JP2015022958A - Positive electrode active material, and lithium battery containing positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material whose discharge capacity is increased than conventional one by being used in a lithium battery.SOLUTION: A positive electrode active material belongs to a space group Fm-3m and is represented by the composition formula (1) : LiNiCoMnTiO(In the composition formula (1), x, y, and z are real numbers satisfying 0<x≤0.05, 0.1<y≤0.2 and 0<z≤0.5. Moreover, in the composition formula (1), a and b are real numbers satisfying 0<a≤2 and 0<b≤4) in which there is deficiency in a part of at least transition metal element selected from the group of nickel, cobalt and manganese.

Description

  The present invention relates to a positive electrode active material that is used in a lithium battery to increase the discharge capacity as compared with the prior art, and a lithium battery including the positive electrode active material.

It is known that a polyanionic compound capable of reversibly inserting and desorbing lithium is used for a positive electrode active material of a lithium battery. Patent Document 1 includes carbon particles and a polyanionic compound having a composition represented by _a chemical formula: Li _a MXO ₄ (M is Mn, Co, Ni, etc.), and has an average primary particle size of 0.03 to 1. An active material comprising 4 μm and compound particles supported on the carbon particles is disclosed.

JP 2010-087772 A

Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄ is known as _{one of} Li _a MXO ₄ type polyanionic compounds described in Patent Document 1. However, in the case of Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄ belonging to the space group Fm-3m, since the discharge capacity may be low, it has not been put into practical use.
The present invention has been accomplished in view of the above circumstances, and provides a positive electrode active material that increases discharge capacity compared to the prior art when used in a lithium battery, and a lithium battery including the positive electrode active material. Objective.

The positive electrode active material of the present invention is represented by the following composition formula (1), which belongs to the space group Fm-3m and is partially deficient in at least one transition metal element selected from the group consisting of nickel, cobalt, and manganese. It is characterized by that.
_{Li a Ni x Co y Mn z} TiO b compositional formula (1)
(In the composition formula (1), x, y, and z are real numbers that satisfy 0 <x ≦ 0.05, 0.1 <y ≦ 0.2, and 0 <z ≦ 0.5. In the composition formula (1), a and b are real numbers that satisfy 0 <a ≦ 2 and 0 <b ≦ 4.)

  The lithium battery of the present invention is a lithium battery comprising a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein the positive electrode contains at least the positive electrode active material. .

  According to the present invention, when the positive electrode active material is used in a lithium battery, it has a lithium ion diffusion hindrance by having a chemical composition in which at least one transition metal element of nickel, cobalt, and manganese is deficient. It can be reduced and the discharge capacity can be increased as compared with the conventional lithium battery.

The arrangement of atoms of _{Li a Ni x Co y Mn z} TiO b according to the present invention is a diagram schematically showing. It is a figure which shows an example of the laminated constitution of the lithium battery of this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. 4 is a graph showing XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1 side by side. 2 is a TEM image of the positive electrode active material of Example 1. 2 is a charge / discharge curve of the lithium battery of Example 2. FIG. 4 is a bar graph comparing the first discharge capacity (actual capacity) of lithium batteries of Example 2 and Comparative Example 2. FIG. The sequence of the conventional _{Li 2 Ni 1/3 Co 1/3 Mn 1/3} TiO 4 atoms is a diagram schematically showing.

1. Positive electrode active material The positive electrode active material of the present invention belongs to the space group Fm-3m, and at least one transition metal element selected from the group consisting of nickel, cobalt, and manganese is partially lost in the following composition formula (1) It is represented by.
_{Li a Ni x Co y Mn z} TiO b compositional formula (1)
(In the composition formula (1), x, y, and z are real numbers that satisfy 0 <x ≦ 0.05, 0.1 <y ≦ 0.2, and 0 <z ≦ 0.5. In the composition formula (1), a and b are real numbers that satisfy 0 <a ≦ 2 and 0 <b ≦ 4.)

