WO2018000023A1

WO2018000023A1 - Printed interdigitated super capacitor and method of manufacture

Info

Publication number: WO2018000023A1
Application number: PCT/AU2017/050628
Authority: WO
Inventors: Uli Kruger; Tanachat POCHANA
Original assignee: Cleanfuture Energy Co Ltd.
Priority date: 2016-06-30
Filing date: 2017-06-21
Publication date: 2018-01-04

Abstract

A super capacitor is constructed by printing an array of parallel connected series capacitor subassemblies onto a flexible substrate, applying an electrolyte on to the printed array, rolling the printed array into a cylinder, and attaching electrodes to first and second ends of the cylinder. Preferably the series capacitor subassemblies comprise a plurality of series connected capacitors formed from an array of interdigitated electrodes and are printed using a rotogravure process.

Description

Printed Interdigitated Super Capacitor and Method of Manufacture

FIELD OF THE INVENTION

[0001] The present invention relates to super capacitors, in particular a printed planar interdigitated super capacitor and method to manufacture same that will allow for the construction of cheap and effective bulk energy storage devices.

BACKGROUND TO THE INVENTION

[0002] In an interdigitated super-capacitor both electrode surfaces reside on the same plane with a minimal separation gap between them. This design offers some advantages over the traditional parallel plate design by enabling improved ionic transfer, better utilisation of electrochemical surface area and electrical double-layer formation across the planar surfaces. It has been found that down scaling this type of capacitor to micro-scale or nano-scale can offer additional advantages such as lower internal resistance and higher specific power densities. Connecting a multiplicity of nano-scaled or micro-scaled interdigitated supercapacitors together to form a

series/parallel circuit will result in a higher capacity and power density over fewer larger devices covering the same area.

[0003] Further significant improvements in power and energy density can be achieved by introducing pseudo-capacitance inducing materials to the electrodes, thereby creating an Interdigitated-Nano-Hybrid-Supercapacitor. Independent research results based on modelling indicate that this kind of approach can yield very high energy densities in the range of 100s of mW/cm³, potentially outperforming existing battery technologies for energy storage and mass energy storage applications.

However, until an actual device consisting of 1000s of multiple layers consisting of 100s of thousands to millions of individual devices per layer is manufactured and performance tested, such results remain speculative. A successful mass storage device based on the Planar Interdigitated Supercapacitor (PIS) must integrate many

thousands of individual nano-scale capacitor circuits into one simple to manufacture package with minimal inactive layer-volume. The manufacturing method must be fast and automated.

[0004] The object of this invention is to provide a bulk energy storage device based on multiple interconnected groups of planar interdigitated supercapacitors that can be quickly and easily constructed and cost effectively mass produced.

SUMMARY OF THE INVENTION

[0005] In a first aspect the invention provides a method of constructing a super capacitor, comprising the steps of printing an array of parallel connected series capacitor subassemblies onto a flexible substrate, applying an electrolyte on to the printed array, rolling the printed array into a cylinder, and attaching electrodes to first and second ends of the cylinder.

[0006] Preferably the array of parallel connected capacitors is formed from a repeated pattern and is produced by a rotogravure process.

[0007] The invention further provides a super capacitor constructed according to the above method.

[0008] It should be noted that any one of the aspects mentioned above may include any of the features of any of the other aspects mentioned above and may include any of the features of any of the embodiments described below as appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows.

[0010] Figure 1 shows a single series connected capacitor.

[0011] Figure 2 shows an abstracted version of the capacitor of Figure 1 .

[0012] Figure 3 shows a rotogravure roller with an engraved drum for printing series capacitors.

[0013] Figure 4 shows a contiguous strip of series capacitors connected in parallel.

[0014] Figure 5 shows a complete capacitor being assembled from a rolled up capacitor strip and two terminal plates. [0015] Figure 6 shows a complete capacitor.

[0016] Figure 7 shows a power storage module comprising multiple capacitors. DRAWING COMPONENTS

[0017] The drawings include the following integers.

