JPH0414757A - Non-aqueous solvent secondary battery - Google Patents

Abstract

PURPOSE:To improve filling density of a positive electrode active material to provide a non-aqueous solvent secondary battery with a positive electrode capacitance improved by providing a positive electrode containing as an active material oxide having manganese property wherein titanium oxide is mixed into manganese oxide and sintered. CONSTITUTION:Oxide having manganese property wherein titanium oxide is mixed into manganese dioxide, spinel structure lithium manganese oxide or oxide with these mixed and sintered is used as an active material. By mixing titanium oxide into manganese oxide and sintering, particles of the manganese oxide can be well sintered with one another by a function of titanium oxide as a sintering assistant, a dense oxide having manganese property can be obtained with large tap density. As a result, by using such an oxide having manganese property in a positive electrode active material, filling density of the positive electrode material in a battery having a constant capacity can be improved so that a high capacitance non-aqueous solvent secondary battery with a positive electrode capacitance improved can be obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a non-aqueous solvent secondary battery, and particularly to a non-aqueous solvent secondary battery with an improved positive electrode active material.

(Prior Art) In recent years, with the development of electronic devices, there has been a demand for the development of secondary batteries that are small, lightweight, have high energy density, and can be repeatedly charged and discharged.

This type of secondary battery uses lithium or lithium alloy as the negative electrode active material, and oxides, sulfides, etc. of molybdenum, vanadium, titanium, niobium, etc. as the positive electrode active material.
Those using selenide etc. are known.

On the other hand, manganese dioxide is used as a positive electrode active material having high energy density and high voltage in non-aqueous solvent-based batteries, and has been put into practical use. Therefore, in a non-aqueous solvent secondary battery having a lithium negative electrode, the use of the manganese dioxide as a positive electrode active material is being considered. However, such non-aqueous solvent secondary batteries have problems in charge/discharge cycle characteristics. That is, the manganese dioxide has a tunnel structure, and as the battery discharges, Li+ ions from the negative electrode enter the tunnel, thereby causing M n 0
The two-crystalline structure expands. The alkali metal ions in this tunnel are in a state where they can easily move, so when this battery is brought into a charged state, Li+ in the tunnel is released,
Correspondingly, the MnO2 crystal structure contracts. For this reason, if MnO2, which is used in conventional non-aqueous solvent secondary batteries, is used as it is as a positive electrode active material in secondary batteries, the initial discharge capacity is large, but as the battery charges and discharges, the crystal structure contracts and expands. There is a problem in that the tunnel structure of M n O□ collapses due to repetition of this process, and as the charge/discharge cycle progresses, the charge/discharge capacity deteriorates significantly.

For this reason, spinel-type lithium manganese oxide (LiMn204), which is made by adding a lithium compound (for example, Li2C03) to manganese dioxide and roasting it at a high temperature of 800 to 1000°C to strengthen the crystal structure, has been used as a positive electrode. Non-aqueous solvent secondary batteries have been proposed that use active materials to improve charge-discharge cycle characteristics.

However, spinel type Li as the positive electrode active material
Mn2O4 has a small tap density, and its theoretical capacity per weight is a constant value of about 148 mAh/g. Furthermore, the manganese dioxide as the positive electrode active material described above also has a small tap density and a theoretical capacity per weight that is approximately constant. Therefore, when these positive electrode active materials with low tap densities are housed in a cylindrical or coin-shaped battery with a spiral structure, there is a limit to the packing density, so there is a problem that sufficient battery capacity cannot be secured. there were.

A non-aqueous solvent secondary battery has also been proposed in which manganese dioxide is mixed with anatase-type titanium oxide as a sub-active material, and this mixture is used as a positive electrode active material to improve charge-discharge cycle characteristics (Japanese Patent Laid-Open Publication No. 64-6384).

(Problems to be Solved by the Invention) The present invention has been made in order to solve the conventional problems, and aims to provide a non-aqueous solvent secondary battery in which the packing density of the positive electrode active material is increased and the positive electrode capacity is improved. That is.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a method for adding titanium oxide to manganese dioxide, spinel-type lithium manganese oxide, or a mixed oxide thereof (hereinafter simply referred to as manganese oxide). This is a non-aqueous solvent secondary battery characterized by comprising a positive electrode containing as an active material a manganese oxide compounded and sintered.

