HK1260389B - Multi-cell ultracapacitor - Google Patents

Description

Multi-cell supercapacitors

Related applications

This application claims priority to U.S. Provisional Application Serial No. 62/339,172, filed May 20, 2016, which is incorporated herein by reference in its entirety.

Background Art

Electric energy storage cells are widely used to provide power to electronic, electromechanical, electrochemical, and other available devices. For example, electric double-layer supercapacitors typically use a pair of polarizable electrodes comprising carbon particles (e.g., activated carbon) impregnated with a liquid electrolyte. Due to the effective surface area of the particles and the small spacing between the electrodes, large capacitance values can be achieved. Nevertheless, problems still exist. For example, many conventional supercapacitors are arranged in rigid metal containers. These containers are typically bulky and must use pre-made fixing points in the circuit or device, which makes it difficult to accommodate supercapacitors of different sizes. Although supercapacitors using flexible housings have also been developed, they tend to still be relatively bulky and have relatively low capacitance and high equivalent series resistance ("ESR"). Therefore, there is currently a need for improved supercapacitors.

Summary of the Invention

According to one embodiment of the present invention, a supercapacitor is disclosed, which includes a first electrochemical cell connected in parallel with a second electrochemical cell (unit cell). The first cell is defined by a first electrode comprising a current collector having opposite sides coated with a carbonaceous material, a second electrode comprising a current collector having opposite sides coated with a carbonaceous material, and a separator located between the first electrode and the second electrode. The second cell is defined by the second electrode, a third electrode comprising a current collector having opposite sides coated with a carbonaceous material, and a separator located between the second electrode and the third electrode. The supercapacitor also includes a non-aqueous electrolyte in ionic contact with the first electrode, the second electrode, and the third electrode, wherein the non-aqueous electrolyte includes a non-aqueous solvent and an ionic liquid. The package encapsulates the first cell, the second cell, and the non-aqueous electrolyte, wherein the package includes a substrate having a thickness of about 20 microns to about 1,000 microns.

Other features and aspects of the present invention are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The remainder of the specification more particularly describes the complete and enabling disclosure of the present invention (including the best mode thereof) for those skilled in the art with reference to the accompanying drawings, in which:

FIG1 is a schematic diagram of an embodiment of a current collector that can be used in a supercapacitor of the present invention;

FIG2 is a schematic diagram of one embodiment of a current collector/carbonaceous coating structure that can be used in a supercapacitor of the present invention; and

FIG3 is a schematic diagram of an embodiment of a supercapacitor according to the present invention.

Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.

DETAILED DESCRIPTION

Those skilled in the art will appreciate that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the invention, which are embodied in the exemplary construction.

In general, the present invention relates to a supercapacitor comprising a high degree of volumetric efficiency (because it is relatively thin in nature) yet still capable of providing a high degree of capacitance. The supercapacitor comprises at least two electrochemical cells, such as a first cell and a second cell. The first cell is defined by a first electrode comprising a current collector having opposite sides coated with a carbonaceous material (e.g., activated carbon particles), a second electrode comprising a current collector having opposite sides coated with a carbonaceous material (e.g., activated carbon particles), and a separator positioned between the first and second electrodes. The second cell is similarly defined by the second electrode, a third electrode comprising a current collector having opposite sides coated with a carbonaceous material (e.g., activated carbon particles), and a separator positioned between the second and third electrodes. To help achieve the desired properties, the first and second cells are connected in parallel. For example, a first terminal (connector) is electrically connected to the first and third electrodes and a second terminal is electrically connected to the second electrode. An electrolyte is also in ionic contact with the first, second, and third electrodes.

The present inventors have discovered that by selectively controlling the properties of the materials used to form the supercapacitor and the manner in which the materials are formed, a variety of beneficial properties can be achieved. For example, the electrolyte is typically non-aqueous in nature and therefore comprises at least one non-aqueous solvent. The electrolyte also comprises at least one ionic liquid that is soluble in the non-aqueous solvent. The electrochemical cell (e.g., electrodes, separator, and electrolyte) is also held in a relatively thin flexible package that encapsulates and seals the components of the supercapacitor. In order to help achieve the desired thickness and volume efficiency, the package is typically formed of a substrate that is relatively thin in nature, for example, having a thickness of about 20 microns to about 1,000 microns, in some embodiments about 50 microns to about 800 microns, and in some embodiments about 100 microns to about 600 microns. The resulting supercapacitor, despite its thin nature, can still exhibit excellent electrical properties, even when exposed to high temperatures. For example, the ultracapacitors may exhibit a capacitance of about 6 farads per cubic centimeter ("F/cm ³ ") or greater, in some embodiments, about 8 F/cm ³ or greater, in some embodiments, about 9 to about 100 F/cm ³ , and in some embodiments, about 10 to about 80 F/cm ³ , measured at a temperature of 23° C., a frequency of 120 Hz, and without an applied voltage. The ultracapacitors may also have a low equivalent series resistance ("ESR"), for example, about 150 milliohms or less, in some embodiments, less than about 125 milliohms, in some embodiments, about 0.01 to about 100 milliohms, and in some embodiments, about 0.05 to about 70 milliohms, measured at a temperature of 23° C., a frequency of 1 kHz, and without an applied voltage.

