JP6043213B2 - Layered lithium composite oxide and manufacturing method thereof, positive electrode active material for secondary battery including the layered lithium composite oxide, positive electrode for secondary battery including the same, and lithium ion secondary battery using the same as the positive electrode - Google Patents

Description

  The present invention relates to a layered lithium composite oxide and a method for producing the same, a positive electrode active material for a secondary battery including the layered lithium composite oxide, a positive electrode for a secondary battery including the same, and a lithium ion secondary battery using the same as a positive electrode .

  Lithium batteries have a high energy density compared to other batteries, are light and can be used for a long time, and are power sources for portable devices such as mobile phones, PHS and small computers, power storage power sources, electric vehicles Development is underway for use as a power source for automobiles.

Such a lithium battery includes a positive electrode made of a positive electrode active material containing a lithium-containing composite oxide, a negative electrode made of a material capable of occluding and releasing lithium such as carbon, and a separator containing a non-aqueous electrolyte. Alternatively, a solid electrolyte is provided as a main component.
Among these constituent elements, those studied as positive electrode active materials include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O _4). ) Etc. In particular, a battery using a lithium cobalt composite oxide as a positive electrode has been developed to obtain excellent initial capacity characteristics and cycle characteristics, and has already been put into practical use.
However, since cobalt is a rare resource, a lithium ion secondary battery using lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode is expensive. Therefore, an alternative material or the like in which at least a part of cobalt is substituted with another element has been demanded, and some proposals have already been made.

  For example, Patent Document 1 discloses a powder containing a lithium transition metal compound having a function capable of inserting / extracting lithium ions, and a third period by SEM-EDX method is formed inside the powder particles. And a compound having a peak derived from at least one element selected from Group 16 elements and at least one element selected from Group 5 to 7 elements in the fifth and sixth periods. The lithium transition metal-based compound powder for a lithium secondary battery positive electrode material is described.

For example, in Patent Document 2, a lithium-containing composite oxide capable of occluding and releasing lithium ions is used as a positive electrode active material, and the filling property represented by (tap density / true density) × 100 [%] is 25% or more and less than 50%. And represented by the composition formula Li _a Mn _x Ni _y X _z O ₂ (X = Co, at least one of Al), 1 ≦ a ≦ 1.2, 0.3 ≦ x ≦ 0.4, 0.36 A positive electrode active material for a non-aqueous lithium secondary battery, which is a composite oxide having a layered rock salt structure in the range of ≦ y ≦ 0.6, 0.1 ≦ z ≦ 0.31, and x + y + z = 1, A positive electrode active material for a lithium secondary battery, characterized in that the crystallite size measured by the Hall method from the integral width of each diffraction peak obtained from a line diffraction pattern is greater than 600 and less than or equal to 760 Have been described.

JP 2011-228292 A Japanese Patent No. 4172024

  However, a battery using the conventional lithium composite oxide described in Patent Documents 1 and 2 as a positive electrode active material has a sufficiently high discharge capacity per volume, and a cycle when used at a temperature higher than room temperature. We found that the characteristics are low and there is room for improvement in the rate characteristics.

  The present invention solves the problems of the conventional lithium composite oxide as described above. That is, when it is used as a positive electrode active material, a lithium ion secondary battery having a high discharge capacity per volume, excellent cycle characteristics when used in a temperature atmosphere higher than room temperature, and excellent rate characteristics is also provided. It is an object to provide a layered lithium composite oxide that can be obtained and a method for producing the same. Moreover, it aims at providing the positive electrode active material containing such a layered lithium complex oxide. Moreover, it aims at providing the positive electrode for lithium ion secondary batteries using this positive electrode active material. Furthermore, it aims at providing the lithium ion secondary battery using this positive electrode.

The inventor has intensively studied to solve the above-mentioned problems, and has completed the present invention.
The present invention includes the following (1) to (7).
(1) A method for producing a layered lithium composite oxide represented by the following formula (I),
A precursor preparation step of obtaining a precursor using a lithium source, a raw material containing M ¹ and a raw material containing M ² ;
A first firing step of firing the precursor in an atmosphere having an oxygen concentration of 5 to 15% by volume to obtain a fired body [1];
A second firing step of firing the fired body [1] in an atmosphere having an oxygen concentration higher than the oxygen concentration in the first firing step to obtain a fired body [2];
A method for producing a layered lithium composite oxide.
Formula (I): Li _{(1 + x)} M ¹ _(1-xp) M ² _p O _(2-a)
However, in formula (I), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al and Cr, and M ² is B, P, S, Pb, Sb, It is at least one element selected from the group consisting of Si and V, and 0 ≦ x ≦ 0.5, 0 ≦ p ≦ 1.0, and 0 ≦ a ≦ 1.0.
(2) The temperature at which the precursor is fired in the first firing step and the temperature at which the fired body [1] is fired in the second firing step are both more than 850 ° C. and less than 1000 ° C. ) For producing a layered lithium composite oxide.
(3) The precursor preparation step is a step of pulverizing and mixing a lithium source, a raw material containing M ¹ and a raw material containing M ² in a solvent, and drying the resulting slurry to obtain the precursor The method for producing a layered lithium composite oxide according to the above (1) or (2).
(4) A layered lithium composite oxide obtained by the production method according to any one of (1) to (3) above.
(5) A positive electrode active material comprising the layered lithium composite oxide according to (4).
(6) A positive electrode for a lithium ion secondary battery comprising the positive electrode active material according to (5) above.
(7) A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to (6) above, a negative electrode, and an electrolytic solution.

  According to the present invention, when used as a positive electrode active material, the lithium ion secondary battery has a high discharge capacity per volume, excellent cycle characteristics when used in a temperature atmosphere higher than normal temperature, and excellent rate characteristics. A layered lithium composite oxide capable of obtaining a secondary battery and a method for producing the same can be provided. Moreover, the positive electrode active material containing such a layered lithium composite oxide can be provided. Moreover, the positive electrode for lithium ion secondary batteries using this positive electrode active material can be provided. Furthermore, a lithium ion secondary battery using this positive electrode can be provided.

2 is an SEM image (5000 times magnified photograph) of a layered lithium composite oxide obtained in Example 1. FIG. 2 is a SEM image (5000 times magnified photograph) of a layered lithium composite oxide obtained in Comparative Example 1.

The present invention will be described.
The present invention is a method for producing a layered lithium composite oxide represented by the following formula (I), wherein a precursor is obtained by using a lithium source, a raw material containing M ¹ and a raw material containing M ² A first firing step of firing the precursor in an atmosphere having an oxygen concentration of 5 to 15% by volume to obtain a fired body [1], and an atmosphere having an oxygen concentration higher than the oxygen concentration in the first firing step A calcined product [1] and a second calcined product [2] to obtain a calcined product [2].
Formula (I): Li _{(1 + x)} M ¹ _(1-xp) M ² _p O _(2-a)
However, in formula (I), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al and Cr, and M ² is B, P, S, Pb, Sb, It is at least one element selected from the group consisting of Si and V, and 0 ≦ x ≦ 0.5, 0 ≦ p ≦ 1.0, and 0 ≦ a ≦ 1.0.
Hereinafter, such a method for producing a layered lithium composite oxide is also referred to as “the production method of the present invention”.

In the production method of the present invention, the precursor is fired in an atmosphere having an oxygen concentration of 5 to 15% by volume, and further fired again in an atmosphere having an oxygen concentration higher than the oxygen concentration to obtain a layered lithium composite oxide. The present inventors have found that a layered lithium composite oxide having a small average primary particle size and a high tap density can be obtained by such a production method.
When such a layered lithium composite oxide is used, a lithium ion secondary battery having high discharge capacity per volume, excellent cycle characteristics when used in a temperature atmosphere higher than room temperature, and excellent rate characteristics can be obtained. The inventor has found that it can be obtained.

  Each process with which the manufacturing method of this invention is provided is demonstrated below.

