JP2001250536A - Method of producing negative electrode plate for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the high load discharge characteristics of a nonaqueous electrolyte secondary battery. SOLUTION: After a negative electrode mixture is applied to a collector and dried, heat treatment of 110 deg.C or higher and 300 deg.C or lower is given to a negative electrode plate to be rolled and molded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a method for producing a negative electrode plate thereof.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery which is small and lightweight, has a high energy density, and can be repeatedly charged and discharged. Research and development of such nonaqueous electrolyte secondary batteries, especially lithium secondary batteries using lithium-containing composite oxides such as lithium cobalt oxide for the positive electrode and carbon materials for the negative electrode, have been actively conducted. I have. However, since this type of battery uses a non-aqueous electrolyte, there is a problem that the ion conductivity is lower than that of an aqueous solution type battery. For this reason, from the viewpoint of current characteristics, many structures have been proposed in which a positive / negative electrode plate is spirally wound as a sheet-like electrode plate to increase the electrode area to form an electrode group.

[0003] Generally, such a sheet-like electrode plate is produced by applying a mixture to a current collector. However, since it is necessary to apply the mixture to the current collector thinly and uniformly, a mixture is required. The agent is a paste by adding a thickener together with an active material, a conductive agent and a binder to a solvent,
A method of coating the current collector is used. Further, in some cases, a method of rolling after coating, in order to increase the filling amount of the active material, has been studied.

[0004]

In a mixture containing a thickener and a binder, the active material is partially covered with the thickener and the binder. In the electrode plate rolled after being applied to the current collector, the thickener intervenes as a film between the current collector and the active material. For this reason, there is a problem that a battery incorporating an electrode plate produced by rolling after application is deteriorated in high-load discharge characteristics. Therefore, it has been devised to provide a non-aqueous electrolyte secondary battery having excellent high-load discharge characteristics by a manufacturing method in which a negative electrode plate is dried under various conditions and then formed into a group.

In Japanese Patent Application Laid-Open No. 11-120996, after a mixture is applied to a current collector, the mixture is heated to 150 ° C. to 350 ° C. in a non-oxidizing atmosphere.
Although there is a description of a non-aqueous electrolyte secondary battery using a negative electrode that has been heat-treated at a temperature of ° C., the details of which step after coating is unclear.

[0006] Further, when the drying conditions in a non-oxidizing atmosphere are carried out on a mass production scale, there are problems related to productivity such as a cost problem by using equipment having a predetermined atmosphere specification and a time required to obtain the atmosphere. appear.

Therefore, there has been a demand for a method of improving high-load discharge characteristics while minimizing problems of cost and productivity reduction as much as possible.

The present invention has been made to solve the above problems, and provides a non-aqueous electrolyte secondary battery capable of improving high load discharge characteristics while minimizing the problems of process cost and productivity reduction. is there.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the above-mentioned problems, a method of manufacturing a negative electrode plate for a non-aqueous electrolyte secondary battery according to the present invention comprises a carbon material capable of occluding and releasing lithium ions, a thickener, and a binder. A method for producing a negative electrode plate having a negative electrode mixture layer containing a binder,
The negative electrode mixture is applied to a current collector, dried, heat-treated at 110 ° C. or more and 300 ° C. or less, and roll-formed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a cylindrical battery according to the present invention. In FIG. 1, a positive electrode plate 1 is made by mixing lithium cobaltate as an active material, carbon powder of acetylene black as a conductive agent, polytetrafluoroethylene (PTFE) resin dispersion as a binder, and carboxymethyl cellulose as a thickener. Knead the aqueous sodium salt solution,
The paste is applied on a metal foil as a current collector,
After drying, heat treatment was performed at 250 ° C. for 10 hours, followed by rolling and cutting to predetermined dimensions. This includes the positive lead 2
Is spot welded. 250 before group composition
The electrode was dried at 10 ° C. for 10 hours.

