JP2001151511A - Lithium manganese double oxide and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive polarity active material for a lithium ion secondary battery excellent in high temperature cycle property. SOLUTION: The lithium manganese double oxide is a spinel type lithium manganese double oxide obtained by replacing a part of manganese site by another element and the replaced elements are distributed to be <=50% in the standard deviation (G) to the average value of the replaced element content in each primary crystal particle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a lithium manganese composite oxide and a secondary battery using the same as a positive electrode active material.

[0002]

2. Description of the Related Art A lithium ion secondary battery, which functions as a battery by a positive electrode and a negative electrode absorbing and releasing lithium ions from each other, has a high voltage and a high energy density, and is used for mobile phones, portable personal computers, video cameras, It can be suitably used for applications such as electric vehicles.

A positive electrode active material for a lithium ion secondary battery and
As a result, the layered composite oxide Li _1-XCoO_Two(0 ≦
x ≦ 1) can obtain a high voltage of 4V class and is high.
Because of its energy density, it has already been widely used
ing. On the other hand, raw material Co is scarce in resources and expensive
Therefore, there is a possibility that demand will increase significantly in the future.
If you think about it, there is concern about the supply of raw materials,
Could soar. Then, Li_1-xCoO_Two
Made of inexpensive Mn as a positive electrode active material
Using lithium manganese composite oxide as positive electrode active material
It is thought that.

[0004] However, the lithium manganese composite oxide has a problem in that the capacity deterioration when repeatedly charged and discharged at a temperature of 50 to 60 ° C is greater than that of the above-mentioned Li _1-x CoO ₂ . . In this regard, in order to (1) improve the crystallinity of the lithium manganese composite oxide, and (2) stabilize the crystal structure, a part of Mn is replaced by one or more elements to increase the capacity. It has been clarified that there is a deterioration suppressing effect. However, such improvement is not yet sufficient, and further improvement is required.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide lithium manganese which is suitable for a positive electrode active material of a lithium ion secondary battery, particularly, a positive electrode active material having excellent cycle characteristics. An object is to provide a composite oxide.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that when a part of the Mn site of the spinel-type lithium manganese composite oxide is substituted with another element, the substitution element between the primary crystal grains is changed. The inventors have found that the distribution state of the content affects the cycle characteristics, and have completed the present invention. That is, the gist of the present invention is a spinel-type lithium manganese composite oxide in which a part of the Mn site is substituted by another element, and the standard deviation σ of the average value of the substituted element content of each primary crystal particle is 50%. As described below, the present invention resides in a lithium manganese composite oxide in which the substitution elements are distributed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. According to the study of the present inventors, the spinel-type lithium manganese composite oxide in which a part of the Mn site is substituted with another element has a uniform distribution of the substitution element (other element) content between the primary crystal grains. In the case where the average content of the substitution element is the same, even when the content distribution between the primary particles is not uniform, the effect of suppressing the elution amount of Mn into the electrolytic solution is large, and as a result, This has the effect of improving the cycle characteristics.

The spinel-type lithium manganese composite oxide in which a part of the Mn site is replaced by another element, which is the object of the present invention, has the following chemical formula (1)

[0009]

## STR2 ## _{Li 1 + x Mn 2-xY} M Y O 4 (1)

(However, 0 <X <0.5, 0 <Y <0.
5, M represents a substitution element). In the above formula, as the substitution element represented by M, B,
Sn, Al, Ti, V, Cr, Fe, Co, Ni, C
Examples include elements selected from u, Zn, Mg, and Ga, and preferably aluminum (Al).

