JP6745929B2 - Method for producing lithium-containing composite oxide, positive electrode for lithium-ion secondary battery, and lithium-ion secondary battery - Google Patents

Description

The present invention relates to a method for producing a lithium-containing composite oxide, a positive electrode for a lithium-ion secondary battery containing the lithium-containing composite oxide obtained by the production method, and a lithium-ion secondary battery having the positive electrode.

As a positive electrode active material included in the positive electrode of a lithium ion secondary battery, a lithium-containing composite oxide, particularly LiCoO _2, is well known. However, in recent years, portable electronic devices and vehicle-mounted lithium-ion secondary batteries have been required to be smaller and lighter, further improving the discharge capacity per unit mass (hereinafter, simply referred to as discharge capacity), There is a demand for further improvement in characteristics (hereinafter, also referred to as cycle characteristics) in which the discharge capacity and the average discharge voltage do not decrease after repeating the charge/discharge cycle.

As a positive electrode active material (lithium-containing composite oxide) capable of improving the discharge capacity and cycle characteristics of a lithium-ion secondary battery, LiCo _1-2x Ni _x Mn _x O ₂ (where 0<x≦0.5 is satisfied. ), a so-called ternary positive electrode active material is proposed. The following method has been proposed as a method for producing a ternary-type positive electrode active material capable of further improving the discharge capacity of a lithium ion secondary battery.
(1) Lithium-containing composite material in which a precursor containing Li, Ni, Mn, and Co is subjected to a primary heat treatment in an oxidizing atmosphere at 300° C. or higher and lower than 800° C., and then a secondary heat treatment is performed in a non-oxidizing atmosphere at 800° C. or higher. Oxide production method (Patent Document 1).

Further, as a positive electrode active material capable of further increasing the discharge capacity of a lithium ion secondary battery, a positive electrode active material having a high content ratio of Li and Mn, that is, a so-called lithium-rich positive electrode active material has been attracting attention. As the lithium-rich positive electrode active material, for example, the followings have been proposed.
(2) It has an α-NaFeO ₂ type crystal structure and is Li _1+α Me _1-α O ₂ (where Me is a transition metal element containing Co, Ni and Mn, α>0, and is relative to the transition metal element). The molar ratio of Li (Li/Me) is 1.2 to 1.6, the molar ratio of Co to the transition metal element (Co/Me) is 0.02 to 0.23, and the ratio of Mn to the transition metal element is A positive electrode active material represented by a molar ratio (Mn/Me) of 0.62 to 0.72 (Patent Document 2).
_{(3) xLi 2 MnO 3 ·} (1-x) LiNi u + Δ Mn u-Δ Co w A y O 2 ( however, A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, One or more elements selected from Ca, Ce, Y, Nb, Cr, Fe and V, x is 0.03 to 0.47, Δ is −0.3 to 0.3, and 2u+w+y. =1, w is 0 to 1, u is 0 to 0.5, and y<0.1.) A lithium-rich composite metal oxide (Patent Document 3).

JP, 2007-214118, A International Publication No. 2012/091015 International Publication No. 2011/031546

However, the ternary positive electrode active material obtained by the method (1) has a low Li and Mn content. Therefore, a lithium ion secondary battery having a positive electrode containing the ternary positive electrode active material cannot sufficiently meet the recent demand for improvement in discharge capacity.
The lithium-rich positive electrode active materials (2) and (3) contain a large amount of Mn as a metal element. Mn in the lithium-rich positive electrode active material is likely to be eluted in the electrolytic solution when it comes into contact with a decomposition product generated from the electrolytic solution by charging at a high voltage. When Mn is eluted in the electrolytic solution, the crystal structure of the positive electrode active material becomes unstable. Therefore, a lithium-ion secondary battery having a positive electrode containing a lithium-rich positive electrode active material is likely to have deteriorated cycle characteristics, especially due to repeated charging/discharging, and improvement of the characteristics is required.

When the present inventors examined the lithium-rich positive electrode active material, the discharge capacity and cycle characteristics of the lithium-ion secondary battery having a positive electrode containing the lithium-rich positive electrode active material were I found that I was dependent. Specifically, when the specific surface area of the lithium-rich positive electrode active material is high, the discharge capacity increases, but the cycle characteristics tend to deteriorate. On the other hand, when the specific surface area of the lithium-rich positive electrode active material is low, the discharge capacity tends to decrease and the cycle characteristics tend to improve. Therefore, it has been difficult to improve both the discharge capacity and the cycle characteristics of the lithium-ion secondary battery with the conventional lithium-rich positive electrode active material.

The present invention relates to a method for producing a lithium-containing composite oxide used in a lithium-rich positive electrode active material capable of enhancing the discharge capacity and cycle characteristics of a lithium-ion secondary battery; the lithium-containing composite oxide obtained by the method. An object of the present invention is to provide a positive electrode for a lithium-ion secondary battery containing: and a lithium-ion secondary battery having the positive electrode.

The inventors of the present invention, when producing a lithium-containing composite oxide containing a large amount of Li and Mn, control the specific surface area of the hydroxide within a specific range to obtain a mixture of the hydroxide and the lithium compound. By adjusting the heat treatment conditions, specifically the atmosphere and the temperature, it is possible to obtain a lithium-containing composite oxide capable of enhancing both the discharge capacity and the cycle characteristics of the lithium-ion secondary battery even if the specific surface area is low. The inventors have found that and have reached the present invention.

That is, the gist of the present invention lies in the following [1] to [10].
[1] Li _1+a MO _b (where M is two or more metal elements (excluding Li)), at least two of which are Ni and Mn, and the molar ratio of Mn to Ni. (Mn/Ni) is 1.1 or more, a is more than 0 and 0.6 or less, and b is the number of moles of O necessary to satisfy the valences of Li and M.). A method for producing a lithium-containing composite oxide, comprising:
A method for producing a lithium-containing composite oxide, comprising the following steps (a) to (d).
(A) A step of obtaining a hydroxide containing Ni and Mn, having a molar ratio of Mn to Ni (Mn/Ni) of 1.1 or more and having a specific surface area of 5 to 80 m ² /g.
(B) The lithium compound and the hydroxide are so adjusted that the molar ratio (Li/M) of Li to the total number of moles of metal elements other than Li contained in the hydroxide is more than 1 and not more than 1.6. Mixing to obtain a mixture.
(C) A step of obtaining a primary heat-treated product by heat-treating the mixture at a temperature of 500 to 700° C. in an atmosphere having an oxygen concentration of 5% by volume or more.
(D) A step of subjecting the primary heat-treated product to secondary heat treatment at a temperature of 800° C. or higher and lower than 950° C. in an atmosphere having an oxygen concentration of less than 5% by volume to obtain the lithium-containing composite oxide.

