JP2019089708A - Method of producing lithium-containing composite oxide, positive electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

To provide a method of producing a lithium-containing composite oxide capable of enhancing cycle characteristics while keeping a high discharge capacity of a lithium ion secondary battery by a lithium-containing composite oxide containing a large amount of Li and Mn and to provide a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery.SOLUTION: There is provided a method of producing a lithium-containing composite oxide of LiMO(M: at least Ni and Mn, Mn/Ni:1.1 or more, 0<a≤0.6, b: the number of moles of O required for satisfying the valence of M), which comprises: (a) a step of obtaining a hydroxide containing Ni and Mn and having a specific surface area of 5 to 80 m/g; (b) a step of mixing a lithium compound and the hydroxide to obtain a mixture; (c) a step of heat-treating the mixture at 500 to 700°C in an atmosphere having an oxygen concentration of 5 vol.% or more to obtain a first heat-treated product; and d) a step of subjecting the heat-treated product to secondary heat treatment at 800°C or more and less than 950°C in an atmosphere having an oxygen concentration of less than 5 vol.% to obtain a lithium-containing composite oxide.SELECTED DRAWING: None

Description

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

As a positive electrode active material contained in the positive electrode of a lithium ion secondary battery, a lithium-containing composite oxide, in particular, LiCoO ₂ is well known. However, in recent years, size reduction and weight reduction are required for portable electronic devices and lithium ion secondary batteries for vehicles, and the discharge capacity per unit mass (hereinafter simply referred to as discharge capacity) is further improved, There is a demand for further improvement of characteristics (hereinafter also referred to as cycle characteristics) in which the discharge capacity and the average discharge voltage do not decrease after repetition of charge and discharge cycles.

As a positive electrode active material (lithium-containing composite oxide) capable of improving the discharge capacity and cycle characteristics of the lithium ion secondary battery, LiCo _1-2x Ni _x Mn _x O ₂ (where 0 <x ≦ 0.5). A so-called ternary positive electrode active material represented by) is proposed. Further, as a method of producing a ternary positive electrode active material capable of further improving the discharge capacity of a lithium ion secondary battery, the following method has been proposed.
(1) A lithium-containing composite in which a precursor containing Li, Ni, Mn and Co is subjected to primary heat treatment in an oxidizing atmosphere at 300 ° C. or more and less than 800 ° C., and then subjected to secondary heat treatment in a nonoxidizing atmosphere at 800 ° C. or more The manufacturing method of an oxide (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 of Li and Mn, that is, a so-called lithium rich positive electrode active material is attracting attention. As a lithium rich system positive electrode active material, the following are proposed, for example.
(2) Li _{1 + α} Me _1-α O ₂ (where Me is a transition metal element including Co, Ni and Mn and has α> 0, and has an α-NaFeO ₂ type crystal structure, with respect to the transition metal element The molar ratio of Li (Li / Me) is 1.2 to 1.6, the molar ratio of Co to transition metal element (Co / Me) is 0.02 to 0.23, Mn to transition metal element The positive electrode active material represented by molar ratio (Mn / Me) is 0.62-0.72.) (Patent document 2).
(3) x Li ₂ MnO _3. (1-x) Li Ni _{u + Δ} Mn _u-Δ Co _w A _y O ₂ (where 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 A lithium-rich composite metal oxide represented by the formula: = 1, w is 0 to 1, u is 0 to 0.5, and y <0.1) (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 content of Li and Mn. Therefore, a lithium ion secondary battery having a positive electrode containing the ternary positive electrode active material can not sufficiently meet the recent demand for improvement in discharge capacity.
The lithium-rich positive electrode active materials of (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 electrolyte when in contact with the decomposition product generated from the electrolyte 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, in the lithium ion secondary battery having a positive electrode containing a lithium-rich positive electrode active material, cycle characteristics are likely to be deteriorated particularly by repeated charge and discharge, and improvement of the characteristics is required.

  When the present inventors examined a lithium-rich positive electrode active material, the discharge capacity and cycle characteristics of a lithium ion secondary battery having a positive electrode containing the lithium-rich positive electrode active material were the same as the specific surface area of the lithium-rich positive electrode active material. 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 is increased, but the cycle characteristics tend to be deteriorated. 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 increase. For this reason, it has been difficult to enhance the characteristics of 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 provides a method for producing a lithium-containing composite oxide used for 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 It is an object of the present invention to provide a positive electrode for a lithium ion secondary battery including: and a lithium ion secondary battery having the positive electrode.