<Precursor preparation step>
The precursor preparation process in the manufacturing method of this invention is demonstrated.
In the precursor preparation step, a lithium source, a raw material containing M ¹ and a raw material containing M ² are prepared.

  As the lithium source, an inorganic or organic compound containing a lithium atom (that is, a lithium compound) can be used. For example, lithium hydroxide, lithium carbonate, lithium nitrate, or lithium acetate can be used. Among these, it is preferable to use lithium hydroxide and / or lithium carbonate. This is because generation of harmful gases can be suppressed.

As the raw material containing M ¹ , a compound containing at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al and Cr can be used, and selected from the group consisting of Mn, Ni and Co. It is preferable to use a compound containing at least one element.
The raw material containing M ¹ may be an assembly of a plurality of types of raw materials. For example, the raw material containing M ¹ may be an assembly of a Mn compound, a Ni compound, and a Co compound.

Specifically, as a material containing M ^1, for example, manganese oxide (such as _{MnO 2, Mn 3 O 4)} , manganese carbonate, manganese carbonate hydrate, manganese hydroxide, manganese oxyhydroxide, basic nickel carbonate, Basic cobalt carbonate, magnesia, hematite, alumina, aluminum hydroxide (Al (OH) ₃ ), chromium oxide, and the like can be used. It is also possible to use a mixture of plural kinds of raw materials as a raw material containing M ^1. For example, MnO ₂ and Mn ₃ O ₄ may be mixed and used as a raw material containing M ¹ .

As a raw material containing M ² , a compound containing at least one element selected from the group consisting of B, P, S, Pb, Sb, Si and V can be used.
The raw material containing M ² may be an assembly of a plurality of types of raw materials, as in the case of the raw material containing M ¹ .

Specifically, as a raw material containing M ² , for example, boric acid (H ₃ BO ₃ ), trioxide diboric acid (B ₂ O ₃ ), P ₂ O ₅ , H ₂ SO ₄ , (NH ₄ ) ₂ SO ₄ , PbO, Sb ₂ O ₃ , SiO ₂ or V ₂ O ₅ can be used.

As will be described later, the layered lithium composite oxide obtained by the production method of the present invention may not contain M ² . In this case, since the raw material containing M ² is not used in the production method of the present invention, it is not necessary to prepare it. Even such a case is within the scope of the present invention. This raw material is always prepared containing a lithium source and M ¹ against.

In the precursor preparation step in the production method of the present invention, a precursor is obtained using the lithium source, the raw material containing M ¹ and the raw material containing M ² . Examples of a method for obtaining a precursor using the lithium source, the raw material containing M ¹ and the raw material containing M ² include a conventionally known precipitation method. Specifically, for example, a precipitate (hydroxide) obtained by making an aqueous solution containing lithium ions alkaline, and an aqueous solution containing M ^{1 in} an ionic state (for example, Mn ions, Ni ions, and Co ions) The precursor can be obtained by mixing the precipitate (hydroxide) obtained by making the alkalinity alkaline.

The lithium source, a method of obtaining a precursor by using a raw material containing the raw material and the M ² containing the M ^1, the lithium source, a raw material containing the raw material and the M ² containing the M ¹ was contained in the solvent The method is preferably a method in which the precursor is obtained by pulverizing and mixing in a state and drying the resulting slurry.

When the precursor is obtained by such a preferable method, at least one of the lithium source, the raw material containing M ¹ and the raw material containing M ² is preferably a solid raw material.

Further, when to be contained in the solvent, a lithium source such as described above, the ratio of raw materials including a raw material and M ² including M ^1, as the lithium composite oxide having a composition represented by the formula (I) is obtained It is preferable to adjust.

The solvent will be described.
The solvent containing the lithium source, the raw material containing M ¹ and the raw material containing M ² is not particularly limited, and for example, a conventionally known solvent such as water (pure water etc.), ethanol, acetone or the like can be used. Is preferably used.
Further, these raw materials are contained so that the solid content concentration in the solvent is preferably 5 to 40% by mass, more preferably 10 to 35% by mass, and further preferably 15 to 25% by mass.

It is preferable that a lithium source, a raw material containing M ¹ and a raw material containing M ² are contained in such a solvent and pulverized and mixed in that state.
The method of pulverization and mixing is not particularly limited, but a wet pulverization method using a wet pulverizer using a bead mill or the like is preferable.

This pulverization and mixing is preferably performed until a slurry having an average particle size (D ₅₀ ) of solids of 0.50 μm or less is obtained. When the average particle diameter (D ₅₀ ) is pulverized and mixed so as to be 0.50 μm or less, the solid content tends to be uniform in the slurry. Moreover, it is because the capacity maintenance rate at high temperature is higher than normal temperature in the obtained lithium ion secondary battery. The average particle diameter is preferably 0.40 μm or less, and more preferably 0.30 μm or less.
The average particle size is preferably 0.10 μm or more, and more preferably 0.15 μm or more. This is because if the particle size is too small by pulverization, handling in the subsequent steps is worsened.

The average particle size (D ₅₀ ) of the solid content in the slurry was determined by adding a sodium hexametaphosphate aqueous solution to the slurry at room temperature in the atmosphere, and dispersing the slurry by ultrasonic dispersion and stirring. The integrated particle size distribution (volume basis) is measured using a laser diffraction / scattering type particle size distribution measuring apparatus, and the median diameter obtained from the particle size distribution is meant.

Further, this pulverization and mixing is preferably performed until a slurry having a D ₉₀ particle size of 0.50 μm or less in solid content is obtained. More preferably the particle size of D ₉₀ is less than 0.40 .mu.m, even more preferably less 0.30 .mu.m. This is because the capacity retention rate at a temperature higher than normal temperature in the obtained lithium ion secondary battery tends to be higher.

The particle size of D ₉₀ in the solid content of the slurry was determined by adding a sodium hexametaphosphate aqueous solution to the slurry at room temperature in the atmosphere, and dispersing the slurry by ultrasonic dispersion and stirring. The integrated particle size distribution (volume basis) is measured using a laser diffraction / scattering particle size distribution measuring apparatus, and the particle size at which the integrated particle size is 90% is meant.

  Next, the slurry thus obtained is dried to obtain a precursor. The slurry can be dried by a drying method using a band dryer or a shelf dryer, but is preferably spray drying. Spray drying is to dry the slurry after spraying it into a mist or while forming a mist. By spray-drying under desired conditions, the particle size of the resulting precursor can be adjusted within a desired range.

  The method of spray drying is not particularly limited. For example, the slurry component is discharged from the slit of the atomizer by allowing the slurry to flow into the atomizer rotating at high speed, and the droplet is dispersed by adjusting to an appropriate drying gas temperature and blowing rate. A method for quickly drying the droplets is mentioned. At this time, the slurry flow rate is preferably 0.5 to 700 kg / h, more preferably 1 to 600 kg / h, still more preferably 300 to 550 kg / h, and the atomizer speed is preferably 10,000 to 40,000 rpm, more preferably 20,000 to 35,000 rpm, more preferably 28,000 to 32,000 rpm. A treatment such as an appropriate temperature and air blowing is performed so as to quickly dry the scattered droplets, but it is preferable to introduce the dry gas in a downward flow from the upper part of the drying tower to the lower part.

  Spray drying is preferably performed using a spray dryer. Moreover, the inlet temperature of the hot air for drying of a spray dryer becomes like this. Preferably it is 60-500 degreeC, More preferably, it is 100-400 degreeC, More preferably, it is 150-250 degreeC, Outlet temperature is preferably 50-250 degreeC, More preferably, it is 80- 200 degreeC, More preferably, you may be 100-160 degreeC.

  A precursor can be obtained by such a precursor preparation step.

<First firing step>
The 1st baking process in the manufacturing method of this invention is demonstrated.
In the first firing step, the precursor obtained by the precursor preparation step as described above is fired in an atmosphere having an oxygen concentration of 5 to 15% by volume.
The present inventors have found that when the precursor is fired in an atmosphere having such an oxygen concentration, a layered lithium composite oxide having a small average primary particle size and a high tap density can be obtained.

