HK1254992A1 - Electrolyte for three-volt ultracapacitor - Google Patents

Description

Electrolyte for three-volt super capacitor

Description of the cases

The present application is a divisional application of an invention patent application having an application date of 2015, 4/8, a national application number of 201380052534.2 and an invention name of "electrolyte for three-volt supercapacitor".

Technical Field

The present invention relates generally to electrical energy storage devices, and more particularly to the design of electrolytes for electrical energy storage devices, such as double layer capacitors.

Background

Electrical energy storage batteries are widely used to provide electrical power to electronic, electromechanical, electrochemical, and other useful devices. Such batteries include primary chemical batteries, secondary (rechargeable) batteries, fuel cells, and various types of capacitors, including supercapacitors. Some characteristics of an electrical energy storage cell include energy density, power density, charging rate, internal leakage current, Equivalent Series Resistance (ESR), and the ability to withstand multiple charge-discharge cycles. Capacitors that can store a relatively large amount of charge are known as ultracapacitors (supercapacitors) for a number of reasons, which have been disbursed in various electrical energy storage cells.

An increase in the operating voltage of the supercapacitor can provide improved energy storage and power capacity. However, various components of the capacitor may exhibit instability when subjected to elevated voltage operating conditions. For example, instabilities in one or more components of the capacitor may contribute to degradation of capacitor performance, including, but not limited to, excessive capacitance decay and Equivalent Series Resistance (ESR) increase over cyclic operation or DC lifetime (also referred to as calendar life), self-discharge, pseudocapacitance, and/or gas formation.

Disclosure of Invention

In some embodiments, the housing component comprises an inner surface exposed to the electrolyte and an outer surface, and wherein the protective coating is applied along at least a portion of the inner surface. The protective coating may comprise a polymeric material or a conductive material. The polymeric material may include at least one of: polyepoxides, polyolefins, polyethylenes, polyimides, polyetheretherketones, polyurethanes, ethylene-propylene rubbers, poly (p-xylylene), Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene (ETFE), fluorinated ethylene-propylene, and/or copolymers thereof. The conductive material may comprise conductive carbon, including graphite.

In some embodiments, the electrolyte comprises a quaternary ammonium salt. The salt may comprise a cation selected from the group consisting of: triethylmethylammonium, spiro- (1,1') -bispyrrolidinium salts and tetraethylammonium. The quaternary ammonium salt may include an anion selected from the group consisting of: tetrafluoroborate and iodide. The electrolyte may include acetonitrile. In some embodiments, the salt concentration of the electrolyte may be between about 0.7 moles/l (M) and about 1.0M. In some embodiments, the salt concentration of the electrolyte may be about 0.8M.

The cation of the electrolyte salt can include a symmetrical cation including, for example, triethylmethylammonium. In some embodiments, the cation of the electrolyte salt can include an asymmetric cation, including, for example, triethylmethylammonium. In some embodiments, the electrolyte salt can include spiro compounds, including symmetric and asymmetric spiro compounds. For example, the electrolyte may include an N-spirobicyclic compound, including a symmetric N-spirobicyclic compound having a 5-membered cyclic ring. In some embodiments, the electrolyte may include an asymmetric spiro compound, including asymmetric spiro compounds having ring structures of unequal sizes. Symmetric spiro compounds may include spiro- (1,1') -dipyrrolidinium tetrafluoroborate (spiro- (1,1') -dipyrrolidinium tetrafluoroborate).

In some embodiments, the separator comprises a film comprising paper. In some embodiments, the separator comprises a membrane comprising cellulose. In some embodiments, the separator comprises a membrane comprising cellulose fibers.

In some embodiments, the positive or negative electrode includes at least one of a current collector and a carbon-based material. The carbon-based material may include at least one of activated carbon, carbon black, and a binder resin.

In some embodiments, the positive or negative electrode includes macroporosity, mesoporosity, and microporosity optimized for ion mobility therein.

In some embodiments, the positive electrode includes a first thickness that is greater than a second thickness of the negative electrode. The first thickness may be greater than the second thickness by about 10%. The first thickness may be greater than the second thickness by about 20%.

In some embodiments, the capacitor includes a first sub-capacitor formed at an interface between the positive electrode and the electrolyte; a second sub-capacitor formed at an interface between the negative electrode and the electrolyte; and a first and second thickness selected by: determining a positive voltage limit of the first sub-capacitor and a negative voltage limit of the second sub-capacitor; dividing the positive voltage limit by the negative voltage limit to obtain a first ratio of the second sub-capacitor to the first sub-capacitor; and setting the relative thicknesses of the positive electrode layer and the negative electrode layer such that the capacitance of the second sub-capacitor is substantially equal to the product of the first ratio and the capacitance of the first sub-capacitor.

In some embodiments, the carbon-based material comprises a treated carbon material having a reduced number of functional groups remaining on the treated carbon material. The treated carbon material may be exposed to a reactive gas and microwave energy at a temperature of at least 300 ℃ to reduce the number of functional groups remaining on the treated carbon material. The functional groups of the treated carbon material may be reduced by about 50%. The functional groups of the treated carbon material may be reduced by about 80%. In some embodiments, the reactant gas comprises hydrogen and nitrogen. In some embodiments, the reactive gas comprises fluorine.

In some embodiments, a separator film for an electrochemical double layer capacitor comprises cellulose fibers.

A capacitor configured to provide desired performance at operating voltages of 3 volts or greater may include a first current collector and a second current collector. In some embodiments, the capacitor includes a positive electrode electrically coupled to the first current collector and a negative electrode electrically coupled to the second current collector, the positive and negative electrodes including a treated carbon material having a reduced number of carbon surface functional groups. In some embodiments, the capacitor comprises a separator positioned between the positive electrode and the negative electrode, the separator comprising cellulose. In some embodiments, the capacitor comprises an electrolyte comprising acetonitrile and spiro- (1,1') -bipyrrolidinium tetrafluoroborate, triethylmethylammonium tetrafluoroborate and/or tetraethylammonium tetrafluoroborate, the electrolyte being in ionic contact with the positive and negative electrodes. In some embodiments, a capacitor includes a housing assembly configured to hold a positive electrode, a negative electrode, a separator, and an electrolyte, the housing assembly including a protective coating on at least a portion of an interior surface exposed to the electrolyte.

One additional embodiment is a method of manufacturing an ultracapacitor configured to operate between about 2.8 volts to about 3 volts. The method includes providing a first current collector and a second current collector separated by a separator in a housing; and adding an electrolyte to the housing, wherein the electrolyte comprises a quaternary ammonium salt in ionic contact with the positive electrode and the negative electrode, wherein the electrolyte comprises less than 1M salt.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages are described herein. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages without necessarily achieving other objects or advantages.

All such embodiments are intended to be within the scope of the invention disclosed herein. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description, taken with the accompanying drawings, wherein the invention is not limited to any particular disclosed embodiment.

