Lithium spinel-type manganese oxide, its manufacturing method, and its uses

Abstract

To provide a spinel-type lithium manganate and a lithium-ion secondary battery having excellent charge / discharge characteristics, especially at high temperatures.SOLUTION: There is provided a spinel-type lithium manganate containing a phosphorus compound and having the following chemical formula: Li1+XMn2-X-YMYO4 (in which, 0.02≤X≤0.20, 0.05≤Y≤0.30, and M is Al or Mg). The BET specific surface area of the phosphorus compound is 10 m2 / g or more and 80 m2 / g or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to spinel-type lithium manganate, a method for producing the same, and its applications, and more specifically, to spinel-type lithium manganate containing a phosphorus compound, a method for producing the same, and lithium-ion secondary batteries. [Background technology]

[0002] Due to their high energy density, lithium-ion rechargeable batteries are widely used as batteries in small electronic devices such as mobile phones. Recently, their application to large-scale applications requiring high capacity and high output, such as stationary and automotive batteries, is progressing, and further performance improvements are expected.

[0003] Currently, for lithium-ion secondary batteries, cobalt-based materials (LiCoO2) are mainly used as the positive electrode material for consumer small batteries such as those in mobile phones, while nickel-based materials (LiNi) are used for stationary and automotive applications. 0.8 Co 0.15 Al 0.05 O2) and nickel-cobalt-manganese ternary materials (LiNi 0.5 Co 0.2 Mn 0.3 O2, etc., is the main material used. However, cobalt and nickel raw materials are scarce and expensive, making it difficult to secure large quantities, and their power output characteristics are not very high.

[0004] On the other hand, spinel-type lithium manganese oxide, a manganese-based material, is readily available in large quantities because its raw material, manganese, is inexpensive and abundant, and it is also highly safe, making it a suitable material for large batteries.

[0005] However, spinel-type lithium manganese oxide has problems with high-temperature stability, that is, with battery characteristics at high temperatures, particularly storage characteristics and charge / discharge characteristics, and solutions to this problem have been considered. For example, Patent Documents 1 and 2 both propose spinel-type lithium manganese oxide containing phosphate, but there is still room for improvement in battery characteristics at high temperatures.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present disclosure is to provide at least one of spinel - type lithium manganate and a method for producing the same, which are excellent in battery characteristics at high temperatures, particularly storage characteristics and charge - discharge characteristics, when used as an electrode of a secondary battery. Furthermore, an electrode using the spinel - type lithium manganate or a lithium - ion secondary battery is provided.

Means for Solving the Problems

[0008] That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows. (1) Spinel - type lithium manganate containing a phosphorus compound and represented by the chemical formula Li 1+X Mn 2-X-Y M Y O4 (where 0.02 ≤ X ≤ 0.20, 0.05 ≤ Y ≤ 0.30, and M is Al or Mg), wherein the BET specific surface area of the phosphorus compound is 10 m 2 / g or more and 80 m 2 / g or less. [[ID=四十]] (2) The spinel - type lithium manganate according to (1), wherein the content of the phosphorus compound is 0.1% by mass or more and 10% by mass or less. (3) The spinel - type lithium manganate according to (1) or (2), wherein the BET specific surface area is 0.2 m 2 / g or more and 1.5 m 2 / g or less. (4) A spinel-type lithium manganate according to any one of (1) to (3), wherein the average particle diameter of the secondary particles is 4.0 μm or more and 20.0 μm or less. (5) A spinel-type lithium manganate according to any one of (1) to (4), wherein the SO4 content is 0.8% by mass or less. (6) A spinel-type lithium manganate according to any one of (1) to (5), wherein the Na content is 3000 ppm by mass or less. (7) A method for producing spinel-type lithium manganate according to any one of (1) to (6), comprising: a firing step of firing a composition comprising a manganese source, a lithium source, and a metal source comprising at least one of aluminum and magnesium at 750°C to 970°C to obtain a fired product; and a phosphorus compound-containing step of containing the phosphorus compound in the fired product. (8) An electrode containing spinel-type lithium manganate as described in any of (1) to (6). (9) A lithium-ion secondary battery including the electrodes described in (8). [Effects of the Invention]

[0009] According to this disclosure, it becomes possible to provide at least one of the spinel-type lithium manganese oxide and a method for producing the same, which exhibits excellent battery characteristics at high temperatures, particularly storage characteristics and charge / discharge characteristics, when used as an electrode for a secondary battery. Furthermore, it becomes possible to provide an electrode using the spinel-type lithium manganese oxide or a lithium-ion secondary battery. [Brief explanation of the drawing]

[0010] [Figure 1] This is a TEM-EDX image of the particle cross-section of spinel-type lithium manganate obtained in Example 1. [Figure 2] This is the XRD pattern of the particle cross-section of spinel-type lithium manganate obtained in Example 1. [Figure 3] This is the XRD pattern of the particle cross-section of spinel-type lithium manganate obtained in Comparative Example 1. [Modes for carrying out the invention]

[0011] This disclosure will be described in detail with reference to one embodiment, but this disclosure is not limited to the following embodiment.