  The oxygen concentration in the atmosphere for firing the precursor is 5 to 15% by volume. The oxygen concentration is preferably 14% by volume or less, and more preferably 12% by volume or less. The oxygen concentration is preferably 6% by volume or more, and more preferably 7% by volume or more. This is because when the precursor is fired in an atmosphere having such an oxygen concentration, a layered lithium composite oxide having a smaller average primary particle size and a higher tap density can be obtained.

In addition, the oxygen concentration of the atmosphere which bakes a precursor shall mean the value obtained by measuring with the following methods.
First, a SUS tube is inserted into a precursor (for example, a precursor packed in a container such as Saya), and the oxygen in the atmosphere of the precursor during firing is reduced by continuously sucking the gas in the SUS tube. An oxygen concentration meter (for example, OXYGEN ANALYZER, LC-750, manufactured by Toray Engineering Co., Ltd.) is connected to the SUS tube so that the measurement can be performed. Here, by immersing at least a part of the SUS tube in water, the temperature of the gas whose oxygen concentration is measured with an oximeter is cooled to about room temperature. Then, the gas in the SUS tube is sucked at 100 ml / min, and the oxygen concentration is measured over time. Usually, the oxygen concentration gradually decreases from the start of firing, and then stabilizes substantially. The oxygen concentration at the time of stabilization is set as the oxygen concentration of the atmosphere in which the precursor is fired. When the oxygen concentration is not stable, the average oxygen concentration at the time of firing is the oxygen concentration of the atmosphere in which the precursor is fired in the present invention.
When the oxygen concentration in the air is measured by this method (that is, when the oxygen concentration is measured by leaving the SUS tube in the air without charging the precursor), the oxygen concentration indicated by the oximeter is 21 volumes. %.

A method for firing the precursor in an atmosphere having an oxygen concentration of 5 to 15% by volume is not particularly limited. For example, there is a method in which the precursor is placed in a sealed container (or a substantially sealed container) and the container is placed in a firing furnace to fire the precursor. When the precursor is baked by such a method, the precursor is baked in an atmosphere having the same oxygen concentration as the atmosphere in the initial stage of the baking. Since it can be 15% by volume, the precursor is fired in an atmosphere having this oxygen concentration.
Further, for example, the precursor can be fired in an atmosphere having an oxygen concentration of 5 to 15% by volume by a method of firing the precursor while blowing an inert gas such as nitrogen or argon into the firing furnace.

  As the firing furnace, for example, a conventionally known tunnel furnace, muffle furnace, rotary kiln, box furnace, tubular furnace or the like can be used.

  The temperature for firing the precursor (hereinafter also referred to as firing temperature [1]) is preferably 600 to 1200 ° C, more preferably more than 850 ° C and less than 1000 ° C, and more preferably 900 to 975 ° C. Further preferred. This is because a layered lithium composite oxide having a smaller average primary particle size and a higher tap density can be obtained. If the firing temperature [1] is too high, oxygen may be released from the crystal structure, and in this case, battery performance may be reduced.

The time for firing the precursor at the firing temperature [1] as described above is preferably 0.1 to 10 hours, more preferably 0.25 to 5 hours, and 0.5 to 4 hours. More preferably.
If the firing time is too long, oxygen may be released from the crystal structure or oxygen deficiency may occur due to sintering between particles, and in this case, battery performance tends to deteriorate.

  A fired body [1] can be obtained by such a first firing step.

<Second firing step>
The 2nd baking process in the manufacturing method of this invention is demonstrated.
In the second firing step, the fired body [1] obtained by the first firing step as described above is fired in an atmosphere having an oxygen concentration higher than the oxygen concentration in the first firing step.
When the fired body [1] is fired in an atmosphere having such an oxygen concentration, a layered lithium composite oxide capable of producing a lithium ion secondary battery having a high initial discharge capacity and high rate characteristics is obtained. The inventor found.

  The oxygen concentration in the atmosphere for firing the fired body [1] is not particularly limited as long as it is higher than the oxygen concentration in the first firing step. For example, when the precursor is fired in an atmosphere having an oxygen concentration of 10% by volume in the first firing step to obtain a fired body [1], in the atmosphere having an oxygen concentration higher than 10% by volume in the second firing step, The fired body [1] is fired.

  The oxygen concentration in the atmosphere when firing the fired body [1] in the second firing step is preferably 15% by volume or more, more preferably 18% by volume or more, and further preferably 20% by volume or more. preferable. The oxygen concentration is preferably 50% by volume or less, more preferably 30% by volume or less, and further preferably 25% by volume or less. This is because a layered lithium composite oxide having a smaller average primary particle size and a higher tap density can be obtained.

  In the second firing step, the fired body [1] is preferably fired in the air atmosphere.

  The method for measuring the oxygen concentration in the atmosphere in which the fired body [1] is fired is the same as the method for measuring the oxygen concentration in the atmosphere in which the precursor is fired in the first firing step.

  The method for adjusting the oxygen concentration in the atmosphere for firing the fired body [1] is not particularly limited. For example, the oxygen concentration in the atmosphere can be adjusted by blowing an inert gas such as nitrogen or argon into the baking furnace and adjusting the amount in the same manner as in the case of baking the aforementioned precursor. Also, for example, if the fired body [1] is placed in an unsealed container and placed in an open firing furnace together with the container and fired, the fired body [1] can be fired in the atmosphere. .

  The same firing furnace as that used in the first firing step can be used.

The temperature for firing the fired body [1] in the second firing step (hereinafter also referred to as firing temperature [2]) is preferably 600 to 1200 ° C, more preferably more than 850 ° C and less than 1000 ° C, More preferably, it is 900-975 degreeC.
This is because a layered lithium composite oxide having a smaller average primary particle size and a higher tap density can be obtained. If the firing temperature [2] is too high, oxygen may be released from the crystal structure, and in this case, battery performance may be reduced.

The time for firing the fired body [1] at the firing temperature [2] as described above is preferably 0.1 to 10 hours, more preferably 0.25 to 5 hours, More preferably, it is ˜4 hours.
If the firing time is too long, oxygen may be released from the crystal structure or oxygen deficiency may occur due to sintering between particles, and in this case, battery performance tends to deteriorate.

  It is preferable that the first baking step and the second baking step are continuously performed by one apparatus.

By such a production method of the present invention, a layered lithium composite oxide represented by the formula (I) can be obtained.
Hereinafter, such a layered lithium composite oxide is also referred to as “the composite oxide of the present invention”.

<Composite oxide of the present invention>
The composite oxide of the present invention will be described. The composite oxide of the present invention is a layered lithium composite oxide.
The layered lithium composite oxide, which is also called α-NaFeO ₂ type, is considered that oxide ions have a hexagonal crystal structure and are cubic close packed.
Further, the layered lithium composite oxide includes a solid solution compound based on LiCoO ₂ or LiNiO ₂ . This solid solution compound includes LiNi _0.5 Mn _0.5 O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O _{2 and the} like. Further, as the solid solution compound, γLi _4/3 M _2/3 O _2. (1-γ) LiMO ₂ (0 <γ < ^1. M is selected from the group consisting of M ¹ and M ² in the composite oxide of the present invention. And at least one of the above embodiments).
Moreover, it is thought that it has the crystal structure of space group R-3m other than the solid solution compound in layered lithium complex oxide.

  The composite oxide of the present invention is a layered lithium composite oxide represented by the following formula (I).

