JP2011251862A - Manganese oxide and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manganese oxide for obtaining lithium manganate which provides excellent charge-discharge cycle characteristic of a secondary battery, and a method for producing the same.SOLUTION: The method for producing the manganese oxide includes: subjecting electrolytic manganese dioxide to reduction treatment followed by neutralizing with ammonia. The the manganese dioxide is preferably reduced so that the manganese valence is 2.7 or more and 3.7 or less. The manganese oxide preferably has a manganese valence of 2.7 or more and 3.7 or less, and has one or more crystal phases selected from the group consisting of manganite (MnOOH), γ-MnOand hausmannite (MnO).

Description

  The present invention relates to a manganese oxide used as a manganese raw material of a lithium-manganese composite oxide used for a positive electrode active material such as a lithium secondary battery, and a method for producing the same.

  At present, spinel-structure lithium manganate mainly containing manganese is widely studied as a positive electrode active material of a lithium ion secondary battery (LIB) (Non-patent Document 1), and various manganese oxides are used as raw materials. (Cited references 1-4).

  Among manganese oxides, electrolytic manganese dioxide is mainly used because it is possible to obtain dense and high energy density lithium manganate and is suitable for resources, safety, and mass production. Usually, electrolytic manganese dioxide is obtained by electrolytic deposition from a manganese sulfate bath and grinding it.

  Therefore, electrolytic manganese dioxide has a very high concentration of impurities, particularly sulfate radical (Patent Document 1), and furthermore, since the particle size distribution is wide, lithium manganate obtained using this as a raw material has a low capacity retention rate. Studies have been made to improve this and to make electrolytic manganese dioxide a manganese raw material suitable for lithium manganate.

For example, a method for producing electrolytic manganese dioxide in which electrolytic conditions such as a high current density of 100 A / m ² or more, addition of phosphoric acid, and use of manganese chloride are controlled has been studied (Patent Document 5). However, since the packing density of electrolytic manganese dioxide obtained under such electrolysis conditions decreases, lithium manganate obtained using this as a raw material also has a low packing density and an extremely low energy density.

  On the other hand, a method of treating electrolytic manganese dioxide after electrolytic deposition with a pH-controlled acid is disclosed (Patent Document 6). However, such treatment hardly improved the physical properties of electrolytic manganese dioxide, and the lithium manganate obtained using this as a raw material did not have a sufficient capacity retention rate.

  Patent Documents 7 and 8 disclose a method in which electrolytic manganese dioxide is mixed with a lithium compound using a manganese oxide obtained by heat treatment. However, although these manganese oxides have a reduced sulfate group concentration, the lithium manganate obtained using this as a raw material still has a low capacity retention rate.

  Further, a manganese oxide having a degree of peroxidation of 1.50 to 1.90 obtained by neutralizing electrolytic manganese dioxide reduced with hydrazine with a lithium salt is disclosed (Patent Document 9). However, the capacity retention rate of lithium manganate obtained using this as a raw material was not sufficient.

  Thus, there has been no manganese oxide from which lithium manganate having a sufficient capacity retention rate has been obtained so far.

Japanese Patent Laid-Open No. 06-150914 JP 2000-281347 A U.S. Pat. No. 2,956,860 JP 2004-292264 A Japanese Patent Laid-Open No. 05-21063 Japanese Patent Laid-Open No. 10-294099 Japanese Patent Laid-Open No. 11-157841 JP2008-156162 Japanese Patent Laid-Open No. 03-233869

M.M. M.M. Thuckeray et al. , J. et al. Electrochem. Soc. , 139, 363 (1992)

  Provided is a manganese oxide suitable as a raw material for lithium manganate excellent in charge / discharge cycle characteristics used as a positive electrode active material of a secondary battery.

  As a result of intensive studies on manganese oxide used as a raw material for lithium manganate, the present inventor has found that conventional electrolytic manganese dioxide and manganese oxide obtained by treating this have reduced sulfate radical concentration. Because of this, there is a physical property change such as an extreme decrease in specific surface area accompanying this, and a physical property such as a wide particle size distribution, so that the crystallinity of lithium manganate obtained using this as a raw material is lowered, and the charge / discharge cycle characteristics are Found it to be lower. Furthermore, the present inventor reduced the electrolytic manganese dioxide to a specific state and then neutralized it with ammonia, thereby solving these problems and obtaining manganese suitable for obtaining lithium manganate having excellent charge / discharge cycle characteristics. As a result, the present invention was completed.