Drawings

These and other features, aspects, and advantages of the present disclosure are described with reference to figures of certain embodiments, which are intended to illustrate certain embodiments, but not to limit the present invention.

Figure 1 is a block diagram showing a simplified cross-sectional view of an exemplary electric double layer supercapacitor.

FIG. 2 is a cutaway perspective view illustrating an exemplary housing assembly for an electric double layer supercapacitor.

Figure 3A shows the capacitive performance of an electric double layer supercapacitor with a barrier film coating a portion of the inner surface of the housing component.

Figure 3B shows the resistance performance of an electric double layer supercapacitor with a barrier film coating a portion of the inner surface of the housing component.

Figure 4 shows the capacitance performance of an electric double layer supercapacitor with reduced electrolyte concentration.

Figure 5 shows a cross-sectional top view of an electric double layer supercapacitor in a jelly-roll configuration.

Figure 6 is a perspective view showing the various layers of an electric double layer supercapacitor in a jelly-roll configuration.

Fig. 7 is a line graph showing the results of modifying the carbon surface characteristics of a supercapacitor electrode.

Figure 8 is a cross-sectional view showing a simplified exemplary electric double layer supercapacitor including asymmetric electrodes.

Detailed Description

While certain embodiments and examples are described below, it will be appreciated by those skilled in the art that the invention extends beyond the specifically disclosed embodiments and/or uses and obvious modifications and equivalents thereof. Therefore, it is intended that the scope of the invention herein disclosed should not be limited by any of the specific embodiments described below.

Figure 1 shows a simplified cross-sectional view of a portion of an exemplary electric double layer supercapacitor 10. The exemplary portion of the double layer supercapacitor 10 includes a first electrode 22, e.g., a positive electrode, having a first active electrode portion 14; and a second electrode 24, such as a negative electrode, having a second active electrode portion 18. Separator 16 is positioned between electrodes 22 and 24 to maintain separation between first electrode 22 and second electrode 24. The electrodes may include current collectors to facilitate electrical contact between the electrodes and an external circuit. Referring to fig. 1, for example, positive electrode 22 includes a first current collector 12 electrically coupled to first active electrode portion 14 and a second current collector 20 electrically coupled to second active electrode portion 18. The separator 16 and the two electrodes 22, 24 may be immersed in an electrolyte (not shown). Electrolyte may permeate into the separator 16 and the active electrode portions 14, 18, for example, to facilitate ion transport between the electrodes 22 and 24.

Embodiments of the present invention relate to techniques for increasing the operating voltage of a supercapacitor to 3 volts or more. These techniques, as described below, allow the supercapacitor to operate at 3 volts or more while minimizing adverse side effects so that such relatively high voltages can be applied across the supercapacitor. In particular, it has been found thatThe increased voltage now causes an increase in the rate of secondary electrochemical reactions occurring within the supercapacitor. For example, a secondary electrochemical reaction may occur between a supercapacitor electrolyte (e.g., an acetonitrile-based electrolyte) and one or more other materials of the supercapacitor. It has been found that these reactions are sensitive to the operating voltage and that the reaction rate can be increased as the voltage across the capacitor is increased. The byproducts of the reaction may contribute to increased accumulation of various constituent gases within the supercapacitor, including, for example, H₂And CO₂This can cause pressure build-up within the device and/or leakage of the device. In addition, in a supercapacitor with an aluminum current collector, the aluminum current collector may contribute to secondary reactions, which may result in an increase in the internal resistance of the device. Ultimately, the secondary reactions can result in physical and/or chemical changes in the carbon-based electrode and electrode structure, which can have a deleterious effect on the performance of the supercapacitor (including, for example, the capacitance of the supercapacitor).

The following techniques, used alone or in combination with one another, may alleviate or mitigate problems caused by: operating at 3 volts or more, particularly at higher temperatures such as 60 ℃, 65 ℃, 70 ℃, 75 ℃ or more, while maintaining more than 80% of its initial capacitance for more than 1500 hours, more than 80% of its initial capacitance for a plurality of cycles (e.g., cycles between the rated voltage and half-voltage of the capacitor), less than 200% of its initial supercapacitor Equivalent Series Resistance (ESR) for more than 1500 hours, and/or less than 200% of its initial supercapacitor Equivalent Series Resistance (ESR) for a plurality of cycles (e.g., cycles between the rated voltage and half-voltage of the capacitor). In some embodiments, the techniques described herein, used alone or in combination with one another, facilitate operation of a supercapacitor at 3 volts while exhibiting a leakage current that is less than a target leakage current for a period of time (e.g., less than 18 milliamps (mA) for a plurality of hours, such as more than 72 hours) and/or exhibiting a self-discharge of less than 25% for a period of time, such as more than 72 hours.

The techniques described herein may also be used alone or in combination with one another to achieve desired operation of the ultracapacitor at greater than or equal to 500k cycles at an operating voltage of 3 volts or more at a temperature of about 65 ℃. For example, a supercapacitor may include one or more of the techniques described herein to enable the supercapacitor to maintain or substantially maintain a capacitance of greater than about 80% of its initial capacitance, and/or less than 200% of its initial equivalent series resistance, when operated at a voltage of 3 volts or more for a period of more than about 1,500 hours and/or greater than or equal to 500k cycles and at a temperature of about 65 ℃. In other embodiments, the ultracapacitor is capable of maintaining at least 75%, 85%, 90%, 95%, or 99% of its initial capacitance when operated at 65 ℃ or more for a period of 1500 hours and/or greater than or equal to 500k cycles.

Definition of

As used herein, capacitance (F-farad) is a measure of energy storage in joules. C-qV

As used herein, voltage is the maximum operating voltage of a single capacitor. The nominal voltage is the voltage under which the performance data is measured. The capacitor may be subjected to voltages exceeding the rated voltage. The effect depends on the time and temperature during this exposure.

As used herein, surge voltage is the maximum voltage at which a supercapacitor can operate in a short time with minimal damage or battery opening.

As used herein, internal resistance (DC) is the resistance R corresponding to all of the resistive components within the ultracapacitor_tot. This measurement is made at the end of the device discharge and in particular a few seconds after the discharge current has stopped flowing, typically 5 seconds (ESR ═ Δ V/abs (i)). Since the time constant of the supercapacitor is about 1 second, it takes about 5 time constants or 5 seconds to effectively remove 99.7% of the stored energy. R_totConsisting of resistance components attributed to contact or interconnect resistance, electrode conduction resistance, electrolyte conduction and ionic resistance, and resistance of other materials.

As used herein, cycle life is the expected performance characteristic of an ultracapacitor when cycled between a rated voltage and half the rated voltage when cycled from the rated voltage to half the rated voltage for 50k cycles, 500k cycles, 1 million (M) cycles, or any number of cycles. In one embodiment, the cycling is performed at a duty cycle and current level such that the internal and/or external bulk temperature of the ultracapacitor does not or substantially does not rise, wherein the ultracapacitor maintains a temperature equal or substantially equal to 65 ℃.

