WO2000016352A1

WO2000016352A1 - A flexible charge storage device

Info

Publication number: WO2000016352A1
Application number: PCT/AU1999/000780
Authority: WO
Inventors: Anthony Michael Vassallo; Clodoveo Simone Sacchetta
Original assignee: Energy Storage Systems Pty. Ltd.
Priority date: 1998-09-16
Filing date: 1999-09-16
Publication date: 2000-03-23
Also published as: US6552895B1; AUPP596598A0; EP1133781A1; EP1133781A4

Abstract

A flexible charge storage device in the form of a supercapacitor (1) includes a flexible capacitive element (2) which is housed within a flexible plastics package (3). Element (2) includes a plurality of interleaved sheet electrodes having an insulator or separator therebetween and which are stacked in a face to face configuration. Alternate electrodes are interconnected by way of respective opposed tabs (4) which extend outwardly from element (2). Supercapacitor (1) also includes a first terminal (5) and a second terminal (6) which are respectively electrically connected with opposed tabs (4). More particularly, electrodes (5, 6) have first ends (7, 8) which are disposed within package (3), and respective second ends (9, 10) which are disposed outside of package (3). Ends (9, 10), in use, are connected to other components in the circuit of interest to allow electrical connection with the electrodes of element (2). Package (3) include a single folded laminar plastics sheet (14) which extends between two ends (15, 16), and which has edges (17, 18, 19 and 20). Ends (15, 16), as well as the portions of both sides (19, 20) which overlap, are fixedly and sealingly abutted against one another by way of heat welding or the like. Accordingly, electrolyte (12) is retained within package (3).

Description

TITLE: A FLEXIBLE CHARGE STORAGE DEVICE

FIELD OF THE INVENTION

The present invention relates to a charge storage device and in particular to a

flexible charge storage device.

The invention has been developed primarily as a supercapacitor and will be

described hereinafter with reference to that application. However, it will be appreciated

that the invention is not limited to this particular field of use and is also suitable for other

energy storage devices such as batteries, capacitors and the like.

BACKGROUND OF THE INVENTION

Known supercapacitors and other energy storage devices are provided in rigid

containers or housings. These containers, particularly for supercapacitors offering large

amounts of charge storage, are often fixedly mounted to other structures of the circuit or

apparatus to which they are incorporated. The containers are generally bulky and

necessitate prefabricated mounting points within the circuit or apparatus. Consequently,

such circuits and apparatus do not easily accommodate a supercapacitor of differing

dimension. In the event such a circuit requires a supercapacitor having different

characteristics from that which was originally intended, the dimensions of the new

capacitor must be very similar to the original.

It is an object of the present invention, at least in the preferred embodiments, to

overcome or substantially ameliorate one or more of the disadvantages of the prior art, or

at least provide a useful alternative. DISCLOSURE OF THE INVENTION

According to a first aspect of the invention there is provided a flexible charge

storage device including:

a first sheet electrode having a first terminal extending therefrom;

a second sheet electrode disposed adjacent the first electrode and having a second

terminal extending therefrom;

a porous separator disposed between the electrodes; and

a sealed package for containing the electrodes, the separator and an electrolyte,

whereby the terminals extend from the package to allow electrical connection to the

respective electrodes.

Preferably, each of the sheets includes two opposed sides, at least one of the sides

of each sheet having a coating containing activated carbon.

Preferably also, the first electrode and the second electrode include respective

first and second aluminium sheets. More preferably, the first and second sheets and the

intermediate separator are together folded.

In a preferred form the charge storage device includes a plurality of first and

second sheets and intermediate separators. More preferably, the sheets and intermediate

separators are stacked. Alternatively, the sheets and the intermediate separators are

wound together.

Preferably also, one of the length and breadth of the package is less than the

respective length and breadth of the first sheet.

Preferably, the package includes a plurality of layers. More preferably, the layer of the package closest to the terminals is polyethylene. Even more preferably, the package is sealingly bonded to the terminals. Most preferably, the package is adhesively

bonded to the terminals.

In a preferred form, the package includes polyethylene and the terminals are

aluminium, wherein the adhesive bond is formed with an adhesive resin. In other

embodiments use is made of an epoxy resin. In other preferred embodiments each

terminal includes a respective plastics sleeve sealingly bonded thereto. In this

embodiment the package is preferably sealingly engaged with the sleeves. In further

embodiments a plastics layer is used in place of the sleeve.

Preferably, the sheets are abutted against the separator.

