JP3030764B2 - Spinel-type lithium manganese oxide, method for producing the same, and use thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel lithium manganese oxide, a method for producing the same, and uses thereof.

[0002] Manganese oxide has long been used as a battery active material, and a lithium manganese composite oxide, which is a composite material of manganese and lithium, has recently attracted attention as an active material for lithium secondary batteries. Material.

[0003] A lithium secondary battery is a new type of secondary battery that is expected to be put to practical use as a battery with high output and high energy density.

[0004]

2. Description of the Related Art Positive electrode materials for lithium secondary batteries are required to have a high voltage operating range, a high discharge capacity, and a high cycle stability. Li and various metals such as Co, Ni, Lithium manganese composite oxides such as Mn have been studied.

LiMn ₂ O ₄ having a spinel structure, which is a kind of composite oxide of lithium and manganese, is known to exhibit a two-stage discharge having a flat portion at around 4 V and around 3 V at the time of discharge. If it is possible to cycle reversibly in the operating region, it is expected that high energy can be taken out, and thus it is considered to be promising as a positive electrode active material.

[0006] Spinel type lithium manganese oxide (Li
Mn ₂ O ₄ ) has been studied in terms of magnetic properties, and has been known as a substance for a long time. For example, J. Phys. Ch
em. Solids, 7 , 351 (1958).
G. FIG. Wickham and W.C. J. Croft reported as a part of the study of the magnetic properties of the Mn-based spinel structure. As a production method, a mixture of lithium carbonate and manganese oxide having a Li / Mn molar ratio of exactly 0.5 was prepared as follows.
A method of heat treatment at 00 to 900 ° C has been reported. Further, another document (Blasse, G. (1958) P
hils Res. Rpts. Suppl. 3 , 1
-139), not only LiMn ₂ O ₄ but also Li ₄ Mn ₅
The magnetic properties of substances having a spinel structure such as O ₁₂ have been reported, and their existence has been confirmed.

As described above, LiMn ₂ O _{4 and the} like have been known as substances for a long time. However, application to a cathode material for a lithium secondary battery has recently been performed. Patent application title: A cathode containing lithium, an anode mainly composed of LiMn ₂ O ₄ , and an organic electrolyte secondary battery comprising an organic electrolyte ・ Japanese Patent Application Laid-Open No. 63-187569 A negative electrode containing lithium or a lithium alloy as an active material ,
Non-aqueous secondary batteries and the like, which include a positive electrode that uses spinel-type LiMn ₂ O ₄ , λ-type manganese dioxide, or a manganese oxide having an intermediate crystal structure as an active material, have been proposed. Further, regarding a method for producing a composite oxide of lithium and manganese, particularly a method for producing a LiMn ₂ O ₄ system,
As described in D. above. G. FIG. The production method reported in Wickham et al.
A mixture having an i / Mn molar ratio of exactly 0.5 was prepared from 800 to
In addition to the method of heat treatment at 900 ° C., for example, Japanese Patent Application Laid-Open No. 63-187569 discloses Mn ₂ O ₃ or MnO ₂ and lithium carbonate in the form of Mn: Li =
2: 1 (molar ratio), 650 ° C. for 6 hours, 850
Method of baking in air at 14 ° C. for 14 hours ・ A method of adding a lithium salt to γ-MnOOH and subjecting it to a heat treatment ・ A method of heating a manganese oxide (MnO ₂ , Mn ₂ O ₃ or Method for calcining a mixture of Mn ₃ O ₄ ) and lithium nitrate (LiNO ₃ ) in air ・ Japanese Patent Laid-Open No. 3-127453 Manganese dioxide (MnO ₂ ) and lithium nitrate (LiN
O ₃ ) is obtained by converting Mn: Li from 2.2: 1.0 to 1.8: 1.0.
Of 880 ° C. or higher in air
For example, there is a method of baking in a temperature range of 00 ° C. or less to form an oxide composed of lithium and manganese.

However, it has been difficult to obtain a high-performance positive electrode active material by the above-mentioned method.

In this regard, the present inventors have proposed that LiMn
_The reason was thought to be that the optimal physical properties that bring out the inherent performance of ₂ O ₄ as a positive electrode active material have not been clarified.

