WO2014156992A1

WO2014156992A1 - Method for producing positive electrode active material

Info

Publication number: WO2014156992A1
Application number: PCT/JP2014/057856
Authority: WO
Inventors: 酒井　智弘
Original assignee: 旭硝子株式会社
Priority date: 2013-03-25
Filing date: 2014-03-20
Publication date: 2014-10-02
Also published as: JPWO2014156992A1; JP6388573B2

Abstract

To obtain a positive electrode active material which has excellent cycle characteristics, while being suppressed in decrease in the discharge voltage. A method for producing a positive electrode active material, which comprises: a step wherein at least one sulfate (A) selected from the group consisting of sulfates of Ni, sulfates of Co and sulfates of Mn and at least one carbonate (B) selected from the group consisting of carbonates of Na and carbonates of K are mixed with each other in the form of an aqueous solution, so that a carbonate compound is precipitated; a step wherein the carbonate compound and an aqueous solution (C) that contains at least one element (Y) selected from the group consisting of Al, F, Si, Zr, Y, Mo, Ce and Ca are mixed with each other; a step wherein the water content is vaporized from the mixture of the carbonate compound and the aqueous solution (C), so that a precursor compound is obtained; and a step wherein the precursor compound and a lithium compound are mixed with each other and fired at 500-1,000°C.

Description

Method for producing positive electrode active material

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

Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and notebook computers. As a positive electrode active material of a lithium ion secondary battery, a positive electrode active material (LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMn ₂ O _4, etc.) made of a composite oxide containing Li and a transition metal element .)It has been known. For example, a lithium ion secondary battery using LiCoO ₂ as a positive electrode active material and using a lithium alloy, graphite, carbon fiber, or the like as a negative electrode can be widely used as a battery having a high energy density because a high voltage of about 4 V can be obtained. Has been.

リチウム Lithium ion secondary batteries for portable electronic devices and in-vehicle use are required to be smaller and lighter. Therefore, the lithium ion secondary battery has a discharge capacity per unit mass (hereinafter simply referred to as “discharge capacity”) and characteristics that make it difficult to reduce the discharge capacity and the average discharge voltage after repeated charge / discharge cycles (hereinafter referred to as “discharge capacity”). It is also called “cycle characteristics”).

As a positive electrode active material having a high discharge capacity, a positive electrode active material made of a composite oxide having a high Li molar ratio to a transition metal element (hereinafter also referred to as “Li-rich positive electrode active material”) has attracted attention.
Patent Document 1 includes a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, and the composition ratio of Li and transition metal element contained in the solid solution is expressed by the composition formula Li _{1 + 1 / 3x} Co _{1-1. A} positive electrode active material satisfying _xy Ni _{y / 2} Mn _{2x / 3 + y / 2} (x + y ≦ 1, 0 ≦ y and 1/3 <x ≦ 2/3) is described.
However, the positive electrode active material of Patent Document 1 is likely to elute Mn into the electrolytic solution by coming into contact with a decomposition product generated from the electrolytic solution by charging at a high voltage. Therefore, the crystal structure of the positive electrode active material tends to become unstable, and sufficient cycle characteristics cannot be obtained.

Patent Document 2 describes a method of doping fluorine by blending a positive electrode active material and LiF or NH ₄ HF ₂ as a powder and heating in order to improve cycle characteristics.
However, in the method of Patent Document 2, fluorine cannot be doped sufficiently uniformly, and it is difficult to obtain sufficient cycle characteristics.

Japanese Unexamined Patent Publication No. 2009-152114 Japanese Special Table 2012-504316

The present invention provides a method for producing a positive electrode active material having excellent cycle characteristics and a small decrease in discharge voltage. Moreover, this invention provides the lithium ion secondary battery which has a positive electrode for lithium ion secondary batteries using the positive electrode active material obtained by the said manufacturing method, and this positive electrode for lithium ion secondary batteries.

The gist of the present invention is as follows.
(1) A method for producing a positive electrode active material comprising the following steps (I) to (IV):
(I) at least one sulfate (A) selected from the group consisting of Ni sulfate, Co sulfate and Mn sulfate;
At least one carbonate (B) selected from the group consisting of Na carbonate and K carbonate,
Mix in the state of aqueous solution,
Depositing a carbonate compound containing at least one transition metal element (X) selected from the group consisting of Ni, Co and Mn.
(II) A step of mixing the carbonate compound with an aqueous solution (C) containing at least one element (Y) selected from the group consisting of Al, F, Si, Zr, Y, Mo, Ce and Ca.
(III) A step of obtaining a precursor compound by volatilizing water from a mixture of the carbonate compound and the aqueous solution (C).
(IV) A step of mixing the precursor compound and the lithium compound and baking at 500 to 1000 ° C.
(2) The method for producing a positive electrode active material according to (1), wherein, in the step (I), the aqueous solution of the sulfate (A) includes a sulfate of Ni, a sulfate of Co, and a sulfate of Mn.

(3) In the step (I), the concentration of the transition metal element (X) composed of Mn, Ni and Co in the aqueous solution of the sulfate (A) is 0.1 to 3 mol / kg, The manufacturing method of the positive electrode active material as described in 1) or (2).
(4) Any one of the above (1) to (3), wherein the concentration of the carbonate (B) in the aqueous solution of the carbonate (B) is 0.1 to 2 mol / kg in the step (I). The manufacturing method of the positive electrode active material of description.

(5) In the step (II), the ratio of the total molar amount of the element (Y) contained in the aqueous solution (C) to the total amount (100 mol) of the transition metal element (X) contained in the carbonate compound ( The method for producing a positive electrode active material according to any one of (1) to (4), wherein Y / X) is 0.01 to 10%.
(6) The process according to any one of (1) to (5), wherein the concentration of the compound containing the element (Y) in the aqueous solution (C) is 0.1 to 50% by mass in the step (II). Of manufacturing positive electrode active material.
(7) In step (II), the compound containing element (Y) is a basic aluminum lactate salt, ammonium hydrogen fluoride, colloidal silica, ammonium zirconium carbonate, yttrium nitrate, hexaammonium heptamolybdate, cerium nitrate, and nitric acid The method for producing a positive electrode active material according to (6), wherein the positive electrode active material is one or more selected from the group consisting of calcium.
(8) The method for producing a positive electrode active material according to any one of (1) to (7) above, wherein in step (II), the carbonate compound and the aqueous solution (C) are mixed by a spray coating method.