Formula (I): Li _{(1 + x)} M ¹ _(1-xp) M ² _p O _(2-a)

  In the formula (I), x is in the range of 0 ≦ x ≦ 0.5, preferably 0 <x ≦ (1/3), and more preferably 0.05 ≦ x ≦ 0.15. preferable.

x means the amount of Li substituted for M ¹ . In the present invention, in the layered lithium composite oxide represented by the formula (I), a part of M ¹ is preferably substituted with Li. That is, it is preferable that excess Li is contained from the theoretical value of the number of atoms (composition ratio) of Li in the composition formula of the lithium composite oxide used as the positive electrode active material of the lithium ion battery. In this case, the structure is such that at least a part of Li is replaced with M ¹ by reducing the amount of M ^{1 by an} amount corresponding to a part or all of the excess Li.
When the substitution amount (x) of Li increases, the charge / discharge capacity of the battery slightly decreases, but the cycle characteristics at a higher temperature than normal temperature tend to be improved. However, even if x is larger than 0.5, the cycle characteristics at a temperature higher than normal temperature tend to be hardly improved. Moreover, when the total amount of Li (1 + x) is less than 1.0, a heterogeneous phase that is an impurity is generated, and the charge / discharge performance of the battery tends to decrease.

In formula (I), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al and Cr, and at least one element selected from the group consisting of Mn, Ni and Co It is preferable that it is an element (element group) containing Mn, Ni and Co.

1-xp which is the abundance of M ¹ is larger than 0. The lower limit of 1-xp is preferably 0.5, and more preferably 0.66. This is because the capacity cannot be maintained if 1-xp is too small.

In the formula (I), the element M ² is at least one element selected from the group consisting of B, P, S, Pb, Sb, Si and V. Of these, B is a preferred element.

(If it contains a plurality of kinds of element as M ² are their sum) p substituted amount of M ² is 0 ≦ p ≦ 1. The upper limit of p is preferably 0.1, and more preferably 0.05. This is because when used as a positive electrode active material, the cycle characteristics at a higher temperature than normal temperature tend to be improved. When the substitution amount p is too high, the discharge capacity of the lithium ion secondary battery when used as the positive electrode active material tends to decrease.
Note that p may be 0. In this case, the layered lithium composite oxide represented by the formula (I) does not contain M ² . That is, the layered lithium composite oxide represented by the formula (I) may have a composition represented by Li _{(1 + x)} M ¹ _(1-x) O _(2-a) .
On the other hand, since 0 <1-xp in the formula (I), the layered lithium composite oxide represented by the formula (I) necessarily contains M ¹ .

In the formula (I), a represents the amount of O (oxygen) deficiency.
In the formula (I), a satisfies 0 ≦ a ≦ 1.0 and is preferably a = 0.
When the amount of oxygen deficiency is small (that is, when a is small), the capacity of 3.2 V or less in the charge / discharge test tends to be small. When the amount of oxygen vacancies is small, the crystal structure is stable, and the cycle characteristics at a temperature higher than normal temperature tend to be improved.

Specifically, as the layered lithium composite oxide represented by the formula (I), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , Li _4/3 M _2/3 O ₂ (M is at least one selected from the group consisting of M ¹ and M ² in the composite oxide of the present invention). .

The composition of the composite oxide of the present invention is specified from the molar ratio determined from the content of each element. Specifically, first, using an ICP emission spectrometer, the contents of Li, M ¹ and M ² in the composite oxide of the present invention are measured. In addition, using an oxygen / nitrogen / hydrogen analyzer, the content of O (oxygen) in the composite oxide of the present invention is measured. Then, the molar ratio ^{(Li: M 1: M 2} : O = 1 + x: 1-x-p: p: 2-a) and this correction value is assumed to identify the composition of the composite oxide of the present invention.

<Tap density>
The tap density of the composite oxide of the present invention is preferably 0.5 to 5.0 g / cc, more preferably 1.0 to 3.0 g / cc, and 2.0 to 2.5 g / cc. More preferably.

  The tap density of the composite oxide of the present invention is measured using a conventionally known bulk density measuring device. Specifically, 10.0 g of the composite oxide powder of the present invention is filled in a 20 ml graduated cylinder, and the volume after shaking 300 times at a predetermined speed is read from the scale and determined.

<Pore volume>
The composite oxide of the present invention has a small pore volume. Since the composite oxide of the present invention has a small pore volume and is dense, it is considered that the tap density is increased.
Preferably the pore volume of the composite oxide of the present invention is 0.01~0.5cm ³ / g, more preferably 0.05~0.31cm ³ / g, 0.10~0. More preferably, it is 25 cm ³ / g.

The pore density of the composite oxide of the present invention is measured by a mercury intrusion method. Specifically, first, 1 g of the composite oxide of the present invention is placed in a crucible, dried at 300 ° C. for 1 hour, then placed in a desiccator and cooled to room temperature. Next, 0.3 g of the cooled sample is collected in a cell, and mercury is pressed into the pores using a known pore distribution measuring device (for example, PM-33GT1LP (manufactured by QUANTA CROME)). Then, the pore volume is measured from the relationship between the pressure applied at that time and the volume of mercury pushed in (invaded). Further, based on the Washburn equation (P · r = −2σcos θ) (where P is pressure, r is pore diameter, σ is surface tension, and θ is contact angle), The pore distribution is obtained by obtaining the pore diameter into which mercury can enter.
The measurement is performed up to a maximum pressure of 32273 psi (pore diameter 5.4 nm), the surface tension of mercury used for analysis is σ = 473 dynes / cm, and the contact angle is θ = 130 °. And the pore volume (cm < ³ > / g) to pore diameter 5.4-2000 nm is measured.

<Particle size>
The composite oxide of the present invention preferably contains secondary particles as a constituent element, and more preferably an aggregate of secondary particles.
Here, it is an aggregate of crystallites (single crystal part), and the smallest particle unit that can be visually recognized by SEM observation at a magnification of 5000 times behaves as a single particle in handling, in which primary particles are sintered and primary particles are sintered. Particles are defined as secondary particles.

The composite oxide of the present invention preferably has an average primary particle diameter of 0.1 to 5.0 μm, more preferably 0.3 to 2.5 μm, 0.5 to More preferably, it is 2.0 μm.
Here, the average particle size of the primary particles means the median size of the primary particles (aggregates of crystallites) described above.
Moreover, the median diameter of the primary particles was photographed with a scanning electron microscope (SEM) at a magnification of 5000 times using the scanning composite electron microscope (SEM), 500 pieces were arbitrarily selected from the obtained photographs, and calipers were used. Then, each projected area circle equivalent diameter is measured to obtain an integrated particle size distribution (volume basis), and an average particle diameter (median diameter) is calculated therefrom to obtain a calculated value.

The composite oxide of the present invention preferably has a standard deviation of the particle diameter of primary particles of 0.001 to 0.8 μm, more preferably 0.001 to 0.5 μm. It is more preferable that it is 001-0.4 micrometer.
Here, the standard deviation of the primary particles is obtained by photographing the composite oxide of the present invention at a magnification of 5000 times using a scanning electron microscope (SEM), as in the case of the median diameter of the primary particles described above. 500 images are arbitrarily selected from the photographs, each projected area circle equivalent diameter is measured using a caliper, a particle size distribution (volume basis) is obtained, and a standard deviation is calculated therefrom to obtain a calculated value.

The composite oxide of the present invention preferably has an average secondary particle size of 2 to 30 μm, more preferably 5 to 20 μm, and still more preferably 8 to 12 μm. Yes.
Here, the secondary particles are obtained by sintering the primary particles as described above.
Moreover, the average particle diameter of secondary particles shall mean the median diameter of secondary particles.

Moreover, the average particle diameter of secondary particles shall mean the value measured by the following method.
First, the composite oxide of the present invention is added to an aqueous sodium hexametaphosphate solution at room temperature in the atmosphere, and is dispersed by ultrasonic dispersion and stirring to form a slurry. Next, after adjusting this slurry to have a transmittance of 80 to 90%, an integrated particle size distribution (volume basis) is measured using a laser diffraction / scattering particle size distribution measuring device. The median diameter obtained from the particle size distribution measured in this manner is defined as the average particle diameter of secondary particles in the composite oxide of the present invention.

<Specific surface area>
The composite oxide of the present invention preferably has a BET specific surface area of 0.1 to 3.0 m ² / g, more preferably 0.2 to 2.0 m ² / g, More preferably, it is from ^{2 to} 1.0 m ² / g.

