JP7831005B2 - Lithium spinel-type manganese oxide, its manufacturing method, and its uses - Google Patents

Description

This disclosure relates to spinel-type lithium manganese oxide, a method for producing the same, and its applications; more specifically, to spinel-type lithium manganese oxide containing a phosphorus compound, a method for producing the same, and lithium-ion secondary batteries.

Lithium-ion rechargeable batteries are widely used in small electronic devices such as mobile phones due to their high energy density. Recently, their application is progressing to larger, high-capacity, and high-output applications, such as stationary and automotive batteries, and further performance improvements are expected.

Currently, for lithium-ion secondary batteries, cobalt-based materials ( _LiCoO₂ ) are mainly used as cathode materials in consumer batteries such as those for mobile phones, while nickel-based materials ( _{LiNi₀.8Co₀.15Al₀.05O₂ )} or _nickel - _cobalt -manganese ternary materials ( _{LiNi₀.5Co₀.2Mn₀.3O₂ , etc.} ) are mainly used for stationary and automotive applications. 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.

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. Furthermore, its superior safety features make it a suitable material for large batteries.

However, spinel-type lithium manganese oxide has problems with high-temperature stability, specifically with its battery characteristics at high temperatures, particularly its storage and charge/discharge properties. Solutions to this problem have been under consideration. For example, Patent Documents 1 and 2 both propose spinel-type lithium manganese oxide containing phosphate, but these still leave room for improvement in high-temperature battery characteristics.

Patent No. 5556983 Japanese Patent Publication No. 2017-31006

The purpose of this disclosure is 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 in a secondary battery. Furthermore, the aim is to provide an electrode using the spinel-type lithium manganese oxide, or a lithium-ion secondary battery.

In other words, the present invention is as claimed, and the gist of this disclosure is as follows.
(1) A spinel-type lithium manganate containing a phosphorus compound and represented by the chemical formula Li _{1 + X} Mn _2-X-Y M _Y O ₄ (wherein 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 ^m² /g or more and 80 ^m² /g or less.
(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 described in (1) or (2), wherein the BET specific surface area is 0.2 ^m² /g or more and 1.5 ^m² /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 making the fired product contain the phosphorus compound.
(8) An electrode containing spinel-type lithium manganate as described in any of (1) to (6).
(9) A lithium-ion secondary battery containing the electrodes described in (8).

According to this disclosure, it becomes possible to provide at least one of the following: a 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 in a secondary battery. Furthermore, it becomes possible to provide an electrode using the spinel-type lithium manganese oxide, or a lithium-ion secondary battery.

This is a TEM-EDX image of a particle cross-section of spinel-type lithium manganate obtained in Example 1. This is the XRD pattern of the particle cross-section of spinel-type lithium manganate obtained in Example 1. This is the XRD pattern of the particle cross-section of spinel-type lithium manganate obtained in Comparative Example 1.

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

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 can achieve the effects of the present invention, but it is preferably an inorganic compound, and more preferably a phosphate salt. Examples include lithium phosphates such as _{Li3PO4 and LiPO3} , sodium phosphates such as _{Na3PO4 , NaH2PO4} , _{and Na2HPO4 , and} potassium phosphates such as _K3PO4 , _KH2PO4 , and _{K2HPO4 .} Preferably _{Li3PO4 and LiPO3} , and more preferably _Li3PO4 . Hereinafter, the phosphorus compound will be described as a _phosphate salt. When a phosphate salt 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, it is possible to obtain excellent storage characteristics and charge/discharge characteristics at high temperatures. There are no particular restrictions on the properties of the phosphate contained, and examples include crystalline, crystalline and porous, crystalline and dense, amorphous, amorphous and porous, and amorphous and dense, but are not limited to these.

The spinel-type lithium manganate of this embodiment is represented by the chemical formula Li₁ _{+X₂Mn₂ -X- Y₁Y₂Y₂O₄} (wherein 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 the 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.