The method for determining the average content of the substitution element in the spinel-type lithium manganese composite oxide in which a part of the Mn site is substituted by another element and the content of the substitution element for each primary particle are not particularly limited. . First, as a method of obtaining the average content, for example, a small amount of a composite oxide sample (0.
About 5 g to 5 g) dissolved in an acid and analyzed by atomic absorption spectrometry, IC
There is a method of measuring by P (inductively coupled plasma) analysis or the like. However, this analysis technique cannot simultaneously measure the substitution element content of each primary particle. On the other hand, the substitution element content of each primary particle can be determined by, for example, Auger electron spectroscopy (AES). AES is a method in which a specific primary particle is spot-irradiated with an electron beam by observation with an electron microscope, and the emitted electrons due to the Auger effect are detected by energy analysis of scattered electrons. AES is preferable because the beam diameter of the electron beam can be reduced to 100 nm or less, and local composition analysis becomes possible. Therefore, it is possible to determine the respective replacement element contents for several to several tens of primary particles selected from a plurality of secondary particles. Further, the average value can be obtained by averaging the measured values. By the way, among the n primary particles, the i-th substituted element content is Xi, and the average substituted element content of the n primary particles is X _AV . , Change (sum of squared deviations)
S and standard deviation σ are calculated according to the following equations.

[0012]

(Equation 1)

The lithium manganese composite oxide according to the present invention has a standard deviation σ obtained as described above of 50% or less, preferably 30% or less, with respect to the average value of the content of the substituted elements. The method for producing a lithium manganese composite oxide in which a part of the Mn site is substituted with another element according to the present invention is not particularly limited, and according to a known method, the composition of the produced oxide becomes as uniform as possible. The lithium compound, the manganese compound, and the replacement element compound may be pulverized, mixed, and fired so that the content distribution of the replacement element between the primary particles is within the above range.

Examples of the lithium compound used as a raw material include one or a mixture of two or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxide and the like and hydrates thereof. As the manganese compound, for example, MnO ₂ , Mn ₂ O ₃ , M
Manganese oxides such as n ₃ O ₄ and MnO, or MnC
1 selected from carbonates such as O ₃ or MnOOH
Species or a mixture of two or more species.

[0015] The other element that replaces part of the manganese site
Compounds include oxides, hydroxides,
Organic acid salts, chlorides, nitrates, sulfates, etc. or their hydration
Things. Specifically, when the substitution element is Al,
Al_TwoO_Three, AlOOH, Al (OH)_Three, Al (CH
_ThreeCOO)_Three, AlCl_Three, Al (NO_Three)_Three・ 9H _Two
O, Al_Two(SO_Four)_ThreeAnd the like, preferably Al
_TwoO_Three, AlOOH, Al (OH)_ThreeIt is.

The proportions of these starting compounds used are Li, M
n and the substitution element M are used so as to have the composition represented by the general formula (1). These starting compounds are first mixed.
In the case of a compound that does not melt at the reaction temperature, it is preferable to reduce the particle diameter to 10 μm or less by means such as pulverization in order to increase the reactivity. The order of pulverization and mixing is not particularly limited, and pulverization and mixing can be performed in an arbitrary order. The method of pulverization and mixing is not particularly limited as long as uniform mixing is possible. Dry or wet methods may be used, and examples thereof include a mixing method using an apparatus such as a ball mill, a vibration mill, and a bead mill.However, the uniformity of the substitution element content distribution among the primary particles of the obtained composite oxide is preferably good. Wet mixing is preferred because it is necessary. When the mixture is wet, when the mixture is dried, the mixture may be granulated to, for example, 1 to 100 μm by means such as spray drying.

The firing temperature of the raw material mixture is usually 500 ° C. or higher, preferably 550 ° C. or higher, and usually 1000 ° C.
Below, especially 950 ° C or less is preferred. If the temperature is too low, a long reaction time is required to obtain a lithium-manganese composite oxide having good crystallinity, which is not preferable. On the other hand, if the temperature is too high, a phase other than the target lithium manganese composite oxide is generated, or a lithium manganese composite oxide having many defects is generated. It is not preferable because it causes deterioration due to collapse of the crystal structure due to discharge. When the temperature is raised from room temperature to the above reaction temperature, the temperature is gradually raised at a temperature of, for example, 5 ° C. or less per minute in order to perform the reaction more uniformly, or the temperature is temporarily stopped on the way, It is preferable to provide a holding time at a constant temperature.

