JP2002226214A - New lithium manganese complex oxide and its production method and application thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a new lithium manganese complex oxide and to provide its production method, furthermore to provide a manganese type lithium secondary cell excellent in high-rate charge and discharge characteristics using the lithium manganese complex oxide as a cathode active material. SOLUTION: The lithium manganese complex oxide which has a spinel type crystal structure is denoted by the formula; Li1+XMn2-Y-ZMZO4+δ(M is one or more elements selected from Ni, Co, Fe, Cr, Cu, B, Al, Ga and In, 0<=X<=1/3, 0<=Y<=1/3, 9<Z<=0.25, -0.14<=δ<=0.5) and its average particle size is 5-20 μm, its BET specific surface area is below 1.0 m2.g-1 and the average crystalline diameter determined by Hall method is above 1,000 angstrom. The production method for the lithium manganese complex oxide and the lithium secondary cell using this lithium manganese complex oxide as a cathode are provided.

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, and more specifically, to a general formula Li _{1 + X} Mn _{2-YZM Z} O _{4+ δ} (where M is Ni, Co, F
e, at least one element selected from the group consisting of Cr, Cu, B, Al, Ga and In, where 0 ≦ X ≦ 1 / 3,0
≦ Y ≦ 1/3, 0 <Z ≦ 0.25, −0.14 ≦ δ ≦
0.5), having an average particle diameter of 5 to 20 μm and a BET
A lithium manganese composite oxide having a spinel type crystal structure having a specific surface area of 1.0 m ² · g ⁻¹ or less and an average crystallite diameter determined by Hall's method of 1000 Å or more, a method for producing the same, and a lithium manganese oxide thereof The present invention relates to a lithium secondary battery used for a positive electrode active material.

A manganese-based material is one of promising materials for various uses because it is inexpensive, is rich in manganese as a raw material, and is environmentally friendly.

[0003] Since lithium secondary batteries can theoretically be constructed with a high energy density, they are being applied to a wide range of fields as new types of secondary batteries for the next generation. Research aimed at improving performance, including those that have been developed, is being pursued.

[0004]

2. Description of the Related Art With the spread of mobile devices for personal use, the development of a small, lightweight, and high energy density lithium secondary battery has been strongly desired, and a carbonaceous material capable of inserting and extracting lithium in a negative electrode. Lithium-ion batteries using Pt have been commercialized.

[0005] At present, lithium cobalt oxide (hereinafter referred to as LiCoO ₂ ) is mainly used as a positive electrode material of a lithium ion battery. However, since a cobalt raw material is expensive, development of an alternative material is desired. I have.

[0006] As a positive electrode material showing a 4 V class electromotive force in place of LiCoO ₂ , lithium nickel oxide (hereinafter referred to as L
iNiO ₂ ) and lithium manganese spinel (hereinafter referred to as LiMn ₂ O ₄ ), which are abundant and inexpensive in terms of resources, have little impact on the environment, and ensure safety when used in batteries. LiMn ₂ O ₄ is considered to be the best cathode material for use as an auxiliary power source for batteries for hybrid-type electric vehicles and fuel cells because of its ease of use. Some have already been put into practical use.

In a hybrid-type battery for an electric vehicle, power assist performance when the vehicle starts or accelerates, and regenerative performance of kinetic energy during deceleration are important, and the ability to input and output a large current in a short time ( = High rate charge / discharge characteristics). Although such demands have been met by optimizing the battery structure and electrode structure, improvement of the positive electrode material itself is important for further improvement of battery performance. Also, LiM
Since the high-temperature stability of n ₂ O ₄ is inferior to LiCoO ₂ and LiNiO ₂ , improvement in this point is also important.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to propose a novel lithium manganese oxide having excellent high-rate charge / discharge characteristics and high-temperature stability, and a method for producing the same.
Another object of the present invention is to provide a high-output lithium secondary battery using the compound as a positive electrode active material.

