JP2018067474A - Method for manufacturing lithium secondary battery electrode material, method for manufacturing lithium secondary battery, and lithium-niobium solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a lithium-niobium solution improved in storage stability; and a technique which can suppress the reduction in discharge capacity and increase the production efficiency concerning a lithium secondary battery electrode and its material.SOLUTION: A method for manufacturing a lithium secondary battery electrode material and its related technique are provided. The method comprises: the step 1 of mixing an aqueous solution with a lithium salt dissolved therein, particles A composed of fine particles including at least one of a niobium oxide and a niobium hydroxide, of which the mode diameter (highest-frequency particle diameter) according to a dynamic light scattering method is 5 to 200 nm, and a lithium secondary battery positive electrode active material to obtain slurry; the step 2 of recovering powder with niobium and lithium deposited on the surface of each particle B of the lithium secondary battery positive electrode active material by applying an evaporation drying method to the slurry; and the step 3 of firing the powder at 150 to 700°C to form a lithium niobate layer on the surface of each particle B of the lithium secondary battery positive electrode active material.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a lithium secondary battery electrode material, a method for producing a lithium secondary battery, and a lithium-niobium solution.

  Lithium ion batteries are characterized by high energy density and high voltage operation. Therefore, it is used for information devices such as mobile phones as secondary batteries that are easy to reduce in size and weight. In recent years, the demand for secondary batteries for large motive power such as for hybrid vehicles has been increasing.

  In a lithium ion battery, a nonaqueous solvent electrolyte in which a salt is dissolved in an organic solvent is generally used as the electrolyte. However, since the nonaqueous solvent electrolyte is flammable, the lithium ion battery needs to solve the safety problem. In order to ensure the safety, for example, measures such as incorporating a safety device into a lithium ion battery are implemented. Further, as a more drastic solution, a method has been proposed in which the above-described electrolyte is made a nonflammable electrolyte, that is, a lithium ion conductive solid electrolyte.

  Generally, the electrode reaction of a battery occurs at the interface between the electrode active material and the electrolyte. Here, when a liquid electrolyte is used as the electrolyte, the liquid electrolyte permeates between the active material particles by forming an electrode containing an electrode active material in the liquid electrolyte, thereby forming a reaction interface. On the other hand, when a solid electrolyte is used as the electrolyte, since the solid electrolyte does not have such a permeation mechanism between the active material particles, the powder containing the electrode active material particles and the solid electrolyte powder are mixed in advance. There is a need to. For this reason, the positive electrode of an all-solid-state lithium ion battery is usually a mixture of a positive electrode active material powder and a solid electrolyte.

  However, in an all-solid-state lithium ion battery, resistance generated when lithium ions move through the interface between the positive electrode active material and the solid electrolyte (hereinafter sometimes referred to as “interface resistance”) tends to increase. When the interfacial resistance increases, performance such as battery capacity in an all-solid-state lithium ion battery decreases.

Here, the following patent document discloses a proposal for reducing the interfacial resistance by coating the surface of lithium cobaltate, which is a positive electrode active material, with lithium niobate and improving the performance of the all-solid-state lithium ion battery. .
Patent Document 1 discloses an aqueous solution containing a peroxo complex of niobic acid ([Nb (O ₂ ) ₄ ] ³⁻ ) or a niobic acid complex having oxalic acid as a ligand and a lithium compound, and lithium-transition metal oxidation. A step of mixing the product powder to obtain a mixture, removing water from the mixture, and forming a peroxo complex of niobic acid ([Nb (O ₂ ) ₄ ] ³⁻ ) on the surface of the lithium-transition metal oxide powder. Alternatively, the method includes a step of obtaining a powder in which a niobic acid complex having oxalic acid as a ligand and a lithium compound are adhered, and a step of heat-treating the powder at 300 ° C. to 700 ° C. -A method for producing transition metal oxide powders is disclosed.

  Patent Document 2 has a spray-drying process in which a solution containing a niobium peroxo complex and lithium is sprayed and the solution is dried in parallel therewith, and a heat treatment process in which heat treatment is performed after the spray-drying process. And the temperature of heat processing is higher than 123 degreeC, and the manufacturing method of the active material composite powder whose temperature is less than 350 degreeC is disclosed.

JP 2012-074240 A Japanese Patent Laying-Open No. 2015-056307

  As a result of investigations by the present inventors, it has been clarified that the niobium peroxo complex forms a precipitate in 4 to 5 hours after the complex is formed unless any treatment is performed. In other words, niobium peroxo complexes have a problem in storage stability. If a solution containing a peroxo complex of niobium with precipitates is used, the coating amount decreases when the surface of lithium cobaltate, which is the positive electrode active material, is coated with lithium niobate, and the coating amount varies. As a result, the discharge capacity may be reduced. For this reason, after producing a peroxo complex of niobium, it becomes necessary to use the complex within a certain period of time, which leads to a decrease in production efficiency.

  Therefore, the present inventors proceeded with the study as a problem to be solved to provide a lithium-niobium solution with improved storage stability.

  As another issue, the present inventors have studied as a problem to be solved to provide a technology capable of suppressing a decrease in discharge capacity and improving production efficiency in a lithium secondary battery electrode and its material.

  As a result of investigations by the present inventors to solve the above problems, niobium-based fine particles (those containing niobium as an element, for example, niobium oxide or niobium hydroxide. The above description is obtained by preparing the fine particles so as to have a predetermined mode diameter and using a lithium-niobium solution containing the fine particles. .

  The inventions that have been found by the inventors to solve the above problems are as follows. In the following, a lithium secondary battery positive electrode will be exemplified as the lithium secondary battery electrode, but the lithium secondary battery positive electrode active material is one of raw materials for obtaining a lithium secondary battery positive electrode material. A lithium secondary battery positive electrode material is obtained by adhering lithium and niobium to the lithium secondary battery positive electrode active material particles and further forming a lithium niobate layer on the surface of the particles.