(9) In step (IV), the ratio (Li / X) of the total molar amount of Li contained in the lithium compound to the total molar amount of transition metal element (X) contained in the precursor compound is 1.1. The method for producing a positive electrode active material according to any one of (1) to (8) above.
(10) In the step (IV), the precursor compound and the lithium compound are mixed, pre-baked at 400 to 700 ° C., and then subjected to main baking at 700 to 1000 ° C. ). The manufacturing method of the positive electrode active material as described in any one of.
(11) The method for producing a positive electrode active material according to any one of (1) to (10), wherein the obtained positive electrode active material is a compound (1) represented by the following formula (1).
_{_{Li 1 + a Y 'b Ni}} c Co d Mn e O 2 + f ··· (1)
(In the formula (1), Y ′ is the element (Y), and a to e are 0.1 ≦ a ≦ 0.6, 0.0001 ≦ b ≦ 0.105, 0.1 ≦ c, respectively. ≦ 0.5, 0 ≦ d ≦ 0.3, 0.2 ≦ e ≦ 0.9, 0.9 ≦ c + d + e ≦ 1.05, and f is Li, element (Y), Ni, Co, and Mn. (The number is determined by the valence.)

(12) A positive electrode current collector, and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer is as defined in any one of (1) to (11) above The positive electrode for lithium ion secondary batteries containing the positive electrode active material obtained by the manufacturing method of description, a electrically conductive material, and a binder.
(13) A lithium ion secondary battery comprising the lithium ion secondary battery positive electrode according to (12), a negative electrode, and a nonaqueous electrolyte.

According to the method for producing a positive electrode active material of the present invention, a positive electrode active material having excellent cycle characteristics and a small decrease in discharge voltage can be obtained.
If the positive electrode for lithium ion secondary batteries of the present invention is used, a lithium ion secondary battery having excellent cycle characteristics and a small decrease in discharge voltage can be obtained.
The lithium ion secondary battery of the present invention has excellent cycle characteristics and a small decrease in discharge voltage.

<Method for producing positive electrode active material>
The method for producing a positive electrode active material of the present invention includes the following steps (I) to (IV).

[Step (I)]
In step (I), sulfate (A) and carbonate (B) are mixed in the form of an aqueous solution. You may use an additive further as needed. Thereby, a carbonate compound containing at least one transition metal element (X) selected from the group consisting of Ni, Co and Mn is deposited.

The aspect which mixes sulfate (A) and carbonate (B) in the state of aqueous solution will not be specifically limited if sulfate (A) and carbonate (B) are in the state of aqueous solution at the time of mixing.
Specifically, since the carbonate compound is easily precipitated and the particle diameter is easily controlled, both the aqueous solution of sulfate (A) and the aqueous solution of carbonate (B) are continuously added to the mixing tank. It is preferable. It is preferable to put ion exchange water, pure water, distilled water, etc. in the mixing tank in advance, and it is more preferable to control the pH using a carbonate (B), an additive described later, or the like.
The pH of the mixed solution in the mixing tank when mixing the sulfate (A) and the carbonate (B) is maintained at 7 to 12 because the carbonate compound containing the transition metal element (X) is likely to precipitate. It is preferable to keep it at 7.5-10.

When two or more kinds of sulfates (A) are used, the aqueous solution of sulfate (A) may be two or more kinds of aqueous solutions separately containing each of the two or more kinds of sulfates (A). It is good also as 1 type of aqueous solution containing the above sulfate (A). Moreover, you may use together the aqueous solution containing 1 type of sulfates (A), and the aqueous solution containing 2 or more types of sulfates (A). The same applies when two types of carbonate (B) are used.

The sulfate (A) is at least one sulfate selected from the group consisting of Ni sulfate, Co sulfate and Mn sulfate.
Examples of the Ni sulfate include nickel sulfate (II) hexahydrate, nickel sulfate (II) heptahydrate, nickel sulfate (II) ammonium hexahydrate, and the like.
Examples of Co sulfate include cobalt sulfate (II) heptahydrate and cobalt sulfate (II) ammonium hexahydrate.
Examples of the sulfate of Mn include manganese sulfate (II) pentahydrate, manganese sulfate (II) ammonium hexahydrate, and the like.

As for sulfate (A), only 1 type may be sufficient and 2 or more types may be sufficient as it.
The sulfate (A) preferably contains Ni sulfate and Mn sulfate from the viewpoint of easily obtaining a lithium ion secondary battery having a high discharge capacity. Ni sulfate, Co sulfate and Mn More preferably, it contains all of the sulfates. That is, the carbonate compound is preferably a carbonate compound containing Ni and Mn as the transition metal element (X), and is a carbonate compound containing all of Ni, Co and Mn as the transition metal element (X). Is more preferable.

The carbonate (B) is at least one carbonate selected from the group consisting of Na carbonate and K carbonate. The carbonate (B) also serves as a pH adjuster for precipitating the carbonate compound containing the transition metal element (X).
Examples of the carbonate of Na include sodium carbonate and sodium hydrogen carbonate.
Examples of the carbonate of K include potassium carbonate and potassium hydrogen carbonate.
As the carbonate (B), sodium carbonate or potassium carbonate is preferable because it is inexpensive and allows easy control of the particle diameter of the carbonate compound. On the other hand, as the carbonate (B), sodium hydrogen carbonate or potassium hydrogen carbonate is preferable in terms of easily increasing the tap density of the carbonate compound. As carbonate (B), only 1 type may be sufficient and 2 or more types may be sufficient.