Further, with the improvement of the above-mentioned manufacturing method, Li
Many proposals have been made on physical properties and the like for Mn ₂ O ₄ to exhibit performance as a positive electrode active material. For example, JP-A-63-274059 discloses a negative electrode active material mainly composed of Li, an anode active material mainly composed of LiMn ₂ O ₄ , and a non-aqueous electrolyte.
n ₂ O ₄ has a half-value width of a diffraction peak at a diffraction angle of 46.1 ° of 1.1 to 1.0 in X-ray diffraction using FeKα ray.
Non-aqueous electrolyte battery characterized by being 2.1 ・. Japanese Patent Application Laid-Open No. 2-139860. A positive electrode, a non-aqueous electrolyte having lithium ion conductivity, and a negative electrode made of lithium or a lithium alloy. In a battery, the positive electrode has a crystal lattice constant a of 8.22.
Angstroms The following LiMn ₂ O ₄ nonaqueous No. electrolyte secondary batteries, JP-A 2-270268, which is a publication _{Li x Mn 2 O 4 1.025 ≦} x ≦ 1.185 and is intended, especially in a lithium secondary battery using a No. 2-270269 discloses Li _x Mn ₂ O ₄ with 0.76 ≦ x ≦ 0.98 in which those-Hei 3-219556 discloses a lithium or a lithium alloy as a negative electrode, a positive electrode active material A lithium secondary battery using LiMn ₂ O ₄ having an average primary particle diameter of 0.5 μm or less.

However, when attempting to use the above-mentioned lithium manganese oxide as a so-called 4 V class positive electrode active material of 3.5 V to 4.5 V, according to the study of the present inventors, at present, charging and discharging have Sacrifice charge / discharge capacity as a positive electrode material for lithium secondary batteries, such as having a large capacity but remarkably deteriorating with the progress of charge / discharge cycles, or having cycle stability but low charge / discharge capacity Thus, no lithium manganese oxide having cycle stability was obtained.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel high-performance lithium manganese oxide as a positive electrode material for a lithium secondary battery, a method for producing the same, and lithium using the lithium manganese oxide as a positive electrode. A secondary battery is provided.

[0013]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the performance inherent in lithium manganese oxide is not exhibited only by making the crystal structure a single phase, but the particle structure, primary particle diameter and When the total balance of the BET specific surface area is important, and when considering the application of lithium manganese oxide to a positive electrode active material, lithium manganese oxide alone is not used as a positive electrode, but a conductive material such as a carbon material. And polytetrafluoroethylene (PTF
Since it is used by mixing with a binder such as E), it has been found that the physical properties of the powder greatly affect the properties.

That is, the present invention relates to a lithium manganese oxide comprising Li, Mn and O, wherein the crystal structure is a spinel structure and the molar ratio of Li to Mn is Li: Mn = 1.
00-1.10: 2.00, Mn oxidation degree is 3.40-
3.60 valence, BET specific surface area is 1 m ² / g or more,
A lithium manganese oxide characterized in that substantially all the primary particles are less than 1 μm and the lattice constant a-axis length is 8.235 to 8.245 angstroms, which solves the above-mentioned problem. In a method for producing a lithium manganese oxide by heating after mixing a manganese compound, a manganese compound and a lithium compound, the manganese compound has a spinel structure, and the degree of oxidation of the manganese element is defined as MnO _x . At least one manganese compound selected from the group consisting of manganese oxides, hydrated manganese oxides, manganese hydroxides and manganate hydroxides in which the value of x when expressed is 1.5 or less; The above-mentioned substance can be produced by a production method which is a compound comprising a system or a Mn-OH compound. A high performance lithium secondary battery using the lithium manganese oxide as a positive electrode active material was found, and the present invention was completed.

Hereinafter, the present invention will be described specifically.

The lithium manganese oxide of the present invention has substantially the same chemical composition and crystal structure as lithium manganese spinel, LiMn ₂ O ₄ and / or LiMn ₂ O ₄ and / or Li ₄ Mn _5, which have long been well known. An intermediate substance of O ₁₂ , and further, the substance contains Mn ₂ O _{3 in an} amount not observed by X-ray diffraction, that is, a lithium manganese oxide composed of Li, Mn and O has a crystal structure of Spinel structure, molar ratio of Li to Mn is Li: Mn
= 1.00 to 1.10: 2.00, the average degree of oxidation of Mn is 3.40 to 3.60.

Further, the physical properties of the powder are such that the BET specific surface area is 1 m ² / g or more, and substantially all the primary particles are 1
It is characterized by being less than μm.

When the BET specific surface area is less than 1 m ² / g, when used as a positive electrode, the utilization rate decreases, and the charge / discharge capacity tends to decrease.

The BET specific surface area is preferably not more than 10 m ² / g.

Further, when the primary particles have a size of 1 μm or more, the charge / discharge capacity tends to decrease with the charge / discharge cycle, which is not preferable.

The primary particles are preferably at least 0.01 μm.

The lithium manganese particles of the present invention are agglomerated particles obtained by aggregating the primary particles, and have an average particle diameter of 1
３０30 μm.

If the average particle size is outside the above range, the charge / discharge capacity is low, or the charge / discharge capacity tends to decrease with the charge / discharge cycle, which is not preferable.

Further, the physical properties of the lithium manganese oxide of the present invention from the crystal plane are such that the crystal structure is a cubic spinel structure, and the a-axis length of the lattice constant is 8.235 Å to 8.245 Å. Is mandatory.

