JP2014044897A - Lithium composite oxide and method for producing the same, positive electrode active material for secondary battery including the lithium composite oxide, positive electrode for secondary battery including the same, and lithium ion secondary battery using the same as positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium composite oxide with which, when the lithium composite oxide is used as a positive electrode active material, a lithium ion secondary battery high in discharge capacity per volume and excellent in cycle characteristics when used in an atmosphere at temperatures higher than room temperature can be obtained.SOLUTION: A hybrid type lithium composite oxide contains, as a main component, a particulate lithium composite oxide comprising a core and a shell covering the core. The core comprises a lithium composite oxide A containing, as a main component, at least one selected from the group consisting of a spinel-type lithium composite oxide, an inverse spinel-type lithium composite oxide, a silicate-type lithium composite oxide, and an olivine-type lithium composite oxide. The shell comprises a lithium composite oxide B containing, as a main component, a layered lithium composite oxide.

Description

  The present invention relates to a lithium composite oxide and a method for producing the same, a positive electrode active material for a secondary battery including the lithium composite oxide, a positive electrode for a secondary battery including the lithium active material, and a lithium ion secondary battery using the positive electrode.

  Lithium batteries have a high energy density compared to other batteries, are light and can be used for a long time, and are power sources for portable devices such as mobile phones, PHS and small computers, power storage power sources, electric vehicles Development is underway for use as a power source for automobiles.

Such a lithium battery includes a positive electrode made of a positive electrode active material containing a lithium-containing composite oxide, a negative electrode made of a material capable of occluding and releasing lithium such as carbon, and a separator containing a non-aqueous electrolyte. Alternatively, a solid electrolyte is provided as a main component.
Among these constituent elements, those studied as positive electrode active materials include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O _4). ) Etc. In particular, a battery using a lithium cobalt composite oxide as a positive electrode has been developed to obtain excellent initial capacity characteristics and cycle characteristics, and has already been put into practical use.
However, since cobalt is a rare resource, a lithium ion secondary battery using a lithium cobalt composite oxide for the positive electrode is expensive. Therefore, an alternative material that is cheaper than cobalt and can realize a high energy density has been demanded, and several proposals have already been made.

  For example, Patent Document 1 discloses a method for producing a composite positive electrode active material for a surface-treated nonaqueous electrolyte secondary battery, in which a positive electrode active material and a surface treatment component are mixed in advance, and then has a high-speed shearing action. A method for producing a positive electrode material, which is a lithium transition metal composite oxide for a non-aqueous electrolytic secondary battery, characterized in that it is coated with an apparatus is described.

Japanese Patent Laid-Open No. 2008-300339

  However, the discharge capacity per volume of the battery using the lithium composite oxide described in Patent Document 1 or the like as the positive electrode active material is not sufficiently high. Further, the present inventor has found that the battery using the lithium composite oxide described in Patent Document 1 or the like as the positive electrode active material has a problem that the cycle characteristics are low when used at a temperature higher than room temperature. .

  The present invention solves the problems of the conventional lithium composite oxide as described above. That is, when it is used as a positive electrode active material, a lithium composite battery capable of obtaining a lithium ion secondary battery having a high discharge capacity per volume and excellent cycle characteristics when used in a temperature atmosphere higher than room temperature. It is an object to provide an oxide and a method for producing the oxide. Moreover, it aims at providing the positive electrode active material containing such a lithium complex oxide. Moreover, it aims at providing the positive electrode for lithium ion secondary batteries using this positive electrode active material. Furthermore, it aims at providing the lithium ion secondary battery using this positive electrode.

The inventor has intensively studied to solve the above-mentioned problems, and has completed the present invention.
The present invention includes the following (1) to (11).
(1) A hybrid type lithium composite oxide mainly composed of particulate lithium composite oxide composed of a core and a shell covering the core,
The core is lithium mainly composed of at least one selected from the group consisting of spinel lithium composite oxide, reverse spinel lithium composite oxide, silicate lithium composite oxide, and olivine lithium composite oxide. Composed of complex oxide A,
The shell is a hybrid type lithium composite oxide comprising a lithium composite oxide B mainly composed of a layered lithium composite oxide.
(2) The hybrid lithium composite oxide according to the above (1), wherein the covering ratio of the shell to the core is 15% or more.
(3) The core is composed of a lithium composite oxide A mainly composed of a lithium composite oxide represented by the following formula (I):
The shell is a hybrid lithium composite oxide according to the above (1) or (2), which is composed of a lithium composite oxide B mainly composed of a lithium composite oxide represented by the following formula (II).
Formula (I): Li _{(x + y)} M ¹ _(2-yp) M ² _p O _(4-a)
Formula (II): Li _{(1 + z)} M ¹ _(1-zq) M ² _q O _(2-b)
However, in Formula (I) and Formula (II), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al, and Cr, and M ² is B, P, Pb , Sb, Si and V, at least one element selected from the group consisting of 1.0 ≦ x ≦ 2.0, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.34, 0 ≦ p ≦ 1 0.0, 0 ≦ q ≦ 1.0, 0 <1-zq, 0 ≦ a ≦ 1.0, and 0 ≦ b ≦ 1.0.
(4) The hybrid according to any one of (1) to (3), wherein the core is made of a lithium composite oxide A mainly composed of a spinel type lithium composite oxide represented by the formula (I). Type lithium composite oxide.
(5) The hybrid lithium composite oxide according to any one of (1) to (4), wherein a mass ratio of the core to the shell is 9.9: 0.1 to 6: 4.
(6) An adjustment step [1] in which the lithium source is pulverized and mixed in a solvent, and the resulting slurry is dried and fired to obtain the lithium composite oxide A;
An adjustment step [2] in which a lithium source is pulverized and mixed in a solvent, and the resulting slurry is dried and fired to obtain the lithium composite oxide B.
After obtaining the mixture containing the lithium composite oxide A and the lithium composite oxide B, a compressive force and a shear force are applied to the mixture, and the mixture according to any one of (1) to (5) above. A mechanofusion process for obtaining a hybrid lithium composite oxide;
A method for producing a hybrid lithium composite oxide.
(7) The mechano-fusion step is
After obtaining a mixture containing the lithium composite oxide A and the lithium composite oxide B, a compressive force and a shear force are applied to the mixture, and then the lithium composite oxide B is further added. The method for producing a hybrid lithium composite oxide according to (6), which is a step of applying a compressive force and a shearing force.
(8) A hybrid lithium composite oxide obtained by the production method described in (6) or (7) above.
(9) A positive electrode active material comprising the hybrid lithium composite oxide according to (1), (2), (3), (4), (5) or (8).
(10) A positive electrode for a lithium ion secondary battery using the positive electrode active material according to (9) above.
(11) A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to (10) above, a negative electrode, and an electrolytic solution.

  According to the present invention, when it is used as a positive electrode active material, a lithium ion secondary battery having a high discharge capacity per volume and excellent cycle characteristics when used in a temperature atmosphere higher than room temperature is obtained. It is possible to provide a lithium composite oxide and a method for producing the same. Moreover, the positive electrode active material containing such a lithium composite oxide can be provided. Moreover, the positive electrode for lithium ion secondary batteries using this positive electrode active material can be provided. Furthermore, a lithium ion secondary battery using this positive electrode can be provided.

2 is a SEM-EDS photograph of the hybrid lithium composite oxide obtained in Example 1. 4 is a SEM-EDS photograph of a hybrid type lithium composite oxide obtained in Example 2. 4 is a SEM-EDS photograph of a hybrid type lithium composite oxide obtained in Example 3.

The present invention will be described.
The present invention relates to a hybrid type lithium composite oxide composed mainly of a particulate lithium composite oxide composed of a core and a shell covering the core, wherein the core is a spinel type lithium composite oxide. , A lithium composite oxide A mainly composed of at least one selected from the group consisting of reverse spinel type lithium composite oxide, silicate type lithium composite oxide, and olivine type lithium composite oxide, The hybrid lithium composite oxide is composed of lithium composite oxide B mainly composed of layered lithium composite oxide.
Hereinafter, such a hybrid lithium composite oxide is also referred to as “the composite oxide of the present invention”.

<Composite oxide of the present invention>
The composite oxide of the present invention has a high tap density, and furthermore, a lithium ion secondary battery using the same as a positive electrode active material has excellent cycle characteristics at a temperature higher than room temperature (about 55 ° C.). Found. Since the tap density (g / ml) is high, the discharge capacity per unit volume (mAh / ml), which is the product of the tap density and the initial discharge capacity (mAh / g), becomes high. For example, when a secondary battery is used as a battery for an electric vehicle, it is important how much electricity can be stored in a limited space. Therefore, it is preferable that the discharge capacity per unit volume be higher. The secondary battery using the composite oxide of the present invention as the positive electrode active material has a high discharge capacity per unit volume and a cycle characteristic at a temperature higher than room temperature (hereinafter also simply referred to as “high temperature cycle characteristic”). Excellent.
The composite oxide of the present invention is presumed that when the surface of the spinel type lithium composite oxide is coated with the layered lithium composite oxide, the elution amount of Mn decreases and the high-temperature cycle characteristics tend to increase. .