Examples of the manganese dioxide include chemically synthesized manganese dioxide, activated chemically treated manganese dioxide, and the like.

The chemically synthesized manganese dioxide is produced, for example, by the method shown below. First, manganese sulfate (MnSO4)
Manganese sulfate is decomposed by heating and concentrating the solution to crystallize manganese sulfate, and roasting it at 800 to 1100°C for 10 minutes or more in an air atmosphere or an oxygen atmosphere with a higher oxygen partial pressure than air. Mn3O4 or M
n20. Prepare manganese oxide whose main component is Here, in the case of manganese oxide whose main component is Mn3O4, the
It is roasted at ℃ to produce manganese oxide whose main component is Mn2O3. Subsequently, the roasted manganese oxide powder is mixed into heated sulfuric acid solution and reacted for a desired time. Next, the reaction product is thoroughly washed with water, neutralized with aqueous ammonia, and further washed with water to obtain chemically synthesized manganese dioxide containing mainly γ-type manganese dioxide.

The activated chemically treated manganese dioxide is produced, for example, by the method shown below. First, natural manganese dioxide is crushed and roasted to produce Mn2o3.

This is further finely pulverized and mixed into a heated mineral acid such as sulfuric acid to convert it into manganese dioxide, which is neutralized and dried to obtain activated chemically treated manganese dioxide.

The spinel type lithium manganese oxide is manufactured, for example, by the method shown below. First, manganese sulfate (M
Dimanganese trioxide (Mn SO4) obtained from crystals
203) A predetermined amount of lithium salt such as lithium carbonate or lithium hydroxide is mixed with chemically synthesized manganese dioxide mainly composed of γ-type or activated chemically treated manganese dioxide obtained from natural manganese dioxide, and heated at 400 to 500°C or eoo~
Spinel type lithium manganese oxide is obtained by heating in a temperature range of 950°C.

When the heating temperature is 400 to 500''C, it is desirable that the mixing ratio of lithium salts (Mn to Li) is 4:1 to 2:i, and the resulting material is a spinel type LiM.
n 204 or spinel type LiMn 20° and M n
It is a mixed oxide with 02. Here, the heating temperature is set to 40
If the heating temperature is lower than 0'C, manganese dioxide will not be sufficiently dehydrated, while if the heating temperature exceeds 500C, dimanganese trioxide (Mn203) will be produced due to thermal decomposition of manganese dioxide.
), indicating a decrease in active material capacity and deterioration in cycle characteristics. Further, when the heating temperature is 600 to 950°C, the mixing ratio of manganese oxide and lithium salt (Mn:L
i) is preferably 2:1, and the resulting material is a spinel-type LiMn2O4 single phase.

From the viewpoint of uniformly dispersing the titanium oxide in the manganese oxide and sintering the particles of the manganese oxide,
Fine particles with a particle size of 1 to 50 μm are preferable, and usually,
A sol obtained by dispersing the titanium oxide in a solvent is used. The amount of titanium oxide blended is 0.5 to 20% by weight, more preferably 1.0 to 5% by weight based on the manganese oxide.
．． Preferably, it is 0% by weight. The reason for this is that if the amount is less than 0.5% by weight, the sinterability between manganese oxide particles cannot be improved, and it becomes difficult to sufficiently increase the amount of positive electrode active material per unit volume, that is, the density. When the amount exceeds 20% by weight, the amount of manganese oxide in the positive electrode active material decreases, and the capacity of the positive electrode active material itself may decrease.

The sintering is preferably performed at a temperature below the thermal decomposition temperature of each manganese oxide. Specifically, when using manganese dioxide, the temperature is preferably 300 to 500°C, and spinel type L
When iMn2O4 is used, it is desirable to carry out the heating at 300 to 900°C.

The positive electrode is usually prepared by preparing a slurry mixture by kneading the positive electrode active material, a conductive material such as acetylene black, a binding agent, etc. in a dispersion solvent, and then coating it on a conductive core such as aluminum. Manufactured by drying. Examples of the binder used here include a terpolymer of ethylene-propylene-cyclic diene, polytetrafluoroethylene, polyacrylic acid, and polyacrylates. Examples of the dispersion solvent include organic solvents and water.

Examples of the active material of the negative electrode used in the nonaqueous solvent secondary battery of the present invention include light metals such as lithium, alloys such as lithium aluminum alloy, carbon materials, and the like.