[2] The method for producing a lithium-containing composite oxide according to [1], wherein the atmosphere in the step (d) has an oxygen concentration of less than 5% by volume and the balance is nitrogen.
[3] The method for producing a lithium-containing composite oxide according to [1] or [2], wherein the step (d) is performed in a closed container.
[4] The method for producing a lithium-containing composite oxide according to any one of [1] to [3], further including the following step (e).
(E) A step of heat-treating the lithium-containing composite oxide after the step (d) at a temperature of 400 to 800° C. in an atmosphere having an oxygen concentration of 5% by volume or more.
[5] The method for producing a lithium-containing composite oxide according to any one of [1] to [4], wherein the lithium-containing composite oxide is a compound represented by the following formula (II).
Li(Li _a Ni _x Co _y Mn _z )O _b ... (II)
However, a is more than 0 and 0.6 or less, x is 0.1 to 0.5, y is 0 to 0.3, z is 0.36 to 0.9, and x+y+z=1. And z/x is 1.1 or more, and b is the number of moles of O necessary to satisfy the valences of Li and M.
[6] The method for producing a lithium-containing composite oxide according to any one of [1] to [5], wherein the lithium-containing composite oxide has a specific surface area of 0.9 to ⁴ m ² /g.
[7] The method for producing a lithium-containing composite oxide according to any one of [1] to [6], wherein the volume-based cumulative 50% diameter D _{50 of the} hydroxide is 3 to 18 μm.
[8] The lithium-containing composite oxide is a secondary particle in which a plurality of primary particles are aggregated, and the volume-based cumulative 50% diameter D ₅₀ of the secondary particle is 3 to 18 μm. [7] A method for producing a lithium-containing composite oxide according to any one of [7].
[9] A positive electrode for a lithium-ion secondary battery, containing the lithium-containing composite oxide obtained by the production method according to any one of [1] to [8].
[10] A lithium ion secondary battery including the positive electrode for a lithium ion secondary battery according to [9].

The manufacturing method of the present invention can provide a lithium-containing composite oxide capable of enhancing both the discharge capacity and the cycle characteristics of a lithium ion secondary battery.
According to the positive electrode for a lithium ion secondary battery of the present invention, both the discharge capacity and the cycle characteristics of the lithium ion secondary battery can be improved.
The lithium ion secondary battery of the present invention has high discharge capacity and cycle characteristics.

The following definitions of terms apply throughout the specification and claims.
The “lithium-containing composite oxide containing a large amount of Li and Mn” means that the respective contents of Li and Mn are in a molar ratio with respect to the total amount (M) of metal elements other than Li in the lithium-containing composite oxide. , Li/M is more than 1 and Mn/M is 0.36 or more.
"Atmosphere in which the oxygen concentration is in a specific range and the balance is nitrogen or argon" means that the components other than oxygen are substantially nitrogen or argon, and the components other than oxygen, nitrogen and argon influence the heat treatment. Means an atmosphere that may be included in a range that does not give.
“D ₅₀ ”means a particle diameter at a point at which 50% is reached in a cumulative volume distribution curve where the total volume distribution of particle size distribution is 100%, that is, a volume-based cumulative 50% diameter. The particle size distribution is obtained from the frequency distribution and cumulative volume distribution curve measured by a laser scattering particle size distribution measuring device. The particle size is measured by sufficiently dispersing the powder in an aqueous medium by ultrasonication or the like and measuring the particle size distribution (for example, using a laser diffraction/scattering type particle size distribution measuring device).
The notation “Li” means that the element is not the elemental metal but Li element unless otherwise specified. The same applies to the notation of other elements such as Ni, Co and Mn.
The composition analysis of the lithium-containing composite oxide and the hydroxide is performed by the inductively coupled plasma analysis method (hereinafter abbreviated as ICP). Moreover, the ratio of the elements of the lithium-containing composite oxide is a value in the lithium-containing composite oxide before the initial charging (also referred to as activation treatment).

<Lithium-containing composite oxide>
The lithium-containing composite oxide obtained by the production method of the present invention (hereinafter referred to as the present production method) is a compound represented by the following formula (I).
Li _1+a MO _b ...(I)

b is the number of moles of oxygen (O) required to satisfy the valences of Li and M.
M represents two or more metal elements (excluding Li), and at least two of the metal elements are Ni and Mn, and may contain other metal elements as necessary.
Examples of other metal elements include Mg, Ca, Ba, Sr, Al, Co, Cr, Fe, Ti, Zr, Y, Nb, Mo, Ta, W, Ce and La. From the viewpoint of easily obtaining a high discharge capacity, Mg, Al, Co, Cr, Fe, Ti or Zr is preferable, and Co is more preferable.
When the other metal element is Co, the lithium-containing composite oxide may contain Co in a molar ratio of Co/M of 0.3 or less.
When the other metal element is other than Co, the total content of the other metal elements other than Co is (molar ratio)/(the total content of the other metal element other than Co)/M of the lithium-containing composite oxide is 0. You may contain in the quantity of 05 or less.

The molar ratio of Mn to Ni (Mn/Ni) in the lithium-containing composite oxide is 1.1 or more, and within this range, the lithium-containing composite oxide is used as a positive electrode active material of a lithium ion secondary battery In this case, the discharge capacity can be increased. In order to increase the charge/discharge efficiency of the lithium ion secondary battery, Mn/Ni of the lithium-containing composite oxide is preferably 5 or less. Mn/Ni is more preferably 1.2 to 4.0, further preferably 1.3 to 3.5.

A in the formula (I) is more than 0 and not more than 0.6, preferably 0.1 to 0.5, and more preferably 0.1 to 0.45. When a is at least the above lower limit value, the discharge capacity of the lithium ion secondary battery having the lithium-containing composite oxide of formula (I) can be increased. If a is not more than the upper limit value, the amount of free lithium on the surface of the lithium-containing composite oxide can be reduced in the present production method. If the amount of free lithium is large, charge/discharge efficiency and rate characteristics may be deteriorated, or decomposition of the electrolytic solution may be promoted, which may cause gas generation of decomposition products.

As the lithium-containing composite oxide, a compound represented by the following formula (II) is preferable from the viewpoint that a lithium ion secondary battery having a high initial discharge capacity and a high initial discharge voltage can be obtained.
Li(Li _a Ni _x Co _y Mn _z )O _b ... (II)

A in formula (II) is the same as a in formula (I).

X in the formula (II) is 0.1 to 0.5, preferably 0.15 to 0.45, and more preferably 0.2 to 0.4. When x is in the above range, the discharge capacity and charge/discharge efficiency of the lithium ion secondary battery having the lithium-containing composite oxide of the formula (II) can be increased.

Y in the formula (II) is 0 to 0.3, preferably 0 to 0.2, and more preferably 0 to 0.15. When y is within the above range, the discharge capacity and charge/discharge efficiency of the lithium ion secondary battery having the lithium-containing composite oxide of the formula (II) can be increased.

Z of the formula (II) is 0.36 to 0.9, preferably 0.5 to 0.8, and more preferably 0.5 to 0.7. When z is in the above range, the discharge capacity and charge/discharge efficiency of the lithium ion secondary battery having the lithium-containing composite oxide of the formula (II) can be increased.

