WO2018167789A2

WO2018167789A2 - A method for the preparation of supercapacitor electrodes and printed electrodes derived therefrom

Info

Publication number: WO2018167789A2
Application number: PCT/IL2018/050300
Authority: WO
Inventors: Ervin TAL-GUTELMACHER; Mordechay Moshkovich; Tamir Stein
Original assignee: POCell Tech Ltd.
Priority date: 2017-03-15
Filing date: 2018-03-15
Publication date: 2018-09-20
Also published as: IL251195A0; WO2018167789A3

Abstract

The present invention provides a method for the preparation of printable electrodes, suitable for use in supercapacitors, and in particular for the application of an electrode composition to heat-sensitive substrates. The method of the invention incudes providing a substantially flat substrate; providing a flowable electrode composition comprising an aqueous electrolyte and a dry matter, wherein the dry matter content (DMC) of the flowable electrode composition ranges from about 25% to about 65% (w/w); placing a thin screen or a stencil having at least one opening over a top surface of the flat substrate; contacting a top surface of the screen or stencil with the flowable composition; removing the thin screen or stencil from the top surface of the substrate; and blotting the substrate and the electrode composition applied thereon under pressure of between about 5 to about 150 bar, thereby obtaining a printed electrode having a DMC of between about 30% (w/w) to about 75% (w/w). The invention further provides printed electrodes, which can be prepared in a highly reproducible manner by the method of the invention.

Description

A METHOD FOR THE PREPARATION OF SUPERCAPACITOR ELECTRODES AND PRINTED ELECTRODES DERIVED THEREFROM

FIELD OF THE INVENTION

The present invention is directed to a method for the preparation of printable electrodes utilized in symmetric or asymmetric supercapacitors. The invention is further directed to printed electrodes prepared by the method of the invention.

BACKGROUND OF THE INVENTION

Ongoing technological advances in such disparate areas as consumer electronics, transportation, and energy generation and distribution are often hindered by the capabilities of current energy storage/conversion systems, thereby driving the search for high-performance power sources that are also economically viable, safe to operate, and have limited environmental impact. Electrochemical capacitors (ECs), also termed electric double-layer capacitor (EDLC), supercapacitors or ultracapacitors, are one class of energy-storage devices that fill the gap between the high specific energy of batteries and the high specific power of conventional electrostatic capacitors.

A basic EDLC cell configuration is a pair of highly porous electrodes, typically including activated carbon, disposed on opposite faces of parallel conductive plates known as current collectors. The electrodes are impregnated with an electrolyte, and separated by a separator consisting of a porous electrically-insulating and ion-permeable membrane. When a voltage is applied between the electrodes, negative ions from the electrolyte flow to the positive electrode while positive ions from the electrolyte flow to the negative electrode, such that an electric double layer is formed at each electrode/electrolyte interface by the accumulated ionic charges. As a result, energy is stored by the separation of positive and negative charges at each interface. The separator prevents electrical contact between the conductive electrodes but allows the exchange of ions. When the EDLC is discharged, such as by powering an external electrical device, the voltage across the electrodes results in current flow as the ions discharge from the electrode surfaces. The EDLC may be recharged and discharged again over multiple charge cycles. Screen printing, as well as other printing techniques, including flexography, gravure, offset lithography, and inkjet, may be utilized for the formation of electrical devices on various substrates, termed printed electronics. By the electronic industry standards, printed electronics are considered to be inexpensive and beneficial for mass production. Screen-printed electrodes (SPEs) are often produced utilizing a thin screen or stencil made of a polymer (usually polyester) or of stainless steel stretched over a wooden or metal frame, and ink comprising carbon-based compounds, such as activated carbon, carbon nanotubes (CNTs), graphite and carbon black. In addition to the carbon-based compounds, binders, viscosifying agents and additional additives are often used in order to achieve a stable, easy to use, printable formulation. Said additives are known to affect the final electrode material properties and dimensions. The quality and the performance of the SPEs depends highly on: (a) the printing conditions, such as the printing speed or the blade size parameters; (b) the ink properties, such as stability, viscosity, and composition (Xu, Yanfei, et al. Adv. Energy Mater. 2013, 3, 1035-1040).

Utilizing printing techniques such as screen printing in the manufacturing process of EDLC electrodes is known to be beneficial in terms of low-cost large scale electrode production. In this technique, a mesh is used to transfer ink onto a substrate, excluding areas made impermeable to ink by a blocking screen or stencil. A blade or a squeegee is then moved across the screen to obtain a homogeneous layer of ink on the surface, followed by separating the screen or stencil from the printed substrate, and drying the resultant ink layer utilizing high temperature (S.H. Wu, Analytica Chimica Acta 687 (2011) 43-49 and H Wei, Analytica Chimica Acta 588 (2007) 297-303) and/or under vacuum conditions (L. Zhang, Int. J. Electrochem. Sci., 6 (2011) 819 - 829).

US Patent No. 3,648,126 is directed to a high capacitance low voltage electrolytic capacitor consisting essentially of a pair of paste electrodes and a separator saturated with electrolyte which functions as an electronic insulator and an ionic conductor. One of said paste electrodes is composed of active carbon and the opposing paste electrode is composed of a powdered metal selected from the group consisting of copper, nickel, cadmium, zinc, iron, manganese, lead, magnesium, titanium, silver, cobalt, indium, selenium and tellurium, said electrodes being prepared by mixing finely divided particulate material of the above electrode materials with electrolyte to form a viscous paste and compressing the paste to form the electrodes. The paste electrode can be deposited on a support surface as a very thin film by known techniques, such as silk screening, spraying, or roll coating. US Patent No. 6,084,766 is directed to a method of making an ultracapacitor electrode comprising applying a film-forming paste to a substrate through a screen at least in part supported by raised spaced ribs to fill spacing on the substrate defined by the ribs. The film is then cured to form a patterned electrode with intervening spacing for accumulation of gas during operation of the electrode in an ultracapacitor.

US Patent No. 8,472, 162 is directed to an energy storage device comprising one or more cells, wherein each cell is defined by a pair of electrodes and a separator placed therebetween, wherein each cell is bounded by two current collectors, the geometric form and size of said separator being identical to the form and size of said current collectors, and wherein in each cell, one electrode is printed on one of said two current collectors and the other electrode is printed on one face of the separator, the two electrodes being electronically insulated by means of said separator, and wherein the peripheral region of the separator, which surrounds the electrode printed thereon, is sealed.

Screen printing technique allows the use of a wide variety of substrates for the printing process such as plastics, fabrics and paper. However, utilizing heating and/or vacuum conditions as a part of the printing process restricts the printing on heat-sensitive materials, and might cause unwanted structural changes to the substrate or to the flowable electrode composition disposed on the substrate, and damage the quality of the final printed electrode product.

US Patent No. 8,083,970 discloses electroconductive printable inks and methods of making and using the same. The electroconductive inks include carbon fibrils, a liquid vehicle, and may include a polymeric binder.

US Patent Application No. 2012/0028127 discloses a graphene based ink for forming electrodes of printable batteries or supercapacitors. The ink comprises titanium dioxide and a binder. The binder may comprise one or more of the following: poly(sodium 4- styrenesulfonate), polyaniline, and poly[2,5-bis(3-sulfonatopropoxy)-l ,4-ethynylphenylene-alt- l,4-ethynylphenylene]sodium salt.

International Patent Application No. 2014/072877 discloses a screen-printable ink comprising nano-graphene platelets, a polymer comprising aniline monomelic units, and at least one solvent.

There remains an unmet need for a controllable screen printing process, which would allow electrode printing on heat-sensitive substrates and promote the fine tuning of the resulted printed electrode composition to achieve improved capacitance and overall performance of a supercapacitor. SUMMARY OF THE INVENTION

The present invention provides a unique method for the preparation of printable electrodes utilized in supercapacitor devices, allowing a low-cost large scale production of said electrodes on a wide range of substrates and with varying electrode components. The beneficial method of the invention further allows the printing of electrodes onto substrates which are heat- sensitive, and promotes the control and fine tuning of the resulted printed electrode composition. Furthermore, the method of the invention facilitates the production of thin printed electrodes, having a reduced internal resistance and an improved overall capacitive performance.

Additionally, the present invention provides highly reproducible printed electrodes, having a chemically stable and tunable final composition, which are prepared by the method of the invention. One of the advantages of the present printing method and the resultant electrodes is that they do not require inclusion of a binder or a thickening agent, thereby reducing the amount of non-conductive components of the electrode, lowering the electrode cost and decreasing its cycle-life degradation.

Thus, according to one aspect, the present invention provides a method for preparing a supercapacitor electrode, comprising the steps of:

(a) providing a substantially flat substrate;

(b) providing a flowable electrode composition comprising an aqueous electrolyte and a dry matter, wherein the dry matter content (DMC) of the flowable electrode composition ranges from about 25% (w/w) to about 65% (w/w);

(c) placing a thin screen or a stencil having at least one opening over a top surface of the substrate;

(d) contacting a top surface of the screen or stencil with the flowable composition of step (b) so that a portion of the composition extrudes through the opening, being applied to the top surface of the substrate in a substantially homogeneous manner;

(e) removing the thin screen or stencil from the top surface of the substrate; and

(f) blotting the substrate and the flowable electrode composition applied thereon under pressure of between about 5 to about 150 bar, thereby obtaining a printed electrode having a DMC of from about 30% (w/w) to about 75% (w/w).