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

That is, the gist of the present invention resides in the following [1] to [10].
[1] Li _{1 + a} MO _b (where M is two or more metal elements (except Li), at least two of the metal elements 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, b is the number of moles of O necessary to satisfy the valences of Li and M. A method of producing a lithium-containing composite oxide,
The manufacturing method of lithium containing complex oxide which has following process (a)-(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 a specific surface area of 5 to 80 m ² / g.
(B) The lithium compound and the hydroxide are selected so that the molar ratio of Li to the total number of moles of metal elements other than Li contained in the hydroxide (Li / M) is more than 1 and not more than 1.6. Mixing to obtain a mixture.
(C) A step of 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 to obtain a primary heat-treated product.
(D) a step of subjecting the first heat-treated product to a second heat treatment at a temperature of 800 ° C. or more and less 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) is an atmosphere in which the oxygen concentration is less than 5% by volume and the balance is nitrogen.
[3] The method for producing a lithium-containing composite oxide of [1] or [2], wherein the step (d) is performed in a closed vessel.
[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 at a temperature of 400 to 800 ° C. in an atmosphere having an oxygen concentration of 5% by volume or more after the step (d).
[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 not more than 0.6, 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 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 specific surface area of the lithium-containing composite oxide is 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, [1] to [1] 7] The manufacturing method of lithium containing complex oxide in any one.
[9] A positive electrode for a lithium ion secondary battery, comprising the lithium-containing composite oxide obtained by the method according to any one of the above [1] to [8].
[10] A lithium ion secondary battery having the positive electrode for a lithium ion secondary battery according to the above [9].

The manufacturing method of the present invention can provide a lithium-containing composite oxide that can increase both the discharge capacity and the cycle characteristics of the 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 characteristic of the lithium ion secondary battery can be enhanced.
The lithium ion secondary battery of the present invention has both high discharge capacity and cycle characteristics.

The following definitions of terms apply throughout the specification and claims.
"Li-containing complex oxide containing a large amount of Li and Mn" means that the content of each of Li and Mn is in molar ratio to the total amount (M) of metal elements other than Li in the lithium-containing complex oxide And Li / M is more than 1 and Mn / M is 0.36 or more.
In the "atmosphere where the oxygen concentration is in a specific range and the balance is nitrogen or argon," the components other than oxygen are substantially nitrogen or argon, and other components other than oxygen, nitrogen and argon affect the heat treatment. Means an atmosphere that may be included without giving
“D ₅₀ ” means the particle diameter of a point at which 50% is obtained in the cumulative volume distribution curve where the total volume of particle size distribution determined on a volume basis is 100%, that is, the 50% diameter at volume basis. The particle size distribution is determined by the frequency distribution and cumulative volume distribution curve measured by a laser scattering particle size distribution measuring apparatus. The particle size is measured by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like to measure the particle size distribution (for example, using a laser diffraction / scattering type particle size distribution measuring apparatus or the like).
The notation “Li” indicates that the element is not elemental Li but the element Li unless otherwise noted. The same applies to the other elements such as Ni, Co and Mn.
Compositional analysis of the lithium-containing composite oxide and hydroxide is carried out by inductively coupled plasma analysis (hereinafter abbreviated as ICP). Further, the ratio of the elements of the lithium-containing composite oxide is a value in the lithium-containing composite oxide before the first charge (also referred to as activation treatment).

Lithium-containing complex 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) necessary to satisfy the valences of Li and M.
M represents two or more types of metal elements (except for Li), and at least two of the metal elements are Ni and Mn, and may contain other metal elements as needed.
Other metal elements include Mg, Ca, Ba, Sr, Al, Co, Cr, Fe, Ti, Zr, Y, Nb, Mo, Ta, W, Ce, La and the like. Mg, Al, Co, Cr, Fe, Ti or Zr are preferable, and Co is more preferable, from the viewpoint that a high discharge capacity can be easily obtained.
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 in the lithium-containing composite oxide is (molar ratio of the other metal elements other than Co) / M 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 If so, the discharge capacity can be increased. In order to increase the charge and discharge efficiency of the lithium ion secondary battery, the Mn / Ni of the lithium-containing composite oxide is preferably 5 or less. Mn / Ni is more preferably 1.2 to 4.0, and still more preferably 1.3 to 3.5.

  A of 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. If a is at least the lower limit value, the discharge capacity of the lithium ion secondary battery having the lithium-containing composite oxide of the formula (I) can be increased. If a is equal to or less 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, the charge / discharge efficiency or rate characteristics may be degraded, or decomposition of the electrolyte may be promoted to cause generation of gas 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 an initial discharge capacity and an 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).

  In the formula (II), x is 0.1 to 0.5, preferably 0.15 to 0.45, and more preferably 0.2 to 0.4. If 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 of Formula (II) is 0-0.3, 0-0.2 are preferable and 0-0.15 are more preferable. If y 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.