In general, the conventional Li ₂ MTiO ₄ -based positive electrode active material can obtain only a practical amount of about half the theoretical capacity. Although the conventional Li ₂ MTiO ₄ positive electrode active material has a lithium ion diffusion path in its chemical structure, there is a problem that a sufficient amount of lithium ions does not diffuse when used in a lithium battery. This is presumably because the diffusion coefficient of lithium ions in the conventional Li ₂ MTiO ₄ positive electrode active material is low, and a sufficient amount of lithium ion diffusion paths are not always secured.
Theoretically, lithium ions should diffuse by 2 moles with respect to ₄ moles of Li ₂ MTiO. However, in the conventional Li ₂ MTiO ₄ positive electrode active material, an example in which 2 mol of lithium ions diffuse is not known. Here, examples in which lithium ions diffuse by 2 moles are examples of a charging reaction involving two electrons as shown in the following formula (A), and two electrons that are the reverse reaction of the following formula (A). It refers to an example of the discharge reaction involved.
_{Li 2 MTiO 4 → MTiO 4 +} 2Li + + 2e - formula (A)

LiCoO ₂ conventionally used in lithium batteries has a rock salt structure in which lithium layers and cobalt layers are alternately stacked. Therefore, in LiCoO ₂ , lithium ions diffuse two-dimensionally in the lithium layer. On the other hand, Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄ has a different chemical structure from LiCoO ₂ .
FIG. 7 is a diagram schematically showing the arrangement of atoms of conventional Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄ . The circles in FIG. 7 represent each atom, the squares separating the circles represent the sites occupied by each atom in the crystal structure, and the thin arrows represent the lithium ion diffusion path. FIG. 7 is a schematic diagram for simply explaining the lithium ion diffusion path, and does not always accurately represent the actual chemical structure of Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO _4. Absent.
As shown in FIG. 7, in the conventional Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄ (300), lithium, nickel, cobalt, manganese, and titanium are irregularly arranged at equivalent sites. Has a structure. Therefore, Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄ does not have an ion diffusion path in which lithium atoms are regularly linked, like the lithium layer in LiCoO ₂ .

  As a result of trial and error aimed at improving the diffusion coefficient of lithium ions, the present inventor diffuses lithium ions through sites normally occupied by transition metal elements such as nickel, cobalt, and manganese, which are obstacles to lithium ion diffusion. I came up with a structure to do. As a result of diligent efforts, the present inventor partially introduces a defect into a site normally occupied by the transition metal element, that is, by removing the transition metal element from a part of the site, Improves lithium ion conductivity of the positive electrode active material and improves the discharge capacity when the positive electrode active material is used in a lithium battery while reducing obstacles and increasing the diffusion path when lithium ions diffuse Succeeded. In addition, when the present inventor uses the positive electrode active material for a lithium battery, the site into which the defect is introduced functions as a site for occluding and releasing lithium ions, which contributes to an improvement in charge / discharge capacity. And the present invention was completed.

  The positive electrode active material according to the present invention is represented by the composition formula (1), belongs to the space group Fm-3m, and lacks a transition metal element. Here, the space group Fm-3m refers to a space group of crystals having a so-called rock salt structure.

In the composition formula (1), x, y, and z are real numbers that satisfy 0 <x ≦ 0.05, 0.1 <y ≦ 0.2, and 0 <z ≦ 0.5. Here, the fact that the sum of x, y, and z is always less than 1 represents a transition metal element defect in the present invention. In the present invention, the composition ratio y of cobalt is larger than the composition ratio x of nickel.
In the composition formula (1), x, y, and z are real numbers that satisfy 0.03 ≦ x ≦ 0.05, 0.12 ≦ y ≦ 0.17, and 0.30 <z ≦ 0.45. Preferably there is.

  In the composition formula (1), a and b are real numbers that satisfy 0 <a ≦ 2 and 0 <b ≦ 4. If a exceeds 2, or b exceeds 4, the chemical structure belonging to the space group Fm-3m may not be maintained. It is preferable that a and b satisfy 1.5 ≦ a ≦ 2 and 3.5 ≦ b ≦ 4.