  Hereinafter, the production method of the present invention will be described.

  The method for producing manganese oxide of the present invention uses electrolytic manganese dioxide as a raw material. Thereby, a manganese oxide with high density is obtained.

The raw material electrolytic manganese dioxide preferably has a BET specific surface area of 30 m ² / g or more, more preferably 35 m ² / g or more, and still more preferably 40 m ² / g or more. When the BET specific surface area is 30 m ² / g or more, the effects of reduction treatment and neutralization treatment with ammonia are easily obtained. On the other hand, the larger the BET specific surface area, the easier the removal of sulfate radicals, but 60 m ² / g or less, preferably 50 m ² / g or less is sufficient.

The raw material electrolytic manganese dioxide preferably has a sulfate radical content of 0.8% or more and 3.0% or less, and preferably 0.8% or more and 2.5% or less, in terms of the SO ₄ / Mn molar ratio. . By making the SO ₄ / Mn molar ratio of electrolytic manganese dioxide within this range, reduction treatment and neutralization treatment with ammonia are easily performed efficiently.

The SO ₄ / Mn molar ratio of electrolytic manganese dioxide can be determined by the following formula.

SO ₄ / Mn molar ratio (%) = (M _{SO 4} / M _Mn ) × 100
M _SO4 : SO ₄ (mol) in electrolytic manganese dioxide
M _Mn : Mn (mol) in electrolytic manganese dioxide

  The raw material electrolytic manganese dioxide preferably has a manganese valence of 3.9 to 4.0. If the manganese valence is 3.9 or more, the sulfate radical removal effect by the reduction treatment is increased.

  The average particle diameter of electrolytic manganese dioxide is preferably about the same as that of the target manganese oxide. For example, the average particle diameter is 1 μm or more and 35 μm or less, preferably 5 μm or more and 25 μm or less.

As the electrolytic manganese dioxide satisfying the above properties, for example, in a manganese sulfate bath electrolysis in which the weight ratio of Mn ²⁺ / H ₂ SO ₄ in the electrolytic solution is 1.0 or more and 4.0 or less, the current density is 0.6 A / dm ^2. beyond 1.1A / dm ² or less, preferably include those crushed electrolytic manganese dioxide obtained in electrolysis conditions of 0.8 a / dm ² or more 0.9 a / dm ² or less of the current density, and washed it can.

The weight ratio of Mn ²⁺ / H ₂ SO ₄ in the electrolytic solution is a value determined by the following formula.

_{C Mn = (C 'F-} Mn /0.90-C' H2SO4) × 54.94
C _H2SO4 = C ′ _H2SO4 × 98.02
Mn ²⁺ / _H 2 SO ₄ weight ratio _{= C Mn /} C _H2SO4
here,
C ′ _F—Mn : Mn concentration in replenisher (mol / L)
C _Mn : Mn concentration in electrolyte (g / L)
C ′ _Mn : Mn concentration in the electrolyte (mol / L)
C _H2SO4 : H ₂ SO ₄ concentration in the electrolyte (g / L)
C _{'H2SO4: H} 2 SO ₄ concentration in the electrolyte (mol / L)
The coefficient 54.94 is the mass number (g / mol) of electrolytic manganese dioxide (MnO ₂ ), and 98.02 is the mass number (g / mol) of sulfuric acid (H ₂ SO ₄ ).

  In this case, the sulfuric acid concentration in the electrolytic solution throughout the electrolysis period may be constant or may be changed.

  In the production method of the present invention, electrolytic manganese dioxide is reduced.

  The reduction treatment is preferably performed until the manganese valence becomes 2.7 to 3.7, more preferably 2.7 to 3.6, and more preferably 2.7 to 3.5. Is more preferable. By carrying out the reduction treatment until the manganese valence becomes 3.7 or less, the sulfate radicals can be sufficiently removed. On the other hand, a manganese oxide having a high density is easily obtained by reducing the manganese valence to 2.7 or more.

  Furthermore, when the raw material electrolytic manganese dioxide contains particles of 1 μm or less, these particles are dissolved and removed as the reduction treatment proceeds. Thereby, the particle size distribution of the manganese oxide after the reduction treatment tends to be more uniform. When the particles of 1 μm or less are dissolved, the BET specific surface area of the manganese oxide after the reduction treatment tends to be lower than that of the raw material electrolytic manganese dioxide, and the average particle diameter tends to be large.

