JP2011134670A - Lithium secondary battery positive electrode active material - Google Patents

Abstract

Provided is a positive electrode active material for a lithium secondary battery, which is a solid solution of LiMO ₂ and Li ₂ MnO ₃ and has excellent battery characteristics in which elution of manganese is suppressed even after repeated charging and discharging with a high rate. To do.
A positive electrode active material for a lithium secondary battery provided by the present invention has a general formula: LiMO ₂ (wherein M is at least one transition metal selected from the group consisting of Co, Ni and Mn) These are solid solution particles of a lithium transition metal composite oxide (320) represented by one or more metal elements including an element) and a lithium manganese oxide (310) represented by Li ₂ MnO _3. Te, closer to the center portion of the solid solution _particles, Li 2 concentration of MnO ₃ is constituted higher than the concentration of LiMO _2, and, the closer to the particle outer surfaces, LiMO ₂ concentrations _Li 2 MnO ₃ It has a concentration gradient that is configured to be higher than the above concentration.
[Selection] Figure 1

Description

  The present invention relates to a positive electrode active material used for a lithium secondary battery and a method for producing the same.

  In recent years, secondary batteries such as lithium secondary batteries and nickel metal hydride batteries have become increasingly important as power sources mounted on vehicles using electricity as a drive source, or power sources mounted on personal computers, portable terminals, and other electrical products. . In particular, a lithium secondary battery (typically a lithium ion battery) that is lightweight and obtains a high energy density is expected to be preferably used as a high-output power source mounted on a vehicle.

A lithium secondary battery includes an electrode having a configuration in which a material (electrode active material) capable of reversibly occluding and releasing lithium ions serving as a charge carrier is held in a conductive member (electrode current collector), and further increases energy. In order to achieve higher density and higher output, electrode active material materials are being studied. As a positive electrode active material constituting a positive electrode of a lithium secondary battery, LiMO ₂ having a layered rock salt structure (M is at least one element of cobalt, nickel, and manganese, for example, Li _x Ni _1/3 Co _1/3 Mn A lithium transition metal composite oxide represented by _1/3 O ₂ ) is known.

In addition, as a conventional technique related to the positive electrode active material for a lithium secondary battery, Patent Document 1 discloses LiMO ₂ having a layered rock salt structure and lithium manganese oxide having a layered rock salt structure (monoclinic system). A positive electrode active material comprising a solid solution (solid phase in which different substances are uniformly dissolved) with Li ₂ MnO ₃ which is a product is disclosed. Furthermore, Patent Document 2 discloses a positive electrode active material which is a composite particle of LiMO ₂ and Li ₂ MnO ₃ and contains LiMO ₂ inside the particle and Li ₂ MnO _{3 on the} surface at a high density. ing.

JP 2006-253119 A JP-A-8-171935

The lithium secondary battery constructed using a positive electrode active material made of a solid solution of LiMO ₂ and Li ₂ MnO ₃ described in Patent Document 1 is a lithium constructed using a positive electrode active material made of a single LiMO _2. Compared to secondary batteries, lithium ion storage can be increased, and it is expected as a positive electrode active material capable of realizing higher capacity or higher energy density. However, manganese is eluted while charging and discharging are repeated, and battery characteristics (for example, cycle characteristics and load characteristics) are deteriorated.
Further, in the case of a positive electrode active material composed of composite particles of LiMO ₂ and _Li 2 MnO ₃ as described in Patent Document 2, because of the presence of _Li 2 MnO ₃ with a high density on the particle surface, more elution of manganese It occurs remarkably and it becomes difficult to maintain good battery characteristics.

The present invention has been made in view of the foregoing, it is an object of a solid solution of LiMO ₂ and Li ₂ MnO _3, elution of manganese is suppressed even after repeating charging and discharging due to high-rate Providing a positive electrode active material for a lithium secondary battery having excellent load characteristics (characteristics for maintaining high capacity even during large current discharge) or cycle characteristics (characteristics for maintaining high capacity even after repeated charge / discharge) It is. Another object is to provide a lithium secondary battery including a positive electrode using such a positive electrode active material.

To achieve the above object, according to the present invention, a general formula: LiMO ₂ (wherein M is one or more transition metal elements including at least one transition metal element selected from the group consisting of Co, Ni and Mn). There is provided a positive electrode active material for a lithium secondary battery comprising solid solution particles of a lithium transition metal composite oxide represented by (a metal element) and a lithium manganese oxide represented by Li ₂ MnO ₃ .
The positive electrode active material disclosed herein is configured such that the closer to the center of the solid solution particle, the higher the concentration of Li ₂ MnO ₃ than the concentration of LiMO ₂ , and the outer surface of the solid solution particle. It is characterized by having a concentration gradient such that the closer the LiMO ₂ concentration is, the higher the Li ₂ MnO ₃ concentration.

In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. In general, a secondary battery referred to as a lithium ion battery is a typical example included in the lithium secondary battery in this specification.
In this specification, the “positive electrode active material” means a positive electrode side capable of reversibly occluding and releasing (typically inserting and desorbing) chemical species (that is, lithium ions) serving as charge carriers in a secondary battery. Refers to the substance.

A positive electrode active material for a lithium secondary battery composed of solid solution particles of LiMO ₂ and Li ₂ MnO ₃ is expected as a positive electrode active material capable of realizing high capacity or high energy density because of a large amount of occlusion of lithium ions. Has been. The positive electrode active material composed of solid solution particles according to the present invention is configured such that the closer to the particle central portion, the higher the concentration of Li ₂ MnO _{3 than} the concentration of LiMO ₂ and the closer to the outer surface of the solid solution particles, ₂ has a concentration gradient such that the concentration of ₂ is higher than the concentration of Li ₂ MnO ₃ . Therefore, a lithium secondary battery constructed using such a positive electrode active material contains the above Li ₂ MnO ₃ at a high concentration in the center of the solid solution particles even if it is used in a mode in which charging and discharging by high rate are repeated. Manganese is difficult to elute from solid solution particles (typically Li ₂ MnO ₃ ). Therefore, according to the present invention, since the collapse of the crystal structure due to elution of manganese is suppressed, an excellent battery characteristic (for example, cycle characteristic, load characteristic) in which an increase in internal resistance is suppressed even after repeated high-rate charge / discharge. A positive electrode active material for a lithium secondary battery that can be realized can be provided.