Housing with internal coating

Referring to fig. 2, electric double layer supercapacitor 29 may include a housing assembly 30 configured to house and hold a positive electrode, a negative electrode, a separator, and an electrolyte, as discussed above with reference to fig. 1. The housing assembly 30 may include one or more walls 32, a base 36, and an upper cover 38 having an exterior surface 40 and an interior surface 42, where the interior surface 42 at least partially defines the housing interior space 34, the interior space 34 configured to hold a positive electrode, a negative electrode, a separator, and an electrolyte. For example, the housing assembly 30 may include a cylindrical container having a sidewall 32, a base 36, and an upper cover 38. The sidewalls 32, base 36, and/or cover 38 may be made of a conductive material. For example, substrate 36 and/or the cover may include conductive materials that allow electrical contact to one or more current collectors (e.g., current collectors 12 and 20, shown in fig. 1) to enable current to flow from the current collectors to an external circuit. The conductive material of the sidewalls 32, base 36, and/or upper cover 38 may include aluminum, nickel, silver, steel, tantalum, other suitable metallic materials, and/or combinations thereof. The housing assembly 30 may also take the form of other shapes (e.g., the housing assembly has a prismatic shape) and this is not limited to a cylindrical shape.

The inner surface 42 of the sidewall 32 may be in contact with the electrolyte. This may result in chemical and/or electrochemical interaction between the electrolyte and the inner surface 42, such as the generation of byproducts that may degrade the performance of the capacitor. In one embodiment of the invention, a barrier film 44 may be applied to at least a portion of the interior surfaces 42 of the housing assembly 30 exposed to the electrolyte to provide a protective coating for one or more of the interior surfaces 42.

The barrier film 44 may be applied to a portion of the inner surface of the sidewall 32, the inner surface of the base 36, and/or the inner surface of the lid 38. In some embodiments, the barrier film 44 may be applied to all or substantially all of the interior surface portions of the housing assembly 30 exposed to the electrolyte. In some embodiments, a portion of the substrate 36 and/or the upper cap 38 is not or substantially not coated with the barrier film 44, for example, to mitigate degradation of the electrical coupling between the active components of the supercapacitor and the external circuit.

In some embodiments, the barrier film 44 is applied to all or substantially all of the inner surface 42 of the sidewall 32, except for the portion of the inner surface 42 of the sidewall 32 that is configured to provide contact between the active components of the supercapacitor and an external circuit. For example, all or substantially all of the inner surface 42 of the sidewall 32 may be coated by the barrier film 44, except for the portion of the inner surface 42 of the sidewall 32 that is configured to provide one or more current collectors electrically coupled to the supercapacitor. In some embodiments, the uncoated portion of the inner surface 42 of the sidewall 32 may have an area configured to provide reduced interference by the barrier film 44 upon electrical coupling between the active component of the ultracapacitor and an external circuit (e.g., an area configured to reduce degradation of electrical coupling between one or more current collectors of the ultracapacitor and the external circuit) while providing a desired coating of the inner surface 42 of the sidewall 32 to facilitate reduced interaction with the electrolyte.

For example, a portion of the inner surface 42 of the sidewall 32 near and/or along the base 36 of the housing 30 (e.g., a portion along the base 36 forming a strip having a width) may not be coated by the barrier film 44. In some embodiments, the uncoated strips have a width of less than about 10 millimeters (mm). For example, the inner surface 42 of the sidewall 32 may form a strip having a width of about 5mm along an uncoated portion of the base 36 of the housing 30. Of course, other shapes and/or sizes of the uncoated portions may also be suitable. In some embodiments, the uncoated portion of the inner surface 42 of the sidewall 32 may be at another location on the sidewall 32.

In some embodiments, barrier film 44 enables a reduction in chemical and/or electrochemical interactions between one or more interior surfaces 42 and the electrolyte (e.g., to help mitigate corrosion of one or more interior surfaces 42). For example, the barrier film 44 may exhibit chemical resistance to the electrolyte and may provide a physical barrier between the interior surface 42 and the electrolyte so as to enable reduced interaction between the interior surface 42 and the electrolyte and reduced generation of byproducts. In some embodiments, the barrier film 44 may prevent or substantially prevent all chemical interactions between the inner surface 42 and the electrolyte, particularly when the inner surface 42 is an aluminum surface.

The barrier film 44 may comprise a material having a desired mechanical strength, sufficient adhesion to the lower interior surface 42 of the housing assembly 30, and/or chemical and/or electrochemical stability with respect to the electrolyte. In some embodiments, the barrier film 44 is free or substantially free of pinholes, cracks, and/or other defects.

The barrier film 44 may have a sufficient thickness to provide the desired separation between the electrolyte and the inner surface 42 while providing a coating having a reduced impact on the volume of the housing interior 34 occupied by the barrier film 44. The volume of the housing interior 34 occupied by the barrier film 44 may reduce the volume available for other components of the ultracapacitor. In some embodiments, barrier film 44 is uniformly or substantially uniformly applied to portions of inner surface 42. A variety of thicknesses may be suitable. For example, the barrier film is about 5 micrometers (μm) to about 40 μm. In some embodiments, the barrier film 44 may have a thickness of about 5 μm to about 55 μm. For example, the barrier film 44 applied to a portion of the inner surface 44 of the sidewall 32 may have a thickness of about 10 μm.

In some embodiments, the barrier film 44 may comprise a non-conductive material, such as a polymeric material. For example, barrier film 44 can include polyepoxides (e.g., epoxies), polyolefins (e.g., polypropylene (PP), Polyethylene (PE), e.g., High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE)), polyimides, Polyetheretherketones (PEEK), polyurethanes, ethylene-propylene rubbers (EPDM, EPR), poly (p-xylylene) (e.g., parylene), fluorinated polymers (e.g., Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene (ETFE), fluorinated ethylene-propylene (FEP)), copolymers thereof, and/or combinations thereof.

In some embodiments, the barrier film 44 may include a conductive film. The conductive film may enable portions of the inner surface 42 to maintain or substantially maintain a desired electrical contact with another ultracapacitor component (e.g., a current collector) and/or an external circuit. In some embodiments, the membrane includes a conductive material, such as a conductive carbon material, that is chemically and/or electrochemically resistant to the electrolyte. The conductive film may be made of graphite (e.g., graphite ink, graphite paste, graphene). For example, the film may comprise a mixture comprising an electrically conductive carbon material (e.g., graphite and/or graphene) and a binder material (e.g., a thermoplastic binder material). In some embodiments, the mixture may be a dispersion of the conductive carbon in a thermoplastic binder, such as a water-based dispersion. For example, the barrier film 44 may be made from a water-based dispersion of graphite in a thermoplastic binder material. The barrier film 44 made of conductive carbon may have a desired conductivity, for example, a sheet resistance of less than about 30 ohms/square ("Ω/sq") at a thickness of about 25 μm.