20 series capacitor

20' series capacitor - abstracted

22 series capacitor negative image

25 rotogravure roller

30, 31 bus strips

40, 50, 60, 70 capacitors

41 , 51 , 61 , 71 , 81 electrode connections

42, 43, 52, 53, 54, 55, 62, 63, 64, 65, 72, 73, 74, 75, 84, 85 electrodes

90 capacitor strip

94 capacitor subassembly

95 end face

100 capacitor

1 10 terminal plate

1 12 metal plate

1 14 punched metal prongs

1 15 tab

1 16 hole

200 power storage module

210 endplates

212 metal sheet

213 punched metal prongs

220 cover

221 , 222 terminals

DETAILED DESCRIPTION OF THE INVENTION

[0018] The following detailed description of the invention refers to the

accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. Dimensions of certain parts shown in the drawings may have been modified and/or exaggerated for the purposes of clarity or illustration.

[0019] The present invention provides a capacitor produced by rotogravure printing electrodes onto a substrate. Each rotation of a rotogravure roller produces a number of interdigitated capacitors in series between two connection bus strips. Successive rotations of the rotogravure roller connect the series capacitors in parallel. The substrate is then rolled up and electrodes attached at either side. The number of capacitors in series determines the working voltage of the capacitor whilst the number of series capacitors connected in parallel determines the total capacitance. The small scale features obtainable by the rotogravure process together with the materials used and tight packing of the capacitor produce a super capacitor of very high energy density.

[0020] The repeated pattern produced by a single rotation of the rotogravure roller, i.e. a series interdigitated capacitor with bus connections, is shown as 20 in Figure 1 . In order to maximise the charge/discharge rate and frequency response as a result of smaller internal resistance of the completed circuit, the interdigitated micro patterns are printed in the smallest possible scale. The current state of the art for rotogravure printing allows 5 micron line width with a 1 micron separation. Alternate electrodes are connected at either end to form opposing electrodes of individual capacitors, with the end capacitors connected to bus strips. The relative scale of the features of the series capacitor 20 in Figure 1 makes it hard to discern them from each other and appreciate the interconnections between them. For representational convenience an abstracted version of the series capacitor is shown as 20' in Figure 2 and will be used to explain the structure.

[0021] The series capacitor 20' comprises bus strips 30 and 31 between which are four series connected capacitors 40, 50, 60 and 70. Each of the capacitors comprises four interdigitated electrodes joined two at a time. The first capacitor 40 is connected to the bus strip 30 by electrode connection 41 which connects to a first end of electrodes 42 and 43 that form a first half of the capacitor 40. The second half of the first capacitor 40 is formed by electrodes 52 and 53 which are joined by a second electrode connection 51 and spaced apart from electrodes 42 and 43. The second electrode connection 51 also connects together electrodes 54 and 55 which form the first half of the second capacitor 50, thus also connecting the first capacitor 40 and the second capacitor 50 in series. The second half of the second capacitor 50 is formed by electrodes 64 and 65 connected by electrode connection 61 . This pattern of

interconnected and spaced electrodes is repeated to produce the four capacitors in series, with capacitor 60 being formed by electrodes 62, 63 and 72, 73 connected by electrode connections 61 and 71 respectively and capacitor 70 being formed by electrodes 74, 75 and 84, 85 connected by electrode connections 71 and 81

respectively. As the basic structure of the capacitor is printed, individual capacitors are well matched to each other allowing them to be connected in series without the need for any balancing circuits.

[0022] The series capacitor 20 in Figure 1 is produced by a negative image 22 on a rotogravure drum 25 as shown in Figure 3. The negative image 22 is preferably formed by laser engraving. The image produces a single series connected capacitor with each revolution. The bus strips 30 and 31 are produced by endless annular patterns thereby joining together the series capacitors in parallel. In alternative embodiments the image on the rotogravure drum produces multiple series connected capacitors in parallel with each revolution.

[0023] The printing medium is either a type of conductive graphene ink, MOF (Metal Organic Framework) ink or Graphene Oxide (GO) ink. If GO is chosen, a suitable surface reduction method must be employed to remove surface oxygen groups in order to increase the conductivity of the material. Reduction may be achieved by Electron beam, Ion beam, Induction, or applied electric current at a prescribed intensity and duration. The specific fluency rate for any of the applied reduction methods is chosen to leave some residual defects in the form of oxygen groups on the electrode surface in order to enhance the wettability and storage capacity of the reduced GO.

