JPWO2015108163A1 - Positive electrode active material and method for producing the same - Google Patents

Abstract

Provided is a positive electrode active material that provides a lithium ion secondary battery having a high discharge capacity and a low DCR. It is a positive electrode active material including secondary particles in which a plurality of primary particles of lithium-containing composite oxide are aggregated, and the lithium-containing composite oxide is aLi (Li1 / 3Mn2 / 3) O2 · (1-a) LiMO2 (however, M represents at least one element selected from Ni, Co and Mn, and 0 <a <1), and the secondary particles have a cross-sectional porosity of 12 to 40%, and A positive electrode active material in which the isolated porosity of the positive electrode active material is 5% or less. And at least two selected from the group consisting of Ni sulfate, Co sulfate and Mn sulfate, and at least one selected from the group consisting of Na carbonate, K carbonate, NaOH and KOH. In the form of an aqueous solution to obtain a coprecipitate, and then the coprecipitate and lithium carbonate are mixed and fired.

Description

  The present invention relates to a positive electrode active material and a method for producing the same.

Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and notebook computers. As a positive electrode active material of a lithium ion secondary battery, a lithium-containing composite oxide containing Li and a transition metal element such as LiCoO ₂ , LiNiO ₂ , and LiNi _0.8 Co _0.2 O ₂ is known.
As the positive electrode active material of a lithium ion secondary _battery, represented by _{LiCo a Ni b Mn c O 2} ( provided that 0 <a <1,0 <b < 1,0 <c <1.) A so-called ternary lithium-containing composite oxide is also known.

Incidentally, in recent years, there has been an increasing demand for miniaturization and weight reduction in lithium ion secondary batteries for portable electronic devices and in-vehicle use, and the discharge capacity per unit mass (hereinafter simply referred to as “discharge capacity”). Further improvement is demanded.
As a positive electrode active material capable of increasing the discharge capacity of a lithium ion secondary battery, a positive electrode active material having a large content of Li and Mn, a so-called lithium-rich positive electrode active material has attracted attention.

As the lithium-rich positive electrode active material, for example, the following (i) and (ii) are proposed.
(I) having an α-NaFeO ₂ type crystal structure, Li _{1 + α} Me _1-α O ₂ (where Me is a transition metal element containing Co, Ni and Mn, α> 0, and 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 molar ratio of Mn to the transition metal element A positive electrode active material represented by a molar ratio (Mn / Me) of 0.62 to 0.72 (Patent Document 1).
_{(Ii) zLi 2 MnO 3 ·} (1-z) LiNi u + △ Mn u- △ Co w A y O 2 ( however, A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti , Ca, Ce, Y, Nb, Cr, Fe and V are one or more elements, z is 0.03 to 0.47, Δ is −0.3 to 0.3, 2u + w + y = 1, w is 0 to 1, u is 0 to 0.5, and y <0.1) (Patent Document 2).

International Publication No. 2012/091015 International Publication No. 2011/031546

  However, the lithium ion secondary battery having the lithium-rich positive electrode active material (i) or (ii) has a high direct current resistance (hereinafter abbreviated as DCR), and as a result, the charge / discharge cycle is repeated. In addition, there is a problem that characteristics for maintaining charge / discharge capacity (hereinafter referred to as cycle characteristics) are lowered.

  An object of this invention is to provide the positive electrode active material which can make high discharge capacity of a lithium ion secondary battery, and can make DCR low, and the manufacturing method of this positive electrode active material.

The present invention achieves the above-mentioned problems and has the following gist.
[1] A positive electrode active material including secondary particles in which a plurality of primary particles of lithium-containing composite oxide are aggregated,
The lithium-containing composite oxide has a general formula aLi (Li _1/3 Mn _2/3 ) O _2. (1-a) LiMO ₂ (where M is at least one element selected from Ni, Co and Mn). Represented by 0 <a <1),
A positive electrode active material characterized in that the secondary particles have a cross-sectional porosity of 12 to 40% and the positive porosity of the positive electrode active material is 5% or less.
[2] The lithium-containing composite oxide has a molar ratio with respect to the total molar amount (X) of Ni, Co, and Mn, the Ni ratio (Ni / X) is 0.15 to 0.5, and the Co ratio (Co / X) is 0 to 0.33, and the Mn ratio (Mn / X) is 0.33 to 0.8.
[3] The molar ratio of Li to the total molar amount (X) of Ni, Co and Mn in the lithium-containing composite oxide, and the Li ratio (Li / X) is 1.1 to 1.7. The positive electrode active material of [1] or [2].
[4] a positive electrode active particle diameter _{D 50} of the substance is 3 to 15 [mu] m, positive electrode active material of any one [1] to [3].
[5] The positive electrode active material according to any one of [1] to [4], wherein the positive electrode active material has a specific surface area of 0.1 to 10 m ² .
[6] Crystal structure of space group C2 / m with respect to integrated intensity (I ₀₀₃ ) of the (003) plane peak attributed to the crystal structure of space group R-3m in the X-ray diffraction pattern of the lithium-containing composite oxide The positive electrode active of any one of [1] to [5] above, wherein the ratio (I ₀₂₀ / I ₀₀₃ ) of the integrated intensity (I ₀₂₀ ) of the peak of the (020) plane belonging to material.
[7] A method for producing a positive electrode active material according to any one of the above [1] to [6], comprising the following steps (I) and (II).
(I) at least two sulfates (A) selected from the group consisting of Ni sulfate, Co sulfate and Mn sulfate;
A step of mixing a carbonate of Na, a carbonate of K, at least one alkali (B) selected from the group consisting of NaOH and KOH in the form of an aqueous solution to precipitate a coprecipitate.
(II) A step of mixing lithium carbonate and the coprecipitate and baking at 500 to 1000 ° C.
[8] The method for producing a positive electrode active material according to the above [7], wherein the total concentration of Ni, Co and Mn in the aqueous solution of the sulfate (A) is 0.1 to 2 mol / kg.
[9] The method for producing a positive electrode active material according to [7] or [8] above, wherein the concentration of alkali (B) in the aqueous solution of alkali (B) is 0.1 to 2 mol / kg.
[10] The above [7] to [7], wherein the ratio of the molar amount of Li contained in the lithium compound to the total molar amount (X) of Ni, Co and Mn contained in the coprecipitate is 1.1 to 1.7. 9] The manufacturing method of the positive electrode active material as described in any one of [9].

  If the positive electrode active material of this invention is used, the discharge capacity of a lithium ion secondary battery can be made high, and DCR can be reduced. Moreover, according to the manufacturing method of the positive electrode active material of this invention, the positive electrode active material which can make high the discharge capacity of a lithium ion secondary battery and can make DCR low can be obtained.

3 is a graph showing an X-ray diffraction pattern of the positive electrode active material of Example 1. 4 is a SEM image of a secondary particle cross section of the positive electrode active material of Example 1. 10 is a SEM image of a secondary particle cross section of the positive electrode active material of Example 8. 10 is a SEM image of a secondary particle cross section of the positive electrode active material of Example 10.

