JP2018120871A - Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a positive electrode active material for a lithium secondary battery, which is low in battery resistance and improved in peel strength; a positive electrode for a lithium secondary battery, which is arranged by use of the positive electrode active material for a lithium secondary battery; and a lithium secondary battery having the positive electrode for a lithium secondary battery.SOLUTION: A positive electrode active material for a lithium secondary battery comprises: secondary particles resulting from the agglomeration of primary particles which allows lithium ions to be doped thereinto or de-doped therefrom. The secondary particles have pores, and satisfy the following requirements (1) and (2) as to a pore distribution obtained according to a method of mercury penetration: (1) the pore distribution has a pore peak in a pore radius range of 10 nm or larger and 200 nm or smaller as to the pore radius of pores which are present in the secondary particles and/or among the secondary particles; and (2) of pores which are present in the secondary particles and/or among the secondary particles, pores having a pore radius of 100 nm or larger and 10 μm or smaller have a total superficial area less than 1.1 m/g.SELECTED DRAWING: None

Description

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

  Lithium composite oxide is used as a positive electrode active material for lithium secondary batteries. Lithium secondary batteries have already been put into practical use not only for small power sources for mobile phones and laptop computers, but also for medium and large power sources for automobiles and power storage.

  In order to improve the performance of lithium secondary batteries such as battery capacity, attempts have been made focusing on the peak position of the pore distribution of the positive electrode active material for lithium secondary batteries (for example, Patent Documents 1 and 2).

JP 2008-243448 A JP-A-9-82312

As the application field of lithium secondary batteries continues to expand, positive electrode active materials for lithium secondary batteries are required not only to improve battery characteristics such as reducing battery resistance, but also to improve productivity. Specifically, as an improvement in productivity, the positive electrode active material is sufficiently adhered to the current collector (in other words, the peel strength of the positive electrode active material with respect to the current collector is high). A positive electrode for a lithium secondary battery can be produced without worrying about dropping or powder adhesion to the roll.
However, the positive electrode active materials for lithium secondary batteries as described in Patent Documents 1 and 2 have room for improvement from the viewpoint of improving productivity as well as improving battery characteristics.
The present invention has been made in view of the above circumstances, and has a low battery resistance and improved peel strength, a positive electrode active material for a lithium secondary battery, and a lithium secondary battery using the positive electrode active material for a lithium secondary battery It is an object to provide a lithium secondary battery having a positive electrode for use and a positive electrode for the lithium secondary battery.

That is, the present invention includes the following [1] to [7].
[1] A positive electrode active material for a lithium secondary battery including secondary particles obtained by agglomerating primary particles capable of doping and dedoping lithium ions, wherein the secondary particles have pores and are mercury intrusion methods The positive electrode active material for a lithium secondary battery, characterized in that the following distributions (1) and (2) are satisfied in the pore distribution obtained by:
(1) The pore radius of one or both of the secondary particles and the pores existing between the secondary particles has a pore peak in the range of 10 nm to 200 nm.
(2) The total surface area of pores having a pore radius of 100 nm or more and 10 μm or less among pores existing in either or both of the secondary particles or the secondary particles is 1.1 m ² / less than g.
[2] The positive electrode active material for a lithium secondary battery according to [1], which is represented by the following composition formula (I).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(However, M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.4, and 0 ≦ w ≦ 0.1 are satisfied.)
[3] The positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the tap density is 2.5 g / cc or less.
[4] The positive electrode active material for a lithium secondary battery according to any one of [1] to [3], wherein the average secondary particle diameter is 3 μm or more and 15 μm or less.
Any one of [1] to [4], wherein [5] (pore surface area with a pore radius of 10 nm to 50 nm) / (pore surface area with a pore radius of 10 nm to 100 μm) is 0.20 or more. The positive electrode active material for lithium secondary batteries as described in any one.
[6] A positive electrode for a lithium secondary battery having the positive electrode active material for a lithium secondary battery according to any one of [1] to [5].
[7] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [6].

  According to the present invention, the positive electrode active material for a lithium secondary battery having low battery resistance and improved peel strength, the positive electrode for a lithium secondary battery using the positive electrode active material for the lithium secondary battery, and the lithium secondary battery A lithium secondary battery having a positive electrode can be provided.

It is a schematic block diagram which shows an example of a lithium ion secondary battery. It is a schematic diagram of the test piece and test apparatus which are used for a peel strength test. It is a schematic diagram of the cross section of the positive electrode to which this invention is applied. It is a schematic diagram of the cross section of the positive electrode which does not apply this invention.

<Positive electrode active material for lithium secondary battery>
The present invention is a positive electrode active material for a lithium secondary battery (hereinafter sometimes referred to as “positive electrode active material”) containing secondary particles formed by agglomerating primary particles capable of doping and dedoping lithium ions. .
The positive electrode active material of the present invention satisfies the following requirements (1) and (2) in the pore distribution obtained by the mercury intrusion method.
(1) The pore radius of one or both of the secondary particles and the pores existing between the secondary particles has a pore peak in the range of 10 nm to 200 nm.
(2) The total surface area of pores having a pore radius of 100 nm or more and 10 μm or less among pores existing in either or both of the secondary particles or the secondary particles is 1.1 m ² / less than g.

≪Measurement of pore distribution by mercury intrusion method≫
The pore peak of the above requirement (1) and the pore surface area of (2) can be calculated from the pore distribution obtained by the mercury intrusion method.
In this embodiment, the pore distribution measurement by the mercury intrusion method is performed by the following method.

First, after evacuating the container containing the positive electrode active material, the container is filled with mercury. Mercury has a high surface tension, and as it is, mercury does not enter the pores on the surface of the positive electrode active material. However, when pressure is applied to the mercury and the pressure is increased gradually, the pores with smaller diameters increase in order from the larger diameter. Mercury gradually penetrates into the pores. If the amount of mercury intrusion is detected while continuously increasing the pressure, a mercury intrusion curve can be obtained from the relationship between the pressure applied to mercury and the amount of mercury intrusion.
Here, assuming that the shape of the pore is cylindrical, the pressure applied to mercury is P, the pore diameter (pore diameter) is D, the surface tension of mercury is σ, and the contact angle between mercury and the sample is θ Then, the pore diameter is represented by the following formula (A).
D = −4σ × cos θ / P (A)

That is, since there is a correlation between the pressure P applied to the mercury and the diameter D of the pore into which mercury enters, the size of the pore radius of the positive electrode active material and its volume are determined based on the obtained mercury intrusion curve. A pore distribution curve representing the relationship between When the length of the pore having the pore diameter D is L, the volume V is represented by the following formula (B).
V = πD2L / 4 (B)
Since the side area of the cylinder S = πDL, it can be expressed as S = 4 V / D. Here, if it is assumed that the volume increase dV in a certain pore diameter range is due to a cylindrical pore having a certain average pore diameter, the specific surface area increased in that section is dA = 4 dV / Dav (Dav is an average) The pore specific surface area ΣA is calculated. In addition, as for the approximate measurement limit of the pore diameter by the mercury intrusion method, the lower limit is about 2 nm or more, and the upper limit is about 200 μm or less. Measurement by the mercury intrusion method can be performed using an apparatus such as a mercury porosimeter. Specific examples of the mercury porosimeter include Autopore III9420 (manufactured by Micromeritics).