According to some embodiments, the electrode is useful in the construction of a single- cell or a multi-cell symmetric or asymmetric supercapacitor. Each possibility represents a separate embodiment of the invention. According to some embodiments, the substrate is essentially inert to alkaline electrolyte. According to some embodiments, the substrate is heat-sensitive. According to some embodiments, the substrate is selected from a separator and a current collector. Each possibility represents a separate embodiment of the invention.

According to some specific embodiments, the substrate is a separator. The separator can comprise a polymer having surface hydroxyl groups. In further embodiments, the separator is made of a material selected from the group consisting of polyvinyl alcohol (PVA), polypropylene or polyethylene coated with hydrophilic materials such as ethyl vinyl alcohol (EVA), PVA and cellulose-based materials.

According to some embodiments, the substrate is a current collector. The current collector can comprise a composite material comprising a mixture of a polymer with conductive particles. According to further embodiments, the substrate is made of a material selected from the group consisting of polyvinyl chloride (PVC), polyethylene and polyaniline. In some related embodiments, the substrate comprises carbon particles embedded therein.

The thickness of the resultant electrode can be controlled, inter alia, by the thickness of the stencil utilized in step (c). Thus, according to some embodiments, the stencil utilized in step (c) of the method as described above, has a thickness of between about 0.01 and about 5 millimeters. In further embodiments, said stencil is a stainless-steel stencil.

In some embodiments, the screen utilized in step (c) of the method as described above comprises a plurality of openings. The thickness of the resulted electrode can be controlled by the number of the openings (corresponding to the mesh number), area of the opening, and/or the thread thickness of the screen. In some embodiments, the mesh number of the screen ranges between about 20 to about 40 mesh. In further embodiments, the thread thickness of the screen ranges from about 0.10 to about 0.40 mm. In further embodiments, the area of an opening of the screen ranges from about 0.1 to about 1 mm². In further embodiments, said screen is a stainless- steel screen.

In some embodiments, the contacting in step (d) comprises applying the flowable electrode composition of step (b) onto the surface of the screen or stencil utilizing a blade or a squeegee. In some specific embodiments, the squeegee comprises a blade. In certain embodiments, the contacting of step (d) comprises applying the flowable electrode composition of step (b) onto the surface utilizing a squeegee having a blade. In further embodiments, the blade of the squeegee has a round or a triangular shape. In some embodiments the blade of the squeegee has a triangular shape selected from isosceles triangle and a right-angled triangle. Each possibility is a separate embodiment of the invention. In certain embodiments, the blade of the squeegee has a triangular shape, wherein the opening angle ranges from about 20 to about 80 degrees. In some embodiments, at least a portion of the squeegee or a surface of the squeegee contacting the top surface of the substrate is made of a metal-based material. In further embodiments, at least a portion of the squeegee blade or a surface of the squeegee blade contacting the top surface of the substrate is made of a metal-based material. In some related embodiments, the metal-based material is stainless-steel. In some specific embodiments, the stainless steel blade surface is coated with polytetrafluoroethylene (PTFE). In some embodiments, the squeegee and/or its blade are characterized by having sheer properties selected from hard-metallic and spring metallic properties. In some embodiments, at least a portion of the squeegee or a surface of the squeegee contacting the top surface of the substrate is made of rubber. In further embodiments, at least a portion of the squeegee blade or a surface of the squeegee blade contacting the top surface of the substrate is made of rubber. In further embodiments, the rubber has a shore hardness of from 30 to 100 on a durometer scale of type A.

According to the principles of the invention, the blotting action is performed in order to remove the excess liquid from the resulted electrode, thereby providing a stable electrode having reproducible composition and efficient capacitive properties. In certain embodiments, blotting of the excess liquid is performed under pressure of between about 5 to about 100 bar. In some specific embodiments, the blotting of the printed surface is performed in a single step. In some embodiments, the blotting is performed in multiple steps utilizing different pressure conditions. Additionally, according to some embodiments, the removal of the excess liquid content from the printed electrode is carried out without drying the printed surface utilizing heat. Accordingly, in some embodiments, the method does not include heating of the substantially flat substrate and/or electrode composition following step (d).

In some embodiments, the flowable electrode composition is characterized by having a viscosity of from about 10,000 to about 10,000,000 cP. In some other embodiments, the flowable electrode composition is characterized by having a viscosity of from about 500,000 to about 2,000,000 cP. In some further embodiments, the flowable electrode composition is characterized by having a viscosity of from about 100,000 to about 1,000,000 cP. In certain such embodiments, the viscosity is measured by Brookfield DV-E viscometer at shear rates of 0.5-10 (1/sec) and temperature of 25°C.

In some embodiments, the aqueous electrolyte of the flowable electrode composition is an alkaline electrolyte. In some embodiments, the alkaline electrolyte of the flowable electrode composition comprises a dissolved salt selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH), and combinations thereof. Each possibility represents a separate embodiment of the invention. In some specific embodiments, the dissolved salt is potassium hydroxide (KOH).

In some embodiments, the dry matter of the flowable electrode composition comprises activated carbon. In further embodiments, the flowable electrode composition is characterized by having a DMC of between about 25% (w/w) and about 50% (w/w).

In some embodiments, the dry matter of the flowable electrode composition comprises a conductive agent selected from the group consisting of carbon nanotubes (CNTs), graphite, carbon black and combinations thereof. Each possibility represents a separate embodiment of the invention. In still further embodiments, the flowable electrode composition is characterized by having a DMC of between about 40% (w/w) and about 65% (w/w).

In some embodiments, the dry matter of the flowable electrode composition comprises a transition metal oxide or sulfide. In some related embodiments, the transition metal sulfide is selected from the group consisting of Mn_nO_x, TiO_x, NiO_x, CoO_x, SnO_x, and combinations thereof, wherein x ranges from 1.5 to 3. In additional related embodiments, the transition metal sulfide is selected from the group consisting of FeS_y, MoS_y, NiS_y, CoS_y, MnS_y, TiS_y, SnS_y and combinations thereof, wherein y ranges from 1.8 to 2.2 and n ranges from 1 to 2. Each possibility represents a separate embodiment of the invention. In some specific embodiments, the transition metal oxide comprises Mn0₂. In further embodiments, the transition metal oxide comprises Ti0₂. In some related embodiments, the flowable electrode composition is characterized by having a DMC of between about 40% (w/w) and about 65% (w/w).

In certain embodiments, the flowable electrode composition comprises the aqueous alkaline electrolyte, activated carbon, transition metal oxide or sulfide, carbon nanotubes (CNTs) and graphite. In further embodiments, the flowable electrode composition as described above is characterized by having a DMC of between about 40% and about 65%. In some related embodiments, the transition metal oxide or sulfide is selected from the group consisting of Mn_nO_x, TiO_x, NiO_x, CoO_x, SnO_x, FeS_y, MoS_y, NiS_y, CoS_y, MnS_y, TiS_y, SnS_y and combinations thereof, wherein x ranges from 1.5 to 3, y ranges from 1.8 to 2.2 and n ranges from 1 to 2. Each possibility represents a separate embodiment of the invention. In some specific embodiments, the transition metal oxide is Mn0₂. In some optional embodiments, the flowable electrode composition further comprises carbon black. In certain embodiments, the flowable electrode composition comprises the aqueous alkaline electrolyte, at least two transition metal oxides or sulfides, carbon nanotubes (CNTs) and graphite. In further embodiments, the flowable electrode composition as described above is characterized by having a DMC of between about 40% and about 65%. In some related embodiments, the transition metal oxide or sulfide is selected from the group consisting of Mn_nO_x, TiO_x, NiO_x, CoO_x, SnO_x, FeS_y, MoS_y, NiS_y, CoS_y, MnS_y, TiS_y, SnS_y and combinations thereof, wherein x ranges from 1.5 to 3, y ranges from 1.8 to 2.2 and n ranges from 1 to 2. Each possibility represents a separate embodiment of the invention. In some specific embodiments, the at least two transition metal oxides include Mn0₂ and Ti0₂.

As mentioned hereinabove, the present printing method and the resultant electrode do not require inclusion of a binder or a thickening agent. Accordingly, in some currently preferred embodiments, the dry matter of the flowable electrode composition comprises less than about 20%) (w/w) of an additive selected from the group consisting of a thickening agent, a binder, an anti-foaming agent and combinations thereof. In further embodiments, the flowable electrode composition is essentially free of an additive selected from the group consisting of a thickening agent, a binder, an anti-foaming agent and combinations thereof. Each possibility represents a separate embodiment of the invention.

In some optional embodiments, the flowable electrode composition further comprises an additive selected from the group consisting of a thickening agent, a binder, an anti-foaming agent and combinations thereof. Each possibility represents a separate embodiment of the invention. In some specific embodiments, the thickening agent is selected from the group consisting of clay, sulfonate, saccharide, polysaccharide, polyacrylic acid based polymers, gelling agent, organosilicon, and combinations thereof. In some other embodiments, the flowable electrode composition comprises a binder selected from the group consisting of an alginate, cellulose- based material, rubber, polyvinyl, PTFE, polyacrylate, and combinations thereof. In some related embodiments, the flowable electrode composition comprises an anti-foaming agent selected from the group consisting of silica, polysilicon polymer, polyethylene glycol, polyethylene glycol copolymer, and combinations thereof. Each possibility represents a separate embodiment of the invention.

