JP2018174161A - 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 having high volume capacity density.SOLUTION: A positive electrode active material for a lithium secondary battery includes active material powder. The active material powder contains secondary particles which are formed through agglomeration of primary powders capable of doping and dedoping of lithium ions and have gaps. Also, the positive electrode active material for the lithium secondary battery satisfies the following two conditions with respect to micropore distribution obtained through a mercury intrusion technique: (1) pore volume distribution has a peak within a pore radius range of 10 nm or more and 200 nm or less; and (2) cumulative pore volume distribution has at least three inflection points within a pore radius range of 10 nm or more and 3000 nm or less.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 nonaqueous electrolyte secondary batteries (hereinafter sometimes referred to as “positive electrode active material”). 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 the lithium secondary battery such as volume capacity density, for example, cited reference 1 describes a positive electrode active material powder in which two types of particle powders having different compressive fracture strengths are mixed.

International Publication No. 2005/020354

As the application field of lithium secondary batteries expands, positive electrode active materials used for lithium secondary batteries are required to have further improved volume capacity density. Here, “volume capacity density” means the battery capacity per unit volume (the amount of power that can be stored). The larger the volume capacity density value, the more suitable for a small battery.
However, the positive electrode active material for a lithium secondary battery as described in Patent Document 1 has room for improvement from the viewpoint of improving the volume capacity density.
The present invention has been made in view of the above circumstances, and has a high volume capacity density positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery using the positive electrode active material for lithium secondary battery, and the lithium It is an object of the present invention to provide a lithium secondary battery having a positive electrode for a secondary battery.

That is, the present invention includes the following [1] to [8].
[1] A positive electrode active material for a lithium secondary battery containing an active material powder containing secondary particles obtained by agglomerating primary particles that can be doped / undoped with lithium ions, wherein the secondary particles have voids inside the particles. The positive electrode active material for lithium secondary batteries which contains particle | grains and satisfy | fills the following requirements (1) and (2) in the pore distribution obtained by the mercury intrusion method of the said positive electrode active material for lithium secondary batteries.
(1) A pore peak has a pore radius in the range of 10 nm to 200 nm.
(2) It has three or more inflection points of the cumulative pore volume in the range where the pore radius is 10 nm or more and 3000 nm or less.
[2] The positive electrode active material for a lithium secondary battery according to [1], which has three inflection points of the cumulative pore volume in the range of 10 nm to 1500 nm in the requirement (2).
[3] The positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the positive electrode active material for a lithium secondary battery 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.)
[4] The positive electrode active material for a lithium secondary battery according to any one of [1] to [3], wherein an average particle diameter of the secondary particles is 1 μm or more and 30 μm or less.
[5] The positive electrode active material for a lithium secondary battery according to any one of [1] to [4], wherein the active material powder includes two or more types of secondary particles having different average secondary particle diameters.
[6] The active material powder includes secondary particles A having an average secondary particle diameter of 1 μm to 10 μm and secondary particles B having an average secondary particle diameter of 5 μm to 30 μm, and the secondary particles A The positive electrode active material for a lithium secondary battery according to [5], wherein a mixing ratio (mass ratio) of the secondary particles B is 20:80 to 50:50.
[7] 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 [6].
[8] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [7].

  According to the present invention, a positive electrode active material for a lithium secondary battery having a high volume capacity density, a positive electrode for a lithium secondary battery using the positive electrode active material for a lithium secondary battery, and a lithium secondary battery having the positive electrode for the lithium secondary battery. A secondary battery can be provided.

It is a schematic block diagram which shows an example of a lithium ion secondary battery. 4 is a graph showing the inflection point of the cumulative pore volume in the range where the pore radius of the positive electrode active material for a lithium secondary battery of Example 1 is 10 nm or more and 3000 nm or less. 6 is a graph showing the inflection point of the cumulative pore volume when the pore radius of the positive electrode active material for a lithium secondary battery of Comparative Example 2 is in the range of 10 nm to 3000 nm. 4 is a graph showing an inflection point of cumulative pore volume in a range where the pore radius of the positive electrode active material for a lithium secondary battery of Comparative Example 1 is 10 nm or more and 3000 nm or less. 4 is a graph showing the particle size distribution of positive electrode active materials for lithium secondary batteries of Examples 1 and 2, Comparative Example 1 and Comparative Example 3.

<Positive electrode active material for lithium secondary battery>
The positive electrode active material for a lithium secondary battery of the present invention is a positive electrode active material for a lithium secondary battery containing an active material powder containing secondary particles formed by agglomerating primary particles that can be doped / undoped with lithium ions. . Moreover, the positive electrode active material for lithium secondary batteries of the present invention includes secondary particles having voids inside the particles, and satisfies the following requirements (1) and (2) in the pore distribution obtained by the mercury intrusion method: .
(1) A pore peak has a pore radius in the range of 10 nm to 200 nm.
(2) It has three or more inflection points of the cumulative pore volume in the range where the pore radius is 10 nm or more and 3000 nm or less.

