WO2018070517A1 - Production method for lithium secondary battery positive electrode active material - Google Patents

Abstract

The present invention relates to a production method for a lithium secondary battery positive electrode active material, the production method including: a mixing step for mixing a lithium compound and a positive electrode active material precursor to obtain a mixture; and a main sintering step for using a rotary kiln to sinter the mixture. The production method is characterized in that the mixture contains more than 0 but no more than 50 mass% of the lithium compound and in that a kiln inner wall of the rotary kiln is formed from a non-metal material.

Description

Method for producing positive electrode active material for lithium secondary battery

The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery.
This application claims priority based on Japanese Patent Application No. 2016-201566 for which it applied to Japan on October 13, 2016, and uses the content here.

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

A method for producing a positive electrode active material for a lithium secondary battery generally includes a step of firing a lithium compound and a precursor that is a metal composite oxide.
In order to improve the performance of the lithium secondary battery such as cycle characteristics, attempts have been made to make the composition of the positive electrode active material for the lithium secondary battery uniform and to reduce the remaining amount of unreacted substances.
For example, Patent Document 1 describes that a positive electrode material with little variation in oxidation could be manufactured with high productivity by performing the firing process using a roller hearth kiln.

JP 2006-4724 A

As the application field of lithium secondary batteries is expanding, positive electrode active materials for lithium secondary batteries are required to have high crystallinity in order to improve various battery characteristics.
However, as described in Patent Document 1, when a roller hearth kiln is used, a long time is required for firing, and crystallinity is not sufficient.
This invention is made | formed in view of the said situation, Comprising: It aims at providing the manufacturing method of the positive electrode active material for lithium secondary batteries which is excellent in crystallinity.

That is, the present invention includes the following [1] to [8].
[1] Production of a positive electrode active material for a lithium secondary battery, comprising: a mixing step of mixing a lithium compound and a positive electrode active material precursor to obtain a mixture; and a main baking step of baking the mixture using a rotary kiln. The lithium compound content in the mixture is more than 0 and 50% by mass or less with respect to the total mass of the mixture, and the furnace inner wall of the rotary kiln is formed of a non-metallic material. A method for producing a positive electrode active material for a lithium secondary battery.
[2] The method for producing a positive electrode active material for a lithium secondary battery according to [1], wherein the main firing step is performed at 750 ° C. or higher and 1000 ° C. or lower.
[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 includes a lithium metal composite oxide represented by the following general formula (I): A method for producing a substance.
Li [Li _x (Ni _(1-yzw) Co _y Mn _z M _w ) _1-x ] O ₂ (I)
(In the general formula (I), −0.1 ≦ x ≦ 0.2, 0 <y ≦ 0.5, 0 <z ≦ 0.8, 0 ≦ w ≦ 0.1, y + z + w <1, M is It represents one or more elements selected from the group consisting of Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V.)
[4] Any one of [1] to [3], including a pre-baking step after the mixing step and before the main baking step, including baking at a temperature lower than the baking temperature of the main baking. The manufacturing method of the positive electrode active material for lithium secondary batteries as described in an item.
[5] Any one or both of the main firing step and the preliminary firing step are performed by ventilating an oxygen-containing gas at a flow rate of 15 Nm ³ / h / m ³ or more. 2. A method for producing a positive electrode active material for a lithium secondary battery according to item 1.
[6] The method for producing a positive electrode active material for a lithium secondary battery according to [5], wherein an oxygen concentration in the oxygen-containing gas is 21% by volume or more based on a total volume of the oxygen-containing gas.
[7] Any of [1] to [6], wherein the content of chromium contained in the positive electrode active material for lithium secondary batteries is 50 ppm or less with respect to the total mass of the positive electrode active material for lithium secondary batteries. The manufacturing method of the positive electrode active material for lithium secondary batteries of Claim 1.
[8] The content of lithium carbonate contained in the positive electrode active material for lithium secondary batteries is 1.0% by mass or less based on the total mass of the positive electrode active material for lithium secondary batteries. [7] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [7].

According to the present invention, a method for producing a positive electrode active material for a lithium secondary battery having excellent crystallinity can be provided.

It is a schematic block diagram which shows an example of a lithium ion secondary battery. It is a schematic block diagram which shows an example of a lithium ion secondary battery. It is the schematic which shows an example of a rotary kiln. It is a schematic sectional drawing of the direction perpendicular | vertical with respect to the longitudinal direction of a rotary kiln. It is a schematic sectional drawing of the longitudinal direction of a rotary kiln.

<Method for producing positive electrode active material for lithium secondary battery>
The method for producing a positive electrode active material for a lithium secondary battery of the present invention (hereinafter also referred to as “positive electrode active material”) is a lithium compound and a positive electrode active material precursor (hereinafter also referred to as “precursor”). And a main firing step in which the mixture is fired using a rotary kiln, and a method for producing a positive electrode active material for a lithium secondary battery, comprising: a lithium compound contained in the mixture The content of is more than 0 and 50% by mass or less with respect to the total mass of the mixture, and the furnace inner wall of the rotary kiln is formed of a non-metallic material.