FIG. 1 is a diagram schematically showing the arrangement of atoms of Li _a Ni _x Co _y Mn _z TiO _{b according to} the present invention. The solid line circles, squares separating the circles, and thin arrows in FIG. 1 are the same as those in FIG. In addition, the broken-line circle in FIG. 1 indicates that the transition metal element in the site is deficient, and the thick arrow superimposed on the broken-line circle indicates the lithium ion diffusion path through the site. Each is shown. FIG. 1 is a schematic diagram for simply explaining the lithium ion diffusion path, and does not necessarily accurately represent the actual chemical structure of the positive electrode active material according to the present invention.
As can be seen from a comparison between FIG. 1 and FIG. 7, Li _a Ni _x Co _y Mn _z TiO _b (100) according to the present invention has a site in which a transition metal element is deficient. Therefore, in the past, lithium ions diffused through a long detour as in the case of sewing between transition metal elements, whereas in the present invention, lithium ions diffused through empty sites, It is considered that the lithium ion diffusion barrier is reduced and the lithium ion conductivity is improved. Although not specifically illustrated in FIG. 1, when the _{Li a Ni x Co y Mn z} TiO b according to the present invention is used for a lithium battery, by which the empty site occluding and releasing lithium ions, conventional The discharge capacity can be improved as compared with lithium batteries.

  The average particle diameter of the positive electrode active material according to the present invention is, for example, preferably in the range of 1 to 50 μm, more preferably in the range of 1 to 20 μm, and particularly preferably in the range of 3 to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because there is. In addition, the average particle diameter of the positive electrode active material according to the present invention is obtained by measuring the particle diameter of the positive electrode active material observed with, for example, a transmission electron microscope (TEM) or a scanning electron microscope (SEM) and averaging the average particle diameter. It can ask for.

The method for producing the positive electrode active material according to the present invention is as follows.
First, a lithium compound, a nickel compound, a cobalt compound, a manganese compound, and a titanium compound are prepared as raw materials. Note that it is not always necessary to prepare all these five types of compounds as raw materials. For example, when the lithium compound contains a cobalt element, it is not always necessary to prepare another cobalt compound.
Examples of the lithium compound include lithium carbonate (Li ₂ CO ₃ ), lithium acetate (CH ₃ CO ₂ Li), lithium nitrate (LiNO ₃ ), and hydrates thereof.
Examples of the nickel compound include nickel hydroxide (II) (Ni (OH) ₂ ), nickel acetate (II) (Ni (CH ₃ CO ₂ ) ₂ ), nickel nitrate (II) (Ni (NO ₃ ) ₂ ). Nickel (II) sulfate (NiSO ₄ ), nickel (II) oxalate (NiC ₂ O ₄ ), nickel chloride (II) (NiCl ₂ ), and hydrates thereof.
Examples of the cobalt compound include cobalt hydroxide (II) (Co (OH) ₂ ), cobalt acetate (II) (Co (CH ₃ CO ₂ ) ₂ ), and cobalt nitrate (II) (Co (NO ₃ ) ₂ ). , Cobalt sulfate (II) (CoSO ₄ ), cobalt oxalate (II) (CoC ₂ O ₄ ), cobalt chloride (II) (CoCl ₂ ), and hydrates thereof.
Examples of the manganese compound include manganese oxide (II) (MnO), manganese (II) acetate (Mn (CH ₃ CO ₂ ) ₂ ), manganese nitrate (II) (Mn (NO ₃ ) ₂ ), manganese sulfate (II ) (MnSO ₄ ), manganese (II) oxalate (MnC ₂ O ₄ ), manganese chloride (II) (MnCl ₂ ), and hydrates thereof.
Examples of the titanium compound include titanium oxide (II) (TiO), titanium dioxide (IV) (TiO ₂ ), tetraisopropyl orthotitanate (Ti (OCH (CH ₃ ) ₂ ) ₄ ), and tetrabutoxy titanium (IV). (Ti (OC ₄ H ₉ ) ₄ ), dititanium trioxide (III) (Ti ₂ O ₃ ), and hydrates thereof.

  The mixing ratio of the raw materials is preferably matched to the composition ratio of each element in the composition formula (1). Specifically, from the above composition formula (1), the ratio of each metal element in the positive electrode active material is Li: Ni: Co: Mn: Ti = a: x: y: z: 1 (a, x, y , Z is as described above). Therefore, what is necessary is just to adjust the mixing ratio of each raw material so that the composition after mixing may follow the ratio of the said metal element.

  When mixing the raw materials, it is preferable to dissolve or disperse the raw materials in an acid solution. The acid solution suitably used in the present invention is not particularly limited as long as it can dissolve most of the above raw materials, and specifically, nitric acid, acetic acid, sulfuric acid, perchloric acid, hydrochloric acid, hypochlorous acid. An acid etc. are mentioned. Of these, nitric acid is preferred from the viewpoint of high ability to dissolve the above-mentioned raw materials.