In a preferable aspect of the positive electrode active material for a lithium secondary battery disclosed herein, the lithium transition metal composite oxide constituting the solid solution particles is an oxide containing all of Ni, Co, and Mn.
An oxide containing all of Ni, Co and Mn as transition metal elements constituting a lithium transition metal composite oxide is a positive electrode having a stable crystal structure, excellent heat resistance, and a large theoretical lithium ion storage capacity. Can be an active material. As a result, a positive electrode active material for a lithium secondary battery that can construct a lithium secondary battery having a higher battery capacity or a higher energy density can be provided.
In still another preferred embodiment, the lithium transition metal composite oxide constituting the solid solution particle is an oxide represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

Moreover, this invention provides the method of manufacturing the positive electrode active material for lithium secondary batteries as another side surface which implement | achieves the said objective. The production method disclosed herein has a general formula: LiMO ₂ (wherein M is one or more metals including at least one transition metal element selected from the group consisting of Co, Ni and Mn) Element comprising a solid solution particle of a lithium transition metal complex oxide represented by Li ₂ MnO ₃ and a lithium manganese oxide represented by Li ₂ MnO ₃ , comprising: These steps are included.
That is, (1) a step of preparing lithium manganese oxide particles represented by the above Li ₂ MnO ₃ , (2) a lithium transition metal composite oxide represented by the above prepared Li ₂ MnO ₃ and the above general formula: LiMO ₂ A step of preparing a raw material mixture by dissolving a starting raw material for constituting the solid solution particles in a water-based solvent, including a lithium source for constituting a solid metal particle and one or more transition metal M element sources ( (Typically, one or two or more gelling agents are added together), (3) a gelation step of gelling the prepared raw material mixture to obtain a gel composition, and (4) the above obtained A firing step of firing the gel-like composition.

According to this manufacturing method, in the raw material preparation step, a state in which the lithium manganese oxide particle surface is coated with a precursor of a lithium transition metal composite oxide (lithium source, transition metal M element source, etc.) is formed. Further, Li ₂ MnO ₃ diffuses outward by the heat treatment in the firing step, and the lithium transition metal composite oxide (typically a precursor) covering the surface of the Li ₂ MnO ₃ faces inward. Spread. As a result, solid solution particles of LiMO ₂ and Li ₂ MnO ₃ are formed, and the concentration of Li ₂ MnO ₃ is configured to be higher than the concentration of LiMO ₂ closer to the center of the particle. The closer to the outer surface, the solid solution particles having a concentration gradient in which the concentration of LiMO ₂ is higher than the concentration of Li ₂ MnO ₃ can be produced. Thus, even if the lithium secondary battery constructed using solid solution particles containing Li ₂ MnO ₃ at a higher concentration as the cathode is closer to the center as a positive electrode active material is used in a mode in which charging and discharging at a high rate are repeated, ₂ Manganese is difficult to elute from MnO ₃ . As a result, according to the present invention, an increase in resistance due to elution of manganese is suppressed even under high-rate charge / discharge, so that a positive electrode for a lithium secondary battery that can realize excellent battery characteristics (for example, cycle characteristics and load characteristics). An active material can be produced.

In a preferable aspect of the production method disclosed herein, the lithium transition metal composite oxide includes an oxide containing all of Ni, Co, and Mn, and therefore includes a nickel source, a cobalt source, and a manganese source. A raw material mixture is prepared using the starting materials. Further, the raw material mixture is prepared so that a preferable lithium transition metal composite oxide constitutes an oxide represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .
An oxide containing all of Ni, Co and Mn as transition metal elements constituting a lithium transition metal composite oxide is a positive electrode having a stable crystal structure, excellent heat resistance, and a large theoretical lithium ion storage capacity. Can be an active material. Therefore, a positive electrode for a lithium secondary battery capable of constructing a lithium secondary battery having a higher battery capacity or a higher energy density by preparing a raw material mixture using starting raw materials including a nickel source, a cobalt source and a manganese source An active material can be produced.

In another preferred embodiment of the production method provided by the present invention, in the gelation step, the prepared raw material mixture is heated to a temperature of room temperature to 100 ° C.
By making the raw material mixture gel at the above temperature, a positive electrode active material composed of solid solution particles of LiMO ₂ and Li ₂ MnO ₃ having a higher energy density can be produced more efficiently.

Furthermore, in another preferable aspect, the lithium manganese oxide particles include (1) a step of preparing a raw material mixture by dissolving a starting material including a lithium source and a manganese source in an aqueous solvent, and (2) the above A step of heating the raw material mixture and pre-baking at 300 ° C. or higher; and (3) a step of heating and baking the pre-baked product to a temperature higher than the pre-baking temperature and not higher than 1000 ° C. Li ₂ MnO ₃ obtained by the production method is used.
The method for producing lithium manganese oxide particles, which are starting materials for solid solution particles, is not particularly limited, but Li ₂ MnO ₃ having a highly crystalline layered rock salt structure (monoclinic system) can be obtained by using the production method described above. It can be manufactured efficiently.

Moreover, this invention provides a lithium secondary battery as another aspect. That is, a lithium secondary battery provided with a positive electrode active material (including a positive electrode active material manufactured by any manufacturing method) disclosed herein is provided. A lithium secondary battery including such a positive electrode can be a battery in which deterioration of battery characteristics (load characteristics or cycle characteristics) is suppressed even when it is used in a mode of being repeated under high-rate output.
Furthermore, according to this invention, the vehicle provided with the lithium secondary battery disclosed here is provided. The lithium secondary battery provided by the present invention may exhibit battery characteristics particularly suitable as a power source for a battery mounted on a vehicle. Therefore, the lithium secondary battery disclosed herein can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle or an electric vehicle.

The concentration gradient of the constituents in solid solution particles of LiMO ₂ and Li ₂ MnO ₃ according to one embodiment is a particle cross-sectional view schematically showing. It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is the III-III sectional view taken on the line in FIG. It is a perspective view which shows typically the state which winds and produces an electrode body. It is a side view showing typically a vehicle (automobile) provided with a lithium secondary battery concerning one embodiment.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The positive electrode active material for a lithium secondary battery provided by the present invention has a general formula: LiMO ₂ (wherein M includes at least one transition metal element selected from the group consisting of Co, Ni, and Mn). It is constituted by solid solution particles of a lithium transition metal composite oxide represented by a seed or two or more metal elements) and a lithium manganese oxide represented by Li ₂ MnO ₃ . Hereinafter, although the said positive electrode active material and the manufacturing method of this active material are demonstrated in detail, it is not intending limiting this invention to this embodiment.

First, the positive electrode active material for a lithium secondary battery according to this embodiment will be described. The positive electrode active material disclosed here is composed of solid solution particles of LiMO ₂ and Li ₂ MnO ₃ as described above. LiMO ₂ and Li ₂ MnO ₃ both have a layered rock-salt crystal structure, and the solid solution particles of LiMO ₂ and Li ₂ MnO ₃ have a large amount of lithium ions that can be occluded or released, thereby increasing the capacity. Alternatively, it is expected as a positive electrode active material for lithium secondary batteries that can realize high energy density.