According to another aspect, the present invention provides a supercapacitor printed electrode having a DMC of from about 30%> (w/w) to about 75% (w/w), wherein said electrode is prepared according to the method of the present invention as described in the various embodiments hereinabove. In some embodiments, the dry matter of the printed electrode comprises from about 50 to about 90 % (w/w) Mn0₂; from about 0.1 to about 10 % (w/w) CNTs; from about 0.5 to about 15 % (w/w) graphite; and from about 0.5 to about 10 % (w/w) activated carbon. In some embodiments, the printed electrode as described above is characterized by having a DMC of from about 35 to about 65% (w/w). In some exemplary embodiments, the printed electrode as described above is characterized by having a DMC of from about 55 to about 60% (w/w).

In some embodiments, the dry matter of the printed electrode comprises from about 60 to about 85 % (w/w) Mn0₂; from about 0.5 to about 15 % (w/w) CNTs; from about 1 to about 25 % (w/w) graphite; and from about 0.5 to about 15 % (w/w) Ti0₂. In some embodiments, the printed electrode as described above is characterized by having a DMC of from about 50 to about 75% (w/w).

In some embodiments, the printed electrode comprises about 30 to about 50 % (w/w) activated carbon and about 50 to about 70 % (w/w) of the alkaline electrolyte. In some embodiments, the printed electrode as described above is characterized by having a DMC of from about 30 to about 50% (w/w).

In some currently preferred embodiments, the dry matter of the printed electrode comprises less than about 20% (w/w) of an additive selected from the group consisting of a thickening agent, a binder, an anti-foaming agent and combinations thereof. In further embodiments, the printed electrode is essentially free of an additive selected from the group consisting of a thickening agent, a binder, an anti-foaming agent and combinations thereof. Each possibility represents a separate embodiment of the invention.

In some embodiments, the printed electrode as described above has a thickness ranging from about 10 micron to about 5 millimeters. In some specific embodiments, the printed electrode has a thickness ranging from about 50 microns to about 2 millimeters. In some other embodiments, the printed electrode has a thickness ranging from about 300 microns to about 1 millimeter. In some further embodiments, the printed electrode has a thickness ranging from about 500 microns to about 1.5 millimeters.

According to some embodiments, the utilized activated carbon is a low purity activated carbon having an ash content of above about 5 % (w/w). In some other embodiments, the activated carbon is a low purity activated carbon having an ash content of above about 10 % (w/w). In some related embodiments, the activated carbon has a surface area of at least about 500 m²/gr. In some other embodiments, the activated carbon has a surface area of at least about 1000 m²/gr. In some other related embodiments, the activated carbon has a porosity/pore volume of about 0.3 to about 0.9 cc/gr.

Further embodiments and the full scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: depicts the capacitance measured for supercapacitors produced by different methods (printed vs. rolled);

Figure 2: depicts the Equivalent Series Resistance (ESR) values measured for supercapacitors produced by different methods (printed vs. rolled);

Figures 3A-3B: depict the capacitance measured for supercapacitors having printed electrode comprising different conductive additives compared with the capacitance measured for supercapacitor with no conductive additives. Figure 3A depicts the relative normalized capacitance value per total weight of all paste components, including electrolyte and additives. Figure 3B depicts the relative normalized capacitance value per weight of the active components of the paste which contribute to the electrochemical activity of the electrode, not including electrolyte or additives;

Figure 4A-4B: depict the Equivalent Series Resistance (ESR) values measured for different supercapacitors having printed electrodes comprising different conductive additives compared with the ESR values measured for a supercapacitor with no conductive additives. Figure 4A depicts the relative ESR measured before charge/discharge cycles. Figure 4B depicts the relative ESR measured after charge/discharge cycles.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method for the preparation of printable electrodes which can be used in supercapacitors allowing a low-cost large scale production of said electrodes on a wide range of substrates without utilizing high temperatures as part of the printing and electrode fixation processes. The method of the invention further enables printing of electrodes onto substrates which are heat-sensitive, such as various polymeric membranes including polyvinyl chloride (PVC) or polyethylene or polyaniline which can be beneficial as structural components in a supercapacitor. Additionally, the method of the present invention promotes the control and fine tuning of the resulted printed electrode thickness and composition (e.g. dry matter content) , which have crucial effect on the internal resistance of the electrode and overall capacitive performance of the supercapacitor.

(a) providing a substrate;

(b) providing a flowable electrode composition having a dry matter content (DMC) of from about 25 to about 65% (w/w);

(c) placing a thin screen or a stencil having at least one opening over the substrate;

(d) contacting the thin screen or stencil with the flowable composition of step (b) so that a portion of the composition extrudes through the opening and being applied to the substrate in a substantially homogeneous manner;

(e) removing the thin screen or stencil from the substrate; and

(f) removing excess liquid content from the substrate and electrode composition applied thereon utilizing blotting under pressure of from about 5 to about 150 bar,

thereby obtaining a printed electrode having a DMC of from about 30 to about 75%.

According to some embodiments, the method is for use in preparing a printable electrode on a suitable substrate useful for the construction of a single-cell or multi-cell symmetric or asymmetric supercapacitor.

According to some embodiments, the substrate is substantially flat. According to some embodiments, the thin screen is substantially flat. As used herein, the term "substantially flat" refers in some embodiments to a substrate and/or a thin screen that assume a generally flat orientation when placed upon a flat supporting surface. In further embodiments the term "substantially flat" refers to a substrate and/or a thin screen having a surface roughness of no greater than about 1 μπι.

According to the principles of the present invention, the method allows the printing of electrodes onto a wide variety of substrates including heat-sensitive substrates, in particular substrates that can be used as a structural component in the supercapacitor. Thus, a suitable substrate for electrode printing can be, for example, a separator or a current collector. According to some embodiments, said substrate is a heat-sensitive substrate. As used herein, the term "heat-sensitive substrate" refers to a substrate that can change its structure, intrinsic properties (such as electric or mechanical properties), degrade or disassemble upon contacting or being in close proximity to a heat source, for example, but not limited to, polymeric films composed of polyvinyl chloride (PVC), polyethylene or polyaniline.

According to the principles of the invention, a suitable substrate is a substrate that is chemically and physically stable, in particular, under alkaline conditions. As the flowable electrode composition used for the printing process can comprise an aqueous alkaline electrolyte, a suitable substrate for said process is a substrate which is essentially inert to such electrolyte. The term "essentially inert" as used herein and in the claims refers to a chemically non-reactive substance, for example, a suitable substrate does not chemically react with alkaline electrolyte or is not being activated by such electrolyte or under alkaline conditions. In further embodiments, the term "essentially inert" refers to a substrate that does not change its intrinsic properties (such as electric or mechanical properties) or structure, or does not degrade or disassemble upon contacting or being in close proximity to the alkaline electrolyte.

According to some specific embodiments, the suitable substrate is a separator. Typically, the separator comprises an inert, electrically-insulating and ion-permeable material. In some embodiments, the separator is porous. In some related embodiments, the separator is an inert membrane, which is ion-permeable (i.e., allowing the exchange of ions therethrough) and electrically-insulating (i.e., preventing the transfer of electrons therethrough). In an optional embodiment, the separator includes multiple layers (e.g., a number of separate ion-permeable and electrically-insulating membranes arranged successively). In some embodiments, the separator substrate is made of a material selected from the group consisting of polyvinyl alcohol (PVA), polypropylene or polyethylene coated with hydrophilic materials such as ethyl vinyl alcohol (EVA), PVA and cellulose-based materials.

According to some embodiments, the suitable substrate is a current collector. Typically, the current collector is made from a conductive material, such as a conductive polymer material, in which the electrical conductivity is anisotropic, such that the conductivity perpendicular to the surface of the current collector sheet is greater than the conductivity along the surface. Alternatively, the current collector can be made from a metal or other material which is inert to the chosen electrolyte as described above. In some embodiments, the current collector is made of a material selected from the group consisting of polyvinyl chloride (PVC), polyethylene and polyaniline. In some additional embodiments, the current collector as described above further comprises carbon particles embedded therein. The substrate can have any shape as known in the art, such as, but not limited to rectangular and cubic shapes. In some embodiments, the substrate comprises a bottom surface and a top surface. In further embodiments, the method comprises placing a thin screen or a stencil having at least one opening over the top surface of the substrate in step (c) and removing the thin screen or stencil from the top surface of the substrate in step (e).

As indicated hereinabove, the method for preparing a printable electrode comprises a step of placing a thin screen or a stencil having at least one opening over the substrate. As used herein, the terms "thin screen" or "stencil" refer to an intermediate object having a defined patterned surface, to which the electrode composition is being applied in order to produce an image or a pattern designed by gaps or openings, allowing the electrode composition to reach only limited parts of the surface of the substrate. In some embodiments the thin screen and/or the stencil have a top surface and a bottom surface. The bottom surface can be configured to contact the substrate and the top surface can be configured to contact the flowable electrode composition. In further embodiments, the method comprises placing a thin screen or a stencil having at least one opening over the substrate in step (c), wherein the bottom surface of the thin screen or stencil contacts the top surface of the substrate. In still further embodiments the method comprises contacting the top surface of the thin screen or stencil with the flowable composition in step (d).