The amount of Ni contained in the sulfate of Ni is preferably 10 to 50 mol% and more preferably 15 to 45 mol% with respect to the total amount (100 mol%) of Ni, Co and Mn contained in the sulfate (A). 20 to 45 mol% is particularly preferable. If the ratio of the amount of Ni is equal to or higher than the lower limit value, a positive electrode active material exhibiting a high discharge voltage is easily obtained. If the ratio of the amount of Ni is not more than the upper limit value, a positive electrode active material exhibiting a high discharge capacity is easily obtained.

The amount of Co contained in the sulfate of Co is preferably 0 to 30 mol% and more preferably 0 to 20 mol% with respect to the total amount (100 mol%) of Ni, Co and Mn contained in the sulfate (A). 0 to 15 mol% is particularly preferable. If the ratio of the amount of Co is not more than the upper limit value, a positive electrode active material exhibiting excellent cycle characteristics can be easily obtained.

The amount of Mn contained in the sulfate of Mn is preferably 20 to 90 mol%, more preferably 35 to 85 mol% with respect to the total amount (100 mol%) of Ni, Co and Mn contained in the sulfate (A). 40 to 80 mol% is particularly preferable. If the ratio of the amount of Mn is not less than the lower limit value, a positive electrode active material exhibiting a high discharge capacity is easily obtained. If the ratio of the amount of Mn is not more than the upper limit value, a positive electrode active material exhibiting a high discharge voltage is easily obtained.

The concentration of the transition metal element (X) in the aqueous solution of the sulfate (A) is preferably from 0.1 to 3 mol / kg, more preferably from 0.5 to 2.5 mol / kg. If the concentration is equal to or higher than the lower limit, productivity is high. If the said density | concentration is below an upper limit, it will be easy to fully dissolve a sulfate (A).
When using 2 or more types of aqueous solution containing a sulfate (A), it is preferable to make the density | concentration of a transition metal element (X) into the said range about each aqueous solution.

The concentration of carbonate (B) in the aqueous solution of carbonate (B) is preferably from 0.1 to 2 mol / kg, more preferably from 0.5 to 2 mol / kg. If the concentration of the carbonate (B) is within the above range, the carbonate compound is likely to precipitate.
When using 2 or more types of aqueous solution containing a sulfate (B), it is preferable to make the density | concentration of a sulfate (B) into the said range about each aqueous solution.

The solvent of the aqueous solution of the sulfate (A) and the aqueous solution of the carbonate (B) may be water alone as long as the sulfate (A) and the carbonate (B) are dissolved. And an aqueous medium containing components other than water.
Examples of components other than water include methanol, ethanol, 1-propanol, 2-propanol, polyol and the like. Examples of the polyol include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, butanediol, glycerin and the like.
The proportion of components other than water in the aqueous medium is preferably 0 to 20% by mass, more preferably 0 to 10% by mass, particularly preferably 0 to 1% by mass, and most preferably not contained. If the ratio of components other than water is less than or equal to the upper limit, it is excellent in terms of environment, handleability, and cost.

When mixing a sulfate (A) and carbonate (B) in the state of aqueous solution, it is preferable to carry out stirring in a mixing tank.
As a stirring apparatus, a three-one motor etc. are mentioned, for example. Examples of the stirring blade include a stirring blade such as an anchor type, a propeller type, and a paddle type.

The temperature of the mixed solution when mixing the sulfate (A) and the carbonate (B) is preferably 20 to 80 ° C., more preferably 25 to 60 ° C., because the carbonate compound is likely to precipitate.
Further, when the sulfate (A) and the carbonate (B) are mixed, it is preferable to perform the mixing under a nitrogen atmosphere or an argon atmosphere from the viewpoint of suppressing the oxidation of the precipitated carbonate compound. From the viewpoint, it is particularly preferable to perform the mixing in a nitrogen atmosphere.

As the additive, for example, ammonia or an ammonium salt may be used in order to adjust the pH and the solubility of the transition metal element (X). Examples of ammonium salts include ammonium chloride, ammonium sulfate, and ammonium nitrate.
Ammonia or ammonium salt is preferably supplied to the mixed solution simultaneously with the supply of sulfate (A).

The preferred ranges of the respective proportions of Ni, Co and Mn in the obtained carbonate compound are the same as the preferred ranges of the respective proportions of Ni, Co and Mn in all the sulfates (A) used as described above. is there. Thereby, it is easy to obtain a spherical carbonate compound having an appropriate particle size.

The particle size (D ₅₀ ) of the carbonate compound is preferably 5 to 20 μm, more preferably 5 to 18 μm, and particularly preferably 7 to 15 μm. Within D ₅₀ of the scope of the carbonate compound, easily controlled within the preferred range of D ₅₀ of the positive electrode active material obtained in later-described step (IV), the positive electrode active material showing sufficient battery characteristics can not be obtained easily .
In the present specification, D ₅₀ means a particle diameter at a point of 50% in a cumulative volume distribution curve with the total volume distribution determined on a volume basis being 100%, that is, a volume-based cumulative 50% diameter. . The particle size distribution is obtained from a frequency distribution and a cumulative volume distribution curve measured with a laser scattering particle size distribution measuring apparatus. The particle size is measured by sufficiently dispersing the powder in an aqueous medium by sonication or the like and measuring the particle size distribution (for example, using a laser diffraction / scattering particle size distribution measuring device Partica LA-950VII manufactured by HORIBA). Used).

The specific surface area of the carbonate compound is preferably 50 ~ 300m ² / g, more preferably 100 ~ 250m ² / g. When the specific surface area of the carbonate compound is within the above range, the aqueous solution (C) in the step (II) described later can easily penetrate into the inside of the particles, and a positive electrode active material exhibiting high discharge capacity and cycle characteristics can be easily obtained.
The specific surface area of the carbonate compound can be measured by the BET method. Specifically, it is measured by the method described in the examples.

