaction tank is controlled, for example, in the range of 20 ° C. to 80 ° C., preferably 30 to 70 ° C., and the pH value in the reaction tank is, for example, pH 9 to pH 13 and preferably pH 11 to pH 13 or less. The temperature is controlled within the range, and the substance in the reaction vessel is appropriately stirred. The reaction tank is of a type in which a formed reaction precipitate overflows for separation.

  By appropriately controlling the concentration of the metal salt to be supplied to the reaction vessel, the stirring speed, the reaction temperature, the reaction pH, and the firing conditions described below, the secondary particle diameter of the lithium metal composite oxide finally obtained in the following step And various physical properties such as pore radius can be controlled. In addition to controlling the above conditions, various gases, for example, an inert gas such as nitrogen, argon, or carbon dioxide, an oxidizing gas such as air or oxygen, or a mixed gas thereof may be supplied into the reaction vessel. . In addition to gases, use oxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorates, hypochlorite, nitric acid, nitric acid, halogen, ozone, etc. to promote oxidation. be able to. In addition to gas, organic acids such as oxalic acid and formic acid, sulfites, hydrazine and the like can be used to promote the reduction state.

  After the above reaction, the obtained reaction precipitate is washed with water and then dried to isolate nickel cobalt manganese hydroxide as a nickel cobalt manganese composite compound. Further, if necessary, washing may be performed with an aqueous solution of weak acid or an alkali solution containing sodium hydroxide or potassium hydroxide. In the above example, a nickel-cobalt-manganese composite hydroxide is manufactured, but a nickel-cobalt-manganese composite oxide may be prepared.

(Production process of lithium metal composite oxide)
After drying the above-mentioned metal composite oxide or metal composite hydroxide, it is mixed with a lithium salt. In the present embodiment, it is preferable to mix an inert flux simultaneously with the mixing.
By calcining the mixture containing the inert flux containing the metal composite oxide or hydroxide, the lithium salt and the inert flux, the mixture is calcined in the presence of the inert flux. By baking in the presence of the inert flux, it is possible to suppress sintering of the primary particles and generation of secondary particles. In addition, the growth of single particles can be promoted.

  In the present embodiment, the drying conditions are not particularly limited. For example, conditions under which the metal composite oxide or the metal composite hydroxide is not oxidized or reduced (the oxide is maintained as an oxide, the hydroxide is a hydroxide) Conditions), conditions under which the metal composite hydroxide is oxidized (the hydroxide is oxidized to the oxide), conditions under which the metal composite oxide is reduced (the oxide is reduced to the hydroxide) )). An inert gas such as nitrogen, helium and argon may be used for conditions where oxidation and reduction are not performed, and oxygen or air may be used for conditions where hydroxides are oxidized. Further, as a condition for reducing the metal composite oxide, a reducing agent such as hydrazine or sodium sulfite may be used in an inert gas atmosphere. As the lithium salt, any one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, and lithium oxide, or a mixture of two or more thereof can be used.

After drying the metal composite oxide or metal composite hydroxide, classification may be performed as appropriate. The above lithium salt and metal composite hydroxide are used in consideration of the composition ratio of the final target. For example, when a nickel-cobalt-manganese composite hydroxide is used, the lithium salt and the metal composite hydroxide are used at a ratio corresponding to the composition ratio of LiNi _a Co _b Mn _c O ₂ (where a + b + c = 1). . The lithium-nickel-cobalt-manganese composite oxide is obtained by calcining a mixture of the nickel-cobalt-manganese metal composite hydroxide and the lithium salt. In the firing, dry air, an oxygen atmosphere, an inert atmosphere, or the like is used according to a desired composition, and a plurality of heating steps are performed if necessary.

  In the present embodiment, by firing the mixture in the presence of the inert flux, the reaction of the mixture can be promoted. The inert flux may remain in the fired lithium metal composite oxide powder, or may be removed by washing with water or the like after firing. In the present embodiment, it is preferable to wash the lithium composite metal oxide after firing using water or the like.

By adjusting the holding temperature in the firing, the particle diameter of the obtained single particles of the lithium metal composite oxide can be controlled within a preferable range of the present embodiment.
In general, the higher the holding temperature, the larger the particle size of the single particle and the smaller the BET specific surface area. The holding temperature in the firing may be appropriately adjusted according to the type of transition metal element used, the type and amount of the precipitant and the inert flux.
In the present embodiment, the setting of the holding temperature may be performed in consideration of the melting point of the inert flux described below, and is performed in the range of the melting point of the inert flux minus 100 ° C. or more and the melting point of the inert flux plus 100 ° C. or less. Is preferred.
Specific examples of the holding temperature include a range of 200 ° C. to 1150 ° C., preferably 300 ° C. to 1050 ° C., and more preferably 500 ° C. to 1000 ° C.