[0024] To produce multiple series capacitors connected in parallel a substrate is passed through a reel to reel printer with the rotogravure roller 25. In practise a continuous strip of series capacitors 20 would be printed and subsequently cut to length to produce the desired capacitance. A strip of four series capacitors 20 on a common printed substrate is shown as 90 in Figure 4. The bus strips 30 and 31 of each individual series capacitor 20 join together to connect the series capacitors in parallel. In practise hundreds of series capacitors would typically be joined together. [0025] The substrate material is chosen to be as thin as possible to minimise dead volume in a completed capacitor. Kaptan 700nm thick has been found to be a viable substrate.

[0026] Once printed the substrate is dried to prevent slumping of the printed lines which could result in touching and short circuiting. Drying methods such as infrared, near infrared, ultra violet, ultrasonic drying, hot air or electron beam curing may be employed. The substrate then passes a separate print roller to deposit two continuous glue lines along the inside edges of each connection bus strip 30 and 31 . The print method of the glue may be rotogravure, flexography or screen printing. An electrolyte layer is applied onto the printed pattern between the glue lines. The electrolyte may be of the aqueous type, but preferably an organic type of electrolyte or ionic liquid in order to achieve a higher potential total voltage for the finished device.

[0027] After the glue and electrolyte have been applied the substrate is rolled up tightly into a cylindrical capacitor subassembly 94 as seen in Figure 5. The glue lines provide a permanent bond between the continuous top side to the bottom side of the substrate. The electrolyte layer is thereby sealed in and entrapped between both sides of the substrate. In the capacitor subassembly 94, each end face 95 represents one side of the overall parallel connected embedded in-series circuits. To make a complete capacitor 100 a connection is made to each end face with a terminal plate 1 10 which comprises a metal plate 1 12 which has been punched to produce a series of sharp metal prongs 1 14. The sharp prongs 1 14 extend perpendicularly from the face of the plate and are arranged in radial patterns along increasing diameters at a substantially equal rate from the centre to the periphery of the plate. A plate 1 10 is pushed against each end face 95 causing the prongs to enter the end grain of the subassembly 94 to make an electrical connection with bus strips 30 and 31 . Before insertion, each terminal connection plate is heated up to a temperature slightly above the melting point of the substrate material. An assembled capacitor 100 is shown in Figure 6. The terminal plates include a tab 1 15 with a hole 1 16 for easy external connection.

[0028] The metal terminal plates 1 10 may be made by stamping and forming and can be made from any conductive metal of sufficient tensile strength. The metal is preferably plated with a highly conductive metal such as gold or zinc. A larger diameter capacitor with a proportionally higher overall current rating requires a larger diameter connection plate with an increased number of power take off prongs in proportion to its size.

[0029] Other structures with multiple capacitors may also be made such as the power storage module 200 shown in Figure 7. A number of capacitor subassemblies 94 are sandwiched between two endplates 210. Similar to the terminal connection plates 1 10, the endplates comprise a metal sheet 212 into which a series of metal prongs 213 have been stamped to connect to the end faces 95 of the subassemblies. The cover 220 conceals voltage control circuitry between the capacitors and the external terminals 221 and 222.

[0030] The reader will now appreciate the present invention which uses readily available printing technology to produce super capacitors with superior energy densities compared to known devices.

[0031] Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in this field.

[0032] In the present specification and claims (if any), the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers.

Claims

1 . A method of constructing a super capacitor, comprising the steps of:

a) printing an array of parallel connected series capacitor subassemblies onto a flexible substrate;

b) applying an electrolyte on to the printed array;

c) rolling the printed array into a cylinder; and

d) attaching electrodes to first and second ends of the cylinder,

wherein the series capacitor subassemblies comprise a plurality of series connected capacitors formed from an array of interdigitated electrodes.

2. A method of constructing a super capacitor as in claim 1 , wherein the array of parallel connected capacitors is formed from a repeated pattern.

3. A method of constructing a super capacitor as in claim 1 , wherein the repeated pattern is produced by a rotogravure process.

4. A super capacitor constructed according to claim 1 .

5. A super capacitor constructed according to claim 2.

6. A super capacitor constructed according to claim 3.