In a preferred form the device, when maintained at 80°C for 100 hours, retains at

least 90% by weight of the electrolyte. Even more preferably, and under the same

conditions, the device retains at least 95% by weight of the electrolyte.

According to a second aspect of the invention there is provided a method of

producing a flexible charge storage device, the method including the steps of:

providing a first sheet electrode having a first terminal extending therefrom;

disposing a second sheet electrode adjacent the first electrode, the second

electrode having a second terminal extending therefrom;

disposing a porous separator between the electrodes; and

sealing the electrodes and the separator in a package containing an electrolyte,

respective electrodes. Preferably, each of the sheets includes two opposed sides, and the method

includes the further step of applying a coating containing activated carbon to at least one

of the sides of each sheet.

Preferably also, the first electrode and the second electrode are respective first

and second aluminium sheets. More preferably, the method includes the step of folding

together the first and second sheets and the intermediate separator.

In a preferred form, the method includes the step of providing a plurality of first

and second sheets and intermediate separators. More preferably, the method includes the

step of stacking the sheets and intermediate separators. Alternatively, the method

includes the step of winding together the sheets and the intermediate separators.

Preferably, the package includes a plurality of layers. More preferably, the layer

of the package closest to the terminals includes polyethylene. In some embodiments that

layer is coated with an ionomer and more preferably coated with SURLYN. Even more

preferably, the method includes the step of sealingly bonding the package to the

terminals. Most preferably, the method includes the step of adhesively bonding the

package to the terminals.

Preferably also, the package includes polyethylene and the terminal is

aluminium, wherein the method includes the step of forming the adhesive bond with a

resin. Examples of commercially available and suitable resins are those which are

marketed under the names NUCREL and PRIMACOR. In other embodiments use is

made of an epoxy resin. In further embodiments the method includes the steps of

sealingly bonding a respective plastics sleeve to each terminal and then sealingly

engaging the package with the sleeves. In a preferred form the method includes the step of abutting the sheets against the

separator.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of

example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic perspective view of a charge storage device according to

the invention;

Figure 2 is a cross section taken along line 2-2 of Figure 1; and

Figure 3 is a graph of the electrolyte weight loss for one of the supercapacitors

according to the invention.

PREFERRED EMBODIMENT OF THE INVENTION

Referring to Figures 1 and 2, a flexible charge storage device in the form a

supercapacitor 1 includes a flexible capacitive element 2 which is housed within a

flexible plastics package 3. Element 2 includes a plurality of interleaved sheet electrodes

having an insulator or separator therebetween and which are stacked in a face to face

configuration. Alternate electrodes are interconnected by way of respective opposed tabs

4 which extend outwardly from element 2.

Supercapacitor 1 also includes a first terminal 5 and a second terminal 6 which

are respectively electrically connected with opposed tabs 4. More particularly,

electrodes 5 and 6 have first ends 7 and 8 which are disposed within package 3, and

respective second ends 9 and 10 which are disposed outside of package 3. Ends 9 and 10, in use, are connected to other components in the circuit of interest to allow electrical

connection with the electrodes of element 2.

In other embodiments the sheet electrodes are folded together, while in further

embodiments they are wound together. In any event, element 2 is flexible in that it is

pliable. In the present embodiment element 2 includes four stacked aluminium sheets

each coated on one side with a thin activated carbon layer. Each sheet is maintained in a

spaced apart configuration from the adjacent sheet by way of intermediate porous

separators. Each sheet electrode is about 40 mm x 40 mm and the total thickness of

element 2 is about 0.5 mm.

In other embodiments both sides of the aluminium sheets include a carbon

coating.

Terminals 5 and 6 are aluminium, although in other embodiments use is made

different conductive materials.

Package 3 contains element 2 which is pre-soaked with an electrolyte 12.

Package 3 is impervious to the electrolyte and, as such, maintains it in contact with the

element 2. In this case, the separator included within element 2 is porous to allow

movement of ions between the adjacent electrodes. The electrolyte should be as

conductive as possible and, in this embodiment, is an organic electrolyte based upon

ethylene carbonate and dimethylcarbonate. In other embodiments other electrolytes are

used such as tetraethylammonium tetrafluoroborate dissolved in propylene carbonate or

acetonitrile at 0.5 to 1.5 M concentration. Other electrolytes would be known to those

skilled in the art. Package 3 include a single folded laminar plastics sheet 14 which extends

between two ends 15 and 16 and which has edges 17, 18, 19 and 20. Ends 15 and 16, as

well as the portions of both sides 19 and 20 which overlap, are fixedly and sealingly

abutted against one another by way of heat welding or the like. Accordingly, electrolyte

12 is retained within package 3. In the configuration shown the approximate length and

breath dimensions of package 3 are both 50 mm.