The thin screen and/or the stencil can have any shape, which is suitable for the preparation of a supercapacitor electrode. In some embodiments, the thin screen and/or the stencil have a rectangular or cubic shape. Each possibility represents a separate embodiment of the invention.

In some embodiments, step (c) comprises placing a stencil over the substrate opening. In some embodiments, the stencil comprises one opening. In certain such embodiments, the shape and/or area of the stencil opening defines the shape and/or area of the electrode. In further embodiments, the stencil has a rectangular shape comprising a rectangular opening (i.e., the stencil is a hollow rectangular frame).

In some embodiments, step (c) comprises placing a thin screen over the substrate opening. In some embodiments, the thin screen comprises a plurality of openings. The thin screen can be made of threads, wherein the openings are open spaces between the threads. In further embodiments, the threads form a grid pattern. In still further embodiments, the thin screen includes a frame, to which the threads are connected. In certain embodiments, the inner perimeter of the frame defines the perimeter and/or shape of the electrode. In certain embodiments, the frame has a rectangular shape.

According to the principles of the present invention, the thickness of the resulted printable electrode can be modified utilizing stencils of different thicknesses or thin screens having varying grid parameters. The advantageous ability to modify and tailor the electrode thickness to the desired electrode composition and operation mode of the supercapacitor may reduce the internal resistance of the electrode and promote the capacitive properties of the device. Additionally, the ability to control the printed electrode thickness is especially important in the case of asymmetric supercapacitor, in which the anode and cathode may be constructed from different materials having distinct densities, mass and charge densities, all of which lead to the need of obtaining different thickness of the anode and cathode in order to allow a balanced and productive operating superconductive cell or device. Thus, according to some embodiments, the stencil utilized in step (c) of the method as described above, has a thickness of between about 0.01 and about 5 millimeters. In further embodiments, the thickness of the stencil ranges from about 0.1 mm to about 1 mm. The term "thickness" as used in connection with the stencil, refers to a distance between the top surface and the bottom surface of the stencil. In some other embodiments, the stencil is made of stainless-steel.

In some embodiments, the thin screen utilized in step (c) of the method as described above comprises a plurality of openings. The thickness of the resulted electrode can be controlled by the number of the openings (corresponding to the mesh number), area of the opening, and/or the thread thickness of the screen. In some embodiments, the mesh number of the screen ranges between about 20 to about 40 mesh. In further embodiments, the thread thickness of the screen ranges from about 0.10 to about 0.40 mm. In further embodiments, the area of an opening of the screen ranges from about 0.1 to about 1 mm². In further embodiments, said screen is a stainless-steel screen.

According to the principles of the invention, the ability to achieve a substantially homogeneous spreading of the flowable electrode composition onto the substrate depends on the consistency of the ink composition and on the physical spreading action of the ink composition onto the top surface of the stencil or thin screen. As used herein, the terms "ink" and "flowable electrode composition" are used interchangeably, and refer to a liquid form of the electrode composition, which can be applied to a thin screen or a stencil in a substantially homogeneous manner to produce a well-defined surface comprising the electrode composition on top of a desired substrate. As used herein, the term "substantially homogeneous" refers to the spreading of the ink on top of the screen or stencil, utilizing a blade of a squeegee. The ink is being applied in a way which allows a uniform thickness of the printed electrode material, with minor fluctuation of about ±1-100 μιη (depending on electrode thickness) throughout the electrode structure.

Thus, in some embodiments, contacting the flowable electrode composition with the stencil and/or thin screen surface as described in step (d) hereinabove, comprises applying the flowable electrode composition onto the surface by utilizing a blade or a squeegee.

In some embodiments, the application of the flowable electrode composition is carried out by a squeegee. In further embodiments, the squeegee has a blade. In some embodiments, the blade of the squeegee has a shape selected from a round shape and a triangular shape. In further embodiments, the blade of the squeegee has a triangular shape, wherein the opening angle ranges from about 20 to about 80 degrees. In certain embodiments, the triangular shape is selected from an isosceles triangle and a right-angle triangle. The term "shape", as used in connection with the squeegee blade, refers to a shape of the cross-section of the blade. The term "opening angle", as used herein refers to an angle of the blade's vertex, which contacts the flowable electrode composition in step (d). In some specific embodiments, the blade of the squeegee as described above is characterized by having a thickness of between about 0.01 to about 5 millimeters. In some related embodiments, the portion of the squeegee or the surface area of the squeegee contacting the surface of the thin screen or stencil is made of a metal -based material. In further embodiments, at least a portion of the squeegee blade or a surface area of the squeegee blade contacting the surface of the substrate is made of a metal-based material. In some related embodiments, the metal-based material is stainless-steel. In some specific and currently preferred embodiments, the stainless steel blade surface is coated with polytetrafluoroethylene (PTFE). Without being bound by theory or mechanism of action, it is postulated that the PTFE coating reduces the adhesion between the ink and the squeegee and allows an improved spreading action. In some embodiments, the squeegee and/or its blade are characterized by having sheer properties selected from hard-metallic and spring metallic properties. In some embodiments, at least a portion of the squeegee or a surface area of the squeegee contacting the surface of the substrate is made of rubber. In further embodiments, at least a portion of the squeegee blade or a surface area of the squeegee blade contacting the surface of the substrate is made of rubber. In further embodiments, the rubber has a shore hardness of between 30 to 100 on a durometer scale of type A.

In some embodiments, the application of the flowable electrode composition is carried out by a blade. The blade utilized in step (d) can have different structures selected from the group consisting of a uniform flat blade, uniform thickness wire shaped blade, a rolling knife apparatus and a wire helically surrounded by a spring. Each possibility is a separate embodiment of the invention.

In some embodiments, the method comprises manually applying the flowable electrode composition onto the substrate by a blade or a squeegee. In some embodiments, the method comprises automated application of the flowable electrode composition onto the substrate by a blade or a squeegee. In certain such embodiments, the blade or the squeegee is connected to a print head. According to certain embodiments, the print head force is between 0 and 60kg. In some embodiments the print head force is about 15kg.

According to some specific embodiments, the printing speed of the electrodes of the invention is between about 100 to about 450 mm/sec. In some further embodiments, the printing speed is between 200 to about 350 mm/sec. In some additional embodiments, the printing speed is between about 250 and about 300 mm/sec. The term "printing speed", as used herein, refers in some embodiments to the speed of applying the flowable electrode composition onto the substrate by a blade or a squeegee. According to some embodiments, step (d) comprising contacting the thin screen or stencil with the flowable electrode composition is repeated at least twice. In further embodiments, step (d) is repeated at least three, four or five times. In further embodiments, step (d) comprises utilizing a blade or a squeegee.

According to some embodiments, about 500 g of ink is being applied to the screen or stencil, and after between about two to about four prints the ink quantity is renewed in order to allow at least about 300 g of ink on the screen or stencil.

In some embodiments, the printing process as described above continues until reaching a loading of the electrode composition of from about 0.01 g/cm² to about 0.5 g/cm² per printed surface, prior to blotting. According to the principles of the invention, a blotting or pressing action is performed in order to remove the excess liquid from the printed electrode and provide a stable electrode having reproducible and efficient capacitive properties. As used herein the term "blotting" refers to the action of attaching or pressing an adsorbing material such as paper or fabric against a surface to remove residual liquid from said surface. The blotting action according to the principles of the present invention provides control over the final electrode composition without the need to heat or dry the substrate under vacuum. The blotting process can be performed in a single step, or in several steps, wherein after each step the adsorbing material can be replaced and renewed to allow a better adsorption in the following step. As used herein the term "excess liquid" refers to residual aqueous electrolyte solution in which the solid electrode components are being mixed in to achieve a flowable electrode composition. It is to be understood, that upon the removal of a portion of said aqueous electrolyte solution utilizing blotting, an increase of the DMC of the printed electrode occurs from between about 25 to about 65% to a DMC value of between about 30 to about 75%.

In some embodiments, the blotting of the excess liquid is performed under pressure of between about 5 to about 150 bar. In some embodiments, the blotting of the excess liquid is performed under pressure of between about 5 to about 100 bar. In further embodiments, the pressure applied during blotting is between about 5 to about 90 bar, between about 10 to about 80 bar, between about 10 to about 60 bar, between about 10 to about 40 bar, between about 10 to about 20 bar, between about 50 to about 150 bar, between about 75 to about 125 bar or between 90 to about 100 bar. Each possibility represents a separate embodiment of the invention.

In some specific embodiments, the blotting of the substantially flat substrate and the flowable electrode composition is performed in a single step. In some embodiments, the blotting of the substantially flat substrate and the flowable electrode composition is performed in multiple steps utilizing different pressure conditions. Thus, in some embodiments, the blotting is performed under low pressure conditions, followed by a separate blotting step preformed under higher pressure conditions. In certain embodiments, the method comprises a first blotting step performed at a pressure of from about 5 bar to about 50 bar and a second blotting step performed at a pressure of from about 50 bar to about 150 bar. The blotting time can range from about 1 sec to about 30 sec. In further embodiments, the blotting time ranges from about 1 sec to about 20 sec or from about 1 sec to about 10 sec. In still further embodiment, each blotting step lasts for from about 1 sec to about 5 sec. Additionally, the advantageous method of the present invention promotes the removal of the excess liquid content from the screen-printed electrode without heat-drying the printed surface. In some embodiments, the method of the invention is carried without drying the printed substrate, wherein said drying utilizes heat. It is to be understood that by avoiding the heating of the substrate after printing, the method of the invention allows the use of heat-sensitive substrates which may be damaged or structurally altered due to the exposure to high temperatures. Flowable electrode composition (ink)

The flowable electrode composition of the invention enables a reproducible and efficient printing process and is characterized by having a balanced viscosity and chemical stability which promote an easy application of the ink onto a thin screen or stencil and the formation of a uniform printed electrode composition on the desired substrate. Preferably, the flowable electrode composition of the invention is aqueous and does not contain hazardous or environmentally unfriendly materials.

