JP7262365B2 - Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, lithium secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for lithium secondary batteries, a positive electrode for lithium secondary batteries, and a lithium secondary battery.

Lithium metal composite oxides are used as positive electrode active materials for lithium secondary batteries (hereinafter sometimes referred to as “positive electrode active materials”). Lithium secondary batteries have already been put to practical use not only as small power sources for mobile phones and notebook computers, but also as medium- and large-sized power sources for automobiles and power storage.

Lithium-metal composite oxides include lithium-cobalt composite oxides, lithium-nickel composite oxides, lithium-nickel-manganese composite oxides, and the like. Patent Literature 1 describes a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a coating layer made of a compound containing aluminum on the surface of these lithium metal composite oxides. In Patent Document 1, by providing such a coating layer, contact of moisture, carbon dioxide, etc. in the air with the central portion of the lithium metal composite oxide is suppressed, and the weather resistance of the positive electrode active material is improved. there is

JP 2017-188211 A

When the coating layer is provided on the surface of the lithium metal composite oxide, it is conceivable that the coating layer is formed unevenly, for example, the coating layer is partially formed or the thickness of the coating layer varies. An uncoated portion formed in such a case or a portion where the coating layer is a thin film becomes a reaction portion with the electrolytic solution. A decomposition reaction of the electrolytic solution occurs at this reaction site, and gas may be generated. The generated gas causes battery swelling.
The present inventors have discovered a new problem of selecting a positive electrode active material having a coating layer, the coating layer being uniformly formed on the surface of the lithium metal composite oxide.

The present invention has been made in view of the above circumstances, and provides a positive electrode active material for a lithium secondary battery that generates less gas and suppresses battery swelling, a positive electrode using the same, and a non-aqueous electrolyte using the same. An object of the present invention is to provide a secondary battery.

That is, the present invention includes the following inventions [1] to [9].
[1] A lithium secondary comprising a coating layer containing a metal composite oxide of lithium and aluminum on the surface of a lithium composite metal compound composed of secondary particles formed by aggregating primary particles capable of doping and dedoping lithium ions. A positive electrode active material for a lithium secondary battery, characterized by containing at least nickel and aluminum as metals other than lithium and satisfying all of the following requirements (1) to (2).
(1) The ratio of the detection intensity of aluminum to the detection intensity of nickel (aluminum The detection intensity of /the detection intensity of nickel) is defined as AR.
The AR when the SEM-EDX measurement is performed at an acceleration voltage of 3 kV is assumed to be _AR3 .
Let _AR10 be the AR when the SEM-EDX measurement is performed at an accelerating voltage of 10 kV.
Calculate the average value [Ave (AR ₃ /AR ₁₀ )] and the standard deviation [σ (AR ₃ /AR ₁₀ )] of the ratio [AR ₃ /AR ₁₀ ] between AR ₃ and AR ₁₀ obtained by the above measurement method. do.
A coefficient of variation <[σ(AR ₃ /AR ₁₀ )]/[Ave(AR ₃ /AR ₁₀ )]> is calculated from the ratio and the standard deviation.
The inverse of the obtained variation coefficient <[Ave( _AR3 / _AR10 )]/[σ( _AR3 / _AR10 )]> is 6.1 or more.
(2) The average value of _AR3 is 0.025 or more.
[2] A lithium secondary comprising a coating layer containing a metal composite oxide of lithium and zirconium on the surface of a lithium composite metal compound composed of secondary particles formed by aggregating primary particles capable of doping and dedoping lithium ions. A positive electrode active material for a lithium secondary battery, characterized by containing at least nickel and zirconium as metals other than lithium and satisfying all of the following requirements (1) to (2).
(1) The ratio of the detection intensity of zirconium and the detection intensity of nickel (zirconium Detected intensity/Nickel detected intensity) is defined as ZR.
The ZR when the SEM-EDX measurement is performed at an acceleration voltage of 5 kV is defined as _ZR5 .
Let ZR ₁₀ be the ZR when the SEM-EDX measurement is performed at an acceleration voltage of 10 kV.
Calculate the average value [Ave (ZR ₅ /ZR ₁₀ )] and the standard deviation [σ (ZR ₅ /ZR ₁₀ )] of the ratio [ZR ₅ /ZR ₁₀ ] between ZR ₅ and ZR ₁₀ obtained by the above measurement method. do.
A coefficient of variation <[σ(ZR ₅ /ZR ₁₀ )]/[Ave (ZR ₅ /ZR ₁₀ )]> is calculated from the ratio and the standard deviation.
The inverse of the obtained variation coefficient <[Ave( _ZR5 / _ZR10 )]/[σ( _ZR5 / _ZR10 )]> is 1.0 or more.
(2) The average value of _ZR5 is 0.002 or more.
[3] A lithium secondary comprising a coating layer containing a metal composite oxide of lithium and tungsten on the surface of a lithium composite metal compound composed of secondary particles formed by agglomeration of primary particles capable of doping and dedoping lithium ions. A positive electrode active material for a lithium secondary battery, characterized by containing at least nickel and tungsten as metals other than lithium and satisfying all of the following requirements (1) to (2).
(1) The ratio of the detection intensity of tungsten to the detection intensity of nickel measured by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) on the particle surface of the positive electrode active material for lithium secondary batteries (tungsten Detected intensity of nickel/Detected intensity of nickel) is defined as WR.
WR ₃ is the WR when the SEM-EDX measurement is performed at an acceleration voltage of 3 kV.
Let WR ₁₀ be the WR when the SEM-EDX measurement is performed at an acceleration voltage of 10 kV.
Calculate the average value [Ave (WR ₃ /WR ₁₀ )] and the standard deviation [σ (WR ₃ /WR ₁₀ )] of the ratio [WR ₃ /WR ₁₀ ] between WR ₃ and WR ₁₀ obtained by the above measurement method. do.
A coefficient of variation <[σ(WR ₃ /WR ₁₀ )]/[Ave(WR ₃ /WR ₁₀ )]> is calculated from the ratio and the standard deviation.
The reciprocal <[Ave(WR ₃ /WR ₁₀ )]/[σ(WR ₃ /WR ₁₀ )]> of the obtained coefficient of variation is 2.5 or more.
(2) The average value of WR ₃ is 0.005 or more.
[4] The positive electrode active material for a lithium secondary battery according to any one of [1] to [3], which has a BET specific surface area of 0.1 m ² /g or more and 2.0 m ² /g or less.
[5] The lithium according to any one of [1] to [4], wherein the content of lithium carbonate is 0.3% by mass or less and the content of lithium hydroxide is 0.3% by mass or less. Positive electrode active material for secondary batteries.
[6] The positive electrode active material for lithium secondary batteries according to any one of [1] to [5], which has a water content of 600 ppm or less.
[7] The lithium secondary battery according to any one of [1] to [6], wherein the lithium composite metal compound has an α-NaFeO ₂ type crystal structure represented by the following compositional formula (A): Positive electrode active material.
Li[ _Lix ( _NiaCobMncM1d ) _{1 -x} ] ^O2 _{( A )}
(where -0.1 ≤ x ≤ 0.2, 0.5 ≤ a < 1, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.1, a + b + c + d = 1 and M ¹ is Mg, Ca, Sr, Ba, Zn, B, Al, Ga, Ti, Zr, Ge, Fe, Cu, Cr, V, W, Mo, Sc, Y, Nb, La, Ta, It is one or more elements selected from the group consisting of Tc, Ru, Rh, Pd, Ag, Cd, In, and Sn.)
[8] The positive electrode active material for a lithium secondary battery according to [7], wherein x in the composition formula (A) satisfies 0<x≤0.1.
[9] A positive electrode for lithium secondary batteries comprising the positive electrode active material for lithium secondary batteries according to any one of [1] to [8].
[10] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [9].

According to the present invention, it is possible to provide a positive electrode active material for a lithium secondary battery that generates less gas and suppresses battery swelling, a positive electrode using the same, and a non-aqueous electrolyte secondary battery using the same.

1 is a schematic configuration diagram showing an example of a lithium ion secondary battery; FIG. 1 is a schematic configuration diagram showing an example of a lithium ion secondary battery; FIG. FIG. 2 is an image of the cross section of the positive electrode active material for a lithium secondary battery of Example 1, obtained by mapping aluminum elements by STEM-EDX. FIG. 10 is an image of the cross section of the positive electrode active material for a lithium secondary battery of Example 3, obtained by mapping aluminum elements by STEM-EDX. FIG. 2 is an image diagram of aluminum element mapping of a cross section of the positive electrode active material for a lithium secondary battery of Comparative Example 1 by STEM-EDX.

<Positive electrode active material for lithium secondary battery>
<<First embodiment>>
In this embodiment, a coating layer containing a metal composite oxide of lithium and aluminum is provided on the surface of a lithium composite metal compound composed of secondary particles formed by aggregating primary particles capable of doping and dedoping lithium ions. It is a positive electrode active material for secondary batteries. The positive electrode active material for a lithium secondary battery of the present embodiment contains at least nickel and aluminum as metals other than lithium. Furthermore, the positive electrode active material for lithium secondary batteries of the present embodiment satisfies all of the following requirements (1) and (2).
(1) The ratio of the detection intensity of aluminum to the detection intensity of nickel (aluminum The detection intensity of /the detection intensity of nickel) is defined as AR.
The AR when the SEM-EDX measurement is performed at an acceleration voltage of 3 kV is assumed to be _AR3 .
Let _AR10 be the AR when the SEM-EDX measurement is performed at an accelerating voltage of 10 kV.
Calculate the average value [Ave (AR ₃ /AR ₁₀ )] and the standard deviation [σ (AR ₃ /AR ₁₀ )] of the ratio [AR ₃ /AR ₁₀ ] between AR ₃ and AR ₁₀ obtained by the above measurement method. do.
A coefficient of variation <[σ(AR ₃ /AR ₁₀ )]/[Ave(AR ₃ /AR ₁₀ )]> is calculated from the ratio and the standard deviation.
The inverse of the obtained variation coefficient <[Ave( _AR3 / _AR10 )]/[σ( _AR3 / _AR10 )]> is 6.1 or more.
(2) The average value of _AR3 is 0.025 or more.

The positive electrode active material for a lithium secondary battery of this embodiment includes a coating layer containing a metal composite oxide of lithium and aluminum on the surface of the lithium composite metal compound.
Each requirement that the positive electrode active material for a lithium secondary battery of this embodiment satisfies will be described.

[Requirements (1)]
In the positive electrode active material for a lithium secondary battery of the present embodiment, when the particle surface of the positive electrode active material is measured by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) under the following conditions, the detection strength of aluminum and the detected intensity ratio AR of nickel satisfies specific requirements. In addition, the positive electrode active material for a lithium secondary battery of the present embodiment includes a coating layer on the surface of the lithium composite metal compound. For this reason, the measurement shall be performed with the coating layer provided.
In the present embodiment, an example of an apparatus used for the measurement of requirement (1) is not limited as long as it can irradiate an electron beam under conditions of accelerating voltages of 3 kV and 10 kV. In this embodiment, a field emission scanning electron microscope secondary electron spectrometer (SEM-EDX; product name S-4800 manufactured by Hitachi High Technologies, Ltd., energy dispersive X-ray analyzer X-Max ^N manufactured by Oxford Instruments ) is preferred.

- Measurement method First, a carbon tape is stuck on the sample stage of the scanning electron microscope, and the positive electrode active material particles are placed thereon. The sample stage is preferably made of carbon.
The positive electrode active material particles arranged as described above are irradiated with an electron beam under conditions of an acceleration voltage of 3 kV or 10 kV and a working distance of 15 mm, and the detection intensity of characteristic X-rays observed for aluminum and nickel is determined.
The ratio of the detected intensity of aluminum to the detected intensity of nickel (detected intensity of aluminum/detected intensity of nickel) at this time is defined as AR. Further, the AR obtained at an acceleration voltage of 3 kV is assumed to be _AR3 . The AR obtained at an accelerating voltage of 10 kV is assumed to be _AR10 .

Here, measurement at an acceleration voltage of 3 kV has high sensitivity to the composition near the surface of the positive electrode active material particles, and AR ₃ means a value that strongly reflects the amount of aluminum near the surface of the positive electrode active material particles (that is, the coating layer).
In the measurement at an acceleration voltage of 10 kV, even the inside of the positive electrode active material particles can be detected, so AR ₁₀ means a value reflecting the amount of aluminum in the entire particle including the vicinity of the surface of the positive electrode active material particles.