The following definitions of terms apply throughout this specification and the claims.
The notation “Li” indicates that the element is not Li alone but a Li element unless otherwise specified. The same applies to other notations such as Ni, Co, and Mn.
The composition analysis of the positive electrode active material is performed by inductively coupled plasma analysis (hereinafter referred to as ICP). The ratio of elements in the positive electrode active material is a value in the positive electrode active material before the first charge.
“Primary particle” means the smallest particle observed by a scanning electron microscope (SEM). The “secondary particle” means a particle in which primary particles are aggregated.
“D ₅₀ ” means a particle diameter at a point of 50% in a cumulative volume distribution curve in which the total volume of particle size distribution obtained on a volume basis is 100%, that is, a volume-based cumulative 50% diameter. The particle size distribution is obtained from a frequency distribution and a cumulative volume distribution curve measured with a laser scattering particle size distribution measuring apparatus. The particle size is measured by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like and measuring the particle size distribution (for example, using a laser diffraction / scattering particle size distribution measuring device).

<Positive electrode active material>
The positive electrode active material (hereinafter referred to as the present active material) of the present invention includes a solid solution lithium-containing composite oxide (1) (hereinafter referred to as a composite oxide (1)).
The composite oxide (1) has the general formula aLi (Li _1/3 Mn _2/3 ) O _2. (1-a) LiMO ₂ (where M is at least one element selected from Ni, Co and Mn). And 0 <a <1.) That is, the composite oxide (1) is a solid solution of Li (Li _1/3 Mn _2/3 ) O ₂ and LiMO ₂ .
Since this active material contains complex oxide (1), the discharge capacity of the lithium ion secondary battery which has this active material can be made high.

  The a in the general formula is preferably 0.1 to 0.78, and more preferably 0.2 to 0.75. When this active material contains the complex oxide (1) in which a is 0.1 or more, the discharge capacity of the lithium ion secondary battery can be easily increased. When the active material contains a composite oxide (1) having a of 0.7 or less, the discharge voltage of the lithium ion secondary battery tends to be high.

  From the viewpoint of increasing the discharge capacity of the lithium ion secondary battery, M of the composite oxide (1) preferably contains Ni and Mn, and more preferably contains Ni, Co, and Mn.

  In the composite oxide (1), each content of Ni, Co and Mn is a molar ratio with respect to the total molar amount (X) of Ni, Co and Mn, and the Ni ratio (Ni / X) is 0.15. It is preferable that -0.5, Co ratio (Co / X) is 0-0.33, and Mn ratio (Mn / X) is 0.33-0.8. When the active material contains the composite oxide (1) in which the Ni ratio, the Co ratio, and the Mn ratio are in the above ranges, the discharge capacity of the lithium ion secondary battery can be easily increased, and the cycle characteristics can be easily improved.

  The Ni ratio is more preferably 0.15 to 0.45, and particularly preferably 0.15 to 0.37. When the active material contains the composite oxide (1) having a Ni ratio of 0.15 or more, the discharge voltage of the lithium ion secondary battery can be easily increased. When the active material contains the composite oxide (1) having a Ni ratio of 0.45 or less, the discharge capacity of the lithium ion secondary battery can be easily increased.

  The Co ratio is more preferably 0 to 0.3, and particularly preferably 0 to 0.25. The positive electrode active material containing the composite oxide (1) whose Co ratio is not more than the upper limit value has better cycle characteristics of the lithium ion secondary battery.

  The Mn ratio is more preferably 0.4 to 0.82, and particularly preferably 0.5 to 0.8. When the active material includes the composite oxide (1) having a Mn ratio of 0.4 or more, the discharge capacity of the lithium ion secondary battery can be easily increased. When this active material contains the complex oxide (1) whose Mn ratio is 0.82 or less, it is easy to increase the discharge voltage of the lithium ion secondary battery.

  In the composite oxide (1), the Li ratio (Li / X) is preferably 1.1 to 1.7 in terms of the molar ratio with respect to the total molar amount (X) of Ni, Co and Mn. The Li ratio is more preferably 1.1 to 1.67, and particularly preferably 1.25 to 1.6. When this active material contains the complex oxide (1) whose Li ratio is in the above range, the discharge capacity of the lithium ion secondary battery can be increased.

  The composite oxide (1) may contain elements other than Li, Ni, Co, and Mn. Examples of other elements include P. When this preferable active material contains the complex oxide (1) containing P, the cycle characteristics of the lithium ion secondary battery can be improved.

Composite oxides (1) has the general _{formula aLi (Li 1/3 Mn 2/3) O} 2 · (1-a) LiNi b Co c Mn d O 2 ( however, b is from 0.33 to 0.6, c is 0 to 0.33, and d is 0.33 to 0.5). Further, b is more preferably 0.33 to 0.5.

The composite oxide (1) is a solid solution of Li (Li _1/3 Mn _2/3 ) O ₂ and LiMO ₂ and has two crystal structures. Li (Li _1/3 Mn _2/3 ) O ₂ has a layered rock salt type crystal structure of the space group C2 / m. The crystal structure of the space group C2 / m is also called a lithium excess phase. LiMO ₂ has a layered rock salt type crystal structure of space group R-3m. It can be confirmed by X-ray diffraction measurement that the complex oxide (1) has these crystal structures.

The (020) plane of the crystal structure of the space group C2 / m with respect to the integrated intensity (I ₀₀₃ ) of the peak of the (003) plane of the crystal structure of the space group R-3m in the X-ray diffraction pattern of the composite oxide (1) The ratio (I ₀₂₀ / I ₀₀₃ ) of the peak integrated intensity (I ₀₂₀ ) is preferably 0.02 to 0.3. In a preferred embodiment of the present active material, the composite oxide (1) having I ₀₂₀ / I ₀₀₃ in the above range includes the above-mentioned two crystal structures in a balanced manner, so that the discharge capacity of the lithium ion secondary battery can be easily increased. . From the viewpoint of increasing the discharge capacity of the lithium ion secondary battery, I ₀₂₀ / I ₀₀₃ is more preferably 0.02 to 0.28, and further preferably 0.02 to 0.25.
X-ray diffraction measurement can be performed by the method described in the examples. The (003) plane peak of the crystal structure of the space group R-3m is a peak appearing at 2θ = 18 to 19 °. The peak on the (020) plane of the crystal structure of the space group C2 / m is a peak that appears at 2θ = 20-21 °.

  The active material includes secondary particles in which a plurality of primary particles of the composite oxide (1) are aggregated. In this active material, the porosity of the cross section of the secondary particles is 12 to 40%. If the active material having a porosity within the above range is used, the DCR of the lithium ion secondary battery can be reduced. The lower limit value of the porosity is preferably 13%, and more preferably 14%. The upper limit value of the porosity of the cross section of the secondary particles is preferably 38% and more preferably 33%.