If the a-axis length of the lattice constant is out of the above range, the ratio of Mn ⁴⁺ and Mn ³⁺ present in the crystal structure is largely out of 1: 1 or Li, M
This is a case where n and O are not present at a predetermined site, and when both are used as a positive electrode active material, performance cannot be exhibited.

The cubic crystallite diameter is preferably 400 to 700 Å, and more preferably 500 to 650 Å.

The crystallite diameter was calculated from the X-ray diffraction peak on the (111) plane using the Scherrer equation.

When the crystallite diameter is smaller than the above range, the crystal is not developed and the performance is hardly obtained. On the other hand, if it is larger than the above range, it is difficult to achieve the above-mentioned powder properties such as BET, primary particle diameter and average particle diameter.

It has been difficult to obtain a lithium manganese oxide having the above physical properties by a conventional production method.

Further, the present inventors have studied the tap density of the powder as an index of the powder filling property.

The tap density of the lithium manganese oxide of the present invention is preferably 1.7 g / cm ³ or more. The tap density is more preferably 1.8 g / cm ³ or more, and still more preferably 1.9 g / cm ³ .

When the tap density is smaller than the above range, it is difficult to mix the positive electrode with a conductive agent such as a carbon material or a binder such as polytetrafluoroethylene (PTFE). Because of its bulkiness, the amount of filling in a certain volume tends to decrease.

As described above, the lithium manganese oxide of the present invention has been difficult to obtain by the conventional production method, but has a fine powder property such as the lithium manganese oxide of the present invention. Those with a high tap density as in the invention are more difficult to obtain by conventional manufacturing methods,
It is difficult to manufacture without the method of the present invention.

The method for producing a lithium manganese oxide according to the present invention is a method for producing a lithium manganese oxide by first mixing a manganese compound and a lithium compound and then subjecting the mixture to a heat treatment, wherein the manganese compound has a spinel structure. At least one selected from the group consisting of manganese oxides, hydrated manganese oxides, manganese hydroxides and manganate hydroxides, wherein the value of x when the degree of oxidation of the manganese element is expressed as MnO _x is 1.5 or less. One manganese compound is a manganese compound which is a compound of Mn-O type or Mn-O-H type, and whose manganese compound has a spinel structure.

In the present invention, a high-performance lithium manganese oxide is obtained by using a manganese oxide having a spinel structure in which the arrangement of oxygen is the same as that of the lithium manganese oxide intended for the manganese compound. It is estimated that it can be. Examples of the manganese oxide having the spinel structure include Mn ₃ O ₄ (mineral name: Hausmannite), and those containing a hydrogen atom in the structure, for example, Mn ₃
Preferred are those represented by the formula of O _4-x (OH) _x (where 0 <x ≦ 4) and hydrous crystals, that is, Mn ₃ O ₄ .nH ₂ O and the like.

The manganese oxide Mn ₃ O ₄ is usually
The Mn compound can be produced by heating the compound to 900 ° C. or higher in the presence of oxygen. However, since the specific surface area is reduced by firing at a high temperature, pulverization or the like is required, which is not preferable.

In the present invention, there is a method for producing Mn ₃ O ₄ by oxidizing manganese hydroxide. Since Mn ₃ O ₄ obtained by this production method is fine particles and is preferable for obtaining the lithium manganese oxide of the present invention, manganese hydroxide is oxidized as a manganese compound having a spinel structure of the present invention. The manufactured manganese compound having a spinel structure is used.

The production method is described in, for example,
No. 296732 discloses dispersing a metal manganese powder in water containing at least one compound selected from the group consisting of a water-soluble amino acid and an ammonium salt, and removing the manganese hydroxide formed in the dispersion. A method for producing fine manganese oxide powder characterized by oxidizing to obtain trimanganese oxide, which is obtained by oxidizing manganese hydroxide with an oxidizing agent or the like in an aqueous solution to obtain Mn ₃ O _4. I just need.

Further, as the manganese compound having a spinel structure of the present invention, the degree of oxidation of manganese element is MnO _x
A manganese compound having a value of x of 1.5 or less is used.

This is not clear, but when the degree of oxidation is higher than 1.5, Mn ₂ O ₃ is liable to be mixed in the manganese oxide having a spinel structure. This is because it is difficult to obtain manganese oxide.

As the manganese compound having a spinel structure according to the present invention, a manganese compound having a specific surface area of 5 m ² / g or more is used.

The manganese compound has a specific surface area of 5
A manganese compound having a spinel structure of m ² / g or more is used. If the specific surface area is less than 5 m ² / g, the reactivity with the lithium salt during production of the lithium manganese oxide is so poor that a uniform product cannot be obtained.

As the lithium compound of the present invention, at least one lithium salt selected from the group consisting of lithium hydroxide, lithium nitrate, lithium chloride and lithium carbonate can be suitably used.