Conventionally, facilities such as a tunnel furnace, a roller hearth kiln, and a rotary kiln are used for the firing process of the lithium compound and the precursor.
Tunnel furnaces and roller hearth kilns have a problem that the firing efficiency is low and further firing takes a long time because the mixture is fired with filling the mixture.
In addition, if the furnace inner wall is made of metal, the rotary kiln has a problem that when fired at a high temperature, the metal is eluted from the member, and the positive electrode active material is contaminated by the eluted metal component.

In the present invention, a firing process of a mixture of a lithium compound and a precursor is performed using a rotary kiln in which a furnace inner wall, which is a portion in contact with the mixture, is formed of a nonmetallic material. For this reason, even if it is a case where it bakes at high temperature, a metal does not elute from a furnace inner wall and a positive electrode active material is not contaminated. In addition, since the present invention bakes a mixture having a lithium compound content of 50% by mass or less based on the total mass of the mixture, the mixture and the baked product do not excessively adhere to the rotary kiln even when baked at a high temperature. It can be fired.
Hereinafter, the manufacturing method of the positive electrode active material for lithium secondary batteries of this invention is demonstrated.

[Mixing process]
This step is a step of mixing the lithium compound and the precursor to obtain a mixture.
In this step, mixing is performed so that the content of the lithium compound in the mixture of the lithium compound and the precursor is more than 0 and 50% by mass or less with respect to the total mass of the mixture.
10 mass% or more is preferable, as for the lower limit of content of the lithium compound with respect to the total mass of the said mixture, 15 mass% or more is more preferable, and 20 mass% or more is especially preferable.
The upper limit of the lithium compound content relative to the total mass of the mixture is preferably 49% by mass or less, more preferably 48% by mass or less, and particularly preferably 47% by mass or less.
The upper limit value and the lower limit value can be arbitrarily combined.
For example, the content of the lithium compound with respect to the total mass of the mixture is preferably 10% by mass to 49% by mass, more preferably 15% by mass to 48% by mass, and still more preferably 20% by mass to 47% by mass. .

In the present invention, the lithium compound content relative to the total mass of the mixture in the mixture is set to the specific content, whereby adhesion of the mixture and the fired product to the inner wall of the rotary kiln can be reduced. For this reason, in the baking process mentioned later, it can bake at high temperature and can obtain the positive electrode active material with high crystallinity.

-Lithium compound The lithium compound used for this invention is demonstrated.
The lithium compound used in the present invention is not particularly limited, and any one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, lithium oxide, or a mixture of two or more thereof. Can be used. In these, any one or both of lithium hydroxide and lithium carbonate are preferable.

-Precursor The precursor is preferably a transition metal compound. The precursor is a group consisting of metals other than lithium, that is, essential metals Ni, Co, Mn, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. It is preferable that it is a transition metal compound containing 1 or more types of arbitrary elements chosen from these. The transition metal compound is preferably a transition metal hydroxide or a transition metal oxide, and specifically, nickel cobalt manganese composite hydroxide or nickel cobalt manganese composite oxide is preferable.
The precursor can be produced by a generally known batch method or coprecipitation method.

[Main firing process]
In the present invention, by using the above specific mixing conditions, firing can be performed at a high temperature in the firing step, and the development of crystals can be favorably progressed.
The main firing step is performed by a rotary kiln in which the furnace inner wall, which is a contact portion with the mixture, is formed from a non-metallic material.
The rotary kiln used in this embodiment will be described with reference to FIGS.
The rotary kiln 40 includes a cylindrical furnace core tube 42, a rotating device (not shown) that rotates the furnace core tube 42, a heat insulating material (not shown) that covers the furnace core tube 42, and the furnace core tube 42. A heater (not shown) for heating, a raw material charging device (not shown) for charging the fired raw material into the furnace core tube 42, and a discharge part (not shown) for discharging the fired product are included. As shown in FIG. 4, the furnace core tube 42 is installed with an inclination so that the outlet side is lower than the inlet side into which the firing raw material is charged. By rotating the furnace core tube 42, the firing raw materials are mixed and fed from the inlet side to the outlet side of the furnace core tube 42, and firing is performed. The oxygen-containing gas is normally ventilated from the outlet side to the inlet side, as indicated by broken line arrows in FIG.
Specifically, in the firing step, the mixture is supplied to the rotary kiln 40 and the furnace core tube 42 constituting the rotary kiln 40 is rotated so that the mixture reaches a predetermined temperature while mixing the mixture. This can be done by heating the rotary kiln. In the present invention, the furnace inner wall 41 means an inner wall of the furnace core tube 42.
Non-metallic materials include silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ ; also referred to as alumina), silicon dioxide (SiO ₂ ), zirconium dioxide (ZrO ₂ ), magnesium oxide (MgO), silicon carbide. A ceramic material such as (SiC) is preferable, and it is particularly preferable that aluminum oxide is contained in an amount of 50% by mass or more based on the total mass of the nonmetallic material.
The filling amount of the mixture with respect to the total internal volume of the rotary kiln is preferably 1% by volume to 50% by volume, more preferably 3% by volume to 30% by volume, and 5% by volume to 20% by volume. Is more preferable.