[0012] The spinel-type lithium manganate of this embodiment has a phosphorus compound on its surface. The phosphorus compound is not particularly limited as long as it provides the effects of the present invention, but it is preferably an inorganic compound, and more preferably a phosphate, such as lithium phosphates such as Li3PO4 and LiPO3, and Na3PO 4、 Examples include sodium phosphates such as NaH2PO4 and Na2HPO4, and potassium phosphates such as K3PO4, KH2PO4, and K2HPO4. Preferably, Li3PO4 and LiPO3, and more preferably Li3PO4. Hereinafter, phosphorus compounds will be referred to as phosphates in this specification. When a phosphate is included in spinel-type lithium manganate, it exhibits excellent battery performance when used as a positive electrode active material for lithium-ion secondary batteries, and in particular, excellent storage characteristics and charge / discharge characteristics can be obtained at high temperatures. There are no particular restrictions on the properties of the contained phosphate, and examples include crystalline, crystalline and porous, crystalline and dense, amorphous, amorphous and porous, and amorphous and dense, but are not limited to these.

[0013] The spinel-type lithium manganate of this embodiment has the chemical formula Li 1+X Mn 2-X-Y M YIt is represented by O4 (wherein the formula 0.02 ≤ X ≤ 0.20, 0.05 ≤ Y ≤ 0.30, and M is Al or Mg). If the value of X is less than 0.02, a decrease in capacity occurs during storage and charging / discharging at high temperatures, and if it exceeds 0.20, sufficient charging / discharging capacity cannot be obtained. Similarly, if the value of Y is less than 0.05, a decrease in capacity occurs during storage and charging / discharging at high temperatures, and if it exceeds 0.30, sufficient charging / discharging capacity cannot be obtained. X and Y can be determined by compositional analysis of spinel-type lithium manganate. Examples of compositional analysis methods include inductively coupled plasma emission spectrometry (hereinafter also referred to as "ICP") and atomic absorption spectrometry.

[0014] The phosphate contained in the spinel-type lithium manganate of this embodiment has a BET specific surface area of ​​10 m². 2 / g or more 80m 2 The amount is less than / g. This allows the reaction in which hydrogen fluoride contained in the electrolyte is captured by the phosphate to proceed rapidly when used as a positive electrode active material in lithium-ion secondary batteries. As a result, manganese leaching caused by the reaction between hydrogen fluoride and spinel-type lithium manganate is suppressed, and excellent storage and charge / discharge characteristics are obtained at high temperatures. The BET specific surface area of ​​the phosphate is 10 m². 2 Because the amount is less than / g, the reaction in which hydrogen fluoride is captured by phosphate does not proceed quickly, and 80m 2 When the value exceeds / g, the electrode density decreases when the spinel-type lithium manganate of this embodiment is used as the positive electrode. The BET specific surface area of ​​the phosphate is 10m². 2 / g or more 50m 2 It is preferable that the amount be less than or equal to / g, and 10m 2 / g or more 30m 2 It is more preferable that the amount is less than or equal to / g. The BET specific surface area of ​​phosphate can be determined by the nitrogen gas adsorption method (BET method).

[0015] In this embodiment, the phosphate content of the spinel-type lithium manganate is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.2% by mass or more and 6% by mass or less. This increases the charge and discharge capacity when the spinel-type lithium manganate of this embodiment is used as the positive electrode active material of a lithium-ion secondary battery. In this embodiment, the phosphate content is the ratio (mass%) of the mass of element P contained in the spinel-type lithium manganate, converted to Li3PO4, relative to the mass of the spinel-type lithium manganate. That is, the phosphate content can be determined by multiplying the concentration (mass%) of element P obtained by ICP measurement by Li3PO4 / P (atomic ratio) and converting it to Li3PO4.

[0016] The phosphate contained in the spinel-type lithium manganate of this embodiment is preferably porous. The porous nature of the phosphate allows for more rapid capture of hydrogen fluoride contained in the electrolyte when used as a positive electrode active material in a lithium-ion secondary battery. As a result, manganese elution due to the reaction between hydrogen fluoride and spinel-type lithium manganate is further suppressed, resulting in excellent storage and charge-discharge cycle characteristics at high temperatures. The porous nature of the phosphate can be determined by cross-sectional TEM-EDX measurement of spinel-type lithium manganate particles.