Among the compounds constituting the solid solution particles, the lithium transition metal composite oxide has a general formula: LiMO ₂ (wherein M includes at least one transition metal element selected from the group consisting of Co, Ni, and Mn). 1 or 2 or more metal elements). For example, lithium nickelate (LiNiO ₂ ), lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), nickel / manganese-based LiNi _x Mn _1-x O ₂ (0 <x <1), Nickel-cobalt-based LiNi _x Co _1-x O ₂ (0 <x <1), cobalt-manganese-based LiCo _x Mn _1-x O ₂ (0 <x <1) A binary lithium transition metal composite oxide containing two kinds of transition metal elements may be used. Alternatively, a ternary lithium transition metal composite oxide LiNi _1-xy Co _x Mn _y O ₂ (0 <x <1, 0 <y) such as nickel / cobalt / manganese containing two or more transition metal elements. <1, 0 <x + y <1). For example, the lithium transition metal composite oxide constituting the solid solution particles is preferably an oxide containing all of Ni, Co, and Mn. Ternary lithium transition metal composite oxides are suitable for high-power applications (for example, in-vehicle use) because of their stable crystal structure, excellent heat resistance, and large theoretical lithium ion storage / release capacity. ing. A suitable example of the ternary lithium transition metal composite oxide is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

  Here, the lithium transition metal composite oxide represented by the formula (1) is at least one transition metal selected from the group consisting of cobalt (Co), nickel (Ni), and manganese (Mn) as the M element. In addition to the elements, a metal element as exemplified below (that is, a transition metal element other than the main constituent metal element and / or a typical metal element) may be contained in a proportion smaller than the molar ratio of each main constituent metal element. Examples of such metal elements include aluminum (Al), iron (Fe) chromium (Cr), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo ), Tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and cerium (Ce).

Moreover, among the compounds constituting the solid solution particles, the other is a lithium manganese oxide represented by Li ₂ MnO ₃ . Lithium manganese oxide has a large lithium storage capacity and a large theoretical capacity (approximately 350 mAh / g). However, in a lithium secondary battery using such an oxide, manganese is eluted during repeated charging and discharging, and battery characteristics (for example, cycle characteristics and load characteristics) may be deteriorated.
However, the positive electrode active material composed of solid solution particles of LiMO ₂ and Li ₂ MnO ₃ disclosed herein has a lithium manganese oxide (Li ₂ MnO ₃ ) 310 closer to the center of the particle as shown in FIG. The concentration of LiMO ₂ (320) is set to be higher than the concentration of lithium transition metal complex oxide (LiMO ₂ ) 320 and closer to the outer surface of the solid solution particles, the concentration of LiMO ₂ (320) is Li ₂ MnO ₃ (310). It has a concentration gradient that is higher than the concentration of. Therefore, even if the lithium secondary battery constructed using such a positive electrode active material is used in a mode in which charging and discharging at high rates are repeated, Li ₂ MnO ₃ (310) present at a high concentration in the center of the solid solution particles. Manganese is difficult to elute. As a result, since an increase in resistance due to the collapse of the crystal structure is suppressed, it can be a positive electrode active material for a lithium secondary battery that can realize excellent battery characteristics (for example, cycle characteristics and load characteristics) even under high-rate charge / discharge. .

Next, a method for producing a positive electrode active material for a lithium secondary battery including solid solution particles of LiMO ₂ and Li ₂ MnO _{3 according} to the present embodiment will be described.
The production method disclosed herein has a general formula: LiMO ₂ (wherein M is one or more metals including at least one transition metal element selected from the group consisting of Co, Ni and Mn) Element of the lithium transition metal complex oxide represented by Li ₂ MnO ₃ and a lithium active metal positive electrode active material for a lithium secondary battery. In general, the production method includes (1) a step of preparing lithium manganese oxide particles represented by Li ₂ MnO ₃ , (2) the prepared Li ₂ MnO _3, and the general formula: LiMO ₂ . A starting material for constituting the solid solution particles including a lithium source for constituting the represented lithium transition metal composite oxide and one or more kinds of transition metal M element sources is dissolved in an aqueous solvent. A step of preparing a raw material mixture (typically adding one or more gelling agents together), (3) a gelling step of gelling the prepared raw material mixture to obtain a gel-like composition And (4) a baking step of baking the gel-like composition obtained above. Details will be described below.

<Preparation of lithium manganese oxide particles>
First, lithium manganese oxide particles represented by Li ₂ MnO ₃ , which is a compound constituting solid solution particles, are prepared (including synthesis or purchase). The lithium manganese oxide particles prepared here may be manufactured by any manufacturing method. For example, lithium manganese oxide particles produced by the following production method can be suitably used.

First, a starting material including a lithium source for constituting lithium manganese oxide particles represented by Li ₂ MnO ₃ and a manganese source (typically together with a gelling agent) is dissolved in an aqueous solvent and the starting material Prepare the mixture. Then, the raw material mixture is heated (for example, room temperature to 100 ° C., preferably approximately 80 ° C.) to evaporate water. Thereafter, the (gel-like) raw material mixture is heated and calcined at 300 ° C. or higher (preferably 300 to 600 ° C., more preferably 450 to 550 ° C., for example, about 500 ° C.). The obtained calcined product is pulverized and further heated to a temperature higher than the calcining temperature and not higher than 1000 ° C. (preferably 700 to 900 ° C., for example, about 800 ° C.), and calcined, thereby Li ₂ MnO. ₃ is obtained. By this production method, lithium manganese oxide particles represented by Li ₂ MnO ₃ having a highly crystalline layered rock salt structure (monoclinic system) can be efficiently produced.

  The aqueous solvent in which the starting material is dissolved is typically water, but may be any water-based solvent as a whole, that is, water or a mixed solvent mainly composed of water can be preferably used. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use a solvent in which about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is a solvent consisting essentially of water.

<Starting material>
Next, a lithium source and one or more transition metal M element sources for constituting a lithium transition metal composite oxide (general formula: LiMO ₂ ) that forms solid solution particles with the lithium manganese oxide particles Starting materials are prepared.

The compound including a lithium source that is one of the above starting materials is not particularly limited as long as it can be dissolved in an aqueous solvent, and various lithium compounds can be used. For example, lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, lithium peroxide, lithium phosphate, lithium oxalate, lithium acetate, or lithium iodide may be used. Particularly preferred examples include hydrates such as lithium acetate dihydrate [Li (CH ₃ COO) · 2H ₂ O].

