Method for producing lithium composite oxide

Abstract

The present invention provides a zigzag LiMnO2-type compound that can be produced on an industrial scale and / or a method for producing the same. A method for producing a manganese oxide-based manganese oxide composite of the composition formula Li, comprising the steps of heating a composition containing at least one manganese source selected from the group consisting of dimanganese trioxide and manganese oxyhydroxide, and at least one lithium source selected from the group consisting of lithium carbonate, lithium hydroxide anhydride, and lithium hydroxide monohydrate in an inert atmosphere to a temperature of 600°C to 750°C, and maintaining the temperature for 6 hours or less. x A method for producing a lithium composite oxide represented by MnO2 (where 0.80≦x≦1.20), which has a zigzag layered structure as a base structure and has domains of an α-NaFeO2 type layered structure.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a lithium composite oxide. [Background technology]

[0002] Lithium composite oxides, specifically lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), etc., are widely used as positive electrode active materials in lithium secondary batteries distributed worldwide. Active research is being conducted on these lithium composite oxides to improve their properties (higher capacity, higher output, cycle stability) and safety.

[0003] Regarding performance enhancement through improvement of the characteristics of positive electrode active materials for lithium secondary batteries, for example, increasing capacity has attracted attention, and a lithium composite oxide represented by LiMnO2, which has a crystal structure based on a zigzag layer structure and domains of an α-NaFeO2-type layer structure (Patent Document 1) has been disclosed.

[0004] Patent Documents 2 and 3 disclose a LiMnO2-type compound characterized by being composed of at least one of orthorhombic and monoclinic crystals, and the discharge capacity of a lithium ion secondary battery produced using this compound was low at about 170 mAh / g. In contrast, Patent Document 1 discloses that the crystal structure is changed by a heat treatment process after mechanical milling, and the discharge capacity is improved to 260 mAh / g. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6956039 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-007297 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-145619 Summary of the Invention [Problem to be solved by the invention]

[0006] The LiMnO2-type compound disclosed in Patent Document 1 is a lithium composite oxide that has a high capacity and is inexpensive compared to cobalt-based or nickel-based lithium composite oxides, but it was believed that it could only be produced by mechanical milling. Mechanical milling is a production method that requires a complicated production process and produces very small amounts. Therefore, it was difficult to produce the LiMnO2-type compound disclosed in Patent Document 1 on an industrial scale.

[0007] An object of the present disclosure is to provide a lithium composite oxide (hereinafter also referred to as a "zigzag LiMnO2-type compound") having a crystal structure in which a zigzag layered structure is used as a matrix structure and which has domains of an α-NaFeO2-type layered structure, and which can be produced on an industrial scale, and / or a method for producing the same. [Means for solving the problem]

[0008] In this disclosure, we have investigated a method for producing a zigzag LiMnO2-type compound. As a result, we have found that a zigzag LiMnO2-type compound, which was previously thought to be obtainable only by mechanical milling, can be produced by a simple production method. Furthermore, we have found that the zigzag LiMnO2-type compound obtained by this production method is suitable for production on an industrial scale. That is, the present invention is as set forth in the claims, and the gist of this disclosure is as follows. [1] A method for producing a manganese-based catalyst comprising the steps of heating a composition containing at least one manganese source selected from the group consisting of dimanganese trioxide and manganese oxyhydroxide, and one or more lithium sources selected from the group consisting of lithium carbonate, lithium hydroxide anhydride, and lithium hydroxide monohydrate in an inert atmosphere to a temperature of 600°C to 750°C, and maintaining the temperature for 6 hours or less, the method comprising the steps of heating a composition containing at least one manganese source selected from the group consisting of dimanganese trioxide and manganese oxyhydroxide in an inert atmosphere to a temperature of 600°C to 750°C, the method comprising the steps of heating a composition containing at least one manganese source selected from the group consisting of dimanganese trioxide and manganese oxyhydroxide, and one or more lithium sources selected from the group consisting of lithium carbonate, lithium hydroxide anhydride, and lithium hydroxide monohydrate in an inert atmosphere to a temperature of 600°C to 750°C, and maintaining the temperature for 6 hours or less, the method comprising the steps of heating a composition containing at least one manganese source selected from the group consisting of dimanganese trioxide and manganese oxyhydroxide, and xA method for producing a lithium composite oxide represented by MnO2 (where 0.80≦x≦1.20), which has a zigzag layered structure as a base structure and has domains of an α-NaFeO2 type layered structure. [2] The method for producing a lithium composite oxide according to the above [1], wherein the inert atmosphere is an argon (Ar) atmosphere or a nitrogen (N2) atmosphere. [3] The method for producing a lithium composite oxide according to the above [1], wherein the inert atmosphere is an argon (Ar) atmosphere. [4] The lithium composite oxide has a span value S obtained by the formula (1) of more than 0 and not more than 15.0, and a BET specific surface area of ​​3.0 m 2 / g or more 20.0m 2 The method for producing a lithium composite oxide according to the above [1] or [2], wherein the lithium composite oxide has a solubility of 1 / g or less. S=(D 90 -D 10 ) / D 50 (1) (In formula (1), D 10 [μm], D 50 [μm] and D 90 [μm] respectively indicate the cumulative 10% particle size, cumulative 50% particle size, and cumulative 90% particle size in the volume-based particle size distribution.) [5] The span value S obtained by formula (1) is greater than 0 and less than 15.0, and the BET specific surface area is 3.0 m 2 / g or more 20.0m 2 / g or less, with the composition formula Li x A lithium composite oxide represented by MnO2 (where 0.80≦x≦1.20), which has a zigzag layered structure as its parent structure and has domains of an α-NaFeO2 type layered structure. S=(D 90 -D 10 ) / D 50 (1) (In formula (1), D 10 [μm], D 50 [μm] and D 90 [μm] respectively indicate the cumulative 10% particle size, cumulative 50% particle size, and cumulative 90% particle size in the volume-based particle size distribution.) [6] The lithium composite oxide according to [5], wherein the half-width of a diffraction peak having a peak top at 2θ=25±1.0° in powder X-ray diffraction using CuKα radiation (1.5418 Å) as an X-ray source is 1.0 or more and 2.0 or less. [Effects of the Invention]