[0017] The BET specific surface area of ​​the spinel-type lithium manganate in this embodiment is 0.2 m². 2 / g or more 1.5m 2 It is preferable that it be less than or equal to / g, and 0.2m 2 / g or more 1.0m 2 It is more preferable that it be less than or equal to / g, and 0.3m 2 / g or more 0.8m 2 It is even more preferable that the amount is less than or equal to / g. This makes it possible to obtain better storage and charge / discharge characteristics at high temperatures when used as a positive electrode active material for lithium-ion secondary batteries.

[0018] In this embodiment, the average particle size of the secondary particles of the spinel-type lithium manganate is preferably 4.0 μm or more and 20.0 μm or less, and more preferably 5.0 μm or more and 15.0 μm or less. This makes it possible to obtain better output characteristics and to improve the packing efficiency of the positive electrode mixture when used as a positive electrode active material in a lithium-ion secondary battery, as the lithium diffusion distance within the spinel-type lithium manganate particles becomes smaller.

[0019] Here, "secondary particles" refer to particles formed when primary particles of LMO powder aggregate and sinter, while "primary particles" refer to independent crystalline particles. In this embodiment, the average particle size of the secondary particles is measured by a particle size distribution analyzer (for example, MicrotracBEL MT3000II). 50 The average particle size of secondary particles is measured by laser diffraction and scattering.

[0020] In this embodiment, the SO4 content of the spinel-type lithium manganese oxide is preferably 0.8% by mass or less, and more preferably 0.5% by mass or less. This increases the charge-discharge capacity when used as a positive electrode active material for lithium-ion secondary batteries, and also provides better storage and charge-discharge characteristics at high temperatures. Examples of SO4 content include 0.01% by mass or more, or 0.02% by mass or more. The SO4 content (by mass) is the ratio (by mass) of the amount of sulfur (S) contained in the spinel-type lithium manganese oxide converted to SO4, relative to the total mass of the spinel-type lithium manganese oxide. That is, the SO4 content can be determined by multiplying the concentration of sulfur (S) obtained by ICP measurement (by mass) by SO4 / S (atomic ratio) to convert it to SO4.

[0021] The state of SO4 contained is not limited; for example, it can be at least one of sulfate ions and a compound containing an SO4 group, specifically Li2SO4, Na2SO4, etc.

[0022] The sodium content of the spinel-type lithium manganate in this embodiment is preferably 3000 ppm by mass or less, more preferably 1500 ppm by mass or less, and even more preferably 1000 ppm by mass or less. This increases the charge-discharge capacity when used as a positive electrode active material in lithium-ion secondary batteries, and also provides better storage and charge-discharge characteristics at high temperatures. Examples of sodium content include 10 ppm by mass or more, or 20 ppm by mass or more. The sodium content can be determined by ICP measurement.

[0023] The state of the contained Na is not limited, and examples include at least one selected from the group consisting of Na metal, Na-containing compounds, and Na ions. Specifically, Na2SO4 is one example.

[0024] The boron content of the spinel-type lithium manganate in this embodiment is preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less, and even more preferably 300 ppm by mass or less. This increases the charge-discharge capacity when used as a positive electrode active material for lithium-ion secondary batteries, and also provides better storage and charge-discharge characteristics at high temperatures. The boron content does not need to be 0 ppm by mass or more; in other words, it does not need to be present in the spinel-type lithium manganate in this embodiment. The boron content can be determined by ICP measurement.

[0025] The state of boron contained is not limited, and examples include at least one selected from the group consisting of boron metal, boron-containing compounds, and boron ions. Specifically, B2O3, Li2B4O7, etc., can be given as examples.

[0026] Next, the method for producing spinel-type lithium manganate according to this embodiment will be described.

[0027] The spinel-type lithium manganate of this embodiment can be produced by a manufacturing method comprising: a mixing step of mixing a manganese source, a lithium source, and a metal M source containing at least one of aluminum and magnesium to obtain a mixture; a firing step of firing the mixture at 750°C to 970°C to obtain a fired product; and a phosphorus compound-containing step of containing a phosphorus compound in the fired product.

[0028] In the mixing step, a mixture is obtained by mixing at least a manganese source, a lithium source, and a metal M source containing at least one of aluminum and magnesium. The mixing method can be either wet mixing or dry mixing, as long as the manganese source, lithium source, and metal M source are uniformly mixed. Wet mixing is preferred because it yields a more uniform mixed powder.

[0029] The source of manganese is not particularly limited and can include, for example, MnO2, Mn3O4, Mn2O3, as well as organic salts such as manganese acetate.

[0030] The lithium source is not particularly limited and can be any lithium salt such as lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium iodide, or lithium oxalate.

[0031] The metal source M includes at least one of a magnesium source and an aluminum source.

[0032] Examples of magnesium sources include at least one of magnesium hydroxide, magnesium oxide, or magnesium carbonate.