In some embodiments, the flowable electrode composition is characterized by having a viscosity of between about 10,000 to about 10,000,000 cP. In some other embodiments, the flowable electrode composition is characterized by having a viscosity of between about 500,000 to about 2,000,000 cP. In some further embodiments, the flowable electrode composition is characterized by having a viscosity of between about 100,000 to about 1,000,000 cP. In certain such embodiments, the viscosity is measured by Brookfield DV-E viscometer at shear rates of 0.5-10 (1/sec) and temperature of 25°C.

A) Electrolyte

According to some embodiments, the flowable electrode composition comprises an aqueous electrolyte. Said aqueous electrolyte can be an alkaline aqueous electrolyte. In further embodiments, the alkaline electrolyte comprises a dissolved salt selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH), and combinations thereof. Each possibility represents a separate embodiment of the invention. In some specific embodiments, the dissolved salt is potassium hydroxide (KOH). In some related embodiments, the aqueous alkaline electrolyte concentration is between about 20 and about 50% (w/w). In certain embodiments, the aqueous alkaline electrolyte concentration is about 30 % (w/w).

The weight percentage of the electrolyte in the flowable electrode composition is complimentary to the DMC value. For example, if the DMC value of the flowable electrode composition ranges from about 25% to about 65% (w/w), the weight percent of the electrolyte ranges from about 35% to about 75% (w/w), B) Carbon-based electrode composition.

In some embodiments, the flowable electrode composition comprises activated carbon and alkaline electrolyte, and is characterized by having a dry matter content (DMC) of between about 25 to about 50%. In certain embodiments, the flowable electrode composition has a DMC of between about 30 to about 36%. In some specific embodiments, the flowable electrode composition comprises activated carbon and alkaline electrolyte, and is characterized by having a DMC of between about 30 to about 40%. In some specific embodiments, the flowable electrode composition comprises activated carbon and alkaline electrolyte, and is characterized by having a DMC of between about 50 to about 60%. In some additional embodiments, the flowable electrode composition further comprises a conductive agent selected from the group consisting of carbon nanotubes (CNTs), graphite, carbon black and combinations thereof. Each possibility represents a separate embodiment of the invention. In some currently preferred embodiments, the flowable electrode composition as described above is characterized by having a viscosity of between about 500,000 to about 2,000,000 cP. In certain such embodiments, the viscosity is measured by Brookfield DV-E viscometer at shear rates of 0.5-10 (1/sec) and temperature of 25°C.

C) Transition metal-based electrode composition.

In some embodiments, the flowable electrode composition comprises a transition metal oxide, sulfide or a combination thereof. Each possibility represents a separate embodiment of the invention. In some embodiments, the flowable electrode composition comprises a transition metal oxide. The transition metal oxide can be selected from Mn_nO_x, TiO_x, NiO_x, CoO_x, SnO_x, and combinations thereof, wherein x ranges from 1.5 to 3. Each possibility represents a separate embodiment of the invention. In certain embodiments, the flowable electrode composition comprises Mn0₂. In additional embodiments, the flowable electrode composition comprises Ti0₂. In further embodiments, the flowable electrode composition comprises Mn0₂ and Ti0₂.

In some embodiments, the flowable electrode composition comprises a transition metal sulfide. The transition metal sulfide can be selected from the group consisting of FeS_y, MoS_y, NiSy, CoSy, MnSy, TiSy, SnSy and combinations thereof, wherein y ranges from 1.8 to 2.2 and n ranges from 1 to 2. Each possibility represents a separate embodiment of the invention.

In some embodiments, the transition metal-based electrode composition further comprises activated carbon. In some embodiments, the transition metal-based electrode composition further comprises a conductive agent selected from the group consisting of carbon nanotubes (CNTs), graphite, carbon black and combinations thereof.

In some embodiments, the flowable electrode composition comprises activated carbon, alkaline electrolyte, transition metal oxide or sulfide, carbon nanotubes (CNTs) and graphite, and is characterized by having a DMC of between about 40 to about 65%. In certain embodiments, the flowable electrode composition has a DMC of between about 50 to about 57%. In some currently preferred embodiments, the transition metal oxide is Mn0₂. In some optional embodiments, the flowable electrode composition further comprises carbon black. In some currently preferred embodiments, the flowable electrode composition as described above is characterized by having a viscosity of between about 100,000 to about 1,000,000 cP. In certain such embodiments, the viscosity is measured by Brookfield DV-E viscometer at shear rates of 0.5-10 (1/sec) and temperature of 25°C.

In some embodiments, the flowable electrode composition comprises the aqueous alkaline electrolyte, at least two transition metal oxides or sulfides, carbon nanotubes (CNTs) and graphite, and is characterized by having a DMC of between about 40 to about 65%. In certain embodiments, the flowable electrode composition has a DMC of between about 50 to about 57%). In certain embodiments, the at least two transition metal oxides comprise Mn0₂ and Ti0₂. In some optional embodiments, the flowable electrode composition further comprises activated carbon, carbon black or a combination thereof. In some currently preferred embodiments, the flowable electrode composition as described above is characterized by having a viscosity of between about 100,000 to about 1,000,000 cP. In certain such embodiments, the viscosity is measured by Brookfield DV-E viscometer at shear rates of 0.5-10 (1/sec) and temperature of 25°C.

D) Activated carbon source

In some embodiments, the activated carbon utilized in the carbon-based and transition metal-based electrode flowable compositions is a low purity activated carbon, which is both environmentally friendly and cost-effective. Thus in some embodiments, the activated carbon utilized for the preparation of the flowable electrode composition is a low purity activated carbon having an ash content of above about 5 %> (w/w). In some related embodiments, the activated carbon has a surface area of at least about 500 m²/gr. In some other embodiments, the activated carbon has a surface area of at least about 1000 m²/gr. In some other related embodiments, the activated carbon has a porosity/pore volume of about 0.3 to about 0.9 cc/gr. The term "low purity activated carbon", as used herein, refers in some embodiment to the ash content of above about 5 % (w/w). In other embodiments, the term refers to the content of impurities of above about 10 % (w/w). Said impurities can be selected from inorganic impurities e.g. metals, oxides and ceramic materials (i.e. silicates). In some embodiments, the activated carbon has an ash content of above about 10 % (w/w). In further embodiments, the activated carbon has an ash content of above 15 % (w/w). In some embodiments, the activated carbon does not contain an ash content of above 20 % (w/w). Without being bound by theory or mechanism of action, it is postulated that activated carbon having above 20 % (w/w) ash will be more prone to go through parasitic reactions, which in turn might cause an increase in the internal resistance of the capacitor comprising said impure activated carbon, and decrease the overall performance of the capacitor. In some embodiments, the activated carbon utilized in the electrode is characterized by having the ash content below about 20 % (w/w). In further embodiments, the ash content is below about 19 % (w/w), below about 18 % (w/w), below about 17 % (w/w), below about 16 % (w/w), or below about 15 % (w/w). Each possibility represents a separate embodiment of the invention.

E) Additional additives

According to the principles of the invention, the flowable electrode composition is chemically stable and is characterized by a balanced viscosity allowing an easy wetting of the desired substrate, and an easy spreading of the ink by using a blade or a squeegee in order to form a substantially homogeneous printed electrode.

Accordingly, in some currently preferred embodiments, the flowable electrode composition comprises less than about 20% (w/w) of a thickening agent of the total weight of the dry matter of the flowable electrode composition. In further embodiments, the flowable electrode composition comprises less than about 15% (w/w), less than about 10% (w/w), less than about 5% (w/w), or less than about 1% (w/w) of a thickening agent of the total weight of the dry matter of the flowable electrode composition. Each possibility represents a separate embodiment of the invention.

In additional currently preferred embodiments, the flowable electrode composition comprises less than about 20% (w/w) of a binder of the total weight of the dry matter of the flowable electrode composition. In further embodiments, the flowable electrode composition comprises less than about 15% (w/w), less than about 10% (w/w), less than about 5% (w/w), or less than about 1% (w/w) of a binder the total weight of the dry matter of the flowable electrode composition. Each possibility represents a separate embodiment of the invention. In additional currently preferred embodiments, the flowable electrode composition comprises less than about 5% (w/w) of an anti-foaming agent of the total weight of the dry matter of the flowable electrode composition. In further embodiments, the flowable electrode composition comprises less than about 1% (w/w) of an anti-foaming agent of the total weight of the dry matter of the flowable electrode composition.

In further embodiments, the flowable electrode composition is essentially free of a thickening agent. In still further embodiments, the flowable electrode composition is essentially free of a binder. In still further embodiments, the flowable electrode composition is essentially free of an anti-foaming agent. The term "essentially free", as used herein, refers in some embodiments to a concentration of a compound, which is not detectable in the composition by conventional techniques.