When mixing the above raw materials, organic substances may be further mixed. The organic substance plays a role of suppressing undesirable particle growth when heat treatment is performed for the purpose of crystallization.
Examples of organic substances that can be mixed with the above raw materials include glycolic acid, citric acid, ascorbic acid, stearic acid, carboxylic acid, and oleic acid. These organic substances may be used alone or in combination of two or more. Among these, it is preferable to use glycolic acid from the viewpoint of good handleability and ease of removal.

  The order of mixing the raw materials and organic substances is not particularly limited. Each of the above raw materials and organic substances may be mixed at one time, or may be mixed one by one in order. In addition, when using the said organic substance, it is preferable to mix raw materials and organic substances other than a titanium compound first, and to mix a titanium compound in the said mixture after that.

  The above mixture may be gelled by distilling off water by heating appropriately while stirring. The heating temperature at this time should just be about 60-100 degreeC.

In this production method, the target positive electrode active material is obtained by heating the mixture (or gel thereof).
The heating method is not particularly limited, but firing is preferably performed in an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere. The firing temperature is preferably 500 to 1,100 ° C, and more preferably 700 to 1,000 ° C. The firing time is preferably 5 to 48 hours, and more preferably 10 to 24 hours.
When an organic substance such as glycolic acid is used, the mixture is preferably preliminarily heat treated to decompose and remove the organic substance, and then the baking is performed. In the preliminary heat treatment, the heating method is not particularly limited, and may be in the air. The firing temperature is preferably 100 to 500 ° C, and more preferably 200 to 400 ° C. The firing time is preferably 5 to 48 hours, and more preferably 10 to 24 hours.

2. The lithium battery of the present invention is a lithium battery comprising a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein the positive electrode contains at least the positive electrode active material. And
Since the positive electrode active material has excellent lithium ion conductivity and high discharge capacity, a lithium battery including the positive electrode active material can exhibit good discharge characteristics.

FIG. 2 is a diagram showing an example of a layer configuration of the lithium battery according to the present invention, and is a diagram schematically showing a cross section cut in the stacking direction. The lithium battery according to the present invention is not necessarily limited to this example.
The lithium battery 200 includes a positive electrode 6 including a positive electrode active material layer 2 and a positive electrode current collector 4, a negative electrode 7 including a negative electrode active material layer 3 and a negative electrode current collector 5, and an electrolyte layer sandwiched between the positive electrode 6 and the negative electrode 7. 1 is provided.
Hereinafter, the positive electrode, the negative electrode, and the electrolyte layer used in the lithium battery according to the present invention, and the separator and battery case suitably used in the lithium battery according to the present invention will be described in detail.

  The positive electrode used in the present invention preferably comprises a positive electrode active material layer containing the positive electrode active material described above, and in addition to this, in general, connected to the positive electrode current collector and the positive electrode current collector. A positive lead is provided.

In the present invention, the above-described positive electrode active material according to the present invention is used. In the present invention, only the positive electrode active material according to the present invention described above may be used alone, or the positive electrode active material may be used in combination with one or more other positive electrode active materials. .
As other positive electrode active materials, specifically, LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoMnO ₄ , Li ₂ NiMn ₃ O ₈ , Li ₃ Fe ₂ (PO ₄ ) _3, Li ₃ V ₂ (PO ₄ ) _{3 and the} like can be mentioned. On the surface of fine particles composed of the positive electrode active material may be coated with LiNbO ₃ or the like.
The total content of the positive electrode active material in the positive electrode active material layer is usually in the range of 50 to 90% by mass.

  The thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the lithium battery, but is preferably in the range of 0.1 to 250 μm, and in the range of 1 to 20 μm. Is particularly preferred, and most preferred is in the range of 3 to 10 μm.

The positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
The conductive material used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved. Examples thereof include carbon black such as acetylene black and ketjen black. it can. Moreover, although the content rate of the electroconductive material in a positive electrode active material layer changes with kinds of electroconductive material, it is in the range of 1-30 mass% normally.