First, [AR ₃ /AR ₁₀ ], which is the ratio of AR ₃ and AR ₁₀ , is obtained.
Next, the average value [Ave (AR ₃ /AR ₁₀ )] of this ratio [AR ₃ /AR ₁₀ ] is calculated. When obtaining the average value, for example, it is preferable to obtain the average value obtained by measuring arbitrary 20 positive electrode active materials. In calculating the average value, the standard deviation [σ(AR ₃ /AR ₁₀ )] of the ratio [AR ₃ /AR ₁₀ ] is also calculated.
Next, the coefficient of variation <[σ(AR ₃ /AR ₁₀ )]/[Ave(AR ₃ /AR ₁₀ )]> is calculated from the above ratio and standard deviation.
Then, the reciprocal <[Ave(AR ₃ /AR ₁₀ )]/[σ(AR ₃ /AR ₁₀ )]> of the obtained coefficient of variation is calculated.

In the present embodiment, <[Ave (AR ₃ /AR ₁₀ )]/[σ (AR ₃ /AR ₁₀ )]> calculated by the above method is 6.1 or more.

However, AR ₃ and AR ₁₀ are to be measured in the same area on the particle surface of the positive electrode active material for lithium secondary batteries. In other words, AR ₃ and AR ₁₀ are to be measured by irradiating the same surface region of the same particle with an electron beam.

In the present embodiment, <[Ave (AR ₃ /AR ₁₀ )]/[σ (AR ₃ /AR ₁₀ )]> is preferably 6.2 or more, more preferably 6.3 or more, and 6.4 or more. Especially preferred.
By measuring <[Ave(AR ₃ /AR ₁₀ )]/[σ(AR ₃ /AR ₁₀ )]>, it is possible to determine whether aluminum is uniformly dispersed. Specifically, the larger the value, the more uniformly distributed the amount of aluminum present in the vicinity of the surface of the positive electrode active material particles (that is, the coating layer).
It is believed that the uniform presence of a certain amount of aluminum on the surface of the positive electrode active material reduces the uncoated or thin coating layer portion. For this reason, it is presumed that the positive electrode active material of the present embodiment suppresses the generation of gas due to contact with the electrolytic solution, and suppresses swelling of the battery.

[Requirement (2)]
In this embodiment, the average AR ₃ is 0.025 or more, preferably 0.027 or more, more preferably 0.03 or more, and particularly preferably 0.035 or more.
When the average AR ₃ is equal to or higher than the above lower limit value, it means that a large amount of aluminum is distributed in the vicinity of the surface of the positive electrode active material (that is, the coating layer).

- Coating layer The positive electrode active material of the present embodiment includes a coating layer containing a metal composite oxide of lithium and aluminum. In this embodiment, the entire surface of the lithium composite metal compound is covered. As long as the above requirements (1) and (2) are satisfied, the entire surface of the lithium mixed metal compound may not be completely covered, or there may be uncovered portions.

The coating layer contains a metal composite oxide of lithium and aluminum. A metal composite oxide of lithium and aluminum is a compound having lithium ion conductivity. As such a compound having lithium ion conductivity, one or more selected from the group consisting of LiAlO ₂ , Li ₅ AlO ₄ and LiAl ₅ O ₈ is preferable, LiAlO ₂ is more preferable, and α-LiAlO ₂ is particularly preferable. preferable.

The coating layer may contain a product obtained by partially reacting a lithium composite metal compound or a lithium composite metal compound with a metal composite oxide of lithium and aluminum, but the metal composite oxide of lithium and aluminum may also be included. The effect of the present invention can be obtained if the substance contains at least 30% or more. The coating layer preferably contains 50% or more of the metal composite oxide of lithium and aluminum, more preferably 70% or more, and even more preferably 90% or more.

Aluminum oxide, aluminum hydroxide, and aluminum nitrate can be used as raw materials for the aluminum constituting the coating layer. From the viewpoint of promoting the formation of a uniform coating layer, the BET specific surface area of the raw material containing aluminum is preferably 10 m ² /g or more, more preferably 30 m ² /g or more.

<<Second embodiment>>
In this embodiment, a coating layer containing a metal composite oxide of lithium and zirconium is provided on the surface of a lithium composite metal compound composed of secondary particles formed by agglomeration of primary particles capable of doping and dedoping lithium ions. The positive electrode active material for a lithium secondary battery of this embodiment contains at least nickel and zirconium as metals other than lithium. Furthermore, the positive electrode active material for lithium secondary batteries of the present embodiment satisfies all of the following requirements (1) and (2).
(1) The ratio of the detection intensity of zirconium and the detection intensity of nickel (zirconium Detected intensity/Nickel detected intensity) is defined as ZR.
The ZR when the SEM-EDX measurement is performed at an acceleration voltage of 5 kV is defined as _ZR5 .
Let ZR ₁₀ be the ZR when the SEM-EDX measurement is performed at an acceleration voltage of 10 kV.
Calculate the average value [Ave (ZR ₅ /ZR ₁₀ )] and the standard deviation [σ (ZR ₅ /ZR ₁₀ )] of the ratio [ZR ₅ /ZR ₁₀ ] between ZR ₅ and ZR ₁₀ obtained by the above measurement method. do.
A coefficient of variation <[σ(ZR ₅ /ZR ₁₀ )]/[Ave (ZR ₅ /ZR ₁₀ )]> is calculated from the ratio and the standard deviation.
The inverse of the obtained variation coefficient <[Ave( _ZR5 / _ZR10 )]/[σ( _ZR5 / _ZR10 )]> is 1.0 or more.
(2) The average value of _ZR5 is 0.002 or more.

The positive electrode active material for a lithium secondary battery of this embodiment includes a coating layer containing a metal composite oxide of lithium and zirconium on the surface of the lithium composite metal compound.
Each requirement that the positive electrode active material for a lithium secondary battery of this embodiment satisfies will be described.

[Requirements (1)]
In the positive electrode active material for a lithium secondary battery of the present embodiment, the detection intensity of zirconium and the detection intensity of nickel when the particle surface is measured by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) under the following conditions satisfies certain requirements. In addition, the positive electrode active material for a lithium secondary battery of the present embodiment includes a coating layer on the surface of the lithium composite metal compound. For this reason, the measurement shall be performed with the coating layer provided.

- Measurement method First, a carbon tape is stuck on the sample stage of the scanning electron microscope, and the positive electrode active material particles are placed thereon. The sample stage is preferably made of carbon.
The positive electrode active material particles arranged as described above are irradiated with an electron beam under conditions of an acceleration voltage of 5 kV or 10 kV and a working distance of 15 mm, and the detection intensity of characteristic X-rays observed for zirconium and nickel is determined.
The ratio of the detected intensity of zirconium and the detected intensity of nickel (detected intensity of zirconium/detected intensity of nickel) at this time is defined as ZR. Further, the ZR obtained at an acceleration voltage of 5 kV is defined as _ZR5 . The ZR obtained at an acceleration voltage of 10 kV is defined as _ZR10 .

Here, measurement at an acceleration voltage of 5 kV is highly sensitive to the composition near the surface of the positive electrode active material particles, and ZR ₅ means a value that strongly reflects the amount of zirconium near the surface of the positive electrode active material particles (that is, the coating layer).
In measurement at an acceleration voltage of 10 kV, even the inside of the positive electrode active material particles can be detected, so ZR ₁₀ means a value reflecting the amount of zirconium in the entire particle including the vicinity of the surface of the positive electrode active material particles.

First, [ZR ₅ /ZR ₁₀ ], which is the ratio of ZR ₅ and ZR ₁₀ , is obtained.
Next, the average value [Ave (ZR ₅ /ZR ₁₀ )] of this ratio [ZR ₅ /ZR ₁₀ ] is calculated. When obtaining the average value, for example, it is preferable to obtain the average value obtained by measuring arbitrary 20 positive electrode active materials. In calculating the average value, the standard deviation [σ(ZR ₅ /ZR ₁₀ )] of the ratio [ZR ₅ /ZR ₁₀ ] is also calculated.
Next, the coefficient of variation <[σ(ZR ₅ /ZR ₁₀ )]/[Ave (ZR ₅ /ZR ₁₀ )]> is calculated from the above ratio and standard deviation.
Then, the reciprocal <[Ave (ZR ₅ /ZR ₁₀ )]/[σ (ZR ₅ /ZR ₁₀ )]> of the obtained coefficient of variation is calculated.

In the present embodiment, <[Ave (ZR ₅ /ZR ₁₀ )]/[σ (ZR ₅ /ZR ₁₀ )]> calculated by the above method is 1.0 or more.

However, ZR ₅ and ZR ₁₀ are measured in the same region on the particle surface of the positive electrode active material for lithium secondary batteries. In other words, ZR ₅ and ZR ₁₀ are to be measured by irradiating the same surface region of the same particle with an electron beam.

In the present embodiment, <[Ave (ZR ₅ /ZR ₁₀ )]/[σ (ZR ₅ /ZR ₁₀ )]> is preferably 1.5 or more, more preferably 2.5 or more, and 3.0 or more. Especially preferred.
By measuring <[Ave (ZR ₅ /ZR ₁₀ )]/[σ (ZR ₅ /ZR ₁₀ )]>, it is possible to determine whether zirconium is uniformly dispersed. Specifically, it means that the larger this value is, the more uniformly the zirconium present in the vicinity of the surface of the positive electrode active material particles (that is, the coating layer) is distributed.
It is believed that the uniform presence of a certain amount of zirconium on the surface of the positive electrode active material reduces the uncoated or thin coating layer portion. For this reason, it is presumed that the positive electrode active material of the present embodiment suppresses the generation of gas due to contact with the electrolytic solution, and suppresses swelling of the battery.

[Requirement (2)]
In this embodiment, the average _ZR5 is 0.002 or more, preferably 0.005 or more, more preferably 0.007 or more, and particularly preferably 0.010 or more.
When the average of ZR ₅ is equal to or higher than the above lower limit, it means that a large amount of zirconium is distributed near the surface of the positive electrode active material (that is, the coating layer).

- Coating layer The positive electrode active material of the present embodiment includes a coating layer containing a metal composite oxide of lithium and zirconium. In this embodiment, the entire surface of the lithium composite metal compound is covered. As long as the above requirements (1) and (2) are satisfied, the entire surface of the lithium mixed metal compound may not be completely covered, or there may be uncovered portions.

The coating layer contains a metal composite oxide of lithium and zirconium. A metal composite oxide of lithium and zirconium is a compound having lithium ion conductivity. As such a compound having lithium ion conductivity, Li ₂ ZrO ₃ or Li ₄ ZrO ₄ is preferable, and Li ₂ ZrO ₃ is more preferable. The coating layer may contain a product obtained by partially reacting a lithium composite metal compound or a lithium composite metal compound with a metal composite oxide of lithium and zirconium. The effect of the present invention can be obtained if the substance contains at least 30% or more. The coating layer preferably contains 50% or more of the metal composite oxide of lithium and zirconium, more preferably 70% or more, and even more preferably 90% or more.

Zirconium oxide can be used as a raw material for the zirconium constituting the coating layer. From the viewpoint of promoting the formation of a uniform coating layer, the raw material containing zirconium preferably has a BET specific surface area of 10 m ² /g or more, more preferably 30 m ² /g or more.

<<Third Embodiment>>
In this embodiment, a coating layer containing a metal composite oxide of lithium and tungsten is provided on the surface of a lithium composite metal compound composed of secondary particles formed by agglomeration of primary particles capable of doping and dedoping lithium ions. The positive electrode active material for a lithium secondary battery of this embodiment contains at least nickel and tungsten as metals other than lithium. The positive electrode active material for lithium secondary batteries of the present embodiment satisfies all of the following requirements (1) and (2).
(1) The ratio of the detection intensity of tungsten to the detection intensity of nickel measured by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) on the particle surface of the positive electrode active material for lithium secondary batteries (tungsten Detected intensity of nickel/Detected intensity of nickel) is defined as WR.
WR ₃ is the WR when the SEM-EDX measurement is performed at an acceleration voltage of 3 kV.
Let WR ₁₀ be the WR when the SEM-EDX measurement is performed at an acceleration voltage of 10 kV.
Calculate the average value [Ave (WR ₃ /WR ₁₀ )] and the standard deviation [σ (WR ₃ /WR ₁₀ )] of the ratio [WR ₃ /WR ₁₀ ] between WR ₃ and WR ₁₀ obtained by the above measurement method. do.
A coefficient of variation <[σ(WR ₃ /WR ₁₀ )]/[Ave(WR ₃ /WR ₁₀ )]> is calculated from the ratio and the standard deviation.
The reciprocal <[Ave(WR ₃ /WR ₁₀ )]/[σ(WR ₃ /WR ₁₀ )]> of the obtained coefficient of variation is 2.5 or more.
(2) The average value of WR ₃ is 0.005 or more.

