Spinel-type lithium manganese oxide and its manufacturing method

Abstract

Provided is a spinel-type lithium manganese oxide having improved long-term stability in charge-discharge cycles at high temperatures. SOLUTION: A spinel-type lithium manganese oxide containing ferrocyanide.

Description

[Technical Field]

[0001] The present disclosure relates to a spinel-type lithium manganese oxide and a method for producing the same. [Background technology]

[0002] Spinel-type lithium manganese oxide (hereinafter referred to as "LMO") has been investigated as a positive electrode active material for lithium-ion secondary batteries (hereinafter referred to as "LIB"). However, manganese leaches out of LMO during charge and discharge, which reduces the charge-discharge cycle stability, especially at high temperatures. Various studies have been conducted to improve the charge-discharge cycle stability at high temperatures.

[0003] For example, Patent Document 1 considers coating the surface of LMO with aluminum, or calcining ammonium dihydrogen phosphate and a manganese source to form a film of an inorganic phosphorus compound (Li3PO4) on the surface of LMO. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-176732 Summary of the Invention [Problem to be solved by the invention]

[0005] However, all of the methods disclosed in Patent Document 1 were insufficient in suppressing manganese leaching from LMO, and LIBs containing such LMOs still had poor long-term stability (hereinafter also referred to as "storage characteristics") in charge-discharge cycles at high temperatures.

[0006] In contrast, the present disclosure aims to provide an LMO with improved storage characteristics compared to manganese leaching suppression using an aluminum coating or a coating of an inorganic phosphorus compound, a method for producing the same, and at least one of a positive electrode active material and a LIB containing the same. [Means for solving the problem]

[0007] In this disclosure, we have focused on additives to LIBs in order to improve storage characteristics. As a result, we have found that the inclusion of specific additives suppresses the elution of manganese from LMO during charge-discharge cycles and can also capture the eluted manganese ions, thereby improving the storage characteristics of LIBs using this as a positive electrode active material.

[0008] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] Lithium manganese spinel oxide containing ferrocyanide. [2] The spinel-type lithium manganese oxide according to [1], wherein the ferrocyanide is an alkali metal salt containing a ferrocyanide ion. [3] The spinel-type lithium manganese oxide according to [2], wherein the alkali metal salt is at least one of a lithium salt and a sodium salt. [4] The spinel-type lithium manganese oxide according to any one of [1] to [3], wherein the content of the ferrocyanide is 0.05% by mass or more and 20% by mass or less. [5] BET specific surface area is 0.1m 2 / g or more 1.5m 2 The spinel-type lithium manganese oxide according to any one of [1] to [4], wherein the value is 0.1 / g or less. [6] The spinel-type lithium manganese oxide according to any one of [1] to [5], having a JIS pH of 9.0 or more and 12.0 or less, as measured in accordance with 5.9.2 (water method) of JIS K1467. [7] The spinel-type lithium manganese oxide according to any one of [1] to [6], which is in powder form. [8] The spinel-type lithium manganese oxide according to any one of [1] to [7], having an average secondary particle diameter of 0.1 μm or more and 25 μm or less. [9] A positive electrode active material containing the spinel-type lithium manganese oxide according to any one of [1] to [8].

[10] A lithium secondary battery comprising the positive electrode active material according to [9]. [Effects of the Invention]

[0009] The present disclosure makes it possible to provide an LMO with improved storage characteristics compared to those achieved by suppressing manganese elution using an aluminum coating or a coating of an inorganic phosphorus compound, a method for producing the same, and at least one of a positive electrode active material and a LIB containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present disclosure will be described in detail below. However, the following description of the constituent elements is an example of an embodiment of the present disclosure, and the present disclosure is not limited to these contents. Furthermore, the present disclosure includes any combination of the configurations and parameters disclosed in this specification, and also includes any combination of the upper and lower limits of the values ​​disclosed in this specification. In this specification, "to" means a numerical range including both ends of the numerical value. [Ferrocyanide-containing LMO] This embodiment relates to an LMO containing ferrocyanide (hereinafter also referred to as "ferrocyanide-containing LMO"). In this embodiment, the LMO itself functions as an electrode active material, causing desorption and insertion of Li ions during charge and discharge. On the other hand, the ferrocyanide is thought to suppress the elution of manganese ions from the LMO surface (hereinafter also referred to as "manganese elution") and further capture the eluted manganese ions. This is thought to suppress the poisoning of the negative electrode by manganese ions and improve storage characteristics.

[0011] In this embodiment, the LMO can be identified by performing powder X-ray diffraction (hereinafter also referred to as "powder XRD") under the following conditions using a general powder X-ray diffractometer (e.g., Ultima IV, manufactured by Rigaku) ​​to obtain an XRD pattern, which can then be compared with the XRD pattern on the JCPDS card (hereinafter also referred to as "reference pattern") to identify its structure.

[0012] Radiation source: CuKα radiation (wavelength λ=1.5405Å) Output: 1.6kW (40mA-40kV) Filter: Kβ filter Divergence slit: 1° Divergence vertical limit slit: 10mm Scattering slit: Open Receiving slit: Open Scanning mode: Continuous Scan speed: 4,000° / min Sampling width: 0.04°(2θ / θ) Accumulation count: 1 time Measurement range: 10-90°(2θ / θ) No. 35-782 (LiMn2O4) is an example of a reference pattern for LMO.

