JP2015099659A - Positive electrode active material, positive electrode, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material capable of achieving a nonaqueous electrolyte secondary battery excellent in the cycle characteristics, storage characteristics and continuous charging characteristics entirely, and to provide a positive electrode containing the positive electrode active material, and a nonaqueous electrolyte secondary battery including the positive electrode.SOLUTION: In a positive electrode active material containing a lithium transition metal oxide, and an oxo acid salt, the peak detected by TEM-EDX analysis of the positive electrode active material cross section, TOF-SIMS of a positive electrode active material in the depth direction, or XPS of positive electrode active material in the depth direction includes peak (A) derived from at least one element selected from a group consisting at least of phosphor, sulfur and boron, and peak (B) derived from at least one element selected from a group consisting transition metals, where at least one peak (A) and at least one peak (B) satisfy a predetermined relationship.

Description

  The present invention relates to a positive electrode active material, a positive electrode including the positive electrode active material, and a nonaqueous electrolyte secondary battery including the positive electrode.

  With the recent development of electronic technology and increasing interest in environmental technology, various electrochemical devices are used. In particular, there are many requests for energy saving, and expectations for what can contribute to it are increasing. Lithium ion secondary batteries, which are representative examples of power storage devices and are also representative examples of nonaqueous electrolyte secondary batteries, have been used mainly as charging places for portable devices, but in recent years, batteries for hybrid vehicles and electric vehicles have been used. The use as is expected.

  However, when a lithium ion secondary battery is used in an automotive application, the temperature and charge / discharge conditions are more severe than those used for a conventional portable device. Therefore, in order to function well as a secondary battery even under such severe conditions, the lithium ion secondary battery is required to further improve durability such as cycle characteristics, storage characteristics, and continuous charge characteristics.

Conventionally, techniques described in Patent Documents 1 and 2 have been proposed with the aim of improving these characteristics. In an example of Patent Document 1, it is described that AlPO ₄ is coated on a positive electrode active material. Patent Document 2 describes that at least one of sulfur (S), phosphorus (P), and fluorine (F) is aggregated on the surface of the positive electrode active material.

  Furthermore, Patent Document 3 describes a production method in which an aqueous solution containing a lithium-containing composite oxide powder and an L element source (boron and / or phosphorus) is mixed, an aqueous medium is removed from the resulting mixture, and firing is performed. .

JP 2003-7299 A JP 2011-82133 A International Publication No. 2006-085588

  However, none of the conventional techniques including those described in Patent Documents 1 to 3 have been found that satisfies all the durability of the cycle characteristics, the storage characteristics, and the continuous charge characteristics.

For example, in Patent Document 1, AlPO ₄ has a problem that the lithium ion conductivity is poor and the conductivity is lowered, and the effect is insufficient. Durability is improved by dissolving a part of the metal element such as aluminum contained in the coating material in the positive electrode active material. However, if the amount of solid solution is small, the cycle characteristics under high temperature or high charging voltage are sufficient. It cannot be improved, and the problem remains that the charge / discharge capacity decreases when the amount of the solid solution is large.

  Further, in Patent Document 2, although durability is improved, the added compound causes problems such as decomposition of the electrolytic solution and generation of gas, or the compound covering the electrode surface and hindering conductivity. However, it is not preferable as a method for improving durability. It is insufficient to satisfy the durability under conditions in which the temperature and charging / discharging conditions are severer than those conventionally used for automobiles and the like.

  Further, in Patent Document 3, although gas generation is suppressed, improvement in cycle characteristics, storage characteristics, and continuous charge characteristics is insufficient.

  Therefore, the present invention has been made in view of the above circumstances, and cycle characteristics, storage characteristics, and continuous charging even when used under severe temperature and charge / discharge conditions equivalent to or higher than those of conventional vehicles. It is an object of the present invention to provide a positive electrode active material capable of realizing a nonaqueous electrolyte secondary battery having excellent characteristics, a positive electrode including the positive electrode active material, and a nonaqueous electrolyte secondary battery including the positive electrode.

  As a result of intensive studies to solve the above problems, the present inventors have found that a transmission electron microscope-energy dispersive X-ray analysis (TEM-EDX; TEM-EDX) of a cross section of a positive electrode active material. ), Time-of-flight secondary ion mass spectrometry (TOF-SIMS) in the depth direction of the positive electrode active material, or X-ray photoelectron spectroscopy (X-) in the depth direction of the positive electrode active material. It has been found that the positive electrode active material having a predetermined peak in ray photoelectron spectroscopy (XPS) can solve the above-described problems, and the present invention. It came to complete.

That is, the present invention is as follows.
[1]
A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by transmission electron microscope-energy dispersive X-ray analysis of the positive electrode active material cross section is at least:
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
A positive electrode active material in which at least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.5
2 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).)
[2]
A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by time-of-flight secondary ion mass spectrometry in the depth direction of the positive electrode active material is at least,
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
A positive electrode active material in which at least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.7
1.5 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).)
[3]
A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by X-ray photoelectron spectroscopy in the depth direction of the positive electrode active material is at least,
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
A positive electrode active material in which at least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6
1.7 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).)
[4]
The positive electrode active material according to any one of [1] to [3], wherein the peak (A) includes at least a peak derived from phosphorus.
[5]
The oxoacid salt is at least (M _x P _y O _{3 + z} ) _n O (x ≧ 1, y ≧ 1, z ≧ 0, n ≧ 1, M is at least one selected from the group consisting of Li and a transition metal The positive electrode active material according to any one of [1] to [4], including an element).
[6]
The oxoacid salt is at least (LiM _x-1 P _y O _{3 + z} ) _n O (x ≧ 1, y ≧ 1, z ≧ 0, n ≧ 1, M is at least one selected from the group consisting of transition metals) The positive electrode active material according to any one of [1] to [5], including an element).
[7]
The positive electrode active material according to any one of [1] to [6], wherein the oxoacid salt includes at least Li ₄ P ₂ O ₇ and / or LiMnPO ₄ .
[8]
The oxoacid salt is
Li ₄ P ₂ O ₇ and / or LiMnPO ₄ ,
At least one compound represented by M _x P _{2 + y} O _{7 + z} (x ≧ 1, y ≧ 0, z ≧ 0, M represents at least one selected from the group consisting of Mn, Ni, Co and Fe) Including,
The positive electrode active material according to any one of [1] to [7] above.
[9]
The oxoacid salt is
Li ₄ P ₂ O ₇ and / or LiMnPO ₄ ,
And at least one compound represented by M ₂ P ₂ O ₇ (M represents at least one selected from the group consisting of Mn, Ni, Co, and Fe).
The positive electrode active material according to any one of [1] to [8] above.
[10]
The positive electrode active material according to any one of [1] to [9], wherein the oxoacid salt is attached to at least a part of the lithium transition metal oxide.
[11]
The positive electrode active material according to any one of [1] to [10], which is for a nonaqueous electrolyte secondary battery.
[12]
A positive electrode comprising the positive electrode active material according to any one of [1] to [11].
[13]
A non-aqueous electrolyte secondary battery comprising at least the positive electrode according to [12], a negative electrode, a non-aqueous electrolyte, and an exterior body.

  According to the present invention, a non-aqueous electrolyte secondary excellent in all of cycle characteristics, storage characteristics and continuous charge characteristics even when used under severe temperature and charge / discharge conditions equal to or higher than conventional, such as automotive applications. A positive electrode active material capable of realizing a battery, a positive electrode including the positive electrode active material, and a nonaqueous electrolyte secondary battery including the positive electrode can be provided.

It is sectional drawing which shows roughly an example of the nonaqueous electrolyte secondary battery in this embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be implemented with appropriate modifications within the scope of the gist thereof.

[Positive electrode active material]
The first aspect of the positive electrode active material of this embodiment is
A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by transmission electron microscope-energy dispersive X-ray analysis of the positive electrode active material cross section is at least:
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
At least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.5
2 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).)

The second aspect of the positive electrode active material of the present embodiment is
A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by time-of-flight secondary ion mass spectrometry in the depth direction of the positive electrode active material is at least,
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
At least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.7
1.5 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).)

Furthermore, the third aspect of the positive electrode active material of the present embodiment is
A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by X-ray photoelectron spectroscopy in the depth direction of the positive electrode active material is at least,
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
At least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6
1.7 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).)

  The positive electrode active material according to the present embodiment includes a lithium transition metal oxide. More preferably, the positive electrode active material according to the present embodiment includes a lithium transition metal oxide and an oxoacid salt present on at least a part of the surface of the lithium transition metal oxide.

[Lithium transition metal oxide]
As the lithium transition metal oxide, known materials that can electrochemically occlude and release lithium ions can be used, and are not particularly limited. Among them, as the lithium transition metal oxide, for example, the following general formula (1):
Li _x Mn _{2- y My} O _z (1)
(In formula (1), M represents at least one element selected from the group consisting of transition metal elements, and 0 <x ≦ 1.3, 0.2 <y <0.8, 3.5 <z. <4.5.)
An oxide represented by the following general formula (2):
_{Li x M y O z (2} )
(In the formula (2), M represents at least one element selected from the group consisting of transition metal elements, and 0 <x ≦ 1.3, 0.8 <y <1.2, 1.8 <z. <2.2.)
A layered oxide represented by the following general formula (3):
_{LiMn 2-x Ma x O 4} (3)
(In formula (3), Ma represents at least one element selected from the group consisting of transition metal elements, and 0.2 ≦ x ≦ 0.7.)
A spinel oxide represented by the following general formula (4):
Li ₂ McO ₃ (4)
(In formula (4), Mc represents at least one element selected from the group consisting of transition metal elements.)
An oxide represented by the following general formula (5):
LiMdO ₂ (5)
(In formula (5), Md represents at least one element selected from the group consisting of transition metal elements.)
A composite oxide with an oxide represented by the following general formula (6):
_{zLi 2 McO 3 - (1-} z) LiMdO 2 (6)
(In formula (6), Mc and Md have the same meanings as in formulas (4) and (5), respectively, and 0.1 ≦ z ≦ 0.9.)
Li-excess layered oxide positive electrode active material represented by the following general formula (7):
LiMb _1-y Fe _y PO ₄ (7)
(In formula (7), Mb represents at least one element selected from the group consisting of Mn and Co, and 0 ≦ y ≦ 1.0.)
And an olivine-type positive electrode active material represented by the following general formula (8):
Li ₂ MePO ₄ F (8)
(In formula (8), Me represents at least one element selected from the group consisting of transition metal elements.). These lithium transition metal oxides are used singly or in combination of two or more.