Non-limiting examples of a thickening agent include clay, sulfonate, saccharide, polysaccharide, polyacrylic acid based polymers, gelling agents, organosilicon and combinations thereof. Non-limiting examples of a binder include alginates (e.g. sodium alginate), cellulose- based materials (e.g. carboxymethyl cellulose (CMC)), rubbers, polyvinyl (such as PVA and PVP), polytetrafluoroethylene (PTFE), and polyacrylate (such as lithium polyacrylate, (LiPAA)) and combination thereof. Non-limiting examples of an anti-foaming agent include silica, polysilicon polymers, polyethylene glycol, polyethylene glycol copolymers and combinations thereof.

However, it is also possible to utilize stabilizers and accommodate them in the flowable ink formulation without jeopardizing the preferred consistency and chemical stability of the flowable electrode composition of the invention. Thus, in some alternative embodiments, the flowable electrode composition further comprises an additive selected from the group consisting of a thickening agent, a binder, an anti-foaming agent or combination thereof. Each possibility represents a separate embodiment of the invention. In some specific embodiments, the thickening agent is selected from the group consisting of clay, sulfonate, saccharide, polysaccharide, polyacrylic acid based polymers, gelling agents, organosilicon and combinations thereof. Each possibility represents a separate embodiment of the invention. In some other embodiments, the flowable electrode composition comprises a binder selected from the group consisting of alginates (e.g. sodium alginate), cellulose-based materials (e.g. carboxymethyl cellulose (CMC)), rubbers, polyvinyl (such as PVA and PVP), polytetrafluoroethylene (PTFE), and polyacrylate (such as lithium polyacrylate, (LiPAA)) and combination thereof. Each possibility represents a separate embodiment of the invention. In some related embodiments, the flowable electrode composition comprises an anti-foaming agent selected from the group consisting of silica, polysilicon polymers, polyethylene glycol, polyethylene glycol copolymers and combinations thereof. Each possibility represents a separate embodiment of the invention.

Printed electrodes

According to another aspect, the present invention provides a printed electrode having a

DMC of between about 30 to about 75%, wherein said electrode is prepared by the method according to the various embodiments of the present invention. In some embodiments, the printed electrode as described above has a thickness ranging from about 10 micron to about 5 millimeters. In some other embodiments, the printed electrode has a thickness ranging from about 50 microns to about 2 millimeters. In some further embodiments, the printed electrode has a thickness ranging from about 300 microns to about 1 millimeters. In some additional embodiments, the printed electrode has a thickness ranging from about 500 microns to about 1.5 millimeters.

A) Carbon-based electrode

In some embodiments, the printed electrode comprises from about 30 to about 50 %

(w/w) activated carbon and from about 50 to about 70 % (w/w) of the alkaline electrolyte. In some specific embodiments, the printed electrode comprises about 35 to about 45 % (w/w) activated carbon and about 55 to about 65 % (w/w) of the alkaline electrolyte. In some exemplary embodiments, the printed electrode as described above is characterized by a DMC of between about 30 to about 50% (w/w). In further embodiments, the printed electrode as described above is characterized by a DMC of between about 30 to about 45%. In some embodiments, the printed electrode has a thickness ranging from about 10 micron to about 5 millimeters. In some other embodiments, the printed electrode has a thickness ranging from about 50 micron to about 2 millimeters. In some additional embodiments, the printed electrode has a thickness ranging from about 500 micron to about 1.5 millimeters.

In some embodiments, the printed electrode comprises about 30 to about 40 % (w/w) activated carbon and about 60 to about 70 % (w/w) of alkaline electrolyte. In some exemplary embodiments, the printed electrode as described above is characterized by a DMC of between about 30 to about 40%. In further embodiments, the printed electrode has a thickness ranging from about 10 micron to about 5 millimeters.

In certain embodiments, the printed electrode consists essentially of the activated carbon and alkaline electrolyte. In other embodiments, the printed electrode comprises activated carbon, alkaline electrolyte and a conductive additive selected from CNTs, graphite, carbon black, and combinations thereof. In further embodiments, the dry matter of the printed electrode comprises from about 75 to about 95 % (w/w) activated carbon and from about 5 to about 25 % (w/w) of the conductive additive selected from CNTs, graphite, carbon black, and combinations thereof. In one specific embodiment, the conductive additive comprises carbon black. In another specific embodiment the conductive additive comprises graphite. In yet another specific embodiment, the conductive additive comprises carbon black, graphite and CNTs. In some related embodiments, the printed electrode as described above is characterized by a DMC of between about 30 to about 50% (w/w).

B) Transition metal-based electrode

In some embodiments, the printed electrode comprises at least one transition metal oxide or sulfide, CNTs, graphite, and alkaline electrolyte. In further embodiments, the printed electrode comprises at least one transition metal oxide or sulfide, CNTs, graphite, activated carbon, and alkaline electrolyte. In additional embodiments, the printed electrode comprises at least two transition metal oxide or sulfide, CNTs, graphite, and alkaline electrolyte.

In some embodiments, the final printed electrode composition comprises:

from about 50 to about 90 % (w/w) Mn0₂;

from about 0.1 to about 10 % (w/w) CNTs;

from about 0.5 to about 15 % (w/w) graphite;

and from about 0.5 to about 10 % (w/w) activated carbon,

of the total weight of the dry matter of the electrode composition.

In certain embodiments, the printed electrode consists essentially of Mn0₂, CNTs, graphite, activated carbon and alkaline electrolyte. In certain embodiments, the printed electrode as described above is characterized by a DMC of between about 35 to about 65% (w/w). In further embodiments, the printed electrode as described above is characterized by a DMC of between about 50 to about 60% (w/w). According to further embodiments, the final printed electrode comprises from about 35 to about 65% (w/w) alkaline electrolyte. According to still further embodiments, the final printed electrode comprises from about 40 to about 60% (w/w) alkaline electrolyte. In certain embodiments, said alkaline electrolyte comprises KOH.

In some embodiments, the final printed electrode comprises

from about 60 to about 85 % (w/w) Mn0₂;

from about 0.5 to about 15 % (w/w) CNTs;

from about 1 to about 25 % (w/w) graphite; and f

rom about 0.5 to about 15 % (w/w) Ti0₂, of the total weight of the dry matter of the electrode composition.

In certain embodiments, the printed electrode as described above is characterized by having a DMC of from about 50 to about 75% (w/w). In further embodiments, the printed electrode is characterized by having a DMC of from about 55 to about 65% (w/w). According to further embodiments, the final printed electrode comprises from about 25 to about 50% (w/w) alkaline electrolyte. According to still further embodiments, the final printed electrode comprises from about 35 to about 45% (w/w) alkaline electrolyte. In certain embodiments, said alkaline electrolyte comprises KOH.

In some currently preferred embodiments, the final printed electrode comprises less than about 20%) (w/w) of a thickening agent of the total weight of the dry matter of the electrode composition. In further embodiments, the final printed electrode comprises less than about 15% (w/w), less than about 10% (w/w), less than about 5% (w/w), or less than about 1% (w/w) of a thickening agent of the total weight of the dry matter of the total weight of the dry matter of the electrode composition. Each possibility represents a separate embodiment of the invention.

In further currently preferred embodiments, the final printed electrode comprises less than about 20% (w/w) of a binder of the total weight of the dry matter of the electrode composition. In further embodiments, the final printed electrode comprises less than about 15% (w/w), less than about 10% (w/w), less than about 5% (w/w), or less than about 1% (w/w) of a binder the total weight of the total weight of the dry matter of the electrode composition. Each possibility represents a separate embodiment of the invention.

In still further currently preferred embodiments, the final printed electrode comprises less than about 5% (w/w) of an anti-foaming agent of the total weight of the dry matter of the electrode composition. In further embodiments, the final printed electrode comprises less than about 1%) (w/w) of an anti-foaming agent of the total weight of the dry matter of the electrode composition.

In further embodiments, the final printed electrode is essentially free of a thickening agent. In still further embodiments, the final printed electrode is essentially free of a binder. In still further embodiments, the final printed electrode is essentially free of an anti-foaming agent and combinations thereof.

In some specific embodiments, the printed electrode has a thickness ranging from about

10 micron to about 5 millimeters. In some other embodiments, the printed electrode has a thickness ranging from about 50 micron to about 2 millimeters. In some additional embodiments, the printed electrode has a thickness ranging from about 300 micron to about 1 millimeter. In some embodiments, the printed electrode prepared by the method according to various embodiments of the invention is porous. The term "porous", as used herein, refers to a structure of interconnected pores or voids such that continuous passages and pathways throughout a material are provided. In some embodiments, the porosity of the electrodes is from about 20% to about 90%, such as, for example, 30% - 80%, or 40% - 70% porosity. Each possibility represents a separate embodiment of the invention.

In some embodiments, the porous electrodes have a high surface area. The term "high surface area", as used in some embodiments, refers to a surface area in the range from about 1 to about 2000 m²/g, such as, for example, 10 - 100 m²/g or 50 -1500 m²/g.

In some embodiments, the terms "porous" and/or "high surface area" encompass materials having micro or nanoparticles.

A supercapacitor comprising the printed electrodes of the invention may be a symmetric or an asymmetric supercapacitor, including at least one electrode as described above. In some embodiments, the supercapacitor of the invention is a symmetric supercapacitor. In some embodiments, the symmetric supercapacitor of the invention comprises two low-purity carbon based electrodes as described above.

