JP6498407B2 - Oxide composite and non-aqueous lithium ion secondary battery - Google Patents

Description

  The present invention relates to an oxide composite useful as a positive electrode active material of a non-aqueous lithium ion secondary battery, and a non-aqueous lithium ion secondary battery using the oxide composite as an active material.

A non-aqueous secondary battery including a composite oxide containing lithium atoms is characterized by light weight, high energy, and long life. For example, it is portable for notebook computers, mobile phones, digital cameras, video cameras, etc. Widely used as a power source for electronic devices. In addition, with the shift to a low environmental impact society, hybrid electric vehicles ("HEV") and plug-in HEVs (Plug-in Hybrid Electric Vehicles, "PHEV"), as well as residential power storage systems It is also attracting attention in the field of power storage.
When a non-aqueous lithium ion secondary battery is installed in a vehicle or residential power storage system such as an automobile, its constituent materials include chemical and electrochemical stability and strength from the viewpoint of cycle performance and long-term reliability. Therefore, a material excellent in corrosion resistance is required. Furthermore, non-aqueous secondary batteries are required to have high electric capacity and high output performance as necessary physical properties.
By the way, as a positive electrode material of a nonaqueous lithium ion secondary battery, rock salt layer type positive electrode materials such as LiCoO ₂ and LiNiO ₂ ; spinel type positive electrode materials such as LiMn ₂ O ₄ ; olivine type positive electrode materials such as LiFePO ₄ are known. It has been.

In addition to being relatively expensive, the layered compound LiCoO ₂ that is a typical positive electrode material has a limitation in the amount of Li extraction because the layered structure collapses when Li is extracted 50% or more during charge and discharge. There is also a problem in terms of capacity. In addition, the theoretical capacity of the olivine-type positive electrode material such as LiFePO ₄ is about 170 mAh / g, whereas a positive electrode material of about 150 mAh / g has already been utilized, and there is almost no room for further capacity improvement. Absent.
In order to increase the electric capacity of the non-aqueous lithium ion secondary battery, Li ₂ M′O ₃ (M ′, which is electrochemically inert but has a high theoretical capacity of about 460 mAh / g, has a Li-rich structure. By using a Li-excess solid solution in which a component having an average oxidation number of tetravalent metal ion) and an electrochemically active LiMO ₂ (M represents a metal ion having an average oxidation number of trivalent) component are combined. There is a disclosure about a technique for obtaining a high electric capacity.

For example, in Patent Document 1, xLiMO ₂ (1-x) Li ₂ M′O ₃ (x is in the range of 0 <x <1; M is one or more trivalent average oxidation numbers including Ni. M ′ is one or more tetravalent metal ions having an average oxidation number including at least Mn.), And a layered compound having a composition composed of LiMO ₂ and Li ₂ M′O ₃ is disclosed. ing.
In Patent Document 2, xLiMO ₂ (1-x) Li ₂ M′O ₃ (x is in the range of 0 <x <1; M represents an ion with an average oxidation number of 3 containing at least Mn; M 'Represents an ion having an average oxidation number of 4 valences), and a layered compound having a composition comprising LiMO ₂ and Li ₂ M′O ₃ is disclosed.
Patent Document 3 discloses a technique of combining F, Cl, and I with Ni, Co, and Mn as essential components.
According to the above Patent Documents 1 to 3, it is explained that high electric capacity can be obtained by each of the above technologies.

Further, in Patent Documents 4 to 6, xLiMO ₂ (1-x) Li ₂ M′O ₃ (M is an ion having an average oxidation number of 3; M ′ is an ion having an average oxidation number of 4). X has a structure represented by 0 <x <1, and Li _{1 + a} Ni _α Mn _β Co _γ O ₂ (a, α, β, and γ are 0.05 <a <0. 25, 0.1 <α <0.4, 0.4 <β <0.65, 0.05 <γ <0.3), and the composition ratio is Li _1.2. It is disclosed that particularly high electric capacity can be obtained when Ni _0.175 Co _0.10 Mn _0.525 O ₂ .

However, the above Li-excess solid solution has a problem that it is difficult to flow a large current at the time of discharge (poor discharge rate characteristics) because the conductivity of the Li ₂ M′O ₃ component is low. In order to solve this problem, attempts have been made to improve rate characteristics by increasing the conductivity of the surface of the Li-excess solid solution. For example, Patent Document 7 discloses a technique for coating an indium compound,
Non-Patent Document 1 reports a technique for coating conductive carbon. Patent Document 8 exemplifies a technique in which an active material having an Li-excess structure is coated with bismuth oxide or the like, and shows a tendency that rate characteristics are improved by this technique.
Furthermore, Patent Document 9 proposes a technique of combining an active material and a specific oxygen storage compound for the purpose of improving battery characteristics. This technique is intended to suppress the generation of oxygen at a high temperature of a thermally unstable Li—Ni composite oxide used as a main component of the positive electrode active material. Although this technique has achieved stabilization of the positive electrode material at a high temperature, it has been shown that the internal resistance of the positive electrode is increased by containing the oxygen storage compound, and the discharge rate is deteriorated.

US Pat. No. 6,667,082 US Pat. No. 6,680,143 US Pat. No. 7,135,252 Special table 2011-519126 gazette Special table 2012-504316 gazette Special table 2012-505520 gazette JP 2013-201119 A Special table 2013-503449 gazette JP 2006-114256 A

Jun Liu et al., Electrochemistry Communications, Vol. 12, 750-753 (2010)

As described above, various attempts have been made to improve the rate characteristics of the positive electrode active material having a Li-excess structure, but none of the effects are sufficient. Therefore, a positive electrode active material having a high electric capacity and excellent discharge rate characteristics is still awaited.
Under such circumstances, the problem to be solved by the present invention is to provide an oxide composite that provides a non-aqueous lithium ion secondary battery in which high discharge capacity and high discharge rate characteristics are compatible, and the oxide composite as an active material. It is providing the non-aqueous lithium ion secondary battery used as.

The present inventor has conducted intensive research and experiments to solve the above problems. As a result, by using a positive electrode active material having a Li-excess structure in combination with a specific other metal oxide, a non-aqueous lithium ion secondary battery having both high discharge capacity and high discharge rate characteristics is obtained. It has been found that the present invention has been achieved.
That is, the present invention is as follows.

[1] The following composition formula (1):
Li ₂ Mn _1-x M ′ _x O _3-α (1)
{In the formula, M ′ is one or more metal elements other than Mn and Li, and satisfies the relationship of 0 ≦ x <1 and 0 ≦ α <1. } Li-containing composite oxide (A) having a layered crystal structure in which Li represented by
An oxide composite comprising at least one metal oxide (B) selected from the group consisting of yttrium, zirconium, and lanthanoid,
The oxide composite, wherein the metal oxide (B) is dispersed in the oxide composite.
[2] The oxide composite according to [1], which is produced by a coprecipitation method, a spray drying method, or a gelation combustion method.

[3] When the Mn line analysis was performed on the lithium-containing composite oxide (A) using an energy dispersive X-ray detector, the following formula: Element dispersion width (%) = (maximum intensity−minimum intensity) / average intensity × 100
The oxide composite according to [1] or [2], wherein the element dispersion width defined by the above is 50% or less.
[4] The content rate of the said metal oxide (B) is 0.5-5.0 mass% with respect to the whole oxide complex, [1]-[3] Any one statement Oxide complex.
[5] The metal oxide (B) according to any one of [1] to [4], wherein the metal oxide (B) is an oxide of a metal including at least one selected from the group consisting of yttrium, zirconium, and cerium. Oxide composite.

[6] The oxide composite according to [5], wherein the metal oxide (B) is an oxide of a metal containing cerium.
[7] The lithium-containing composite oxide (A)
A layered crystal structure represented by the composition formula (1);
The following composition formula (2):
Li _{1 + k} Mn _2-y Me ′ _y O _4-γ (2)
{In the formula, Me ′ is one or more metal elements other than Mn and Li, and satisfies the relationship of 0 ≦ k <1, 0 ≦ y ≦ 0.5, and 0 ≦ γ <1. } And the following composition formula (3):
LiMeO ₂ (3)
{Wherein Me is one or more metal elements other than Li. } It has a crystal structure in which one or more types of crystal structures selected from a layered crystal structure in which Li represented in a layer is arranged in a layer form are described in any one of [1] to [6] Oxide complex.