In some embodiments, the barrier film 44 may include a non-conductive film, a conductive film, and/or combinations thereof. For example, the barrier film 44 may include only non-conductive materials (e.g., one or more polymer films), only conductive materials (e.g., one or more conductive films made of conductive carbon materials), or non-conductive films on conductive films (e.g., one or more polymer films on one or more conductive carbon-based films). For example, a portion of the inner surface 42 may be coated with a barrier film 44, the barrier film 44 including a conductive film beneath the polymer film that helps reduce interference generated by the polymer film having electrical contact between the portion of the inner surface 42 and the current collector of the supercapacitor.

In some embodiments, the aluminum interior surface may be anodized to form a protective oxide barrier. In some embodiments, the stainless steel inner surface may be passivated to provide a barrier layer.

Fig. 3A shows the capacitive performance (e.g., capacitance decay performance) of a supercapacitor whose inner surface of the housing is partially coated with a barrier film. The barrier film is a conductive barrier film made of a carbon material including graphite. The supercapacitor has portions of the inner surface of the housing side walls coated by a barrier film to reduce interaction between the side walls and the electrolyte while also reducing interference with the electrical coupling between the active components of the capacitor and the external circuit. A comparison is exhibited between a supercapacitor with a barrier coating and a control supercapacitor without a barrier film on any portion of the inner surface of its housing. Figure 3A shows that ultracapacitors coated with a graphite conducting barrier film have improved capacitance over time. For example, a supercapacitor coated with the barrier film on the inner surface of its side wall was found to retain about 75% of its capacitance when operated at 3 volts and 65 ℃ for 1000 hours, compared to an uncoated supercapacitor which retained only about 68% of its capacitance when operated at the same conditions for 1000 hours. The coated supercapacitor was found to be able to operate for about 1500 hours until the same approximate 68% capacitance was reached, indicating that the coating extended the capacitive life of supercapacitors operating at 3 volts and 65 ℃.

Figure 3B shows the electrostatic resistance performance (e.g., ESR) of a supercapacitor whose inner surface of the outer shell is coated with a barrier film made of carbon graphite, as compared to a supercapacitor without the barrier film. Fig. 3B shows that the coated supercapacitor is able to maintain a reduced ESR over time compared to the uncoated supercapacitor. As shown, the ESR of the coated supercapacitor operated at 3 volts and 65 ℃ for 1500 hours was lower than the ESR of the uncoated supercapacitor operated under the same conditions for only 1000 hours.

Suitable methods of applying the barrier film 44 to the interior surface portions of the housing assembly 30 may include, for example, dipping, spraying, brushing, liquid dispersion coating, vapor deposition, spin coating, wiping, painting, and/or dripping.

Electrolyte

As described herein, an electric double layer supercapacitor includes an electrolyte capable of transporting ions between a positive electrode (e.g., positive electrode 22 shown in fig. 1) and a negative electrode (e.g., positive electrode 24 shown in fig. 1). The electrolyte may be a solution having a solvent and a salt, wherein the salt provides an ionic species to facilitate ionic conductivity and contact between the positive and negative electrodes. Suitable electrolytes may also exhibit low viscosity and/or a high degree of ionic conductivity, thereby achieving reduced internal resistance of the capacitor and increased capacitor voltage during charging and discharging of the capacitor. For example, increased solubility of the salt in the solvent may enable increased ionic conductivity between the positive and negative electrodes. Suitable electrolytes may exhibit chemical and/or electrochemical stability under the operating conditions of the supercapacitor and can withstand repeated charge discharge cycles of the supercapacitor.

Electrolyte with acetonitrile solvent and various salts

One embodiment of the invention is a supercapacitor that exhibits stable performance when operated at 3 volts or more and includes an electrolyte having a salt that exhibits increased solubility in an electrolyte solvent and that may be chemically and/or electrochemically stable at an operating voltage of 3 volts. The electrolyte can achieve enhanced ionic mobility and/or can exhibit enhanced chemical and/or electrochemical stability under operating conditions of the supercapacitor. In one embodiment, the capacitor electrolyte solvent is acetonitrile.

In some embodiments, the electrolyte salt can include an ionic liquid. For example, suitable electrolyte salts may include ionic liquids that exhibit desirable stability at operating voltages of 3 volts or more, provide sufficient ionic conductivity between the electrodes of the supercapacitor, and/or exhibit desirable solubility in acetonitrile electrolyte solvents.

The electrolyte salt may include a quaternary ammonium salt having a desired solubility in acetonitrile solvent.

In some embodiments, the cation of the electrolyte salt comprises spiro- (1,1') -bipyrrolidinium (SPB), Triethylmethylammonium (TEMA), and/or Tetraethylammonium (TEA). In some embodiments, the anion of the electrolyte salt comprises tetrafluoroborate and/or iodonium. For example, the electrolyte may comprise a salt comprising: spiro- (1,1') -bispyrrolidinium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, spiro- (1,1') -bispyrrolidinium iodide, triethylmethylammonium iodide and/or tetraethylammonium iodide. For example, electrolytes comprising triethylmethylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, and/or spiro- (1,1') -bipyrrolidinium tetrafluoroborate can provide electrolytes having increased salt solubility and improved chemical and/or electrochemical stability at increased operating voltages, wherein the electrolyte comprises an acetonitrile solvent.

In some embodiments, the cation of the electrolyte salt can include a symmetrical cation, including, for example, triethylmethylammonium. In some embodiments, the cation of the electrolyte salt can include an asymmetric cation, including, for example, triethylmethylammonium. In some embodiments, the electrolyte salt can include spiro compounds, including symmetric and asymmetric spiro compounds. For example, the electrolyte may include an N-spirobicyclic compound, including a symmetric N-spirobicyclic compound having a 5-membered cyclic ring. In some embodiments, the electrolyte may include an asymmetric spiro compound, including asymmetric spiro compounds having ring structures of unequal sizes. Symmetric spiro compounds may include spiro- (1,1') -bispyrrolidinium tetrafluoroborate.

Electrolyte with reduced salt concentration

Another embodiment of the invention is a supercapacitor that can provide desired operation at an operating voltage of 3 volts or more, wherein the supercapacitor includes an electrolyte having a reduced salt concentration compared to a typical supercapacitor. The electrolyte may include a salt having improved solubility in an electrolyte solvent, such as a salt having improved solubility in an acetonitrile-based solvent, so that the electrolyte may have a reduced salt concentration while maintaining or substantially maintaining a desired ionic conductivity between the positive and negative electrodes of the supercapacitor. This allows a reduction in ion concentration while providing sufficient ion transport between the electrodes without starving the supercapacitor. An electrolyte with a reduced salt concentration may enable reduced chemical interaction between the electrolyte and one or more other components of the ultracapacitor. The reduced chemical interactions may, for example, enable reduced byproduct generation rates and thus provide improved supercapacitor performance.