The step (I) preferably includes a step of removing the aqueous solution by filtration or centrifugation after the carbonate compound is precipitated. For filtration or centrifugation, a pressure filter, a vacuum filter, a centrifugal classifier, a filter press, a screw press, a rotary dehydrator, or the like can be used.
The obtained carbonate compound is preferably washed in order to remove impurity ions. Examples of the method for washing the carbonate compound include a method in which pressure filtration and dispersion in distilled water are repeated.
The carbonate compound may be dried as necessary after washing.
The drying temperature of the carbonate compound is preferably 60 to 200 ° C, more preferably 80 to 130 ° C. If the said drying temperature is more than a lower limit, a carbonate compound can be dried in a short time. If the said drying temperature is below an upper limit, the oxidation of a carbonate compound can be suppressed.
The drying time of the carbonate compound is preferably 1 to 300 hours, more preferably 5 to 120 hours.

[Step (II)]
In step (II), the carbonate compound obtained in step (I) and the aqueous solution (C) are mixed.
Examples of the method for mixing the carbonate compound and the aqueous solution (C) include a spray coating method and a dipping method. Especially, since an element (Y) is provided more uniformly to a carbonate compound, a spray coating method is preferable.
When the aqueous solution (C) is spray coated on the carbonate compound, the aqueous solution (C) is spray coated on the carbonate compound being stirred, or the aqueous solution (C) is spray coated on the carbonate compound and then they are stirred. It is more preferable.
For stirring the carbonate compound and the aqueous solution (C), a Ladige mixer, a rocking mixer, a Nauta mixer, a spiral mixer, a spray dryer, a V mixer, or the like can be used.
The aqueous solution (C) may be spray coated with the carbonate compound spread thinly.

The aqueous solution (C) is an aqueous solution containing at least one element (Y) selected from the group consisting of Al, F, Si, Zr, Y, Mo, Ce and Ca.
The aqueous solution (C) can be obtained, for example, by dissolving a compound containing the element (Y) in water.
Examples of the compound containing the element (Y) include basic aluminum lactate, ammonium hydrogen fluoride, colloidal silica, ammonium zirconium carbonate, yttrium nitrate, hexaammonium heptamolybdate, cerium nitrate, and calcium nitrate.
The compound containing the element (Y) contained in the aqueous solution (C) may be one type or two or more types.

The concentration of the compound containing the element (Y) in the aqueous solution (C) is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and particularly preferably 1 to 20% by mass. If the said density | concentration is more than a lower limit, it will be easy to provide an element (Y) to a carbonate compound uniformly. If the said density | concentration is below an upper limit, it will be easy to melt | dissolve the compound containing an element (Y) fully.

In the step (II), the ratio of the total molar amount of the element (Y) contained in the aqueous solution (C) to the total amount (100 mol) of the transition metal element (X) contained in the carbonate compound (Y / X) is preferably 0.01 to 10%, more preferably 0.1 to 5%, and particularly preferably 0.5 to 3%. When the Y / X is not less than the lower limit, a positive electrode active material exhibiting excellent cycle characteristics can be easily obtained. If Y / X is less than or equal to the upper limit value, impurities are hardly generated after firing in step (IV), and excellent electrical characteristics are easily obtained.

[Step (III)]
In the step (III), the precursor compound is obtained by volatilizing water from the mixture of the carbonate compound and the aqueous solution (C) obtained in the step (II).
Step (III) may be performed simultaneously with the above-described step (II), or step (III) may be performed after step (II). When step (III) is not performed, much water remains in the precursor compound. If a large amount of moisture remains in the precursor compound, lithium carbonate is likely to be dissolved in moisture in the step (IV) to be described later. When aggregation of lithium carbonate occurs, the distribution of Li and element (Y) in the positive electrode active material becomes non-uniform, and a positive electrode active material having sufficient cycle characteristics cannot be obtained.
In addition, since the above-mentioned bad influence is small, 30 mass% or less is preferable with respect to the total mass of a precursor compound, and, as for the moisture content which remains in the precursor compound obtained by process (III), 15 mass% or less is more. Preferably, 5 mass% or less is especially preferable.
The amount of water remaining can be measured by the Karl Fischer method.

Examples of the method for volatilizing moisture include a method of drying by heating.
The heating temperature in step (III) is preferably 60 to 200 ° C, more preferably 80 to 130 ° C. If heating temperature is more than a lower limit, the moisture content in the obtained precursor compound will decrease, and the positive electrode active material which shows the outstanding cycling characteristics will be easy to be obtained. When the heating temperature is equal to or lower than the upper limit value, the precursor compound is hardly thermally deteriorated.
Although the heating time varies depending on the heating temperature, it is preferably 1 to 300 hours, more preferably 1 to 120 hours.

[Step (IV)]
In step (IV), the precursor compound obtained in step (III) and the lithium compound are mixed and fired at 500 to 1000 ° C.
As the lithium compound, at least one selected from the group consisting of lithium carbonate, lithium hydroxide and lithium nitrate is preferable, and lithium carbonate is more preferable because it is inexpensive.
Examples of the method of mixing the precursor compound and lithium carbonate include a method using a rocking mixer, a nauta mixer, a spiral mixer, a cutter mill, a V mixer, and the like.

In step (IV), the ratio (Li / X) of the total molar amount of Li contained in the lithium compound to the total molar amount of transition metal element (X) contained in the precursor compound is preferably 1.1 or more. If the said ratio is more than a lower limit, a high discharge capacity will be obtained.
The Li / X is more preferably from 1.1 to 1.6, and particularly preferably from 1.1 to 1.4. When Li / X is not more than the upper limit value, a high discharge capacity is easily obtained.

An electric furnace, a continuous firing furnace, a rotary kiln or the like can be used for the firing apparatus. Since the precursor compound is oxidized during firing, the firing is preferably performed in the air, and particularly preferably performed while supplying air.
The air supply rate is preferably 10 to 200 mL / min, more preferably 40 to 150 mL / min per 1 L of the furnace internal volume.
By supplying air at the time of firing, the transition metal element (X) in the precursor compound is sufficiently oxidized, and a positive electrode active material having high crystallinity and a target crystal phase is obtained.