  The holding time at the holding temperature is, for example, from 0.1 hour to 20 hours, and preferably from 0.5 hour to 10 hours. The rate of temperature rise to the holding temperature is usually 50 ° C./hour to 400 ° C./hour, and the rate of temperature drop from the holding temperature to room temperature is usually 10 ° C./hour to 400 ° C./hour. As the firing atmosphere, air, oxygen, nitrogen, argon, or a mixed gas thereof can be used.

  The lithium metal composite oxide obtained by calcination is appropriately classified after pulverization to obtain a positive electrode active material applicable to a lithium secondary battery.

  The inert flux that can be used in the present embodiment is not particularly limited as long as it does not easily react with the mixture during firing. In the present embodiment, a fluoride of one or more elements selected from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr and Ba (hereinafter referred to as “A”), a chloride of A , A carbonate of A, a sulfate of A, a nitrate of A, a phosphate of A, a hydroxide of A, a molybdate of A, and a tungstate of A. .

Examples of the fluoride of A include NaF (melting point: 993 ° C.), KF (melting point: 858 ° C.), RbF (melting point: 795 ° C.), CsF (melting point: 682 ° C.), CaF ₂ (melting point: 1402 ° C.), MgF ₂ (Melting point: 1263 ° C.), SrF ₂ (melting point: 1473 ° C.) and BaF ₂ (melting point: 1355 ° C.).

The chlorides of A include NaCl (melting point: 801 ° C.), KCl (melting point: 770 ° C.), RbCl (melting point: 718 ° C.), CsCl (melting point: 645 ° C.), CaCl ₂ (melting point: 782 ° C.), MgCl ₂ (Melting point: 714 ° C.), SrCl ₂ (melting point: 857 ° C.) and BaCl ₂ (melting point: 963 ° C.).

As carbonates of A, Na ₂ CO ₃ (melting point: 854 ° C.), K ₂ CO ₃ (melting point: 899 ° C.), Rb ₂ CO ₃ (melting point: 837 ° C.), Cs ₂ CO ₃ (melting point: 793 ° C.) , CaCO ₃ (melting point: 825 ° C.), MgCO ₃ (melting point: 990 ° C.), SrCO ₃ (melting point: 1497 ° C.) and BaCO ₃ (melting point: 1380 ° C.).

As the sulfate of A, Na ₂ SO ₄ (melting point: 884 ° C.), K ₂ SO ₄ (melting point: 1069 ° C.), Rb ₂ SO ₄ (melting point: 1066 ° C.), Cs ₂ SO ₄ (melting point: 1005 ° C.) , CaSO ₄ (melting point: 1460 ° C.), MgSO ₄ (melting point: 1137 ° C.), SrSO ₄ (melting point: 1605 ° C.) and BaSO ₄ (melting point: 1580 ° C.).

As nitrates of A, NaNO ₃ (melting point: 310 ° C.), KNO ₃ (melting point: 337 ° C.), RbNO ₃ (melting point: 316 ° C.), CsNO ₃ (melting point: 417 ° C.), Ca (NO ₃ ) ₂ (melting point : 561 ° C), Mg (NO ₃ ) ₂ , Sr (NO ₃ ) ₂ (melting point: 645 ° C) and Ba (NO ₃ ) ₂ (melting point: 596 ° C).

As the phosphate of A, Na ₃ PO ₄ , K ₃ PO ₄ (melting point: 1340 ° C.), Rb ₃ PO ₄ , Cs ₃ PO ₄ , Ca ₃ (PO ₄ ) ₂ , Mg ₃ (PO ₄ ) ₂ ( Melting point: 1184 ° C), Sr ₃ (PO ₄ ) ₂ (melting point: 1727 ° C) and Ba ₃ (PO ₄ ) ₂ (melting point: 1767 ° C).

Examples of the hydroxide of A include NaOH (melting point: 318 ° C.), KOH (melting point: 360 ° C.), RbOH (melting point: 301 ° C.), CsOH (melting point: 272 ° C.), Ca (OH) ₂ (melting point: 408 ° C.) ), Mg (OH) ₂ (melting point: 350 ° C.), Sr (OH) ₂ (melting point: 375 ° C.) and Ba (OH) ₂ (melting point: 853 ° C.).