In some embodiments, an electrolyte having a reduced salt concentration enables the electrolyte to have reduced electrolyte concentration non-uniformity. The non-uniformity may result from non-uniform current density within the supercapacitor. The electrolyte concentration non-uniformity may promote precipitation of salts on one or more electrode surfaces. This precipitation can, for example, block one or more electroactive sites on the electrode and negatively impact the performance of the supercapacitor. By using an electrolyte with a reduced salt concentration, the ultracapacitor may avoid electrolyte concentration non-uniformity when operated at elevated voltages, such as at high current charge and discharge cycles.

The electrolyte may include spiro- (1,1') -dipyrrolidinium tetrafluoroborate, tetraethylammonium Tetrafluoroborate (TEA), triethylmethylammonium Tetrafluoroborate (TEMA), spiro- (1,1') -dipyrrolidinium iodide, triethylmethylammonium iodide, and/or tetraethylammonium iodide in a solvent comprising acetonitrile. In this embodiment, the electrolyte may have a concentration in the range of about 0.5 moles/l (M) to about 1.0M, including from about 0.7M to about 0.9M. For example, the electrolyte may include tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, and/or a 0.8M solution of spiro- (1,1') -bipyrrolidinium tetrafluoroborate in acetonitrile.

Fig. 4 is a line graph showing a comparison of capacitive performance between ultracapacitors with different electrolyte concentrations. As shown, several supercapacitors with 0.8M tetraethylammonium tetrafluoroborate in acetonitrile (TEA) electrolyte solutions were compared to several supercapacitors with 1.0M TEA to measure the decay in capacitance over time. Each supercapacitor was operated at 3.0 volts and 65 ℃. As shown, the supercapacitor with a reduced electrolyte concentration of 0.8M was found to have a reduced capacitance fade over time compared to the supercapacitor with 1M TEA electrolyte. As shown at 500 hours, the supercapacitor with 0.8M TEA had a capacitance decay of about 78%, while the supercapacitor with 1.0M TEA was found to have a capacitance decay of about 84%.

Other suitable solvents may include gamma-butyrolactone, dimethoxyethane, N-dimethylformamide, hexamethyl-phosphonotriamine (hexamethylene-phosphotriamide), propylene carbonate, dimethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, dimethyl sulfite, sulfolane (tetramethylene sulfone), nitromethane, and/or dioxolane. Other suitable salts may include methyltriethylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, tetraalkyl phosphonium salts (e.g., tetraethylphosphonium tetrafluoroborate, tetrapropylphosphonium tetrafluoroborate, tetrabutylphosphonium tetrafluoroborate, tetrahexylphosphonium tetrafluoroborate, tetraethylphosphonium hexafluorophosphate, tetraethylphosphonium trifluoromethylsulfonate) and/or lithium salts (e.g., lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate).

Partition board

As described herein, an electric double layer capacitor may have a separator immersed in an electrolyte and positioned between positive and negative electrodes (e.g., the positive and negative electrodes 22, 24 shown in fig. 1). The separator enables electrical insulation of one electrode from the other in a supercapacitor, for example to prevent electrical short circuits between the positive and negative electrodes, while allowing ion transport between the two electrodes. For example, the separator may include a porous material having sufficient wettability for the electrolyte to facilitate ion transfer between the positive and negative electrodes. The separator may be made of a material having mechanical strength, chemical stability, and/or electrochemical stability, including, for example, a material that maintains or substantially maintains its physical, electrical, and/or chemical properties under the conditions of the manufacturing process and/or the operating conditions of the capacitor. In some embodiments, the separator is made of cellulose including, for example, cellulose fibers.

The separator may have an optimized thickness to provide sufficient separation between the electrodes of the supercapacitor while having a reduced volume (e.g., so that the supercapacitor has a reduced volume and/or weight, and/or the supercapacitor has an increased volume for its other components). For example, the separator may have a thickness of about 20 μm to about 50 μm. For example, the separator made of cellulose may have a thickness of about 30 μm.

Electrode for electrochemical cell

The capacitance of an electric double layer supercapacitor depends, at least in part, on the surface area available for storing charge, and in particular the surface area available on the electrodes of the capacitor. Referring to fig. 5, an electric double layer supercapacitor 50 is shown having a separator 54 positioned between a positive electrode 52 and a negative electrode 56. In this case, the supercapacitor 50 is shown wound or rolled into a "jelly roll" configuration. The jelly-roll type structure may enable increased surface area storage in tight spaces. In some embodiments, the positive electrode 52 and/or the negative electrode 56 constitute the active portion of the supercapacitor, which contains a porous material having a very large effective area per unit volume (i.e., a very large normalized effective surface area).

Optimized electrode carbon microporosity, mesoporosity and macroporosity

In another embodiment, a supercapacitor operating at 3 volts may have one or more carbon based layers (e.g., carbon based layers 82, 84 of fig. 6) in a supercapacitor electrode comprising a carbon material having a desired microporosity (e.g., pores having a diameter of less than about 2 nanometers (nm)), mesoporosity (e.g., pores having a diameter of about 2nm to about 50 nm), and/or macroporosity (e.g., pores having a diameter of greater than about 50 nm). For example, the electrodes may be made at least in part from activated carbon having optimized microporosity, mesoporosity, and/or macroporosity to achieve improved performance at three volts or more. The micro-, meso-, and/or macro-porosity of the carbon-based layer may be optimized to facilitate ion mobility within the layer and/or capacitance values of the layer. Ions within the electrolyte of the capacitor may migrate within the electrodes of the capacitor after a number of charge-discharge cycles, becoming trapped within the pores (e.g., micropores) of the electrodes. The trapped ions may become unavailable for further charge-discharge cycles and may at least partially contribute to deterioration of the operational characteristics of the capacitor, including, for example, an increase in the Equivalent Series Resistance (ESR) value and/or a decrease in the capacitive performance. In some embodiments, the carbon material may have a reduced microporosity to reduce the space into which ions may be trapped. Reducing the microporosity of the carbon-based layer can facilitate the entry of ions into the active surface of the electrode. The carbon-based layer may have an optimized micro-, meso-, and/or macro-porosity to reduce ion capture within the pores of the carbon-based layer while providing the desired carbon-based layer capacitance performance.

In some embodiments, the carbon-based layer may have a microporosity of about 60% to about 85%, such as about 70% or about 75% or about 80%. In some embodiments, the carbon-based layer may have a mesoporosity of about 10% to about 35%, such as about 20% to about 25%. In some embodiments, the carbon-based layer may have a macroporosity of less than about 5%, for example, about 1%. In some embodiments, a decrease in microporosity and an increase in microporosity can provide improved ESR performance and/or capacitance performance. For example, a reduction in microporosity of about 20% to about 25% can contribute to a reduction in the ESR value of an ultracapacitor operating at 3 volts or more and at about 65 ℃ of about 20% to about 30%. In some embodiments, the carbon-based layer of the electrode may have a microporosity in the range of about 70% to about 85%, a mesoporosity in the range of about 10% to about 30%, and a macroporosity in the range of less than about 5% (e.g., about 1%).