  The reduction treatment is preferably performed using a reducing agent. As the reducing agent, those not containing metal ions are preferable, and hydrazine, formalin, hydrogen peroxide, oxalic acid compounds, and formic acid compounds are preferable, and hydrazine, formalin, and hydrogen peroxide are more preferable. Furthermore, hydrazine is particularly preferable because it has a high boiling point and can be used in a wide temperature range.

  The reducing agent is preferably used as an aqueous solution. By using an aqueous solution, the concentration of the reducing agent can be adjusted as appropriate.

The amount of the reducing agent used is preferably such that the manganese valence of the reduced manganese oxide falls within the above range. For example, when hydrazine (N ₂ H ₄ ) is used as the reducing agent, the electrolysis used N ₂ H ₄ may be 0.03 mol or more and 0.3 mol or less, preferably 0.06 mol or more and 0.3 mol or less, with respect to 1 mol of manganese dioxide (MnO ₂ ).

  The reduction treatment can be appropriately used such as a method of reducing by adding electrolytic manganese dioxide to an aqueous solution containing a reducing agent, an electrolytic manganese dioxide dispersion, and a method of reducing by dropping a reducing agent. It is preferable to reduce manganese by dispersing manganese in water and adding a reducing agent dropwise thereto. Thereby, dissolution of particles of 1 μm or less is easily promoted.

  In the reduction treatment, the reaction temperature is preferably 50 ° C. or higher and 90 ° C. or lower, more preferably 60 ° C. or higher and 90 ° C. or lower, and still more preferably 70 ° C. or higher and 90 ° C. or lower. When the reaction temperature is 50 ° C. or higher, the reduction reaction is easily promoted. On the other hand, if the reaction temperature is 90 ° C. or less, the reduction reaction is sufficiently easy to proceed.

  The time for the reduction treatment is not limited as long as the manganese valence is in the above range, and can be 1 hour or more and 5 hours or less.

  The pH of the reduction treatment varies depending on the reducing agent used, but 2 ≦ pH ≦ 9 is preferable. You may adjust pH by adding the alkali compound (ammonia etc.) which does not contain a metal ion as needed.

In the reduction treatment, electrolytic manganese dioxide having γ-MnO ₂ as the main crystal phase is reduced. Therefore, the crystal phase of the manganese oxide obtained gamma-MnO _2, manganite (MnOOH), hausmannite _(Mn 3 _{O 4)} easily has one or more kinds of, also of gamma-MnO ₂ than this It is easy to contain a reduced phase (γ-MnO _2-x ). More preferably, the manganese oxide after the reduction treatment contains manganite (MnOOH) and / or a reduced phase (γ-MnO _2-x ) of house mannite (Mn ₃ O ₄ ) and γ-MnO _2. More preferably, it contains a reduced phase (γ-MnO _2-x ) of knight (MnOOH) and γ-MnO ₂ . On the other hand, β-MnO ₂ and Mn ₂ O ₃ which are thermal decomposition products of γ-MnO ₂ are not generated.

  In the method of the present invention, the reduction treatment is followed by neutralization with ammonia.

  The reason why more efficient sulfate radical removal can be achieved by neutralization with ammonia after the reduction treatment is unknown, but the sulfate radical tends to be detached due to the change of particles due to the reduction treatment, and neutralization with ammonia. It is considered that the sulfate ions are more easily removed as compared with the case where neutralization treatment with ammonia is performed without performing the reduction treatment, because the counter ions (positively charged ions) existing in the treatment are easily affected. Therefore, in the production method of the present invention, it is important to neutralize the manganese oxide after the reduction treatment with ammonia.

  Manganese oxide obtained without neutralization with ammonia after reduction treatment, such as neutralized with strong alkali sodium hydroxide or potassium hydroxide, treated directly with aqueous lithium salt solution or mixed with lithium compound The effect of the present invention cannot be obtained if it is not subjected to neutralization treatment. The reason for this is not clear, but when these are fired, the crystallinity of the resulting lithium manganate may have decreased due to, for example, a side reaction of the lithium compound or a non-uniform reaction between lithium and manganese. Conceivable.

  The reduction treatment and the neutralization treatment with ammonia can be performed by either a batch method or a continuous method.