  Z of Formula (II) is 0.36-0.9, 0.5-0.8 are preferable and 0.5-0.7 are more preferable. If 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 (Mn / Ni) in the lithium-containing composite oxide described above.

The lithium-containing composite oxide is preferably a secondary particle 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. If D ₅₀ of the secondary particles of the lithium-containing composite oxide is in the range can be increased and the discharge capacity of the lithium ion secondary battery.

_{D 50} of the primary particles of the lithium-containing composite oxide, 10 to 500 nm is preferable. If D ₅₀ of the primary particles of the lithium-containing composite oxide is in the range, when producing a lithium ion secondary battery, the electrolytic solution is easily spreads sufficiently between the positive electrode active material in the positive electrode.

The specific surface area of the lithium-containing composite oxide is preferably ^{0.9~4m 2 / g, 1~3m 2 /} g is more preferable. If 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 be reduced. When the specific surface area of the lithium-containing composite oxide exceeds 4 m ² / g, the cycle characteristics may be deteriorated.
The specific surface area of the lithium-containing composite oxide is a value measured by the BET method (Brunauer, Emmet, Teller). In the measurement of the specific surface area, nitrogen is used as an adsorption gas. 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 as it is or after surface treatment.
The surface treatment is a treatment for attaching a substance (surface adhesion substance) having a composition different from the substance constituting the lithium-containing composite oxide to the surface of the lithium-containing composite oxide. As the surface adhesion substance, for example, 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, sulfate) Magnesium, calcium sulfate, aluminum sulfate, etc.), carbonates (calcium carbonate, magnesium carbonate, etc.), etc. may be mentioned.

  0.01 mass% or more is preferable with respect to lithium containing complex oxide, as for the quantity of a surface adhesion substance, 0.05 mass% or more is more preferable, and 0.1 mass% or more is especially preferable. 10 mass% or less is preferable with respect to lithium containing complex oxide, as for the quantity of a surface adhesion substance, 5 mass% or less is more preferable, and 3 mass% or less is especially preferable. By the presence of the surface adhesion substance on the surface of the lithium-containing composite oxide, the oxidation reaction of the non-aqueous electrolyte on the surface of the lithium-containing composite oxide can be suppressed, and the battery life can be improved.

  The manufacturing method of lithium containing complex oxide and the surface treatment of lithium containing complex oxide obtained by this manufacturing method are demonstrated below.

<Method of producing lithium-containing composite oxide>
The present 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 a specific surface area of 5 to 80 m ² / g.
(B) mixing the lithium compound and the hydroxide such that the molar ratio of Li to the total number of moles of the metal element other than Li contained in the hydroxide (Li / M) is more than 1 and not more than 1.6 To obtain a mixture.
(C) A step of 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 to obtain a primary heat-treated product.
(D) a step of obtaining a lithium-containing composite oxide by performing a secondary heat treatment on the primary heat-treated product at a temperature of 800 ° C. or more and less than 950 ° C. in an atmosphere having an oxygen concentration of less than 5% by volume.

(Step (a))
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 a specific surface area of 5 to 80 m ² / g. . The hydroxides also include partially oxidized oxyhydroxides.
If it manufactures using this hydroxide, lithium containing complex oxide with high Mn / Ni will be obtained. Furthermore, if it manufactures using this hydroxide, the specific surface area of lithium containing complex oxide can be included in a desired range, and the discharge capacity of the lithium ion secondary battery which has the obtained lithium containing complex oxide And cycle characteristics can be increased.

  The metal elements contained in the hydroxide include at least Ni and Mn, and may contain other metal elements as needed. Other metal elements include Mg, Ca, Ba, Sr, Al, Co, Cr, Fe, Ti, Zr, Y, Nb, Mo, Ta, W, Ce, La and the like. Mg, Al, Co, Cr, Fe, Ti or Zr are preferable, and Co is more preferable, from the viewpoint that a high discharge capacity can be easily obtained.

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

_{D 50} of the hydroxide is preferably 3～18Myuemu, more preferably 3 to 15 [mu] m, 3 to 12 [mu] m is particularly preferred. If D ₅₀ of the hydroxide within the range, the D ₅₀ of the lithium-containing composite oxide in a desired range. Lithium-containing composite oxide D ₅₀ is 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. If the specific surface area of the hydroxide is within the above range, the specific surface area of the resulting lithium-containing composite oxide can be controlled within the appropriate range. The lithium-containing composite oxide having an appropriate specific surface area can enhance both the discharge capacity and the cycle characteristics of the lithium ion secondary battery.

As a method of preparing the hydroxide, coprecipitation method is preferable from the viewpoint of easily adjusting the ratio of the metal element to a desired range and adjusting the specific surface area of the hydroxide.
The coprecipitation method is a method of precipitating a hardly soluble compound (coprecipitate) containing a desired two or more metal elements from a solution containing two or more 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 vessel, mixed, and reacted while maintaining the pH in the mixed solution constant. And co-precipitates containing If the pH of the mixture is above 10, the coprecipitate is considered as a hydroxide.