[Requirement (1)]
In the present embodiment, the secondary particles of the positive electrode active material are fine voids in which the particle surface and the inside of the particles communicate with each other inside the secondary particles (hereinafter sometimes referred to as “secondary particle fine voids”). have. The secondary particles of the positive electrode active material have fine voids (hereinafter sometimes referred to as “secondary particle gaps”) between the secondary particles. In the present embodiment, in the pore distribution obtained by the mercury intrusion method, either one or both of the fine pores in the secondary particles and the secondary particle gaps are narrow in the range where the pore radius is 10 nm or more and 200 nm or less. Has a pore peak.
The pore radius of the pore peak of the fine pores in the secondary particles is preferably 20 nm or more, more preferably 30 nm or more, and particularly preferably 40 nm or more.
Further, the pore radius of the fine pores in the secondary particles is preferably 180 nm or less, more preferably 150 nm or less, and particularly preferably 120 nm or less.
The upper limit value and the lower limit value can be arbitrarily combined.

  In the present embodiment, when the pore radius of the fine voids in the secondary particles is in the specific range, a positive electrode active material in which the electrolytic solution easily permeates and the direct current resistance is low can be obtained.

  In the present embodiment, the pore peak of the fine voids in the secondary particles is preferably in the specific range.

[Requirement (2)]
In the present embodiment, in the pore distribution obtained by the mercury intrusion method, one or both of the fine pores in the secondary particles and the secondary particle gaps are pores having a pore radius in the range of 100 nm to 10 μm. The surface area S is less than 1.1 m ² / g.
Pore surface area S is preferably 1.0 m ² / g or less, more preferably 0.9 m ² / g, and particularly preferably 0.85 m ² / g.
The pore surface area S is preferably 0.01 m ² / g or more, more preferably 0.1 m ² / g or more, and particularly preferably 0.15 m ² / g or more.
The upper limit value and the lower limit value can be arbitrarily combined.

  In this embodiment, when the pore surface area S is not more than the above upper limit value, the permeability of the binder is improved, and the binder component can be present at the interface with the current collector. This point will be described with reference to the drawings.

  In the present embodiment, the pore surface area S in the range where the pore radius of the gap between the secondary particles is 100 nm or more and 10 μm or less is preferably in the specific range.

  In this embodiment, in the pore distribution obtained by the mercury intrusion method, the pore peak having a pore radius in the range of 10 nm or more and 100 nm or less is a peak derived from the fine voids in the secondary particles.

FIG. 3 is a cross-sectional view of the positive electrode in which the positive electrode mixture including the positive electrode active material 11, the conductive material 12, and the binder 13 satisfying the requirement (2) of the present embodiment is prepared and the positive electrode mixture is supported on the current collector 10. It is a schematic diagram.
As shown in FIG. 3, in the positive electrode active material satisfying the requirement (2) of the present embodiment, the binder component easily penetrates into the gap between the secondary particles, and a large amount of the binder component can be arranged at the interface with the current collector 10. it can. For this reason, it is guessed that the binder component which contributes to adhesion | attachment with the electrical power collector 10 and positive electrode mixture increases, and a positive electrode with high peeling strength can be obtained.

  On the other hand, when the present invention is not applied, as shown in FIG. 4, the binder 13 hardly penetrates into the gap between the secondary particles and hardly reaches the interface with the current collector 10. For this reason, it is considered that a sufficient binder component for adhering the current collector 10 and the positive electrode mixture cannot be secured, and the peel strength is lowered.

In the present embodiment, the lithium metal composite oxide powder is represented by the following general formula (I).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(However, M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.4, and 0 ≦ w ≦ 0.1 are satisfied.)

In the sense of obtaining a lithium secondary battery having high cycle characteristics, x in the composition formula (I) is preferably more than 0, more preferably 0.01 or more, and further preferably 0.02 or more. . In the sense of obtaining a lithium secondary battery with higher initial Coulomb efficiency, x in the composition formula (I) is preferably 0.1 or less, more preferably 0.08 or less, and 0.06. More preferably, it is as follows.
The upper limit value and the lower limit value of x can be arbitrarily combined.

In the sense of obtaining a lithium secondary battery having low battery resistance, y in the composition formula (I) is preferably 0.005 or more, more preferably 0.01 or more, and 0.05 or more. More preferably it is. In the sense of obtaining a lithium secondary battery having high thermal stability, y in the composition formula (I) is more preferably 0.35 or less, and further preferably 0.33 or less.
The upper limit value and the lower limit value of y can be arbitrarily combined.

In the sense of obtaining a lithium secondary battery having high cycle characteristics, z in the composition formula (I) is preferably 0.01 or more, more preferably 0.03 or more, and 0.1 or more. More preferably it is. In addition, z in the composition formula (I) is preferably 0.4 or less, and preferably 0.38 or less in order to obtain a lithium secondary battery having high storage characteristics at a high temperature (for example, in an environment of 60 ° C.). Is more preferable, and it is still more preferable that it is 0.35 or less.
The upper limit value and lower limit value of z can be arbitrarily combined.

In the sense of obtaining a lithium secondary battery having low battery resistance, w in the composition formula (I) is preferably more than 0, more preferably 0.0005 or more, and 0.001 or more. Further preferred. In the sense of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, w in the composition formula (I) is preferably 0.09 or less, more preferably 0.08 or less, and 0 More preferably, it is 0.07 or less.
The upper limit value and the lower limit value of w can be arbitrarily combined.

  M in the composition formula (I) represents one or more metals selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. .

  In order to obtain a lithium secondary battery having high cycle characteristics, M in the composition formula (I) is preferably Ti, Mg, Al, W, B, Zr, and lithium secondary having high thermal stability. In terms of obtaining a battery, Al, W, B, and Zr are preferable.

(Tap bulk density of positive electrode active material)
In this embodiment, the tap bulk density of the positive electrode active material for a lithium secondary battery is preferably 2.5 g / cc or less in order to obtain a lithium secondary battery having a high electrode density.
The tap bulk density can be measured based on JIS R 1628-1997.
In the present specification, “heavy loading density” corresponds to the tap bulk density in the above JIS R 1628-1997.

(Average particle size)
In the present embodiment, the average particle diameter of the lithium metal composite oxide powder is preferably 3 μm or more, more preferably 4 μm or more, in order to improve the handling properties of the positive electrode active material for a lithium secondary battery. More preferably, it is 5 μm or more. Further, in the sense of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, it is preferably 15 μm or less, more preferably 13 μm or less, and further preferably 12 μm or less.
The upper limit value and the lower limit value of the average particle diameter can be arbitrarily combined.
In the present invention, the “average particle diameter” of the lithium metal composite oxide powder refers to a value measured by the following method (laser diffraction scattering method).