  Further, the transition metal M element source is not particularly limited, but as a preferable specific example, the lithium transition metal composite oxide may include nickel (Ni), cobalt (Co), and manganese (Mn). Starting materials including a nickel source, a cobalt source and a manganese source are preferred in order to constitute an oxide containing any of them. Examples of the compound containing the transition metal M element include compounds such as hydroxides, oxides, various salts (for example, carbonates), halides (for example, fluorides) of various transition metal elements that can be dissolved in an aqueous solvent. Can be selected.

For example, as the compound including the nickel source, for example, compounds such as nickel acetate, nickel oxalate, nickel carbonate, nickel oxide, nickel sulfate, nickel nitrate, nickel hydroxide, and nickel oxyhydroxide can be used. A particularly preferable example is nickel acetate (II) tetrahydrate [Ni (CH ₃ COO) ₂ .4H ₂ O].

Examples of the compound containing the cobalt source include compounds such as cobalt acetate, cobalt oxalate, cobalt carbonate, cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt hydroxide, and cobalt oxyhydroxide. A particularly preferred example is cobalt (II) acetate tetrahydrate [Co (CH ₃ COO) ₂ .4H ₂ O].

Furthermore, as a compound containing the said manganese source, compounds, such as manganese acetate, manganese oxalate, manganese carbonate, manganese oxide, manganese sulfate, manganese nitrate, manganese hydroxide, manganese oxyhydroxide, can be used, for example. Particularly preferable examples include manganese acetate (II) tetrahydrate [Mn (CH ₃ COO) ₂ .4H ₂ O] or manganese sulfate.

  Here, as the transition metal M, in addition to at least one transition metal element selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn), one or more metals An elemental metal element (that is, a transition metal element other than the main constituent metal element and / or a typical metal element) may be contained in a proportion smaller than the molar ratio of the constituent metal elements. Examples of such metal elements include aluminum (Al), iron (Fe) chromium (Cr), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo ), Tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), cerium (Ce), and the like.

<Preparation of raw material mixture>
Subsequently, each starting material including the prepared lithium manganese oxide particles, the lithium source for constituting the lithium transition metal composite oxide, and the transition metal M element source is weighed. The mixing ratio of each starting material can be appropriately adjusted according to the composition ratio of the M element of the lithium transition metal composite oxide (LiMO ₂ ) constituting the solid solution particles. Then, each starting material is mixed with an aqueous solvent and sufficiently diffused or permeated to prepare a material mixture. As a result, a state in which the surface of the lithium manganese oxide particles is coated with a precursor of a lithium transition metal composite oxide (lithium source, transition metal M element source, etc.) is formed.

Here, in order to promote the gelation described later, a gelling agent may be added here together with the above starting materials. As a gelling agent, glycolic acid (C ₂ H ₄ O ₃ ), malic acid (C ₄ H ₆ O ₅ ), citric acid (C ₆ H ₈ O ₇ ), hydroxycarboxylic acid or a derivative thereof is preferably used. Can do. The addition amount of a gelling agent is not specifically limited, It is good to adjust suitably so that a desired gel form may be exhibited.
In the mixing, stirring (including kneading and pulverization) may be performed as necessary. The apparatus used for mixing is not particularly limited. For example, by using a planetary mixer, a planetary stirrer, a desper, a ball mill, a kneader, a mixer, etc., the above raw material mixture can be uniformly diffused or permeated and stabilized. A mixed state can be formed.

<Gelification>
Next, the raw material mixture is gelled to prepare a gel composition. By heating (drying) the raw material mixture at a temperature at which the aqueous solvent evaporates, gelation can be promoted. The heating temperature is not particularly limited, but it is preferably an aqueous solvent by heating in a temperature range from room temperature to 100 ° C. (typically 20 to 90 ° C., preferably 50 to 90 ° C., about 80 ° C.). A part (or all) of the solvent volatilizes and can be changed from a sol state in which particles are dispersed to a gel state having no fluidity.
Moreover, what is necessary is just to adjust heating time suitably, confirming the dry state of a raw material mixture. In addition, as a heating method, any heating (drying) means such as hot air, vacuum, infrared rays, far-infrared rays and the like can be suitably used. Furthermore, the atmosphere at the time of heating may be put in an atmosphere of an inert gas such as nitrogen gas, or in a sealed container as needed depending on the type of solvent and starting material used.

<Baking>
Next, firing will be described. After the aqueous solvent of the raw material mixture is evaporated and gelled, the obtained gel composition is fired. The firing is desirably performed in an oxidizing atmosphere, for example, the air or an atmosphere richer in oxygen than the air. The firing temperature is a temperature of 1000 ° C. or less, and it is typically preferable to heat the material to 700 to 900 ° C., for example, about 800 ° C. for firing. Further, the firing time is not particularly limited, but after the temperature has been raised to the set temperature, firing can be performed in the temperature range for about 5 to 24 hours.

By performing such heat treatment, lithium manganese oxide particles (Li ₂ MnO ₃ ) diffuse outward and the precursor of the lithium transition metal composite oxide covering the surface of Li ₂ MnO ₃ faces inward. Spread. As a result, as shown in FIG. 1, the concentration of lithium manganese oxide (Li ₂ MnO ₃ ) 310 is higher than the concentration of lithium transition metal composite oxide (LiMO ₂ ) 320 as it is closer to the center of the particle. cage, and, the closer to the outer surface of the solid solution _particles, LiMO ₂ (320) and _Li 2 MnO ₃ having a concentration gradient in which the concentration of LiMO 2 (320) is configured higher than the concentration of _Li 2 _MnO 3 (310) Solid solution particles with (310) can be produced. Thus, the solid solution particle which Li ₂ MnO ₃ (310) contains at a higher concentration as it is closer to the center has a structure in which manganese is less likely to be eluted from Li ₂ MnO ₃ . As a result, a lithium secondary battery constructed using such solid solution particles as a positive electrode active material suppresses an increase in resistance associated with elution of manganese even under high-rate charge / discharge. Characteristic, load characteristic).

In addition, after baking, it is preferable to grind | pulverize a baked material (solid solution particle) as needed. By pulverizing, granulating and classifying the fired product by an appropriate means, a powder of solid solution particles of granular LiMO ₂ and Li ₂ MnO ₃ having a desired average particle size and / or particle size distribution can be obtained. .