[0009]

Means for Solving the Problems As a result of diligent studies aimed at simultaneously improving the high-rate charge / discharge characteristics and high-temperature stability of LiMn ₂ O ₄ , the average oxidation number of manganese was 8%.
/ 3 or more manganese compound, lithium compound and N
By baking a mixture with at least one metal material selected from i, Co, Fe, Cr, Cu, B, Al, Ga, and In by a predetermined method, a general formula Li _{1 + X} Mn is obtained.
_{2-YZ M Z O 4+ δ} ( wherein M is Ni, Co, Fe, Cr, C
at least one selected from u, B, Al, Ga, and In, and 0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <
Z ≦ 0.25, −0.14 ≦ δ ≦ 0.5), the average particle diameter is 5 to 20 μm, and the BET specific surface area is 1.0 m ^2.
G- ¹ or less, a novel spinel-type lithium manganese composite oxide having an average crystallite diameter of 1000 angstroms or more determined by the Hall method can be synthesized, and this can be used as a positive electrode of a lithium secondary battery. The inventors have found that a manganese-based lithium secondary battery having both high-rate charge / discharge characteristics and high-temperature stability can be constituted by using the active material, and have completed the present invention.

Hereinafter, the present invention will be described specifically.

The general formula Li _{1 + X} Mn _2-YZ M _Z O _{4+ δ} (where M is Ni, Co, Fe, Cr, Cu, B, Al, Ga,
At least one element selected from In,
0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦ 0.25
−0.14 ≦ δ ≦ 0.5) and an oxide having a spinel-type crystal structure. The compound of the present invention comprises lithium,
Manganese, metal element M (where M is Ni, Co, F
e, at least one element selected from the group consisting of e, Cr, Cu, B, Al, Ga, and In), and oxygen.
Lithium occupies the 8a site at the tetrahedral position and manganese and metal element M, or manganese and metal element M, or lithium and manganese and metal element M occupies the 16d site at the octahedral position in the cubic densely packed oxygen array. If the occupancy of each site of lithium, manganese, and the metal element M is within the range of the above general formula, the oxide will have a spinel crystal structure.

The lithium manganese oxide according to the present invention includes Ni, C and the like in addition to lithium, manganese and oxygen.
It is important to include at least one or more elements selected from o, Fe, Cr, Cu, B, Al, Ga, and In. By including these elements, stability at high temperatures is improved.

It is essential that the lithium manganese oxide of the present invention has an average particle diameter of 5 to 20 μm. If the average particle size is less than 5 μm, the stability at high temperatures is remarkably reduced, and in addition, the workability at the time of producing an electrode is not preferable. On the other hand, when the thickness exceeds 20 μm, the high-rate charge / discharge characteristics are significantly reduced.

The lithium manganese oxide of the present invention is
It is essential that the ET specific surface area be 1.0 m ² · g ^-1 or less. The larger the BET specific surface area, the better the contact with the electrolytic solution and the conductive material, which is advantageous for high-rate charge / discharge performance, but lowers high-temperature stability and deteriorates workability during electrode fabrication. The BET specific surface area is 1.0m
² · g ^-1 or less is good.

[0015] The lithium manganese oxide of the present invention is H
It is essential that the average crystallite diameter determined by the All method is 1000 Å or more. If the average crystallite diameter is in the above range, the average particle diameter and BET of the present invention
Good high-rate charge / discharge characteristics can be achieved even in the range of the specific surface area.

In the lithium manganese oxide having a spinel structure, the charge / discharge reaction proceeds as lithium at the 8a site diffuses in the solid phase through the empty 16c site. It is considered that the ease of movement of lithium ions, that is, the high-rate charge / discharge performance is affected by the degree of development of the lithium diffusion path inside the solid phase. Therefore, the higher the crystal structure, the better the high-rate charge / discharge performance. It is thought to be.
For use in hybrid-type electric vehicle batteries, it is necessary to charge or discharge at least 5C (conditions for charging or discharging the battery capacity in 1/5 hour), and details are unknown. When the average crystallite diameter determined by the Hall method was 1000 angstroms or more, remarkable improvement in high rate characteristics was observed. The average crystallite diameter is an index indicating the degree of repetitive development of the unit cell,
The larger the value, the more developed the crystal. The Hall method of the present invention can be applied to the diffraction of each diffraction peak obtained by powder X-ray diffraction measurement, for example, as described on page 75 and subsequent pages of X-ray diffraction guide revised 4th edition (Rigaku Corporation). In this method, the average crystallite diameter is determined from the position and the spread of the peak, that is, the half width.

In the case of a layered structure LiCoO ₂ or LiNiO ₂ , two-dimensional lithium diffusion in the solid phase occurs, whereas in the spinel structure, three-dimensionally developed lithium diffusion paths cause the lithium diffusion in the solid phase. It is easily assumed that the high-rate characteristics are excellent, but as in the present invention, the average particle diameter is 5 to 20 μm, the BET specific surface area is 1.0 m ² · g ⁻¹ or less, and the average crystallite diameter is 1000 Å or more. By doing so, it is possible for the first time to achieve both easy electrode fabrication and high-rate charge / discharge characteristics.