It is preferable to perform this baking process at 750 degreeC or more and 1000 degrees C or less.
By setting the firing temperature to a high temperature range of 750 ° C. or higher and 1000 ° C. or lower, a positive electrode active material with high crystallinity can be produced.
In this embodiment, the temperature of a baking process means the temperature of the mixture baked.

[Pre-baking step]
In the present invention, it is preferable to include a preliminary firing step in which firing is performed at a temperature lower than the firing temperature of the main firing after the mixing step and before the main firing step. The pre-firing may be performed at a temperature lower than that of the main calcination, and is preferably 80 ° C. to 200 ° C. lower than the main calcination temperature, and preferably 100 ° C. to 150 ° C. lower.
By performing preliminary firing, a positive electrode active material containing a lithium metal composite oxide having high crystallinity can be obtained, and unreacted materials can be reduced.
The firing furnace in the preliminary firing step is not particularly limited, but it is preferable to use a rotary kiln. The main firing step and the preliminary firing step may be the same rotary kiln or different rotary kilns, but are preferably performed using the same rotary kiln from the viewpoint of performing the firing step continuously.
The contact part with the said mixture of the baking furnace used for a preliminary baking process may be metal materials, such as Inconel, such as silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ ; also referred to as alumina), etc. A non-metallic material may be used.

Wherein one or both of the firing step and the pre-baking step is preferably conducted by passing an oxygen-containing gas at 15Nm ³ / h / ^{m 3} or more ^flow, is 16Nm ³ / h / ^m 3 or more More preferred. The upper limit value is not particularly limited, for example, 150Nm ³ / h / ^{m 3} or less, 130Nm ³ / h / ^{m 3} or less include 120Nm ³ / h / ^{m 3} or less.
The upper limit value and the lower limit value can be arbitrarily combined.
For example, the flow rate ^is preferably 15Nm ³ / h / ^m 3 or more 150Nm ³ / h / ^{m 3} or ^less, more preferably 16Nm ³ / h / ^m 3 or more 130Nm ³ / h / ^{m 3} or less 16 Nm ³ / h / m ³ or more and 120 Nm ³ / h / m ³ or less.
As another aspect of this embodiment, the flow rate ^is preferably 40Nm ³ / h / ^m 3 or more 200Nm at ³ / h / ^{m 3} or ^less, 80Nm ³ / h / ^m 3 or more 180Nm ³ / h / m It is more preferably ³ or less, and further preferably 130 Nm ³ / h / m ³ or more and 160 Nm ³ / h / m ³ or less.
It is preferable that one or both of the main firing step and the preliminary firing step be performed at an oxygen concentration in the oxygen gas of 21% by volume or more based on the total volume of the oxygen-containing gas. As a method for producing the oxygen-containing gas having the above oxygen concentration, it can be obtained by mixing a gas other than oxygen and oxygen gas at a predetermined ratio. The gas other than oxygen and the flow rate of oxygen gas can be controlled by a known flow meter. Moreover, you may use air as it is.
In this invention, it is preferable to implement this baking process on said ventilation | gas_flowing conditions.

The firing time is preferably 1 hour or more and 10 hours or less, more preferably 1 hour or more and 8 hours or less, and more preferably 1 hour or more and 5 hours or less. Is particularly preferred.
In the present invention, when pre-baking is performed, the time from the start of temperature increase in the pre-baking step to the end of the main baking step is performed within the above time.
More specifically, the pre-baking step is preferably 30 minutes to 3 hours, more preferably 1 hour to 2.5 hours.
Moreover, it is preferable to make this baking process into 30 minutes or more and 3 hours or less, and it is more preferable to set it as 1 to 2.5 hours.
As another aspect of the present invention, the holding time after reaching the target temperature in the firing step is preferably 1 hour or more and 10 hours or less, more preferably 1 hour or more and 8 hours or less, and more preferably 1 hour or more and 6 hours or less. More preferred is a time or less. The rate of temperature rise to the target temperature is preferably 20 ° C./hour or more and 2000 ° C./hour or less, more preferably 50 ° C./hour or more and 1000 ° C./hour or less, and 100 ° C./hour or more. More preferably, it is set to 800 ° C./hour or less.
In the present invention, the main firing step is carried out using a rotary kiln in which the furnace inner wall, which is the part in contact with the mixture, is formed from a non-metallic material.
Metal rotary kilns need to be fired at a temperature at which metal elution does not occur, but when using a rotary kiln in which the furnace inner wall, which is the part in contact with the mixture, is made of a non-metallic material, metal elution The baking temperature can be set to a high temperature without considering the above. Therefore, the firing process can be performed at a higher temperature when a rotary kiln having a furnace inner wall made of a non-metallic material is used than when a rotary kiln made of metal is used for the furnace inner wall. For this reason, the positive electrode active material containing a highly crystalline lithium metal composite oxide can be obtained in a short baking process.