“Porosity of the cross section of the secondary particles” is a value calculated as follows. An image obtained by binarizing the SEM image obtained by observing the cross section of the secondary particles (for example, the portion where the primary particles are present is white, the void portion where the primary particles are not present and the outside of the secondary particles are black) )) Using image analysis software, fill the outer part of the secondary particle and the part connected to the outer part of the void part in the secondary particle with the third color (color other than white and black). . The total number of dots of the portion where the primary particles are present (white portion) in the secondary particle cross section is N _A , the portion not filled in the third color in the void portion of the secondary particle cross section, that is, the secondary particle cross section the total number of partial dots in the (black portion) which is not connected to the outer side in the gap portion as N _B, obtains the void ratio (%) by the following equation (1). The porosity is obtained for a total of 20 secondary particles, and the average of these is taken as the porosity of the cross section of the secondary particles.
(Porosity) = N _B / (N _A + N _B ) × 100 (1)

The isolated porosity of the active material is 5% or less. Since this active material has an isolated porosity of 5% or less, the DCR of the lithium ion secondary battery can be reduced. The isolated porosity is preferably 4% or less, and more preferably 3% or less.
Moreover, it is preferable that this active material has a hole (henceforth a through-hole) which has a hollow part inside a secondary particle, and leads from the exterior to a hollow part. It is preferable that the positive electrode active material has a through hole because the isolated porosity is reduced.

The “isolated porosity of the positive electrode active material” is a value calculated as follows. The apparent density d1 of the positive electrode active material is measured using nitrogen gas by a pycnometer method. Also, the lattice constant of the positive electrode active material is measured by X-ray diffraction, and the theoretical crystal density d2 is calculated from the lattice constant. The isolated porosity (%) is calculated by the following equation (2).
(Isolated porosity) = (d2-d1) / d2 × 100 (2)

  The active material may be the composite oxide (1) as the active material, or may have a coating on the surface of the composite oxide (1) as the active material. The active material having a coating on the surface of the composite oxide (1) is preferable because it can improve the cycle characteristics of the lithium ion secondary battery. When the surface of the composite oxide (1) has a coating, the contact frequency between the composite oxide (1) and the electrolyte decreases, and as a result, transition metal elements such as Mn in the composite oxide (1) are reduced. It is thought that elution can be reduced.

As the coating existing on the surface of the composite oxide (1) of the active material, the cycle characteristics can be improved without lowering other battery characteristics, so that Al compounds (Al ₂ O ₃ , AlOOH, Al (OH ₃ ) is preferred.
The coating may be present on the surface of the complex oxide (1), may be present on the entire surface of the complex oxide (1), or may be present on a part of the complex oxide (1).

D _{50 of the} present active material is preferably 3 to 15 μm. Within D ₅₀ of the range, easily increase the discharge capacity of the lithium ion battery. D _{50 of the} present active material is more preferably 5 to 15 μm, and particularly preferably 6 to 12 μm.

The specific surface area of the active material is preferably 0.1 to 10 m ² / g. When the specific surface area of this active material is 0.1 m ² / g or more, the discharge capacity of the lithium ion secondary battery can be increased. When the specific surface area of this active material is 10 m ² / g or less, the cycle characteristics of the lithium ion secondary battery can be improved. The specific surface area of the active material is more preferably ^{0.5~7m 2 / g, 0.5~5m 2 /} g is particularly preferred. The specific surface area of the active material is measured by the method described in the examples.

<Method for producing positive electrode active material>
The method for producing a positive electrode active material of the present invention (hereinafter referred to as the present production method) preferably has the following steps (I) and (II).
(I) a group consisting of at least two sulfates (A) selected from the group consisting of Ni sulfate, Co sulfate and Mn sulfate, Na carbonate, K carbonate, NaOH and KOH A step of mixing at least one alkali (B) selected from the above in the form of an aqueous solution and reacting in the mixed solution to precipitate a coprecipitate containing a metal.
(II) A step of mixing the metal-containing coprecipitate and lithium carbonate and baking at 500 to 1000 ° C.

[Step (I)]
In step (I), sulfate (A) and alkali (B) are mixed in the form of an aqueous solution and reacted in the mixed solution. Thereby, a coprecipitate containing at least two kinds of transition metal elements selected from the group consisting of Ni, Co and Mn is deposited. In step (I), other solutions may be mixed as necessary.

The aspect which mixes sulfate (A) and alkali (B) in the state of aqueous solution will not be specifically limited if sulfate (A) and alkali (B) are in the state of aqueous solution at the time of mixing.
Specifically, since the coprecipitate is easy to precipitate and the particle size of the coprecipitate is easy to control, both the aqueous solution of sulfate (A) and the aqueous solution of alkali (B) are continuously added to the reaction tank. It is preferable to add to. It is preferable to put ion exchange water, pure water, distilled water, etc. in the reaction tank in advance. Furthermore, it is more preferable to control the pH in the reaction vessel using alkali (B) or other solutions.
The pH of the mixed solution when the sulfate (A) and the alkali (B) are mixed is preferably maintained at a value set in the range of 7 to 12, since the coprecipitate is easily precipitated. It is more preferable to maintain the set value of 10.

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

  The sulfate (A) preferably includes Ni sulfate and Mn sulfate, and more preferably includes all of Ni sulfate, Co sulfate, and Mn sulfate. That is, the coprecipitate obtained in the step (I) is preferably a coprecipitate containing Ni and Mn, and more preferably a coprecipitate containing all of Ni, Co and Mn.

  The aqueous solution of sulfate (A) may be a separate aqueous solution of each of two or more sulfates (A), or a single aqueous solution containing two or more sulfates (A). Moreover, you may use together the aqueous solution containing 1 type of sulfates (A), and the aqueous solution containing 2 or more types of sulfates (A). The same applies when two types of alkalis (B) are used.

  The ratio of Ni contained in the sulfate (A) is preferably 0.15 to 0.5 in terms of a molar ratio with respect to the total molar amount of Ni, Co and Mn contained in the sulfate (A). If the ratio of Ni is 0.15 to 0.5, a composite oxide (1) having a desired composition can be obtained. For the same reason, the Ni ratio is more preferably 0.15 to 0.45, and particularly preferably 0.15 to 0.37.

  The ratio of Co contained in the sulfate (A) is preferably 0 to 0.33 in terms of a molar ratio with respect to the total molar amount of Ni, Co and Mn contained in the sulfate (A). If the ratio of Co is 0 to 0.33, a composite oxide (1) having a desired composition can be obtained. For the same reason, the proportion of Co is more preferably 0 to 0.3, and particularly preferably 0 to 0.25.

  The ratio of Mn contained in the sulfate (A) is preferably 0.33 to 0.8 in terms of a molar ratio with respect to the total molar amount of Ni, Co and Mn contained in the sulfate (A). If the ratio of Mn is 0.33 to 0.8, a composite oxide (1) having a desired composition can be obtained. For the same reason, the ratio of Mn is more preferably 0.4 to 0.82, and particularly preferably 0.5 to 0.8.

The total concentration of Ni, Co and Mn in the aqueous solution of sulfate (A) is preferably 0.1 to 2 mol / kg, and more preferably 0.5 to 1.6 mol / kg. If the concentration is equal to or higher than the lower limit, productivity is high. When the concentration of sulfate (A) is 2 mol / kg or less, sulfate (A) can be sufficiently dissolved in water.
When using 2 or more types of aqueous solution containing a sulfate (A), it is preferable to make the density | concentration of a transition metal element (X) into the said range about each aqueous solution.