The lithium manganese oxide of the present invention comprises a manganese compound having an average manganese oxidation number of 8/3 or more;
Lithium compound, Ni, Co, Fe, Cr, Cu,
A mixture with at least one or more metal materials selected from B, Al, Ga, and In is first fired at a temperature of 500 ° C. or less, and then a second temperature at a temperature of more than 500 ° C. and 950 ° C. or less. It is synthesized by firing and then cooling to 500 ° C. at a rate of 20 ° C. or less per hour. By first performing the first baking at a temperature of 500 ° C. or less, the compounding reaction with the manganese compound, lithium compound, and metal element M easily proceeds uniformly, and the second baking is performed at a temperature exceeding 500 ° C. and 950 ° C. or less. By firing the
A lithium manganese composite oxide having a sufficiently developed crystal structure can be synthesized. Further, since lithium manganese oxide exhibits a property of releasing and absorbing oxygen at a high temperature, cooling after the second baking is performed by 1 in consideration of re-absorption of oxygen in the temperature decreasing process.
It is important to perform the reaction at a rate of 20 ° C. or less per hour for synthesizing a lithium manganese composite oxide having a uniform crystal structure. Note that the firing is preferably performed in the air or in a gas stream having an oxygen content of 18% or more, and in particular, this condition is more preferable in the second firing.

In the synthesis of the lithium manganese oxide of the present invention, it is important to use a manganese compound having an average manganese oxidation number of 8/3 or more. The manganese compound used in the synthesis has an average oxidation number of manganese in the compound of 8 /
Any three or more may be used. Although not limiting the present invention, examples of the oxide include oxides such as various crystalline forms of manganese dioxide, manganese trioxide, hydrated manganese oxide (MnOOH), and manganese tetraoxide, and manganese compounds. The average oxidation number of manganese synthesized by heat treatment at a temperature of 500 ° C. or more is 8/3
The above manganese oxides are exemplified. Although the details are unknown, among these, the use of manganese trioxide facilitates the synthesis of a lithium manganese composite oxide having a uniform crystal structure.

As the lithium compound used in the synthesis, any compound may be used as long as the compound starts to form a complex at a temperature of 500 ° C. or less with a compound having an average oxidation number of manganese of 8/3 or more. Although the present invention is not limited thereto, for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium iodide and the like are exemplified. In order to perform mixing more uniformly, the average particle diameter is 10 μm. It is preferable to use the following lithium compounds.

As the metal element M used for the synthesis, any compound may be used as long as it is a compound which starts a complexing reaction with a manganese raw material and a lithium raw material at a temperature of 500 ° C. or less. Without limiting the invention, for example, Ni, Co,
Examples thereof include carbonates, nitrates, hydroxides, and oxides of Fe, Cr, Cu, B, Al, Ga, and In.

As the negative electrode of the lithium secondary battery of the present invention, a lithium metal, a lithium alloy, or a compound capable of storing and releasing lithium, which has previously stored lithium, can be used.

The lithium alloy is not limited to the present invention, and examples thereof include a lithium / tin alloy, a lithium / aluminum alloy, and a lithium / lead alloy.

The compound capable of inserting and extracting lithium is not limited to the present invention, and examples thereof include carbon materials such as graphite and graphite, iron oxides and cobalt oxides.

The electrolyte of the lithium secondary battery of the present invention is not particularly limited. Examples thereof include carbonates such as prolene carbonate and diethyl carbonate; sulfolane such as sulfolane and dimethyl sulfoxide; lactones such as γ-butyrolactone; Dissolve at least one lithium salt such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, trifluoromethanesulfonic acid, etc. in at least one organic solvent such as ether such as dimethyl sulfoxide. In addition, inorganic and organic lithium-ion conductive solid electrolytes and the like can be used.

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

In the drawing, 1: positive electrode lead wire, 2: positive electrode current collecting mesh, 3: positive electrode, 4: separator, 5: negative electrode, 6: negative electrode current collecting mesh, 7: negative electrode lead wire,
8: Container.

Examples will be shown below as specific examples of the present invention, but the present invention is not limited by these examples.

Incidentally, the powder X-ray diffraction measurement and the calculation of the average crystallite diameter ε in Examples and Comparative Examples of the present invention were performed by the following methods.