[0013] The LMO in the ferrocyanide-containing LMO of this embodiment has the general formula Li 1+X Mn 2-X-Y M Y O4 (wherein 0.02≦X≦0.20, 0.05≦Y≦0.30, M=at least one of Mg and Al), and LMO represented by the general formula Li 1+X Mn 2-X-Y M Y It is more preferable that the LMO is a substituted LMO represented by the formula O4 (wherein 0.05≦X≦0.15, 0.05≦Y≦0.10, and M=at least one of Mg and Al). When the LMO is a substituted LMO, manganese elution is more easily suppressed.

[0014] The composition of the LMO contained in the ferrocyanide-containing LMO of this embodiment is represented by the composition formula Li1+X Mn 2-X―Y M Y O4 and calculated from the contents (mol) of Li, Mn, and M (=Al and Mg) obtained by composition analysis.

[0015] The composition of the ferrocyanide-containing LMO in this embodiment can be determined by quantifying Li, Mn, Al, Mg, and Fe by ICP measurement using a general inductively coupled plasma atomic emission spectrometer (e.g., ICP-AES, manufactured by PerkinElmer Japan). Prior to ICP measurement, the measurement sample may be dissolved in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide, and, if necessary, may be dissolved by acid decomposition under pressure.

[0016] In this embodiment, the ferrocyanide is a hexacyanidoferrate (II) ion ([Fe(CN)6] 4- ) (hereinafter also referred to as "ferrocyanide ion") as an anion, and examples thereof include alkali metal salts containing ferrocyanide ions, and further include one or more selected from the group consisting of lithium ferrocyanide, sodium ferrocyanide, and potassium ferrocyanide, with at least one of lithium ferrocyanide and sodium ferrocyanide being preferred.

[0017] The content of ferrocyanide ions contained in the ferrocyanide-containing LMO of this embodiment is preferably 0.05% by mass or more or 0.1% by mass or more, and is preferably 20% by mass or less or 10% by mass or less, for example, 0.05% by mass or more and 20% by mass or less, or 0.1% by mass or more and 10% by mass or less.

[0018] In this embodiment, the ferrocyanide may be contained in a state that can suppress the elution of manganese, for example, one or more selected from the group consisting of a state in which the ferrocyanide is contained in the LMO as particles, a state in which the ferrocyanide is attached to the surface of the LMO, a state in which the ferrocyanide coats the surface of the LMO, and a state in which the ferrocyanide is chemically incorporated into the LMO structure. The chemical interaction between the ferrocyanide and manganese can more efficiently suppress the elution of manganese.

[0019] The composition of the ferrocyanide-containing LMO of this embodiment is determined by the following formula (1).

[0020] Ferrocyanide-containing LMOs = LMO + ferrocyanide (1) The mass percentage (mass%) of ferrocyanide in formula (1) is calculated by converting the mass% of Fe obtained by composition analysis using the formula weight of ferrocyanide (Fe(CN)6; 211.85 g / mol) and the atomic weight of Fe (55.845 g / mol). The LMO (mass%) in formula (1) is calculated by subtracting the mass% of ferrocyanide from the ferrocyanide-containing LMO, which is set to 100 mass%.

[0021] The ferrocyanide-containing LMO of this embodiment preferably contains no substances other than LMO and ferrocyanide, but may contain unavoidable impurities as long as the effects are not impaired.

[0022] The BET specific surface area of ​​the ferrocyanide-containing LMO of this embodiment is 0.1 m 2 / g or more or 0.2m 2 / g or more, and 2.0m 2 / g or less or 1.5m 2 / g or less, and 2 / g or more 2.0m 2 / g or less, or 0.2m 2 / g or more 1.5m 2When the BET specific surface area is in this range, it is possible to suppress the elution of manganese from the ferrocyanide-containing LMO while exhibiting sufficient input / output characteristics and capacity.

[0023] In this embodiment, the BET specific surface area can be measured by a common measuring device (e.g., Macsorb, manufactured by MOUNTECH) using a 30% nitrogen-70% helium mixed gas as the adsorption gas by the one-point method specified in 7.3 of JIS Z8830. The measurement sample is placed in a glass cell for BET specific surface area measurement and subjected to a dehydration treatment at 150°C for 20 minutes in a nitrogen flow atmosphere as pretreatment.

[0024] In order to more easily suppress gelation when used as a positive electrode active material, the pH (hereinafter also simply referred to as "pH") of the ferrocyanide-containing LMO of this embodiment, measured by a method based on JIS K1467, 5.9.2, water method, is preferably 9.0 or more or 9.5 or more, and is preferably 12.0 or less or 11.5 or less, for example, 9.0 or more and 12.0 or less, or 9.5 or more and 11.5 or less.