[8] A positive electrode active material comprising the oxide composite according to any one of [1] to [7].
[9] A non-aqueous lithium ion secondary battery comprising the positive electrode active material according to [8].

  The oxide composite according to the present invention is an oxide composite in which a lithium-containing composite oxide having a Li-excess structure and a specific metal oxide are combined, and when this is used as a positive electrode active material, a high discharge capacity is obtained. And a high discharge rate characteristic can be obtained.

It is sectional drawing which shows roughly an example of the non-aqueous secondary battery in this embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention. In addition, the range described using "-" in this specification includes the numerical value described before and behind that.

The oxide composite in the present embodiment has the following composition formula (1):
Li ₂ Mn _1-x M ′ _x O _3-α (1)
{In the formula, M ′ is one or more metal elements other than Mn and Li, and satisfies the relationship of 0 ≦ x <1 and 0 ≦ α <1. } Li-containing composite oxide (A) having a layered structure in which Li represented by
An oxide composite containing at least one metal oxide (B) selected from the group consisting of yttrium, zirconium, and lanthanoids.

<Lithium-containing composite oxide (A)>
The lithium-containing composite oxide (A) can achieve the object of the present invention if the layered crystal structure represented by the composition formula (1) is present inside the crystal. However, from the viewpoint of increasing the electrical activity when the oxide composite of the present embodiment is used as a positive electrode active material, and stabilizing the crystal structure of the lithium-containing composite oxide itself,
A layered crystal structure represented by the composition formula (1);
The following composition formula (2):
Li _{1 + k} Mn _2-y Me ′ _y O _4-γ (2)
{In the formula, Me ′ is one or more metal elements other than Mn and Li, and satisfies the relationship of 0 ≦ k <1, 0 ≦ y ≦ 0.5, and 0 ≦ γ <1. } And the following composition formula (3):
LiMeO ₂ (3)
{Wherein Me is one or more metal elements other than Li. } Is preferably an oxide composite having a crystal structure in which one or more crystal structures selected from a layered crystal structure in which Lis are arranged in a layer form are solid-solved.

Examples of M ′ in the composition formula (1) include Ni, Co, Al, Mn, Mo, W, Ce, Nb, Mg, Fe, Cu, Ti, Sn, Pb, V, Zn, Ga, Ge, and Zr. It is 1 or more types chosen from. Among these, one or more selected from Fe, Co, and Ni is more preferable, one or more selected from Co and Ni is still more preferable, and Ni is particularly preferable.
As Me ′ in the composition formula (2), for example, one or more selected from Ni, Co, Al, Fe, Ti, and Mg is preferable, and Ni is particularly preferable.
Me in the composition formula (3) is preferably at least one selected from Mn, Ni, Co, Ti, Al, Mg, Mo, W, and V.
Based on the above structure, elements such as V, Fe, Al, Mg, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, Y, and Ca are dissolved in oxides or in other forms. An oxide composite added or added can also be used.

The lithium-containing composite oxide (A) in the present embodiment is preferably a metal element having high dispersibility. High dispersibility of the metal element means that the metal contained in the lithium-containing composite oxide (A) is uniformly distributed along the radial direction of the lithium-containing composite oxide (A) particles. Say.
When the lithium-containing composite oxide (A) having a low element dispersibility is used, a specific metal element may be solidified to promote the growth of a crystal phase different from that intended by the present embodiment. . Such another crystal phase serves as a resistance inside the active material and causes a decrease in electric capacity. Therefore, when the lithium-containing composite oxide (A) having sufficiently high element dispersibility is used, a high battery capacity can be obtained without formation of a resistance component, so that the rate characteristics do not deteriorate. Moreover, in a preferable aspect in the present embodiment, another crystal structure having an electrochemically active crystal structure can be used as a solid solution in the lithium-containing composite oxide (A). In this case, by keeping the element dispersibility of the lithium-containing composite oxide (A) high, a sufficiently high electrochemical activity can be maintained, so that a high discharge capacity can be obtained and the deterioration of rate characteristics can be suppressed. It can be done.

The dispersibility of the metal element in the lithium-containing composite oxide (A) is evaluated using, for example, a transmission electron microscope (TEM) / scanning transmission electron microscope (STEM) equipped with an energy dispersive X-ray detector (EDX). can do. Specifically, an appropriate region is selected from the field of view observed in the STEM, and element analysis is performed on the region using an EDX detector, and evaluation is performed using an appropriate analysis method such as point analysis, element mapping, or line analysis. be able to. Preferably, line analysis is used. In the line analysis, a line range of about several μ without a void of powder particles is selected from the field of view of the STEM, and the X-ray intensity of each metal element is measured every several tens of nm along the line. And the highest intensity | strength, the minimum intensity | strength, and average intensity | strength are calculated | required for every metal kind, and the element dispersion width of each metal can be calculated | required according to following Numerical formula (1).
Element dispersion width (%) = (maximum strength−minimum strength) / average strength × 100 (1)
The above operation may be performed by arbitrarily selecting several lines, and an average value thereof may be obtained as an evaluation value of the element dispersion width.

The element dispersion width is preferably as small as possible for any element, but a preferable range is selected in consideration of the complexity of the preparation method and the like. In order to obtain a sufficient discharge capacity, it is preferably 50% or less;
In order to maintain the preferable solid solution state of the crystal phase and obtain sufficient rate characteristics, it is preferably 30% or less; and the heterogeneous growth due to the bias of elements during repeated charge and discharge is suppressed, and sufficient In order to obtain the discharge capacity and rate characteristics, it is most preferably 20% or less.
The element dispersion width can be defined for all of the metal element species contained in the lithium-containing composite oxide (A), but if Ni, Co, and Mn are examined, the lithium-containing composite oxide (A) You can know the metal distribution situation. More simply, by examining Mn, the metal distribution in the lithium-containing composite oxide (A) can be generally known.

<Metal oxide (B)>
The metal oxide (B) is an oxide of at least one metal selected from the group consisting of yttrium, zirconium, and lanthanoids. Such metal oxides are known as having the property of occluding oxygen atoms.
The metal oxide (B) is used to enhance the rate characteristics of the non-aqueous lithium ion secondary battery, and constitutes an oxide composite together with the lithium-containing composite oxide (A).
A lithium ion secondary battery obtained by applying a lithium-containing composite oxide having an Li-excess structure to a positive electrode active material requires an electrical activation process in order to use a high electric capacity. That is, a high electric capacity can be obtained by performing a first charge at a high voltage and causing a crystal structure change accompanying oxygen desorption.

  When the oxide composite as the positive electrode active material contains the metal oxide (B) together with the lithium-containing composite oxide (A), the effect of the metal oxide (B) on the improvement of the rate characteristics is clarified. I don't know. However, the inventor believes that this action is related to oxygen release in the activation process. If the positive electrode active material having a Li-excess structure contains the metal oxide (B), oxygen released in the activation process can be absorbed by the oxygen storage property. Therefore, there are advantageous effects such as suppression of physical damage such as generation of fine cracks on the active material surface, promotion of progress of oxygen desorption from Li-rich structure, suppression of electrolyte modification and decomposition by active oxygen, etc. Can be obtained. As a result, it is considered that an increase in resistance on the surface and inside of the active material in the activation process is suppressed. In addition to these, since the ionic conductivity of the metal oxide (B) itself is high, the lithium ion conductivity of the oxide composite containing the metal oxide (B) may be improved. It is considered that the rate characteristics are improved by combining these actions and reducing the resistance around the positive electrode active material including the oxide composite of the present embodiment.

The metal oxide (B) is preferably a metal oxide containing at least one selected from the group consisting of yttrium, zirconium, and cerium. Most preferably, a metal oxide containing cerium is used.
The metal oxide (B) is used in a state where it is homogeneously present with the lithium-containing composite oxide (A) in the oxide composite according to the present embodiment, or in a state where the lithium-containing composite oxide (A) is coated. Can do.

