WO2017150522A1

WO2017150522A1 - Positive electrode active material for lithium secondary battery

Info

Publication number: WO2017150522A1
Application number: PCT/JP2017/007756
Authority: WO
Inventors: 徹也光本; 大輔鷲田; 松嶋　英明
Original assignee: 三井金属鉱業株式会社
Priority date: 2016-02-29
Filing date: 2017-02-28
Publication date: 2017-09-08
Also published as: JPWO2017150522A1; JP6343411B2

Abstract

Provided is a positive electrode active material for a lithium secondary battery, said material including active particles that are represented by the general formula Li_1±xCo_yM_1-x-yO₂ (In the formula, 0.95 ≤ 1±x ≤ 1.05, y ≥ 0.8, 1-x-y > 0, and M is any one or a combination of two or more elements from the group consisting of Mn, Ni, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce), have a layered crystal structure, and are provided, on the surface thereof, with a surface part in which any one or a combination of two or more elements (referred to as "surface element A") from the group consisting of Al, Ti, and Zr is present, and being characterized in that the ratio (A/(Co+M)) of the atomic ratio of surface element A to the total of the atomic ratios of Co and M as measured by XPS is 0.07-0.8, the amount of surface lithium impurities is less than 0.15 wt%, and the peak integrated intensity ratio (003)/(104) as measured by XRD is 1.15-3.00.

Description

Positive electrode active material for lithium secondary battery

The present invention relates to a positive electrode active material for a lithium secondary battery that can be used as a positive electrode active material for a lithium secondary battery.

Lithium batteries, especially lithium secondary batteries, have features such as high energy density and long life, so they can be used for home appliances such as video cameras, portable electronic devices such as notebook computers and mobile phones. Used as a power source. Recently, the lithium secondary battery is also applied to a large battery mounted on an electric vehicle (EV), a hybrid electric vehicle (HEV), or the like.

A lithium secondary battery is a secondary battery with a structure in which lithium is melted as ions from the positive electrode during charging, moves to the negative electrode and is stored, and reversely, lithium ions return from the negative electrode to the positive electrode during discharging. It is known to be caused by the potential of the positive electrode material.

As positive electrode active materials for lithium secondary batteries, lithium manganese oxide (LiMn ₂ O ₄ ) having a spinel structure and lithium metal composite oxides such as LiCoO ₂ , LiNiO ₂ and LiMnO ₂ having a layered crystal structure are known. It has been. For example, LiCoO ₂ has a layered crystal structure in which lithium atom layers and cobalt atom layers are alternately stacked via oxygen atom layers, has a large charge / discharge capacity, and is excellent in diffusibility of lithium ion storage / desorption. Therefore, many of the commercially available lithium secondary batteries employ a lithium cobalt metal composite oxide having a layered crystal structure such as LiCoO ₂ as a positive electrode active material.

A lithium metal composite oxide having a layered crystal structure such as LiCoO ₂ or LiNiO ₂ is represented by a general formula LiMO ₂ (M: transition metal). The crystal structure of these lithium metal composite oxides having a layered crystal structure belongs to the space group R-3m ("-" is usually attached to the upper part of "3" and indicates reversal. The same applies hereinafter). The Li ion, Me ion, and oxide ion occupy the 3a site, 3b site, and 6c site, respectively. It is known that a layer composed of Li ions (Li layer) and a layer composed of Me ions (Me layer) exhibit a layered crystal structure in which they are alternately stacked via O layers composed of oxide ions.

When a lithium metal composite oxide having such a layered crystal structure is used as a positive electrode active material for a lithium secondary battery, the lithium metal composite oxide and the electrolyte solution chemically react, particularly when charged and discharged at high temperatures. However, since the reactants change on the surface of the positive electrode active material, the battery capacity and life characteristics are deteriorated.

As an example of means for solving such a problem, it is conceivable to coat the particle surface of a lithium metal composite oxide having a layered crystal structure with a metal or a metal oxide.
For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2001-291518), the surface of a lithium metal composite oxide having a layered crystal structure is composed of Mg, Al, Co, K, Na, Ca, Si, Ti, and V. A positive electrode active material for a lithium secondary battery comprising a metal oxide or composite metal oxide layer selected from the group is disclosed.

In Patent Document 2 (Japanese Patent Laid-Open No. 2005-310744), a lithium metal composite oxide particle powder having a layered crystal structure is dispersed in an isopropyl alcohol solution and stirred, followed by heat treatment at 600 ° C. A positive electrode active material having a particle surface coated with aluminum is disclosed.

In Patent Document 3 (Japanese Patent Laid-Open No. 2005-322616), a lithium metal composite oxide having a layered crystal structure and powdered metal aluminum are added to water to form a slurry, and further stirred to dissolve the metal aluminum. A lithium-containing composite oxide in which the surface of the composite oxide obtained by drying at 80 ° C. is covered with a layer containing aluminum hydroxide, aluminum oxide and lithium carbonate is disclosed.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2005-346955) is obtained by adding aluminum stearate to a lithium metal composite oxide having a layered crystal structure, mixing and crushing with a ball mill, and heat-treating at 600 ° C. A lithium-containing composite oxide in which an aluminum compound is modified on the particle surface is disclosed.

Patent Document 5 (WO 2007/142275) discloses a positive electrode active in which lithium metal composite oxide particles having a layered crystal structure are subjected to surface modification in which a specific surface region contains a relatively high specific concentration of aluminum. Lithium metal composite oxide particles having a layered crystal structure as a substance, the surface layer containing aluminum, and the aluminum content within 5 nm of the surface layer is atomic ratio relative to the total of Ni and element M A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by comprising surface-modified lithium-containing composite oxide particles of 0.8 or more is disclosed.

Patent Document 6 (Japanese Patent Application Laid-Open No. 2008-153017) discloses a layered crystal from the viewpoint of using as a positive electrode active material coated with a lithium composite oxide surface having a specific composition and a specific particle size and particle size distribution. A lithium metal composite oxide having a structure, having an average particle size D50 of 3 to 15 μm, a minimum particle size of 0.5 μm or more, a maximum particle size of 50 μm or less, and D10 / D50 of 0 A substance (A is Ti, Sn, Mg, A) on the surface of the lithium composite oxide for a non-aqueous electrolyte secondary battery composed of particles having a particle diameter of .60 to 0.90 and D10 / D90 of 0.30 to 0.70. Disclosed is a positive electrode active material for a non-aqueous electrolyte secondary battery characterized by having a structure coated with a compound comprising at least one element selected from the group consisting of Zr, Al, Nb and Zn) That.

In Patent Document 7 (Japanese Patent Laid-Open No. 4-329267), a LiCoO ₂ metal oxide is immersed in a 20% NaOH aqueous solution at a temperature of about 80 ° C. to perform an alkali treatment, whereby the surface of the metal oxide is treated. A LiCoO ₂ metal oxide that has been subjected to a coupling treatment using a titanate coupling agent with an increased OH group concentration is disclosed.

JP 2001-291518 A JP 2005-310744 A JP 2005-322616 A JP 2005-346955 A WO2007 / 142275 JP 2008-153017 A JP-A-4-329267

As described above, when the particle surface of the lithium metal composite oxide is coated with a metal or metal oxide in order to suppress the reaction between the electrolytic solution and the lithium metal composite oxide, the rate characteristics of the battery are reduced. This creates a new problem.

Therefore, the present invention relates to a positive electrode active material containing a lithium metal composite oxide having a layered crystal structure, and when used as a positive electrode active material of a lithium secondary battery, suppresses the reaction with the electrolytic solution and improves the battery life characteristics. A new positive electrode active material for a lithium secondary battery that can be improved and has a rate characteristic equivalent to or higher than that of a positive electrode active material that has been surface-treated as previously proposed. To do.

Also, in the case of lithium cobalt metal composite oxides, it was found that when used at a high potential in a high temperature environment, the cycle characteristics were severely deteriorated during cycle evaluation, and there was a big problem in cycle characteristics.