[Requirement (1)]
The positive electrode active material for a lithium secondary battery according to the present embodiment has a pore peak in a pore radius range of 10 nm to 200 nm. The pore peak in this range is a pore peak derived from a fine void (hereinafter referred to as “a fine void in the secondary particle”) where the particle surface communicates with the inside of the secondary particle. It means that secondary particles having fine voids in secondary particles are included.

[Requirement (2)]
The positive electrode active material for a lithium secondary battery of the present embodiment has three or more inflection points of the cumulative pore volume in the range where the pore radius is 10 nm or more and 3000 nm or less.
In the present embodiment, the “inflection point” means a point where the sign of the second-order derivative changes.

In the present embodiment, the three inflection points of requirement (2) are calculated by the following method.
First, by measuring the pore distribution, 71 points of data are measured so that the pore radius is equidistant between 0.0018 μm and 246.9 μm when the pore radius is the logarithmic axis and the horizontal axis.
The cumulative pore volume is calculated from each data plot, and the point where the sign of the second-order derivative changes is counted as the inflection point.
In this embodiment, it is preferable to carry out the pore distribution measurement a plurality of times and confirm that the inflection point appears with good reproducibility. In addition, it is determined that a portion having no restriction is derived from a noise peak and is not counted as an inflection point.

  In addition to the first inflection point derived from the fine voids of the secondary particles having voids therein, the at least three inflection points of the requirement (2) include fine voids (hereinafter referred to as “two” An inflection point derived from a secondary particle having a large particle diameter, or a secondary particle having a large particle diameter or a secondary particle having a large particle diameter among secondary particle gaps. Two or more inflection points selected from a gap formed between secondary particles having a small particle diameter and an inflection point caused by a gap formed between secondary particles having a small particle diameter. In the present embodiment, there may be four or more inflection points.

  The positive electrode active for the lithium secondary battery of the present embodiment satisfying the requirement (2) by realizing a state in which the secondary particles have voids and the large secondary particles and the small secondary particles coexist. A substance can be obtained. The method for controlling the requirements (1) and (2) within the scope of the present invention will be described in detail later, and specifically, there is a method of broadening the particle size distribution. A method of mixing powders having different average secondary particle diameters is preferable.

  In the present embodiment, it is preferable to have three or more inflection points of the cumulative pore volume in the range where the pore radius is 10 nm or more and 1500 nm or less.

-Pore distribution measurement by mercury intrusion method The pore peak of the above requirement (1) and the cumulative pore volume 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 = πD ² L / 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).

  The positive electrode active material for a lithium secondary battery according to this embodiment includes secondary particles having voids inside the particles. When secondary particles having voids inside the particles are included, the density of the positive electrode active material for a lithium secondary battery tends to decrease and the volume capacity density tends to decrease. According to the present embodiment, even when secondary particles having voids are included inside the particles, the positive electrode active for lithium secondary batteries having a high volume capacity density is satisfied by satisfying the requirements (1) and (2). Can provide material.

The positive electrode active material for a lithium secondary battery according to this embodiment is preferably 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.)

From the viewpoint 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. . Further, from the viewpoint of obtaining a lithium secondary battery having 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.

Further, from the viewpoint of obtaining a lithium secondary battery with 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. Further, from the viewpoint 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.

Further, from the viewpoint of obtaining a lithium secondary battery having high cycle characteristics, z in the composition formula (I) is preferably 0 or more, more preferably 0.03 or more, and 0.1 or more. Is more preferable. Further, from the viewpoint of obtaining a lithium secondary battery having high storage characteristics at a high temperature (for example, in an environment of 60 ° C.), z in the composition formula (I) is preferably 0.4 or less, and 0.38 or less. 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.

Further, from the viewpoint of obtaining a lithium secondary battery with 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. Further, from the viewpoint 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. .

  Further, from the viewpoint of obtaining a lithium secondary battery with high cycle characteristics, M in the composition formula (I) is one or more metals selected from the group consisting of Ti, Mg, Al, W, B, and Zr. From the viewpoint of obtaining a lithium secondary battery with high thermal stability, it is preferably one or more metals selected from the group consisting of Al, W, B, and Zr.