X-ray powder diffraction measurement Measurement model MXS3 manufactured by Mac Science Inc. Irradiation Cu Kα ray Measurement mode Step scan Scan condition 0.04 ° as 2θ Measurement time 5 seconds Measurement range 2θ from 5 ° to 80 ° Calculation of average crystallite diameter Hall's method: β · cos θ / λ
= 2 · η · sin θ / λ + 1 / ε The profile of two or more diffraction lines is measured, and β · cos θ / λ is set to 2 on the Y axis.
The reciprocal of the intercept of the straight line obtained by plotting η · sin θ / λ on the X axis is the average crystallite diameter value ε.

Here, β: half width, λ: measured X-ray wavelength,
θ: Black angle of diffraction line ε: Average size of crystallite diameter, η: Non-uniform strain value of crystal

The BET specific surface area was measured by a nitrogen adsorption method, and the average particle diameter was measured by a Microtrac.

[0033]

EXAMPLES [Production of lithium manganese composite oxide] Example 1 (Synthesis of LiMn _1.8 Al _0.2 O ₄ )
iMn _1.8 Al _0.2 O ₄ was prepared by the following method.

Li: Mn: Al molar ratio of lithium carbonate, aluminum hydroxide and manganese trioxide is 1.0:
After mixing at 1.8: 0.2, the first baking was performed in air at 450 ° C. for 12 hours. Next, after the temperature was lowered to room temperature, pulverization and mixing were performed, and then the second firing was performed at 800 ° C. in the air for 24 hours. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel structure. Table 1 shows the value of ε, the average particle diameter, and the BET specific surface area as a result of the chemical composition analysis of the product.

Example 2 (Synthesis of LiMn _1.8 Ni _0.5 O ₄ ) As Example 2, cobalt hydroxide was used as the metal element and Li: M was used in a molar ratio of Li: M.
A lithium manganese composite oxide was synthesized in the same manner as in Example 1 except that the n: Ni ratio was mixed so as to be 1.0: 1.8: 0.5. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel structure. As a result of chemical composition analysis of the obtained compound, the value of ε, the average particle diameter, and the BET specific surface area are shown in Table 1.

Example 3 (Synthesis of LiMn _1.9 Co _0.1 O ₄ ) As Example 3, a 9: 9 hydrate of iron nitrate was used as a metal element, and Li: M was used in a molar ratio.
A lithium manganese composite oxide was synthesized in the same manner as in Example 1, except that the n: Fe ratio was mixed so as to be 1.0: 1.9: 0.1. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel structure. As a result of the chemical composition analysis, Table 1 shows the value of ε, the average particle diameter, and the BET specific surface area.

Example 4 (Synthesis of LiMn _1.8 Cr _0.2 O ₄ ) As Example 4, chromium trioxide was used as the metal element and Li: M was used in a molar ratio of Li: M.
A lithium manganese composite oxide was synthesized in the same manner as in Example 1, except that the n: Cr ratio was mixed so as to be 1.0: 1.8: 0.2. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel crystal structure. As a result of chemical composition analysis of the obtained compound, the value of ε, the average particle diameter, and the value of the BET specific surface area are shown in Table 1.

Example 5 (Synthesis of LiMn _1.8 Cu _0.2 O ₄ ) As Example 5, using a copper nitrate trihydrate as a metal material, a molar ratio of Li: M
A lithium manganese composite oxide was synthesized in the same manner as in Example 1, except that the n: Cu ratio was mixed so as to be 1.0: 1.8: 0.2. From the result of the powder X-ray diffraction measurement, it was found from the result of the powder X-ray diffraction measurement that the obtained compound had a spinel crystal structure. As a result of chemical composition analysis of the obtained compound, the value of ε, the average particle diameter, and the value of the BET specific surface area are shown in Table 1.

Comparative Example 1 As Comparative Example 1, LiMn was prepared in the same manner as in Example 1 except that the cooling rate after the second baking was 100 ° C. per hour.
n _1.8 Al _0.2 O ₄ was synthesized. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound was a spinel single phase. As a result of the chemical composition analysis, Table 1 shows the value of ε, the average particle diameter, and the value of the BET specific surface area.

[Structure of Battery] Examples 1 to 5 and Comparative Example 1
Was mixed with a mixture of polytetrafluoroethylene and acetylene black (trade name: TAB-2) as conductive agents at a weight ratio of 2: 1. After 75 mg of the mixture was formed into a pellet on a 16 mmφ mesh (SUS 316) at a pressure of 1 ton · cm ⁻² , a vacuum drying treatment was performed at 200 ° C. for 5 hours.