As the lithium compound used in the present invention, any compound can be used as long as it decomposes at a temperature lower than the firing temperature. In particular, in order to obtain a lithium manganese oxide at a low temperature, the lithium compound is lithium nitrate. It is preferred to use In addition, when firing, N
From the viewpoint that toxic gases such as O _x and SO _x are not released, it is also preferable to use lithium carbonate, lithium hydroxide and lithium hydroxide hydrate as the lithium compound.

In the present invention, the manganese compound and the lithium compound described above are mixed.

In the present invention, the mixing of the manganese compound and the lithium compound is performed by mixing Li and Mn in a molar ratio of Li: Mn.
= 1.0: 2.0 to 1.2: 2.0.

The mixing may be performed by any method capable of forming the manganese compound and the lithium compound into a uniform mixture, such as wet mixing and dry mixing using a ball mill or the like. The manganese compound and the lithium compound may be mixed with a slurry. The dried product may be spray-dried to obtain a uniform mixture.

Subsequently, in the present invention, the mixture is heat-treated. According to the method of the present invention, for example, when lithium nitrate is used, in the air atmosphere, the temperature near the melting temperature of lithium nitrate is obtained by the heat treatment. From 260 ° C., generation of lithium manganese oxide was confirmed by X-ray, and lithium manganese oxide can be produced at a lower temperature than when other manganese oxides are used. From this, it can be said that the method for producing a lithium manganese oxide of the present invention is a very energy-efficient production method.

As described above, according to the manufacturing method of the present invention,
Although lithium manganese oxide can be produced from a low temperature, when heat treatment is performed in an air atmosphere, the heat treatment temperature is preferably 500 to 850 ° C. because the degree of oxidation of the Mn element is high.

The heat treatment is performed at a temperature of 200 ° C. or more and less than 500 ° C. at least once,
It is more preferable to perform the heat treatment again in the following,
After heat treatment at a temperature of at least 500 ° C. and less than 500 ° C., and mixing again,
It is particularly preferable to perform the heat treatment at 500 to 850 ° C.

It is also preferable to perform heat treatment while mixing in a rotary kiln without performing the above-described firing method for mixing again.

The atmosphere during the heat treatment is usually an air atmosphere, but it is preferable to use an atmosphere containing a small amount of oxygen, such as N ₂ , Ar, reduced pressure, and vacuum, in order to lower the firing temperature.

Further, according to the present invention, in the above-mentioned method for producing a lithium manganese oxide, after mixing the manganese compound and the lithium compound, pressing the resulting mixture under pressure, and then performing heat treatment, the tap density can be reduced. 1.7g
/ Cm ³ or more can be obtained.

In the pressure molding, after mixing the manganese compound and the lithium compound, the resulting mixture is subjected to pressure molding. The molding pressure may be any pressure at which a molded body can be obtained,
Forming under pressure with a pressure of at least kg / cm ² is a powder having a tap density of 1.7 g / cm ³ or more, which is easy to handle when performing a heat treatment because the molded body maintains a stable shape. Preferred for obtaining body. In particular, it is preferable to perform pressure molding at a pressure of 1 ton / cm ² or more.

The heat treatment of the molded body is the same as in the above-mentioned production method. In this case as well, if the heat treatment is too high, the tap density becomes high, but the composition tends to be distorted due to scattering of Li and the primary particle diameter tends to be large.
0-850 degreeC is preferable and 650-800 degreeC is especially preferable.

Further, as described above, the heat treatment was performed for 200 hours.
After the heat treatment at least once at a temperature of 500 ° C. or more and less than 500 ° C.,
In the case where the mixing is performed again and the heat treatment is performed at 500 to 850 ° C., it is particularly preferable that the molding is performed again after the completion of the remixing after the heat treatment at 200 ° C. to less than 500 ° C.

Although the lithium manganese oxide having a spinel structure produced as described above is more agglomerated than when heat-treated with a powder, the agglomeration is loosened by simple crushing, and the fine powder is filled. It becomes a lithium manganese oxide having a good spinel structure.

In the present invention, the lithium manganese oxide having a spinel structure produced as described above is used as a positive electrode active material.

As the negative electrode active material used in the lithium secondary battery of the present invention, a material capable of inserting and extracting metallic lithium and lithium or lithium ions can be used. Examples thereof include metallic lithium, a lithium / aluminum alloy, a lithium / tin alloy, a lithium / lead alloy, and a carbon-based material electrochemically doped with and dedoped with lithium ions.

The electrolyte used in the lithium secondary battery of the present invention is not particularly limited. Examples thereof include electrolytes in which a lithium salt is dissolved in an organic solvent such as carbonates, sulfolanes, lactones, and ethers. Alternatively, a lithium ion conductive solid electrolyte can be used.

A battery shown in FIG. 1 was constructed using the lithium manganese oxide of the present invention as a positive electrode active material.