In the present embodiment, from the viewpoint of enhancing the handleability of the positive electrode active material for lithium secondary batteries, the average particle size of the positive electrode active material for lithium secondary batteries is preferably 1 μm or more, and more preferably 4 μm or more. Preferably, it is 5 μm or more. From the viewpoint of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, it is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 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 positive electrode active material powder for a lithium secondary battery 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 a positive electrode active material powder for a lithium secondary battery was put into 50 ml of a 0.2 mass% sodium hexametaphosphate aqueous solution, A dispersion in which 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 (D ₅₀ ) viewed from the fine particle side at the time of 50% accumulation was taken as the average particle diameter of the positive electrode active material powder for a lithium secondary battery.

  In this embodiment, it is preferable that the positive electrode active material for lithium secondary batteries contains an active material powder containing two or more types of secondary particles having different average secondary particle diameters. Specifically, the active material powder is preferably mixed with secondary particles A having an average secondary particle diameter of 1 μm to 10 μm and secondary particles B having an average secondary particle diameter of 5 μm to 30 μm. Here, either the secondary particle A or the secondary particle B is a secondary particle having an intraparticle void.

  When the secondary particles A and the secondary particles B are mixed, the mixing ratio (mass ratio) is preferably 20:80 to 50:50. Whether or not the mixed active material is a mixture of the secondary particles A and the secondary particles B is measured by measuring the particle size distribution and observing the peak caused by the secondary particles A and the peak caused by the secondary particles B. This can be confirmed.

(Layered structure)
The crystal structure of the positive electrode active material for a lithium secondary battery is a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure.

The hexagonal crystal structures are P3, P3 ₁ , P3 ₂ , R3, P-3, R-3, P312, P321, P3 ₁ 12, P3 ₁ 21, P3 ₂ 12, P3 ₂ 21, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P6 ₁ , P6 ₅ , P6 ₂ , P6 ₄ , P6 ₃ , P-6, P6 / m, P6 ₃ / m, P622, P6 ₁ 22, P6 ₅ 22, P6 ₂ 22, P6 ₄ 22, P6 ₃ 22, P6 mm, P6 cc, P6 ₃ cm, P6 ₃ mc, P- It belongs to any one space group selected from the group consisting of 6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P6 ₃ / mcm, and P6 ₃ / mmc.

The monoclinic crystal structure is P2, P2 ₁ , C2, Pm, Pc, Cm, Cc, P2 / m, P2 ₁ / m, C2 / m, P2 / c, P2 ₁ / c, C2 / It belongs to any one space group selected from the group consisting of c.

  Among these, from the viewpoint of obtaining 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.

[Method for producing positive electrode active material for lithium secondary battery]
In producing the positive electrode active material for a lithium secondary battery of the present invention, first, a metal other than lithium, that is, an essential metal composed of Ni, Co and Mn, and Fe, Cu, Ti, Mg, Al, W , B, Mo, Nb, Zn, Sn, Zr, Ga, and V, it is preferable to prepare a metal composite compound containing any one or more arbitrary metals, and to fire the metal composite compound 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 _a Co _b Mn _c (OH) ₂ A metal composite hydroxide represented by the formula (where a + b + c = 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 the solute of the cobalt salt solution, for example, any one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used. As the manganese salt that is the solute of the manganese salt solution, for example, any of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate can be used. The above metal salt is used in a proportion corresponding to the composition ratio of Ni _a Co _b Mn _c (OH) ₂ .
Moreover, water is used as a solvent.

  The complexing agent can form a complex with nickel, cobalt, and manganese ions in an aqueous solution. For example, an ammonium ion supplier (ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.) ), Hydrazine, 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.

In addition to the nickel salt solution, cobalt salt solution, and manganese salt solution, when a complexing agent is continuously supplied to the reaction vessel, nickel, cobalt, and manganese react to form Ni _a Co _b Mn _c (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.

  The secondary particle diameter of the lithium metal composite oxide finally obtained in the following steps 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, etc. Various physical properties such as pore radius can be controlled. In addition to the control of the above conditions, various gases, for example, an inert gas such as nitrogen, argon or carbon dioxide, an oxidizing gas such as air or oxygen, or a mixed gas thereof may be supplied into the reaction vessel. . In addition to gases, oxidants such as hydrogen peroxide and other peroxide salts, permanganate and other peroxide salts, perchlorate, hypochlorite, nitric acid, halogen, and ozone are used. 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, a metal composite compound having a small secondary particle size can be easily obtained. On the other hand, when the reaction pH is lowered, a metal composite compound having a large secondary particle size is easily obtained. Moreover, when the oxidation state in the reaction vessel is increased, a metal composite compound having many voids is easily obtained. On the other hand, when the oxidation state is lowered, a dense metal composite compound is easily obtained. Since the reaction conditions depend on the size of the reaction tank used, the reaction conditions may be optimized while monitoring various physical properties of the finally obtained lithium composite oxide.