  Using a laser diffraction particle size distribution analyzer (manufactured by HORIBA, Ltd., model number: LA-950), 0.1 g of lithium metal composite oxide powder was put into 50 ml of a 0.2 mass% sodium hexametaphosphate aqueous solution, and the powder was dispersed. A dispersion was obtained. The particle size distribution of the obtained dispersion is measured to obtain a volume-based cumulative particle size distribution curve. In the obtained cumulative particle size distribution curve, the value of the particle diameter (D50) viewed from the fine particle side at the time of 50% accumulation was taken as the average particle diameter of the lithium metal composite oxide powder.

  In this embodiment, when preparing a paste-like electrode mixture using a lithium metal composite oxide powder, in order to increase the stability of paste viscosity over time (pore surface area with a pore radius of 10 nm to 50 nm) / (Pore surface area having a pore radius of 10 nm to 100 μm) is preferably 0.20 or more, more preferably 0.25 or more, and further preferably 0.30 or more.

(Layered structure)
The crystal structure of the lithium nickel composite oxide is a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure.

  The hexagonal crystal structures are P3, P31, P32, R3, P-3, R-3, P-312, P321, P3112, P3121, P3212, P3221, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P61, P65, P62, P64, P63, P-6, P6 / m, P63 / m, P622, From P6122, P6522, P6222, P6422, P6322, P6mm, P6cc, P63cm, P63mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P63 / mcm, P63 / mmc It belongs to any one space group selected from the group.

  The monoclinic crystal structure is composed of P2, P21, C2, Pm, Pc, Cm, Cc, P2 / m, P21 / m, C2 / m, P2 / c, P21 / c, and C2 / c. It belongs to any one space group selected from the group.

  Among these, in order to obtain a lithium secondary battery having a high discharge capacity, the crystal structure is a hexagonal crystal structure belonging to the space group R-3m or a monoclinic crystal belonging to C2 / m. A crystal structure is particularly preferred.

The lithium compound used in the present invention is any one of lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium hydroxide, lithium oxide, lithium chloride, lithium fluoride, or a mixture of two or more. can do. In these, any one or both of lithium hydroxide and lithium carbonate are preferable.
The lithium carbonate component contained in the lithium metal composite oxide powder is preferably 0.4% by mass or less, and 0.39% by mass or less in order to improve the handling property of the positive electrode active material for a lithium secondary battery. Is more preferable, and it is especially preferable that it is 0.38 mass% or less.
Moreover, it is preferable that the lithium hydroxide component contained in the lithium metal composite oxide powder is 0.35% by mass or less, and 0.25% by mass or less in order to improve the handling property of the positive electrode active material for a lithium secondary battery. It is more preferable that it is, and it is especially preferable that it is 0.2 mass% or less.

[Method for producing positive electrode active material for lithium secondary battery]
In producing the positive electrode active material for lithium secondary battery of the present invention (hereinafter sometimes referred to as “lithium metal composite oxide”), it is first composed of a metal other than lithium, that is, Ni, Co, and Mn. And a metal composite compound containing any metal selected from the group consisting of essential metals and Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V The metal composite compound is preferably fired with an appropriate lithium salt. As a metal complex compound, a metal complex hydroxide or a metal complex oxide is preferable. Below, an example of the manufacturing method of a positive electrode active material is divided and demonstrated to the manufacturing process of a metal composite compound, and the manufacturing process of a lithium metal composite oxide.

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

First, a nickel salt solution, a cobalt salt solution, a manganese salt solution, and a complexing agent are reacted by a coprecipitation method, in particular, a continuous method described in JP-A-2002-201028, and Ni _x Co _y Mn _z (OH). ₂ A composite metal hydroxide represented by the formula (where x + y + z = 1) is produced.

  Although it does not specifically limit as nickel salt which is the solute of the said nickel salt solution, For example, any one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used. As the cobalt salt that is a 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 a solute of the manganese salt solution, for example, any one of manganese sulfate, manganese nitrate, and manganese chloride can be used. The above metal salt is used in a proportion corresponding to the composition ratio of NixCoyMnz (OH) 2. Moreover, water is used as a solvent.

  The complexing agent is capable of forming a complex with nickel, cobalt, and manganese ions in an aqueous solution. For example, an ammonium ion supplier (ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, Examples include ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine.

  During the precipitation, an alkali metal hydroxide (for example, sodium hydroxide or potassium hydroxide) is added if necessary to adjust the pH value of the aqueous solution.

When the complexing agent is continuously supplied to the reaction vessel in addition to the nickel salt solution, the cobalt salt solution, and the manganese salt solution, nickel, cobalt, and manganese react to form Ni _x Co _y Mn _z (OH) _2. Is manufactured. During the reaction, the temperature of the reaction vessel is controlled within a range of, for example, 20 ° C. or more and 80 ° C. or less, preferably 30 to 70 ° C., and the pH value in the reaction vessel is, for example, a pH of 9 or more and pH 13 or less, preferably a range of pH 11-13. The substance in the reaction vessel is appropriately stirred. The reaction vessel is of a type that causes the formed reaction precipitate to overflow for separation.

  By appropriately controlling the concentration of metal salt to be supplied to the reaction tank, the stirring speed, the reaction temperature, the reaction pH, the firing conditions described later, and the like, the above-mentioned requirements (1 ), Various physical properties such as pore radius and average secondary particle diameter shown in (2) can be controlled. In particular, in order to achieve the desired pore radius shown in the above requirements (1) and (2), in addition to controlling the above conditions, inert gases such as nitrogen, argon, carbon dioxide, etc. Bubbling with an oxidizing gas such as gas, air, oxygen, or a mixed gas thereof may be used in combination. Use peroxides such as hydrogen peroxide, peroxides such as permanganate, perchlorates, hypochlorites, nitric acid, halogens, ozone, etc. to promote the oxidation state in addition to gases. be able to. In addition to gases, organic acids such as oxalic acid and formic acid, sulfites, hydrazine and the like can be used to promote the reduced state.

For example, when the reaction pH in the reaction vessel is increased, the primary particle diameter of the metal composite compound is decreased, and a metal composite compound having a high BET specific surface area is easily obtained. On the other hand, when the reaction pH is lowered, a metal composite compound having a low BET specific surface area is easily obtained. Moreover, when the oxidation state in the reaction vessel is increased, a metal composite oxide having many voids is easily obtained. On the other hand, when the oxidation state is lowered, a dense metal oxide is easily obtained.
Ultimately, each condition of the reaction pH and oxidation state is precisely controlled so that the metal composite compound has the desired physical properties, but the oxidizing gas is introduced into the reaction vessel while passing an inert gas such as nitrogen gas. By continuously venting, the pore diameter of the voids of the metal composite compound can be controlled. When air is used as the oxidizing gas, the ratio A / B between the air flow rate A (L / min) and the reaction vessel volume B (L) is preferably greater than 0 and less than 0.020.
The pore radius shown in the above requirements (1) and (2) of the lithium metal composite oxide powder in the present invention is determined by controlling the firing conditions and the like to be described later using the metal composite compound. Can be within the range.

