JPH03214562A - Manufacture of positive electrode for secondary battery with non-aqueous electrolyte - Google Patents

Abstract

PURPOSE:To enhance the capacity retention characteristic as required associate with progress of the charge/discharge cycles, by mixing heat treated manganese dioxide or complex oxides of lithium and manganese dioxide, with an electroconduction auxiliary agent, binder and water, subjecting the admixture to the drying process at a specified temp., and using this to the positive electrode. CONSTITUTION:A battery is composed of a battery case 1, sealing plate 2, lithium alloy 3, gasket 4, separator 6, and pos. electrode black mix 6. Manganese dioxide or a complex oxide of lithium and manganese dioxide having undergone a heat treatment at a temp. between 200 and 430 deg.C is mixed with an electroconduction auxiliary agent, binder, and water, and the resultant mixture is heat treated under the drying condition between 60 and 180 deg.C. A pos. electrode thus formed is used to assemble a battery. This pos. electrode leaves a bound water of manganese dioxide, which stabilizes crystals of manganese dioxide. This enhances the capacity retention characteristic associate with the progress of charge/discharge cycles.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a positive electrode for a secondary battery using a non-aqueous electrolyte and using metallic lithium, a lithium alloy, or linear graphite as the negative electrode.

Conventional technology A secondary battery using a non-aqueous electrolyte uses metallic lithium, lithium alloy, or near graphite for the negative electrode, and MnO2, TiS2, or v20, for the positive electrode.
There are some that use These batteries are advantageous in that they have a higher energy density and better storage stability than secondary batteries that use aqueous solutions.

Among these, manganese dioxide has a particularly high voltage,
It is considered to be promising as a positive electrode for non-aqueous electrolyte secondary batteries because it is an abundant resource and inexpensive. When manganese dioxide is used as a positive electrode active material in a non-aqueous electrolyte battery, it is necessary to perform water removal treatment because lithium, which is a negative electrode active material, is highly reactive with water. Furthermore, by heat treatment at 200° C. to 430° C., the crystal structure of manganese dioxide changes, changing to a crystal structure in which lithium ions can easily diffuse.

Specifically, γ or γ-β type manganese dioxide heat-treated at a temperature of 200°C to 350°C, or β-type manganese dioxide heat-treated at a temperature of 350°C to 430°C is used. In addition, lithium-manganese dioxide composite oxide is made by inserting lithium into the crystal lattice of manganese dioxide to stabilize its crystal structure, with the aim of improving the capacity retention characteristics as the charge/discharge cycle of manganese dioxide progresses. . Specifically, it is obtained by mixing manganese dioxide and lithium hydroxide (LiOH) and firing the mixture at 200°C to 450°C.

Then, in order to manufacture a positive electrode for a battery, the above-mentioned manganese dioxide or lithium-mancanthic dioxide composite oxide, a conductive additive, and a binder are mixed, and a positive electrode is formed. However, in this step, the dehydrated manganese dioxide and lithium manganese dioxide composite oxide end up adsorbing water again. Therefore, in order to remove the re-adsorbed water before incorporating this positive electrode into a battery, heat treatment has conventionally been performed at temperatures exceeding 200° C. and up to 320° C.

Problems to be Solved by the Invention The positive electrode of a non-aqueous electrolyte secondary battery that has been subjected to the conventional drying process as described above has the problem that its discharge capacity decreases significantly as the charge/discharge cycle progresses. .

Means for Solving the Problems The present invention uses a lithium-manganese dioxide composite oxide or manganese dioxide heat-treated at a temperature of over 200°C to about 430°C as a positive electrode active material, and uses this positive electrode active material as a positive electrode active material. The present invention attempts to solve the above-mentioned problems by providing a non-aqueous electrolyte secondary battery that uses a positive electrode that has been dried at a temperature of over 60° C. to 180° C. after adding moisture.

The present inventor has developed a positive electrode made of a mixture of manganese dioxide, a conductive agent, a binder, and water dried under reduced pressure at a temperature of over 200° C. to 430° C., and a lithium manganese dioxide composite oxide and a conductive agent. A detailed and systematic experiment on the influence of the drying conditions of a positive electrode made of a mixture of a binder, a binder, and water on the capacity retention characteristics of a non-aqueous electrolyte secondary battery as the charging/discharging cycle progresses. As a result of our investigation, we found the following phenomenon.

