JP7271848B2 - Method for producing positive electrode active material for lithium ion secondary battery - Google Patents

Description

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

2. Description of the Related Art In recent years, with the spread of mobile devices such as mobile phones and laptop computers, there is a strong demand for the development of small and lightweight secondary batteries with high energy density.
Also, eco-friendly vehicles called xEV are shifting from hybrid vehicles (HEV) to plug-in hybrid vehicles (PHEV) and electric vehicles (BEV) that require high-capacity secondary batteries. BEVs travel a shorter distance on a single charge than gasoline-powered vehicles, and in order to improve this, there is a demand for high-capacity secondary batteries.

As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery.
This lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution, and the like, and the active material of the negative electrode and the positive electrode is a material capable of desorbing and intercalating lithium.
Furthermore, lithium ion secondary batteries are currently being actively researched and developed. Since a high voltage can be obtained, it is being put to practical use as a battery having a high energy density.

Materials mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO ₂ ), lithium-nickel-cobalt-manganese composite oxide (LiNi _{1/ 3} Co _1/3 Mn _1/3 O ₂ ), lithium-manganese composite oxide using manganese (LiMn ₂ O ₄ ), and the like.

Among these, lithium-nickel composite oxide (LiNiO ₂ ) has a high capacity and a high output, and is attracting attention as a material that satisfies the characteristics required as a positive electrode active material for secondary batteries of future eco-friendly automobiles. and demand is growing rapidly.
Furthermore, with the recent increase in demand for XEVs, there is a demand for lower prices. As a result, there is an increasing demand for lower cost secondary batteries, which is one of the reasons for the high cost of eco-friendly vehicles. It is

This lithium-nickel composite oxide is produced by mixing a nickel-containing compound such as nickel composite hydroxide or nickel composite oxide with a lithium compound to prepare a lithium mixture (raw material mixture), and then firing the lithium mixture. Obtainable.
The firing of the lithium mixture is performed, for example, at a temperature of about 650° C. or higher and 1100° C. or lower for 3 hours or longer. During this firing step, the lithium compound reacts (sinters) with the nickel-containing compound to obtain a lithium-nickel composite oxide with high crystallinity.

Firing of the lithium mixture is generally carried out by placing the powder of the lithium mixture in a container such as a sagger and firing it in a firing furnace. However, when the powder is placed in a container and fired, the heat conduction is poor and the replacement of the generated gas with the reaction gas is also poor. Time for temperature rise and reaction is required, and the total baking time including these becomes very long.
Therefore, several proposals have been made so far regarding the firing conditions for efficiently firing the powder of the lithium mixture.

For example, in Patent Document 1, in the step of filling a mixture (powder) obtained by mixing a nickel composite compound and a lithium compound into a sintering vessel and sintering, oxygen is sufficiently diffused into the mixture. A method of sintering the mixture as efficiently as possible by specifying the minimum holding time and the range of oxygen concentration to be held in a specific temperature range for the amount of filling (thickness when the mixture is placed in the sintering container). It is shown.

Further, in Patent Document 2, in addition to normal heater heating, microwave heating is used to bake the raw material to promote heat conduction in the raw material in the baking process, thereby shortening the baking time and reducing the raw material. A method is presented to achieve increased loading to obtain high quality positive electrode active materials for lithium ion batteries at low manufacturing costs.

JP 2011-146309 A JP 2011-210463 A

However, in the technique described in Patent Document 1, the diffusion time of oxygen increases as the amount of the mixture piled up increases, so even if an attempt is made to improve productivity by increasing the amount of the mixture piled up, a significant improvement in productivity cannot be expected. .
Further, in the technique described in Patent Document 2, there is a possibility that the raw material may ignite due to bumping of moisture in the raw material due to microwaves or concentration of microwaves. In addition, in the case of mass production, a fairly large microwave transmission device is required, the cost of introducing the device is high, and there is concern that the device may be damaged by a large amount of microwaves. It is also necessary to comply with the Radio Law, such as measures against radio wave leakage.

Under such circumstances, in view of the above problems, the present invention aims to provide a simple method for producing a positive electrode active material for lithium ion secondary batteries, which can further improve productivity.

A first invention of the present invention includes nickel (Ni), cobalt (Co), and other elements (M), and the atomic ratio of each element is Ni:Co:M=(1-x -y): x: y (where 0.01 ≤ x ≤ 0.35, 0.03 ≤ y ≤ 0.35, M is at least one of transition metals, alkaline earth metals, base metals, and semimetals) and a mixing step of mixing nickel composite oxide particles represented by and a lithium compound powder to obtain a lithium mixture, and a firing step of firing the lithium mixture in an oxidizing atmosphere, wherein the firing step includes the A method for producing a positive electrode active material for a lithium ion secondary battery, characterized in that the step involves stirring the lithium mixture at least once every time the furnace temperature is raised by 150°C during the firing process. is.

The second invention of the present invention is that the amount of the lithium mixture to be stirred in one stirring operation in the stirring operation of the lithium mixture of the first invention is 30% or more of the total amount of the lithium mixture subjected to the firing treatment. A method for producing a positive electrode active material for a lithium ion secondary battery, characterized by comprising:

A third invention of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery, wherein the oxidizing atmosphere in the first and second inventions has an oxygen concentration of 80% by volume or more.