In the formula (II), the total amount (x+y+z) of x, y and z is 1. z/x is the same as the molar ratio of Mn to Ni in the lithium-containing composite oxide (Mn/Ni).

The lithium-containing composite oxide is preferably secondary particles in which a plurality of primary particles are aggregated.
The D ₅₀ of the secondary particles of the lithium-containing composite oxide is preferably 3 to 18 μm, more preferably 3 to 15 μm, and particularly preferably 3 to 12 μm. When the D _{50 of the} secondary particles of the lithium-containing composite oxide is within the above range, the lithium ion secondary battery can have a high discharge capacity.

The D ₅₀ of the primary particles of the lithium-containing composite oxide is preferably 10 to ₅₀₀ nm. When the D _{50 of the} primary particles of the lithium-containing composite oxide is within the above range, the electrolyte solution can easily be sufficiently distributed between the positive electrode active materials in the positive electrode when the lithium ion secondary battery is manufactured.

The specific surface area of the lithium-containing composite oxide is preferably 0.9 to ⁴ m ² /g, more preferably 1 to ³ m ² /g. When the specific surface area of the lithium-containing composite oxide is within the above range, both the discharge capacity and the cycle characteristics of the lithium ion secondary battery can be increased. If the specific surface area of the lithium-containing composite oxide is less than 0.9 m ² /g, the discharge capacity may decrease. If the specific surface area of the lithium-containing composite oxide exceeds 4 m ² /g, the cycle characteristics may deteriorate.
The specific surface area of the lithium-containing composite oxide is a value measured by the BET method (Brunauer, Emmet, Teller). Nitrogen is used as an adsorption gas in the measurement of the specific surface area. Specifically, it is calculated by the method described in the examples.

The lithium-containing composite oxide can be used as a positive electrode active material for a lithium ion secondary battery, either as it is or after surface treatment.
The surface treatment is a treatment for adhering a substance (surface-adhering substance) having a composition different from that of the substance forming the lithium-containing composite oxide onto the surface of the lithium-containing composite oxide. Examples of the surface-adhering substance include oxides (aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, etc.), sulfates (sodium sulfate, potassium sulfate, sulfuric acid). Magnesium, calcium sulfate, aluminum sulfate, etc.), carbonates (calcium carbonate, magnesium carbonate, etc.) and the like.

The amount of the surface-adhering substance is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more, based on the lithium-containing composite oxide. The amount of the surface-adhering substance is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 3% by mass or less, based on the lithium-containing composite oxide. The presence of the surface-adhering substance on the surface of the lithium-containing composite oxide can suppress the oxidation reaction of the non-aqueous electrolytic solution on the surface of the lithium-containing composite oxide and improve the battery life.

The method for producing the lithium-containing composite oxide and the surface treatment of the lithium-containing composite oxide obtained by the production method will be described below.

<Method for producing lithium-containing composite oxide>
This manufacturing method is a method including the following steps (a) to (d).
(A) A step of obtaining a hydroxide containing Ni and Mn, having a molar ratio of Mn to Ni (Mn/Ni) of 1.1 or more and having a specific surface area of 5 to 80 m ² /g.
(B) A lithium compound and a hydroxide are mixed so that the molar ratio (Li/M) of Li to the total number of moles of metal elements other than Li contained in the hydroxide is more than 1 and 1.6 or less. To obtain a mixture.
(C) A step of obtaining a primary heat-treated product by heat-treating the mixture at a temperature of 500 to 700° C. in an atmosphere having an oxygen concentration of 5% by volume or more.
(D) A step of subjecting the primary heat-treated product to secondary heat treatment at a temperature of 800° C. or higher and lower than 950° C. in an atmosphere having an oxygen concentration of less than 5% by volume to obtain a lithium-containing composite oxide.

(Process (a))
The step (a) is a step of obtaining a hydroxide containing Ni and Mn, having a molar ratio of Mn to Ni (Mn/Ni) of 1.1 or more and having a specific surface area of 5 to 80 m ² /g. .. The hydroxide also includes oxyhydroxide which is partially oxidized.
A lithium-containing composite oxide having a high Mn/Ni can be obtained by using the hydroxide. Furthermore, if the hydroxide is used for production, the specific surface area of the lithium-containing composite oxide can be kept within a desired range, and the discharge capacity of the lithium-ion secondary battery having the obtained lithium-containing composite oxide. And both cycle characteristics can be improved.

The metal element contained in the hydroxide contains at least Ni and Mn, and may contain other metal elements as necessary. Examples of other metal elements include Mg, Ca, Ba, Sr, Al, Co, Cr, Fe, Ti, Zr, Y, Nb, Mo, Ta, W, Ce and La. From the viewpoint of easily obtaining a high discharge capacity, Mg, Al, Co, Cr, Fe, Ti or Zr is preferable, and Co is more preferable.

The molar ratio of Mn to Ni contained in the hydroxide (Mn/Ni) is 1.1 or more, preferably 1.1 to 5, more preferably 1.2 to 4, and 1.3 to 3.5. Is more preferable. When the Mn/Ni of the hydroxide is in this range, the discharge capacity is high when the lithium-containing composite oxide produced by using this hydroxide is used as the positive electrode active material of the lithium ion secondary battery. it can.

The D ₅₀ of the hydroxide is preferably 3 to 18 μm, more preferably 3 to 15 μm, and particularly preferably 3 to 12 μm. If D ₅₀ of the hydroxide within the range, the D ₅₀ of the lithium-containing composite oxide in a desired range. The lithium-containing composite oxide having D ₅₀ in the desired range can increase the discharge capacity of the lithium ion secondary battery.

The specific surface area of the hydroxide is 5~80m ² / g, preferably from ^{10~60m 2 / g, 20~40m 2 /} g is more preferable. When the specific surface area of the hydroxide is within the above range, the specific surface area of the obtained lithium-containing composite oxide can be controlled within an appropriate range. The lithium-containing composite oxide having an appropriate specific surface area can improve both the discharge capacity and the cycle characteristics of the lithium ion secondary battery.

As a method for preparing the hydroxide, the coprecipitation method is preferable because it is easy to adjust the ratio of the metal element to a desired range and the specific surface area of the hydroxide is easily adjusted.
The coprecipitation method is a method of precipitating a sparingly soluble compound (coprecipitate) containing a desired two or more kinds of metal elements from a solution containing two or more kinds of metal elements. As an example of the coprecipitation method, an aqueous solution of a metal salt containing a metal element and a pH adjusting solution are added to a reaction tank, mixed, and allowed to react with each other while keeping the pH in the mixed solution constant, to react with the metal element. A method of precipitating a coprecipitate containing When the pH of the mixed solution is 10 or more, the coprecipitate is regarded as a hydroxide.

Examples of the metal salt include nitrates, acetates, chlorides and sulphates of metal elements, and the sulphate is preferable from the viewpoint of relatively low material cost and excellent battery characteristics. As the metal salt used in the present production method, a sulfate of Ni, a sulfate of Mn, and a sulfate of Co are more preferable.