The alkali (B) is at least one selected from the group consisting of Na carbonate, K carbonate, NaOH and KOH. Alkali (B) also serves as a pH adjuster for precipitating the coprecipitate. When Na carbonate or K carbonate is used as the alkali (B), a coprecipitate of a carbonate compound containing metal is obtained. Further, when NaOH or KOH is used as the alkali (B), a metal-containing hydroxide coprecipitate is obtained.
Alkali (B) may be used alone or as a mixture of two or more. From the viewpoint of ease of production of the composite oxide (1), the alkali (B) is preferably at least one carbonate selected from the group consisting of Na carbonate and K carbonate.
Examples of the carbonate of Na include sodium carbonate and sodium hydrogen carbonate.
Examples of the carbonate of K include potassium carbonate and potassium hydrogen carbonate.
As the carbonate, sodium carbonate and potassium carbonate are preferable because they are inexpensive and easy to control the particle size of the coprecipitate.

The concentration of alkali (B) in the aqueous solution of alkali (B) is preferably 0.1 to 2 mol / kg, more preferably 0.5 to 1.6 mol / kg. When the concentration of the alkali (B) is 0.1 to 2 mol / kg, the coprecipitate is likely to be precipitated by the coprecipitation reaction.
When using 2 or more types of aqueous solution containing an alkali (B), it is preferable to make the density | concentration of an alkali (B) into the said range about each aqueous solution.

Other solutions that may be mixed in step (I) include, for example, an aqueous solution containing ammonia or an ammonium salt. These function to adjust the pH and the solubility of the transition metal element. Examples of ammonium salts include ammonium chloride, ammonium sulfate, and ammonium nitrate.
Ammonia or ammonium salt is preferably supplied to the mixed solution simultaneously with the supply of sulfate (A).

As a solvent for the aqueous solution of sulfate (A), the aqueous solution of alkali (B), and other solutions, water is preferable. If the sulfate (A) and the alkali (B) can be dissolved, a mixed medium containing an aqueous medium other than water up to 20% with respect to the total mass of the solvent may be used as the solvent.
Examples of components other than water include methanol, ethanol, 1-propanol, 2-propanol, polyol and the like. Examples of the polyol include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, butanediol, glycerin and the like.

When mixing a sulfate (A) and an alkali (B) in the state of aqueous solution, it is preferable to carry out stirring in a reaction tank.
Examples of the stirring device include a three-one motor. Examples of the stirring blade include a stirring blade such as an anchor type, a propeller type, and a paddle type.

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

  As a preferable method for mixing the sulfate (A) and the alkali (B) in the state of an aqueous solution to precipitate a coprecipitate, the mixed solution in the reaction vessel is filtered using a filter medium (filter cloth or the like). A method in which the precipitation reaction is performed while concentrating the coprecipitate (hereinafter referred to as a concentration method), and the mixed solution in the reaction vessel is extracted together with the coprecipitate without using a filter medium to keep the concentration of the carbonate compound low. However, there are two types of methods (hereinafter referred to as overflow method) in which the precipitation reaction is performed.

Step (I) is preferably a concentration method. The secondary particles of the lithium-containing composite oxide obtained by the concentration method and using the coprecipitate are likely to have a porosity of the cross section of the secondary particles satisfying the above range. Moreover, the positive electrode active material obtained using the coprecipitate obtained by the concentration method tends to satisfy the above range in the isolated porosity of the positive electrode active material.
This is considered as follows. In the concentration method, since the solid content concentration of the coprecipitate in the mixed solution in the reaction tank is high, the primary particles of the coprecipitate are aggregated, and secondary particles of the dense coprecipitate are easily formed. Secondary particles of the coprecipitate are likely to aggregate. When the secondary particles of the coprecipitate aggregate, the particle surface becomes dense. For example, in the case where the coprecipitate is a carbonate compound, in the step (II), when the lithium compound and the carbonate compound are mixed and the mixture is baked, if the particle surface is dense, the lithium compound is transformed into Li Does not easily enter the inside of the carbonic acid compound. Therefore, while carbonic acid is removed by firing, atoms inside the carbonic acid compound tend to move to the surface of the carbonic acid compound to form a lithium-containing composite oxide. As a result, the secondary particles of the lithium-containing composite oxide obtained after calcination have a reduced volume reduction from the mixture, and a hollow portion and a hole communicating from the outside to the hollow portion are formed. The porosity and the isolated porosity of the positive electrode active material tend to satisfy the above range.

  On the other hand, in the overflow method, the precipitated coprecipitate is withdrawn from time to time together with the mixed solution, so that the solid content concentration of the coprecipitate in the mixed solution in the reaction vessel is low. For this reason, the secondary particles of the coprecipitate are less likely to agglomerate, and spherical and uniform secondary particles of the coprecipitate having many pores into which Li can enter are likely to be formed. For example, when the coprecipitate is a carbonate compound, when the carbonate compound and the lithium compound are mixed in step (II) and the mixture is baked, the carbonate is removed while the secondary compound of the carbonate compound is removed. There is a tendency that Li intrudes into the particles to form a lithium-containing composite oxide. Therefore, it is considered that the secondary particles of the lithium-containing composite oxide obtained after calcination are greatly reduced in volume from the mixture before calcination and are likely to be solid particles.

Furthermore, desired hollow particles can be easily obtained by controlling the conditions of the precipitation reaction.
A longer reaction time is preferred. Thereby, the particle surface of a coprecipitate tends to become dense. As a result, it tends to become hollow particles after firing.
It is preferable that the initial pH of the reaction vessel is high. Thereby, the ionic strength in a reaction tank becomes high and aggregation of a coprecipitate tends to advance. As a result, it tends to become hollow particles after firing.
Higher control pH during the reaction and higher reaction temperature are preferred. Thereby, aggregation of a coprecipitate tends to advance. As a result, there is a tendency to become hollow particles after firing.

  The preferred ranges of the respective proportions of Ni, Co and Mn in the coprecipitate obtained are the same as the preferred ranges of the respective proportions of Ni, Co and Mn in all the sulfates (A) used.

The D ₅₀ of the coprecipitate is preferably 3 to 15 μm, more preferably 6 to 15 μm, and particularly preferably 6 to 12 μm. Within D ₅₀ is the range of the coprecipitate, easily controlled within the preferred range of D ₅₀ of the positive electrode active material, easy positive electrode active material was obtained showing a sufficient battery characteristics.

The specific surface area of a coprecipitate is preferably ^{50~300m 2 / g, 100~250m 2 /} g is more preferable. If the specific surface area of the coprecipitate is within the above range, the positive electrode active material is easy to control the specific surface area of the positive electrode active material within the above range, and a lithium ion secondary battery exhibiting high discharge capacity and cycle characteristics is obtained. Easy to manufacture.
In addition, the specific surface area of a coprecipitate means the value measured after drying the said coprecipitate at 120 degreeC for 15 hours. The specific surface area of the coprecipitate can be measured by the BET method.