Sheet 14, in this embodiment, includes four layers which have a combined

thickness of about 100 microns. In other embodiments however, use is made of a sheet

having a thickness in the range of 30 microns to 1 mm. Preferably, however, to optimise

the flexibility and barrier properties of sheet 14 its total thickness is in the range of 50

microns to 200 microns.

In this embodiment the first or innermost layer of sheet 14 is polyethylene which

is heat sealable and chemically unaffected by electrolyte 12. In other embodiments

where use is made of alternative electrolytes it may be necessary to select an alternative

innermost layer. The layer adjacent the polyethylene is ethylene vinyl alcohol which

acts as a solvent and oxygen barrier. A layer of nylon is then utilised. This layer

provides further solvent resistance and mechanical strength. The next or outermost layer

in this embodiment is a barrier or protective layer and is preferably constructed from

polyethylene. In other embodiments the outer layer is constructed of protective material

other than polyethylene.

Not only does package 3 contain electrolyte 12, it prevents the ingress of water or

other contaminants in to the electrolyte. Moreover, package 3 provides for a more

effective sealing engagement with terminals 5 and 6. In this embodiment, where the terminals are made from aluminium and the inner layer of sheet 14 is polyethylene, the

two are adhered together. Most preferably the adhesive is epoxy resin.

In another embodiment the packaging includes a surlyn coating and the resin

selected from one of the commercially available resins such as the resins that are

marketed under the names NUCREL and PRIMACOR.

To further enhance the sealing engagement some embodiments make use of

pretreating the polyethylene surfaces by exposure to a corona discharge.

In alternative embodiments respective plastics sleeves or layers are initially

bonded to terminals 5 and 6. The preferred sleeve is made from polyethylene, although

other embodiments utilise other polymers such as polyethylene acrylic acid. The sleeves

are heat bonded to the terminals. Thereafter, package 3 is heat sealed to the sleeves to

form a sealed container for electrolyte 12.

In some embodiments the sleeve or layer is adhesively bonded to the terminals

with a resin.

A number of embodiments of the invention were tested for electrolyte retention

at elevated temperatures. The first test was conducted using a package of the preferred

embodiment measuring 50 mm x 50 mm and containing dimethylcarbonate solvent. The

supercapacitor was maintained at 80 C and the weight loss of electrolyte was found to

be 1.9%, 3.2%, 7.3% and 13.1% at 100 hours, 200 hours, 600 hours and 1000 hours

respectively.

The second test was conducted with another supercapacitor that provides about

15 Farads at 2.5 Volts. The electrolyte weight loss for the capacitor is plotted against

time and illustrated in Figure 3. This supercapacitor has the following structure: four aluminium sheets, each being about 70 mm by 60 mm and including

respective opposed carbon coatings;

two terminals being integrally formed with and extending away from the

respective sheets;

a separator for maintaining the sheets being in a fixed spaced apart configuration;

a multi-layer laminate packaging including an aluminium layer and an outer

surlyn layer;

an acetonitrile solvent containing a 1 M solution of tetraethylammonium

tetrafluoroborate;

a PRIMACOR resin for sealing the package against itself and the terminals;

a total weight of about 6 grams; and

overall dimensions of about 80 mm x 70 mm x 2mm.

In some embodiments package 3 includes different or additional layers.

Different polymers are used if specific operating temperatures are envisaged.

Supercapacitor 1 weighs approximately 5 grams and includes a capacitance of

about 3 Farads at 2.5 Volts. As would be appreciated by a skilled addressee many other

configurations are available. The present configuration, however, is particularly suited

to mobile communications, self propelled toys, and automotive applications. In one

specific embodiment, supercapacitor 1 is placed in parallel with a standard mobile

telephone battery. Such an arrangement not only extends the life of the battery but will

quickly recharge. The compact and flexible nature of the capacitor and its package 3

allows them to be placed in confined spaces and in many different configurations.

Moreover, so far as the space available permits, additional like capacitors can be added in parallel to further the available charge storage capacity for the electronic device. In

some cases, capacitor 1 is contained within the housing of the mobile telephone, while in

other embodiments it is contained within the housing of the battery. However, in still

further embodiments, supercapacitor 1 is maintained in the cavity between the mobile

telephone and the battery and, as such can be retro fitted to existing mobile telephones.