The present invention has the general formula Li _{1 ± x} Co _y M _1-xy O ₂ (where 0.95 ≦ 1 ± x ≦ 1.05, y ≧ 0.8, 1-xy> 0, M is Mn, Ni, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re And a surface of a particle comprising a lithium cobalt metal composite oxide having a layered crystal structure represented by any one or a combination of two or more of the group consisting of Ce and Ce (referred to as “constituent element M”) For a lithium secondary battery including particles having a surface portion in which any one or a combination of two or more of the group consisting of Al, Ti and Zr (referred to as “surface element A”) is present A positive electrode active material,
The atomic ratio of Co and the atomic ratio of M (constituent element M is 2) measured by X-ray photoelectron spectroscopy (XPS) (hereinafter also referred to as “XPS”). The ratio (A / (Co + M)) of the atomic ratio of the surface element A (the total of the atomic ratio when the surface element A is two or more) to the total of the total of the atomic ratio in the case of more than one type is 0.07 Greater than 0.8 and
The amount of surface lithium impurities is less than 0.15 wt%, and
In an X-ray diffraction pattern measured by a powder X-ray diffractometer (XRD: X-Ray Diffractometer, hereinafter also referred to as “XRD”) using a CuKα1 ray, a (003) plane with respect to an integrated intensity of a peak derived from the (104) plane A positive electrode active material for a lithium secondary battery is proposed, characterized in that the ratio (003) / (104) of the integrated intensity of the peak derived from is larger than 1.15 and smaller than 3.00.

According to the positive electrode active material proposed by the present invention, when used as a positive electrode active material of a lithium secondary battery, it is possible to suppress the reaction with the electrolytic solution and improve the life characteristics in high temperature use under a high temperature environment. At the same time, the rate characteristics can be made equal to or higher than those of the conventional positive electrode active material subjected to the surface treatment. Therefore, the positive electrode active material proposed by the present invention is a battery for consumer use such as a mobile phone, a battery for vehicle use, particularly a battery mounted on an electric vehicle (EV) or a hybrid electric vehicle (HEV). It is particularly excellent as a positive electrode active material.

In an Example, it is a figure for demonstrating the structure of the cell for electrochemical evaluation produced by battery characteristic evaluation.

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiment.

<This positive electrode active material>
The positive electrode active material for a lithium secondary battery according to an example of the embodiment of the present invention has a general formula (1): Li _{1 ± x} Co _y M _1-xy O ₂ (where 0.95 ≦ 1 ± x ≦ 1.05, y ≧ 0.8, 1-xy> 0, M is Mn, Ni, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re and Ce, any one kind or a combination of two or more kinds (this is referred to as “constituent element M”). Any one of the group consisting of Al, Ti and Zr on the surface of the particles composed of lithium cobalt metal composite oxide having a layered crystal structure (referred to as “the present lithium cobalt metal composite oxide particles”) Grain having a surface portion on which one type or a combination of two or more types (referred to as “surface element A”) exists Is (the "particles" as referred) cathode active material for a lithium secondary battery containing (referred to as "MotoTadashi electrode active material").

The present positive electrode active material may contain other components in addition to the present particles. However, from the viewpoint of effectively obtaining the characteristics of the present particles, the present particles preferably occupy 80 wt% or more, particularly 90 wt% or more, and more preferably 95 wt% or more (including 100 wt%).

<This particle>
The present particle is a particle having a surface portion containing the surface element A on the surface of the present lithium cobalt metal composite oxide particle.
As long as this particle | grain is provided with the said surface part, it may be provided with the other layer and another part.

(The present lithium cobalt metal composite oxide particles)
The lithium cobalt metal composite oxide particles have a general formula (1): Li _{1 ± x} Co _y M _1-xy O ₂ (where 0.95 ≦ 1 ± x ≦ 1.05, y ≧ 0. 8, 1-xy> 0, M is Mn, Ni, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb A layered crystal structure represented by any one or a combination of two or more of the group consisting of Mo, In, Ta, W, Re, and Ce (referred to as “constituent element M”). It is a particle made of a lithium cobalt metal composite oxide.

In the general formula (1): Li _{1 ± x} Co _y M _1-xy O ₂ , “1 ± x” is 0.95 to 1.05, particularly 0.97 or more or 1.03 or less, It is preferably 0.98 or more and 1.02 or less.

“M” in the above formula (1) is Mn, Ni, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb, Any one or a combination of two or more selected from the group consisting of Mo, In, Ta, W, Re, and Ce may be used.

In the above formula (1), y ≧ 0.8 may be satisfied, especially y ≧ 0.9, particularly y ≧ 0.95, and more preferably y ≧ 0.97.
In the above formula (1), 1-xy is 0.25 or less, preferably less than 0.15, more preferably less than 0.10, and even more preferably less than 0.05.
In the above general formula (1), the atomic ratio of the oxygen amount is described as “2” for convenience, but may have some non-stoichiometry.

The present lithium cobalt metal composite oxide particles may contain inevitable impurities. For example, each element of inevitable impurities may be contained if it is 0.17 wt% or less. This is because it is considered that the amount of this amount hardly affects the characteristics of the present lithium cobalt metal composite oxide particles.

(Surface part)
As for the surface portion, any one or a combination of two or more of the group consisting of Al, Ti, and Zr (referred to as “surface element A”) exists on the surface of the lithium cobalt metal composite oxide particles. It is preferable to do this.
The surface portion described here is characterized in that a portion having a higher concentration of the surface element A than the inside of the particle is provided on the particle surface.

The thickness of the surface portion is preferably 1 nm to 300 nm from the viewpoints of suppressing the reaction with the electrolytic solution to improve the life characteristics and maintaining or improving the rate characteristics, and more preferably 4 nm or more or 220 nm or less. Among these, it is preferable that it is 8 nm or more or 150 nm or less.

If the surface portion is present on the surface of the lithium cobalt metal composite oxide particles, when used as a positive electrode active material of a lithium secondary battery, the life characteristics are improved by suppressing reaction with the electrolyte solution, Compared to a conventionally proposed positive electrode active material subjected to a surface treatment, the rate characteristics can be made equal or better. Therefore, the present lithium cobalt metal composite oxide is suitable for use as a positive electrode active material of a lithium secondary battery, and is used for consumer use batteries such as mobile phones and in-vehicle batteries, in particular, electric vehicles (EV: Electric Vehicle). ) And hybrid electric vehicles (HEV: Hybrid Electric Vehicle) are particularly excellent as positive electrode active materials for batteries.

Whether or not the surface portion where the surface element A exists is present on the surface of the lithium cobalt metal composite oxide particle is determined by whether or not the concentration of the surface element A is higher on the particle surface than inside the particle. can do. Specifically, for example, when the particle is observed with a scanning transmission electron microscope (STEM), the determination can be made based on whether or not the peak of the surface element A is observed on the surface of the particle.

In particular, the atomic ratio of the surface element A (surface element) to the sum of the atomic ratio of Co, which is a constituent element, and the atomic ratio of M (total of atomic ratios when there are two or more constituent elements M) measured by XPS When A is 2 or more, the ratio (A / (Co + M)) of the sum of atomic ratios is preferably larger than 0.07 and smaller than 0.8.
If the surface element A is present to such an extent that the ratio (A / (Co + M)) is smaller than 0.8, it is possible to suppress the reaction with the electrolytic solution and improve the life characteristics. Further, the rate characteristics can be made equal to or higher than those of conventionally proposed positive electrode active materials subjected to surface treatment.
From this point of view, the ratio (A / (Co + M)) is preferably larger than 0.07 and smaller than 0.8, more preferably larger than 0.10 and smaller than or equal to 0.6, more preferably larger than 0.12 and larger than 0.4. Hereinafter, among them, it is more preferably greater than 0.15 and not greater than 0.3.

Thus, in order to adjust the ratio (A / (Co + M)) to be larger than 0.07 and smaller than 0.8, for example, when the present lithium cobalt metal composite oxide particles are surface-treated, the surface treatment is performed. The amount of the surface element A in the agent may be adjusted, and the subsequent heat treatment temperature may be adjusted. However, it is not limited to these methods.