The electrolytes of the non-aqueous electrolyte used in the non-aqueous solvent secondary battery according to the present invention include LiPF6LiC, pO4, LiB
Examples include lithium salts such as F4 and LiCF3SO3. Examples of the solvent for the electrolytic solution include propylene carbonate (PC), ethylene carbonate (EP), tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, and 1,2-dimethoxyethane (DME). These solvents can be used alone or in a mixture of two or more, and from the viewpoint of prolonging the charge/discharge cycle life, a mixed solvent of propylene carbonate and 1,2-dimethoxyethane, a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran, etc. A mixed solvent of ethylene carbonate and 1,2-dimethoxyethane, a mixed solvent of propylene carbonate and tetrahydrofuran are desirable.

(Function) According to the present invention, by blending titanium oxide with manganese oxide and sintering the mixture, particles of the manganese oxide can be sintered well due to the action of the titanium oxide as a sintering aid. , a dense manganese oxide with a large tap density is obtained. As a result, by using such a manganese oxide as a positive electrode active material, it is possible to increase the packing density of the positive electrode active material in a battery of a certain volume. You can get batteries.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Example 1 First, a manganese sulfate (MnSO<) solution was heated and concentrated to form manganese sulfate crystals, and this was heated to 1050
By roasting at ℃ for 60 minutes, Mn3O4
A manganese oxide containing as the main component was obtained. The roasted manganese oxide was mixed into a 3M sulfuric acid solution at 90"C and reacted for 2 hours. The reaction product (M n 203 ) was thoroughly washed with water, neutralized with aqueous ammonia, and further washed with water. Then γ
Chemically synthesized manganese dioxide with a lump density of 1.91 g/cc was synthesized mainly from molds.

Titanium oxide sol [
TiO2 10% by weight] 20g was blended (3.3% by weight of titanium oxide with respect to the amount of manganese dioxide) and 4% by weight in air.
Sintered at 20℃ for 12 hours to achieve tap density of 2.2
0 g/ce of manganese oxide was obtained. When the crystal structure of this manganese oxide was investigated by X-ray diffraction, it was found that the crystal structure of the chemically synthesized manganese dioxide (γ-βM n
It was confirmed that there was no change in 02).

90% by weight of the sintered powder as a positive electrode active material, 7% by weight of acetylene black as a conductive material, and 3% by weight of an ethylene-propylene-cyclic diene terpolymer as an adhesive are kneaded in an organic solvent to form a slurry. A positive electrode mixture was prepared, and this positive electrode mixture was coated on an aluminum substrate with a thickness of 100 μm, air-dried, and then pressurized to a constant thickness.
0.26+a after heating and drying at 200℃ for 10 hours
A plate-shaped positive electrode having a positive electrode mixture layer with a thickness of m was manufactured.

Using the obtained positive electrode, a non-aqueous electrolyte secondary battery of single cell (AA) size as shown in FIG. 1 was assembled.

That is, the non-aqueous electrolyte secondary battery 1 includes a bottomed cylindrical stainless steel container 3 with an insulator 2 arranged at the bottom and which also serves as a negative electrode terminal.
has. In this container 3, an electrode group 4 is housed. This electrode group 4 includes a negative electrode 5, a separator 6, and a positive electrode 7.
It has a structure in which a strip-like material in which the following layers are laminated in this order is spirally wound so that the negative electrode 6 is located on the outside. The negative electrode 5 is formed from a strip-shaped lithium foil. The separator 6 is formed from a polypropylene porous film impregnated with an electrolytic solution. The electrolytic solution contains lithium hexafluorophosphate (L i P F b ) as an electrolyte in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane (volume ratio 50:50) at a concentration of 0.5 molar. . In the container 3 above the electrode group 4, an insulating plate 8 with an open center is arranged.

An insulating sealing body 9 is provided at the upper opening of the container 3.
It is crimped and fixed airtight. A positive electrode terminal IO is fitted into the central opening of the insulating sealing plate 8. This positive electrode terminal lO is connected to the positive electrode lead 11 of the positive electrode 7 of the electrode group 4.
connected via. Note that the negative electrode 5 of the electrode group 4
is connected to the container 3, which is a negative terminal, via negative terminals (not shown).