A fourth invention of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery, wherein the baking temperature in the baking step in the first to third inventions is 650° C. or more and 1100° C. or less. is.

A fifth aspect of the present invention is a lithium ion secondary battery characterized in that the firing time, which is the holding time at the firing temperature in the firing step in the first to fourth aspects, is 15 minutes or more and 180 minutes or less. It is a manufacturing method of the positive electrode active material for.

A sixth aspect of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery, comprising crushing, washing, and drying the fired product obtained in the firing step in the first to fifth aspects of the invention. be.

ADVANTAGE OF THE INVENTION According to this invention, the simple manufacturing method of the positive electrode active material for lithium ion secondary batteries with higher productivity can be provided.

It is a figure which shows an example of the manufacturing method of the positive electrode active material for lithium ion secondary batteries. It is a figure which shows an example of the manufacturing method of nickel composite oxide. FIG. 4 is a diagram showing an example of a treatment process for a lithium-nickel composite oxide after firing; FIG. 3 is a diagram showing a secondary battery for evaluation used in Examples.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. In the drawings, they may be represented schematically or may be represented by changing the scale as appropriate.

1. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Batteries The present embodiment is a method for producing a positive electrode active material for lithium ion secondary batteries containing a lithium-nickel composite oxide (hereinafter also simply referred to as "positive electrode active material"). be.
The lithium-nickel composite oxide has an atomic ratio of lithium (Li), nickel (Ni), cobalt (Co), and other elements (M) of Li:Ni:Co:M=s:(1- xy):x:y (0.93<s<1.03, 0.01≤x≤0.35, 0.03≤y≤0.35). The lithium-nickel composite oxide (hereinafter also simply referred to as "composite oxide") may have a layered crystal structure and may contain secondary particles formed by agglomeration of primary particles.

FIG. 1 is a diagram showing an example of a method for producing a positive electrode active material according to this embodiment.
As shown in FIG. 1, the method for producing a positive electrode active material includes, for example, obtaining a lithium mixture containing a nickel composite oxide and a lithium compound (mixing step: step S10), and firing the mixture. obtaining a sintered body (sintering step: step S20). Each step will be described below.

[Mixing step: step S10]
First, the mixing step (step S10) of mixing a nickel composite oxide and a lithium compound to obtain a lithium mixture will be described.
In the production method of the present embodiment, by using a nickel composite oxide as a raw material, it is possible to obtain a highly crystalline lithium-nickel composite oxide in a very short time with high productivity. Each raw material used in the mixing step (step S10) will be described below.

(Nickel composite oxide)
A nickel composite oxide is an oxide containing nickel, cobalt, and other elements (hereinafter also referred to as “nickel composite oxide”).
The nickel composite oxide includes, for example, nickel (Ni), cobalt (Co), and other element M, and the atomic ratio (molar ratio) of each element is Ni:Co:M=(1−x −y): x:y (0.01≦x≦0.35, 0.03≦y≦0.35). Also, the element M may be at least one of transition metals, alkaline earth metals, base metals, and semimetals. In addition, the ratio of each element contained in the nickel composite oxide is inherited to the lithium-nickel composite oxide. Therefore, the composition of the entire nickel composite oxide can be the same as the composition of the metals other than lithium in the lithium-nickel composite oxide to be obtained.

Further, the nickel composite oxide contains nickel (Ni), cobalt (Co), and aluminum (Al), and the atomic ratio (molar ratio) of each element is Ni:Co:Al=(1−x -y): x:y (0.01≤x≤0.10, 0.03≤y≤0.10).

In addition, the nickel composite oxide may contain nickel (Ni), cobalt (Co), aluminum (Al), and other element M, and the atomic number ratio (molar ratio) of each element is Ni:Co : Al: M = (1-xy): x: y: z (0.03 ≤ x ≤ 0.10, 0.03 ≤ y ≤ 0.10, 0 ≤ z ≤ 0.10) may Also, the element M may be at least one of transition metals, alkaline earth metals, base metals, and semimetals.

A nickel composite oxide can be obtained, for example, by oxidizing a nickel composite hydroxide used as a precursor of a positive electrode active material.
When the nickel composite oxide is used, the amount of water vapor generated during firing of the lithium mixture is reduced, the reaction proceeds remarkably, and the firing time can be greatly shortened.

An example of a method for producing a nickel composite oxide will be described below. Note that the nickel composite oxide may be obtained by other production methods.
FIG. 2 is a diagram showing an example of a method for producing a nickel composite oxide.
For example, a nickel composite oxide can be obtained by a method comprising oxidative roasting (step S2) of a nickel composite hydroxide obtained by crystallization (step S1), as shown in FIG. The nickel composite hydroxide obtained by crystallization has a uniform composition throughout the particles, and the finally obtained positive electrode active material also has a uniform composition. Incidentally, the nickel composite oxide may be obtained by a method other than crystallization. Each step of producing the nickel composite oxide will be described below.

[Crystallization step; Step S1]
Nickel composite hydroxide supplies a neutralizing agent or the like to an aqueous solution containing, for example, a salt containing nickel (Ni salt), a salt containing cobalt (Co salt), and a salt containing aluminum (Al salt). and crystallize (step S1).