<Crystal structure>
Regarding the crystal structure of the present lithium cobalt metal composite oxide particles, in the X-ray diffraction pattern measured by XRD using the CuKα1 line, the integration of the (003) plane-derived peak with respect to the integrated intensity of the (104) plane-derived peak The intensity ratio (003) / (104) is preferably greater than 1.15.
The closer the ratio (003) / (104) is to 1.00, the larger the proportion occupied by the rock salt structure. It was found that if the ratio (003) / (104) is greater than 1.15, the proportion occupied by the rock salt structure is reduced, and the rate characteristics can be improved.
From this point of view, regarding the present positive electrode active material, the ratio (003) / (104) is preferably greater than 1.15, more preferably greater than 1.20, and more preferably greater than 1.30. preferable.
On the other hand, it was found that when the ratio (003) / (104) is greater than 3.00, the anisotropy of expansion / contraction due to the insertion / desorption of lithium increases, so that the cycle characteristics deteriorate.
From this viewpoint, it is preferable that the ratio (003) / (104) is less than 3.00, particularly 2.50 or less, more preferably less than 2.00. Preferably it is less than 1.70.

For the present positive electrode active material, in order to make the ratio (003) / (104) larger than 1.15 and smaller than 3.00, the firing conditions are adjusted or the amount of the solvent or water in the surface treatment is adjusted. Just do it. However, it is not limited to such a method.

<Amount of surface lithium impurities>
The positive electrode active material preferably has a surface lithium impurity amount of 0.15 wt% or less.
If the amount of surface lithium impurities is 0.15 wt% or less, it is preferable because the unreacted residual lithium reacts with the electrolytic solution to suppress a reaction that causes deterioration of life characteristics.
From this point of view, the surface lithium impurity amount of the present positive electrode active material is preferably 0.15 wt% or less, more preferably greater than 0 wt% or even more preferably 0.10 wt% or less.
Here, it is considered that the above surface lithium impurities are derived from Li that remains without reacting when fired. Therefore, in order to adjust the surface lithium impurity amount to the above range, the raw material mixing conditions and the firing conditions are adjusted and reacted sufficiently, and the unreacted components are further reacted by adjusting the surface treatment conditions and the heat treatment conditions. You may adjust to. However, the present invention is not limited to this.

<Specific surface area>
The positive electrode active material preferably has a specific surface area (SSA) of 0.1 to 2 m ² / g.
If the specific surface area (SSA) of the present positive electrode active material is 0.1 to 2 m ² / g, a sufficient reaction field for Li insertion / desorption can be secured, and the rate characteristics can be maintained. preferable.
From this viewpoint, the specific surface area (SSA) of the present positive electrode active material is preferably 0.1 to 2 m ² / g, more preferably 1.5 m ² / g or less, particularly 1.3 m ² / g or less. Of these, 1.0 m ² / g or less is more preferable.
In order to set the specific surface area of the present lithium cobalt metal composite oxide powder within the above range, it is preferable to adjust the firing conditions and the crushing conditions. However, it is not limited to these adjustment methods.

<Surface LiOH amount>
In the present positive electrode active material, the LiOH amount measured by the following measurement method is preferably less than 0.07 wt%, and more preferably less than 0.05 wt%, from the viewpoint of improving the rate characteristics.

In the present positive electrode active material, in order to make the surface LiOH amount less than 0.07 wt%, it is preferable to react the unreacted components sufficiently by adjusting the surface treatment conditions and heat treatment conditions. However, it is not limited to these adjustment methods.

<Surface Li ₂ CO ₃ content>
In the present positive electrode active material, the amount of Li ₂ CO ₃ measured by the following measurement method is less than 0.15 wt%, particularly less than 0.13 wt%, and particularly less than 0.10 wt% from the viewpoint of improving the rate characteristics. Is preferred.

In this positive electrode active material, in order to make the amount of Li ₂ CO ₃ less than 0.15 wt%, it is preferable to react the unreacted components sufficiently by adjusting the surface treatment conditions and heat treatment conditions. However, it is not limited to these adjustment methods.

(Measurement method of surface LiOH amount, surface Li ₂ CO ₃ amount)
Titration is performed according to the following procedure with reference to the Winkler method. 10.0 g of a sample is dispersed in 50 ml of ion-exchanged water, immersed for 15 minutes, filtered, and the filtrate is titrated with hydrochloric acid. Titration was performed using an automatic titrator (“AT-700” manufactured by Kyoto Electronics Industry Co., Ltd.). While measuring the pH, the surface LiOH amount and the surface Li ₂ CO ₃ amount are calculated based on the titer up to pH 8.5 and the titer up to pH 4.25.

<Tap density>
The positive electrode active material preferably has a tap density of 2.0 g / cm ³ or more, particularly 2.1 g / cm ³ or more or 3.2 g / cm ³ or less, and more preferably 2.2 g / cm ³ or more. It is particularly preferably 1 g / cm ³ or less, more preferably 2.2 g / cm ³ or more, or 3.0 g / cm ³ or less.
Thus, if the tap density of the present positive electrode active material is 2.0 g / cm ³ or more, the electrode density can be increased, and thus the volume energy density can be increased.
In order to set the tap density of the positive electrode active material to 2.0 g / cm ³ or more, the material is baked at a high temperature of 700 ° C. or higher, or a substance that increases the reactivity at the time of baking, such as a boron compound or a fluorine compound The positive electrode active material is preferably produced by firing and using dense raw materials. However, it is not limited to these adjustment methods.

<Application>
The positive electrode active material can be produced, for example, by mixing a conductive material made of carbon black or the like and a binder made of Teflon (registered trademark) binder or the like. At this time, the present positive electrode active material and another positive electrode active material may be used in combination as necessary.
Such a positive electrode mixture is used for the positive electrode, for example, a material that can occlude / desorb lithium such as lithium or carbon is used for the negative electrode, and lithium hexafluorophosphate (LiPF ₆ ) or the like is used for the non-aqueous electrolyte. A lithium secondary battery can be constructed using a lithium salt dissolved in a mixed solvent such as ethylene carbonate-dimethyl carbonate. However, the present invention is not limited to the battery having such a configuration.

Lithium batteries equipped with this positive electrode active material as at least one of the positive electrode active materials exhibit excellent life characteristics (cycle characteristics) when repeatedly used for charge and discharge. It is particularly excellent in the use of a positive electrode active material of a lithium battery used as a power source for driving a motor mounted on an electric vehicle (EV: Electric Vehicle) or a hybrid electric vehicle (HEV: Hybrid Electric Vehicle).

A “hybrid vehicle” is a vehicle that uses two power sources, an electric motor and an internal combustion engine.
The term “lithium battery” is intended to encompass all batteries containing lithium or lithium ions in the battery, such as lithium primary batteries, lithium secondary batteries, lithium ion secondary batteries, and lithium polymer batteries.

<Manufacturing method>
As an example of the method for producing the present positive electrode active material, for example, a particle powder of the above lithium cobalt metal composite oxide having a layered crystal structure using a surface treatment agent containing at least one of aluminum, titanium, and zirconium (“ After the surface treatment (referred to as “the surface treatment step”) of the present lithium cobalt metal composite oxide particle powder ”, the lithium cobalt metal composite oxide particle powder after the surface treatment is subjected to a heat treatment (“ heat treatment step ”). Can be mentioned). However, it is not limited to such a method.
However, since the surface treatment step and the heat treatment step only have to be provided, other steps may be further provided. For example, a crushing step may be inserted after the heat treatment step, or a crushing step or a classification step may be inserted before the surface treatment step. Moreover, you may add another process.
Moreover, it is not the intention which limits the manufacturing method of this positive electrode active material to this method.

(Method for producing the present lithium cobalt metal composite oxide particle powder)
The present lithium cobalt metal composite oxide particle powder can be obtained by mixing raw materials, granulating and drying as necessary, firing, heat treatment as necessary, and further pulverizing as necessary.
However, the lithium cobalt metal composite oxide powder obtained by purchasing or the like can be used as the present lithium cobalt metal composite oxide particle powder after being subjected to a predetermined treatment.