[0025] In order to facilitate the preparation of a positive electrode for a LIB, the average secondary particle diameter of the ferrocyanide-containing LMO of this embodiment is preferably 0.1 μm or more, 0.5 μm or more, or 1 μm or more, and is preferably 40 μm or less, 30 μm or less, or 25 μm or less, such as 0.1 μm or more and 40 μm or less, 0.5 μm or more and 30 μm or less, or 1 μm or more and 25 μm or less.

[0026] The average secondary particle diameter in this embodiment is a particle diameter corresponding to the 50% volume diameter (hereinafter also referred to as "D50") in a cumulative volume particle diameter distribution curve determined under the following conditions using a general laser diffraction / scattering device (for example, MT3000II series, manufactured by MicrotracBEL).

[0027] Light source: Semiconductor laser Particle refractive index: 2.20 Measurement approximation: Non-spherical approximation Dispersion medium: Ethanol The form of the ferrocyanide-containing LMO of this embodiment may be any form that can be used as a positive electrode active material, such as powder, pellet, sheet, or fiber. Powder form is preferred because it is easy to handle when used as a positive electrode active material.

[0028] The method for producing the ferrocyanide-containing LMO of this embodiment may be any method as long as it can produce a ferrocyanide-containing LMO that satisfies the above-mentioned configuration, but examples include a production method that includes a step of mixing a ferrocyanide source with a spinel-type lithium manganese oxide.

[0029] In the step of mixing the ferrocyanide with the spinel-type lithium manganese oxide (hereinafter also referred to as the "mixing step"), the mixing can bring the ferrocyanide into a state in which it can suppress the elution of manganese.

[0030] The temperature during mixing is not particularly limited as long as the LMO and ferrocyanide source can be mixed, but it may be 0°C or higher, or even room temperature (20±10°C), and is preferably 0°C or higher and 100°C or lower, more preferably 0°C or higher and 70°C or lower, and even more preferably 0°C or higher and 40°C or lower.

[0031] This state can be adjusted by the mixing method and degree. For example, by increasing the amount of ferrocyanide source added and mixed, a wider area of ​​the LMO surface can be brought into contact with the ferrocyanide source, making it easier to suppress manganese elution. By increasing the mixing time, the ferrocyanide source tends to be highly dispersed on the LMO. Furthermore, by increasing the load during mixing, the LMO and ferrocyanide source tend to adhere more strongly, improving handleability when used as a positive electrode active material.

[0032] Examples of equipment used for mixing include one or more selected from the group consisting of a mortar, a container rotary mixer, a ribbon mixer, a high-speed rotary impact grinder, and a ball mill. Examples of mortars include an alumina mortar, an agate mortar, and an iron mortar, with an alumina mortar or an agate mortar being preferred. The mixing time in the mortar is preferably 10 seconds or more, 20 seconds or more, or 1 minute or more, and preferably 2 hours or less, 1 hour or less, or 30 minutes or less, such as 10 seconds to 2 hours, 20 seconds to 1 hour, or 1 minute to 2 hours. Setting the mixing time within this range allows for both workability and mixability while maintaining the particle structure of the LMO. An automatic mortar may also be used. The mixing may also be performed in the presence of a solvent.

[0033] In the mixing step, the LMO, the ferrocyanide source, and the solvent may be mixed as a slurry, which allows the ferrocyanide to be coated on the surface of the LMO in the form of a film.

[0034] The solvent is not particularly limited as long as it is a solvent in which the LMO and ferrocyanide source can be dispersed, and examples thereof include at least one of water and ethanol.

[0035] A method for forming a slurry state includes adding LMO to a ferrocyanide source solution. The concentration of the ferrocyanide source solution is sufficient if the ferrocyanide is uniformly dispersed, and for example, the ferrocyanide ion concentration may be 1% by mass or more and 10% by mass or less. To uniformly disperse the ferrocyanide source, the ferrocyanide solution may be irradiated with ultrasonic waves.

[0036] A slurry state can be obtained by adding LMO powder to the obtained ferrocyanide source solution. The LMO slurry concentration can be any concentration that allows ferrocyanide ions and LMO to be mixed uniformly, for example, 10% by mass to 60% by mass. To achieve uniform mixing, the slurry can be stirred with a rotary stirring blade.

[0037] In the liquid phase method, it is preferable to remove the solvent after mixing. Any method may be used to remove the solvent, and drying in the air is an example. In this case, the drying temperature is not particularly limited, but is preferably 50°C or higher and 200°C or lower.

[0038] When the resulting ferrocyanide-containing LMO is used as a positive electrode active material for a LIB, good charge-discharge characteristics are likely to be obtained. Therefore, the LMO to be subjected to the mixing step preferably has at least one of the following physical properties, more preferably has two or more of the following physical properties, and even more preferably has all of the following physical properties.

[0039] The average secondary particle diameter of the LMO is preferably 0.1 μm or more, 0.5 μm or more, or 1 μm or more, and is preferably 40 μm or less, 30 μm or less, or 25 μm or less, such as 0.1 μm or more and 40 μm or less, 0.5 μm or more and 30 μm or less, or 1 μm or more and 25 μm or less.