In some other embodiments, the supercapacitor of the invention is an asymmetric supercapacitor, in which the asymmetric electrode configuration may increase the energy density stored in the capacitor. In some embodiments, the asymmetric supercapacitor of the invention comprises a first low-purity carbon based electrode as described above (serving as an anode) and a second electrode comprising a transitional metal-based composition as described above (serving as a cathode).

As used herein and in the appended claims the singular forms "a", "an," and "the" include plural references unless the content clearly dictates otherwise. It should be noted that the term "and" or the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise. As used herein, the term "about", when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of +/-10%, more preferably +1-5%, even more preferably +/-1%, and still more preferably +/-0.1% from the specified value, as such variations are appropriate to perform the disclosed methods. The following examples are presented in order to more fully illustrate some embodiments of the invention. They should, in no way be construed, however, as limiting the broad scope of the invention. One skilled in the art can readily devise many variations and modifications of the principles disclosed herein without departing from the scope of the invention. EXAMPLES

Example 1 : Preparation of flowable electrode compositions

An activated carbon electrode (anode) can be prepared with different DMC values and may contain conductive additives and/ or stabilizers such as binders. The basic flowable electrode composition was prepared with two different DMC values while avoiding the use of stabilizers or conductive additives. The preparation of these flowable compositions was carried as follows:

a) Preparation of activated carbon-based electrode flowable composition having a DMC of 34-35% (w/w):

The preparation of 10 Kg of flowable activated carbon (AC) composition was carried out utilizing 30 % (w/w) KOH electrolyte solution which was prepared using a titration against a known standard solution. 3.45 Kg of AC was mixed with 6.15 Kg of electrolyte solution in a pot and mixed in a mixer using an anchor stirrer at a starting speed of about 500 RPM for 15 minutes. The mixer speed was elevated up to 1500-2000 RPM, and then decreased to 500 RPM for 5 minutes for the composition stabilization. The obtained carbon-based flowable electrode composition had a DMC of 34.5%, and it was stored at 23 °C for 1 week prior to use.

b) Preparation of activated carbon-based flowable electrode composition having a DMC of 33-33.5%):

The preparation of 10 Kg flowable activated carbon (AC) composition was similar to the preparation path described in paragraph (a) hereinabove, utilizing 3.3 Kg activated carbon (AC) mixed together with 6.7 Kg of 30 % (w/w) KOH electrolyte solution to obtain a final flowable electrode composition having a DMC of 33% (w/w).

Transition metal-based electrode (cathode) can be prepared with different DMC values, transition metal oxides or sulfides, and carbon materials and may contain stabilizers such as binders. Two flowable electrode compositions were prepared with different DMC values and different dry matter constituents while avoiding the use of stabilizers. The preparation of these flowable compositions was carried as follows: c) preparation of transition metal-based flowable electrode composition having a DMC of 55% (w/w):

The preparation procedure included the following steps: 1) calculating and weighting the desired amounts of Mn0₂, SWCNT, graphite and activated carbon; 2) placing the ingredients into a polypropylene beaker; 3) using a mixer, to mix the ingredients for about 2 minutes; 4) adding electrolyte while mixing; 5) continuing mixing for 20 minutes to form a homogeneous mixture

Flowable composition preparation: 850 g Mn0₂, 50 g activated carbon and 50 g graphite were inserted into a polypropylene beaker and were mixed together for about 0.5 hr at room temperature. 50 g MWCNT were added to the mixture at mixed together to obtain a homogenized mixture. 1200 g 6.7M KOH electrolyte was added in a stepwise manner during stirring. The mixture was further mixed for about 20 minutes to achieve a homogenized mixture. d) preparation of transition metal-based flowable electrode composition having a DMC of 53% (w/w):

The preparation procedure included the following steps: 1) mixing 6000 g Mn0₂, 375 g

MWCNTs, and 750 g graphite by means of mixer; 2) adding 1920 g of 30 % (w/w) KOH electrolyte solution to the above solid mixture; 3) mixing the above mixture by means of a mixer for 2 hours at lOOrpm; 4) dispersing 375 g Ti0₂ in 4731 g of the KOH electrolyte solution; 5) adding the dispersion of Ti0₂ in the KOH electrolyte to the mixture obtained in step 3 and mixing for another 2 hours at 100 rpm.

Example 2: Printing process

a) Flowable composition (ink) final preparation prior to use:

The flowable compositions were prepared according to Example 1 hereinabove and were kept in a refrigerator until use. Prior to the printing process, the composition was placed at room temperature for 10 minutes and mixed at 500 RPM for 5 minutes before printing.

b) Printing:

Printing speed back and forth was 300 mm/sec and the print head force was 10 kg. The angle of the triangular squeegee blade (made of 316 stainless steel coated with Teflon (PTFE)) was adjusted to an angle of 10° vertical to the printing plane. The stencil thickness utilized for the transition metal -based electrode was 1.2 mm and 1.5 mm for the carbon-based electrodes. About 500 g of ink was applied to the stencil, and every 2-3 prints the ink quantity was renewed, in order to allow at least 300 g of ink on the stencil. The squeegee operated in a double stroke mode; (a) the carbon-based electrode composition having a DMC of 34-35% (w/w) was applied by 3-5 double strokes; (b) the carbon-based flowable electrode composition having a DMC of 33-33.5% (w/w) was applied by a single double stroke; (c) the transition metal-based flowable electrode composition having a DMC of 55% (w/w) was applied by a single double stroke; and (d) the transition metal-based flowable electrode composition having a DMC of 53% (w/w) was applied by a single double stroke . Each printed electrode was transferred immediately to a blotting station. The transition metal-based electrode and the carbon-based electrode with the flowable electrode composition having a DMC of 34-35% (w/w) underwent a single stage blotting process at high pressure of 30 bar for 5 seconds. The carbon-based electrode with the flowable electrode composition having a DMC of 33-33.5%) (w/w) required a delicate blotting process including two steps: 1) at low pressures for a short duration (e.g., 10-40 bar for 1-3 seconds), 2) removal and replacement of the extraction paper media, followed by a second blotting at high pressure (e.g., 100 bar for 5 seconds).

Results:

a) The carbon-based electrode with the flowable electrode composition having a DMC of 33-33.5%) (w/w) yielded a uniform stencil-printing product, which had up to about 1.2 mm thickness without significant smears after fixation. The final DMC of the solid electrode was 40% (w/w).

b) The carbon-based electrode with the flowable electrode composition having a DMC of 35%) (w/w) yielded a uniform stencil -printing product, which had up to about 1.5 mm thickness without significant smears after fixation. The final DMC of the solid electrode was 40 % (w/w).

c) The transition metal -based electrode having a DMC of 55% (w/w) yielded a uniform stencil-printing product, which had up to 1 mm thickness without significant smears after fixation, with a final DMC of the solid electrode of 60% (w/w).

d) The transition metal-based electrode having a DMC of 53% (w/w) yielded a uniform stencil -printing product, which had up to 1 mm thickness without significant smears after fixation, with a final DMC of the solid electrode of 60% (w/w).

Example 3 : Comparison between screen printed electrodes and rolled electrodes

In order to study the effect of the electrode manufacturing technique on the electrode characteristics, the internal resistance and overall capacitance of the electrodes were tested. ESR was measured utilizing 1kHz AC -impedance multiohmeter. Fresh cells where measured once before charge/discharge cycles and again afterwards. Capacitance was calculated from charge/discharge cycles performed under constant current regime at 10 and 50 mA/cm2 between 0.4-1.2V and between 1.2-1.4V. The mass of the rolled electrodes was 30 g and the mass of the screen printed electrodes was 34 g and the DMC values were similar for both printed and rolled electrodes (47% (w/w)). The size of the supercapacitors tested was 100 cm2, and they consisted of single cells.

Results:

According to Figure 1, the capacitance values for the printed and rolled electrodes were highly similar, with lower than 5 % differences between the two distinct electrode sources, which was within the standard deviation region (SD). In Figure 1, measurements carried between 0.4-1.2 V exhibited a 1% and 0.4% difference for 1 and 5 A, respectively. Measurements carried between 1.2-.1.4V exhibited a 3 and 4.5% difference for 1 and 5 A, respectively.

According to the difference in the ESR values demonstrated in Figure 2, there is a 16 and 19%) difference between the ESR values for the rolled and the printed electrodes, from the ESR values before and after the measurement, respectively. These variations are related mainly to the difference in the weight (and thickness) of the electrodes between the rolled and the printed electrodes as the cells composed of printed electrodes were 12%> higher in weight than the rolled electrodes cells. If these weight variations are taken into consideration utilizing normalization of the data, the ESR differences decreases to less than 7%>, which are considered as similar values.

Example 4: conductive additives for activated carbon electrode

In order to improve the overall performance of the supercapacitor comprising the printable electrode of the invention, several compositions of carbon additives were examined. The studied electrodes were activated carbon-based electrodes, further comprising graphite, CNT, carbon black (CB) or combinations thereof according to the compositions specified in Table 1.

The capacitance and internal resistance were measured for seven different 6 cm² supercapacitor cells, where each had a distinct electrode composition as described in Table 1. The capacitance was measured at RT at 0.1, 0.5 and 1 Amp constant currents (3 cycles in each current regime) for each supercapacitor. The DMC of all measured samples was 39%> (w/w) per electrodes for cell assembly. All samples were tested in symmetrical Carbon-Carbon cells. ESR was measured before and after charge/discharge cycle performed under constant current regime between 0.4- 1.2V and between 0.4- 1.4V.