Examples of the lithium compound used as a raw material of the present lithium cobalt metal composite oxide particle powder include lithium hydroxide (including LiOH and LiOH.H ₂ O), lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), Examples thereof include lithium oxide (Li ₂ O), other fatty acid lithium, lithium halide, and the like.
The type of cobalt compound used as a raw material for the lithium cobalt metal composite oxide particle powder is not particularly limited, and for example, basic cobalt carbonate, cobalt nitrate, cobalt chloride, cobalt oxyhydroxide, cobalt hydroxide, cobalt oxide, etc. should be used. Among these, basic cobalt carbonate, cobalt hydroxide, cobalt oxide, and cobalt oxyhydroxide are preferable.

In addition, hydroxide salts, carbonates, nitrates, etc. of the M element in the above formula (1) can be used as raw materials for the present lithium cobalt metal composite oxide particle powder.

As a raw material mixing method, dry mixing or wet mixing can be performed. As dry mixing, it can be mixed using a ball mill or a precision mixer.
As the wet mixing, it is preferable to add a liquid medium such as water or a dispersant to make a slurry. And when employ | adopting the spray-drying method mentioned later, it is preferable to grind | pulverize the above-mentioned obtained slurry with a wet grinder. However, dry pulverization may be performed. In such mixing of raw materials, the maximum particle size (Dmax) of the raw material is 20 μm or less, in particular, 10 μm or less before mixing the raw materials in order to improve the homogeneity at the time of mixing the raw materials except for the raw material coarse powder. In particular, it is preferable to adjust so as to be 5 μm or less.

After mixing the raw materials, it is preferable to granulate as necessary.
The granulation method may be either wet or dry as long as various raw materials are dispersed in the granulated particles without being separated. Extrusion granulation method, rolling granulation method, fluidized granulation method, mixed granulation method, spraying method A dry granulation method, a pressure molding granulation method, or a flake granulation method using a roll or the like may be used.
At this time, when wet granulation is performed, it is necessary to sufficiently dry before firing. As a drying method at this time, it may be dried by a known drying method such as a spray heat drying method, a hot air drying method, a vacuum drying method, a freeze drying method, etc., among which the spray heat drying method is preferable.
The spray heat drying method is preferably carried out using a heat spray dryer (spray dryer) (referred to herein as “spray drying method”).
However, it is also possible to produce a coprecipitated powder to be fired by, for example, a so-called coprecipitation method (referred to herein as “coprecipitation method”). In the coprecipitation method, after the raw material is dissolved in a solution, the coprecipitation powder can be obtained by adjusting the conditions such as pH and causing precipitation.

In the spray drying method, the powder strength is relatively low, and voids tend to occur between the particles. Therefore, when the spray drying method is adopted, the crushing strength after the crushing step after the firing step, which will be described later, is higher than that of a conventional crushing method, for example, a crushing method using a coarse crusher having a rotation speed of about 1000 rpm. It is preferable to employ a high grinding method.

In the firing step for obtaining the present lithium cobalt metal composite oxide particle powder, it is preferable to calcine at 500 to 870 ° C. as necessary, followed by firing at 700 to 1000 ° C. It is also possible to perform the main baking at 700 to 1000 ° C. without performing the preliminary baking.
By calcining, a gas (for example, CO ₂ ) generated from a component contained in the raw material can be extracted. And in this baking, the crystallinity of particle | grains can be raised or it can adjust to the desired particle size by baking at high temperature rather than temporary baking.

The pre-baking is performed at a temperature of 500 to 870 ° C. in a baking furnace in an air atmosphere, an oxygen gas atmosphere, an atmosphere in which an oxygen partial pressure is adjusted, a carbon dioxide gas-containing atmosphere, or other atmosphere ( : Means the temperature when a thermocouple is brought into contact with the fired product in the firing furnace.) Among them, 600 ° C. or more or 870 ° C. or less, especially 650 ° C. or more or 770 ° C. or less, 0.5 to 30 hours Baking is preferably performed so as to hold.
The kind of baking furnace is not specifically limited. For example, it can be fired using a rotary kiln, a stationary furnace, or other firing furnace.

The main baking is performed at a temperature of 700 to 1000 ° C. in a baking furnace in an air atmosphere, an oxygen gas atmosphere, an atmosphere in which an oxygen partial pressure is adjusted, a carbon dioxide gas-containing atmosphere, or other atmosphere (: It means the temperature when a thermocouple is brought into contact with the fired product in the firing furnace.), Preferably 750 ° C. or higher or 950 ° C. or lower, more preferably 800 ° C. or higher or 950 ° C. or lower, and even more preferably 830 ° C. The baking is preferably performed at 910 ° C. or lower for 0.5 to 30 hours. At this time, it is preferable to select a firing condition in which a fired product including a plurality of metal elements can be regarded as a single phase of a lithium cobalt metal composite oxide having a target composition.
The kind of baking furnace is not specifically limited. For example, it can be fired using a rotary kiln, a stationary furnace, or other firing furnace.

In the case of performing main baking without pre-baking, the temperature is 700 to 1000 ° C., particularly 750 ° C. or higher or 950 ° C. or lower, particularly 800 ° C. or higher or 950 ° C. or lower, and more preferably 830 ° C. or higher or 910 ° C. or lower. The main calcination is preferably performed so as to hold for 5 to 30 hours.

The heat treatment after firing for obtaining the present lithium cobalt metal composite oxide particle powder is preferably performed when the crystal structure needs to be adjusted. As the heat treatment atmosphere at that time, it is preferable to perform the heat treatment under the conditions of an oxidizing atmosphere such as an air atmosphere, an oxygen gas atmosphere, or an atmosphere with an adjusted oxygen partial pressure.

The pulverization after the firing or the heat treatment is preferably performed using a high-speed rotary pulverizer or the like. If pulverization is performed by a high-speed rotary pulverizer, it is possible to pulverize a portion where the particles are aggregated or weakly sintered, and to suppress distortion of the particles. However, the present invention is not limited to a high-speed rotary pulverizer.

An example of the high-speed rotary pulverizer is a pin mill. The pin mill is known as a rotary disk crusher, and is a type of crusher that draws in powder from a raw material supply port by rotating a rotating disk with pins to make the inside negative pressure. Therefore, since the fine particles have a light mass, they easily get on the air current and pass through the clearance in the pin mill, while the coarse particles are reliably crushed. Therefore, when pulverizing with a pin mill, aggregation between particles and weakly sintered portions can be surely solved, and distortion can be suppressed from entering into the particles.
The rotational speed of the high-speed rotary pulverizer is preferably 4000 rpm or more, more preferably 5000 rpm or more or 12000 rpm or less, and particularly preferably 7000 rpm or more or 10000 rpm or less.

Since the classification after firing has the technical significance of adjusting the particle size distribution of the agglomerated powder and removing foreign matter, it is preferable to classify by selecting a sieve having a preferred size.

The lithium cobalt metal composite oxide particles thus produced preferably have a moisture content of 50 to 1000 ppm measured at 110 to 300 ° C. by the Karl Fischer method. If the moisture content is 50 ppm or more, the reaction with the coupling agent among the surface treatment agents can be enhanced, and the surface treatment effect can be enhanced. On the other hand, if the water content is 1000 ppm or less, it is preferable in that the battery characteristics can be made equal or more.
From this point of view, the water content of the present lithium cobalt metal composite oxide particle powder is preferably 50 to 1000 ppm, more preferably 50 ppm or more and 700 ppm or less, especially 50 ppm or more and 500 ppm or less, and more preferably 400 ppm or less. Is more preferable.
The water content measured at 110 to 300 ° C. by the Karl Fischer method is measured in a device at 110 ° C. in a nitrogen atmosphere using a Karl Fischer moisture meter (for example, CA-100 manufactured by Mitsubishi Chemical Corporation). This is the amount of water released when a sample is heated for 45 minutes, then heated to 300 ° C. and heated at 300 ° C. for 45 minutes.
The water measured at 110 to 300 ° C. by the Karl Fischer method is considered to be mainly water chemically bonded to the lithium cobalt metal composite oxide particle powder.

As means for adjusting the water content of the present lithium cobalt metal composite oxide particle powder to the above range, the present lithium cobalt metal composite oxide particle powder produced as described above is mainly dried or dehumidified. And a method for controlling the humidity in storage. However, it is not limited to such a method.