The composite oxide of the present invention will be described.
The composite oxide of the present invention is mainly composed of a particulate lithium composite oxide composed of a core and a shell covering the core.

In the composite oxide of the present invention, the core is in a state where the shell covers the core, but the coverage (the coverage of the shell with respect to the core) is preferably 15% or more, and more preferably 18% or more. Preferably, it is more preferably 20% or more.
This is because it is possible to obtain a lithium ion secondary battery having a higher discharge capacity per volume and a more excellent cycle characteristic when used in a temperature atmosphere higher than room temperature.

The covering ratio of the shell to the core means a value obtained by measuring as follows.
X-ray photoelectron spectroscopy (XPS) measurement of each of the composite oxide and the layered lithium composite oxide of the present invention is performed, and the surface composition ratio of each Co / Mn is calculated from the spectrum area of Co _2p and Mn _3p . Then, the coverage is calculated from the following equation.
Coverage (%) = (Co / Mn composition ratio of composite oxide of the present invention) / (Co / Mn composition ratio of layered lithium composite oxide) × 100

Moreover, it is preferable that mass ratio of the said core and the said shell is 9.9: 0.1-6: 4, and it is more preferable that it is 9.5: 0.5-6.5: 3.5. 9: 1 to 7: 3 is more preferable.
This is because it is possible to obtain a lithium ion secondary battery having a higher discharge capacity per volume and a more excellent cycle characteristic when used in a temperature atmosphere higher than room temperature.

  The composite oxide of the present invention has a particulate lithium composite oxide composed of the core and the shell as a main component. Here, the “main component” has a content of 70% by mass or more. Means that. That is, in the composite oxide of the present invention, the content of the particulate lithium composite oxide composed of the core and the shell is 70% by mass or more. This content is preferably 80% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 99% by mass or more, and 100% by mass. That is, the composite oxide of the present invention is more preferably composed of a particulate lithium composite oxide substantially composed of the core and the shell. Here, “substantially” means that impurities and damages inevitably included from the raw materials and the manufacturing process can be included. In the following description of the present invention, “main component” and “substantially” are used in this sense.

  The composite oxide of the present invention may include other than the particulate lithium composite oxide composed of the core and the shell. For example, the thing only of the said core (thing which does not have a shell), and the thing only of the said shell (thing which does not have a core) are mentioned.

<Core>
The core in the composite oxide of the present invention will be described.
In the composite oxide of the present invention, the core is at least one selected from the group consisting of spinel type lithium composite oxide, reverse spinel type lithium composite oxide, silicate type lithium composite oxide, and olivine type lithium composite oxide. It consists of lithium composite oxide A whose main component is one.

The spinel-type lithium composite oxide has a cubic structure and has a space group Fd-3m symmetry. In an ideal structure, it is considered that O (oxygen) which is an anion is close-packed in cubic, and cations are filled in the gaps.
In addition, a substitution-type spinel lithium composite oxide, which is sometimes referred to as a 5V type or 5V class, which has a high operating potential of 5V level, is also included in the spinel type lithium composite oxide in the present invention.
The spinel type lithium composite oxide is preferably a spinel type lithium composite oxide represented by the formula (I).
The spinel type lithium composite oxide represented by the formula (I) will be described in detail later.

The reverse spinel type lithium composite oxide takes a space group Fd-3m, and in the general formula of LiAMB ₄ (M is a transition element), A is a tetrahedral site, and M (transition element) and lithium are octahedral sites randomly. The structure which occupies is provided.
The reverse spinel type lithium composite oxide is preferably a reverse spinel type lithium composite oxide represented by the formula (I).
The reverse spinel type lithium composite oxide represented by the formula (I) will be described in detail later.

The silicate-type lithium composite oxide is expressed as Li ₂ MSiO ₄ (M: transition element such as Mn, Fe, Co, Ni, etc.), crystallographically belonging to orthorhombic crystal, space group Pmn2 ₁ , The structure is similar to Li ₃ PO ₄ . Oxygen atoms are bonded to Si by covalent bonds to form (SiO ₄ ) ^4- polyanions.
The silicate type lithium composite oxide is preferably a silicate type lithium composite oxide represented by the formula (I).
The silicate type lithium composite oxide represented by the formula (I) will be described in detail later.

The olivine type lithium composite oxide is expressed as LiMPO ₄ (M: transition element such as Mn, Fe, Co, Ni, etc.), crystallographically belonging to orthorhombic, space group Pnma (No. 62), MO ₆ octahedrons are connected zigzag by vertex sharing, forming a layer parallel to the bc plane, and this octahedron and PO ₄ tetrahedron are joined by vertex sharing, thereby forming a three-dimensional network. , M and P have a structure having a bond through O.
The olivine-type lithium composite oxide is preferably an olivine-type lithium composite oxide represented by the formula (I).
The olivine type lithium composite oxide represented by the formula (I) will be described in detail later.

  The core is preferably made of a lithium composite oxide A mainly composed of a lithium composite oxide represented by the following formula (I).

Formula (I): Li _{(x + y)} M ¹ _(2-yp) M ² _p O _(4-a)

  In the formula (I), x is in the range of 1.0 ≦ x ≦ 2.0, preferably 1.0 ≦ x ≦ 1.2, and 1.0 ≦ x ≦ 1.1. Is more preferable, and it is more preferable that x = 1.0. The closer x is to 1.0, the closer the lithium composite oxide is to the spinel type. The closer x is to 2.0, the closer the lithium composite oxide is to the silicate type.

In the formula (I), y is in the range of 0 ≦ y ≦ 0.2, preferably 0 <y ≦ 0.2, and more preferably 0.03 ≦ y ≦ 0.15.
y means the amount of Li substituted for M ¹ . In the composite oxide of the present invention, in the lithium composite oxide represented by the formula (I), a part of M ¹ is preferably substituted with Li. That is, it is preferable that excess Li is contained from the theoretical value of the number of atoms (composition ratio) of Li in the composition formula of the lithium composite oxide used as the positive electrode active material of the lithium ion battery. In this case, the structure is such that at least a part of Li is replaced with M ¹ by reducing the amount of M ^{1 by an} amount corresponding to a part or all of the excess Li.
When the substitution amount (y) of Li increases, the charge / discharge capacity of the battery slightly decreases, but the cycle characteristics at a higher temperature than normal temperature tend to be improved. However, even if y is larger than 0.2, the cycle characteristics at a temperature higher than normal temperature tend to be hardly improved. Moreover, when Li total amount (x + y) becomes less than 1.0, the heterogeneous phase which becomes an impurity will be produced | generated and there exists a tendency for the charge / discharge performance of a battery to fall.

In the formula (I), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al and Cr, and preferably contains Mn and / or Al.

2-yp which is the abundance of M ¹ is larger than 0. The lower limit of 2-yp is preferably 0.66, and more preferably 0.8. This is because the capacity cannot be maintained if 2-yp is too small.
Moreover, although the upper limit of 2-yp is 2.0, it is preferable that it is 1.95, and it is more preferable that it is 1.90. This is because if 2-yp is too large, the cycle characteristics deteriorate.

When M ¹ contains Mn, the formula (I) can be expressed as the following formula (I-1).
Formula _{(I-1): Li (} x + y) Mn (2-ypr) M 11 r M 2 p O (4-a)
In Formula (I-1), M ¹¹ is an element other than Mn in M ¹ , that is, at least one element selected from the group consisting of Ni, Co, Mg, Fe, Al, and Cr, and r is a substitution of M ¹¹ Means quantity, 0 ≦ r ≦ 2.0.
In addition, 0 <2-ypr. The preferable upper limit and the preferable lower limit of 2-ypr are the same as those of 2-yp described above.

(If it contains a plurality of kinds of element as M ^11, their sum) r is a replacement amount of M ¹¹ is preferably 0 ≦ r ≦ 1.0, more preferably 0.02 ≦ r ≦ 0.2, further Preferably it is about 0.1. This is because when used as a positive electrode active material, a certain discharge capacity can be secured and cycle characteristics at a temperature higher than normal temperature can be maintained. If the amount of M ¹¹ substitution is too large, the cycle characteristics at a higher temperature than the normal temperature of the battery when used as the positive electrode active material are improved, but the discharge capacity of the battery may be reduced.

In the formula (I), the element M ² is at least one element selected from the group consisting of B, P, Pb, Sb, Si and V. Of these, B is a preferred element.

(If it contains a plurality of kinds of element as M ² are their sum) p substituted amount of M ² is 0 ≦ p ≦ 1.0, preferably the upper limit is 0.1, 0.05 It is more preferable that This is because when used as a positive electrode active material, the cycle characteristics at a higher temperature than normal temperature tend to be improved. When the substitution amount p is too high, the discharge capacity of the lithium ion secondary battery when used as the positive electrode active material tends to decrease.
Note that p may be 0. In this case, the lithium composite oxide represented by the formula (I) does not contain M ² . That is, the lithium composite oxide represented by the formula (I) may have a composition represented by Li _{(x + y)} M ¹ _(2-y) O _(4-a) .