The above “homogeneously existing state” means a state in which primary particles of the lithium-containing composite oxide (A) and primary particles of the metal oxide (B) are uniformly mixed. In the state where the metal oxide (B) is present homogeneously in the oxide composite, the content ratio of the metal oxide (B) is 0.5 to 5.0 with respect to the entire oxide composite. It is preferable that it is mass%, More preferably, it is 1.0 to 4.0 weight%. In order to fully express the effect of using the metal oxide (B), it is preferably used in an amount of 0.5% by mass or more. In order to avoid a decrease in capacity, it is preferably used at 5.0% by mass or less.
The “coated state” means a state in which the metal oxide (B) is unevenly distributed on the surface of the lithium-containing composite oxide (A). The content ratio of the metal oxide (B) in the coated state is preferably 0.1 to 0.6% by mass, more preferably 0.2 to 0. 0% with respect to the whole oxide composite. 5% by mass. It is used in an amount of 0.1% by mass or more in order to sufficiently obtain the effects of the present invention, and is used in an amount of 0.6% by mass or less in order to suppress an increase in resistance derived from the electron conductivity of the oxide composite surface.
This “covered state” is preferably an embodiment in which the metal oxide (B) covers only a part of the surface of the lithium-containing composite oxide (A). When the metal oxide (B) uniformly covers the entire surface of the lithium-containing composite oxide (A), the effects of the present invention may not be sufficiently exhibited, which is not preferable.

  Whether the metal oxide (B) is included in a "homogeneously present" state or a "covered state" depends on the desired oxide composite particle size, specific surface area, required density, etc. Thus, it can be set appropriately and used properly.

<Method for producing oxide composite>
There is no limitation in particular as a manufacturing method of an oxide composite, It can implement by a well-known method.
In order to create a state in which the metal oxide (B) is present homogeneously with the lithium-containing composite oxide (A) in the oxide composite, for example, by a coprecipitation method, a spray drying method, a gelation combustion method, etc. Can be manufactured;
In order to produce an oxide composite in which the metal oxide (B) is coated with the lithium-containing composite oxide (A), for example, a lithium-containing composite oxide (A) prepared in advance is used as a metal oxide. It can manufacture by the method (coating method) etc. which calcinate after making the solution containing the precursor of (B) contact.

[In homogeneous state]
(1) Coprecipitation method Manufacture of an oxide composite by a coprecipitation method can be performed according to a conventional method. For example, an aqueous solution containing a metal salt that is a precursor of the lithium-containing composite oxide (A) and a metal salt that is a precursor of the metal oxide (B) in a predetermined ratio is prepared, and an alkali is added to the aqueous solution. In addition, the resulting precipitate can be dried and fired. A part of the metal salt may be post-added to the precipitate caused by the alkali, pulverized and mixed as necessary, and then subjected to firing.

The metal salt that is a precursor of the lithium-containing composite oxide (A) is a metal salt included in the composition formula (1), specifically, for example, a Li salt, a Ni salt, a Co salt, a Mn salt, or the like;
The metal salt that is a precursor of the metal oxide (B) is an yttrium salt, a zirconium salt, or a lanthanoid salt. These salts may be hydroxides other than nitrates, sulfates, acetates, carbonates and the like.
Examples of the alkali include aqueous solutions of Na ₂ CO ₃ , NaOH, KOH, NH ₄ OH, and the like. The liquid during the coprecipitation operation is preferably carried out by adjusting the pH to 5.0 to 13.0, more preferably from 6.0 to 12.0.

The obtained precipitate is preferably dried at 100 to 150 ° C, more preferably 105 to 130 ° C, preferably 30 minutes to 24 hours, more preferably 4 to 12 hours. The recovered dried precipitate is then fired. This firing can be performed in an atmosphere in which oxygen exists in an appropriate heating apparatus such as a heating furnace.
In order to make the state of crystal growth, element dispersibility, particle shape, particle size, etc. of the finally obtained lithium-containing composite oxide (A) preferable, firing is divided into primary firing and secondary firing. You may go. In this case, the primary firing is performed in an atmosphere in which oxygen is present, in the range of 300 ° C. to 650 ° C., preferably in the range of 400 ° C. to 600 ° C., preferably 30 minutes to 24 hours, more preferably 2 hours to 12 hours. Done on condition. After the powder obtained by the primary firing is pulverized and mixed, the secondary firing is performed. The secondary firing is preferably performed in the range of 650 ° C to 1,200 ° C. The firing temperature is preferably 650 ° C. or higher from the viewpoint of sufficient crystal growth, and should be 1,200 ° C. or lower in order to avoid a decrease in rate characteristics due to the specific surface area of the powder becoming too small. preferable. From the viewpoint that sufficient crystal growth can be obtained and good characteristics can be obtained in the rate characteristics, the temperature is more preferably 700 ° C. to 1,000 ° C., and most preferably 750 ° C. to 950 ° C.
If a preferable state can be obtained in the element dispersion state, particle shape, size, and degree of crystal growth, primary firing may be omitted and only secondary firing may be performed.

(2) Spray-drying method The spray-drying method contains, for example, a metal salt that is a precursor of the lithium-containing composite oxide (A) and a metal salt that is a precursor of the metal oxide (B) in a predetermined ratio. The solution or suspension is prepared, spray-dried, and then baked. A part of the metal salt may be post-added to a powder obtained by spray drying, and pulverized and mixed as necessary, and then subjected to firing. The solvent for the solution or suspension is preferably water.
The conditions of the coprecipitation method can be employed as they are, respectively, as the type of raw material metal salt, the concentration of metal salt in the solution, and the firing conditions in the spray drying method. The metal salt concentration in the case of using a suspension instead of the solution may be considered according to the case of the solution.

(3) Gelled Combustion Method The gelled combustion method is a method in which a combustible gel comprising a metal salt having an oxidizable ligand and a metal salt having a combustible ligand is heat-treated to produce the combustible gel. Is a technology for obtaining a homogeneous and fine fine powder oxide by instantly thermally decomposing.
Examples of the metal salt having an oxidizable ligand include nitrates and sulfates;
Examples of the metal salt having a flammable ligand include citrate, acetate, glycine salt, oxalate,
Each can be mentioned. These salts may be anhydrous salts or hydrated salts. Most preferably, nitrate is used as the metal salt having an oxidizing ligand, and acetate is used as the metal salt having a combustible ligand.

The ratio of the metal salt having an oxidizable ligand to the metal salt having a flammable ligand depends on the state of thermal decomposition during heat treatment and the desired oxidation / reduction state of the resulting oxide composite. It can be determined as appropriate. That is, when the final metal oxide is desired to be reduced, the ratio of the metal salt having a flammable ligand is increased, and when it is desired to be oxidized, the metal having an oxidizable ligand is used. It is preferable to increase the salt ratio.
The use ratio of the metal salt having an oxidizable ligand to the metal salt having a flammable ligand is the ratio of the metal salt having a flammable ligand / the metal salt having an oxidizable ligand. The ratio is preferably in the range of 2 to 5 (molar ratio), more preferably in the range of 2.5 to 3.5.

In the gelation combustion method,
First, an aqueous solution containing a metal salt having an oxidizing ligand as described above and a metal salt having a combustible ligand in a predetermined ratio is prepared.
The water is then removed from the aqueous solution to form a homogeneous combustible gel and the combustible gel is heat treated. The powder obtained by this heat treatment may be further pulverized and stirred and then sintered to adjust crystal growth.
The metal salt concentration in the metal salt aqueous solution is preferably 0.1 to 50% by mass as the total concentration of the metal salt having an oxidizable ligand and the metal salt having a flammable ligand, More preferably, it is 0.5-30 mass%. This solution may be aged after preparation for the purpose of obtaining a more stable combustible gel. This aging is performed by continuing the stirring of the solution in the range of 10 minutes to 20 hours, for example, at 50 to 80 ° C. for the purpose of promoting the growth of a preferable complex salt by the oxidizing ligand and the flammable ligand. be able to.