(Surface treatment process)
As a method of surface-treating the present lithium cobalt metal composite oxide particle powder produced as described above, a surface treatment agent containing at least one of aluminum, titanium and zirconium is obtained as described above. The lithium cobalt metal composite oxide powder may be contacted.
For example, an organometallic compound containing at least one of aluminum, titanium, and zirconium, such as a titanium coupling agent, an aluminum coupling agent, a zirconium coupling agent, a titanium-aluminum coupling agent, a titanium-zirconium coupling agent, or an aluminum. A surface treatment agent such as zirconium coupling agent or titanium / aluminum / zirconium coupling agent is dispersed in an organic solvent to form a dispersion, and the dispersion and the lithium cobalt metal composite oxide obtained as described above. A method of performing surface treatment by bringing particle powder into contact with each other can be mentioned.

Examples of the surface treatment agent include compounds having an organic functional group and a hydrolyzable group in the molecule. Among these, those having phosphorus (P) in the side chain are preferable. The coupling agent having phosphorus (P) in the side chain is particularly excellent in binding property with the binder because of better compatibility with the binder.

In the surface treatment step, it is preferable that a surface treatment agent equivalent to 0.1 to 20 wt% is brought into contact with 100 wt% of the lithium cobalt metal composite oxide powder, particularly 0.5 wt% or more or 10 wt% or less, of which 1 wt%. % Or more, or 5 wt% or less, more preferably 1 wt% or more or 3 wt% or less of the surface treatment agent is more preferably brought into contact with the lithium cobalt metal composite oxide powder.

More specifically, for example, the ratio of the total number of moles of aluminum, titanium and zirconium in the surface treatment agent to the number of moles of the present lithium cobalt metal composite oxide powder {(M / lithium cobalt metal composite oxide powder) × 100 (M: Al, Ti, Zr)} is 0.005 to 4%, especially 0.04% or more or 2% or less, and more preferably 0.08% or more or 1% or less. Thus, it is preferable that the lithium cobalt metal composite oxide powder and the surface treatment agent are brought into contact with each other so that the content is 0.08% or more or 0.6% or less.

The amount of the dispersion in which the surface treatment agent is dispersed in an organic solvent or water is 0.2 to 20 wt%, particularly 1 wt% or more or 15 wt% or less with respect to 100 wt% of the present lithium cobalt metal composite oxide powder. It is preferable that the amount is adjusted to 2 wt% or more or 10 wt% or less, more preferably 2 wt% or more or 7 wt% or less, and this amount of dispersion is brought into contact with the lithium cobalt metal composite oxide powder.

In the case of a lithium cobalt metal composite oxide having a layered crystal structure, if the amount of the organic solvent or water to be brought into contact is large, lithium in the layered crystal structure will be eluted. The amount of dispersion dispersed in a solvent or water is preferably limited as described above.
Moreover, the surface treatment agent is mixed with the atmosphere or oxygen by bringing a small amount of the surface treatment agent or a dispersion in which the surface treatment agent is dispersed in an organic solvent or water into contact with the lithium cobalt metal composite oxide powder. Can be brought into contact with the lithium cobalt metal composite oxide powder. As a result, oxygen can be left on the particle surface, which can be assumed to contribute to the supply of oxygen consumed in the oxidation reaction of the organic matter during the subsequent heat treatment.
At this time, the dispersion in which the above amount of the surface treatment agent or the surface treatment agent is dispersed in an organic solvent is not brought into contact with the lithium cobalt metal composite oxide powder at one time and mixed, but divided into several times. It is preferable to repeat the process of contacting and mixing.

In addition, it is also possible to dry-process using inorganic compound powder as a surface treatment agent. However, when inorganic compound powder is used, it is based on the total of the atomic ratio of Co, which is a constituent element, and the atomic ratio of M (total of atomic ratios when there are two or more constituent elements M) measured by XPS. Control the ratio (A / (Co + M)) of the atomic ratio of the surface element A (the total of the atomic ratios when there are two or more surface elements A), the thickness of the surface portion, etc. It is preferable to adjust the conditions.

(Surface treatment)
When performing the surface treatment using the surface treatment agent as described above, in order to volatilize the organic solvent or water, it is preferable to heat and dry at 40 to 120 ° C. and then perform the heat treatment in the next step. Depending on the type of the surface treatment agent, it is preferable to perform the adhesion treatment at 120 ° C. or more and less than 900 ° C. Depending on the type of the surface treatment agent, the adhesion treatment and the heat treatment step can be performed simultaneously.

(Heat treatment process)
In the heat treatment step after the surface treatment step, the surface-treated lithium cobalt metal composite oxide powder is higher than 700 ° C. and lower than 900 ° C. (in a fired product in the furnace) in an atmosphere having an oxygen concentration of 20 to 100%. It is preferable to perform heat treatment so that the temperature when the thermocouple is brought into contact, that is, the product temperature, is maintained for a predetermined time. When the temperature is 900 ° C. or higher, the surface treatment element diffuses into the crystal structure, and the ratio (A / (Co + M)) of the atomic ratio of the surface element A (the total of the atomic ratios when the surface element A is two or more types). Is unfavorable because it becomes smaller.
By such heat treatment, the organic solvent or water can be volatilized or the side chain of the surface treatment agent can be decomposed, and aluminum, titanium, or zirconium in the surface treatment agent can be diffused deeper from the surface. It is possible to suppress the reaction with the electrolytic solution and improve the life characteristics, and the rate characteristics can be equal to or higher than that of the conventional positive electrode active material subjected to the surface treatment. .
Furthermore, it is preferable to set the heat treatment temperature to be equal to or lower than the main firing temperature, since the crushing load after the heat treatment can be reduced.

From the viewpoint of further enhancing the effect of such heat treatment, the treatment atmosphere in the heat treatment step is preferably an oxygen-containing atmosphere. Among them, an oxygen-containing atmosphere having an oxygen concentration of 20 to 100% is preferable, and 30% or more or 100% or less, especially 50% or more or 100% or less, more preferably 60% or more or 100% or less, Of these, an oxygen-containing atmosphere of 80% or more or 100% or less is more preferable.

Further, the treatment temperature in the heat treatment step is preferably higher than 700 ° C. and lower than 900 ° C. (meaning the temperature when a thermocouple is brought into contact with the fired product in the firing furnace). Or 880 ° C. or lower, more preferably 850 ° C. or lower, more preferably 720 ° C. or higher, or lower than 800 ° C.
Furthermore, the treatment time in the heat treatment step is preferably 0.5 to 20 hours, depending on the treatment temperature, and is preferably 1 hour or more or 10 hours or less, more preferably 3 hours or more or 10 hours or less. Is more preferable.
The type of furnace is not particularly limited. For example, it can be fired using a rotary kiln, a stationary furnace, or other firing furnace.

(Disintegration)
After the heat treatment step, the lithium cobalt metal composite oxide powder may be crushed.
At this time, it is preferable to crush the lithium cobalt metal composite oxide powder at a crushing strength at which the change rate of the specific surface area (SSA) before and after crushing is 100 to 250%.
Crushing after heat treatment is preferably performed so that the new surface under the surface treatment layer is not exposed so as to maintain the effect of the surface treatment, so that the change rate of the specific surface area (SSA) before and after crushing is It is preferably 100 to 200%, more preferably 175% or less, more preferably 150% or less, and even more preferably 125% or less.

As a preferable example of such a crushing method, a crushing device (for example, a pin mill) that crushes with a pin attached to a crushing plate that rotates at high speed in a relative direction can be used.
When crushing in the step after the surface treatment, it is preferable to crush at 4000 to 7000 rpm, particularly 6500 rpm or less, and especially 6000 rpm or less so as not to scrape the surface portion.

¡After crushing as described above, classification may be performed as necessary. The classification at this time has the technical significance of adjusting the particle size distribution of the agglomerated powder and removing foreign matter, and therefore, it is preferable to classify by selecting a sieve having a preferred size.