Examples of the molybdate salt of A include Na ₂ MoO ₄ (melting point: 698 ° C.), K ₂ MoO ₄ (melting point: 919 ° C.), Rb ₂ MoO ₄ (melting point: 958 ° C.), Cs ₂ MoO ₄ (melting point: 956 ° C.) ), CaMoO ₄ (melting point: 1520 ° C.), MgMoO ₄ (melting point: 1060 ° C.), SrMoO ₄ (melting point: 1040 ° C.) and BaMoO ₄ (melting point: 1460 ° C.).

Examples of the tungstate of A include Na ₂ WO ₄ (melting point: 687 ° C.), K ₂ WO ₄ , Rb ₂ WO ₄ , Cs ₂ WO ₄ , CaWO ₄ , MgWO ₄ , SrWO ₄ and BaWO _4. .

In the present embodiment, two or more of these inert fluxes can be used. When two or more kinds are used, the melting point may be lowered. In addition, among these inert fluxes, as the inert flux for obtaining a lithium metal composite oxide powder having higher crystallinity, carbonates and sulfates of A, any of chlorides of A or a mixture thereof. A combination is preferred. A is preferably one or both of sodium (Na) and potassium (K). That is, among the above, particularly preferred inert fluxes are one or more selected from the group consisting of NaCl, KCl, Na ₂ CO ₃ , K ₂ CO _3, Na ₂ SO _4, and K ₂ SO _4. .
By using these inert fluxes, the average crushing strength of the obtained lithium metal composite oxide can be controlled within the preferred range of the present embodiment.

In this embodiment, when one or both of K ₂ SO ₄ and Na ₂ SO ₄ are used as the inert flux, the average crushing strength of the obtained lithium metal composite oxide is preferable in this embodiment. Can be controlled to a range.

In the present embodiment, the amount of the inert flux present during firing may be appropriately selected. In order to make the average crushing strength of the obtained lithium metal composite oxide fall within the range of the present embodiment, the amount of the inert flux at the time of firing is 0.1 parts by mass or more based on 100 parts by mass of the lithium compound. It is more preferable that the amount is 1 part by mass or more. If necessary, an inert flux other than the above-mentioned inert fluxes may be used in combination. Examples of the melting agent include ammonium salts such as NH ₄ Cl and NH ₄ F.

<Lithium secondary battery>
Next, a description will be given of a positive electrode using the positive electrode active material for a lithium secondary battery containing the positive electrode active material powder of the present embodiment, and a lithium secondary battery having the positive electrode, while describing the configuration of the lithium secondary battery.

  One example of the lithium secondary battery of the present embodiment includes a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolytic solution disposed between the positive electrode and the negative electrode.

  1A and 1B are schematic diagrams illustrating an example of the lithium secondary battery of the present embodiment. The cylindrical lithium secondary battery 10 of the present embodiment is manufactured as follows.

  First, as shown in FIG. 1A, a pair of band-shaped separators 1, a band-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a band-shaped negative electrode 3 having a negative electrode lead 31 at one end are separated into a separator 1, a positive electrode 2, and a separator 1. An electrode group 4 is obtained by laminating and winding the negative electrode 1 and the negative electrode 3 in this order.

  Next, as shown in FIG. 1B, after housing the electrode group 4 and an insulator (not shown) in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with the electrolytic solution 6, and the positive electrode 2 and the negative electrode 3 are formed. An electrolyte is placed between them. Further, by sealing the upper portion of the battery can 5 with the top insulator 7 and the sealing body 8, the lithium secondary battery 10 can be manufactured.

  As the shape of the electrode group 4, for example, a columnar shape such that a cross-sectional shape when the electrode group 4 is cut in a direction perpendicular to a winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners Can be mentioned.

  Further, as the shape of the lithium secondary battery having such an electrode group 4, IEC60086, which is a standard for batteries defined by the International Electrotechnical Commission (IEC), or a shape defined by JIS C8500 can be adopted. . For example, a shape such as a cylindrical shape and a square shape can be given.

  Further, the lithium secondary battery is not limited to the above-described wound type configuration, and may be a stacked type configuration in which a stacked structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of the stacked lithium secondary battery include a so-called coin battery, a button battery, and a paper (or sheet) battery.

Hereinafter, each configuration will be described in order.
(Positive electrode)
The positive electrode of the present embodiment can be manufactured by first preparing a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder, and supporting the positive electrode mixture on a positive electrode current collector.

(Conductive material)
As the conductive material of the positive electrode of this embodiment, a carbon material can be used. Examples of the carbon material include graphite powder, carbon black (for example, acetylene black), and a fibrous carbon material. Carbon black is a fine particle and has a large surface area.By adding a small amount to the positive electrode mixture, the conductivity inside the positive electrode can be increased, and the charge / discharge efficiency and output characteristics can be improved. Both the binding force between the positive electrode mixture and the positive electrode current collector and the binding force inside the positive electrode mixture decrease, which causes an increase in internal resistance.