The positive electrode active material for a lithium secondary battery of this embodiment includes a coating layer containing a metal composite oxide of lithium and tungsten on the surface of the lithium composite metal compound.
Each requirement that the positive electrode active material for a lithium secondary battery of this embodiment satisfies will be described.

[Requirements (1)]
In the positive electrode active material for lithium secondary batteries of the present embodiment, when the particle surface is measured by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) under the following conditions, the detection intensity of tungsten and the detection of nickel The intensity ratio WR meets certain requirements. In addition, the positive electrode active material for a lithium secondary battery of the present embodiment includes a coating layer on the surface of the lithium composite metal compound. For this reason, the measurement shall be performed with the coating layer provided.

- Measurement method First, a carbon tape is stuck on the sample stage of the scanning electron microscope, and the positive electrode active material particles are placed thereon. The sample stage is preferably made of carbon.
The cathode active material particles arranged as described above are irradiated with an electron beam under conditions of an acceleration voltage of 3 kV or 10 kV and a working distance of 15 mm, and the detection intensity of characteristic X-rays observed for tungsten and nickel is determined.
The ratio of the detected intensity of tungsten to the detected intensity of nickel (detected intensity of tungsten/detected intensity of nickel) at this time is defined as WR. Further, the WR obtained at an acceleration voltage of 3 kV is defined as WR ₃ . Let WR ₁₀ be the WR obtained at an acceleration voltage of 10 kV.

Here, measurement at an acceleration voltage of 3 kV has high sensitivity to the composition near the surface of the positive electrode active material particles, and WR ₃ means a value that strongly reflects the amount of tungsten near the surface of the positive electrode active material particles (that is, the coating layer).
Measurement at an acceleration voltage of 10 kV can detect even the inside of the positive electrode active material particle, so WR ₁₀ means a value reflecting the amount of tungsten in the entire particle including the vicinity of the surface of the positive electrode active material particle.

First, [WR ₃ /WR ₁₀ ], which is the ratio of WR ₃ and WR ₁₀ , is obtained.
Next, the average value [Ave (WR ₃ /WR ₁₀ )] of this ratio [WR ₃ /WR ₁₀ ] is calculated. When obtaining the average value, for example, it is preferable to obtain the average value obtained by measuring arbitrary 20 positive electrode active materials. In calculating the average value, the standard deviation [σ(WR ₃ /WR ₁₀ )] of the ratio [WR ₃ /WR ₁₀ ] is also calculated.
Next, the coefficient of variation <[σ(WR ₃ /WR ₁₀ )]/[Ave(WR ₃ /WR ₁₀ )]> is calculated from the ratio and the standard deviation.
Then, the reciprocal <[Ave(WR ₃ /WR ₁₀ )]/[σ(WR ₃ /WR ₁₀ )]> of the obtained coefficient of variation is calculated.

In the present embodiment, <[Ave (WR ₃ /WR ₁₀ )]/[σ (WR ₃ /WR ₁₀ )]> calculated by the above method is 2.5 or more.

However, WR ₃ and WR ₁₀ are measured in the same region on the particle surface of the positive electrode active material for lithium secondary batteries. In other words, WR ₃ and WR ₁₀ are to be measured by irradiating the same surface region of the same particle with an electron beam.

In the present embodiment, <[Ave (WR ₃ /WR ₁₀ )]/[σ (WR ₃ /WR ₁₀ )]> is preferably 2.6 or more, more preferably 3.5 or more, and 4.5 or more. Especially preferred.
By measuring <[Ave(WR ₃ /WR ₁₀ )]/[σ(WR ₃ /WR ₁₀ )]>, it can be determined whether tungsten is uniformly dispersed. Specifically, it means that the larger this value is, the more uniformly the tungsten present in the vicinity of the surface of the positive electrode active material particles (that is, the coating layer) is distributed.

It is believed that the uniform presence of a certain amount of tungsten on the surface of the positive electrode active material reduces the uncoated or thin coating layer portion. For this reason, it is presumed that the positive electrode active material of the present embodiment suppresses the generation of gas due to contact with the electrolytic solution, and suppresses swelling of the battery.

[Requirement (2)]
In the present embodiment, the average of WR ₃ is 0.005 or more, preferably 0.006 or more, more preferably 0.010 or more, and particularly preferably 0.015 or more.
When the average of WR ₃ is equal to or higher than the lower limit, it means that a large amount of tungsten is distributed in the vicinity of the surface of the positive electrode active material (that is, the coating layer).

- Coating layer The positive electrode active material of the present embodiment includes a coating layer containing a metal composite oxide of lithium and tungsten. In this embodiment, the entire surface of the lithium composite metal compound is covered. As long as the above requirements (1) and (2) are satisfied, the entire surface of the lithium mixed metal compound may not be completely covered, or there may be uncovered portions.

The coating layer contains a metal composite oxide of lithium and tungsten. A metal composite oxide of lithium and tungsten is a compound having lithium ion conductivity. As the compound _having lithium ion conductivity _{, one} or _more selected from _the group _{consisting of Li2WO4} , _Li4WO5 , _{Li6W2O9 , Li2W2O7} and _Li2W4O13 is preferred, _one or more selected _{from the} group consisting of _{Li2WO4 , Li4WO5} and _{Li6W2O9 is} more preferred, and _Li2WO4 or _Li4WO5 is particularly _preferred .

The coating layer may contain a product obtained by partially reacting a lithium composite metal compound or a lithium composite metal compound with a lithium-tungsten metal composite oxide. The effect of the present invention can be obtained if the substance contains at least 30% or more. The coating layer preferably contains 50% or more of the metal composite oxide of lithium and tungsten, more preferably 70% or more, and even more preferably 90% or more.

Tungsten oxide can be used as a raw material for the tungsten forming the coating layer. From the viewpoint of promoting the formation of a uniform coating layer, the BET specific surface area of the raw material containing tungsten is preferably 0.5 m ² /g or more, more preferably 1 m ² /g or more.

・BET specific surface area In the first to third embodiments, the specific surface area of the positive electrode active material is preferably 0.1 m ² /g or more, more preferably 0.2 m ² /g or more, and more preferably 0.3 m ² / g or more is particularly preferred.
Also, it is preferably 2.0 m ² /g or less, more preferably 1.9 m ² /g or less, and particularly preferably 1.8 m ² /g or less.
The above upper limit and lower limit can be combined arbitrarily.
In the present embodiment, it is preferably 0.1 m ² /g or more and 2.0 m ² /g or less, more preferably 0.2 m ² /g or more and 1.0 m ² /g or less, and 0.3 m ² /g or more1. 8 m ² /g or less is particularly preferred.

When the BET specific surface area is within the above range, the battery can have a higher capacity.

Content of lithium carbonate In the first to third embodiments, the content of lithium carbonate is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and particularly preferably 0.15% by mass or less. .

Content of lithium hydroxide In the first to third embodiments, the content of lithium hydroxide is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and 0.15% by mass or less. Especially preferred.

The amounts of lithium carbonate and lithium hydroxide are obtained as converted values from the results of neutralization titration.

When the contents of lithium carbonate and lithium hydroxide are equal to or less than the above upper limits, the generation of gas can be further suppressed.

- Moisture Content In the first to third embodiments, the moisture content is preferably 600 ppm or less, more preferably 590 ppm or less, and particularly preferably 580 ppm or less.
The water content can be measured using a coulometric Karl Fischer moisture meter (831 Coulometer, manufactured by Metrohm).

If the water content is equal to or less than the above upper limit, the generation of gas can be further suppressed.

Lithium Composite Metal Compound In the first to third embodiments, the lithium composite metal compound preferably has an α-NaFeO2 type crystal structure represented by the following compositional formula (A).
Li _{[ Lix} ( _NiaCobMncM1d ) _1-x ] _{O2 ( A} )
(where -0.1 ≤ x ≤ 0.2, 0.5 ≤ a < 1, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.1, a + b + c + d = 1 and M1 is Mg, Ca, Sr, Ba, Zn, B, Al, Ga, Ti, Zr, Ge, Fe, Cu, Cr, V, W, Mo, Sc, Y, Nb, La, Ta, Tc , Ru, Rh, Pd, Ag, Cd, In, and Sn.)

In the positive electrode active material for a lithium secondary battery of the present embodiment, from the viewpoint of obtaining a lithium secondary battery with high high voltage cycle characteristics, x in the composition formula (A) preferably exceeds 0, and is 0.01 or more. It is more preferably 0.02 or more.
From the viewpoint of obtaining a lithium secondary battery with a higher initial coulombic efficiency, x in the composition formula (A) is preferably 0.18 or less, more preferably 0.15 or less, and 0.1. More preferably:
The upper limit and lower limit of x can be combined arbitrarily. The combination of the upper limit value and the lower limit value preferably satisfies 0<x≦0.2, more preferably 0.01 or more and 0.18 or less, and particularly preferably 0.02 or more and 0.15 or less.
As used herein, "high cycle characteristics" means high discharge capacity retention.

Further, from the viewpoint of obtaining a lithium secondary battery with a high capacity, a in the composition formula (A) preferably exceeds 0.70, more preferably 0.72 or more, and 0.75 or more. is more preferred. Further, from the viewpoint of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, a in the composition formula (A) is preferably 0.92 or less, more preferably 0.91 or less, and 0 0.9 or less is more preferable.
The upper limit and lower limit of a can be combined arbitrarily.
In the present embodiment, an example of a combination of the upper limit and the lower limit is preferably more than 0.70 and 0.92 or less, more preferably 0.72 or more and 0.91 or less, and further 0.75 or more and 0.9 or less. preferable.

In addition, from the viewpoint of obtaining a lithium secondary battery with high high-voltage cycle characteristics, b in the composition formula (A) is preferably 0.07 or more, more preferably 0.1 or more, and 0.13. It is more preferable that it is above. From the viewpoint of obtaining a lithium secondary battery with high thermal stability, b in the composition formula (A) is preferably 0.25 or less, more preferably 0.23 or less, and 0.20. More preferably:
The upper limit and lower limit of b can be combined arbitrarily.
In the present embodiment, an example of a combination of the upper limit value and the lower limit value is preferably 0.07 or more and 0.25 or less, more preferably 0.1 or more and 0.23 or less, and further preferably 0.13 or more and 0.20 or less. .

In addition, from the viewpoint of obtaining a lithium secondary battery with high high-voltage cycle characteristics, c in the composition formula (A) is preferably 0.01 or more, more preferably 0.02 or more, and 0.03. It is more preferable that it is above. In addition, from the viewpoint of obtaining a lithium secondary battery that can be stably stored at high temperatures (for example, in an environment of 60° C.), c in the composition formula (A) is preferably 0.18 or less, and is 0.15 or less. is more preferable, and 0.10 or less is even more preferable.
The upper limit and lower limit of c can be combined arbitrarily.
In the present embodiment, the combination of the upper limit and the lower limit is preferably 0.01 or more and 0.18 or less, more preferably 0.02 or more and 0.15 or less, and even more preferably 0.03 or more and 0.10 or less. .

M1 in the composition formula (A) is Mg, Ca, Sr, Ba, Zn, B, Al, Ga, Ti, Zr, Ge, Fe, Cu, Cr, V, W, Mo, Sc, Y, Nb, One or more elements selected from the group consisting of La, Ta, Tc, Ru, Rh, Pd, Ag, Cd, In, and Sn.
From the viewpoint of improving the handleability of the positive electrode active material for lithium secondary batteries, d in the composition formula (A) is preferably greater than 0, more preferably 0.001 or more, and 0.003 or more. is more preferred. Further, from the viewpoint of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, d in the composition formula (A) is preferably 0.08 or less, more preferably 0.07 or less, It is more preferably 0.06 or less.
The upper limit and lower limit of d can be combined arbitrarily.
In the present embodiment, examples of combinations of upper and lower limits are more than 0 and preferably 0.08 or less, more preferably 0.001 or more and 0.07 or less, and even more preferably 0.003 or more and 0.06 or less. .

Further, from the viewpoint of obtaining a lithium secondary battery with high high-voltage cycle characteristics, M1 in the composition formula (A) is preferably any one of Al, Zr, W, Mo, and Nb, and is thermally stable. Any one of Mg, Al, Zr, and W is preferable from the viewpoint of obtaining a lithium secondary battery with high resistance.

<Method for producing positive electrode active material for lithium secondary battery>
A positive electrode active material for a lithium secondary battery of the present invention comprises a step of producing a composite metal compound containing nickel, cobalt and manganese, and a step of producing a lithium composite metal compound using the composite metal compound and a lithium compound. is preferred.