[0009] The present disclosure can provide at least one of a lithium composite oxide having a crystal structure in which a zigzag layered structure is used as a matrix structure and which has domains of an α-NaFeO type layered structure, which can be produced on an industrial scale, and a method for producing the same. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing a zigzag layer structure. [Figure 2] Schematic diagram showing a layered structure (2a) and a rock salt structure (2b). [Figure 3] FIG. 1 is a diagram showing XRD patterns of Examples 1 to 4 and Comparative Examples 1 to 3. [Figure 4] 1 shows photographs of the morphology of Example 1 and Comparative Example 1 observed by a scanning electron microscope (SEM). [Figure 5] 1 shows photographs of the morphology of Examples 1, 3, and 4 and Comparative Example 2 observed by a scanning electron microscope (SEM). [Figure 6] FIG. 2 is a graph showing charge-discharge characteristics of Example 1 and Comparative Example 1. [Figure 7] FIG. 1 is a graph showing cycle characteristics of Example 1 and Comparative Example 1. [Figure 8] FIG. 1 is a graph showing charge-discharge characteristics of Examples 1, 3, and 4. [Figure 9] FIG. 1 is a graph showing the cycle characteristics of Examples 1, 3, and 4. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment for carrying out the present disclosure (hereinafter referred to as "the present embodiment") will be described in detail using an example. The present embodiment is an example for explaining the present disclosure, and is not intended to limit the present disclosure to the following content. The present disclosure includes any combination of the configurations and numerical values ​​disclosed in this specification, and also includes any combination of the numerical values ​​disclosed in this specification.

[0012] The production method of this embodiment is a production method characterized by comprising the steps of heating a composition containing a manganese source of at least any one of dimanganese trioxide and manganese oxyhydroxide, and one or more lithium sources selected from the group consisting of lithium carbonate, lithium hydroxide anhydride, and lithium hydroxide monohydrate, in an inert atmosphere to an ultimate temperature of 600°C or higher and 750°C or lower, and maintaining the ultimate temperature for 6 hours or shorter.

[0013] In the manufacturing method of this embodiment, a composition containing at least one of dimanganese trioxide (MnO) and manganese oxyhydroxide (MnOOH) as a manganese source is used as the raw material composition. The oxidation number of the compound used as the manganese source must not change during heat treatment in an inert atmosphere. Furthermore, manganese must diffuse during heat treatment. Therefore, at least one of dimanganese trioxide and manganese oxyhydroxide, which have the same trivalent manganese oxidation number as the manganese after heat treatment and do not have oxidizing or reducing ability, is used. Among these, dimanganese trioxide is preferred as the manganese source because it is easy to control the particle shape.

[0014] In the manufacturing method of this embodiment, a composition containing one or more lithium sources selected from the group consisting of lithium carbonate (Li2CO3), anhydrous lithium hydroxide (LiOH), and lithium hydroxide monohydrate (LiOH·1H2O) is used as the raw material composition. The compound used as the lithium source is a lithium compound that is highly reactive and allows lithium to easily diffuse during heat treatment in an inert atmosphere, and must lack oxidizing or reducing capabilities. Therefore, the lithium source may be one or more selected from the group consisting of lithium carbonate, anhydrous lithium hydroxide, and lithium hydroxide monohydrate. Among these, lithium hydroxide monohydrate is preferred as the lithium source because of its high reactivity in the temperature range of the heat treatment and its resistance to moisture contamination even when handled in an air atmosphere.

[0015] The manganese source may be dimanganese trioxide and manganese oxyhydroxide, and the lithium source may be two or more selected from the group consisting of lithium carbonate, lithium hydroxide anhydrous, and lithium hydroxide monohydrate.

[0016] The ratio of manganese to lithium in the zigzag LiMnO2-type compound of this embodiment may be approximately the same as the ratio of manganese to lithium in the composition of the target zigzag LiMnO2-type compound, and for example, the lithium (Li) / manganese (Mn) substance ratio may be 0.8 to 1.2. To achieve this substance ratio, the mixture ratio may be changed depending on the amounts of manganese and lithium in the manganese source and lithium source.