  As metal salts, nitrates of metal elements, acetates, chlorides and sulfates may be mentioned, and sulfates are preferable in terms of relatively inexpensive material cost and excellent battery characteristics can be obtained. As a metal salt used in this manufacturing 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) ammonium sulfate hexahydrate.
Examples of the sulfate of Co include cobalt (II) sulfate heptahydrate, cobalt (II) ammonium sulfate hexahydrate and the like.
Examples of the sulfate of Mn include manganese (II) sulfate pentahydrate, manganese (II) ammonium sulfate hexahydrate and the like.

  0.1-3 mol / kg is preferable and, as for the density | concentration of the sum total of the metallic element of the aqueous solution of a metal salt, 0.5-2.5 mol / kg is more preferable. If the total concentration of the metal elements is equal to or more than the lower limit value, it is preferable because the productivity is excellent. If the concentration of the metal element is equal to or less 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.
As an aqueous medium other than water, methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, butanediol, glycerin and the like can be mentioned. The proportion of the aqueous medium other than water is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass, with respect to 100 parts by mass of water from the viewpoints of safety, environment, handleability, and cost. 1 part by mass is particularly preferred.

In the step (a), as the pH adjusting solution, an aqueous solution containing a strong alkali is preferable.
The strong alkali is preferably at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide.
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 to mix the aqueous solution of the metal salt and the pH adjusting solution while stirring in the reaction vessel.
As a stirring apparatus, a three-one motor etc. are mentioned. As a stirring blade, an anchor type, a propeller type, a paddle type, etc. are mentioned.
The reaction temperature is preferably 20 to 80 ° C., and more preferably 25 to 60 ° C. from the viewpoint of reaction promotion.

It is preferable to carry out the mixing of the aqueous solution of the metal salt and the pH adjusting solution under a nitrogen atmosphere or an argon atmosphere from the viewpoint of suppressing the oxidation of the hydroxide, and in terms of cost, it is particularly preferable to carry out under a nitrogen atmosphere. preferable.
During the mixing of the metal salt aqueous solution and the pH adjusting solution, it is preferable to maintain the pH in the reaction tank at a set pH in the range of 10 to 12 in order to appropriately advance the coprecipitation reaction.

  The obtained hydroxide 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 or filtrate when the hydroxide is dispersed in distilled water is 50 mS / m or less, more preferably 20 mS / m or less preferable.

After washing, the hydroxide may be dried if necessary.
60-200 degreeC is preferable and 80-130 degreeC of a drying temperature is more preferable. If the drying temperature is equal to or higher than the lower limit value, the drying time can be shortened. If drying temperature is below the said upper limit, advancing of the oxidation of a hydroxide can be suppressed.
The drying time may be appropriately set according to the amount of hydroxide, preferably 1 to 300 hours, and more preferably 5 to 120 hours.

(Step (b))
In the step (b), the lithium compound and the hydroxide obtained in the step (a) are added in a molar ratio of Li to the total number of metal elements other than Li contained in the hydroxide (Li / M) of 1 It is a process of mixing so that it may be over 1.6 or less to obtain a mixture.

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

  The amount of lithium compound in the mixture is appropriately adjusted in accordance with the total number of moles of the metal element 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. If Li / M is 1.6 or less, Li (free lithium) that does not contribute to the crystal structure of the lithium-containing composite oxide can be reduced when firing. If there is a large amount of free lithium, the charge / discharge efficiency and rate characteristics of the lithium ion secondary battery may be degraded, and decomposition of the electrolyte is promoted at the time of use of the lithium ion secondary battery to cause generation of decomposition product gas and May be 1.1-1.5 are preferable and 1.1-1.45 of Li / M are more preferable.

(Step (c))
The step (c) is a step of subjecting the mixture obtained in the step (b) to a primary heat treatment of an oxide at a temperature of 500 to 700 ° C. in an atmosphere having an oxygen concentration of 5 vol% or more. .

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 the air. Moreover, it is more preferable to perform primary heat processing, supplying air.

The temperature of the primary heat treatment is 500 to 700 ° C., preferably 500 to 600 ° C. If 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 highly thermally treated primary heat treatment product can be obtained.
The time of primary heat treatment is preferably 3 to 10 hours. If the time of the primary heat treatment is within the above range, the reaction between the hydroxide and the lithium compound can sufficiently proceed, and a highly heat-treated primary heat-treated product can be obtained.
When the crystallinity of the primary heat treatment product is low and the primary heat treatment product has a different phase, the discharge capacity of the lithium ion secondary battery may be reduced.