Hereinafter, solid solution particles of lithium transition metal composite oxide (LiMO ₂ ) and lithium manganese oxide particles (Li ₂ MnO ₃ ) obtained by the production method disclosed herein are used as electrode active materials for lithium secondary batteries. A positive electrode and an embodiment of a lithium secondary battery including the positive electrode will be described with respect to a rectangular lithium secondary battery including a wound electrode body. However, the present invention is intended to be limited to such an example. is not.
Further, matters other than the matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, the configuration and manufacturing method of an electrode body, a general configuration related to construction of a lithium secondary battery and other batteries) Technology, etc.) can be understood as a design matter of those skilled in the art based on the prior art in the field. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

2 is a perspective view schematically showing a rectangular lithium secondary battery according to an embodiment, and FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is a perspective view schematically showing a state in which the electrode body is wound and manufactured.
As shown in FIGS. 2 and 3, the lithium secondary battery 100 according to the present embodiment includes a rectangular parallelepiped battery case 10 and a lid 14 that closes the opening 12 of the case 10. A flat electrode body (wound electrode body 20) and an electrolyte can be accommodated in the battery case 10 through the opening 12. The lid 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection, and a part of the terminals 38 and 48 protrudes to the surface side of the lid 14. Also, some of the external terminals 38 and 48 are connected to the internal positive terminal 37 or the internal negative terminal 47, respectively, inside the case.

  Next, the wound electrode body 20 according to the present embodiment will be described with reference to FIGS. 3 and 4. As shown in FIG. 2, the wound electrode body 20 includes a sheet-like positive electrode sheet 30 having a positive electrode active material layer 34 on the surface of a long positive electrode current collector 32, a long sheet-like separator 50, a long A sheet-like negative electrode sheet 40 having a negative electrode active material layer 44 on the surface of a long negative electrode current collector 42 is formed. As shown in FIG. 3, in the cross-sectional view in the winding axis direction R, the positive electrode sheet 30 and the negative electrode sheet 40 are stacked via two separators 50. 50, the negative electrode sheet 40, and the separator 50 are laminated in this order. The laminate is wound around a shaft core (not shown) in a cylindrical shape, and is formed into a flat shape by squashing the obtained wound electrode body 20 from the side surface direction.

As shown in FIG. 4, the wound electrode body 20 according to the present embodiment has a positive electrode active material layer formed on the surface of the positive electrode current collector 32 at the center in the winding axis direction R. 34 and the negative electrode active material layer 44 formed on the surface of the negative electrode current collector 42 overlap each other to form a densely stacked portion. Further, in a cross-sectional view in the direction along the winding axis direction R, the exposed portion of the positive electrode current collector 32 (positive electrode active material layer) without forming the positive electrode active material layer 34 at one end in the direction R. The non-forming portion 36) is laminated in a state of protruding from the separator 50 and the negative electrode sheet 40 (or a dense laminated portion of the positive electrode active material layer 34 and the negative electrode active material layer 44). That is, a positive electrode current collector laminated portion 35 formed by laminating the positive electrode active material layer non-forming portion 36 in the positive electrode current collector 32 is formed at the end of the electrode body 20. Also, the other end of the electrode body 20 has the same configuration as that of the positive electrode sheet 30, and the negative electrode active material layer non-formation portion 46 in the negative electrode current collector 42 is laminated to form the negative electrode current collector lamination portion 45. ing.
Here, as the separator 50, a separator having a width larger than the width of the laminated portion of the positive electrode active material layer 34 and the negative electrode active material layer 44 and smaller than the width of the electrode body 20 is used, and the positive electrode current collector 32 and the negative electrode The current collectors 42 are disposed so as to be sandwiched between the stacked portions of the positive electrode active material layer 34 and the negative electrode active material layer 44 so as not to contact each other and cause an internal short circuit.

The positive electrode (typically, positive electrode sheet 30) of the lithium secondary battery according to the present embodiment has a configuration in which a positive electrode active material layer 34 containing a positive electrode active material is formed on a long positive electrode current collector 32. Prepare. As the positive electrode current collector 32, a conductive member made of a highly conductive metal is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector 32 may vary depending on the shape of the lithium secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. Further, as the positive electrode active material, solid solution particles of LiMO ₂ and Li ₂ MnO ₃ disclosed herein (including solid solution particles produced by the production method disclosed herein) are used.

  In addition to the above-described positive electrode active material, the positive electrode active material layer 34 may contain one or more kinds of conductive materials and binders that can be blended in a general lithium secondary battery as necessary. it can. As such a conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. In addition, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof. In addition, only 1 type may be used among these, or 2 or more types may be used together.

  Moreover, as the binder, the same binder as that used for the positive electrode of a general lithium secondary battery can be appropriately employed. For example, it is preferable to select a polymer that is soluble or dispersible in the solvent used. When an aqueous solvent is used, cellulose polymers such as carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC); polyvinyl alcohol (PVA); polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer Water-soluble or water-dispersible polymers such as fluorine resins such as (FEP); vinyl acetate copolymers; rubbers such as styrene butadiene rubber (SBR) and acrylic acid-modified SBR resins (SBR latex); be able to. When a non-aqueous solvent is used, a polymer such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC) can be preferably used. Such a binder may be used individually by 1 type, and may be used in combination of 2 or more type. In addition to the function as a binder, the polymer material exemplified above may be used for the purpose of exhibiting the function as a thickener or other additive of the above composition.

Next, a method for producing the positive electrode of the lithium secondary battery according to this embodiment will be described.
First, a positive electrode active material (solid solution particles of LiMO ₂ and Li ₂ MnO ₃ disclosed herein), a conductive material, a binder, and the like are mixed with an appropriate solvent (aqueous solvent or non-aqueous solvent) to obtain a paste. Alternatively, a slurry-like composition for forming a positive electrode active material layer (hereinafter referred to as “positive electrode active material layer forming paste”) is prepared. As for the blending ratio of each constituent material, for example, the ratio of the positive electrode active material in the positive electrode active material layer is preferably about 50% by mass or more (typically 50 to 95% by mass), and about 70 to 95% by mass. % (For example, 75 to 90% by mass) is more preferable. The proportion of the conductive material in the positive electrode active material layer can be, for example, about 2 to 25% by mass, and preferably about 2 to 20% by mass. Furthermore, in the composition using the binder, the proportion of the binder in the positive electrode active material layer can be, for example, about 1 to 10% by mass, and usually about 2 to 5% by mass. The paste prepared by mixing the constituent materials in this way is applied to the positive electrode current collector 32, and after the solvent is evaporated and dried, the paste is compressed (pressed). Thereby, the positive electrode of the lithium secondary battery in which the positive electrode active material layer is formed on the positive electrode current collector is obtained.

  As a solvent used for preparing the positive electrode active material layer forming paste, either an aqueous solvent or a non-aqueous solvent can be used. As described above, the aqueous solvent only needs to be water-based as a whole, that is, water or a mixed solvent mainly composed of water can be preferably used. As a preferable example of the non-aqueous solvent, N- Examples thereof include methyl-2-pyrrolidone (NMP), methyl ethyl ketone, toluene and the like.