  The proportion of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less based on 100 parts by mass of the positive electrode active material. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, the ratio can be reduced.

(binder)
As the binder included in the positive electrode of the present embodiment, a thermoplastic resin can be used. Examples of the thermoplastic resin include polyvinylidene fluoride (hereinafter, may be referred to as PVdF), polytetrafluoroethylene (hereinafter, may be referred to as PTFE), and ethylene tetrafluoride / propylene hexafluoride / vinylidene fluoride. Fluororesins such as copolymers, propylene hexafluoride / vinylidene fluoride copolymers, and ethylene tetrafluoride / perfluorovinyl ether copolymers; polyolefin resins such as polyethylene and polypropylene;

  These thermoplastic resins may be used as a mixture of two or more kinds. By using a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the whole positive electrode mixture is 1% by mass to 10% by mass, and the ratio of the polyolefin resin is 0.1% by mass to 2% by mass, whereby the positive electrode It is possible to obtain a positive electrode mixture in which both the adhesion to the current collector and the bonding force inside the positive electrode mixture are high.

(Positive electrode current collector)
As the positive electrode current collector included in the positive electrode of this embodiment, a belt-shaped member using a metal material such as Al, Ni, and stainless steel as a forming material can be used. Above all, it is preferable to use Al as a forming material and process it into a thin film in that it is easy to process and inexpensive.

  As a method for supporting the positive electrode mixture on the positive electrode current collector, there is a method in which the positive electrode mixture is pressure-formed on the positive electrode current collector. In addition, the positive electrode mixture is paste-formed using an organic solvent, the obtained positive electrode mixture paste is applied to at least one surface of the positive electrode current collector, dried, pressed and fixed, so that the positive electrode A mixture may be carried.

  When the positive electrode mixture is made into a paste, usable organic solvents include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; methyl acetate And amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

  Examples of a method of applying the paste of the positive electrode mixture to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method.

The positive electrode can be manufactured by the method described above.
(Negative electrode)
The negative electrode of the lithium secondary battery of the present embodiment may be any type as long as it is possible to dope and dedope lithium ions at a lower potential than the positive electrode, and the negative electrode mixture containing the negative electrode active material is supported on the negative electrode current collector. And an electrode composed of the negative electrode active material alone.

(Negative electrode active material)
Examples of the negative electrode active material of the negative electrode include carbon materials, chalcogen compounds (oxides, sulfides, and the like), nitrides, metals, and alloys, which can be doped and dedoped with lithium ions at a lower potential than the positive electrode. Can be

  Examples of the carbon material that can be used as the negative electrode active material include graphite such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and organic polymer compound fired bodies.

Examples of oxides that can be used as the negative electrode active material include oxides of silicon represented by the formula SiO _x such as SiO ₂ and SiO (where x is a positive real number); TiO _x such as TiO ₂ and TiO (here, , X is a positive real number); a vanadium oxide represented by the formula VO _x (where x is a positive real number) such as V ₂ O ₅ and VO ₂ ; Fe ₃ O ₄ , Fe ₂ O ₃ , FeO, etc., an iron oxide represented by the formula FeO _x (where x is a positive real number); SnO ₂ , SnO represented by the formula SnO _x (where x is a positive real number) Oxides of tin; oxides of tungsten represented by the general formula WO _x (where x is a positive real number) such as WO ₃ and WO ₂ ; lithium and titanium such as Li ₄ Ti ₅ O ₁₂ and LiVO ₂ Or a composite metal oxide containing vanadium. It is possible.

Examples of the sulfide usable as the negative electrode active material include titanium sulfide represented by the formula TiS _x (where x is a positive real number) such as Ti ₂ S ₃ , TiS ₂ , and TiS; V ₃ S ₄ , VS _2. Vanadium sulfide represented by the formula VS _x (where x is a positive real number) such as VS; FeS _x (where x is a positive real number) such as Fe ₃ S ₄ , FeS ₂ , and FeS A sulfide of iron represented by the formula: MoS _x such as Mo ₂ S ₃ , MoS ₂ (where x is a positive real number); a sulfide of molybdenum represented by the formula SnS _x such as SnS _{2 or} SnS x is represented sulfides of tin is a positive real number); WS ₂ wherein WS _x (wherein, etc., x is sulfides of tungsten represented by a positive real number); _Sb 2 _{S 3,} etc. formula SbS _x (wherein Where x is a positive real number) and sulfide of antimony represented by the following formula: Se ₅ S ₃ , selenium sulfide represented by the formula SeS _x (where x is a positive real number) such as SeS ₂ and SeS.