This was used for the positive electrode in FIG. 1, 3 for the negative electrode in FIG. 1, a lithium piece cut out of a lithium foil (thickness 0.2 mm) for the negative electrode in FIG. 1, and propylene carbonate for the electrolyte. the volume ratio of dimethyl carbonate 1: 2 mixed solvent of, impregnated with organic electrolyte prepared by dissolving lithium hexafluorophosphate in a concentration of 1 mol · dm ^-3 to 4 of the separator of Figure 1, the cross-sectional area 2 cm ² The battery shown in FIG.

[Evaluation of Rate Characteristics] First, using the battery prepared by the above method, charging and discharging for 5 cycles were performed at a constant current of 0.4 mA · cm ⁻² and a battery voltage of 4.5 V to 3.5 V. Repeated. Next, after charging the battery at a constant current of 0.4 mA · cm ⁻² until the battery voltage becomes 4.5 V,
Discharge was performed to 3.5 V at a constant current of 5 mA · cm ⁻² . Table 1, the ratio of the discharge capacity at 5 mA · cm ^-2 to the discharge capacity at 0.4 mA · cm ^-2 at the fifth cycle, i.e. exhibited a capacity retention rate.

[0043]

[Table 1] Each of the lithium manganese oxides synthesized in Examples 1 to 5 showed a high capacity retention of about 95%. On the other hand, the capacity retention of the lithium manganese composite oxide synthesized in the comparative example was 90%.

[0044]

As described above, a manganese compound having an average manganese oxidation number of 8/3 or more, a lithium compound, Ni, Co, Fe, Cr, Cu, B, Al, G
a, by baking a mixture with at least one or more metal materials selected from In, a general formula Li _{1 + X} Mn _2-YZ
M _Z O _{4+ δ} (where M is Ni, Co, Fe, Cr, Cu,
At least one selected from the group consisting of B, Al, Ga, and In, and 0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦
0.25, −0.14 ≦ δ ≦ 0.5), the average particle diameter is 5 to 20 μm, and the BET specific surface area is 1.0 m ² · g.
^-1 or less, the average crystallite diameter determined by the Hall method is 10
It is possible to synthesize a novel lithium manganese composite oxide having a spinel-type crystal structure of not less than 00 angstroms, and this cannot be achieved with conventional materials by using this as a positive electrode active material of a lithium secondary battery. In addition, they have found that a manganese-based lithium secondary battery having both high-rate charge / discharge characteristics and high-temperature stability can be constructed.

The finding of a lithium manganese composite oxide having excellent high-rate charge / discharge characteristics is an industrially useful finding.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a battery constituted by an example and a comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode lead 2 positive electrode current collecting lead 3 positive electrode 4 separator 5 negative electrode 6 negative electrode current collecting mesh 7 negative electrode lead 8 container

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H01M 4/58 H01M 4/58

Claims (4)

[Claims] 1. The general formula Li _{1 + X} Mn _2-YZ M _Z O _{4+ δ} (where M is Ni, Co, Fe, Cr, Cu, B, Al, Ga,
At least one element selected from In,
0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦ 0.25
−0.14 ≦ δ ≦ 0.5), and the average particle diameter is 5 to 5.
20 μm, the BET specific surface area is 1.0 m ² · g ⁻¹ or less, and the average crystallite diameter determined by the Hall method is 1
A lithium manganese composite oxide having a spinel-type crystal structure, wherein the lithium manganese composite oxide has a molecular weight of 000 Å or more. 2. A manganese compound having an average manganese oxidation number of 8/3 or more, a lithium compound, Ni, Co, Fe,
First, a mixture with at least one or more elemental compounds selected from Cr, Cu, B, Al, Ga, and In is mixed with 50
After performing the first baking at a temperature of 0 ° C. or less, the second baking is performed at a temperature of more than 500 ° C. and 950 ° C. or less, and then a rate of 20 ° C. or less per hour to cool to 500 ° C. The method for producing a lithium manganese composite oxide according to claim 1, wherein the method is performed. 3. The method for producing a lithium manganese composite oxide according to claim 2, wherein the manganese compound having an average oxidation number of 8/3 or more is manganese trioxide. 4. A lithium-manganese composite oxide according to claim 1, wherein at least one or more substances selected from lithium, lithium alloys and compounds capable of inserting and extracting lithium are used as a negative electrode, a non-aqueous electrolyte is used as an electrolyte, and the lithium-manganese composite oxide according to claim 1 is used as a positive electrode. Lithium secondary battery.