  Among these, the lithium transition metal compound containing manganese represented by the general formulas (1), (3), and (7) is preferable. By using such a lithium transition metal oxide, even when used under severe temperature and charge / discharge conditions, cycle characteristics, storage characteristics, and continuous charge characteristics tend to be more excellent.

  The transition metal contained in the lithium transition metal compound, such as M, Ma, Mc, Md, and Me, refers to a metal contained in the group consisting of Group 3 elements to Group 11 elements. Such a transition metal is not particularly limited, but for example, at least one metal selected from the group consisting of Ni, Mn, Co, and Fe is preferable.

[Oxo acid salt]
The positive electrode active material according to this embodiment includes an oxoacid salt. Furthermore, the oxoacid salt is more preferably contained on the surface of the positive electrode active material, and the cycle characteristics, storage characteristics, and continuous charge characteristics tend to be more excellent by being contained on the surface of the positive electrode active material.

When the oxoacid salt contains a compound containing peak (A) and peak (B), from the viewpoint of further improving lithium ion conductivity, (M _x P _y O _{3 + z} ) _n O (x ≧ 1, y ≧ 1) , Z ≧ 0, n ≧ 1, M represents at least one element selected from the group consisting of Li and transition metals), M _x P _{2 + y} O _{7 + z} (x ≧ 1, y ≧ 0, z ≧ 0) , M represents at least one element selected from the group consisting of Li and transition metals), and M _x P _{3 + y} O _{10 + z} (x ≧ 1, y ≧ 0, z ≧ 0, M consists of Li and transition metals) It is preferable that at least one element selected from the group consisting of at least one element selected from the group is included. These oxo acid salts are preferably condensed phosphates.

The oxo acid salt preferably contains at least Li, and (LiM _x-1 P _y O _{3 + z} ) _n O (x ≧ 1, y ≧ 1, z ≧ 0, n ≧ 1, M is a transition metal) LiM _x-1 P _{2 + y} O _{7 + z} (x ≧ 1, y ≧ 0, z ≧ 0, M represents at least one element selected from the group consisting of transition metals) And LiM _x-1 P _{3 + y} O _{10 + z} (x ≧ 1, y ≧ 0, z ≧ 0, M represents at least one element selected from the group consisting of transition metals). By including Li in the oxoacid salt, cycle characteristics, storage characteristics, and continuous charge characteristics tend to be more excellent even when used under severe temperature and charge / discharge conditions.

The oxo acid salt preferably contains at least Li ₄ P ₂ O ₇ and / or LiMnPO ₄ . By including such Li ₄ P ₂ O ₇ and / or LiMnPO ₄ , cycle characteristics, storage characteristics, and continuous charge characteristics tend to be more excellent.

Also, oxo acid salt in _addition to the Li ₄ P 2 _{O 7} and / or _{LiMnPO 4, M x P 2 +} y O 7 + z (M represents Mn, Ni, the at least one selected from the group consisting of Co and Fe It is preferable that at least one compound represented by By containing _{M x P 2 + y O 7} + z compound represented by the cycle characteristics, storage characteristics and continuous charge characteristics are more excellent trend.

Furthermore, in addition to Li ₄ P ₂ O ₇ and / or LiMnPO ₄ , the oxoacid salt is M ₂ P ₂ O ₇ (M represents at least one selected from the group consisting of Mn, Ni, Co, and Fe) It is preferable to contain at least one compound represented by By including the compound represented by M ₂ P ₂ O ₇ , cycle characteristics, storage characteristics, and continuous charge characteristics tend to be more excellent.

[Physical properties of positive electrode active material]
In the first aspect of the present embodiment, the peak detected by transmission electron microscope-energy dispersive X-ray (TEM-EDX) analysis of the cross section of the positive electrode active material is selected from the group consisting of at least phosphorus, sulfur and boron. A peak (A) derived from at least one element and a peak (B) derived from at least one element selected from the group consisting of transition metals, at least one peak (A), and at least one peak The peak (B) satisfies the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.5
2 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. I _{(B) 50 nm} indicates the intensity of the peak (B) in a cross section at a depth of 50 nm from the surface of the positive electrode active material, and I _{(B) 5 nm} indicates a depth of 5 nm from the surface of the positive electrode active material. (Indicates the intensity of peak (B).)

In the second aspect of the present embodiment, the peak detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in the depth direction of the positive electrode active material is at least from the group consisting of phosphorus, sulfur, and boron. A peak (A) derived from at least one selected element and a peak (B) derived from at least one element selected from the group consisting of transition metals, at least one peak (A), and at least 1 Two peaks (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.7
1.5 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. I _{(B) 50 nm} indicates the intensity of the peak (B) in a cross section at a depth of 50 nm from the surface of the positive electrode active material, and I _{(B) 5 nm} indicates a depth of 5 nm from the surface of the positive electrode active material. (Indicates the intensity of peak (B).)

Furthermore, in the third aspect of the present embodiment, the peak detected by X-ray photoelectron spectroscopy (XPS) in the depth direction of the positive electrode active material is at least one selected from the group consisting of phosphorus, sulfur and boron. A peak (A) derived from one element and a peak (B) derived from at least one element selected from the group consisting of transition metals, at least one peak (A), and at least one peak (B ) Satisfies the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6
1.7 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. I _{(B) 50 nm} indicates the intensity of the peak (B) in a cross section at a depth of 50 nm from the surface of the positive electrode active material, and I _{(B) 5 nm} indicates a depth of 5 nm from the surface of the positive electrode active material. (Indicates the intensity of peak (B).)

  By satisfying the above relational expression, when used in a secondary battery, the cathode active material is excellent in all of cycle characteristics, storage characteristics, and continuous charge characteristics.

(Peak (A))
The peak (A) is a peak derived from at least one element selected from the group consisting of phosphorus, sulfur and boron, which is detected by TEM-EDX analysis, TOF-SIMS, or XPS. The peak (A) preferably includes a peak derived from phosphorus from the viewpoint of lithium ion conductivity.

In TEM-EDX, I _{(A) 50 nm} / I _{(A) 5 nm} is 0.00001 or more and 0.5 or less, preferably 0.001 or more and 0.5 or less, more preferably 0.01 or more. 0.5 or less. Here, I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. The strength of is shown. That is, the positive electrode active material according to the present embodiment is configured such that at least one element selected from the group consisting of phosphorus, sulfur, and boron decreases at a certain rate from the surface toward the center of the positive electrode active material. It is. When I _{(A) 50 nm} / I _{(A) 5 nm} is 0.00001 or more and 0.5 or less, cycle characteristics and storage characteristics are further improved. On the other hand, when I _{(A) 50 nm} / I _{(A) 5 nm} exceeds 0.5, cycle characteristics and storage characteristics deteriorate, and when I _{(A) 50 nm} / I _{(A) 5 nm} falls below 0.00001. Charge / discharge capacity decreases.

In TOF-SIMS, I _{(A) 50 nm} / I _{(A) 5 nm} is 0.00001 or more and 0.7 or less, preferably 0.001 or more and 0.7 or less, more preferably 0.01 or more. 0.7 or less. Here, I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. The strength of is shown. That is, the positive electrode active material according to the present embodiment is configured such that at least one element selected from the group consisting of phosphorus, sulfur, and boron decreases at a certain rate from the surface toward the center of the positive electrode active material. It is. When I _{(A) 50 nm} / I _{(A) 5 nm} is 0.00001 or more and 0.7 or less, cycle characteristics and storage characteristics are further improved. On the other hand, when I _{(A) 50 nm} / I _{(A) 5 nm} exceeds 0.7, cycle characteristics and storage characteristics deteriorate, and when I _{(A) 50 nm} / I _{(A) 5 nm} falls below 0.00001. Charge / discharge capacity decreases.

In XPS, I _{(A) 50 nm} / I _{(A) 5 nm} is 0.00001 or more and 0.6 or less, preferably 0.001 or more and 0.6 or less, and more preferably 0.01 or more and 0.00. 6 or less. Here, I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. The strength of is shown. That is, the positive electrode active material according to the present embodiment is configured such that at least one element selected from the group consisting of phosphorus, sulfur, and boron decreases at a certain rate from the surface toward the center of the positive electrode active material. It is. When I _{(A) 50 nm} / I _{(A) 5 nm} is 0.00001 or more and 0.6 or less, cycle characteristics and storage characteristics are further improved. On the other hand, when I _{(A) 50 nm} / I _{(A) 5 nm} exceeds 0.6, cycle characteristics and storage characteristics deteriorate, and when I _{(A) 50 nm} / I _{(A) 5 nm} falls below 0.00001. Charge / discharge capacity decreases.

(Peak (B))
The peak (B) is a peak derived from at least one element selected from the group consisting of transition metals, which is detected by TEM-EDX analysis, TOF-SIMS, or XPS.
The transition metal derived from the peak (B) is preferably a metal constituting a lithium transition metal oxide or a metal derived from a lithium transition metal oxide. When the transition metal derived from the peak (B) is a metal constituting a lithium transition metal oxide or a metal derived from a lithium transition metal oxide, the particle interface resistance between the positive electrode active materials and the lithium transition metal oxide There is a tendency for the interfacial resistance between the oxoacid salt and the oxoacid salt to decrease. In addition, when the oxoacid salt is present on the surface of the positive electrode active material, by using the metal constituting the lithium transition metal oxide, the binding force between the lithium transition metal oxide and the oxoacid salt is further improved, and the cycle characteristics Tend to improve.
The peak (B) preferably includes a peak derived from at least one metal selected from the group consisting of Ni, Mn, Co, and Fe from the viewpoint of lithium ion conductivity.