[0017] The zigzag LiMnO2-type compound used in the manufacturing method of this embodiment may be manufactured by any method, provided that the manganese source and the lithium source are mixed together. The mixing method may be at least one of dry mixing and wet mixing, with dry mixing being preferred, as long as the manganese source and the lithium source are homogeneous.

[0018] In the manufacturing method of this embodiment, the temperature increase and heat treatment are performed in an inert atmosphere. Examples of the inert atmosphere include a nitrogen atmosphere and an argon atmosphere, and an argon atmosphere is preferable. This makes it more difficult for the oxidation number of manganese to change before and after the heat treatment.

[0019] In the manufacturing method of this embodiment, the temperature is raised to a target temperature of 600°C or higher and 750°C or lower. If the target temperature is lower than 600°C, a portion of the manganese source will remain unreacted and will be mixed into the zigzag LiMnO2-type compound after firing. On the other hand, if the target temperature exceeds 750°C, crystal growth of the zigzag LiMnO2-type compound will proceed excessively, and the charge / discharge capacity of a lithium secondary battery using the resulting zigzag LiMnO2-type compound as the positive electrode active material will likely decrease. The target temperature is more preferably 650°C or higher and 700°C or lower.

[0020] The rate of temperature rise to the target temperature is not particularly limited, but may be, for example, 10° C. / min or more and 20° C. / min or less to allow for appropriate crystal growth. The rate of temperature rise may also be changed during the temperature rise.

[0021] In the manufacturing method of this embodiment, the temperature increase and heat treatment may be carried out in a general-purpose firing furnace, and after the temperature is increased to the target temperature, the temperature may be decreased to any desired temperature, for example, 100°C or less, or even room temperature (20±10°C). The temperature decrease rate is not particularly limited, but may be, for example, 4°C / min to 10°C / min to promote appropriate crystal growth. The temperature decrease rate may also be changed during the temperature decrease.

[0022] In the manufacturing method of this embodiment, the holding time at the ultimate temperature is 6 hours or less. If the holding time exceeds 6 hours, crystal growth is unnecessarily promoted, and a lithium secondary battery using the zigzag LiMnO2-type compound of this embodiment as a cathode active material will not achieve high capacity. Since a cathode active material that exhibits high capacity is more easily obtained, a short holding time is preferable; therefore, 3 hours or less is preferred, 1 hour or less is more preferred, and the holding time may be 0 hours (i.e., no holding at the ultimate temperature). Examples of holding times include 0 minutes to 6 hours, or 0 minutes to 3 hours.

[0023] The production method of this embodiment is a simple production method that simply involves heat-treating a composition containing a manganese source and a lithium source, so it is easy to use general-purpose, large-scale equipment, and the production process is simple. Therefore, compared to conventional mechanochemical methods, large-scale production is possible and the production cost is lower, making it very easy to apply to industrial production. Therefore, the zigzag LiMnO2-type compound obtained by the production method of this embodiment is a zigzag LiMnO2-type compound that can be easily produced industrially due to its production method.

[0024] The zigzag LiMnO2 type compound of this embodiment has the composition formula Li x MnO2 (where 0.80≦x≦1.20), where x is 0.80 or more, 0.90 or more, or 0.95 or more, and 1.20 or less, 1.10 or less, or 1.05 or less, and is preferably 0.80 or more and 1.20 or less, 0.90 or more and 1.10 or less, or 0.95 or more and 1.05 or less.

[0025] The composition of the zigzag LiMnO2-type compound of this embodiment is determined by ICP measurement using a general inductively coupled plasma optical emission spectrometer (e.g., OPTIMA5300DV, manufactured by PerkinElmer Japan) to quantify Li and Mn. Next, the concentration (mass%) of each element determined by ICP measurement is divided by the atomic weight of each element, and converted into the amount of substance to determine the content (mol) of each element, and the composition formula can be determined. Note that ICP measurement can be performed on a measurement solution prepared by dissolving a sample in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide.

[0026] The zigzag LiMnO2-type compound of this embodiment has a zigzag layered structure as a base structure and an α-NaFeO2-type layered structure domain. By having such a structure, the resulting lithium secondary battery does not require an initial activation charge-discharge cycle, and can exhibit high capacity from the initial cycle. Therefore, it is advantageous in terms of reducing energy costs compared to orthorhombic LiMnO2, which requires several tens of charge-discharge cycles to exhibit high capacity.

[0027] A schematic diagram of the zigzag layered structure is shown in Figure 1. Schematic diagrams of the layered structure and the rock salt structure are shown in Figure 2 (2a) and (2b), respectively. Figures 1 and 2 show that the zigzag layered structure is a crystalline structure in which the layers of the α-NaFeO2 layered structure grow alternately and regularly, forming a zigzag layered structure.