In the drawing, 1: lead wire for positive electrode, 2:
Positive electrode collecting mesh, 3: Positive electrode, 4: Separator, 5:
Negative electrode, 6: negative electrode current collector mesh, 7: negative electrode lead wire,
8: Container.

In the present invention, the positive electrode active material described above,
Using a negative electrode active material and a lithium salt-containing non-aqueous electrolyte,
The conventional lithium secondary battery using the spinel-structured lithium manganese composite oxide cannot achieve 3.5 to 4.
It is possible to obtain a high-performance lithium secondary battery exhibiting a stable charge-discharge cycle with a high discharge capacity at an operating potential of about 5 V.

Examples will be described below, but the present invention is not limited to these examples.

[0065]

EXAMPLES Each measurement in Examples and Comparative Examples of the present invention was measured under the following conditions.

The XRD pattern was measured under the following conditions.

Measurement model: Mac Science, Inc. MXP-3 Irradiated X-ray: Cu Kα ray Measurement mode: Step scan Scan condition: 0.04 degrees per second Measurement time: 3 seconds Measurement range: 5 to 80 degrees as 2θ ・ Lattice constant Is measured by WPPF (Whole Powder Pattern F)
It was calculated by analyzing at 2θ = 15 to 80 ° by the itting method.

The crystallite diameter was calculated from Scherrer's equation.

Composition analysis was performed by ICP spectroscopy.

The degree of oxidation of the Mn element was determined by the oxalic acid method.

The primary particle diameter was determined from an SEM observation image.

The secondary particle size was measured with a Microtrac particle size distribution meter (manufactured by Nikkiso Co., Ltd.).

The average diameter used was the average volume diameter.

The BET specific surface area was measured using nitrogen gas.

The tap density was measured under the following conditions.

Measurement model: Tsutsui Physical and Chemical Instruments Co., Ltd. Powder reduction degree measuring instrument (Tapping type) Model TPM-3 Measurement conditions: Measure density after tapping 6 times / 10 seconds, 60 minutes “Synthesis of lithium manganese oxide” As Examples 1 to 8 and Comparative Examples 1 to 7, lithium manganese oxide was synthesized by the following method.

Example 1 Mn ₃ O ₄ (manufactured by Tosoh Corporation, trade name: Brownox) having a BET specific surface area of 20 m ² / g and an oxidation degree of MnO _1.34 as MnO _x, and lithium nitrate as Li and Mn
After the mixture was well mixed in a mortar at a molar ratio of Li: Mn = 1.025: 2.0, the temperature was raised from room temperature to 264 ° C. in the air in 2.5 hours, and kept at 264 ° C. for 24 hours. Take out and let cool, mix well in a mortar, and then 450 ° C
The temperature was raised for 4.5 hours, kept at 450 ° C. for 24 hours, taken out, allowed to cool, and mixed well in a mortar. Further, the temperature of the mixture was raised from room temperature to 650 ° C. over 6.5 hours.
It was kept at 0 ° C. for 24 hours.

From the X-ray diffraction pattern of the obtained compound,
L of JCPDS card 35-782 already from 264 ℃
It showed the same pattern as iMn ₂ O ₄ . From the analysis values, Li and Mn are in a molar ratio of Li: Mn = 1.01:
2.0, and the degree of oxidation of Mn was 1.75 when represented as MnO _x .

The primary particle size was 0.2 μm, and the secondary particle size was 16 μm.

The a-axis length of the lattice constant was 8.242 angstroms, and the crystallite diameter was 580 angstroms.

Example 2 A 2 mol / dm ³ manganese nitrate aqueous solution 6 in a nitrogen atmosphere
0 ml is 2 mol / dm ³ of lithium hydroxide 50
0 ml, and after adding aqueous hydrogen peroxide to the solution containing the formed precipitate of manganese hydroxide, the mixture was filtered, washed, dried at 110 ° C., and treated with M having a specific surface area of 30 m ² / g.
n ₃ O ₄ was obtained.

Using this Mn ₃ O ₄ , a heat treatment was performed under the same heat treatment conditions as in Example 1.

The obtained compound was prepared according to JCPDS Card 35-
782 shows the same pattern as LiMn ₂ O _4, and the analysis results show that Li and Mn are in a molar ratio of Li: Mn = 1.02: 2.
0 and the degree of oxidation of Mn is expressed as x = MnO _x
1.76.

Example 3 A 0.25 mol / dm ³ aqueous glycine solution 2 was prepared by referring to the method disclosed in Japanese Patent Application Laid-Open No. 2-296732.
While maintaining dm ³ at 50 ° C., 100 g of Mn powder passed through a 100-mesh sieve was added, and the mixture was stirred for 6 hours while stirring while blowing air at 2 L / min. After passing the product through a 200-mesh sieve, it is filtered, washed with water and dried to give a specific surface area of 10 m ³ / g.
Mn ₃ O ₄ powder was obtained.