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. Drying conditions are not particularly limited, but, for example, conditions where the metal composite oxide or hydroxide is not oxidized / reduced (the oxide is maintained as an oxide, the hydroxide is maintained as a hydroxide) In any condition of the condition that the metal composite hydroxide is oxidized (hydroxide is oxidized to an oxide) and the condition that the metal composite oxide is reduced (the oxide is reduced to hydroxide) Good. An inert gas such as nitrogen, helium and argon may be used for conditions where oxidation / reduction is not performed, and oxygen or air may be used for conditions where hydroxide is oxidized. 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 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 metal composite hydroxide are used in a proportion corresponding to the composition ratio of LiNi _a Co _b Mn _c O ₂ (where a + b + c = 1). . A lithium-nickel cobalt manganese composite oxide is obtained by firing a mixture of a nickel cobalt manganese metal composite 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.

  There is no restriction | limiting in particular as a calcination temperature of the said metal complex oxide or hydroxide, and lithium compounds, such as lithium hydroxide and lithium carbonate. For example, the temperature is preferably 600 ° C. or higher and 1100 ° C. or lower, more preferably 750 ° C. or higher and 1050 ° C. or lower, and further preferably 800 ° C. or higher and 1025 ° C. or lower.

  The firing time is preferably 3 hours to 50 hours. When the firing time is 50 hours or less, the volatilization of Li can be suppressed, and deterioration of battery performance can be prevented. If the firing time is 3 hours or longer, the crystal development tends to proceed well. 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.

-Control method of requirement (1) and requirement (2) In this embodiment, among the lithium metal composite oxides obtained by the above method, a lithium metal composite having a void in the particle and having a small particle diameter By mixing the oxide and the lithium metal composite oxide having a large particle size, a positive electrode active material for a lithium secondary battery that satisfies the requirements (1) and (2) can be obtained.

  In this embodiment, it is preferable to mix two or more types of secondary particles having different average secondary particle diameters. Specifically, it is preferable to mix the secondary particles A having an average secondary particle diameter of 1 μm to 10 μm and the secondary particles B having an average secondary particle diameter of 5 μm to 30 μm. Here, either the secondary particle A or the secondary particle B is a secondary particle having an intraparticle void.

  When the secondary particles A and the secondary particles B are mixed, the mixing ratio (mass ratio) is preferably 20:80 to 50:50.

-Other control methods of requirement (1) and requirement (2) Further, in the present embodiment, among the lithium metal composite oxides obtained by the above method, a material having a wide secondary particle size distribution (particle size distribution) By using (a material in which is broad), the requirements (1) and (2) may be controlled within the desired range of the present invention.
In order to widen the particle size distribution, for example, in the production process of the metal composite hydroxide, the state in which crystals tend to grow and the state in which nuclei are likely to be generated change with time by raising and lowering the reaction pH. A wide lithium metal composite oxide can be obtained.

  In addition to the above method, in the production process of the metal composite hydroxide, two reaction tanks having different reaction pHs are provided, the reaction pH is lowered in the first-stage reaction tank, and 1 in the second-stage reaction tank. A lithium metal composite oxide having a wide particle size distribution can be obtained by making the reaction pH higher than that in the stage reaction vessel.

    In order to widen the particle size distribution, for example, in the pulverization step after firing, there is a method of appropriately adjusting the pulverization time, the rotational speed of the pulverization mill, and the pulverization processing type (dry pulverization or wet pulverization).

<Lithium secondary battery>
Next, while explaining the configuration of the lithium secondary battery, the positive electrode using the positive electrode active material for the secondary battery of the present invention as the positive electrode active material of the lithium secondary battery, and the lithium secondary battery having the positive electrode will be described. .

  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.

The oxide can be used as an anode active _material, (wherein, x represents a positive real number) SiO 2, SiO, etc. formula SiO _x oxides of silicon represented _by; TiO 2, TiO, etc. formula TiO _x (wherein , X is a positive real number); oxide of titanium represented by formula VO _x (where x is a positive real number) such as V ₂ O ₅ and VO ₂ ; 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) Oxide of tin; tungsten oxide represented by general formula WO _x (where x is a positive real number) such as WO ₃ and WO ₂ ; lithium and titanium such as Li ₄ Ti ₅ O ₁₂ and LiVO ₂ Or a metal composite oxide containing vanadium. It is possible.

Examples of sulfides that can be used as the negative electrode active material 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 , VS _2, VS and other vanadium sulfides represented by the formula VS _x (where x is a positive real number); Fe ₃ S ₄ , FeS ₂ , FeS and other formulas FeS _x (where x is a positive real number) Iron sulfide represented; Mo ₂ S ₃ , MoS _{2 and the} like MoS _x (where x is a positive real number) Molybdenum sulfide; SnS _2, SnS and other formula SnS _x (where, a sulfide of tin represented by x is a positive real number; a sulfide of tungsten represented by a formula WS _x (where x is a positive real number) such as WS ₂ ; a formula SbS _x such as Sb ₂ S ₃ (here And x is a positive real number) antimony sulfide; Se ₅ S ₃ , selenium sulfide represented by the formula SeS _x (where x is a positive real number) such as SeS ₂ and SeS.