In producing the positive electrode active material for a lithium secondary battery of the present invention, first, metals other than lithium, that is, containing at least Ni, Co and Mn, and Fe, Cu, Ti, Mg, Al, W, B, A composite metal compound containing any one or more of Mo, Nb, Zn, Sn, Zr, Ga and V is prepared. The composite metal compound is then calcined with a suitable lithium salt.
As the composite metal compound, a composite metal hydroxide or a composite metal oxide is preferable.
An example of the method for producing the positive electrode active material will be described below by dividing into a process for producing a composite metal compound and a process for producing a lithium mixed metal oxide.

(Manufacturing process of composite metal compound)
A composite metal compound can be produced by a generally known batch coprecipitation method or continuous coprecipitation method. Hereinafter, the production method will be described in detail, taking as an example a composite metal hydroxide containing nickel, cobalt and manganese as metals.

First, a nickel salt solution, a cobalt salt solution, a manganese salt solution, and a complexing agent are reacted by a coprecipitation method, particularly a continuous method described in JP-A-2002-201028, to form a nickel-cobalt-manganese composite metal hydroxide. manufacture.

The nickel salt that is the solute of the nickel salt solution is not particularly limited, but for example, any one of nickel sulfate, nickel nitrate, nickel chloride and nickel acetate can be used. As the cobalt salt that is the solute of the cobalt salt solution, for example, any one of cobalt sulfate, cobalt nitrate, and cobalt chloride can be used. As the manganese salt that is the solute of the manganese salt solution, for example, any one of manganese sulfate, manganese nitrate, and manganese chloride can be used. The above metal salts are used in a proportion corresponding to the composition ratio of the formula (A). Also, water is used as a solvent.

The complexing agent is one capable of forming complexes with ions of nickel, cobalt, and manganese in an aqueous solution, such as ammonium ion donors (ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, Ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine.

During precipitation, alkali metal hydroxides (eg sodium hydroxide, potassium hydroxide) are added, if necessary, to adjust the pH value of the aqueous solution.

In addition to the nickel salt solution, the cobalt salt solution, and the manganese salt solution, when the complexing agent is continuously supplied to the reaction tank, nickel, cobalt, and manganese react to produce a nickel-cobalt-manganese composite metal hydroxide. be done.
During the reaction, the temperature of the reaction vessel is controlled, for example, within the range of 20°C or higher and 80°C or lower, preferably 30°C or higher and 70°C or lower.

For example, when the temperature of the aqueous solution is 40° C., the pH value in the reaction tank is controlled within the range of pH 9 or more and pH 13 or less, preferably pH 11 or more and pH 13 or less. By controlling the pH within the above range, the desired secondary particles of the present invention having highly reactive surfaces can be produced.
The materials in the reaction vessel are appropriately agitated. The temperature of the reaction tank is maintained at 40° C. or higher, and each solution is added under conditions such that the ratio of the weight of the nickel, cobalt, and manganese as metals to the weight of the alkali metal hydroxide is 0.9 or higher. By mixing and stirring, the sphericity of the secondary particles can be controlled within the desired range of the present invention, and the lithium composite metal compound and the coating material raw material can be uniformly mixed in the coating layer forming step described later. can make it easier to do. The reactor can be of the overflow type to separate the reaction sediment formed.

In addition, while maintaining an inert atmosphere, the inside of the reaction tank is kept in an atmosphere containing an appropriate amount of oxygen or in the presence of an oxidizing agent, so that the reaction between the lithium composite metal compound and the coating material raw material in the step of forming the coating layer, which will be described later, proceeds. can be made easier. In order to create an oxygen-containing atmosphere in the reaction vessel, an oxygen-containing gas may be introduced into the reaction vessel. The oxygen-containing gas includes oxygen gas, air, or a mixed gas of these and an oxygen-free gas such as nitrogen gas. From the viewpoint of facilitating adjustment of the oxygen concentration in the oxygen-containing gas, a mixed gas is preferred among the above.

By appropriately controlling the concentration of the metal salt supplied to the reaction vessel, the stirring speed, the reaction temperature, the reaction pH, and the firing conditions described later, the finally obtained positive electrode active material for lithium secondary batteries has desired physical properties. can be controlled.

After the above reaction, the obtained reaction precipitate is washed with water and then dried to isolate the nickel-cobalt-manganese composite hydroxide as the nickel-cobalt-manganese composite compound. In addition, if necessary, it may be washed with weak acid water or an alkaline solution containing sodium hydroxide or potassium hydroxide. In addition, in the above example, a nickel-cobalt-manganese composite hydroxide is produced, but a nickel-cobalt-manganese composite oxide may be prepared. When preparing a nickel-cobalt-manganese composite oxide from a nickel-cobalt-manganese composite hydroxide, an oxidization step is performed in which the nickel-cobalt-manganese composite oxide is calcined at a temperature of 300° C. or more and 800° C. or less for 1 hour or more and 10 hours or less. may

(Manufacturing process of lithium composite metal oxide)
Mixing step After drying the composite metal oxide or hydroxide, it is mixed with a lithium salt.
As the lithium salt, one or a mixture of two or more of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, and lithium oxide may be used.

After drying the composite metal oxide or hydroxide, it may be appropriately classified. The above lithium salt and composite metal hydroxide are used in consideration of the composition ratio of the final product. For example, when nickel-cobalt-manganese composite hydroxide is used, the lithium salt and the composite metal hydroxide are used at a ratio corresponding to the composition ratio of the formula (A).

- Main firing step A lithium-nickel-cobalt-manganese composite metal oxide is obtained by firing a nickel-cobalt-manganese composite metal oxide or a mixture of a hydroxide and a lithium salt. For firing, dry air, an oxygen atmosphere, an inert atmosphere, or the like is used depending on the desired composition, and if necessary, a main firing step having a plurality of heating steps is carried out.

The firing temperature of the composite metal oxide or hydroxide and the lithium compound such as lithium hydroxide and lithium carbonate is not particularly limited, but is preferably 700° C. or higher and 1100° C. or lower, and 750° C. or higher and 1050° C. ° C. or less, and more preferably 800° C. or higher and 1025° C. or lower. Here, the firing temperature is the maximum temperature of the holding temperature in the main firing step (hereinafter sometimes referred to as the maximum holding temperature), and in the case of the main firing step having a plurality of heating steps, It means the temperature when heated at the maximum holding temperature.

The firing time is preferably 3 hours or more and 50 hours or less. If the baking time exceeds 50 hours, the battery performance tends to be substantially inferior due to volatilization of lithium. If the baking time is less than 3 hours, the crystal growth is poor and the battery performance tends to be poor.

In the present embodiment, the heating rate in the heating step to reach the maximum holding temperature is preferably 180° C./hr or higher, more preferably 200° C./hr or higher, and particularly preferably 250° C./hr or higher.
The rate of temperature increase in the heating step to reach the maximum holding temperature is calculated from the time from the time the temperature rise is started until the temperature reaches the holding temperature, which will be described later.
A positive electrode active material for a lithium secondary battery having secondary particles with high surface reactivity can be produced by setting the temperature increase rate within the above specific range.

-Washing step After firing, the obtained fired product may be washed. Pure water or an alkaline cleaning liquid can be used for cleaning.
Examples of alkaline cleaning solutions include LiOH (lithium hydroxide), NaOH (sodium hydroxide), KOH ( _potassium hydroxide), _Li2CO3 (lithium carbonate), _{Na2CO3 (} sodium carbonate), and _{K2CO3 .} (potassium carbonate) and (NH ₄ ) ₂ CO ₃ (ammonium carbonate). Ammonia can also be used as the alkali.

In the cleaning step, the cleaning liquid and the lithium composite metal compound can be brought into contact with each other by adding the lithium composite metal compound to an aqueous solution of each cleaning liquid and stirring, or by using the aqueous solution of each cleaning liquid as shower water to remove the lithium composite metal. A method of applying to a compound, a method of adding a lithium mixed metal compound to an aqueous solution of the cleaning solution and stirring, separating the lithium mixed metal compound from the aqueous solution of each cleaning solution, and then separating the aqueous solution of each cleaning solution as shower water. A method of applying to the later lithium composite metal compound can be mentioned.

- Coating Layer Forming Step When forming a coating layer on the surface of the positive electrode active material for a lithium secondary battery, first, the coating material raw material and the lithium composite metal compound are mixed. Next, a coating layer made of the lithium mixed metal compound can be formed on the surfaces of the primary particles or secondary particles of the lithium mixed metal compound by heat treatment as necessary.
Depending on the coating material raw material, in the mixing step of mixing the composite metal oxide or hydroxide and the lithium salt, by adding and mixing the coating material raw material, after the main firing step, the primary particles of the lithium composite metal compound or A coating layer made of a lithium composite metal compound can be formed on the surface of the secondary particles.

The coating material raw material can be any one of oxides, hydroxides, carbonates, nitrates, sulfates, halides, oxalates, or alkoxides of aluminum, titanium, zirconium, or tungsten, and must be oxides. is preferred.

In order to more efficiently coat the surface of the lithium mixed metal compound with the raw material for the coating material, the raw material for the coating material is preferably finer than the secondary particles of the lithium mixed metal compound. Specifically, the average secondary particle size of the coating material raw material is preferably 1 μm or less, more preferably 0.1 μm or less.

The raw materials for the coating material and the lithium composite metal compound are uniformly mixed until lump-like aggregates disappear. The mixing apparatus is not limited as long as the coating material raw material and the lithium composite metal compound can be uniformly mixed, but mixing using a Loedige mixer is preferable. In the mixing step of mixing the composite metal oxide or hydroxide and the lithium salt, the same applies when adding and mixing the coating material raw material.

Further, by performing the mixing in an atmosphere containing water or water and carbon dioxide gas, the coating layer can be adhered more firmly to the surface of the lithium composite metal compound.
The coating layer can be adhered more firmly to the surface of the lithium mixed metal compound by keeping the raw material for the coating material and the lithium mixed metal compound in an atmosphere containing water or water and carbon dioxide gas after mixing.

The heat treatment conditions (temperature, holding time) in the heat treatment optionally performed after mixing the coating material raw material and the lithium composite metal compound may vary depending on the type of the coating material raw material.
For example, when aluminum is used as the coating raw material, it is preferable to bake at a temperature of 600° C. or higher and 800° C. or lower for 4 hours or longer and 10 hours or shorter. Firing under these high-temperature, long-time firing conditions enables control within the ranges of the above requirements (1) and (2). If the firing temperature is higher than 800° C., the raw material of the coating material may form a solid solution with the lithium composite metal compound, failing to form a coating layer. If the baking time is shorter than 4 hours, the diffusion of the coating raw material is insufficient, and the coating layer may not be uniformly formed.

A positive electrode active material for a lithium secondary battery can also be obtained by forming a coating layer on the surface of the lithium composite metal compound by using techniques such as sputtering, CVD, and vapor deposition.

In some cases, a positive electrode active material for a lithium secondary battery can be obtained by mixing and calcining the composite metal oxide or hydroxide, the lithium salt, and the raw material for the coating material.

A positive electrode active material for a lithium secondary battery comprising a coating layer on the surfaces of primary particles or secondary particles of a lithium composite metal compound is appropriately pulverized and classified to obtain a positive electrode active material for a lithium secondary battery.

<Lithium secondary battery>
Next, while explaining the structure of the lithium secondary battery, a positive electrode using the positive electrode active material for a lithium secondary battery of the present invention as a positive electrode active material for a lithium secondary battery, and a lithium secondary battery having this positive electrode will be explained. do.

An example of the lithium secondary battery of the present embodiment has a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolytic solution placed between the positive electrode and the negative electrode.

1A and 1B are schematic diagrams showing an example of the lithium secondary battery of this embodiment. The cylindrical lithium secondary battery 10 of this embodiment is manufactured as follows.

First, as shown in FIG. 1A, a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are arranged as follows: 1 and the negative electrode 3 are stacked in this order and wound to form an electrode group 4 .

Next, as shown in FIG. 1B, after housing the electrode group 4 and an insulator (not shown) in the battery can 5, the can bottom is sealed, the electrode group 4 is impregnated with the electrolyte solution 6, and the positive electrode 2 and the negative electrode 3 are separated. Place the electrolyte between Further, by sealing the upper portion of the battery can 5 with the top insulator 7 and the sealing member 8, the lithium secondary battery 10 can be manufactured.

As for the shape of the electrode group 4, for example, the cross-sectional shape when the electrode group 4 is cut in the direction perpendicular to the winding axis is a columnar shape such as a circle, an ellipse, a rectangle, or a rectangle with rounded corners. can be mentioned.

In addition, as the shape of the lithium secondary battery having such an electrode group 4, a shape defined by IEC60086, which is a standard for batteries defined by the International Electrotechnical Commission (IEC), or JIS C 8500 can be adopted. . For example, shapes such as a cylindrical shape and a rectangular shape can be mentioned.