The lithium metal composite oxide obtained by firing is appropriately classified after pulverization, and used as a positive electrode active material for a lithium secondary battery applicable to a lithium secondary battery. Through the classification step, the positive electrode active material for a lithium secondary battery is generally classified into 200 to 400 mesh.
One aspect of the present invention is a method for producing a positive electrode active material for a lithium secondary battery, which further includes a pulverization and classification step in addition to the mixing step and the main firing step described above.

<Positive electrode active material for lithium secondary battery>
The positive electrode active material for lithium secondary batteries produced by the method for producing a positive electrode active material for lithium secondary batteries of the present invention will be described.

In order to increase the energy density of the lithium secondary battery, the positive electrode active material for the lithium secondary battery preferably includes a lithium metal composite oxide represented by the following composition formula (I).
Li [Li _x (Ni _(1-yzw) Co _y Mn _z M _w ) _1-x ] O ₂ (I)
(In the general formula (I), −0.1 ≦ x ≦ 0.2, 0 <y ≦ 0.5, 0 <z ≦ 0.8, 0 ≦ w ≦ 0.1, y + z + w <1, M is It represents one or more elements selected from the group consisting of Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V.)

In the sense of obtaining a lithium secondary battery having high cycle characteristics, x in the composition formula (I) is preferably 0 or more, more preferably 0.01 or more, and further preferably 0.02 or more. preferable. In the sense of obtaining a lithium secondary battery with higher initial Coulomb efficiency, x in the composition formula (I) is preferably 0.18 or less, more preferably 0.15 or less, More preferably, it is as follows.
The upper limit value and the lower limit value of x can be arbitrarily combined.
For example, x is preferably 0 or more and 0.18 or less, more preferably 0.01 or more and 0.15 or less, and further preferably 0.02 or more and 0.1 or less.
In the present specification, “high cycle characteristics” means that the discharge capacity retention ratio is high.

In order to obtain a lithium secondary battery having high cycle characteristics, y in the composition formula (I) is preferably 0.13 or more, and more preferably 0.14 or more. In order to obtain a lithium secondary battery having high thermal stability, y in the composition formula (I) is preferably 0.35 or less, more preferably 0.3 or less, and 0.25. More preferably, it is as follows.
The upper limit value and the lower limit value of y can be arbitrarily combined.
For example, y is preferably from 0.13 to 0.35, more preferably from 0.14 to 0.3, and even more preferably from 0.14 to 0.25.

In the sense of obtaining a lithium secondary battery having high cycle characteristics, z in the composition formula (I) is preferably 0.1 or more, more preferably 0.15 or more, and 0.2 or more. More preferably. In addition, z in the composition formula (I) is preferably 0.35 or less, and preferably 0.32 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 further more preferable that it is 0.30 or less.
The upper limit value and lower limit value of z can be arbitrarily combined.
For example, z is preferably 0.1 or more and 0.35 or less, more preferably 0.15 or more and 0.32 or less, and further preferably 0.2 or more and 0.30 or less.

In the sense of improving the handling properties of the positive electrode active material for lithium secondary batteries, w in the composition formula (I) is preferably more than 0, more preferably 0.001 or more, and 0.005 or more. Is more preferable. 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 0.04 or less, more preferably 0.03 or less, More preferably, it is 0.02 or less.
The upper and lower limits of w can be combined arbitrarily.
For example, the above is preferably more than 0 and 0.04 or less, more preferably from 0.001 to 0.03, and further preferably from 0.005 to 0.02.

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

In the present invention, a lithium compound and a positive electrode active material precursor are prepared so that the produced positive electrode active material for a lithium secondary battery includes a lithium metal composite oxide having a desired composition represented by the composition formula (I). Can be mixed.

(Layered structure)
The crystal structure of the positive electrode active material 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, 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.

In the present embodiment, the crystallinity of the positive electrode active material is such that the half width of the diffraction peak in the range of 2θ = 18.7 ± 1 ° of the X-ray diffraction pattern obtained by X-ray diffraction measurement using CuKα rays, and 2θ It can be evaluated by the half-value width of the diffraction peak within the range of 44.4 ± 1 °.
The range of the half width of the diffraction peak within the range of 2θ = 18.7 ± 1 ° is preferably 0.01 to 0.20, more preferably 0.02 to 0.19, and 0 More preferably, it is 0.03 to 0.18.
The range of the half value width of the diffraction peak within the range of 2θ = 44.4 ± 1 ° is preferably 0.01 to 0.25, more preferably 0.02 to 0.22. More preferably, it is 0.03 to 0.20.