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

Next, the present invention will be further described based on examples and comparative examples. However, the present invention is not limited to the following examples.

<Example 1>
Lithium carbonate, cobalt oxyhydroxide, and magnesium oxide were weighed so that the molar ratio was Li: Co: Mg = 0.999: 0.997: 0.004.

After mixing the weighed raw materials with a precision mixer, a mixed raw material was obtained. The obtained mixed raw material was baked at 850 ° C. for 22 hours in an air atmosphere using a stationary electric furnace. The fired lump obtained by firing was put in a mortar and crushed with a pestle and classified with a sieve having an opening of 53 μm, and the lithium cobalt metal composite oxide powder under the sieve was recovered.

The obtained lithium cobalt metal composite oxide powder had a water content of 241 ppm measured at 110 to 300 ° C. by the Karl Fischer method.
As a result of chemical analysis of the lithium cobalt metal composite oxide powder obtained by firing, Li: 7.0%, Co: 60.9%, and Mg: 0.1%.

Next, a titanium coupling agent (Ajinomoto Fine Techno Co., Ltd. Preneact (registered trademark) KR-46B) (3.0 wt%) as a surface treatment agent and isopropyl alcohol (7.6 wt%) as a solvent are mixed and mixed in a solvent. A dispersion in which an aluminum coupling agent was dispersed was prepared. Thereafter, 10.6 wt% of the dispersion was added to 100 wt% of the lithium cobalt metal composite oxide powder obtained by firing, and mixed using a cutter mill (Milcer 720G manufactured by Iwatani Corporation).
Next, it vacuum-dried at 100 degreeC for 1 hour. Then, lithium carbonate was added so that it might become 3.9 wt% with respect to an aluminum coupling agent, and it mixed using the cutter mill. After mixing, heat treatment was performed in an atmosphere having an oxygen concentration of 98% so as to maintain the product temperature at 730 ° C. for 5 hours to obtain a lithium cobalt metal composite oxide powder.
The lithium cobalt metal composite oxide obtained by the heat treatment was classified with a sieve having an opening of 53 μm to obtain a lithium cobalt metal composite oxide powder (sample) under the sieve.

<Example 2>
Zirconium coupling agent (KENRICH PETROCHMICALS, INC. Ken-React (registered trademark) NZ12) was used as the surface treatment agent, and the amount of lithium carbonate added after vacuum drying was 3.0% with respect to the zirconium coupling agent. A lithium cobalt metal composite oxide powder (sample) was obtained in the same manner as in Example 1 except that the content was changed to%.

<Example 3>
A lithium cobalt metal composite oxide powder (sample) was obtained in the same manner as in Example 2 except that the surface treatment and vacuum drying were followed by heat treatment without adding lithium carbonate and the heat treatment temperature was changed to 770 ° C. It was.

<Comparative Example 1>
Lithium carbonate and cobalt oxyhydroxide were weighed so that the molar ratio was Li: Co = 1.000: 1.000.

The weighed raw material was put into a PP container, Zr balls were added and ball mill mixing was performed to obtain a mixed raw material. The obtained mixed raw material was baked at 850 ° C. for 22 hours in an air atmosphere using a stationary electric furnace. The fired lump obtained by firing was put in a mortar and crushed with a pestle and classified with a sieve having an opening of 53 μm, and the lithium cobalt metal composite oxide powder under the sieve was recovered.
As a result of chemical analysis of the obtained lithium cobalt metal oxide powder (sample), they were Li: 7.0 and Co: 59.4%.

<Comparative example 2>
Lithium carbonate and cobalt oxyhydroxide were weighed so that the molar ratio was Li: Co = 1.002: 0.998.

The weighed raw material was put into a PP container, Zr balls were added and ball mill mixing was performed to obtain a mixed raw material. The obtained mixed raw material was baked for 22 hours at 1000 ° C. in an air atmosphere using a stationary electric furnace. The fired lump obtained by firing was put in a mortar and crushed with a pestle and classified with a sieve having an opening of 53 μm, and the lithium cobalt metal composite oxide powder under the sieve was recovered.
As a result of chemical analysis of the obtained lithium cobalt metal oxide powder (sample), they were Li: 7.1 and Co: 59.5%.

<Comparative Example 3>
The lithium cobalt metal oxide powder prepared in Comparative Example 2 was placed in a 20% NaOH aqueous solution at 80 ° C. and subjected to alkali treatment while stirring. At this time, the slurry concentration was set to 33%. After the alkali treatment, it was filtered and the resulting cake was dried at 120 ° C. After drying, it was classified with a sieve having an opening of 53 μm, and the lithium cobalt metal composite oxide powder under the sieve was recovered.

<Comparative example 4>
Titanium coupling agent (Ajinomoto Fine Techno Co., Ltd. Preneact (registered trademark) KR-44) 0.1 wt% as a surface treatment agent and isopropyl alcohol as a solvent with respect to the lithium cobalt metal oxide powder produced in Comparative Example 3 0.25 wt% was mixed to prepare a dispersion in which an aluminum coupling agent was dispersed in a solvent. Thereafter, 0.35 wt% of the dispersion was added to 100 wt% of the lithium cobalt metal composite oxide powder obtained by firing, and mixed using a cutter mill (Milcer 720G manufactured by Iwatani Corporation).
Next, it vacuum-dried at 100 degreeC for 1 hour, and heat-processed in air | atmosphere so that the product temperature might be maintained at 900 degreeC for 30 minutes, and obtained lithium cobalt metal complex oxide powder.
The lithium cobalt metal composite oxide obtained by the heat treatment was classified with a sieve having an opening of 53 μm to obtain a lithium cobalt metal composite oxide powder (sample) under the sieve.

<Analysis of surface portion and measurement method of thickness of surface portion>
A cross section near the particle surface of the lithium cobalt metal complex oxide (sample) is observed with a transmission electron microscope (“JEM-ARM200F” manufactured by JEOL Ltd.) and energy dispersive X-ray analysis (EDS: Energy dispersive X -ray spectrometry).
As a result, for the lithium cobalt metal composite oxide (sample) obtained in each example obtained in the above examples, a layer containing a large amount of Al element, Ti element, or Zr element exists on the surface of each particle. I was able to confirm that.
The thickness of the surface portion was measured by performing line analysis at the particle surface portion, and measuring the length of both ends of the peak of the Al element, Ti element, or Zr element as the thickness of the surface portion.

<Analysis by XPS>
The ratio of the existing elements in the depth direction was analyzed while sputtering the lithium cobalt metal complex oxide (sample) by XPS (“XPS Quantam 2000” manufactured by ULVAC-PHI). The equipment specifications and conditions used for the measurement are as follows.
X-ray source: AlKα1 (1486.8 eV)
Tube voltage: 15 kV
Tube current: 3mA
X-ray irradiation area: 200μmφ
Measurement conditions: Narrow measurement for state / semi-quantitative path energy: 23.5 eV
Measurement interval: 0.1 eV
Sputtering rate: 1-10nm / min (SiO2 conversion)

The XPS data was analyzed using data analysis software ("Multipack Ver6.1A" manufactured by ULVAC-PHI). The trajectory used for the calculation was determined for each element, and the analysis was performed considering the sensitivity coefficient.
Co: 2p1 Sensitivity coefficient 1.056
Al: 2p sensitivity coefficient 0.256
Ti: 2p Sensitivity coefficient 2.077
Zr: 3d impression coefficient 2.767

As a result, for each lithium cobalt metal composite oxide (sample) obtained in the above example, the ratio of the atomic ratio of the surface element A to the total of the atomic ratio of Co, which is a constituent element, and the atomic ratio of M (A / (Co + M)) was confirmed to be larger than 0.07 and smaller than 0.8.

<Surface LiOH amount / Surface Li ₂ CO ₃ amount>
Titration was performed according to the following procedure with reference to the Winkler method. 10.0 g of a sample is dispersed in 50 ml of ion-exchanged water, immersed for 15 minutes, filtered, and the filtrate is titrated with hydrochloric acid. At that time, the titration was performed using an automatic titrator (“AT-700” manufactured by Kyoto Electronics Industry Co., Ltd.). While measuring the pH, the amount of surface LiOH and the amount of surface Li ₂ CO ₃ were calculated based on the titration amount up to pH 8.5 and the titration amount up to pH 4.25.