Further, the lithium secondary battery is not limited to the wound type structure described above, and may have a layered structure in which a layered structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of laminated lithium secondary batteries include so-called coin-type batteries, button-type batteries, and paper-type (or sheet-type) batteries.

Hereinafter, each configuration will be described in order.
(positive electrode)
The positive electrode of the present embodiment can be manufactured by first preparing a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder, and supporting the positive electrode mixture on a positive electrode current collector.

(Conductive material)
A carbon material can be used as the conductive material of the positive electrode of the present embodiment. Examples of carbon materials include graphite powder, carbon black (eg, acetylene black), and fibrous carbon materials. Since carbon black is fine particles and has a large surface area, adding a small amount to the positive electrode mixture can increase the conductivity inside the positive electrode and improve the charge-discharge efficiency and output characteristics. Both the binding force between the positive electrode mixture and the positive electrode current collector and the binding force inside the positive electrode mixture are reduced, which causes an increase in internal resistance.

The ratio of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. If a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, this ratio can be lowered.

(binder)
A thermoplastic resin can be used as the binder of the positive electrode of the present embodiment.
This thermoplastic resin is polyvinylidene fluoride (hereinafter sometimes referred to as PVdF).
), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), ethylene tetrafluoride/propylene hexafluoride/vinylidene fluoride copolymer, propylene hexafluoride/vinylidene fluoride copolymer, tetrafluoride fluororesins such as ethylene chloride/perfluorovinyl ether copolymers; polyolefin resins such as polyethylene and polypropylene;

These thermoplastic resins may be used in combination of two or more. By using a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the entire positive electrode mixture is 1% by mass or more and 10% by mass or less, and the ratio of the polyolefin resin is 0.1% by mass or more and 2% by mass or less. It is possible to obtain a positive electrode mixture having both high adhesion to the current collector and high bonding strength inside the positive electrode mixture.

(Positive electrode current collector)
As the positive electrode current collector included in the positive electrode of the present embodiment, a strip-shaped member made of a metal material such as Al, Ni, or stainless steel can be used. Among them, it is preferable to use Al as a forming material and process it into a thin film because it is easy to process and inexpensive.

As a method for supporting the positive electrode mixture on the positive electrode current collector, there is a method of pressure-molding the positive electrode mixture on the positive electrode current collector. In addition, the positive electrode mixture is made into a paste using an organic solvent, and the obtained positive electrode mixture paste is applied to at least one side of a positive electrode current collector, dried, and pressed to adhere, thereby forming a positive electrode on the positive electrode current collector. A mixture may be supported.

When the positive electrode mixture is made into a paste, organic solvents that can be used include amine-based solvents such as N,N-dimethylaminopropylamine and diethylenetriamine; ether-based solvents such as tetrahydrofuran; ketone-based solvents such as methyl ethyl ketone; ester solvents such as dimethylacetamide; amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP);

Examples of the method for applying the positive electrode mixture paste to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method.

A positive electrode can be manufactured by the method mentioned above.
(negative electrode)
The negative electrode included in the lithium secondary battery of the present embodiment may be capable of doping and dedoping lithium ions at a potential lower than that of the positive electrode, and the negative electrode mixture containing the negative electrode active material is supported on the negative electrode current collector. and an electrode composed solely of the negative electrode active material.

(Negative electrode active material)
Examples of the negative electrode active material that the negative electrode has include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, or alloys that can be doped and undoped with lithium ions at a potential lower than that of the positive electrode. be done.

Examples of carbon materials that can be used as the negative electrode active material include graphite such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and baked organic polymer compounds.

Examples of oxides _that can be used as the negative electrode active material include oxides of silicon represented by the formula SiO _x (where x is a positive real number) such as SiO ₂ and SiO _; , x is a positive real number); V ₂ O ₅ , VO _2, etc. Vanadium oxide represented by the formula VO _x (where x is a positive real number); Fe ₃ O ₄ , Fe ₂ O ₃ , FeO, etc. Iron oxide represented by the formula FeO _x (where x is a positive real number); SnO ₂ , SnO, etc. represented by the formula SnO _x (where x is a positive real number) oxides of tin such as WO ₃ and WO ₂ ; oxides of tungsten represented by the general formula WO _x (where x is a positive real number); lithium and titanium such as Li ₄ Ti ₅ O ₁₂ and LiVO ₂ or a composite metal oxide containing vanadium;

Sulfides that can be used as negative electrode active materials include titanium sulfides represented by the formula TiS _x (where x is a positive real number) such as Ti ₂ S ₃ , TiS ₂ and TiS; V ₃ S ₄ and VS. _2, Vanadium sulfide represented by _the formula VS _x (where x is a positive real number) _such as _{VS ;} Molybdenum sulfide represented by the formula MoS _x (where x is a positive real number) such as Mo ₂ S ₃ and MoS ₂ ; SnS _{2 and} SnS etc. Formula SnS _x (where, sulfides of tin represented by the _{formula WS x} (where x is a positive real number); sulfides of tungsten represented by the formula WS _x (where _x is a positive real number); selenium sulfide represented _by the formula SeS _x (where x is a positive real number), such as _Se5S3 , _SeS2 , SeS, etc.; can be mentioned.

Nitrides that can be used as negative electrode active materials include Li ₃ N and Li _3-x A _x N (where A is either one or both of Ni and Co and 0<x<3). Lithium-containing nitrides such as

These carbon materials, oxides, sulfides and nitrides may be used alone or in combination of two or more. Moreover, these carbon materials, oxides, sulfides and nitrides may be either crystalline or amorphous.

Metals that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

Alloys that can be used as negative electrode active materials include lithium alloys such as Li—Al, Li—Ni, Li—Si, Li—Sn, and Li—Sn—Ni; silicon alloys such as Si—Zn; - tin alloys such as Co, Sn-Ni, Sn-Cu, Sn-La; alloys such as Cu ₂ Sb, La ₃ Ni ₂ Sn ₇ ;

These metals and alloys are mainly used alone as electrodes after being processed into a foil shape, for example.

Among the above negative electrode active materials, the potential of the negative electrode hardly changes from the uncharged state to the fully charged state during charging (good potential flatness), the average discharge potential is low, and the capacity retention rate when repeatedly charged and discharged is low. A carbon material containing graphite as a main component, such as natural graphite or artificial graphite, is preferably used for reasons such as high (good cycle characteristics). The shape of the carbon material may be, for example, flaky such as natural graphite, spherical such as mesocarbon microbeads, fibrous such as graphitized carbon fiber, or aggregates of fine powder.

The negative electrode mixture may contain a binder, if necessary. Binders may include thermoplastic resins, specifically PVdF, thermoplastic polyimides, carboxymethyl cellulose, polyethylene and polypropylene.

(Negative electrode current collector)
Examples of the negative electrode current collector of the negative electrode include a band-shaped member made of a metal material such as Cu, Ni, or stainless steel. Among them, it is preferable to use Cu as a forming material and process it into a thin film because it is difficult to form an alloy with lithium and is easy to process.

As a method for supporting the negative electrode mixture on such a negative electrode current collector, as in the case of the positive electrode, a method of pressure molding, a paste using a solvent or the like is applied to the negative electrode current collector, dried and then pressed. A method of crimping can be mentioned.

(separator)
The separator of the lithium secondary battery of the present embodiment may be in the form of a porous film, nonwoven fabric, or woven fabric made of a material such as a polyolefin resin such as polyethylene or polypropylene, a fluororesin, or a nitrogen-containing aromatic polymer. can be used. Moreover, the separator may be formed using two or more of these materials, or the separator may be formed by laminating these materials.

In the present embodiment, the separator has a permeation resistance of 50 seconds/100 cc or more and 300 seconds/100 cc according to the Gurley method defined in JIS P 8117 in order to allow the electrolyte to pass through the separator well when the battery is used (during charging and discharging). It is preferably 50 seconds/100 cc or more and 200 seconds/100 cc or less.

The porosity of the separator is preferably 30% by volume or more and 80% by volume or less, more preferably 40% by volume or more and 70% by volume or less. The separator may be a laminate of separators with different porosities.

(Electrolyte)
The electrolytic solution of the lithium secondary battery of this embodiment contains an electrolyte and an organic solvent.

Electrolytes contained in the electrolytic solution include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiN ( _{SO2CF3 )} ( _COCF3 ), Li _{( C4F9SO3} ), _LiC ( _{SO2CF3 ) 3} , _Li2B10Cl10 , LiBOB (where BOB is _bis (oxalato) _borate ), LiFSI (where FSI is bis(fluorosulfonyl)imide), lower aliphatic carboxylic acid lithium salts, _LiAlCl4 and other lithium salts, and mixtures of two or more thereof may be used. Among them, the electrolyte is at least selected from the group consisting of _LiPF6 , _LiAsF6 , _LiSbF6 , _LiBF4 , _{LiCF3SO3 ,} LiN( _{SO2CF3 ) 2} and LiC( _SO2CF3 ) ₃ containing fluorine _. It is preferred to use one containing one.

Examples of the organic solvent contained in the electrolytic solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di (Methoxycarbonyloxy) carbonates such as ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, 2- ethers such as methyltetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; - Carbamates such as 2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, 1,3-propanesultone, or those obtained by further introducing a fluoro group into these organic solvents (one of the hydrogen atoms of the organic solvent above substituted with a fluorine atom) can be used.

As the organic solvent, it is preferable to use a mixture of two or more of these. Among them, a mixed solvent containing carbonates is preferable, and a mixed solvent of a cyclic carbonate and a non-cyclic carbonate and a mixed solvent of a cyclic carbonate and an ether are more preferable. A mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable as the mixed solvent of the cyclic carbonate and the non-cyclic carbonate. The electrolyte using such a mixed solvent has a wide operating temperature range, does not easily deteriorate even when charging and discharging at a high current rate, does not easily deteriorate even after long-term use, and uses natural graphite as an active material for the negative electrode. , and has many features of being resistant to decomposition even when graphite materials such as artificial graphite are used.

Further, as the electrolytic solution, it is preferable to use an electrolytic solution containing a fluorine-containing lithium salt such as LiPF ₆ and an organic solvent having a fluorine substituent, since the safety of the obtained lithium secondary battery is enhanced. Mixed solvents containing fluorine-substituted ethers such as pentafluoropropylmethyl ether and 2,2,3,3-tetrafluoropropyldifluoromethyl ether and dimethyl carbonate do not retain their capacity even when charged and discharged at a high current rate. It is more preferable because of its high retention rate.

A solid electrolyte may be used in place of the above electrolytic solution. Examples of solid electrolytes that can be used include organic polymer electrolytes such as polyethylene oxide polymer compounds and polymer compounds containing at least one of polyorganosiloxane chains and polyoxyalkylene chains. In addition, a so-called gel type in which a non-aqueous electrolyte is held in a polymer compound can also be used. Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ SP ₂ S ₅ , Li ₂ S—B ₂ S ₃ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS Inorganic solid electrolytes containing sulfides such as ₂ - _{Li 2} SO ₄ and Li ₂ S--GeS ₂ --P ₂ S ₅ may be mentioned, and mixtures of two or more of these may be used. By using these solid electrolytes, the safety of the lithium secondary battery can sometimes be improved.

Moreover, in the lithium secondary battery of the present embodiment, when a solid electrolyte is used, the solid electrolyte may serve as a separator, in which case the separator may not be required.

The positive electrode active material in this embodiment satisfies all requirements (1) to (2). The positive electrode active material having such a structure means a structure in which a coating layer is uniformly formed on the surface of the lithium metal composite compound. With such a structure, there are no or very few places where the electrolyte and the lithium metal composite compound are in direct contact, so generation of gas due to contact with the electrolyte can be suppressed. Therefore, a lithium secondary battery manufactured using the positive electrode active material of the present embodiment can suppress battery swelling.

EXAMPLES Next, the present invention will be described in more detail by way of examples.

<Composition analysis>
The composition analysis of the lithium metal composite oxide powder produced by the method described below was carried out by dissolving the obtained lithium metal composite oxide powder in hydrochloric acid and then using an inductively coupled plasma emission spectrometer (SII Nanotechnology Co., Ltd. manufactured by SPS3000).

<Measurement of moisture content>
The water content was measured using a coulometric Karl Fischer moisture meter (831 Coulometer, manufactured by Metrohm).

<BET specific surface area measurement>
After drying 1 g of the lithium metal composite oxide powder at 105° C. for 30 minutes in a nitrogen atmosphere, measurement was performed using Macsorb (registered trademark) manufactured by Mountech.