  According to a first aspect of the present invention, an aqueous solution containing particles A that are niobium source particles having a mode diameter (mode particle diameter) of 5 to 200 nm by a dynamic light scattering method and lithium ions is obtained by using a lithium secondary solution. And a step of forming a lithium niobate layer on the surface of the particles B of the lithium secondary battery active material, and a method for producing a lithium secondary battery electrode material.

The second invention of the present invention is a particle composed of an aqueous solution in which a lithium salt is dissolved and at least one of niobium oxide and niobium hydroxide, and has a mode diameter (mode particle diameter) determined by a dynamic light scattering method. Step 1 of mixing a particle A having a thickness of 5 to 200 nm and a positive electrode active material for a lithium secondary battery to obtain a slurry;
Recovering powder in a state where niobium and lithium are adhered to the surface of the particles B of the lithium secondary battery positive electrode active material by applying an evaporation to dryness method to the slurry; and
And a step 3 of firing the powder at 150 to 700 ° C. to form a lithium niobate layer on the surface of the particles B of the lithium secondary battery positive electrode active material. is there.

A third invention of the present invention is a particle composed of an aqueous solution in which a lithium salt is dissolved and at least one of niobium oxide and niobium hydroxide, and has a mode diameter (mode particle diameter) determined by a dynamic light scattering method. Step 1 of mixing particles A having a diameter of 5 to 200 nm to obtain a slurry;
A step 2 of spraying the slurry on the positive electrode active material of the lithium secondary battery to recover the powder in a state where niobium and lithium are adhered to the surface of the particles B of the lithium secondary battery positive electrode active material;
And a step 3 of forming the lithium niobate layer on the surface of the particles B of the lithium secondary battery positive electrode active material by firing the powder at 150 to 700 ° C. .

  4th invention of this invention is invention of 2nd or 3rd, Comprising: The said lithium salt is lithium hydroxide.

  A fifth invention of the present invention is any one of the first to fourth inventions, wherein the particle A is composed of niobium hydroxide.

  6th invention of this invention is invention in any one of 1st-5th, Comprising: The film thickness of the lithium niobate layer in the said process 3 shall be 2-100 nm.

  7th invention of this invention is a method of manufacturing a lithium secondary battery provided with a positive electrode, a negative electrode, and the electrolyte which contacts the said positive electrode and the said negative electrode, Comprising: The electrode which produces the said positive electrode and the said negative electrode The positive electrode is a method for manufacturing a lithium secondary battery obtained by the method for manufacturing a lithium secondary battery electrode material according to any one of the first to sixth aspects.

  The eighth invention of the present invention is a lithium-niobium solution containing lithium and niobium, wherein a mode diameter (by dynamic light scattering method) of particles A composed of the niobium in the lithium-niobium solution ( Lithium-niobium solution having a most frequent particle size) of 5 to 200 nm.

  A ninth invention of the present invention is the invention described in the eighth invention, wherein the particles A are composed of niobium hydroxide.

  With the lithium-niobium solution according to the present invention, the storage stability can be improved.

  In addition, the technology relating to the lithium secondary battery electrode and the material thereof according to the present invention can suppress the reduction of the discharge capacity and improve the production efficiency.

FIG. 2 schematically shows a cross-sectional view illustrating a method for assembling an all-solid-state lithium ion secondary battery.

Hereinafter, the present embodiment will be described in the following order.
1. 1. Manufacturing method of positive electrode material for lithium secondary battery 1-1. Slurry preparation process 1-2. Adhesion process 1-3. Firing process
1-4. Other 2. 2. Manufacturing method of lithium secondary battery Advantages of the embodiment 4. Modifications etc. In this specification, “to” refers to a value that is greater than or equal to a predetermined value and less than or equal to a predetermined value.

<1. Method for producing lithium secondary battery positive electrode material>
1-1. Slurry preparation step In this step (step 1), the mode diameter (mode particle by the dynamic light scattering method is a fine particle composed of an aqueous solution in which a lithium salt is dissolved and at least one of niobium oxide and niobium hydroxide. Fine particles (particle A. hereinafter referred to as fine particles) having a diameter of 5 to 200 nm and a lithium secondary battery positive electrode active material (hereinafter also simply referred to as positive electrode active material) are mixed to obtain a slurry.

  Hereinafter, these substances to be mixed will be described in detail.

(Aqueous solution in which lithium salt is dissolved)
The lithium salt in the “aqueous solution in which the lithium salt is dissolved” used in this step functions as a lithium source. The lithium source is not particularly limited as long as it is soluble in an aqueous solution and adheres to a particle B (hereinafter referred to as a particle) of a lithium secondary battery positive electrode active material (described later). May be adopted. For example, examples of the lithium source include inorganic lithium salts such as lithium hydroxide (LiOH), lithium nitrate (LiNO ₃ ), lithium sulfate (Li ₂ SO ₄ ), and lithium carbonate (Li ₂ CO ₃ ). Note that the lithium salt is preferably lithium hydroxide in view of the fact that the lithium source preferably has less impurities other than lithium and is water-soluble.

(Niobium fine particles)
The “fine particles composed of at least one of niobium oxide and niobium hydroxide” used in this step have a mode diameter (mode particle diameter) of 5 to 200 nm by a dynamic light scattering method, and are lithium secondary batteries. As long as it adheres to the particles of the positive electrode active material (described later), it may be fine particles composed of niobium oxide, fine particles composed of niobium hydroxide, or fine particles mixed with both. Good. However, in this step, as an example, wet pulverization is performed when a slurry is produced, and niobium hydroxide is preferable in terms of pulverizability at that time.

