Battery having a sheet current collector fluid-tightly separating basic cells

A small battery and an electric double layer capacitor exhibit adequate cell voltage and capacitor withstand voltage. Specifically, the battery or electric double layer capacitor includes basic cells having a pair of electrodes oppositely laminated via the separator, and an electrolyte are packaged in a resin sheet package. The basic cells are laminated in series via a sheet current collector. The sheet current collector extends to an edge of the resin sheet package around the periphery of the basic cells laminated on both sides of the current collector. The sheet current collector is glued or fused to the resin sheet in its edge. The adjacent basic cells via the sheet current collector are fluid-tightly separated within the resin sheet package.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a battery and an electric double layer capacitor which are packaged in a resin sheet.

2. Description of the Related Art

Recent downsizing and weight reduction of mobile devices in information communication applications have led to intensive attempts to develop smaller and lighter batteries and electric double layer capacitors while being capable of rapid charge/discharge.

For meeting the needs for smaller and lighter batteries and electric double layer capacitors, it has been proposed to use a laminated film composed of a polymer film layer and a metal foil layer as an outer package material. For improving rapid charge/discharge properties, a metal plate made of, for example, copper having a smaller electric resistance is employed as a terminal.

Japanese Laid-open Patent Publication No. 8-83596 has disclosed a thin card battery wherein a closed battery package consisting of laminated films comprises laminated layers of a cathode, a separator and an anode as well as an electrolyte. Such a battery, however, comprises only one basic cell in which a cathode and an anode are oppositely placed via a separator. Thus, an increased voltage requires connecting a plurality of cells in series outside the package, which makes size reduction of a product difficult. Furthermore, when an electrolyte is acidic and a terminal is a metal plate made of, e. g., copper in the battery, an internal resistance is increased probably due to corrosion of the metal terminal plate caused by its contact with the acidic electrolyte.

Japanese Laid-open Patent Publication No. 6-29154 has disclosed an output terminal in an electric double layer capacitor, which acts as an external terminal by being contacted with a polarizable electrode impregnated with a highly corrosive electrolyte. The output terminal has a configuration where a corrosion-resistant conductive sheet covers an outer surface of the metal terminal plate except an external lead. An electric double layer capacitor produced using such a terminal, however, has an increased outer diameter by an increase in a thickness because both sides of the metal terminal plate is covered by the conductive sheet.

Japanese Laid-open Patent Publication No. 4-237109 has disclosed an electric double layer capacitor having a configuration in which a plurality of devices comprising a gasket are laminated and a sheet of current collector is disposed between two devices, and has described that such a configuration may increase a withstand voltage and reduce the number of current collector, resulting in a smaller thickness. Such a configuration, however, still comprises a gasket contributing to a larger outer diameter of a product. Thus, the configuration is insufficiently effective in size reduction.

In Japanese Patent Application No. 2001-103629 (Japanese Laid-open Patent Publication No. 2002-298798), we have proposed a battery and an electric double layer capacitor, in which a metal terminal plate except its lead is sealed by heat sealing between a conductive rubber and an outer laminated material. Such a configuration may be used to prevent corrosion of the metal terminal plate even when the electrolyte is acidic and to reduce a product size because of absence of a gasket. The battery and the electric double layer capacitor, however, have a single basic cell in which a pair of electrodes are oppositely placed via a separator, so that an increased voltage requires connecting a plurality of batteries or capacitors in series outside the closed package. There is, therefore, room for improvement in size reduction of a product for producing a battery or capacitor having a desired voltage or withstand voltage.

SUMMARY OF THE INVENTION

An objective of this invention is to provide a small battery or electric double layer capacitor having an adequate cell voltage or capacitor withstand voltage, in which performance degradation due to corrosion of a terminal can be prevented even when an electrolyte is acidic.

This invention relates to a battery in which basic cells comprising a separator, a cathode and an anode oppositely laminated via the separator, and an electrolyte are packaged in a resin sheet package, wherein

the basic cells are laminated in series via a sheet current collector;

the sheet current collector extends to an edge of the resin sheet package around the periphery of the basic cells laminated on both sides of the current collector;

the sheet current collector is glued or fused to the resin sheet in its edge; and

the adjacent basic cells via the sheet current collector are fluid-tightly separated within the resin sheet package.

