Method for manufacturing layered composite metal oxide crystalline materials
A method for producing layered composite metal oxide crystals at lower temperatures and normal pressure addresses the scalability issues of existing high-temperature and high-pressure synthesis methods, enabling cost-effective production for lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- HOKKAIDO UNIVERSITY
- Filing Date
- 2022-03-17
- Publication Date
- 2026-05-15
AI Technical Summary
Current methods for producing layered composite metal oxide crystals for lithium-ion secondary batteries require high-temperature calcination or high-pressure hydrothermal synthesis, making them unsuitable for large-scale, cost-effective production.
A method involving the calcination of a mixture containing monovalent anion salts of lithium, sodium, and transition metals at temperatures between 150°C and 400°C in the presence of water molecules and oxygen, allowing for the production of layered composite metal oxide crystals under normal pressure.
Enables the low-cost, large-scale synthesis of layered composite metal oxide crystals suitable for lithium-ion secondary batteries, with improved energy efficiency and reduced environmental impact.
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Abstract
Description
[Technical Field]
[0001] This invention relates to a method for producing layered composite metal oxide crystalline materials, which can be used as positive electrode materials for lithium-ion secondary batteries, under milder conditions. [Background technology]
[0002] To realize a sustainable, low-carbon society, the spread of renewable energy sources such as solar and wind power is being promoted. However, since the amount of electricity generated by these renewable energy sources is dependent on the weather, it is necessary to also introduce stationary energy storage systems to ensure a stable energy supply. In the automotive sector, too, there is a surge in the development of electric vehicles and plug-in hybrid vehicles equipped with storage batteries in order to reduce carbon dioxide emissions.
[0003] Lithium-ion secondary batteries are the primary type of rechargeable battery currently under development. Lithium-ion secondary batteries use materials with a host structure that allows for the insertion or removal of lithium ions as active materials for the positive and negative electrodes, and charge and discharge are performed by the exchange of lithium ions between these electrodes. As the positive electrode material for lithium-ion secondary batteries, layered crystals of lithium cobalt oxide (LiCoO2) are mainly used because they are relatively easy to synthesize and handle, and exhibit good battery characteristics such as a high operating voltage and excellent cycle life. Layered crystals of lithium cobalt oxide have a crystalline structure in which CoO2 layers and lithium ions are alternately stacked, and lithium ions are removed from or transferred between these CoO2 layers.
[0004] Layered lithium cobalt oxide crystals are generally produced by solid-phase methods that involve high-temperature calcination processes of 700-900°C, and it is known that low-activity spinel crystals are produced at relatively low-temperature calcination of 300-600°C (Non-Patent Literature 1). However, large-scale synthesis involving high-temperature calcination processes requires a great deal of energy, so a more energy-saving method for producing lithium cobalt oxide crystals has been proposed using the flux method (Non-Patent Literature 2). However, even this method requires calcination at 500°C.
[0005] On the other hand, Patent Document 1 discloses a method for producing a single-layered alkali metal oxide material at a relatively low temperature of about 50 to 150°C by hydrothermal synthesis using oxyhydroxides of transition metals as raw materials. However, this method requires the reaction to be carried out under high pressure for a long period of time, for example, about 5 days at about 6.5 atmospheres or 2 days at about 30 to 35 atmospheres, and also requires a sealed container that can withstand high pressure, making it unsuitable for large-scale synthesis. [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Special Publication No. 10-510239 [Non-patent literature]
[0007] [Non-Patent Document 1] ARIYOSHI Kingo et al., J. Phys. Chem. C, 2020, 124, 8170-8177 [Non-Patent Document 2] T.YODA et al.,RSC Adv.,2015,5,96002-96007 [Overview of the project] [Problems that the invention aims to solve]
[0008] As described above, the layered composite metal oxide crystal material useful as a cathode material for a lithium ion secondary battery is produced through a firing process at high temperature or a hydrothermal synthesis at high pressure for a long time. However, for mass synthesis, it is necessary to develop a synthesis process at a lower cost under lower temperature and normal pressure. Therefore, an object of the present invention is to provide a method for producing a layered composite metal oxide crystal material that can be used as a cathode material for a lithium ion secondary battery under milder conditions, and a method for producing a cathode and a lithium ion secondary battery using the method.