In TEM-EDX, I _{(B) 50 nm} / I _{(B) 5 nm} is 2.0 or more and 10000 or less, preferably 2.0 or more and 1000 or less, more preferably 2.0 or more and 100 or less. . Here, I _{(B) 50 nm} indicates the intensity of the peak (B) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(B) 5 nm} indicates the peak (B) at a depth of 5 nm from the surface of the positive electrode active material. The strength of is shown. That is, the positive electrode active material according to the present embodiment is configured such that at least one element selected from the group consisting of transition metals increases at a certain rate from the surface toward the center of the positive electrode active material. As described above, when I _{(B) 50 nm} / I _{(B) 5 nm} is 2.0 or more and 10,000 or less, cycle characteristics and storage characteristics are further improved. In contrast, when I _{(B) 50 nm} / I _{(B) 5 nm} exceeds 10,000, the charge / discharge capacity decreases, and when I _{(B) 50 nm} / I _{(B) 5 nm} is less than 2.0, cycle characteristics and storage are reduced. Characteristics are degraded.

In TOF-SIMS, I _{(B) 50 nm} / I _{(B) 5 nm} is 1.5 or more and 10000 or less, preferably 1.5 or more and 1000 or less, and more preferably 1.5 or more and 100 or less. . Here, I _{(B) 50 nm} indicates the intensity of the peak (B) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(B) 5 nm} indicates the peak (B) at a depth of 5 nm from the surface of the positive electrode active material. The strength of is shown. That is, the positive electrode active material according to the present embodiment is configured such that at least one element selected from the group consisting of transition metals increases at a certain rate from the surface toward the center of the positive electrode active material. As described above, when I _{(B) 50 nm} / I _{(B) 5 nm} is 1.5 or more and 10,000 or less, cycle characteristics and storage characteristics are further improved. On the other hand, when I _{(B) 50 nm} / I _{(B) 5 nm} exceeds 10,000, the charge / discharge capacity decreases, and when I _{(B) 50 nm} / I _{(B) 5 nm} falls below 1.5, cycle characteristics and storage are reduced. Characteristics are degraded.

In XPS, I _{(B) 50 nm} / I _{(B) 5 nm} is 1.7 or more and 10,000 or less, preferably 1.7 or more and 1000 or less, and more preferably 1.7 or more and 100 or less. Here, I _{(B) 50 nm} indicates the intensity of the peak (B) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(B) 5 nm} indicates the peak (B) at a depth of 5 nm from the surface of the positive electrode active material. The strength of is shown. That is, the positive electrode active material according to the present embodiment is configured such that at least one element selected from the group consisting of transition metals increases at a certain rate from the surface toward the center of the positive electrode active material. Thus, when I _{(B) 50 nm} / I _{(B) 5 nm} is 1.7 or more and 10,000 or less, cycle characteristics and storage characteristics are further improved. On the other hand, when I _{(B) 50 nm} / I _{(B) 5 nm} exceeds 10,000, the charge / discharge capacity decreases, and when I _{(B) 50 nm} / I _{(B) 5 nm} falls below 1.7, cycle characteristics and storage are reduced. Characteristics are degraded.

In TEM-EDX, the combination of I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} is 0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0. 5 and 2.0 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000, preferably 0.001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.5, and 2.0 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 1000, more preferably 0.01 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.5 and 2.0 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 100. When the combination of the TEM-EDX intensity ratios of the peak (A) and the peak (B) is in such a range, the cycle characteristics, the storage characteristics, and the continuous charge characteristics are further improved. The reason for this is not necessarily clear, but ionic conductivity is improved by setting the TEM-EDX intensity ratio (I _{(A) 50 nm} / I _{(A) 5 nm} ) of peak (A) to 0.00001 or more and 0.5 or less. The TEM-EDX intensity ratio (I _{(B) 50 nm} / I _{(B) 5 nm} ) of the peak (B) is set to 2.0 or more and 10,000 or less to suppress metal elution from the positive electrode active material. It is done. In addition, by simultaneously adjusting the intensity ratio of peak (A) and peak (B) to a specific range, the reaction active sites on the positive electrode surface can be stabilized, and side reactions such as decomposition of the electrolyte can be suppressed. It is thought that you can.

In TOF-SIMS, the combination of I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} is 0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0. 7 and 1.5 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000, preferably 0.001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.7, and 1.5 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 1000, more preferably 0.01 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.7, and 1.5 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 100. When the combination of the TOF-SIMS intensity ratios of the peak (A) and the peak (B) is within such a range, cycle characteristics, storage characteristics, and continuous charge characteristics are further improved. The reason for this is not necessarily clear, but ion conductivity is improved by setting the TOF-SIMS intensity ratio (I _{(A) 50 nm} / I _{(A) 5 nm} ) of peak (A) to 0.00001 or more and 0.7 or less. In addition, it is considered that metal elution from the positive electrode active material is suppressed by setting the TEM-EDX intensity ratio (I _{(B) 50 nm} / I _{(B) 5 nm} ) of the peak (B) to 1.5 or more and 10,000 or less. It is done. In addition, by simultaneously adjusting the intensity ratio of peak (A) and peak (B) to a specific range, the reaction active sites on the positive electrode surface can be stabilized, and side reactions such as decomposition of the electrolyte can be suppressed. It is thought that you can.

In XPS, the combination of I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} is 0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6 and 1.7 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000, preferably 0.001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6 and 1.7 ≦ I _{(B 50 nm} / I _{(B) 5 nm} ≦ 1000, more preferably 0.01 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6 and 1.7 ≦ I _{(B) 50 nm} / I _{(B ) 5 nm} ≦ 100. When the combination of the XPS intensity ratios of the peak (A) and the peak (B) is within such a range, the cycle characteristics, the storage characteristics, and the continuous charge characteristics are further improved. The reason for this is not necessarily clear, but by increasing the XPS intensity ratio (I _{(A) 50 nm} / I _{(A) 5 nm} ) of peak (A) to 0.00001 or more and 0.6 or less, ion conductivity is improved. It is considered that elution of metal from the positive electrode active material is suppressed by setting the XPS intensity ratio (I _{(B) 50 nm} / I _{(B) 5 nm} ) of peak (B) to 1.7 or more and 10,000 or less. In addition, by simultaneously adjusting the intensity ratio of peak (A) and peak (B) to a specific range, the reaction active sites on the positive electrode surface can be stabilized, and side reactions such as decomposition of the electrolyte can be suppressed. It is thought that you can.

Peak (A) and peak (B) can be measured by any of TEM-EDX, TOF-SIMS, or XPS. The intensity of each peak (I _{(A) 50 nm} , I _{(A) 5 nm} , I _{(B) 50 nm,} and I _{(B) 5 nm} ) can be measured by the method described in Examples. In addition, as a method for producing a cross section of the positive electrode active material for analysis, a conventionally known method can be used. For example, the cross section of the positive electrode active material can be manufactured by processing the positive electrode active material with a focused ion beam (FIB). For example, when measuring phosphorus at peak (A), TEM-EDX confirms the phosphorus atom, TOF-SIMS confirms the sum of the fragment ions based on the phosphorus monomer, and XPS confirms the X-ray irradiation. The energy of photoelectrons based on phosphorus is confirmed, and the intensity is calculated. The fragment ion based on the monomer of phosphorus is a fragment ion composed of one phosphorus element and another element among the fragment ions, and indicates, for example, PO ₂ or PO ₃ . Specifically, the photoelectron energy based on phosphorus is photoelectron energy of 130 ± 10 eV. Boron and sulfur elements and transition metals can be measured in the same manner. Compared to TEM-EDX, TOF-SIMS and XPS tend to have slightly larger values for I _{(A) 50 nm} / I _{(A) 5 nm} , and slightly for I _{(B) 50 nm} / I _{(B) 5 nm.} Tend to take a small value. Furthermore, compared with XPS, TOF-SIMS has a tendency that I _{(A) 50 nm} / I _{(A) 5 nm} has a slightly larger value, and I _{(B) 50 nm} / I _{(B) 5 nm} has a slightly smaller value. Tend to take. These reasons include the detection range and detection sensitivity of each measurement. There is a tendency for slight differences to occur due to differences in the detection range and detection sensitivity of each measurement. In TEM-EDX, 0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.5, 2.0 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000, in TOF-SIMS, 0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.7, 1.5 ≦ I _{(B) 50 nm} / I _{( B) 5 nm} ≦ 10000, in XPS, 0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6, 1.7 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000 By satisfying this, cycle characteristics, storage characteristics and continuous charge characteristics tend to be excellent.

  Since the element derived from the peak (A) and the element derived from the peak (B) are contained in both the lithium transition metal oxide and the oxo acid salt, the interface resistance between the lithium transition metal oxide and the oxo acid salt And the cycle characteristics, storage characteristics, and high-speed charge / discharge characteristics tend to be further improved.

  The intensity ratio of peak (A) and peak (B) in any of the measurement methods of TEM-EDX, TOF-SIMS, or XPS is, for example, treating a positive electrode active material precursor such as a lithium transition metal oxide with an acid. In the method for producing a positive electrode active material having an acid treatment step and a baking step of baking the positive electrode active material after the acid treatment, it can be controlled by adjusting the conditions of the acid treatment step and / or the baking step. There is no particular restriction. Hereinafter, the manufacturing method of a positive electrode active material is demonstrated.

[Method for producing positive electrode active material]
Although it does not specifically limit as a manufacturing method of the positive electrode active material which concerns on this embodiment, For example, the acid treatment process which processes positive electrode active material precursors, such as a lithium transition metal oxide, with an acid, and the positive electrode active material after acid treatment And a firing step of firing.

(Acid treatment process)
The acid treatment step is a step of treating a positive electrode active material precursor such as a lithium transition metal oxide with an acid. Although it does not specifically limit as a processing method, For example, the method of mixing the aqueous solution containing an acid or the organic solvent containing an acid with respect to a positive electrode active material precursor, Solid acid and a positive electrode active material precursor are mixed mechanically. And a method of bringing a gaseous acid into contact with the positive electrode active material precursor by vapor deposition or sputtering.