This invention also relates to the battery as described above, wherein

at each of the top side and the bottom side of a laminated structure comprising the laminated basic cells, is disposed a metal terminal plate with a lead extending to the outside of resin sheet package;

each of the top side and the bottom side of the laminated structure has a sheet current collector, which is glued or fused to the internal surface of the resin sheet package such that the sheet current collector covers the metal terminal plate except its lead.

This invention also relates to the battery as described above, wherein the resin sheet is a laminated sheet consisting of a resin film and a metal film.

This invention relates to an electric double layer capacitor in which basic cells comprising a pair of polarizable electrodes oppositely laminated via the separator, and an electrolyte are packaged in a resin sheet package, wherein

the basic cells are laminated in series via a sheet current collector;

the sheet current collector extends to an edge of the resin sheet package around the periphery of the basic cells laminated on both sides of the current collector;

the sheet current collector is glued or fused to the resin sheet in its edge; and

the adjacent basic cells via the sheet current collector are fluid-tightly separated within the resin sheet package.

This invention also relates to the electric double layer capacitor as described above, wherein

at each of the top side and the bottom side of a laminated structure comprising the laminated basic cells, is disposed a metal terminal plate with a lead extending to the outside of resin sheet package;

each of the top side and the bottom side of the laminated structure has a sheet current collector, which is glued or fused to the internal surface of the resin sheet package such that the sheet current collector covers the metal terminal plate except its lead.

This invention also relates to the electric double layer capacitor as described above, wherein the resin sheet is a laminated sheet consisting of a resin film and a metal film.

According to the present invention, a plurality of basic cells can be electrically laminated in series via current collectors without using a gasket, and the laminate can be packaged and sealed using a laminated sheet as an outer package material. The number of the laminated basic cells may be appropriately determined to provide a battery or electric double layer capacitor having an required cell voltage or capacitor withstand voltage, respectively. Furthermore, because of absence of a gasket, a volumetric efficiency can be improved and a smaller device can be provided. Even when using an acidic electrolyte, corrosion of a terminal can be prevented and performance deterioration can be, therefore, minimized. Furthermore, this invention can eliminate production steps associated with a gasket so that a production time may be reduced.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be described.

FIG. 1shows a structure of a basic cell where a pair of electrodes are oppositely placed via a separator. In the figure, the symbols indicate the following meanings;1: a cathode and2: an anode, in which both are polarizable electrodes in an electric double layer capacitor, and3: a porous separator. The cathode1and the anode2are oppositely placed via the separator and contain an electrolyte within them.

An active material in an electrode may be, for a battery, any known organic or inorganic material which can be involved in a redox reaction and, for an electric double layer capacitor, a material capable of storing a charge when being contacted with an electrolyte such as activated carbon powders, activated carbon fibers, solid activated carbon and a composite of activated carbon and polyacene.

For example, a cathodic active material may be an indole trimer represented by chemical formula (1):

An anodic active material may be a polyphenylquinoxaline represented by chemical formula (2):

An electrode used in this invention, specifically a solid electrode having a desired electrode density and a film thickness, may be formed by, for example, placing an electrode material in a mold having a defined size/shape and by molding the material using a hot press. Alternatively, an electrode material is mixed with a solvent to give a paste, which is then deposited by printing on a current collector to form an electrode.

A separator prevents short-circuit caused by contact between a pair of electrodes and allows electrolyte ions to pass through it. It may be a nonwoven fabric or porous film which may be impregnated with an electrolyte.

An electrolyte may be selected from aqueous acidic solutions such as sulfuric acid; aqueous alkaline solutions such as an aqueous potassium hydroxide solution; and non-aqueous electrolytes such as a mixture of an organic solvent (e. g., propylene carbonate) and an electrolyte (e. g., a quaternary ammonium salt).

FIG. 2shows a schematic cross-section of a battery having a laminated structure as an embodiment of this invention where three basic cells illustrated inFIG. 1are laminated in series. For a metal terminal plate6inFIG. 2, only its lead6ais shown and the remaining part is omitted. The metal terminal plate6may be disposed as illustrated inFIG. 3.

In this invention, basic cells are laminated in series via sheet current collectors4b, and packaged in a resin sheet5.

The resin sheet5is fluid-tightly glued or fused in a sealing area in its edge to form an outer package. InFIG. 2, the symbol7indicates a fusion area. This outer package may be a pair of piled resin sheets, which are glued or fused in a sealing area in its edge, or a folded resin sheet glued or fused in a sealing area in its edge.