[0028] Furthermore, the zigzag LiMnO2 type compound of this embodiment has a span value S obtained by the following formula of more than 0 and not more than 15.0, and a BET specific surface area of ​​3.0 m 2 / g or more 20.0m 2 / g or less, with the composition formula Li x Preferably, the lithium composite oxide is represented by the formula (x) and has a zigzag layered structure as a matrix and an α-NaFeO2-type layered structure domain, where x is 0.80≦x≦1.20. This makes it easier to obtain a lithium secondary battery with higher output characteristics than conventional zigzag LiMnO2-type compounds. S=(D 90 -D 10 ) / D 50 (In the formula, D 10 [μm], D 50 [μm] and D 90 The values ​​[μm] respectively represent the cumulative 10% particle size, cumulative 50% particle size, and cumulative 90% particle size in the volume-based particle size distribution.) The span value of the zigzag LiMnO2-type compound of this embodiment is preferably greater than 0, and is preferably 15.0 or less, 12.5 or less, or 10.0 or less, and is preferably greater than 0 and 15.0 or less, greater than 0 and 12.5 or less, or greater than 0 and 10.0 or less. The span value is an index indicating the spread of the particle size distribution, and a smaller span value indicates a more uniform particle size distribution. When the span value of the zigzag LiMnO2-type compound of this embodiment is within this range, the mixture with the conductive material is uniform, making it easier to form a conductive path. As a result, the electrical conductivity of the resulting lithium secondary battery is likely to be high.

[0029] Above D 10 [μm], D 50[μm] and D 90 [μm] indicates the particle diameter when the cumulative value from the smallest particle side is 10 volume %, 50 volume %, and 90 volume %, respectively, and D 10 [μm]≦D 50 [μm]≦D 90 The relationship is [μm].

[0030] D of the zigzag LiMnO2 type compound of this embodiment 10 is preferably 1 μm or more and 10 μm or less or 5 μm or less, and more preferably 1 μm or more and 10 μm or less, or 1 μm or more and 5 μm or less.

[0031] D of the zigzag LiMnO2 type compound of this embodiment 50 is preferably 5 μm or more or 8 μm or more, and 15 μm or less or 12 μm or less, and more preferably 5 μm or more and 15 μm or less, or 8 μm or more and 12 μm or less.

[0032] D of the zigzag LiMnO2 type compound of this embodiment 90 is preferably 10 μm or more or 15 μm or more, and 50 μm or less or 30 μm or less, and more preferably 10 μm or more and 50 μm or less, or 15 μm or more and 30 μm or less.

[0033] In this embodiment, D 10 [μm], D 50 [μm] and D 90 The particle size distribution [μm] may be measured using a general laser diffraction / scattering particle size distribution measuring device (for example, MT3000II series, manufactured by MicrotracBEL) under the following conditions. Light source: Semiconductor laser Calculation mode: HRA Measurement time: 30 seconds Measurement approximation: non-spherical approximation Solvent: Water Refractive index of solvent: 1.33 Refractive index of powder sample: 2.46 The particle size retention rate [%] of the zigzag LiMnO2-type compound of this embodiment is preferably 20% or more, 50% or more, or 80% or more, and is preferably 100% or less, such as 20% or more and 100% or less, 50% or more and 100% or less, or 80% or more and 100% or less. By achieving these particle size retention rates, disintegration of secondary particles can be suppressed during the preparation of a positive electrode for a lithium secondary battery, and a conductive path between the positive electrode active material and the conductive material can be maintained. As a result, the electrical conductivity of the resulting lithium secondary battery is likely to be high.

[0034] In this embodiment, the particle size retention rate was determined by pressing the zigzag LiMnO2-type compound of this embodiment at 3 t / cm using a general uniaxial pressure molding machine (for example, a mini press set manufactured by Riken Kiki Co., Ltd.). 2 When pellets were made by uniaxial pressing at a pressure of D 50 This is a value that indicates the rate of change of and can be calculated using the following formula. Grain size retention rate [%] = (D of the zigzag LiMnO2 type compound of this embodiment after uniaxial pressing) 50 [μm]) / (D of the zigzag LiMnO2-type compound of this embodiment before uniaxial pressing 50 [μm]) x 100 D of the zigzag LiMnO2-type compound of this embodiment after uniaxial pressing 50 The D was measured by crushing the pellets of the zigzag LiMnO2-type compound of this embodiment after uniaxial pressing in a mortar to obtain a powder similar to that of the zigzag LiMnO2-type compound of this embodiment before uniaxial pressing, and using the laser diffraction / scattering particle size distribution measuring device. 50 is.

[0035] The BET specific surface area of ​​the zigzag LiMnO2-type compound of this embodiment is 3.0 m 2 / g or more, and 2 / g or less or 15.0m 2 / g or less, and 2 / g or more 20.0m 2 / g or less, or 3.0m 2 / g or more 15.0m 2When the BET specific surface area is within this range, the capacity of the resulting lithium secondary battery tends to be high.

[0036] In this embodiment, the BET specific surface area can be measured using a general measuring device (for example, MICROMETRICS Desorb III manufactured by Shimadzu Corporation) and a mixed gas of 30% nitrogen and 70% helium as the adsorption gas, according to the method specified in JIS Z8830.

[0037] The BET specific surface area may be measured after pre-treatment in which the zigzag LiMnO2 type compound of this embodiment is placed in a glass cell for BET specific surface area measurement and dehydrated at 150°C for 30 minutes in a nitrogen flow atmosphere.