Step (I) preferably includes a step of removing the aqueous solution by filtration or centrifugation after obtaining the coprecipitate. For filtration or centrifugation, a pressure filter, a vacuum filter, a centrifugal classifier, a filter press, a screw press, a rotary dehydrator, or the like can be used.
The obtained coprecipitate is preferably washed to remove impurity ions. Examples of the method for washing the coprecipitate include a method of repeating pressure filtration and dispersion in distilled water.
It is preferable to dry the coprecipitate after washing.
When drying, 60-200 degreeC is preferable and, as for drying temperature, 80-130 degreeC is more preferable. If the said drying temperature is more than a lower limit, a coprecipitate can be dried in a short time. If the said drying temperature is below an upper limit, the oxidation of a coprecipitate can be suppressed.
When drying, the drying time is preferably 1 to 300 hours, more preferably 5 to 120 hours.

[Step (II)]
In step (II), the coprecipitate obtained in step (I) and the lithium compound are mixed and baked at 500 to 1000 ° C. Thereby, the complex oxide (1) is formed.
The lithium compound is preferably at least one selected from the group consisting of lithium carbonate, lithium hydroxide and lithium nitrate, and lithium carbonate is more preferable from the viewpoint of ease of handling.
Examples of the method for mixing the coprecipitate and lithium carbonate include a method using a rocking mixer, a nauta mixer, a spiral mixer, a cutter mill, a V mixer, and the like.

  In the step (II), the ratio (mixing ratio) of the molar amount of Li contained in the lithium compound to the total molar amount (X) of Ni, Co and Mn contained in the coprecipitate is 1.1 to 1.7. Preferably, 1.1 to 1.67 is more preferable, and 1.25 to 1.6 is particularly preferable. When the mixing ratio is within the above range, the Li ratio of the composite oxide (1) can be set to a desired range, and a positive electrode active material exhibiting a high discharge capacity is easily obtained.

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

A calcination temperature is 500-1000 degreeC, 600-1000 degreeC is preferable and 800-950 degreeC is especially preferable. When the firing temperature is within the above range, a complex oxide (1) having high crystallinity can be obtained.
The higher the firing temperature, the easier the atoms in the coprecipitate move to the surface of the coprecipitate. As a result, the porosity of the cross section of the secondary particles and the isolated porosity of the positive electrode active material tend to satisfy the above range. On the other hand, if the firing temperature is too high, a hetero phase such as spinel is generated in the composite oxide, which is not preferable.

The firing time is preferably 4 to 40 hours, and more preferably 4 to 20 hours.
When the firing time is increased, atoms inside the coprecipitate can move to the surface of the coprecipitate. Therefore, the porosity of the cross section of the secondary particles and the isolated porosity of the positive electrode active material tend to satisfy the above range.

Firing may be one-step firing at 500 to 1000 ° C., or two-step firing in which main firing is performed at 700 to 1000 ° C. after preliminary firing at 400 to 700 ° C. Among these, two-stage firing is preferable because Li easily diffuses uniformly into the lithium-containing composite oxide.
400-700 degreeC is preferable and the temperature of the temporary baking in the case of two-step baking has more preferable 500-650 degreeC. Moreover, 700-1000 degreeC is preferable and the temperature of the main baking in the case of two-stage baking has more preferable 800-950 degreeC.

In addition, the manufacturing method of complex oxide (1) contained in this active material is not limited to an above described method.
For example, the coprecipitate obtained in step (I) is mixed with a phosphate aqueous solution (phosphoric acid aqueous solution, ammonium dihydrogen phosphate aqueous solution, diammonium hydrogen phosphate aqueous solution, etc.), and the water is volatilized. Also good. By this step, the primary particles of the positive electrode active material can be doped with P (phosphorus).

Examples of the method for forming a coating on the surface of the secondary particles include a powder mixing method, a gas phase method, a spray coating method, and an immersion method. These methods will be described using an example in which an Al compound is used as a coating.
The powder mixing method is a method in which secondary particles and an Al compound are mixed and then heated. The vapor phase method is a method in which an organic compound containing Al such as aluminum ethoxide, aluminum isopropoxide, aluminum acetylacetonate, etc. is vaporized, and the organic compound is brought into contact with the surface of secondary particles to cause a reaction. The spray coating method is a method of heating after spraying a solution containing Al onto secondary particles.
In addition, an Al water-soluble compound (aluminum acetate, aluminum oxalate, aluminum citrate, aluminum lactate, basic aluminum lactate, aluminum nitrate, etc.) for forming an Al compound is dissolved in the secondary particles after firing in a solvent. After the contacted aqueous solution is brought into contact by a spray coating method or the like, a coating containing an Al compound may be formed on the surface of the secondary particles by heating to remove the solvent.

  Since this active material is a lithium-rich positive electrode active material, a lithium ion secondary battery having a high discharge capacity can be obtained. In addition, this active material satisfies the condition that the porosity of the cross section of the secondary particles is 12 to 40% and the isolated porosity of the positive electrode active material is 5% or less. Thereby, DCR of the lithium ion secondary battery which has this active material can be made low.

Japanese Patent Application Laid-Open No. 2011-119092 discloses Li _{1 + m} Ni _p Co _q Mn _r M ¹ _s O ₂ having a hollow part inside a secondary particle and having a through hole penetrating from the outside to the hollow part. M ¹ is at least one selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, Ta, W, Cu, Zn, Ga, In, Sn, La, and Ce. 0 ≦ m ≦ 0.2, 0.1 ≦ p ≦ 0.9, 0 ≦ q ≦ 0.5, 0 ≦ r ≦ 0.5, 0 ≦ s ≦ 0 0.02, and p + q + r + s = 1)), a so-called ternary positive electrode active material is disclosed.
Further, WO 2012/153379, the same hollow portion and the through-hole in the secondary particles are _{formed, Li 1 + e Ni f Co} g Mn (1-f-g) M 2 h O 2 ( where M ² is at least one selected from the group consisting of Zr, W, Mg, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B, and F, and 0 ≦ e ≦ 0.2 And 0.1 <f <0.9, 0.1 <g <0.4, and 0 ≦ h ≦ 0.01.) The substance is disclosed.
In addition, in International Publication No. 2013/031478, Li _{1 + i} Ni _j Co _k Mn _(1- jk ₎ W _β M ³ _γ O ₂ (in which similar hollow portions and through holes are formed in the secondary particles. M ² is at least one selected from the group consisting of Zr, Mg, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B, and F, and 0 ≦ i ≦ 0.2 0.1 <j <0.9, 0.1 <k <0.4, 0.0005 ≦ β ≦ 0.01, and 0 ≦ γ ≦ 0.1. A so-called ternary positive electrode active material represented by
In addition, International Publication No. 2012/169083 includes Li _{1 + δ} Ni _ε Mn _η Co _ζ M ⁴ _φ O ₂ (where M ⁴ is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, At least one selected from the group consisting of W, ε + η + ζ + φ = 1, −0.05 ≦ δ ≦ 0.50, 0.3 ≦ ε ≦ 0.7, 0.1 ≦ η ≦ 0.55, 0 ≦ ζ ≦ 0.4, and 0 ≦ φ ≦ 0.1), and has a hollow portion and a hexagonal layered crystal lithium nickel manganese composite oxide A so-called ternary positive electrode active material composed of a single material layer is disclosed.