Means for Solving the Problems
[0009] The present inventors have conducted intensive studies to solve the above problems. As a result, they have found that a layered composite metal oxide crystal material containing lithium and a transition metal can be produced under relatively low temperature and normal pressure by using a specific raw material compound, and thus completed the present invention. Hereinafter, the present invention will be described.
[0010] [1] A method for producing a layered composite metal oxide crystal material, where the layered composite metal oxide crystal material is composed of a composite metal oxide represented by the following formula, Li x MO y [wherein, M represents one or more transition metals, and a part of M may be substituted with Al and / or Mg, x represents a number of 1 or more and 2 or less, y represents a number of 2 or more and 3 or less, the value of x + n (n represents the average valence of the transition metal M) is 2 × y.] A method comprising a step of firing a mixture containing a monovalent anion salt of lithium, a monovalent anion salt of sodium and / or potassium, and a monovalent anion salt of a transition metal at 150°C or higher and 400°C or lower in the presence of water molecules and oxygen. [2] The method according to [1], wherein one or more salts selected from the group consisting of the monovalent anionic salt of lithium, the monovalent anionic salt of sodium and / or potassium, and the monovalent anionic salt of the transition metal are hydrates. [3] The method according to [1], wherein the mixture includes water. [4] The method according to any one of [1] to [3], wherein the molar ratio of the monovalent anionic salt of sodium and / or potassium to the monovalent anionic salt of lithium is 0.1 or more and 5 or less. [5] The method according to any one of the above [1] to [4], wherein firing is performed at atmospheric pressure. [6] The method according to any one of claims [1] to [5], wherein the mixture further comprises a monovalent anionic salt of aluminum and / or magnesium, in which case a portion of M is substituted with Al and / or Mg. [7] A method for manufacturing a positive electrode, A step of producing a layered composite metal oxide crystal material by any of the methods described in [1] to [6] above, A step of preparing a positive electrode slurry by mixing the layered composite metal oxide crystal material with at least a solvent and a binder. The process of coating the positive electrode slurry onto the positive electrode current collector, and A method characterized by including a step of drying the positive electrode slurry coated onto the positive electrode current collector. [8] A method for manufacturing a lithium-ion secondary battery, A step of manufacturing a positive electrode on a positive electrode current collector by the method described in [7] above, A process for manufacturing a negative electrode on a negative electrode current collector, A process of obtaining a winding body by winding the positive electrode current collector having a positive electrode and the negative electrode current collector having a negative electrode via a separator, and A method characterized by including the steps of placing the wound body inside a battery container and injecting an electrolyte solution into the battery container. [Effects of the Invention]
[0011] According to the method of the present invention, it is possible to easily manufacture layered composite metal oxide crystalline materials containing lithium and transition metals at relatively low temperatures without requiring high pressure, simply by using specific raw material compounds. Therefore, the present invention is extremely useful industrially as it enables the low-cost, large-scale synthesis of layered composite metal oxide crystalline materials useful as cathode materials for lithium-ion secondary batteries and the like. [Brief explanation of the drawing]
[0012] [Figure 1] Figure 1 shows the results of analyzing LiCoO2 powders of the present invention examples and comparative examples using X-ray diffraction. [Figure 2] Figure 2 shows the results of charge-discharge tests of half-cells having electrodes made from LiCoO2 powder in the examples and comparative examples of the present invention. [Figure 3] Figure 3 shows the results of analyzing the LiNi1 / 3Mn1 / 3Co1 / 3O2 powder of the present invention example by X-ray diffraction. [Figure 4] Figure 4 shows the results of analyzing the LiCoO2 powder of the present invention example by X-ray diffraction. [Figure 5] Figure 5 shows the results of a charge-discharge test of a half-cell having electrodes made from LiCoO2 powder according to an example of the present invention. [Figure 6] Figure 6 shows the results of analyzing the LiCoO2 powder of the present invention example by X-ray diffraction. [Modes for carrying out the invention]
[0013] The method for producing a layered composite metal oxide crystal material according to the present invention includes the step of calcining a mixture containing a monovalent anionic salt of lithium, a monovalent anionic salt of sodium and / or potassium, and a monovalent anionic salt of a transition metal at a temperature of 150°C or higher and 400°C or lower in the presence of water molecules and oxygen.