  The fine particles described above also have a great feature in that the mode diameter (mode diameter) by the dynamic light scattering method is 5 to 200 nm (hereinafter also simply referred to as mode diameter). By the way, in this specification, the size of “particles composed of at least one of niobium oxide and niobium hydroxide” is defined so that the mode diameter is in the nano-order of 5 to 200 nm, so that it is referred to as fine particles. .

  If the mode diameter is 5 nm or more, the time required for the pulverization step can be set to an appropriate length, productivity can be improved, and the accompanying increase in the amount of impurities can be suppressed. . Moreover, if it is 200 nm or less, it becomes possible to cover the surface of the positive electrode active material particles with lithium and niobium (lithium niobate in this embodiment).

Lithium niobate is defined as a composite oxide having an atomic ratio of Li and Nb of 1: 1. A typical composition formula is LiNbO ₃ , and the crystal structure may be amorphous, but may be crystalline. I can take it. The atomic ratio of lithium and niobium in the lithium niobate layer on the particle surface can be obtained by controlling the charged amount of the niobium source and the lithium source in the slurry preparation step so that the atomic ratio of Li and Nb is 1: 1.

  In addition, there is no limitation in particular in the method for producing said fine particle. For example, as shown in the items of Examples described later, wet pulverization may be performed on niobium oxide, otherwise the above-described fine particles may be produced by a neutralization method, or a commercially available niobium colloid liquid From the above, the above fine particles may be produced. Further, when the above-described fine particles are produced, for example, when wet pulverization is employed, wet pulverization may be performed on niobium oxide or niobium hydroxide (so-called niobium source) alone. In the item of Example, wet grinding is performed by this method.

  In the present embodiment, a mixture of the fine particles thus obtained and an aqueous solution in which the lithium salt is dissolved is referred to as a “lithium-niobium solution”. -Also referred to as "niobium solution manufacturing method".

  Note that the mode diameter (mode particle diameter) of the fine particles composed of at least one of niobium oxide and niobium hydroxide by the dynamic light scattering method hardly changes even when an aqueous solution in which a lithium salt is dissolved is mixed. Since lithium is dissolved by ions, it is not detected by the dynamic light scattering method. Fine particles composed of at least one of niobium oxide and niobium hydroxide are detected by the dynamic light scattering method.

  Further, the wet pulverization may be performed in the state where the lithium source described above is added to the niobium source, and the solution after the wet pulverization is also a “lithium-niobium solution” after all. There is no change.

  Incidentally, in this embodiment, the mode diameter referred to here is an aqueous solution after wet pulverization is performed on the niobium source alone, and a commercially available particle size measuring device by a dynamic light scattering method (Otsuka Electronics in the examples described later). It is the mode particle diameter obtained when measured using FPAR-1000 (manufactured by FPAR-1000, measurement ambient temperature 25 ° C.)

(Lithium secondary battery positive electrode active material (positive electrode active material))
The positive electrode active material used in this step is not particularly limited as long as it is a material that can be used as a positive electrode active material of a lithium ion secondary battery. As such a material, in addition to lithium cobaltate (LiCoO ₂ ), positive electrode active materials for secondary batteries include lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₄ ), and transition metals of these active materials. Part substituted with Al, Ti, Cr, Fe, Zr, Y, W, Ta, Nb (LiNi _0.95 Al _0.05 O ₂ etc.), and an active material (LiNi _0.95 ) combined with these active materials _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.5 Mn _{1 .5} O ₄ etc.).

  That is, in this step, a slurry is obtained by mixing the aqueous solution in which the lithium salt is dissolved, the fine particles, and the positive electrode active material. When obtaining a slurry, the same method as in Example 1 described later, that is, a so-called lithium-niobium solution in which an aqueous solution in which a lithium salt is dissolved and the above-described fine particles are heated, is heated with respect to the solution. An active material may be added to obtain a slurry. However, as a specific operation of this slurrying, a known work may be used, or these substances may be simply mixed.

1-2. Attachment process In this process (process 2), there is no limitation in a specific method if said slurry (aqueous solution) can be made to adhere to a positive electrode active material. In the present embodiment, the powder in a state where niobium and lithium are attached to the surface of the positive electrode active material particles is collected by applying the evaporation to dryness method to the slurry. The specific method is as described in the item of the examples described later. For example, a powdered positive electrode active material is added to the solution while the lithium-niobium solution is heated. And by evaporating a water | moisture content, powder is produced and this is collect | recovered. The particles constituting the powder are in a state where niobium and lithium are attached to the surfaces of the particles of the positive electrode active material.

  In addition, instead of applying the evaporation to dryness method to the above slurry, the slurry in which the positive electrode active material is not mixed with the above slurry (Nb—Li raw material liquid as referred to in Example 1 described later) and the positive electrode active The rolling coating method (so-called spray drying method) may be applied in a state where the substance is separated. Thus, niobium and lithium can be attached to the particles of the positive electrode active material powder. Whether or not niobium and lithium are attached to the powder particles of the positive electrode active material can be measured by a general surface analysis method (X-ray photoelectron spectroscopy or Auger electron spectroscopy). It can be measured with a microscope (especially using TEM-EELS, EDX, etc.).

1-3. Firing process
In this step (step 3), the powder recovered as described above is fired at 150 to 700 ° C. to form a lithium niobate layer on the surface of the positive electrode active material particles.

When the firing temperature is 150 ° C. or higher, it becomes possible to improve the crystallinity of lithium niobate in the lithium niobate layer, that is, the lithium niobate layer is suitable as a reaction suppression layer with the solid electrolyte in the secondary battery. Function. Moreover, if it is 700 degrees C or less, it can suppress reacting with a positive electrode active material, and it becomes possible to suppress the fall of discharge capacity.
The firing atmosphere is not particularly limited, but an oxygen atmosphere or an air atmosphere is preferable. This is because atmosphere control is easier than in a non-oxidizing atmosphere such as a nitrogen or hydrogen atmosphere.