[0038] In the powder X-ray diffraction pattern of the zigzag LiMnO2-type compound of this embodiment, using CuKα radiation (1.5418 Å) as an X-ray source, the diffraction peak observed at 2θ=25±1.0° has a full width at half maximum (hereinafter also simply referred to as "FWHM") of preferably 1.0 or more or 1.2 or more, and preferably 2.5 or less or 2.3 or less, such as 1.0 to 2.5 or 1.2 to 2.3. When the FWHM is within this range, the rate characteristics of the resulting lithium secondary battery tend to be improved.

[0039] In this embodiment, the FWHM can be determined from a powder X-ray diffraction (hereinafter also referred to as "XRD") pattern measured using a general X-ray measurement device (for example, D2 PHASER, manufactured by Bruker) under the following conditions: X-ray source: CuKα ray=1.5418Å Output: 1.6kW (40mA-40kV) Divergence slit: 1° Divergence vertical limit slit: 10mm Scattering slit: Open Receiving slit: Open Scan width: 0.04°(2θ / θ) Scan speed: 4° / min Measurement range: 10 to 90° (2θ / θ) The obtained XRD pattern is analyzed using the attached analysis software (PDXL2), and the integral width of the peak at 2θ=25±1.0° is taken as the FWHM.

[0040] The zigzag LiMnO2 type compound of this embodiment can be used as a positive electrode active material for lithium secondary batteries. [Example]

[0041] The present disclosure will be described in more detail below with reference to examples, but the present disclosure should not be construed as being limited to these examples. Furthermore, the "sample" described below refers to the zigzag LiMnO2-type compound in each example and comparative example.

[0042] <Powder X-ray diffraction> The 2θ angle of the diffraction peak for each plane of the sample was measured by XRD using an X-ray diffractometer (trade name: Bruker D2 PHASER (Cu Kα=1.54184 Å)) under the following conditions: X-ray source: CuKα ray=1.5418Å Output: 1.6kW (40mA-40kV) Divergence slit: 1° Divergence vertical limit slit: 10mm Scattering slit: Open Receiving slit: Open Scan speed: 4° / min Scan width: 0.04°(2θ / θ) Measurement range: 10 to 90° (2θ / θ) The obtained XRD pattern was analyzed using the attached analysis software (PDXL2), and the integral width of the peak at 2θ=25±1.0° was taken as the FWHM of the sample.

[0043] <Particle size distribution> The volume-based particle size distribution of the sample was measured using a particle size distribution measuring device (trade name: MT3000II series, manufactured by MicrotracBEL). The measurement was carried out after adding an appropriate amount of pure water to the sample and subjecting it to ultrasonic dispersion for 5 minutes. The sample was dispersed by the sample circulator attached to the device, and the measurement was carried out under the following conditions. Light source: semiconductor laser Calculation mode: HRA Measurement time: 30 seconds Measurement approximation: non-spherical approximation Dispersion medium: water Refractive index of the dispersion medium: 1.33 Refractive index of the sample: 2.46 The cumulative 10% particle size (D 10 ) [μm], cumulative 50% particle size (D 50 ) [μm] and cumulative 90% particle size (D 90 ) [μm] in the volume-based particle size distribution of the sample were calculated by the software attached to the device, and the span value S was obtained according to the above formula (1).

[0044] <Composition analysis> The composition of the sample was determined by quantifying Li and Mn by ICP measurement using an inductively coupled plasma optical emission spectrometer (trade name: OPTIMA5300DV, manufactured by PerkinElmer Japan).

[0045] ICP measurement was carried out on the dissolution solution obtained by dissolving the sample in a hydrochloric acid-hydrogen peroxide mixed aqueous solution. The content (mol) of Li and Mn in the sample was obtained by dividing the concentration (mass%) of each element determined by ICP measurement by the atomic weight of each element and converting it to the amount of substance, and the general formula of the composition of the sample was obtained.

[0046] <BET specific surface area> 0.3 g of the sample was placed in a glass cell for BET specific surface area measurement, and pretreated by dehydration treatment at 150 °C for 30 minutes in a nitrogen flowing atmosphere.

[0047] Using a BET measurement device (trade name: MICROMETRICS DesorbIII, manufactured by Shimadzu Corporation), the BET specific surface area of the pretreated sample was measured by the one-point method in accordance with 7.3 of JIS Z8830. During the measurement, a mixed gas of 30% by volume of nitrogen and 70% by volume of helium was used as the adsorption gas.

[0048] <Scanning electron microscope> The morphology of the sample was observed by a scanning electron microscope (SEM). For the measurement, a scanning electron microscope (trade name: JEOL JCM-6000, manufactured by JEOL) was used.

[0049] <Fabrication of electrodes> The positive electrode active material, conductive material (acetylene black), and binder (PVdF) were weighed at a mass ratio of 80:10:10, respectively. The binder was dissolved in an organic solvent (N-methylpyrrolidone), and the positive electrode active material and the conductive material were mixed therein to prepare a positive electrode material ink. The obtained positive electrode material ink was applied to a current collector (aluminum foil), dried in an air atmosphere at 60 °C, and then dried under reduced pressure at 150 °C for 12 hours to fabricate an electrode.