<Measurement of Lithium Carbonate Amount and Lithium Hydroxide Amount>
20 g of a positive electrode active material for a lithium secondary battery and 100 g of pure water were placed in a 100 ml beaker and stirred for 5 minutes. After stirring, the positive electrode active material for lithium secondary batteries was filtered, 0.1 mol/L hydrochloric acid was added dropwise to 60 g of the remaining filtrate, and the pH of the filtrate was measured with a pH meter. Assuming that the titration amount of hydrochloric acid at pH = 8.3 ± 0.1 is Aml and the titration amount of hydrochloric acid at pH = 4.5 ± 0.1 is Bml, the positive electrode activity for lithium secondary batteries is calculated from the following formula. The concentrations of lithium carbonate and lithium hydroxide remaining in the material were calculated. In the following formulas, the molecular weights of lithium carbonate and lithium hydroxide were calculated assuming that each atomic weight was H: 1.000, Li: 6.941, C: 12, and O: 16.
Lithium carbonate concentration (%) =
0.1 x (BA) / 1000 x 73.882 / (20 x 60/100) x 100 lithium hydroxide concentration (%) =
0.1×(2A−B)/1000×23.941/(20×60/100)×100

<Scanning electron microscope - measurement by energy dispersive X-ray analysis (SEM-EDX)> The surface of the aluminum positive electrode active material was measured by a field emission scanning electron microscope secondary electron spectrometer (SEM-EDX; manufactured by Hitachi High Technologies, Ltd.) , product name S-4800, Oxford Instruments energy dispersive X-ray spectrometer X-Max ^N ), the particle surface of the positive electrode active material is measured, and the ratio of the detection intensity of aluminum to the detection intensity of nickel (the detection intensity of aluminum / nickel detection intensity) was defined as AR.
The AR when the SEM-EDX measurement was performed at an acceleration voltage of 3 kV was defined as AR ₃ .
The AR when the SEM-EDX measurement was performed at an acceleration voltage of 10 kV was defined as _AR10 .
Calculate the average value [Ave (AR ₃ /AR ₁₀ )] and the standard deviation [σ (AR ₃ /AR ₁₀ )] of the ratio [AR ₃ /AR ₁₀ ] between AR ₃ and AR ₁₀ obtained by the above measurement method. bottom.
A coefficient of variation <[σ(AR ₃ /AR ₁₀ )]/[Ave(AR ₃ /AR ₁₀ )]> was calculated from the ratio and the standard deviation.

・ Tungsten The surface of the positive electrode active material is subjected to a field emission scanning electron microscope secondary electron spectrometer (SEM-EDX; manufactured by Hitachi High Technologies, product name S-4800, Oxford Instruments Energy dispersive X-ray analyzer X- Max ^N ), and the ratio of the detected intensity of tungsten to the detected intensity of nickel (detected intensity of tungsten/detected intensity of nickel) was defined as WR.
The WR when the SEM-EDX measurement was performed at an acceleration voltage of 3 kV was defined as WR ₃ .
The WR when the SEM-EDX measurement was performed at an acceleration voltage of 10 kV was defined as WR ₁₀ .
Calculate the average value [Ave (WR ₃ /WR ₁₀ )] and the standard deviation [σ (WR ₃ /WR ₁₀ )] of the ratio [WR ₃ /WR ₁₀ ] between WR ₃ and WR ₁₀ obtained by the above measurement method. bottom.
A coefficient of variation <[σ(WR ₃ /WR ₁₀ )]/[Ave(WR ₃ /WR ₁₀ )]> was calculated from the ratio and the standard deviation.

・ Zirconium The surface of the positive electrode active material is subjected to a field emission scanning electron microscope secondary electron spectrometer (SEM-EDX; Hitachi High Technologies, product name S-4800, Oxford Instruments Energy Dispersive X-ray Analyzer X- Max ^N ), and the ratio of the detected intensity of zirconium to the detected intensity of nickel (detected intensity of zirconium/detected intensity of nickel) was defined as ZR.
The ZR when the SEM-EDX measurement was performed at an acceleration voltage of 5 kV was defined as ZR ₅ .
The ZR when the SEM-EDX measurement was performed at an acceleration voltage of 10 kV was defined as _ZR10 .
Calculate the average value [Ave (ZR ₅ /ZR ₁₀ )] and the standard deviation [σ (ZR ₅ /ZR ₁₀ )] of the ratio [ZR ₅ /ZR ₁₀ ] between ZR ₅ and ZR ₁₀ obtained by the above measurement method. bottom.
A coefficient of variation <[σ(ZR ₅ /ZR ₁₀ )]/[Ave (ZR ₅ /ZR ₁₀ )]> was calculated from the ratio and the standard deviation.

<Preparation of positive electrode for lithium secondary battery>
A lithium metal composite oxide, a conductive material (acetylene black), and a binder (PVdF) obtained by the production method described later are mixed into a positive electrode active material for a lithium secondary battery: conductive material: binder = 92:5:3 (mass ratio). A pasty positive electrode mixture was prepared by adding and kneading so as to have a composition of N-methyl-2-pyrrolidone was used as an organic solvent when preparing the positive electrode mixture.

The obtained positive electrode mixture was applied to an Al foil having a thickness of 40 μm as a current collector and vacuum-dried at 150° C. for 8 hours to obtain a positive electrode for a lithium secondary battery. The electrode area of this positive electrode for a lithium secondary battery was 1.65 cm ² .

<Preparation of negative electrode for lithium secondary battery>
Next, artificial graphite (MAGD manufactured by Hitachi Chemical Co., Ltd.) as a negative electrode active material, CMC (manufactured by Daiichi Kogyo Yaku Co., Ltd.) and SBR (manufactured by Nippon A&L Co., Ltd.) as binders, negative electrode active material: CMC: A pasty negative electrode mixture was prepared by adding and kneading so as to obtain a composition of SRR=98:1:1 (mass ratio). Ion-exchanged water was used as a solvent when preparing the negative electrode mixture.

The resulting negative electrode mixture was applied to a Cu foil having a thickness of 12 μm as a current collector and vacuum-dried at 60° C. for 8 hours to obtain a negative electrode for a lithium secondary battery. The electrode area of this negative electrode for lithium secondary battery was 1.77 cm ² .

<Production of lithium secondary battery (coin-type full cell)>
The following operations were performed in an argon atmosphere glove box.
The positive electrode for the lithium secondary battery prepared in "(2) Preparation of the positive electrode for the lithium secondary battery" is placed on the lower lid of the part for the coin-type battery R2032 (manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down. A laminated film separator (polyethylene porous film laminated with a heat-resistant porous layer (thickness: 16 μm)) was placed thereon. 300 μl of electrolytic solution was injected here. The electrolytic solution is 16:10 of ethylene carbonate (hereinafter sometimes referred to as EC), dimethyl carbonate (hereinafter sometimes referred to as DMC) and ethylmethyl carbonate (hereinafter sometimes referred to as EMC). : 74 (volume ratio) 1% by volume of vinylene carbonate (hereinafter sometimes referred to as VC) is added to a mixed solution, and LiPF ₆ is dissolved so as to be 1.3 mol / l (hereinafter, LiPF ₆ /EC+DMC+EMC) was used.
Next, place the negative electrode for lithium secondary battery prepared in <Preparation of negative electrode for lithium secondary battery> on the upper side of the laminated film separator, cover it with a gasket, and crimp it with a crimping machine to Model full cell R2032, hereinafter sometimes referred to as "full cell".
) was made.

<Discharge test>
Using the full cell produced in <Production of lithium secondary battery (coin-type full cell)>, an initial charge/discharge test was performed under the conditions shown below.

<Charge/discharge test conditions>
Test temperature: 25°C
Maximum charge voltage 4.2V, charge time 6 hours, charge current 0.2CA, constant current constant voltage charge Minimum discharge voltage 2.7V, discharge time 5 hours, discharge current 0.2CA, constant current discharge

<DC resistance measurement>
Assuming that the discharge capacity measured above is 100% for the depth of charge (hereinafter sometimes referred to as SOC), the battery resistance at 100% SOC was measured at 25°C. In addition, the adjustment to each SOC was performed in a 25 degreeC environment. Battery resistance measurement is carried out by placing a full cell with adjusted SOC in a constant temperature bath at 25 ° C. for 2 hours, discharging at 20 μA for 15 seconds, standing for 5 minutes, charging at 20 μA for 15 seconds, standing for 5 minutes, and standing at 40 μA for 15 seconds. Discharge, rest for 5 minutes, charge for 30 seconds at 20 μA, rest for 5 minutes, discharge for 15 seconds at 80 μA, rest for 5 minutes, charge for 60 seconds at 20 μA, rest for 5 minutes, discharge for 15 seconds at 160 μA, rest for 5 minutes , charging at 20 μA for 120 seconds, and standing for 5 minutes. The battery resistance is obtained by calculating an approximate curve using the least squares approximation method from a plot of the battery voltage and each current value measured 10 seconds after 20, 40, 80, and 120 μA discharge, and calculating the slope of this approximate curve. battery resistance.

<Production of lithium secondary battery (laminate cell)>
<Preparation of positive electrode for lithium secondary battery> Place the positive electrode for lithium secondary battery with the aluminum foil side facing down on an aluminum laminate film, and place it on a laminated film separator (polyethylene porous film (thickness 27 μm). )) was placed. Next, the negative electrode for lithium secondary battery prepared in <Preparation of negative electrode for lithium secondary battery> was placed on the upper side of the laminated film separator with the copper foil side facing up, and an aluminum laminate film was placed thereon. Furthermore, the parts were heat-sealed while leaving the part where the electrolytic solution was injected. Then, it was transferred to a dry bench in a dry atmosphere with a dew point temperature of minus 50°C or less, and 1 mL of the electrolytic solution was injected using a vacuum injector. The electrolytic solution is 16:10 of ethylene carbonate (hereinafter sometimes referred to as EC), dimethyl carbonate (hereinafter sometimes referred to as DMC) and ethylmethyl carbonate (hereinafter sometimes referred to as EMC). : 74 (volume ratio) 1% by volume of vinylene carbonate (hereinafter sometimes referred to as VC) is added to a mixed solution, and LiPF ₆ is dissolved so as to be 1.3 mol / l (hereinafter, LiPF ₆ /EC+DMC+EMC) was used.
Finally, the electrolyte injection part was heat-sealed to produce a laminate cell.

<Measurement of gas expansion volume>
An X-ray CT scan was performed on the laminate cell produced as described above, and the laminate cell volume before the test was calculated. Then, charging and discharging were performed under the following test conditions, the laminate cell volume was measured again, and the volume difference before and after the test was calculated. The difference in volume (cm ³ ) before and after the test was divided by the amount (g) of the positive electrode material present in the laminate cell to obtain the volume of gas swelling per positive electrode material (cm ³ /g).

<Test conditions>
Charge/discharge times: 50 times Test temperature: 60°C
Charge maximum voltage 4.2V, charge time 2.5 hours, charge current 0.5CA, constant current constant voltage charge Minimum discharge voltage 2.7V, discharge time 1 hour, discharge current 1CA, constant current discharge

(Example 1)
Production of positive electrode active material 1 for lithium secondary battery [Nickel-cobalt-manganese composite hydroxide production process]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 0.510:0.225:0.265 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reactor under stirring so that the pH of the solution in the reactor when measured at 40° C. was 11.2. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and various liquid amounts are adjusted so that the reaction time is 11 hours to obtain nickel-cobalt-manganese composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain a nickel-cobalt-manganese composite hydroxide 1.

[Mixing process]
The nickel-cobalt-manganese composite hydroxide 1 obtained as described above and the lithium carbonate powder were weighed and mixed so that the molar ratio was Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 930° C. for 5 hours in an oxygen atmosphere to obtain a fired product 1.
The composition analysis of the obtained baked product 1 was performed, and when it corresponded to the composition formula (A), x = 0.032, a = 0.512, b = 0.223, c = 0.265, d = 0 0.000.

[Coating process]
The fired product 1 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, and mixed using a Loedige mixer in an atmosphere containing water and carbon dioxide gas. A positive electrode active material 1 for a lithium secondary battery was obtained by heat-treating at °C for 5 hours.

Evaluation of Positive Electrode Active Material 1 for Lithium Secondary Battery The particle cross section of the obtained positive electrode active material 1 for lithium secondary battery was subjected to aluminum element mapping by STEM-EDX, and a coating layer containing the aluminum element was uniformly formed on the particle surface. Confirmed that The results are shown in FIG.

(Example 2)
Production of positive electrode active material 2 for lithium secondary battery [mixing step]
Nickel-cobalt-manganese composite hydroxide 1 and lithium carbonate powder were weighed and mixed in a molar ratio of Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 910° C. for 5 hours in an oxygen atmosphere to obtain fired product 2 .
The composition analysis of the obtained fired product 2 was performed, and when it corresponded to the composition formula (A), x = 0.024, a = 0.511, b = 0.224, c = 0.265, d = 0 0.000.