Various embodiments of the present invention will now be described in greater detail.

I. Electrodes

As noted above, the electrodes used in electrochemical cells typically include current collectors. The current collectors of one or more batteries can be formed from the same or different materials. In any case, each current collector is typically formed from a substrate containing a conductive metal (e.g., aluminum, stainless steel, nickel, silver, palladium, etc. and their alloys). Aluminum and aluminum alloys are particularly suitable for use in the present invention. The substrate can be in the form of a foil, sheet, plate, mesh, etc. The substrate can also have a relatively small thickness, such as about 200 microns or less, in some embodiments about 1 to about 100 microns, in some embodiments about 5 to about 80 microns, and in some embodiments about 10 to about 50 microns. Although not mandatory, the surface of the substrate can optionally be roughened, for example, by washing, etching, sandblasting, etc.

In certain embodiments, the current collector may include a plurality of fibrous tentacles extending outwardly from the substrate. Although not wishing to be bound by theory, it is believed that these tentacles can effectively increase the surface area of the current collector and also improve the adhesion of the current collector to the corresponding electrode. This can allow the use of a relatively low binder content in the first electrode and/or the second electrode, which can improve charge transfer and reduce interfacial resistance, and as a result, lead to very low ESR values. The tentacles are typically formed of a material that includes carbon and/or a reaction product of carbon with the conductive metal. For example, in one embodiment, the material includes a carbide of the conductive metal, such as aluminum carbide (Al ₄ C ₃ ). For example, referring to Figure 1 , an embodiment of a current collector is shown, which includes a plurality of tentacles 21 extending outwardly from a substrate 1. If desired, the tentacles 21 can optionally extend from a seed portion 3 embedded in the substrate 1. Similar to the whiskers 21 , the seed portion 3 may also be formed of a material including carbon and/or a reaction product of carbon and the conductive metal, such as a carbide of the conductive metal (eg, aluminum carbide).

The manner in which the tentacles are formed on the substrate may be varied as desired. For example, in one embodiment, the conductive metal of the substrate is reacted with a hydrocarbon compound. Examples of such hydrocarbon compounds may include, for example, alkane compounds such as methane, ethane, propane, n-butane, isobutane, pentane, etc.; olefin compounds such as ethylene, propylene, butene, butadiene, etc.; alkyne compounds such as acetylene; and derivatives or any combination thereof. It is generally desirable that the hydrocarbon compound is in gaseous form during the reaction. Therefore, it may be desirable to use hydrocarbon compounds such as methane, ethane, and propane that are in gaseous form when heated. Although not required, the hydrocarbon compound is typically used in the range of about 0.1 parts to about 50 parts by weight, and in some embodiments, about 0.5 parts by weight to about 30 parts by weight, based on 100 parts by weight of the substrate. To initiate the reaction by the hydrocarbon and the conductive metal, the substrate is typically heated in an atmosphere at a temperature of about 300° C. or higher, in some embodiments about 400° C. or higher, and in some embodiments, from about 500° C. to about 650° C. The heating time depends on the exact temperature selected, but is typically in the range of about 1 hour to about 100 hours. The atmosphere typically contains a relatively low amount of oxygen to minimize the formation of a dielectric film on the substrate surface. For example, the oxygen content of the atmosphere may be about 1% by volume or less.

The electrodes used in the supercapacitor also include a carbonaceous material coated on the opposite side of the current collector. Although they can be formed of the same or different types of materials and can include one or more layers, the carbonaceous coatings each typically include at least one layer including activated particles. For example, in certain embodiments, the activated carbon layer can be directly located above the current collector and can optionally be the only layer of the carbonaceous coating. Examples of suitable activated carbon particles may include, for example, coconut shell-based activated carbon, petroleum coke-based activated carbon, asphalt-based activated carbon, polyvinylidene chloride-based activated carbon, phenolic resin-based activated carbon, polyacrylonitrile-based activated carbon, and activated carbon from natural sources such as coal, charcoal (charcoal) or other natural organic sources.

In certain embodiments, to help improve the ion mobility of certain types of electrolytes after undergoing one or more charge-discharge cycles, it may be desirable to selectively control certain aspects of the activated carbon particles, such as their particle size distribution, surface area, and pore size distribution. For example, at least 50% by volume of the particles (D50 size) may have a size ranging from about 0.01 to about 30 microns, in some embodiments from about 0.1 to about 20 microns, and in some embodiments from about 0.5 to about 10 microns. At least 90% by volume of the particles (D90 size) may similarly have a size ranging from about 2 to about 40 microns, in some embodiments from about 5 to about 30 microns, and in some embodiments from about 6 to about 15 microns. The BET surface area may also be in the range of about 900 m ² /g to about 3,000 ^{m 2} /g, in some embodiments from about 1,000 m ² /g to about 2,500 ^{m 2} /g, and in some embodiments from about 1,100 m ² /g to about 1,800 ^{m 2} /g.