After the above reaction, the obtained reaction precipitate is washed with water and then dried to isolate nickel cobalt manganese hydroxide as a nickel cobalt manganese composite compound. Moreover, you may wash | clean with the alkaline solution containing weak acid water, sodium hydroxide, or potassium hydroxide as needed.
In the above example, nickel cobalt manganese composite hydroxide is manufactured, but nickel cobalt manganese composite oxide may be prepared.

(Production process of lithium metal composite oxide)
The metal composite oxide or hydroxide is dried and then mixed with a lithium salt. The drying conditions are not particularly limited. For example, the metal composite oxide or hydroxide is not oxidized / reduced (oxide → oxide, hydroxide → hydroxide), and the metal composite hydroxide is oxidized. Any of the conditions (hydroxide → oxide) and the conditions under which the metal composite oxide is reduced (oxide → hydroxide) may be used. An inert gas such as nitrogen, helium, or an inert gas such as argon may be used for conditions where oxidation / reduction is not performed. Under conditions where hydroxide is oxidized, oxygen or air may be used in an atmosphere. good. As a condition for reducing the metal composite oxide, a reducing agent such as hydrazine or sodium sulfite may be used in an inert gas atmosphere. As the lithium salt, any one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, lithium oxide, or a mixture of two or more can be used.
Classification may be appropriately performed after the metal composite oxide or hydroxide is dried. The above lithium salt and metal composite metal hydroxide are used in consideration of the composition ratio of the final object. 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 LiNixCoyMnzO2 (wherein x + y + z = 1). A lithium-nickel cobalt manganese composite oxide is obtained by firing a mixture of a nickel cobalt manganese composite metal hydroxide and a lithium salt. For the firing, dry air, an oxygen atmosphere, an inert atmosphere, or the like is used according to a desired composition, and a plurality of heating steps are performed if necessary.

  The firing temperature of the metal composite oxide or hydroxide and a lithium compound such as lithium hydroxide or lithium carbonate is not particularly limited, but the above requirements (1) and (2) of the lithium metal composite oxide are satisfied. In order to make it the specific range of this invention, it is preferable that it is 600 degreeC or more and 1100 degrees C or less, It is more preferable that it is 750 degreeC or more and 1050 degrees C or less, 800 degreeC-1025 degreeC are further more preferable.

  The firing time is preferably 3 hours to 50 hours. When the firing time exceeds 50 hours, there is no problem in battery performance, but the battery performance tends to be substantially inferior due to volatilization of Li. If the firing time is less than 3 hours, the crystal growth is poor and the battery performance tends to be poor. In addition, it is also effective to perform temporary baking before the above baking. The temperature for such preliminary firing is preferably in the range of 300 to 850 ° C. for 1 to 10 hours.

  The lithium metal composite oxide obtained by firing is appropriately classified after pulverization, and used as a positive electrode active material applicable to a lithium secondary battery.

<Lithium secondary battery>
Next, while explaining the configuration 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 of the lithium secondary battery, and a lithium secondary battery having the positive electrode will be described. To do.

  An example of the lithium secondary battery of the present embodiment includes a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

  FIG. 1 is a schematic diagram showing an example of the lithium secondary battery of the present embodiment. The cylindrical lithium secondary battery 10 of this embodiment is manufactured as follows.

  First, as shown in FIG. 1 (a), a pair of separators 1 having a strip shape, a strip-like positive electrode 2 having a positive electrode lead 21 at one end, and a strip-like negative electrode 3 having a negative electrode lead 31 at one end, 2, separator 1, and negative electrode 3 are laminated in this order and wound to form electrode group 4.

  Next, as shown in FIG. 1B, after the electrode group 4 and an insulator (not shown) are accommodated in the battery can 5, the bottom of the can is sealed, and the electrode group 4 is impregnated with the electrolytic solution 6, An electrolyte is disposed between the negative electrode 3 and the negative electrode 3. Furthermore, the lithium secondary battery 10 can be manufactured by sealing the upper part of the battery can 5 with the top insulator 7 and the sealing body 8.

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

  Moreover, as a shape of the lithium secondary battery having such an electrode group 4, a shape defined by IEC 60086 or JIS C 8500, which is a standard for a battery defined by the International Electrotechnical Commission (IEC), can be adopted. . For example, cylindrical shape, square shape, etc. can be mentioned.

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

Hereafter, each structure is demonstrated in order.
(Positive electrode)
The positive electrode of the present embodiment can be produced by first adjusting 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)
As the conductive material included in the positive electrode of the present embodiment, a carbon material can be used. Examples of the carbon material include graphite powder, carbon black (for example, acetylene black), and a fibrous carbon material. Since carbon black is fine and has a large surface area, adding a small amount to the positive electrode mixture can improve 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 proportion 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. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, this ratio can be lowered.

(binder)
As the binder included in the positive electrode of the present embodiment, a thermoplastic resin can be used.
This thermoplastic resin is sometimes referred to as polyvinylidene fluoride (hereinafter referred to as PVdF).
), Polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, propylene hexafluoride / vinylidene fluoride copolymer, tetrafluoroethylene Fluorine resins such as fluorinated ethylene / perfluorovinyl ether copolymers; Polyolefin resins such as polyethylene and polypropylene.

  These thermoplastic resins may be used as a mixture of two or more. By using a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the whole 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. A positive electrode mixture having both high adhesion to the current collector and high bonding strength inside the positive electrode mixture can be obtained.

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

  Examples of the method of supporting the positive electrode mixture on the positive electrode current collector include a method of pressure-molding the positive electrode mixture on the positive electrode current collector. Also, the positive electrode mixture is made into a paste using an organic solvent, and the resulting positive electrode mixture paste is applied to at least one surface side of the positive electrode current collector, dried, pressed and fixed, whereby the positive electrode current collector is bonded to the positive electrode current collector. A mixture may be supported.

  When the positive electrode mixture is made into a paste, usable organic solvents include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; methyl acetate And amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

  Examples of the method of 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 this embodiment is only required to be able to dope and dedope lithium ions at a lower potential than 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 made of a negative electrode active material alone.

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

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

  Examples of oxides that can be used as the negative electrode active material include oxides of silicon represented by the formula SiOx such as SiO2 and SiO (where x is a positive real number); formula TiOx such as TiO2 and TiO (where x is positive) Oxide of titanium represented by the formula VOx (where x is a positive real number); FeOx such as Fe3O4, Fe2O3, and FeO (where x is a real number) Is an oxide of iron represented by SnO2, SnO, etc. SnOx represented by the formula SnOx (where x is a positive real number); WO3, WO2, etc. x is a positive real number); a composite metal oxide containing lithium and titanium or vanadium such as Li4Ti5O12 and LiVO2;

  Examples of sulfides that can be used as the negative electrode active material include titanium sulfides represented by the formula TiSx (where x is a positive real number) such as Ti2S3, TiS2, and TiS; formula VSx such as V3S4, VS2, and VS (where , X is a positive real number); a sulfide of vanadium represented by a formula FeSx (where x is a positive real number) such as Fe3S4, FeS2, and FeS; a formula MoSx such as Mo2S3 and MoS2 Here, molybdenum sulfide represented by x is a positive real number; tin sulfide represented by the formula SnSx (where x is a positive real number) such as SnS2 and SnS; and WSx such as WS2 (where x is a positive real number) , X is a positive real number); a sulfide of tungsten represented by a formula SbSx such as Sb2S3 (where x is a positive real number); a formula Se such as Se5S3, SeS2, SeS x (wherein, x represents a positive real number) sulfide selenium represented by; and the like.