These documents all describe a ternary positive electrode active material having a hollow portion. However, in these documents, a lithium-rich positive electrode active material that has a hollow portion inside the secondary particles and the porosity of the cross section of the secondary particles and the isolated porosity of the positive electrode active material satisfy the above ranges is used. Is not listed. Moreover, it is not disclosed that a lithium ion secondary battery can have a high discharge capacity and a low DCR by using such a lithium-rich positive electrode active material. Further, since a lithium ion secondary battery using a ternary positive electrode active material has a low DCR, it can be said that lowering the DCR of a lithium ion secondary battery is a problem inherent to the lithium rich positive electrode active material.
The present invention solves a problem peculiar to the case of using a lithium-rich positive electrode active material that can increase the discharge capacity of a lithium ion secondary battery but cannot lower DCR, and the present invention can solve the problem. Is difficult to predict from the descriptions of JP 2011-119092 A, International Publication No. 2012/169083, International Publication No. 2013/031478, and International Publication No. 2012/169083.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description. Examples 1 to 7 and 12 are examples, and examples 8 to 11 and 13 are comparative examples. Examples 14 and 15 are reference examples.
[Specific surface area]
The specific surface area was measured by a nitrogen adsorption BET (Brunauer, Emmett, Teller) method using a specific surface area measuring device (manufactured by Mountec, device name: HM model-1208). Deaeration was performed at 200 ° C. for 20 minutes.

[Particle size]
Sufficiently disperse particles in water by ultrasonic treatment, and measure with a laser diffraction / scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., apparatus name: MT-3300EX) to obtain a frequency distribution and a cumulative volume distribution curve A volume-based particle size distribution was obtained. In the obtained cumulative volume distribution curve was, points cumulative volume becomes 50% (average) particle diameter is D _50.

[X-ray diffraction]
X-ray diffraction measurement was performed with an X-ray diffractometer (manufactured by Rigaku Corporation, apparatus name: SmartLab). Table 1 shows the measurement conditions. The measurement was performed at 25 ° C. The obtained X-ray diffraction pattern was subjected to peak search using integrated powder X-ray analysis software PDXL2 manufactured by Rigaku Corporation. From there, the integrated intensity (I ₀₀₃ ) of the peak of the (003) plane attributed to the crystal structure of the space group R-3m and the integrated intensity of the peak of the (020) plane attributed to the crystal structure of the space group C2 / m ( I ₀₂₀ ) was determined, and the ratio (I ₀₂₀ / I ₀₀₃ ) was calculated.

[Porosity]
A sample obtained by polishing a positive electrode active material embedded with an epoxy resin with diamond abrasive grains was used, and the cross section of secondary particles was observed by SEM. Next, in the image obtained by binarizing the obtained SEM image by the image analysis software, the outer part of the secondary particle and the part connected to the outer part of the void part in the secondary particle are displayed in the third color (green). ). Next, the total number of dots of the portion where the primary particles are present (white portion) in the secondary particle cross section is N _A , and the portion not filled in the third color in the void portion in the secondary particle cross section, ie, the second the total number of dots of the following particle cross section which is not connected to the outer side in the gap portion of the (black portion) as N _B, the porosity (%) was determined by the following equation (1). The porosity was determined for a total of 20 secondary particles, and the average value of these was taken as the porosity of the cross section of the secondary particles.
(Porosity) = N _B / (N _A + N _B ) × 100 (1)

[Isolated porosity]
The apparent density d1 of the positive electrode active material was measured using nitrogen gas by a pycnometer method using a fully automatic pycnometer (Ultrapyc 1200e, manufactured by QUANTACHROME). Further, the lattice constant of the secondary particles was obtained from the result of X-ray diffraction, and the theoretical crystal density d2 of the positive electrode active material was obtained by calculation from the lattice constant. Next, the isolated porosity (%) was calculated by the following formula (2).
(Isolated porosity) = (d2-d1) / d2 × 100 (2)

[Composition analysis]
The composition of the lithium-containing composite oxide contained in the positive electrode active material is a value calculated from the amount of sulfate and lithium compound charged. _{aLi (Li 1/3 Mn 2/3) O} 2 · (1-a) LiNi b Co c Mn a of when expressed in d _{O 2,} b, was calculated c and d.

[Charge capacity, discharge capacity, charge / discharge efficiency]
(Manufacture of positive electrode sheet)
The positive electrode active material obtained in each example, acetylene black as a conductive material, and polyvinylidene fluoride (binder) were weighed so that the mass ratio was 80:10:10, and these were added to N-methylpyrrolidone. A slurry was prepared.
Next, the slurry was coated on one side of an aluminum foil (positive electrode current collector) having a thickness of 20 μm with a doctor blade. The gap of the doctor blade was adjusted so that the sheet thickness after rolling was 30 μm. After drying this at 120 degreeC, roll press rolling was performed twice and the positive electrode body sheet | seat was produced.
(Manufacture of lithium secondary batteries)
The obtained positive electrode sheet was punched into a circle with a diameter of 18 mm as a positive electrode, and a stainless steel simple sealed cell type lithium secondary battery was assembled in an argon glove box. A stainless steel plate having a thickness of 1 mm was used as the negative electrode current collector, and a metal lithium foil having a thickness of 500 μm was formed on the negative electrode current collector to form a negative electrode. As the separator, porous polypropylene having a thickness of 25 μm was used. In addition, a solution in which LiPF ₆ was dissolved in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1 so that the concentration was 1 mol / dm ³ was used as an electrolytic solution.

(Measuring method)
The battery characteristics (charge capacity, discharge capacity, and charge / discharge efficiency) of the lithium secondary batteries having the positive electrode active materials of Examples 1 to 13 were measured under the following conditions. After constant current charging to 4.6V with a load current of 20 mA per 1 g of the positive electrode active material, 4.6 V constant voltage charging was performed. The constant current charge and the constant voltage charge were combined for 23 hours. Then, it discharged to 2.0V with the load current of 20 mA per 1g of positive electrode active materials, and performed first charge / discharge. The ratio of the discharge capacity to the charge capacity at that time was defined as the charge / discharge efficiency.
The battery characteristics of the lithium secondary batteries having the positive electrode active materials of Examples 14 and 15 were measured under the following conditions. After constant current charging to 4.3 V with a load current of 16 mA per 1 g of the positive electrode active material, constant voltage charging of 4.3 V was performed until the current value reached 1.6 mA per 1 g of the positive electrode active material. Then, it discharged to 2.0V with the load current of 16 mA per 1g of positive electrode active materials, and performed initial charge / discharge. The ratio of the discharge capacity to the charge capacity at that time was defined as the charge / discharge efficiency.

[DCR]
The DCR of the lithium secondary battery having the positive electrode active material of Examples 1 to 13 was measured under the following conditions. After the first charge / discharge, a 3.75 V constant current / constant voltage charge was performed for 3 and a half hours, and then the battery was discharged for 1 minute at a load current of 60 mA per 1 g of the positive electrode active material. The DCR value was calculated by dividing the voltage drop 10 seconds after the start of discharge by the current value.
The DCR of the lithium secondary battery having the positive electrode active material of Examples 14 and 15 was measured under the following conditions. After the first charge / discharge, a 3.75 V constant current / constant voltage charge was performed for 3 and a half hours, and then the battery was discharged for 1 minute at a load current of 52 mA per 1 g of the positive electrode active material. The DCR value was calculated by dividing the voltage drop 10 seconds after the start of discharge by the current value.