[0040] The BET specific surface area of ​​LMO is 0.05m 2 / g or more or 0.1m 2 / g or more, and 2.0m 2 / g or less or 1.5m 2 / g or less, and 0.05m 2 / g or more 2.0m 2 / g or less, or 0.1m 2 / g or more 1.5m 2 / g or less.

[0041] The pH of the LMO is preferably 8.00 or higher or 9.50 or higher, and is preferably 12.0 or lower or 11.5 or lower, such as 9.00 or higher and 12.0 or higher, or 9.50 or higher and 11.5 or lower.

[0042] The ferrocyanide source to be subjected to the mixing step may be at least one of a ferrocyanide and a precursor thereof.

[0043] The ferrocyanide source used in the composite step may be any ferrocyanide capable of producing the desired composite oxide. Specific examples of the ferrocyanide source include one or more selected from the group consisting of lithium hexacyanoferrate(II) (Li4[Fe(CN)6]·nH2O), sodium hexacyanoferrate(II) decahydrate (Na4[Fe(CN)6]·10H2O), and potassium hexacyanoferrate(II) trihydrate (K4[Fe(CN)6]·3H2O), with at least one of sodium hexacyanoferrate(III) decahydrate and lithium hexacyanoferrate(II) being preferred.

[0044] The average secondary particle diameter of the ferrocyanide source is preferably 0.01 μm or more, 0.05 μm or more, or 0.1 μm or more, and is preferably 30 μm or less, 20 μm or less, or 15 μm or less, such as 0.01 μm or more and 30 μm or less, 0.05 μm or more and 20 μm or less, or 0.1 μm or more and 15 μm or less.

[0045] The ratio of the average secondary particle size of the ferrocyanide source to the average secondary particle size of the LMO (ferrocyanide source / LMO; hereinafter also referred to as the "average secondary particle size ratio") is preferably 0.01 or more, or 0.02 or more, and preferably 10.0 or less, or 8.0 or less, for example, 0.01 or more and 10.0 or less, or 0.02 or more and 8.0 or less. Having the average secondary particle size ratio within this range facilitates homogeneity of the ferrocyanide source and LMO when mixed. The amount of the ferrocyanide source mixed is preferably 0.1% by mass or more, or 0.2% by mass or more, or 0.3% by mass or more, and is preferably 15% by mass or less, 12% by mass or less, or 10% by mass or less, for example, 0.1% by mass or more and 15% by mass or less, or 0.2% by mass or more and 12% by mass or less, or 0.3% by mass or more and 10% by mass or less. When the amount of the ferrocyanide source is within this range, the effect of improving the storage characteristics by mixing the ferrocyanide source can be more easily obtained.

[0046] The method for producing ferrocyanide-containing LMO of this embodiment may further include a classification step after the mixing step in order to make the particle size uniform.

[0047] The classification method is not particularly limited as long as the particle size of the ferrocyanide-containing LMO of this embodiment is uniform, but examples include at least one of sieve classification and air classification. From the viewpoint of production cost, a vibrating sieve is preferred. The sieve openings can be 10 μm or more and 1 mm or less, and the powder that falls through the sieve can be collected. [Example]

[0048] The present disclosure will be described below with reference to examples, but the present disclosure is not limited to these examples.

[0049] <XRDパターン> Powder X-ray diffraction (hereinafter also referred to as "powder XRD") was performed using a powder X-ray diffractometer (Ultima IV, manufactured by Rigaku) ​​under the following conditions to obtain an XRD pattern and identify the crystal structure of the sample.

[0050] Radiation source: CuKα radiation (wavelength λ=1.5405Å) Output: 1.6kW (40mA-40kV) Filter: Kβ filter Divergence slit: 1° Divergence vertical limit slit: 10mm Scattering slit: Open Receiving slit: Open Scanning mode: Continuous Scan speed: 4,000° / min Sampling width: 0.04°(2θ / θ) Accumulation count: 1 time Measurement range: 10-90°(2θ / θ) <Composition> The composition of the sample was determined by quantifying Li, Mn, Al, P, and Fe by ICP measurement using an inductively coupled plasma atomic emission spectrometer (ICP-AES, manufactured by PerkinElmer Japan). Prior to the measurement, the sample was dissolved in a mixed aqueous solution of hydrochloric acid and hydrogen peroxide to prepare a measurement solution. The concentration (mass%) of each element determined by ICP measurement was divided by the atomic weight of each element, and the content (mol) of each element in the sample was calculated by converting it into the amount of substance.

[0051] Also, according to the above method, LMO was identified from the XRD pattern, and the general formula of LMO was determined from the content of each obtained element.

[0052] <Content ratio> The content of each component in the LMO containing ferrocyanide was determined from the above formula (1). Also, the content of the ferrocyanide was determined from the following formula (2).

[0053] Content of ferrocyanide [mass%] ={(W Fe ×M1 / M2) / W ICP}×100 (2) In formula (2), W Fe is the amount of Fe [g] determined from ICP measurement, M1 is the amount of substance of ferrocyanide ions [211.85 [g / mol]], M2 is the atomic weight of iron (Fe) [[55.845 g / mol]], and W ICP is the sample mass [g] subjected to ICP measurement.