The firing temperature is 500 to 1000 ° C., preferably 600 to 1000 ° C., and particularly preferably 800 to 950 ° C. When the firing temperature is within the above range, a positive electrode active material with high crystallinity can be obtained.
The firing time is preferably 4 to 40 hours, and more preferably 4 to 20 hours.

The firing may be one-stage firing at 500 to 1000 ° C., or two-stage firing in which main firing is performed at 700 to 1000 ° C. after preliminary firing at 400 to 700 ° C. Among these, two-stage firing is preferable because Li easily diffuses uniformly into the positive electrode active material.
In the case of the two-stage firing, the temperature for temporary firing is preferably 400 to 700 ° C, more preferably 500 to 650 ° C. Further, the temperature of the main firing in the case of two-stage firing is preferably 700 to 1000 ° C., and more preferably 800 to 950 ° C.

The positive electrode active material obtained by the production method of the present invention is a positive electrode active material made of a composite oxide containing Li, a transition metal element (X), and an element (Y).
The obtained positive electrode active material is particulate. The particle shape of the positive electrode active material is not particularly limited, and examples thereof include a spherical shape, a needle shape, and a plate shape. Especially, since the filling property of a positive electrode active material becomes high at the time of manufacture of a positive electrode, the particle shape of a positive electrode active material has a more preferable spherical shape.

The D ₅₀ of the positive electrode active material is preferably 4 to 20 μm, more preferably 5 to 18 μm, and particularly preferably 6 to 15 μm. Within D ₅₀ is the range of the positive electrode active material, high discharge capacity can be easily obtained.
The positive electrode active material is preferably secondary particles in which primary particles having a particle diameter D ₅₀ of 10 to 500 nm are aggregated. As a result, when a lithium ion secondary battery is manufactured, the electrolyte is easily spread between the positive electrode active materials in the positive electrode. It is preferable that the element (Y) is uniformly distributed in the secondary particles from the viewpoint that the decrease in the discharge voltage can be sufficiently suppressed.

The specific surface area of the positive electrode active material is preferably 0.1 ~ ^15m 2 / g, more preferably 2 ~ ^10m 2 / g, particularly preferably 4 ~ ^8m 2 / g. If the specific surface area is not less than the lower limit, a high discharge capacity is easily obtained. If the specific surface area is not more than the upper limit value, excellent cycle characteristics can be easily obtained.
The specific surface area is measured by the method described in Examples.

The molar ratio (Li / X) of the Li content to the content of the transition metal element (X) in the positive electrode active material is preferably 1.1 or more, more preferably 1.1 or more and 1.6 or less. 1 or more and 1.4 or less are especially preferable. If Li / X is 1.1 or more and 1.6 or less, a higher discharge capacity can be obtained.

The ratio (Y / X) of the content molar amount of the element (Y) to the content (100 mol) of the transition metal element (X) in the positive electrode active material is preferably 0.01 to 10%, preferably 0.1 to 5% Is more preferable, and 0.5 to 3% is particularly preferable. If Y / X is not less than the lower limit, excellent cycle characteristics can be easily obtained. If Y / X is not more than the upper limit value, excellent electrical characteristics can be easily obtained.

As the positive electrode active material of the present invention, the compound (1) represented by the following formula (1) is preferable.
_{_{Li 1 + a Y 'b Ni}} c Co d Mn e O 2 + f ··· (1)
In the above formula (1), Y ′ is the element (Y), and a to e are 0.1 ≦ a ≦ 0.6, 0.0001 ≦ b ≦ 0.105, and 0.1 ≦ c ≦, respectively. 0.5, 0 ≦ d ≦ 0.3, 0.2 ≦ e ≦ 0.9, 0.9 ≦ c + d + e ≦ 1.05, and f is the value of Li, element (Y), Ni, Co, and Mn A numerical value determined by a number.
The compound (1) has a high effect of suppressing a decrease in discharge voltage due to the cycle when 0.0001 ≦ b ≦ 0.105. The cause of the effect is not clear, but it is presumed that the crystal structure change due to the cycle is suppressed by the element (Y) being precipitated at the crystal interface of the positive electrode active material.

Since a of the compound (1) becomes a positive electrode active material having a high initial discharge capacity and initial discharge voltage, 0.1 ≦ a ≦ 0.4 is more preferable.
In the compound (1), b is preferably 0.001 ≦ b ≦ 0.1, and more preferably 0.005 ≦ b ≦ 0.03, since both the initial discharge capacity and the cycle characteristics can be achieved.
For the same reason as a, c of the compound (1) is more preferably 0.15 ≦ c ≦ 0.45, and particularly preferably 0.2 ≦ c ≦ 0.4.
For the same reason as a, d of the compound (1) is more preferably 0 ≦ d ≦ 0.2, particularly preferably 0 ≦ d ≦ 0.15.
For the same reason as a, e of the compound (1) is more preferably 0.35 ≦ e ≦ 0.85, and particularly preferably 0.4 ≦ e ≦ 0.8.

According to the production method of the present invention described above, a positive electrode active material having excellent cycle characteristics and a small decrease in discharge voltage can be obtained. Although the factor for obtaining the positive electrode active material by the production method of the present invention is not clear, the specific surface area of the carbonate compound obtained in the step (I) is large, and the carbonate compound and the aqueous solution (C) are used in the step (II). When mixing, it is considered that the aqueous solution (C) can penetrate uniformly into the pores of the carbonate compound. Thereby, it is considered that the positive electrode active material in which the element (Y) is uniformly diffused and distributed to the inside of the particles is obtained by the firing in the step (IV).

<Positive electrode for lithium ion secondary battery>
The positive electrode for a lithium ion secondary battery of the present invention has a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. A well-known aspect can be employ | adopted for the positive electrode for lithium ion secondary batteries of this invention except using the positive electrode active material obtained with the manufacturing method of this invention.