  In the production method of the present invention, it is preferable to wash and dry after the neutralization treatment with ammonia. Washing and drying are not particularly limited as long as the physical properties of the manganese oxide obtained by the reduction treatment and the neutralization treatment with ammonia are not significantly changed and impurities are not mixed, but the drying temperature is 100 ° C. Or less, more preferably 70 ° C. or more and 90 ° C. or less. If a drying temperature is 100 degrees C or less, it will be easy to dry, without impairing the characteristic of the manganese oxide of this invention.

  Next, the manganese oxide of the present invention will be described.

In the present invention, the manganese valence is 2.7 or more and 3.7 or less, and any one or more crystal phases selected from the group consisting of manganite (MnOOH), γ-MnO ₂ and house mannite (Mn ₃ O ₄ ) are used. It has manganese oxide.

  The manganese oxide of the present invention has a manganese valence of 2.7 to 3.7, preferably 2.7 to 3.6, and more preferably 2.7 to 3.5. preferable. The manganese valence of the manganese oxide of the present invention is within this range, which is different from manganese dioxide having a manganese valence of 3.9 to 4.0.

The manganese oxide of the present invention has one or more crystal phases selected from the group consisting of manganite (MnOOH), γ-MnO ₂ and house mannite (Mn ₃ O ₄ ), and reduces γ-MnO ₂ . More preferably, it has a phase (γ-MnO _2-x ). Furthermore, it is preferable to have a reduced phase (γ-MnO _2-x ) of house mannite (Mn ₃ O ₄ ) and / or manganite (MnOOH) and γ-MnO ₂ , manganite (MnOOH) and it is even more preferred to have gamma-MnO ₂ of the reduced phase _{(γ-MnO 2-x)} . Furthermore, it is preferable that neither β-MnO ₂ nor Mn ₂ O ₃ is contained.

The sulfate radical concentration of the manganese oxide of the present invention is preferably 0.7% or less, more preferably 0.6% or less in terms of the SO ₄ / Mn molar ratio. When a manganese oxide having a SO ₄ / Mn molar ratio of 0.7% or less is used as a raw material, the crystallite diameter of the obtained lithium manganate tends to be large, and the charge / discharge cycle characteristics are likely to be improved. The lower the sulfate radical concentration, the better. However, the SO ₄ / Mn molar ratio is preferably 0.1% or more, and more preferably 0.15% or more, so that highly crystalline lithium manganate can be obtained. .

  For the same reason, the sodium concentration of the manganese oxide of the present invention is preferably 0.1% or less and more preferably 0.08% or less in terms of Na / Mn molar ratio. The sodium concentration is preferably low, but is preferably 0.01% or more, and more preferably 0.06% or more, and thus a highly crystalline lithium manganate can be obtained.

Incidentally, _SO 4 / Mn mole ratio and Na / Mn molar ratio of manganese oxide can be determined by the following equation.

SO ₄ / Mn molar ratio (%) = (M _{SO 4} / M _Mn ) × 100
Na / Mn molar ratio (%) = (M _Na / M _Mn ) × 100
M _SO4 : SO ₄ (mol) in manganese oxide
M _Na : Na (mol) in manganese oxide
M _Mn : Mn (mol) in manganese oxide

The manganese oxide of the present invention preferably has a BET specific surface area of 25 m ² / g or more and 50 m ² / g or less, and more preferably 25 m ² / g or more and 40 m ² / g or less. When the BET specific surface area is 25 m ² / g or more, the reactivity with the lithium compound tends to be high, and the crystallinity of the resulting lithium manganate tends to be high. On the other hand, if it is 50 m < ² > / g or less, it will react easily with a lithium compound.

  In the manganese oxide of the present invention, particles having a particle size of 1 μm or less are preferably 5% or less in volume fraction, more preferably 1% or less, and still more preferably substantially free. When the particle size of 1 μm or less is 5% or less in terms of volume fraction, the particle size of the manganese oxide becomes more uniform, and the reaction with the lithium compound easily proceeds uniformly. Thereby, it is easy to obtain lithium manganate having a large crystallite and excellent capacity retention.