[Example 1]
Nickel sulfate (II) hexahydrate, cobalt sulfate (II) heptahydrate, manganese sulfate (II) pentahydrate so that the ratio of Ni, Co and Mn is as shown in Table 2. And it melt | dissolved in distilled water so that the total density | concentration of Ni, Co, and Mn might be 1.5 mol / L, and sulfate aqueous solution was obtained. Further, 1271 g of sodium carbonate was dissolved in 6729 g of distilled water to prepare a carbonate aqueous solution (pH adjusting solution).
Next, distilled water is put into a 2 L baffled glass reaction vessel and heated to 25 ° C. with a mantle heater, and the addition rate is 5.0 g while stirring the solution in the reaction vessel with a two-stage inclined paddle type stirring blade. The aqueous sulfate solution was added at a rate of 25 minutes per minute. During the addition of the sulfate aqueous solution, a pH adjusting solution was added so as to keep the pH in the reaction vessel at 8.5, thereby precipitating a carbonate compound (coprecipitate) containing Ni, Co and Mn. The initial pH of the mixed solution was 7.0. During the precipitation reaction, nitrogen gas was flowed into the reaction vessel at a flow rate of 2 L / min so that the precipitated coprecipitate was not oxidized. Moreover, the concentration method was employ | adopted for precipitation reaction, and the liquid was continuously extracted using the filter cloth so that the liquid quantity in a reaction tank might not exceed 2L during reaction.

The obtained coprecipitate was repeatedly washed with pressure filtration and dispersed in distilled water to remove impurity ions. Washing was terminated when the electrical conductivity of the filtrate was less than 20 mS / m. Next, the coprecipitate after washing was dried at 120 ° C. for 15 hours.
Next, the coprecipitate after drying and lithium carbonate were mixed with the mixing ratio (Li / X) of Li to the total molar amount (X) of the transition metal elements in the coprecipitate at a value shown in Table 2. The mixture was calcined at 600 ° C. for 5 hours in the atmosphere and then calcined at 900 ° C. for 16 hours to obtain a lithium-containing composite oxide. This lithium-containing composite oxide was used as a positive electrode active material.

[Examples 2 to 7, 11]
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the precipitation reaction conditions and the lithiation conditions were changed as shown in Table 2. These lithium-containing composite oxides were used as positive electrode active materials.
In Example 11, ammonium sulfate was dissolved in distilled water so as to have a concentration of 0.75 mol / L to prepare an aqueous ammonium sulfate solution. The aqueous ammonium sulfate solution together with the aqueous sulfate solution was combined with the total molar amount of transition metal elements in the carbonate compound ( It was added over 28 hours so that the molar ratio (NH ⁴⁺ / X) of ammonium ion to X) was as shown in Table 2.

[Example 8]
Under the precipitation reaction conditions, a coprecipitate was obtained in the same manner as in Example 1 except that the overflow method was adopted and the filter cloth was not used for extracting the liquid from the reaction tank. A carbonate compound overflowed during 15 to 18 hours from the start of the reaction was used.
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the lithiation conditions were changed as shown in Table 2. The obtained lithium-containing composite oxide was used as a positive electrode active material.

[Example 9]
Precipitation reaction conditions and lithiation conditions were as shown in Table 2, and a lithium-containing composite oxide was obtained in the same manner as in Example 8 except that a coprecipitate overflowed during 12 to 15 hours from the start of the reaction was used. The obtained lithium-containing composite oxide was used as a positive electrode active material.

[Example 10]
Nickel sulfate (II) hexahydrate, cobalt sulfate (II) heptahydrate, manganese sulfate (II) pentahydrate so that the ratio of Ni, Co and Mn is as shown in Table 2. And it melt | dissolved in distilled water so that the total density | concentration of Ni, Co, and Mn might be 1.5 mol / L, and sulfate aqueous solution was obtained. In addition, a 48% sodium hydroxide aqueous solution by mass was prepared as a pH adjusting solution.
Next, distilled water is put into a 2 L baffled glass reaction vessel and heated to 50 ° C. with a mantle heater, and the sulfate solution is added while stirring the solution in the reaction vessel with a two-stage inclined paddle type stirring blade. It was added for 28 hours at a rate of 5.0 g / min. Further, a pH adjusting solution was added so as to keep the pH of the mixed solution at 10.0, thereby precipitating a hydroxide (coprecipitate) containing Ni, Co and Mn. The initial pH of the mixture was 10.0. During the precipitation reaction, nitrogen gas was flowed into the reaction vessel at a flow rate of 2 L / min so that the precipitated hydroxide was not oxidized.

The obtained coprecipitate was repeatedly washed with pressure filtration and dispersed in distilled water to remove impurity ions. Washing was terminated when the electrical conductivity of the filtrate was less than 20 mS / m. The coprecipitate after washing was dried at 120 ° C. for 15 hours.
Next, the dried coprecipitate and lithium carbonate were mixed so that the mixing ratio of Li to the total amount of transition metal element (X) contained in the coprecipitate (Li / X) was as shown in Table 2. The mixture was calcined at 600 ° C. for 5 hours in the atmosphere and then calcined at 850 ° C. to obtain a lithium-containing composite oxide. The obtained lithium-containing composite oxide was used as a positive electrode active material.

[Example 12]
Nickel sulfate (II) hexahydrate and manganese sulfate (II) pentahydrate were mixed so that the ratio of Ni and Mn was as shown in Table 2, and the total concentration of Ni and Mn was 1.5 mol. / L was dissolved in distilled water to obtain a sulfate aqueous solution. In addition, a 48% sodium hydroxide aqueous solution by mass was prepared as a pH adjusting solution. Ammonium sulfate was dissolved in distilled water to a concentration of 0.75 mol / L to prepare an aqueous ammonium sulfate solution.
Next, distilled water is put into a 2 L baffled glass reaction vessel and heated to 50 ° C. with a mantle heater, and the sulfate solution is added while stirring the solution in the reaction vessel with a two-stage inclined paddle type stirring blade. An aqueous ammonium sulfate solution was added at a rate of 5.0 g / min for 28 hours at an addition rate such that the molar ratio (NH ⁴⁺ / X) of ammonium ions to the total moles (X) of transition metal elements in the coprecipitate was as shown in Table 2. . In addition, a pH adjusting solution was added so as to keep the pH of the mixed solution at 11.0 to precipitate a hydroxide (coprecipitate) containing Ni, Co and Mn. The initial pH of the mixture was 11.0. During the precipitation reaction, nitrogen gas was flowed into the reaction vessel at a flow rate of 2 L / min so that the precipitated hydroxide was not oxidized.