[Coating process]
The fired product 2 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, and mixed using a Loedige mixer in an atmosphere containing water and carbon dioxide gas. A positive electrode active material 2 for a lithium secondary battery was obtained by heat-treating at °C for 5 hours.

(Example 3)
Production of positive electrode active material 3 for lithium secondary battery [Nickel-cobalt-manganese composite hydroxide production process]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 0.510:0.225:0.265 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reaction tank under stirring so that the pH of the solution in the reaction tank when measured at 40° C. was 12.4. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and the amount of various liquids is adjusted so that the reaction time is 20 hours to obtain nickel-cobalt-manganese composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-manganese composite hydroxide 3.

[Mixing process]
The nickel-cobalt-manganese composite hydroxide 3 obtained as described above and the lithium carbonate powder were weighed and mixed so that the molar ratio was Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 870° C. for 10 hours in an air atmosphere to obtain a fired product 3 .
The composition analysis of the obtained baked product 3 was performed, and when it corresponded to the composition formula (A), x = 0.030, a = 0.516, b = 0.222, c = 0.262, d = 0 0.000.

[Coating process]
The baked product 3 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, dry-mixed using a VG mixer, and heat-treated at 760° C. for 5 hours in an air atmosphere to produce a lithium secondary battery. A positive electrode active material 3 for

Evaluation of positive electrode active material 3 for lithium secondary battery The particle cross section of the obtained positive electrode active material 3 for lithium secondary battery was subjected to aluminum element mapping by STEM-EDX, and a coating layer containing aluminum element was uniformly formed on the particle surface. Confirmed that The results are shown in FIG.

(Example 4)
Production of positive electrode active material 4 for lithium secondary battery [Nickel-cobalt-manganese composite hydroxide production process]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 0.550:0.210:0.240 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reaction tank under stirring so that the pH of the solution in the reaction tank when measured at 40° C. was 11.8. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and various liquid amounts are adjusted so that the reaction time is 17 hours or longer to obtain nickel-cobalt-manganese composite hydroxide particles, which are then added with a sodium hydroxide solution. After washing, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-manganese composite hydroxide 4 .

[Mixing process]
The nickel-cobalt-manganese composite hydroxide 4 obtained as described above and the lithium carbonate powder were weighed and mixed so that the molar ratio was Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the above mixing step was fired at 910° C. for 5 hours in an oxygen atmosphere to obtain fired product 4 .
The composition analysis of the obtained baked product 4 was performed, and when it corresponded to the composition formula (A), x = 0.034, a = 0.553, b = 0.207, c = 0.240, d = 0 0.000.

[Coating process]
The fired product 4 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, and mixed using a Loedige mixer in an atmosphere containing water and carbon dioxide gas. A positive electrode active material 4 for a lithium secondary battery was obtained by heat-treating at °C for 5 hours.

(Example 5)
Production of positive electrode active material 5 for lithium secondary battery [Nickel-cobalt-aluminum composite hydroxide production process]
After water was put into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was kept within the range of 40 to 45°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and an aluminum sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and aluminum atoms was 0.880:0.090:0.030 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reactor under stirring, and the pH of the solution in the reactor measured at 40° C. was 12.1 to 12.0. An aqueous sodium hydroxide solution was added dropwise at appropriate times so as to achieve a range of 5. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and the amounts of various liquids are adjusted so that the reaction time is 13 hours to obtain nickel-cobalt-aluminum composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-aluminum composite hydroxide 5 .

[Mixing process]
The nickel-cobalt-aluminum composite hydroxide 5 obtained as described above and the lithium hydroxide powder were weighed and mixed so that the molar ratio was Li/(Ni+Co+Al)=1.06.

[Baking process]
After that, the mixture obtained in the above mixing step was fired at 720° C. for 6 hours in an oxygen atmosphere to obtain fired product 5 .
The composition analysis of the obtained baked product 5 was performed, and when it corresponded to the composition formula (A), x = 0.005, a = 0.883, b = 0.088, c = 0.000, d = 0 0.029.

[Coating process]
The calcined product 5 and aluminum oxide were weighed so that Al[1]/(Ni+Co+Al[2])=0.015, dry-mixed using a Loedige mixer, and subjected to oxygen atmosphere at 720° C. for 5 hours. A lithium metal composite oxide Al-coated powder 5 was obtained by heat treatment. Here, Al[1] represents aluminum derived from aluminum oxide, which is the coating source, and Al[2] represents aluminum derived from the fired material 5 .

[Washing process]
After that, the obtained lithium metal composite oxide aluminum-coated powder 5 was washed with water. The washing step was carried out by adding the lithium metal composite oxide aluminum-coated powder 5 to pure water, stirring the resultant slurry for 20 minutes, and dehydrating the slurry.

[Drying process]
Thereafter, the wet cake obtained in the dehydration step was vacuum-dried at 80° C. for 15 hours and at 150° C. for 8 hours to obtain positive electrode active material 5 for a lithium secondary battery.

(Example 6)
Production of positive electrode active material 6 for lithium secondary battery [Nickel-cobalt composite hydroxide production process]
After water was introduced into a reaction vessel equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained within the range of 50-55°C.

A nickel sulfate aqueous solution and a cobalt sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms to cobalt atoms was 0.890:0.110 to prepare a mixed raw material solution.

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reactor under stirring, and the pH of the solution in the reactor measured at 40° C. was 11.8 to 12.0. An aqueous sodium hydroxide solution was added dropwise at appropriate times so as to achieve a range of 5. Then, an oxidizing gas obtained by mixing nitrogen gas with air was passed through, and various liquid amounts were adjusted so that the reaction time was 19 hours to obtain nickel-cobalt composite hydroxide particles, which were washed with a sodium hydroxide solution. After that, by dehydrating and isolating with a centrifuge and drying at 105° C., a nickel-cobalt composite hydroxide 6 was obtained.

[Mixing process]
The nickel-cobalt composite hydroxide 6 obtained as described above and the lithium hydroxide powder were weighed and mixed so that the molar ratio was Li/(Ni+Co)=1.04.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 720° C. for 6 hours in an oxygen atmosphere to obtain a fired product 6 .
The composition analysis of the obtained baked product 6 was performed, and when it corresponded to the composition formula (A), x = 0.021, a = 0.890, b = 0.110, c = 0.000, d = 0 0.000.

[Coating process]
The baked product 6 and aluminum oxide were weighed so that Al/(Ni+Co)=0.015, dry-mixed using a Loedige mixer, and heat-treated at 720° C. for 5 hours in an oxygen atmosphere to produce lithium metal. A composite oxide aluminum-coated powder 6 was obtained.

[Washing process]
After that, the obtained lithium metal composite oxide aluminum-coated powder 6 was washed with water. The washing step was carried out by adding the lithium metal composite oxide aluminum-coated powder 6 to pure water, stirring the obtained slurry liquid for 20 minutes, and dehydrating the liquid.

[Drying process]
After that, the wet cake obtained in the dehydration step was vacuum-dried at 80° C. for 15 hours and at 150° C. for 8 hours to obtain positive electrode active material 6 for a lithium secondary battery.

(Example 7)
Production of positive electrode active material 7 for lithium secondary battery [Nickel-cobalt-manganese composite hydroxide production process]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 0.550:0.210:0.240 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reaction tank under stirring so that the pH of the solution in the reaction tank when measured at 40° C. was 11.7. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and the amounts of various liquids are adjusted so that the reaction time is 12 hours to obtain nickel-cobalt-manganese composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-manganese composite hydroxide 7 .

[Mixing process]
The nickel-cobalt-manganese composite hydroxide 7 obtained as described above and the lithium carbonate powder were weighed and mixed in a molar ratio of Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the above mixing step was fired at 940° C. for 5 hours in an oxygen atmosphere to obtain fired product 7 .
The composition analysis of the obtained baked product 7 was performed, and when it corresponded to the composition formula (A), x = 0.041, a = 0.549, b = 0.209, c = 0.242, d = 0 0.000.

[Tungsten coating process]
The baked product 7 obtained as described above was heated to 105° C., and an alkaline solution in which tungsten oxide was dissolved in an aqueous lithium hydroxide solution was sprayed for 1 hour while mixing using a Loedige mixer. At this time, the concentration of tungsten in the alkaline solution was adjusted so that the molar ratio W/(Ni+Co+Mn)=0.005. Through this process, lithium metal composite oxide tungsten-coated powder 7 was obtained.

[Aluminum coating step]
Lithium metal composite oxide tungsten-coated powder 7 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, and mixed in an atmosphere containing water and carbon dioxide using a Lödige mixer. and a heat treatment at 760° C. for 5 hours in an air atmosphere to obtain a positive electrode active material 7 for a lithium secondary battery.

(Example 8)
Production of positive electrode active material 8 for lithium secondary battery [Nickel-cobalt-manganese composite hydroxide production process]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 0.550:0.210:0.240 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reaction tank under stirring so that the pH of the solution in the reaction tank when measured at 40° C. was 12.0. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and the amount of various liquids is adjusted so that the reaction time is 20 hours to obtain nickel-cobalt-manganese composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-manganese composite hydroxide 8 .

[Mixing process]
The nickel-cobalt-manganese composite hydroxide 8 obtained as described above and the lithium carbonate powder were weighed and mixed so that the molar ratio was Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the above mixing step was fired at 850° C. for 10 hours in an air atmosphere to obtain a fired product 8 .
The composition analysis of the obtained baked product 8 was performed, and when it corresponded to the composition formula (A), x = 0.035, a = 0.549, b = 0.209, c = 0.241, d = 0 0.000.

[Zirconium coating step]
The fired product 8 obtained as described above and the zirconium oxide powder were dry-mixed so that the atomic ratio of zirconium atoms to the total of nickel atoms, cobalt atoms and manganese atoms was 0.300 mol%, thereby producing a lithium metal composite. A zirconium oxide coated powder 8 was obtained.

[Aluminum coating step]
Lithium metal composite oxide zirconium-coated powder 8 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, and mixed using a Loedige mixer in an atmosphere containing water and carbon dioxide gas. and a heat treatment at 850° C. for 10 hours in an air atmosphere to obtain a positive electrode active material 8 for a lithium secondary battery.

(Comparative example 1)
Production of positive electrode active material 9 for lithium secondary battery [Nickel-cobalt-manganese composite hydroxide production process]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 0.510:0.225:0.265 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reaction tank while stirring so that the pH of the solution in the reaction tank when measured at 40° C. was 11.5. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and various liquid amounts are adjusted so that the reaction time is 11 hours to obtain nickel-cobalt-manganese composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-manganese composite hydroxide 9 .

[Mixing process]
The nickel-cobalt-manganese composite hydroxide 9 obtained as described above and the lithium carbonate powder were weighed and mixed in a molar ratio of Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 870° C. for 10 hours in an oxygen atmosphere to obtain fired product 9 .
The composition analysis of the obtained baked product 9 was performed, and when it corresponded to the composition formula (A), x = 0.034, a = 0.514, b = 0.224, c = 0.262, d = 0 0.000.

[Coating process]
The baked product 9 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, dry-mixed using an FM mixer, and heat-treated at 760° C. for 3 hours in an air atmosphere to produce a lithium secondary battery. A positive electrode active material 9 for

Evaluation of Positive Electrode Active Material 9 for Lithium Secondary Battery When the particle cross section of the obtained positive electrode active material 9 for lithium secondary battery was subjected to aluminum element mapping by STEM-EDX, the coating layer containing the aluminum element was found to be lumpy on the particle surface. It was confirmed that the particles existed in a shape and were non-uniformly formed. The results are shown in FIG.

(Comparative example 2)
Production of positive electrode active material 10 for lithium secondary battery [mixing step]
Nickel-cobalt-manganese composite hydroxide 9 and lithium carbonate powder were weighed and mixed in a molar ratio of Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 870° C. for 5 hours in an oxygen atmosphere to obtain fired product 10 .
The composition analysis of the obtained fired product 10 was performed, and when it corresponded to the composition formula (A), x = 0.029, a = 0.512, b = 0.224, c = 0.264, d = 0 0.000.

[Coating process]
The baked product 10 and aluminum oxide were weighed so that Al/(Ni+Co+Mn)=0.01, dry-mixed using an FM mixer, and heat-treated at 760° C. for 3 hours in an air atmosphere to produce a lithium secondary battery. A positive electrode active material 10 for

(Comparative Example 3)
Production of positive electrode active material 11 for lithium secondary battery [Nickel-cobalt-manganese composite hydroxide production process]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 0.510:0.225:0.265 to prepare a mixed raw material solution. .