[0054] <BET specific surface area> 1.5 g of the sample was placed in a glass cell for BET specific surface area measurement, and dehydration treatment was performed at 150°C for 20 minutes in a nitrogen flow atmosphere for pretreatment.

[0055] Using a BET measuring device (Macsorb, manufactured by MOUNTECH), the BET specific surface area of the pretreated sample was measured by the one-point method according to 7.3 of JIS Z8830. During the measurement, a mixed gas of 30% by volume of nitrogen - 70% by volume of helium was used as the adsorption gas.

[0056] <ph> The JIS-pH of the sample was measured according to the water method specified in 5.9.2 of JIS K1467.

[0057] <Average secondary particle diameter> Using a particle size distribution analyzer (MT3000II series, manufactured by MicrotracBEL), D50 was calculated from the volume frequency distribution curve obtained under the following conditions, and this was taken as the average secondary particle diameter of the sample. Prior to measurement, the sample was mixed with a dispersion medium (ethanol) to obtain a slurry, which was pretreated by irradiating it with ultrasound for 3 minutes.

[0058] Light source: Semiconductor laser Particle refractive index: 2.20 Measurement approximation: Non-spherical approximation Dispersion medium: Ethanol <Lithium secondary battery> According to the following procedure, lithium ion secondary batteries were fabricated using the ferrocyanide-containing LMO obtained in the examples or the LMO obtained in the comparative examples as the positive electrode active material.

[0059] <<Positive Electrode>> 4.7 g of positive electrode active material, 0.15 g of acetylene black, 1.5 g of a 10 mass % polyvinylidene fluoride / N-methyl-2-pyrrolidone solution (0.15 g as polyvinylidene fluoride), and 1.23 mL of N-methyl-2-pyrrolidone were weighed to obtain a composition with a mass ratio of positive electrode active material:acetylene black:polyvinylidene fluoride = 94:3:3. The obtained composition was mixed in a planetary centrifugal mixer (AR-310, manufactured by Thinky) to prepare a positive electrode mixture.

[0060] The weight of the positive electrode active material per unit area of ​​the obtained positive electrode mixture was 15.0±3.5 mg / cm 2 After drying, the mixture was punched out into a rectangle of 60 mm length x 30 mm width, and the positive electrode active material density was 2.5±0.1 g / cm. 3 , or 3.0±0.1g / cm 3 After the roll press, a 10 mm long portion was peeled off from the top end of the positive electrode composite coating, and the portion was dried at 120°C for 2 hours under vacuum. An aluminum tab was spot-welded to any location within the region where the positive electrode active material was peeled off to form a positive electrode.

[0061] <<Negative Electrode>> The negative electrode was prepared by weighing 4.0 g of negative electrode active material (artificial graphite), 2.1 g of a 10 mass % polyvinylidene fluoride / N-methyl-2-pyrrolidone solution (0.21 g of polyvinylidene fluoride), and 3.2 mL of N-methyl-2-pyrrolidone (graphite:polyvinylidene fluoride = 95:5 (mass ratio)), and mixing the resulting composition in a planetary centrifugal mixer (AR-310, manufactured by Thinky) to prepare a negative electrode mixture. The weight of the negative electrode active material per unit volume of the resulting negative electrode mixture was 5.5 mg / cm. 2 After drying, the copper foil was punched out into a rectangle measuring 62 mm in length and 32 mm in width, and the weight of the negative electrode material per unit area of ​​the negative electrode mixture was 1.4±0.1 g / cm. 3 After the roll press, a 10 mm long portion was peeled off from the top end of the negative electrode active material-coated portion, and the portion was dried in a vacuum at 120°C for 5 hours. After drying, a nickel tab was spot-welded to any location within the region where the negative electrode active material was peeled off, to obtain a negative electrode.

[0062] <<Lithium secondary battery>> Positive electrode, negative electrode, and electrolyte (a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1:1) containing 1 mol / dm LiPF6 3 A lithium secondary battery consisting of a single-layer laminate cell was fabricated using 0.2±0.05 mL of a solution of 1% by mass of ethylenediaminetetraacetic acid and vinylene carbonate (and 1% by mass of vinylene carbonate dissolved therein) and a separator (product name: ceramic coated wet separator for lithium ion secondary batteries SH716E14, manufactured by Shenzhen Senior Technology Material). <Storage characteristics> The storage characteristics of the prepared single-layer laminate cell were measured under the following conditions: The measurements were carried out by a cycle test using a charge-discharge device (BTS2004W, manufactured by Nagano Corporation).

[0063] <<1 cycle>> Measurement mode: Constant current / constant voltage charge-constant current discharge Voltage range: 4.2V-3.0V Current value: 4±1mA Measurement temperature: 24℃ <<2 to 100 cycles>> Measurement mode: Constant current / constant voltage charge-constant current discharge Voltage range: 4.2V-3.0V Current value: 0.2C (2, 10, 20, 50, and 100 cycles) 1C (cycles other than those mentioned above) Measurement temperature: 60℃ The constant voltage charge was terminated when the charging current decreased to 1 / 20 of that during constant current charge. A current value of 1 C corresponds to the discharge capacity of a lithium secondary battery when charged and discharged for 1 hour at a current value of 20±4 mA.