[0033] Examples of aluminum sources include at least one of aluminum hydroxide, aluminum oxyhydroxide, or aluminum oxide.

[0034] The mixture may contain binders, conductive additives, and other additives as needed. For example, it is preferable to mix in a boron compound as a flux. This can reduce the BET specific surface area of ​​the spinel-type lithium manganate in this embodiment. The boron compound is not particularly limited and examples include H3BO3, B2O3, Li2O·nB2O3 (n=1~5), etc.

[0035] The firing process involves firing the mixture obtained in the mixing process to obtain a fired product. The firing temperature is between 750°C and 970°C. A firing temperature below 750°C increases the BET specific surface area of ​​the spinel-type lithium manganate. As a result, when used as a positive electrode active material in lithium-ion secondary batteries, manganese leaching is more likely to occur, leading to a decrease in storage characteristics and charge / discharge characteristics. A firing temperature above 970°C increases the oxygen deficiency of the spinel-type lithium manganate. As a result, when used as a positive electrode active material in lithium-ion secondary batteries, storage characteristics and charge / discharge characteristics tend to decrease. Furthermore, it is preferable to perform the firing at a temperature between 800°C and 950°C. The firing time is preferably between 3 hours and 12 hours to reduce manufacturing costs.

[0036] The firing atmosphere is not particularly limited, but it is preferable to carry it out in air or in a high-concentration oxygen atmosphere (including a pure oxygen atmosphere), that is, in an oxygen atmosphere with an oxygen content of 18 vol% or more and 100 vol% or less.

[0037] The phosphorus compound-containing step is a step in which a phosphorus compound is incorporated into the calcined product obtained in the calcination step. Hereinafter, in this specification, the phosphorus compound-containing step will be referred to as the phosphate-containing step. There are no particular limitations on the method for incorporating phosphate into the calcined product, but one example is a crystallization method in which a solution of a lithium compound and a solution of a phosphorus compound are added and mixed, followed by filtration and drying.

[0038] There are no particular restrictions on the lithium compound as long as it is water-soluble. Examples include lithium hydroxide, lithium carbonate, lithium nitrate, lithium chloride, lithium iodide, and lithium oxalate.

[0039] There are no particular restrictions on the phosphorus compound as long as it is water-soluble. Examples include lithium phosphates such as Li3PO4 and LiPO3, sodium phosphates such as Na3PO4, NaH2PO4, and Na2HPO4, potassium phosphates such as K3PO4, KH2PO4, and K2HPO4, magnesium phosphates such as Mg3(PO4)2, MgHPO4, and Mg(H2PO4)2, and ammonium phosphoric acid such as NH4H2PO4 and (NH4)2HPO4.

[0040] Methods for adding a lithium compound solution and a phosphate compound solution to spinel-type lithium manganate include adding the lithium compound solution to the spinel-type lithium manganate and then adding the phosphate compound solution, and preparing a slurry of spinel-type lithium manganate and then simultaneously adding the lithium compound solution and the phosphate compound solution. When adding the lithium compound solution and the phosphate compound solution to spinel-type lithium manganate, it is preferable to maintain a pH of 7 or higher in the solution to suppress the detachment of lithium from the spinel-type lithium manganate.

[0041] Examples of solutions to which lithium compounds and phosphate compounds are added include pure water and water.

[0042] Since spinel-type lithium manganate tends to solidify with other secondary particles during calcination, it is preferable to crush it to obtain the desired particle size. For crushing, shearing force is preferred to further suppress the generation of fine powder.

[0043] It is preferable to pass the spinel-type lithium manganate through a sieve to remove coarse particles that exceed the thickness of the positive electrode. The sieve opening is preferably 200 μm or less, and more preferably 150 μm or less.

[0044] By using the lithium manganese phosphate containing phosphate of the present embodiment as the positive electrode of a lithium ion secondary battery, it becomes possible to construct a lithium ion secondary battery having storage characteristics and charge-discharge characteristics at high temperatures, which could not be obtained conventionally.

[0045] As the configuration of the lithium ion secondary battery other than the positive electrode, there is no particular limitation. For the negative electrode, materials that occlude and release Li, such as carbon-based materials, tin oxide-based materials, Li4Ti5O 12 , SiO, materials that form an alloy with Li, etc. can be mentioned. Examples of the material that forms an alloy with Li include silicon-based materials and aluminum-based materials. Examples of the electrolyte include an organic electrolyte solution in which a Li salt and various additives are dissolved in an organic solvent, a solid electrolyte having Li ion conductivity, and a combination thereof.

Example

[0046] Next, the present disclosure will be described with specific examples, but the present disclosure should not be construed as being limited to these examples.