Examples of the sulfate of Ni include nickel (II) sulfate hexahydrate, nickel (II) sulfate heptahydrate, and nickel (II) sulfate ammonium hexahydrate.
Examples of the Co sulfate include cobalt (II) sulfate heptahydrate, cobalt (II) sulfate ammonium hexahydrate, and the like.
Examples of the Mn sulfate include manganese (II) sulfate pentahydrate, ammonium manganese (II) sulfate hexahydrate, and the like.

The total concentration of metal elements in the aqueous solution of the metal salt is preferably 0.1 to 3 mol/kg, more preferably 0.5 to 2.5 mol/kg. When the total concentration of the metal elements is at least the lower limit value described above, the productivity is excellent, which is preferable. When the concentration of the metal element is not more than the upper limit value, the metal salt can be sufficiently dissolved in water, which is preferable.

The aqueous solution of the metal salt may contain an aqueous medium other than water.
Examples of the aqueous medium other than water include methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, butanediol, glycerin and the like. From the viewpoint of safety, environment, handleability, and cost, the proportion of an aqueous medium other than water is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass, and 0 to 100 parts by mass of water. 1 part by mass is particularly preferred.

In the step (a), the pH adjusting liquid is preferably an aqueous solution containing a strong alkali.
As the strong alkali, at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide is preferable.
An aqueous ammonia solution or an aqueous ammonium sulfate solution may be added to the mixed solution in order to adjust the solubility of the metal element.

It is preferable that the aqueous solution of the metal salt and the pH adjusting liquid are mixed while stirring in a reaction tank.
Examples of the stirring device include a three-one motor. Examples of the stirring blade include an anchor type, a propeller type, and a paddle type.
From the viewpoint of accelerating the reaction, the reaction temperature is preferably 20 to 80°C, more preferably 25 to 60°C.

The mixing of the aqueous solution of the metal salt and the pH adjusting liquid is preferably performed under a nitrogen atmosphere or an argon atmosphere from the viewpoint of suppressing the oxidation of hydroxide, and from the viewpoint of cost, it is particularly preferable to perform under a nitrogen atmosphere. preferable.
During the mixing of the aqueous solution of the metal salt and the pH adjusting liquid, it is preferable to keep the pH in the reaction tank at the set pH in the range of 10 to 12 from the viewpoint of appropriately promoting the coprecipitation reaction.

The hydroxide obtained is preferably washed to remove impurity ions. Examples of the washing method include a method in which pressure filtration and dispersion in distilled water are repeated. In the case of washing, it is preferable to repeat until the electric conductivity of the supernatant liquid or the filtrate when the hydroxide is dispersed in distilled water becomes 50 mS/m or less, more preferably 20 mS/m or less. preferable.

After washing, the hydroxide may be dried if necessary.
The drying temperature is preferably 60 to 200°C, more preferably 80 to 130°C. When the drying temperature is at least the lower limit value, the drying time can be shortened. When the drying temperature is at most the above upper limit value, the progress of oxidation of hydroxide can be suppressed.
The drying time may be appropriately set depending on the amount of hydroxide, and is preferably 1 to 300 hours, more preferably 5 to 120 hours.

(Process (b))
In the step (b), the lithium compound and the hydroxide obtained in the step (a) have a molar ratio (Li/M) of Li of 1 to the total number of moles of metal elements other than Li contained in the hydroxide. This is a step of obtaining a mixture by mixing so as to have a super 1.6 or less.

The lithium compound is not particularly limited as long as it is mixed with a hydroxide and heat-treated in steps (c) and (d) described below to obtain a lithium-containing composite oxide. As the lithium compound, lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate are preferable, and lithium carbonate is more preferable because it is inexpensive.

The amount of the lithium compound in the mixture is appropriately adjusted according to the total number of moles of metal elements contained in the hydroxide. When Li/M is more than 1, a lithium-containing composite oxide containing a large amount of Li and Mn can be obtained. When Li/M is 1.6 or less, Li (free lithium) that does not contribute to the crystal structure of the lithium-containing composite oxide when fired can be reduced. If the amount of free lithium increases, the charge/discharge efficiency and rate characteristics of the lithium-ion secondary battery may deteriorate, and the decomposition of the electrolyte is promoted during use of the lithium-ion secondary battery, causing the generation of decomposition product gas. May be. 1.1-1.5 are preferable and, as for Li/M, 1.1-1.45 are more preferable.

(Process (c))
The step (c) is a step of primary heat treating the mixture obtained in the step (b) at a temperature of 500 to 700° C. in an atmosphere having an oxygen concentration of 5% by volume or more to obtain a primary heat-treated oxide product. ..

The primary heat treatment is performed in an electric furnace, a continuous firing furnace, a rotary kiln or the like.
The primary heat treatment may be performed in an atmosphere having an oxygen concentration of 5% by volume or more, and is preferably performed in air. In addition, the primary heat treatment is more preferably performed while supplying air.

The temperature of the primary heat treatment is 500 to 700°C, preferably 500 to 600°C. When the temperature of the primary heat treatment is within the above range, the reaction between the hydroxide and the lithium compound can proceed uniformly, and a primary heat treatment product with high crystallinity can be obtained.
The time of the primary heat treatment is preferably 3 to 10 hours. When the time of the primary heat treatment is within the above range, the reaction between the hydroxide and the lithium compound can be sufficiently advanced, and the primary heat treatment product having high crystallinity can be obtained.
When the crystallinity of the primary heat-treated product is low and the primary heat-treated product has a different phase, it may cause a decrease in the discharge capacity of the lithium ion secondary battery.

(Process (d))
The step (d) is a step of secondarily heat-treating the primary heat-treated product at a temperature of 800° C. or higher and lower than 950° C. in an atmosphere having an oxygen concentration of less than 5% by volume to obtain a lithium-containing composite oxide.

The secondary heat treatment of the step (d) is preferably performed in a container capable of hermetically closing the furnace, and more preferably performed in a container capable of evacuating the furnace. Examples of the container include a Tammann tube type atmospheric electric furnace and the like. By using the container, the secondary heat treatment can be performed while maintaining the atmosphere in which the oxygen concentration is less than 5% by volume.

The oxygen concentration in the atmosphere of the secondary heat treatment in step (d) is less than 5% by volume, preferably 1% by volume or less, more preferably 0.5% by volume or less, and further preferably 0.01% by volume or less. When the oxygen concentration in the atmosphere of step (d) is within the above range, the discharge capacity and cycle characteristics of the lithium ion secondary battery having the positive electrode containing the lithium-containing composite oxide after the secondary heat treatment can be improved.