Examples of the nitride that can be used as the negative electrode active material include Li ₃ N and Li _3-x A _x N (where A is one or both of Ni and Co, and 0 <x <3). And lithium-containing nitrides.

  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. It can also be mentioned; -Co, Sn-Ni, Sn -Cu, tin alloys such as _Sn-La; Cu 2 _Sb, alloys such as 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 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 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 (SO ₂ CF ₃ ) (COCF ₃ ), Li (C ₄ F ₉ SO ₃ ), LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiBOB (where BOB is bis (oxalato) borate LiFSI (here, FSI is bis (fluorosulfonyl) imide), lithium salt such as lower aliphatic carboxylic acid lithium salt, LiAlCl _4, and a mixture of two or more of these May be used. Among them, the electrolyte is at least selected from the group consisting of LiPF ₆ containing fluorine, LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) _3. It is preferable to use one containing one kind.

  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 LiPF ₆ 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 above-described lithium metal composite oxide of the present embodiment, 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.
(1) Evaluation of positive electrode active material for lithium secondary battery / Measurement of average secondary particle diameter 0.1 g of positive electrode active material powder for lithium secondary battery to be measured was put into 50 ml of 0.2% by mass sodium hexametaphosphate aqueous solution. A dispersion in which the powder was dispersed was obtained. About the obtained dispersion liquid, the particle size distribution was measured using the master sizer 2000 (laser diffraction scattering particle size distribution measuring apparatus) by Malvern, and the volume-based cumulative particle size distribution curve was obtained. In the obtained cumulative particle size distribution curve, the value of the particle diameter (D ₅₀ ) viewed from the fine particle side at 50% accumulation was taken as the average secondary particle diameter.

  From the number of peak tops in the volume-based cumulative particle size distribution curve, the number of powders having different average secondary particle diameters contained in the positive electrode active material powder for lithium secondary batteries can be determined. If two or more kinds of powders having different average secondary particle diameters contained in the positive electrode active material powder for a lithium secondary battery are used, two or more peak tops are observed.

Measurement of particle size distribution of positive electrode active material for lithium secondary battery 0.1 g of positive electrode active material powder for lithium secondary battery to be measured was put into 50 ml of 0.2 mass% sodium hexametaphosphate aqueous solution, and the powder was dispersed. A dispersion was obtained. About the obtained dispersion liquid, the particle size distribution was measured using the master sizer 2000 (laser diffraction scattering particle size distribution measuring apparatus) by Malvern.

Composition analysis The composition analysis of the positive electrode active material powder for lithium secondary battery produced by the method described below is performed by dissolving the obtained positive electrode active material powder for lithium secondary battery in hydrochloric acid and then performing inductively coupled plasma emission spectrometry. The measurement was performed using an apparatus (SPS3000, manufactured by SII Nano Technology).

-Measurement of pore distribution of positive electrode active material for lithium secondary battery by mercury porosimetry The positive electrode active material for lithium secondary battery was dried at 120 ° C for 4 hours as a pretreatment. 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: 0.432 psia to 59245.2 psia

The data measurement points in the pore distribution measurement were 71 points, and when the pore radius was a logarithmic axis and a horizontal axis, the pore radius was set to be equally spaced between 0.0018 μm and 246.9 μm. The cumulative pore volume was calculated from each data plot, and the point at which the sign of the second-order derivative changed was counted as the inflection point. The pore distribution measurement was performed several times, and it was confirmed that an inflection point appeared with good reproducibility.
It was decided that the places without restrictions were derived from noise peaks and were not counted as inflection points.

(2) Production 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 the production method described later are used as a positive electrode active material for lithium secondary battery: A paste-like positive electrode mixture was prepared by adding and kneading so that the composition of conductive material: binder = 92: 5: 3 (mass ratio) was obtained. 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 .

(3) Production of negative electrode for lithium secondary battery Next, artificial graphite (MAGD manufactured by Hitachi Chemical Co., Ltd.) as a negative electrode active material, and CMC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and SBR (Nippon A & L Co., Ltd.) as binders. Was prepared so as to have a composition of negative electrode active material: CMC: SRR = 98: 1: 1 (mass ratio), and kneaded to prepare a paste-like negative electrode mixture. 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 100 ° 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 .