(Step (d))
The step (d) is a step of subjecting the primary heat treatment product to secondary heat treatment at a temperature of 800 ° C. or more and less than 950 ° C. in an atmosphere having an oxygen concentration of less than 5 vol% to obtain a lithium-containing composite oxide.

  The secondary heat treatment in the step (d) is preferably performed in a container which can seal the inside of the furnace, more preferably in a container which can make the inside of the furnace vacuum. Examples of the container include a Tamman tube atmosphere electric furnace and the like. By using the container, the secondary heat treatment can be performed while maintaining the atmosphere having an oxygen concentration of less than 5% by volume.

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

  The atmosphere for the secondary heat treatment in the 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 in the above range and the balance is nitrogen or argon is preferable. In terms of ease of 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 more and less than 950 ° C., preferably 800 to 900 ° C. If the temperature of the secondary heat treatment is within the above range, the effects of the secondary heat treatment can be sufficiently exhibited. The discharge capacity and cycle characteristics of a lithium ion secondary battery having a positive electrode containing a lithium-containing composite oxide after secondary heat treatment can be enhanced.
The time of the secondary heat treatment of the step (d) is preferably 4 to 20 hours. If the time of the secondary heat treatment is within the above range, a lithium-containing composite oxide with high crystallinity can be obtained.

  In the present production method, it is preferable to carry out the other steps after carrying out the steps (a) to (d). As another process, the process (process (e)) which heats lithium containing complex oxide again, the process (step (f)) which surface-treats lithium containing complex oxide, etc. are mentioned. The other steps may be performed one by one or all. In addition, the order of performing the other steps is not limited.

(Step (e))
The step (e) is a step of heat treatment at a temperature of 400 to 800 ° C. in an atmosphere having an oxygen concentration of 5% by volume or more. When step (e) is carried out, Li (hereinafter referred to as free Li) attached to the surface of the lithium-containing composite oxide without entering the crystal of the lithium-containing composite oxide can be reduced. As a result, the slurry at the time of preparation of the electrode is less likely to gel and handling of the slurry becomes easy. Free Li is often present on the surface of the lithium-containing composite oxide as a lithium compound.
As for the temperature of process (e), 450-750 degreeC is more preferable, and 500-700 degreeC is further more preferable. The heat treatment time of 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 obtained by dispersing the lithium-containing composite oxide in water and stirring, and then filtering to obtain the amount of Li contained in the obtained filtrate. The method of measuring the amount of Li contained in the filtrate is calculated by the method described in the examples.

(Step (f))
Step (f) is a step of surface-treating the lithium-containing composite oxide obtained by the present production method. In the surface treatment, for example, a liquid (coating liquid) containing a predetermined amount of surface adhesion substance is sprayed onto the positive electrode active material, the solvent of the coating liquid is removed by firing, or the positive electrode active material is immersed in the coating liquid It can be carried out by performing solid-liquid separation by filtration and removal of the solvent by calcination.

(Mechanism of action)
In the present 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 to a specific range, and the hydroxide and the lithium compound The heat treatment conditions, specifically the atmosphere and the temperature, of the mixture obtained by mixing are set to specific conditions. As a result, since the specific surface area of the lithium-containing composite oxide can be reduced, it is possible to obtain a lithium-containing composite oxide capable of enhancing the cycle characteristics of the lithium ion secondary battery. Furthermore, even if the specific surface area is low, it is possible to obtain a lithium-containing composite oxide that can increase the discharge capacity of the lithium ion secondary battery.

<Positive electrode for lithium ion secondary battery>
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, a positive electrode active material. Specifically, a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder obtained by the present manufacturing method is formed on a positive electrode current collector.

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

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

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

(Method of manufacturing positive electrode)
The positive electrode for a lithium ion secondary battery can be produced, for example, by the following method.
The positive electrode active material, the conductive material and the binder are dissolved or dispersed in a medium to obtain a slurry. The obtained slurry is applied to a positive electrode current collector, and the medium is removed by drying or the like to form a layer of a positive electrode active material. As needed, after forming the layer of a positive electrode active material, you may roll with a roll press etc. Thereby, the positive electrode for lithium ion secondary batteries 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 to a positive electrode current collector to obtain a positive electrode for a lithium ion secondary battery.

(Mechanism of action)
In the present positive electrode described above, since the lithium-containing composite oxide obtained by the present manufacturing method is included, both the discharge capacity and the cycle characteristics of the lithium ion secondary battery can be enhanced. That is, the lithium-containing composite oxide obtained by the present manufacturing method has both the high discharge capacity and the cycle characteristics of a lithium ion secondary battery by the lithium-containing composite oxide (lithium-rich positive electrode active material) containing a large amount of Li and Mn. Can be raised. By including such a lithium-containing composite oxide, the present positive electrode can enhance both the discharge capacity and the cycle characteristics of the lithium ion secondary battery.