[0047] <Composition analysis> The composition, phosphate content, SO4 content, Na content, and boron content of the spinel-type lithium manganate obtained in the examples and comparative examples were analyzed with an inductively coupled plasma optical emission spectrometer (trade name: ICP-AES, manufactured by PerkinElmer Japan) after dissolving the spinel-type lithium manganate in a sulfuric acid-hydrogen peroxide mixed aqueous solution or a hydrochloric acid-hydrogen peroxide mixed aqueous solution.

[0048] <Identification of crystal phase by XRD> The identification of the crystal phase of the spinel-type lithium manganate obtained in the examples and comparative examples was performed by powder XRD measurement (trade name: Ultima IV, manufactured by Rigaku). The measurement conditions were as follows.

[0049] · Target: Cu · Output: 1.6 kW (40 mA - 40 kV) · Filter: Kβ filter • Divergent slit: 1° • Divergence vertical limiting slit: 10mm • Scattering slit: Open • Light-receiving slit; open • Scanning mode: Continuous • Scan speed: 4,000° / min • Sampling width: 0.04° (2θ / θ) • Number of times accumulated: 1 • Measurement range: 10-90° (2θ / θ) <Measurement of BET specific surface area of ​​phosphates and spinel-type lithium manganate> 1.5 g of spinel-type lithium manganate obtained in the examples and comparative examples was placed in a glass cell for BET specific surface area measurement and dehydrated under a nitrogen stream at 150°C for 30 minutes to remove moisture adhering to the powder particles. The BET specific surface area of ​​the treated sample was measured using a single-point method with a BET measuring device (product name: MICROMERITICS DeSorbIII, manufactured by Shimadzu Corporation) using a mixed gas of 30% nitrogen and 70% helium as the adsorption gas.

[0050] Furthermore, the BET specific surface area of ​​spinel-type lithium manganate, which does not contain phosphate (i.e., after the calcination process and immediately before the phosphate-containing process), was measured in advance, and the BET specific surface area of ​​phosphate (Li3PO4) was calculated based on the following formula.

[0051] BET specific surface area of ​​Li3PO4 [m²] 2 [g] = ((BET specific surface area of ​​Li3PO4-containing spinel-type lithium manganate [m²] 2 [g]-(BET specific surface area of ​​spinel-type lithium manganate that does not contain Li3PO4 [m²] 2 / g])) / (Li3PO4 content (mass%) / 100) <Measurement of cross-sectional TEM-EDX> Cross-sectional TEM-EDX measurements were performed on spinel-type lithium manganate particles using a field emission transmission electron microscope (product name: JEM-2100F, manufactured by JEOL) and an energy-dispersive X-ray spectrometer (product name: JED-2300T, manufactured by JEOL). Prior to the measurements, the samples were cut using a beam cutter.

[0052] <Measurement of secondary particle size> Using a particle size distribution analyzer (product name: MT3000II series, manufactured by MicrotracBEL), the average particle size (D) of secondary particles of spinel-type lithium manganese oxide was determined. 50 ) was measured.

[0053] <Battery Performance Evaluation> For the positive electrode, 4.7 g of spinel-type lithium manganate obtained in the examples and comparative examples, 0.15 g of acetylene black (product name: Denka Black Li-400, manufactured by Denka), 1.434 mL of 10% by mass polyvinylidene fluoride / N-methyl-2-pyrrolidone solution (0.15 g of polyvinylidene fluoride) (weight ratio: lithium spinel-type lithium manganate: acetylene black: polyvinylidene fluoride = 94:3:3), and 1.23 mL of N-methyl-2-pyrrolidone were mixed in a rotary-orbit mixer (product name: AR-310, manufactured by Shinki) to prepare a positive electrode slurry. The resulting positive electrode slurry was applied to aluminum foil, dried at 120°C for 10 minutes, punched out into a rectangle measuring 60 mm in length and 30 mm in width, and roll-pressed. The coated positive electrode mixture was peeled off the aluminum foil using N-methyl-2-pyrrolidone to a size of 50 mm vertically and 30 mm horizontally. An aluminum tab was welded to the peeled area, and it was vacuum-dried at 150°C for 5 hours before use. The coating amount was 15 mg / cm² of spinel-type lithium manganate. 2 This was done so that the positive electrode mixture density was 2.4 g / cm³. 3 That's what I decided.

[0054] For the negative electrode, 4.0 g of artificial graphite, 2.008 mL of a 10% polyvinylidene fluoride / N-methyl-2-pyrrolidone solution (0.210 g of polyvinylidene fluoride) (weight ratio of graphite:polyvinylidene fluoride = 95:5), and 3.160 mL of N-methyl-2-pyrrolidone were mixed in a rotation-orbit mixer (product name: AR-310, manufactured by Sinky) to prepare a negative electrode slurry. The resulting negative electrode slurry was applied to copper foil, dried at 120°C for 10 minutes, punched out into a rectangle measuring 62 mm in length and 32 mm in width, and roll-pressed. The applied negative electrode slurry was peeled from the copper foil using N-methyl-2-pyrrolidone to a size of 52 mm in length and 32 mm in width. Nickel tabs were welded to the peeled portion, and after vacuum drying at 150°C for 5 hours, it was used. The application amount of artificial graphite was 5.5 mg / cm². 2 This was done so that the density of the negative electrode mixture was 1.3 g / cm³. 3 That's what I decided.