(4) Production of lithium secondary battery (coin-type half cell) The following operation was performed in a glove box in 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 electrolytic solution was 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) 30:35. : 35 (volume ratio) a mixture of LiPF ₆ dissolved to 1.0 mol / l (hereinafter sometimes referred to as LiPF ₆ / EC + DMC + EMC) was used.
Next, using lithium metal as the negative electrode, the negative electrode is placed on the upper side of the laminated film separator, covered with a gasket, and then caulked with a caulking machine to form a lithium secondary battery (coin type half cell R2032, hereinafter "half cell"). Was prepared.

(5) Volume Capacity Density Test Using the half cell produced in “(4) Production of lithium secondary battery (coin-type half cell)”, a charge / discharge test was carried out under the following conditions to calculate the volume capacity density.
<Charge / discharge test>
Test temperature 25 ° C
Charge maximum voltage 4.3V, charge time 6 hours, charge current 1.0CA, constant current constant voltage charge discharge minimum voltage 2.5V, discharge time 5 hours, discharge current 1.0CA, constant current discharge <volume capacity density calculation >
From the discharge capacity discharged to 1.0 C and the mass per unit volume of the positive electrode material, the volume capacity density was determined based on the following calculation formula.
Volume capacity density (mAh / cm ³ ) = specific capacity of positive electrode material (mAh / g) × electrode density (g / cm ³ )

(Production Example 1)
1. Production of lithium nickel cobalt manganese composite oxide 1
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 30 ° 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 55:21:24 to prepare a mixed raw material solution.

  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 added dropwise at an appropriate time so that the pH of the solution in the reaction tank becomes 13.0 to obtain nickel cobalt manganese composite hydroxide particles, washed, dehydrated with a centrifuge, washed, dehydrated, The nickel cobalt manganese composite hydroxide 1 was obtained by isolating and drying at 105 ° C.

  Nickel-cobalt-manganese composite hydroxide 1 and lithium carbonate powder were weighed and mixed so that Li / (Ni + Co + Mn) = 1.06, and then fired at 690 ° C. for 5 hours in an air atmosphere. The target lithium nickel cobalt manganese composite oxide 1 was obtained by firing at 875 ° C. for 10 hours in an atmosphere. It was 4.6 micrometers as a result of measuring the average secondary particle diameter of the obtained lithium nickel cobalt manganese complex oxide 1.

(Production Example 2)
1. Production of lithium nickel cobalt manganese composite oxide 2
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 60 ° 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 55:21:24 to prepare a mixed raw material solution.

  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 vessel becomes 11.9 to obtain nickel cobalt manganese composite hydroxide particles, washed, dehydrated with a centrifuge, washed, dehydrated, The nickel cobalt manganese composite hydroxide 2 was obtained by isolating and drying at 105 ° C.

  Nickel-cobalt-manganese composite hydroxide 2 and lithium carbonate powder were weighed and mixed so that Li / (Ni + Co + Mn) = 1.06, and then fired at 690 ° C. for 5 hours in an air atmosphere. The target lithium nickel cobalt manganese composite oxide 2 was obtained by firing at 875 ° C. for 10 hours in an atmosphere. The average secondary particle diameter of the obtained lithium nickel cobalt manganese composite oxide 2 was measured and found to be 11.6 μm.

(Production Example 3)
1. Production of lithium nickel cobalt manganese composite oxide 3
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 were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 55:21:24 to prepare a mixed raw material solution.

  Next, with stirring, this mixed raw material solution and ammonium sulfate aqueous solution were continuously added as a complexing agent to the reaction vessel, and air was mixed with nitrogen gas so that the oxygen concentration was 3.7%. An oxygen-containing gas 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, dehydrated with a centrifuge, washed, dehydrated, The nickel cobalt manganese composite hydroxide 3 was obtained by isolation and drying at 105 ° C.

  Nickel cobalt manganese composite hydroxide 3 and lithium carbonate powder were weighed and mixed so that Li / (Ni + Co + Mn) = 1.07, then fired at 760 ° C. for 3 hours in an air atmosphere, The target lithium nickel cobalt manganese composite oxide 3 was obtained by firing at 850 ° C. for 10 hours in an atmosphere. The average secondary particle diameter of the obtained lithium nickel cobalt manganese composite oxide 3 was measured and found to be 3.6 μm.

(Production Example 4)
1. Production of lithium nickel cobalt manganese composite oxide 4
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 were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 55:21:24 to prepare a mixed raw material solution.

  Next, with stirring, this mixed raw material solution and ammonium sulfate aqueous solution were continuously added as a complexing agent to the reaction vessel, and air was mixed with nitrogen gas so that the oxygen concentration was 8.6%. An oxygen-containing gas 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 12.0 to obtain nickel cobalt manganese composite hydroxide particles, washed, dehydrated with a centrifuge, washed, dehydrated, The nickel cobalt manganese composite hydroxide 4 was obtained by isolating and drying at 105 ° C.