In the formula (I), a represents the amount of O (oxygen) deficiency.
In the formula (I), a satisfies 0 ≦ a ≦ 1.0 and is preferably a = 0.
When the amount of oxygen deficiency is small (that is, when a is small), the capacity of 3.2 V or less in the charge / discharge test tends to be small. When the amount of oxygen vacancies is small, the crystal structure is stable, and the cycle characteristics at a temperature higher than normal temperature tend to be improved.

The lithium composite oxide represented by the formula (I) includes the spinel lithium composite oxide represented by the formula (I), the reverse spinel lithium composite oxide represented by the formula (I), and the formula (I). It is preferably a silicate type lithium composite oxide represented by formula (I) or an olivine type lithium composite oxide represented by formula (I).
Among these, the lithium composite oxide represented by the formula (I) is more preferably a spinel type lithium composite oxide represented by the formula (I).
That is, it is preferable that the core is made of a lithium composite oxide A whose main component is a spinel type lithium composite oxide represented by the formula (I).

Spinel type lithium composite oxide represented by formula (I), reverse spinel type lithium composite oxide represented by formula (I), silicate type lithium composite oxide represented by formula (I), or formula Specifically, as the olivine type lithium composite oxide represented by (I), LiMn _2−α M _α O ₄ (M: at least one selected from the group consisting of Ni, Co, Mg, Fe, Al and Cr) Two elements), LiMnMPO ₄ (M: at least one element selected from the group consisting of Ni, Co and Fe), Li ₂ MSiO ₄ (M: selected from the group consisting of M ¹ and M ² in the composite oxide of the present invention) More specifically, LiMn ₂ O ₄ , Li _1.03 Mn _1.86 Al _0.10 O ₄ , Li _1.06 Mn _1.83 Al _0.10 B _0.01 O ₄ , LiMn (Ni, Co) VO ₄ Exemplified .

<Shell>
The shell in the composite oxide of the present invention will be described.
In the composite oxide of the present invention, the shell is composed of a lithium composite oxide B mainly composed of a layered lithium composite oxide.

The layered lithium composite oxide is considered to be an α-NaFeO ₂ type (space group R-3m), in which oxide ions have a hexagonal crystal structure and are cubic close packed.
Further, a solid solution compound based on LiCoO ₂ or LiNiO ₂ is also included in the layered lithium composite oxide in the present invention. This solid solution compound includes LiNi _0.5 Mn _0.5 O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O _{2 and the} like. The solid solution compound of LiNi _0.5 Mn _0.5 O ₂ and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ has a hexagonal structure in which oxide ions, also called space group R-3m, have cubic close packing. It is thought that there is. Further, as the solid solution compound, γLi _4/3 M _2/3 O _2. (1-γ) LiMO ₂ (0 <γ < ^1. M is selected from the group consisting of M ¹ and M ² in the composite oxide of the present invention. And at least one of the above embodiments).
The layered lithium composite oxide is preferably a layered lithium composite oxide represented by the formula (II).
The layered lithium composite oxide represented by the formula (II) will be described in detail later.

  The shell is preferably made of a lithium composite oxide B mainly composed of a lithium composite oxide represented by the following formula (II).

Formula (II): Li _{(1 + z)} M ¹ _(1-zq) M ² _q O _(2-b)

In the formula (II), z is in the range of 0 ≦ z ≦ 0.34, preferably 0 <z ≦ (1/3), and more preferably 0.05 ≦ z ≦ 0.15. preferable.
z means the amount of Li substituted for M ¹ . In the composite oxide of the present invention, in the lithium composite oxide represented by the formula (II), a part of M ¹ is preferably substituted with Li. That is, it is preferable that excess Li is contained from the theoretical value of the number of atoms (composition ratio) of Li in the composition formula of the lithium composite oxide used as the positive electrode active material of the lithium ion battery. In this case, the structure is such that at least a part of Li is replaced with M ¹ by reducing the amount of M ^{1 by an} amount corresponding to a part or all of the excess Li.
When the substitution amount (z) of Li increases, the charge / discharge capacity of the battery slightly decreases, but the cycle characteristics at a higher temperature than normal temperature tend to be improved. However, even if z is larger than 0.34, the cycle characteristics at a temperature higher than normal temperature tend to be hardly improved. Further, when the total amount of Li (1 + z) is less than 1.0, a heterogeneous phase that is an impurity is generated, and the charge / discharge performance of the battery tends to be reduced.

In the formula (II), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al and Cr, and at least one element selected from the group consisting of Mn, Ni and Co It is preferable that

Note that M ¹ in the formula (I), the M ¹ in Formula (II), may be different even in the same. For example, M ¹ in formula (I) is Mn (for example, lithium composite oxide is Li _1.03 Mn _1.87 Al _0.10 O ₄ ), and M ¹ in formula (II) is Ni and Co (for example, lithium composite oxide is LiNi _0.5 Co _0.5 O ₂ ), Mn, Ni and Co (for example, lithium composite oxide may be LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ).

1-zq which is the abundance of M ¹ is larger than 0. The lower limit of 1-zq is preferably 0.5, and more preferably 0.66. This is because the capacity cannot be maintained if 1-zq is too small.

In the formula (II), the element M ² is at least one element selected from the group consisting of B, P, Pb, Sb, Si and V. Of these, B is a preferred element.

Note that the M ² in formula (I), the M ² of Formula (II), may be different even in the same. For example, M ² in formula (I) is Al (for example, lithium composite oxide is Li _1.03 Mn _1.87 Al _0.10 O ₄ ), and M ² in formula (II) is Ni, Co, Mn (for example, lithium composite oxide is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ).

(If it contains a plurality of kinds of element as M ² are their sum) q is a replacement amount of M ² is 0 ≦ q ≦ 1, preferably the upper limit is 0.1, are 0.05 It is more preferable. This is because when used as a positive electrode active material, the cycle characteristics at a higher temperature than normal temperature tend to be improved. When the substitution amount q is too high, the discharge capacity of the lithium ion secondary battery when used as the positive electrode active material tends to decrease.
Note that q may be 0. In this case, the lithium composite oxide represented by the formula (II) does not contain M ² . That is, the lithium composite oxide represented by the formula (II) may have a composition represented by Li _{(1 + z)} M ¹ _(1-z) O _(2-b) .
On the other hand, since 0 <1-zq in the formula (II), the lithium composite oxide represented by the formula (II) necessarily includes M ¹ .

In the formula (II), b represents the amount of O (oxygen) deficiency.
In the formula (II), b satisfies 0 ≦ b ≦ 1.0 and is preferably b = 0.
When the amount of oxygen deficiency is small (that is, when b is small), the capacity of 3.2 V or less in the charge / discharge test tends to be small. When the amount of oxygen vacancies is small, the crystal structure is stable, and the cycle characteristics at a temperature higher than normal temperature tend to be improved.

  The lithium composite oxide represented by the formula (II) is preferably a layered lithium composite oxide represented by the formula (II).

Specifically, as the layered lithium composite oxide represented by the formula (II), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiMn _1/3 Ni _1/3 Co _1/3 O ₂ Li _4/3 M _2/3 O ₂ (M is at least one selected from the group consisting of M ¹ and M ² in the composite oxide of the present invention).

  In the composite oxide of the present invention, each of the lithium composite oxide A constituting the core and the lithium composite oxide B constituting the shell is preferably an aggregate of secondary particles.

  Here, it is an aggregate of crystallites (single crystal part), and the smallest particle unit that can be visually recognized by SEM observation at a magnification of 5000 times behaves as a single particle in handling, in which primary particles are sintered and primary particles are sintered. Particles are defined as secondary particles.

In the composite oxide of the present invention, the average particle diameter of primary particles of the lithium composite oxide A constituting the core is preferably 0.1 to 5.0 μm, more preferably 0.8 to 4.0 μm. Preferably, it is 2.0-3.0 micrometers.
In the composite oxide of the present invention, the average particle diameter of primary particles of the lithium composite oxide B constituting the shell is preferably 0.01 to 5.0 μm, more preferably 0.02 to 3.0 μm. Preferably, it is 0.03-1.0 micrometer.
Here, the average particle size of the primary particles means the median size of the primary particles (aggregates of crystallites) described above.

  The median diameter of the primary particles was obtained by taking a photograph of the composite oxide of the present invention at a magnification of 300,000 using a scanning electron microscope (SEM), arbitrarily selecting 500 pieces from the obtained photograph, Measure the projected particle equivalent circle diameter of primary particles in each of lithium composite oxide A or lithium composite oxide B to obtain the integrated particle size distribution (volume basis), and calculate the average particle diameter (median diameter) from it. To obtain the value.

In the composite oxide of the present invention, the average particle diameter of the secondary particles of the lithium composite oxide A constituting the core is preferably 2 to 30 μm, more preferably 8 to 20 μm, and about 17 μm. Is more preferable.
In the composite oxide of the present invention, the average particle diameter of the secondary particles of the lithium composite oxide B constituting the shell is preferably 2 to 20 μm, more preferably 3 to 10 μm, and about 6 μm. Is more preferable.