The combustible gel can be obtained by a method in which one or more operations selected from heating and reduced pressure are applied to the solution to remove the solvent and dry.
The heat treatment of the combustible gel is preferably performed at 300 ° C to 500 ° C. A temperature of 300 ° C. or higher is used in order to sufficiently decompose the ligand contained in the gel, and a temperature of 500 ° C. or lower is used from the viewpoint of avoiding nonuniform particle size and metal distribution. Most preferably, it is the range of 300 to 400 degreeC. The rate of temperature increase during the heat treatment is controlled in the range of 10 ° C./hour to 200 ° C./hour. From the viewpoint of homogeneous thermal decomposition, the rate of temperature rise is preferably slow. However, it is carried out at a rate of 10 ° C./hour or more from the viewpoint of efficiency, and can be operated at a temperature of 200 ° C./hour or less in order to obtain a homogeneous pyrolytic powder. It is preferably operated at a temperature rising rate in the range of 50 ° C / hour to 150 ° C / hour.

After the heat treatment, pulverization / mixing operation is preferably performed for the purpose of further improving the homogeneity of the finally obtained oxide composite. The powder after the pulverization / mixing operation can be further subjected to a sintering operation in the range of 500 ° C. to 1,000 ° C. in order to optimize the particle size and crystal growth of the oxide composite. In order to sufficiently grow the crystal, conditions of 500 ° C. or higher are preferable, and in order to avoid problems such as excessive crystal growth, conditions of 1,000 ° C. or lower are preferable. More preferably, the temperature is 700 ° C to 950 ° C. The sintering time is preferably 30 minutes to 36 hours, more preferably 3 to 12 hours.
If the final oxide composite can be obtained in a preferable state, it can be a condition for performing only the heat treatment, or after the heat treatment, the operation of pulverization and mixing is omitted, and the heat treatment and the firing are performed. The ligation operation can be carried out continuously.

  Any of the above methods can create a state in which the metal oxide (B) is present homogeneously with the lithium-containing composite oxide (A) in the oxide composite.

[When covered]
In order to produce an oxide composite in which the metal oxide (B) is coated with the lithium-containing composite oxide (A), for example, a lithium-containing composite oxide (A) prepared in advance is used as a metal oxide. For example, a method (coating method) of baking after bringing the solution containing the precursor (B) into contact can be used.
In order to produce the lithium-containing composite oxide (A) in advance, the precursor of the lithium-containing composite oxide (A) is used without using the metal salt that is the precursor of the metal oxide (B) as the metal salt of the raw material. Other than using only the metal salt that is a body, it can be performed by a method according to the coprecipitation method, spray drying method, or gelation combustion method in the case of creating the homogeneous state.

As the solution containing the precursor of the metal oxide (B), an aqueous solution containing a metal salt which is a precursor of the metal oxide (B) can be preferably used. The metal salt concentration in the aqueous solution is preferably 0.1 to 50% by mass, more preferably 0.5 to 30% by mass.
The contact between the solution and the lithium-containing composite oxide (A) can be performed, for example, at 40 to 90 ° C., preferably 50 to 80 ° C., for example, for 1 to 10 hours, preferably 2 to 5 hours.
Firing after the contact can be performed, for example, at 500 to 1,000 ° C., preferably 700 to 950 ° C., for example, for 30 minutes to 36 hours, preferably for 3 to 12 hours.
As described above, an oxide composite in which the metal oxide (B) covers the surface of the lithium-containing composite oxide (A) can be produced.

<Non-aqueous lithium ion secondary battery>
The non-aqueous lithium ion secondary battery in the present embodiment is a battery using the above-described oxide composite as a positive electrode active material, for example, a lithium ion secondary battery schematically showing a cross-sectional view in FIG. Can do.
The lithium ion secondary battery 100 shown in FIG.
Separator 110;
A positive electrode 120 and a negative electrode 130 sandwiching the separator 110 from both sides;
Furthermore, a positive electrode current collector 140 (arranged outside the positive electrode) and a negative electrode current collector 150 (arranged outside the negative electrode) sandwiching the laminate,
And a battery exterior 160 that accommodates them. A laminate in which the positive electrode 120, the separator 110, and the negative electrode 130 are stacked is impregnated with an electrolytic solution. As each of these members, those similar to those provided in the conventional lithium ion secondary battery can be used except that the oxide composite of the present embodiment is used as the positive electrode active material. Things.

[Positive electrode]
The positive electrode is not particularly limited as long as it functions as a positive electrode of a non-aqueous lithium ion secondary battery, except that the oxide composite of the present embodiment is used as a positive electrode active material. can get.
First, a positive electrode mixture-containing paste is prepared by dispersing a positive electrode mixture in which the positive electrode active material is mixed together with other components (for example, a conductive additive, a binder, etc.) used as necessary in a solvent. Next, this positive electrode mixture-containing paste is applied to a positive electrode current collector, dried to form a positive electrode mixture layer, and further pressurized to adjust the thickness as necessary to produce a positive electrode.

Examples of the conductive aid used as necessary in the production of the positive electrode include graphite; carbon black typified by acetylene black and ketjen black; carbon fiber and the like. The number average particle diameter (primary particle diameter) of the conductive assistant is preferably 10 nm to 10 μm, more preferably 20 nm to 1 μm.
Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene butadiene rubber, and fluorine rubber.
The solid content concentration in the positive electrode mixture-containing paste is preferably 30 to 80% by mass, more preferably 40 to 70% by mass.
The positive electrode current collector is made of a metal foil such as an aluminum foil or a stainless steel foil. These materials may be carbon coated or those materials processed into a mesh shape.

[Negative electrode]
The negative electrode is not particularly limited as long as it functions as a negative electrode of a non-aqueous lithium ion secondary battery, and a known one can be used.
The negative electrode preferably contains at least one material selected from the group consisting of a material capable of inserting and extracting lithium ions as a negative electrode active material and metallic lithium. Such materials include metal lithium, metal materials such as a material containing an element capable of forming an alloy with lithium, and the like;
For example, amorphous carbon (hard carbon), artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, glassy carbon, organic polymer compound fired body, mesocarbon microbead, carbon fiber, activated carbon, graphite, carbon colloid, Examples thereof include carbon materials typified by carbon black. Among these, examples of the coke include pitch coke, needle coke, and petroleum coke. The fired body of an organic polymer compound is obtained by firing and polymerizing a polymer material such as phenol resin or furan resin at an appropriate temperature. In addition to carbon, the carbon material may contain a heterogeneous compound containing O, B, P, N, S, SiC, B ₄ C, or the like. As content of a different compound, it is preferable that it is 0-10 mass% with respect to the whole negative electrode active material. The metal material capable of forming an alloy with lithium may be a single metal or a semimetal, an alloy, or a compound, and one or more of these phases may be combined. It may be at least partly.

The number average particle diameter (primary particle diameter) of the negative electrode active material is preferably 0.1 μm to 100 μm, more preferably 1 μm to 10 μm.
A negative electrode is obtained as follows, for example.
First, a negative electrode mixture-containing paste is prepared by dispersing a negative electrode mixture prepared by mixing the negative electrode active material together with other components (for example, a conductive additive and a binder) used as necessary in a solvent. Next, this negative electrode mixture-containing paste is applied to a negative electrode current collector, dried to form a negative electrode mixture layer, and further pressurized to adjust the thickness as necessary to produce a negative electrode.
Here, the solid content concentration in the negative electrode mixture-containing paste is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass. The negative electrode current collector is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.
Examples of the conductive aid used as necessary in the production of the negative electrode include graphite; carbon black typified by acetylene black and ketjen black; carbon fiber and the like. The number average particle diameter (primary particle diameter) of the conductive assistant is preferably 0.1 μm to 100 μm, more preferably 1 μm to 10 μm. Examples of the binder include PVDF, PTFE, polyacrylic acid, styrene butadiene rubber, and fluorine rubber.

[Electrolyte]
The electrolyte used for the non-aqueous lithium ion secondary battery in the present embodiment is not particularly limited as long as it contains at least a non-aqueous solvent and a lithium salt and acts as an electrolyte for the non-aqueous secondary battery. Well-known ones can be used. The electrolyte solution preferably does not contain moisture, but may contain a very small amount of moisture as long as it does not inhibit the desired effect. Such water content is, for example, 0 to 100 ppm with respect to the total amount of the electrolytic solution.
There is no restriction | limiting in particular as a non-aqueous solvent, For example, an aprotic solvent is mentioned, Among these, an aprotic polar solvent is preferable.