In the present invention, since the inner wall of the furnace where the mixture contacts is performed using a rotary kiln formed of a non-metallic material, the main baking step is performed at 750 ° C. to 1000 ° C. in order to increase the crystallinity of the positive electrode active material. Even when firing at a high temperature, the elution of metal from the material of the firing furnace can be reduced. For this reason, when attention is paid to chromium which is a kind of metal impurity, a positive electrode active material in which the chromium content is reduced can be manufactured.
The content of chromium with respect to the total mass of the positive electrode active material for lithium secondary batteries contained in the positive electrode active material for lithium secondary batteries produced according to the present invention is preferably 50 ppm or less, and is 45 ppm or less. Is more preferable, and 40 ppm or less is particularly preferable.
The measurement of the chromium content relative to the total mass of the positive electrode active material for lithium secondary batteries contained in the positive electrode active material for lithium secondary batteries is performed by contacting the powder of the positive electrode active material for lithium secondary batteries with hydrochloric acid. And then dissolved by an inductively coupled plasma optical emission spectrometer.

The method for producing a positive electrode active material for a lithium secondary battery according to the present invention can be fired at a high temperature because the inner wall of the furnace, which is a part in contact with the mixture, is carried out using a rotary kiln formed of a nonmetallic material. . For this reason, decomposition | disassembly of the lithium carbonate in a raw material is accelerated | stimulated, and the residual amount of lithium carbonate in the positive electrode active material manufactured is reduced.
1.0 mass% or less is preferable with respect to the total mass of the positive electrode active material contained in the positive electrode active material for lithium secondary batteries manufactured by this invention, and 0.99 mass% or less is preferable. More preferred is 0.95% by mass or less. Although the lower limit of content of lithium carbonate with respect to the total mass of a positive electrode active material is not specifically limited, For example, 0.05 mass% or more, 0.10 mass% or more, 0.2 mass% or more is mentioned.
The upper limit value and the lower limit value can be arbitrarily combined.
For example, the lithium carbonate content with respect to the total mass of the positive electrode active material is preferably 0.05% by mass or more and 1.0% by mass or less, and is 0.10% by mass or more and 0.99% by mass or less. More preferably, the content is 0.2% by mass or more and 0.95% by mass or less.
The content of the lithium carbonate component contained in the positive electrode active material for a lithium secondary battery can be determined by neutralization titration with an acidic solution. Specifically, the positive electrode active material for a lithium secondary battery is contact-treated with pure water, and the lithium carbonate component is eluted in pure water. By neutralizing and titrating the eluate with an acidic solution such as hydrochloric acid, the content of the lithium carbonate component can be determined. A more specific operation and a method for calculating the content of the lithium carbonate component will be described in Examples.

In contrast to the present invention, when the main calcination is carried out by filling a mixture in a roller sheath such as a roller hearth kiln, the oxygen-containing gas does not sufficiently reach the mixture filled in the bottom of the sheath, and lithium carbonate Since the decomposition of the metal does not proceed uniformly, a large amount of lithium carbonate tends to remain in the produced positive electrode active material.

<Lithium secondary battery>
Next, while explaining the configuration of the lithium secondary battery, the positive electrode using the positive electrode active material for lithium secondary battery manufactured by the method for manufacturing the positive electrode active material for lithium secondary battery of the present invention, and lithium having this positive electrode The secondary battery 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 electrolytic solution disposed between the positive electrode and the negative electrode.

1A and 1B are schematic views 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. 1A, 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, a separator 1, a positive electrode 2, and a 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, the electrode group 4 is impregnated with the electrolytic solution 6, the positive electrode 2, the negative electrode 3, An electrolyte is placed between the two. 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.

Further, 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 this embodiment can be manufactured 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, by adding a small amount to the positive electrode mixture, the conductivity inside the positive electrode can be improved and the charge / discharge efficiency and output characteristics can be improved. 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 total mass of the positive electrode mixture is 1% by mass to 10% by mass, and the ratio of the polyolefin resin is 0.1% by mass to 2% by mass In addition, a positive electrode mixture having both high adhesion to the positive electrode 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 composed of the 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 graphite 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 composite metal 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.

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

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, Sn -Tin alloys such as Co, Sn-Ni, Sn-Cu, Sn-La; alloys such as Cu ₂ Sb, La ₃ Ni ₂ Sn ₇ ;

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

Among the 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: 2009 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.

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 with respect to the total volume of the separator. 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, as the electrolyte, at least selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) ₃ containing fluorine. 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-dimethyla Amides such as toamide; 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.