  Examples of the nitride that can be used as the negative electrode active material include lithium-containing nitrides such as Li3N and Li3-xAxN (where A is one or both of Ni and Co, and 0 <x <3). Can be mentioned.

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

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

  Examples of alloys that can be used as the negative electrode active material include lithium alloys such as Li—Al, Li—Ni, Li—Si, Li—Sn, and Li—Sn—Ni; silicon alloys such as Si—Zn; Sn—Mn and Sn. -Tin alloys such as Co, Sn-Ni, Sn-Cu, Sn-La; alloys such as Cu2Sb, La3Ni2Sn7;

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

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

  The negative electrode mixture may contain a binder as necessary. Examples of the binder include thermoplastic resins, and specific examples include PVdF, thermoplastic polyimide, 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, and stainless steel. In particular, it is preferable to use Cu as a forming material and process it into a thin film from the viewpoint that it is difficult to make an alloy with lithium and it is easy to process.

  As a method of supporting the negative electrode mixture on such a negative electrode current collector, as in the case of the positive electrode, a method using pressure molding, pasting with a solvent, etc., applying to the negative electrode current collector, drying and pressing. The method of crimping is mentioned.

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

  In the present embodiment, the separator allows the electrolyte to permeate well when the battery is used (during charging / discharging). Therefore, the air resistance according to the Gurley method defined in JIS P 8117 is 50 seconds / 100 cc or more, 300 seconds / 100 cc. Or less, more preferably 50 seconds / 100 cc or more and 200 seconds / 100 cc or less.

  Moreover, 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 having different porosity.

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

  The electrolyte contained in the electrolyte includes LiClO4, LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN (SO2CF3) 2, LiN (SO2C2F5) 2, LiN (SO2CF3) (COCF3), Li (C4F9SO3), LiC (SO2CF3) 3, Li2B10Cl10, LiBOB (where BOB is bis (oxalato) borate), LiFSI (here, FSI is bis (fluorosulfonyl) imid), lower aliphatic lithium carboxylate, A lithium salt such as LiAlCl 4 may be mentioned, and a mixture of two or more of these may be used. Among them, it is preferable to use an electrolyte containing at least one selected from the group consisting of LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN (SO2CF3) 2, and LiC (SO2CF3) 3 containing fluorine.

  Examples of the organic solvent contained in the electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di- Carbonates such as (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2- Ethers such as methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amides; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by further introducing a fluoro group into these organic solvents ( One obtained by substituting one or more hydrogen atoms in the organic solvent with fluorine atoms 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 cyclic carbonate and acyclic carbonate and a mixed solvent of cyclic carbonate and ether are more preferable. As a mixed solvent of cyclic carbonate and acyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable. The electrolyte using such a mixed solvent has a wide operating temperature range, hardly deteriorates even when charged and discharged at a high current rate, hardly deteriorates even when used for a long time, and natural graphite as an active material of the negative electrode. Even when a graphite material such as artificial graphite is used, it has many features that it is hardly decomposable.

  Further, as the electrolytic solution, it is preferable to use an electrolytic solution containing a lithium salt containing fluorine such as LiPF6 and an organic solvent having a fluorine substituent because the safety of the obtained lithium secondary battery is increased. A mixed solvent containing dimethyl carbonate and ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether is capable of capacity even when charging / discharging at a high current rate. Since the maintenance rate is high, it is more preferable.

A solid electrolyte may be used instead of the above electrolytic solution. As the solid electrolyte, for example, an organic polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Moreover, what is called a gel type which hold | maintained the non-aqueous electrolyte in the high molecular compound can also be used. The _{Li 2 S-SiS 2, Li} 2 S-GeS 2, Li 2 S-P 2 S 5, Li 2 S-B 2 S 3, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 S-SiS _{2 -Li 2 SO 4, Li 2} S-GeS 2 -P 2 S 5 inorganic solid electrolytes containing a sulfide, and the like, may be used a mixture of two or more thereof. By using these solid electrolytes, the safety of the lithium secondary battery may be further improved.

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

  Since the positive electrode active material having the above-described configuration uses the lithium-containing composite metal oxide of the present embodiment described above, the life of the lithium secondary battery using the positive electrode active material can be extended.

  Moreover, since the positive electrode having the above-described configuration has the above-described positive electrode active material for a lithium secondary battery according to this embodiment, the life of the lithium secondary battery can be extended.

  Furthermore, since the lithium secondary battery having the above-described configuration has the above-described positive electrode, the lithium secondary battery has a longer life than the conventional one.

  Next, the present invention will be described in more detail with reference to examples.

  In this example, evaluation of a positive electrode active material for a lithium secondary battery and production evaluation of a positive electrode for a lithium secondary battery and a lithium secondary battery were performed as follows.

<Measurement of pore distribution of mercury positive electrode active material for lithium secondary battery>
As a pretreatment, the positive electrode active material for a lithium secondary battery was dried at 120 ° C. for 4 hours. Using Autopore III9420 (manufactured by Micromeritics), pore distribution measurement was performed under the following measurement conditions. The surface tension of mercury was 480 dynes / cm, and the contact angle between mercury and the sample was 140 °.

Measurement condition
Measurement temperature: 25 ° C
Measurement pressure: 1.07 psia to 59256.3 psia

<Measurement of Heavy Density of Positive Electrode Active Material for Lithium Secondary Batteries (hereinafter, referred to as “tap bulk density”)>
The weight density was measured based on JIS R 1628-1997.

<Measurement of average particle diameter of positive electrode active material for lithium secondary battery>
The average particle size was measured using a laser diffraction particle size distribution analyzer (LA-950, manufactured by HORIBA, Ltd.), 0.1 g of a positive electrode active material powder for a lithium secondary battery, and 50 ml of a 0.2 mass% sodium hexametaphosphate aqueous solution. And a dispersion liquid in which the powder was dispersed was obtained. The particle size distribution of the obtained dispersion is measured to obtain a volume-based cumulative particle size distribution curve. In the obtained cumulative particle size distribution curve, the value of the particle diameter (D50) viewed from the fine particle side at 50% accumulation was taken as the average particle diameter of the positive electrode active material for a lithium secondary battery.

<BET specific surface area of positive electrode active material for lithium secondary battery>
1 g of the positive electrode active material powder for a lithium secondary battery was dried at 105 ° C. for 30 minutes in a nitrogen atmosphere, and then measured using Macsorb (registered trademark) manufactured by Mountec.