As a specific example, an aqueous solution containing a nickel salt, a cobalt salt and an aluminum salt is neutralized with an alkaline aqueous solution in the presence of a complexing agent such as an ammonium ion donor while being stirred, and a crystallization reaction is carried out. can be manufactured by The nickel composite hydroxide obtained by the crystallization method is composed of secondary particles in which primary particles are agglomerated, and the positive electrode active material obtained by using the nickel composite hydroxide particles as a precursor also has agglomerated primary particles. It is composed of secondary particles.

As the metal salt used when preparing the aqueous solution containing the metal salt, for example, sulfates, nitrates and chlorides of Ni, Co and Al can be used. Moreover, the aqueous solution of the metal salt may contain a salt containing a metal M other than nickel, cobalt, and aluminum.

The nickel composite hydroxide can contain nickel (Ni), cobalt (Co), and optionally other metals (M), where the molar ratio of each element is Ni:Co:M=(1- xy): x:y (0.01≤x≤0.35, 0.03≤y≤0.35).
The ratio of each element contained in the nickel composite hydroxide is inherited to the nickel composite oxide and the lithium-nickel composite oxide. Therefore, the composition of the nickel composite hydroxide as a whole can be the same as the composition of the metals other than lithium in the lithium-nickel composite oxide to be obtained.

The crystallization method is not particularly limited, and for example, a continuous crystallization method, a batch method, or the like can be used. The continuous crystallization method is, for example, a method of continuously recovering nickel composite hydroxide that overflows from a reaction vessel, and can easily produce a large amount of nickel composite hydroxide having the same composition. In addition, the nickel composite oxide obtained by the continuous crystallization method has a wide particle size distribution, and the particle size distribution affects even the positive electrode active material. The volumetric energy density of the battery is increased. In addition, the particle size of nickel compound hydroxide is 1 micrometer or more and 50 micrometers or less, for example.

The batch method can obtain a nickel composite hydroxide having a more uniform particle size and a narrow particle size distribution. A molded body obtained using a nickel composite hydroxide obtained by a batch method can more uniformly react with a lithium compound during firing. In addition, the nickel composite hydroxide obtained by the batch method can reduce contamination of fine powder, which is one of the causes of deterioration of cycle characteristics and output characteristics when used in secondary batteries.

[Oxidizing Roasting Step: Step S2]
Next, nickel composite oxide is obtained by subjecting the nickel composite hydroxide to oxidizing roasting (heat treatment) (step S2).
The conditions for the oxidizing roasting are not particularly limited as long as most of the nickel composite hydroxide is converted to the nickel composite oxide. Preferably. If the temperature of oxidizing roasting is less than 600° C., moisture may remain in the nickel composite hydroxide (precursor) and oxidation may not proceed sufficiently. On the other hand, if the oxidizing roasting temperature exceeds 800° C., the composite oxides may bond together to form coarse particles. On the other hand, if the oxidizing roasting temperature is too high, it consumes a lot of energy, which lowers the productivity from the viewpoint of cost, making it industrially unsuitable.

The oxidative roasting time is preferably, for example, 0.5 hours or more and 3.0 hours or less. If the oxidative roasting time is less than 0.5 hours, the nickel composite hydroxide may not be sufficiently oxidized. On the other hand, if the oxidizing roasting time exceeds 3.0 hours, the energy cost increases and the productivity decreases, which is industrially unsuitable.

(lithium compound)
The lithium compound is not particularly limited, and a known lithium compound can be used. For example, lithium hydroxide, lithium nitrate, lithium carbonate, lithium acetate, or a mixture thereof can be used. Among these, lithium hydroxide and lithium carbonate are preferably used.

As lithium hydroxide, hydrates such as lithium hydroxide-hydrate (LiOH.H ₂ O) and anhydrides such as anhydrous lithium hydroxide (LiOH) can be used. Lithium hydroxide having a moisture content of 1.5% or less and a total carbon content of 1.0% or less is more preferable.

Lithium hydroxide having a moisture content of 1.5% or less and a total carbon of 1.0% or less can be obtained, for example, by heat-treating lithium hydroxide-hydrate (LiOH.H ₂ O). When such lithium hydroxide is used, generation of moisture is suppressed in the firing step (step S20), thereby promoting the synthesis reaction of the lithium-nickel composite oxide and shortening the firing time.

The moisture content is obtained by vacuum-drying the lithium hydroxide to be measured at 200° C. for 8 hours, and measuring the weight before and after vacuum drying, with the moisture content of the obtained lithium hydroxide being 0% by mass. Calculated. Note that the moisture content is an amount including water of hydration, and for example, lithium hydroxide-hydrate has a moisture content of about 43% by mass. Further, total carbon (total carbon content) is a value that can be measured by a high-frequency combustion-infrared absorption method.

(lithium mixture)
A lithium mixture is obtained by mixing a nickel composite oxide and a lithium compound.
The mixing ratio of the nickel composite oxide and the lithium compound is determined by the ratio (Li/Me ratio) is in the range of more than 0.93 and less than 1.03.

If the Li/Me ratio is 0.93 or less, a part of the nickel composite oxide remains unreacted in the firing step (step S20), and sufficient battery performance may not be obtained. On the other hand, when the Li/Me ratio is 1.03 or more, sintering is promoted in the firing step (step S20), and the fired product becomes hard and difficult to crush, and the resulting lithium-nickel composite oxide The particle size and crystallite size of the particles become too large, and sufficient battery performance may not be obtained.