  The average particle size of the manganese oxide of the present invention is preferably more than 1 μm and not more than 35 μm, more preferably not less than 5 μm and not more than 30 μm, and still more preferably not less than 5 μm and not more than 25 μm. When the average particle size exceeds 1 μm, secondary aggregation of manganese oxide is easily suppressed, and the particle size of lithium manganate obtained using such manganese oxide as a raw material becomes uniform, and particle size control becomes easy. . On the other hand, when the particle size is 35 μm or less, the particle size of the obtained lithium manganate is a particle size suitable for use as a positive electrode active material.

  The manganese content of the manganese oxide of the present invention is preferably 58 wt% or more and 67 wt% or less, more preferably more than 60 wt% and 67 wt% or less.

The tap density of the manganese oxide of the present invention is preferably 1.5 g / cm ³ or more. Thereby, the density of the lithium manganate which uses this as a raw material also becomes high.

  The manganese oxide obtained by the manganese oxide of the present invention and the production method of the present invention can be mixed and reacted with a lithium compound to obtain lithium manganate having an excellent capacity retention rate.

  The lithium compound to be reacted with the manganese oxide is not particularly limited, and examples thereof include lithium hydroxide, lithium carbonate, and lithium nitrate.

  Moreover, in the range which does not impair the characteristic of this invention, you may add metal compounds, such as nickel, cobalt, and aluminum, with a manganese oxide and a lithium compound.

  The mixing method of the manganese oxide and the lithium compound is not limited as long as the two can be mixed uniformly, but the method of simply dry-mixing the manganese oxide and the lithium compound, or mixing the manganese oxide and the lithium compound to form a slurry. Examples of the granulation method include spray drying. Since the manganese oxide of the present invention has few impurities and does not contain particles of 1 μm or less, even simple dry mixing can be sufficiently and uniformly mixed with the lithium compound.

  The manganese oxide and lithium compound of the present invention produce lithium manganate by firing. As firing conditions, general conditions can be applied. For example, firing can be performed at a temperature of 700 ° C. or more and 1000 ° C. or less in an aerobic atmosphere such as air or oxygen.

  The obtained lithium manganate preferably has a crystallite size of 240 mm or more, and particularly preferably 260 mm or more. When the crystallite diameter is 240 mm or more, charge / discharge cycle characteristics excellent as a positive electrode active material can be obtained.

  Thus, the manganese oxide of the present invention is suitable as a raw material for lithium manganate, particularly lithium manganate having a spinel structure.

  The lithium manganate using the manganese oxide of the present invention as a raw material can be used as a positive electrode active material for a secondary battery such as a lithium ion secondary battery.

  When constituting a secondary battery using lithium manganate made from the manganese oxide of the present invention as a positive electrode active material, commonly used negative electrode active materials, electrolytes, separators, etc. can be used. As active materials, metallic lithium and lithium ions or materials capable of occluding and releasing lithium ions, metallic lithium, lithium / aluminum alloys, lithium / tin alloys, lithium / lead alloys and electrochemically inserting / extracting lithium ions. Carbon materials and electrolytes that can be released include carbonates, sulfolanes, lactones, lithium salt dissolved in an organic solvent such as ether condyles, lithium ion conductive solid electrolytes, and polyethylene as a separator. Further, a microporous film made of polypropylene or the like can be used.

  By using lithium manganate made from the manganese oxide of the present invention as a positive electrode active material, it has excellent charge / discharge cycle performance, and has a high capacity retention rate of 98.0% or more according to the evaluation method described later. A secondary battery having discharge cycle performance can be configured.

Powder X-ray diffraction pattern of manganese oxide (in the figure, upper figure: Example 1, middle figure: Example 2, lower figure: raw material (electrolytic manganese dioxide)) Particle size distribution curve of manganese oxide of Example 2 and raw material (electrolytic manganese dioxide) (in the figure, ●: raw material (electrolytic manganese dioxide), ▲: Example 2) Particle form of raw material (electrolytic manganese dioxide) used in Example 1 (scale is 5 μm in the figure) Particle form of manganese oxide of Example 2 (scale is 5 μm in the figure) Powder X-ray diffraction pattern of lithium manganate (in the figure, upper figure: Example 1, middle figure: Example 2, lower figure: Comparative Example 1)

  EXAMPLES Next, although an Example demonstrates this invention, this invention is not limited to these Examples.

(Average particle size and particle size distribution)
Manganese oxide and lithium manganate 0.5g are put into 50mL of 0.1N-ammonia water, and the dispersion slurry prepared by ultrasonic irradiation for 10 seconds is put into Microtrac HRA (manufactured by HONEWELL) in a predetermined amount, and laser The volume distribution was measured by a diffraction method, and the average particle size and the particle size distribution were obtained.