[0050] <Fabrication of Li counter electrode battery> Using the electrode fabricated by the above method as the positive electrode, a solution in which LiPF6 was dissolved at a concentration of 1.0 M in a solution obtained by mixing EC and DMC at a volume ratio of 3:7 as the electrolyte, a polyolefin porous membrane (trade name: Celgard 2500, manufactured by Celgard) as the separator, and a lithium foil as the negative electrode, a two-electrode electrochemical cell (Li counter electrode battery) was fabricated.

[0051] <Evaluation of cycle characteristics> Using a charge-discharge evaluation device (trade name: TOSCAT-3100, manufactured by Toyo System Co., Ltd.), a charge-discharge test of the Li counter electrode battery was conducted. The measurement was carried out at a measurement temperature of 25 °C and a voltage range of 4.8 V - 1.5 V, and charge-discharge was performed at a current density of 25 mA / g (Example 1 and Comparative Example 1) or 10 mA / g (Examples 1, 3, and 4).

[0052] <Measurement of rate characteristics> The rate characteristics of the Li counter electrode battery were evaluated using a charge / discharge device (product name: BTS2004W, manufactured by NAGANO Corporation).

[0053] The measurements were performed by performing two cycles of constant-current constant-voltage charge-constant-current discharge at a temperature of 25°C, a voltage range of 2.0V-4.5V, and a current density of 6mA / g, followed by one cycle at a voltage range of 2.0V-4.5V and a current density of 0.03C, and one cycle at a current density of 0.3C. The discharge capacities 0.03C [mAh / g] and C0.3C [mAh / g] at 0.03C and 0.3C were measured. The current value at which the discharge capacity at a current density of 6mA / g could be charged and discharged in one hour was defined as 1C, and the current densities at 0.03C and 0.3C were calculated.

[0054] In addition, the average discharge voltage V 0.03C [V] and V 0.3C [V] was calculated, and the rate characteristics were calculated using the following formula. E 0.03C [mWh / g]=C 0.03C [mAh / g]×V 0.03C [V] E 0.3C [mWh / g]=C 0.3C [mAh / g]×V 0.3C [V] R[%]=E 0.3C [mWh / g] / E 0.03C [mWh / g] x 100 where E 0.03C [mWh / g] and E 0.3C [mWh / g] represents the energy density of the Li counter electrode battery at 0.03 C and 0.3 C, respectively, and R [%] represents the rate characteristic.

[0055] Example 1 Manganese carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.) was calcined in an air atmosphere at 600°C for 12 hours to prepare Mn2O3. The prepared Mn2O3 was mixed with LiOH·1H2O (Fujifilm Wako Pure Chemical Industries, Ltd.) so that the lithium (Li) / manganese (Mn) mass ratio was 1.0, and the mixture was pressed into a uniaxial press (Mini Press Set, Riken Kikai Co., Ltd.) at a density of 3 t / cm. 2 The pellets were heated in an argon atmosphere to 700°C at a rate of 10°C / min, and then cooled to room temperature at a rate of 4°C / min without holding the temperature after reaching 700°C, thereby obtaining a zigzag LiMnO2-type compound of this example.

[0056] Example 2 The zigzag LiMnO2 type compound of this example was obtained in the same manner as in Example 1, except that after the temperature reached 700°C, it was held at 700°C for 1 hour.

[0057] Example 3 2.0 mol / dm -3 manganese nitrate aqueous solution, and 1.2 mol / dm -3 Manganese carbonate was obtained by mixing the manganese carbonate with an aqueous ammonium bicarbonate solution. The manganese carbonate was calcined in an air atmosphere at 600°C for 12 hours to produce Mn2O3. The prepared Mn2O3 was mixed with LiOH·1H2O so that the lithium (Li) / manganese (Mn) mass ratio was 1.0, and pellets were produced using the uniaxial press molding machine described above. The produced pellets were heated in an argon atmosphere to 700°C at a rate of 10°C / min, and then, without holding at 700°C, were cooled to room temperature at a rate of 4°C / min, resulting in the zigzag LiMnO2-type compound of this example.

[0058] Example 4 The zigzag LiMnO2 type compound of this example was obtained in the same manner as in Example 3, except that in the heat treatment, after the temperature reached 700°C, it was held at 700°C for 1 hour.

[0059] Example 5 2.0 mol / dm -3 Instead of the manganese nitrate solution of 2.0 mol / dm-3 The zigzag LiMnO2-type compound of this example was obtained in the same manner as in Example 3, except that the manganese sulfate aqueous solution was used, the prepared Mn2O3 and LiOH·1H2O were mixed in a substance ratio of 1:2.1, and the temperature decrease rate in the heat treatment was set to 5°C / min.

[0060] The composition of the zigzag LiMnO2 type compound in this example is LiMnO2, and D 10 , D 50 and D 90 were 0.61 μm, 0.93 μm, and 2.03 μm, respectively, the particle size retention was 99%, and the FWHM was 1.6°.