That is, in the manganese dioxide heat-treated at a temperature exceeding 200° C. and up to 430° C. and the lithium-manganese dioxide composite oxide immediately after synthesis, moisture that adversely affects lithium batteries is sufficiently removed. However, in order to manufacture a positive electrode, water must be added and thoroughly stirred to uniformly mix this heat-treated manganese dioxide or lithium-manganese dioxide composite oxide, conductive additive, and binder. . Since the manganese dioxide and lithium-manganese dioxide composite oxide from which water has been removed in this process adsorb water again, it is necessary to perform heat treatment again to remove water. Generally, this heat treatment is performed at a temperature exceeding 200°C and up to 320°C. This is because a drying temperature of 200°C or less is insufficient to completely remove the bound water of manganese dioxide and lithium-manganese dioxide composite oxide, and if the drying temperature exceeds 320°C, manganese dioxide crystals This is because the structure may change or the binder may decompose, causing the mixture to lose its shape, making it difficult to assemble the battery. However, batteries are assembled using positive electrodes prepared at temperatures above 200°C and up to 320°C.
When charging and discharging the battery, it was found that there was a problem with the capacity retention characteristics as the charge/discharge cycle progressed.

Therefore, the present inventor mixed manganese dioxide or lithium-manganese dioxide composite oxide heat-treated at a temperature of over 200°C to 430°C, a conductive additive, a binder, and water, and then heated the mixture at a temperature of over 60°C. When a battery was assembled using a positive electrode that had been heat-treated under dry conditions up to 180°C and charged and discharged, it was found that the capacity retention characteristics improved dramatically as the charge-discharge cycle progressed.

According to the present invention, a positive electrode that has been dried at 180°C or lower, which is an insufficient temperature to completely remove the bound water of manganese dioxide and lithium-manganese dioxide composite oxide, The combined oxides of manganese dioxide and lithium-manganese dioxide composite oxides exhibit better capacity retention characteristics as the charge-discharge cycle progresses than positive electrodes in which the bound water of the composite oxides is almost completely removed. It is presumed that there is a close correlation with the capacity retention characteristics as the cycle progresses. In other words, bound water occupies a certain position within a crystal and is necessary for stabilizing the crystal lattice.

A positive electrode heat-treated under conventional drying conditions has an unstable crystal structure because the bound water of manganese dioxide has been removed, and as the charge/discharge cycle progresses, the crystals collapse and the discharge capacity decreases. . This positive electrode can be used for primary batteries, but is not suitable for secondary batteries. However, by leaving the bound water of manganese dioxide as in the dry-treated positive electrode of the present invention, this bound water stabilizes the crystals of manganese dioxide, resulting in extremely excellent capacity retention as the charge/discharge cycle progresses. This seems to indicate the characteristics.

The positive electrode drying treatment conditions of the present invention are preferably 180° C. or lower, but ideally 120° C. exhibits the best discharge capacity and capacity retention characteristics as the charge/discharge cycle progresses. A positive electrode dried under a drying condition of 60° C. or lower exhibits excellent cycle capacity Il retention characteristics, but has problems in long-term storage stability and discharge capacity because water adsorbed on the surface of manganese dioxide is insufficiently removed. At 180° C. or higher, the removal of bound water progresses, so that the capacity retention characteristics deteriorate as the cycle progresses.

Example Hereinafter, the present invention will be explained in detail using preferred embodiments.

[Battery A1] (Embodiment of the present invention) Manganese dioxide obtained by heat-treating γ-type manganese dioxide at 375° C. for 5 hours under reduced pressure of 50 mmHg or less and then heat-treating it at 375° C. for 5 hours in air is used.

To 100 parts by weight of this heat-treated manganese dioxide, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added and kneaded well. A positive electrode mixture was prepared by drying with warm air for several hours. Then, 107 mg of the positive electrode mixture was weighed and wrapped in a 180-mesh nickel net to produce 2 tons/c.
A positive electrode is formed by pressure molding at m2. The dimensions of the positive electrode are diameter 1
The thickness is approximately 5.0 mm and the thickness is 0.6 mm. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 20° C. for 3 hours.