Here, the secondary particles are obtained by sintering the primary particles as described above.
Moreover, the average particle diameter of secondary particles shall mean the median diameter of secondary particles.

Moreover, the average particle diameter of secondary particles shall mean the value measured by the following method.
First, in a room temperature atmosphere, lithium composite oxide A constituting the core or lithium composite oxide B constituting the shell is added to an aqueous solution of sodium hexametaphosphate and dispersed by ultrasonic dispersion and stirring to form a slurry. . Next, after adjusting this slurry to have a transmittance of 80 to 90%, an integrated particle size distribution (volume basis) is measured using a laser diffraction / scattering particle size distribution measuring device. The median diameter obtained from the particle size distribution measured in this manner is defined as the secondary particle diameter.

The average particle diameter (median diameter) of the composite oxide of the present invention is preferably 2 to 30 μm, more preferably 5 to 20 μm, and still more preferably about 17 μm.
This is because it is possible to obtain a lithium ion secondary battery having a higher discharge capacity per volume and a more excellent cycle characteristic when used in a temperature atmosphere higher than room temperature.

In addition, the average particle diameter (median diameter) of the composite oxide of the present invention means a value measured by the following method.
First, the composite oxide of the present invention is added to an aqueous sodium hexametaphosphate solution at room temperature in the atmosphere, and is dispersed by ultrasonic dispersion and stirring to form a slurry. Next, after adjusting this slurry to have a transmittance of 80 to 90%, an integrated particle size distribution (volume basis) is measured using a laser diffraction / scattering particle size distribution measuring device. The median diameter obtained from the particle size distribution measured in this way is defined as the average particle diameter in the composite oxide of the present invention.

BET specific surface area of the composite oxide of the present invention is preferably 0.3~5.00m ² / g, more preferably 1.0~3.0m ² / g, 1.5~2 More preferably, it is 5 m ² / g.

In the composite oxide of the present invention, BET specific surface area of the lithium composite oxide A constituting the core is preferably one of 0.1~2.0m ² / g, 0.2~1.0m ² / g is more preferable, and 0.3 to 0.4 m ² / g is even more preferable.
In the composite oxide of the present invention, the BET specific surface area of the lithium composite oxide B constituting the shell is preferably 0.1 to 5.0 m ² / g, and preferably 0.2 to ^2.5 m ² / g. g is more preferable, and 0.5 to 1.5 m ² / g is more preferable.

The BET specific surface area is a value obtained by BET one-point measurement by a continuous flow method. Specifically, both the adsorption gas and the carrier gas to be used are a mixed gas of nitrogen, air and helium. The sample is degassed by heating with the mixed gas at a temperature of 450 ° C. or lower, and then cooled with liquid nitrogen. The mixed gas is adsorbed, the adsorbed nitrogen gas is desorbed by returning to room temperature, detected by a thermal conductivity detector, the amount is obtained as a desorption peak, and the specific surface area of the sample is calculated. Such a BET specific surface area can be measured using a known BET powder specific surface area measuring device.
In the present invention, the simple description of “specific surface area” means “BET specific surface area”.

  The tap density of the composite oxide of the present invention is preferably 1.5 to 8.0 g / cc, more preferably 2.0 to 5.0 g / cc, and about 2.5 g / cc. More preferably.

In the composite oxide of the present invention, the tap density of the lithium composite oxide A constituting the core is preferably 1.0 to 8.0 g / cc, and preferably 1.5 to 5.0 g / cc. More preferably, it is 1.8 g / cc.
In the composite oxide of the present invention, the tap density of the lithium composite oxide B constituting the shell is preferably 0.5 to 3.0 g / cc, more preferably 1.0 to 2.0 g / cc. Preferably, it is 1.3 g / cc.

  The tap density can be measured using a conventionally known bulk density measuring device. Specifically, 10.0 g of a measurement object (a composite oxide of the present invention, a lithium composite oxide A constituting a core, or a lithium composite oxide B constituting a shell) is filled in a 20 ml graduated cylinder. The volume after shaking 60 times at a predetermined speed is read from the scale and the tap density is obtained.

The initial discharge capacity of the secondary battery using the composite oxide of the present invention as the positive electrode active material is 90 mAh / g or more, preferably 100 mAh / g or more, more preferably 105 mAh / g or more, more preferably 108 mAh / g. g or more, more preferably 110 mAh / g or more.
In the present invention, the initial discharge capacity (mAh / g) of the lithium ion secondary battery is measured as follows.
First, 85% by mass of the composite oxide of the present invention, 7.5% by mass of acetylene black, and 7.5% by mass of polyvinylidene fluoride are weighed and dispersed in normal methylpyrrolidone to obtain a mixture. Then, the obtained mixture is applied on an Al foil so as to have a thickness of about 0.1 mm, vacuum-dried at about 110 ° C., and then punched out using a 14 mmφ punch to produce a positive electrode.
Next, after the obtained positive electrode was used as a test electrode, the test electrode and a lithium metal foil (thickness 0.2 μm) were stacked in a coin-type battery case via a separator (trade name: Cell Guard). Then, an electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 1 was injected to prepare a test coin cell.
Next, the initial discharge capacity of the test coin cell created in this way is measured. Specifically, a constant current charge of 0.5 mA / cm ² (that is, a reaction for releasing lithium ions from the positive electrode) is performed at an upper limit of 4.3 V, and a constant current of 0.5 mA / cm ² (equivalent to 0.1 C). The initial discharge capacity (mAh / g) per unit mass of the positive electrode active material when the discharge (that is, the reaction for occluding lithium ions in the positive electrode) is performed at a lower limit of 3.0 V is measured.
In the present invention, the value obtained by measuring in this way is defined as the initial discharge capacity.

In addition, the cycle capacity maintenance rate at a temperature higher than room temperature of the secondary battery using the composite oxide of the present invention as the positive electrode active material is 88% or more, preferably 90.0% or more, more preferably 91.%. It can be 0% or more.
In the present invention, the cycle capacity retention rate (%) at a temperature higher than the room temperature of the secondary battery is measured as follows.
First, a test coin cell is prepared by the same method as that for measuring the initial discharge capacity (mAh / g) of the lithium ion secondary battery.
Then, the obtained lithium battery was placed in a constant temperature bath at 55 ° C., and constant current charging of 0.5 mA / cm ² was repeated at an upper limit of 4.3 V and a lower limit of 3.0 V, and the first cycle discharge capacity (initial discharge) The ratio (percentage,%) of the discharge capacity at the 100th cycle to the capacity) is defined as the cycle capacity maintenance rate at a temperature higher than room temperature.

  Although it does not specifically limit the manufacturing method of the complex oxide of this invention, It is preferable to manufacture with the manufacturing method of this invention demonstrated below.

<Production method of the present invention>
The method for producing the composite oxide of the present invention will be described.
In the method for producing a composite oxide of the present invention, the lithium composite oxide A is obtained by pulverizing and mixing in a state where a lithium source is contained in a solvent, and drying and firing the obtained slurry to obtain the lithium composite oxide A [1]. And adjusting step [2] to obtain the lithium composite oxide B by pulverizing and mixing in a state where the lithium source is contained in a solvent, and drying and firing the obtained slurry, and the lithium composite oxide A After obtaining a mixture containing the lithium composite oxide B, a mechanofusion step of obtaining a composite oxide of the present invention by applying a compressive force and a shearing force to the mixture, and a hybrid lithium composite oxidation It is a manufacturing method of a thing.
Hereinafter, such a production method is also referred to as a “production method of the present invention”.

  Each process with which the manufacturing method of this invention is provided is demonstrated below.

<Adjustment step [1]>
The adjustment process [1] in the production method of the present invention will be described.
In the adjustment step [1], first, a lithium source is contained in the solvent.

  As the lithium source, an inorganic or organic compound containing a lithium atom (that is, a lithium compound) can be used. For example, lithium hydroxide, lithium carbonate, lithium nitrate, or lithium acetate can be used. Among these, it is preferable to use lithium hydroxide and / or lithium carbonate. This is because generation of harmful gases can be suppressed.

In the adjustment step [1], in addition to the lithium source, it is preferable to further contain a raw material containing M ¹ and / or a raw material containing M ² in the solvent.

As the raw material containing M ¹ , a compound containing at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al, and Cr can be used.
The raw material containing M ¹ preferably contains a manganese source.
As the manganese source, an inorganic or organic compound containing a manganese atom (that is, a manganese compound) can be used. For example, manganese oxide, manganese carbonate, manganese carbonate hydrate, manganese hydroxide, manganese oxyhydroxide can be used. Among these, it is preferable to use manganese oxide, and it is more preferable to use Mn ₃ O ₄ . This is because a lithium ion secondary battery that can be obtained at low cost as an industrial raw material and has a higher capacity retention rate tends to be obtained.