[0014] The layered composite metal oxide crystalline material according to the present invention is a composite oxide of lithium and a transition metal, and the monovalent anionic salt of lithium is an important raw material containing lithium that constitutes the target compound.
[0015] The counter anions constituting monovalent anionic salts of lithium, sodium and / or potassium, and transition metals are not particularly limited as long as they are monovalent anions and can form salts with lithium ions, sodium ions and / or potassium ions, and transition metal ions, for example, hydroxide ions (OH) - ), nitrate ion (NO3 - ), halide ions, cyanide ions (CN - ), acetate ion (CH3CO2 - ), bicarbonate ions (HCO3) - Examples of halide ions include fluoride ions, chloride ions, bromide ions, and iodide ions, with chloride ions, bromide ions, and iodide ions being preferred. Preferred anions include hydroxide ions, nitrate ions, and halide ions, with hydroxide ions and nitrate ions being more preferred, and hydroxide ions being even more preferred. Furthermore, when using monovalent anionic salts of aluminum and / or magnesium, the anions of the salts may be the same as those listed above.
[0016] Monovalent anionic salts of sodium and / or potassium have the effect of lowering the overall melting point when mixed with monovalent anionic salts of lithium, and may promote the reaction of monovalent anionic salts of lithium and / or transition metals at relatively low temperatures by forming a molten salt with the monovalent anionic salt of lithium. For example, according to the lithium hydroxide-sodium hydroxide phase diagram, the lowest eutectic point is observed when lithium hydroxide:sodium hydroxide = 3:7 (molar ratio), which is 493K (220℃) (A. Kacprzak et al., Journal of Power Sources, 239 (2013), 409-414). However, according to the inventors' experimental findings, it was a surprising result that layered composite metal oxide crystalline material could be successfully produced by firing at a low temperature of 300℃ even at compositions far outside the eutectic point, such as lithium hydroxide:sodium hydroxide = 3:1 (molar ratio) (Example 1).
[0017] The amount of sodium and / or potassium monovalent anionic salt used can be adjusted as appropriate within the range in which the reaction according to the present invention proceeds. For example, it can be used in an amount of 0.1 to 5 moles per mole of lithium monovalent anionic salt. If the ratio is 0.1 moles or more, the reaction-promoting effect of sodium and / or potassium monovalent anionic salt can be more reliably exerted. On the other hand, if the ratio is 5 moles or less, it becomes possible to suppress the residue of sodium and / or potassium monovalent anionic salt in the layered composite metal oxide crystal material, which is the target compound. Preferably, the above ratio is 0.2 moles or more, more preferably 0.25 moles or more, even more preferably 0.3 moles or more, and also preferably 2.5 moles or less, more preferably 1 mole or less, and even more preferably 0.5 moles or less. Note that sodium monovalent anionic salt or potassium monovalent anionic salt may be used alone, or both may be used in combination.
[0018] The layered composite metal oxide crystalline material according to the present invention is a composite oxide of lithium and a transition metal, and the monovalent anionic salt of the transition metal is an important raw material containing the transition metal that constitutes the target compound.
[0019] The transition metal is not particularly limited, but for example, one or more first transition metals selected from scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc can be used, with one or more first transition metals selected from manganese, cobalt, and nickel being preferred, and at least cobalt and / or nickel being preferred. In addition, monovalent anionic salts of magnesium and / or aluminum may be used in combination.
[0020] Only one type of transition metal may be used, or two or more types of transition metals may be used in combination. When two or more types of transition metals are used in combination, there is no particular upper limit on the number of transition metals, but for example, it can be set to 5 or less. Preferably, the number is 4 or less, and more preferably 1, 2, or 3. In addition, in the layered composite metal oxide crystalline material according to the present invention, a portion of the transition metal may be substituted with Al and / or Mg, and may be particularly substituted with Al. When a portion of the transition metal is substituted with Al and / or Mg, the ratio of Al and Mg to the total of 100 mol% of the transition metal, Al, and Mg can be 1 mol% or more and 10 mol% or less. Preferably, the ratio is 2 mol% or more, more preferably 3 mol% or more, preferably 8 mol% or less, and more preferably 6 mol% or less. The ratio can be adjusted to, for example, 3.5 ± 0.5 mol% or 5.0 ± 0.5 mol%.