The negative electrode plate 3 is formed by kneading flaky graphite capable of absorbing and releasing lithium, a water-soluble dispersion of styrene butadiene rubber as a binder, and an aqueous solution of sodium carboxymethyl cellulose as a thickener to form a paste. After coating on a metal foil as a current collector and drying,
Heat treatment was performed at 180 ° C. for 6 hours, followed by rolling and cutting to predetermined dimensions. In this case, the negative electrode lead 4 is attached by spot welding. Further, the electrode plate was dried at 110 ° C. for 6 hours before forming the group.

A separator 5 made of polypropylene was arranged between the positive and negative electrode plates and spirally wound to form an electrode plate group.

An upper insulating plate 6 and a lower insulating plate 7 are arranged above and below the electrode group, respectively, and inserted into the battery case 8. Then, a predetermined amount of electrolyte is injected into the battery case 8, and a polypropylene gasket 9 is formed.
The sealing plate 10 was sealed with a battery case 8 through the above to obtain a completed battery. As the electrolytic solution, a solution prepared by dissolving 1.3 mol of lithium hexafluorophosphate as an electrolyte in a mixed solvent of ethylene carbonate and ethyl methyl carbonate was used. The battery size is a cylinder 18650 type.

The battery assembled in this manner was used as the battery of the present invention.

Next, after coating and drying when producing a negative electrode plate,
A battery was fabricated in the same manner as described above except that rolling was performed without heat treatment, and this was used as a conventional battery.

The discharge characteristics of these batteries after storage were evaluated. The battery was stored at 60 ° C. for 20 days under a charged condition. The test conditions were a charging current of 0.2 C and a final voltage of 4.2.
V constant current constant voltage charge, discharge current 0.2C, 1.0C,
2.0C, constant voltage discharge with a final voltage of 3.0V, 20 ° C
And repeated charging and discharging.

Table 1 shows the discharge characteristics of the conventional battery and the battery of the present invention after storage.

[0019]

[Table 1]

From the results shown in Table 1, the conventional battery prepared by rolling and forming without heat treatment after coating and drying when forming a negative electrode plate, and the present invention formed by rolling and forming after heat treatment were performed. A clear difference was observed between the battery and the battery in terms of discharge performance, especially in high-load discharge characteristics.

It is considered that this is because the thermal decomposition of the thickener and the binder is effectively performed by the heat treatment after the application, and the excess thickener and the binder are removed.

Further, since the copper foil is rolled after annealing and softening by the heat treatment, it is considered that the mechanical adhesion between the current collector and the mixture is improved and the current collecting effect is also improved. .

This is also confirmed by a cross-sectional photograph of the electrode plate. FIG. 2 shows an example of the discharge curves of the battery of the conventional example and the battery of the present invention.

Next, as a study on the heat treatment conditions, after measuring the heat treatment temperature, the treatment time, and the weight reduction ratio of the negative electrode mixture, a battery was prepared in the same manner as in the above example except for the heat treatment conditions, and the battery characteristics were evaluated. went. (Table 2)
Shown in Regarding the heat treatment time, conditions were examined up to 720 minutes as the time when the amount of change in the weight loss rate became almost zero.

[0025]

[Table 2]

Under heat treatment conditions in which the heat treatment temperature is 110 ° C. or more and 300 ° C. or less (the weight loss is 0.6 ± 0.2%), the discharge characteristics are improved as compared with the conventional example, and the heat treatment temperature is lower than 110 ° C. or 300 ° C. Under the heat treatment conditions above ℃ (area where the weight loss rate is 0.8% or more or below 0.4%), the result that the discharge characteristics deteriorated was obtained.

In the region where the heat treatment temperature is higher than 300 ° C., the degree of oxidative discoloration of the copper foil is large, and lithium ions are trapped in a negatively reversible form due to the formation of a polymer with lithium ions due to solvation of an electrolytic solution on the copper foil surface. As a result, it is considered that the discharge capacity itself is reduced.