As a raw material containing M ¹ , for example, basic nickel carbonate, basic cobalt carbonate, magnesia, hematite, alumina, aluminum hydroxide (Al (OH) ₃ ), chromium oxide, or the like can be used. Among these, a compound containing Al is preferably used, and aluminum hydroxide (Al (OH) ₃ ) can be more preferably used. This is because a lithium ion secondary battery that can be obtained industrially at low cost, is relatively easily replaced with Mn in the crystal structure, and has a higher capacity retention rate can be obtained.

As a raw material containing M ² , a compound containing at least one element selected from the group consisting of B, P, Pb, Sb, Si and V can be used. The element M ² is preferably B.
For example, when M ² contains B, boric acid (H ₃ BO ₃ ) or triboric diboric acid (B ₂ O ₃ ) can be used as a raw material containing boron, and boric acid (H ₃ BO ₃ ). Is preferably used. This is because it can be obtained at low cost as an industrial raw material.
As the raw material containing M ^2, or the like can be used _{P 2 O 5, PbO, Sb} 2 O 3, SiO 2 and V ₂ O _5.
When M ² contains B, the inventor presumes that the sinterability at the time of firing increases, the particle diameter grows, and contributes to the improvement of the capacity retention rate of the obtained lithium ion secondary battery. ing.

In the production method of the present invention, the raw material containing M ² promotes the generation and growth of spinel crystals during firing described later. That is, it is considered that the oxide of the element M ² acts as a flux in the process of forming the spinel crystal, thereby promoting the generation and growth of the crystal, and further promoting the growth of the primary particles that are aggregates of crystallites.

When a lithium source and a raw material containing M ¹ and / or a raw material containing M ² are used, the ratio of the above-described lithium source to be contained in the solvent, the raw material containing M ¹ and the raw material containing M ² is expressed by the formula ( It is preferable to adjust so as to obtain a lithium composite oxide having a composition represented by I).

A solvent containing a lithium source (preferably a raw material containing M ¹ and a raw material containing M ² ) is not particularly limited. For example, a conventionally known solvent such as water (pure water or the like), ethanol, acetone or the like may be used. Although it is possible, it is preferable to use water.
Further, these raw materials are contained so that the solid content concentration in the solvent is preferably 5 to 40% by mass, more preferably 10 to 35% by mass, and further preferably 15 to 25% by mass.

In the adjustment step [1], a lithium source (preferably a raw material containing M ¹ and a raw material containing M ² ) is contained in the solvent, and pulverized and mixed in that state.
The method of pulverization and mixing is not particularly limited, but a wet pulverization method using a wet pulverizer using a bead mill or the like is preferable.
Further, this pulverization is preferably performed until a slurry having an average particle size (D ₅₀ ) of solids of 0.50 μm or less is obtained. When the average particle diameter (D ₅₀ ) is pulverized and mixed so as to be 0.50 μm or less, the solid content tends to be uniform in the slurry. Moreover, it is because the capacity maintenance rate at high temperature is higher than normal temperature in the obtained lithium ion secondary battery. The average particle diameter is preferably 0.40 μm or less, and more preferably 0.30 μm or less.
The average particle size is preferably 0.10 μm or more, and more preferably 0.15 μm or more. This is because if the particle size is too small by pulverization, handling in the subsequent steps will be worsened.

The average particle size (D ₅₀ ) of the solid content in the slurry was determined by adding a sodium hexametaphosphate aqueous solution to the slurry at room temperature in the atmosphere, and dispersing the slurry by ultrasonic dispersion and stirring. The integrated particle size distribution (volume basis) is measured using a laser diffraction / scattering type particle size distribution measuring apparatus, and the median diameter obtained from the particle size distribution is meant.

This pulverization is preferably performed until a slurry having a D ₉₀ particle size of 0.50 μm or less in solid content is obtained. More preferably the particle size of D ₉₀ is less than 0.40 .mu.m, even more preferably less 0.30 .mu.m. This is because the capacity retention rate at a temperature higher than normal temperature in the obtained lithium ion secondary battery tends to be higher.

The particle size of D ₉₀ in the solid content of the slurry was determined by adding a sodium hexametaphosphate aqueous solution to the slurry at room temperature in the atmosphere, and dispersing the slurry by ultrasonic dispersion and stirring. The integrated particle size distribution (volume basis) is measured using a laser diffraction / scattering type particle size distribution measuring device, and the particle size at which the integrated particle size distribution is 90% is meant.

  Next, the slurry thus obtained is dried to obtain a precursor. The slurry can be dried by a drying method using a band dryer or a shelf dryer, but is preferably spray drying. Spray drying is to dry the slurry after spraying it into a mist or while forming a mist. By spray-drying under desired conditions, the particle size of the resulting precursor can be adjusted within a desired range.

The method of spray drying is not particularly limited. For example, the slurry is caused to flow into the atomizer rotating at high speed, thereby causing the slurry component droplets to be discharged from the slit of the atomizer, and then sprayed using an appropriate drying gas temperature or air flow rate. A method for quickly drying the droplets is mentioned. At this time, the slurry flow rate is preferably 0.5 to 700 kg / h, more preferably 1 to 600 kg / h, still more preferably 300 to 550 kg / h, and the atomizer speed is preferably 10,000 to 40,000 rpm, more preferably 20,000 to 35,000 rpm, more preferably 28,000 to 32,000 rpm. A treatment such as an appropriate temperature and air blowing is performed so as to quickly dry the scattered droplets, but it is preferable to introduce the dry gas in a downward flow from the upper part of the drying tower to the lower part.
Spray drying is preferably performed using a spray dryer. Moreover, the inlet temperature of the hot air for drying of a spray dryer becomes like this. Preferably it is 60-500 degreeC, More preferably, it is 250-450 degreeC, More preferably, it is 300-400 degreeC, Outlet temperature is preferably 80-250 degreeC, More preferably, it is 100- 200 degreeC, More preferably, you may be 130-160 degreeC.

Next, the precursor obtained as described above is fired.
Here, the firing method is not particularly limited as long as it is performed in an oxygen-containing atmosphere, and examples thereof include conventionally known methods such as a firing method using a tunnel furnace, a muffle furnace, a rotary kiln, and the like.

Moreover, it is preferable that a calcination temperature is 600-1200 degreeC. Moreover, it is preferable that it is 650 degreeC or more, It is more preferable that it is 700 degreeC or more, It is further more preferable that it is 750 degreeC or more. When the precursor contains boron, the present inventor has found that when it is fired at 650 to 900 ° C., cycle characteristics at a temperature higher than room temperature tend to be improved.
Moreover, it is preferable that a calcination temperature is 850 degrees C or less. When the firing temperature is too high, oxygen is released from the crystal structure, and the battery performance tends to deteriorate.

  The time for firing the precursor at the firing temperature as described above is preferably 0.1 to 8 hours, more preferably 0.5 to 7 hours, and more preferably 0.5 to 4 hours, More preferably, it is 1.5 to 2.5 hours.

  The lithium composite oxide A can be obtained by such an adjustment step [1].

<Adjustment step [2]>
The adjustment process [2] in the production method of the present invention will be described.
In the adjustment step [2], a lithium source is first contained in a solvent.
In the adjustment step [2], in addition to the lithium source, it is preferable to further contain a raw material containing M ¹ and / or a raw material containing M ² in the solvent.

As the lithium source, the raw material containing M ¹ and the raw material containing M ² , those used in the adjusting step [1] can be used.

When a lithium source and a raw material containing M ¹ and / or a raw material containing M ² are used, the ratio of the above-described lithium source to be contained in the solvent, the raw material containing M ¹ and the raw material containing M ² is expressed by the formula ( It is preferable to adjust so as to obtain a lithium composite oxide having a composition represented by II).

The solvent containing a lithium source (preferably further containing a raw material containing M ¹ and a raw material containing M ² ) can be the same as in the aforementioned adjustment step [1]. The same applies to the solid content concentration in the solvent.

  Further, the pulverization and mixing can be performed in the same manner as in the adjustment step [1] described above. The same applies to the degree of grinding.

  Also, the method of obtaining the precursor by drying the slurry can be the same as in the above-mentioned adjustment step [1].

Further, the method for firing the precursor may be the same as in the adjustment step [1] described above.
However, the firing temperature is preferably 800 to 1400 ° C. Moreover, it is preferable that it is 850 degreeC or more, It is more preferable that it is 900 degreeC or more, It is further more preferable that it is 930 degreeC or more.
The firing temperature is preferably 1200 ° C. or lower, more preferably 1100 ° C. or lower, and further preferably 1000 ° C. or lower. When the firing temperature is too high, oxygen is released from the crystal structure, and the battery performance tends to deteriorate.

  The time for firing the precursor at the firing temperature as described above is preferably 0.1 to 8 hours, more preferably 0.5 to 7 hours, and more preferably 0.5 to 4 hours, More preferably, it is 1.5 to 2.5 hours.

  The lithium composite oxide B can be obtained by such an adjustment step [2].