[0055] The above-mentioned positive and negative electrodes are combined with a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1:2) and LiPF6 at a concentration of 1 mol / dm³. 3 Laminate cells were fabricated using 0.24 mL of dissolved electrolyte and a separator punched into a rectangle measuring 65 mm vertically and 35 mm horizontally (product name: ceramic coated wet separator SH716E14, manufactured by Shenzhen Senior Technology Material). For battery evaluation, the laminate cell was sandwiched between two acrylic plates and tightened with a torque pressure of 1 N / m using four screws that penetrated the acrylic plates.

[0056] Furthermore, a CR2032 type coin cell was fabricated using a separator (product name: Cellguard, manufactured by Polypore) with the above positive electrode punched out to 15.96 mmφ and the Li metal punched out to 16 mmφ as the negative electrode.

[0057] Using the fabricated CR2032 coin cell, a constant current charge-discharge cycle was performed at 24°C with a current of 0.6mA between cell voltages of 4.3V and 3.0V, and the charged capacity was defined as the initial capacity.

[0058] Next, aging was performed using the fabricated laminate cells. The aging process involved charging the cells at 24°C with a constant current until they reached 10% of their initial capacity, followed by a 9-hour pause. Then, they were charged again with a constant current until they reached 60% of their initial capacity, followed by a 24-hour pause. After that, they were charged with a constant current and voltage until the cell voltage reached 4.2V, and then discharged with a constant current until it reached 3.0V. The current during charging and discharging was set at a rate of 0.1C relative to the initial capacity, and the termination condition for constant voltage charging was when the charging current decreased to a rate of 0.005C.

[0059] After the aging process was complete, the cell capacity was checked. At 24°C, with the cell voltage between 4.2V and 3.0V, one cycle of constant current / constant voltage charging and constant current discharging was performed, and the discharge capacity was defined as the cell capacity. The charging and discharging currents were set at a rate of 0.2C relative to the initial capacity, and the termination condition for constant voltage charging was when the charging current decreased to a rate of 0.01C.

[0060] After confirming the cell capacity, storage tests and charge-discharge cycle tests were performed.

[0061] The storage test involved charging the fabricated laminate cells to 4.2V at 24°C, then storing them at 60°C for 7 days. Next, the cells were discharged to 3.0V, and then a constant current / constant voltage charging-constant current discharging cycle was performed between 4.2V and 3.0V. The discharge capacity was defined as the recovery capacity, and the ratio of the recovery capacity to the cell capacity was defined as the storage capacity recovery rate. The charging and discharging currents were set at a time rate of 0.2C relative to the cell capacity, and the termination condition for constant voltage charging was when the charging current decreased to a time rate of 0.01C.

[0062] The charge-discharge cycle test involved performing 50 cycles of constant-current / constant-voltage charging and constant-current discharging on the fabricated laminate cells at 45°C with cell voltages of 4.2V and 3.0V. The charge-discharge cycle retention rate was defined as the ratio of the capacity at cycle 50 to the capacity at cycle 1. The charging and discharging currents were set at a rate of 0.5C relative to the cell capacity, and the termination condition for constant-voltage charging was defined as when the charging current decreased to a rate of 0.025C.

[0063] Example 1 A mixture was obtained by mixing 80.00 g of electrolytic manganese dioxide with an average particle size of 12.0 μm, 18.80 g of Li2CO3 with an average particle size of 3 μm, 1.56 g of Mg(OH)2 (manufactured by Wako Pure Chemical Industries, average particle size of 0.07 μm), and 0.24 g of H3BO3 (manufactured by Kishida Chemical Co., Ltd.) that had been ground in an agate mortar. This mixture was calcined in a box furnace at 930°C for 6 hours while circulating air at a rate of 5 L / min, then heat-treated at 600°C for 24 hours, and cooled to room temperature to obtain spinel-type lithium manganate. The heating rate to 930°C was 100°C / hr, the cooling rate from 930°C to 600°C was 20°C / hr, and the cooling rate from 600°C to room temperature was 100°C / hr. The obtained spinel-type lithium manganate was crushed using a powerful, compact crusher (product name: Rotary Crusher, manufactured by Osaka Chemical).