Activated carbon particles can also include holes with certain size distribution except having certain size and surface area.For example, the amount of the hole (i.e. " micropore ") of size less than about 2 nanometers can provide about 50 volume % of total pore volume or less, about 30 volume % or less and 0.1 volume %-15 volume % in some embodiments.Similarly, the amount of the hole (i.e. " mesopore ") of size between about 2 nanometers and about 50 nanometers can be about 20 volume % to about 80 volume %, about 25 volume % to about 75 volume % and about 35 volume % to about 65 volume % in some embodiments.Finally, the amount of the hole (i.e. " macropore ") of size greater than about 50 nanometers can be about 1 volume % to about 50 volume %, about 5 volume % to about 40 volume % and about 10 volume % to about 35 volume % in some embodiments. The carbon particles may have a total pore volume in the range of about 0.2 cm ³ /g to about 1.5 cm ³ /g, and in some embodiments, about 0.4 cm ³ /g to about 1.0 cm ³ /g, and a median pore width of about 8 nanometers or less, in some embodiments, from about 1 to about 5 nanometers, and in some embodiments, from about 2 to about 4 nanometers. The pore size and total pore volume may be measured using nitrogen adsorption and analyzed by the Barrett-Joyner-Halenda ("BJH") technique, as is known in the art.

A unique aspect of the present invention is that the electrode does not need to be included in a large amount of adhesives conventionally used in the electrodes of supercapacitors. That is, the adhesive can be present in the first and/or second carbonaceous coating in an amount of about 60 parts or less, in some embodiments 40 parts or less, and in some embodiments about 1-about 25 parts per 100 parts of carbon. The adhesive can, for example, constitute about 15 weight % or less of the total weight of the carbonaceous coating, in some embodiments about 10 weight % or less, and in some embodiments about 0.5 weight % to about 5 weight %. Nevertheless, when used, any of a variety of suitable adhesives can be used in the electrode. For example, in certain embodiments, a water-insoluble organic adhesive can be used, such as styrene-butadiene copolymer, polyvinyl acetate homopolymer, vinyl acetate ethylene copolymer, vinyl acetate acrylic copolymer, ethylene-vinyl chloride copolymer, ethylene-vinyl chloride-vinyl acetate terpolymer, acrylic polyvinyl chloride polymer, acrylic polymer, nitrile polymer, fluoropolymer such as polytetrafluoroethylene or polyvinylidene fluoride, polyolefin, and mixtures thereof. Water-soluble organic adhesives can also be used, such as polysaccharides and derivatives thereof. In a specific embodiment, the polysaccharide can be a nonionic cellulose ether, such as alkyl cellulose ethers (such as methyl cellulose and ethyl cellulose); hydroxyalkyl cellulose ethers (such as hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl hydroxybutyl cellulose, hydroxyethyl hydroxypropyl cellulose, hydroxyethyl hydroxybutyl cellulose, hydroxyethyl hydroxypropyl hydroxybutyl cellulose, etc.); alkyl hydroxyalkyl cellulose ethers (such as methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, ethyl hydroxypropyl cellulose, methyl ethyl hydroxyethyl cellulose and methyl ethyl hydroxypropyl cellulose); carboxyalkyl cellulose ethers (such as carboxymethyl cellulose); etc., as well as protonated salts of any of the foregoing substances, such as sodium carboxymethyl cellulose.

If desired, other materials may also be used within the activated carbon layer of the carbonaceous material. For example, in certain embodiments, a conductivity enhancer may be used to further increase electrical conductivity. Exemplary conductivity enhancers may include, for example, carbon black, graphite (natural or artificial), graphite, carbon nanotubes, nanowires or nanotubes, metal fibers, graphene, and the like, and mixtures thereof. Carbon black is particularly suitable. The conductivity enhancer, when used, typically constitutes about 60 parts or less, in some embodiments 40 parts or less, and in some embodiments about 1 to about 25 parts per 100 parts of activated carbon particles in the carbonaceous coating. The conductivity enhancer may, for example, constitute about 15 weight % or less, in some embodiments about 10 weight % or less, and in some embodiments about 0.5 weight % to about 5 weight % of the total weight of the carbonaceous coating. Similarly, activated carbon particles typically constitute 85 weight % or more, in some embodiments about 90 weight % or more, and in some embodiments about 95 weight % to about 99.5 weight % of the carbonaceous coating.