  The mixing method of the acid and the positive electrode active material precursor is not particularly limited, but it is preferable to stir and mix the secondary particles of the positive electrode active material precursor with such a strength that the secondary particles of the positive electrode active material precursor are not pulverized. In addition, when the acid and the positive electrode active material precursor are mixed in a solid state, it is preferable to mix them with such a strength that the secondary particles are not pulverized and with a relatively large force. An apparatus that can be used for stirring and mixing is not particularly limited, and examples thereof include a mixer, a planetary ball mill, a jet mill, and a magnetic stirrer.

  When the acid is brought into mechanical mixing contact, the acid is preferably in a solid state. When the acid is solid particles, the average particle diameter of the acid is not particularly limited, but is preferably 0.1 to 100 μm, more preferably 10 to 50 μm. When the average particle size of the solid acid is 0.1 μm or more, the acid and the positive electrode active material precursor tend to be more uniformly contacted. Further, when the average particle size of the solid acid is 100 μm or less, battery characteristics such as discharge characteristics tend to be maintained better. The average particle size of the solid acid can be measured by using a laser diffraction particle size distribution measuring apparatus as the average particle size of the median diameter (d50) in which the large particles and the small particles are equivalent.

  Even if the acid and the positive electrode active material precursor are mixed or contacted non-uniformly, the effect can be obtained, but it is more preferable to mix or contact uniformly.

  When using the aqueous solution containing an acid or the organic solvent containing an acid, it is preferable to pass through the drying process which removes a solvent from the mixture after an acid treatment process. The drying method is not particularly limited, but from the viewpoint of uniformly treating the positive electrode active material precursor, it is preferable to gradually remove the solvent by heating or the like after the completion of stirring. Alternatively, the positive electrode active material precursor may be dipped in an aqueous solution containing an acid or an organic solvent containing an acid, filtered to remove the solvent, and then dried.

As the acid used in the acid treatment step, an inorganic acid or an organic acid in which a part of protons of the acid may be substituted with an alkali metal and / or an alkaline earth metal can be used, and is not particularly limited. Specific examples thereof include H ₃ PO ₄ , H ₃ BO ₃ , H ₂ CO ₃ , H ₂ SiO ₃ , HAsO, H ₃ AsO ₃ , H ₃ AsO ₄ , HBrO, HCN, HCNO, HIO, HClO, H _2. MoO ₄ , HN ₃ , H ₂ N ₂ O ₂ , HSCN, HNO ₂ , H ₃ PO ₃ , H ₄ P ₂ O ₇ , H ₅ P ₃ O ₁₀ , H ₂ S, H ₂ SO ₃ , H ₂ SO ₄ , H ₂ Se, H ₂ SeO ₃ , H ₂ SiO ₂ (OH) ₂ , H ₂ TeO ₃ , H ₂ TeO ₄ , H ₃ VO ₄ , H ₂ WO ₄ , HAgO, H ₃ AlO ₃ , HCrO ₄ , H _{2 GeO 3, HSbO 2, HTe} , H 3 AuO 3, and one or more members selected from the group consisting of _H 3 GaO ₃ are preferred.

  Among these, the acid dissociation constant (pKa) of the acid used is preferably 12.01 or less, and more preferably from the viewpoint of more easily adjusting the intensity ratio between the peak (A) and the peak (B). 65 or less, more preferably 2.12 or less. By treating the positive electrode active material precursor with an acid having a pKa of 12.01 or less, a slight amount of the transition metal constituting the positive electrode active material precursor is eluted, or the elements and acids constituting the positive electrode active material precursor Form an intermediate. By baking in such a state in which eluted metals and / or intermediates are mixed, there are regions where the intensity ratios of the peak (A) and the peak (B) are different from 5 nm to 50 nm from the surface of the positive electrode active material. Preferably, an oxo acid salt containing an eluting metal and / or an intermediate as a constituent element is attached to the surface of the lithium transition metal oxide. By having such an oxo acid salt, the surface of the positive electrode active material tends to be stabilized and the cycle characteristics and the like tend to be further improved.

  In the case of using an acid-containing aqueous solution or an acid-containing organic solvent, the peak (A) and the peak (A) from the positive electrode active material surface to the inside of the positive electrode active material (for example, 5 nm depth and 50 nm depth from the positive electrode active material surface) From the viewpoint of forming a gentle atomic concentration gradient so that the strength of B) is different, the pH of the aqueous solution containing acid or the organic solvent containing acid is preferably 6.0 or less, more preferably 1.0 or more. 3.0 or less.

  As the acid, it is preferable to use an acid that condenses during firing, and as such an acid, an acid having one or more hydroxyl groups in the chemical formula is preferable. Specific examples thereof include phosphoric acid, boric acid and sulfuric acid, and phosphoric acid is more preferable. Condensation of the acid during firing causes the oxoacid salt to adhere more uniformly to the surface of the lithium transition metal oxide, so even when the secondary battery is used under harsh temperature and charge / discharge conditions, cycle characteristics and storage There exists a tendency to obtain the positive electrode active material which can implement | achieve the secondary battery which is more excellent in a characteristic and continuous charge characteristic. Moreover, the intermediate body produced | generated by the reaction of an acid and a positive electrode active material precursor may contain the hydroxyl group.

  When an acid that condenses during firing is used, the chain length of the condensate is increased by the progress of the condensation, so that the oxo acid salt has a glass transition point and may be amorphous. Such an amorphous oxoacid salt is preferable because it is advantageous in terms of lithium ion conduction. Therefore, from the viewpoint of further improving the lithium ion conductivity, it is preferable to form an oxoacid salt having a glass transition point on the surface of the lithium transition metal oxide at a temperature lower than the temperature of the firing step, and among these, an oxoacid containing phosphorus It is more preferable to have a salt on the surface.

  The glass transition point of the oxo acid salt is preferably 400 to 1000 ° C, preferably 400 to 900 ° C, and preferably 400 to 800 ° C.

Further, from the viewpoint of forming a uniform oxo acid salt, it is preferable that the acid and the intermediate produced by the acid have a melting point below the temperature of the firing step. Such an acid is not particularly limited, and examples thereof include phosphoric acid and boric acid. Further, as the intermediate, it is not particularly limited, for _{example, LiH 2 PO 4, Li 2} HPO 4 and LiHSO ₄ and the like.

  The melting point of the oxoacid salt is preferably 400 ° C to 1000 ° C, preferably 400 to 900 ° C, and preferably 400 to 800 ° C.

  The melting point and glass transition point of the oxoacid salt can be detected by thermogravimetric-differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC). Whether the oxoacid salt is amorphous or not is determined by X-ray diffraction analysis (X-ray diffraction: XRD), a broad peak appearing in a diffraction angle range of 15 ° to 30 °, or a TEM electron beam. It can be confirmed by a diffraction image.

  The amount of the acid to be used is not particularly limited, but preferably 0.01 to 10% by mass with respect to 100% by mass of the positive electrode active material precursor from the viewpoint of achieving the effect more effectively and reliably and from the viewpoint of cost. More preferably, it is 0.1-10 mass%, More preferably, it is 0.1-1 mass%. In addition, in the case where the positive electrode active material precursor is treated by charging and discharging by adding an acid during the production of the battery, the positive electrode active material precursor amount included in the positive electrode included in the nonaqueous electrolyte secondary battery is 100% by mass. The content is preferably 0.01 to 10% by mass, more preferably 0.1 to 10% by mass, and still more preferably 0.1 to 1% by mass.

  The elution amount of the constituent metal of the positive electrode active material precursor in the acid treatment step is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass. When the elution amount is 0.01% by mass or more, it can have a region where the intensity ratio of the peak (A) and the peak (B) is specific from 5 nm to 50 nm from the surface of the positive electrode active material. Preferably, in the case of a structure in which an oxoacid salt is attached to at least a part of the lithium transition metal oxide, the effect of the deposit tends to be further improved. Moreover, when the elution amount is 10% by mass or less, it is possible to further suppress deterioration of the battery characteristics due to deterioration of the crystal structure of the positive electrode active material precursor. In the acid treatment step, the constituent metal of the positive electrode active material precursor is eluted and then fired in a state containing the eluted constituent metal, so that the oxoacid salt having a small contact resistance and a good interface is a lithium transition metal oxide. A positive electrode active material formed on the surface can be obtained. As the positive electrode active material precursor, it is preferable to use a lithium transition metal oxide such as a spinel oxide containing manganese or a Li-excess solid solution. When these lithium transition metal oxides are used, the effect of dramatically suppressing transition metal elution from the lithium transition metal oxide generated during charging and discharging is exhibited.

(Baking process)
The positive electrode active material precursor is preferably subjected to a firing step after being brought into contact with an acid. By firing the positive electrode active material after the acid treatment, the metal eluted from the positive electrode active material precursor and / or the intermediate between the element constituting the positive electrode active material precursor and the acid reacts on the surface of the positive electrode active material. A strong oxoacid salt can be formed on the surface of the active material. Thereby, there exists a tendency for the cycling characteristics etc. of the positive electrode active material obtained to improve more.

  The firing temperature is preferably 400 ° C. or higher and 1000 ° C. or lower, more preferably 600 ° C. or higher and 900 ° C. or lower, and further preferably 700 ° C. or higher and 900 ° C. or lower. When the firing temperature is 400 ° C. or higher, the binding force between the formed oxoacid salt and the lithium transition metal oxide is further improved, the contact resistance is further decreased, and the cycle characteristics and the high-speed charge / discharge characteristics are further improved. is there. Moreover, it exists in the tendency which can suppress more that the primary particle growth rate increases and the crystal particle of a positive electrode active material becomes too large because a calcination temperature is 1000 degrees C or less. Moreover, when the firing temperature is 1000 ° C. or less, the amount of Li deficiency locally increases and the structural instability tends to be further suppressed. Furthermore, when the firing temperature is 1000 ° C. or lower, element substitution between the site occupied by the Li element and the site occupied by the transition metal can be suppressed, so that the Li conduction path is maintained and the discharge capacity is also maintained. As a result, oxygen desorption from the positive electrode active material, a decrease in crystal stability, a decrease in charge / discharge cycle performance, a change in the composition of the positive electrode active material due to the volatilization of Li, and a battery performance due to a higher density of positive electrode active material particles. It tends to be possible to further suppress the decrease. Moreover, when the firing temperature is 700 ° C. or higher and 900 ° C. or lower, the binding force between the oxoacid salt and the positive electrode active material is further improved, and the cycle characteristics and the high-speed charge / discharge characteristics tend to be further improved.