(Measurement of crystal phase)
Manganese oxide and lithium manganate were measured using a general X-ray diffractometer (MXP-3 manufactured by Mac Science). A CuKα ray (λ = 1.5405 mm) is used as the radiation source, the measurement mode is step scan, the scan condition is 0.04 ° per second, the measurement time is 3 seconds, and the measurement range is 2 ° to 5 ° to 80 °. Measured with

(Calculation of crystallite diameter)
The full width at half maximum of the 400 diffraction peak (peak near 2θ = 44 °) of the spinel structure lithium manganate (space group Fd-3m) was measured, and the crystallite diameter was calculated by the Scherrer equation.

(BET specific surface area)
The BET specific surface areas of manganese oxide and lithium manganate were measured by BET single point nitrogen adsorption. In addition, the sample used for the measurement of the BET specific surface area was deaerated by heating at 150 ° C. for 40 minutes prior to the measurement of the BET specific surface area.

(Measurement of chemical composition)
The chemical composition of the raw material electrolytic manganese dioxide, manganese oxide and lithium manganate was measured using ICP emission analysis.

(Measurement of capacity maintenance rate)
The battery characteristic test was performed by the method shown below. A mixture of lithium manganate, polytetrafluoroethylene as a conductive agent, and acetylene black (trade name: TAB-2) is mixed at a weight ratio of 4: 1 and meshed at a pressure of 1 ton / cm ² (manufactured by SUS316). ) After being molded into a pellet shape on top, it was dried under reduced pressure at 200 ° C. to produce a positive electrode for a battery.

Electrolysis in which lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / dm ^{3 in} the obtained positive electrode for a battery, a negative electrode comprising a metal lithium foil (thickness 0.2 mm), and A battery was obtained using the liquid.

Using the obtained battery, the battery voltage was charged and discharged 50 times at a constant current of 1.0 mA / cm ² between 4.2 V and 3.0 V at room temperature. The 10th and 50th discharge capacities (mAh / g) were Q ₁₀ and Q ₅₀ , respectively, and the ratio of these ratios was 100 × Q ₅₀ / Q ₁₀ (%).

Example 1
(Manufacture of electrolytic manganese dioxide)
Electrolysis was performed for 10 days so that the current density was 0.83 A / dm ² , the electrolysis temperature was 95 ° C., the electrolytic replenisher was a manganese sulfate solution having a manganese concentration of 47 g / l, and the sulfuric acid concentration in the electrolyte solution was 20 g / l. . The weight ratio of Mn ²⁺ / H ₂ SO ₄ in the electrolytic solution during the electrolysis period was 2.1. The electrolytic manganese dioxide lump that was electrolytically deposited was pulverized with a roller mill and then washed to obtain electrolytic manganese dioxide. The average particle diameter of the obtained electrolytic manganese dioxide was 25 μm. The crystal phase of the obtained electrolytic manganese dioxide is shown in FIG. 1, the particle size distribution is shown in FIG. 2, and the particle morphology is shown in FIG.

The obtained electrolytic manganese dioxide had a crystal phase of γ-MnO ₂ , manganese had a chemical composition of 60% by weight of manganese, 2% by weight of sulfate radical, and a SO ₄ / Mn molar ratio of 2.1%. The BET specific surface area was 48 m ² / g, and the volume fraction of particles of 1 μm or less was 10%.

(Manufacture of manganese oxide)
50 ml of pure water was added to 10 g of electrolytic manganese dioxide to obtain a manganese dioxide dispersion. While this was stirred and maintained at 70 ° C., a 5 wt% hydrazine aqueous solution was dropped at a dropping rate of 0.5 g / min to perform a reduction treatment.

The amount of dripping is MnO ₂ + 1 / 4N ₂ H ₄ → MnOOH + 1 / 4N ₂ when the reaction proceeds completely (N ₂ H ₄ 0.25 mol with respect to 1 mol of MnO ₂ ) and the reduction rate is 100%. The rate was 150% (N ₂ H ₄ 0.375 mol relative to 1 mol of MnO ₂ ).

  After completion of dropping, the mixture was further stirred and held at 70 ° C. for 1 hour, and then separated by filtration to obtain a cake. The cake after separation was immersed in 50 ml of 0.1N ammonia water and stirred at room temperature for 1 hour for alkali treatment.