As known to those skilled in the art, the specific manner in which the carbonaceous material is applied to the face of the current collector may be different, such as printing (e.g., gravure printing), spraying, slot-die coating, drip coating, dip coating, etc. Regardless of the manner in which it is applied, in order to remove moisture from the coating, the resulting electrode is typically dried at a temperature of, for example, about 100° C. or higher, in some embodiments about 200° C. or higher, and in some embodiments about 300° C. to about 500° C. The electrode can also be pressed (e.g., calendered) to optimize the volumetric efficiency of the supercapacitor. After any optional pressing, the thickness of each carbonaceous coating can generally vary based on the desired electrical properties and operating range of the supercapacitor. However, typically, the thickness of the coating is about 20-about 200 microns, 30-about 150 microns, and in some embodiments about 40-about 100 microns. The coating may be present on one or both sides of the current collector. Regardless, the thickness of the entire electrode (including the current collector and carbonaceous coating after optional pressing) typically ranges from about 20 to about 350 microns, in some embodiments, from about 30 to about 300 microns, and in some embodiments, from about 50 to about 250 microns.

II. Non-aqueous electrolytes

As noted above, the electrolyte used in supercapacitors is typically non-aqueous in nature and therefore comprises at least one non-aqueous solvent. In order to help widen the operating temperature range of supercapacitors, it is typically desirable as follows: the non-aqueous solvent has a relatively high boiling temperature, for example, about 150°C or greater, about 200°C or greater in some embodiments, and about 220°C to about 300°C in some embodiments. Particularly suitable high boiling point solvents may include, for example, cyclic carbonate solvents, such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc. Propylene carbonate is particularly suitable due to its high electrical conductivity and decomposition voltage and its ability to be used under a wide temperature range. Of course, other non-aqueous solvents may also be used individually or in combination with cyclic carbonate solvents. Examples of such solvents may include, for example, open-chain carbonates (e.g., dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, etc.), aliphatic monocarboxylic acid esters (e.g., methyl acetate, methyl propionate, etc.), lactone solvents (e.g., butyrolactone, valerolactone, etc.), nitriles (e.g., acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, etc.), amides (e.g., N,N-dimethylformamide, N,N-diethylacetamide, N-methylpyrrolidone), alkanes (e.g., nitromethane, nitroethane, etc.), sulfur compounds (e.g., sulfolane, dimethyl sulfoxide, etc.); and the like.

The electrolyte further comprises at least one ionic liquid that is soluble in the non-aqueous solvent. Although the concentration of the ionic liquid can vary, it is generally desirable that the ionic liquid be present in a relatively high concentration. For example, the ionic liquid may be present in an amount of about 0.8 moles (M) or greater, in some embodiments about 1.0 M or greater, in some embodiments about 1.2 M or greater, and in some embodiments about 1.3 to about 1.8 M per liter of electrolyte.

The ionic liquid is typically a salt having a relatively low melting temperature, for example, about 400°C or less, in some embodiments about 350°C or less, in some embodiments about 1°C to about 100°C, and in some embodiments about 5°C to about 50°C. The salt comprises a cationic species and a counterion. Cationic species include compounds having at least one heteroatom (e.g., nitrogen or phosphorus) as a "cationic center." Examples of such heteroatom compounds include, for example, unsubstituted or substituted organic quaternary ammonium compounds such as ammonium (e.g., trimethylammonium, tetraethylammonium, etc.), pyridine pyridazine pyrimidine (pyramidinium), pyrazine imidazole pyrazolazole triazole thiazole quinoline piperidine pyrrolidine, quaternary ammonium spirocyclic compounds in which two or more rings are connected together by spiro atoms (e.g., carbon, heteroatoms, etc.), quaternary ammonium fused ring structures (e.g., quinoline isoquinoline, etc.), etc. For example, in a specific embodiment, the cationic species may be an N-spiro bicyclic compound, such as a symmetrical or asymmetrical N-spiro bicyclic compound having a cyclic ring. An example of such a compound has the following structure:

wherein m and n are independently a number from 3 to 7, and in some embodiments, from 4 to 5 (eg, pyrrolidine or piperidine).

Suitable counterions for cationic species may also include halides (e.g., chloride, bromide, iodide, etc.); sulfates or sulfonates (e.g., methylsulfate, ethylsulfate, butylsulfate, hexylsulfate, octylsulfate, hydrogensulfate, methanesulfonate, dodecylbenzenesulfonate, dodecylsulfate, trifluoromethanesulfonate, heptadecafluorooctanesulfonate, sodium dodecylethoxysulfate, etc.); sulfosuccinates; amides (e.g., dicyanamide); imides (e.g., bis(pentafluoroethylsulfonyl)imide, bis(trifluoromethylsulfonyl)imide, bis(trifluoromethylsulfonyl)imide, borate (e.g., tetrafluoroborate, tetracyanoborate, bis(oxalato)borate, bis(salicylate)borate, etc.); phosphate or phosphite (e.g., hexafluorophosphate, diethylphosphate, bis(pentafluoroethyl)phosphite, tris(pentafluoroethyl)-trifluorophosphate, tris(nonafluorobutyl)trifluorophosphate, etc.); antimonate (e.g., hexafluoroantimonate); aluminate (e.g., tetrachloroaluminate); fatty acid carboxylates (e.g., oleate, isostearate, pentafluorooctanoate, etc.); cyanate; acetate; etc., and any combination of the foregoing.