The nitride can be used as a negative electrode active _{material, Li 3 N, Li 3-} x A x N ( wherein, A is one or both of Ni and Co, which is 0 <x <3.) And other lithium-containing nitrides.

  These carbon materials, oxides, sulfides, and nitrides may be used alone or in combination of two or more. In addition, these carbon materials, oxides, sulfides, and nitrides may be either crystalline or amorphous.

  Examples of the metal that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

Examples of alloys usable as the negative electrode active material include lithium alloys such as Li-Al, Li-Ni, Li-Si, Li-Sn, and Li-Sn-Ni; silicon alloys such as Si-Zn; Sn-Mn, Sn It can also be mentioned; -Co, Sn-Ni, Sn -Cu, tin alloys such as _Sn-La; Cu 2 _Sb, alloys such as La 3 _Ni 2 Sn _7.

  These metals and alloys are mainly used alone as electrodes after being processed into a foil shape, for example.

  Among the above negative electrode active materials, the potential of the negative electrode hardly changes from an uncharged state to a fully charged state during charging (good potential flatness), the average discharge potential is low, and the capacity retention rate when repeatedly charged and discharged is low. A carbon material containing graphite as a main component, such as natural graphite or artificial graphite, is preferably used for reasons such as high (good cycle characteristics). The shape of the carbon material may be any of, for example, a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder.

  The negative electrode mixture may contain a binder, if necessary. Examples of the binder include thermoplastic resins, and specific examples include PVdF, thermoplastic polyimide, carboxymethylcellulose, polyethylene, and polypropylene.

(Negative electrode current collector)
Examples of the negative electrode current collector included in the negative electrode include a band-shaped member formed of a metal material such as Cu, Ni, and stainless steel. Among them, a material formed into a thin film using Cu as a forming material is preferable in that it is difficult to form an alloy with lithium and is easy to process.

  As a method of supporting the negative electrode mixture on such a negative electrode current collector, similarly to the case of the positive electrode, a method by pressure molding, forming a paste using a solvent or the like, applying the paste on the negative electrode current collector, drying and pressing. There is a method of crimping.

(Separator)
Examples of the separator included in the lithium secondary battery of the present embodiment include, for example, a porous film, a nonwoven fabric, and a woven fabric made of a material such as a polyolefin resin such as polyethylene and polypropylene, a fluororesin, and a nitrogen-containing aromatic polymer. Can be used. Further, a separator may be formed by using two or more of these materials, or a separator may be formed by laminating these materials.

  In the present embodiment, the separator has a gas permeability resistance of 50 seconds / 100 cc or more and 300 seconds / 100 cc according to the Gurley method specified in JIS P 8117 in order to allow the electrolyte to pass well when the battery is used (during charge / discharge). Or less, more preferably 50 seconds / 100 cc or more and 200 seconds / 100 cc or less.

  The porosity of the separator is preferably 30% by volume or more and 80% by volume or less, more preferably 40% by volume or more and 70% by volume or less. The separator may be a laminate of separators having different porosity.

(Electrolyte)
The electrolytic solution of the lithium secondary battery of the present embodiment contains an electrolyte and an organic solvent.

As the electrolyte contained in the electrolyte, LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (COCF ₃ ), Li (C ₄ F ₉ SO ₃ ), LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiBOB (here, BOB is bis (oxalato) borate ), LiFSI (here, FSI is bis (fluorosulfonyl) imide), lithium salts of lower aliphatic carboxylic acids, lithium salts such as LiAlCl _4, and a mixture of two or more of these. May be used. Among them, the electrolyte is at least selected from the group consisting of LiPF ₆ containing fluorine, LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) _3. It is preferable to use one containing one kind.

  Examples of the organic solvent contained in the electrolytic solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-diethyl carbonate. Carbonates such as (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, Ethers such as methyltetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amides; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propanesultone; or those obtained by further introducing a fluoro group into these organic solvents ( In which one or more of the hydrogen atoms of the organic solvent are substituted with a fluorine atom) can be used.

  As the organic solvent, it is preferable to use a mixture of two or more of these. Among them, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate and a mixed solvent of cyclic carbonate and ether are more preferable. As the mixed solvent of the cyclic carbonate and the non-cyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is preferable. The electrolytic solution using such a mixed solvent has a wide operating temperature range, hardly deteriorates even when charged and discharged at a high current rate, hardly deteriorates even when used for a long time, and natural graphite as an active material of the negative electrode. It has many features that it is hardly decomposable even when a graphite material such as artificial graphite is used.