<Mechanofusion process>
The mechanofusion process in the production method of the present invention will be described.
In the mechanofusion step, after obtaining a mixture containing the lithium composite oxide A and the lithium composite oxide B, compressive force and shear force are applied to the mixture.

  The mixture is preferably obtained by mixing the lithium composite oxide A and the lithium composite oxide B.

The mixing ratio of the lithium composite oxide A and the lithium composite oxide B in obtaining the mixture is not particularly limited, but the mass ratio thereof (mass of lithium composite oxide A: mass of lithium composite oxide B) 9.9: 0.1-0.1: 9.9 (preferably 9.9: 0.1-5: 5, more preferably 9.9: 0.1-6: 4) Is more preferable.
This is because, with such a mixing ratio, a lithium ion secondary battery having a higher discharge capacity per volume and a more excellent cycle characteristic when used in a temperature atmosphere higher than normal temperature can be obtained.

After obtaining the mixture, compressive force and shear force are applied to the mixture.
A method for applying the compressive force and the shearing force is not particularly limited, and the compressive force and the shearing force can be applied to the mixture using a conventionally known mechanofusion device.
The mechanofusion device is a device that applies a compressive force and a shearing force by pressing a raw material fixed inside the rotating container with an inner piece by a centrifugal force of the rotating container and sandwiching it between the rotating container.

When such a mechanofusion apparatus is used to apply a compressive force and a shearing force to the mixture, preferred operating conditions are as follows.
It is preferable that 80-100 cc of the mixture is filled in a rotating container, the rotation is performed at 5000-7000 rpm, the temperature rise stops, the current value of the apparatus decreases, and the process is terminated when it becomes constant.

  After the mechanofusion step obtains a mixture containing the lithium composite oxide A and the lithium composite oxide B, a compressive force and a shear force are applied to the mixture, and then the lithium composite oxide B is further added. It is preferable to add the compression force and the shearing force again.

For example, first, the mixing ratio of the lithium composite oxide A and the lithium composite oxide B contained in the composite oxide of the present invention obtained by the mechanofusion process (the mass of the lithium composite oxide A: the lithium composite oxide B (Mass) becomes 9.9: 0.1-0.1: 9.9 (preferably 9.9: 0.1-5: 5, more preferably 9.9: 0.1-6: 4). Thus, the lithium composite oxide A and the lithium composite oxide B are weighed.
Next, a part of the lithium composite oxide B (for example, about 20 to 80% by mass, preferably about 40 to 60% by mass, more preferably about 50% by mass) is mixed with the lithium composite oxide A to obtain a mixture. .
Next, compressive force and shearing force are applied to the mixture using a mechanofusion device or the like.
Next, it is preferable to add the remaining lithium composite oxide B and apply compressive force and shear force again.
This is because it is possible to obtain a lithium ion secondary battery having a higher discharge capacity per volume and a more excellent cycle characteristic when used in a temperature atmosphere higher than room temperature.

  The composite oxide of the present invention can be obtained by such a mechanofusion process.

<Positive electrode active material of the present invention>
The positive electrode active material of the present invention will be described.
The positive electrode active material of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery using the composite oxide of the present invention.
The positive electrode active material of the present invention preferably contains 80% by mass or more of the composite oxide of the present invention, more preferably 90% by mass or more, and substantially 100% by mass, that is, from the composite oxide of the present invention. More preferably.

<Positive electrode of the present invention and manufacturing method thereof>
The positive electrode of the present invention may be in the same mode as, for example, a conventionally known positive electrode, as long as the positive electrode active material of the present invention is used. For example, what formed the layer which consists of what added the conductive support agent, the binder, etc. and mixed with the positive electrode active material of this invention as needed on a collector is mentioned. Specifically, an ink (slurry) is prepared by kneading a conductive additive, a binder, and an organic solvent such as N-methylpyrrolidone with the positive electrode active material of the present invention, and this ink is applied to the aluminum foil of the current collector. After applying and drying, it can be obtained by applying to a roller press. By applying to a roller press, the contact between the positive electrode active material and the current collector can be improved and the density of the positive electrode active material can be increased. Moreover, after fully mixing a conductive support agent and a binder with the positive electrode active material of this invention, it shape | molds in a sheet form with a roller press, and can obtain a positive electrode.
Here, examples of the conductive assistant include graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black and ketjen black.
Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluorine rubber, styrene butadiene, cellulose resin, and polyacrylic acid.
Further, the current collector is not limited, and for example, a conventionally known net shape, sheet shape, or film shape can be used.

<Secondary battery of the present invention>
The secondary battery of the present invention will be described.
The secondary battery of the present invention may have the same configuration as a normal lithium ion secondary battery except that the positive electrode of the present invention is used as a positive electrode, and may be a cylindrical type, a square type, a coin type, a button type, or the like. It's okay. That is, the positive electrode, the negative electrode, and the non-aqueous electrolyte are the main battery components, and these components are enclosed in, for example, a battery can. Each of the positive electrode and the negative electrode acts as a lithium ion carrier, and the lithium ions are occluded in the negative electrode during charging and detached from the negative electrode during discharging.

A negative electrode is not specifically limited, For example, the aspect similar to a conventionally well-known negative electrode may be sufficient. For example, as the negative electrode active material, a lithium alloy represented by lithium or lithium-aluminum can be used, and graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Carbon-based materials that can reversibly occlude and release lithium ions such as mesocarbon microbeads, carbon fibers, and activated carbon can also be used. For example, the same current collector as that of the positive electrode can be used.
When the negative electrode active material is lithium or a lithium alloy, the negative electrode can be used as it is, or can be manufactured by pressure bonding to a current collector. In addition, when the negative electrode active material is a carbon-based material (graphite, carbon black, etc.) capable of occluding and releasing lithium ions, a binder similar to that for the positive electrode is added to the negative electrode active material and mixed as necessary. Then, paste it into a paste using a solvent, apply the obtained negative electrode mixture-containing paste to a negative electrode current collector made of copper foil, etc., dry it to form a negative electrode mixture layer, and press-mold as necessary It can manufacture by passing through a process.

  As the non-aqueous electrolyte, an organic electrolyte, a polymer electrolyte, a solid electrolyte, or the like can be used. Here, the organic electrolyte is a lithium salt added to a non-aqueous solvent, and the polymer electrolyte is a lithium salt added to a polymer compound.

Here, as the lithium salt, for example, LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Examples thereof include LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) ₂ . Among these, LiBF ₄ (lithium tetrafluoroborate) is less reactive with moisture present in the electrolyte, so it has better safety, cycle characteristics, rate characteristics (high rate discharge characteristics), initial characteristics, etc. It is easy to obtain an excellent lithium battery.
The concentration of the lithium salt in the organic electrolyte is preferably 0.1 to 3.0 mol / l, more preferably 0.2 to 2.0 mol / l. This is because the ionic conductivity of the non-aqueous electrolyte is increased, lithium salts are hardly precipitated in the non-aqueous electrolyte, and a lithium battery having high-performance battery performance can be obtained.

  As the non-aqueous solvent of the organic electrolyte, for example, a conventionally known one can be used, and a mixed solvent of ethylene carbonate, γ-butyrolactone, propylene carbonate and vinylene carbonate can be preferably used. Since ethylene carbonate, γ-butyrolactone and propylene carbonate have a high dielectric constant, they can reliably cause ionic conduction. Further, by containing vinylene carbonate in a non-aqueous solvent, ethylene carbonate, γ -Since the film | membrane derived from vinylene carbonate which can suppress reliably decomposition | disassembly of butyrolactone and propylene carbonate can be formed on a negative electrode, it can fully charge.

  The organic electrolyte may contain another organic solvent in addition to the lithium salt and the non-aqueous solvent.

When the non-aqueous electrolyte is a polymer electrolyte, it includes a matrix polymer compound that is gelled with a plasticizer (non-aqueous electrolyte). Examples of the matrix polymer compound include ethers such as polyethylene oxide and cross-linked products thereof. Fluorine-based resins such as vinyl resins, polymethacrylate resins, polyacrylate resins, polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers can be used alone or in combination.
Among these, from the viewpoint of oxidation-reduction stability, it is preferable to use a fluorine-based resin such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

The production of the polymer electrolyte is not particularly limited, and examples thereof include a method in which a polymer compound constituting a matrix, a lithium salt, and a solvent are mixed and heated to melt and dissolve. In addition, after dissolving a polymer compound, a lithium salt, and a solvent in an organic solvent for mixing, the organic solvent for mixing is evaporated, a polymerizable monomer, a lithium salt, and a solvent are mixed, and ultraviolet rays, electron beams, or molecules are mixed. Examples include a method of polymerizing a polymerizable monomer by irradiating a line and the like to obtain a polymer.
10-90 mass% is preferable and, as for the ratio of the solvent in a polymer electrolyte, 30-80 mass% is more preferable. With such a ratio, the electrical conductivity is high, the mechanical strength is strong, and the film is easily formed.