  Specific examples of the non-aqueous solvent include, for example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, Trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, trifluoromethylethylene carbonate, fluoroethylene carbonate, cyclic carbonate represented by 1,2-difluoroethylene carbonate; γ-butyrolactone, γ- Lactones typified by valerolactone; sulfur compounds typified by sulfolane and dimethyl sulfoxide; cyclic ethers typified by tetrahydrofuran, 1,4-dioxane and 1,3-dioxane; methyl ethyl carbonate, dimethyl Chain carbonates typified by til carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, methyl trifluoroethyl carbonate; acetonitrile, propiononitrile, butyronitrile, Mononitriles such as valeronitrile and acrylonitrile; alkoxy-substituted nitriles represented by methoxyacetonitrile and 3-methoxypropionitrile; cyclic nitriles represented by benzonitrile; ethers represented by dimethyl ether; represented by methyl propionate And a chain ether carbonate compound typified by dimethoxyethane. Moreover, the halide represented by these fluorides is also mentioned. These are used singly or in combination of two or more.

In order to increase the ionization degree of the lithium salt that contributes to charge / discharge of the non-aqueous lithium ion secondary battery, the non-aqueous solvent preferably contains at least one selected from a cyclic aprotic polar solvent and a cyclic carbonate. More preferably, both of these are included. From the viewpoint of improving the solubility, conductivity, and ionization degree of the lithium salt, a mixed solvent of two or more of the above non-aqueous solvents is preferable.
The lithium salt is not particularly limited as long as it is used in an electrolyte solution for a non-aqueous secondary battery, and any lithium salt may be used. The lithium salt is preferably contained in the nonaqueous electrolytic solution at a concentration of 0.1 to 3 mol / L, and more preferably 0.5 to 2 mol / L. When the concentration of the lithium salt is within the above range, the electric conductivity of the electrolytic solution is kept high, and at the same time, the charge / discharge efficiency of the nonaqueous secondary battery tends to be kept high.
The lithium salt in the present embodiment is not particularly limited, but is preferably an inorganic lithium salt. The inorganic lithium salt is not particularly limited as long as it is used as a normal non-aqueous electrolyte, and any one may be used. Specific examples of such inorganic lithium salts include, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , Li ₂ B ₁₂ F _b H _12-b. In addition to [b is an integer of 0 to 3], a lithium salt bonded to a polyvalent anion and the like can be mentioned.

These inorganic lithium salts are used singly or in combination of two or more. Among these, it is preferable to use an inorganic lithium salt having a fluorine atom as the inorganic lithium salt in that a passive film can be formed on the surface of the positive electrode current collector and an increase in internal resistance can be suppressed. Further, an inorganic lithium salt having a phosphorus atom together with a fluorine atom is more preferable, and LiPF ₆ is particularly preferable.
The content of the inorganic lithium salt is preferably 0.1 to 40% by mass, more preferably 1 to 30% by mass, and 5 to 25% by mass with respect to the total amount of the nonaqueous electrolytic solution. Is more preferable.

  The non-aqueous electrolyte solution of the non-aqueous lithium ion secondary battery in the present embodiment only needs to contain at least a non-aqueous solvent and a lithium salt, but may further optionally contain additives. . The additive may substantially overlap in function with the non-aqueous solvent. The additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte solution and the non-aqueous secondary battery in the present embodiment, but also includes a substance that does not directly participate in the electrochemical reaction. One additive is used alone, or two or more additives are used in combination.

  Specific examples of the additive include, for example, 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1, 3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5 , 5-tetrafluoro-1,3-dioxolan-2-one, fluoroethylene carbonate represented by 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; vinylene carbonate, 4 , 5-Dimethyl vinylene carbonate, cyclic carbonate containing unsaturated bond typified by vinyl ethylene carbonate; γ-butyrolactone, γ-valerolactone, γ-caprolacto , .Delta.-valerolactone, .delta.-caprolactone, lactones represented by ε- caprolactone, cyclic ethers typified by 1,2-dioxane;

Methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, n-propyl formate, n-propyl acetate, n-propyl propionate, n-propyl butyrate, isopropyl formate, isopropyl acetate, isopropyl propionate, isopropyl butyrate, n-butyl formate, n-butyl acetate, n-butyl propionate, n-butyl butyrate, isobutyl formate, Isobutyl acetate, isobutyl propionate, isobutyl butyrate, sec-butyl formate, sec-butyl acetate, sec-butyl propionate, sec-butyl butyrate, tert-butyl forme Tert-butyl acetate, tert-butyl propionate, tert-butyl butyrate, methyl pivalate, n-butyl pivalate, n-hexyl pivalate, n-octyl pivalate, dimethyl oxalate, ethyl methyl oxalate, diethyl Carboxylic acid esters represented by oxalate, diphenyl oxalate, malonic acid ester, fumaric acid ester, maleic acid ester;

Amides represented by N-methylformamide, N, N-dimethylformamide, N, N-dimethylacetamide; ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-methylsulfolane, 3-sulfolene , 1,3-propane sultone, 1,4-butane sultone, 1,3-propanediol sulfate, tetramethylene sulfoxide, cyclic sulfur compounds represented by thiophene 1-oxide; represented by monofluorobenzene, biphenyl, fluorinated biphenyl Nitro compounds typified by nitromethane; Schiff bases; Schiff base complexes; oxalato complexes. These are used singly or in combination of two or more.
Although there is no restriction | limiting in particular about content of the additive in the non-aqueous electrolyte in this embodiment, It is preferable that it is 0.1-30 mass% with respect to the whole quantity of a non-aqueous electrolyte, 0.1-10 mass % Is more preferable.

[Separator]
The nonaqueous lithium ion secondary battery in the present embodiment preferably includes a separator between the positive electrode and the negative electrode from the viewpoint of preventing safety between the positive and negative electrodes, providing safety by shutting down, and the like. The separator may be the same as that provided in a known non-aqueous lithium ion secondary battery. The separator is preferably an insulating thin film having high ion permeability and excellent mechanical strength.
Examples of the separator of the non-aqueous lithium ion secondary battery in the present embodiment include a microporous film made of a polyolefin resin such as polyethylene and polypropylene;
A structure containing a mixture of a resin such as cellulose, aromatic polyamide, fluororesin or polyolefin and one or more inorganic materials such as alumina and silica;
A structure formed by coating the surface of a nonwoven fabric, papermaking, porous membrane or the like with a mixture of the resin and an inorganic material;
Examples include a solid electrolyte film.
The separator may be a single microporous membrane or a laminate of a plurality of microporous membranes, or may be a laminate of two or more microporous membranes.

<Production method of battery>
The non-aqueous lithium ion secondary battery in the present embodiment is manufactured by a known method using the above-described electrolytic solution, a positive electrode manufactured using the oxide composite, a negative electrode, and, if necessary, a separator. For example, a positive electrode and a negative electrode are laminated with a separator interposed therebetween,
A mode in which the laminate is wound to form a wound body of the laminate;
A mode in which the multilayer body is bent to form a multilayered multilayer body in which separators are interposed between a plurality of alternately stacked positive and negative electrodes;
The electrode laminate is constituted by, for example, an embodiment in which the laminate is laminated in a plurality of layers, and is formed into a multilayered laminate in which separators are interposed between a plurality of alternately stacked positive and negative electrodes. Next, the electrode laminate is accommodated in a battery case (exterior), an electrolyte solution is injected into the case, and the laminate is immersed in the electrolyte solution and sealed, whereby the non-aqueous two-layer battery of this embodiment is sealed. A secondary battery can be produced. Alternatively, an electrolyte membrane containing a gelled electrolyte solution is prepared in advance, and a positive electrode, a negative electrode, the electrolyte membrane, and, if necessary, a separator are formed according to the above-described method to form a porous electrode laminate. Thereafter, a method of manufacturing the non-aqueous lithium ion secondary battery by accommodating the electrode stack in a battery case is also possible.