  Nickel-cobalt-manganese composite hydroxide 1 and lithium carbonate powder were weighed and mixed so that Li / (Ni + Co + Mn) = 1.07, and then fired at 760 ° C. for 5 hours in an air atmosphere. The target lithium nickel cobalt manganese composite oxide 4 was obtained by firing at 850 ° C. for 10 hours in an atmosphere. As a result of measuring the average secondary particle diameter of the obtained lithium nickel cobalt manganese composite oxide 4, it was 8.9 μm.

Example 1
1. Production of positive electrode active material 1 for lithium secondary battery Lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 as secondary particles A, and lithium nickel cobalt manganese composite oxide 2 produced in Production Example 2 as secondary particles B Was mixed at a mixing ratio of secondary particles A and secondary particles B of 25/75 to obtain a 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 positive electrode active material 1 for a lithium secondary battery was performed to correspond to the composition formula (I). As a result, x = 0.029, y = 0.207, z = 0.239, and w = 0. . The average secondary particle size was 9.6 μm.

The positive electrode active material 1 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. A graph showing the relationship between the cumulative pore volume and the pore radius is shown in FIG. As shown in FIG. 2, there were three inflection points of the cumulative pore volume in the range where the pore radius was 10 nm or more and 1500 nm or less (requirement (2)).
The volume capacity density (mAh / cm ³⁾ was 457mAh / cm ^3.

(Example 2)
1. Production of cathode active material 2 for lithium secondary battery Lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 as secondary particles A, and lithium nickel cobalt manganese composite oxide 2 produced in Production Example 2 as secondary particles B And mixing the secondary particles A and the secondary particles B at a mixing ratio of 50/50 to obtain a 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 positive electrode active material 1 for a lithium secondary battery was performed to correspond to the composition formula (I). As a result, x = 0.031, y = 0.208, z = 0.340, and w = 0. . The average secondary particle size was 7.6 μm.

The positive electrode active material 2 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. A graph showing the relationship between the cumulative pore volume and the pore radius is shown in FIG. As shown in FIG. 2, there were three inflection points of the cumulative pore volume in the range where the pore radius was 10 nm or more and 1500 nm or less (requirement (2)).
The volume capacity density (mAh / cm ³⁾ was 455mAh / cm ^3.

(Example 3)
1. Production of cathode active material 3 for lithium secondary battery Lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 as secondary particles A, and lithium nickel cobalt manganese composite oxide 2 produced in Production Example 4 as secondary particles B And mixing the secondary particles A and the secondary particles B at a mixing ratio of 25/75 to obtain a 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 positive electrode active material 3 for a lithium secondary battery was performed, and when it was made to correspond to the composition formula (I), x = 0.038, y = 0.208, z = 0.244, w = 0. . The average secondary particle size was 7.6 μm.

The positive electrode active material 3 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. A graph showing the relationship between the cumulative pore volume and the pore radius is shown in FIG. As shown in FIG. 2, there were three inflection points of the cumulative pore volume in the range where the pore radius was 10 nm or more and 1500 nm or less (requirement (2)).
The volume capacity density (mAh / cm ³⁾ was 434mAh / cm ^3.

Example 4
1. Production of cathode active material 4 for lithium secondary battery Lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 as secondary particles A, and lithium nickel cobalt manganese composite oxide 2 produced in Production Example 4 as secondary particles B Were mixed at a mixing ratio of secondary particles A and secondary particles B of 50/50 to obtain a 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 positive electrode active material 4 for a lithium secondary battery was performed to correspond to the composition formula (I). As a result, x = 0.037, y = 0.209, z = 0.243, and w = 0. . The average secondary particle size was 6.3 μm.

The positive electrode active material 4 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. A graph showing the relationship between the cumulative pore volume and the pore radius is shown in FIG. As shown in FIG. 2, it had three inflection points of the cumulative pore volume in the range where the pore radius was 10 nm or more and 1500 nm or less (requirement (2)).
The volume capacity density (mAh / cm ³⁾ was 438mAh / cm ^3.

(Comparative Example 1)
1. Production of positive electrode active material 5 for lithium secondary battery
The lithium nickel cobalt manganese composite oxide 2 produced in Production Example 2 was used as the 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 positive electrode active material 5 for a lithium secondary battery was performed to correspond to the composition formula (I). As a result, x = 0.027, y = 0.206, z = 0.237, and w = 0. . The average secondary particle size was 11.6 μm.

The positive electrode active material 5 for a lithium secondary battery does not have a pore peak in the range of 10 nm to 200 nm in the pore distribution obtained by the mercury intrusion method, and as shown in the graph shown in FIG. Had an inflection point of the cumulative pore volume only in the range of 300 nm to 2000 nm.
The volume capacity density (mAh / cm ³⁾ was 432mAh / cm ^3.