A resin sheet is preferably a laminated sheet. Specifically, a laminated sheet having a laminated structure of a resin film and metal film may be used. For example, the laminated sheet may have a three layer structure of an outer package resin film, a metal film and a fusing resin film. Alternatively, it may have a four layer structure for, e. g., preventing short-circuit. Examples of the resin film include a polyethylene resin, an ethylene copolymer resin and a polypropylene resin, and examples of the metal film include aluminum and an aluminum alloy. In particular, a fusing resin film is preferably a resin exhibiting good heat-sealing performance and adhesiveness to a metal; suitably a polypropylene resin and an ionomer resin which is a type of ethylene copolymer resin.

A current collector used in this invention may be a rubber sheet which is endowed with electroconductivity by adding, e. g., carbon.

The current collectors4binserted between the basic cells in this invention are disposed such that the basic cells are liquid-tightly separated from each other. Specifically, the current collectors4bwhich lie between the basic cells extend to the edge of the resin sheet package around its periphery and glued or fused in the edge of the resin sheet package. For example, during the sealing area in the edge of the resin sheet is fused for forming an outer package, the edge of the extended part of the current collector piled on the edge of the resin sheet may be simultaneously fused to unite them. In this process, when three or more basic cells are laminated via two or more current collectors, it is preferable that an insulating resin is inserted between the current collectors for preventing these current collectors from coming into contact each other. The resin which may be inserted between the current collectors may be the fusing resin film described above, which can ensure insulation between the current collectors and adequate fusion of the current collector edge piled on the edge of the resin sheet during fusing the edge of the resin sheet.

When an electrolyte is acidic in this invention, it is preferable that a sheet current collector4ais disposed on the electrode in each of the top and the bottom layers in a laminated structure in which basic cells are laminated and each of these sheet current collectors4ais glued or fused to the inner surface5of the resin sheet package such that it covers the metal terminal plate6except its lead6aas illustrated inFIG. 3. Thus, such a configuration can prevent corrosion of the metal terminal plate due to contact between the metal terminal plate and the acidic electrolyte.

EXAMPLES

This invention will be further described with reference to Examples.

In this example, a battery shown inFIG. 2was fabricated, which had a laminated structure of three basic cells in series.

As a cathode1, a 10 cm2solid electrode was formed by adding a conduction aid and a binder to a cathodic active material, the indole trimer represented by chemical formula (1) (R at 5-position in the indole unit is —CN and the remaining Rs are —H: 5-cyanoindole trimer); stirring and blending the mixture by a blender to give an electrode powder; placing 0.5 g of the powder in a mold; and pressing it by a hot press.

As an anode2, a 10 cm2solid electrode was formed by adding a conduction aid to an anodic active material, the polyphenylquinoxaline represented by chemical formula (2); stirring and blending the mixture by a blender to give an electrode powder; placing 0.5 g of the powder in a mold; and pressing it by a hot press.

Current collectors4a,4bwere conductive rubber sheets and laminated sheets5were laminates of an aluminum foil and a resin film.

As shown inFIG. 3, the surface of a metal terminal plate6except a lead6awas liquid-tightly packaged in the laminated sheet5and the current collectors4aconsisting of the conductive rubber sheet. This configuration can prevent corrosion of the metal terminal plate due to contact between the metal terminal plate and an acidic electrolyte. Thus, two sheets were prepared, in which the metal terminal plate6, the current collector4aand the laminated sheet5are integrated.

On the current collector4ain one of two laminated sheets5prepared above were laminated, via the current collectors4b, three basic cells in series, which were covered by the laminated sheet5such that the other current collector4awas disposed on the cells. Then, to the vacuumed product was added a given amount of 20 wt % aqueous sulfuric acid solution as an electrolyte for immersion of the electrolyte. Then, a sealing area to be a fused area7was sealed by vacuum heat fusion. A lead6awas drawn outside from a part of the fused area7.

The current collectors4bconsisting of a conductive rubber sheet had such a size that they can be extended to the edge of a laminated sheet package (outer package), and were overlapped in the edge of two laminated sheets, i. e., the sealing area. Furthermore, between the current collectors were inserted ionomer films and these were fused together.

In the configuration of this example, adjacent basic cells are fully separated by the current collector4bwhich lies between them so that the electrolyte is isolated by the current collector4bwhich lies between the basic cells.