[0064] From the results of the cycle test, the value calculated using the following formula was taken as the storage property (%).

[0065] (Storage characteristics (%)) = (Discharge capacity at 100th cycle (mAh / g)) / (1st cycle discharge capacity (mAh / g)) x 100 Synthesis Example 1 A 2.0 mol / L aqueous manganese sulfate solution was added to 7.3 L of pure water at 80° C. while stirring and bubbling with air.

[0066] Air bubbling was performed at a feed rate of 0.5 L / min, and the manganese sulfate aqueous solution was added at a feed rate of 12 g / min (0.565 L / h), and the sodium hydroxide aqueous solution was added at a feed rate of 7 g / min (0.347 L / h). The manganese sulfate aqueous solution was terminated when 16 L of the manganese sulfate aqueous solution had been added. The addition was performed so that the pH of the reaction slurry was 7.5±0.5. If the pH was outside the 7.5±0.5 range, the pH was adjusted by adding 20% ​​by mass of sodium hydroxide aqueous solution as needed.

[0067] The reaction was carried out continuously, i.e., by simultaneously adding raw materials, reacting, and discharging the product, and the raw material addition rate and the product discharge rate were adjusted appropriately so that the residence time of the added manganese sulfate aqueous solution (reaction liquid volume [L] / raw material addition rate [L / h], where the raw material addition rate is the sum of the addition rates of the manganese sulfate aqueous solution and the sodium hydroxide aqueous solution) was 8 hours. The resulting reaction slurry was filtered and dried in the air at 110°C for 15 hours to obtain Mn3O4 powder.

[0068] 100 g of the obtained Mn3O4, 28.62 g of lithium carbonate, 5.155 g of aluminum hydroxide, 0.451 g of boric acid, and zirconia balls with a diameter of 10 mm as grinding media were placed in a wide-mouth bottle and dry-ground and mixed at 250 rpm for 60 minutes to obtain a mixed powder.

[0069] The resulting mixed powder was filled into an alumina sagger and fired under the following firing conditions.

[0070] Firing atmosphere: Air flow atmosphere (flow rate: 8 L / min) Firing temperature: 930℃ Baking time: 6 hours Heating rate: 100°C / hour After firing, the temperature was lowered to 700°C at a rate of 20°C / hour, and then annealed by maintaining that temperature for 24 hours. After annealing, the temperature was lowered from 700°C to room temperature (25°C) at a rate of 100°C / hour, and the fired powder was recovered and crushed using a hammer crusher to obtain crushed powder.

[0071] The crushed powder was dispersed in pure water to form a slurry, which was then filtered and dried in air at 120°C for 20 hours to obtain a dry powder. The dried powder was crushed in a rotary crusher, then subjected to a vibrating sieve treatment using a sieve with 32 μm openings for 5 minutes, and the powder that fell through the sieve was collected and used as the powder of this synthesis example.

[0072] The powder in this synthesis example has an average secondary particle diameter of 16.0 μm and a BET specific surface area of ​​0.38 m 2 The solubility in water of 10.1% by mass was 1.02 g / g and the pH was 10.1. The XRD pattern was the same as that of JCPDS card No. 35-782 (LiMn2O4).

[0073] In addition, as a result of composition analysis, the general formula of the LMO powder in this synthesis example is Li 1.09 Mn 1.81 Al 0.10 It was O4.

[0074] Synthesis Example 2 A mixed slurry was obtained by mixing 1533 g of electrolytic manganese dioxide, 363 g of lithium carbonate, 69 g of aluminum hydroxide, 5.76 g of boric acid, 3.06 g of trilithium phosphate, and 7893 g of pure water. The mixed slurry was subjected to a pulverization and mixing process for 3 hours using a pulverizer (Dyno Mill, manufactured by Shinmaru Enterprises). The obtained precursor slurry was spray-dried under the following conditions to recover a dry powder.

[0075] Spray pressure: 0.3MPa Feeding rate: 8230g / hour Inlet temperature: 200℃ Outlet temperature: 120℃ The obtained dry powder was placed in an alumina sagger and fired under the following firing conditions.

[0076] Firing atmosphere: Air flow atmosphere (flow rate: 5 L / min) Firing temperature: 900℃ Baking time: 6 hours Heating rate: 100°C / hour After firing, the temperature was decreased to 600°C at a rate of 20°C / hour and annealed at that temperature for 24 hours. After annealing, the temperature was decreased from 600°C to room temperature (25°C) at a rate of 100°C / hour, and the powder was recovered and crushed using a hammer crusher.

[0077] 100 g of the crushed powder was mixed with 300 g of pure water and stirred for 1 hour to form a slurry, which was then filtered and dried in an air atmosphere at 120°C for 20 hours. After that, the mixture was crushed in a rotary crusher, and then subjected to a vibrating sieve treatment using a sieve with 40 μm openings for 5 minutes. The powder that fell through the sieve was collected and used as the powder of this synthesis.