The atmosphere for the secondary heat treatment in step (d) is preferably an atmosphere in which the oxygen concentration is within the above range and the balance is an inert gas. As such an atmosphere, an atmosphere in which the oxygen concentration is within the above range and the balance is nitrogen or argon is preferable. From the viewpoint of easy handling and manufacturing cost, an atmosphere in which the balance is nitrogen is more preferable. The atmosphere of step (d) can be controlled by the purity of the gas used.

The temperature of the secondary heat treatment of the step (d) is 800°C or higher and lower than 950°C, preferably 800 to 900°C. When the temperature of the secondary heat treatment is within the above range, the effect of the secondary heat treatment can be sufficiently exhibited. The discharge capacity and cycle characteristics of the lithium ion secondary battery having the positive electrode containing the lithium-containing composite oxide after the secondary heat treatment can be improved.
The time of the secondary heat treatment in step (d) is preferably 4 to 20 hours. When the time of the secondary heat treatment is within the above range, a lithium-containing composite oxide having high crystallinity can be obtained.

In this manufacturing method, it is preferable to perform other steps after performing steps (a) to (d). Other steps include a step of heating the lithium-containing composite oxide again (step (e)), a step of surface-treating the lithium-containing composite oxide (step (f)), and the like. Any one of the other steps may be performed, or all of them may be performed. The order of performing other steps is not limited.

(Process (e))
The step (e) is a step of performing heat treatment at a temperature of 400 to 800° C. in an atmosphere having an oxygen concentration of 5% by volume or more. By performing the step (e), Li (hereinafter referred to as free Li) that does not enter the crystal of the lithium-containing composite oxide and is attached to the surface of the lithium-containing composite oxide can be reduced. As a result, the slurry at the time of manufacturing the electrode is unlikely to gel, and the handling of the slurry becomes easy. Free Li is often present on the surface of the lithium-containing composite oxide as a lithium compound.
The temperature of step (e) is more preferably 450 to 750°C, further preferably 500 to 700°C. The heat treatment time of the step (e) is preferably 0.1 to 20 hours, more preferably 0.5 to 10 hours.

The reduction of free Li is evaluated by calculating the molar ratio of the amount of free Li to the amount of Li contained in the lithium-containing composite oxide. The amount of free Li is the amount of Li contained in the obtained filtrate after dispersing the lithium-containing composite oxide in water and stirring. The method for measuring the amount of Li contained in the filtrate is calculated by the method described in Examples.

(Process (f))
Step (f) is a step of surface-treating the lithium-containing composite oxide obtained by this production method. The surface treatment is, for example, spraying a liquid (coating liquid) containing a predetermined amount of surface-adhering substance on the positive electrode active material and removing the solvent of the coating liquid by firing, or immersing the positive electrode active material in the coating liquid, It can be carried out by performing solid-liquid separation by filtration and solvent removal by calcination.

(Mechanism of action)
In the production method described above, when producing a lithium-containing composite oxide containing a large amount of Li and Mn, the specific surface area of the hydroxide is controlled within a specific range, and the hydroxide and the lithium compound are combined. The heat treatment conditions of the mixture obtained by mixing, specifically, the atmosphere and the temperature are set to specific conditions. As a result, the specific surface area of the lithium-containing composite oxide can be reduced, so that the lithium-containing composite oxide that can improve the cycle characteristics of the lithium-ion secondary battery can be obtained. Furthermore, even if the specific surface area is low, it is possible to obtain a lithium-containing composite oxide capable of increasing the discharge capacity of a lithium ion secondary battery.

<Lithium-ion secondary battery positive electrode>
The positive electrode for a lithium ion secondary battery of the present invention (hereinafter referred to as the present positive electrode) contains the lithium-containing composite oxide obtained by the present production method, that is, the positive electrode active material. Specifically, the positive electrode active material layer containing the positive electrode active material, the conductive material, and the binder obtained by the present manufacturing method is formed on the positive electrode current collector.

(Conductive material)
Examples of the conductive material include carbon black (acetylene black, Ketjen black, etc.), graphite, vapor grown carbon fiber, carbon nanotube, and the like.

(Binder)
As the binder, a fluorine-based resin (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyolefin (polyethylene, polypropylene, etc.), a polymer or copolymer having an unsaturated bond (styrene/butadiene rubber, isoprene rubber, butadiene rubber, etc.) ), acrylic acid-based polymers or copolymers (acrylic acid copolymers, methacrylic acid copolymers, etc.) and the like.

(Positive electrode current collector)
Examples of the positive electrode current collector include aluminum foil and stainless steel foil.

(Manufacturing method of positive electrode)
The positive electrode for a lithium ion secondary battery can be manufactured by the following method, for example.
A positive electrode active material, a conductive material and a binder are dissolved or dispersed in a medium to obtain a slurry. The obtained slurry is applied to the positive electrode current collector, and the medium is removed by drying or the like to form a layer of the positive electrode active material. If necessary, the positive electrode active material layer may be formed and then rolled by a roll press or the like. As a result, a positive electrode for a lithium ion secondary battery is obtained.
Alternatively, a kneaded material is obtained by kneading the positive electrode active material, the conductive material and the binder with a medium. The obtained kneaded product is rolled into a positive electrode current collector to obtain a positive electrode for a lithium ion secondary battery.

(Mechanism of action)
Since the positive electrode described above includes the lithium-containing composite oxide obtained by the present manufacturing method, both the discharge capacity and the cycle characteristics of the lithium ion secondary battery can be improved. That is, the lithium-containing composite oxide obtained by the present production method has both high discharge capacity and cycle characteristics of a lithium-ion secondary battery using a lithium-containing composite oxide containing a large amount of Li and Mn (lithium-rich positive electrode active material). Can be higher. By including such a lithium-containing composite oxide, the present positive electrode can improve both the discharge capacity and the cycle characteristics of the lithium ion secondary battery.

<Lithium-ion secondary battery>
The lithium ion secondary battery of the present invention (hereinafter referred to as the present battery) has the present positive electrode. Specifically, it has the present positive electrode, a negative electrode, and a nonaqueous electrolyte.

(Negative electrode)
The negative electrode contains a negative electrode active material. Specifically, a negative electrode active material layer containing a negative electrode active material and, if necessary, a conductive material and a binder is formed on a negative electrode current collector.

Negative electrode active material:
The negative electrode active material may be any material that can absorb and release lithium ions at a relatively low potential. Examples of the negative electrode active material include lithium metal, lithium alloys, lithium compounds, carbon materials, oxides mainly containing metals of Group 14 of the periodic table, oxides mainly containing metals of Group 15 of the periodic table, carbon compounds, and silicon carbide compounds. , Silicon oxide compounds, titanium sulfide, boron carbide compounds and the like.

Examples of the carbon material of the negative electrode active material include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic high carbons. Examples thereof include calcined molecular compounds (phenolic resins, furan resins, etc., which are calcined at an appropriate temperature to be carbonized), carbon fibers, activated carbon, carbon blacks, and the like.

Examples of the metal of Group 14 of the periodic table used for the negative electrode active material include Si and Sn, and Si is preferable.
Examples of other negative electrode active materials include oxides such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide and tin oxide, and other nitrides.