A volumetric efficiency for the battery of this example (a rate of the volume of the basic cell laminate to that of the outer package consisting of the laminated sheets) was 62.5%. An ESR (equivalent series resistance) for the battery was 60 mΩ. A time taken until sealing in the battery production was 20 min.

In the configuration of this example, a volumetric efficiency was improved because of absence of a gasket. Furthermore, since the basic cells could be directly laminated via a sheet of current collector, the number of current collectors could be reduced in comparison with a battery using a gasket and thus a resistance could be correspondingly reduced (reduction in an ESR). A production time could be reduced because the process dispensed with steps associated with a gasket (vulcanization adhesion, cooling, etc.).

A battery was fabricated as described in Example 1, except that an electrode weight was 1.0 g for both cathode and anode.

A volumetric efficiency of the battery of Example 2 was 87.5%. An ESR for the battery was 120 mΩ. A time taken until sealing in the battery production was 20 min. In the configuration of this example, a volumetric efficiency was improved; a cell ESR could be reduced; and a production time could be reduced.

A battery was fabricated as described in Example 1, except that ten basic cells were laminated in series and sealed.

A volumetric efficiency of the battery of Example 3 was 90.5%. An ESR for the battery was 200 mΩ. A time taken until sealing in the battery production was 20 min. In the configuration of this example, a volumetric efficiency was improved; a cell ESR could be reduced; and a production time could be reduced.

An electric double layer capacitor having a structure as described in Example 1 was fabricated, except that basic cells in which polarizable electrodes were oppositely placed via a separator, were substituted for the basic cells in the battery in Example 1.

A polarizable electrode was produced by mixing activated carbon with the appropriate amounts of carbon powders as a conduction aid and a binder, mixing the mixture with a solvent to form a paste, depositing the paste on the current collector by printing to given size and film thickness, and then dried the product at 120° C. for 1 hour.

On one side of the current collector4awas deposited a polarizable electrode while on both sides of the current collector4bwere polarizable electrodes. These current collectors with the polarizable electrodes were laminated such that the polarizable electrodes were oppositely placed via a separator to form a laminated structure where three basic cells were laminated in series via the current collectors4b. Then, the laminated structure was packaged in a laminated sheet. Then, to the vacuumed product was added a given amount of 20 wt % aqueous sulfuric acid solution as an electrolyte for impregnation with the electrolyte. Then, a sealing area to be a fused area7was sealed by vacuum heat fusion. A lead6awas drawn outside from a part of the fused area7.

The current collectors4bconsisting of a conductive rubber sheet had such a size that they can be extended to the edge of a laminated sheet package (outer package), and were overlapped in the edge of two laminated sheets, i. e., the sealing area. Furthermore, between the current collectors were inserted ionomer films and these were fused together.

A volumetric efficiency for the electric double layer capacitor of Example 4 was 62.5%. An ESR for the electric double layer capacitor was 45 mΩ. A time taken until sealing in the production was 110 min. In the configuration of this example, a volumetric efficiency was improved; a capacitor ESR could be reduced; and a production time could be reduced.

Comparative Example 1

In this comparative example, a battery (FIG.5) where three unit cells (FIG. 4) comprising one basic cell were laminated in series, was fabricated.

A cathode1with a size of 10 cm2was formed by adding an appropriate amount of carbon powders as a conduction aid to a cathodic active material, the cyanoindole trimer represented by chemical formula (1) (R at 5-position in the indole unit is —CN and the remaining Rs are —H: 5-cyanoindole trimer) and pressing 0.5 g of the powders by a hot press.

An anode2with a size of 10 cm2was formed by adding an appropriate amount of carbon powders as a conduction aid to an anodic active material, the polyphenylquinoxaline represented by chemical formula (2) and pressing 0.5 g of the powders by a hot press.

A rim type gasket8was fused by pressure with one current collector4consisting of a conductive rubber sheet. Inside of the gasket, a cathode1and an anode2were oppositely placed via a separator3. Over the product was placed the other current collector4consisting of a conductive rubber sheet and the laminate was sealed by pressing. In this process, sealing was conducted while forming an inlet for injecting an electrolyte. The product was subject to vulcanization adhesion at 120° C. at a pressure of 3 kgf/cm2(2.94×105Pa) for 2 hours. Then, a 20 wt % aqueous sulfuric acid solution as an electrolyte was injected into the vacuumed product for impregnation with the electrolyte. Then, the inlet was sealed with a plastic material.