The firing time is usually from 1 hour to 100 hours. If the time is too short, a lithium manganese composite oxide having good crystallinity cannot be obtained, and an excessively long reaction time is not practical. In order to obtain a lithium manganese composite oxide having few crystal defects, it is preferable to slowly cool to a certain temperature after the above reaction, and to cool at 800 ° C., preferably 5 ° C./min. It is preferable to gradually cool at the following cooling rate. The heating device used for firing is not particularly limited as long as the above-described temperature and atmosphere can be achieved, and for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, and the like can be used.

In the lithium manganese oxide thus produced, primary particles having a particle size of 0.1 to 3 μm are aggregated.
It is preferably composed of secondary particles having a particle size of 1 to 100 μm and having a specific surface area of 0.1 to ⁵ m ² / g by nitrogen adsorption. The size of the primary particles can be controlled by the degree of pulverization of the raw material, the firing temperature, the firing time, and the like. The particle size of the secondary particles can be controlled by the conditions for pulverizing the raw material, the conditions for spray-drying when performing spray-drying, the conditions for pulverization after calcination, and the classification conditions. The specific surface area can be controlled by the particle size of the primary particles and the particle size of the secondary particles.
It is reduced by increasing the particle size of the secondary particles and / or the particle size of the secondary particles.

A secondary battery can be manufactured using the lithium manganese oxide of the present invention in which a part of the Mn site is replaced by another element as a positive electrode active material. As an example of the secondary battery of the present invention, a secondary battery including a positive electrode, a negative electrode, an electrolytic solution, and a separator may be mentioned. An electrolyte exists between the positive electrode and the negative electrode, and the separator does not contact the positive electrode and the negative electrode. So be placed between them. As the positive electrode, the lithium manganese oxide (positive electrode active material) obtained according to the present invention, a conductive material, a binder, and a solvent for uniformly dispersing the lithium manganese oxide are mixed in a certain amount, and then mixed on a current collector. Apply. As the conductive material used here, natural graphite, artificial graphite, acetylene black, etc., as the binder polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc., dispersed Solvents include N-methylpyrrolidone, tetrahydrofuran, dimethylformamide and the like, but are not limited thereto. Examples of the material of the current collector include aluminum and stainless steel. After being coated on the current collector, it is dried and usually consolidated by a roller press or other methods.

On the other hand, as the negative electrode, a material obtained by applying a carbon-based material (natural graphite, pyrolytic carbon, or the like) on a current collector such as Cu, a lithium metal foil, a lithium-aluminum alloy, or the like can be used.

The electrolytic solution used in the present invention is a non-aqueous electrolytic solution. Specifically, as the electrolytic salt, LiClO ₄ , LiA
sF ₆ , LiPF ₆ , LiBF ₄ , LiBr, LiCF
₃ SO _{3 and the} like, and as a solvent constituting the electrolytic solution, tetrahydrofuran, 1,4-dioxane, dimethylformamide, acetonitrile, benzonitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene Examples thereof include carbonate, but are not limited thereto. These solvents may be used alone or as a mixture of two or more.

Examples of the separator used in the present invention include a polymer such as Teflon, polyethylene, polypropylene, and polyester, a nonwoven fabric filter such as glass fiber, and a composite nonwoven fabric filter of glass fiber and polymer fiber. In this manner, the secondary battery prepared using the positive electrode active material obtained by the present invention can obtain a secondary battery having a high capacity retention rate after a high-temperature charge / discharge cycle, as is clear from the examples. Can be