Since the required Li/Me ratio varies depending on the configuration of the secondary battery, etc., the Li/Me ratio can be appropriately set within the above range according to the requirements. The value of the Li/Me ratio may be, for example, 0.95 or more and less than 1.03, may be 1.0 or more and less than 1.03, or may be more than 1.0 and less than 1.03. There may be.

Moreover, since the Li/Me ratio does not substantially change before and after the firing step (step S20), the Li/Me ratio in the lithium mixture is substantially maintained in the lithium-nickel composite oxide. Therefore, the mixing ratio of the nickel composite oxide and the lithium compound can be appropriately adjusted so as to be the same as the Li/Me ratio in the lithium-nickel composite oxide to be obtained.

A general mixer can be used for mixing the nickel composite oxide and the lithium compound, for example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, or the like can be used. Moreover, this mixing should be sufficiently mixed so that the skeleton of the nickel composite oxide is not destroyed. Insufficient mixing may cause problems such as variation in the Li/Me ratio among individual particles and failure to obtain sufficient battery characteristics.

[Baking process: step S20]
Next, the obtained lithium mixture is fired at 650° C. or higher and 1100° C. or lower in an oxygen atmosphere (baking step, step S20).
In the firing of this lithium mixture, the nickel composite oxide and the lithium compound in the mixture react to form a lithium-nickel composite oxide.
In particular, by stirring the lithium mixture during this firing, a lithium-nickel composite oxide (positive electrode active material) that has high crystallinity and battery characteristics equivalent to or better than conventional firing time in a much shorter time than conventional firing time. can be obtained.

By the way, the firing conditions may be any conditions as long as the nickel composite oxide reacts with the lithium compound to form the lithium-nickel composite oxide. It is preferable to hold (baking time) at a predetermined temperature (baking temperature) within the temperature range of 3 hours or less.

If the firing temperature is lower than 650° C., the diffusion of lithium is not sufficiently performed, and particles of unreacted lithium compound remain, or the crystal structure of the lithium-nickel composite oxide is not sufficiently arranged, resulting in the obtained A secondary battery using a positive electrode active material may not have sufficient battery characteristics.
On the other hand, if the firing temperature exceeds 1100° C., intense sintering occurs between the lithium-nickel composite oxide particles and abnormal grain growth may occur, resulting in a decrease in the specific surface area. In addition, the specific surface area of the positive electrode active material may be reduced, the resistance of the positive electrode in the secondary battery may be increased, and the battery capacity may be reduced. Incidentally, the firing temperature can be appropriately adjusted according to the composition.

For example, when aluminum is used as the other element M, the temperature may be 700° C. or higher and 800° C. or lower, or 730° C. or higher and 770° C. or lower.
When manganese is used as another element M, the temperature may be 800° C. or higher and 1100° C. or lower, or 850° C. or higher and 950° C. or lower.

The time during which the lithium mixture is held at the firing temperature (hereinafter also referred to as "firing time") is not particularly limited as long as a highly crystalline lithium-nickel composite oxide is formed. When aluminum is used for M, the time is preferably 120 minutes or less, more preferably 60 minutes or less, and even more preferably 30 minutes or less.
When manganese is used as another element M, the time is preferably 420 minutes or less, more preferably 300 minutes or less, and even more preferably 180 minutes or less.
In the present embodiment, it is preferable that a lithium-nickel composite oxide having high crystallinity is obtained with a firing time of 15 to 180 minutes depending on the firing temperature and composition presented, and the firing time is within that range. While maintaining the crystallinity in , the shorter the time, the more productivity can be expected, which is preferable.

The atmosphere during firing is preferably an oxidizing atmosphere having an oxygen concentration higher than the atmospheric atmosphere, more preferably an atmosphere having an oxygen concentration of 80% by volume or more, and may have an oxygen concentration of 100% by volume. . That is, the lithium mixture is preferably carried out in an oxygen stream.
If the oxygen concentration in the atmosphere during firing is less than 80% by volume, the amount of oxygen required for the reaction between the nickel composite oxide and the lithium compound cannot be supplied, and it takes a long time to form the lithium-nickel composite oxide. , when the oxygen concentration is lower than that in the atmosphere, the lithium-nickel composite oxide may not be sufficiently formed.

The firing furnace is not particularly limited as long as it can be heated in an oxygen stream, and a vertical furnace, a rotary hearth furnace, a roller hearth kiln, and the like can be used.

(Stirring operation)
In the stirring operation during firing, the stirring method is not particularly limited as long as the lithium mixture can be stirred. Preferably, the method is a stirring method in which 30% or more of the lithium mixture is stirred in one stirring, more preferably a method in which 50% or more is stirred, and further preferably a method in which 70% or more is stirred. .

In addition, the frequency of the stirring operation does not need to be stirred at all from the start of temperature rise to the end of temperature drop in the baking process, and it is sufficient if it can be mixed as necessary. Stirring treatment is preferably performed until about the middle of the firing time at the temperature. Preferably, it is preferable to adopt a method of stirring each time the temperature inside the furnace rises to a certain temperature during the heating process. Preferably, it is more preferably once or more per 50°C. In addition, while the sintering temperature is being maintained, the stirring operation may be performed on a time base at fixed intervals.