In the event the mobile telephone includes the necessary voltage regulation

circuitry it can be powered by the supercapacitor only.

Another application of supercapacitor 1 is in combination with the laptop

computers and other electronic equipment. Other applications include portable power

tools and other cordless electric devices. Again, although supercapacitor 1 will

advantageously operate in parallel with an existing battery, it is, in some embodiments,

utilised as the sole power source.

Although the invention has been described with reference to specific examples, it

will be appreciated by those skilled in the art that it may be embodied in many other

forms.

Claims

1. A flexible charge storage device including:

a first sheet electrode having a first terminal extending therefrom;

terminal extending therefrom;

a porous separator disposed between the electrodes; and

a sealed package for contaimng the electrodes, the separator and an electrolyte,

respective electrodes.

2. A device according to claim 1 wherein each of the sheets includes two opposed

sides, at least one of the sides of each sheet having a coating containing activated carbon.

3. A device according to claim 1 or claim 2 wherein the first electrode and the

second electrode include respective first and second aluminium sheets.

4. A device according to claim 3 wherein the first and second sheets and the

intermediate separator are together folded.

5. A device according to claim 3 including a plurality of like first sheets, a plurality

of like second sheets and a plurality of intermediate separators.

6. A device according to claim 3 or claim 5 wherein the sheets and intermediate

separators are stacked.

7. A device according to claim 3 or claim 5 wherein the sheets and the intermediate

separators are wound together.

8. A device according to any one of the preceding claims wherein one of the length

and breadth of the package is less than the respective length and breadth of the first

sheet.

9. A device according to any one of the preceding claims wherein the package

includes a plurality of layers.

10. A device according to claim 9 wherein the layer of the package closest to the

terminals includes polyethylene.

11. A device according to claim 10 wherein the layer closest to the terminals

includes an ionomer coating.

12. A device according to claim 11 wherein the ionomer coating is a SURLYN

coating.

13. A device according to claim 9 wherein the package is sealingly bonded to the

terminals.

14. A device according to claim 11 wherein the package is adhesively bonded to the

terminals.

15. A device according to claim 13 wherein the package includes a ionomer coating

and the terminals are aluminium, wherein the adhesive bond is formed with an adhesive

resin.

16. A device according to claim 13 wherein the ionomer coating is a SURLYN

coating.

17. A device according to claim 15 wherein the resin is an epoxy resin.

18. A device according to claim 15 wherein each terminal includes a respective

plastics sleeve sealingly bonded thereto.

19. A device according to claim 18 wherein the package is sealingly engaged with

the sleeves.

20. A device according to claim 15 including a plastics sheet disposed in sealing

abutment with the terminals and the package.

21. A device according to any one of the preceding claims wherein the sheets are

abutted against the separator.

22. A device according to any one of the preceding claims which, when maintained

at 80┬░C for 100 hours, retains at least 90% by weight of the electrolyte.

23. A device according to claim 22 which, under the same conditions, retains at least

95% by weight of the electrolyte.

24. A device according to any one of claims 1 to 21 which, when maintained at 70┬░C

for 1000 hours, retains at least 99% by weight of the electrolyte.

25. A method of producing a flexible charge storage device, the method including

the steps of:

providing a first sheet electrode having a first terminal extending therefrom;

disposing a second sheet electrode adjacent the first electrode, the second

electrode having a second terminal extending therefrom;

disposing a porous separator between the electrodes; and

respective electrodes.

26. A method according to claim 25 wherein each of the sheets includes two opposed

sides, and the method includes the further step of applying a coating containing activated

carbon to at least one of the sides of each sheet.

27. A method according to claim 25 or claim 26 wherein the first electrode and the

second electrode are respective first and second aluminium sheets and the method

includes the step of folding together the first and second sheets and the intermediate

separator.

28. A method according to claim 27 including the step of providing a plurality of like

first sheets, a plurality of like second sheets and a plurality of intermediate separators.

29. A method according to claim 28 including the step of stacking the sheets and

intermediate separators.

30. A method according to claim 28 including the step of winding together the sheets

and the intermediate separators.

31. A method according to any one of claims 25 to 28 wherein the package includes

a plurality of layers one of which is polyethylene and the method includes the step of

disposing the polyethylene layer of the package closest to the terminals.

32. A method according to claim 31 including the step of sealingly bonding the

package to the terminals.

33. A method according to claim 32 including the step of adhesively bonding the

package to the terminals.