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to any examples as long as the gist is not exceeded. Example 1 Mn ₂ O ₃ , AlOOH, and LiOH were each represented by a composition in a final spinel-type lithium manganese composite oxide,
Li: Mn: Al was weighed so as to be 1.04: 1.84: 0.12 (molar ratio), and pure water was added thereto to prepare a slurry having a solid concentration of 30% by weight. While stirring this slurry, using a circulating medium stirring wet pulverizer,
After pulverizing until the average particle diameter of the solid content in the slurry becomes 0.5 μm, the slurry is spray-dried using a two-fluid nozzle spray type spray dryer, and further dried in an air atmosphere.
Baking was performed at 00 ° C. for 10 hours. As a result, substantially spherical granulated particles having an average particle diameter of about 8 μm were obtained. X-ray diffraction measurement confirmed that the powder had a cubic spinel-type lithium manganese composite oxide structure. In addition,
The particle size distribution was measured using a laser diffraction scattering type particle size distribution analyzer (LA910 manufactured by HORIBA). 1 g of the composite oxide powder thus obtained was dissolved in an acid, and the composition was analyzed by atomic absorption spectrometry.
The composition was n: Al = 1.04: 1.85: 0.11 (molar ratio).

Next, as a result of observation with a scanning electron microscope (SEM), the primary particles constituting the composite oxide granulated particles had a particle diameter of 0.2 to 1.0 μm. Regarding the Al content in the primary particles, Auger
The measurement was performed by electron spectroscopy. With respect to a total of four granulated particles, for each granulated particle, three primary particles constituting the granulated particle were selected, and for a total of 12 primary particles, Aug was determined.
er electron spectroscopy (measuring device: MIC manufactured by VG)
ROLAB310-F). As the information, the signal strength value for Al and Mn can be obtained, and the signal strength value of Al / M
n as a measure of Al content in Table 1
It was shown to. The standard deviation of these measurements from the mean is
It was 24.5%.

The above-mentioned lithium manganese composite oxide powder is mixed with acetylene black powder and polytetrafluoroethylene powder in a weight ratio of 75: 20: 5, kneaded in a mortar to form a sheet, and then with a 12 mmφ punch. Punching was performed to produce a 17.0 mg disk-shaped positive electrode mixture sheet.
This positive electrode mixture sheet was pressure-bonded to a 16 mmφ aluminum mesh using a hand press to form a positive electrode. Also,
As the negative electrode agent, fine graphite powder was prepared by mixing polyvinylidene fluoride (PVDF) and N-methyl-2-pyrrolidone (NM
This was mixed with P) to form a coating solution. This coating solution was applied on a Cu sheet, dried, and punched into a disk shape with a 12 mmφ punch to obtain a negative electrode. The net weight of the negative electrode active material in the negative electrode was 4.80 mg. The electrode produced in this manner was connected to CR203 via a polyethylene separator.
It was assembled into a type 2 (diameter 20 mm × thickness 3.2 mm) coin battery. At that time, ethylene carbonate (EC): diethyl carbonate (DEC) = 3:
A solution obtained by dissolving 1M-LiPF ₆ in 1 liter of the 7 composition solution was used. Four batteries were prepared, and one of the batteries was charged to 4.2 V, and the battery was charged at 80 ° C.
For 7 days. After the storage was completed, the battery was disassembled to collect the electrolytic solution, and the amount of Mn contained in the electrolytic solution was measured to be 0.18 μmol / ml.
On the other hand, for the remaining three batteries, a 1C charge / discharge cycle test in a range of 3.0 to 4.2 V was performed in a thermostat at 50 ° C. The initial discharge capacity in the first cycle of the three battery tests was 95 mAh / g, and the average value of the capacity retention rate after 50 cycles (discharge capacity in the 50th cycle / discharge capacity in the first cycle) was 89%. Met.