Negative electrode conductive material, binder:
As the conductive material and binder for the negative electrode, the same materials as those for the positive electrode can be used.

Negative electrode current collector:
Examples of the negative electrode current collector include metal foils such as nickel foil and copper foil.

Negative electrode manufacturing method:
The negative electrode can be manufactured, for example, by the following method.
A negative electrode active material, a conductive material and a binder are dissolved or dispersed in a medium to obtain a slurry. The medium is removed by applying the obtained slurry to a negative electrode current collector, drying, pressing, etc. to obtain a negative electrode.

(Non-aqueous electrolyte)
Examples of the non-aqueous electrolyte include a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in an organic solvent; an inorganic solid electrolyte; a solid or gel polymer electrolyte in which an electrolyte salt is mixed or dissolved.

Organic solvent:
Examples of the organic solvent include those known as organic solvents for non-aqueous electrolyte solutions. Specifically, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, diethyl ether, sulfolane, methylsulfolane, acetonitrile, acetic acid ester, butyric acid. Examples thereof include esters and propionic acid esters. From the viewpoint of voltage stability, cyclic carbonates (propylene carbonate, etc.) and chain carbonates (dimethyl carbonate, diethyl carbonate, etc.) are preferable. As the organic solvent, one type may be used alone, or two or more types may be mixed and used.

Inorganic solid electrolyte:
The inorganic solid electrolyte may be any material having lithium ion conductivity.
Examples of the inorganic solid electrolyte include lithium nitride and lithium iodide.

Solid polyelectrolyte:
Examples of the polymer used for the solid polymer electrolyte include ether polymer compounds (polyethylene oxide, crosslinked products thereof, etc.), polymethacrylate ester polymer compounds, acrylate polymer compounds and the like. The polymer compounds may be used alone or in combination of two or more.
Gel polyelectrolyte:
Examples of the polymer used for the gel polymer electrolyte include fluorine-based polymer compounds (polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, etc.), polyacrylonitrile, acrylonitrile copolymer, ether-based polymer compound ( Polyethylene oxide, its cross-linked product, etc.) and the like. Examples of the monomer to be copolymerized with the copolymer include polypropylene oxide, methyl methacrylate, butyl methacrylate, methyl acrylate and butyl acrylate.
As the polymer compound, a fluorine-based polymer compound is preferable from the viewpoint of stability against redox reaction.

Electrolyte salt:
Any electrolyte salt may be used as long as it is used in a lithium ion secondary battery. Examples of the electrolyte salt include LiClO ₄ , LiPF ₆ , LiBF ₄ , CH ₃ SO ₃ Li, and the like.

(Separator)
A separator may be interposed between the positive electrode and the negative electrode to prevent a short circuit. The separator may be a porous film. The non-aqueous electrolyte is used by impregnating the porous membrane. In addition, a gelled electrolyte obtained by impregnating a porous membrane with a non-aqueous electrolyte may be used as the gel electrolyte.

(Battery exterior body)
Examples of the material of the battery exterior body include nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a resin material, a film material, and the like.

(shape)
Examples of the shape of the lithium ion secondary battery include a coin shape, a sheet shape (film shape), a folding shape, a winding bottomed cylindrical shape, a button shape, and the like, and can be appropriately selected according to the application.

(Mechanism of action)
Since the present battery described above has the present positive electrode, both the discharge capacity and the cycle characteristics are high. That is, the lithium-containing composite oxide obtained by the present production method is a lithium-containing composite oxide containing a large amount of Li and Mn (lithium-rich positive electrode active material) while maintaining a high discharge capacity of a lithium-ion secondary battery, The cycle characteristics can be improved. By having a positive electrode containing such a lithium-containing composite oxide, the present battery can have improved discharge capacity and cycle characteristics.

The present invention will be described below with reference to examples.
Examples 1 to 6 and Examples 13 to 15 are examples, and Examples 7 to 12 are comparative examples.

(Specific surface area)
The specific surface areas of the hydroxide (coprecipitate) and the lithium-containing composite oxide were calculated by a nitrogen adsorption BET (Brunauer, Emmett, Teller) method using a specific surface area measuring device (HM model-1208 manufactured by Mountech Co., Ltd.). .. Deaeration was performed under the conditions of 200° C. and 20 minutes.

(Particle size)
A hydroxide (coprecipitate) or a lithium-containing composite oxide is sufficiently dispersed in water by ultrasonication, and a laser diffraction/scattering type particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., MT-3300EX) is used for measurement. A volume-based particle size distribution was obtained by obtaining a frequency distribution and a cumulative volume distribution curve. The particle diameter at the point at which 50% was obtained in the obtained cumulative volume distribution curve was defined as D ₅₀ .

(Composition analysis)
The composition analysis of the hydroxide (coprecipitate) and the lithium-containing composite oxide was performed by a plasma emission spectrometer (SII3 Nanotechnology SPS3100H).

(Manufacture of positive electrode)
A lithium-containing composite oxide, acetylene black, and a solution (solvent: N-methylpyrrolidone) containing 12.0 mass% of polyvinylidene fluoride were mixed, and N-methylpyrrolidone was further added to prepare a slurry. The mass ratio of the lithium-containing composite oxide, acetylene black, and polyvinylidene fluoride was 80:10:10.
The slurry was applied on one side of a 20 μm thick aluminum foil (positive electrode current collector) using a doctor blade. The gap during coating was 200 μm. After drying at 120° C., roll press rolling was performed twice to produce a positive electrode.

(Manufacture of lithium secondary battery)
As the negative electrode, a negative electrode active material layer made of a metal lithium foil having a thickness of 500 μm and a negative electrode current collector made of a stainless plate having a thickness of 1 mm was prepared.
As the separator, 25 μm-thick porous polypropylene was prepared.
A LiPF6 solution having a concentration of 1 mol/dm3 was prepared as the non-aqueous electrolyte. A mixed solution of ethylene carbonate and diethyl carbonate (volume ratio 1:1) was used as a solvent of the non-aqueous electrolyte.
Using the positive electrode, the negative electrode, the separator, and the nonaqueous electrolytic solution, a stainless steel simple closed cell type lithium secondary battery was assembled in an argon glove box.

(Discharge capacity)
The lithium secondary battery was charged to 4.6 V at a load current of 20 mA per 1 g of the lithium-containing composite oxide and discharged to 2.0 V at a load current of 20 mA per 1 g of the lithium-containing composite oxide to measure the discharge capacity.

(Cycle characteristics)
Next, 100 g of a charge/discharge cycle was performed in which 1 g of the lithium-containing composite oxide was charged to 4.6 V at a load current of 200 mA, and 1 g of the lithium-containing composite oxide was discharged at a high rate to 2.0 V at a load current of 200 mA. At this time, the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was defined as the cycle maintenance rate.