<Calculation of surface lithium impurity amount>
The surface lithium impurity amount was obtained by adding the amount of lithium hydroxide and the amount of lithium carbonate calculated from the above titration.

<Measurement of D50>
About lithium cobalt metal complex oxide powder (sample) obtained in Examples and Comparative Examples, using an automatic sample feeder for laser diffraction particle size distribution measuring device (“Microtorac SDC” manufactured by Nikkiso Co., Ltd.), lithium cobalt metal complex Oxide powder (sample) is put into a water-soluble solvent, 40W ultrasonic wave is irradiated for 360 seconds at a flow rate of 40%, and the particle size distribution is measured using a laser diffraction particle size distribution measuring instrument “MT3000II” manufactured by Nikkiso Co., Ltd. D50 was determined from the measured volume-based particle size distribution chart.
The water-soluble solvent used in the measurement was passed through a 60 μm filter, the solvent refractive index was 1.33, the particle permeability was transmissive, the particle refractive index was 2.46, the shape was non-spherical, and the measurement range was 0.133. ˜704.0 μm, the measurement time was 30 seconds, and the average value measured twice was D50.

<Measurement of specific surface area>
The specific surface areas of the lithium cobalt metal composite oxide powders (samples) obtained in the examples and comparative examples were measured as follows.
First, 2.0 g of a sample (powder) was weighed into a glass cell (standard cell) for a fully automatic specific surface area measuring device Macsorb (manufactured by Mountec Co., Ltd.), and set in an autosampler. After replacing the inside of the glass cell with nitrogen gas, heat treatment was performed at 250 ° C. for 15 minutes in the nitrogen gas atmosphere. Thereafter, cooling was performed for 4 minutes while flowing a mixed gas of nitrogen and helium. After cooling, the sample (powder) was measured by the BET single point method.
Note that a mixed gas of 30% nitrogen and 70% helium was used as the adsorption gas during cooling and measurement.

<Measurement of tap density>
30 g of the lithium cobalt metal composite oxide obtained in Examples and Comparative Examples was placed in a 150 ml glass graduated cylinder, using a shaking specific gravity measuring instrument (KRS-409, manufactured by Kuramochi Scientific Instruments) at a stroke of 60 mm. The powder packing density when tapped 350 times was determined as the tap density.

<X-ray diffraction>
X-ray diffraction measurement was performed on the lithium cobalt metal composite oxides obtained in Examples and Comparative Examples, and peak search was performed on the obtained X-ray diffraction patterns using the integrated powder X-ray analysis software PDXL2 manufactured by Rigaku Corporation. . Data processing is performed automatically for background removal and Kα2 removal, and the ratio of the integrated intensity of the peak derived from the (003) plane to the integrated intensity of the peak derived from the (104) plane belonging to the crystal structure of the space group R-3m (003) / (104) was calculated.

The XRD measurement was performed under the following measurement condition 1 using an apparatus name “Ultima IV, manufactured by Rigaku Corporation” to obtain an XRD pattern. The equipment specifications and conditions used for the measurement are as follows.
= XRD measurement conditions =
Radiation source: CuKα (line focal point), wavelength: 1.541836Å
Operation axis: 2θ / θ, Measurement method: Continuous, Count unit: cps
Start angle: 15.0 °, end angle: 120.0 °, integration count: 1 sampling width: 0.01 °, scan speed: 1.0 ° / min
Voltage: 40 kV, current: 40 mA
Divergence slit: 0.2 mm, Divergence length restriction slit: 2 mm
Scattering slit: 2 °, light receiving slit: 0.15 mm
Offset angle: 0 °
Goniometer radius: 285 mm, optical system: concentrated method attachment: ASC-48
Slit: D / teX Ultra slit detector: D / teX Ultra
Incident monochrome: CBO
Ni-Kβ filter: No rotation speed: 50 rpm

<Battery characteristics evaluation>
Using the lithium cobalt metal composite oxide powder prepared in Examples and Comparative Examples as a positive electrode active material, a 2032 type coin battery and a cell for electrochemical evaluation TOMCEL (registered trademark) shown in FIG. 1 were prepared. Using this, the following battery performance evaluation test, rate characteristic evaluation test, and cycle characteristic evaluation test were conducted.

(Production of coin battery)
89 parts by mass of lithium manganese composite oxide powder (sample) prepared in Examples and Comparative Examples as a positive electrode active material, 5 parts by mass of acetylene black, and 6 parts by mass of polyvinylidene fluoride (PVDF) were weighed and mixed. Then, 100 parts by mass of 1-methyl-2-pyrrolidone (NMP) was added thereto, and a positive electrode mixture slurry (solid content concentration: 50% by mass) using a planetary agitation / defoaming device (Mazerustar KK-50S manufactured by Kurabo Industries) Adjusted.
At this time, PVDF was dissolved in NMP in advance, and the positive electrode active material and acetylene black were added and kneaded to prepare a positive electrode mixture slurry (solid content concentration 50 mass%).
After coating this positive electrode mixture slurry on an aluminum foil as a current collector at a conveying speed of 20 cm / min using a coating machine, the coating machine is used to hold 70 ° C. for 2 minutes. After heating as described above, drying was performed so as to hold 120 ° C. for 2 minutes to form a positive electrode mixture layer to obtain an aluminum foil with a positive electrode mixture layer. Next, the aluminum foil with the positive electrode mixture layer was punched out to 13 mmφ after punching the electrode into a size of 50 mm × 100 mm and using a roll press machine to press and dense with a press linear pressure of 3 t / cm. Next, in a vacuum state, the mixture was heated from room temperature to 200 ° C. and dried by heating so as to be held at 200 ° C. for 6 hours to obtain a positive electrode.
The negative electrode was made of metallic Li of φ14 mm × thickness 0.6 mm, and a separator in which an electrolytic solution in which LiPF ₆ was dissolved to 1 mol / L was placed in a carbonate-based mixed solvent was placed to prepare a 2032 type coin battery. .

(Battery performance evaluation test)
Using the 2032 type coin battery prepared as described above, initial activation was performed by the method described below. The battery was charged at a constant current and a constant potential to 4.3 V at 0.1 C at 25 ° C., and then discharged at a constant current to 3.0 V at 0.1 C. This was repeated for 3 cycles. The actually set current value was calculated from the content of the positive electrode active material in the positive electrode.

(Rate characteristics evaluation test)
As described above, a rate characteristic evaluation test was performed using a coin battery after evaluating the discharge capacity. After constant current and constant potential charging to 4.3 V at 25 ° C. and 0.1 C, constant current discharging was performed to 3.0 V at 5 C. In the above evaluation, a discharge capacity of 5C up to 4.3-3.0V was obtained. The 5 C discharge capacity / 0.1 C discharge capacity × 100 was calculated as an index of rate characteristics. The larger the value, the better the rate characteristics.

(Cycle life evaluation test)
As described above, a cycle life characteristic evaluation test was performed using a coin battery after evaluating the discharge capacity. Under an environment of 25 ° C., the charge / discharge range is 4.3 V to 3.0 V, the charge is performed at a constant current of 0.1 C constant current and the discharge is performed at a constant current of 0.1 C for one cycle, and then at 1 C. The charge / discharge cycle was performed 98 times.
The percentage (%) of the numerical value obtained by dividing the discharge capacity at the 99th cycle by the discharge capacity at the second cycle was determined as the cycle life characteristic value.
Table 1 shows the life characteristic values (4.3 V capacity retention rate @ 25 ° C.) of each Example and Comparative Example as relative values when the cycle life characteristic value of Comparative Example 4 is 100.