Further, as the electrolyte, it is preferable to use an electrolyte containing a lithium salt containing fluorine such as LiPF ₆ and an organic solvent having a fluorine substituent, since the safety of the obtained lithium secondary battery is enhanced. A mixed solvent containing an ether having a fluorine substituent such as pentafluoropropyl methyl ether or 2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate has a high capacity even when charged and discharged at a high current rate. It is more preferable because the maintenance ratio is high.

A solid electrolyte may be used instead of the above electrolyte. As the solid electrolyte, for example, an organic polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound containing at least one polyorganosiloxane chain or a polyoxyalkylene chain can be used. Further, a so-called gel type in which a non-aqueous electrolyte is held in a polymer compound can also be used. Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—P ₂ S ₅ , Li ₂ S—B ₂ S ₃ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS _{2 -Li 2 SO 4, Li 2} S-GeS 2 -P 2 S 5 inorganic solid electrolytes containing a sulfide, and the like, may be used a mixture of two or more thereof. By using these solid electrolytes, the safety of the lithium secondary battery may be further improved.

  Further, in the lithium secondary battery of the present embodiment, when a solid electrolyte is used, the solid electrolyte may serve as a separator, and in that case, the separator may not be required.

  Next, the present invention will be described in more detail with reference to examples.

≫Measurement of average crush strength 強度
The “average crush strength” of the single particles contained in the positive electrode active material was measured by the following method.

First, a test pressure (load) is applied to one arbitrarily selected single particle using a “micro compression tester MCT-510” manufactured by Shimadzu Corporation for the positive electrode active material powder, and the displacement amount of the single particle is measured. It was measured. When the test pressure is gradually increased, the pressure value at which the displacement becomes maximum while the test pressure is almost constant is defined as the test force (P), and the equation of Hiramatsu et al. Vol. 81, (1965)), the crushing strength (St) is calculated. This operation was performed five times in total, and the average crushing strength was calculated from the average value of the five crushing strengths.
St = 2.8 × P / (π × d × d) (d: single particle diameter) (A)

_{«(D 90 -D 10) /} D measurement of _50»
The ratio (D ₉₀ / D ₁₀ ) of the 90% cumulative volume particle size D ₉₀ and the 10% cumulative volume particle size D ₁₀ of the lithium metal composite oxide powder was calculated by the following method.
First, 0.1 g of lithium metal composite oxide powder was added to 50 ml of a 0.2% by mass aqueous solution of sodium hexametaphosphate to obtain a dispersion in which the powder was dispersed.
Next, the particle size distribution of the obtained dispersion was measured using Microtrack MT3300EXII (laser diffraction scattering particle size distribution analyzer) manufactured by Microtrack Bell Co., Ltd., and a volume-based cumulative particle size distribution curve was obtained.
In the obtained cumulative particle size distribution curve, the value of the particle diameter as viewed from the fine particle side at the time of 10% accumulation is 10% cumulative volume particle size D ₁₀ (μm), and the particle as viewed from the fine particle side at the time of 50% accumulation. The value of the diameter is 50% cumulative volume particle size D ₅₀ (μm), the value of the particle size as viewed from the fine particle side at 90% accumulation is 90% cumulative volume particle size D ₉₀ (μm), and the ratio (D ₉₀ −D) ₁₀₎ was calculated _{/ D 50.}

≫Measurement of single particle size≪
The average particle size of the single particles was determined by the following method.
First, the positive electrode active material powder was placed on a conductive sheet stuck on a sample stage, and an electron beam having an acceleration voltage of 20 kV was irradiated using JSM-5510 manufactured by JEOL Ltd. to perform SEM observation. 50 single particles were arbitrarily extracted from an image (SEM photograph) obtained by the SEM observation, and for each single particle, the distance between parallel lines separated by a parallel line obtained by drawing a projected image of the single particle from a certain direction ( (Diameter in a fixed direction) was measured as the particle diameter of a single particle. The arithmetic average of the particle diameters of the obtained single particles was defined as the average single particle diameter of the positive electrode active material powder.

≫Measurement of float electric quantity≫
"Float electricity quantity" was measured by the following method.
A lithium secondary battery (coin-type cell) was produced using the positive electrode active material obtained by the method described below. For the positive electrode, a positive electrode active material for a lithium secondary battery: a conductive material: a binder = 92: 5: 3 (mass ratio) comprising a positive electrode active material obtained by a method described below, a conductive material (acetylene black), and a binder (PVdF). ) To obtain a paste-like positive electrode mixture.