(Example 1)
Process (a):
Nickel (II) sulphate hexahydrate, cobalt (II) sulphate heptahydrate and manganese (II) sulphate pentahydrate so that the molar ratios of Ni, Co and Mn are as shown in Table 1. In addition, it was dissolved in distilled water so that the total amount of sulfate (total concentration of metal elements) was 1.5 mol/kg to obtain a sulfate aqueous solution.
As the pH adjusting liquid, an aqueous sodium hydroxide solution in which sodium hydroxide was dissolved in distilled water to a concentration of 48% by mass was used.
Ammonium sulfate was dissolved in distilled water to a concentration of 0.75 mol/kg to obtain an ammonium sulfate aqueous solution.

Distilled water was put into a 2 L baffled glass reaction tank and heated to 50° C. with a mantle heater. While stirring the solution in the reaction tank with a paddle type stirring blade, 5.0 g/min of a sulfate aqueous solution and 0.5 g/min of an ammonium sulfate aqueous solution were added, and the pH of the mixed solution was adjusted to 11.0. A pH adjusting solution was added so as to keep the hydroxide (coprecipitate) containing Ni, Co and Mn precipitated. While the raw material solution was being added, nitrogen gas was caused to flow in the reaction tank at a flow rate of 1.0 L/min. Further, the liquid was continuously withdrawn so that the liquid amount in the reaction tank did not exceed 2 L. In order to remove impurity ions from the obtained hydroxide, pressure filtration and dispersion in distilled water were repeated for washing. When the electric conductivity of the filtrate reached 20 mS/m, the washing was terminated and the filtrate was dried at 120°C for 15 hours.

Step (b):
The hydroxide (18.00 g) after washing and drying was mixed with lithium carbonate (8.66 g) having a Li content of 26.9 mol/kg to obtain a mixture.

Step (c):
In an electric furnace, while supplying air, the mixture was subjected to primary heat treatment in air at 600° C. for 5 hours to obtain a primary heat treated product.

Step (d):
In a Tammann tube atmosphere electric furnace, the primary heat-treated product was subjected to secondary heat treatment at 850° C. for 16 hours in an atmosphere having an oxygen concentration of 0.01% by volume and the balance being nitrogen to obtain a lithium-containing composite oxide. Obtained.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 2)
Process (a):
Nickel (II) sulphate hexahydrate and manganese (II) sulphate pentahydrate were added such that the molar ratios of Ni and Mn were as shown in Table 1 and the total amount of sulphate (of the total metal elements It was dissolved in distilled water so that the concentration) would be 1.5 mol/kg to obtain a sulfate aqueous solution.
A hydroxide containing Ni and Mn was obtained in the same manner as in Example 1.

Step (b):
The obtained hydroxide (30.00 g) was mixed with lithium carbonate (19.25 g) having a Li content of 26.9 mol/kg to obtain a mixture. The steps (c) and (d) were performed in the same manner as in Example 1. The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 3)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the temperature of the secondary heat treatment in step (d) was 800°C.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 4)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the temperature of the secondary heat treatment in step (d) was 900°C.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 5)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the atmosphere for the secondary heat treatment in step (d) was an atmosphere in which the oxygen concentration was 0.5% by volume and the balance was nitrogen.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 6)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the atmosphere of the secondary heat treatment in the step (d) was an atmosphere having an oxygen concentration of 1% by volume and the balance being nitrogen.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 7)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the atmosphere of the secondary heat treatment in step (d) was air.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 8)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the atmosphere of the secondary heat treatment in step (d) was air and the temperature was 1000°C.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 9)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the temperature of the secondary heat treatment in step (d) was 950°C.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 10)
A lithium-containing composite oxide was obtained in the same manner as in Example 2 except that the atmosphere of the secondary heat treatment in step (d) was air.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 11)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the atmosphere of the secondary heat treatment in step (d) was an atmosphere having an oxygen concentration of 10% by volume and the balance being nitrogen.
The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

(Example 12)
Process (a):
Nickel (II) sulphate hexahydrate, cobalt (II) sulphate heptahydrate and manganese (II) sulphate pentahydrate so that the molar ratios of Ni, Co and Mn are as shown in Table 1. In addition, it was dissolved in distilled water so that the total amount of sulfate (total concentration of metal elements) was 1.5 mol/kg to obtain a sulfate aqueous solution.
As the pH adjusting liquid, an aqueous sodium carbonate solution in which sodium carbonate was dissolved in distilled water so that the concentration became 1.5 mol/L was used.
Ammonium sulfate was dissolved in distilled water to a concentration of 0.375 mol/kg to obtain an ammonium sulfate aqueous solution.

Distilled water was put into a 2 L glass reaction tank equipped with a baffle and heated to 30° C. with a mantle heater. While stirring the solution in the reaction tank with a paddle type stirring blade, an aqueous solution of sulfate was added at a rate of 2.5 g/min and an aqueous solution of ammonium sulfate was added at a rate of 0.5 g/min, and the pH of the mixed solution was adjusted to 10.0. An aqueous carbonate solution was added so as to keep the solution, and a carbonate (coprecipitate) containing Ni, Co and Mn was deposited. While the raw material solution was being added, the liquid was continuously extracted so that the liquid amount in the reaction tank did not exceed 2 L. In order to remove impurity ions from the obtained carbonate, pressure filtration and dispersion in distilled water were repeated for washing. When the electric conductivity of the supernatant was 20 mS/m, the washing was completed and the supernatant was dried at 120°C for 15 hours.

Step (b):
A carbonate (18.00 g) after washing and drying was mixed with lithium carbonate (7.29 g) having a Li content of 26.9 mol/kg to obtain a mixture. The steps (c) and (d) were performed in the same manner as in Example 1. The production conditions of the lithium-containing composite oxide and the evaluation results of the lithium secondary battery are shown in Tables 1 and 2.

In Examples 1 to 6, hydroxide was used in the steps (a) and (b) as the production conditions of the lithium-containing composite oxide, and the atmosphere in the step (d) was an atmosphere having an oxygen concentration of less than 5% by volume. The heat treatment temperature is 800° C. or higher and lower than 950° C. The lithium secondary battery having the lithium-containing composite oxide obtained under these conditions has a high discharge capacity and a high cycle retention rate.
Comparing Examples 1 and 2 with Example 8, the specific surface areas of the obtained lithium-containing composite oxides are the same, but the lithium secondary batteries having the lithium-containing composite oxides obtained in Examples 1 and 2 are High discharge capacity and cycle maintenance rate. From this, it can be said that the discharge capacity and cycle retention rate of the lithium secondary battery having the lithium-containing composite oxide are affected by the manufacturing conditions of the lithium-containing composite oxide.
Comparing Examples 1 and 2 with Example 12, Examples 1 and 2 have a high specific surface area of the lithium-containing composite oxide and a high discharge capacity of the lithium secondary battery having the obtained lithium-containing composite oxide. Comparing the production conditions of Examples 1 and 2 and Example 12, the conditions are the same except that the type of compound obtained in step (a) is different. From this, by using the hydroxide in the steps (a) and (b) in the production of the lithium-containing composite oxide, the discharge capacity and the cycle maintenance rate of the lithium secondary battery having the lithium-containing composite oxide obtained can be improved. It can be said that it can be raised.