  After the alkali treatment, the solution was separated by filtration, and repulp washed with 50 ml of pure water. After separation by filtration, the cake was dried in air at 60 ° C. overnight to obtain manganese oxide. The results are shown in Table 1.

The manganese oxide of the obtained manganese oxide has a valence of 2.8, the crystal phase is house mannite (Mn ₃ O ₄ ) as the main crystal phase, and in addition to that, a reduced phase (γ-MnO ₂₎ of γ-MnO _{2. 2-x} ) and its reduced compounds, but not β-MnO ₂ and Mn ₂ O ₃ .

The BET specific surface area was 35 m ² / g, which was lower than that of the raw material electrolytic manganese dioxide, and particles of 1 μm or less were not detected.

  In addition, the filtrate after hydrazine reduction showed pH 5.8, and as a result of filtrate composition analysis, elution of electrolytic manganese dioxide into the filtrate was not observed.

(Manufacture of lithium manganate)
The obtained manganese oxide and lithium carbonate having an average particle size of 3.5 μm were dry-mixed and mixed so that the (lithium / manganese) molar ratio = 0.54. 100 g of the mixture was placed in an alumina crucible and baked at 850 ° C. for 1 day in air in a muffle furnace to obtain lithium manganate. The results are shown in Table 1.

  The obtained lithium manganate crystal phase was a spinel phase single phase. Furthermore, in the X-ray diffraction measurement, all diffraction peaks were indexed with a spinel structure (space group: Fd3-m), and peaks derived from the byproduct layer were not included. The obtained lithium manganate had a high capacity retention rate.

Example 2
(Manufacture of manganese oxide)
Manganese oxide was obtained in the same manner as in Example 1 except that electrolytic manganese dioxide obtained by the same method as in Example 1 was used, and the amount of hydrazine aqueous solution added was reduced to a reduction rate of 65%.

  The crystal phase of the obtained manganese oxide is shown in FIG. 1, the particle size distribution is shown in FIG. 2, the particle morphology is shown in FIG. 4, and the results are shown in Table 1.

Manganese valence of the resulting manganese oxide is 3.4, the crystalline phase manganite a (MnOOH) as the main crystal phase, other than the well gamma-MnO ₂ in the reduction phase _{(γ-MnO 2-x)} And its reducing compound, but β-MnO ₂ and Mn ₂ O ₃ were not included. The BET specific surface area was 29 m ² / g, which was lower than the raw material electrolytic manganese dioxide. In addition, the particle | grains of 1 micrometer or less were not contained.

  The filtrate after hydrazine reduction had a pH of 5.1, and the dissolution rate of electrolytic manganese dioxide into the filtrate was 0.5%.

(Manufacture of lithium manganate)
Lithium manganate was obtained in the same manner as in Example 1 using the obtained manganese oxide. The results are shown in Table 1.

  The obtained lithium manganate crystal phase was a spinel phase single phase. Furthermore, in the X-ray diffraction measurement, all diffraction peaks were indexed with a spinel structure (space group: Fd3-m), and peaks derived from the byproduct layer were not included.

Comparative Example 1
(Manufacture of manganese oxide)
The electrolytic manganese dioxide obtained by the same method as in Example 1 was used, and after stirring and washing with 0.1N-ammonia water having a weight 5 times the weight of electrolytic manganese dioxide, filtration, separation, and 60 ° C. And dried overnight to obtain the manganese oxide of Comparative Example 1. The results are shown in Table 1.

The manganese valence of the obtained manganese oxide was 4.0, the removal of sulfate radical did not proceed sufficiently, and the SO ₄ / Mn molar ratio was high. Furthermore, it contained many particles of 1 μm or less.

(Manufacture of lithium manganate)
Lithium manganate was obtained in the same manner as in Example 1 using the obtained manganese oxide. The results are shown in Table 1.

  The obtained lithium manganate crystal phase was a spinel phase single phase. Furthermore, in the X-ray diffraction measurement, all diffraction peaks were indexed with a spinel structure (space group: Fd3-m), and peaks derived from the byproduct layer were not included.

Comparative Example 2
(Manufacture of manganese oxide)
Electrolytic manganese dioxide was obtained in the same manner as in Example 1, and manganese oxide was obtained in the same manner as in Example 1 except that 0.1N sodium hydroxide solution was used instead of 0.1N ammonia water. It was.