In some embodiments, a densified carbon-based layer having an optimized composition, packing density, microporosity, and/or macroporosity is adhered to one or more surfaces of a current collector (e.g., current collectors 84, 82 shown in fig. 6). For example, the first and/or second carbon-based layers may be adhered to the surface of the current collector via a lamination process. The first and/or second carbon-based layers may be adhered directly or indirectly to a surface of a current collector, for example, optionally including an adhesive layer (e.g., a conductive adhesive layer) to promote adhesion between the surface of the current collector and the carbon-based layer and/or to achieve reduced sheet resistance. For example, the adhesive layer includes a solvent, an adhesive component (e.g., a thermoplastic material), and/or a conductivity enhancer (e.g., graphite and/or other conductive carbon powder). The adhesive layer is also commercially available. For example, a first compacted carbon-based layer having an optimized composition, packing density, microporosity, and/or macroporosity can be adhered to a first surface of a current collector, and a second compacted carbon-based layer having an optimized composition, packing density, microporosity, and/or macroporosity can be adhered to a second surface of the current collector opposite the first surface. In some embodiments, the carbon-based layer has an optimized composition, packing density, microporosity, and/or macroporosity to achieve improved equivalent series resistance, structural integrity of the carbon-based layer, improved ion mobility, and/or extended supercapacitor cycle life.

Asymmetric electrode thickness

In one embodiment of the invention, a supercapacitor includes a positive electrode having a thickness greater than a thickness of a negative electrode. As shown in fig. 8, the electric double layer capacitor 150 may include a positive electrode 152 having a first thickness T1 and a negative electrode 154 having a second thickness T2. In some embodiments, the first thickness T1 of the positive electrode 152 is greater than the second thickness T2 of the negative electrode 154.

For example, a first sub-capacitor may be formed at the interface between the positive electrode 152 and an electrolyte (e.g., the electrolyte 26 shown in fig. 1), and a second sub-capacitor may be formed at the interface between the negative electrode 154 and the electrolyte. An exemplary method of selecting the first thickness T1 and the second thickness T2 includes: determining a positive voltage limit of the first sub-capacitor and a negative voltage limit of the second sub-capacitor; dividing the positive voltage limit by the negative voltage limit to obtain a first ratio of the second sub-capacitor to the first sub-capacitor; and setting the relative thicknesses of the positive electrode layer and the negative electrode layer such that the capacitance of the second sub-capacitor is substantially equal to the product of the first ratio and the capacitance of the first sub-capacitor. Further embodiments of one or more methods for determining first thickness T1 and second thickness T2 are provided in U.S. patent application publication No. 2006/0148112, which is incorporated by reference herein in its entirety.

In some embodiments, the carbon-based layer of positive electrode 152 (e.g., the carbon-based layer may be made of activated carbon, binder material, and/or conductive additives) may have a thickness that is about 20 μm to about 100 μm greater than a thickness of the carbon-based layer of negative electrode 154. For example, the carbon-based layer thickness of the positive electrode 152 may be about 80 μm to about 200 μm, and the carbon-based layer thickness of the negative electrode 154 may be about 60 μm to about 160 μm. For example, the first thickness T1 of the positive electrode 152 can include the current collector thickness of the positive electrode 152 and the carbon-based layer thickness on each of the two opposing surfaces of the current collector. The second thickness T2 of the negative electrode 154 may include the current collector thickness of the negative electrode 154 and the carbon-based layer thickness on each of the two opposing surfaces of the current collector of the negative electrode 154.

In some embodiments, the percentage by which the first thickness T1 of the positive electrode 152 is greater than the second thickness T2 of the negative electrode 154 is in the range of about 15% to about 40%, including about 20% to about 30%. For example, the first thickness T1 is about 25% greater than the second thickness T2. For example, the first thickness T1 is about 35% greater than the second thickness T2.

In some embodiments, supercapacitors having asymmetric electrodes (e.g., positive and negative electrodes having different thicknesses) may exhibit improved capacitive and/or resistive performance. For example, a supercapacitor with a positive electrode thicker than the negative electrode may exhibit an improvement in capacitive performance of about 5% to about 10% and/or an improvement in resistive performance of 5% to about 10% when operated at 3 volts or more and at a temperature of about 65 ℃.

Carbon surface modification

Reduction of carbon surface functional groups

In one embodiment of the invention, the carbon used in one or more electrodes of the supercapacitor is treated to reduce the number of carbon surface functional groups, thereby achieving improved supercapacitor performance. As described herein, in some embodiments, the electrodes (e.g., the positive and/or negative electrodes 152, 154 shown in fig. 8) comprise activated carbon. The high surface area on the activated carbon may be produced via chemical and/or thermal oxidation process processes. Incomplete oxidation of carbon can produce oxygen-containing functional groups on the carbon surface, including carboxyl, carboxylate, hydroxyl, lactone, quinones, and phenols. Residual oxygen can lead to detrimental performance characteristics of the capacitor. For example, residual oxygen can cause capacitive decay upon cycling, self-discharge, pseudocapacitance, gas formation at high potential voltages, and/or enhanced hydrophilic surface properties, which stimulate moisture adsorption. In some embodiments, surface functional groups with nitrogen (N) and/or hydrogen (H) can degrade the performance of the supercapacitor during its operation.

In some embodiments, the treated carbon material used in an electrode (e.g., the positive and/or negative electrodes 152, 154 shown in fig. 8) comprises a reduced number of surface functional groups. For example, the activated carbon material used in the electrode may be exposed to a reactive gas (e.g., comprising CO) at a temperature of at least 300 ℃₂And/or N₂The reaction gas) and microwave energy to reduce the number of functional groups remaining on the treated carbon material. In some embodiments, the reaction gas comprises a reducing gas. In some embodiments, the electrode carbon material may be treated with a reaction gas comprising a reducing gas at elevated temperatures to achieve, for example, a reduction in the number of functional groups on the carbon surface. For example, the electrode carbon material may be treated at a temperature in the range of about 300 ℃ to about 1000 ℃, including about 500 ℃ to about 1000 ℃. For example, the activated carbon material of the electrode may be treated with a reducing gas at a temperature in the range of about 500 ℃ to about 1000 ℃ to achieve a reduction in the number of functional groups on the surface of the activated carbon. Further description of methods for carbon surface modification is provided in U.S. patent application publication No. 2009/0097188, which is incorporated herein by reference in its entirety.

In some embodiments, the treated carbon material may have less than about 1% hydrogen-containing functional groups (e.g., less than about 0.5%), less than about 0.5% nitrogen-containing functional groups (e.g., less than about 0.1%), and/or less than about 5% oxygen-containing functional groups (e.g., less than about 3%). In some embodiments, the treated carbon material may have a reduction in the number of functional groups on one or more surfaces of the treated activated carbon of about 20% to about 50%. For example, the treated carbon material may have about 30% fewer hydrogen-containing functional groups.