[0021] The amount of monovalent anionic salt of the transition metal used can be adjusted as appropriate within the range in which the reaction according to the present invention proceeds. For example, it can be used in amounts of 0.1 moles or more and 1 mole or less per mole of lithium monovalent anionic salt. If the ratio is 0.1 moles or more, a sufficient amount of layered composite metal oxide crystalline material can be obtained more reliably without any problems. On the other hand, if the ratio is 1 mole or less, the layered composite metal oxide crystalline material can be theoretically synthesized. The above ratio is preferably 0.2 moles or more, more preferably 0.5 moles or more, preferably 0.9 moles or less, more preferably 0.8 moles or less, and even more preferably 0.7 moles or less. Note that only one type of monovalent anionic salt of the transition metal may be used alone, or two or more types may be used in combination. When producing a layered composite metal oxide crystalline material in which a portion of the transition metal is substituted with Al and / or Mg, the amount of monovalent anionic salt of Al and / or Mg used should be determined according to the ratio of Al and Mg to the total of 100 mol% of the desired transition metal and Al and Mg.
[0022] In the present invention, a mixture containing a monovalent anionic salt of lithium, a monovalent anionic salt of sodium and / or potassium, and a monovalent anionic salt of a transition metal is calcined in the presence of water molecules. Although the role of water molecules in the reaction according to the present invention is not entirely clear, it is thought that the monovalent anionic salts of sodium and / or potassium act as proton-releasing Brønsted acids in the molten salt formed by calcination, promoting the dissolution and recrystallization of the transition metal in the molten salt, thereby playing an important role in the progress of the reaction at relatively low temperatures and the growth of the product crystals.
[0023] The phrase "in the presence of water molecules" is not particularly limited as long as water molecules are present in the reaction system according to the present invention. For example, one or more starting material compounds selected from monovalent anionic salts of lithium, sodium and / or potassium, and monovalent anionic salts of transition metals may be used as hydrates. Stable compounds such as monohydrates or dihydrates may be used as hydrates. For example, it is preferable to use a hydrate of a monovalent anionic salt of lithium. When a monovalent anionic salt of lithium is used, the dehydration reaction proceeds by calcination, leaving a monovalent anion, and it is thought that a product of higher purity can be obtained.
[0024] Alternatively, a mixture containing a monovalent anionic salt of lithium, a monovalent anionic salt of sodium and / or potassium, and a monovalent anionic salt of a transition metal may be mixed with water to form a slurry. In this case, for example, the amount of water used can be between 1 mole and 5 moles relative to the total number of moles of the monovalent anionic salt of lithium, a monovalent anionic salt of sodium and / or potassium, and a monovalent anionic salt of the transition metal. The ratio is preferably 4 moles or less, and more preferably 2 moles or less. Alternatively, a hydrate may be used as one or more raw material compounds selected from the monovalent anionic salt of lithium, a monovalent anionic salt of sodium and / or potassium, and a monovalent anionic salt of a transition metal, and the mixture may be made into a slurry by adding water. In this case, it is preferable to adjust the total number of moles of water molecules in the hydrate and the separately added water molecules to within the above range.
[0025] The slurry may be molded into a desired shape. Furthermore, even when using hydrates as raw material compounds without adding water, the mixture may be pressure-molded into a desired shape to increase the contact area between the raw material compounds and ensure a smooth solid-phase reaction. In the case of a slurry, the contact area between the raw material compounds is high even without molding, and the solid-phase reaction is expected to proceed smoothly.
[0026] In this invention, the above mixture is calcined in the presence of oxygen. For example, the mixture may be calcined in the atmosphere, or if oxygen is insufficient during calcination in the atmosphere, oxygen may be supplied to the mixture. However, the oxygen partial pressure during the calcination process in this invention does not need to be high; the mixture may be calcined at an oxygen partial pressure of approximately atmospheric pressure.
[0027] The present invention enables the successful production of layered composite metal oxide crystalline materials by firing at relatively low temperatures, specifically between 150°C and 400°C. From the viewpoint of manufacturing cost, a firing temperature of 350°C or lower is preferred, 300°C or lower is more preferred, and 280°C or 250°C or lower is even more preferred. From the viewpoint of molten salt formation, a lower limit of firing temperature of 180°C or higher or 200°C or higher is preferred, and 220°C or higher is more preferred. Furthermore, by using a monovalent anionic salt of sodium and a monovalent anionic salt of potassium in combination, it is possible to further reduce the firing temperature.