  In addition, as a method of apply | coating the said paste to a positive electrode electrical power collector, the technique similar to a conventionally well-known method can be employ | adopted suitably. For example, the paste can be suitably applied to the positive electrode current collector by using an appropriate application device such as a slit coater, a die coater, a gravure coater, or a comma coater. Moreover, when drying a solvent, it can dry favorably by using natural drying, a hot air, low-humidity air, a vacuum, infrared rays, far-infrared rays, and an electron beam individually or in combination. Furthermore, as a compression method, a conventionally known compression method such as a roll press method or a flat plate press method can be employed. In adjusting the thickness, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to compress a plurality of times until a desired thickness is obtained.

  Next, the negative electrode of the lithium secondary battery according to this embodiment will be described. The negative electrode (typically, the negative electrode sheet 40) may have a configuration in which a negative electrode active material layer 44 is formed on a long negative electrode current collector 42 (for example, a copper foil). As the negative electrode current collector serving as the base material of the negative electrode, a conductive member made of a highly conductive metal is preferably used. For example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector may vary depending on the shape of the lithium secondary battery and the like, and is not particularly limited.

  The negative electrode active material layer formed on the surface of the negative electrode current collector contains a negative electrode active material capable of inserting and extracting lithium ions serving as charge carriers. As the negative electrode active material, one or more of materials conventionally used in lithium secondary batteries can be used without particular limitation. An example is carbon particles. A particulate carbon material (carbon particles) containing a graphite structure (layer structure) at least partially is preferably used. Any carbon material of a so-called graphitic material (graphite), a non-graphitizable carbonaceous material (hard carbon), a graphitizable carbonaceous material (soft carbon), or a combination of these materials is preferably used. obtain. Among these, graphite particles can be preferably used. Graphite particles (eg, graphite) are excellent in conductivity because they can suitably occlude lithium ions as charge carriers. Further, since the particle size is small and the surface area per unit volume is large, it can be a negative electrode active material more suitable for high-power charge / discharge.

  In addition to the negative electrode active material, the negative electrode active material layer may contain an optional component such as a binder as necessary. As such a binder, the same binder as that used for the negative electrode of a general lithium secondary battery can be adopted as appropriate, and functions as the binder listed in the components of the positive electrode described above. The various polymer materials obtained can be suitably used.

  Next, a method for producing a negative electrode for a lithium secondary battery according to this embodiment will be described. In order to form a negative electrode active material layer on the surface of the negative electrode current collector, first, the negative electrode active material is mixed with the appropriate solvent (aqueous solvent or non-aqueous solvent) together with a binder or the like to form a paste or slurry. The negative electrode active material layer forming composition (hereinafter referred to as “negative electrode active material layer forming paste”) is prepared. As for the blending ratio of each constituent material, for example, the ratio of the negative electrode active material in the negative electrode active material layer is preferably about 50% by mass or more, and is about 85 to 99% by mass (for example, 90 to 97% by mass). It is more preferable. Further, the ratio of the binder in the negative electrode active material layer can be, for example, about 1 to 15% by mass, and is usually preferably about 3 to 10% by mass. The paste thus prepared is applied to the negative electrode current collector, the solvent is volatilized and dried, and then compressed (pressed). Thereby, the negative electrode of the lithium secondary battery which has the negative electrode active material layer formed using this paste on a negative electrode collector is obtained. In addition, the application | coating, drying, and the compression method can use a conventionally well-known means similarly to the manufacturing method of the above-mentioned positive electrode.

  A rough procedure for constructing the lithium secondary battery 100 according to an embodiment will be described using the positive electrode sheet and the negative electrode sheet thus manufactured. The prepared positive electrode sheet 30 and negative electrode sheet 40 are stacked and wound together with two separators 50, and are crushed and crushed from the stacking direction to form the electrode body 20 into a flat shape and accommodate it in the battery case 10. After injecting the electrolyte, the lid 14 is attached to the case opening 12 and sealed, whereby the lithium secondary battery 100 of this embodiment can be constructed. There is no particular limitation on the structure, size, material (for example, metal or laminate film) of the battery case 10 and the like.

  Moreover, as a suitable separator sheet 50 used between the positive / negative electrode sheets 30 and 40, what was comprised with porous polyolefin resin is mentioned. For example, a porous separator sheet made of synthetic resin (for example, made of polyolefin such as polyethylene) can be suitably used. When a solid electrolyte or a gel electrolyte is used as the electrolyte, there may be a case where a separator is unnecessary (that is, in this case, the electrolyte itself can function as a separator).

Moreover, the electrolyte can use the thing similar to the nonaqueous electrolyte conventionally used for a lithium secondary battery without limitation. Such an electrolyte typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. The non-aqueous solvent is selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), N, N-dimethylformamide (DMF), ethyl methyl carbonate (EMC), and the like. 1 type or 2 types or more can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). _3. Lithium compounds (lithium salts) such as LiI can be used. In addition, the density | concentration of support salt may be the same as that of the nonaqueous electrolyte solution used with the conventional lithium secondary battery, and there is no restriction | limiting in particular. An electrolyte containing an appropriate lithium compound (supporting salt) at a concentration of about 0.1 to 5 mol / L can be used.

  As described above, the lithium secondary battery 100 constructed in this way has a high battery capacity or a high energy density. Therefore, the lithium secondary battery 100 is particularly preferably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. obtain. Therefore, as schematically shown in FIG. 5, the present invention provides a vehicle 1 (typically an automobile, particularly a hybrid) provided with such a lithium secondary battery (typically a battery pack formed by connecting a plurality of series batteries) 100 as a power source. Automobiles, electric vehicles, automobiles equipped with electric motors such as fuel cell vehicles).

In the following test examples, a positive electrode active material for a lithium secondary battery comprising solid solution particles of LiMO ₂ and Li ₂ MnO ₃ disclosed herein (including solid solution particles produced by the production method disclosed herein) The lithium secondary battery (sample battery) was constructed using it, and its performance was evaluated.

<Example>
Implementation of solid solution particles (concentration gradient) of lithium transition metal composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese oxide (Li ₂ MnO ₃ ) by the following procedure A positive electrode active material for a lithium secondary battery according to an example was synthesized.