The shape of the non-aqueous lithium ion secondary battery of the present embodiment is not particularly limited, and for example, a cylindrical shape, an elliptical shape, a rectangular tube shape, a button shape, a coin shape, a flat shape, a laminate shape, and the like are suitably employed. .
The non-aqueous lithium-on secondary battery in the present embodiment can function as a battery by initial charging, but is stabilized by decomposition of a part of the electrolyte during the initial charging. Although there is no restriction | limiting in particular about the method of initial charge in this embodiment, It is preferable that initial charge is performed at 0.001-0.3C, It is more preferable to be performed at 0.002-0.25C, 0.003 More preferably, it is carried out at ~ 0.2C. In addition, it is also preferable that the initial charging is performed via the constant voltage charging in the middle.
In addition, the constant current value which discharges rated capacity in 1 hour is 1C. By setting a long voltage range in which the lithium salt is involved in the electrochemical reaction, SEI (Solid Electrolyte Interface) is formed on the electrode surface, and an effect of suppressing an increase in internal resistance including the positive electrode is obtained. In addition, the reaction product is not firmly fixed only to the negative electrode, but also has a good effect on members other than the negative electrode such as the positive electrode and the separator in some form. Therefore, it is very effective to perform the initial charge in consideration of the electrochemical reaction of the lithium salt dissolved in the electrolytic solution.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said embodiment. The present invention can be variously modified without departing from the gist thereof.

  Examples of the present invention will be specifically described below with reference to Examples and the like, but the present invention is not limited to these.

<Preparation of lithium-containing composite oxide by gelation combustion method>
A lithium-containing composite oxide having a composition represented by Li _1.2 Ni _0.175 Co _0.10 Mn _0.525 O ₂ was prepared by gelation combustion method.
Li (CH ₃ COO) · 2H ₂ O and LiNO ₃ as the Li source
As Ni source of Ni _{(NO 3) 2 · 6H 2} O,
Co (NO ₃ ) ₂ .6H ₂ O as the Co source and Mn (CH ₃ COO) ₂ .4H ₂ O as the Mn source,
By using each of them, adjusting the usage ratio of Li (CH ₃ COO) · 2H ₂ O and LiNO ₃ , the CH ₃ COO / NO ₃ ratio of the entire raw material becomes 3/1 (molar ratio), and further the salt An aqueous solution in which the above raw materials were dissolved in a proportion corresponding to the above composition was prepared so that the total concentration of

While stirring the container containing this aqueous solution, it was heated at 80 ° C. for 3 hours to obtain a combustible gel. The obtained gel was heat-treated in the atmosphere under the conditions of an ultimate temperature of 400 ° C., a temperature rising time from room temperature to 400 ° C. of 3 hours, and a holding time of 30 minutes at 400 ° C. to obtain a sponge-like powder. During the heat treatment, the temperature of the gel was continuously measured. As a result, a rapid temperature increase was observed at 230 ° C., and it was confirmed that the gel was thermally decomposed instantaneously at this temperature.
Next, after the obtained sponge-like powder was pulverized with a mortar and pestle, the temperature reached 860 ° C., the temperature rising time from room temperature to the temperature reached 1.5 hours, and the holding time at the temperature reached 5 hours in the atmosphere. 1 g of lithium-containing composite oxide was obtained by sintering.

(Measurement of metal composition ratio)
The metal composition ratio of the lithium-containing composite oxide obtained above was examined by emission spectroscopic measurement using ICP (high frequency inductively coupled plasma) as a light source.
As a result of ICP measurement, it was found that the obtained composite oxide had an atomic ratio of Li: Ni: Co: Mn = 1.2: 0.175: 0.10: 0.525 (molar ratio). It was confirmed that the desired composition was obtained.

ICP measurements were performed as follows:
0.05 g of complex oxide finely pulverized in an agate mortar was placed in a Teflon (registered trademark) container, 8 mL of aqua regia was added, and microwave heating was performed to dissolve uniformly. An ICP measurement sample was prepared by adding ultrapure water to this solution to make 100 g. About this sample, it measured on the following conditions using the ICP-emission-spectral-analysis apparatus.
Measurement conditions: For water solvent, using cyclone chamber Plasma gas (PL1): 13 (L / min)
Sheath gas (G1): 0.3 (L / min)
Nebulizer gas pressure: 3.0 (bar)
Nebulizer flow rate: 0.2 (L / min)
High frequency power: 1.0 (kW)
A quantitative value was calculated by comparing the obtained result with the analytical value of a commercially available standard solution for atomic absorption analysis.

<Evaluation of metal element dispersibility>
The dispersibility of the metal element in the lithium-containing composite oxide was evaluated as follows.
0.2 g of the lithium-containing composite oxide obtained above was placed in a pressurizable tablet molding container having a diameter of 13 mm, and pressurized with a pressure of 20 MPa to obtain a press-molded body (tablet). 3100FEF transmission electron microscope / scanning transmission electron microscope apparatus (TEM / STEM) manufactured by JEOL Co., Ltd. equipped with an energy dispersive X-ray detector (EDX) using a sample obtained by performing Os vapor deposition on this pressure molded body. STEM observation was performed under the conditions of an acceleration voltage of 5 kV.

For the bright field image of TEM and the dark field image of STEM, the field of view about 10 μm wide is observed, and the line range of 3 μm length is selected in the area without the voids of the powder particles, and line analysis is performed. did. That is, X-ray intensities of Ni, Co, and Mn were measured every 20 nm with an EDX detector along the selected 3 μm line.
And the highest intensity | strength, the lowest intensity | strength, and average intensity | strength were investigated for every metal seed | species, and these elements were substituted into following Numerical formula (1), and the element dispersion width | variety was calculated | required.
Element dispersion width (%) = (maximum strength−minimum strength) / average strength × 100 (1)
The element dispersion widths of the lithium-containing composite oxide by the gelation combustion method were Co: 12.3%, Ni: 15.9%, and Mn: 11.8%.

<Preparation of lithium-containing composite oxide by coprecipitation method>
A lithium-containing composite oxide having a composition represented by Li _1.2 Ni _0.175 Co _0.10 Mn _0.525 O ₂ was prepared by a coprecipitation method using transition metal nitrate and Li carbonate as raw materials.
NiSO ₄ · 6H ₂ O, CoSO ₄ · 7H ₂ O, and MnSO ₄ · 5H ₂ O are dissolved in distilled water at a ratio corresponding to the above composition and the sulfate concentration is 2 mol / L in total. An aqueous sulfate solution was obtained.
Alternatively, the _Na 2 CO ₃ and _NH 4 OH, _Na 2 CO ₃ concentration was dissolved in distilled water to a concentration of 2.5 mol / L and _NH 4 OH is a 1mol / L, _Na 2 CO _{A 3} / NH ₄ OH aqueous solution was prepared.

Next, the Na ₂ CO ₃ / NH ₄ OH aqueous solution was gradually added to the sulfate aqueous solution with stirring to obtain a metal carbonate precipitate. The obtained metal carbonate was collected by filtration, washed several times with distilled water, and then dried at 110 ° C. for 16 hours. After drying, the mass was measured, and Li ₂ CO ₃ was mixed in a proportion corresponding to the above composition. After sufficiently mixing and stirring using a mortar, the first stage baking was performed in the atmosphere at 500 ° C. for 5 hours. Next, the mixture was pulverized and mixed again in a mortar, and the second stage baking was performed at 900 ° C. for 5 hours to obtain 5 g of a lithium-containing composite oxide.

As a result of ICP measurement by the same method as described above, the obtained lithium-containing composite oxide was Li: Ni: Co: Mn = 1.2: 0.175: 0.10: 0.525 (molar ratio). It was confirmed that the desired composition was obtained.
Further, when element dispersibility was measured by the same method as described above, the element dispersion width of this lithium-containing composite oxide was Co: 29.7%, Ni: 29.9%, and Mn: 28.9%. there were.