Using this Mn ₃ O ₄ , heat treatment was performed under the same heat treatment conditions as in Example 1.

The product was a JCPDS card 35-782.
A pattern similar to that of LiMn ₂ O ₄ was obtained.
The molar ratio of i and Mn is Li: Mn = 1.01: 2.0, and the degree of oxidation of Mn is x = 1.7 when expressed as MnO _x.
It was 4.

Example 4 The conditions were the same as in Example 1 except that lithium hydroxide was used as the lithium raw material.

The product was the same as in Example 1.

The a-axis length of the lattice constant was 8.239 angstroms, and the crystallite diameter was 570 angstroms.

Example 5 Example 1 except that lithium carbonate was used as a lithium raw material.
The same conditions were used. The product was similar to Example 1.

The a-axis length of the lattice constant was 8.240 angstroms, and the crystallite diameter was 580 angstroms.

Example 6 In Example 1, after mixing the Li raw material and the Mn raw material,
After forming a 20 mmφ pellet at a pressure of 1 t / cm ² ,
The temperature is raised from room temperature to 750 ° C. in the air in 7 hours,
After maintaining at 24 ° C. for 24 hours, the temperature was lowered to room temperature in 7 hours, and the obtained heat-treated product was crushed in a mortar to obtain a target lithium manganese oxide.

The product showed an X-ray diffraction pattern similar to that of LiMn ₂ O ₄ of JCPDS card 35-782. From the analytical values, Li and Mn were in a molar ratio of Li: Mn = 1.01: 2.
00, the degree of oxidation of Mn is x = 1.76 when expressed as MnO _x , and the tap density is 1.9 g / c.
m ³ .

The a-axis length of the lattice constant was 8.243 angstroms, and the crystallite diameter was 580 angstroms.

Example 7 The conditions were the same as in Example 6, except that lithium hydroxide was used as the lithium raw material.

The product showed the same X-ray diffraction pattern as that of LiMn ₂ O _4.
i: Mn = 1.02: 2.00, the degree of oxidation of Mn was x = 1.77 when expressed as MnO _x , and the tap density was 1.8 g / cm ³ .

The a-axis length of the lattice constant was 8.240 angstroms, and the crystallite diameter was 590 angstroms.

Example 8 Lithium carbonate was used as a lithium raw material, and the molding pressure was 2 t.
/ Cm ² and other conditions were the same as in Example 6.

The product showed an X-ray diffraction pattern similar to that of LiMn ₂ O _4.
i: Mn = 1.00: 2.00, the degree of oxidation of Mn was x = 1.77 when expressed as MnO _x , and the tap density was 1.9 g / cm ³ .

The a-axis length of the lattice constant was 8.242 angstroms, and the crystallite diameter was 600 angstroms.

Comparative Example 1 As a manganese compound, a BET specific surface area was 20 m ² / g,
Γ-MnOOH of MnO1.51 (manufactured by Tosoh Corporation,
Product name: Manga Night) and use lithium nitrate as Li
And the molar ratio of Mn is Li: Mn = 1.025: 2.0
After mixing well in a mortar at the ratio of
The temperature was raised to 0 ° C in 8.5 hours, and kept at 850 ° C for 24 hours.

The product showed a pattern similar to that of LiMn ₂ O ₄ of JCPDS card 35-782. From the analysis results, Li and Mn were in a molar ratio of Li: Mn = 0.99: 2.0.
And the degree of oxidation of Mn is expressed as x = MnO _x
1.74.

The a-axis length of the lattice constant was 8.248 angstroms, and the crystallite diameter was 720 angstroms.

Comparative Example 2 As a manganese compound, a BET specific surface area of 20 m ² / g,
Γ-MnOOH of MnO1.51 (manufactured by Tosoh Corporation,
(Product name: Manga Night) was used under the same conditions as in Example 1.

At 264 ° C., β-MnO ₂ was produced, and at 450 ° C., the LiMn of JCPDS card 35-782 was obtained.
It becomes a broad peak close to n ₂ O ₄ and JC at 650 ° C.
A pattern similar to that of LiMn ₂ O ₄ of the PDS card 35-782 was shown. Also, from the analysis values, Li and Mn were in a molar ratio of Li: Mn = 1.02: 2.0, and the degree of oxidation of Mn was x = 1.76 when expressed as MnO _x .

The a-axis length of the lattice constant was 8.246 angstroms, and the crystallite diameter was 600 angstroms.

Comparative Example 3 The same conditions as in Example 1 were used except that EMD (Electrolytic manganese dioxide manufactured by Tosoh Corporation, trade name: HHU) having a BET specific surface area of 30 m ² / g was used as the manganese compound.