The BET specific surface area is a value obtained by BET one-point measurement by a continuous flow method. Specifically, both the adsorption gas and the carrier gas to be used are a mixed gas of nitrogen, air and helium. The sample is degassed by heating with the mixed gas at a temperature of 450 ° C. or lower, and then cooled with liquid nitrogen. The mixed gas is adsorbed, the adsorbed nitrogen gas is desorbed by returning to room temperature, detected by a thermal conductivity detector, the amount is obtained as a desorption peak, and the specific surface area of the sample is calculated. Such a BET specific surface area can be measured using a known BET powder specific surface area measuring device.
In the present invention, the simple description of “specific surface area” means “BET specific surface area”.

<Crystal structure>
The composite oxide of the present invention preferably has a specific crystal structure.
Specifically, the Miller index is (012) with respect to the peak intensity at the crystal lattice plane where the Miller index is (101), which is obtained from a chart obtained by performing powder X-ray diffraction measurement on the composite oxide of the present invention. It is preferable that the peak intensity ratio ((012) / (101)) in a certain crystal lattice plane is small. Further, it is preferable that the ratio ((003) / (104)) of the peak intensity at the crystal lattice plane with the Miller index (003) to the peak intensity at the crystal lattice plane with the Miller index (104) is large. Furthermore, it is preferable that the peak intensity ratio ((012) / (101)) is small and the peak intensity ratio ((003) / (104)) is large.

More specifically, the peak intensity ratio ((012) / (101)) is preferably 0.25 to 0.40. The ratio of peak intensity ((012) / (101)) is more preferably 0.36 or less.
The peak intensity ratio ((003) / (104)) is preferably 1.00 or more, more preferably 1.10 or more, and further preferably 1.15 or more. This peak intensity ratio ((003) / (104)) may be 2.00 or less.
The composite oxide of the present invention showing such a peak intensity ratio has a higher discharge capacity per volume when it is used as a positive electrode active material, and cycle characteristics when used in a temperature atmosphere higher than room temperature. The present inventor has found that a lithium ion secondary battery that is more excellent in terms of the rate characteristics can be obtained.

  In addition, when calculating | requiring said peak intensity ratio, powder X-ray-diffraction measurement uses a sample horizontal type | mold multipurpose X-ray-diffraction apparatus (For example, the Rigaku Co., Ltd. product, X-RAY DIFFRACTMETER, RINT-Ultima). Further, Cu—Kα ray is used for the measurement, and the measurement is performed in the range of 2θ = 15 to 80 °.

<Initial discharge capacity>
The initial discharge capacity of the secondary battery using the composite oxide of the present invention as the positive electrode active material can be 151 mAh / g or more, preferably 152 mAh / g or more, more preferably 165 mAh / g or more.

In the present invention, the initial charge / discharge capacity (mAh / g) of the lithium ion secondary battery is measured as follows.
First, 85% by mass of the composite oxide of the present invention, 7.5% by mass of acetylene black, and 7.5% by mass of polyvinylidene fluoride are weighed and dispersed in normal methylpyrrolidone to obtain a mixture. Then, the obtained mixture is applied on an Al foil so as to have a thickness of about 0.1 mm, vacuum-dried at about 110 ° C., and then punched out using a 14 mmφ punch to produce a positive electrode.
Next, after the obtained positive electrode was used as a test electrode, the test electrode and a lithium metal foil (thickness 0.2 μm) were stacked in a coin-type battery case via a separator (trade name: Cell Guard). Then, an electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate having a volume ratio of 1: 1 was injected to prepare a test coin cell.
Next, the initial charge / discharge capacity of the test coin cell created in this way is measured. Specifically, the charging / discharging rate is 0.2 C, the charging end voltage is 4.3 V, the current density is 0.5 mA / cm ^2, and the constant current / constant voltage charging (after the voltage becomes 4.3 V). Is charged at a constant voltage of 4.3 V), the discharge end voltage is 3.0 V, and the current density is 0.5 mA / cm ² . The initial charge capacity (mAh / g) and the initial discharge capacity (mAh / g) are measured. The charging is terminated when 10 hours have elapsed from the start of charging or when the current reaches 0.001C.
In the present invention, the value obtained by measuring in this way is defined as the initial charge / discharge capacity.

<High temperature cycle characteristics>
The secondary battery using the composite oxide of the present invention as the positive electrode active material has a cycle capacity maintenance rate at a temperature higher than room temperature of 89.0% or higher, preferably 90.0% or higher, more preferably 91.%. It can be 0% or more.

In the present invention, the cycle capacity retention rate (%) at a temperature higher than the room temperature of the secondary battery is measured as follows.
First, a test coin cell is prepared by the same method as that for measuring the initial charge / discharge capacity (mAh / g) of the lithium ion secondary battery.
Then, the test coin cell is placed in a constant temperature bath of 60 ° C., and the charge / discharge rate is 0.2 C, the charge end voltage is 4.3 V, and the discharge end voltage is 3 as in the measurement of the initial charge / discharge capacity. A constant current charge of 0.5 mA / cm ² is performed 100 times under the condition of potential regulation up to 0.0 V, and the cycle capacity maintenance rate at a temperature higher than room temperature is obtained by the following formula.
Cycle capacity retention rate (%) = (100th discharge capacity / first discharge capacity) × 100

<Rate characteristics>
The rate capacity maintenance rate of the secondary battery using the composite oxide of the present invention as the positive electrode active material can be 80.0% or more, preferably 81.0% or more, more preferably 84.0% or more.

In the present invention, the rate capacity maintenance rate (%) of the secondary battery is measured as follows.
First, a test coin cell is manufactured by the same method as that for measuring the initial charge / discharge capacity.
In the case of the measurement of the initial charge / discharge capacity, the charge / discharge rate is set to 0.2C, but only the rate at the time of discharge is set to 5C. Test and measure initial discharge capacity.
The ratio between the initial discharge capacity obtained by conducting the constant current discharge test at 5C and the discharge capacity when the initial charge / discharge capacity is measured and the constant current discharge test is performed at 0.2C. (Percentage) is obtained as the rate capacity maintenance rate.

<Positive electrode active material of the present invention>
The positive electrode active material of the present invention will be described.
The positive electrode active material of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery using the composite oxide of the present invention.
The positive electrode active material of the present invention preferably contains 80% by mass or more of the composite oxide of the present invention, more preferably 90% by mass or more, and substantially 100% by mass, that is, from the composite oxide of the present invention. More preferably, it becomes substantially.

In addition to the composite oxide of the present invention, the positive electrode active material of the present invention can contain LTO (Li ₄ Ti ₅ O ₁₂ ), a solid electrolyte described later, and other oxides not containing lithium. Moreover, what apply | coated the material represented to these to the surface of the complex oxide of this invention can also be used as a positive electrode active material of this invention.

<Positive electrode of the present invention and manufacturing method thereof>
The positive electrode of the present invention may be in the same mode as, for example, a conventionally known positive electrode, as long as the positive electrode active material of the present invention is used. For example, what formed the layer which consists of what added the conductive support agent, the binder, etc. and mixed with the positive electrode active material of this invention as needed on a collector is mentioned. Specifically, an ink (slurry) is prepared by kneading a conductive additive, a binder, and an organic solvent such as N-methylpyrrolidone with the positive electrode active material of the present invention, and this ink is applied to the aluminum foil of the current collector. After applying and drying, it can be obtained by applying to a roller press. By applying to a roller press, the contact between the positive electrode active material and the current collector can be improved and the density of the positive electrode active material can be increased. Moreover, after fully mixing a conductive support agent and a binder with the positive electrode active material of this invention, it shape | molds in a sheet form with a roller press, and can obtain a positive electrode.
Here, examples of the conductive assistant include graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black and ketjen black.
Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluorine rubber, styrene butadiene, cellulose resin, and polyacrylic acid.
Further, the current collector is not limited, and for example, a conventionally known net shape, sheet shape, or film shape can be used.