[Production of positive electrode active material (synthesis)]
First, lithium manganese oxide (Li ₂ MnO ₃ ) particles were synthesized. That is, lithium acetate dihydrate [Li (CH ₃ COO) 2H ₂ O] as a lithium source and manganese acetate (II) tetrahydrate [Mn (CH ₃ COO) _2. 4H ₂ O], and a starting material for constituting lithium manganese oxide was prepared. The starting material and glycolic acid (C ₂ H ₄ O ₃ ) were added and dissolved in pure water, and the raw material mixture was prepared by sufficiently stirring. Next, the raw material mixture was heated (dried) to 80 ° C. to evaporate the water and gelled. And it heated at 500 degreeC, calcinated for 5 hours, and pulverized (stirred) with the ball mill. Further, the pulverized product was heated to 800 ° C. and baked for 5 hours to synthesize lithium manganese oxide (Li ₂ MnO ₃ ). The obtained fired product was pulverized to obtain lithium manganese oxide (Li ₂ MnO ₃ ) particles.

As a lithium source for constituting the lithium manganese oxide (Li ₂ MnO ₃ ) particles prepared above and a lithium transition metal composite oxide represented by the general formula: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ Lithium acetate dihydrate [Li (CH ₃ COO) 2H ₂ O] and nickel acetate (II) tetrahydrate as a nickel source [Ni (CH ₃ COO) ₂ 4H ₂ O] Cobalt acetate (II) tetrahydrate [Co (CH ₃ COO) ₂ .4H ₂ O] as a cobalt source and manganese acetate (II) tetrahydrate [Mn (CH ₃ COO as a manganese source) ) ₂ · 4H ₂ O] and is, 1: 1: 0.33: 0.33: so that the molar ratio of 0.33 were weighed, to prepare a starting material. A starting material mixture was prepared by dissolving the starting material for constituting the solid solution particles in pure water together with glycolic acid (corresponding to 0.2 mol of the above molar ratio) as a gelling agent and sufficiently stirring.
Next, the raw material mixture was heated (dried) to 80 ° C. to evaporate the water and gelled. And by heating to 800 ° C. and firing for 5 hours, the concentration of Li ₂ MnO ₃ is higher than the concentration of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the particle is closer to the center of the particle. And the closer to the outer surface of the solid solution particle, the lithium transition metal composite oxidation having a concentration gradient in which the concentration of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is higher than the concentration of Li ₂ MnO ₃ Solid solution particles of the product (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese oxide (Li ₂ MnO ₃ ) were synthesized. The obtained solid solution particles were pulverized to an appropriate particle size.

[Production of positive electrode]
Next, the positive electrode of the lithium secondary battery for a test was produced.
First, in forming the positive electrode active material layer in the positive electrode, a positive electrode active material layer forming paste was prepared. The synthesized solid solution particles as the positive electrode active material, acetylene black as the conductive material, and polyvinylidene fluoride (PVDF) as the binder are such that the mass% ratio of these materials is 85: 10: 5. The positive electrode active material layer forming paste was prepared by weighing and mixing with N-methylpyrrolidone (NMP).
And the said paste was apply | coated to the aluminum foil as a positive electrode electrical power collector, and the water | moisture content in this paste was dried (evaporated). Furthermore, it was stretched into a sheet shape with a roller press, and an active material layer was formed on the surface of the positive electrode current collector. And it punched circularly with the punch of diameter 15mm, and prepared the positive electrode.

[Production of negative electrode]
Next, a negative electrode for a lithium secondary battery for testing was prepared. A lithium metal foil was prepared and punched out with a punch having a diameter of 15 mm to prepare a negative electrode.

[Construction of lithium secondary battery]
A 2032 type (diameter 20 mm, thickness 3.2 mm) coin-type test lithium secondary battery was constructed using the positive electrode and negative electrode prepared above. That is, a circular positive electrode and a separator impregnated with an electrolyte are laminated and arranged inside an outer can that forms a positive electrode-side outer sheath, and after pressing the periphery of the separator with a gasket, a circular negative electrode, A spacer for adjusting the thickness and a leaf spring were sequentially arranged on the separator. Then, the inside of the accommodated outer can was closed with an outer lid, and the outer can and the peripheral edge of the outer lid were sealed to construct a lithium secondary battery for testing.
As the electrolyte, a composition in which 1 mol / L LiPF6 was dissolved in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was used. As the separator, a porous sheet made of polypropylene was used.

<Comparative Example 1>
In Comparative Example 1, a positive electrode was produced in the same procedure as in the Example, except that the lithium manganese oxide (Li ₂ MnO ₃ ) synthesized in the above example was used as the positive electrode active material. Moreover, the lithium secondary battery for a test was constructed | assembled in the same procedure using the battery constituent material same as an Example.

<Comparative Example 2>
[Production of positive electrode active material (synthesis)]
In Comparative Example 2, a solid solution in which lithium transition metal composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese oxide (Li ₂ MnO ₃ ) were uniformly dissolved by the following procedure. A positive electrode active material for lithium secondary battery composed of particles (no concentration gradient) was synthesized.
First, lithium acetate dihydrate as a lithium source [Li (1) so that LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and Li ₂ MnO ₃ constituting the solid solution particles are 1: 1. CH ₃ COO) · 2H ₂ O], nickel acetate (II) tetrahydrate as a nickel source [Ni (CH ₃ COO) ₂ · 4H ₂ O], and cobalt acetate (II) · as a cobalt source Weighing tetrahydrate [Co (CH ₃ COO) ₂ .4H ₂ O] and manganese acetate (II) tetrahydrate [Mn (CH ₃ COO) ₂ .4H ₂ O] as a manganese source. The starting material was prepared. A starting material mixture for preparing the solid solution particles was dissolved in pure water together with glycolic acid as a gelling agent and sufficiently stirred to prepare a starting material mixture.
Next, the raw material mixture was heated (dried) to 80 ° C. to evaporate the water and gelled. And it heated at 500 degreeC and pre-baked for 5 hours, and it grind | pulverized (stirred) using the ball mill. Further, the pulverized product is heated to 800 ° C. and fired for 5 hours, whereby lithium transition metal composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese oxide (Li ₂ MnO _3). ) And solid solution particles that were uniformly melted. The obtained solid solution particles were pulverized to an appropriate particle size.

Using the synthesized lithium transition metal composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese oxide (Li ₂ MnO ₃ ) solid solution particles (no concentration gradient) as the positive electrode active material A positive electrode was produced in the same procedure as in Example except that it was used. Moreover, the lithium secondary battery for a test which concerns on the comparative example 2 was constructed | assembled in the same procedure using the battery constituent material same as an Example.

[Load characteristics]
Each of the test lithium secondary batteries according to Examples and Comparative Examples 1 and 2 constructed as described above is subjected to an appropriate conditioning treatment, and then loaded characteristics (characteristics for maintaining high capacity even during large current discharge) ) The test was conducted. The load characteristics of each battery were measured by performing the following operations and determining the discharge capacity at each operation.