[0064] Next, 72.0 g of the obtained spinel-type lithium manganate was mixed with 72 mL of pure water and 18 mL of a 2.0 mol / L LiOH (Kishida Chemical Co., Ltd.) aqueous solution. At room temperature, while stirring at 600 rpm, 10 mL of a 26% by mass H3PO4 (Kishida Chemical Co., Ltd.) aqueous solution was added at a rate of 0.056 mL / min. After that, the mixture was filtered and dried, and coarse particles were removed by passing it through a sieve with a mesh size of 32 μm to obtain the spinel-type lithium manganate of this example.

[0065] From the ICP measurement results, the composition of the obtained spinel-type lithium manganate is the stoichiometric composition Li 1+X Mn 2-X-Y M Y Assuming we take O4, Li 1.08 Mn 1.86 Mg 0.06 The result was O4. The measurement results for phosphate content, BET specific surface area of ​​phosphate, average particle size of spinel-type lithium manganate secondary particles, SO4 content, Na content, and boron content (hereinafter also simply referred to as "measurement results") are shown in Table 1, and the battery performance evaluation results are shown in Table 2.

[0066] [Table 1]

[0067] [Table 2]

[0068] Furthermore, TEM-EDX images of the cross-section of spinel-type lithium manganate particles are shown in Figure 1. Figure 1(A) shows the mapping results for element P, and Figure 1(B) shows the mapping results for element Mn. It was confirmed that phosphate (Li3PO4) is present on the surface of the spinel-type lithium manganate particles. In addition, XRD measurements detected two peak patterns from spinel-type lithium manganate: JCPDS No. 35-782 (LiMn2O4, peak positions: 2θ=18.6°, 30.7°, 36.1°, 37.8°, 43.9°, 48.1°, 58.1°, 63.8°, 67.1°, 75.6°, 76.6°) and No. 25-1030 (Li3PO4, peak positions: 2θ=16.9°, 22.4°, 23.4°, 25.0°, 29.2°, 33.9°). Figure 2 shows the XRD peak pattern of Example 1.

[0069] Example 2 Lithium spinel-type manganese oxide was obtained in the same manner as in Example 1, except that the concentration of the LiOH aqueous solution was 1.0 mol / L and the concentration of the H3PO4 aqueous solution was 13% by mass.

[0070] The composition of the obtained spinel-type lithium manganate is Li 1.08 Mn 1.86 Mg 0.06 The result was O4. The measurement results are shown in Table 1, and the battery performance is shown in Table 2. In addition, from the XRD measurement, two peak patterns were detected in the obtained spinel-type lithium manganate: JCPDS No. 35-782 (LiMn2O4) and No. 25-1030 (Li3PO4).

[0071] Example 3 Lithium spinel-type manganese oxide was obtained using the same method as in Example 1, except that the concentration of the LiOH aqueous solution was 0.50 mol / L and the concentration of the H3PO4 aqueous solution was 6.5% by mass.

[0072] The composition of the obtained spinel-type lithium manganate is Li 1.08 Mn 1.86 Mg 0.06 The result was O4. The measurement results are shown in Table 1, and the battery performance is shown in Table 2. In addition, from the XRD measurement, two peak patterns were detected in the obtained spinel-type lithium manganate: JCPDS No. 35-782 (LiMn2O4) and No. 25-1030 (Li3PO4).

[0073] Comparative Example 1 A mixture was obtained by mixing 75.00g of Mn3O4 with an average particle size of 4.0 μm, 21.48g of Li2CO3 with an average particle size of 3 μm, 1.70g of Mg(OH)2 (manufactured by Wako Pure Chemical Industries, average particle size of 0.07 μm), and 0.60g of H3BO3 (manufactured by Kishida Chemical Co., Ltd.) that had been ground in an agate mortar. This mixture was calcined in a box furnace at 850°C for 6 hours while air was flowed through it at a rate of 5 L / min, then calcined at 600°C for 24 hours, and cooled to room temperature to obtain spinel-type lithium manganese oxide. The heating rate from room temperature to 850°C was 100°C / hr, the cooling rate from 850°C to 600°C was 20°C / hr, and the cooling rate from 600°C to room temperature was 100°C / hr. The obtained spinel-type lithium manganate was crushed using a powerful, compact crusher (product name: Rotary Crusher, manufactured by Osaka Chemical).

[0074] Next, Li3PO4 film was deposited onto the obtained spinel-type lithium manganese oxide using a powder barrel sputtering apparatus manufactured by Toyoshima Seisakusho. A Li3PO4 sintered body was used as the target, the power supply was RF, the output during film deposition was 2kW, the deposition time was 8 hours, and the gas used was 100% Ar.

[0075] The composition of the obtained spinel-type lithium manganate is Li 1.09 Mn 1.85 Mg 0.06 The result was O4. The measurement results are shown in Table 1, and the battery performance is shown in Table 2. In addition, from the XRD measurement, two peak patterns were detected in the obtained spinel-type lithium manganate: JCPDS No. 35-782 (LiMn2O4) and No. 25-1030 (Li3PO4).