The resulting manganese oxide powder crystal phase is the main crystal phase manganite (MnOOH), γ-MnO ₂ in the reduction phase otherwise _{(γ-MnO 2-x)} and contains the reducing compound However, β-MnO ₂ and Mn ₂ O ₃ were not contained.

  The filtrate after hydrazine reduction showed pH 5.1, and the dissolution rate of electrolytic manganese dioxide into the filtrate was 0.5%.

(Manufacture of lithium manganate)
Lithium manganate was obtained in the same manner as in Example 1 using the obtained manganese oxide. The results are shown in Table 1.

  The obtained lithium manganate crystal phase was a spinel phase single phase. Furthermore, in the X-ray diffraction measurement, all diffraction peaks were indexed with a spinel structure (space group: Fd3-m), and peaks derived from the byproduct layer were not included.

  The capacity retention rate of the obtained lithium manganate was as low as 96.9%.

Comparative Example 3
(Manufacture of manganese oxide)
Electrolytic manganese dioxide was obtained in the same manner as in Example 1, and manganese oxide was obtained in the same manner as in Example 1 except that immersion in ammonia water and stirring were not performed. The results are shown in Table 1. When alkali treatment was not performed, removal of sulfate radicals was insufficient, and the resulting manganese oxide had a high sulfuric acid concentration.

Crystal phase of manganese oxide, manganite (MnOOH) is the main crystalline phase, but other in gamma-MnO ₂ in the reduction phase _{(γ-MnO 2-x)} and contained the reducing compound, beta- MnO ₂ and Mn ₂ O ₃ were not included.

  The filtrate after hydrazine reduction showed pH 5.1, and as a result of filtrate composition analysis, the dissolution rate of electrolytic manganese dioxide into the filtrate was 0.5%.

(Manufacture of lithium manganate)
Lithium manganate was obtained in the same manner as in Example 1 using the obtained manganese oxide. The results are shown in Table 1.

  The obtained lithium manganate crystal phase was a spinel phase single phase. Furthermore, in the X-ray diffraction measurement, all diffraction peaks were indexed with a spinel structure (space group: Fd3-m), and peaks derived from the byproduct layer were not included.

  The obtained lithium manganate crystallites were small, and the capacity retention rate was as low as 97.3%.

  The charge / discharge cycle characteristics of a lithium secondary battery using lithium manganate obtained using the manganese oxide of the present invention as a raw material as a positive electrode active material were high.

  By mixing the manganese oxide of the present invention with a lithium compound as a raw material, lithium manganate having high crystallinity, less fine powder, and excellent charge / discharge cycle characteristics can be obtained. By using the lithium manganate thus obtained as a positive electrode active material, a lithium ion secondary battery having high charge / discharge cycle characteristics can be obtained.

Claims (10)

  A method for producing manganese oxide, comprising reducing electrolytic manganese dioxide and then neutralizing with ammonia.   The method for producing a manganese oxide according to claim 1, wherein the manganese valence is reduced to 2.7 or more and 3.7 or less.   The method for producing a manganese oxide according to claim 1 or 2, wherein the reduction treatment is performed with an aqueous hydrazine solution. Manganese oxide having a manganese valence of 2.7 or more and 3.7 or less and any one or more crystal phases selected from the group consisting of manganite (MnOOH), γ-MnO ₂ and house mannite (Mn ₃ O ₄ ) . 5. The manganese oxide according to claim 4, wherein the SO ₄ / Mn molar ratio is 0.7% or less and the Na / Mn molar ratio is 0.1% or less.   6. The manganese oxide according to claim 4, wherein particles of 1 μm or less have a volume fraction of 5% or less.   A method for producing lithium manganate, comprising mixing the manganese oxide according to any one of claims 4 to 6 and a lithium compound, followed by heat treatment.   A method for producing lithium manganate, comprising reducing and treating electrolytic manganese dioxide, mixing and baking a manganese oxide obtained by neutralizing with ammonia, washing and drying, and a lithium compound.   The method for producing a lithium manganate compound according to claim 7 or 8, wherein the manganese valence of the manganese oxide is reduced to 2.7 or more and 3.7 or less.   The method for producing lithium manganate according to claim 8 or 9, wherein the reduction treatment is performed with an aqueous hydrazine solution.

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