<Production of positive electrode for peel strength test>
A positive electrode active material for lithium secondary battery, a conductive material (acetylene black), and a binder (PVdF) obtained by a manufacturing method described later, a positive electrode active material for lithium secondary battery: conductive material: binder = 90: 5: 5 ( In addition, a paste-like positive electrode mixture was prepared by kneading at 5000 rpm for 3 minutes using a fill mix 30-25 type (manufactured by Primex). When preparing the positive electrode mixture, N-methyl-2-pyrrolidone was used as the organic solvent. The paste-like positive electrode mixture was applied to an aluminum current collector foil having a thickness of 20 μm and dried with hot air at 90 ° C. After drying with warm air, the obtained positive electrode was cut into a width of 25 mm and a length of 100 mm, and pressed at a load of 0.3 MPa using a roll press machine (manufactured by Tester Sangyo). Then, the positive electrode for peel strength tests was obtained by vacuum-drying at 150 degreeC for 8 hours. The obtained positive electrode had a positive electrode mixture layer thickness of about 35 μm and a supported amount of the positive electrode active material for a lithium secondary battery of 7 mg / cm ² .

<Measurement of peel strength>
A method for measuring the peel strength will be described with reference to FIG.
FIG. 2A shows a secondary battery electrode 1 including an electrode mixture layer 3 laminated on a current collector 2. The current collector has a width l2 of 25 mm and a length l4 of 100 mm. The current collector thickness l1 was 20 μm, the electrode mixture layer thickness l3 was about 35 μm, and the length l5 was 70 mm.
In the secondary battery electrode 1, one end 2 a of the current collector 2 and one end 3 a of the electrode mixture layer 3 are aligned. On the other hand, the other end 2b of the current collector 2 is located at a position away from the other end 3b of the electrode mixture layer 3 in plan view.
FIG. 2B shows a peel strength measuring device.
The surface of the electrode mixture layer 3 and the substrate 5 (glass epoxy copper-clad laminate MCL-E-67, manufactured by Meiden Kasei Kogyo Co., Ltd.) are used. , Manufactured by Nichiban Co., Ltd.) to form a test piece. In that case, it fixed so that the end 5a of the board | substrate 5, the end 2a of the electrical power collector 2, and the end 3a of the electrode mixture layer 3 might align.
The current collector 1 was peeled from the electrode mixture layer 3 from one end of the electrode, and the substrate was fixed to the holding part 6 below the vertical tensile strength tester (Autograph DSS-500, manufactured by Shimadzu Corporation).
An aluminum foil 2 was added to the current collector 1, and the other end 2 b of the aluminum foil 2 was folded back to the side opposite to the electrode mixture 3, and the other end 2 b of the aluminum foil 2 was fixed to the upper grip 7.
The electrode mixture of the secondary battery electrode and the current collector are pulled by a 180 ° peel test in which the current collector 1 is pulled upward (in the direction indicated by reference numeral 8 in FIG. 2B) at a pulling speed of 100 mm / min. The strength (N) was measured.
From the tensile strength (N) and the electrode width (25 mm), the peel strength (N / m) between the electrode mixture and the current collector was calculated.

<Composition analysis>
The composition analysis of the lithium metal composite oxide powder produced by the method described below is performed by dissolving the obtained lithium metal composite oxide powder in hydrochloric acid and then using an inductively coupled plasma emission spectrometer (SII Nanotechnology, Inc.). Manufactured by SPS3000).

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

  The obtained positive electrode mixture was applied to an Al foil having a thickness of 40 μm serving 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 the positive electrode for the lithium secondary battery was 1.65 cm 2.

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

The obtained negative electrode mixture was applied to a 12 μm thick Cu foil serving 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 the negative electrode for a lithium secondary battery was 1.77 cm ² .

<Production of lithium secondary battery (coin-type full cell)>
The following operations were performed in a glove box with an argon atmosphere.
Place the positive electrode for the lithium secondary battery prepared in “(2) Preparation of the positive electrode for the lithium secondary battery” with the aluminum foil surface facing downward on the lower lid of the part for the coin-type battery R2032 (manufactured by Hosen Co., Ltd.). Then, a laminated film separator (a heat-resistant porous layer laminated on a polyethylene porous film (thickness: 16 μm)) was placed thereon. 300 μl of electrolyte was injected here. The electrolyte was 16:10 of ethylene carbonate (hereinafter sometimes referred to as EC), dimethyl carbonate (hereinafter sometimes referred to as DMC), and ethyl methyl carbonate (hereinafter sometimes referred to as EMC). : 74 (volume ratio) 1 volume% of vinylene carbonate (hereinafter sometimes referred to as VC) is added to a mixed solution, and LiPF ₆ is dissolved to 1.3 mol / l (hereinafter referred to as LiPF _6). / EC + DMC + EMC).
Next, the negative electrode for lithium secondary battery prepared in <Preparation of negative electrode for lithium secondary battery> is placed on the upper side of the laminated film separator, the upper lid is put through a gasket, and it is caulked with a caulking machine. Type full cell R2032, hereinafter sometimes referred to as "full cell".
) Was produced.

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

<Charge / discharge test conditions>
Test temperature: 25 ° C
Charging maximum voltage 4.2V, charging time 6 hours, charging current 0.2CA, constant current constant voltage charging Discharging minimum voltage 2.7V, discharging time 5 hours, discharging current 0.2CA, constant current discharging

<DC resistance measurement>
The discharge capacity measured above was taken as 100% charge depth (hereinafter sometimes referred to as SOC), and the battery resistance at 100% SOC was measured at 25 ° C. In addition, adjustment to each SOC was performed in a 25 ° C. environment. For battery resistance measurement, a full cell with SOC adjusted in a constant temperature bath at 25 ° C. was left for 2 hours, discharged at 20 μA for 15 seconds, left for 5 minutes, charged at 20 μA for 15 seconds, left at 5 μm, left at 40 μA for 15 seconds. Discharge for 5 minutes, charge at 20 μA for 30 seconds, leave for 5 minutes, discharge at 80 μA for 15 seconds, leave for 5 minutes, charge at 20 μA for 60 seconds, leave for 5 minutes, discharge at 160 μA for 15 seconds, leave for 5 minutes , Charging at 20 μA for 120 seconds, and standing for 5 minutes. The battery resistance was calculated from the plot of the battery voltage after 10 seconds measured at the time of discharging at 20, 40, 80, and 120 μA and each current value by using the least square approximation method, and this inclination was defined as the battery resistance. .

Example 1
1. Manufacture of positive electrode active material 1 for lithium secondary battery After putting water in the reaction tank provided with the stirrer and the overflow pipe, sodium hydroxide aqueous solution was added and liquid temperature was hold | maintained at 50 degreeC.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. The air flow rate was adjusted so that the ratio A / B between the air flow rate A (L / min) and the reaction volume B (L) was 0.013, and the reaction vessel was continuously vented. A sodium hydroxide aqueous solution is dripped in a timely manner so that the pH of the solution in the reaction tank is 12.0 to obtain nickel cobalt manganese composite hydroxide particles, which are washed with a sodium hydroxide solution, dehydrated with a centrifuge, and then simply removed. The nickel cobalt manganese composite hydroxide 1 was obtained by separating and drying at 105 ° C.