FIG. 3 is a diagram showing an example of the process of treating the lithium-nickel composite oxide obtained after sintering.
As shown in FIG. 3, in the method for producing a positive electrode active material according to the present embodiment, the lithium-nickel composite oxide (fired product) obtained after the firing step (step S20) is pulverized to crush the pulverized product (lithium-nickel composite oxide powder) (crushing step: step S30), washing and filtering the crushed material (washing step: step S40), and drying the washed lithium-nickel composite oxide (drying Step: step S50). Note that the method for producing a positive electrode active material according to the present embodiment may not include the above crushing (step S30), water washing (step S40), and drying step (step S50). At least one step may be provided among the steps. Each step will be described below.

[Crushing step: step S30]
The lithium-nickel composite oxide (fired product) obtained after firing (step S20) may be further pulverized (step S30).
By this pulverization, the secondary particles of the lithium-nickel composite oxide that have aggregated or lightly sintered are separated from each other, and the average particle size and particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range. can. In addition, crushing refers to applying mechanical energy to aggregates composed of multiple secondary particles generated by sintering necking between secondary particles during firing, and almost without destroying the secondary particles themselves. It refers to the operation of separating and loosening aggregates.

As the crushing method, known means can be used, for example, a pin mill, a hammer mill, a crusher with a classifying function, or the like can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

[Water washing step: step S40]
The crushed material obtained may then be washed with water (step S40).
By washing the lithium-nickel composite oxide (crushed material) with water, excess lithium and impurities on the surface of the lithium-nickel composite oxide particles are removed, resulting in a positive electrode active material for lithium-ion secondary batteries with higher capacity and higher thermal stability. can be obtained. Here, the washing method is not particularly limited, and a known technique is used.

As a water washing method, for example, the lithium-nickel composite oxide (crushed material) is put into water to form a slurry, and the slurry is stirred so that excess lithium on the surface of the lithium-nickel composite oxide particles is sufficiently removed. is preferred. After stirring, solid-liquid separation is performed, and drying (step S50) is performed as described later to obtain a lithium-nickel composite oxide.

As for the slurry concentration, it is preferable to add 0.5 to 2 parts by mass of lithium-nickel composite oxide (crushed material) to 1 part by mass of water.
As for the slurry concentration, if the amount of pulverized material added to 1 part by mass of water exceeds 2 parts by mass, the viscosity becomes very high and stirring becomes difficult, and the alkalinity (pH) in the liquid is high. The rate of dissolution of deposits from the powder may be slow, and even if peeling occurs, it may become difficult to separate from the powder. On the other hand, when the slurry concentration is less than 0.5 parts by mass with respect to 1 part by mass of water, the amount of lithium eluted is large because the slurry is too dilute, and the crystals of the lithium nickel composite oxide (crushed material) Detachment of lithium from the lattice also occurs, making crystals more likely to collapse, and the high-pH aqueous solution (slurry) absorbs carbon dioxide gas in the atmosphere, causing lithium carbonate to form on the surface of the lithium-nickel composite oxide. may re-deposit.

The washing liquid used in the water washing step (step S40) is not particularly limited, and for example, water may be used. When water is used, for example, water with an electrical conductivity of less than 10 μS/cm is preferable, and water with an electrical conductivity of 1 μS/cm or less is more preferable. When water having an electrical conductivity measurement of less than 10 μS/cm is used, deterioration of battery performance due to adhesion of impurities to the positive electrode active material can be further suppressed.

When the slurry is subjected to solid-liquid separation, it is preferable that the amount of adhering water remaining on the particle surfaces of the lithium-nickel composite oxide is small. When a large amount of adhering water is present, lithium dissolved in the liquid (in the slurry) may be reprecipitated, increasing the amount of lithium present on the surface of the lithium-nickel composite oxide after drying (step S50). For the solid-liquid separation, a centrifugal machine, a filter press, etc., which are commonly used are used.

[Drying process: step S50]
After washing with water (step S40), it may be dried to obtain a lithium-nickel composite oxide (positive electrode active material) (step S50). Drying conditions are not particularly limited as long as at least part of the moisture in the lithium-nickel composite oxide is removed. In the drying step (step S50), for example, the lithium-nickel composite oxide (powder) after filtration (solid-liquid separation) is dried in a gas atmosphere that does not contain compound components containing carbon and sulfur, or in a vacuum atmosphere. It is preferable to carry out the reaction at a predetermined temperature using a machine.

The drying temperature is preferably 80° C. or higher and 550° C. or lower, more preferably 120° C. or higher and 350° C. or lower. When the drying temperature is 80° C. or higher, the positive electrode active material after washing with water (step S40) is quickly dried, and it is possible to suppress the occurrence of a lithium concentration gradient between the particle surface and the inside of the particle. On the other hand, when the drying temperature exceeds 550°C, the surface of the lithium-nickel composite oxide is expected to be in a state close to the stoichiometric ratio or in a state close to the charged state due to the desorption of lithium. There is a possibility that the crystal structure will collapse and the battery characteristics of the secondary battery will deteriorate.
Moreover, the drying temperature is more preferably 120° C. or higher and 350° C. or lower from the viewpoint of productivity and heat energy cost.

[Characteristics of positive electrode active material]
According to the method for producing a positive electrode active material according to the present embodiment described above, a lithium-nickel composite oxide (positive electrode active material) with excellent crystallinity can be obtained with high productivity by firing in a very short time. The characteristics of the lithium-nickel composite oxide (positive electrode active material) obtained by the manufacturing method according to this embodiment will be described below.