[0076] Comparative Example 2 A mixture was obtained by dissolving 100.0 g of electrolytic manganese dioxide with an average particle size of 12 μm, 23.7 g of lithium carbonate with an average particle size of 3 μm, 4.3 g of aluminum hydroxide with an average particle size of 3 μm, 0.9 g of trilithium phosphate (manufactured by Wako Pure Chemical Industries), and 1.8 g of H3BO3 (manufactured by Wako Pure Chemical Industries) in 98.2 g of pure water to make a 1.8 mass% aqueous solution, and then mixing 0.11 g of this solution. This mixture was calcined in a box-type furnace at 800°C for 20 hours while circulating air at a rate of 5 L / min, and then cooled to room temperature to obtain spinel-type lithium manganese oxide. Both the heating rate and cooling rate were set to 100°C / hr. Next, the mixture was crushed using a powerful small-scale pulverizer (product name: rotary crusher, manufactured by Osaka Chemical Co., Ltd.) and passed through a sieve with a mesh size of 32 μm to obtain spinel-type lithium manganese oxide.

[0077] The composition of the obtained spinel-type lithium manganate is Li 1.07 Mn 1.84 Al 0.09 The result was O4. The measurement results are shown in Table 1, and the battery performance is shown in Table 2. In addition, from the XRD measurement, two peak patterns were detected in the obtained spinel-type lithium manganate: JCPDS No. 35-782 (LiMn2O4) and No. 25-1030 (Li3PO4).

[0078] Comparative Example 3 Lithium spinel-type lithium manganate was obtained using the same method as in Example 1, except that LiOH and H3PO4 were not added to the spinel-type lithium manganate.

[0079] The composition of the obtained spinel-type lithium manganate is Li 1.08 Mn 1.86 Mg 0.06 The result was O4. The measurement results are shown in Table 1, and the battery performance is shown in Table 2. Furthermore, from the XRD measurement, the obtained spinel-type lithium manganate was JCPDS No. 35-782 (LiMn2O4) single phase. Figure 3 shows the XRD peak pattern of Comparative Example 3. In Table 1, the column for phosphate BET specific surface area is shown as "-", indicating that it was not measured because it did not contain phosphate (Li3PO4). [Industrial applicability]

[0080] The spinel-type lithium manganate of this embodiment has a uniquely large BET specific surface area due to its phosphate content, and can therefore be used as a positive electrode active material for lithium-ion secondary batteries that exhibits excellent battery performance at high temperatures, particularly in terms of storage characteristics and charge / discharge characteristics. [Explanation of symbols]

[0081] 1… Spinel-type lithium manganate 2…Lithium phosphate (Li3PO4)

Claims

1. A phosphorus compound that is a phosphate salt, wherein the content of the phosphorus compound is 0.1% by mass or more and 10% by mass or less, the chemical formula Li １＋Ｘ Mn ２－Ｘ－Ｙ M Ｙ O ４ A spinel-type lithium manganate represented by the formula (wherein 0.02 ≤ X ≤ 0.20, 0.05 ≤ Y ≤ 0.30, and M is Al or Mg), The BET specific surface area of ​​the phosphorus compound obtained by the following formula (1) is 10 m². ２ / g or more 80m ２ Lithium spinel-type manganese oxide with a concentration of less than / g. The BET specific surface area of ​​phosphorus compounds [m² / g] = (BET specific surface area of ​​spinel-type lithium manganate containing phosphorus compounds [m² / g] - BET specific surface area of ​​spinel-type lithium manganate not containing phosphorus compounds [m² / g]) / (Phosphorus compound content [mass%] / 100) (1)

2. BET specific surface area is 0.2 m² ２ / g or more 1.5m ２ The spinel-type lithium manganate according to claim 1, wherein the amount is less than or equal to / g.

3. The spinel-type lithium manganate according to claim 1 or 2, wherein the average particle diameter of the secondary particles is 4.0 μm or more and 20.0 μm or less.

4. SO ４ The spinel-type lithium manganate according to any one of claims 1 to 3, wherein the content of

5. The spinel-type lithium manganate according to any one of claims 1 to 4, wherein the Na content is 3000 ppm by mass or less.

6. A method for producing spinel-type lithium manganate according to any one of claims 1 to 5, comprising: a firing step of firing a composition comprising a manganese source, a lithium source, and a metal source comprising at least one of aluminum and magnesium at 750°C to 970°C to obtain a fired product; and a phosphorus compound-containing step of containing a phosphorus compound in the fired product.

7. A positive electrode active material comprising spinel-type lithium manganate according to any one of claims 1 to 5.

8. An electrode comprising the positive electrode active material according to claim 7.

9. A lithium-ion secondary battery comprising the electrode described in claim 8.

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