<Secondary battery of the present invention>
The secondary battery of the present invention will be described.
The secondary battery of the present invention may have the same configuration as a normal lithium ion secondary battery except that the positive electrode of the present invention is used as a positive electrode, and may be a cylindrical type, a square type, a coin type, a button type, or the like. It's okay. That is, the positive electrode, the negative electrode, and the non-aqueous electrolyte are the main battery components, and these components are enclosed in, for example, a battery can. Each of the positive electrode and the negative electrode acts as a lithium ion carrier, and the lithium ions are occluded in the negative electrode during charging and detached from the negative electrode during discharging.

A negative electrode is not specifically limited, For example, the aspect similar to a conventionally well-known negative electrode may be sufficient. For example, as the negative electrode active material, a lithium alloy represented by lithium or lithium-aluminum can be used, and graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Carbon-based materials that can reversibly occlude and release lithium ions such as mesocarbon microbeads, carbon fibers, and activated carbon can also be used. For example, the same current collector as that of the positive electrode can be used.
When the negative electrode active material is lithium or a lithium alloy, the negative electrode can be used as it is, or can be manufactured by pressure bonding to a current collector. In addition, when the negative electrode active material is a carbon-based material (graphite, carbon black, etc.) capable of occluding and releasing lithium ions, a binder similar to that for the positive electrode is added to the negative electrode active material and mixed as necessary. Then, paste it into a paste using a solvent, apply the obtained negative electrode mixture-containing paste to a negative electrode current collector made of copper foil, etc., dry it to form a negative electrode mixture layer, and press-mold as necessary It can manufacture by passing through a process.

  As the non-aqueous electrolyte, an organic electrolyte, a polymer electrolyte, a solid electrolyte, or the like can be used. Here, the organic electrolyte is a lithium salt added to a non-aqueous solvent, and the polymer electrolyte is a lithium salt added to a polymer compound.

Here, as the lithium salt, for example, LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Examples thereof include LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) ₂ . Among these, LiBF ₄ (lithium tetrafluoroborate) is less reactive with moisture present in the electrolyte, so it has better safety, cycle characteristics, rate characteristics (high rate discharge characteristics), initial characteristics, etc. It is easy to obtain an excellent lithium battery.
The concentration of the lithium salt in the organic electrolyte is preferably 0.1 to 3.0 mol / l, more preferably 0.2 to 2.0 mol / l. This is because the ionic conductivity of the non-aqueous electrolyte is increased, lithium salts are hardly precipitated in the non-aqueous electrolyte, and a lithium battery having high-performance battery performance can be obtained.

  As the non-aqueous solvent of the organic electrolyte, for example, a conventionally known one can be used, and a mixed solvent of ethylene carbonate, γ-butyrolactone, propylene carbonate and vinylene carbonate can be preferably used. Since ethylene carbonate, γ-butyrolactone and propylene carbonate have a high dielectric constant, they can reliably cause ionic conduction. Further, by containing vinylene carbonate in a non-aqueous solvent, ethylene carbonate, γ -Since the film | membrane derived from vinylene carbonate which can suppress reliably decomposition | disassembly of butyrolactone and propylene carbonate can be formed on a negative electrode, it can fully charge.

  The organic electrolyte may contain another organic solvent in addition to the lithium salt and the non-aqueous solvent.

When the non-aqueous electrolyte is a polymer electrolyte, it includes a matrix polymer compound that is gelled with a plasticizer (non-aqueous electrolyte). Examples of the matrix polymer compound include ethers such as polyethylene oxide and cross-linked products thereof. Fluorine-based resins such as vinyl resins, polymethacrylate resins, polyacrylate resins, polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers can be used alone or in combination.
Among these, from the viewpoint of oxidation-reduction stability, it is preferable to use a fluorine-based resin such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

The production of the polymer electrolyte is not particularly limited, and examples thereof include a method in which a polymer compound constituting a matrix, a lithium salt, and a solvent are mixed and heated to melt and dissolve. In addition, after dissolving a polymer compound, a lithium salt, and a solvent in an organic solvent for mixing, the organic solvent for mixing is evaporated, a polymerizable monomer, a lithium salt, and a solvent are mixed, and ultraviolet rays, electron beams, or molecules are mixed. Examples include a method of polymerizing a polymerizable monomer by irradiating a line and the like to obtain a polymer.
10-90 mass% is preferable and, as for the ratio of the solvent in a polymer electrolyte, 30-80 mass% is more preferable. With such a ratio, the electrical conductivity is high, the mechanical strength is strong, and the film is easily formed.

Solid electrolytes include, for example, oxide-based quenching glasses containing lithium ions, glass-based solid electrolytes such as sulfide-based oxysulfide-based superionic conductive glasses, and high concentrations of Li salts dissolved and dispersed in polymers such as polyethers. Examples include molecular solid electrolytes.
The polymer solid electrolyte may be in the form of a gel containing a solvent component.

The secondary battery of the present invention preferably has a separator that prevents direct contact between the positive electrode and the negative electrode.
A separator is not specifically limited, For example, a conventionally well-known thing can be used, for example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane that combines these.
In the case where an organic electrolyte or a polymer electrolyte is used as the nonaqueous electrolyte, a separator is usually used. However, in the case of a solid electrolyte, the solid electrolyte may be used without using the separator.

  The manufacturing method of the secondary battery of this invention is not specifically limited, For example, it can manufacture by a conventionally well-known method. For example, it can be manufactured by injecting a non-aqueous electrolyte before or after laminating the positive electrode of the present invention and the negative electrode via a lithium battery separator, and finally sealing with an exterior material. . Examples of the exterior material include a metal-resin composite film having a configuration in which nickel-plated iron, stainless steel, aluminum, and metal foil are sandwiched between resin films.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Example 1>
[Preparation of lithium composite oxide]
Lithium hydroxide (LiOH.H ₂ O) and lithium carbonate (Li ₂ CO ₃ ) as the lithium source, nickel hydroxide (Ni (OH) ₂ ) as the nickel source, Co ₃ O ₄ as the cobalt source, and electrolytic dioxide as the manganese source Manganese (γ-MnO ₂ ) was prepared. Each raw material was weighed so that the composition of the finally obtained lithium composite oxide was Li _1.0 Ni _0.5 Co _0.2 Mn _0.3 O ₂ .

  Next, these weighed raw materials were mixed, and after adding pure water so that the solid content concentration was 33.3% by mass, a wet pulverizer (manufactured by Ashizawa Finetech Co., Ltd .: Star Mill Lab Star LMZ-) was added. 06) to obtain a slurry. Here, it grind | pulverized until the average particle diameter (median diameter) of solid content in a slurry became 0.20 micrometer or less. In the pulverization, a 600 ml vessel was used.

  In addition, the average particle diameter (median diameter) of the solid content in the slurry was determined using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd .: LA-950v2). Specifically, an aqueous sodium hexametaphosphate solution is added to the slurry at room temperature in the atmosphere, dispersed by ultrasonic dispersion and stirring, adjusted to have a transmittance of 30 to 60%, and then refracted using the above apparatus. The integrated particle size distribution (volume basis) was measured and obtained under the condition of a rate of 2.20.

  Next, the slurry after pulverization was spray-dried using a disk-type spray dryer (Okawara Kako Co., Ltd .: L-8 type spray dryer). Here, air was used as the drying gas. The bag filter differential pressure was adjusted to 0.15 kPa, and the drying gas inlet temperature was adjusted to 200 ° C. The slurry flow rate was 2 kg / h, and the air pressure of the two-fluid nozzle protruding the slurry / air was 0.05 MPa. By performing such spray drying, a particulate precursor was obtained.

  Next, the obtained precursor was put into a substantially sealed container, and the container was placed in a firing furnace. Then, the firing furnace was heated to 950 ° C. at 200 ° C./h, the precursor was fired at 950 ° C. for 2 hours, and then cooled to room temperature by allowing to cool in the room. Here, when the oxygen concentration in the atmosphere for firing the precursor was measured by the method described above, the oxygen concentration was 11% by volume.