(composition)
The lithium-nickel composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and other elements (M), and the molar ratio of each metal element is Li:Ni:Co:M=s : (1-xy): x: y (where 0.93 < s < 1.03, 0.01 ≤ x ≤ 0.35, 0.03 ≤ y ≤ 0.35, M is a transition metal, at least one of alkaline earth metals, base metals, and semimetals).

(Lithium seat occupancy rate)
The lithium nickel composite oxide has, for example, a lithium site occupancy of 95% or more, preferably 96% or more, more preferably 96% or more, which is a lithium-based layer obtained from Rietveld analysis of an X-ray diffraction pattern. 97% or more. When the lithium seat occupancy is within the above range, the sintering reaction between the precursor and the lithium compound is sufficiently performed in the firing step (step S20), and the lithium-nickel composite oxide has high crystallinity. show. When a highly crystalline lithium-nickel composite oxide is used as a positive electrode active material for a secondary battery, it exhibits excellent battery characteristics (high battery capacity, etc.).

(Initial charge/discharge efficiency)
The initial charge/discharge efficiency (initial discharge capacity/initial charge capacity) of a 2032-type coin-type battery for evaluation (see FIG. 4) produced using a lithium-nickel composite oxide as a positive electrode active material is, for example, 85% or more. , preferably 89% or more, more preferably 89.5% or more. When the initial charge-discharge efficiency is within the above range, the sintering reaction between the precursor and the lithium compound is sufficiently performed in the firing step (step S30), and the lithium-nickel composite oxide has high crystallinity. show. For the initial discharge capacity efficiency, the coin-type battery used in the example was left for about 24 hours after it was manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was set to 0.1 mA/ It is a value obtained by measuring the capacity when charged to a cut-off voltage of 4.3 V as cm ² , discharged to a cut-off voltage of 3.0 V after resting for 1 hour.

2. Lithium Ion Secondary Battery A method for manufacturing a lithium ion secondary battery according to the present embodiment (hereinafter also referred to as a “method for manufacturing a secondary battery”) uses a positive electrode, a negative electrode, and a non-aqueous electrolyte to produce a lithium ion secondary battery. obtaining a battery, wherein the positive electrode is obtained using the positive electrode active material obtained by the manufacturing method described above. A secondary battery obtained by the manufacturing method according to the present embodiment may include, for example, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolytic solution, or may include a positive electrode, a negative electrode, and a solid electrolyte. Also, the secondary battery may be composed of components similar to those of a known lithium-ion secondary battery.

Hereinafter, as an example of a method of manufacturing a secondary battery according to the present embodiment, constituent materials of a secondary battery using a non-aqueous electrolytic solution and a method of manufacturing the same will be described. It should be noted that the embodiments described below are merely examples, and the manufacturing method of the secondary battery is based on the embodiments described herein, and various changes and improvements are made based on the knowledge of those skilled in the art. It can be implemented in the form of Moreover, the secondary battery obtained by the manufacturing method according to the present embodiment is not particularly limited in its application.

(positive electrode)
The positive electrode contains the positive electrode active material described above. A positive electrode can be manufactured, for example, as follows. Note that the method for producing the positive electrode is not limited to the following examples, and other methods may be used.

First, the above positive electrode active material, conductive material, and binder (binder) are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment, etc. are added, and this is kneaded to obtain a positive electrode mixture. Make a paste. The constituent material of the positive electrode mixture paste is not particularly limited, and materials equivalent to known positive electrode mixture pastes may be used.

The mixing ratio of each material in the positive electrode mixture paste is not particularly limited, and is appropriately adjusted according to the required performance of the secondary battery. The mixture ratio of the materials can be in the same range as the positive electrode mixture paste for known secondary batteries. The content of the active material may be 60 to 95 parts by mass, the content of the conductive material may be 1 to 20 parts by mass, and the content of the binder may be 1 to 20 parts by mass.

Examples of conductive materials that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black.

Binders (binders) play a role in binding active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulose resin. , polyacrylic acid, etc. can be used.

If necessary, a solvent for dispersing the positive electrode active material, the conductive material, and the activated carbon and dissolving the binder (binder) may be added to the positive electrode mixture paste. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone (NMP) may be used. In addition, activated carbon may be added to the positive electrode mixture in order to increase the electric double layer capacity.

Next, the obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil, dried, and the solvent is dispersed to prepare a sheet-like positive electrode. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery, and used for manufacturing the battery.

(negative electrode)
Metallic lithium, a lithium alloy, or the like may be used for the negative electrode. For the negative electrode, a negative electrode active material capable of intercalating and deintercalating lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste. It may be applied to a surface, dried, and optionally compressed to increase electrode density.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. Similar to the positive electrode, a fluorine-containing resin such as PVDF can be used as the negative electrode binder. Further, organic solvents such as N-methyl-2-pyrrolidone can be used as solvents for dispersing these active materials and binders.

(separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, for example, a non-aqueous electrolytic solution can be used.
As the non-aqueous electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent can be used. Further, as the non-aqueous electrolytic solution, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid is a salt that is composed of cations and anions other than lithium ions and that is liquid even at room temperature.