[Positive electrode current collector]
Examples of the positive electrode current collector include an aluminum foil and a stainless steel foil.

[Positive electrode active material layer]
The positive electrode active material layer is a layer containing a positive electrode active material obtained by the production method of the present invention, a conductive material, and a binder. The positive electrode active material layer may contain other components such as a thickener as necessary.
Examples of the conductive material include carbon materials such as acetylene black, graphite, and ketjen black. The conductive material may be one type or two or more types.
Examples of the binder include fluorine-based resins (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyolefins (polyethylene, polypropylene, etc.), polymers having unsaturated bonds, and copolymers (styrene-butadiene rubber, isoprene rubber). , Butadiene rubber, etc.), acrylic acid polymers and copolymers (acrylic acid copolymers, methacrylic acid copolymers, etc.). The binder may be one type or two or more types.
The positive electrode active material may be one type or two or more types.

Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and polyvinylpyrrolidone. One thickener may be used, or two or more thickeners may be used.

[Method for producing positive electrode for lithium ion secondary battery]
The manufacturing method of the positive electrode for lithium ion secondary batteries can employ | adopt a well-known manufacturing method except using the positive electrode active material obtained by the manufacturing method of this invention. For example, the following method is mentioned as a manufacturing method of the positive electrode for lithium ion secondary batteries.
A positive electrode active material, a conductive material and a binder are dissolved or dispersed in a medium to obtain a slurry, or a positive electrode active material, a conductive material and a binder are kneaded with a medium to obtain a kneaded product. Subsequently, the positive electrode active material layer is formed by coating the obtained slurry or kneaded material on the positive electrode current collector.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention has the above-mentioned positive electrode for lithium ion secondary batteries of this invention, a negative electrode, and a non-aqueous electrolyte.

[Negative electrode]
The negative electrode is formed by forming a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector.
Examples of the negative electrode current collector include metal foils such as nickel foil and copper foil.
The negative electrode active material may be any material that can occlude and release lithium ions at a relatively low potential. For example, an oxide mainly composed of lithium metal, lithium alloy, carbon material, periodic table 14 or group 15 metal. , Silicon carbide compounds, silicon oxide compounds, titanium sulfide, boron carbide compounds and the like. Further, as the negative electrode active material, iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, tin oxide, and other oxides and other nitrides may be used.

Examples of the carbon material for the negative electrode active material include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, and glassy carbons. Organic polymer compound fired bodies obtained by firing and polymerizing organic polymer compounds (phenol resin, furan resin, etc.) at an appropriate temperature, carbon fibers, activated carbon, carbon blacks and the like.
Examples of the metal of Group 14 of the periodic table include Si and Sn. Among these, Si is preferable as the metal of Group 14 of the periodic table.

The negative electrode is obtained, for example, by preparing a slurry by mixing a negative electrode active material with an organic solvent, applying the prepared slurry to a negative electrode current collector, drying, and pressing.

Examples of the non-aqueous electrolyte include a non-aqueous electrolyte obtained by dissolving an electrolyte salt in an organic solvent, a solid electrolyte containing an electrolyte salt, a solid electrolyte obtained by mixing or dissolving an electrolyte salt in a polymer electrolyte, a polymer compound, and the like. Or a gel electrolyte etc. are mentioned.

As the organic solvent, known organic solvents for non-aqueous electrolytes can be employed, for example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, Examples thereof include γ-butyrolactone, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, acetic acid ester, butyric acid ester, and propionic acid ester. Among these, from the viewpoint of voltage stability, the organic solvent is preferably a cyclic carbonate such as propylene carbonate, or a chain carbonate such as dimethyl carbonate or diethyl carbonate. 1 type may be sufficient as an organic solvent, and 2 or more types may be sufficient as it.

As the solid electrolyte, any material having lithium ion conductivity may be used, and either an inorganic solid electrolyte or a polymer solid electrolyte may be used.
Examples of the inorganic solid electrolyte include lithium nitride and lithium iodide.
Examples of the polymer solid electrolyte include an electrolyte containing an electrolyte salt and a polymer compound that dissolves the electrolyte salt. Examples of the polymer compound that dissolves the electrolyte salt include ether polymer compounds (poly (ethylene oxide), cross-linked poly (ethylene oxide), etc.), poly (methacrylate) ester polymer compounds, and acrylate polymer compounds. Etc.

The matrix of the gel electrolyte may be any matrix that absorbs the non-aqueous electrolyte and gels, and various polymer compounds can be used. Examples of the polymer compound include fluorine-based polymer compounds (poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), etc.), polyacrylonitrile, a copolymer of polyacrylonitrile, an ether-based compound, and the like. And high molecular compounds (polyethylene oxide, polyethylene oxide copolymers, and crosslinked products of the copolymers, etc.). Examples of the monomer copolymerized with polyethylene oxide include methyl methacrylate, butyl methacrylate, methyl acrylate, and butyl acrylate.
As the matrix of the gel electrolyte, a fluorine-based polymer compound is particularly preferable among the polymer compounds from the viewpoint of stability against redox reaction.

As the electrolyte salt, known ones used in lithium ion secondary batteries can be used, and examples thereof include LiClO ₄ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, and the like.

The shape of the lithium ion secondary battery is not particularly limited, and shapes such as a coin shape, a sheet shape (film shape), a folded shape, a wound type bottomed cylindrical shape, a button shape, and the like can be appropriately selected depending on the application.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description. Examples 1 to 8 are examples, and examples 9 to 18 are comparative examples.
[Specific surface area (SSA)]
The specific surface area of the positive electrode active material was measured by a BET (Brunauer, Emmett, Teller) method using a specific surface area measuring device (device name: HM model-1208) manufactured by Mountec.
[Average particle diameter (D ₅₀ )]
The particle size (D ₅₀ ) of the positive electrode active material is determined by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like, and measuring the scattering particle size distribution (HORIBA: laser diffraction / scattering particle size distribution measurement). The measurement was performed using the apparatus Partica LA-950VII. In the cumulative volume distribution curve in which the total volume of the particle size distribution obtained on a volume basis was 100%, 50% was defined as the volume-based cumulative 50% diameter (D ₅₀ ).