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

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

Negative electrode active material:
The negative electrode active material may be any material that can occlude and release lithium ions at a relatively low potential. As the negative electrode active material, lithium metal, lithium alloy, lithium compound, carbon material, oxide mainly composed of metal of periodic table group 14, oxide mainly composed of metal of periodic table group 15, carbon compound, silicon carbide compound And silicon oxide compounds, titanium sulfide, and boron carbide compounds.

  As a carbon material of the negative electrode active material, non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic high materials A molecular compound fired body (phenol resin, furan resin, etc. fired and carbonized at an appropriate temperature), carbon fiber, activated carbon, carbon blacks, etc. may be mentioned.

As a metal of periodic table 14 group used for a negative electrode active material, Si and Sn are mentioned, and Si is preferable.
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 of the negative electrode and the binder, the same materials as those of the positive electrode can be used.

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

Production method of negative electrode:
The negative electrode can be produced, for example, by the following method.
The negative electrode active material, the conductive material and the binder are dissolved or dispersed in a medium to obtain a slurry. The medium is removed by coating the obtained slurry on a negative electrode current collector, drying, pressing or the like to obtain a negative electrode.

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

Organic solvent:
As an organic solvent, what is well-known as an organic solvent for non-aqueous electrolytes is mentioned. Specifically, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, acetate, butyric acid Ester, propionic acid ester and the like can be mentioned. From the viewpoint of voltage stability, cyclic carbonates (such as propylene carbonate) and linear carbonates (such as dimethyl carbonate and diethyl carbonate) are preferable. An organic solvent may be used individually by 1 type, and may mix and use 2 or more types.

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

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

Electrolyte salt:
The electrolyte salt may be any one 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. A porous membrane is mentioned as a separator. The non-aqueous electrolyte is used by impregnating the porous membrane. Further, a porous membrane impregnated with a non-aqueous electrolytic solution and gelled may be used as a gel electrolyte.

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

(shape)
The shape of the lithium ion secondary battery may, for example, be a coin, a sheet (film), a fold, a winding type, a bottomed cylindrical, a button, or the like, which can be appropriately selected according to the application.

(Mechanism of action)
In the present battery described above, since the present positive electrode is provided, both the discharge capacity and the cycle characteristics are high. That is, the lithium-containing composite oxide obtained by the present manufacturing method maintains the high discharge capacity of the lithium ion secondary battery due to the lithium-containing composite oxide (lithium-rich positive electrode active material) containing a large amount of Li and Mn. Cycle characteristics can be enhanced. By having a positive electrode containing such a lithium-containing composite oxide, the present battery can enhance both the discharge capacity and the cycle characteristics.

Hereinafter, the present invention will be described using 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 area of the hydroxide (coprecipitate) and the lithium-containing composite oxide was calculated by the nitrogen adsorption BET (Brunauer, Emmett, Teller) method using a specific surface area measurement device (manufactured by MUNTECH Co., Ltd., HM model-1208) . Degassing was performed at 200 ° C. for 20 minutes.

(Particle size)
The hydroxide (coprecipitate) or lithium-containing composite oxide is sufficiently dispersed in water by ultrasonic treatment, and measurement is performed using a laser diffraction / scattering particle size distribution measuring device (MT-3300EX, manufactured by Nikkiso Co., Ltd.), A volume-based particle size distribution was obtained by obtaining frequency distribution and cumulative volume distribution curve. Particle size of the point to be 50% in the obtained cumulative volume distribution curve was D _50.

(Composition analysis)
The compositional analysis of the hydroxide (coprecipitate) and the lithium-containing composite oxide was performed using a plasma emission analyzer (SPS3100H, manufactured by SII Nanotechnology Inc.).

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

(Manufacturing of lithium secondary battery)
A negative electrode was prepared in which the negative electrode active material layer was a metal lithium foil having a thickness of 500 μm and the negative electrode current collector was a stainless plate having a thickness of 1 mm.
A 25 μm thick porous polypropylene was prepared as a separator.
As a non-aqueous electrolytic solution, a LiPF 6 solution with a concentration of 1 mol / dm 3 was prepared. A mixed solution of ethylene carbonate and diethyl carbonate (1: 1 by volume ratio) was used as a solvent of the non-aqueous electrolyte.
Using the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte, a stainless steel simple closed cell 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, discharged to 2.0 V at a load current of 20 mA per 1 g of the lithium-containing composite oxide, and the discharge capacity was measured.