The firing time is preferably 1 hour to 8 hours, more preferably 1 to 5 hours, and further preferably 3 to 5 hours. When the firing time is 1 hour or longer, I _{(A) 50 nm} / I _{(A) 5 nm} becomes larger, and the charge / discharge capacity tends to increase. Moreover, I _{(B) 50nm} / I _{(B) 5nm} becomes small because baking time is 1 hour or more, and it exists in the tendency for cycling characteristics and a storage characteristic to improve. Further, when the firing time is 8 hours or less, I _{(A) 50 nm} / I _{(A) 5 nm} becomes smaller, and the cycle characteristics, storage characteristics and the like tend to be improved. Moreover, I _{(B) 50nm} / I _{(B) 5nm} becomes large by making baking time into 8 hours or less, and it exists in the tendency for metal elution to be suppressed. Furthermore, Li volatilization and excessive oxygen desorption can be suppressed, and battery performance tends to be further improved.

The rate of temperature increase in the firing step is preferably 1 ° C / min to 50 ° C / min, more preferably 1 ° C / min to 20 ° C / min. When the rate of temperature increase is 50 ° C./min or less, the oxoacid salt binds more uniformly to the lithium transition metal oxide, and the cycle characteristics and the high-speed charge / discharge characteristics tend to be further improved. Further, when the rate of temperature rise is 1 ° C./min or more, I _{(A) 50 nm} / I _{(A) 5 nm} is reduced, and the cycle characteristics, storage characteristics, etc. tend to be further improved.

  The temperature lowering rate in the firing step is preferably 1 ° C./min to 25 ° C./min, more preferably 1 ° C./min to 10 ° C./min. When the temperature lowering rate is 25 ° C./min or less, the contact resistance at the interface between the formed oxoacid salt and the lithium transition metal oxide can be reduced, and the cycle characteristics and the high-speed charge / discharge characteristics tend to be improved. . Moreover, when the temperature lowering rate is 1 ° C./min or more, the process is shortened and the productivity tends to be further improved.

  The atmosphere at the time of firing may be an oxygen atmosphere or a nitrogen atmosphere, and is not particularly limited. However, firing in the atmosphere in which both insertion and desorption of oxygen can occur on the surface and inside of the positive electrode active material is more preferable.

The specific surface area of the positive electrode active material is preferably 0.1 m ² / g or more, and more preferably 0.6 m ² / g or more. The specific surface area of the positive electrode active material is preferably 10.0 m ² / g or less. When the specific surface area of the positive electrode active material is 0.1 m ² / g or more, battery characteristics such as discharge characteristics tend to be more excellent. On the other hand, when the specific surface area of the positive electrode active material is 10.0 m ² / g or less, cycle characteristics and storage characteristics tend to be more excellent.

[Nonaqueous electrolyte secondary battery]
The nonaqueous electrolyte secondary battery according to the present embodiment includes at least a positive electrode including the positive electrode active material according to the present embodiment, a negative electrode, a nonaqueous electrolyte, and an exterior body. Thus, it is preferable that the positive electrode active material which concerns on this embodiment is an object for nonaqueous electrolyte secondary batteries. This realizes a non-aqueous electrolyte secondary battery with excellent cycle characteristics, storage characteristics, and continuous charge characteristics even when used under severe temperature and charge / discharge conditions equivalent to or higher than those of conventional applications. can do.

  FIG. 1 is a schematic cross-sectional view showing an example of a nonaqueous electrolyte secondary battery in the present embodiment. A non-aqueous electrolyte secondary battery 100 shown in FIG. 1 includes a separator 110, a positive electrode 120 and a negative electrode 130 that sandwich the separator 110 from both sides, and a positive electrode current collector 140 that sandwiches a laminate thereof (arranged outside the positive electrode). ), A negative electrode current collector 150 (arranged outside the negative electrode), and a battery exterior 160 that accommodates them. A laminate in which the positive electrode 120, the separator 110, and the negative electrode 130 are laminated is impregnated with an electrolytic solution.

[Positive electrode]
The positive electrode according to the present embodiment includes the positive electrode active material according to the present embodiment, and can include a conductive material, a binder, and a current collector as necessary. The positive electrode preferably contains a lithium transition metal oxide containing manganese from the viewpoint of cost.

  As the conductive material that can be included in the positive electrode, a known material that can conduct electrons can be used, and is not particularly limited. Among these, as the conductive material, non-graphitic carbonaceous materials such as activated carbon, various cokes, carbon black and acetylene black, and graphite are preferable. These are used singly or in combination of two or more.

  The binder that can be included in the positive electrode can be a known material that can bind at least two of the positive electrode active material, the conductive material that can be included in the positive electrode, and the current collector that can be included in the positive electrode, There is no particular limitation. Among these, as the binder, polyvinylidene fluoride and fluororubber are preferable. A binder is used individually by 1 type or in combination of 2 or more types.

  The current collector that can be included in the positive electrode is not particularly limited, and examples thereof include metal foils such as aluminum, titanium, and stainless steel, expanded metal, punch metal, foam metal, carbon cloth, and carbon paper. These are used singly or in combination of two or more.

[Negative electrode]
The negative electrode used in the present embodiment preferably includes a negative electrode active material, a binder, and a current collector.

  As the negative electrode active material that can be contained in the negative electrode, a known material that can electrochemically occlude and release lithium ions can be used. Among them, the negative electrode active material is not particularly limited, but for example, carbon materials such as graphite powder, mesophase carbon fibers, and mesophase microspheres, and metals, alloys, oxides, and nitrides are preferable. These are used singly or in combination of two or more.

  As the binder that can be included in the negative electrode, a known material that can bind at least two of the negative electrode active material, the conductive material that can be included in the negative electrode, and the current collector that can be included in the negative electrode can be used. There is no particular limitation. Among these, carboxymethyl cellulose, styrene-butadiene crosslinked rubber latex, acrylic latex, and polyvinylidene fluoride are preferable as the binder. These are used singly or in combination of two or more.

  The current collector that can be included in the negative electrode is not particularly limited, and examples thereof include metal foils such as copper, nickel, and stainless steel, expanded metal, punch metal, foam metal, carbon cloth, and carbon paper. These are used singly or in combination of two or more.

[Nonaqueous solvent]
The electrolyte (salt) used for the non-aqueous electrolyte in the present embodiment is not particularly limited, and a conventionally known one can be used. Specific examples thereof include LiPF ₆ (lithium hexafluorophosphate), LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{2k + 1} [k is an integer of 1 to 8], LiN (SO ₂ C _k F _{2k + 1} ) ₂ [k is an integer of 1 to 8], LiPF _n (C _k F _{2k + 1} ) _6-n [n is an integer of 1 to 5, k is an integer of 1 to 8], LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , LiBF ₄ , LiAlO ₄ , LiAlCl ₄ , Li ₂ B ₁₂ F _b H _12-b [b is an integer from 0 to 3], LiBF _q (C _s F _{2s + 1} ) _{4 -Q} [q is an integer of 1 to 3, s is an integer of 1 to 8], LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiB (C ₃ O ₄ H ₂ ) ₂ , LiPF ₄ (C ₂ O ₂ ) and the like. These electrolytes are used singly or in combination of two or more. Among these, LiPF ₆ is preferable from the viewpoint of more effectively and reliably achieving the object of the present invention.

  The non-aqueous solvent used in the non-aqueous electrolyte in the present embodiment is not particularly limited, and a conventionally known one can be used. As the non-aqueous solvent, for example, an aprotic polar solvent is preferable. Specific examples thereof include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, trifluoromethylethylene carbonate, fluoroethylene. Cyclic carbonates such as carbonate and 4,5-difluoroethylene carbonate; lactones such as γ-butyrolactone and γ-valerolactone; cyclic sulfones such as sulfolane; cyclic ethers such as tetrahydrofuran and dioxane; ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl Propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, Chain carbonates such as tilpropyl carbonate and methyl trifluoroethyl carbonate; Nitriles such as acetonitrile; Chain ethers such as dimethyl ether; Chain carboxylic acid esters such as methyl propionate; Chain ether carbonate compounds such as dimethoxyethane . These are used singly or in combination of two or more.

  Note that the nonaqueous electrolyte of the present embodiment may be a liquid or a solid electrolyte.

〔separator〕
As a separator that can be used in the present embodiment, a conventionally known separator used for a nonaqueous electrolyte secondary battery can be used, and is not particularly limited. Examples of the separator include microporous membranes of polyolefin resins such as polyethylene and polypropylene, used for conventional non-aqueous electrolyte secondary batteries; resins such as cellulose, aromatic polyamide, fluororesin and polyolefin, and alumina and silica. Structures such as nonwoven fabrics, papermaking, porous membranes, etc., containing or coated with a mixture of one or more inorganic substances; solid electrolyte films. Any separator may be used as long as it has a high ion permeability and has a function of electrically isolating the positive electrode and the negative electrode.

[Exterior body]
A conventionally well-known thing can be used for the exterior body used for this embodiment, and it does not restrict | limit in particular. Although it does not specifically limit as a material of an exterior body, For example, the laminate film which coat | covered metal, such as stainless steel, iron, and aluminum, and the surface of the metal with resin.

  The non-aqueous electrolyte secondary battery of the present embodiment may have the same configuration as a conventionally known one except that it has the above-described configuration. Examples of the nonaqueous electrolyte secondary battery of the present embodiment include a lithium ion secondary battery and a lithium ion capacitor.