Solid electrolytes include, for example, oxide-based quenching glasses containing lithium ions, glass-based solid electrolytes such as sulfide-based oxysulfide-based superionic conductive glasses, and high concentrations of Li salts dissolved and dispersed in polymers such as polyethers. Examples include molecular solid electrolytes.
The polymer solid electrolyte may be in the form of a gel containing a solvent component.

The secondary battery of the present invention preferably has a separator that prevents direct contact between the positive electrode and the negative electrode.
A separator is not specifically limited, For example, a conventionally well-known thing can be used, for example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane that combines these.
In the case where an organic electrolyte or a polymer electrolyte is used as the nonaqueous electrolyte, a separator is usually used. However, in the case of a solid electrolyte, the solid electrolyte may be used without using the separator.

  The manufacturing method of the secondary battery of this invention is not specifically limited, For example, it can manufacture by a conventionally well-known method. For example, it can be manufactured by injecting a non-aqueous electrolyte before or after laminating the positive electrode of the present invention and the negative electrode via a lithium battery separator, and finally sealing with an exterior material. . Examples of the exterior material include a metal-resin composite film having a configuration in which nickel-plated iron, stainless steel, aluminum, and metal foil are sandwiched between resin films.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Example 1>
[Preparation of lithium composite oxide A]
Lithium hydroxide (LiOH.H ₂ O) was prepared as a lithium source, electrolytic manganese dioxide (γ-MnO ₂ ) was prepared as a manganese source, and aluminum hydroxide (Al (OH) ₃ ) was prepared as an aluminum source. Each raw material was weighed so that the composition of the finally obtained lithium composite oxide was Li _1.03 Mn _1.87 Al _0.10 O ₄ .

  Next, these weighed raw materials were mixed, and after adding pure water so that the solid content concentration was 33.3% by mass, a wet pulverizer (manufactured by Ashizawa Finetech Co., Ltd .: Star Mill Lab Star LMZ-) was added. 06) to obtain a slurry. Here, it grind | pulverized until the average particle diameter (median diameter) of solid content in a slurry became 0.35 micrometer. In the pulverization, a 600 ml vessel was used.

  In addition, the average particle diameter (median diameter) of the solid content in the slurry was determined using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd .: LA-950v2). Specifically, an aqueous sodium hexametaphosphate solution is added to the slurry at room temperature in the atmosphere, dispersed by ultrasonic dispersion and stirring, adjusted to have a transmittance of 30 to 60%, and then refracted using the above apparatus. The integrated particle size distribution (volume basis) was measured and obtained under the condition of a rate of 2.20.

  Next, the slurry after pulverization was spray-dried using a disk-type spray dryer (Okawara Kako Co., Ltd .: L-8 type spray dryer). Here, air was used as the drying gas. Further, the cyclone differential pressure was adjusted to 0.7 kPa, and the drying gas inlet temperature was adjusted to 200 ° C. The slurry flow rate was 3 kg / h, and the atomizer speed was 28,000 rpm. By performing such spray drying, a particulate precursor [1] was obtained.

  Next, the obtained precursor [1] was fired in air at 830 ° C. for 2 hours to obtain a spinel type lithium composite oxide having a target composition.

About the obtained spinel type complex oxide, the average particle diameter (median diameter) was calculated | required using the laser diffraction / scattering type particle size distribution measuring apparatus (Horiba Seisakusho: LA-950v2). Specifically, an aqueous sodium hexametaphosphate solution is added to the slurry at room temperature in the atmosphere, dispersed by ultrasonic dispersion and stirring, adjusted to have a transmittance of 30 to 60%, and then refracted using the above apparatus. The cumulative particle size distribution (volume basis) was measured and obtained under the condition of a rate of 2.2.
As a result, the average particle size was 16.6 μm.

Moreover, the tap density of the obtained spinel-type complex oxide was measured using a bulk density measuring device (manufactured by Tsutsui Rikenki Co., Ltd.). Specifically, 10.0 g of spinel-type complex oxide powder was filled in a 20 ml graduated cylinder, and the volume after shaking 60 times at a predetermined speed was read from the scale to obtain the tap density.
As a result, the tap density of the spinel complex oxide was 1.80 g / cc.

[Preparation of lithium composite oxide B]
Next, lithium hydroxide (LiOH.H ₂ O) as a lithium source, nickel oxide (NiO) as a nickel source, Co ₃ O ₄ as a cobalt source, and electrolytic manganese dioxide (γ-MnO ₂ ) as a manganese source were prepared. Each raw material was weighed so that the composition of the finally obtained lithium composite oxide was LiNi _0.5 Co _0.2 Mn _0.3 O ₂ .

Then, as in the case of the above-described spinel type lithium composite oxide, after mixing the raw materials, pure water is added so that the solid content concentration is 33.3% by mass, and pulverization is performed using the same wet pulverizer, The slurry was pulverized until a similar average particle size of solid content was obtained.
In addition, the measuring method of the average particle diameter (median diameter) of the solid content in the slurry is the same.

  Next, as in the case of the above-described spinel type lithium composite oxide, the pulverized slurry was spray dried using a disk type spray dryer to obtain a particulate precursor [2]. The operating conditions of the disk type spray dryer were the same.

  Next, the obtained precursor [2] was fired in air at 950 ° C. for 2 hours to obtain a layered lithium composite oxide.

About the obtained layered lithium complex oxide, it calculated | required using the average particle diameter (median diameter) by the method similar to the case of the above-mentioned spinel type complex oxide.
As a result, the average particle size was 5.9 μm.

Moreover, the tap density of the obtained layered composite oxide was measured using a bulk density measuring device (manufactured by Tsutsui Rikenki Co., Ltd.). Specifically, 10.0 g of layered composite oxide powder was filled in a 20 ml graduated cylinder, and the volume after shaking 60 times at a predetermined speed was read from the scale to determine the tap density.
As a result, the tap density of the layered composite oxide was 1.30 g / cc.

[Adjustment of hybrid type complex oxide]
Next, 130 g of spinel-type lithium composite oxide and 7.2 g of layered lithium composite oxide were put into a mechanofusion apparatus (MECHANO FUSION AMS-Mini manufactured by Hosokawa Micron Corporation).
And when the operation was started at a rotational speed of 7000 rpm, the temperature in the device increased, and the current value indicating the load on the device temporarily became 3.6 A, but then the current value gradually decreased, Five minutes after the start of operation, the temperature in the apparatus was stable at 68.0 ° C. and the current value was 2.6 A, so the operation was interrupted.

  Next, 7.2 g of layered lithium composite oxide was charged into the mechanofusion apparatus, and the operation was restarted under the same conditions. Thereafter, similarly, although the current value indicating the load of the apparatus temporarily became 3.6 A, the current value gradually decreased thereafter, and the temperature inside the apparatus was 68.0 ° C. after 5 minutes from the start of operation. Since the current value was stabilized at 2.6 A, the operation was stopped and the processing was completed.

Such a treatment was performed to obtain a hybrid lithium composite oxide in which a layered lithium composite oxide layer was formed on the surface of the spinel lithium composite oxide.
The mass ratio of the spinel lithium composite oxide to the layered lithium composite oxide in the obtained hybrid lithium composite oxide is 9: 1.

About the obtained hybrid type complex oxide, the average particle diameter (median diameter) was determined using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd .: LA-950v2). Specifically, an aqueous sodium hexametaphosphate solution is added to the slurry at room temperature in the atmosphere, dispersed by ultrasonic dispersion and stirring, adjusted to have a transmittance of 30 to 60%, and then refracted using the above apparatus. The cumulative particle size distribution (volume basis) was measured and obtained under the condition of a rate of 2.2.
As a result, the average particle size of the hybrid composite oxide was 17.4 μm.

The tap density of the obtained hybrid type complex oxide was measured using a bulk density measuring device (manufactured by Tsutsui Rikenki Co., Ltd.). Specifically, 10.0 g of hybrid type complex oxide powder was filled in a 20 ml graduated cylinder, and the volume after shaking 60 times at a predetermined speed was read from the scale to determine the tap density.
As a result, the tap density of the hybrid type complex oxide was 2.5 g / cc.

About the obtained hybrid type complex oxide, it observed by 3300 times using SEM-EDS.
The obtained electron microscope image is shown in FIG.
1A is a cross-sectional photograph of one hybrid composite oxide, FIG. 1B is a Co element distribution, FIG. 1C is a Mn element distribution, and FIG. 1D is a Ni element distribution. Yes.
As can be seen from FIG. 1, although the Mn element is distributed almost uniformly, Co and Ni are unevenly distributed on the outer edge side.
Thus, in the hybrid type composite oxide, a layer made of a layered lithium composite oxide (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) is formed on the surface of the spinel type lithium composite oxide (Li _1.03 Mn _1.87 Al _0.10 O ₄ ). It was confirmed that this was the case.

  Next, a lithium ion secondary battery was produced using the hybrid composite oxide obtained by such a method, and the battery was evaluated.