  Next, the powder of the fired body [1] obtained was crushed with an agate mortar. Thereafter, the fired body [1] was further fired in the air at 950 ° C. for 4 hours, allowed to cool indoors, and then cooled to room temperature to obtain a layered lithium composite oxide having a target composition. In addition, when the oxygen concentration of the atmosphere which bakes sintered body [1] was measured by the above-mentioned method, oxygen concentration was 21 volume%.

<Measurement of average particle diameter>
The average particle diameter (median diameter) of the obtained layered lithium composite oxide was determined using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd .: LA-950v2). Specifically, an aqueous sodium hexametaphosphate solution is added to the slurry at room temperature in the atmosphere, dispersed by ultrasonic dispersion and stirring, adjusted to have a transmittance of 30 to 60%, and then refracted using the above apparatus. The cumulative particle size distribution (volume basis) was measured and obtained under the condition of a rate of 2.2.
As a result, the average particle size was 10.2 μm.

<Measurement of tap density>
The tap density of the obtained layered lithium composite oxide was measured using a bulk density measuring device (manufactured by Tsutsui Chemical Co., Ltd.). Specifically, 10.0 g of layered lithium composite oxide powder was filled in a 20 ml graduated cylinder, the volume after being shaken 300 times at a predetermined speed was read from the scale, and the tap density was determined.
As a result, the tap density of the layered lithium composite oxide was 2.3 g / cc.

<Measurement of pore volume>
The pore volume of the obtained layered lithium composite oxide was measured by the mercury intrusion method described above.
As a result, the pore volume of the layered lithium composite oxide was 0.23 cm ³ / g.

<Powder X-ray diffraction measurement>
The obtained layered lithium composite oxide was subjected to powder X-ray diffraction measurement, and peak intensities at crystal lattice planes with Miller indices of (012), (101), (003) and (104) were measured. The powder X-ray diffraction measurement uses a sample horizontal multi-purpose X-ray diffraction apparatus (manufactured by Rigaku Corporation, X-RAY DIFFRACMETTER, RINT-Ultima). Measured in range.
Then, the ratio ((012) / (101)) of the peak intensity on the crystal lattice plane with the Miller index (012) to the peak intensity on the crystal lattice plane with the Miller index (101) was obtained. Further, the ratio ((003) / (104)) of the peak intensity on the crystal lattice plane with the Miller index (003) to the peak intensity on the crystal lattice plane with the Miller index (104) was obtained.
Each is shown in Table 1.

<SEM image>
The obtained layered lithium composite oxide was observed using an SEM to obtain an enlarged photograph (5,000 times). As shown in FIG.

  Next, a lithium ion secondary battery was produced using the obtained layered lithium composite oxide, and battery evaluation was performed.

<Measurement of initial charge / discharge capacity>
A layered lithium composite oxide was weighed in a proportion of 85% by mass, acetylene black was 7.5% by mass, and polyvinylidene fluoride was 7.5% by mass and dispersed in normal methylpyrrolidone to obtain a mixture. Then, the obtained mixture was applied on an Al foil so as to have a thickness of about 0.1 mm, vacuum-dried at about 110 ° C., and then punched using a 14 mmφ punch to produce a positive electrode.
The obtained positive electrode was used as a test electrode, and this test electrode and a lithium metal foil (thickness 0.2 μm) were stacked and arranged in a coin-type battery case via a separator (trade name: Cell Guard). An electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of 1: 1 ethylene carbonate and diethyl carbonate was injected to prepare a test coin cell.
The initial charge / discharge capacity of the test coin cell thus prepared was measured. Specifically, the charging / discharging rate is 0.2 C, the charging end voltage is 4.3 V, the current density is 0.5 mA / cm ^2, and the constant current / constant voltage charging (after the voltage becomes 4.3 V). Is charged at a constant voltage of 4.3 V), the discharge end voltage is 3.0 V, and the current density is 0.5 mA / cm ² . Initial charge capacity (mAh / g) and initial discharge capacity (mAh / g) were measured. The charging was terminated when 10 hours passed from the start of charging or when the current reached 0.001C.
The results are shown in Table 1.

<Evaluation of rate characteristics>
A test coin cell was produced by the same method as that for measuring the initial charge / discharge capacity.
In the case of the above initial charge / discharge capacity measurement, the charge / discharge rate was set to 0.2C, but only the rate at the time of discharge was set to 5C. A test was conducted to measure the discharge capacity.
The discharge capacity when the constant current discharge test was conducted at 5C thus obtained, and the discharge capacity when the constant current discharge test was conducted at 0.2C obtained by measuring the initial charge / discharge capacity The ratio (percentage) was calculated as the rate capacity maintenance rate. The rate capacity maintenance rate is expressed by the following equation.
Rate capacity retention rate (%) = (discharge capacity at 5 C / discharge capacity at 0.2 C) × 100

<Measurement of 60 ° C / 100 cycle capacity retention rate>
A test coin cell was produced in the same manner as in the case of measuring the initial charge / discharge capacity.
And the coin cell for a test is installed in a 60 degreeC thermostat, and similarly to the measurement of said initial stage charge / discharge capacity, a charge / discharge rate shall be 0.2C, a charge end voltage may be set to 4.3V, and a discharge end voltage may be 3 A constant current charge of 0.5 mA / cm ² was performed 100 times under the condition of potential regulation up to 0.0 V, and the high-temperature cycle capacity retention rate was determined by the following equation.
High-temperature cycle capacity retention rate (%) = (100th discharge capacity / first discharge capacity) × 100
The measurement results are shown in Table 1.

<Example 2>
The same raw materials as in Example 1 (lithium hydroxide, lithium carbonate, nickel hydroxide, Co ₃ O ₄ , electrolytic manganese dioxide) were prepared, and the composition of the lithium composite oxide finally obtained from each raw material was Weighed so that Li _1.10 Ni _0.30 Co _0.30 Mn _0.30 O ₂ .
The subsequent operations were the same as in Example 1. That is, the weighed raw material was wet pulverized to obtain a slurry, and then the slurry was spray-dried to obtain a precursor, and this precursor was put in a substantially sealed container under the same conditions as in Example 1. By firing, a layered lithium composite oxide having a target composition was obtained. When the oxygen concentration in the atmosphere for firing the precursor was measured, as in Example 1, the oxygen concentration when firing the precursor was 11% by volume, and the oxygen concentration when firing the fired body [1] was 21%.

  And about the obtained layered lithium complex oxide, when the tap density was measured by the method similar to Example 1, the tap density of the layered lithium complex oxide was 2.1 g / cc.

Further, the pore volume of the obtained layered lithium composite oxide was measured by the same method as in Example 1.
As a result, the pore volume of the layered lithium composite oxide was 0.24 cm ³ / g.

Further, for the obtained layered lithium composite oxide, the peak intensity ratio ((012) / (101)) was determined by the same powder X-ray diffraction method as in Example 1. Further, the ratio ((003) / (104)) of the peak intensity on the crystal lattice plane with the Miller index (003) to the peak intensity on the crystal lattice plane with the Miller index (104) was obtained.
Each is shown in Table 1.

In addition, a lithium ion secondary battery was produced by using the obtained layered lithium composite oxide in the same manner as in Example 1. Then, the initial charge / discharge capacity, the rate capacity retention rate, and the high temperature cycle capacity retention rate were measured in the same manner as in Example 1.
The measurement results are shown in Table 1.

<Comparative Example 1>
A precursor was obtained in the same manner as in Example 1.
Then, the obtained precursor is put in an unsealed container, this container is placed in an open-type firing furnace, heated to 950 ° C. at 200 ° C./h, and at 950 ° C. for 2 hours in the air. After firing, it was cooled to room temperature by allowing it to cool in the room. And the obtained baked powder was crushed with the agate mortar. Then, again, similarly, it baked at 950 degreeC for 4 hours in the open-type baking furnace, and it cooled to room temperature by standing to cool indoors, and obtained the layered lithium complex oxide of the target composition. In addition, when the oxygen concentration of the atmosphere which bakes the precursor and the baking powder obtained by baking a precursor was measured, oxygen concentration was 21 volume% in any baking.