Three unit cells thus prepared were laminated in series. On both sides of the laminate were disposed metal terminal plates. The laminate was then packaged in a laminated sheet and was sealed by vacuum hot fusion using an ionomer fusion film. From a part of the fused area, a lead (not shown) was drawn outside.

A volumetric efficiency for the battery in Comparative Example 1 was 33.1%. A battery ESR was 68 mΩ. A time taken until sealing in the production was 205 min.

Comparative Example 2

A battery was fabricated as described in Comparative Example 1 except that an electrode weight was 1.0 g for both cathode and anode.

A volumetric efficiency for the battery in Comparative Example 2 was 39.7%. A battery ESR was 136 mΩ. A time taken until sealing in the production was 205 min.

Comparative Example 3

A battery was fabricated as described in Comparative Example 1 except that ten unit cells were laminated in series and sealed.

A volumetric efficiency for the battery in Comparative Example 3 was 39.7%. A battery ESR was 212 mΩ. A time taken until sealing in the production was 205 min.

Comparative Example 4

An electric double layer capacitor was fabricated as described in Comparative Example 1, except that basic cells in which polarizable electrodes were oppositely placed via a separator, were substituted for the basic cells in the battery in Comparative Example 1.

A polarizable electrode was produced by mixing activated carbon with the appropriate amounts of carbon powders as a conduction aid and a binder, mixing the mixture with a solvent to form a paste, depositing the paste on the current collector by printing to given size and film thickness, and then dried the product at 120° C. for 1 hour.

Then, as described in Comparative Example 1, a gasket and a current collector were subject to vulcanization fusion and a 40 wt % aqueous sulfuric acid solution as an electrolyte was injected to form an electric double layer capacitor comprising one basic cell.

Three electric double layer capacitors were laminated in series, metal terminal plates were disposed on both sides, the product was packaged in a laminated sheet and sealing was conducted by vacuum heat fusion using an ionomer fusion film. From a part of the fused area, a lead was drawn outside.

A volumetric efficiency for the battery in Comparative Example 4 was 33.1%. An ESR of the electric double layer capacitor was 53 mΩ. A time taken until sealing in the production was 205 min.

The results in these examples and comparative examples are summarized in the tables below.

TABLE 2Examples 1 to 3Step 15 minMetal terminal plates are packagedin a laminate of a conductive rubbersheet and a laminated sheet, andtheir sheet are fused and sealed byheat.Step 25 minAn electrode is formed by hot pressmolding.Step 35 minA laminate of basic cells is formedwithin a laminated sheet package.Step 45 minAn electrolyte is injected andsealing is conducted.Total20 min

TABLE 3Example 4Step 15 minMetal terminal plates are packagedin a laminate of a conductive rubbersheet and a laminated sheet, andtheir sheet are fused and sealed byheat.Step 25 minA polarizable electrode is depositedon a current collector.Step 390 minThe product was dried at 120° C. andcooled.Step 45 minA laminate of basic cells is formedwithin a laminated sheet package.Step 55 minAn electrolyte is injected andsealing is conducted.Total110 min

TABLE 4Comparative Examples 1 to 3Step 15 minAn electrode is formed by hot pressmolding.Step 25 minA gasket and one current collectorare fused by pressure. Insidegasket, basic cells are formed. Onthe gasket is pressure-fused theother current collector forsealing.Step 3120 minThe gasket and the currentcollectors are subject tovulcanization adhesion at 120° C.Step 460 minThe product is cooled.Step 510 minAn electrolyte is injected and aninlet is sealed.Step 65 minMetal terminal plates are disposed.The product is packaged in alaminated sheet and sealed.Total205 min

TABLE 5Comparative Example 4Step 15 minA polarizable electrode is depositedon a current collector.Step 25 minA gasket and one current collectordeposited are fused by pressure.Inside the gasket, a separator isplaced on the electrode. On thegasket is pressure-fused the othercurrent collector for sealing.Step 3120 minThe gasket and the currentcollectors are subject tovulcanization adhesion at 120° C.Step 460 minThe product is cooled.Step 510 minAn electrolyte is injected and aninlet is sealed.Step 65 minMetal terminal plates are disposed.The product is packaged in alaminated sheet and sealed.Total205 min