<Preparation of lithium-containing composite oxide by solid phase synthesis method>
A lithium-containing composite oxide having a composition represented by Li _1.2 Ni _0.175 Co _0.10 Mn _0.525 O ₂ was prepared using a solid phase synthesis method. The solid phase synthesis method is a method generally used for the synthesis of a lithium-containing layered compound.
Ni, Co, and Mn hydroxides corresponding to the above composition were placed in a zirconia container (12 ml) together with seven zirconia balls (diameter 1 cm), and a planetary ball mill (manufactured by Fritsch, Model P- 5) was mixed at 250 rpm for 6 hours to obtain a metal hydroxide mixture. Thereafter, an amount of lithium carbonate corresponding to the above composition was added, mixed in a mortar, and then fired at the first stage for 5 hours at 500 ° C. in the atmosphere. Next, after pulverizing and mixing again in a mortar, the second-stage firing was performed at 900 ° C. in the air for 5 hours to obtain 1 g of the target lithium-containing composite oxide.

As a result of ICP (high frequency inductively coupled plasma) measurement by the same method as described above, the obtained lithium-containing composite oxide was Li: Ni: Co: Mn = 1.2: 0.175: 0.10: 0. It had an atomic ratio of .525 (molar ratio) and was confirmed to have the desired composition.
When the element dispersibility was evaluated by the same method as described above, the element dispersion width of this lithium-containing composite oxide was Co: 83.9%, Ni: 59.5%, and Mn 57.8%. .

<Production of non-aqueous lithium ion secondary battery>
The characteristics of non-aqueous lithium ion secondary batteries using the oxide composites prepared in the following examples and comparative examples as positive electrode active materials were evaluated by the following procedures.

(1) Electrode preparation (1-1) Preparation of positive electrode The oxide composite prepared in each example or comparative example was used as a positive electrode active material, and an acetylene black powder having a number average particle diameter of 48 nm as a conductive auxiliary agent was used. Then, polytetrafluoroethylene (PTFE) as a binder was mixed at a mass ratio of 4: 5: 1. The resulting mixture was mixed on a mortar while containing ethanol, pressurized with a pestle, and stretched into a sheet. This sheet was allowed to stand at room temperature for 2 hours to remove the solvent, and then 20 mg was cut out to obtain a positive electrode sheet. A positive electrode (P) was obtained by pressure-bonding the cut-out positive electrode sheet at 2 ton / cm ² on one surface of an aluminum mesh with a 15.958 mmφ, and then vacuum drying.

(1-2) Production of negative electrode Graphite carbon powder having a number average particle diameter of 12.7 μm and graphite carbon powder having a number average particle diameter of 6.5 μm as a negative electrode active material, and a carboxymethyl cellulose solution (solid content concentration of 1.83 as a binder) Mass%), and diene rubber (glass transition temperature: −5 ° C., number average particle size upon drying: 120 nm, dispersion medium: water, solid content concentration 40 mass%),
A slurry was prepared by mixing so that the total solid content concentration was 45% by mass at a solid content mass ratio of 90: 10: 1.44: 1.76. This slurry was applied to one side of a 10 μm thick copper foil, allowed to stand at 60 ° C. for 10 hours to remove the solvent, and then rolled with a roll press to obtain a negative electrode (N).
This negative electrode (N) has an active material mass per unit area of 5.0 mg / cm ² ± 3%, an active material thickness of 40 μm ± 3%, and an active material density of 1.25 g / cm ³ ± 3. %, And the coating width was 150 mm with respect to the copper foil width of 200 mm.

(2) Preparation of electrolyte solution Using a solvent in which ethyl methyl carbonate (EMC) and ethylene carbonate (EC) are mixed at a volume ratio of 7: 3 as a solvent, LiPF ₆ is a concentration of 1 mol / L as a lithium salt. Thus, an electrolytic solution was prepared.

(3) Production of battery for evaluation The positive electrode (P) obtained as described above and the negative electrode (N) obtained as described above are punched into a disk shape having a diameter of 16 mm and are made of polyethylene. A laminated body was obtained by superimposing on both sides of a separator (film thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm). The laminate was inserted into a SUS coin-type battery case. Next, 0.1 mL of the electrolyte solution was injected into the battery case and the laminate was immersed in the electrolyte solution, and then the battery case was sealed. Then, it hold | maintained at 25 degreeC for 24 hours, and obtained the small evaluation battery (non-aqueous lithium ion secondary battery) by fully making an electrolyte solution acclimatize to a laminated body.
See also the attached FIG. 1 for the structure of this non-aqueous lithium ion secondary battery.

<Evaluation of non-aqueous lithium ion secondary battery>
(1) Evaluation of rate characteristics For non-aqueous lithium ion secondary batteries produced as described above using the oxide composites prepared in Examples 1 to 4 and Comparative Examples 1 to 3, respectively, were identified according to the following procedure. The discharge capacity at each discharge current was measured to evaluate the rate characteristics.
The measurement was performed using a charge / discharge device ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. and a thermostatic chamber IN-804 (trade name) manufactured by Yamato Scientific Co., Ltd.
For each non-aqueous lithium ion secondary battery, constant current charging was performed at a current value of 0.2 mA (0.1 C Rate) to reach 4.7 V, and then constant voltage charging was performed at a voltage value of 4.7 V. Charging was performed so that the total charging time of current charging and constant voltage charging was 8 hours. After the charge, constant current discharge was performed up to 2.0 V at a current value of 0.2 mA (0.1 C Rate), and the initial discharge capacity was obtained.

Next, after performing constant current charging and constant voltage charging in the same manner as described above, a constant current discharge is performed to 2.0 V at a current value of 0.6 mA (0.3 C Rate), and a discharge capacity at 0.3 C Rate. Asked. Furthermore, after performing constant current charge and constant voltage charge in the same manner as described above, constant current discharge was performed up to 2.0 V at a current value of 10 mA (5 C Rate), and the discharge capacity at 5 C Rate was obtained.
The ambient temperature of the battery during the charge / discharge operation was set to 25 ° C.
Using the values obtained above, the discharge capacity ratio was determined according to the following formula.
Discharge capacity ratio = [discharge capacity at 5C rate] / [discharge capacity at 0.3C rate]

[Example 1]
<Preparation of CeO ₂ containing oxide complex by gel combustion method>
A lithium-containing composite oxide containing 1.59% by mass of CeO ₂ and represented by Li _1.2 Ni _0.175 Co _0.10 Mn _0.525 O ₂ by a gelled combustion method is used as a base. An oxide composite was prepared.
As the Li source, Li (CH ₃ COO) .2H ₂ O and LiNO ₃ are used.
As the Ni source _{Ni (NO 3) 2 · 6H} 2 O,
As a Co source, Co (NO ₃ ) ₂ · 6H ₂ O is used.
Mn (CH ₃ COO) ₂ .4H ₂ O as the Mn source, and CeO ₂ nanosol as the Ce source (Taki Chemical Co., Ltd. Nidral B-10 CeO ₂ 10.3% by mass, average particle size 20 nm) The
Each is used, and by adjusting the usage ratio of Li (CH ₃ COO) · 2H ₂ O and LiNO ₃ , the CH ₃ COO / NO ₃ ratio of the entire raw material becomes 3/1 (molar ratio), and further CeO ₂ containing CeO ₂ nanosol so that the ratio of ₂ corresponds to 1.59% by mass with respect to the total amount of the final oxide composite, and the total salt concentration is 30% by mass, A mixed solution in which the above raw materials were dissolved or dispersed at a ratio corresponding to the above composition was prepared. Next, the container containing the above mixture was heated at 80 ° C. for 3 hours with stirring to obtain a combustible gel. The obtained gel was heat-treated under the conditions of an ultimate temperature of 400 ° C., a temperature rising time from room temperature to 400 ° C. of 3 hours, and a holding time of 30 minutes at 400 ° C. to obtain a sponge-like powder. Next, the obtained sponge-like powder was pulverized using a mortar and then sintered under the conditions of an ultimate temperature of 880 ° C., a temperature rise time from room temperature to the ultimate temperature of 1.5 hours, and an ultimate temperature holding time of 5 hours. As a result, 1 g of an oxide composite containing CeO ₂ was obtained.
As a result of ICP measurement, the resulting oxide composite had an atomic ratio of Li: Ni: Co: Mn: Ce = 1.2: 0.175: 0.10: 0.525: 0.008 (molar ratio). It was confirmed that the desired composition was obtained.