Examples of the binder used in the present invention include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). In addition, the content of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content rate of a binder is in the range of 1-10 mass% normally.
In addition, a dispersion medium such as N-methyl-2-pyrrolidone or acetone may be used for preparing the positive electrode active material.

  The positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer. Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Among these, aluminum and SUS are preferable. Moreover, as a shape of a positive electrode electrical power collector, foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.

  The method for producing the positive electrode used in the present invention is not particularly limited as long as it is a method capable of obtaining the positive electrode. In addition, after forming a positive electrode active material layer, in order to improve an electrode density, you may press a positive electrode active material layer.

  The negative electrode used in the present invention preferably comprises a negative electrode active material layer containing a negative electrode active material, and in addition to this, in general, a negative electrode current collector, and a negative electrode lead connected to the negative electrode current collector Is provided.

The negative electrode active material used in the present invention is not particularly limited as long as it can occlude and / or release lithium ions. For example, lithium metal, a lithium alloy, a metal oxide containing lithium element, and lithium element can be used. Examples thereof include metal sulfides contained, metal nitrides containing lithium element, and carbon materials such as graphite. The negative electrode active material may be in the form of a powder or a thin film.
Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy. Moreover, as a metal oxide containing a lithium element, lithium titanium oxide etc. can be mentioned, for example. Examples of the metal nitride containing a lithium element include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. As the negative electrode active material, lithium coated with a solid electrolyte can also be used.

The negative electrode active material layer may contain only the negative electrode active material, or may contain at least one of a conductive material and a binder in addition to the negative electrode active material. For example, when the negative electrode active material has a foil shape, a negative electrode active material layer containing only the negative electrode active material can be obtained. On the other hand, when the negative electrode active material is in a powder form, a negative electrode active material layer having a negative electrode active material and a binder can be obtained. Note that the conductive material and the binder are the same as the conductive material or the binder contained in the positive electrode active material layer described above, and thus description thereof is omitted here.
Although it does not specifically limit as a film thickness of a negative electrode active material layer, For example, it is preferable to exist in the range of 10-100 micrometers, especially in the range of 10-50 micrometers.

  The electrode active material layer of at least one of the positive electrode and the negative electrode can also be configured to contain at least an electrode active material and an electrode electrolyte. In this case, as the electrode electrolyte, a solid electrolyte such as a solid oxide electrolyte or a solid sulfide electrolyte as described later, a gel electrolyte, or the like can be used.

  As the material for the negative electrode current collector, the same materials as those for the positive electrode current collector described above can be used. Moreover, as a shape of a negative electrode collector, the thing similar to the shape of the positive electrode collector mentioned above is employable.

  The method for producing the negative electrode used in the present invention is not particularly limited as long as the method can obtain the negative electrode. In addition, after forming a negative electrode active material layer, in order to improve an electrode density, you may press a negative electrode active material layer.

The electrolyte layer used in the present invention is held between the positive electrode and the negative electrode, and functions to exchange lithium ions between the positive electrode and the negative electrode.
For the electrolyte layer, an electrolytic solution, a gel electrolyte, a solid electrolyte, or the like can be used. These may be used alone or in combination of two or more.

As the electrolytic solution, a non-aqueous electrolytic solution and an aqueous electrolytic solution can be used.
As the non-aqueous electrolyte, one containing a lithium salt and a non-aqueous solvent is usually used. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO _4, and LiAsF ₆ ; LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ (Li-TFSA), LiN (SO ₂ C ₂ F ₅ ) Organic lithium salts such as ₂ and LiC (SO ₂ CF ₃ ) ₃ can be mentioned. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl carbonate, butylene carbonate, γ-butyrolactone, and sulfolane. , Acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO) and A mixture thereof can be exemplified. The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 to 3 mol / kg.

  In the present invention, for example, an ionic liquid or the like may be used as the nonaqueous electrolytic solution or the nonaqueous solvent. Examples of the ionic liquid include N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) amide (PP13TFSA), N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) amide (P13TFSA), N-butyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) amide (P14TFSA), N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) amide (DEMETFSA) N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) amide (TMPATFSA) and the like.

As the aqueous electrolyte, one containing a lithium salt and water is usually used. Examples of the lithium salt include lithium salts such as LiOH, LiCl, LiNO ₃ , and CH ₃ CO ₂ Li.