[0061] Comparative Example 1 In this comparative example, a lithium composite oxide was obtained using a method similar to Comparative Example 2 of Japanese Patent Application No. 2020-089664. Specifically, 2.08 g of Mn2O3 and 1.00 g of Li2CO3 were weighed, placed in a mortar, and crushed and mixed. Then, pellets were produced using the uniaxial press molding machine described above. The pellets were then fired in an argon atmosphere at 900°C for 12 hours. Next, the LiMnO2 with a zigzag layered structure was subjected to mechanical milling. Mechanical milling was performed using a ball mill at a rotation speed of 600 rpm for 36 hours. This mechanical milling yielded LiMnO2 with a rock salt structure.

[0062] Next, LiMnO2 having a rock salt structure was heated to 700°C at a rate of 10°C / min in an argon atmosphere, held at 700°C for 12 hours, and then cooled to room temperature at a rate of 10°C / min, thereby obtaining a zigzag LiMnO2-type compound for this comparative example.

[0063] Comparative Example 2 The zigzag LiMnO2 type compound of this comparative example was obtained in the same manner as in Example 3, except that the heat treatment temperature reached 800°C.

[0064] Comparative Example 3 A zigzag LiMnO2 type compound of this comparative example was obtained in the same manner as in Example 1, except that in the heat treatment, once the temperature reached 700°C, it was held for 12 hours.

[0065] Comparative Example 4 Manganese carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.) was calcined in an air atmosphere at 700°C for 12 hours to produce Mn2O3. The prepared Mn2O3 was mixed with lithium carbonate (Li2CO3; Rare Metallic Co., Ltd.) in a mortar so that the Li / Mn molar ratio of the metal composition was 1.0. After mixing, the mixture was heated to 900°C at 10°C / min in an argon atmosphere, held at 900°C for 12 hours, and then cooled to room temperature at 10°C / min.

[0066] Next, mechanical milling was carried out in the same manner as in Comparative Example 1 to obtain a zigzag LiMnO2 type compound of this comparative example.

[0067] D of the lithium composite oxide of this comparative example 10 , D 50 and D 90 were 0.43 μm, 0.58 μm, and 8.18 μm, respectively, the particle size retention was 98%, and the FWHM was 2.5°.

[0068] Comparative Example 5 In this comparative example, a zigzag LiMnO2-type compound was obtained using a method similar to Example 1 of Japanese Patent Application No. 2023-065577. Specifically, electrolytic manganese dioxide (MnO2) was calcined at 600°C for 12 hours to produce Mn2O3. 662 g of the Mn2O3 thus produced, 338 g of lithium hydroxide monohydrate (LiOH·HO), and 4000 mL of pure water were mixed to prepare 5 kg of slurry, which was then pulverized for 2 hours using a mill (product name: Dynomill Multi-Lab model, manufactured by Shinmaru Enterprises).

[0069] Next, the slurry was spray-dried using a spray dryer (product name: SB39, manufactured by PRIS) under conditions of a 90-type nozzle spray pressure of 0.2 MPa, a solution rate of 3 kg / h, and a hot air inlet temperature of 220° C. After spray-drying, the temperature was increased to 700° C. at a rate of 10° C. / min in a nitrogen atmosphere, and after reaching 700° C., the temperature was maintained for 2 hours, followed by a heat treatment of decreasing the temperature to room temperature at a rate of 5° C. / min, thereby obtaining a zigzag LiMnO2-type compound of this comparative example.

[0070] The composition of the zigzag LiMnO2 type compound of this comparative example is Li 1.01 MnO2 and D 10 , D 50 and D 90 were 2.8 μm, 9.5 μm, and 19.1 μm, respectively, the particle size retention was 10%, and the FWHM was 2.1°.

[0071] The evaluation results of the zigzag LiMnO2 type compounds obtained in Example 5 and Comparative Example 4 are shown in the table below. [Table 1]

[0072] The XRD patterns of the zigzag LiMnO2-type compounds of Examples 1 to 5 and Comparative Examples 1 to 4 were found to have strong peaks in the orthorhombic (010), (011), (200), and (021) planes, and a weak peak in the monoclinic (001) plane. That is, it was confirmed that the crystal structure of the zigzag LiMnO2-type compounds prepared in the present examples has a zigzag layered structure as the parent structure and domains of an α-NaFeO2-type layered structure. The XRD patterns of the zigzag LiMnO2-type compounds of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Figure 3.

[0073] In Comparative Example 1, the weak and broad peak of the (110) plane means that the sample has domains of the α-NaFeO2-type layer structure, whereas a strong and clear peak of the (110) plane in the XRD pattern means that the sample has relatively few domains of the α-NaFeO2-type layer structure.

[0074] The (110) plane peaks in the XRD patterns of Examples 1 to 4 were broad, whereas the (110) plane peaks were sharp in Comparative Examples 2 and 3. That is, the crystal structures of Examples 1 to 4 had many domains of the α-NaFeO2-type layered structure, similar to Comparative Example 1, and were structures having a zigzag layered structure as the parent structure and domains of the α-NaFeO2-type layered structure, whereas the crystal structures of Comparative Examples 2 to 3 had relatively few domains of the α-NaFeO2-type layered structure and were closer to a crystal structure with a zigzag layered structure.