<Measurement of initial discharge capacity>
A hybrid type composite oxide was weighed in a proportion of 85% by mass, acetylene black was 7.5% by mass and polyvinylidene fluoride was 7.5% by mass and dispersed in normal methylpyrrolidone to obtain a mixture. Then, the obtained mixture was applied on an Al foil so as to have a thickness of about 0.1 mm, vacuum-dried at about 110 ° C., and then punched using a 14 mmφ punch to produce a positive electrode.
The obtained positive electrode was used as a test electrode, and this test electrode and a lithium metal foil (thickness 0.2 μm) were stacked and arranged in a coin-type battery case via a separator (trade name: Cell Guard). An electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of 1: 1 ethylene carbonate and dimethyl carbonate was injected to prepare a test coin cell.
The initial discharge capacity of the test coin cell thus prepared was measured. Specifically, a constant current charge of 0.5 mA / cm ² (that is, a reaction for releasing lithium ions from the positive electrode) is performed at an upper limit of 4.3 V, and a constant current of 0.5 mA / cm ² (equivalent to 0.1 C). The initial discharge capacity (mAh / g) per unit mass of the positive electrode active material when discharging (that is, the reaction of occluding lithium ions in the positive electrode) at a lower limit of 3.0 V was measured.
The results are shown in Table 1.

<Measurement of 55 ° C and 100 cycle capacity retention rate>
A test coin cell was placed in a constant temperature bath at 55 ° C., and 0.5 mA / cm ² under the conditions of potential regulation up to a charging potential of 4.3 V and a discharging potential of 3.0 V, as in the measurement of the initial charge / discharge capacity. The constant current charging was performed 100 times, and the capacity retention rate was obtained by the following equation.
Capacity retention rate (%) = (100th discharge capacity / first discharge capacity) × 100
The measurement results are shown in Table 1.

<Example 2>
In Example 1 above, 130 g of spinel-type lithium composite oxide and 7.2 g of layered lithium composite oxide were introduced into the mechanofusion apparatus for treatment, and 7.2 g of layered lithium composite oxide was further introduced in the middle. Thus, a hybrid lithium composite oxide having a mass ratio of 9: 1 spinel lithium composite oxide and layered lithium composite oxide was obtained.
Example 2 is the same as Example 1, except that 130 g of spinel-type lithium composite oxide and 8.1 g of layered lithium composite oxide are charged into the mechanofusion apparatus for treatment, and further, the layered lithium composite oxide is further processed along the way. 24.4 g of oxide is divided into three times (8.1 g × 3 times) and the treatment is performed, and a hybrid type in which the mass ratio of the spinel type lithium composite oxide and the layered lithium composite oxide is 8: 2 A lithium composite oxide was obtained.

And similarly to the case of Example 1, the obtained hybrid type complex oxide was observed by 3300 times using SEM-EDS.
The obtained electron microscope image is shown in FIG.
2 (a) is a cross-sectional photograph of a single hybrid composite oxide, FIG. 2 (b) is a Co element distribution, FIG. 2 (c) is a Mn element distribution, and FIG. 2 (d) is a Ni element distribution. Yes.
FIG. 2 shows that Co and Ni are unevenly distributed on the outer edge side although Mn element is distributed almost uniformly.
Thus, in the hybrid type composite oxide, a layer made of a layered lithium composite oxide (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) is formed on the surface of the spinel type lithium composite oxide (Li _1.03 Mn _1.87 Al _0.10 O ₄ ). It was confirmed that this was the case.

<Example 3>
In Example 1 above, 130 g of spinel-type lithium composite oxide and 7.2 g of layered lithium composite oxide were introduced into the mechanofusion apparatus for treatment, and 7.2 g of layered lithium composite oxide was further introduced in the middle. Thus, a hybrid lithium composite oxide having a mass ratio of 9: 1 spinel lithium composite oxide and layered lithium composite oxide was obtained.
Example 3 is the same as Example 1, except that 130 g of spinel-type lithium composite oxide and 11.1 g of layered lithium composite oxide are put into the mechanofusion apparatus for treatment, and further, the layered lithium composite oxide is further processed along the way. 44.6 g of the oxide is divided into four times (11.1 g × 4 times) and the treatment is performed, and the hybrid type in which the mass ratio of the spinel type lithium composite oxide to the layered lithium composite oxide is 7: 3 A lithium composite oxide was obtained.

And similarly to the case of Example 1, the obtained hybrid type complex oxide was observed by 3300 times using SEM-EDS.
The obtained electron microscope image is shown in FIG.
3A is a cross-sectional photograph of one hybrid composite oxide, FIG. 3B is a Co element distribution, FIG. 3C is a Mn element distribution, and FIG. 3D is a Ni element distribution. Yes.
FIG. 3 shows that although Mn elements are distributed almost uniformly, Co and Ni are unevenly distributed on the outer edge side.
Thus, in the hybrid type composite oxide, a layer made of a layered lithium composite oxide (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) is formed on the surface of the spinel type lithium composite oxide (Li _1.03 Mn _1.87 Al _0.10 O ₄ ). It was confirmed that this was the case.

<Comparative Example 1>
In the same manner as in Example 1, a spinel type lithium composite oxide and a layered lithium composite oxide were obtained.
Then, 130 g of spinel type lithium composite oxide and 14.4 g of layered lithium composite oxide were put into a sample bottle and mixed by shaking for a sufficient time.

Next, tap density was measured for the mixture of the obtained spinel-type lithium composite oxide and layered lithium composite oxide using a bulk density measuring device (manufactured by Tsutsui Chemical Co., Ltd.). Specifically, 10.0 g of hybrid type complex oxide powder was filled in a 20 ml graduated cylinder, and the volume after shaking 60 times at a predetermined speed was read from the scale to determine the tap density.
As a result, the tap density was 1.70 g / cc.

Next, using the obtained mixture of the spinel type lithium composite oxide and the layered lithium composite oxide, a lithium ion secondary battery was produced in the same manner as in Example 1, and the battery was evaluated.
Table 1 shows the measurement results of the initial discharge capacity (mAh / g) and the 55 ° C./100 cycle capacity retention rate.

Claims (11)

A hybrid lithium composite oxide mainly composed of a particulate lithium composite oxide composed of a core and a shell covering the core,
The core is lithium mainly composed of at least one selected from the group consisting of spinel lithium composite oxide, reverse spinel lithium composite oxide, silicate lithium composite oxide, and olivine lithium composite oxide. Composed of complex oxide A,
The shell is a hybrid type lithium composite oxide comprising a lithium composite oxide B mainly composed of a layered lithium composite oxide.   The hybrid lithium composite oxide according to claim 1, wherein a covering ratio of the shell to the core is 15% or more. The core is composed of a lithium composite oxide A mainly composed of a lithium composite oxide represented by the following formula (I):
3. The hybrid lithium composite oxide according to claim 1, wherein the shell is made of a lithium composite oxide B mainly composed of a lithium composite oxide represented by the following formula (II).
Formula (I): Li _{(x + y)} M ¹ _(2-yp) M ² _p O _(4-a)
Formula (II): Li _{(1 + z)} M ¹ _(1-zq) M ² _q O _(2-b)
However, in Formula (I) and Formula (II), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al, and Cr, and M ² is B, P, Pb , Sb, Si and V, at least one element selected from the group consisting of 1.0 ≦ x ≦ 2.0, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.34, 0 ≦ p ≦ 1 0.0, 0 ≦ q ≦ 1.0, 0 <1-zq, 0 ≦ a ≦ 1.0, and 0 ≦ b ≦ 1.0.   The hybrid lithium composite oxide according to any one of claims 1 to 3, wherein the core is made of a lithium composite oxide A whose main component is a spinel lithium composite oxide represented by the formula (I).   The hybrid lithium composite oxide according to any one of claims 1 to 4, wherein a mass ratio of the core and the shell is 9.9: 0.1 to 6: 4. An adjustment step [1] in which a lithium source is pulverized and mixed in a solvent, and the resulting slurry is dried and fired to obtain the lithium composite oxide A;
An adjustment step [2] in which a lithium source is pulverized and mixed in a solvent, and the resulting slurry is dried and fired to obtain the lithium composite oxide B.
The hybrid lithium according to any one of claims 1 to 5, wherein after obtaining a mixture containing the lithium composite oxide A and the lithium composite oxide B, a compressive force and a shear force are applied to the mixture. A mechanofusion process for obtaining a composite oxide;
A method for producing a hybrid lithium composite oxide. The mechano-fusion process is
After obtaining a mixture containing the lithium composite oxide A and the lithium composite oxide B, a compressive force and a shear force are applied to the mixture, and then the lithium composite oxide B is further added. The method for producing a hybrid lithium composite oxide according to claim 6, which is a step of applying a compressive force and a shearing force.   A hybrid lithium composite oxide obtained by the production method according to claim 6 or 7.   A positive electrode active material comprising the hybrid lithium composite oxide according to claim 1, 2, 3, 4, 5 or 8.   The positive electrode for lithium ion secondary batteries using the positive electrode active material of Claim 9.   The lithium ion secondary battery which has a positive electrode for lithium ion secondary batteries of Claim 10, a negative electrode, and electrolyte solution.