The gel electrolyte used in the present invention is usually gelled by adding a polymer to a non-aqueous electrolyte solution. The non-aqueous gel electrolyte is prepared by adding a polymer such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyurethane, polyacrylate, and / or cellulose to the non-aqueous electrolyte solution described above. It is obtained by gelling. In the present invention, a LiTFSA (LiN (CF ₃ SO ₂ ) ₂ ) -PEO-based non-aqueous gel electrolyte is preferable.

As the solid electrolyte, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer electrolyte, or the like can be used.
Specific examples of the sulfide-based solid electrolyte include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₃ , Li ₂ S—P ₂ S ₃ —P ₂ S ₅ , and Li ₂ S—SiS. _{2, Li 2 S-Si 2} S, Li 2 S-B 2 S 3, Li 2 S-GeS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 S-SiS 2 -P 2 S 5 _{, Li 2 S-SiS 2 -Li} 4 SiO 4, Li 2 S-SiS 2 -Li 3 PO 4, Li 3 PS 4 -Li 4 GeS 4, Li 3.4 P 0.6 Si 0.4 S 4, Examples include Li _3.25 P _0.25 Ge _0.76 S ₄ , Li _4-x Ge _1-x P _x S _{4, and the} like.
Specifically, as the oxide-based solid electrolyte, LiPON (lithium phosphate oxynitride), Li _1.3 Al _0.3 Ti _0.7 (PO ₄ ) ₃ , La _0.51 Li _0.34 TiO Examples include _0.74 , Li ₃ PO ₄ , Li ₂ SiO ₂ , Li ₂ SiO _{4 and the} like.
The polymer electrolyte usually contains a lithium salt and a polymer. As the lithium salt, at least one of the above-described inorganic lithium salt and organic lithium salt can be used. The polymer is not particularly limited as long as it forms a complex with a lithium salt, and examples thereof include polyethylene oxide.

  The lithium battery according to the present invention may include a separator impregnated with an electrolytic solution between the positive electrode and the negative electrode. Examples of the separator include porous films such as polyethylene and polypropylene; and nonwoven fabrics such as a resin nonwoven fabric and a glass fiber nonwoven fabric.

  The lithium battery according to the present invention usually includes a battery case that houses the positive electrode, the negative electrode, the electrolyte layer, and the like. Specific examples of the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminate type.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

1. Synthesis of positive electrode active material [Example 1]
First, lithium acetate (CH ₃ CO ₂ Li), nickel (II) acetate (Ni (CH ₃ CO ₂ ) ₂ ), cobalt acetate (II) (Co (CH ₃ CO ₂ ) ₂ ), manganese acetate in nitric acid (II) (Mn (CH ₃ CO ₂ ) ₂ ) and glycolic acid (CH ₂ (OH) CO ₂ H) were dissolved. The mixing ratio (molar ratio) of the metal compound at this time was lithium acetate: nickel acetate (II): cobalt acetate (II): manganese acetate (II) = 2: 0.05: 0.15: 0.38. . Thus, when the molar ratio of lithium is set to 2, the total molar ratio of nickel, cobalt, and manganese is less than 1, so that a part of these transition metal elements is lost in the positive electrode active material obtained. It was made to become.

Titanium dioxide (IV) (TiO ₂ ) was added and dispersed in the resulting solution. At this time, when the addition amount (molar ratio) of lithium acetate was 2, the addition amount (molar ratio) of titanium oxide was set to 1.
By stirring the solution to which titanium oxide was added while maintaining at 80 ° C., the water was appropriately evaporated to cause gelation. The obtained gel was collected and heat treated at 350 ° C. for 10 hours in the air to remove organic substances such as glycolic acid. The powder obtained after the heat treatment was further heat-treated at 900 ° C. for 10 hours under an argon atmosphere, so that the positive electrode active material (Li ₂ Ni _0.05 Co _0.15 Mn _0.38 TiO ₄ ) of Example 1 was obtained. Synthesized.