Example 2 Mn ₂ O ₃ , AlOOH, and LiOH were combined with each other in the final spinel-type lithium manganese composite oxide by the following composition:
Li: Mn: Al was weighed so as to be 1.04: 1.84: 0.12 (molar ratio), and pure water was added thereto to prepare a slurry having a solid concentration of 30% by weight. While stirring this slurry, using a circulating medium stirring wet pulverizer,
After pulverizing until the average particle diameter of the solid content in the slurry becomes 1.2 μm, the slurry is spray-dried using a two-fluid nozzle spray type spray dryer, and further dried in an air atmosphere.
Baking was performed at 00 ° C. for 10 hours. As a result, substantially spherical granulated particles having an average particle diameter of about 8 μm were obtained. X-ray diffraction measurement confirmed that the particles had a cubic spinel-type lithium manganese composite oxide structure. The particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (LA910 manufactured by HORIBA). 1 g of the composite oxide powder thus obtained was dissolved in an acid, and the composition was analyzed by atomic absorption spectrometry.
The composition was n: Al = 1.04: 1.85: 0.11 (molar ratio).

Next, as a result of SEM observation, the primary particles constituting the composite oxide granulated particles have a particle diameter of 0.2 to 0.2.
It was found to be 2.0 μm, but the Al content in the primary particles was similar to that of Example 1 except for Auger.
Measurements were made by electron spectroscopy. The results are shown in Table 1. The standard deviation of these measurements from the mean is 43
%Met.

On the other hand, using the composite oxide powder, four coin-type batteries were prepared in the same manner as in Example 1, and one of the batteries was charged to 4.2 V, and the charged state was maintained. It was stored in a thermostat at 80 ° C. for 7 days. After the storage was completed, the battery was disassembled to collect the electrolytic solution, and the amount of Mn contained in the electrolytic solution was measured.
ml. On the other hand, for the remaining three batteries, 50
A 1C charge / discharge cycle test in the range of 3.0 to 4.2 V was carried out in a constant temperature bath at ℃. The initial discharge capacity in the first cycle of these three battery tests was 95 mAh / g,
The average value of the capacity retention ratio (discharge capacity at the 50th cycle / discharge capacity at the first cycle) at the end of the cycle was 87%.

Comparative Example 1 Mn ₂ O ₃ , AlOOH, LiO
H is represented by the formula: Li: Mn: Al = 1.04:
The mixture was weighed so as to be 1.84: 0.12 (molar ratio), and was dry-mixed with a ball mill. The mixed powder was finally fired at 900 ° C. for 10 hours. The obtained positive electrode active material powder had a cubic spinel-type lithium manganate structure by X-ray diffraction. From the results of the particle size distribution measurement and the SEM observation, the primary particles of about 1.0 μm were aggregated, and the average particle diameter of the aggregate was 10 μm. Further, 1 g of the composite oxide powder thus obtained was dissolved in an acid, and the composition was analyzed by an atomic absorption method.
Mn: Al = 1.04: 1.85: 0.11 (molar ratio)
The composition was as follows. Next, with respect to the Al content in the primary particles of the composite oxide powder, selected from four aggregated particles,
In the same manner as in Example 1 for a total of 12 primary particles,
The measurement was performed by Auger electron spectroscopy. The results are shown in Table 1. The standard deviation for these measurements is 10
2.7%.

On the other hand, using the present composite oxide as a positive electrode active material,
Insert a CR2032 type coin battery in the same procedure as in the embodiment.
Each of the batteries was assembled, and one of the batteries was charged up to 4.2 V, and stored in a constant temperature bath at 80 ° C. for 7 days in a charged state. After the storage was completed, the battery was disassembled to collect the electrolytic solution, and the amount of Mn contained in the electrolytic solution was measured.
It was 2 μmol / ml. On the other hand, the remaining three batteries were subjected to a 1C charge / discharge cycle test in a range of 3.0 to 4.2 V in a constant temperature bath at 50 ° C. The initial discharge capacity in the first cycle of these three battery tests was 94 mAh / g.
Although there was no significant difference from the Example and Example, the average value of the capacity retention rate after 50 cycles (discharge capacity at 50th cycle / discharge capacity at 1st cycle) was as low as 81%.