Example 2 Chemical synthesis of mainly γ type in Example 1 Dimanganese trioxide (Mn2on
) Mix 14g of lithium carbonate with Bog (Mn: L
i -2:1), heated in air at 850°C for 2 hours, cooled, mixed again, and heated at 850°C in air.
After reheating at ℃ for 2 hours, the tap density is 1.14g.
/cc of synthetic powder was obtained. When this synthesized powder was examined by X-ray diffraction, it was confirmed that LiMn20 was a single phase. Titanium oxide sol [T
i0210% by weight] was blended (titanium oxide! 5% by weight with respect to the amount of manganese dioxide) and heated at 600°C in air.
, after sintering for 12 hours, the tap density was 1.80g/
A manganese oxide of ec was obtained. Xlt! The crystal structure of this manganese oxide! When investigated by jI diffraction method,
It was confirmed that there was no change in the crystal structure of the LiMn2O4 single phase.

In addition to using this manganese oxide as the positive electrode active material,
A non-aqueous electrolyte secondary battery similar to that in Example 1 was assembled.

Example 3 8.5 g of lithium carbonate was mixed with γ-type chemically synthesized manganese dioxide GOg similar to that synthesized in Example 1 (Mn
: Li-3:l) in air at 450℃,
Heated for 3 hours, cooled, mixed again, and heated again in air at 450°C for 3 hours until the tap density was 1.
．． A synthetic powder of 43 g/cc was obtained. When this synthetic powder was examined by X-ray diffraction, it was found that spinel-type LiMn2O4
It was confirmed that it was a mixed oxide of γ-βM n O2. Titanium oxide sol [Ti02
10 wt.
After sintering for 2 hours, the tap density is 1.57g/cc.
of manganese oxide was obtained.

When the crystal structure of this manganese oxide was examined by X-ray diffraction, it was confirmed that there was no change in the crystal structure of the mixed oxide.

A non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that this manganese oxide was used as the positive electrode active material.

Comparative Example 1 Example 1 except that the same chemically synthesized γ-type manganese dioxide synthesized in Example 1, which had been heated and dehydrated in air at 450°C for 12 hours, was used as the positive electrode active material. A non-aqueous electrolyte secondary battery similar to that was assembled.

Comparative Example 2 Spinel type LiMn2O similar to that synthesized in Example 2
A non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1, except that No. 4 was used as the positive electrode active material.

Regarding the nonaqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, the battery voltage was set to 2.0 mA at a current of 100 mA. 3 from OV.
Charge to 3V and battery voltage to 3.3 with current 300a+A
2 from v. The discharge to Ov was repeated, and the discharge capacity at a predetermined number of charge/discharge cycles was measured.

The results are shown in FIG.

As is clear from FIG. 2, the battery of Example 1 is the same as that of Comparative Example 1.
It can be seen that the battery of Example 2 has a larger discharge capacity than the battery of Comparative Example 2, and the battery of Example 3 also has a larger discharge capacity. The reason for this is that particles of each manganese oxide, which is the positive electrode active material of the batteries of Examples 1 to 3, are sintered together using titanium oxide as a sintering aid, and as a result, the filling per unit volume of the positive electrode active material is This is due to increased density.

Note that, although the batteries of Examples 1 to 3 are all cylindrical, similar effects can be obtained with coin-shaped batteries.

[Effects of the Invention] As detailed above, according to the present invention, the packing density of the positive electrode active material can be increased, and the positive electrode capacity can be improved to provide a high-capacity non-aqueous solvent secondary battery. .

[Brief explanation of the drawing]

Figure 1 is a partial cross-sectional view showing the non-aqueous solvent secondary battery of Example 1, and Figure 2 is the discharge versus number of charge/discharge cycles in the non-aqueous solvent secondary batteries of Examples 1 to 3 and Comparative Example 1.2. FIG. 3 is a characteristic diagram showing changes in capacitance. 1... Non-aqueous electrolyte secondary battery, 2... Insulator, 3...
・Stainless steel container, 4... Electrode group, 5... Negative electrode, 6
... Separator, 7... Positive electrode, 8... Insulating plate, 9
... Insulating sealing body, 10 ... Positive electrode terminal, 11 ... Positive electrode lead. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] A non-aqueous solvent secondary comprising a positive electrode containing as an active material a manganese oxide obtained by blending titanium oxide with manganese dioxide, spinel-type lithium manganese oxide, or a mixed oxide thereof and sintering the same. battery.