More specifically, the aluminum foil surface is placed on the lower lid of a coin cell (manufactured by Hosen Co., Ltd.) for the coin-type battery R2032, and a laminated film separator (on a porous film made of polypropylene, A heat resistant porous layer is laminated (thickness: 25 μm). Here, 300 μL of the electrolyte is injected. The electrolytic solution used was prepared by dissolving LiPF ₆ in a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate to a concentration of 1.0 mol / L.
Next, using metallic lithium as the negative electrode, the negative electrode was placed on the upper side of the laminated film separator, covered with a gasket, covered with a cover, and caulked with a caulking machine to form a lithium secondary battery (coin-type battery R2032; hereinafter, referred to as “coin cell”). ).

Further, a test was performed as follows using the obtained coin cell.
That is, constant-current constant-voltage charging was performed at a test temperature of 60 ° C., a maximum charging voltage of 4.3 V, a charging time of 60 hours, and a charging current of 0.05 CA.
In the constant current / constant voltage charging, the integrated amount of electricity for 30 hours after the shift to the constant voltage mode of 4.3 V was calculated as the float amount of electricity (mAh / g).

<< Example 1 >>
1. Production of Positive Electrode Active Material 1 After water was poured into a reaction vessel equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added, and the liquid temperature was maintained at 50 ° C.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed such that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms becomes 0.60: 0.20: 0.20, and the mixed raw material liquid is obtained. Prepared.

  Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent to the reaction vessel with stirring, and nitrogen gas was continuously passed through the reaction vessel. An aqueous solution of sodium hydroxide is added dropwise at appropriate times so that the pH of the solution in the reaction vessel becomes 11.7, to obtain nickel-cobalt-manganese composite hydroxide particles, which are washed and then dehydrated by a centrifugal separator. By isolating and drying at 105 ° C., a nickel-cobalt-manganese composite hydroxide 1 was obtained.

The nickel / cobalt / manganese composite hydroxide particles 1, the lithium carbonate powder and the potassium sulfate powder were mixed with Li / (Ni + Co + Mn) = 1.20, K ₂ SO ₄ / (Li ₂ CO ₃ + K ₂ SO ₄ ) = 0.1 (mol) / Mol), and then calcined at 925 ° C for 8 hours under an air atmosphere to obtain a lithium metal composite oxide powder. The slurry prepared by mixing the powder and pure water so that the ratio of the powder weight to the total amount is 0.3 is stirred for 20 minutes, then dehydrated, isolated, and dried at 105 ° C. A positive electrode active material 1 was obtained.

2. Evaluation of Positive Electrode Active Material 1 The composition analysis of the positive electrode active material 1 was performed, and according to the composition formula (I), x = 0.02, y = 0.20, z = 0.20, and w = 0. Was.

As a result of the SEM observation of the positive electrode active material 1, the particle diameter of the independently existing single particle was 2 μm. The average crushing strength of the single particles contained in the positive electrode active material 1 was 127 MPa, (D ₉₀ −D ₁₀ ) / D ₅₀ was 1.2, and the float charge was 7.66 mAh / g.

<< Example 2 >>
1. Production of Positive Electrode Active Material 2 An aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate were mixed such that the atomic ratio of nickel, cobalt, and manganese was 0.88: 0.08: 0.04. A nickel cobalt manganese composite hydroxide 2 was obtained in the same manner as in Example 1 except for the above.

Nickel-cobalt-manganese composite hydroxide 2, lithium hydroxide monohydrate powder and potassium sulfate powder were mixed with Li / (Ni + Co + Mn) = 1.20, LiOH / (LiOH + K ₂ SO ₄ ) = 0.10 (mol / mol), and calcined at 820 ° C. for 6 hours in an oxygen atmosphere to obtain the obtained lithium metal composite oxide powder. The slurry prepared by mixing the powder and pure water so that the ratio of the powder weight to the total amount is 0.3 is stirred for 20 minutes, then dehydrated, isolated, and dried at 105 ° C. As a result, a positive electrode active material 2 was obtained.

2. Evaluation of Positive Electrode Active Material 2 A composition analysis of the positive electrode active material 2 was performed. According to the composition formula (I), x = 0.02, y = 0.08, z = 0.04, and w = 0. Was.

As a result of the SEM observation of the positive electrode active material 2, the particle diameter of the independently existing single particle was 3 μm. The average crushing strength of the single particles contained in the positive electrode active material 2 was 126 MPa, (D ₉₀ −D ₁₀ ) / D ₅₀ was 1.9, and the float charge was 7.68 mAh / g.

Example 3
1. Production of Positive Electrode Active Material 3 The same operation as in Example 2 was performed except that the nickel-cobalt-manganese composite hydroxide 2 was calcined at 760 ° C. for 6 hours in an oxygen atmosphere to obtain an obtained lithium metal composite oxide powder. Thus, a positive electrode active material 3 was obtained.