  The nonaqueous electrolyte secondary battery of this embodiment is excellent in all of cycle characteristics, storage characteristics, and continuous charge characteristics even when used under severe temperature and charge / discharge conditions equal to or higher than those of conventional applications, such as automobile applications. It will be.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Example 1>
<Synthesis of LiMn ₂ O ₄ >
Lithium carbonate (Wako Pure Chemical Industries, Ltd.) and manganese carbonate (II) n hydrate (Wako Pure Chemical Industries, Ltd.) were weighed so that the molar ratio of lithium: manganese was 1: 2. Dry mixed for hours. Then, the obtained mixture was baked at 1000 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material precursor represented by LiMn ₂ O ₄ .

<Acid treatment of positive electrode active material precursor>
35 g of the positive electrode active material precursor obtained as described above was stirred for 1 hour in 50 mL of an aqueous H ₃ PO ₄ solution having a concentration of 0.6% by mass. At this time, the acid was 0.86% by mass with respect to 100% by mass of the positive electrode active material precursor. Then, only water was removed from the solution by reducing the pressure at 60 ° C. Then, it dried at 100 degreeC under vacuum for 2 hours. The obtained dried product was calcined at 800 ° C. for 5 hours in the air to obtain a target positive electrode active material. The firing was performed at a temperature increase rate of 10 ° C./min and a temperature decrease rate of 10 ° C./min. The specific surface area of the positive electrode active material was measured with nitrogen using an autosorb-1 manufactured by Cantachrome Co. and calculated by the BET method. The obtained positive electrode active material had a nitrogen adsorption specific surface area of 1.8 m ² / g. The obtained active material was acid-decomposed with microwaves (TOPwave (registered trademark) manufactured by Analiquiena), the amount of P was measured using ICP-AES (Optima 8300 manufactured by Perkin Elmer), and H ₃ PO ₄ added. It was confirmed that all of P was contained in the positive electrode active material. Moreover, the cross section of the positive electrode active material was produced by FIB (SMI4050 by Hitachi High-Tech Science Co., Ltd.) processing. Positive electrode active material The obtained positive electrode active material cross section was analyzed by TEM-EDX (JEM-2100, manufactured by JEOL Ltd.), and the element strength ratio I _{(A) of} peak (A) and peak (B _{) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} were calculated. Further, using TOF-SIMS (nanoTOF manufactured by ULVAC-PHI), I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I ₍ sputtering the surface of the positive electrode active material with Ar ₂₅₀₀ ⁺ beam. _{B) 5 nm} was calculated. The peak (A) is the sum of the intensities of PO ₂ and PO ₃ based on m / z = 63 and 79, and the peak (B) is m / z = 87 and 103 based on MnO ₂ , MnO _3. The sum of the intensities was used. Here, m is mass and z is electric charge. Further using XPS (Thermo Fisher Scientific Inc. _Escalab250), while sputtering the surface of the positive electrode active material by _{Ar 2500} ⁺ beam _{I (A) 50nm / I (} A) 5nm and _{I (B)} 50nm / _{I ( B) 5 nm} was calculated. As the peak (A), the photoelectron energy intensity based on P observed at 135 eV was used, and as the peak (B), the sum of the photoelectron energy intensity based on Mn observed at 642 eV and 654 eV was used.

Moreover, the compound produced | generated after passing through an acid treatment and a baking process was confirmed with the following method. After filtering the solution was stirred for LiMn ₂ O ₄ in H ₃ PO _4, results of ICP-AES analysis of the filtrate, the filtrate was confirmed that Li, Mn, P is present. Since Li and Mn are not contained other than the positive electrode active material precursor, it was considered to be derived from the positive electrode active material precursor. Subsequently, the water obtained by removing the water from the filtrate and drying was calcined at 800 ° C. for 5 hours in the air. From the XRD diffraction peak of the powder after firing, it was confirmed that LiMnPO ₄ , Li ₄ P ₂ O ₇ , and Mn ₂ P ₂ O ₇ were contained. Furthermore, since the XRD halo was confirmed, it was confirmed that an amorphous component was contained.

<Preparation of positive electrode>
With the positive electrode active material obtained as described above, graphite powder (TIMCAL, KS-6) and acetylene black powder (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, and a binder A certain polyvinylidene fluoride solution (manufactured by Kureha, L # 7208) was mixed at a mass ratio of 80: 5: 5: 10 in terms of solid content. To the obtained mixture, N-methyl-2-pyrrolidone as a dispersion solvent was added so as to have a solid content of 35% by mass and further mixed to prepare a slurry solution. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was dried and removed, followed by rolling with a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a positive electrode.

<Production of negative electrode>
Graphite powder as negative electrode active material (Osaka Gas Chemical Co., OMAC1.2H / SS) and graphite powder (manufactured by TIMCAL, SFG6) and styrene butadiene rubber as binder (SBR, Asahi Kasei Chemicals Co., Ltd., L-1571) ) And carboxymethyl cellulose ammonium (Daicel Chemical Industries, Ltd., DN-400H) were mixed at a solid content weight ratio of 90: 10: 1.5: 1.8. The obtained mixture was added to water as a dispersion solvent so that the solid content concentration was 45% by mass to prepare a slurry-like solution. This slurry-like solution was applied to one side of a copper foil having a thickness of 18 μm, and the solvent was removed by drying, followed by rolling with a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a negative electrode.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 so as to be 1 mol / L to obtain an electrolyte solution that was a nonaqueous electrolyte. .

<Production of battery>
A laminate in which the positive electrode and the negative electrode produced as described above are superimposed on both sides of a separator (thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm) made of a polypropylene microporous film is made of stainless steel. It was inserted into a disc-shaped battery case (exterior body) made by the manufacturer. Next, 0.5 mL of the above electrolytic solution was injected therein, and the laminate was immersed in the electrolytic solution, and then the battery case was sealed to produce a nonaqueous electrolyte secondary battery.

<Battery evaluation>
-Initial charging / discharging The obtained non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as "battery") is accommodated in a thermostatic bath (manufactured by Futaba Kagaku, PLM-73S, manufactured by Futaba Kagaku) and charged. It connected to the discharge device (ASKA Electronics Co., Ltd. charge / discharge device ACD-01). Next, the battery was charged with a constant current of 0.05 C, reached 4.2 V, charged for 2 hours with a constant voltage of 4.2 V, and discharged to 3.0 V with a constant current of 0.3 C. 1C is a current value at which the battery is discharged in one hour.

・ Continuous charge characteristic test The battery after the above initial charge / discharge is housed in a thermostat set to 50 ° C. (Futaba Kagaku Co., Ltd., thermostat PLM-73S), and a charge / discharge device (Aska Electronics Co., Ltd., charge / discharge). Connected to device ACD-01). Next, the battery was charged with a constant current of 0.5 C, reached 4.2 V, charged with a constant voltage of 4.2 V for 6 hours, and the current value after 6 hours was confirmed as a leakage current value. Thereafter, the battery was discharged to 3.0 V with a constant current of 0.5C. The results are shown in Table 1.

-Cycle test The battery after the above-mentioned continuous charge characteristic test is accommodated in a thermostat set to 50 ° C (manufactured by Futaba Kagaku Co., thermostat PLM-73S), and a charge / discharge device (manufactured by Asuka Electronics Co., Ltd., charge / discharge device). ACD-01). The battery was then charged to 4.2V with a constant current of 0.5C and discharged to 3.0V with a constant current of 0.5C. The discharge capacity at this time was confirmed as the discharge capacity of the first cycle. This series of charging and discharging was defined as one cycle, and charging and discharging were further performed for 28 cycles. Subsequently, the battery was charged with a constant current of 0.1 C, reached 4.2 V, charged with a constant voltage of 4.2 V for 1 hour, and discharged to 3.0 V with a constant current of 0.1 C ( 30th cycle). The discharge capacity at this time was confirmed as the discharge capacity at the 30th cycle. The capacity retention rate was calculated from the discharge capacity at the first and 30th cycles. The results are shown in Table 1.

Storage test The battery after the above initial charge / discharge is housed in a thermostatic chamber (Futaba Scientific Co., Ltd., thermostatic chamber PLM-73S) set at 50 ° C., and the charge / discharge device (Asuka Electronics Co., Ltd., charge / discharge device ACD). −01). Next, the battery was charged with a constant current of 0.5 C, and after reaching 4.2 V, it was charged with a constant voltage of 4.2 V for 1 hour. Then, it discharged to 3.0V with a constant current of 0.5C. The discharge capacity at that time was confirmed as the discharge capacity before storage. Next, the battery was charged at a constant current of 0.5 C, reached 4.2 V, charged at a constant voltage of 4.2 V for 1 hour, and stored as it was in a thermostat for 5 days. Then, after discharging to 3.0V with a constant current of 0.5C, the battery was charged with a constant current of 0.5C, and after reaching 4.2V, it was charged with a constant voltage of 4.2V for 1 hour. Then, it discharged to 3.0V with a constant current of 0.5C. The discharge capacity at the time of the last discharge was confirmed as the discharge capacity after storage. The capacity retention rate was calculated from the discharge capacity before storage and the discharge capacity after storage. The results are shown in Table 1.

<Example 2>
A non-aqueous electrolyte secondary battery was fabricated and evaluated using the positive electrode active material treated in the same manner as in Example 1 except that the concentration of the H ₃ PO ₄ aqueous solution was changed to 0.3 mass%. The results are shown in Table 1. In addition, the acid used was 0.43 mass% with respect to 100 mass% of positive electrode active material precursors.

Note that the amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₃ PO ₄ P was contained. Further, the element intensity ratio I (A) of the peak (A) _{50 nm} / I _{(A) 5 nm} and the peak (B) I _{(B) 50 nm} / I _{(B) 5 nm} by TEM-EDX and the oxo acid salt formed Was confirmed by the same method as in Example 1.