Moreover, although it is the film thickness of the lithium niobate layer formed in the surface of the particle | grains of a positive electrode active material in this process, it is preferable to set it as 2-100 nm.
If the thickness of the lithium niobate layer is 2 nm or more, the lithium niobate layer is preferable because it functions as a reaction suppression layer with the solid electrolyte in the secondary battery. On the other hand, when the thickness is 100 nm or less, the resistance can be suppressed to an appropriate value, and the conductivity of lithium ions can be improved.

The control of the film thickness can be appropriately adjusted according to the concentration of the substance constituting the slurry. In the present embodiment, the film thickness can be controlled by adjusting the amounts of the lithium source and niobium source with respect to the amount of the positive electrode active material. A method for calculating the film thickness will be described in detail in Example 1 described later.
Whether or not a lithium niobate layer is formed on the powder particles of the positive electrode active material can be measured by a general surface analysis method (X-ray photoelectron spectroscopy or Auger electron spectroscopy). It can be measured with an electron microscope (especially using TEM-EELS, EDX, etc.).

1-4. Others In this embodiment, a lithium secondary battery positive electrode material can be manufactured through the above-described steps. Of course, known processes other than the processes described above, known additives, and the like may be appropriately employed.

<2. Manufacturing method of lithium secondary battery>
This embodiment also has a great technical feature as a method for manufacturing a lithium secondary battery. For example, after the positive electrode is obtained by the above-described method for producing a positive electrode material for a lithium secondary battery, a negative electrode is prepared (the steps for preparing the positive electrode and the negative electrode are collectively referred to as an electrode preparation step), and An electrolyte in contact with the positive electrode and the negative electrode may be obtained, and lithium secondary electrons may be produced therefrom. In addition, the manufacturing method of a positive electrode is as having shown above, What is necessary is just to employ | adopt a well-known thing as a specific manufacturing method of the other lithium secondary electron.

<3. Advantages of the embodiment>
As a result of intensive studies by the present inventors, it has been clarified that the niobium peroxo complex produces a precipitate in 4 to 5 hours after the preparation of the complex unless any treatment is performed. In the first place, instead of preparing a peroxo complex of niobium, the microparticles related to niobium are prepared so as to have a predetermined mode diameter, and a lithium-niobium solution containing this is used.

  In this way, the problem that occurred in the first place when the niobium peroxo complex was adopted, that is, when the surface of lithium cobaltate, which is the positive electrode active material, was coated with lithium niobate, the amount of coating was reduced. As a result, it is possible to prevent the possibility that the discharge capacity is lowered as a result. Accordingly, after producing a niobium peroxo complex, the necessity of using the complex within a certain period of time does not occur, and a reduction in production efficiency can be suppressed.

At that time, if the mode diameter of the niobium-related fine particles (niobium source) is 5 nm or more, the time required for the pulverization process can be set to an appropriate length, and the productivity can be improved. Thus, the increase in the amount of impurities can be suppressed. If the mode diameter is 200 nm or less, the surfaces of the positive electrode active material particles can be covered with lithium and niobium (LiNbO ₃ in the present embodiment).

  As a result, the storage stability of the lithium-niobium solution according to the present embodiment can be improved.

  Moreover, if it is the technique regarding the lithium secondary battery positive electrode and its material according to this embodiment, the fall of discharge capacity can be suppressed and production efficiency can be improved.

  Further, as a secondary effect, it is not necessary to employ a niobium peroxo complex as in the prior art, so that it is possible to eliminate the influence of hydrogen peroxide added to the peroxo complex solution. For example, hydrogen peroxide self-decomposes in a solution depending on the storage environment, and heat generation and foaming occur in the solution. Then, when industrially producing or storing a niobium peroxo complex solution as in the prior art, problems such as handling and corrosion of equipment may occur. However, according to the present embodiment, it is not necessary to employ a niobium peroxo complex, so that such a problem does not occur in the first place.

<4. Modified example>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  For example, in the present embodiment, the aqueous solution in which the lithium salt is dissolved in Step 1 is the object to be mixed, but a simple lithium salt before dissolution may be the object to be mixed. In that case, the solution is added to the mixing target. Further, a “solution containing a lithium source” may be used as a mixing target regardless of whether or not the lithium salt is dissolved.

  In the present embodiment, fine particles composed of at least one of niobium oxide and niobium hydroxide are employed, but fine particles of one or more other niobium-containing compounds may be employed as the niobium source.

  If the slurry shown in the present embodiment is prepared in advance, the step 2 can be performed as it is.

In step 2, the evaporation to dryness method or the rolling coating method is employed, but other methods may be employed. For example, pan coating or fluid coating may be employed.
The configuration reflecting each of the above modifications is as follows.
“From a mixture of a lithium source, a niobium source particle having a mode diameter (mode particle diameter) of 5 to 200 nm by a dynamic light scattering method, and a lithium secondary battery active material, Recovering the powder in a state where niobium and lithium are attached to the surface of the lithium secondary battery active material particles;
Firing the powder and forming a lithium niobate layer on the surface of the lithium secondary battery active material particles;
A method for producing a lithium secondary battery electrode material (or related technology). ]
In addition, the lithium secondary battery positive electrode material obtained from the lithium-niobium solution described above also has the technical features of the present invention described above. The same applies to the lithium secondary battery, and the configuration will be described as follows.
“A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte that contacts the positive electrode and the negative electrode, wherein the positive electrode is obtained from the lithium secondary battery positive electrode material, a lithium secondary battery. battery. ]

  Hereinafter, examples and comparative examples according to the present invention will be described.

Example 1
[Preparation of raw materials for lithium secondary battery positive electrode active material]
In a reaction vessel using a glass beaker having a capacity of 1 liter, 200 g of pure water and 90 g of ammonium nitrate were placed and stirred at 50 ° C. and 700 rpm to dissolve the ammonium nitrate. On the other hand, as a raw material liquid, a liquid prepared by dissolving 355 g of cobalt nitrate hexahydrate in 126 g of pure water was prepared.

  The raw material liquid was added to the reaction tank at 1.3 g / min. Meanwhile, an aqueous caustic soda solution having a concentration of 48% was added so that the pH in the tank was 11. Stirring was continued at 700 rpm during addition of the raw material liquid, and the temperature in the tank was kept at 50 ° C. When the addition of the raw material liquid was completed, the temperature and stirring were maintained for 30 minutes as they were, followed by cooling to 30 ° C.

The slurry obtained in the reaction vessel was filtered, the filtrate was washed with water and dried at 120 ° C. for 6 hours to obtain cobalt hydroxide powder. After this cobalt hydroxide powder and lithium hydroxide monohydrate were mixed so that the Co: Li molar ratio was 1: 1.03, this mixture was calcined at 900 ° C. for 2 hours in air, and the average A powder of lithium cobaltate (LiCoO ₂ ) having a particle diameter of 5.1 μm and a BET specific surface area of 0.23 m ² / g was obtained.

  The average particle diameter of the positive electrode active material particles was calculated from the average value of the Heywood diameters of 100 particles observed with a field emission scanning electron microscope (SEM) (S-4700 manufactured by Hitachi, Ltd.). The BET specific surface area was determined by the BET single point method after deaeration at 105 ° C. for 20 minutes using a BET specific surface area measuring device (4 Sorb US manufactured by Yuasa Ionics Co., Ltd.). Hereinafter, unless otherwise specified, it is assumed that the average particle diameter and the BET specific surface area are obtained by the same method.

[Preparation of Nb-Li raw material liquid]
Niobate _{(Nb 2 O 5 · 6.1H 2} O (Nb 2 O 5 content of 70.7%)) in a bead mill method using φ0.1mm zirconia beads 0.21 g, _{H 2} O in 5 hours ( 300 min) A niobic acid dispersion liquid was obtained by pulverization. When the particle size of this dispersion was measured by a dynamic light scattering method (FPAR-1000 manufactured by Otsuka Electronics Co., Ltd., measurement atmosphere temperature: 25 ° C.), the mode diameter (mode particle diameter) of the fine particles was 20 nm. To this niobic acid dispersion, 0.047 g of lithium hydroxide monohydrate (LiOH.H ₂ O) was added to obtain a dispersion containing lithium and particulate niobic acid. This was used as the Nb-Li raw material solution (the lithium-niobium solution described above).

[Coating of Nb-Li on active material]
The Nb—Li raw material liquid immediately after production was heated to 90 ° C., 30 g of the lithium cobaltate powder was added thereto, and the mixture was stirred using a stirrer to obtain a slurry (step 1).

  The slurry was continuously heated, and the temperature was maintained at 90 ° C. until it was judged that the moisture was lost by visual observation. Thereafter, the powder was heated in the atmosphere at 140 ° C. for 1 hour and dried (evaporation to dryness method) to obtain a dry powder (step 2).

  The obtained dry powder was fired in air at 400 ° C. for 3 hours to obtain lithium cobaltate powder whose surface was coated with lithium niobate (step 3). This was designated as coated active material a.

In addition, separately from the coated active material a, the Nb—Li raw material liquid that has passed for two weeks has been used, and lithium niobate is coated on lithium cobaltate in the same manner as the coated active material a. A lithium layer was formed. This was designated as coated active material b. The BET specific surface area of the lithium cobaltate powder was a BET specific surface area of 0.23 m ² / g for both of the coated active materials a and b. The BET specific surface area was determined by the BET one-point method after deaeration at 105 ° C. for 20 minutes using a BET specific surface area measuring device (4 Sorb US manufactured by Yuasa Ionics Co., Ltd.).

  The average thickness of the lithium niobate layer calculated from the amount of lithium and niobium used was 5 nm for both the coated active materials a and b. The film thickness was calculated as follows.

Niobic acid (Nb ₂ O ₅ · 6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) is 0.21 g, and two Nb are present in the formula, so Nb is present in 0.0011 mol. Since lithium hydroxide monohydrate (LiOH.H ₂ O) is 0.047 g, there is 0.0011 mol of Li. Lithium niobate (LiNbO ₃ ) produced from these becomes 0.0011 mol, and 0.165 g of lithium niobate is present in the slurry in Step 1. Since the density of lithium niobate is 4.65 g / cm ³ , the volume of the lithium niobate layer is 3.5556 × 10 ⁻⁸ m ³ . On the other hand, since the positive electrode active material in this example is 30 g of lithium cobaltate (LiCoO ₂ ) having a BET specific surface area of 0.23 m ² / g, the total surface area of the positive electrode active material is 6.9 m ² . As a result, the film thickness is calculated by dividing the volume of the lithium niobate layer by the total surface area of the positive electrode active material. The film thickness of the lithium niobate layer thus obtained is referred to as the average film thickness in this example. The average film thickness of the lithium niobate layer in this example was 5 nm.

[Production of all-solid-state lithium ion secondary battery]
[1] Sulfide-based solid electrolyte P ₂ S ₅ (manufactured by Aldrich) 0.927 g and Li ₂ S (manufactured by Aldrich) 0.573 g together with a zirconia ball φ10 mm and a planetary ball mill (manufactured by Fritsch, P-7) The mixture was stirred and mixed at 350 rpm in an argon gas atmosphere for 35 hours to obtain a pale yellow sulfide-based solid electrolyte powder.