[0078] The powder in this synthesis example has an average secondary particle diameter of 14.8 μm and a BET specific surface area of ​​0.60 m 2 / g and pH 10.1, and its X-ray diffraction pattern was equivalent to that of JCPDS Card No. 35-782 (LiMn2O4).

[0079] In addition, as a result of composition analysis, the general formula of the LMO powder in this synthesis example is Li 1.07 Mn 1.83 Al 0.10 It was O4.

[0080] Synthesis Example 3 (Ferrocyanide Source Powder 1) 25 g of sodium hexacyanoferrate(II) decahydrate (Na4[Fe(CN)6]·10H2O, Fujifilm Wako Pure Chemical Industries, Ltd.) and 10 mm diameter YTZ balls as grinding media were placed in a wide-mouth bottle and crushed at 250 rpm for 10 minutes to obtain ferrocyanide source powder 1.

[0081] The average secondary particle diameter of the ferrocyanide source powder 1 was 3.4 μm.

[0082] Synthesis Example 4 (Ferrocyanide Source Powder 2) An aqueous solution of K4[Fe(CN)6] was prepared by mixing 12 g of potassium hexacyanoferrate(II) trihydrate (K4[Fe(CN)6] 3H2O, Fujifilm Wako Pure Chemical Industries, Ltd.) and 50 mL of pure water. On the other hand, an aqueous solution of LiClO4 was prepared by mixing 12.09 g of LiClO4 (product name: LiClO4, 98.0%+, Fujifilm Wako Pure Chemical Industries, Ltd.) and 30 mL of pure water.

[0083] The resulting K4[Fe(CN)6] aqueous solution and LiClO4 aqueous solution were mixed and stirred at 600 rpm for 1 hour to obtain a slurry.

[0084] The resulting slurry was filtered, and the filtrate was recovered and allowed to stand at 10°C for 20 hours. The precipitate formed upon standing was removed by filtration, and the filtrate was recovered. The filtrate was heated to 100°C and concentrated until the liquid volume was 50 mL. After concentration, the filtrate was cooled again to 10°C and allowed to stand for 20 hours. After standing, the precipitate formed was further filtered, and the filtrate was recovered. The filtrate was heated to 100°C and further concentrated until the liquid volume was 20 mL, and then cooled again to 10°C and allowed to stand for 20 hours. After standing, the white precipitate formed was further filtered, and the filtrate was recovered. The filtrate was dried at 180°C to obtain a dry powder.

[0085] The obtained dry powder was crushed in a mortar and then further crushed for 20 seconds in a small crusher (trade name: Coffee Grinder, manufactured by Russell Hobbs) to obtain ferrocyanide source powder 2.

[0086] The average secondary particle size of the ferrocyanide source powder was 6.6 μm.

[0087] Example 1 The LMO powder of Synthesis Example 1 and ferrocyanide source powder 1 were weighed out to a total of 15 g, with a mass ratio of LMO powder of Synthesis Example 1:ferrocyanide source powder 1 of 98:2, and mixed in an agate mortar at room temperature. Next, a vibrating sieve treatment was carried out for 5 minutes using a sieve with 40 μm openings, and the powder that fell through the sieve was collected to obtain the ferrocyanide-containing LMO of this example.

[0088] The ferrocyanide-containing LMO of this example has an average secondary particle diameter of 16.1 μm and a BET specific surface area of ​​0.37 m 2 / g and pH was 10.3.

[0089] The ferrocyanide ion content in the ferrocyanide-containing LMO of this example was 0.4 mass %.

[0090] The storage characteristics of the obtained ferrocyanide-containing LMO were measured using it as a positive electrode active material.

[0091] Example 2 The ferrocyanide-containing LMO of this example was obtained in the same manner as in Example 1, except that the LMO powder of Synthesis Example 1:ferrocyanide source powder 1 were weighed out so as to achieve a mass ratio of 96:4.

[0092] The ferrocyanide-containing LMO of this example has an average secondary particle diameter of 14.8 μm and a BET specific surface area of ​​0.47 m 2 / g and pH was 10.4.

[0093] The ferrocyanide ion content in the ferrocyanide-containing LMO of this example was 1.4 mass %.

[0094] The storage characteristics of the obtained ferrocyanide-containing LMO were measured using it as a positive electrode active material.

[0095] Example 3 The ferrocyanide-containing LMO of this example was obtained in the same manner as in Example 1, except that the LMO powder of Synthesis Example 1 and the ferrocyanide source powder were weighed out to a mass ratio of 1:94:6.

[0096] The ferrocyanide-containing LMO positive powder of this example has an average secondary particle diameter of 14.3 μm and a BET specific surface area of ​​0.52 m 2 / g and pH was 10.4.

[0097] The ferrocyanide ion content in the ferrocyanide-containing LMO of this example was 2.0 mass %.

[0098] The storage characteristics of the obtained ferrocyanide-containing LMO were measured using it as a positive electrode active material.

[0099] Example 4 0.3 g of the ferrocyanide source powder 1 and 10 g of pure water were mixed and subjected to ultrasonic irradiation for 1 minute to obtain a ferrocyanide source slurry.