Several examples of suitable ionic liquids can include, for example, spiro-(1,1′)-bipyrrolidine tetrafluoroborate, triethylmethylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, spiro-(1,1′)-bipyrrolidine iodide, triethylmethylammonium iodide, tetraethylammonium iodide, methyltriethylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, and the like.

III. Partition

As noted above, the electrochemical cell of the present invention further comprises a separator located between the two electrodes. The separator can electrically insulate one electrode from the other electrode to help prevent electrical short circuits but still allow ions to be transported between the two electrodes. For example, in certain embodiments, a separator comprising a cellulose fiber material (e.g., air-laid paper webs, wet-laid paper webs, etc.), a non-woven fiber material (e.g., a polyolefin non-woven web), a textile fabric, a membrane (e.g., a polyolefin membrane), etc., can be used. For use in supercapacitors, cellulose fiber materials, such as those comprising natural fibers, synthetic fibers, etc., are particularly suitable. Specific examples of cellulose fibers suitable for use in the separator may include, for example, hardwood pulp fibers, softwood pulp fibers, rayon fibers, regenerated cellulose fibers, etc. Regardless of the specific material used, the separator typically has a thickness of about 5 to about 150 microns, in some embodiments about 10 to about 100 microns, and in some embodiments about 20 to about 80 microns.

IV. Housing

The supercapacitor of the present invention uses a housing that holds the electrodes, electrolyte, and separator of each electrochemical cell within it. The manner in which the components are inserted into the housing can vary, as is known in the art. For example, the electrodes and separator can first be folded, wound, or otherwise contacted together to form an electrode assembly. The electrolyte can optionally be impregnated into the electrodes of the assembly. In one embodiment, the electrodes, separator, and optional electrolyte can be wound into an electrode assembly having a "jelly-roll" configuration.

Regardless, the housing is typically in the form of a flexible package that encapsulates the components of the supercapacitor. The package comprises a substrate that may include any number of layers required to achieve the desired level of barrier properties, such as one or more layers, in some embodiments two or more layers, and in some embodiments two to four layers. Typically, the substrate includes a barrier layer that may comprise a metal such as aluminum, nickel, tantalum, titanium, stainless steel, or the like. Such a barrier layer is generally impermeable to the electrolyte, thereby inhibiting its leakage, and is also generally impermeable to water and other contaminants. If desired, the substrate may also include an outer layer that serves as a protective layer for the package. In this manner, the barrier layer faces the electrochemical cell and the outer layer faces the exterior of the package. The outer layer may be formed, for example, from a polymer film such as those formed from polyolefins (e.g., ethylene copolymers, propylene copolymers, propylene homopolymers, etc.), polyesters, or the like. Particularly suitable polyester films may include, for example, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, or the like.

If desired, the substrate may further include a sealing layer. The sealing layer may be continuous across the entire package so that it faces the electrochemical cell. Alternatively, a sealing layer may be used only at the edges of the capacitor to help seal the package at and around the terminals. In any case, the sealing layer may comprise a heat-sealable polymer. Suitable heat-sealable polymers may include, for example, vinyl chloride polymers, vinyl chloridine polymers, ionomers, and the like, and combinations thereof. Ionomers are particularly suitable. For example, in one embodiment, the ionomer may be a copolymer containing α-olefins and (meth) acrylic acid repeating units. Specific α-olefins may include ethylene, propylene, 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene having one or more methyl, ethyl or propyl substituents; 1-hexene having one or more methyl, ethyl or propyl substituents; 1-heptene having one or more methyl, ethyl or propyl substituents; 1-octene having one or more methyl, ethyl or propyl substituents; 1-nonene having one or more methyl, ethyl or propyl substituents; 1-decene substituted with ethyl, methyl or dimethyl; 1-dodecene; and styrene. Ethylene is particularly suitable. As noted, the copolymer may also contain (meth)acrylic acid repeating units. As used herein, the term "(meth)acrylic" includes monomers of acrylic and methacrylic acids, and their salts or esters, such as monomers of acrylates and methacrylates. Examples of such (meth)acrylic monomers may include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, isobornyl acrylate, n-hexyl acrylate, 2-ethylbutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-decyl acrylate, methylcyclohexyl acrylate, cyclopentyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, methacrylic acid, methyl methacrylate ... The ionomer may be 2-hydroxyethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, isopentyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, 2-ethylbutyl methacrylate, methylcyclohexyl methacrylate, cinnamyl methacrylate, crotyl methacrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, 2-ethoxyethyl methacrylate, isobornyl methacrylate, and the like, and combinations thereof. Typically, the α-olefin/(meth)acrylic acid copolymer is at least partially neutralized with a metal ion to form the ionomer. Suitable metal ions may include, for example, alkali metals (e.g., lithium, sodium, potassium, etc.), alkaline earth metals (e.g., calcium, magnesium, etc.), transition metals (e.g., manganese, zinc, etc.), and the like, and combinations thereof. The metal ions may be provided as ionic compounds such as metal formates, acetates, nitrates, carbonates, bicarbonates, oxides, hydroxides, alkoxides, and the like.