[0075] The morphology of the zigzag LiMnO2 type compounds of Example 1 and Comparative Example 1 was observed using a scanning electron microscope (SEM), and the results are shown in FIG.

[0076] The morphology of the zigzag LiMnO2-type compounds of Examples 1, 3, and 4 and Comparative Example 2 was observed using a scanning electron microscope (SEM), and the results are shown in Figure 5. It was found that in Comparative Example 2, in which the heat treatment temperature was increased, the primary particles grew and coarse primary particles were present. It is known that LiMnO2, which has a zigzag layered structure as its parent structure and domains of an α-NaFeO2-type layered structure, can achieve high capacity by controlling the crystallinity, and Comparative Example 2, in which the primary particles grew, is considered unsuitable for achieving high capacity.

[0077] The zigzag LiMnO2-type compounds of Example 1 and Comparative Example 1 were charged and discharged at a temperature of 25°C, a voltage range of 4.8 V to 1.5 V, and a current density of 25 mA / g. The cycle performance evaluation results are shown in Figures 6 and 7. It was found from Figures 6 and 7 that the zigzag LiMnO2-type compound of Example 1 exhibited high capacity and excellent cycle stability, similar to the zigzag LiMnO2-type compound of Comparative Example 1. However, compared to the manufacturing method of Comparative Example 1 ("calcination" → "mechanical milling" → "heat treatment"), the manufacturing method of Example 1 is simpler in that it does not require mechanical milling and requires only one heat treatment in the manufacturing process.

[0078] The zigzag LiMnO2-type compounds of Examples 1, 3, and 4 were charged and discharged at a temperature of 25°C, a voltage range of 4.8 V to 1.5 V, and a current density of 10 mA / g. The results of cycle performance evaluation are shown in Figures 8 and 9. Figures 8 and 9 show that the zigzag LiMnO2-type compounds of Examples 3 and 4 exhibit high capacity and excellent cycle stability, similar to the zigzag LiMnO2-type compound of Example 1.

[0079] From Table 1, it is clear that the zigzag LiMnO2 type compound of Example 5 exhibits superior rate characteristics compared to Comparative Example 4.

[0080] The entire contents of the claims, specification, abstract and drawings of Japanese Patent Application No. 2024-102168, filed on June 25, 2024, are hereby incorporated by reference as the disclosure of the specification of the present invention. [Industrial Applicability]

[0081] The method for producing a zigzag LiMnO2-type compound according to the present disclosure can produce a zigzag LiMnO2-type compound more easily than conventional production methods, and the resulting zigzag LiMnO2-type compound can be used as a positive electrode active material for lithium secondary batteries.

Claims

1. The method is characterized by comprising the step of heating a composition containing at least one manganese source, dimanganese trioxide and manganese oxyhydroxide, and one or more lithium sources selected from the group consisting of lithium carbonate, anhydrous lithium hydroxide, and lithium hydroxide monohydrate, in an inert atmosphere to a target temperature of 600°C to 750°C, and holding the temperature at the target temperature for 6 hours or less. The span value S obtained by the following formula (1) is greater than 0 and less than or equal to 15.0, and the BET specific surface area is 3.0 m² / g or more and less than or equal to 20.0 m² / g, and the composition formula Li ｘ MnO ２ (However, 0.80 ≤ x ≤ 1.20) is shown, and the matrix structure is a zigzag layered structure, with α-NaFeO ２ A method for producing lithium composite oxide having a layered structure domain. S=(D 90 - D 10 ) / D 50 (1) (In formula (1), D 10 [μm], D 50 [μm], and D 90 [μm] represent the cumulative 10% particle diameter, cumulative 50% particle diameter, and cumulative 90% particle diameter, respectively, in the volume-based particle size distribution.)

2. The inert atmosphere is an argon (Ar) atmosphere or a nitrogen (N) atmosphere. ２ A method for producing a lithium composite oxide according to claim 1, wherein the atmosphere is such that

3. The method for producing a lithium composite oxide according to claim 1, wherein the inert atmosphere is an argon (Ar) atmosphere.

4. The span value S obtained by formula (1) is greater than 0 and less than or equal to 15.0, and the BET specific surface area is 3.0 m ２ / g or more and 20.0 m ２ / g or less, and the composition formula is Li ｘ MnO ２ (where 0.80 ≦ x ≦ 1.20), which is represented by a lithium composite oxide having a zigzag layered structure as the mother structure and a domain of an α-NaFeO ２ -type layered structure. S=(D ９０ -D １０ ) / D ５０ (1) (In formula (1), D １０ [μm], D ５０ [μm] and D ９０ [μm] represents the cumulative 10% particle diameter, cumulative 50% particle diameter, and cumulative 90% particle diameter in the volume-based particle size distribution, respectively.

5. The lithium composite oxide according to claim 4, wherein in powder X-ray diffraction using CuKα rays (1.5418 Å) as the X-ray source, the full width at half maximum of the diffraction peak having a peak top at 2θ = 25 ± 1.0° is 1.0 or more and 2.0 or less.

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