[2] Negative electrode A negative electrode was obtained by pressing a lithium foil (φ6 mm, thickness 0.1 mm) against indium foil (φ8 mm, thickness 0.1 mm) and diffusing lithium in indium.

[3] Positive electrode mixture A mixture obtained by mixing 60 mg of the positive electrode active material powder obtained in the above steps 1 to 3, 39 mg of the sulfide-based solid electrolyte, and 1 mg of a conductive agent (Ketchan Black, Lion EJ300J). 7 mg was taken out and pressed with a molding load of 10 kN to obtain a positive electrode mixture composed of a molded body of φ8 mm × thickness 0.1 mm.

[4] Battery assembly
FIG. 1 schematically shows a cross-sectional view illustrating a method for assembling an all solid lithium ion secondary battery. Inside a polyethylene cylinder 1 having an inner diameter of 10 mm and a height of 12 mm, a positive electrode current collector 2 made of stainless steel, the positive electrode mixture 3, and 60 mg of the sulfide solid electrolyte 4 are placed, and a load of 36 kN is applied. Thus, a pressure-molded body was obtained. The negative electrode 5 and the negative electrode current collector 6 made of stainless steel are set on the molded body, and a pressure P of 20 kN is applied thereto to perform pressure molding. A secondary battery was produced. The thicknesses of the positive electrode layer, the electrolyte layer, and the negative electrode layer of the obtained battery are about 100 μm, 500 μm, and 100 μm, respectively. The electrode area on the positive electrode side is 0.5 cm ² (φ8 mm). In FIG. 1, the thickness (length in the vertical direction in the figure) is exaggerated with respect to the cell diameter.
[Battery evaluation]
About the produced battery, the following discharge capacity A and B was investigated and the change rate was calculated | required.

[1] Discharge capacity A
In an all-solid-state battery manufactured using the coated active material a, after charging at a constant current up to 3.8 V at a current density of 0.1 mA / cm ^2, at 3.8 V until the current density reaches 0.001 mA / cm ^2. A constant voltage charge was performed. Thereafter, discharging was performed at 0.1 mA / cm ² from 3.8 V to 2.0 V (from Li to 4.4 V to 2.6 V), and the discharge capacity was measured. The discharge capacity per unit mass of the positive electrode active material was defined as “discharge capacity A”.

[2] Discharge capacity B
The discharge capacity of the all solid state battery produced using the coated active material b was measured under the same conditions as the discharge capacity A. The discharge capacity per unit mass was defined as “discharge capacity B”.

[3] Rate of change
The rate of change (%) was determined by the following equation (1).

Rate of change (%) = (discharge capacity A−discharge capacity B) / discharge capacity A × 100 (1)
It can be said that the smaller the rate of change, the higher the storage stability of the Nb—Li raw material liquid. Table 1 below shows the rate of change and various other conditions and results. In Example 1, the discharge capacity A was 130 mAh, the discharge capacity B was 128 mAh, and the rate of change was 2%, showing good values.

(Examples 2 to 4)
In Examples 2 to 4, as shown in Table 1, in [Preparation of Nb—Li raw material liquid], niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7% )) And the amount of lithium hydroxide monohydrate (LiOH.H ₂ O) were changed from Example 1, and accordingly, the average film thickness of the lithium niobate layer formed after Step 3 Also changed. Other than that was the same as Example 1.

In Example 2, the amount of niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) was 0.42 g, and lithium hydroxide monohydrate (LiOH The amount of H ₂ O) was 0.094 g. The average film thickness of the lithium niobate layer was 10 nm. In Example 2, the discharge capacity A was 132 mAh, the discharge capacity B was 132 mAh, and the rate of change was 0%.

In Example 3, the amount of niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) was 0.84 g, and lithium hydroxide monohydrate (LiOH The amount of H ₂ O) was 0.188 g. The average film thickness of the lithium niobate layer was 20 nm. In Example 3, the discharge capacity A was 131 mAh, the discharge capacity B was 131 mAh, and the rate of change was 0%, showing good values.

In Example 4, the amount of niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) was 2.1 g, and lithium hydroxide monohydrate (LiOH The amount of H ₂ O) was 0.47 g. The average film thickness of the lithium niobate layer was 50 nm. In Example 4, the discharge capacity A was 125 mAh, the discharge capacity B was 123 mAh, and the rate of change was 2%.

(Examples 5-7)
In Examples 5 to 7, unlike Example 1, in [Coating of Nb—Li on active material], lithium cobaltate powder as the positive electrode active material was changed to 500 g, and instead of evaporation to dryness, In order to apply the dynamic coating method, a tumbling fluidized coating apparatus (MP-01, manufactured by POWREC Co., Ltd.) was adopted (described as “spray drying” in Table 1). That is, instead of applying the evaporation and drying method to the slurry prepared in Step 1 of Example 1, the positive electrode active material is not mixed with the above slurry (Nb—Li as in Example 1). In a state where the raw material liquid) and the positive electrode active material (lithium cobaltate powder 500 g) were separated, the rolling coating method was applied to both.

Further, in the same manner as in Examples 2 to 4, the amount of niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content: 70.7%)) in [Preparation of Nb—Li raw material liquid] And the amount of lithium hydroxide monohydrate (LiOH.H ₂ O) was changed from Example 1, and accordingly, the average film thickness of the lithium niobate layer formed after Step 3 was also changed. . Other than that was the same as Example 1.

In Example 5, the amount of niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) was 3.5 g, and lithium hydroxide monohydrate (LiOH The amount of H ₂ O) was 0.78 g. The average thickness of the lithium niobate layer was 5 nm. In Example 5, the discharge capacity A was 130 mAh, the discharge capacity B was 128 mAh, and the rate of change was 2%, showing good values.

In Example 6, the amount of niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) was 0.84 g, and lithium hydroxide monohydrate (LiOH The amount of H ₂ O) was 0.188 g. The average film thickness of the lithium niobate layer was 10 nm. In Example 6, the discharge capacity A was 132 mAh, the discharge capacity B was 132 mAh, and the rate of change was 0%.

In Example 7, the amount of niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) was 2.1 g, and lithium hydroxide monohydrate (LiOH The amount of H ₂ O) was 0.47 g. The average film thickness of the lithium niobate layer was 20 nm. In Example 7, the discharge capacity A was 131 mAh, the discharge capacity B was 130 mAh, and the rate of change was 1%, showing good values.

(Examples 8 to 9)
In Examples 8 to 9, the firing temperature in Step 3 of [Coating of Nb—Li on active material] was varied from Example 1. Other than that was the same as Example 1.

  In Example 8, the firing temperature in Step 3 was 200 ° C. In Example 8, the discharge capacity A was 132 mAh, the discharge capacity B was 132 mAh, and the rate of change was 0%.

  In Example 9, the firing temperature in Step 3 was 500 ° C. In Example 9, the discharge capacity A was 123 mAh, the discharge capacity B was 122 mAh, and the rate of change was 1%, showing good values.

(Examples 10 to 11)
In Examples 10 to 11, unlike Example 1, niobium oxide sol having an average particle diameter of 20 nm measured by a target light scattering method (multiple) as niobium-related fine particles in [Preparation of Nb—Li raw material liquid] The product name Bilal Nb-G6000 manufactured by Ki Chemical Co., Ltd.

  In Example 10, 0.094 g of lithium hydroxide was dissolved in 4.87 g of the niobium oxide sol, thereby preparing a Nb—Li raw material liquid. Other than that was the same as Example 2.

  In Example 10, the discharge capacity A was 132 mAh, the discharge capacity B was 132 mAh, and the rate of change was 0%, showing good values.

  In Example 11, 0.47 g of lithium hydroxide was dissolved in 24.38 g of the niobium oxide sol to prepare an Nb—Li raw material liquid. Other than that was the same as Example 4.

  In Example 11, the discharge capacity A was 124 mAh, the discharge capacity B was 122 mAh, and the rate of change was 2%.

(Examples 12 to 13)
In Examples 12 to 13, the niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) in [Preparation of Nb—Li raw material liquid] in Example 1 The pulverization time was 10 hours (600 min), and the mode diameter of the fine particles was 10 nm.

  Example 12 was the same as Example 2 except that the pulverization time was 10 hours and the mode diameter of the fine particles was 10 nm as described above.

  In Example 12, the discharge capacity A was 130 mAh, the discharge capacity B was 130 mAh, and the rate of change was 0%, showing good values.

  Example 13 was the same as Example 4 except that the pulverization time was 10 hours and the mode diameter of the fine particles was 10 nm as described above.

  In Example 13, the discharge capacity A was 124 mAh, the discharge capacity B was 121 mAh, and the rate of change was 2%, showing good values.

(Examples 14 to 15)
In Examples 14 to 15, in Example 1, the positive electrode active material was lithium cobaltate (LiCoO ₂ ), but the ternary positive electrode material NCM (LiNiCoMnO ₂ ) (MHI BET specific surface area 0.284 m ² / G) was the positive electrode active material.

  Example 14 was the same as Example 2 except that 30 g of NCM was added as the positive electrode active material as described above.

  In Example 14, the discharge capacity A was 145 mAh, the discharge capacity B was 144 mAh, and the rate of change was 1%, showing good values.

  Example 15 was the same as Example 4 except that 30 g of NCM was added as the positive electrode active material as described above.

  In Example 15, the discharge capacity A was 140 mAh, the discharge capacity B was 138 mAh, and the rate of change was 1%, showing good values.

(Examples 16 to 17)
In Examples 16 to 17, the niobic acid (Nb ₂ O ₅ .6.1H ₂ O (Nb ₂ O ₅ content 70.7%)) in [Preparation of Nb—Li raw material liquid] in Example 1 was used. The pulverization time was 0.5 hours (30 min), and the mode diameter of the fine particles was 100 nm.

  Example 16 was the same as Example 2 except that the pulverization time was 0.5 hour and the mode diameter of the fine particles was 100 nm as described above.

  In Example 16, the discharge capacity A was 125 mAh, the discharge capacity B was 123 mAh, and the rate of change was 2%.

  Example 17 was the same as Example 4 except that the pulverization time was 0.5 hour and the mode diameter of the fine particles was 100 nm as described above.

  In Example 17, the discharge capacity A was 118 mAh, the discharge capacity B was 115 mAh, and the rate of change was 3%, showing good values.

(Comparative Examples 1-3)
In Comparative Examples 1 to 3, unlike each example, niobium-based fine particles were not used as the niobium source, but instead a niobium peroxo complex was used.

In Comparative Example 1, as [Preparation of Nb—Li complex solution], an aqueous hydrogen peroxide solution was prepared by adding 11.6 g of hydrogen peroxide solution having a concentration of 30% by mass to 20 g of pure water. To the aqueous hydrogen peroxide solution, niobate _{(Nb 2 O 5 · 6.1H 2} O (Nb 2 O 5 content of 70.7%)) was added 0.42 g. After addition of the niobic acid, 1.92 g of ammonia water having a concentration of 28% by mass was further added and sufficiently stirred to obtain a transparent solution. Into the obtained transparent solution, 0.094 g of lithium hydroxide monohydrate (LiOH.H ₂ O) was added to obtain an aqueous solution containing lithium and a niobic acid complex. It was the same as that of Example 2 except having used the said aqueous solution instead of the Nb-Li raw material liquid in each Example.