It is preferable to use a mixture of two or more of these as the organic solvent. Of these, 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 ethers are more preferable. As a mixed solvent of a cyclic carbonate and an 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 compound 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 ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate 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. Also 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 this 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-containing composite metal oxide of the present embodiment, the lithium secondary battery using the positive electrode active material suppresses side reactions occurring inside the battery. be able to.

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 lithium secondary battery can suppress side reactions occurring inside the battery.

Furthermore, since the lithium secondary battery having the above-described configuration has the above-described positive electrode, it becomes a lithium secondary battery in which side reactions occurring inside the battery are suppressed as compared with the related art.

Next, the embodiment of the present invention will be described in more detail with reference to examples.
In this example, the firing raw material and the positive electrode active material for a lithium secondary battery were evaluated as follows.

(1) Composition analysis in positive electrode active material for lithium secondary battery (ICP emission analysis)
The composition analysis of the positive electrode active material for a lithium secondary battery was performed using an inductively coupled plasma emission analyzer (manufactured by Perkin Elmer, Optima 7300 DV) after dissolving a metal oxide powder in hydrochloric acid. The content of chromium as an impurity was calculated from the amount of chromium obtained above. Moreover, the lithium amount derived from lithium carbonate measured by the method described later was subtracted from the lithium amount obtained above to obtain the lithium amount of the lithium metal composite oxide. The values of x, y, z, and w in the general formula (I) were determined from the nickel amount, cobalt amount, manganese amount, M amount, and lithium amount of the lithium metal composite oxide obtained above. .

(2) Determination of residual lithium carbonate in positive electrode active material for lithium secondary battery (neutralization titration)
20 g of a positive electrode active material for a lithium secondary battery and 100 g of pure water were placed in a 100 mL beaker and stirred for 5 minutes. After stirring, the positive electrode active material for a lithium secondary battery was filtered, 0.1 mol / L hydrochloric acid was added dropwise to 60 g of the remaining filtrate, and the pH of the filtrate was measured with a pH meter. The positive electrode activity for a lithium secondary battery is calculated from the following formula using the hydrochloric acid titration at pH = 8.3 ± 0.1 AmL and the hydrochloric acid titration at B = 4.5 ± 0.1 hr as BmL. The concentration of lithium carbonate remaining in the material was calculated. In the following formula, the molecular weight of lithium carbonate was calculated by setting each atomic weight as Li; 6.941, C; 12, O;
Lithium carbonate concentration (%) = 0.1 × (BA) /1000×73.882/ (20 × 60/100) × 100

(3) Powder X-ray diffraction measurement of a positive electrode active material for a lithium secondary battery A powder X-ray diffraction measurement of a positive electrode active material for a lithium secondary battery was performed using a powder X-ray diffraction apparatus (manufactured by Rigaku Corporation, Ultimate IV, sample horizontal type). ). The obtained positive electrode active material for a lithium secondary battery is filled in a dedicated substrate and measured using a Cu—Kα ray source in a diffraction angle range of 2θ = 10 ° to 90 °. A diffraction pattern was obtained. From the powder X-ray diffraction pattern, a peak in the range of 2θ = 18.7 ± 1 ° (hereinafter also referred to as peak A), a peak in the range of 2θ = 44.6 ± 1 ° (hereinafter, peak B) Half-width) was calculated.

Example 1
[Mixing process]
Lithium carbonate (Li ₂ CO ₃ ) and nickel cobalt manganese composite metal hydroxide (Ni _0.55 Co _0.21 Mn _0.24 (OH) ₂ ) have a molar ratio of Li: Ni: Co: Mn of 1 .05: 0.55: 0.21: 0.24 and they were dry mixed to obtain a mixture. In addition, lithium carbonate content contained in the said mixture is 29.7 mass% from mixing ratio.
[Pre-baking step]
Next, the mixture was placed in a rotary kiln whose inner wall of the furnace was alumina and baked at 790 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product obtained in the preliminary firing step is placed in the rotary kiln and fired at 900 ° C. for 2 hours while a gas containing 21% by volume of oxygen is vented at 108.7 Nm ³ / h per 1 m ³ of the furnace volume. It was.
Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 2 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.25 mass%. In the general formula (I), x was 0.03, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.129 and 0.152, respectively.

(Example 2)
[Mixing process]
Lithium carbonate (Li ₂ CO ₃ ) and nickel cobalt manganese composite metal hydroxide (Ni _0.55 Co _0.21 Mn _0.24 (OH) ₂ ) have a molar ratio of Li: Ni: Co: Mn of 2 20: 0.55: 0.21: 0.24, and they were dry mixed to obtain a mixture. In addition, lithium carbonate content contained in the said mixture is 46.6 mass% from mixing ratio.
[Pre-baking step]
Next, the mixture was placed in a rotary kiln whose inner wall of the furnace was alumina and baked at 790 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in the rotary kiln and fired at 850 ° C. for 2 hours while a gas containing 100% by volume of oxygen was vented by 150.1 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 4 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.92 mass%. In the general formula (I), x was 0.37, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.160 and 0.208, respectively.