<Example 3>
A non-aqueous electrolyte secondary battery was produced using the positive electrode active material treated in the same manner as in Example 1 except that an aqueous H ₃ BO ₃ solution having a concentration of 0.4 mass% was used instead of H ₃ PO ₄ . Battery evaluation was performed. The results are shown in Table 1. In addition, the acid used was 0.57 mass% with respect to 100 mass% of positive electrode active material precursors.

In addition, the amount of B in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of B in the added H ₃ BO ₃ was contained. In addition, the element intensity ratio I (A) of peak (A) _{50 nm} / I _{(A) 5 nm} , I _{(B) 50 nm} / I _{(B) 5 nm} of peak (B), and the oxo acid salt produced are the same as in Example 1. It confirmed by the same method. As the peak of the TOF-SIMS (A) was used intensity of m / z = 43 based on the BO _2. As the XPS peak (A), the photoelectron energy intensity based on B observed at 193 eV was used.

<Example 4>
A non-aqueous electrolyte secondary battery was produced using the positive electrode active material treated in the same manner as in Example 1 except that an aqueous H ₂ SO ₄ solution having a concentration of 0.3% by mass was used instead of H ₃ PO ₄ . Battery evaluation was performed. The results are shown in Table 1. In addition, the acid used was 0.43 mass% with respect to 100 mass% of positive electrode active material precursors.

Note that the amount of S in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₂ SO ₄ S was contained. In addition, the element intensity ratio I (A) of peak (A) _{50 nm} / I _{(A) 5 nm} , I _{(B) 50 nm} / I _{(B) 5 nm} of peak (B), and the oxo acid salt produced are the same as in Example 1. It confirmed by the same method. As the peak of the TOF-SIMS (A) was used the sum of the intensities of m / z = 64, and 80 based on the SO _2, and SO _3. As the XPS peak (A), the photoelectron energy intensity based on S observed at 168 eV was used.

<Example 5>
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the firing temperature during the acid treatment was changed to 600 ° C., and the battery was evaluated. The results are shown in Table 1.

Note that the amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₃ PO ₄ P was contained. The element intensity ratio I _{(A) of} the peak (A) and the peak (B) I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} are the same as in Example 1 by TEM-EDX. Confirmed with. Furthermore, the produced oxo acid salt was confirmed by the same method as in Example 1 except that the firing temperature was 600 ° C.

<Example 6>
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the firing temperature during the acid treatment was changed to 1000 ° C., and the battery was evaluated. The results are shown in Table 1.

Note that the amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₃ PO ₄ P was contained. The element intensity ratio I _{(A) of} the peak (A) and the peak (B) I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} are the same as in Example 1 by TEM-EDX. Confirmed with. Further, the produced oxo acid salt was confirmed by the same method as in Example 1 except that the firing temperature was 1000 ° C.

<Example 7>
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the firing time during the acid treatment was changed to 1 hour, and the battery was evaluated. The results are shown in Table 1.

Note that the amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₃ PO ₄ P was contained. The element intensity ratio I _{(A) of} the peak (A) and the peak (B) I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} are the same as in Example 1 by TEM-EDX. Confirmed with. Further, the produced oxo acid salt was confirmed by the same method as in Example 1 except that the firing time was 1 hour.

<Example 8>
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the firing time during the acid treatment was changed to 8 hours, and the battery was evaluated. The results are shown in Table 1.

Note that the amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₃ PO ₄ P was contained. The element intensity ratio I _{(A) of} the peak (A) and the peak (B) I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} are the same as in Example 1 by TEM-EDX. Confirmed with. Further, the produced oxo acid salt was confirmed by the same method as in Example 1 except that the firing time was 8 hours.

<Example 9>
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the firing temperature drop rate during the acid treatment was changed to 1 ° C./min, and the battery was evaluated. The results are shown in Table 1.

Note that the amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₃ PO ₄ P was contained. The element intensity ratio I _{(A) of} the peak (A) and the peak (B) I _{(A) 50 nm} / I _{(A) 5 nm} and I _{(B) 50 nm} / I _{(B) 5 nm} are the same as in Example 1 by TEM-EDX. Confirmed with. Furthermore, the oxo acid salt to be produced was confirmed by the same method as in Example 1 except that the temperature lowering rate was 1 ° C./min.

<Example 10>
<Synthesis of LiMn _1.95 B _0.05 O ₄ >
Lithium carbonate (Wako Pure Chemical Industries, Ltd.) Manganese (II) n hydrate (Wako Pure Chemical Industries, Ltd.) and diboron trioxide (Wako Pure Chemical Industries, Ltd.), Lithium: Manganese: Boron Were weighed so that the molar ratio was 1: 1.95: 0.05, and dry-mixed for 1 hour. Then, the obtained mixture was baked at 1000 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material precursor represented by LiMn _1.95 B _0.05 O ₄ .

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 3 except that the positive electrode active material precursor was changed to LiMn _1.95 B _0.05 O _{4 in} which part of Mn was replaced with boron. Battery evaluation was performed. The results are shown in Table 1.

In addition, the nitrogen adsorption specific surface area of the obtained positive electrode active material was 0.6 m ² / g. The amount of B in the positive electrode active material obtained by the same method as in Example 3 was measured, and it was confirmed that all of B in the added H ₃ BO ₃ was contained. In addition, the element intensity ratio I (A) of peak (A) _{50 nm} / I _{(A) 5 nm} , I _{(B) 50 nm} / I _{(B) 5 nm} of peak (B), and the oxo acid salt produced are the same as in Example 3. It confirmed by the same method.

<Example 11>
<Synthesis of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ >
Nickel (II) sulfate hexahydrate (Wako Pure Chemical Industries, Ltd.) and manganese (II) sulfate pentahydrate (Wako Pure Chemical Industries, Ltd.) in a 1: 1: 1 molar ratio of transition metal elements )) And cobalt sulfate (II) heptahydrate (Wako Pure Chemical Industries, Ltd.) are dissolved in water to prepare a nickel-manganese-cobalt mixed aqueous solution so that the total metal ion concentration is 2 mol / L. did. Subsequently, this nickel-manganese-cobalt mixed aqueous solution was dropped into 3000 mL of a 1 mol / L sodium carbonate aqueous solution heated to 70 ° C. at an addition rate of 12.5 mL / min for 120 minutes. At the time of dropping, nitrogen at a flow rate of 200 mL / min was bubbled into the aqueous solution with stirring. As a result, a precipitated substance was generated, and the obtained precipitated substance was sufficiently washed with distilled water and dried to obtain a nickel-manganese-cobalt compound. The obtained nickel-manganese-cobalt compound and lithium carbonate (Wako Pure Chemical Industries, Ltd.) were weighed so that the molar ratio of lithium: nickel: manganese: cobalt was 3: 1: 1: 1. After time dry mixing, the obtained mixture was baked at 950 ° C. for 5 hours in the air to obtain a positive electrode active material precursor represented by LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1 except that the positive electrode active material precursor was changed to LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . . The results are shown in Table 3.

In addition, the nitrogen adsorption specific surface area of the obtained positive electrode active material was 1.0 m ² / g. The amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added H ₃ PO ₄ P was adhered. In addition, the element intensity ratio I (A) of peak (A) _{50 nm} / I _{(A) 5 nm} , I _{(B) 50 nm} / I _{(B) 5 nm} of peak (B), and the oxo acid salt produced are the same as in Example 1. It confirmed by the same method. In addition, as a peak (B) other than Mn in TOF-SIMS, Ni uses the sum of the intensities of NiO ₂ and NiO ₃ based on m / z = 90 and 106, and Co is m based on CoO ₂ and CoO _3. The sum of the intensities of / z = 91 and 107 was used. As a peak (A) other than Mn of XPS, Ni used the sum of photoelectron energy intensities of 855 eV and 862 eV, and Co used the sum of photoelectron energy intensities of 780 eV and 795 eV.

<Example 12>
<Synthesis of Li _1.2 Ni _0.175 Co _0.100 Mn _0.525 O ₂ >
Lithium nitrate (Wako Pure Chemical Industries, Ltd.), nickel nitrate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.), cobalt nitrate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.) and Manganese (II) nitrate hexahydrate (Wako Pure Chemical Industries, Ltd.) was weighed so as to have a composition ratio of Li _1.2 Ni _0.175 Co _0.100 Mn _0.525 O ₂ , and the total amount of nitrate Distilled water was added to give a concentration of 40% by mass as a nitrate aqueous solution. Next, the obtained aqueous solution was dried at 260 ° C. for 2 hours to remove water, and then the powder was recovered to obtain a dried product. Subsequently, by holding the dried body at 500 ° C., the nitric acid content held by the metal other than lithium was removed. The obtained dry powder was once taken out from the container, pulverized and mixed, then fired at 830 ° C., and a positive electrode active material precursor represented by Li _1.2 Ni _0.175 Co _0.100 Mn _0.525 O ₂ was obtained. Obtained.

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the positive electrode active material precursor was changed to Li _1.2 Ni _0.175 Co _0.100 Mn _0.525 O ₂ , and the following battery Evaluation was performed. The results are shown in Table 3.

In addition, the nitrogen adsorption specific surface area of the obtained positive electrode active material was 4.2 m ² / g. The amount of P in the positive electrode active material obtained by the same method as in Example 1 was measured, and it was confirmed that all of the added P of H ₃ PO ₄ was contained. In addition, the element intensity ratio I (A) of peak (A) _{50 nm} / I _{(A) 5 nm} , I _{(B) 50 nm} / I _{(B) 5 nm} of peak (B), and the oxo acid salt produced are the same as in Example 1. It confirmed by the same method.

<Battery evaluation>
-Initial charging / discharging The obtained non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as "battery") is accommodated in a thermostatic bath (manufactured by Futaba Kagaku, PLM-73S, manufactured by Futaba Kagaku) and charged. It connected to the discharge device (ASKA Electronics Co., Ltd. charge / discharge device ACD-01). Next, the battery was charged at a constant current of 0.05 C, reached 4.7 V, charged at a constant voltage of 4.7 V for 2 hours, and discharged to 2.0 V at a constant current of 0.3 C. 1C is a current value at which the battery is discharged in one hour.