The negative electrode was a 0.4 mm thick lithium-aluminum alloy plate (8
0wt$Li) was punched out to a diameter of 16 mm in an argon-substituted dry box. In addition, the electrolyte is 2 methyltetrahydrofuran (2Me-T}IF
) in which 1.5 mol/liter of lithium hexafluoroarsenate (LiAsF6) was dissolved was used, and a micro bolus separator of polypropylene (Zieragaard 2400) and a nonwoven fabric of polypropylene were used for the separator, with an outer diameter of 20. A battery with a height of 0 mm and a height of 2.0 mm was created. This invention battery is referred to as (A1).

FIG. 5 is a longitudinal sectional view of the battery. In this figure, l is a case that also serves as a positive electrode terminal, which is made by punching an organic electrolyte-resistant stainless steel plate using a press, and 2 is a sealing plate that also serves as a negative electrode terminal, which is made by stamping the same material. The material lithium-aluminum alloy 3 is pressure-bonded.

5 is a separator made of polypropylene impregnated with an organic electrolyte; 6 is a positive electrode mixture; the open end of the battery case 1, which also serves as a positive electrode terminal, is swaged inward, and the sealing plate 2, which also serves as a negative electrode terminal, is attached via a gasket 4; By tightening the periphery, it is hermetically sealed.

[Battery A2] (Example of the present invention) γ-type manganese dioxide was heat-treated at 375°C for 5 hours under reduced pressure of 50 mmHg or less, and then heated in air for 3 hours.
Manganese dioxide heat-treated at 75° C. for 5 hours is used. 5 parts by weight of acetylene black (conductivity aid) and 4 parts by weight of this heat-treated manganese dioxide.
After adding 2 parts by weight of fluorinated ethylene (binder) and thoroughly kneading, the mixture was dried with hot air at 60° C. for 4 hours to prepare a positive electrode mixture.

Then, weigh 107 mg of the positive electrode mixture and
Wrapped in a mesh nickel net, 2 tons/cm2
Pressure mold it to make a positive electrode. The dimensions of the positive electrode are 15 mm in diameter.
0mm thickness sail is about 6mm. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 60° C. for 3 hours. Example 1 except for using this positive electrode
I made a similar battery.

This invention battery is referred to as (A2).

[Battery A3 (Example of the present invention) γ-type manganese dioxide was heat-treated at 375°C for 5 hours under reduced pressure of 50 mmH3 or less, and then heated in air for 3 hours.
Manganese dioxide heat-treated at 75° C. for 5 hours is used. 5 parts by weight of acetylene black (conductivity aid) and 4 parts by weight of this heat-treated manganese dioxide.
After adding 2 parts by weight of fluorinated ethylene (binder) and thoroughly kneading, the mixture was dried with hot air at 120° C. for 4 hours to prepare a positive electrode mixture. Then, we weighed 107 mg of the positive electrode mixture and wrapped it in a 180 mesh nickel net, making it 2 tons/107 mg each.
A positive electrode is formed by pressure molding in cm2. The dimensions of the positive electrode are approximately 15.0 mm in diameter and 0.6 mm in thickness. Before this positive electrode was incorporated into a battery, it was again subjected to hot air drying treatment at 120° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This invention battery is referred to as (A3).

[Battery A4 (Embodiment of the present invention) γ-type manganese dioxide was heat-treated at 375° C. for 5 hours under reduced pressure of 50 mmHg or less, and then manganese dioxide was used which was heat-treated at 375° C. for 5 hours in air.

Acetylene black (conductivity aid) for 100 parts by weight of this heat-treated manganese dioxide
5 parts by weight and 1 part of polytetrafluoroethylene (binder) were added and thoroughly kneaded, followed by hot air drying at 180° C. for 4 hours to prepare a positive electrode mixture. Then, 107 mg of the positive electrode mixture was weighed out, wrapped in a 180-mesh nickel mesh, and press-molded at 2 tons/cm2 to form a positive electrode. The dimensions of the positive electrode are 15.0 mm in diameter and 0.6 mm in thickness.
That's about it. Before incorporating this positive electrode into the battery,
Hot air drying treatment was performed at 80° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This invention battery is designated as (A4).

[Battery A5] (Comparative Example) After heat-treating γ-type mankan dioxide at 375° C. for 5 hours under reduced pressure of 50 mmHg or less, manganese dioxide which was heat-treated at 375° C. for 5 hours in air is used.

To 100 parts by weight of this heat-treated manganese dioxide, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of Bois tetrafluoroethylene (binder) were added and kneaded well. A positive electrode mixture was prepared by drying with hot air for a period of time. Then, 107 mg of the positive electrode mixture was weighed out and wrapped in a 180-mesh nickel net, resulting in 2 tons/
cm2 and pressure molded to form a positive electrode. The dimensions of the positive electrode are approximately 15.0 mm in diameter and 0.6 mm in thickness. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 230° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This comparison battery (
A5).