If the heat treatment temperature is lower than 110 ° C., it is considered that the heat treatment is insufficient and the thermal decomposition of the excessive thickener and binder on the active material is not promoted, and it becomes a discharge inhibiting element and the high-load discharge characteristics deteriorate. Can be Therefore, a temperature range of 110 ° C. or more and 300 ° C. or less at which heat treatment of the mixture can be performed without causing extreme discoloration of the copper foil is preferable.

From the two viewpoints of reducing the processing time as much as possible from the viewpoint of high-efficiency production and reducing the influence on the heat treatment variation due to the temperature variation of the heat treatment furnace from the viewpoint of process stability, the heat treatment temperature is determined as follows. More preferably, the temperature is set to 150 ° C. or more and 300 ° C. or less.

In performing this heat treatment on a mass-production scale, a continuous furnace has higher productivity than a batch furnace, and any apparatus capable of performing a predetermined intake and exhaust can be used without any problem such as uneven heat treatment. Since there is no need for equipment costs (e.g., vacuum or rare gas), problems in productivity and cost can be reduced to a relatively small extent.

In the present embodiment, styrene butadiene rubber was used as the rubber polymer, but acrylonitrile butadiene rubber, methyl methacrylate butadiene rubber, methyl methacrylate-sodium methacrylate rubber, methyl methacrylate-methacrylic acid were used. Lithium rubber,
Similar results could be obtained for ammonium methacrylate-lithium methacrylate rubber and methyl methacrylate-lithium methacrylate-ammonium methacrylate rubber.

Further, a rubber in which part of all methyl groups of styrene butadiene rubber, methyl methacrylate rubber, and methyl methacrylate rubber is substituted by any of sodium salt, lithium salt and ammonium salt or a combination thereof is preferable. .

In this embodiment, sodium carboxymethylcellulose was used as the negative electrode thickener. However, methylcellulose, lithium carboxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, polyacrylic acid, polyethylene glycol, and polyethylene oxide were used. Similar results could be obtained with either of the above.

Also preferred are sodium carboxymethylcellulose and lithium carboxymethylcellulose.

In this embodiment, a cylindrical battery is used, but a prismatic or stacked battery may of course be used.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical battery of the present invention.

FIG. 2 is a diagram showing discharge characteristics of a battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Positive electrode lead 3 Negative electrode plate 4 Negative electrode lead 5 Separator 6 Upper insulating plate 7 Lower insulating plate 8 Battery case 9 Gasket 10 Sealing plate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Arataki 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Terms (reference) 5H029 AJ03 AK03 AL07 AM03 AM05 AM07 BJ02 CJ02 CJ03 CJ22 DJ08 EJ12 HJ14 5H050 AA08 BA17 CA08 CB08 DA03 DA11 EA23 GA02 GA03 GA22 HA14

Claims (3)

[Claims] 1. A method for producing a negative electrode plate, comprising: a negative electrode mixture layer containing a carbon material capable of occluding and releasing lithium ions, a thickener and a binder formed on a current collector, wherein the carbon material is For a non-aqueous electrolyte secondary battery, a negative electrode mixture containing a thickener and a binder is applied to a current collector, dried, and then heat-treated at 110 to 300 ° C., and then roll-molded. Manufacturing method of negative electrode plate. 2. A binder comprising styrene butadiene rubber,
Acrylonitrile butadiene rubber, methyl methacrylate butadiene rubber, methyl methacrylate rubber, selected from rubbers in which some of the total methyl groups in the rubber of methyl methacrylate have been replaced by sodium salts, lithium salts and ammonium salts or any combination thereof The method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery according to claim 1, which is at least one of the following: 3. The thickener is any one of methylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, lithium carboxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, polyacrylic acid, polyethylene glycol, and polyethylene oxide. A method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery according to claim 1.