(Example 3)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln whose inner wall is alumina, and baked at 850 ° C. for 2 hours while a gas containing 21% by volume of oxygen was passed through 107.2 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 10 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.16 mass%. In the general formula (I), x was 0.03, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.152 and 0.185, respectively.

Example 4
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln having an inner wall made of alumina, and baked at 850 ° C. for 2 hours while a gas containing 60% by volume of oxygen was vented by 107.2 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 31 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.19 mass%. In the general formula (I), x was 0.04, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.153 and 0.194, respectively.

(Example 5)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln having an inner wall made of alumina, and baked at 850 ° C. for 2 hours while a gas containing 100% by volume of oxygen was passed through 46.5 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 49 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.15 mass%. In the general formula (I), x was 0.04, y was 0.22, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.152 and 0.178, respectively.

(Example 6)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln having an inner wall made of alumina, and baked at 850 ° C. for 2 hours while a gas containing 21% by volume of oxygen was vented at 46.5 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 20 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.51 mass%. In the general formula (I), x was 0.04, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.149 and 0.182, respectively.

(Example 7)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln having an inner wall made of alumina, and baked at 850 ° C. for 2 hours while a gas containing 21% by volume of oxygen was passed through 17.9 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 19 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.90 mass%. In the general formula (I), x was 0.03, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.161 and 0.200, respectively.

(Example 8)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was put into a rotary kiln whose inner wall of the furnace was alumina, and baked at 850 ° C. for 2 hours while a gas containing 100% by volume of oxygen was passed through 17.9 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 45 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.53 mass%. In the general formula (I), x was 0.03, y was 0.21, z was 0.24, and w was 0. Moreover, as a result of performing powder X-ray diffraction, the half width of the peak A and the peak B was 0.151 and 0.184, respectively.

(Comparative Example 1)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln whose inner wall of the furnace was Inconel, and fired at 730 ° C. for 2 hours while a gas containing 21% by volume of oxygen was passed through 22.6 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 55 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 5.31 mass%. In the general formula (I), x was 0.02, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.458 and 0.639, respectively.

(Comparative Example 2)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln whose inner wall of the furnace was Inconel, and fired at 730 ° C. for 4 hours while a gas containing 21% by volume of oxygen was passed through 22.6 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 60 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 3.43 mass%. In the general formula (I), x was 0.03, y was 0.22, z was 0.24, and w was 0. Moreover, as a result of performing powder X-ray diffraction, the half width of the peak A and the peak B was 0.415 and 0.578, respectively.

(Comparative Example 3)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was placed in a rotary kiln having an inner wall of SUS310, and fired at 730 ° C. for 5 hours while a gas containing 21% by volume of oxygen was passed through 22.6 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 320 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 1.13 mass%. In the general formula (I), x was 0.02, y was 0.21, z was 0.24, and w was 0. Moreover, as a result of performing powder X-ray diffraction, the half width of the peak A and the peak B was 0.214 and 0.261, respectively.

(Comparative Example 4)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was filled into a sheath whose inner wall is alumina, and was heated at 850 ° C. at 2850 Nm ³ / h with a roller hearth kiln and a gas containing 21% by volume of oxygen per 1 m ³ of the furnace volume. Time firing was performed. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 10 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 1.01 mass%. In the general formula (I), x was 0.04, y was 0.21, z was 0.24, and w was 0. Moreover, as a result of performing powder X-ray diffraction, the half width of the peak A and the peak B was 0.225 and 0.278, respectively.

(Comparative Example 5)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was filled into a sheath whose inner wall is alumina, and was heated at 850 ° C. while a roller hearth kiln was ventilated with 29.7 Nm ³ / h of gas containing 21% by volume of oxygen per 1 m ³ of the furnace volume. Time firing was performed. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing neutralization titration on the positive electrode active material for a lithium secondary battery, the lithium carbonate content was 0.67% by mass. In the general formula (I), x was 0.02, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.129 and 0.150, respectively.

(Comparative Example 6)
[Mixing process]
Lithium carbonate (Li ₂ CO ₃ ) and nickel cobalt manganese composite metal hydroxide (Ni _0.55 Co _0.21 Mn _0.24 (OH) ₂ ) are mixed with a molar ratio of Li: Ni: Co: Mn of 3 0.000: 0.55: 0.21: 0.24, and these were dry mixed to obtain a mixture. In addition, lithium carbonate content contained in the said mixture is 54.3 mass% from mixing ratio. In the general formula (I), x was 0.50, y was 0.21, z was 0.24, and w was 0. The mixture was calcined at 850 ° C. for 2 hours in a rotary kiln having an inner wall of alumina of a furnace while a gas containing 21% by volume of oxygen was vented at 17.9 Nm ³ / h per m ³ of the furnace volume. However, the mixture and the fired product adhered to the wall of the furnace core tube and could not be discharged.