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reaction tank under stirring so that the pH of the solution in the reaction tank when measured at 40° C. was 11.8. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and the amount of various liquids is adjusted so that the reaction time is 20 hours to obtain nickel-cobalt-manganese composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, it was dehydrated and isolated by a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-manganese composite hydroxide 11 .

[Mixing process]
The nickel-cobalt-manganese composite hydroxide 11 obtained as described above and the lithium carbonate powder were weighed and mixed so that the molar ratio was Li/(Ni+Co+Mn)=1.07.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 720° C. for 3 hours in an oxygen atmosphere to obtain fired product 11 .
The composition analysis of the obtained fired product 11 was performed, and when it corresponded to the composition formula (A), x = 0.024, a = 0.519, b = 0.222, c = 0.259, d = 0 0.000.

[Coating process]
The baked product 11 and aluminum oxide were weighed so that Al/(Ni + Co + Mn) = 0.01, and mixed using a Loedige mixer in an atmosphere containing water and carbon dioxide gas. A positive electrode active material 11 for a lithium secondary battery was obtained by heat-treating at °C for 5 hours.

(Comparative Example 4)
Production of positive electrode active material 12 for lithium secondary battery [Nickel-cobalt composite hydroxide production process]
After water was introduced into a reaction vessel equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained within the range of 50-55°C.

A nickel sulfate aqueous solution and a cobalt sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms to cobalt atoms was 0.890:0.110 to prepare a mixed raw material solution.

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reactor under stirring, and the pH of the solution in the reactor measured at 40° C. was 11.8 to 12.0. An aqueous sodium hydroxide solution was added dropwise at appropriate times so as to achieve a range of 5. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and various liquid amounts are adjusted so that the reaction time is 19 hours or longer to obtain nickel-cobalt composite hydroxide particles, which are washed with a sodium hydroxide solution. After that, the nickel-cobalt composite hydroxide 12 was obtained by dehydrating and isolating with a centrifugal separator and drying at 105°C.

[Mixing process]
The nickel-cobalt composite hydroxide 12 obtained as described above and the lithium hydroxide powder were weighed and mixed so that the molar ratio was Li/(Ni+Co)=1.07.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 720° C. for 6 hours in an oxygen atmosphere to obtain fired product 12 .

[Washing process]
After that, the baked product 12 obtained was washed with water. The washing step was carried out by adding the fired product 12 to pure water, stirring the resulting slurry for 20 minutes, and dehydrating the slurry.

[Drying process]
After that, the wet cake obtained in the dehydration step was vacuum-dried at 80° C. for 15 hours and at 150° C. for 8 hours to obtain washed and dried powder 12 of lithium metal composite oxide.
The composition analysis of the obtained washed dried powder 12 of lithium metal composite oxide was carried out to correspond to the composition formula (A). 0.000, d=0.000.

[Coating process]
The washed dried powder 12 of lithium metal composite oxide and aluminum oxide were weighed so that Al/(Ni+Co)=0.015, dry-mixed using a Lödige mixer, and subjected to oxygen atmosphere at 720° C. for 5 hours. A positive electrode active material 12 for a lithium secondary battery was obtained by heat treatment.

(Comparative Example 5)
Production of positive electrode active material 13 for lithium secondary battery [Manufacturing process of nickel-cobalt-manganese-aluminum composite hydroxide]
After putting water into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 60°C.

An aqueous nickel sulfate solution, an aqueous cobalt sulfate solution, an aqueous manganese sulfate solution, and an aqueous aluminum sulfate solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, manganese atoms, and aluminum atoms was 0.855:0.095:0.020:0.030. to prepare a mixed raw material liquid.

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reaction tank while stirring so that the pH of the solution in the reaction tank when measured at 40° C. was 10.2. An aqueous sodium hydroxide solution was added dropwise at appropriate times. Then, an oxidizing gas obtained by mixing nitrogen gas with air is passed through, and the amounts of various liquids are adjusted so that the reaction time is 11 hours to obtain nickel-cobalt-manganese-aluminum composite hydroxide particles, which are then treated with a sodium hydroxide solution. After washing, it was dehydrated and isolated with a centrifugal separator, and dried at 105° C. to obtain nickel-cobalt-manganese-aluminum composite hydroxide 13 .

[Mixing process]
The nickel-cobalt-manganese-aluminum composite hydroxide 13 obtained as described above and the lithium hydroxide powder were weighed and mixed so that the molar ratio was Li/(Ni+Co+Mn+Al)=1.00, and then oxidized. Tungsten powder was dry-mixed so that the atomic ratio of tungsten atoms to the sum of nickel atoms, cobalt atoms, manganese atoms and aluminum atoms was 0.5 mol %.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 770° C. for 5 hours in an oxygen atmosphere to obtain fired product 13 .
The composition analysis of the obtained baked product 13 was performed, and when it corresponded to the composition formula (A), x = 0.000, a = 0.864, b = 0.093, c = 0.018, d = 0 0.024.
Tungsten is not included in d because it exists on the particle surface.

[Coating process]
The baked product 13 and aluminum oxide were weighed so that Al[1]/(Ni+Co+Mn+Al[2])=0.02, and mixed in an atmosphere containing water and carbon dioxide using a Lödige mixer. and a heat treatment at 770° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material 13 for a lithium secondary battery.
Here, Al[1] represents aluminum derived from aluminum oxide, which is the coating source, and Al[2] represents aluminum derived from the fired product 13 .

(Comparative Example 6)
Production of positive electrode active material 14 for lithium secondary battery [mixing step]
Nickel-cobalt-manganese-aluminum composite hydroxide 13 and lithium hydroxide powder are weighed and mixed so that the molar ratio is Li/(Ni+Co+Mn+Al)=1.02, and further, tungsten oxide powder is mixed with nickel atoms and cobalt atoms. and were dry-mixed so that the atomic ratio of tungsten atoms to the sum of manganese atoms and aluminum atoms was 0.125 mol %.

[Baking process]
After that, the mixture obtained in the mixing step was fired at 770° C. for 5 hours in an oxygen atmosphere to obtain fired product 14 .
The composition analysis of the obtained fired product 14 was performed, and when it corresponded to the composition formula (A), x = 0.005, a = 0.864, b = 0.093, c = 0.018, d = 0 0.025.
Tungsten is not included in d because it exists on the particle surface.

[Coating process]
The baked product 14 and aluminum oxide were weighed so that Al[1]/(Ni+Co+Mn+Al[2])=0.02, and mixed in an atmosphere containing water and carbon dioxide using a Lödige mixer. A positive electrode active material 14 for a lithium secondary battery was obtained by heat-treating at 770° C. for 5 hours in an oxygen atmosphere.
Here, Al[1] represents aluminum derived from aluminum oxide as a coating source, and Al[2] represents aluminum derived from the fired product 14 .

(Comparative Example 7)
Production of Positive Electrode Active Material 15 for Lithium Secondary Battery A positive electrode active material 15 for lithium secondary battery was obtained by heat-treating the lithium metal composite oxide zirconium-coated powder 8 at 850° C. for 10 hours in an air atmosphere.

For Examples 1 to 8 and Comparative Examples 1 to 7, coating method, moisture content, BET specific surface area, lithium carbonate content, lithium hydroxide content, average value of AR ₃ when forming an aluminum coating layer, AR ₃ and AR ₁₀ ratio (AR ₃ /AR ₁₀ ) reciprocal average value of variation coefficient [(AR ₃ /AR ₁₀ ) / σ (AR ₃ /AR ₁₀ )], average value of WR ₃ when a tungsten coating layer is formed , the reciprocal average value of the coefficient of variation of the ratio of WR ₃ to WR ₁₀ (WR ₃ /WR ₁₀ ) [(WR ₃ /WR ₁₀ )/σ(WR ₃ /WR ₁₀ )], The average value of ZR ₅ and the reciprocal average value of the coefficient of variation of the ratio of ZR ₅ to ZR ₁₀ (ZR ₅ /ZR ₁₀ ) [(ZR ₅ /ZR ₁₀ )/σ(ZR ₅ /ZR ₁₀ )] battery swelling amount , Tables 1 and 2.

As shown in Tables 1 and 2, Examples 1 to 8 to which the present invention was applied had lower battery swelling amounts of 0.2 cm ³ /g or less than Comparative Examples 1 to 7 to which the present invention was not applied. .

DESCRIPTION OF SYMBOLS 1... Separator, 2... Positive electrode, 3... Negative electrode, 4... Electrode group, 5... Battery can, 6... Electrolytic solution, 7... Top insulator, 8... Sealing body, 10... Lithium secondary battery, 21... Positive electrode lead, 31 …negative lead

Claims (4)

A BET specific surface area of 0.51 m ² /g or more, satisfying all of the following requirements (1) to (2),
A method for producing a positive electrode active material for a lithium secondary battery , wherein the water content is 600 ppm or less ,
A heat treatment step of mixing a lithium composite metal compound containing at least Ni and Li with a coating material raw material containing Al and heat-treating the mixture,
A method for producing a positive electrode active material for a lithium secondary battery, wherein the lithium composite metal compound and the raw material for the coating material are mixed using a Loedige mixer .
(1) The ratio of the detection intensity of aluminum to the detection intensity of nickel (aluminum The detection intensity of /the detection intensity of nickel) is defined as AR.
The AR when the SEM-EDX measurement is performed at an acceleration voltage of 3 kV is assumed to be _AR3 .
Let _AR10 be the AR when the SEM-EDX measurement is performed at an accelerating voltage of 10 kV.
The average value [Ave (AR ₃ /AR ₁₀ )] and the standard deviation [σ (AR ₃ /AR ₁₀ )] of the ratio [AR ₃ /AR ₁₀ ] between AR ₃ and AR ₁₀ obtained by the SEM-EDX measurement are calculate.
A coefficient of variation <[σ(AR ₃ /AR ₁₀ )]/[Ave(AR ₃ /AR ₁₀ )]> is calculated from the ratio and the standard deviation.
The inverse of the obtained variation coefficient <[Ave( _AR3 / _AR10 )]/[σ( _AR3 / _AR10 )]> is 6.1 or more.
(2) The average value of _AR3 is 0.025 or more. A BET specific surface area of 0.51 m ² /g or more, satisfying all of the following requirements (1) to (2),
A method for producing a positive electrode active material for a lithium secondary battery , wherein the water content is 600 ppm or less ,
A heat treatment step of mixing a lithium composite metal compound containing at least Ni and Li with a coating material raw material containing W and heat-treating the mixture,
A method for producing a positive electrode active material for a lithium secondary battery, wherein the lithium composite metal compound and the raw material for the coating material are mixed using a Loedige mixer .
(1) The ratio of the detection intensity of tungsten to the detection intensity of nickel measured by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) on the particle surface of the positive electrode active material for lithium secondary batteries (tungsten Detected intensity of nickel/Detected intensity of nickel) is defined as WR.
WR ₃ is the WR when the SEM-EDX measurement is performed at an acceleration voltage of 3 kV.
Let WR ₁₀ be the WR when the SEM-EDX measurement is performed at an acceleration voltage of 10 kV.
Average value [Ave (WR ₃ /WR ₁₀ )] and standard deviation [σ (WR ₃ /WR ₁₀ )] of the ratio [WR ₃ /WR ₁₀ ] of WR ₃ and WR ₁₀ obtained by the SEM-EDX measurement Calculate
A coefficient of variation <[σ(WR ₃ /WR ₁₀ )]/[Ave(WR ₃ /WR ₁₀ )]> is calculated from the ratio and the standard deviation.
The reciprocal <[Ave(WR ₃ /WR ₁₀ )]/[σ(WR ₃ /WR ₁₀ )]> of the obtained coefficient of variation is 2.5 or more.
(2) The average value of WR ₃ is 0.005 or more. 3. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1 , wherein the lithium composite metal compound has an α-NaFeO2 type crystal structure represented by the following compositional formula (A).
Li _{[ Lix} ( _NiaCobMncM1d )1-x] _{O2 ( A} )
(where -0.1 ≤ x ≤ 0.2, 0.5 ≤ a < 1, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.1, a + b + c + d = 1 and M1 is Mg, Ca, Sr, Ba, Zn, B, Al, Ga, Ti, Zr, Ge, Fe, Cu, Cr, V, W, Mo, Sc, Y, Nb, La, Ta, Tc , Ru, Rh, Pd, Ag, Cd, In, and Sn.) 4. Any one of claims 1 to 3 , wherein the lithium carbonate content of the positive electrode active material for a lithium secondary battery is 0.3% by mass or less, and the lithium hydroxide content is 0.3% by mass or less. A method for producing the positive electrode active material for a lithium secondary battery according to claim 1.

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