In one embodiment, supercapacitors having varying functional groups are tested for pressure values, and the pressure of each supercapacitor within the device is gradually accumulated over time. The following table shows the carbon functional modifications for each carbon tested. Each stress test was performed at 3 volts and 65 ℃.

As shown in fig. 7, improved performance of the electrode with carbon having a reduced concentration of surface functional groups was found. For example, at 3 volts and 65 ℃, carbon 1 was found to have an internal cell pressure of only about 4.5 bar after 250 hours of operation, in contrast to carbon 3, which was found to have an internal pressure of over 7 bar after the same time of operation. This indicates that carbon electrodes with reduced surface functional group concentrations were found to provide a device that can operate for longer periods of time while reducing internal pressure within the supercapacitor package.

Modification of carbon surface functional groups to reduce electrochemical potential of electrodes

One embodiment of the invention includes a supercapacitor configured to operate at an operating voltage of 3 volts or greater, wherein the supercapacitor includes one or more electrodes comprising a carbon material treated with a reactive gas to maintain the one or more electrodes at a reduced electrochemical potential during operation of the supercapacitor. For example, one or more surface functional groups of the electrode carbon material may be modified to change the electrochemical potential of the electrode. In some embodiments, the carbon material of the electrode may be treated with a reactive gas comprising fluorine and/or nitrogen to modify the surface characteristics of the carbon. Electrode carbon materials treated with a reactant gas comprising fluorine and/or carbon may enable the electrode to maintain or substantially maintain a lower electrochemical potential during operation of the supercapacitor than the voltage at which one or more secondary side reactions may occur, thereby facilitating, for example, improved performance of the electrode at increased operating voltages. For example, a positive electrode of a supercapacitor comprising a carbon material treated with a reaction gas comprising fluorine and/or nitrogen is capable of maintaining or substantially maintaining a lower electrochemical potential during operation of the supercapacitor than a voltage at which one or more secondary parasitic reactions may occur, thereby facilitating, for example, improved performance of the supercapacitor at increased operating voltages.

In some embodiments, the electrode carbon material may be treated with a reactive gas to add one or more beneficial functional groups to one or more surfaces of the carbon material. For example, one or more surfaces of the activated carbon material of the electrode may be modified to improve the wettability, conductivity, and/or resistance of the electrode.

Carbon surface coatings

In one embodiment of the invention, a supercapacitor configured to provide desired operation at an operating voltage of 3 volts or more comprises one or more electrodes comprising a carbon material treated to provide a protective coating on one or more surfaces of the carbon material. In some embodiments, one or more electrodes of a supercapacitor comprise a treated carbon material to provide one or more coatings on the surface of the carbon material to reduce chemical degradation of the carbon surface. Suitable materials for protecting the carbon surface from degradation may include, for example, materials that have electrochemical stability at the temperatures at which the supercapacitor operates and/or that maintain or substantially maintain the carbon surface area and/or ion mobility within the electrode. The treated carbon material may include any carbon material used to make electrodes, including, for example, activated carbon, graphite, and/or carbon black.

For example, the protective coating may comprise a porous ceramic material. In some embodiments, the protective coating comprises a metallic material that can protect the carbon surface and/or provide increased electrical conductivity to the treated carbon material (e.g., a carbon surface decorated with a metal of silver atoms). In some embodiments, the protective coating comprises silicon carbide and/or a metal oxide (e.g., tin oxide, titanium oxide, zinc oxide).

The one or more protective coatings can be applied to the carbon material prior to its incorporation into the supercapacitor electrode and/or after the carbon material is incorporated into the electrode (e.g., in situ). For example, in situ modification of the carbon surface may include the use of one or more electrolyte additives (e.g., one or more additives as described herein). The one or more additives may form a protective coating on one or more surfaces of the carbon material, for example, to achieve a reduction in byproduct formation and/or a reduction in carbon surface contamination.

Improved 3V super capacitor

One embodiment is an electric double layer supercapacitor configured to provide desired operation at an elevated operating voltage, such as an operating voltage of 3 volts (V), which may include one or more of the features described herein. The device may operate at 65 ℃ for more than 1500 hours, and/or greater than or equal to 500k cycles, for example, while maintaining more than 80% of its initial capacitance and/or less than about 200% of its initial equivalent series resistance. In this embodiment, the electric supercapacitor includes an electrolyte comprising tetraethylammonium tetrafluoroborate and/or spiro- (1,1') -bipyrrolidinium tetrafluoroborate at a concentration of about 0.8mol/l (m) in acetonitrile. In addition, the device is placed within a housing component having a barrier film on the interior surface of the housing exposed to the electrolyte. This barrier film protects the device from reactions between the electrolyte and the metallic inner surface of the capacitor case.

The separator made of cellulose fibers is within the device, and the cellulose fibers also reduce the rate of any reaction that may degrade the separator. In addition to these features, the device also includes an electrode having a carbon layer with optimized composition, fill density, microporosity, and/or macroporosity and thus the carbon electrode is configured to provide the most advantageous characteristics when operated at 3.0 volts.

In addition, the thickness of the positive electrode is made thicker than the thickness of the negative electrode anode to provide the desired operation at elevated operating voltages.

While the invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while several variations of the embodiments of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed embodiments of the invention. Therefore, it is intended that the scope of the invention herein disclosed should not be limited by the particular embodiments described above.

The headings provided herein are for convenience only if any and do not necessarily affect the scope or meaning of the devices and methods disclosed herein.

Claims (42)

1. An ultracapacitor, comprising:

a first current collector and a second current collector;

a positive electrode electrically coupled to the first current collector;

a negative electrode electrically coupled to the second current collector, wherein at least one of the positive electrode and the negative electrode comprises a carbon-based layer having a mesopore fraction of about 20% to about 25% and a micropore fraction of about 70% to about 80%;

a separator positioned between the positive electrode and the negative electrode;

an electrolyte in ionic contact with the positive electrode and the negative electrode; and

a housing assembly holding the positive electrode, the negative electrode, the separator, and the electrolyte, and wherein the ultracapacitor is capable of operating at 3 volts at a temperature of 65 ℃ or greater while maintaining less than 200% of its initial equivalent series resistance for more than 1500 hours.

2. The ultracapacitor of claim 1, wherein the ultracapacitor is further capable of operating greater than 10 at 25 degrees celsius⁶Cycle life of one cycle.

3. The ultracapacitor of claim 1, wherein the ultracapacitor is capable of operating at 65 ℃ for a cycle life of greater than 500k cycles.

4. The ultracapacitor of claim 1, wherein the electrolyte comprises a quaternary ammonium salt.

5. The supercapacitor of claim 4 wherein said quaternary ammonium salt comprises a cation selected from the group consisting of: spiro- (1,1') -bipyrrolidinium, triethylmethylammonium and tetraethylammonium.

6. The supercapacitor of claim 4 wherein said quaternary ammonium salt comprises an anion selected from the group consisting of: tetrafluoroborate and iodide.