[Composition analysis (Ni, Co, Mn)]
As the composition of the carbonate compound, the Ni ratio, the Co ratio, and the Mn ratio with respect to the total of Ni, Co, and Mn were analyzed. The analysis was performed with a plasma emission analyzer (manufactured by SII Nanotechnology, model name: SPS3100H).

[Example 1]
Step (I):
Nickel sulfate (II) hexahydrate, cobalt sulfate (II) heptahydrate, and manganese sulfate (II) pentahydrate, the Ni ratio is 33 mol% and the Co ratio is 4.1 mol% Then, 2 kg of an aqueous sulfate solution was prepared by dissolving in distilled water so that the Mn ratio was 62.9 mol% and the total amount of sulfate was 1.5 mol / kg. Further, 99.1 g of ammonium sulfate was dissolved in 900.9 g of distilled water to prepare a 0.75 mol / kg ammonium sulfate aqueous solution. Moreover, 381.2 g of sodium carbonate was dissolved in 2018.8 g of distilled water to prepare an aqueous carbonate solution (pH adjusting solution).
Subsequently, distilled water is put into a 2 L baffled glass mixing tank, heated to 50 ° C. with a mantle heater, and stirred with a paddle type stirring blade, the aqueous sulfate solution is 5.0 g / min, and the aqueous ammonium sulfate solution is added. Each was added for 6 hours at a rate of 0.5 g / min. During the addition of the sulfate aqueous solution, a carbonate aqueous solution (pH adjusting solution) was added so as to keep the pH in the mixing tank at 8.0, thereby precipitating a carbonate compound containing Ni, Co and Mn. Further, during the precipitation reaction, the liquid was continuously extracted using a filter cloth so that the amount of liquid in the mixing tank did not exceed 2 L.
In order to remove impurity ions from the obtained carbonate compound, pressure filtration and dispersion in distilled water were repeated to wash the carbonate compound. When the electrical conductivity of the filtrate reached 20 mS / m, the washing was finished and dried at 120 ° C. for 15 hours to obtain a carbonate compound. Table 1 shows the composition analysis results of Ni, Co, and Mn of the obtained carbonate compound.

Step (II) and step (III):
In 18 g of the obtained carbonate compound, the ratio (Y / X) of the total molar amount of the element (Y) to the total amount (100 mol) of the transition metal element (X) contained in the carbonate compound is 1 mol%. Thus, an aqueous solution in which 0.077 g of a basic aluminum lactate salt (trade name “Taxelum KML16”, manufactured by Taki Chemical Co., Ltd.) was dissolved in 3.6 g of distilled water was spray-coated. Then, it dried at 90 degreeC for 3 hours, and obtained the precursor compound.

Process (IV):
The precursor compound so that the molar ratio (Li / X) of the total amount of Li contained in lithium carbonate is 1.275 with respect to the total amount of the transition metal element (X) contained in the precursor compound. And 7.15 g of lithium carbonate were mixed. Further, using an electric furnace (FO510, manufactured by Yamato Scientific Co., Ltd.), while the atmosphere is flowing at 133 mL / min per 1 L of internal volume, pre-baking is performed at 600 ° C. for 5 hours, followed by main baking at 850 ° C. for 16 hours. An active material was obtained.
The specific surface area of the obtained positive electrode active material is shown in Table 1.

[Examples 2 to 17]
In the step (II), a positive electrode active material was obtained in the same manner as in Example 1 except that the compound shown in Table 1 was used instead of the basic aluminum lactate salt and the element (Y) shown in Table 1 was doped.
Table 1 shows the composition analysis result of the obtained carbonate compound and the specific surface area of the positive electrode active material.

[Example 18]
A positive electrode active material was obtained in the same manner as in Example 1 except that Step (II) and Step (III) were not performed.
Table 1 shows the composition analysis result of the obtained carbonate compound and the specific surface area of the positive electrode active material.

In addition, the raw material compound in Table 1 is a compound used for dope of an element (Y) in process (II). Moreover, the symbol in Table 1 shows the following meaning.
KML16: Trade name “Takiseram KML16”, manufactured by Taki Chemical Co., Ltd.
AT50: Product name “Adelite”, manufactured by ADEKA Corporation.
Bay coat 20: Trade name “Bay coat 20”, manufactured by Nippon Light Metal Co., Ltd.
Ti (OBu) ₄ : tetra-n-butyl titanate.

[Evaluation of cycle characteristics]
(Manufacture of positive electrode sheet)
A positive electrode active material obtained in each example, acetylene black as a conductive material, and polyvinylidene fluoride (binder) were added to N-methylpyrrolidone at a mass ratio of 80:10:10 to prepare a slurry.
Next, the slurry was coated on one side of an aluminum foil (positive electrode current collector) having a thickness of 20 μm with a doctor blade, dried at 120 ° C., and then subjected to roll press rolling twice to produce a positive electrode sheet. .
(Manufacture of lithium ion secondary batteries)
The obtained positive electrode sheet was punched into a circular shape with a diameter of 18 mm as a positive electrode, and a stainless steel simple sealed cell type lithium ion secondary battery was assembled in a glove box under argon. A stainless steel plate having a thickness of 1 mm was used as the negative electrode current collector, and a metal lithium foil having a thickness of 500 μm was formed on the negative electrode current collector to form a negative electrode. As the separator, porous polypropylene having a thickness of 25 μm was used. In addition, a solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a mass ratio of 1: 1 so that the concentration was 1 mol / dm ³ was used as an electrolytic solution.
(Measurement of discharge capacity maintenance rate)
The obtained lithium ion secondary battery was connected to a charge / discharge evaluation apparatus (manufactured by Toyo System Co., Ltd., apparatus name: TOSCAT-3000), and charged / discharged at a load current of 0.1 C per 1 g of the positive electrode active material to activate. Processed. Thereafter, a charging / discharging cycle of charging to 4.5 V with 1 C load current per 1 g of the positive electrode active material and discharging to 2.0 V with 1 C load current per 1 g of the positive electrode active material was repeated 100 times. In addition, 1C means the amount of current that can discharge the theoretical capacity of the positive electrode in one hour.
The discharge capacity at the time of the activation treatment is “initial discharge capacity”, the discharge capacity at the third cycle is “pre-cycle discharge capacity”, the discharge capacity at the 100th cycle is “post-cycle discharge capacity”, and the post-cycle discharge capacity is The ratio of discharge capacity was defined as “discharge capacity maintenance ratio”.
Table 2 shows the measurement results of the initial discharge capacity, the pre-cycle discharge capacity, the post-cycle discharge capacity, and the discharge capacity retention rate in each example.
Table 3 shows the composition represented by the above formula (1) and the particle diameter (D ₅₀ ) (μm) of the positive electrode active material obtained in each example.