The phosphate contained in the spinel-type lithium manganate of this embodiment has a BET specific surface area of 10 ^m² /g or more and 80 ^m² /g or less. 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 a lithium-ion secondary battery. As a result, manganese elution 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. If the BET specific surface area of the phosphate is less than 10 ^m² /g, the reaction in which hydrogen fluoride is captured by the phosphate does not proceed rapidly, and if it exceeds 80 ^m² /g, the electrode density decreases when the spinel-type lithium manganate of this embodiment is used as the positive electrode. Preferably, the BET specific surface area of the phosphate is 10 ^m² /g or more and 50 ^m² /g or less, and more preferably 10 ^m² /g or more and 30 ^m² /g or less. The BET specific surface area of phosphates can be determined using the nitrogen gas adsorption method (BET method).

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 weight ratio) and converting _{it to Li₃PO₄} .

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 caused by 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 the spinel-type lithium manganate particles.

The BET specific surface area of the spinel-type lithium manganate in this embodiment is preferably 0.2 ^m² /g or more and 1.5 ^m² /g or less, more preferably 0.2 ^m² /g or more and 1.0 ^m² /g or less, and even more preferably 0.3 ^m² /g or more and 0.8 ^m² /g or less. This makes it possible to obtain better storage characteristics and charge/discharge characteristics at high temperatures when used as a positive electrode active material in lithium-ion secondary batteries.

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 allows for a smaller lithium diffusion distance within the spinel-type lithium manganate particles when used as a positive electrode active material in a lithium-ion secondary battery, resulting in superior output characteristics and improved packing efficiency of the positive electrode mixture.

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

In this embodiment, the _SO₄ content of the spinel-type lithium manganate 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. _{The SO₄} content can be exemplified as 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 manganate, converted to _SO₄ , relative to the mass of the spinel-type lithium manganate. 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 .

The state of _the contained _SO₄ is not limited, and examples include at least one of sulfate ions and compounds containing an _SO₄ group, specifically _Li₂SO₄ , _Na₂SO₄ , _etc.

The sodium (Na) 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 allows for a larger charge-discharge capacity when used as a positive electrode active material in lithium-ion secondary batteries, and enables superior 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.

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.

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 allows for a larger charge-discharge capacity when used as a positive electrode active material in lithium-ion secondary batteries, and enables superior 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 of this embodiment. The boron content can be determined by ICP measurement.

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, examples include _{B₂O₃ and Li₂B₄O ₷ .}

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

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 calcination step of calcining the mixture at 750°C to 970°C to obtain a calcined product; and a phosphorus compound-containing step of incorporating a phosphorus compound into the calcined product.

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 or dry, 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.

The source of manganese is not particularly limited _and includes, for example, _MnO₂ , _Mn₃O₄ , _{Mn₂O₃ ,} as well as organic salts such as manganese acetate.

The lithium source is not particularly limited; examples include lithium salts such as lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium iodide, and lithium oxalate.

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

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

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

The mixture may optionally contain a binder, a conductive additive, and other additives. 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 to ₅ ) _, etc.

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 and charge/discharge characteristics. A firing temperature exceeding 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 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 and 12 hours to reduce manufacturing costs.

The firing atmosphere is not particularly limited, but it is preferable to perform the firing in air or a high-concentration oxygen atmosphere (including a pure oxygen atmosphere), i.e., in an oxygen atmosphere with an oxygen content of 18 vol% or more and 100 vol% or less.

The phosphorus compound incorporation 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 incorporation step will be referred to as the phosphate incorporation step. The method for incorporating phosphate into the calcined product is not particularly limited, but for example, a crystallization method can be used, in which a solution of a lithium compound and a solution of a phosphorus compound are added and mixed, followed by filtration and drying.

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.

There are no particular restrictions on phosphorus compounds as long as _they are 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 .}

Methods for adding solutions of lithium compounds and phosphate compounds to spinel-type lithium manganese include adding the lithium compound solution to the spinel-type lithium manganese and then adding the phosphate compound solution, and simultaneously adding the lithium compound solution and phosphate compound solution after preparing a slurry of spinel-type lithium manganese. When adding the lithium compound solution and phosphate compound solution to spinel-type lithium manganese, 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 manganese.

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

Since spinel-type lithium manganate tends to solidify 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.