<XRD measurement of oxide composite>
The XRD analysis of the oxide composite prepared above was performed under the following conditions using the oxide composite pulverized in a mortar as a measurement sample.
Detector: Semiconductor detector Tube: Cu
Tube voltage: 40 kV
Tube current: 40 mA
Divergent slit: 0.3 °
Step width: 0.02 ° / step
Measurement time: 3 sec
In the obtained XRD pattern, in addition to the peak of the lithium-containing oxide, peaks were observed at 2θ = 28.56 ° and 33.08 °, and thus the formation of CeO ₂ was observed.

[Example 2]
Preparation is performed in the same manner as in Example 1 except that the amount of CeO ₂ nanosol used is an amount corresponding to 3.13% by mass in terms of CeO ₂ with respect to the finally obtained oxide composite. As a result, an oxide composite was obtained. From the measurement results of ICP and XRD, it was confirmed to be an oxide composite containing a predetermined amount of CeO ₂ .

[Example 3]
In this example, surface coating with CeO ₂ was performed on the lithium-containing composite oxide prepared in <Preparation of lithium-containing composite oxide by coprecipitation method>.
Corresponding to 0.31% by mass in terms of CeO ₂ with respect to the finally obtained oxide composite _{Ce (NO 3) 3 · 6H} 2 O, and the entire _{CH 3} COO / NO 3 ratio 3/1 ( An aqueous solution having a total salt concentration of 1% by weight was prepared using an amount of Li (CH ₃ COO) · 2H ₂ O in a molar ratio). To this aqueous solution, 1 g of the lithium-containing composite oxide powder prepared in <Preparation of lithium-containing composite oxide by coprecipitation method> was added. The obtained mixture was put into a 100 ml eggplant flask, and water was distilled off for about 30 minutes under the conditions of a bath temperature of 80 ° C., a rotation speed of 50 rpm, and a pressure of 200 mHg using an evaporator to obtain a dry powder. Next, the obtained powder was sintered under the conditions of a temperature rising time of 3.0 hours, an ultimate temperature of 400 ° C., and a holding time of 0.5 hours, whereby the oxide composite surface-coated with CeO ₂ Got.
As a result of ICP measurement, it was confirmed that the oxide composite contained a predetermined amount of Ce.
Further, when observed by SEM under the following conditions, the coating of CeO ₂ does not exist uniformly on the surface of the lithium-containing composite oxide, but covers only a part of the surface. It was confirmed.
<SEM observation>
Apparatus: VE-9800 manufactured by KEYENCE Corporation
Acceleration voltage: 2.6 KV
Spot diameter: 6 (set value of the device)
Degree of vacuum: 3Pa
Detector: Secondary electron detector A sample was fixed to a sample stage using a conductive double-sided tape, and observed at a magnification of 10,000 times under non-deposition conditions.

[Example 4]
In this example, surface coating with CeO ₂ and Y ₂ O ₃ was performed on the lithium-containing composite oxide prepared in <Preparation of lithium-containing composite oxide by coprecipitation method>.
Using Ce (NO ₃ ) ₃ · 6H ₂ O as the Ce source and Y (NO ₃ ) ₃ · 6H ₂ O as the Y source, an oxide composite that finally obtains the sum of CeO ₂ and Y ₂ O ₃ Preparation was carried out in the same manner as in Example 3 except that the raw material was used in an amount and a proportion such that the molar ratio of Ce / Y was 99/1 with respect to the body, and the Ce / Y molar ratio was 99/1. An oxide composite surface-coated with ₂ and Y ₂ O ₃ was obtained.
As a result of ICP measurement, it was confirmed that the obtained oxide composite contained a predetermined amount of Ce and Y. As a result of SEM observation, it was confirmed that the CeO ₂ coating was not uniform and only a part of the surface of the lithium-containing composite oxide was coated.

[Comparative Example 1]
In Comparative Example 1, a non-aqueous lithium ion secondary battery was produced using the lithium-containing composite oxide obtained in <Preparation of lithium-containing composite oxide by gelation combustion method> as a positive electrode active material, and evaluated. did.

[Comparative Example 2]
In Comparative Example 2, a non-aqueous lithium ion secondary battery was produced and evaluated using the lithium-containing composite oxide obtained in <Preparation of lithium-containing composite oxide by coprecipitation method> as a positive electrode active material as it was. .

[Comparative Example 3]
In Comparative Example 3, a non-aqueous lithium ion secondary battery was produced using the lithium-containing composite oxide obtained in <Preparation of lithium-containing composite oxide by solid-phase synthesis method> as a positive electrode active material and evaluated. did.

  Initial discharge capacity of non-aqueous lithium ion secondary batteries produced in Examples 1 to 4 and Comparative Examples 1 to 3, discharge capacity at 0.3 C, discharge capacity at 5 C, and 5 C / 0.3 C discharge capacity ratio Is shown in Table 1.

  From the results shown in Table 1, the lithium ion secondary battery using an active material using an oxide composite containing a predetermined metal oxide of the present invention has a high electric capacity and a high rate characteristic. It was confirmed that both capacity and high rate characteristics were compatible.

Nonaqueous lithium ion secondary batteries obtained using the oxide composite of the present invention as a positive electrode active material include, for example, mobile devices such as mobile phones, mobile audio devices, personal computers, and IC tags;
Rechargeable batteries for automobiles such as hybrid cars, plug-in hybrid cars, and electric cars;
Furthermore, it can be suitably used in a residential power storage system.

100 Nonaqueous lithium ion secondary battery 110 Separator 120 Positive electrode 130 Negative electrode 140 Positive electrode current collector 150 Negative electrode current collector 160 Battery exterior

Claims (8)

The following composition formula (1):
Li ₂ Mn _1-x M ′ _x O _3-α (1)
{In the formula, M ′ is one or more metal elements other than Mn and Li, and satisfies the relationship of 0 ≦ x <1 and 0 ≦ α <1. Lithium-containing composite oxide Li represented has a layered crystal structure arranged in a layered in} and (A),
An oxide complex comprising metallic oxide and (B),
The metal oxide (B) is an oxide of a metal containing cerium, and the metal oxide (B) is present homogeneously with the lithium-containing composite oxide (A) in the oxide composite. Or the lithium-containing composite oxide (A) is coated, and
When lithium-containing composite oxide (A) was subjected to Mn line analysis using an energy dispersive X-ray detector, the following formula: Element dispersion width (%) = (maximum intensity−minimum intensity) / average intensity × 100
An oxide composite for a positive electrode active material of a non-aqueous lithium ion secondary battery, wherein the element dispersion width defined by the above is 50% or less.   The oxide composite according to claim 1, wherein the content of the metal oxide (B) is 0.5 to 5.0 mass% with respect to the entire oxide composite. The oxide composite according to claim 1, which is the metal oxide (B) cerium oxide. The lithium-containing composite oxide (A) is
A layered crystal structure represented by the composition formula (1);
The following composition formula (2):
Li _{1 + k} Mn _2-y Me ′ _y O _4-γ (2)
{In the formula, Me ′ is one or more metal elements other than Mn and Li, and satisfies the relationship of 0 ≦ k <1, 0 ≦ y ≦ 0.5, and 0 ≦ γ <1. } And the following composition formula (3):
LiMeO ₂ (3)
{Wherein Me is one or more metal elements other than Li. The oxidation according to any one of claims 1 to 3, which has a crystal structure in which one or more crystal structures selected from a layered crystal structure in which Li represented by Compound complex.   A positive electrode active material for a non-aqueous lithium ion secondary battery, comprising the oxide composite according to claim 1.   A non-aqueous lithium ion secondary battery comprising the positive electrode active material according to claim 5.   The flammable gel comprising a metal salt having an oxidizable ligand and a metal salt having a flammable ligand is subjected to heat treatment to thermally decompose the flammable gel. A method for producing an oxide composite, comprising obtaining the oxide composite according to any one of the above. A precipitate obtained by adding an alkali to an aqueous solution containing a metal salt that is a precursor of the lithium-containing composite oxide (A) is dried and fired to obtain the lithium-containing composite oxide (A).
Next, the lithium-containing composite oxide (A) is baked after contacting with a solution containing a precursor of the metal oxide (B), thereby oxidizing according to any one of claims 1 to 4. A method for producing an oxide composite, characterized in that an oxide composite is obtained.

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