(Reference example)
[Mixing process]
A mixture was obtained in the same manner as in Example 1.
[Pre-baking step]
The mixture described in Example 1 was placed in a rotary kiln having an inner wall of Inconel and baked at 730 ° C. for 2 hours.
[Main firing process]
Subsequently, the fired product was put into a rotary kiln whose inner wall of the furnace was alumina, and baked at 850 ° C. for 4 hours while a gas containing 21% by volume of oxygen was vented at 17.9 Nm ³ / h per 1 m ³ of the furnace volume. Then, it cooled to room temperature and this was crushed and the positive electrode active material for lithium secondary batteries was obtained. As a result of performing ICP emission analysis on the positive electrode active material for a lithium secondary battery, the chromium content was 13 ppm. Moreover, as a result of performing neutralization titration, lithium carbonate content was 0.10 mass%. In the general formula (I), x was 0.02, y was 0.21, z was 0.24, and w was 0. Further, as a result of powder X-ray diffraction, the half widths of peak A and peak B were 0.149 and 0.183, respectively.

Tables 1 to 3 below collectively describe the conditions and results of Examples, Comparative Examples, and Reference Examples. In the table, RK indicates a rotary kiln, and RHK indicates a roller hearth kiln.

As shown in Tables 1 to 3 below, Examples 1 to 8 to which the present invention is applied can produce a positive electrode active material having a small peak half-value width, that is, high crystallinity, in a short baking time. did it.
Further, in Examples 1 to 8 to which the present invention was applied, the chromium content was low.
In contrast, Comparative Examples 1 to 3 in which the main firing step was performed with a metal rotary kiln had a high chromium content and a large peak half-value width. Moreover, although the comparative example 4 which used the roller hearth kiln for the main baking process and made the baking time of 2 hours has a large peak half value width and the comparative example 5 has a small peak half value width, the main baking time required 10 hours.
In Reference Example 1, the main calcination was performed for 4 hours using a rotary kiln in which the inner wall of the furnace, which is the part in contact with the mixture, was formed from a non-metallic material. When Reference Example 1 and Example 1 were compared, the peak half-value widths were comparable. That is, a positive electrode active material with high crystallinity could be produced in a short (2 hours) firing time.

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, 40 ... rotary kiln, 41 ... furnace inner wall, 42 ... furnace core tube, 50 ... firing raw material

Claims (8)

1. A mixing step of mixing a lithium compound and a positive electrode active material precursor to obtain a mixture;
   A main baking step of baking the mixture using a rotary kiln;
   A method for producing a positive electrode active material for a lithium secondary battery, comprising:
   The content of the lithium compound contained in the mixture is more than 0 and 50% by mass or less with respect to the total mass of the mixture,
   A method for producing a positive electrode active material for a lithium secondary battery, wherein a furnace inner wall of the rotary kiln is formed of a non-metallic material.
2. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the main firing step is performed at 750 ° C. or more and 1000 ° C. or less.
3. The manufacturing method of the positive electrode active material for lithium secondary batteries of Claim 1 or 2 with which the said positive electrode active material for lithium secondary batteries contains the lithium metal complex oxide 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)
   (In the general formula (I), −0.1 ≦ x ≦ 0.2, 0 <y ≦ 0.5, 0 <z ≦ 0.8, 0 ≦ w ≦ 0.1, y + z + w <1, M is It represents one or more elements selected from the group consisting of Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V.)
4. The lithium according to any one of claims 1 to 3, further comprising a pre-baking step of baking at a temperature lower than a baking temperature of the main baking after the mixing step and before the main baking step. A method for producing a positive electrode active material for a secondary battery.
5. The method according to any one of claims 1 to 4, wherein one or both of the main baking step and the preliminary baking step are performed by ventilating an oxygen-containing gas at a flow rate of 15 Nm ³ / h / m ³ or more. A method for producing a positive electrode active material for a lithium secondary battery.
6. The method for producing a positive electrode active material for a lithium secondary battery according to claim 5, wherein the oxygen concentration in the oxygen-containing gas is 21% by volume or more based on the total volume of the oxygen-containing gas.
7. The content of chromium contained in the positive electrode active material for a lithium secondary battery is 50 ppm or less with respect to the total mass of the positive electrode active material for the lithium secondary battery. Manufacturing method of positive electrode active material for lithium secondary battery.
8. The content of lithium carbonate contained in the positive electrode active material for a lithium secondary battery is 1.0% by mass or less based on the total mass of the positive electrode active material for the lithium secondary battery. The manufacturing method of the positive electrode active material for lithium secondary batteries of Claim 1.

Images