It is preferable to pass the spinel-type lithium manganese oxide through a sieve to remove coarse particles exceeding the thickness of the positive electrode. The sieve opening is preferably 200 μm or less, and more preferably 150 μm or less.

By using the phosphate-containing spinel-type lithium manganese oxide of this embodiment as the positive electrode of a lithium-ion secondary battery, it becomes possible to construct a lithium-ion secondary battery with superior storage characteristics and charge/discharge characteristics at high temperatures, which were not achievable with conventional methods.

There are no particular restrictions on the composition of lithium-ion secondary batteries other than the positive electrode, but the negative electrode can be made of a material that intercepts and deintercepts Li, such as carbon-based materials, tin oxide-based materials, _{Li₄Ti₅O₁₂} , _SiO₂ , _or materials that form alloys with Li. Examples of materials that form alloys with Li include silicon-based materials and aluminum-based materials. Examples of electrolytes include organic electrolytes obtained by dissolving Li salts and various additives in an organic solvent, solid electrolytes that conduct Li ions, or combinations thereof.

Next, the present disclosure will be described with specific embodiments, but the present disclosure is not intended to be limited to these embodiments.

<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 using a dielectric-coupled plasma atomic emission spectrometer (product 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.

<Identification of crystalline phases by XRD>
The crystalline phases of spinel-type lithium manganate obtained in the examples and comparative examples were identified by powder XRD measurement (product name: Ultima IV, manufactured by Rigaku). The measurement conditions were as follows.

Target: Cu
Output: 1.6 kW (40 mA - 40 kV)
• Filter: Kβ filter • Divergence slit: 1°
- Divergence vertical limiting slit: 10 mm
• Scattering slit: Open • Receiving slit: Open • Scanning mode: Continuous • Scanning speed: 4,000°/min • Sampling width: 0.04° (2θ/θ)
• Number of cumulative measurements: 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.

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 the phosphate ( _Li3PO4 ) was calculated based on the _following formula.

The BET specific surface area _{of Li₃PO₄} [ ^m² /g] = ((BET specific surface area of _{Li₃PO₄ -} containing spinel-type lithium manganate [ ^m² /g]) - (BET specific surface area of _Li₃PO₄ -free spinel-type lithium _manganate [ ^m² /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.

<Measurement of secondary particle size>
The average particle size ( _D50 ) of secondary particles of spinel-type lithium manganate was measured using a particle size distribution analyzer (product name: MT3000II series, manufactured by MicrotracBEL).

<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 rotation-orbit mixer (product name: AR-310, manufactured by Thinky) to prepare a positive electrode slurry. The obtained 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 from 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 portion, and the mixture was vacuum-dried at 150°C for 5 hours before use. The coating amount was set so that the amount of spinel-type lithium manganate was 15 mg/ ^cm² . The density of the positive electrode mixture was 2.4 g/ ^cm³ .

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 obtained 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 vacuum-dried at 150°C for 5 hours before use. The coating amount was set to 5.5 mg/ ^cm² of artificial graphite. The density of the negative electrode mixture was set to 1.3 g/ ^cm³ .

A laminate cell was fabricated using the above-mentioned positive and negative electrodes, 0.24 mL of an electrolyte solution prepared by dissolving 1 mol/ ^dm³ of _LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1:2), and a separator punched out in 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.

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

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

Next, aging was performed using the fabricated laminated 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. Finally, 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 charging and discharging currents were 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.

After the aging process was complete, cell capacity was checked. The cell capacity was checked at 24°C, with the cell voltage between 4.2V and 3.0V. A constant current/constant voltage charging-constant current discharge cycle 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. The termination condition for constant voltage charging was when the charging current decreased to a rate of 0.01C.

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

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, followed by one cycle of constant-current/constant-voltage charging and discharging 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.

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 the point when the charging current decreased to a rate of 0.025C.

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.), which had been ground in an agate mortar, in a mortar. This mixture was calcined in a box-type 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 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).

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 (manufactured by Kishida Chemical Co., Ltd.) aqueous solution. At room temperature, while stirring at 600 rpm, 10 mL of a 26% by _{mass H₃PO₄} (manufactured by 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.