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; and ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. can also be used.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , composite salts thereof, and the like can be used. Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

A solid electrolyte may be used as the non-aqueous electrolyte. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes.
The oxide-based solid electrolyte is not particularly limited, and for example, one containing oxygen (O) and having lithium ion conductivity and electronic insulation can be preferably used. For example, lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li ₃ PO ₄ , Li ₄ SiO ₄ - Li ₃ VO ₄ , Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₂ O—B ₂ O ₃ —ZnO, Li _1+X Al _X Ti _2-X (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _2/3-X TiO ₃ (0≦ _{X ≦ 2 / 3 ) , Li5La3Ta2O12 , Li7La3Zr2O12 , Li6BaLa2Ta2O12 , Li3.6Si0.6P0.4O4 , etc.} mentioned.

The sulfide-based solid electrolyte is not particularly limited, and for example, one containing sulfur (S) and having lithium ion conductivity and electronic insulation can be preferably used.
Examples of such sulfide-based solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ SP ₂ S ₅ , LiI _{-Li2S - B2S3} , _Li3PO4 -Li2S _- Si2S, _Li3PO4 - _Li2S - _{SiS2 , LiPO4 - Li2S} - _SiS , LiI- _Li2S- P ₂ O ₅ , LiI—Li ₃ PO ₄ —P ₂ S ₅ and the like.

Inorganic solid electrolytes other than those described above may be used, such as Li ₃ N, LiI, Li ₃ N--LiI--LiOH, and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt).

(Battery shape and configuration)
The shape of the lithium-ion secondary battery of the present embodiment, which is composed of the positive electrode, the negative electrode, and the non-aqueous electrolyte described above, can be various shapes such as a cylindrical shape and a laminated shape.
Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicated with the positive electrode current collector and the outside. A current collecting lead or the like is used to connect between the positive electrode terminal and between the negative electrode current collector and the negative electrode terminal leading to the outside, and the battery case is sealed to complete the lithium ion secondary battery.
Note that when a solid electrolyte is employed, the solid electrolyte may also serve as a separator.

EXAMPLES The present invention will be specifically described below using Examples, but the present invention is not limited to these Examples.
The performance of the positive electrode active material obtained by this embodiment, the positive electrode mixture paste using this positive electrode active material, and the lithium ion secondary battery were measured. In this example, each sample of special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. was used for the production of the composite hydroxide and the production of the positive electrode active material and the secondary battery.

[Production and Evaluation of Secondary Battery for Evaluation]
A 2032-type coin-type battery (see FIG. 4) was produced by the following method, and battery characteristics of the positive electrode active material were evaluated.

(Production of coin-type battery)
52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa to prepare a positive electrode PE (evaluation electrode). bottom. The produced positive electrode PE was dried in a vacuum dryer at 120° C. for 12 hours.

For the negative electrode NE used in the fabrication, a negative electrode sheet in which a copper foil was coated with graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride was punched into a disc shape with a diameter of 14 mm.
As the electrolytic solution, an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiPF ₆ as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used.
A polyethylene porous film having a film thickness of 25 μm was used as the separator SE.

Using these dried positive electrode PE, negative electrode NE, separator SE, and electrolytic solution, a coin-type battery 1 was assembled in an Ar atmosphere glove box with a controlled dew point of -80°C.
As for its structure, as shown in FIG.
The case 2 has a hollow cathode can PC with one end open, and an anode can NC arranged in the opening of the cathode can PC. , a space for accommodating the electrode 3 is formed between the negative electrode can PC and the positive electrode can PC. The electrode 3 is composed of a positive electrode PE, a separator SE, and a negative electrode NE, which are stacked in this order, with the positive electrode PE in contact with the inner surface of the positive electrode can PC and the negative electrode NE with the inner surface of the negative electrode can NC. It is housed in case 2 as shown. A gasket GA is provided between the positive electrode can PC and the negative electrode can NC to ensure their airtightness.

Using the produced coin-type battery 1, the following battery characteristics were measured.
(initial discharge capacity)
For the initial discharge capacity, the coin-type battery 1 was left for about 24 hours after production, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was 0.1 mA / cm ² and the cutoff voltage was 4. The battery was charged to 3 V, rested for 1 hour, and then discharged to a cut-off voltage of 3.0 V. The capacity was taken as the initial discharge capacity.

A nickel composite oxide obtained by oxidizing and roasting a nickel composite hydroxide having a composition ratio of Ni:Co:Al=88:9:3 in a rotary kiln and having a moisture content of 1.5% or less and a total carbon of 1.5%. 0% or less lithium hydroxide was mixed so that the Li/Me ratio was 1.03 to prepare a lithium mixture.

8 kg of the produced lithium mixture powder was placed in a sagger having a width of 330 mm, a depth of 330 mm, and a height of 110 mm. This sagger was placed in a furnace at room temperature, and oxygen was introduced into the furnace to create an atmosphere with an oxygen concentration of 80% by volume or more. After that, while maintaining the oxygen concentration of 80% by volume or more, the lithium mixture is stirred once every time the temperature is raised by 150 ° C. with a stirring jig installed in the furnace, and the temperature is raised at a rate of 10 ° C./min. The temperature was raised to a certain 760°C. The stirring amount of the lithium mixture in one stirring was 30 to 50% of the total lithium mixture. After reaching a firing temperature of 760° C., this firing temperature was held for 60 minutes.