2. Evaluation of Positive Electrode Active Material 3 A composition analysis of the positive electrode active material 3 was performed. According to the composition formula (I), x = 0.02, y = 0.08, z = 0.04, and w = 0. Was.

  As a result of the SEM observation of the positive electrode active material 3, the particle size of the independently existing single particles was 1.8 μm. The average crushing strength of the single particles contained in the positive electrode active material 3 was 102 MPa, (D90-D10) / D50 was 1.7, and the float charge was 7.57 mAh / g.

<< Comparative Example 1 >>
1. Production of Positive Electrode Active Material 4 A positive electrode active material 4 was obtained in the same manner as in Example 1 except that K ₂ SO ₄ was not added at the time of firing the positive electrode active material and the firing temperature was 850 ° C.

2. Evaluation of Positive Electrode Active Material 4 The composition analysis of the positive electrode active material 4 was made to correspond to the composition formula (I), whereupon x = 0, y = 0.20, z = 0.20, and w = 0.

As a result of SEM observation of the positive electrode active material 4, independent single particles were not included. _{(D 90 -D 10) / D} 50 is 1.9, the float electric amount was 11.3mAh / g.

<< Comparative Example 2 >>
1. Production of Positive Electrode Active Material 5 A positive electrode active material 5 was obtained in the same manner as in Example 2, except that K ₂ SO ₄ was not added at the time of firing the positive electrode active material and the firing temperature was 760 ° C.

2. Evaluation of Positive Electrode Active Material 5 A composition analysis of the positive electrode active material 5 was made to correspond to the composition formula (I). As a result, x = 0.02, y = 0.08, z = 0.04, and w = 0. Was.

As a result of the SEM observation of the positive electrode active material 5, independent single particles were not included. _{(D 90 -D 10) / D} 50 is 1.8, the float electric amount was 14.3mAh / g.

<< Comparative Example 3 >>
1. Production of Positive Electrode Active Material 6 A positive electrode active material 6 was obtained in the same manner as in Example 1 except that K ₂ SO ₄ was not added at the time of firing the positive electrode active material and the firing temperature was set at 925 ° C.

2. Evaluation of Positive Electrode Active Material 6 A composition analysis of the positive electrode active material 6 was performed to correspond to the composition formula (I). As a result, x = −0.01, y = 0.20, z = 0.20, and w = 0. there were.

As a result of SEM observation of the positive electrode active material 6, the particle diameter of the independently existing single particle was 1 μm. The average crushing strength of the single particles contained in the positive electrode active material 6 was 71.9 MPa, (D ₉₀ −D ₁₀ ) / D ₅₀ was 11.0, and the float charge was 9.9 mAh / g.

  Table 1 below summarizes the results of Examples 1 to 3 and Comparative Examples 1 to 3.

  As shown in the above results, it was confirmed that the positive electrode active materials of Examples 1 to 3 to which the present invention was applied were those which generated little amount of float electricity and had little decomposition reaction with the electrolytic solution.

  DESCRIPTION OF SYMBOLS 1 ... Separator, 2 ... Positive electrode, 3 ... Negative electrode, 4 ... Electrode group, 5 ... Battery can, 6 ... Electrolyte, 7 ... Top insulator, 8 ... Sealing body, 10 ... Lithium secondary battery, 21 ... Positive electrode lead, 31 … Negative electrode lead

Claims (7)

Primary particles,
Secondary particles formed by aggregation of the primary particles,
The primary particles or the single particles that are present independently of the secondary particles, and a lithium metal composite oxide powder composed of:
A lithium metal composite oxide powder represented by the following composition formula (I), wherein the average crushing strength of the single particles exceeds 80 MPa.
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(Where M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, La and V; −0.1 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, and 0 ≦ w ≦ 0.1.)   2. The lithium metal composite oxide powder according to claim 1, wherein in the composition formula (I), 0 <x ≦ 0.1 and 0 <y ≦ 0.4. A value obtained by subtracting the lithium metal composite oxide 90% cumulative volume particle size _{D 90} 10% cumulative volume particle size _{D 10} of the powder, the ratio of 50% cumulative volume particle size _{D 50 (D 90 -D 10 /} D 50) The lithium metal composite oxide powder according to claim 1 or 2, which is less than 2.0.   The lithium metal composite oxide powder according to any one of claims 1 to 3, wherein the average particle diameter of the single particles is 0.5 µm or more and 7 µm or less.   A positive electrode active material for a lithium secondary battery, comprising the lithium metal composite oxide powder according to claim 1.   A positive electrode comprising the positive electrode active material for a lithium secondary battery according to claim 5.   A lithium secondary battery having the positive electrode according to claim 6.

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