  And about the obtained layered lithium complex oxide, when the tap density was measured by the method similar to Example 1, the tap density of the layered lithium complex oxide was 1.5 g / cc.

Further, the pore volume of the obtained layered lithium composite oxide was measured by the same method as in Example 1.
As a result, the pore volume of the layered lithium composite oxide was 0.32 cm ³ / g.
The presence of pores derived from the voids between the primary particles was confirmed near 500 nm.

Further, for the obtained layered lithium composite oxide, the peak intensity ratio ((012) / (101)) was determined by the same powder X-ray diffraction method as in Example 1. Further, the ratio ((003) / (104)) of the peak intensity on the crystal lattice plane with the Miller index (003) to the peak intensity on the crystal lattice plane with the Miller index (104) was obtained.
Each is shown in Table 1.

  Moreover, about the obtained layered lithium complex oxide, it observed using SEM and the enlarged photograph (5000 times) was obtained. As shown in FIG.

In addition, a lithium ion secondary battery was produced by using the obtained layered lithium composite oxide in the same manner as in Example 1. Then, the initial charge / discharge capacity, the rate capacity retention rate, and the high temperature cycle capacity retention rate were measured in the same manner as in Example 1.
The measurement results are shown in Table 1.

<Comparative example 2>
A precursor was obtained in the same manner as in Example 2.
Then, as in Comparative Example 1, the obtained precursor was put in an unsealed container, this container was placed in an open firing furnace, fired under the same conditions as in Comparative Example 1, and crushed. Firing was performed again to obtain a layered lithium composite oxide having a target composition. In addition, when the oxygen concentration of the atmosphere which bakes the precursor and the baking powder obtained by baking a precursor was measured, oxygen concentration was 21 volume% in any baking.

  Then, when the tap density of the obtained layered lithium composite oxide was measured in the same manner as in Example 1, the tap density of the layered lithium composite oxide was 1.4 g / cc.

Further, the pore volume of the obtained layered lithium composite oxide was measured by the same method as in Example 1.
As a result, the pore volume of the layered lithium composite oxide was 0.33 cm ³ / g.
The presence of pores derived from the voids between the primary particles was confirmed near 500 nm.

Further, for the obtained layered lithium composite oxide, the peak intensity ratio ((012) / (101)) was determined by the same powder X-ray diffraction method as in Example 1. Further, the ratio ((003) / (104)) of the peak intensity on the crystal lattice plane with the Miller index (003) to the peak intensity on the crystal lattice plane with the Miller index (104) was obtained.
Each is shown in Table 1.

In addition, a lithium ion secondary battery was produced by using the obtained layered lithium composite oxide in the same manner as in Example 1. Then, the initial charge / discharge capacity, the rate capacity retention rate, and the high temperature cycle capacity retention rate were measured in the same manner as in Example 1.
The measurement results are shown in Table 1.

<Comparative Example 3>
A precursor was obtained in the same manner as in Example 1.
Next, the obtained precursor was put in an unsealed container, and this container was placed in a firing furnace. Then, while blowing nitrogen into the firing furnace, the temperature was raised to 950 ° C. at 200 ° C./h, firing was performed at 950 ° C. for 2 hours, and then cooled to room temperature by being allowed to cool indoors. And the obtained baked powder was crushed with the agate mortar. After that, the pulverized fired powder is placed in the firing furnace again, fired at 950 ° C. for 4 hours while blowing nitrogen into the firing furnace, and allowed to cool to room temperature by being allowed to cool indoors. A layered lithium composite oxide was obtained. In addition, when the oxygen concentration of the atmosphere which bakes the precursor and the baking powder obtained by baking a precursor was measured, oxygen concentration was 11 volume% in any baking.

  And about the obtained layered lithium complex oxide, when the tap density was measured by the method similar to Example 1, the tap density of the layered lithium complex oxide was 2.3 g / cc.

Further, the pore volume of the obtained layered lithium composite oxide was measured by the same method as in Example 1.
As a result, the pore volume of the layered lithium composite oxide was 0.24 cm ³ / g.

Further, for the obtained layered lithium composite oxide, the peak intensity ratio ((012) / (101)) was determined by the same powder X-ray diffraction method as in Example 1. Further, the ratio ((003) / (104)) of the peak intensity on the crystal lattice plane with the Miller index (003) to the peak intensity on the crystal lattice plane with the Miller index (104) was obtained.
Each is shown in Table 1.

In addition, a lithium ion secondary battery was produced by using the obtained layered lithium composite oxide in the same manner as in Example 1. Then, the initial charge / discharge capacity, the rate capacity retention rate, and the high temperature cycle capacity retention rate were measured in the same manner as in Example 1.
The measurement results are shown in Table 1.

  From Table 1, it can be seen that in Examples 1 and 2, the tap density is high and the initial discharge capacity per volume is high. It can also be seen that both the rate capacity retention rate and the high temperature cycle capacity retention rate are excellent.

  In Comparative Example 3, the initial discharge capacity per volume was low, and the rate capacity retention rate and the high temperature cycle capacity retention rate were both low. Thus, even if the oxygen concentration when the precursor is fired in the first firing step is 5 to 15% by volume, the oxygen concentration when firing the fired body [1] in the second firing step is the first firing. It was confirmed that the performance of the obtained layered lithium composite oxide was not excellent unless the oxygen concentration in the process was higher.

  Further, comparing FIG. 1 with FIG. 2, it can be seen that FIG. 1 (Example 1) is denser than FIG. 2 (Comparative Example 1).

Claims (6)

A method for producing a layered lithium composite oxide represented by the following formula (I):
A precursor preparation step of obtaining a precursor using a lithium source, a raw material containing M ¹ and a raw material containing M ² (however, a raw material containing M ² may not be used) ;
A first firing step of firing the precursor in an atmosphere having an oxygen concentration of 5 to 15% by volume to obtain a fired body [1];
A second firing step of firing the fired body [1] in an atmosphere having an oxygen concentration higher than the oxygen concentration in the first firing step to obtain a fired body [2];
A method for producing a layered lithium composite oxide.
Formula (I): Li _{(1 + x)} M ¹ _(1-xp) M ² _p O _(2-a)
However, in formula (I), M ¹ is at least one element selected from the group consisting of Mn, Ni, Co, Mg, Fe, Al and Cr, and M ² is B, P, S, Pb, Sb, It is at least one element selected from the group consisting of Si and V, and 0 ≦ x ≦ 0.5, 0 ≦ p ≦ 1.0, and 0 ≦ a ≦ 1.0.   The temperature for firing the precursor in the first firing step and the temperature for firing the fired body [1] in the second firing step are both more than 850 ° C and less than 1000 ° C. A method for producing a layered lithium composite oxide. The precursor preparation step is obtained by pulverizing and mixing a lithium source, a raw material containing M ¹ and a raw material containing M ² (however, a raw material containing M ² may not be used) in a solvent. The method for producing a layered lithium composite oxide according to claim 1 or 2, wherein the slurry is dried to obtain the precursor.   The manufacturing method of a positive electrode active material which uses the manufacturing method as described in any one of Claims 1-3, and obtains a positive electrode active material using it after obtaining a layered lithium complex oxide.   The manufacturing method of the positive electrode for lithium ion secondary batteries which obtains the positive electrode for lithium ion secondary batteries using the positive electrode active material by the manufacturing method of Claim 4.   Lithium ion which obtains a lithium ion secondary battery using the positive electrode for lithium ion secondary batteries, the negative electrode, and electrolyte solution after obtaining the positive electrode for lithium ion secondary batteries by the manufacturing method of Claim 5 A method for manufacturing a secondary battery.