(Cycle characteristics)
Next, charge and discharge cycles of charging to 4.6 V with a load current of 200 mA per 1 g of the lithium-containing composite oxide and high rate discharge to 2.0 V with a load current of 200 mA per 1 g of the lithium-containing composite oxide were repeated 100 times. At this time, the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was taken as the cycle maintenance rate.

(Example 1)
Process (a):
Nickel (II) sulfate hexahydrate, cobalt (II) sulfate heptahydrate and manganese (II) sulfate pentahydrate are prepared so that the molar ratio of Ni, Co and Mn is as shown in Table 1; And it melt | dissolved in distilled water so that the total amount (the density | concentration of the sum total of a metallic element) of sulfate might be 1.5 mol / kg, and the sulfate aqueous solution was obtained.
As a pH adjusting solution, 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 aqueous ammonium sulfate solution.

  Distilled water was placed in a 2 L baffled glass reaction vessel and heated to 50 ° C. with a mantle heater. While stirring the solution in the reaction vessel with a paddle type stirring blade, 5.0 g / min of an aqueous sulfate solution and 0.5 g / min of an aqueous ammonium sulfate solution are added, and the pH of the mixture is brought to 11.0. A pH adjusting solution was added to keep the same to precipitate hydroxides (coprecipitates) containing Ni, Co and Mn. During the addition of the raw material solution, nitrogen gas was flowed into the reaction vessel at a flow rate of 1.0 L / min. In addition, the liquid was continuously withdrawn so that the liquid volume in the reaction tank did not exceed 2 liters. In order to remove impurity ions from the obtained hydroxide, pressure filtration and dispersion in distilled water were repeated to perform washing. The washing was ended when the conductivity of the filtrate reached 20 mS / m, and dried at 120 ° C. for 15 hours.

Process (b):
After washing and drying, the hydroxide (18.00 g) and lithium carbonate having a Li content of 26.9 mol / kg (8.66 g) were mixed to obtain a mixture.

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

Process (d):
The primary heat-treated product is subjected to secondary heat treatment at 850 ° C. for 16 hours in an atmosphere containing 0.01% by volume of oxygen and the balance of nitrogen in a Tamman tube atmosphere electric furnace, and the lithium-containing composite oxide is Obtained.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(Example 2)
Process (a):
Nickel (II) sulfate hexahydrate and manganese (II) sulfate pentahydrate were mixed in such a manner that the molar ratio of Ni and Mn was as shown in Table 1, and the total amount of sulfates (total of metal elements It was dissolved in distilled water such that the concentration (concentration) was 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.

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

(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 the step (d) was 800 ° C.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(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 the step (d) was changed to 900 ° C.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(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 the step (d) was changed to an atmosphere in which the oxygen concentration is 0.5% by volume and the remainder is nitrogen.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(Example 6)
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 the step (d) was changed to an atmosphere in which the oxygen concentration is 1% by volume and the balance is nitrogen.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(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 the step (d) was changed to air.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(Example 8)
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 the step (d) was air, and the temperature was 1000 ° C.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(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 the step (d) was changed to 950 ° C.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(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 the step (d) was changed to air.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(Example 11)
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 the step (d) was changed to an atmosphere in which the oxygen concentration is 10% by volume and the remainder is nitrogen.
Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

(Example 12)
Process (a):
Nickel (II) sulfate hexahydrate, cobalt (II) sulfate heptahydrate and manganese (II) sulfate pentahydrate are prepared so that the molar ratio of Ni, Co and Mn is as shown in Table 1; And it melt | dissolved in distilled water so that the total amount (the density | concentration of the sum total of a metallic element) of sulfate might be 1.5 mol / kg, and the sulfate aqueous solution was obtained.
As a pH adjusting solution, an aqueous sodium carbonate solution in which sodium carbonate was dissolved in distilled water to a concentration of 1.5 mol / L was used.
Ammonium sulfate was dissolved in distilled water to a concentration of 0.375 mol / kg to obtain an aqueous ammonium sulfate solution.

  Distilled water was placed in a 2 L baffled glass reaction vessel and heated to 30 ° C. with a mantle heater. While stirring the solution in the reaction vessel with a paddle-type stirring blade, 2.5 g / min of an aqueous sulfate solution and 0.5 g / min of an aqueous ammonium sulfate solution were added, and the pH of the mixture was adjusted to 10.0. An aqueous carbonate solution was added to keep the mixture, to precipitate a carbonate (coprecipitate) containing Ni, Co and Mn. While the raw material solution was added, the liquid was continuously withdrawn so that the liquid volume in the reaction tank did not exceed 2 liters. In order to remove impurity ions from the obtained carbonate, pressure filtration and dispersion in distilled water were repeated to perform washing. The washing was ended when the conductivity of the supernatant liquid reached 20 mS / m, and dried at 120 ° C. for 15 hours.