  The nickel-cobalt-manganese composite hydroxide 1 and lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.08, and then at 760 ° C. for 5 hours in an air atmosphere. Baking was further performed at 875 ° C. for 10 hours in an air atmosphere to obtain a target positive electrode active material 1 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 1 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 1 for a lithium secondary battery was conducted, and when it was made to correspond to the composition formula (I), x = 0.036, y = 0. 211, z = 0.238, and w = 0.

The pore peak of the positive electrode active material 1 for lithium secondary batteries measured by pore distribution measurement by the mercury intrusion method is 56 nm, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 0.854 m ² / g.
Moreover, the tap bulk density of the positive electrode active material 1 for lithium secondary batteries was 1.47 g / cc, and D50 was 4.6 μm.
The pore surface area having a pore radius of 10 nm to 50 nm / the pore surface area having a pore radius of 10 nm to 100 μm was 0.17.

  Moreover, the peel strength of the positive electrode active material 1 for a lithium secondary battery was 189 N / m, and the direct current resistance was 14.1Ω.

(Example 2)
1. Production of Positive Electrode Active Material 2 for Lithium Secondary Battery After water was put in a reaction vessel equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added to keep the liquid temperature at 50 ° C.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. The air flow rate was adjusted so that the ratio A / B between the air flow rate A (L / min) and the reaction volume B (L) was 0.006, and the reaction vessel was continuously vented. A sodium hydroxide aqueous solution is dropped in a timely manner so that the pH of the solution in the reaction tank becomes 12.5 to obtain nickel cobalt manganese composite hydroxide particles, washed with a sodium hydroxide solution, dehydrated with a centrifuge, The nickel cobalt manganese composite hydroxide 2 was obtained by isolating and drying at 105 ° C.

  The nickel-cobalt-manganese composite hydroxide 2 and lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.10, and then at 760 ° C. for 5 hours in an air atmosphere. Firing was further performed at 875 ° C. for 10 hours in an air atmosphere to obtain a target positive electrode active material 2 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 2 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 2 for a lithium secondary battery was conducted, and when it was made to correspond to the composition formula (I), x = 0.049, y = 0. 209, z = 0.242, w = 0.

The pore peak of the positive electrode active material 2 for a lithium secondary battery measured by pore distribution measurement by the mercury intrusion method is 71 nm, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 0.487 m ² / g.
Moreover, the tap bulk density of the positive electrode active material 2 for a lithium secondary battery was 1.89 g / cc, and D50 was 6.6 μm.
The pore surface area having a pore radius of 10 nm to 50 nm / the pore surface area having a pore radius of 10 nm to 100 μm was 0.30.

  Further, the peel strength of the positive electrode active material 2 for a lithium secondary battery was 279 N / m, and the DC resistance was 15.6Ω.

(Example 3)
1. Manufacture of positive electrode active material 3 for lithium secondary battery After putting water in the reaction tank provided with the stirrer and the overflow pipe, the sodium hydroxide aqueous solution was added and liquid temperature was hold | maintained at 50 degreeC.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. Example 2 except that the air flow rate was adjusted so that the ratio A / B between the air flow rate A (L / min) and the reaction volume B (L) was 0.011, and the reaction vessel was continuously vented. The nickel cobalt manganese composite hydroxide 3 was obtained.

  The nickel-cobalt-manganese composite hydroxide 3 and lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.05, and then at 760 ° C. for 5 hours in an air atmosphere. Firing was further performed at 875 ° C. for 10 hours in an air atmosphere to obtain a target positive electrode active material 3 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 3 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 3 for lithium secondary battery was performed, and when it was made to correspond to the composition formula (I), x = 0.025, y = 0. 209, z = 0.240, w = 0.

The pore peak of the positive electrode active material 3 for a lithium secondary battery measured by pore distribution measurement by the mercury intrusion method is 108 nm, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 0.669 m ² / g.
Moreover, the tap bulk density of the positive electrode active material 3 for lithium secondary batteries was 1.85 g / cc, and D50 was 6.6 μm.
The pore surface area having a pore radius of 10 nm to 50 nm / the pore surface area having a pore radius of 10 nm to 100 μm was 0.35.

  Further, the peel strength of the positive electrode active material 3 for a lithium secondary battery was 214 N / m, and the DC resistance was 14.6Ω.

Example 4
1. Manufacture of positive electrode active material 4 for lithium secondary battery After putting water in the reaction tank provided with the stirrer and the overflow pipe, the sodium hydroxide aqueous solution was added and liquid temperature was hold | maintained at 50 degreeC.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. Example 2 except that the air flow rate was adjusted so that the ratio A / B of the air flow rate A (L / min) to the reaction volume B (L) was 0.005 and the reaction vessel was continuously vented. Thus, nickel cobalt manganese composite hydroxide 4 was obtained.

  The nickel cobalt manganese composite hydroxide 4 and lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.05, and then at 760 ° C. for 5 hours in an air atmosphere. Firing was further performed at 875 ° C. for 10 hours in an air atmosphere to obtain a target positive electrode active material 4 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 4 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 4 for lithium secondary battery was performed, and when it was made to correspond to composition formula (I), x = 0.020, y = 0. 208, z = 0.240, w = 0.

The pore peak of the positive electrode active material 4 for a lithium secondary battery measured by pore distribution measurement by the mercury intrusion method is 108 nm, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 0.484 m ² / g.
Moreover, the tap bulk density of the positive electrode active material 4 for lithium secondary batteries was 1.92 g / cc, and D50 was 7.1 μm.
The pore surface area with a pore radius of 10 nm to 50 nm / the pore surface area of a pore radius of 10 nm to 100 μm was 0.48.

  The peel strength of the positive electrode active material 4 for a lithium secondary battery was 272 N / m, and the direct current resistance was 15.1Ω.

(Example 5)
1. Manufacture of positive electrode active material 5 for lithium secondary battery After putting water in the reaction tank provided with the stirrer and the overflow pipe, sodium hydroxide aqueous solution was added and liquid temperature was hold | maintained at 50 degreeC.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. Example 2 except that the air flow rate was adjusted so that the ratio A / B of the air flow rate A (L / min) to the reaction volume B (L) was 0.009 and the reaction vessel was continuously vented. The nickel cobalt manganese composite hydroxide 5 was obtained.

  The nickel-cobalt-manganese composite hydroxide 5 and lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.06, and then at 760 ° C. for 5 hours in an air atmosphere. Firing was further performed at 875 ° C. for 10 hours in an air atmosphere to obtain a target positive electrode active material 5 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 5 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 5 for lithium secondary battery was performed, and when it was made to correspond to composition formula (I), x = 0.028, y = 0. 208, z = 0.241, w = 0.

The pore peak of the positive electrode active material 5 for lithium secondary batteries measured by pore distribution measurement by the mercury intrusion method is 89 nm, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 0.546 m ² / g.
Moreover, the tap bulk density of the positive electrode active material 5 for lithium secondary batteries was 1.81 g / cc, and D50 was 6.7 μm.
The pore surface area with a pore radius of 10 nm to 50 nm / the pore surface area of a pore radius of 10 nm to 100 μm was 0.20.

  Further, the peel strength of the positive electrode active material 5 for a lithium secondary battery was 194 N / m, and the DC resistance was 14.8Ω.