[Battery 86] (Comparative Example) After heat-treating γ-type manganese dioxide at 375° C. for 5 hours under reduced pressure of 50 mm}Ig or less, manganese dioxide heat-treated at 375° C. for 5 hours in air is used.

To 100 parts by weight of this heat-treated manganese dioxide, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added, kneaded well, and heated at 300°C. A positive electrode mixture was prepared by drying with hot air for 4 hours. Then, 107 mg of the positive electrode mixture was weighed out, wrapped in a 180-mesh nickel mesh, and pressure-molded at 2 tons/cm2 to form a positive electrode. The dimensions of the positive electrode are 15.0 mm in diameter and 0.0 mm in thickness. It is about 6 mm. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 300° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This comparison battery is designated as (86).

[Battery Bl] (Example of the present invention) Lithium-
Synthesize manganese dioxide composite oxide. Acetylene black (conductivity aid) for 100 parts by weight of this positive electrode active material.
After adding 5 parts by weight of and 2 parts by weight of polytetrafluoroethylene (binder) and thoroughly kneading, the mixture was dried with warm air at 20° C. for 4 hours to prepare a positive electrode mixture. Then, 107 mg of the positive electrode mixture was weighed out, wrapped in a 180-mesh nickel mesh, and press-molded at 2 tons/cm2 to form a positive electrode. The dimensions of the positive electrode are approximately 15.0 mm in diameter and 6 mm in thickness. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 20° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode.

This invention battery is referred to as (B1).

[Battery B2] (Wood Invention Example) After mixing 100 g of chemical manganese dioxide and 25 g of lithium hydroxide in a mortar, a lithium-manganese dioxide composite oxide is synthesized by heat-treating the mixture in air at 375° C. for 20 hours. To 100 parts by weight of this positive electrode active material, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added and kneaded well, and then heated at 60°C for 4 hours. A positive electrode mixture was prepared by drying with hot air. Then, 107 mg of the positive electrode mixture was weighed out, wrapped in a 180-mesh nickel mesh, and press-molded at 2 tons/cm2 to form a positive electrode. The dimensions of the positive electrode are approximately 15.0 mm in diameter and 0.6 mm in thickness. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 60° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This invention battery is referred to as (B2).

[Battery B3 (Example of the present invention), chemical manganese dioxide 100g and lithium hydroxide 25g
After mixing in a mortar, it was heated at 375℃ in air for 20 minutes.
A lithium-manganese dioxide composite oxide is synthesized by heat treatment for a period of time. To 100 parts by weight of this positive electrode active material, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added and kneaded well, and then heated at 120°C for 4 hours. A positive electrode mixture was prepared by drying with hot air. Then, 107 mg of the positive electrode mixture was weighed and wrapped in a 180 mesh nickel net.
A positive electrode is formed by pressure molding at 2 tons/cm2.

The dimensions of the positive electrode are approximately 15.0 mm in diameter and 6 cm thick.

Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 120° C. for 3 hours. A battery similar to Example 1 was produced except for using this positive electrode. This invention battery is designated as (B3).

[Battery B4 (Embodiment of the present invention) 100 g of chemical manganese dioxide and 25 g of lithium hydroxide are mixed in a mortar, and then heat treated in air at 375° C. for 20 hours to synthesize a lithium-manganese dioxide composite oxide. To 100 parts by weight of this positive electrode active material, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added, kneaded well, and then heated at 180°C for 4 hours. A positive electrode mixture was prepared by drying with hot air. Then, 107 mg of the positive electrode mixture was weighed and wrapped in a 180-mesh nickel net, and the dimensions of the electrode were approximately 15.0 mm in diameter and 0.6 mm in thickness. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 180° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This invention battery is designated as (B4).

[Battery B5 (Comparative Example) 100 g of chemical manganese dioxide and 25 g of lithium hydroxide are mixed in a mortar and then heat treated in air at 375° C. for 20 hours to synthesize a lithium-manganese dioxide composite oxide. To 100 parts by weight of this positive electrode active material, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added and kneaded well, and then heated at 230°C for 4 hours. A positive electrode mixture was prepared by drying with hot air. Then, 107 mg of the positive electrode mixture was weighed and wrapped in a 180-mesh nickel net.
A positive electrode is formed by pressure molding at ton/cm2. The dimensions of the positive electrode are 15mm in diameter. 0mm thickness sail is about 6mm. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 230° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This comparative battery is referred to as (B5).