[0028] The firing time can be adjusted as appropriate within a range in which firing proceeds sufficiently and the target compound, a layered composite metal oxide crystalline material, is obtained in good condition. For example, it can be between 10 minutes and 50 hours. Preferably, the firing time is 20 minutes or more, more preferably 25 minutes or more, preferably 40 hours or less, more preferably 30 hours or less, and even more preferably 20 hours or less or 15 hours or less.
[0029] After calcination, it is preferable to perform the usual post-processing. For example, it is preferable to remove residual raw material compounds, such as monovalent anionic salts of lithium and monovalent anionic salts of sodium and / or potassium, by grinding the calcined mixture and then washing it with a highly polar solvent. Examples of solvents used for washing include water; alcohol-based solvents such as methanol, ethanol, and 2-propanol; nitrile-based solvents such as acetonitrile, propionitrile, and valeronitrile; ether-based solvents such as diethyl ether and tetrahydrofuran; and mixtures thereof. After washing, the product and solvent can be separated by filtration or centrifugation. Any remaining solvent may be removed by heating or reduced pressure.
[0030] The layered composite metal oxide crystal material produced by the method of the present invention is composed of a composite metal oxide represented by the following formula. Li x MO y [In the formula, M represents one or two or more transition metals, a part of M may be substituted with Al and / or Mg, x represents a number of 1 or more and 2 or less, y represents a number of 2 or more and 3 or less, and the value of x + n (n represents the average valence of the transition metal M) is 2 × y, that is, x + n = 2 × y.]
[0031] As described above, when M is two or more transition metals, the upper limit of the number of transition metals is not particularly limited, but for example, it can be 5 or less. As the number, 4 or less is preferable, and 1 or 2 or 3 is more preferable. As the number of transition metals, 1 or 2 is preferable. Also, a part of M may be substituted with Al and / or Mg, and particularly may be substituted with Al. When a part of M is substituted with Al and / or Mg, the ratio of Al and Mg to the total 100 mol% of the transition metal, Al, and Mg can be 1 mol% or more and 10 mol% or less. As the ratio, 2 mol% or more is preferable, 3 mol% or more is more preferable, 8 mol% or less is preferable, and 6 mol% or less is more preferable. The ratio can be adjusted to, for example, 3.5 ± 0.5 mol% or 5.0 ± 0.5 mol%.
[0032] As the reaction mechanism according to the present invention, although it is not necessarily clear, first, it is considered that after M(OH)2 or M(OH)3 is generated, lithium ions are substituted. Therefore, it is preferable to use a monovalent anion salt of lithium in an amount of 1-fold mol or more with respect to 1 mol of the monovalent anion salt of the transition metal. As the ratio, 1.2-fold mol or more is preferable, and 1.4-fold mol or more is more preferable. Also, as the layered composite metal oxide crystal material produced by the method of the present invention, a so-called lithium-excess system material in which LiMO2 is solid-dissolved in Li2MO3 is also conceivable.
[0033] Examples of chemical formulas for the layered composite metal oxide crystal material according to the present invention include LiCoO2, LiNiO2, LiMnO2, and Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, LiNi p Mn q Co r O2[p+q+r=1, for example, p=q=r=1 / 3; p=0.8, q=0.1, r=0.1; p=0.6, q=0.2, r=0.2; p=0.5, q=0.2, r=0.3], LiNi p Co q Al r One example is O2[p+q+r=1, for instance, p=0.815, q=0.15, r=0.035].
[0034] For example, in a lithium-ion secondary battery, during charging, lithium ions are detached from the layered composite metal oxide crystal material of the positive electrode, generating C6Li at the carbon negative electrode, and during discharge, lithium ions generated from the negative electrode are inserted into the positive electrode.
[0035] The layered composite metal oxide crystalline material produced by the present invention can be used, for example, as a positive electrode active material for the positive electrode of a lithium-ion secondary battery. Therefore, a positive electrode can be manufactured by mixing the layered composite metal oxide crystalline material with at least a solvent and a binder to form a positive electrode slurry, coating the positive electrode slurry onto a positive electrode current collector, and then drying it.
[0036] Examples of binders used in the positive electrode slurry include polyvinylidene fluoride and its copolymers, carboxymethylcellulose, styrene-butadiene rubber, polyimide, polytetrafluoroethylene, and mixtures thereof. Examples of solvents used in the positive electrode slurry include water; nitrogen-containing organic solvents such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; and mixtures thereof.
[0037] The cathode slurry may contain not only a layered composite metal oxide crystal material and a binder, but also general additive components. Examples of additive components in the cathode slurry include conductive materials. Examples of conductive materials include acetylene black, Ketjenblack, graphite, carbon materials such as carbon nanofibers.
[0038] Common examples of positive electrode current collectors to which the positive electrode slurry is coated include aluminum foil, etched aluminum foil, and aluminum foil coated with conductive paste.
[0039] A lithium-ion secondary battery can be manufactured using the positive electrode described above. Specifically, a negative electrode can be manufactured on a negative electrode current collector, a winding can be obtained by winding a positive electrode current collector having a positive electrode and a negative electrode current collector having a negative electrode via a separator, the winding can be placed in a battery container, and an electrolyte solution can be injected into the battery container to manufacture a lithium-ion secondary battery.
[0040] The negative electrode can be manufactured by preparing the negative electrode slurry in the same manner as the positive electrode slurry, except that the negative electrode active material is used instead of the layered composite metal oxide crystal material used as the positive electrode active material. The negative electrode slurry is then coated onto a negative electrode current collector and dried. Examples of negative electrode active materials include carbon materials such as graphite, as well as materials containing Si and / or Sn and exhibiting basic properties, such as Si, SiCuAl, SiNiAg, and CoSn2. Copper foil can be used as the negative electrode current collector.
[0041] A microporous membrane made of polyolefin is generally used as a separator in lithium-ion secondary batteries. The winding is manufactured by using a winding machine to wind the positive and negative electrodes, which have been cut to a size that fits inside the battery container, while stacking them with the separator in between. Next, the winding is placed inside the battery container, each electrode is welded to the cap of the battery container, and if a separator is used, the electrolyte is injected into the battery container and the cap is welded to obtain a lithium-ion secondary battery. Alternatively, the electrolyte can be injected through an inlet provided in the cap after it has been welded.
[0042] This application claims the benefit of priority based on Japanese Patent Application No. 2021-45633, filed on 19 March 2021. The entire specification of Japanese Patent Application No. 2021-45633, filed on 19 March 2021, is incorporated herein by reference. [Examples]
[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.
[0044] Example 1 Lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and cobalt hydroxide (manufactured by Kojun Chemical Laboratory Co., Ltd.) were mixed in a mortar in a molar ratio of LiOH·H2O:NaOH:Co(OH)2 = 1.5:0.5:1.0. This raw material was then pelletized into 5mm x 30mm x 5mm rectangular parallelepipeds using a cemented carbide die (manufactured by Sansho Industry Co., Ltd.) at a pressure of 10MPa. Although a pressure of 10MPa was applied for pelletizing, pelletizing was not essential, and the pressure was only applied for a short time, so productivity was not reduced by the pressure load. The obtained pellets were calcined in a tubular furnace ("ARF-40KC," manufactured by Asahi Rika Seisakusho Co., Ltd.) at 300°C for 12 hours under an oxygen flow of 100 mL / min. After calcination, the pellets were crushed, washed with dehydrated ethanol to remove LiOH and NaOH, and then dried at 25°C for 15 minutes to obtain LiCoO2 powder.
[0045] Example 2 LiCoO2 powder was obtained in the same manner as in Example 1, except that the molar ratio of the raw materials was changed to LiOH·H2O:NaOH:Co(OH)2 = 1.5:1.5:1.0.
[0046] Example 3 LiCoO2 powder was obtained in the same manner as in Example 1, except that the molar ratio of the raw materials was changed to LiOH·H2O:NaOH:Co(OH)2 = 1.5:3.5:1.0.
[0047] Comparative Example 1 LiCoO2 powder was obtained in the same manner as in Example 1, except that sodium hydroxide was not used.
[0048] Comparative Example 2 LiCoO2 powder was obtained in the same manner as in Example 3, except that anhydrous lithium hydroxide was used instead of lithium hydroxide monohydrate as a raw material.