・ Continuous charge characteristic test The battery after the above initial charge / discharge is housed in a thermostat set to 50 ° C. (Futaba Kagaku Co., Ltd., thermostat PLM-73S), and a charge / discharge device (Aska Electronics Co., Ltd., charge / discharge). Connected to device ACD-01). Next, the battery was charged with a constant current of 0.5 C, reached 4.5 V, charged with a constant voltage of 4.5 V for 6 hours, and the current value after 6 hours was confirmed as a leakage current value. Thereafter, the battery was discharged to 2.0 V at a constant current of 0.5C. The results are shown in Table 3.

-Cycle test The battery after the above-mentioned continuous charge characteristic test is accommodated in a thermostat set to 50 ° C (manufactured by Futaba Kagaku Co., thermostat PLM-73S), and a charge / discharge device (manufactured by Asuka Electronics Co., Ltd., charge / discharge device). ACD-01). The battery was then charged to 4.5V with a constant current of 0.5C and discharged to 2.0V with a constant current of 0.5C. The discharge capacity at this time was confirmed as the discharge capacity of the first cycle. This series of charging and discharging was defined as one cycle, and charging and discharging were further performed for 28 cycles. Subsequently, the battery was charged at a constant current of 0.1 C, reached 4.5 V, charged at a constant voltage of 4.5 V for 1 hour, and discharged to 2.0 V at a constant current of 0.1 C ( 30th cycle). The discharge capacity at this time was confirmed as the discharge capacity at the 30th cycle. The capacity retention rate was calculated from the discharge capacity at the first and 30th cycles. The results are shown in Table 3.

Storage test The battery after the above initial charge / discharge is housed in a thermostatic chamber (Futaba Scientific Co., Ltd., thermostatic chamber PLM-73S) set at 50 ° C., and the charge / discharge device (Asuka Electronics Co., Ltd., charge / discharge device ACD). −01). Next, the battery was charged with a constant current of 0.5 C, reached 4.5 V, charged with a constant voltage of 4.5 V for 1 hour, and then discharged to 2.0 V with a constant current of 0.5 C. The discharge capacity at that time was confirmed as the discharge capacity before storage. Next, the battery was charged with a constant current of 0.5 C, reached 4.5 V, charged with a constant voltage of 4.5 V for 1 hour, and stored as it was in a thermostatic bath for 5 days. Then, after discharging to 2.0V with a constant current of 0.5C, charging with a constant current of 0.5C, after reaching 4.5V, charging with a constant voltage of 4.5V for 1 hour, then 0.5C Was discharged at a constant current of 2.0 V. The discharge capacity at the time of the last discharge was confirmed as the discharge capacity after storage. The capacity retention rate was calculated from the discharge capacity before storage and the discharge capacity after storage. The results are shown in Table 3.

<Comparative Example 1>
The battery was evaluated in the same manner as in Example 1 except that a non-aqueous electrolyte secondary battery was produced using LiMn ₂ O ₄ that was not subjected to acid treatment and baking as the positive electrode active material. The results are shown in Table 1.

<Comparative Example 2>
The battery was evaluated in the same manner as in Example 1 except that a non-aqueous electrolyte secondary battery was produced using LiMn ₂ O ₄ that was not subjected to the firing step as the positive electrode active material. The results are shown in Table 1.

<Comparative Example 3>
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the firing temperature was changed to 1050 ° C. for 30 hours, and the battery was evaluated. The results are shown in Table 1.

<Comparative Example 4>
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the firing conditions were changed to 500 ° C., 12 hours, and the temperature rising rate was 0.2 ° C./min, and the battery was evaluated. The results are shown in Table 1.

<Comparative Example 5>
Using a positive electrode active material treated in the same manner as in Example 1 except that the firing conditions were changed to 900 ° C. for 3 hours using (NH ₄ ) ₂ HPO ₄ aqueous solution instead of H ₃ PO ₄ , non-aqueous An electrolyte secondary battery was produced and evaluated. The results are shown in Table 1.

<Comparative Example 6>
A mixed aqueous solution of (NH ₄ ) ₂ HPO ₄ and Al (NO ₃ ) ₃ was used instead of H ₃ PO ₄ , and the same treatment as in Example 1 was performed except that the firing conditions were changed to 400 ° C. for 5 hours. Using the positive electrode active material, a non-aqueous electrolyte secondary battery was produced and evaluated. The results are shown in Table 1.

<Comparative Example 7>
The battery was evaluated in the same manner as in Example 10, except that LiMn _1.95 B _0.05 O ₄ not subjected to the acid treatment and the firing step was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced. It was. The results are shown in Table 1.

<Comparative Example 8>
As the positive electrode active material, except that a non-aqueous electrolyte secondary battery using _LiNi 1/3 _Mn 1/3 _Co 1/3 _{O 2} is not performed acid treatment and firing step in the same manner as in Example 11 Battery evaluation was performed. The results are shown in Table 3.

<Comparative Example 9>
The battery evaluation was performed in the same manner as in Example 11 except that a non-aqueous electrolyte secondary battery was produced using LiNi _1/3 Mn _1/3 Co _1/3 O ₂ that was not subjected to the firing step as the positive electrode active material. went. The results are shown in Table 3.

<Comparative Example 10>
Example 12 except that a non-aqueous electrolyte secondary battery was produced using Li _1.2 Ni _0.175 Co _0.100 Mn _0.525 O ₂ without the acid treatment and the firing step as the positive electrode active material. The battery was evaluated in the same manner as above. The results are shown in Table 3.

<Comparative Example 11>
Except that a non-aqueous electrolyte secondary battery was fabricated using Li _1.2 Ni _0.175 Co _0.100 Mn _0.525 O ₂ that was not _subjected to the firing step as the positive electrode active material, the same as in Example 12. The battery was evaluated. The results are shown in Table 3.

Positive electrode: LiMn ₂ O ₄
* Amount of acid used per 100% by mass of positive electrode active material precursor

Positive electrode: LiMn ₂ O ₄
* Amount of acid used per 100% by mass of positive electrode active material precursor

Positive electrode: LiNi _1/3 Mn _1/3 Co _1/3 O ₂ or Li _1.2 Ni _0.175 Co _0.100 Mn _0.525 O ₂
* Amount of acid used per 100% by mass of positive electrode active material precursor

  The nonaqueous electrolyte secondary battery of the present invention has industrial applicability to various consumer equipment power supplies and automobile power supplies.

  DESCRIPTION OF SYMBOLS 100 ... Nonaqueous electrolyte secondary battery, 110 ... Separator, 120 ... Positive electrode, 130 ... Negative electrode, 140 ... Positive electrode collector, 150 ... Negative electrode collector, 160 ... Battery exterior.

Claims (13)

A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by transmission electron microscope-energy dispersive X-ray analysis of the positive electrode active material cross section is at least:
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
A positive electrode active material in which at least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.5
2.0 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).) A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by time-of-flight secondary ion mass spectrometry in the depth direction of the positive electrode active material is at least,
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
A positive electrode active material in which at least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.7
1.5 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).) A positive electrode active material comprising a lithium transition metal oxide and an oxoacid salt,
The peak detected by X-ray photoelectron spectroscopy in the depth direction of the positive electrode active material is at least,
A peak (A) derived from at least one element selected from the group consisting of phosphorus, sulfur and boron;
A peak (B) derived from at least one element selected from the group consisting of transition metals,
A positive electrode active material in which at least one peak (A) and at least one peak (B) satisfy the following relational expression.
0.00001 ≦ I _{(A) 50 nm} / I _{(A) 5 nm} ≦ 0.6
1.7 ≦ I _{(B) 50 nm} / I _{(B) 5 nm} ≦ 10000
(I _{(A) 50 nm} indicates the intensity of the peak (A) at a depth of 50 nm from the surface of the positive electrode active material, and I _{(A) 5 nm} indicates the peak (A) at a depth of 5 nm from the surface of the positive electrode active material. shows the intensity _{of, I (B) 50nm,} the indicates the intensity of the peak in the positive electrode active material surface than 50nm depth _{(B), I (B)} 5nm is definitive the depth of the positive electrode active 5nm than material surface Indicates the intensity of peak (B).)   The positive electrode active material according to claim 1, wherein the peak (A) includes at least a peak derived from phosphorus. The oxoacid salt is at least (M _x P _y O _{3 + z} ) _n O (x ≧ 1, y ≧ 1, z ≧ 0, n ≧ 1, M is at least one selected from the group consisting of Li and a transition metal The positive electrode active material according to any one of claims 1 to 4, comprising an element). The oxoacid salt is at least (LiM _x-1 P _y O _{3 + z} ) _n O (x ≧ 1, y ≧ 1, z ≧ 0, n ≧ 1, M is at least one selected from the group consisting of transition metals) The positive electrode active material of any one of Claims 1-5 containing an element. The positive electrode active material according to claim 1, wherein the oxoacid salt includes at least Li ₄ P ₂ O ₇ and / or LiMnPO ₄ . The oxoacid salt is
Li ₄ P ₂ O ₇ and / or LiMnPO ₄ ,
At least one compound represented by M _x P _{2 + y} O _{7 + z} (x ≧ 1, y ≧ 0, z ≧ 0, M represents at least one selected from the group consisting of Mn, Ni, Co and Fe) Including,
The positive electrode active material of any one of Claims 1-7. The oxoacid salt is
Li ₄ P ₂ O ₇ and / or LiMnPO ₄ ,
And at least one compound represented by M ₂ P ₂ O ₇ (M represents at least one selected from the group consisting of Mn, Ni, Co, and Fe).
The positive electrode active material of any one of Claims 1-8.   The positive electrode active material according to claim 1, wherein the oxoacid salt is attached to at least a part of the lithium transition metal oxide.   The positive electrode active material of any one of Claims 1-10 which is an object for nonaqueous electrolyte secondary batteries.   The positive electrode containing the positive electrode active material of any one of Claims 1-11.   A nonaqueous electrolyte secondary battery comprising at least the positive electrode according to claim 12, a negative electrode, a nonaqueous electrolyte, and an exterior body.