  In Comparative Example 1, the discharge capacity A was 132 mAh, the discharge capacity B was 110 mAh, the rate of change was 17%, and the storage stability was not good.

In Comparative Example 2, as [Preparation of Nb—Li Complex Solution], a hydrogen peroxide aqueous solution in which 23.2 g of 30% by mass hydrogen peroxide solution was added to 40 g of pure water was prepared. To the aqueous hydrogen peroxide solution, 0.84 g of niobic acid (Nb ₂ O ₅ · 6.1H ₂ O (Nb ₂ O ₅ content: 70.7%)) was added. After addition of the niobic acid, 3.84 g of ammonia water having a concentration of 28% by mass was further added and sufficiently stirred to obtain a transparent solution. To the obtained transparent solution, 0.188 g of lithium hydroxide monohydrate (LiOH.H ₂ O) was added to obtain an aqueous solution containing lithium and a niobic acid complex. It was the same as that of Example 3 except having used the said aqueous solution instead of the Nb-Li raw material liquid in each Example.

  In Comparative Example 2, the discharge capacity A was 130 mAh, the discharge capacity B was 90 mAh, the rate of change was 31%, and the storage stability was not good.

In Comparative Example 3, as [Preparation of Nb—Li Complex Solution], a hydrogen peroxide aqueous solution was prepared by adding 193.3 g of hydrogen peroxide solution having a concentration of 30% by mass to 333.3 g of pure water. To the aqueous hydrogen peroxide solution, 7.00 g of niobic acid (Nb ₂ O ₅ · 6.1H ₂ O (Nb ₂ O ₅ content: 70.7%)) was added. After the addition of niobic acid, 32.0 g of ammonia water having a concentration of 28% by mass was further added and stirred sufficiently to obtain a transparent solution. Lithium hydroxide monohydrate (LiOH.H ₂ O) 1.56 g was added to the obtained transparent solution to obtain an aqueous solution containing lithium and a niobic acid complex. The aqueous solution was the same as Example 6 (rolling coating) except that the aqueous solution was used in place of the Nb—Li raw material liquid in each Example.

  In Comparative Example 3, the discharge capacity A was 132 mAh, the discharge capacity B was 105 mAh, the rate of change was 20%, and the storage stability was not good.

(Summary)
As a result, it was confirmed that the storage stability could be improved with the Nb—Li raw material solution of each of the above examples, that is, a lithium-niobium solution.

  Moreover, it has confirmed that regarding the lithium secondary battery positive electrode of each said Example and its material, the fall of discharge capacity could be suppressed and production efficiency could be improved.

DESCRIPTION OF SYMBOLS 1 ... Polyethylene cylinder 2 ... Positive electrode collector 3 ... Positive electrode compound material 4 ... Sulfide type solid electrolyte 5 ... Negative electrode 6 ... Negative electrode collector

Claims (9)

  An aqueous solution containing particles A to be a niobium source and having a mode diameter (mode particle diameter) of 5 to 200 nm by a dynamic light scattering method and lithium ions is attached to an active material for a lithium secondary battery, and And a step of forming a lithium niobate layer on the surface of the particle B of the active material for a lithium secondary battery. A particle A composed of an aqueous solution in which a lithium salt is dissolved, at least one of niobium oxide and niobium hydroxide, and having a mode diameter (mode particle diameter) of 5 to 200 nm by a dynamic light scattering method; Step 1 of mixing a lithium secondary battery positive electrode active material to obtain a slurry;
Recovering powder in a state where niobium and lithium are adhered to the surface of the particles B of the lithium secondary battery positive electrode active material by applying an evaporation to dryness method to the slurry; and
And a step 3 of forming the lithium niobate layer on the surface of the particle B of the lithium secondary battery positive electrode active material by firing the powder at 150 to 700 ° C. A particle A composed of an aqueous solution in which a lithium salt is dissolved and at least one of niobium oxide and niobium hydroxide and having a mode diameter (mode particle diameter) of 5 to 200 nm by a dynamic light scattering method; Step 1 to obtain a slurry by mixing
A step 2 of spraying the slurry on the positive electrode active material of the lithium secondary battery to recover the powder in a state where niobium and lithium are adhered to the surface of the particles B of the lithium secondary battery positive electrode active material;
Step 3 of firing the powder at 150 to 700 ° C. to form a lithium niobate layer on the surface of the particle B of the lithium secondary battery positive electrode active material;
A method for producing a lithium secondary battery electrode material.   The method for producing a lithium secondary battery electrode material according to claim 2 or 3, wherein the lithium salt is lithium hydroxide.   The method for producing a lithium secondary battery electrode material according to any one of claims 1 to 4, wherein the particles A are composed of niobium hydroxide.   6. The method for producing a lithium secondary battery electrode material according to claim 1, wherein in step 3, the thickness of the lithium niobate layer is 2 to 100 nm. A method for producing a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte that contacts the positive electrode and the negative electrode,
An electrode manufacturing step of manufacturing the positive electrode and the negative electrode;
Have
The said positive electrode is a manufacturing method of a lithium secondary battery obtained by the manufacturing method of the lithium secondary battery electrode material in any one of Claims 1 thru | or 6. A lithium-niobium solution containing lithium and niobium,
A lithium-niobium solution having a mode diameter (mode particle diameter) of 5 to 200 nm according to a dynamic light scattering method of particles A composed of the niobium in the lithium-niobium solution.   The lithium-niobium solution according to claim 8, wherein the particles A are composed of niobium hydroxide.

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