[0049] Test Example 1: X-ray Diffraction The LiCoO2 powders prepared in Examples 1-3 and Comparative Examples 1 and 2 were analyzed by X-ray diffraction. The results are shown in Figure 1. As shown in Figure 1, the crystallinity was remarkably low when sodium hydroxide was not used (Comparative Example 1), and it is presumed that Co3O4 and spinel-type Li2Co2O4 were formed as by-products in addition to layered LiCoO2. Furthermore, when calcined in the absence of water molecules (Comparative Example 2), the crystallinity was also low, similar to Comparative Example 1, and the growth of layered LiCoO2 crystals did not proceed sufficiently. In contrast, clear crystallinity was confirmed in the LiCoO2 powders of Examples 1-3. However, when the Li / Na ratio in the raw materials used was 1.5 / 3.5 (Example 3), rock salt-type CoO was confirmed as a by-product.
[0050] Test Example 2: Charge / Discharge Test A coated electrode was prepared by mixing synthesized LiCoO2 powder, acetylene black (manufactured by Denka Co., Ltd.) as a conductive material, and polyvinylidene fluoride (manufactured by Kureha Corporation) as a binder in a mass ratio of 85:10:5. A half-cell was then constructed using lithium metal as the counter electrode, and a charge-discharge test was performed. The results for the LiCoO2 powder of Example 1 are shown in Figure 2(2), and the results for the LiCoO2 powder of Comparative Example 1 are shown in Figure 2(1). As shown in Figure 2, the electrode made from LiCoO2 powder in Comparative Example 1 showed a significant degradation in charge / discharge capacity after repeated charge and discharge cycles. Although not evident from X-ray diffraction analysis, it is possible that phases other than layered crystals were formed. In contrast, the electrode made from LiCoO2 powder in Example 1 produced approximately 120 mAhg -1 The required charge / discharge capacity was achieved, and almost no capacity degradation was observed even after repeating the charge / discharge cycle five times.
[0051] Example 4 Ni instead of Co(OH)2 as the transition metal hydroxide 1 / 3 Mn 1 / 3 Co 1 / 3 Except for using (OH)2, the same procedure as in Example 1 was followed, and LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 powder was obtained.
[0052] Example 5 Anhydrous lithium hydroxide, sodium hydroxide, cobalt hydroxide, and water were mixed in a molar ratio of LiOH·H2O:NaOH:Co(OH)2:H2O = 1.5:0.5:1.0:4.5 to obtain a slurry. LiCoO2 powder was obtained in the same manner as in Example 1, except that the obtained slurry was used.
[0053] Example 6 LiCoO2 powder was obtained in the same manner as in Example 5, except that lithium hydroxide monohydrate was used instead of lithium hydroxide anhydrous, and the molar ratio of the raw materials was changed to LiOH·H2O:NaOH:Co(OH)2:H2O = 1.5:0.5:1.0:3.0.
[0054] Test Example 3: X-ray Diffraction LiNi produced in Example 4 1 / 3 Mn 1 / 3 Co 1 / 3 O2 powder was analyzed by X-ray diffraction. The results showed LiNi 0.33 Mn 0.33 Co 0.34Figure 3 shows the X-ray diffraction pattern data for O2 and Mn2CoO4 (Powder Diffraction File (PDF) 04-014-8375 and 04-022-4484). The LiCoO2 powders produced in Examples 5 and 6 were analyzed by X-ray diffraction. The results, along with the X-ray diffraction pattern data of LiCoO2 (PDF 04-008-6329), are shown in Figure 4. As shown in Figures 3 and 4, the LiNi of Example 4 1 / 3 Mn 1 / 3 Co 1 / 3 Clear crystallinity was observed in the O2 powder and the LiCoO2 powders of Examples 5 and 6.
[0055] Test Example 4: Charge / Discharge Test Electrodes were prepared from the LiCoO2 powders manufactured in Examples 5 and 6 in the same manner as in Test Example 2, and subjected to charge-discharge tests. The results for the LiCoO2 powder of Example 5 are shown in Figure 5(1), and the results for the LiCoO2 powder of Example 6 are shown in Figure 5(2). As shown in Figure 5, electrodes made from LiCoO2 powder produced from a raw material slurry containing water produced 110-120 mAhg -1 The required charge / discharge capacity was achieved, and almost no capacity degradation was observed even after repeating the charge / discharge cycle five times.