(Example 6)
1. Manufacture of positive electrode active material 6 for lithium secondary battery After putting water in the reaction tank provided with the stirrer and the overflow pipe, sodium hydroxide aqueous solution was added and liquid temperature was hold | maintained at 50 degreeC.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. Example 2 except that the air flow rate was adjusted so that the ratio A / B of the air flow rate A (L / min) to the reaction volume B (L) was 0.018 and the reaction vessel was continuously vented. Thus, nickel cobalt manganese composite hydroxide 6 was obtained.

  The nickel cobalt manganese composite hydroxide 6 and lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.07, and then at 760 ° C. for 5 hours in an air atmosphere. Firing was further performed at 875 ° C. for 10 hours in an air atmosphere to obtain a target positive electrode active material 6 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 6 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 6 for a lithium secondary battery was conducted and made to correspond to the composition formula (I). As a result, x = 0.039, y = 0. 209, z = 0.241, w = 0.

The pore peak of the positive electrode active material 6 for lithium secondary batteries measured by pore distribution measurement by the mercury intrusion method is 108 nm, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 0.896 m ² / g.
Moreover, the tap bulk density of the positive electrode active material 6 for lithium secondary batteries was 1.70 g / cc, and D50 was 6.2 μm.
The pore surface area having a pore radius of 10 nm to 50 nm / the pore surface area having a pore radius of 10 nm to 100 μm was 0.05.

  Further, the peel strength of the positive electrode active material 6 for a lithium secondary battery was 166 N / m, and the DC resistance was 14.7Ω.

(Comparative Example 1)
1. Manufacture of positive electrode active material 7 for lithium secondary battery After putting water in the reaction tank provided with the stirrer and the overflow pipe, the sodium hydroxide aqueous solution was added and liquid temperature was hold | maintained at 50 degreeC.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. The air flow rate was adjusted so that the ratio A / B between the air flow rate A (L / min) and the reaction volume B (L) was 0.025, and the reaction vessel was continuously vented. A sodium hydroxide aqueous solution is dropped in a timely manner so that the pH of the solution in the reaction tank becomes 12.5 to obtain nickel cobalt manganese composite hydroxide particles, washed with a sodium hydroxide solution, dehydrated with a centrifuge, The nickel cobalt manganese composite hydroxide 7 was obtained by isolating and drying at 105 ° C.

  The nickel-cobalt-manganese composite hydroxide 7 and lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.06, and then at 760 ° C. for 5 hours in an air atmosphere. Firing was further performed at 875 ° C. for 10 hours in an air atmosphere to obtain a target positive electrode active material 7 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 7 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 7 for a lithium secondary battery was conducted and made to correspond to the composition formula (I). As a result, x = 0.029, y = 0. 210, z = 0.241, w = 0.

The pore peak of the positive electrode active material 7 for a lithium secondary battery measured by pore distribution measurement by the mercury intrusion method is 108 nm, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 1.14 m ² / g.
Moreover, the tap bulk density of the positive electrode active material 7 for lithium secondary batteries was 1.51 g / cc, and D50 was 5.7 μm.
The pore surface area having a pore radius of 10 nm to 50 nm / the pore surface area having a pore radius of 10 nm to 100 μm was 0.05.

  Further, the peel strength of the positive electrode active material 7 for a lithium secondary battery was 35 N / m, and the direct current resistance was 14.1Ω.

(Comparative Example 2)
1. Manufacture of positive electrode active material 8 for lithium secondary battery After water was put into a reaction vessel equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added to keep the liquid temperature at 50 ° C.

  A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms is 0.55: 0.21: 0.24. It was adjusted.

  Next, under stirring, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent, and nitrogen gas was continuously passed through the reaction vessel. A sodium hydroxide aqueous solution is dropped in a timely manner so that the pH of the solution in the reaction tank is 13.0 to obtain nickel cobalt manganese composite hydroxide particles, washed with a sodium hydroxide solution, dehydrated with a centrifuge, The nickel cobalt manganese composite hydroxide 8 was obtained by isolating and drying at 105 ° C.

  The nickel cobalt manganese composite hydroxide 8 and the lithium carbonate powder obtained as described above were weighed and mixed so that Li / (Ni + Co + Mn) = 1.06, and then at 760 ° C. for 5 hours in an air atmosphere. Firing was further performed at 875 ° C. for 10 hours in an air atmosphere, and in addition, baking was performed at 900 ° C. for 10 hours in the air atmosphere to obtain a target positive electrode active material 8 for a lithium secondary battery.

2. Evaluation of Positive Electrode Active Material 8 for Lithium Secondary Battery The composition analysis of the obtained positive electrode active material 8 for lithium secondary battery was performed, and when it was made to correspond to the composition formula (I), x = 0.031, y = 0. 207, z = 0.236, w = 0.

There is no pore peak of the positive electrode active material 8 for a lithium secondary battery measured by pore distribution measurement by the mercury intrusion method, and the pore surface area in the range of the pore radius of 100 nm to 10 μm is 0.732 m ² / g. there were.
Moreover, the tap bulk density of the positive electrode active material 8 for lithium secondary batteries was 1.62 g / cc, and D50 was 5.5 μm.
The pore surface area having a pore radius of 10 nm to 50 nm / the pore surface area having a pore radius of 10 nm to 100 μm was 0.00.

  Further, the peel strength of the positive electrode active material 8 for a lithium secondary battery was 210 N / m, and the DC resistance was 17.2Ω.

As shown in the above results, Examples 1 to 5 to which the present invention was applied all had a peel strength as high as 150 N / m or higher and a direct current resistance as low as 16Ω or less.
On the other hand, Comparative Example 1 to which the present invention was not applied had a very low peel strength of 35 N / m, and Comparative Example 2 had a DC resistance greatly exceeding 16Ω.

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

Claims (7)

A positive electrode active material for a lithium secondary battery comprising secondary particles formed by agglomeration of primary particles that can be doped and dedoped with lithium ions, wherein the secondary particles have pores and are obtained by a mercury intrusion method. A positive electrode active material for a lithium secondary battery, characterized by satisfying the following requirements (1) and (2) in a fine pore distribution.
(1) The pore radius of one or both of the secondary particles and the pores existing between the secondary particles has a pore peak in the range of 10 nm to 200 nm.
(2) The total surface area of pores having a pore radius of 100 nm or more and 10 μm or less among pores existing in either or both of the secondary particles or the secondary particles is 1.1 m ² / less than g. The positive electrode active material for lithium secondary batteries according to claim 1, represented by the following composition formula (I).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(However, M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.4, and 0 ≦ w ≦ 0.1 are satisfied.)   The positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the tap bulk density is 2.5 g / cc or less.   The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3, wherein an average secondary particle diameter is 3 µm or more and 15 µm or less.   5. (Pore surface area having a pore radius of 10 nm to 50 nm) / (Pore surface area of a pore radius of 10 nm to 100 μm) is 0.20 or more. Positive electrode active material for lithium secondary battery.   The positive electrode for lithium secondary batteries which has the positive electrode active material for lithium secondary batteries of any one of Claims 1-5.   A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 6.

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