The sagger was then cooled to room temperature in an oxygen atmosphere. After cooling, it was pulverized, washed with water, and dried to obtain a lithium-nickel composite oxide.
The crystallite size and Li site occupancy of the resulting lithium-nickel composite oxide were measured with an X-ray diffractometer. A coin-type battery was produced using the obtained lithium-nickel composite oxide as a positive electrode active material, and the initial discharge capacity was measured.
These measurement results are shown in Table 1.

The heating rate is 30° C./min, the firing time is 30 minutes, the stirring frequency is once for each 100° C. temperature rise, and the amount of lithium mixture stirred in one stirring is 70 to 90% of the total lithium mixture. A lithium-nickel composite oxide was obtained in the same manner as in Example 1, except that
Table 1 shows the crystallite size, Li site occupancy, and initial discharge capacity of the obtained lithium-nickel composite oxide.

A lithium-nickel composite was produced in the same manner as in Example 1, except that the composition ratio of the nickel composite hydroxide was Ni:Co:Al=91:4:5, the firing temperature was 740° C., and the Li/Me ratio was 1.02. An oxide was obtained.
Table 1 shows the crystallite size, Li site occupancy, and initial discharge capacity of the obtained lithium-nickel composite oxide.

The heating rate is 30° C./min, the firing time is 30 minutes, the stirring frequency is once for each 100° C. temperature rise, and the amount of lithium mixture stirred in one stirring is 70 to 90% of the total lithium mixture. A lithium-nickel composite oxide was obtained in the same manner as in Example 3, except that
Table 1 shows the crystallite size, Li site occupancy, and initial discharge capacity of the obtained lithium-nickel composite oxide.

The composition ratio of the nickel composite hydroxide is Ni:Co:Mn=55:20:25, lithium carbonate is used instead of lithium hydroxide, the firing temperature is 950° C., the firing time is 3 hours, and the stirring frequency is 100. A lithium-nickel composite oxide was obtained in the same manner as in Example 1, except that the stirring was performed once every time the temperature was raised to 0 C, and the amount of the lithium mixture stirred in one stirring was set to 70 to 90% of the total lithium mixture.
Table 1 shows the crystallite size, Li site occupancy, and initial discharge capacity of the obtained lithium-nickel composite oxide.

(Comparative example 1)
A lithium-nickel composite oxide was obtained in the same manner as in Example 1, except that stirring was not performed during firing.
Table 1 shows the crystallite size, Li site occupancy, and initial discharge capacity of the obtained lithium-nickel composite oxide.

(Comparative example 2)
A lithium-nickel composite oxide was obtained in the same manner as in Example 3, except that stirring was not performed during firing.
Table 1 shows the crystallite size, Li site occupancy, and initial discharge capacity of the obtained lithium-nickel composite oxide.

(Comparative Example 3)
A lithium-nickel composite oxide was obtained in the same manner as in Example 5, except that stirring was not performed during firing.
Table 1 shows the crystallite size, Li site occupancy, and initial discharge capacity of the obtained lithium-nickel composite oxide.

(Evaluation results)
The lithium-nickel composite oxides obtained in Examples have a sufficiently large crystallite diameter and a high lithium site occupancy rate, despite the fact that the heating rate is high and the firing time is short. ing.
Moreover, it was shown that the secondary batteries using the lithium-nickel composite oxides obtained in Examples 1 to 5 as positive electrode active materials had very high initial charge/discharge capacities.
As described above, according to the production method of the present embodiment, by firing the lithium mixture while stirring, it is possible to fire the lithium mixture in an extremely short time, and the productivity can be greatly improved. It is clear that significant cost savings are possible.

S10 Mixing step S20 Firing step S1 Crystallization step S2 Oxidizing roasting step S30 Crushing step S40 Water washing step S50 Drying step 1 Coin type battery 2 Case PC Positive electrode can NC Negative electrode can GA Gasket 3 Electrode PE Positive electrode NE Negative electrode SE Separator

Claims (6)

Nickel (Ni), cobalt (Co), and other elements (M) are included, and the atomic ratio of each element is Ni: Co: M = (1-xy): x: y (however, , 0.01≦x≦0.35, 0.03≦y≦0.35, and M is at least one selected from transition metals, alkaline earth metals, base metals, and semimetals. and a mixing step of mixing the lithium compound powder to obtain a lithium mixture;
and a firing step of firing the lithium mixture in an oxidizing atmosphere,
For a lithium ion secondary battery, wherein the firing step is a step that involves stirring the lithium mixture at least once every time the temperature in the furnace is increased by 150 ° C. during the firing process. A method for producing a positive electrode active material. 2. The lithium according to claim 1 , wherein the amount of the lithium mixture to be stirred in one stirring operation in the stirring operation of the lithium mixture is 30% or more of the total amount of the lithium mixture subjected to the firing treatment. A method for producing a positive electrode active material for an ion secondary battery. 3. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein said oxidizing atmosphere has an oxygen concentration of 80% by volume or more. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3 , characterized in that the baking temperature in the baking step is 650°C or higher and 1100°C or lower. The positive electrode active for a lithium ion secondary battery according to any one of claims 1 to 4 , wherein the baking time, which is the holding time at the baking temperature in the baking step, is 15 minutes or more and 180 minutes or less. A method of making a substance. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5 , comprising crushing, washing and drying the fired product obtained in the firing step.

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