Process (b):
After washing and drying, the carbonate (18.00 g) and lithium carbonate (7.29 g) having a Li content of 26.9 mol / kg were mixed to obtain a mixture. Steps (c) and (d) were performed in the same manner as Example 1. Tables 1 and 2 show production conditions of the lithium-containing composite oxide and evaluation results of the lithium secondary battery.

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

When Example 1 and Example 9 are compared, Example 1 has a high specific surface area of the obtained lithium-containing composite oxide, and has a high discharge capacity and cycle retention rate of the lithium secondary battery. Comparison of the production conditions of Example 1 and Example 9 is the same except that the temperature of the heat treatment in step (d) is different. From this, by setting the temperature of the heat treatment in 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.
When Example 1 and Example 7 are compared, Example 1 has a low specific surface area of the obtained lithium-containing composite oxide and a high cycle retention rate of the lithium secondary battery. When the manufacturing conditions of Example 1 and Example 7 are compared, it is the same except the atmosphere of the heat processing of a process (d) differing. From this, by setting the atmosphere of the heat treatment of 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 made 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 content)
After dispersing 1 g of the lithium-containing composite oxide in 10 g of distilled water and stirring for 30 minutes, it was filtered through a membrane filter. An additional 60 g of distilled water was added to the filtrate to measure the pH. The pH at this time was taken as the initial pH.
Next, titration was performed to pH 4.0 with 0.02 mol / L hydrochloric acid using the filtrate to which distilled water was added. At this time, it is assumed that the titration volume from the initial pH to pH 8.5 corresponds to the neutralization of LiOH and Li2CO3, and the titration volume of pH 8.5 to 4.0 corresponds to the neutralization of Li2CO3, and is included in the filtrate. The content of LiOH and Li ₂ CO ₃ was 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 taken as the free LiOH ratio. The sum of free LiOH ratio and 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 lithium-containing composite oxide is the free Li ratio And

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

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

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

  As shown in Table 3, it is understood 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 step (e) is performed at a temperature of 550 ° C. or higher.

The lithium-containing composite oxide obtained by the present production method is useful as a positive electrode active material for a lithium ion secondary battery.
Japanese Patent Application No. 2013-223344 filed on October 28, 2013,
And the specification, claims and abstract of Japanese Patent Application No. 2014-116015 filed on Jun. 4, 2014, the entire contents of which are incorporated herein by reference.
It is what it takes.

Claims (10)

Li _{1 + a} MO _b (where M is two or more metal elements (excluding Li), at least two of the metal elements are Ni and Mn, and the molar ratio of Mn to Ni (Mn / Li) containing lithium represented by 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 valence of Li and M. A method of producing a composite oxide, comprising
The manufacturing method of lithium containing complex oxide which has following process (a)-(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 a specific surface area of 5 to 80 m ² / g.
(B) The lithium compound and the hydroxide are selected so that the molar ratio of Li to the total number of moles of metal elements other than Li contained in the hydroxide (Li / M) is more than 1 and not more than 1.6. Mixing to obtain a mixture.
(C) A step of 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 to obtain a primary heat-treated product.
(D) a step of subjecting the first heat-treated product to a second heat treatment at a temperature of 800 ° C. or more and less than 950 ° C. in an atmosphere having an oxygen concentration of less than 5% by volume to obtain the lithium-containing composite oxide.   The method for producing a lithium-containing composite oxide according to claim 1, wherein the atmosphere in the step (d) is an atmosphere in which the oxygen concentration is less than 5% by volume and the balance is nitrogen.   The method for producing a lithium-containing composite oxide according to claim 1, wherein the step (d) is performed in a closed vessel. Furthermore, the manufacturing method of lithium containing complex oxide as described in any one of Claims 1-3 which has following process (e).
(E) A step of heat treating the lithium-containing composite oxide at a temperature of 400 to 800 ° C. in an atmosphere having an oxygen concentration of 5% by volume or more after the step (d). The method for producing a lithium-containing composite oxide according to any one of claims 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 not more than 0.6, 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 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. The method for producing a lithium-containing composite oxide according to any one of claims 1 to 5, wherein the specific surface area of the lithium-containing composite oxide is 0.9 to ⁴ m ² / g. The method for producing a lithium-containing composite oxide according to any one of claims 1 to 6, wherein the volume-based cumulative 50% diameter D _{50 of the} hydroxide is 3 to 18 μm. 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. The manufacturing method of lithium containing complex oxide as described in one term.   The positive electrode for lithium ion secondary batteries containing the lithium containing complex oxide obtained by the manufacturing method as described in any one of Claims 1-8.   The lithium ion secondary battery which has a positive electrode for lithium ion secondary batteries of Claim 9.