For example, referring to FIG3 , an embodiment of an ultracapacitor 101 is shown that includes a flexible package 103. In the embodiment shown, the package 103 encloses three electrochemical cells 104, 105, and 106, but it should be understood that any number of cells can be used in the present invention. The first cell 104 is defined by a first electrode 110, a second electrode 120, and a separator located between the electrodes 110 and 120. The second cell 105 is defined by a second electrode 120, a third electrode 130, and a separator 114 located between the electrodes 120 and 130. The third cell 106 is defined by a third electrode 130, a fourth electrode 140, and a separator 116 located between the electrodes 130 and 140. An electrolyte (not shown) is also located within the package 103. The electrochemical cells 104, 105, and 106 are connected in parallel via a first terminal 162 and a second terminal 164. For example, the first terminal 162 is electrically connected to the lead line 163 connected to the first electrode 110 and the lead line 165 connected to the third electrode 130. Similarly, the second terminal 164 is electrically connected to the lead line 167 connected to the second electrode 120 and the lead line 169 connected to the fourth electrode 140.

The package 103 generally includes a substrate extending between the two ends and having an edge around the terminals 162 and 164. As noted herein, the substrate may include multiple layers to provide desired sealing. The layers may be continuous or discontinuous over the entire package. For example, in the embodiment shown, the substrate includes a discontinuous sealing layer 150 that is only located at the edge of the package 103. However, the remainder of the substrate is continuous over the entire package.

As noted above, the resulting supercapacitors can exhibit a wide variety of beneficial electrical properties such as improved capacitance and ESR values. Notably, the supercapacitors can exhibit excellent electrical properties even when exposed to high temperatures. For example, the supercapacitors can be placed in contact with an atmosphere having a temperature of about 80° C. or higher, in some embodiments about 100° C. to about 150° C., and in some embodiments about 105° C. to about 130° C. (e.g., 85° C. or 105° C.). The capacitance and ESR values can be stably maintained at such temperatures for a considerable period of time, such as about 100 hours or longer, in some embodiments about 300 hours to about 5000 hours, and in some embodiments about 600 hours to about 4500 hours (e.g., 168, 336, 504, 672, 840, 1008, 1512, 2040, 3024, or 4032 hours).

For example, in one embodiment, the ratio of the capacitance value of the supercapacitor after being exposed to a hot atmosphere (e.g., 85°C or 105°C) for 1008 hours to the capacitance value of the supercapacitor when initially exposed to the hot atmosphere is about 0.75 or greater, in some embodiments, about 0.8-1.0, and in some embodiments, about 0.85-1.0. Such high capacitance values can also be maintained under various extreme conditions (e.g., when a voltage is applied and/or in a humid atmosphere). For example, the ratio of the capacitance value of the supercapacitor after being exposed to a hot atmosphere (e.g., 85°C or 105°C) and an applied voltage to the initial capacitance value of the supercapacitor when exposed to the hot atmosphere but before the voltage is applied may be about 0.60 or greater, in some embodiments, about 0.65-1.0, and in some embodiments, about 0.7-1.0. The voltage may be, for example, about 1 volt or greater, in some embodiments, about 1.5 volts or greater, and in some embodiments, about 2 to about 10 volts (e.g., 2.1 volts). For example, in one embodiment, the above-mentioned ratio can be maintained for 1008 hours or longer. The supercapacitor can also maintain the above-mentioned capacitance value when exposed to high humidity levels, for example, when placed in contact with an atmosphere having a relative humidity of about 40% or greater, in some embodiments about 45% or greater, in some embodiments about 50% or greater, and in some embodiments about 70% or greater (e.g., about 85%-100%). The relative humidity can be determined, for example, according to Method A (2007) of ASTM E337-02. For example, the ratio of the capacitance value of the supercapacitor after exposure to a hot atmosphere (e.g., 85°C or 105°C) and high humidity (e.g., 85%) to the initial capacitance value of the supercapacitor when exposed to the hot atmosphere but before exposure to high humidity can be about 0.7 or greater, in some embodiments about 0.75-1.0, and in some embodiments about 0.80-1.0. For example, in one embodiment, the ratio can be maintained for 1008 hours or longer.