Table 1 : Carbon-based electrode compositions

Results:

Results of the various samples' tests are presented in Figures 3 and 4 as compared to a sample without conductive additives.

According to Figure 3, all samples demonstrate similar capacitance to the capacitance measured for the sample comprising no conductive additives. Figure 3A demonstrates the relative normalized capacitance value per total weight of all paste components, including electrolyte and additives. Figure 3B demonstrates the relative normalized capacitance value per weight of the active components of the paste which contribute to the electrochemical activity of the electrode, not including electrolyte or additives. The active components as referred to in the normalization done for this example are activated carbon and/or transition metal oxide (i.e. Mn0₂), and the additives can be conductive or non-conductive additives. According to Figure 4, samples 3, 4 and 7 exhibit reduced ESR values compared to the other measured samples and to the additive-free sample.

It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and sub-combinations of various features described hereinabove as well as variations and modifications. Therefore, the invention is not to be constructed as restricted to the particularly described embodiments, and the scope and concept of the invention will be more readily understood by references to the claims, which follow.

Claims

1. A method for preparing a supercapacitor electrode, comprising the steps of:

(a) providing a substantially flat substrate;

(b) providing a flowable electrode composition comprising an aqueous electrolyte and a dry matter, wherein the dry matter content (DMC) of the flowable electrode composition ranges from about 25% to about 65% (w/w);

(c) placing a thin screen or a stencil having at least one opening over a top surface of the flat substrate;

(d) contacting a top surface of the screen or stencil with the flowable composition of step (b) so that a portion of the composition extrudes through the opening being applied to the top surface of the substrate in a substantially homogeneous manner;

(f) blotting the substrate and the flowable electrode composition applied thereon under pressure of from about 5 to about 150 bar;

thereby obtaining a printed electrode having a DMC of between about 30% (w/w) to about 75% (w/w).

2. The method according to claim 1, wherein the substrate is heat-sensitive

3. The method according to any one of claims 1 and 2, wherein the substrate is selected from a separator and a current collector.

4. The method according to claim 3, wherein the substrate is a separator made of a material selected from the group consisting of polyvinyl alcohol (PVA), polypropylene, polyethylene coated with a hydrophilic material selected from the group consisting of PVA, ethyl vinyl alcohol (EVA), and cellulose-based materials.

5. The method according to claim 3, wherein the substrate is a current collector made of a material selected from the group consisting of polyvinyl chloride (PVC), polyethylene and polyaniline.

6. The method according to claim 5, wherein the current collector further comprises carbon particles embedded therein.

7. The method according to any one of claims 1 to 6, wherein the stencil of step (c) has a thickness ranging from about 0.01 to about 5 millimeters

8. The method according to claim 7, wherein said stencil is a stainless-steel stencil.

9. The method according to any one of claims 1 to 8, wherein the contacting of step (d) comprises applying the flowable electrode composition of step (b) onto the surface of the screen or stencil utilizing a blade or a squeegee.

10. The method according to claim 9, wherein the contacting of step (d) comprises applying the flowable electrode composition of step (b) onto the surface utilizing a squeegee having a blade, wherein said blade has a round shape or a triangular shape.

11. The method according to claim 10, wherein the triangular shape is selected from an isosceles triangle and a right-angled triangle.

12. The method according to any one of claims 10 and 11, wherein at least a portion of the blade or a surface of the blade contacting the top surface of the substrate is made of a metal- based material.

13. The method according to claim 12, wherein the metal -based material is stainless-steel.

14. The method according to claim 13, wherein the stainless-steel surface of the blade is coated with Teflon.

15. The method according to any one of claims 1 to 14, wherein the blotting is performed under the pressure of from about 5 to about 100 bar.

16. The method according to any one of claims 1 to 15, wherein said method is carried out without drying the printed substrate, wherein said drying utilizes heat.

17. The method according to any one of claims 1 to 16, wherein the blotting of the substantially flat substrate and the flowable electrode composition is performed in a single step.

18. The method according to any one of claims 1 to 16, wherein the blotting of the substantially flat substrate and the flowable electrode composition is performed in multiple steps utilizing different pressure conditions.

19. The method according to any one of claims 1 to 18, wherein the flowable electrode composition is characterized by having a viscosity of between about 10,000 to about 10,000,000 cP, wherein the viscosity is measured by Brookfield DV-E viscometer at shear rates of 0.5-10 (1/sec) and temperature of 25°C.

20. The method according to claim 19, wherein the flowable electrode composition is characterized by having a viscosity of from about 100,000 to about 2,000,000 cP.

21. The method according to any one of claims 1 to 20, wherein the aqueous electrolyte is an alkaline electrolyte.

22. The method according to claim 21, wherein the alkaline electrolyte comprises a dissolved salt selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH), and combinations thereof.

23. The method according to claim 22, wherein the dissolved salt is potassium hydroxide (KOH).

24. The method according to any one of claims 1 to 23, wherein the dry matter of the flowable electrode composition comprises activated carbon.

25. The method according to any one of claims 1 to 24, wherein the dry matter of the flowable electrode composition comprises a conductive agent selected from the group consisting of carbon nanotubes (CNTs), graphite, carbon black and combinations thereof.

26. The method according to any one of claims 1 to 25, wherein the dry matter of the flowable electrode composition comprises a transition metal oxide or sulfide.

27. The method according to claim 26, wherein the transition metal oxide or sulfide is selected from the group consisting of Mn_nO_x, TiO_x, NiO_x, CoO_x, SnO_x, FeS_y, MoS_y, NiS_y, CoS_y, MnS_y, TiS_y, SnS_y and combinations thereof, wherein x ranges from 1.5 to 3, y ranges from 1.8 to 2.2 and n ranges from 1 to 2.

28. The method according to claim 24, wherein the flowable electrode composition is characterized by having a DMC of between about 25 to about 50% (w/w).

29. The method according to any one of claims 25 to 27, wherein the flowable electrode composition is characterized by having a DMC of between about 40 to about 65% (w/w).

30. The method according to any one of claims 1 to 27, wherein the flowable electrode composition comprises the aqueous alkaline electrolyte, activated carbon, transition metal oxide or sulfide, carbon nanotubes (CNTs) and graphite, and is characterized by having a DMC of between about 40 to about 65% (w/w).

31. The method according to any one of claims 1 to 27, wherein the flowable electrode composition comprises the aqueous alkaline electrolyte, at least two transition metal oxides or sulfides, carbon nanotubes (CNTs) and graphite, and is characterized by having a DMC of between about 40 to about 65% (w/w).

32. The method according to any one of claims 30 and 31, wherein the transition metal oxide comprises Mn0₂.

33. The method according to any one of claims 31 and 32, wherein the transition metal oxide further comprises Ti0₂.

34. The method according to any one of claims 30 to 33, wherein the flowable electrode composition further comprises carbon black.

35. The method according to any one of claims 1 to 34, wherein the flowable electrode composition comprises less than about 20% (w/w) of an additive selected from the group consisting of a thickening agent, a binder, an anti-foaming agent and combinations thereof.

36. The method according to claim 35, wherein the flowable electrode composition is essentially free of an additive selected from the group consisting of thickening agent, a binder, an anti-foaming agent and combinations thereof.

37. A supercapacitor printed electrode having a DMC of from about 30% (w/w) to about 75%) (w/w), wherein said electrode is prepared according to any one of claims 1 to 36.

38. The printed electrode of claim 37, wherein the dry matter of said electrode comprises: from about 50 to about 90 % (w/w) Mn0₂;

from about 0.1 to about 10 % (w/w) CNTs;

from about 0.5 to about 15 % (w/w) graphite; and

from about 0.5 to about 10 % (w/w) activated carbon.

39. The printed electrode of claim 38, wherein said electrode is characterized by having a DMC of from about 35 to about 65% (w/w).

40. The printed electrode of claim 37, wherein the dry matter of said electrode comprises: from about 60 to about 85 % (w/w) Mn0₂;

from about 0.5 to about 15 % (w/w) CNTs;

from about 1 to about 25 % (w/w) graphite; and

from about 0.5 to about 15 % (w/w) Ti0₂.

41. The printed electrode of claim 40, wherein said electrode is characterized by having a DMC of from about 50 to about 75% (w/w).

42. The printed electrode of claim 37, wherein said electrode comprises from about 30 to about 50 % (w/w) activated carbon and from about 50 to about 70 % (w/w) of the aqueous alkaline electrolyte.

43. The printed electrode of claim 37, wherein said electrode is characterized by having a DMC of from about 30 to about 50% (w/w).

44. The printed electrode according to any one of claims 37 to 43, wherein the dry matter of the electrode comprises less than about 20% (w/w) of an additive selected from the group consisting of thickening agent, a binder, an anti-foaming agent and combinations thereof.

45. The printed electrode according to claim 44, being essentially free of an additive selected from the group consisting of thickening agent, a binder, an anti-foaming agent and combinations thereof.

46. The printed electrode according to any one of claim 37 to 45, wherein said electrode has a thickness ranging from about 10 micron to about 5 millimeters.

47. The printed electrode according to claim 46, wherein said electrode has a thickness ranging from about 50 micron to about 2 millimeters.