(Production of cell for electrochemical evaluation)
89 parts by mass of lithium manganese composite oxide powder (sample) prepared in Examples and Comparative Examples as a positive electrode active material, 5 parts by mass of acetylene black, and 6 parts by mass of polyvinylidene fluoride (PVDF) were weighed and mixed. Then, 100 parts by mass of 1-methyl-2-pyrrolidone (NMP) was added thereto, and a positive electrode mixture slurry (solid content concentration: 50% by mass) using a planetary agitation / defoaming device (Mazerustar KK-50S manufactured by Kurabo Industries) Adjusted.
At this time, PVDF was dissolved in NMP in advance, and the positive electrode active material and acetylene black were added and kneaded to prepare a positive electrode mixture slurry (solid content concentration 50 mass%).
After coating this positive electrode mixture slurry on an aluminum foil as a current collector at a conveying speed of 20 cm / min using a coating machine, the coating machine is used to hold 70 ° C. for 2 minutes. After heating as described above, drying was performed so as to hold 120 ° C. for 2 minutes to form a positive electrode mixture layer to obtain an aluminum foil with a positive electrode mixture layer. Next, the aluminum foil with the positive electrode mixture layer was punched into a size of 50 mm × 100 mm, press-thickened at a press linear pressure of 3 t / cm using a roll press machine, and then punched out to 16 mmφ. Next, in a vacuum state, the substrate was heated from room temperature to 200 ° C. and dried by heating so as to be held at 200 ° C. for 6 hours.
For the negative electrode 6, metal Li of φ19 mm × thickness 0.6 mm was used.
As the separator 4, a separator made of a microporous polypropylene resin in which an electrolytic solution in which LiPF ₆ was dissolved at 1 mol / L in a carbonate-based mixed solvent was impregnated was used.
And as shown in FIG. 1, the positive electrode 3 which consists of the said positive electrode compound material was arrange | positioned in the inner center of the lower body 1 made from an organic electrolyte-resistant stainless steel. A separator 4 was disposed on the upper surface of the positive electrode 3, and the separator was fixed by a spacer 5. Further, on the upper surface of the separator, a negative electrode 6 in which metal Li is fixed to the lower surface side is arranged, a spacer 7 that also serves as a negative electrode terminal is arranged, and the upper body 2 is put on the top and tightened with a screw to seal the battery. Thus, an electrochemical evaluation cell TOMCEL (registered trademark) was produced.

(Battery performance evaluation test)
Using the electrochemical evaluation cell prepared as described above, initial activity was performed by the method described below. The battery was charged at a constant current and a constant potential to 4.3 V at 0.1 C at 25 ° C., and then discharged at a constant current to 3.0 V at 0.1 C. This was repeated for 3 cycles. The actually set current value was calculated from the content of the positive electrode active material in the positive electrode.

(High temperature high potential cycle life evaluation: 45 ° C high temperature cycle characteristics)
A charge / discharge test was conducted by the method described below using the electrochemical cell after the initial activity as described above, and the high-temperature cycle life characteristics were evaluated.
Place the cell in an environmental testing machine set so that the environmental temperature for charging and discharging the battery is 45 ° C., prepare to charge and discharge, and let it stand for 4 hours so that the cell temperature becomes the environmental temperature, then charge and discharge range Was set to 4.5 V to 3.0 V, charging was performed at a constant current constant potential of 0.1 C and discharging was performed for one cycle at a constant current of 0.1 C, and then charging and discharging cycles were performed 60 times at 1 C.
The percentage (%) of the numerical value obtained by dividing the discharge capacity at the 61st cycle by the discharge capacity at the 2nd cycle was determined as the high temperature cycle life characteristic value.
In Table 1, the life characteristic values (4.5 V capacity retention rate @ 45 ° C.) of each Example and Comparative Example are shown as relative values when the high temperature cycle life characteristic value of Comparative Example 4 is 100.

(Discussion)
From the above-mentioned Examples / Comparative Examples and the test results conducted by the inventors so far, any one of the group consisting of Al, Ti and Zr is formed on the surface of the particles made of lithium cobalt metal composite oxide having a layered crystal structure. Or the atomic ratio of Co and the atomic ratio of M, measured by XPS, for a positive electrode active material for a lithium secondary battery including active particles having a surface portion in which one or two or more combinations exist Ratio (A / (Co + M)) of the atomic ratio of surface element A (the total of atomic ratios when there are two or more surface elements A) to the total of (the total of atomic ratios when there are two or more constituent elements M) ) Is larger than 0.07 and smaller than 0.8, the reaction with the electrolytic solution can be suppressed and the life characteristics can be improved, and the rate characteristics can be compared with that of the conventionally proposed positive electrode active material subjected to the surface treatment. Shi I knew that I could do more than that.

Furthermore, in the X-ray diffraction pattern measured by a powder X-ray diffractometer (XRD) using CuKα1 rays, the ratio of the integrated intensity of the peak derived from the (003) plane to the integrated intensity of the peak derived from the (104) plane (003 ) / (104) is larger than 1.15 and smaller than 3.00, it was found that rate characteristics can be improved.

The above examples are an example of a lithium cobalt metal complex oxide having a layered crystal structure having a specific composition, as a result of addition the inventors of the above embodiment has performed a number of tests, the general formula Li _{1 ± x} Co _y M _1-xy O ₂ (where 0.95 ≦ 1 ± x ≦ 1.05, y ≧ 0.8, 1-xy> 0, M is Mn, Ni, Na , Mg, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce Particles made of a lithium cobalt metal composite oxide having a layered crystal structure represented by any one kind or a combination of two or more kinds (referred to as “constituent element M”) are used as a core material, Any one or a combination of two or more of the group consisting of Al, Ti and Zr (this In the positive electrode active material for a lithium secondary battery including particles having a surface portion in which surface element A ”is present), the atomic ratio of surface element A to at least the total of the atomic ratio of Co and the atomic ratio of M (A / (Co + M)) is larger than 0.07 and smaller than 0.8, the amount of surface lithium impurities is less than 0.15 wt%, and the integrated intensity of the peak derived from the (104) plane is ( When the ratio (003) / (104) of the integrated intensity of the peak derived from the (003) plane is larger than 1.15 and smaller than 3.00, any of the elements listed as the constituent element M can stabilize the crystal structure. As a result, it has been found that rate characteristics and cycle characteristics can be improved, for example, the above example uses Mg as the constituent element M. Considering the difference from Co and the ion radius. By designing the number of moles of constituent elements used, Mn, Ni, Na, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb, It is considered that the same effect as in the above embodiment can be obtained even when any one or a combination of two or more of the group consisting of Mo, In, Ta, W, Re, and Ce is used. it can.

Claims

General formula Li 1 ± x Co y M 1-xy O 2 (where 0.95 ≦ 1 ± x ≦ 1.05, y ≧ 0.8, 1-xy> 0, M is Mn Ni, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce Al, on the surface of the particle composed of a lithium cobalt metal composite oxide having a layered crystal structure represented by any one kind or a combination of two or more kinds of groups (referred to as “constituent element M”) A positive electrode active material for a lithium secondary battery comprising particles having a surface portion in which any one or a combination of two or more of the group consisting of Ti and Zr (referred to as “surface element A”) is present. There,
Measured by X-ray photoelectron spectroscopy (XPS) with respect to the sum of the atomic ratio of Co, which is a constituent element of the above general formula, and the atomic ratio of M (the sum of atomic ratios when there are two or more constituent elements M) The ratio (A / (Co + M)) of the atomic ratio of the surface element A (the total of the atomic ratios when there are two or more surface elements A) is greater than 0.07 and less than 0.8;
The amount of surface lithium impurities is less than 0.15 wt%, and
In the X-ray diffraction pattern measured by a powder X-ray diffractometer (XRD) using CuKα1 line, the ratio of the integrated intensity of the peak derived from the (003) plane to the integrated intensity of the peak derived from the (104) plane (003) / (104) is larger than 1.15 and smaller than 3.00, The positive electrode active material for lithium secondary batteries characterized by the above-mentioned.
The positive electrode active material for a lithium secondary battery according to claim 1, wherein the tap density is 2.0 g / cm 3 or more.
A lithium secondary battery comprising the positive electrode active material for a lithium secondary battery according to claim 1 or 2 as a positive electrode active material.
A lithium secondary battery for a hybrid electric vehicle or an electric vehicle, comprising the positive electrode active material for a lithium secondary battery according to claim 1 or 2 as a positive electrode active material.