[0056] Example 7 A raw material was obtained by mixing lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), potassium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and cobalt hydroxide (manufactured by Kojun Chemical Laboratories Co., Ltd.) in a mortar and pestle in a molar ratio of LiOH·H2O:NaOH:KOH:Co(OH)2 = 1.5:0.25:0.25:1.0. Using this raw material, LiCoO2 powder was obtained in the same manner as in Example 1, except that the calcination temperature was changed from 300°C to 250°C.
[0057] Example 8 A raw material was obtained by mixing lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), potassium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and cobalt hydroxide (manufactured by Kojun Chemical Laboratories Co., Ltd.) in a mortar and pestle in a molar ratio of LiOH·H2O:NaOH:KOH:Co(OH)2 = 1.5:0.25:0.25:1.0. Using this raw material, LiCoO2 powder was obtained in the same manner as in Example 1, except that the calcination temperature was changed from 300°C to 200°C.
[0058] Example 9 A raw material was obtained by mixing lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), potassium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and cobalt hydroxide (manufactured by Kojun Chemical Laboratories Co., Ltd.) in a mortar and pestle in a molar ratio of LiOH·H2O:NaOH:KOH:Co(OH)2 = 1.5:0.45:0.05:1.0. Using this raw material, LiCoO2 powder was obtained in the same manner as in Example 1, except that the calcination temperature was changed from 300°C to 200°C.
[0059] Test Example 5: X-ray Diffraction The LiCoO2 powders prepared in Examples 7-9 were analyzed by X-ray diffraction. The results are shown in Figure 6. As shown in Figure 6, it was revealed that by using potassium hydroxide in addition to lithium hydroxide monohydrate and sodium hydroxide, crystalline LiCoO2 powder can be produced even at lower calcination temperatures.
Claims
1. A method for producing a layered composite metal oxide crystalline material, The aforementioned layered composite metal oxide crystalline material is composed of a composite metal oxide represented by the following formula, Li x MO y [In the formula, M represents one or more transition metals, and some of M may be substituted with Al and / or Mg. x represents a number between 1 and 2, y represents a number between 2 and 3, The value of x + n (where n represents the average valence of the transition metal M) is 2 × y. In the presence of water molecules and oxygen, a mixture containing a monovalent anionic salt of lithium, a monovalent anionic salt of sodium and / or potassium, and a monovalent anionic salt of a transition metal is heated to a temperature of 150°C or higher. This process includes firing at temperatures below 400°C. A method characterized by using 0.2 molars or more of the monovalent anionic sodium and / or potassium salts relative to the monovalent lithium anionic salt.
2. The method according to claim 1, wherein a hydrate is used as one or more salts selected from the group consisting of lithium hydroxide, sodium hydroxide and / or potassium hydroxide, and monovalent anionic salts of transition metals.
3. The method according to claim 1, wherein the aforementioned mixture includes water.
4. The method according to any one of claims 1 to 3, wherein the molar ratio of the monovalent anionic salt of sodium and / or potassium to the monovalent anionic salt of lithium is 5 molars or less.
5. The method according to any one of claims 1 to 4, wherein firing is performed at atmospheric pressure.
6. The method according to any one of claims 1 to 5, wherein a portion of M is substituted with Al and / or Mg, and the mixture further comprises a monovalent anionic salt of aluminum and / or magnesium.
7. A method for manufacturing a positive electrode, A step of producing a layered composite metal oxide crystal material by the method of any one of claims 1 to 6, A step of preparing a positive electrode slurry by mixing the layered composite metal oxide crystal material with at least a solvent and a binder. The process of coating the positive electrode slurry onto the positive electrode current collector, and A method characterized by including a step of drying the positive electrode slurry coated onto the positive electrode current collector.
8. A method for manufacturing lithium-ion secondary batteries, A step of manufacturing a positive electrode on a positive electrode current collector by the method of claim 7, A process for manufacturing a negative electrode on a negative electrode current collector, A process of obtaining a winding body by winding the positive electrode current collector having a positive electrode and the negative electrode current collector having a negative electrode via a separator, and A method characterized by including the steps of placing the wound body inside a battery container and injecting an electrolyte solution into the battery container.