The ESR can also be maintained stably at such temperatures for a considerable period of time, such as described above. For example, in one embodiment, the ratio of the ESR of the supercapacitor after exposure to a hot atmosphere (e.g., 85°C or 105°C) for 1008 hours to the ESR of the supercapacitor when initially exposed to the hot atmosphere is about 1.5 or less, in some embodiments about 1.2 or less, and in some embodiments about 0.2 to about 1. It is worth noting that such low ESR values can also be maintained under various extreme conditions (e.g., when a high voltage is applied and/or in a humid atmosphere, as described above). For example, the ratio of the ESR of the supercapacitor after exposure to a hot atmosphere (e.g., 85°C or 105°C) and an applied voltage to the initial ESR of the supercapacitor when exposed to the hot atmosphere but before the voltage is applied can be about 1.8 or less, in some embodiments about 1.7 or less, and in some embodiments about 0.2 to about 1.6. For example, in one embodiment, the ratios described above can be maintained for 1008 hours or longer. The supercapacitor can also maintain the ESR values described above when exposed to high humidity levels. For example, the ratio of the ESR of the ultracapacitor after exposure to a hot atmosphere (e.g., 85° C. or 105° C.) and high humidity (e.g., 85%) to the initial capacitance of the ultracapacitor when exposed to the hot atmosphere but before exposure to high humidity may be about 1.5 or less, in some embodiments about 1.4 or less, and in some embodiments, from about 0.2 to about 1.2. For example, in one embodiment, this ratio may be maintained for 1008 hours or longer.

The present invention may be better understood with reference to the following examples.

Test Method

Equivalent series resistance (ESR)

The equivalent series resistance can be measured using a Keithley 3330 Precision LCZ meter with a DC bias of 0.0 volts, 1.1 volts, or 2.1 volts (a 0.5 volt peak-to-peak sinusoidal signal). The operating frequency is 1 kHz. Multiple temperatures and relative humidity levels can be tested. For example, the temperature can be 23°C, 85°C, or 105°C, and the relative humidity can be 25% or 85%.

capacitance

Capacitance can be measured using a Keithley 3330 Precision LCZ meter with a DC bias of 0.0 volts, 1.1 volts, or 2.1 volts (a 0.5 volt peak-to-peak sinusoidal signal). The operating frequency is 120 Hz. Various temperatures and relative humidity levels can be tested. For example, the temperature can be 23°C, 85°C, or 105°C, and the relative humidity can be 25% or 85%.

Example

The ability to form an electrochemical cell according to the present invention was demonstrated. Initially, each face of two aluminum current collectors (12-50 μm thick) containing aluminum carbide whiskers was coated with a mixture of 10-40 wt% activated carbon particles, 2-10 wt% styrene-butadiene copolymer, and 5-40 wt% sodium carboxymethylcellulose. The activated carbon particles had a D50 size of about 5-20 μm and a BET surface area of about 1300-2200 ^{m 2} /g. The activated carbon particles contained pores less than 2 nanometers in an amount less than 10% by volume, pores 2-50 nanometers in an amount of about 40-70% by volume, and pores greater than 50 nm in an amount of about 20-50% by volume. The resulting coatings were each about 12-200 μm thick. The electrodes were then rolled and dried under vacuum at a temperature of 70°C-150°C. Once formed, the two electrodes were assembled with an electrolyte and a separator (cellulose material having a thickness of 25 μm). The electrolyte contains 5-azaspiro[4,4]-nonane tetrafluoroborate in propylene carbonate at a concentration of 1.05-2.5M. The resulting strips are cut into individual electrodes and assembled by stacking the electrodes alternately with a separator in between. Once the electrode stack is complete, all electrode terminals are welded to a single aluminum terminal. The assembly is then placed in a plastic/aluminum/plastic laminate packaging material and all edges except one are heat-sealed together. Next, the electrolyte is injected into the package through the open edge. The electrolyte-filled package is then placed under vacuum and the last edge is heat-sealed to complete the final package. The resulting battery is formed and tested for capacitance and ESR. The results are listed in Tables 1-6 below:

Table 1: Average ESR (milliohms) of 24 samples at 0.0 volt bias

Time (hours) 0 168 336 504 672 840 1008 1512 2040 3024 4032 85℃ 65 61 59 62 64 63 64 64 62 62 64 105℃ 62 54 52 57 60 60 60 58 58 57 58

Table 2: Average capacitance of 24 samples at 0.0 volt bias

Table 3: Average ESR (milliohms) of 16 samples at 0.0 volt bias

Time (hours) 0 168 336 504 672 840 1008 85°C, 85% relative humidity 121 133 144 152 166 177 187

Table 4: Average capacitance of 16 samples at 0.0 volt bias

Table 5: Average ESR (milliohms) of 10 samples at 2.1V bias

Time (hours) 0 168 336 504 672 840 1008 85℃ 146 163 167 169 171 173 175

Table 6: Average capacitance of 16 samples at 2.1V bias

These and other variations and modifications of the present invention may be practiced by those of ordinary skill in the art without departing from the spirit and scope of the present invention. Additionally, it should be understood that various aspects of the various embodiments may be interchangeable in whole or in part. Furthermore, those of ordinary skill in the art will recognize that the foregoing description is by way of example only and is not intended to constitute a further limitation of the invention described in the appended claims.