[Comparative Example 1]
First, in acetone, lithium carbonate (Li ₂ CO ₃ ), nickel hydroxide (II) (Ni (OH) ₂ ), cobalt hydroxide (II) (Co (OH) ₂ ), manganese oxide (II) (MnO ) And titanium dioxide (IV) (TiO ₂ ). The mixing ratio (molar ratio) of the metal compound at this time was as follows: lithium carbonate: nickel hydroxide (II): cobalt hydroxide (II): manganese oxide (II): titanium dioxide (IV) = 1: (1/3) : (1/3) :( 1/3): 1. Thus, in the positive electrode active material obtained by making the total molar ratio of nickel, cobalt, and manganese equal to 1 when the molar ratio of lithium is 2 (that is, the molar ratio of lithium carbonate is 1), The composition was such that the transition metal element was not lost.

The obtained dispersion was subjected to a ball mill, and the metal compound in the dispersion was pulverized and mixed at 200 rpm for 3 hours. After ball milling, acetone in the dispersion was distilled off. The obtained powder was heat-treated at 900 ° C. for 24 hours under an argon atmosphere to synthesize the positive electrode active material (Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄ ) of Comparative Example 1.

2. XRD Measurement of Positive Electrode Active Material For the positive electrode active materials of Example 1 and Comparative Example 1, X-ray diffraction (XRD) measurement was performed. Detailed measurement conditions are as follows.
X-ray diffractometer RINT-2500 (Rigaku)
Measurement range 2θ = 10-100 °
Measurement interval 0.02 °
Scanning speed 2 ° / min
Measurement voltage 50kV
Measurement current 300mA

FIG. 3 is a graph showing the XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1 side by side.
As can be seen from the lower spectrum of FIG. 3, in the XRD pattern of Comparative Example 1, sharp peaks are observed at 2θ = 38 °, 43 °, 63 °, 76 °, 80 °, and 95 °, respectively. These peaks indicate that the crystal structure of the positive electrode active material of Comparative Example 1 belongs to the space group Fm-3m. The peak at 2θ = 38 ° is the diffraction of (111) plane, the peak at 2θ = 43 ° is the diffraction of (200) plane, the peak at 2θ = 63 ° is the diffraction of (220) plane, and 2θ = 76. The peak at ° is attributed to diffraction on the (311) plane, and the peak at 2θ = 80 ° is attributed to diffraction at the (222) plane.
On the other hand, as can be seen from the upper spectrum of FIG. 3, in the XRD pattern of Example 1, as in Comparative Example 1, 2θ = 38 °, 43 °, 63 °, 76 °, 80 °, and 95 °. Each sharp peak is observed. Therefore, FIG. 3 shows that the crystal structure of the positive electrode active material of Example 1 also belongs to the space group Fm-3m.
As described above, even if a part of the transition metal element is missing as in Example 1 (that is, even if the sum of the composition ratios of nickel, cobalt, and manganese is less than 1), It was confirmed that a crystal structure belonging to the same space group Fm-3m was taken.

3. TEM observation and EDS measurement of positive electrode active material The mass ratio of nickel, cobalt, manganese, and titanium in the positive electrode active material was measured by TEM observation and EDS measurement. Detailed measurement conditions are as follows.
Using a field emission transmission electron microscope (manufactured by JEOL Ltd., model number: JEM-2100F, attached with Cs correction), TEM observation was performed at an acceleration voltage of 200 kV and a magnification of 450,000 times.
Energy dispersive X-ray spectroscopy (EDS) using a field emission transmission electron microscope (manufactured by JEOL, model number: JEM-2100F, with Cs correction) equipped with a UTW type Si (Li) semiconductor detector (manufactured by JEOL) ), And the mass ratio of nickel, cobalt, manganese, and titanium at the measurement points was calculated.

FIG. 4 is a TEM image (magnification 450,000 times) of the positive electrode active material of Example 1 obtained under the above observation conditions.
A thin and bright portion having a diameter of about 200 nm, which is seen in the center of FIG. 4, is a positive electrode active material. Regarding the surface (measurement point 1 in FIG. 4) and the inside (measurement point 2 in FIG. 4) of the positive electrode active material, mass ratios of nickel, cobalt, manganese, and titanium were measured. The results are shown in Table 1 below.

Table 1 shows the composition ratio (x, y, z) calculated from the semi-quantitative result in addition to the semi-quantitative result of each element by EDS analysis. From the results of Table 1 above, the positive electrode active material of Example 1 has almost no difference in composition between the surface and the inside, and each composition on the surface and inside is the target Li ₂ Ni _0.05 Co. It can be seen that it is substantially equal to _0.15 Mn _0.38 TiO ₄ (ie, x = 0.05, y = 0.15, z = 0.38).