Based on the ICP measurement results, the composition of the obtained spinel-type lithium manganate was assumed to be the stoichiometric composition Li _{1 + X} Mn _2-X-Y M _Y O ₄ , with Li _1.08 Mn _1.86 Mg _0.06 O _4. The measurement results for phosphate content, BET specific surface area of phosphate, average particle size of spinel-type lithium manganate secondary particles, SO ₄ content, Na content, and boron content (hereinafter simply referred to as "measurement results") are shown in Table 1, and the battery performance evaluation results are shown in Table 2.

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 revealed that spinel-type lithium manganate was identified as 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. Two peak patterns were detected: _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.

Example 2
Lithium spinel-type manganate 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.

The composition of the obtained spinel-type lithium manganate was Li _1.08 Mn _1.86 Mg _0.06 O _4. 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 (LiMn ₂ O ₄ ) and No. 25-1030 (Li ₃ PO ₄ ).

Example 3
Lithium spinel-type manganate was obtained in the same manner 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.

The composition of the obtained spinel-type lithium manganate was Li _1.08 Mn _1.86 Mg _0.06 O _4. 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 (LiMn ₂ O ₄ ) and No. 25-1030 (Li ₃ PO ₄ ).

Comparative Example 1 A mixture was obtained by mixing 75.00 _g of _Mn₃O₄ with an average particle size of 4.0 μm, 21.48 g _{of Li₂CO₃} with an average particle size of 3 μm, 1.70 g of Mg(OH) _₂ (manufactured by Wako Pure Chemical Industries, average particle size of 0.07 μm), and 0.60 g _{of H₃BO₃} (manufactured by Kishida Chemical) 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 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 manganate. 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 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).

Next, _Li3PO4 was deposited onto the obtained spinel-type lithium manganate 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 deposition was 2 kW, the deposition time was 8 hours, _and the gas used was 100% Ar.

The composition of the obtained spinel-type lithium manganate was Li _1.09, Mn _1.85 , Mg _0.06 , O _4. 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 (LiMn ₂ O ₄ ) and No. 25-1030 (Li ₃ PO ₄ ).

Comparative Example 2
A mixture was obtained by mixing 0.11 _g of a 1.8% by mass aqueous solution prepared 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. 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 manganate. 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 manganate.

The composition of the obtained spinel-type lithium manganate was Li _1.07 Mn _1.84 Al _0.09 O _4. 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 (LiMn ₂ O ₄ ) and No. 25-1030 (Li ₃ PO ₄ ).

Comparative Example 3
Lithium spinel-type lithium manganate was obtained in the same manner as in Example 1, except that LiOH and _H₃PO₄ were not added to _the spinel-type lithium manganate.

The composition of the obtained spinel-type lithium manganate was Li _1.08 Mn _1.86 Mg _0.06 O _4. 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 (LiMn ₂ O ₄ ) 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 (Li ₃ PO ₄ ).

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

1. Spinel _- type lithium manganate 2. Lithium phosphate ( _Li₃PO₄ )

Claims (9)

A spinel-type lithium manganate represented by the chemical formula Li _1+X Mn _2-X-Y M _Y O ₄ (wherein 0.02 ≤ X ≤ 0.20, 0.05 ≤ Y ≤ 0.30, and M is Al or Mg), which contains a phosphorus compound that is a phosphate salt, and the content of the phosphorus compound is 0.1% by mass or more and 10% by mass or less,
A spinel-type lithium manganate obtained by the following formula (1), wherein the BET specific surface area of the phosphorus compound is 10 ^m² /g or more and 80 ^m² /g or less.
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)
The spinel-type lithium manganate according to claim 1, wherein the BET specific surface area is 0.2 ^m² /g or more and 1.5 ^m² /g or less. 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. The spinel-type lithium manganate according to any one of claims 1 to 3 , wherein the _SO₄ content is 0.8% by mass or less. 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. 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. A positive electrode active material comprising spinel-type lithium manganate according to any one of claims 1 to 5 . An electrode comprising the positive electrode active material according to claim 7. A lithium-ion secondary battery comprising the electrode described in claim 8.