  Under a temperature condition of 25 ° C., a constant current charge was performed up to 4.3 V at 1/3 C, and then a constant current discharge was performed up to 2.5 V at 1 C. Subsequently, after performing constant current charge to 4.3V at 1 / 3C, operation which performed constant current discharge to 2.5V at 20C was performed. And the ratio of the discharge capacity when discharging at 20 C to the discharge capacity when discharging at 1 C was calculated as load characteristics. The results are shown in Table 1.

As shown in Table 1, the lithium secondary battery using the lithium manganese oxide (Li ₂ MnO ₃ ) according to the comparative example had the lowest load characteristics. Moreover, even if it is a solid solution particle of lithium transition metal complex oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese oxide (Li ₂ MnO ₃ ), the solid solution particle having a concentration gradient Than the lithium secondary battery according to Comparative Example 2 in which the solid solution particles having a concentration gradient and uniformly mixed are used as the positive electrode active material. It was confirmed that the load characteristics were further excellent.

[Cycle characteristics]
Next, a cycle characteristic test of the test lithium secondary batteries according to the above-constructed Examples and Comparative Examples 1 and 2 was performed. Specifically, each battery was installed in a constant temperature bath at 60 ° C., and after performing a constant current charge to 4.8 V at 1/3 C, an operation of performing a constant current discharge at 1/3 C to 2.5 V was performed.
Under the measurement environment as it is, after performing constant current charging to 4.3 V at 1 C, constant current discharging was performed at 1 C to 2.5 V. This cycle was repeated 50 times. The ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle was calculated as the capacity retention rate. The results are shown in Table 2.

As shown in Table 2, the lithium secondary battery using the lithium manganese oxide (Li ₂ MnO ₃ ) according to the comparative example had the lowest capacity retention rate after cycling. Moreover, even if it is a solid solution particle of lithium transition metal complex oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese oxide (Li ₂ MnO ₃ ), the solid solution particle having a concentration gradient The capacity of the lithium secondary battery according to the example according to the present invention is significantly higher than that of the lithium secondary battery according to the comparative example 2 using the solid solution particles that are uniformly melted without a concentration gradient, It was confirmed that the cycle characteristics were more excellent.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here. For example, the battery of the various content from which an electrode body structural material and electrolyte differ may be sufficient. Further, the size and other configurations of the battery can be appropriately changed depending on the application (typically for in-vehicle use).

For lithium secondary batteries comprising solid solution particles of lithium transition metal composite oxide (LiMO ₂ ) and lithium manganese oxide (Li ₂ MnO ₃ ) (including solid solution particles produced by the production method disclosed herein) Since the lithium secondary battery constructed using the positive electrode active material is excellent in battery characteristics as described above, it can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 5, the present invention provides a vehicle 1 (typically an automobile, particularly a hybrid) provided with such a lithium secondary battery (typically a battery pack formed by connecting a plurality of series batteries) 100 as a power source. Automobiles, electric vehicles, automobiles equipped with electric motors such as fuel cell vehicles).

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Battery case 12 Opening part 14 Cover body 20 Winding electrode body 30 Positive electrode sheet 32 Positive electrode collector 34 Positive electrode active material layer 35 Positive electrode collector lamination | stacking part 36 Positive electrode active material layer non-formation part 37 Positive electrode current collection terminal 38 External positive electrode current collector terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 45 Negative electrode current collector laminated portion 46 Negative electrode active material layer non-formation portion 47 Negative electrode current collector terminal 48 External negative electrode current collector terminal 50 Separator 100 Lithium secondary Battery 310 Lithium manganese oxide (Li ₂ MnO ₃ )
320 Lithium transition metal composite oxide (LiMO ₂ )
R Winding axis direction

Claims (10)

Lithium represented by the general formula: LiMO ₂ (wherein M is one or more metal elements including at least one transition metal element selected from the group consisting of Co, Ni and Mn) A positive electrode active material for a lithium secondary battery comprising solid solution particles of a transition metal composite oxide and lithium manganese oxide represented by Li ₂ MnO ₃ ,
The closer to the center portion of the solid solution particles, the _Li 2 has a concentration of MnO ₃ is configured higher than the concentration of the LiMO _2, and, the closer to the outer surface of the solid solution particles, the concentration of the LiMO ₂ is the A positive electrode active material for a lithium secondary battery, characterized by having a concentration gradient configured to be higher than the concentration of Li ₂ MnO ₃ .   2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium transition metal composite oxide constituting the solid solution particles is an oxide containing all of Ni, Co, and Mn. The positive electrode active for a lithium secondary battery according to claim 2, wherein the lithium transition metal composite oxide constituting the solid solution particle is an oxide represented by LiNi _1/3 Co _1/3 Mn _1/3 O _2. material. Lithium represented by the general formula: LiMO ₂ (wherein M is one or more metal elements including at least one transition metal element selected from the group consisting of Co, Ni and Mn) A method for producing a positive electrode active material for a lithium secondary battery comprising solid solution particles of a transition metal composite oxide and lithium manganese oxide represented by Li ₂ MnO ₃ , comprising the following steps:
Preparing lithium manganese oxide particles represented by Li ₂ MnO ₃ ;
Includes the prepared lithium manganese oxide particles, a lithium source for constituting the lithium transition metal composite oxide represented by the general formula: LiMO ₂ , and one or more transition metal M element sources A step of preparing a raw material mixture by dissolving a starting raw material for constituting the solid solution particles in an aqueous solvent;
A gelation step of gelling the prepared raw material mixture to obtain a gel-like composition; and
A firing step of firing the obtained gel-like composition;
Manufacturing method.   The lithium transition metal composite oxide forms an oxide containing all of Ni, Co, and Mn, so that a raw material mixture is prepared using starting materials including a nickel source, a cobalt source, and a manganese source. 4. The production method according to 4. The lithium transition metal composite _oxide to prepare a raw material mixture so as to form an oxide represented by _{LiNi 1/3 Co 1/3 Mn 1/3 O 2} , The method according to claim 5.   The manufacturing method according to any one of claims 4 to 6, wherein in the gelation step, the prepared raw material mixture is heated to a temperature of room temperature to 100 ° C. The lithium manganese oxide particles are prepared by dissolving a starting material including a lithium source and a manganese source in an aqueous solvent to prepare a raw material mixture;
Heating the raw material mixture and pre-baking at 300 ° C. or higher; and heating the pre-baked product to a temperature higher than the pre-baking temperature and not higher than 1000 ° C .;
Is _Li 2 MnO ₃ obtained by the production method comprising use the method according to any one of claims 4-7.   A lithium secondary comprising a positive electrode using the positive electrode active material according to any one of claims 1 to 3 or the positive electrode active material obtained by the production method according to any one of claims 4 to 8 as the positive electrode active material. battery. A vehicle comprising the lithium secondary battery according to claim 9.

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