[0100] To the resulting ferrocyanide source slurry, 14.7 g of the LMO powder of Synthesis Example 1 was added, and the mixture was stirred at 170 rpm for 10 minutes to obtain a mixed slurry. The mixed slurry was dried overnight at 120°C in an air atmosphere, then crushed in a mortar and subjected to a vibrating sieve treatment using a 40 μm mesh sieve for 5 minutes, and the powder remaining under the sieve was collected to obtain the ferrocyanide-containing LMO of this example.

[0101] The ferrocyanide-containing LMO of this example has an average secondary particle diameter of 15.1 μm and a BET specific surface area of ​​0.45 m 2 / g and pH was 10.4.

[0102] The ferrocyanide ion content in the ferrocyanide-containing LMO of this example was 0.9 mass %.

[0103] The storage characteristics of the obtained ferrocyanide-containing LMO were measured using it as a positive electrode active material.

[0104] Example 5 A total of 10 g of the LMO powder of Synthesis Example 2 and the ferrocyanide source powder 2 were weighed out so that the mass ratio of the LMO powder of Synthesis Example 2: the ferrocyanide source powder 2 was 98:2, and the mixture was crushed for 5 minutes using a small crusher. After crushing, the mixture was subjected to a vibrating sieve treatment using a sieve with 40 μm openings for 5 minutes to obtain the positive electrode active material of this example.

[0105] The ferrocyanide-containing LMO of this example has an average secondary particle diameter of 16.3 μm and a BET specific surface area of ​​0.75 m 2 / g and pH was 10.4.

[0106] The ferrocyanide ion content in the ferrocyanide-containing LMO of this example was 1.5 mass %. The storage characteristics of the obtained ferrocyanide-containing LMO were measured using it as a positive electrode active material.

[0107] Example 6 0.2 g of the ferrocyanide source powder 2 and 10 g of pure water were mixed, and then ultrasonic waves were irradiated for 1 minute to obtain an aqueous ferrocyanide source solution.

[0108] To the obtained aqueous ferrocyanide source solution, 9.8 g of the LMO powder of Synthesis Example 2 was added, and the mixture was stirred at a stirring speed of 170 rpm for 10 minutes to obtain a mixed slurry.

[0109] The mixed slurry was dried in the air at 120°C for 15 hours, then crushed in a small grinder for 5 minutes and subjected to a vibrating sieve treatment using a sieve with 40µm openings for 5 minutes to obtain the ferrocyanide-containing LMO of this example.

[0110] The ferrocyanide-containing LMO of this example has an average secondary particle diameter of 16.0 μm and a BET specific surface area of ​​0.87 m 2 / g and pH was 10.3.

[0111] The ferrocyanide ion content in the ferrocyanide-containing LMO of this example was 1.7 mass %.

[0112] The storage characteristics of the obtained ferrocyanide-containing LMO were measured using it as a positive electrode active material.

[0113] Comparative Example 1 The powder of Synthesis Example 1 was used as the positive electrode active material of this comparative example, and the storage characteristics were measured.

[0114] Comparative Example 2 The powder of Synthesis Example 2 was used as the positive electrode active material of this comparative example, and the storage characteristics were measured.

[0115] Comparative Example 3 The storage characteristics were measured in the same manner as in Comparative Example 2, except that 0.038 g of Na4[Fe3(CN)6]·10H2O was added to the electrolyte.

[0116] The battery performance of LIBs using the positive electrode active materials of the examples and comparative examples is shown in the table below.

[0117] [Table 1] From Table 1, it was confirmed that the use of LMO containing ferrocyanide as a positive electrode active material improved the storage characteristics of LIBs using this positive electrode active material at high temperatures, regardless of the amount of ferrocyanide, the method of incorporation, or the cation species of the ferrocyanide.

[0118] It was also confirmed that the inclusion of ferrocyanide in LMO improved the storage characteristics of the LIB compared to when ferrocyanide was added to the electrolyte.< / ph>

Claims

1. Spinel-type lithium manganese oxide containing ferrocyanide.

2. 2. The lithium manganese spinel of claim 1, wherein the ferrocyanide is an alkali metal salt containing a ferrocyanide ion.

3. The alkali metal salt is at least one of a lithium salt and a sodium salt.

4. The spinel-type lithium manganese oxide according to claim 1.

5. The spinel-type lithium manganate according to claim 1 or 2, wherein the content of the ferrocyanide is 0.05% by mass or more and 20% by mass or less.

6. BET specific surface area is 0.1m ２ / g or more 1.5m ２ The spinel-type lithium manganese oxide according to claim 1 or 2, wherein the SiO 2 content is 1 / g or less.

7. 3. The spinel-type lithium manganese oxide according to claim 1, wherein the JIS pH measured according to JIS K1467 5.9.2 (water method) is 9.0 or more and 12.0 or less.

8. 3. The spinel-type lithium manganese oxide according to claim 1, which is in the form of a powder.

9. 3. The spinel-type lithium manganese oxide according to claim 1, wherein the average secondary particle diameter is 0.1 μm or more and 25 μm or less.

10. A positive electrode active material comprising the spinel-type lithium manganese oxide according to claim 1 or 2.

11. A lithium secondary battery comprising the positive electrode active material according to claim 9.

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