Comparing Example 1 and Example 9, in Example 1, the obtained lithium-containing composite oxide has a high specific surface area, and the lithium secondary battery has a high discharge capacity and a high cycle retention rate. Comparing the manufacturing conditions of Example 1 and Example 9, they are the same except that the temperature of the heat treatment of step (d) is different. From this, by setting the temperature of the heat treatment in the step (d) to a predetermined temperature range, the specific surface area of the lithium-containing composite oxide can be made a desired size, and the lithium secondary battery having the obtained lithium-containing composite oxide can be obtained. It can be said that the discharge capacity and the cycle maintenance rate can be increased.
Comparing Example 1 and Example 7, in Example 1, the specific surface area of the obtained lithium-containing composite oxide is low, and the cycle retention rate of the lithium secondary battery is high. Comparing the manufacturing conditions of Example 1 and Example 7, they are the same except that the atmosphere of the heat treatment of step (d) is different. From this, by setting the atmosphere of the heat treatment of the step (d) to an atmosphere having an oxygen concentration of less than 5% by volume, the specific surface area of the lithium-containing composite oxide can be set to a desired size, and the obtained lithium-containing composite oxide is obtained. It can be said that the cycle maintenance rate of the lithium secondary battery can be increased.

(Measurement of free Li amount)
1 g of the lithium-containing composite oxide was dispersed in 10 g of distilled water, stirred for 30 minutes, and then filtered with a membrane filter. Further, 60 g of distilled water was added to the filtrate to measure the pH. The pH at this time was defined as the initial pH.
Next, the filtrate containing distilled water was titrated with 0.02 mol/L hydrochloric acid to pH 4.0. At this time, assuming that the titration amount from the initial pH to pH 8.5 corresponds to the neutralization of LiOH and Li2CO3, and the titration amount of pH 8.5 to 4.0 corresponds to the neutralization of Li2CO3, it is included in the filtrate. The contents of LiOH and Li ₂ CO _{3 that} were generated were determined.
The molar ratio of LiOH in the filtrate to the amount of Li contained in 1 g of the lithium-containing composite oxide was defined as the free LiOH ratio. The free Li ratio is the sum of the free LiOH ratio and the free Li ₂ CO ₃ ratio, where the molar ratio of the amount of Li contained in Li ₂ CO _{3 in} the filtrate to the amount of Li contained in 1 g of the lithium-containing composite oxide is the free Li ₂ CO ₃ ratio. And

(Example 13)
The steps (a) to (d) were performed in the same manner as in Example 1, and then the following step (e) was performed.
Process (e):
While supplying air in an electric furnace, the lithium-containing composite oxide was heat-treated in air at 450° C. for 5 hours to obtain a lithium-containing composite oxide. Table 3 shows the free Li ratio of the obtained lithium-containing composite oxide and the evaluation results of the lithium secondary battery having the lithium-containing composite oxide.

(Example 14)
In step (e), a lithium-containing composite oxide was obtained in the same manner as in Example 13 except that the heat treatment temperature was 550°C. Table 3 shows the free Li ratio of the obtained lithium-containing composite oxide and the evaluation results of the lithium secondary battery having the lithium-containing composite oxide.

(Example 15)
A lithium-containing composite oxide was obtained in the same manner as in Example 13 except that the heat treatment temperature was 650° C. in the step (e). Table 3 shows the free Li ratio of the obtained lithium-containing composite oxide and the evaluation results of the lithium secondary battery having the lithium-containing composite oxide.

As shown in Table 3, it can be seen that the step (e) contributes to the reduction of the free Li ratio of the lithium-containing composite oxide. In particular, it was shown that the effect of reducing the free Li ratio becomes remarkable when the step (e) is performed at a temperature of 550° C. or higher.

The lithium-containing composite oxide obtained by this production method is useful as a positive electrode active material for a lithium ion secondary battery.
In addition, Japanese Patent Application No. 2013-223344 filed on October 28, 2013,
And the entire contents of the specification, claims and abstract of Japanese Patent Application No. 2014-116015 filed on June 4, 2014 are cited herein as disclosure of the specification of the present invention.
It is something to incorporate.

Claims (7)

A lithium-containing composite oxide represented by the following formula (II) and having a specific surface area of 1 to ³ m ² /g.
Li(Li _a Ni _x Co _y Mn _z )O _b ... (II)
(In Formula (II), a is more than 0 and is 0.6 or less, x is 0.1 to 0.5, y is 0 to 0.3, and z is 0.36 to 0. 9, (x+y+z) is 1, the molar ratio of Mn to Ni (Mn/Ni) is 1.2 to 3.5 , and b satisfies the valences of Li, Ni, Co, and Mn. Is the number of moles of O necessary for.) The lithium-containing composite oxide is a secondary particle in which a plurality of primary particles are aggregated,
The _{D 50} of the secondary particles is 3～18Myuemu, lithium-containing complex oxide according to claim 1. The lithium-containing composite oxide comprises a surface-adhering substance on the surface,
The surface-adhering substance is
Group consisting of aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, calcium carbonate, magnesium carbonate The lithium-containing composite oxide according to claim 1 or 2, which is one or more selected from the following. The lithium-containing composite oxide according to claim 3, wherein the amount of the surface-adhering substance present is 0.01% by mass or more and 5% by mass or less with respect to the lithium-containing composite oxide. The lithium-containing composite oxide according to any one of claims 1 to 4, wherein a free lithium ratio measured by the following measuring method is 0.71 mol% or less.
(Measuring method)
1 g of the lithium-containing composite oxide is dispersed in 10 g of distilled water, stirred for 30 minutes, and then filtered with a membrane filter. Add 60 g of distilled water to the filtrate and measure the pH. The pH at this time is the initial pH.
Next, the filtrate containing distilled water is used to perform titration with 0.02 mol/L hydrochloric acid until the pH reaches 4.0. At this time, it is assumed that the titration amount from the initial pH to pH 8.5 corresponds to the neutralization of LiOH and Li ₂ CO ₃ , and the titration amount of pH 8.5 to 4.0 corresponds to the neutralization of Li ₂ CO _3. Then, the contents of LiOH and Li ₂ CO ₃ contained in the filtrate are obtained.
The molar ratio of LiOH in the filtrate to the amount of Li contained in 1 g of the lithium-containing composite oxide is defined as the free LiOH ratio. The molar ratio of the amount of Li contained in Li ₂ CO ₃ in the filtrate to the amount of Li contained in 1 g of the lithium-containing composite oxide is defined as the free Li ₂ CO ₃ ratio. The sum of the free LiOH ratio and the free Li ₂ CO ₃ ratio is defined as the free lithium ratio. A positive electrode for a lithium ion secondary battery, comprising the lithium-containing composite oxide according to claim 1. A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 6.