(Comparative Example 2)
1. Production of positive electrode active material 6 for lithium secondary battery
The lithium nickel cobalt manganese composite oxide 4 produced in Production Example 4 was used as the 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 positive electrode active material 6 for a lithium secondary battery was performed, and when it was made to correspond to the composition formula (I), x = 0.034, y = 0.208, z = 0.245, and w = 0. . The average secondary particle size was 8.9 μm.

The positive electrode active material 6 for a lithium secondary battery has a pore peak in the range of 10 nm to 100 nm in the pore distribution obtained by the mercury intrusion method, and the pore radius is as shown in the graph of FIG. Each had an inflection point of the cumulative pore volume in the range of 10 nm to 100 nm and in the range of 200 nm to 1500 nm.
The volume capacity density (mAh / cm ³⁾ was 417mAh / cm ^3.

(Comparative Example 3)
1. Production of positive electrode active material 7 for lithium secondary battery
The lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 was used as the 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 positive electrode active material 7 for a lithium secondary battery was performed, and when it was made to correspond to the composition formula (I), x = 0.035, y = 0.210, z = 0.242, and w = 0. . The average secondary particle size was 3.6 μm.

The positive electrode active material 7 for a lithium secondary battery has a pore peak in a range of 10 nm to 100 nm in a pore distribution obtained by a mercury intrusion method, a pore radius in a range of 10 nm to 100 nm, and 150 nm or more. Each had an inflection point of the cumulative pore volume in the range of 1000 nm or less.
The volume capacity density (mAh / cm ³⁾ was 431mAh / cm ^3.

(Comparative Example 4)
1. Production of positive electrode active material 8 for lithium secondary battery
Using the lithium nickel cobalt manganese composite oxide 3 produced in Production Example 1 as the secondary particles A and the lithium nickel cobalt manganese composite oxide 2 produced in Production Example 2 as the secondary particles B, the secondary particles A and the secondary particles The mixture ratio with B was mixed at 25/75 to obtain a 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 positive electrode active material 8 for a lithium secondary battery was performed, and when it was made to correspond to the composition formula (I), x = 0.028, y = 0.207, z = 0.237, and w = 0. . The average secondary particle size was 9.9 μm.

The positive electrode active material 8 for a lithium secondary battery has no pore peak in the pore distribution obtained by the mercury intrusion method, and has two cumulative pore volumes in the range of the pore radius of 100 nm to 1500 nm. Had inflection points.
The volume capacity density (mAh / cm ³⁾ was 420 mAh / cm ^3.

  The results of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1.

  As shown in Table 1 above, Examples 1 to 4 to which the present invention was applied had higher volume capacity density than Comparative Examples 1 to 4 to which the present invention was not applied.

-Result of particle size distribution measurement In FIG. 5, the result of the particle size distribution measurement of Examples 1-2 and Comparative Examples 1 and 3 is described. In Examples 1 and 2, peaks due to the mixed metal oxides could be confirmed. On the other hand, in Comparative Examples 1 and 3, only one peak was confirmed.

  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 (8)

A positive electrode active material for a lithium secondary battery containing an active material powder containing secondary particles formed by agglomerating primary particles that can be doped and dedoped with lithium ions, including secondary particles having voids inside the particles The positive electrode active material for lithium secondary batteries satisfying the following requirements (1) and (2) in the pore distribution obtained by the mercury intrusion method of the positive electrode active material for lithium secondary batteries.
(1) A pore peak has a pore radius in the range of 10 nm to 200 nm.
(2) It has three or more inflection points of the cumulative pore volume in the range where the pore radius is 10 nm or more and 3000 nm or less.   2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein in the requirement (2), the inflection point of the cumulative pore volume is in a range of 10 nm to 1500 nm. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, wherein the positive electrode active material for lithium secondary batteries 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.)   4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein an average particle diameter of the secondary particles is 1 μm or more and 30 μm or less.   The said active material powder is a positive electrode active material for lithium secondary batteries of any one of Claims 1-4 containing two or more types of secondary particles from which an average secondary particle diameter differs.   The active material powder includes secondary particles A having an average secondary particle diameter of 1 μm to 10 μm and secondary particles B having an average secondary particle diameter of 5 μm to 30 μm, and the secondary particles A and the secondary particles The positive electrode active material for a lithium secondary battery according to claim 5, wherein the mixing ratio (mass ratio) of the secondary particles B is 20:80 to 50:50.   The positive electrode for lithium secondary batteries which has the positive electrode active material for lithium secondary batteries of any one of Claims 1-6.   A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 7.

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