Comparative Example 2 The compositions of Mn ₂ O ₃ , AlOOH and LiOH in the final spinel type lithium manganese composite oxide were as follows:
Li: Mn: Al was weighed so as to be 1.04: 1.84: 0.12 (molar ratio), and pure water was added thereto to prepare a slurry having a solid concentration of 30% by weight. This slurry was not subjected to wet pulverization, but was subjected to a stirring treatment with a stirring blade for 30 minutes, followed by spray drying, and further at 900 ° C. in the air atmosphere.
For 10 hours. As a result, although the sphericity was very poor, granulated particles having an average particle size of about 8 μm were obtained.
As a result of measuring the line diffraction, it was confirmed that it had a structure of a cubic spinel-type lithium manganese composite oxide. 1 g of the composite oxide powder thus obtained was dissolved in an acid, and the composition was analyzed by atomic absorption spectrometry.
The composition was i: Mn: Al = 1.04: 1.85: 0.11 (molar ratio).

Next, as a result of the SEM observation, the particle diameter of the primary particles constituting the composite oxide granulated particles was 0.5 to 0.5%.
It was found to be 3.0 μm. The Al content in the primary particles was measured by Auger electron spectroscopy in the same manner as in Example 1. The results are shown in Table 1. The standard deviation of these measurements from the mean is 72%
Met.

On the other hand, using the composite oxide powder as the positive electrode active material, four coin-type batteries were produced in the same manner as in Example 1,
One of the batteries was charged to 4.2 V, and stored in a constant temperature bath at 80 ° C. for 7 days while being charged. After the storage was completed, the battery was disassembled to collect the electrolytic solution, and the amount of Mn contained in the electrolytic solution was measured.
ml. On the other hand, for the remaining three batteries, 50
A 1C charge / discharge cycle test in the range of 3.0 to 4.2 V was carried out in a constant temperature bath at ℃. The initial discharge capacity in the cycle of these three battery tests was 95 mAh / g, and the average value of the capacity retention rate after 50 cycles (discharge capacity in the 50th cycle / discharge capacity in the first cycle) was 83%. Met.

[0035]

[Table 1]

[0036]

As is clear from the examples, the lithium secondary battery using the lithium manganese composite oxide according to the present invention as an active material, in which the content of Al partially substituted for Mn sites is uniformly distributed, according to the present invention. In comparison with the battery using the composite oxide of the comparative example in which the distribution of the Al content was non-uniform, the amount of Mn dissolved in the electrolytic solution when charging and discharging were repeated was suppressed, and after 50 cycles at 50 ° C. The capacity retention rate is excellent.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Keiji Yamahara 1000-term Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory F-term (reference) 4G048 AA04 AA05 AC06 AD06 5H003 AA04 BB05 BC01 BC06 BD00 5H014 AA01 AA06 EE10 HH00 5H029 AJ05 AK03 AL06 AM03 AM04 AM05 AM07 DJ16 DJ17 HJ00 HJ02

Claims (6)

[Claims] 1. A spinel-type lithium-manganese composite oxide in which a part of an Mn site is substituted with another element, wherein a standard deviation σ of the average value of the substituted element content of each primary crystal particle is 50% or less. A lithium manganese composite oxide characterized in that the substitution elements are distributed such that 2. A lithium-manganese composite oxide is represented by the following general formula (1) ## STR1 ## _{Li 1 + X Mn 2-XY} M Y O 4 (1) ( where, 0 <X <0.5,0 < 2. The lithium manganese composite oxide according to claim 1, wherein Y <0.5 and M represents a substitution element. 3. The method according to claim 1, wherein the substitution element is B, Sn, Al, Ti,
V, Cr, Fe, Co, Ni, Cu, Zn, Mg, Ga
The lithium manganese composite oxide according to claim 1, wherein the lithium manganese composite oxide is an element selected from the group consisting of: 4. The lithium-manganese composite oxide according to claim 3, wherein the substitution element is Al. 5. A positive electrode for a lithium ion secondary battery, wherein the lithium manganese composite oxide according to claim 1 is used as an active material. 6. A lithium ion secondary battery using the positive electrode according to claim 5.