The obtained coprecipitate was repeatedly washed with pressure filtration and dispersed in distilled water to remove impurity ions. Washing was terminated when the electrical conductivity of the filtrate was less than 20 mS / m. The coprecipitate after washing was dried at 120 ° C. for 15 hours.
Next, the dried coprecipitate and lithium carbonate were mixed so that the mixing ratio of Li to the total amount of transition metal element (X) contained in the coprecipitate (Li / X) was as shown in Table 2. The mixture was calcined at 600 ° C. for 5 hours in the air atmosphere and then calcined at 935 ° C. to obtain a lithium-containing composite oxide. The obtained lithium-containing composite oxide was used as a positive electrode active material.

[Example 13]
A lithium-containing composite oxide was obtained in the same manner as in Example 12 except that the precipitation reaction conditions and the lithiation conditions were as shown in Table 2. The obtained lithium-containing composite oxide was used as a positive electrode active material.

[Examples 14 and 15]
A lithium-containing composite oxide is prepared by mixing a hydroxide of Ni: Co: Mn = 5: 2: 3 and lithium carbonate in a molar ratio of Ni, Co, and Mn and calcining under the conditions shown in Table 2. Got. The obtained lithium-containing composite oxide was used as a positive electrode active material.

Table 3 shows D _{50 of} the positive electrode active material obtained in each example, specific surface area, apparent density d1, porosity of the cross section of the secondary particles, and isolated porosity of the positive electrode active material. As a representative example of the X-ray diffraction pattern of the positive electrode active material, the X-ray diffraction pattern of the positive electrode active material of Example 1 is shown in FIG. In addition, as shown in FIG. 1, the values of I ₀₀₃ , I ₀₂₀ , I ₀₂₀ / I ₀₀₃ calculated from the X-ray diffraction patterns of the positive electrode active materials obtained in the respective examples, and the positive electrode active materials are expressed as aLi (Li _{1 /} Table 3 shows the values of a, b, c and d when expressed as ₃ Mn _2/3 ) O _2. (1-a) LiNi _b Co _c Mn _d O ₂ .
Moreover, SEM images of Examples 1, 8, and 10 are shown in FIGS. 2 to 4 as representative examples of the secondary particle cross section of the positive electrode active material. The “OF method” in Table 2 means that the overflow method was adopted for the precipitation reaction.

As shown in Table 3 and FIGS. 2 to 4, the positive electrode active materials of Examples 1 to 7 and 12 have a porosity of 12 to 40% in the cross section of the secondary particles of the lithium-containing composite oxide contained in the positive electrode active material. And the isolated porosity of the positive electrode active material is 5% or less. Therefore, as shown in Table 4, the lithium secondary batteries having the positive electrode active materials of Examples 1 to 7 and 12 have low DCR and high discharge capacity and charge / discharge efficiency.
On the other hand, the lithium secondary batteries having Examples 8, 9, 11 and 13 which are so-called solid positive electrode active materials having a low porosity of the cross section of the secondary particles have a high discharge capacity but a high DCR.
Moreover, although the porosity of the cross section of the secondary particle is 12 to 40%, the lithium secondary battery having the positive electrode active material of Example 10 in which the isolated porosity of the positive electrode active material is more than 5% has a high DCR. This is considered to be caused by a hollow but no through-hole and a high isolated porosity.

Furthermore, in the case of a ternary positive electrode active material, there is almost no change in the DCR of the lithium secondary battery between Example 14 with a porosity of 12% or more and Example 15 with a porosity of less than 12%. As described above, in the case of the ternary positive electrode active material, even if the porosity of the secondary particles is controlled, the effect of reducing the DCR of the lithium secondary battery having the positive electrode active material is not seen.
From the above, when a lithium-rich positive electrode active material is used, the positive electrode active material is contained by controlling the porosity of secondary particles and the isolated porosity of the positive electrode active material to a predetermined size. It can be said that a remarkable effect of reducing the DCR of the lithium secondary battery is exhibited. That is, this effect is not seen in the ternary positive electrode active material, but is a unique effect in the lithium-rich positive electrode active material.

The positive electrode active material of the present invention is used as a positive electrode active material of a lithium ion secondary battery used in a wide field such as for portable electronic devices and in-vehicle use.
It should be noted that the entire content of the specification, claims, drawings and abstract of Japanese Patent Application No. 2014-008063 filed on January 20, 2014 is cited herein as the disclosure of the specification of the present invention. Incorporated.

Claims (10)

Including secondary particles in which a plurality of primary particles of lithium-containing composite oxide are aggregated,
The lithium-containing composite oxide has the general formula aLi (Li _1/3 Mn _2/3 ) O _2. (1-a) LiMO ₂ (where M is at least one element selected from Ni, Co and Mn). Represented by 0 <a <1),
The secondary particle has a cross-sectional porosity of 12 to 40%, and an isolated porosity of the positive electrode active material is 5% or less.   In the lithium-containing composite oxide, the Ni molar ratio (Ni / X) to the total molar amount (X) of Ni, Co and Mn is 0.15 to 0.5, and the Co molar ratio (Co / X) is The positive electrode active material according to claim 1, wherein the positive electrode active material is 0 to 0.33 and the Mn molar ratio (Mn / X) is 0.33 to 0.8.   The positive electrode according to claim 1 or 2, wherein a molar ratio (Li / X) of Li to a total molar amount (X) of Ni, Co, and Mn in the lithium-containing composite oxide is 1.1 to 1.7. Active material. A particle diameter _{D 50} of the positive electrode active material is 3 to 15 [mu] m, positive active material according to any one of claims 1-3. The positive electrode active material according to claim 1, wherein the positive electrode active material has a specific surface area of 0.1 to 10 m ² . In the X-ray diffraction pattern of the lithium-containing composite oxide, it belongs to the crystal structure of the space group C2 / m with respect to the integrated intensity (I ₀₀₃ ) of the (003) plane peak attributed to the crystal structure of the space group R-3m. The positive electrode active material according to claim 1, wherein a ratio (I ₀₂₀ / I ₀₀₃ ) of integrated intensity (I ₀₂₀ ) of a peak of (020) plane is 0.02 to 0.3. It is a manufacturing method of the positive electrode active material as described in any one of Claims 1-6, Comprising: The following process (I)
And a method for producing a positive electrode active material having (II).
(I) at least two sulfates (A) selected from the group consisting of Ni sulfate, Co sulfate and Mn sulfate;
A step of depositing a coprecipitate by mixing at least one alkali (B) selected from the group consisting of Na carbonate, K carbonate, NaOH and KOH in the form of an aqueous solution.
(II) The process of mixing the said coprecipitate and lithium carbonate, and baking at 500-1000 degreeC.   The manufacturing method of the positive electrode active material of Claim 7 whose density | concentration which added Ni, Co, and Mn in the aqueous solution of a sulfate (A) is 0.1-2 mol / kg.   The manufacturing method of the positive electrode active material of Claim 7 or 8 whose density | concentration of the alkali (B) in the aqueous solution of an alkali (B) is 0.1-2 mol / kg.   The ratio of the molar amount of Li contained in the lithium compound to the total molar amount (X) of Ni, Co and Mn contained in the coprecipitate is 1.1 to 1.7. The manufacturing method of the positive electrode active material of description.

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