7. The ultracapacitor of claim 1, wherein the electrolyte comprises acetonitrile.

8. The ultracapacitor of claim 1, wherein a salt concentration of the electrolyte is between 0.7 moles/l (M) and 1.0M.

9. The supercapacitor of claim 1 wherein at least one of said positive electrode and said negative electrode has a carbon-based layer comprising a microporosity of 60% to 85%.

10. The ultracapacitor of claim 9, wherein the carbon-based layer comprises a microporosity of between 70% and 80%.

11. The ultracapacitor of claim 1, wherein the carbon-based layer comprises a mesoporosity of between 10% and 35%.

12. The ultracapacitor of claim 11, wherein the carbon-based layer comprises a mesoporosity between 20% and 25%.

13. The ultracapacitor of claim 1, wherein the carbon-based layer comprises a macroporosity of less than 5%.

14. The ultracapacitor of claim 13, wherein the carbon-based layer comprises a macroporosity of less than 1%.

15. The ultracapacitor of claim 1, wherein the positive electrode comprises a first thickness and the negative electrode comprises a second thickness, wherein the first thickness of the positive electrode is greater than the second thickness of the negative electrode.

16. The ultracapacitor of claim 15, wherein the first thickness is greater than 10 percent greater than the second thickness.

17. An ultracapacitor, comprising:

a first current collector and a second current collector;

a positive electrode electrically coupled to the first current collector;

a negative electrode electrically coupled to the second current collector, wherein at least one of the positive electrode and the negative electrode comprises a treated carbon material having about 10% to about 60% less of at least one functional group on a surface of the treated carbon material than untreated carbon material;

a separator positioned between the positive electrode and the negative electrode;

an electrolyte in ionic contact with the positive electrode and the negative electrode; and

a housing assembly holding the positive electrode, the negative electrode, the separator, and the electrolyte, wherein the ultracapacitor is configured to operate at 3 volts or more at 65 ℃ and maintain greater than 80% of its initial capacitance for more than 1500 hours.

18. The ultracapacitor of claim 17, wherein the ultracapacitor is further capable of operating greater than 10 at 25 degrees celsius⁶Cycle life of one cycle.

19. The ultracapacitor of claim 17, wherein the ultracapacitor is capable of operating at 65 ℃ for a cycle life of greater than 500k cycles.

20. The ultracapacitor of claim 17, wherein the electrolyte comprises a quaternary ammonium salt.

21. The supercapacitor of claim 20 wherein said quaternary ammonium salt comprises a cation selected from the group consisting of: spiro- (1,1') -bipyrrolidinium, triethylmethylammonium and tetraethylammonium.

22. The ultracapacitor of claim 20, wherein the quaternary ammonium salt comprises an anion selected from the group consisting of: tetrafluoroborate and iodide.

23. The ultracapacitor of claim 17, wherein the electrolyte comprises acetonitrile.

24. The ultracapacitor of claim 17, wherein a salt concentration of the electrolyte is between 0.7 moles/l (M) and 1.0M.

25. The ultracapacitor of claim 17, wherein the positive electrode comprises a first thickness and the negative electrode comprises a second thickness, wherein the first thickness of the positive electrode is greater than the second thickness of the negative electrode.

26. The ultracapacitor of claim 25, wherein the first thickness is greater than 10 percent greater than the second thickness.

27. The supercapacitor of claim 17 wherein the positive electrode or the negative electrode comprises a treated carbon material having 30% fewer hydrogen-containing functional groups than an untreated carbon material.

28. An ultracapacitor, comprising:

a first current collector and a second current collector;

a positive electrode electrically coupled to the first current collector;

a negative electrode electrically coupled to the second current collector, wherein at least one of the positive electrode and the negative electrode comprises a treated carbon material having at least one functional group on a surface of the treated carbon material, less than about 1% of the functional groups containing hydrogen, less than about 0.5% of the functional groups containing nitrogen, or less than about 5% of the functional groups containing oxygen;

a separator positioned between the positive electrode and the negative electrode;

an electrolyte in ionic contact with the positive electrode and the negative electrode; and

a housing assembly holding the positive electrode, the negative electrode, the separator, and the electrolyte, wherein the ultracapacitor is capable of operating at 3 volts at a temperature of 65 ℃ or greater while maintaining less than 200% of its initial equivalent series resistance for more than 1500 hours.

29. The ultracapacitor of claim 28, wherein the ultracapacitor is capable of operating at 65 ℃ for a cycle life of greater than 500k cycles.

30. The ultracapacitor of claim 28, wherein the positive electrode comprises a first thickness and the negative electrode comprises a second thickness, wherein the first thickness of the positive electrode is greater than the second thickness of the negative electrode.

31. The ultracapacitor of claim 30, wherein the first thickness is greater than 10 percent greater than the second thickness.

32. The supercapacitor of claim 28 wherein said positive electrode or said negative electrode comprises a treated carbon material having less than 1% hydrogen-containing functional groups.

33. The supercapacitor of claim 28 wherein the positive electrode or the negative electrode comprises a treated carbon material having less than 5% oxygen-containing functional groups.

34. The supercapacitor of claim 28 wherein said positive electrode or said negative electrode comprises a treated carbon material having less than 0.5% nitrogen-containing functional groups.

35. An ultracapacitor, comprising:

a first current collector and a second current collector;

a positive electrode electrically coupled to the first current collector;

a negative electrode electrically coupled to the second current collector;

a separator positioned between the positive electrode and the negative electrode;

an electrolyte in ionic contact with the positive electrode and the negative electrode, wherein the electrolyte comprises less than 1M salt; and

a housing assembly holding the positive electrode, the negative electrode, the separator, and the electrolyte, wherein the ultracapacitor is configured to operate at about 2.8 volts to about 3 volts, and,

wherein the ultracapacitor is further configured to operate at 65 ℃ for a cycle life of greater than 500k cycles.

36. The supercapacitor of claim 35 wherein said quaternary ammonium salt comprises a cation selected from the group consisting of: spiro- (1,1') -bipyrrolidinium, triethylmethylammonium and tetraethylammonium.

37. The ultracapacitor of claim 35, wherein the quaternary ammonium salt comprises an anion selected from the group consisting of: tetrafluoroborate and iodide.

38. The ultracapacitor of claim 35, wherein the electrolyte further comprises acetonitrile.

39. The ultracapacitor of claim 35, wherein a salt concentration of the electrolyte is about 0.8M.

40. The ultracapacitor of claim 35, wherein the positive electrode and the negative electrode each independently comprise a dry electrode film comprising carbon and a binder.

41. The ultracapacitor of claim 35, wherein the ultracapacitor is configured to operate at 3 volts or more at 65 ℃ and maintain greater than 80% of its initial capacitance for more than 1500 hours.

42. The ultracapacitor of claim 35, wherein the ultracapacitor is capable of operating at 3 volts at a temperature of 65 ℃ or greater while maintaining less than 200 percent of its initial equivalent series resistance for more than 1500 hours.