Claims (23)

1. Supercapacitors, including: A first electrochemical cell is defined by a first electrode comprising a current collector having an opposite side coated with a carbonaceous material, a second electrode comprising a current collector having an opposite side coated with a carbonaceous material, and a separator located between the first electrode and the second electrode. A second electrochemical cell connected in parallel with the first cell, wherein the second cell is defined by the second electrode, a third electrode comprising a current collector having an opposite side coated with a carbonaceous material, and a separator located between the second electrode and the third electrode; The carbonaceous material comprising the first electrode, the second electrode, the third electrode, or combinations thereof includes activated carbon particles; the activated carbon particles comprise a plurality of pores, wherein the amount of pores having a size of 2 nanometers or smaller is 50 vol% or less of the total pore volume, the amount of pores having a size of 2 nanometers to 50 nanometers is 20 vol% to 80 vol% of the total pore volume, and the amount of pores having a size of 50 nanometers or larger is 1 vol% to 50 vol% of the total pore volume; A non-aqueous electrolyte in ionic contact with the first, second, and third electrodes, wherein the non-aqueous electrolyte comprises a non-aqueous solvent and an ionic liquid, the ionic liquid comprising cationic species including organic quaternary ammonium compounds; and A package encapsulating a first electrochemical cell, a second electrochemical cell, and a non-aqueous electrolyte, wherein the package includes a substrate having a thickness of 20 micrometers to 1,000 micrometers; wherein the capacitor exhibits a capacitance of 6 farads/cm³ or greater at 23°C, 120 Hz, and without applied voltage. 2. The supercapacitor of claim 1, wherein the capacitor exhibits a capacitance of 9-100 farads/cm³ at 23°C and 120Hz without applied voltage. 3. The supercapacitor of claim 1, wherein the supercapacitor exhibits an ESR of 150 milliohms or less at a temperature of 23°C, a frequency of 1 kHz, and without applied voltage. 4. The supercapacitor of claim 1, wherein the current collector of the first electrode, the second electrode, the third electrode, or a combination thereof comprises a conductive metal. 5. The supercapacitor of claim 4, wherein the conductive metal is aluminum or an alloy thereof. 6. The supercapacitor of claim 4, wherein a plurality of fibrous tendrils extend outward from the conductive metal. 7. The supercapacitor of claim 6, wherein the tendrils comprise a carbide of the conductive metal. 8. The supercapacitor of claim 1, wherein at least 50% by volume of the active carbon particles have a size of 0.01-30 micrometers. 9. The supercapacitor of claim 1, wherein the non-aqueous solvent comprises propylene carbonate. 10. The supercapacitor of claim 1, wherein the ionic liquid comprises anti-charged ions. 11. The supercapacitor of claim 1, wherein the organic quaternary ammonium compound has the following structure: Where m and n are independent numbers from 3 to 7. 12. The supercapacitor of claim 1, wherein the ionic liquid is present at a concentration of 1.0 M or greater. 13. The supercapacitor of claim 1, wherein the separator of the first electrochemical cell, the second electrochemical cell, or both comprises cellulose fiber material. 14. The supercapacitor of claim 1, wherein the substrate of the package comprises a barrier layer. 15. The supercapacitor of claim 14, wherein the barrier layer comprises a metal. 16. The supercapacitor of claim 14, wherein the substrate further comprises an outer layer. 17. The supercapacitor of claim 16, wherein the outer layer comprises a film comprising polyolefin, polyester, or a combination thereof. 18. The supercapacitor of claim 14, wherein the substrate further comprises a sealing layer. 19. The supercapacitor of claim 18, wherein the sealing layer comprises an ionomer. 20. The supercapacitor of claim 1, wherein the first and second electrochemical cells are stacked together. 21. The supercapacitor of claim 1, further comprising a first terminal electrically connected to the first electrode and the third electrode, and a second terminal electrically connected to the second electrode. 22. The supercapacitor of claim 1, further comprising a third electrochemical cell defined by the third electrode, a fourth electrode comprising a current collector having opposite sides coated with a carbonaceous material, and a separator located between the third electrode and the fourth electrode. 23. The supercapacitor of claim 22, further comprising a first terminal electrically connected to the first electrode and the third electrode, and a second terminal electrically connected to the second electrode and the fourth electrode.