4). Production of lithium battery [Example 2]
First, the positive electrode active material of Example 1 above as the positive electrode active material, acetylene black (trade name: HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material, and PVdF (manufactured by Kureha Co., Ltd., KR) as the binder. Polymer # 7305) was prepared for each. The positive electrode active material, the conductive material, and the binder were mixed so as to be positive electrode active material: conductive material: binder = 85% by mass: 10% by mass: 5% by mass to prepare a positive electrode mixture. . Further, N-methyl-2-pyrrolidone (manufactured by Nacalai Tesque) was appropriately added as a dispersion medium to the positive electrode mixture.
An aluminum foil was prepared as a positive electrode current collector.
A lithium metal foil (made by Honjo Metal) was prepared as the negative electrode. Moreover, SUS foil was prepared as a negative electrode collector.
As the electrolytic solution, 1 mol / L LiPF ₆ (solvent EC: DMC = 1: 1, manufactured by Kishida Chemical Co., Ltd.) was prepared.
A coin cell (SUS2032 type) was prepared as a battery case. The above materials were housed in a battery case in the order of aluminum foil, positive electrode mixture layer, electrolytic solution, lithium metal foil, and SUS foil, to produce a lithium battery of Example 2.
All the above steps were performed in a glove box under a nitrogen atmosphere.

[Comparative Example 2]
In Example 2, the same material as in Example 2 was used, except that the positive electrode active material in Comparative Example 1 was used instead of the positive electrode active material in Example 1 as a positive electrode active material. 2 lithium batteries were produced.

5. Charge / Discharge Test of Lithium Battery A charge / discharge test was performed on the lithium batteries of Example 2 and Comparative Example 2. Specifically, first, charging was performed in a constant current mode with 4.8V as the upper limit. Next, the battery was discharged to 2 V, and the obtained capacity was defined as the discharge capacity.

5 is a charge / discharge curve of the lithium battery of Example 2. FIG. FIG. 6 is a bar graph comparing the first discharge capacities (actual capacities) of the lithium batteries of Example 2 and Comparative Example 2.
6, the actual capacity of the lithium battery of Comparative Example 2 is 200 mAh / g, whereas the actual capacity of the lithium battery of Example 2 is 235 mAh / g, which is 18% higher than that of Comparative Example 2.
Thus, the reason why a high discharge capacity was obtained in the lithium battery of Example 2 was that the positive electrode active material (Example 1) used in Example 2 partially contained transition metal elements (Ni, Co, Mn). By having a deficient structure, it is possible to reduce obstacles when lithium ions diffuse, and to use the deficient site as a site for insertion and desorption of lithium ions, resulting in improved lithium ion conductivity. However, it is presumed that the number of sites where lithium ions are occluded and released is increased.

  Further, as can be seen from FIG. 5, the potential of the lithium battery of Example 2 during charging is 4 V or more. Therefore, it turns out that the positive electrode for lithium batteries containing the positive electrode active material which concerns on this invention has very high charge / discharge capacity also in what is called a high potential positive electrode.

_{Li a Ni x Co y Mn z} TiO b according to 1 the electrolyte layer 2 cathode active material layer 3 anode active material layer 4 cathode current collector 5 negative electrode current collector 6 positive 7 negative 100 invention
200 Lithium battery 300 Conventional Li ₂ Ni _1/3 Co _1/3 Mn _1/3 TiO ₄

Claims (2)

The positive electrode is represented by the following composition formula (1), which belongs to the space group Fm-3m and is partially deficient in at least one transition metal element selected from the group consisting of nickel, cobalt, and manganese. Active material.
_{Li a Ni x Co y Mn z} TiO b compositional formula (1)
(In the composition formula (1), x, y, and z are real numbers that satisfy 0 <x ≦ 0.05, 0.1 <y ≦ 0.2, and 0 <z ≦ 0.5. In the composition formula (1), a and b are real numbers that satisfy 0 <a ≦ 2 and 0 <b ≦ 4.) A lithium battery comprising a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode,
The said positive electrode contains the positive electrode active material of the said Claim 1 at least, The lithium battery characterized by the above-mentioned.