The product was prepared at 264 ° C. using X
A line diffraction pattern remained, and generation of LiMn ₂ O ₄ was not observed. At 650 ° C, JCPDS card 35-782
Shows a pattern similar to that of LiMn ₂ O _4, and from the analysis values, Li and Mn are in a molar ratio of Li: Mn = 1.01: 2.
0 and the degree of oxidation of Mn is expressed as x = MnO _x
1.77.

The a-axis length of the lattice constant was 8.246 angstroms, and the crystallite diameter was 510 angstroms.

Comparative Example 4 The EMD used in Comparative Example 3 was heated at 1000 ° C. for 24 hours, then taken out and quenched at room temperature to obtain a specific surface area of 0.5 m ² /
g, when the degree of oxidation of Mn is expressed as MnOx, x = 1.3.
Mn ₃ O ₄ which was No. 2 was synthesized.

The same conditions as in Example 1 were used, except that this Mn ₃ O ₄ was used as a manganese compound.

At 264 ° C., Mn ₃ O _{4 as} a raw material remained in the X-ray diffraction pattern at 264 ° C., and the behavior was clearly different from that of Example 1. At 650 ° C, JCPDS card 3
5-782 shows a pattern similar to that of LiMn2O4,
Also, from the analysis values, Li and Mn are in a molar ratio of Li: Mn =
1.01: 2.0, and the degree of oxidation of Mn was 1.77 when expressed as MnOx.

Comparative Example 5 The same procedure as in Example 1 was carried out except that Mn ₂ O ₃ having a specific surface area of 3.5 m ² / g and an oxidation degree of Mn of MnO _x where x = 1.50 was used as the manganese compound. The conditions were the same.

The product showed 264, 45 in the X-ray diffraction pattern.
At 0 ° C., Mn ₂ O _{3 as} a raw material was confirmed. 650 ° C
Shows a pattern similar to that of LiMn2O4 of the JCPDS card 35-782. From the analysis values, Li and Mn are in a molar ratio of Li: Mn = 1.03: 2.0, and the degree of oxidation of Mn is equal to MnOx. X = 1.77.

The a-axis length of the lattice constant was 8.246 angstroms, and the crystallite diameter was 530 angstroms.

Comparative Example 6 The same conditions as in Example 6 were adopted except that the temperature of the heat treatment was raised from room temperature to 900 ° C. in the air in 9 hours, kept at 900 ° C. for 24 hours, and then lowered to room temperature in 9 hours. I went in.

The a-axis length of the lattice constant was 8.250 angstroms, and the crystallite diameter was 740 angstroms.

Comparative Example 7 The same conditions as in Example 6 were used except that γ-MnOOH (manufactured by Tosoh Corporation, trade name: Manganite) was used as a manganese raw material.

The product showed the same X-ray diffraction pattern as that of LiMn ₂ O _4.
i: Mn = 1.00: 2.00, and the degree of oxidation of Mn was x = 1.76 when expressed as MnOx.

The a-axis length of the lattice constant was 8.246 angstroms, and the crystallite diameter was 560 angstroms.

The chemical analysis values of the products of Examples 1 to 8 and Comparative Examples 1 to 7 are shown in Table 1 below.

[0122]

[Table 1]

The primary particles, secondary particles, BET specific surface area, tap density, lattice constant a-axis length, and crystallite diameter of the products of Examples 1 to 8 and Comparative Examples 1 to 7 are shown in Table 2 below. It was shown to.

[0124]

[Table 2]

[Construction of Battery] The lithium manganese oxide obtained in Examples 1 to 8 and Comparative Examples 1 to 7 and a mixture of polytetrafluoroethylene and acetylene black (trade name: TAB-2) as conductive agents were used. Were mixed at a weight ratio of 2: 1. At a pressure of 1 ton / cm ² , the mixture is
After being formed into a pellet on a mesh (SUS316) having a diameter of mm, the resultant was dried under reduced pressure at 200 ° C. for 24 hours.

This was used for the positive electrode 3 in FIG.
For the negative electrode, a lithium piece cut out from a lithium foil (thickness: 0.2 mm) was used, and for the electrolyte, lithium hexafluorophosphate dissolved at a concentration of 1 mol / dm ^{3 in} a propylene carbonate solvent was used. The battery shown in FIG. 1 having a cross-sectional area of 2.5 cm ² was formed by impregnating the separator of FIG.

[Evaluation of Battery Characteristics] A battery was manufactured using the lithium manganese oxide prepared in each of Examples and Comparative Examples as a positive electrode active material. The battery voltage was 4.5 V at a constant current of 1.0 mA / cm ^2. The charge and discharge were repeated between 3.5 V and 3.5 V.

Table 3 shows the discharge capacity (first cycle), the discharge capacity retention ratio (% of the discharge capacity at the 20th cycle relative to the first cycle) and the tap density.

[0129]

[Table 3]

[0130] As shown in Table 3, Examples 1 to 5 had high performance.

