Metal working – Barrier layer or semiconductor device making – Barrier layer device making
Reexamination Certificate
2003-02-19
2004-08-10
Nguyen, Ha Tran (Department: 2812)
Metal working
Barrier layer or semiconductor device making
Barrier layer device making
C361S502000
Reexamination Certificate
active
06773468
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to energy storage devices, and specifically, to electrochemical capacitors, and to a method for preparing the same. In particular, the invention relates to the production of electrochemical capacitors or batteries based on aqueous electrolyte, and to an improved method of encapsulation thereof.
BACKGROUND OF THE INVENTION
There exists a need, in many different technological areas, for using electrochemical capacitors or batteries having small dimensions as energy storage devices.
In their most usual configuration, electrochemical capacitors, also known in the art as double layer capacitors, comprises a pair of flat electrodes saturated with a suitable electrolyte, wherein said electrodes are separated by a separating medium disposed therebetween. The separating medium, which may be either a porous sheet (known in the art as a separator), or a membrane, prevents the passage of electrical current in the form of electrons between the electrodes, while allowing ionic current to flow therebewteen, due to the porous nature of the separator or the gel type matrix of the membrane. Each of the flat electrodes is placed on a surface of a suitable plate, said plate often being referred to in the art as a current collector. The appropriately sealed capacitor is electrically connected to a suitable load by means of external terminals.
The electrical capacity of the above-described system is attributed to the double-layer formed at the interface of the solid electrode and the electrolyte solution following the application of electrical potential on the pair of electrodes.
Electrochemical capacitors are generally divided into two distinct categories, according to the type of electrolyte used for preparing the electrode, which may be either an aqueous or organic electrolyte solution. The former type may generate up to 1.2 volt per cell, whereas the latter type typically provides about 2.5 to 3.0 volts per cell.
The operating voltage of electrochemical capacitors may be increased by assembling a plurality of individual capacitors described above in series, to obtain an arrangement known in the art as a bipolar capacitor. The art has suggested numerous types of electrochemical capacitors, attempting to improve, inter alia, the structural features of the capacitor, the chemical composition of the electrode material placed therein and of the adhesives used for sealing said capacitor, and the processes for fabricating the same.
Attempts to fabricate a single electrochemical capacitor and a bipolar arrangement based thereon have met with two main difficulties. The first difficulty is related to the attachment of the electrode to the current collector plate, or its deposition thereon. The second difficulty relates to the sealing of the circumferential region of the electrochemical capacitor, in order to prevent the seepage of the electrolyte solution from the electrochemical cell.
U.S. Pat. No. 3,536,963 discloses an electrochemical capacitor comprising electrodes which are made by mixing activated carbon particles with an aqueous electrolyte (e.g., sulfuric acid), to obtain a viscous paste, which is subsequently compressed to form the electrodes. Each of the electrodes is placed within an annular gasket which is affixed to a circular current collector plate, following which the separator is interposed between the electrodes.
U.S. Pat. No. 4,604,788 discloses a chemical composition for carbon paste electrodes comprising activated carbon particles, aqueous electrolyte and fumed silica, to provide a pumpable carbon-electrolyte mix. The fabrication of the capacitor involves the filling of an electrode cavity with the pumpable mixture, following which excess water is removed by a procedure described in the patent.
U.S. Pat. No. 6,212,062 discloses an electrochemical capacitor based on a solution of organic electrolyte, and a method for fabricating the same.
It is an object of the present invention to provide an improved, economically superior and industrially applicable method for manufacturing energy storage devices that comprise an aqueous electrolyte, such as electrochemical capacitors or batteries, which method is based on printing techniques.
It is another object of the present invention to provide a printable composition suitable for the preparation of electrodes for use in electrochemical capacitors, which printable composition may be easily and conveniently applied in the production of said capacitors by means of various printing techniques.
It is yet another object of the present invention to provide an electrochemical capacitor featuring novel electrode composition and improved structural characteristics.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a method for preparing energy storage devices that contain electrochemical cells, and specifically, double layer capacitors, comprising the steps of:
a) Providing a printable composition suitable for use as an electrode, comprising an active material, which is preferably in the form of carbon particles in admixture with an aqueous electrolyte;
b) Placing a first template on one face of a current collector, wherein said first template is provided in the form of a sheet consisting of region(s) permeable to said printable composition, and masked region(s), non-permeable to said composition, wherein said masked region(s) of said first template include the margins thereof;
c) Applying said printable composition through said first template onto said face of said current collector, thereby forming well-defined electrode region(s) thereon;
d) Repeating steps b) and c) to produce a second current collector identical to the current collector of step (c);
e) Placing a second template on a face of a separating medium which may be either a porous film or a membrane, wherein said second template is provided in the form of a sheet consisting of masked and non-masked region(s), wherein said second template is essentially complementary to said first template, such that said masked regions on said second template correspond with the permeable regions of the first template;
f) Blocking the pores of said separating medium in those regions thereof which correspond with those regions of the current collector that have no electrodes printed thereon, and subsequently applying through the non-masked regions of said second template one or more adhesive materials onto said face of said separating medium;
g) Attaching the adhesive face of said separating medium to the first current collector, such that the non-masked region(s) on said face of said separating medium coincide with the electrode(s) printed on the face of said first current collectors, with respect to position, geometric form and size;
h) Repeating steps e) and f) with respect to the second face of said separating medium;
i) Placing said second current collector on said second face of said separator, such that the non-masked regions on said second face of said separator coincide with the electrode(s) printed on the face of said second current collector, with respect to position, geometric form and size.
As used herein, the term “printable composition” refers to a mixture exhibiting the necessary physical properties for application in printing techniques, such as screen-printing, stencil-printing and roller-coating. The inventor has surprisingly found that it is possible to improve the flowability properties and the thixotropicity of the composition used to prepare the electrodes according to the invention, thus rendering said composition particularly suitable for screen-printing applications, by mixing the active components (e.g., the carbon material and the aqueous electrolyte) in specific weight ratios and by introducing into the composition a combination of specific additives.
According to a particularly preferred embodiment of the invention, the printable composition used for preparing the electrodes comprises high surface area activated carbon particles and an aqueous electrolyte, wherein the preferred weight ratio between said a
Cellergy Ltd.
Nguyen Ha Tran
Nixon & Vanderhye P.C.
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