As shown in Table 2, Examples 1 to 8 using positive electrode active materials doped with at least one selected from the group consisting of Al, F, Si, Zr, Y, Mo, Ce, and Ca as elements (Y) The lithium ion secondary battery has a high discharge capacity retention rate compared to the lithium ion secondary batteries of Examples 9 to 17 doped with an element other than the element (Y) and Example 18 not doped, and the cycle Excellent characteristics.

According to the present invention, a positive electrode active material for a lithium ion secondary battery having a high discharge capacity and excellent cycle characteristics can be obtained. The positive electrode active material can be suitably used for forming a positive electrode for a lithium ion secondary battery used for electronic devices such as mobile phones and small and light lithium ion secondary batteries for vehicles.
It should be noted that the entire contents of the specification, claims and abstract of Japanese Patent Application No. 2013-061398 filed on March 25, 2013 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims

A method for producing a positive electrode active material, comprising the following steps (I) to (IV):
(I) at least one sulfate (A) selected from the group consisting of Ni sulfate, Co sulfate and Mn sulfate;
At least one carbonate (B) selected from the group consisting of Na carbonate and K carbonate,
Mix in the state of aqueous solution,
Depositing a carbonate compound containing at least one transition metal element (X) selected from the group consisting of Ni, Co and Mn.
(II) A step of mixing the carbonate compound with an aqueous solution (C) containing at least one element (Y) selected from the group consisting of Al, F, Si, Zr, Y, Mo, Ce and Ca.
(III) A step of obtaining a precursor compound by volatilizing water from a mixture of the carbonate compound and the aqueous solution (C).
(IV) A step of mixing the precursor compound and the lithium compound and baking at 500 to 1000 ° C.
2. The method for producing a positive electrode active material according to claim 1, wherein in step (I), the aqueous solution of the sulfate (A) contains Ni sulfate, Co sulfate, and Mn sulfate. 3.
The concentration of the transition metal element (X) composed of Mn, Ni and Co in the aqueous solution of the sulfate (A) in the aqueous solution of the sulfate (A) is 0.1 to 3 mol / kg in the step (I). The manufacturing method of the positive electrode active material of description.
The positive electrode active material according to any one of claims 1 to 3, wherein in step (I), the concentration of the carbonate (B) in the aqueous solution of the carbonate (B) is 0.1 to 2 mol / kg. Manufacturing method.
In the step (II), the ratio of the total molar amount of the element (Y) contained in the aqueous solution (C) to the total amount (100 mol) of the transition metal element (X) contained in the carbonate compound (Y / X The method for producing a positive electrode active material according to any one of claims 1 to 4, wherein 0.01) to 10% is 0.01 to 10%.
6. The production of a positive electrode active material according to claim 1, wherein the concentration of the compound containing the element (Y) in the aqueous solution (C) is 0.1 to 50% by mass in the step (II). Method.
In the step (II), the compound containing the element (Y) is composed of a basic aluminum lactate salt, ammonium hydrogen fluoride, colloidal silica, ammonium zirconium carbonate, yttrium nitrate, hexaammonium heptamolybdate, cerium nitrate, and calcium nitrate. The method for producing a positive electrode active material according to claim 6, wherein the positive electrode active material is one or more selected from the group.
The method for producing a positive electrode active material according to any one of claims 1 to 7, wherein in step (II), the carbonate compound and the aqueous solution (C) are mixed by a spray coating method.
In step (IV), the ratio (Li / X) of the total molar amount of Li contained in the lithium compound to the total molar amount of the transition metal element (X) contained in the precursor compound is 1.1 or more. The method for producing a positive electrode active material according to any one of claims 1 to 8.
The process according to any one of claims 1 to 9, wherein in the step (IV), the precursor compound and the lithium compound are mixed and pre-baked at 400 to 700 ° C, followed by main baking at 700 to 1000 ° C. The manufacturing method of the positive electrode active material of description.
The method for producing a positive electrode active material according to any one of claims 1 to 10, wherein the obtained positive electrode active material is a compound (1) represented by the following formula (1).
Li 1 + a Y 'b Ni c Co d Mn e O 2 + f ··· (1)
(In the formula (1), Y ′ is the element (Y), and a to e are 0.1 ≦ a ≦ 0.6, 0.0001 ≦ b ≦ 0.105, 0.1 ≦ c, respectively. ≦ 0.5, 0 ≦ d ≦ 0.3, 0.2 ≦ e ≦ 0.9, 0.9 ≦ c + d + e ≦ 1.05, and f is Li, element (Y), Ni, Co, and Mn. (The number is determined by the valence.)
A positive electrode current collector, and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer is obtained by the production method according to any one of claims 1 to 11. The positive electrode for lithium ion secondary batteries containing the obtained positive electrode active material, the electrically conductive material, and the binder.
A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 12, a negative electrode, and a nonaqueous electrolyte.