Furthermore, Examples 6 to 8 have characteristics similar to those of the samples of Examples 1 to 5, but as shown in Table 3, the tap density is high, so that they have high filling properties, and Large filling amount.

Although some of the comparative examples had a large tap density, they were produced by the conventional method, and thus had a small discharge capacity and a low capacity retention rate.

[0133]

Industrial Applicability The lithium manganese oxide of the present invention has high electrochemical performance which exhibits high discharge capacity and stable charge / discharge cyclability, and its manufacturing method is based on a manganese compound having a spinel structure and a lithium compound. It is possible by mixing and heat-treating.Furthermore, in the production method of the present invention, after the mixture is subjected to pressure molding, by performing a heat treatment, a lithium manganese oxide having a high filling property can be produced. . Further, when the lithium manganese oxide of the present invention is used as a positive electrode active material of a lithium secondary battery, an operation of 3.5 to 4.5 V, which cannot be achieved by a conventional lithium secondary battery using a lithium manganese oxide, is performed. In addition to exhibiting a stable charge-discharge cycle property with a high discharge capacity in the potential region, the lithium manganese oxide of the present invention has a high filling property, so that a high-capacity lithium secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a battery constituted by an example and a comparative example.

──────────────────────────────────────────────────続 き Continued on front page (56) References Journal of Power Sources, vol. 41, No. 3, p305-314 (1993) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 45/00 H01M 4/02 H01M 4/58 CA (STN)

Claims (13)

(57) [Claims] 1. A Li, lithium-manganese oxide comprising Mn and O, the molar ratio of the crystal structure is spinel structure, Li and Mn Li: Mn = 1.00 ~1.10:
2.00, Mn oxidation degree 3.40-3.60 valence, BE
T specific surface area is not less 1 m ² / g or more, Ri substantially all of the primary particles is 1μm below der, the lattice constant a-axis length 8.23
Lithium manganese oxide having a particle size of 5 to 8.245 angstroms . 2. The lithium manganese oxide according to claim 1, wherein the primary particles are aggregated, and the average particle diameter of the aggregated particles is 1 to 30 μm. 3. The lithium manganese oxide according to claim 1, wherein the cubic spinel structure according to claim 1 has a crystallite diameter of 400 to 700 angstroms. 4. A lithium-manganese oxide according to claim 1 to 3 in which the tap density is equal to or is 1.7 g / cm ³ or more. 5. A method for producing a lithium manganese oxide by mixing a manganese compound and a lithium compound, followed by heat treatment, wherein the manganese compound is spinel
Structure, and the degree of oxidation of the manganese element was expressed as MnO _x
Wherein at least one manganese compound selected from the group consisting of manganese oxide, hydrated manganese oxide, manganese hydroxide and manganate hydroxide, wherein the value of x is 1.5 or less; The method for producing a lithium manganese oxide according to any one of claims 1 to 4 , which is a compound comprising an Mn-OH compound. 6. The manganese compound according to claim 5 ,
Claim the use of a spinel structure prepared by oxidizing a manganese hydroxide manganese compound 5
The method for producing a lithium manganese oxide according to the above. 7. A method for producing a lithium manganese oxide, comprising using a manganese compound having a spinel structure having a specific surface area of 5 m ² / g or more as the manganese compound according to claim 5 or 6. 8. A lithium compound is lithium hydroxide according to claim 5, lithium nitrate, claim 5-7, characterized in that at least one lithium salt selected from the group consisting of lithium chloride and lithium carbonate Production method of lithium manganese oxide. 9. The temperature of the heat treatment according to claim 5 is 50.
The method for producing a lithium manganese oxide according to claim 5 , wherein the temperature is 0 ° C. or more and 850 ° C. or less. 10. The method for producing a lithium manganese oxide according to claim 5 , wherein the heat treatment is performed at 200 ° C. or more and 500 ° C.
500 ° C or more after heat treatment at least once at less than
The heat treatment is performed again at 50 ° C. or less.
10. The method for producing a lithium manganese oxide according to any one of 5 to 9 . 11. The method for producing a lithium manganese oxide according to claim 5 , wherein the heat treatment is performed at 200 ° C. or more and 500 ° C.
The method for producing a lithium manganese oxide according to any one of claims 5 to 10 , wherein the heat treatment is performed at least once at a temperature lower than 500C and then the mixing is performed again, and then the heat treatment is performed at a temperature of 500C to 850C. The manufacturing method according to claim 12] Lithium manganese oxide in claim 5, claim wherein after mixing the manganese compound and the lithium compound, after the resulting mixture was pressure-molded, the heat treatment is performed 5 12. The method for producing a lithium manganese oxide according to any one of items 11 to 11 . 13. The lithium secondary battery, characterized by the use of lithium-manganese oxide according as the positive electrode active material to claim 1-4.