[Battery B6 (Comparative Example) After mixing 100 g of chemical manganese dioxide and 25 g of lithium hydroxide in a mortar, a lithium-manganese dioxide composite oxide is synthesized by heat-treating the mixture in air at 375° C. for 20 hours. To 100 parts by weight of this positive electrode active material, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added and thoroughly kneaded.
A positive electrode mixture was prepared by drying with hot air at 00° C. for 4 hours. Then, the positive electrode mixture was weighed in units of 107 B, wrapped in a 180-mesh nickel mesh, and press-molded at 2 tons/cm2 to form a positive electrode. The dimensions of the positive electrode are approximately 15.0 mm in diameter and 0.6 mm in thickness. Before incorporating this positive electrode into a battery, it was again subjected to hot air drying treatment at 300° C. for 3 hours. A battery similar to that of Example 1 was produced except for using this positive electrode. This comparative battery is referred to as (B6).

Figures 1 and 2 are capacity retention characteristic diagrams as the charge/discharge cycle progresses when these batteries are charged and discharged in a 20'C constant temperature bath under the following conditions.

Charge end voltage 3.4V, discharge end voltage 2. Ov, charging/discharging current! ，? It says 1.8mAC1.0mA/cm. As is clear from Figures 1 and 2, the battery of the present invention (
AIXA2XA3) (A4XBIXB2XB3) (84
) has improved capacity retention characteristics as the charge/discharge cycle progresses compared to the comparative battery (A5XA68B5) (36).

Figures 3 and 4 show the relationship between the discharge capacity at the 100th cycle in Figures 1 and 2 and the heat treatment temperature. As is clear from these results, it can be seen that the positive electrode subjected to conventional heat treatment conditions of 200° C. to 300° C. has a small discharge capacity and is unsuitable for use as a secondary battery.

The positive electrode drying treatment conditions of the present invention are preferably 180° C. or lower, but ideally 120° C. exhibits the most convenient capacity retention characteristics as the charging/discharging cycle progresses.

Positive electrodes dried at temperatures below 60°C exhibit excellent capacity retention characteristics as the charge/discharge cycle progresses, but long-term storage and charge/discharge capacity are affected due to insufficient removal of water adsorbed on the surface of manganese dioxide. There's a problem. At temperatures above 180°C, removal of bound water progresses, resulting in a decrease in capacity retention characteristics as the cycle progresses.

In this example, a case was explained in which hot air drying in air was used as the drying condition, but reduced pressure, oxidation, reduction,
A similar effect can be obtained by heat treatment in an inert atmosphere. Further, in this example, after adding water to the positive electrode active material, drying was performed twice, and the second drying process was to remove surface adsorbed water adsorbed from the atmosphere during pellet molding. Therefore, if these operations are performed in a dry atmosphere, there is no need to carry out the drying process twice.

Effects of the Invention As mentioned above, a non-woven fabric characterized in that a heat-treated manganese dioxide or lithium-manganese dioxide composite oxide conductive aid, a binder, and water are mixed and then dried at a temperature of 200°C or less. By using the positive electrode of an aqueous electrolyte secondary battery, the capacity retention characteristics of this type of battery as the charge/discharge cycle progresses can be dramatically improved, and its industrial value is extremely large.

[Brief explanation of drawings]

Figures 1 and 2 show the relationship between charge/discharge cycles and discharge capacity. Figures 3 and 4 are relationship diagrams between heat treatment temperature and discharge capacity at the 100th cycle. FIG. 5 is a longitudinal cross-sectional view of the battery in the example. 1 Battery case, 2 11 mouth plate, 3-11 lithium alloy, 4-1- gasket, 5 Separator 6 Positive electrode mixture punch Σ Cycle teaching (box 0 Masaken wr wet friend ("C) Four positive gutter # Ren 5M wide (゜C la

Claims (1)

[Claims] Lithium-manganese dioxide composite oxide, or 200
The positive electrode active material is manganese dioxide that has been heat-treated at a temperature of over 60°C to about 430°C, and after adding moisture to this positive electrode active material, it is dried at a temperature of over 60°C to 180°C. A method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery.