Composite electrode

This application claims the benefit of U.S. Provisional Patent Application No. 62/429,727, entitled Composite Electrode, filed December 2, 2016, the entirety of which is incorporated herein by reference.

Carbon nanotubes (hereafter referred to as CNTs) are carbon structures that exhibit a variety of properties, many of which suggest opportunities for improvement in a variety of technology areas. These areas include electronic materials, optical materials, and conductive and other materials. For example, CNTs have been shown to be useful for energy storage in capacitors.

However, CNTs are typically expensive to produce and present special challenges in electrode manufacturing. Thus, there is a need for electrode materials that exhibit the advantageous properties of CNTs while reducing the amount of CNTs contained in the material.

Applicants have developed composite electrode structures that exhibit advantageous properties, in some embodiments, the electrodes exhibit the advantageous properties of CNTs while mitigating the amount of CNTs contained in the material, e.g., less than 10% by weight.

Electrodes of the type described herein can be used in ultracapacitors to provide high performance (e.g., high operating voltage, high operating temperature, high energy density, high power density, low equivalent series resistance, etc.).

In one embodiment, a device is disclosed that includes an active storage layer including a network of carbon nanotubes defining spaces and a carbonaceous material disposed in the spaces and bounded by the network of carbon nanotubes, the active layer configured to provide energy storage.

In some embodiments, the active layer is substantially free of binders. In some embodiments, the active layer consists essentially or otherwise of carbonaceous material. In some embodiments, the active layer is bonded by electrostatic forces between the carbon nanotubes and the carbonaceous material. In some embodiments, the carbonaceous material comprises activated carbon.

In some embodiments, the carbonaceous material comprises nano forms of carbon other than carbon nanotubes.

In some embodiments, the carbon nanotube network comprises less than 50% by weight of the active layer, less than 10% by weight of the active layer, less than 5% by weight of the active layer, or less than 1% by weight of the active layer.

Some embodiments include an adhesion layer, such as, for example, a layer consisting essentially or otherwise of carbon nanotubes, hi some embodiments, the adhesion layer is disposed between the active layer and the conductive layer.

In some embodiments, the surface of the conductive layer facing the adhesive layer comprises a rough or textured portion. In some embodiments, the surface of the conductive layer facing the adhesive layer comprises a nanostructured portion. In some embodiments, the nanostructured portion comprises a carbide nanowhisker. These nanowhiskers are thin elongated structures (e.g., nanorods) that generally extend from the surface of the conductive layer 102. The nanowhiskers have a radial thickness of 100 nm, 50 nm, 25 nm, 10 nm or less, such as in the range of 1 nm to 100 nm, or any subrange thereof. The nanowhiskers have a longitudinal length that is several times their radial thickness, such as 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 1 μm, 5 μm, 10 μm or more, such as in the range of 20 nm to 100 μm, or any subrange thereof.

In some embodiments, the active layer is annealed to reduce the presence of impurities.

In some embodiments, the active layer is compressed to deform at least a portion of the carbon nanotube network and the carbonaceous material.

Some embodiments include an electrode comprising an active layer. Some embodiments include an ultracapacitor comprising the electrode. In some embodiments, the ultracapacitor has an operating voltage of 1.0V, 2.0V, 2.5V, 3.0V, 3.1V, 3.2V, 3.5V, 4.0V or greater.

In some embodiments, the ultracapacitor has a lifespan of at least 1000 hours at a maximum operating temperature of at least 250° C. and an operating voltage of at least 1.0V. In some embodiments, the ultracapacitor has a lifespan of at least 1000 hours at a maximum operating temperature of at least 250° C. and an operating voltage of at least 2.0V. In some embodiments, the ultracapacitor has a lifespan of at least 1000 hours at a maximum operating temperature of at least 250° C. and an operating voltage of at least 3.0V. In some embodiments, the ultracapacitor has a lifespan of at least 1000 hours at a maximum operating temperature of at least 250° C. and an operating voltage of at least 4.0V. In some embodiments, the ultracapacitor has a lifespan of at least 1000 hours at a maximum operating temperature of at least 300° C. and an operating voltage of at least 1.0V. In some embodiments, the ultracapacitor has a lifespan of at least 1000 hours at a maximum operating temperature of at least 300° C. and an operating voltage of at least 2.0V. In some embodiments, the ultracapacitor has a lifespan of at least 1000 hours at a maximum operating temperature of at least 300° C. and an operating voltage of at least 3.0V. In some embodiments, the ultracapacitor has a life span of at least 1000 hours at a maximum operating temperature of at least 300° C. and an operating voltage of at least 4.0V.

In another aspect, a method includes dispersing carbon nanotubes in a solvent to form a dispersion, mixing the dispersion with a carbonaceous material to form a slurry, applying the slurry to a layer, and drying the slurry to substantially remove the solvent to form an active layer comprising a network of carbon nanotubes defining voids and a carbonaceous material disposed in the voids and bound by the network of carbon nanotubes. Some embodiments include forming or applying the layer of carbon nanotubes and providing an adhesion layer on the conductive layer.

In some embodiments, the applying step includes applying a slurry onto the adhesive layer.

Various embodiments may include any of the elements or features described herein, either alone or in any suitable combination.

<figref num="1">FIG. 2 is a schematic diagram of an electrode.</figref><figref num="2">1 is a detailed view depiction of the active layer of an electrode.</figref><figref num="3">FIG. 2 is a schematic diagram of a two-side electrode.</figref><figref num="4">1 is a flow chart illustrating a method of making an active layer of an electrode.</figref><figref num="5">1 is a flow chart illustrating a method of creating an adhesion layer on an electrode.</figref><figref num="6">FIG. 1 is a schematic diagram of a typical mixing device.</figref><figref num="7A">FIG. 1 is a schematic diagram of a coating apparatus featuring a slot die.</figref><figref num="7B">FIG. 1 is a schematic diagram of a coating apparatus featuring a doctor blade.</figref><figref num="8A">1 is a schematic diagram of an ultracapacitor.</figref><figref num="8B">FIG. 1 is a schematic diagram of an ultracapacitor without a separator.</figref>

With reference to FIG. 1 , an exemplary embodiment of an electrode 100 is disclosed for use in an energy storage device, such as an ultracapacitor or a battery. The electrode includes a conductive layer 102 (also referred to herein as a current collector), an adhesion layer 104, and an active layer 106. When used in an ultracapacitor of the type described herein, the active layer 106 functions as an energy storage medium, for example, by providing a surface interface to an electrolyte (not shown) in the form of an electric double layer (often referred to in the art as a Helmholtz layer). In some embodiments, the adhesion layer 104 can be omitted, for example, if the active layer 106 exhibits good adhesion to the conductive layer 102.

In some embodiments, the active layer 106 is thicker than the adhesive layer 104, e.g., 1.5, 2.0, 5.0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 500, 1000 times or even greater than the thickness of the adhesive layer 104. For example, in some embodiments, the thickness of the active layer 106 is in the range of 1.5 to 1000 times (or any subrange thereof, e.g., 5 to 100 times) the thickness of the adhesive layer 104. For example, in some embodiments, the active layer 106 has a thickness in the range of 0.5 to 2500 μm or any subrange thereof, e.g., 5 μm to 150 μm. In some embodiments, the adhesive layer 104 has a thickness in the range of 0.5 μm to 50 μm or any subrange thereof, e.g., 1 μm to 5 μm.

With reference to FIG. 2, in some embodiments, the active layer 106 is comprised of a carbonaceous material 108 (e.g., activated carbon) bound by a matrix 110 of CNTs 112 (e.g., a web or network formed of CNTs). In some embodiments, the CNTs 112 forming the matrix 110 lie primarily parallel to the major surfaces of the active layer 106, for example when the length of the CNTs is longer than the thickness of the active layer 106. As shown, the CNTs 112 form straight segments, but in some embodiments, when long CNTs are used, some or all of the CNTs instead have a curved, snake-like shape. For example, in cases where the carbonaceous material 108 comprises clumps of activated carbon, the CNTs 112 can bend and wrap around between the clumps.

In some embodiments, the active layer is substantially free of other bonding materials, such as, for example, polymeric materials, adhesives, etc. In other words, in such embodiments, the active layer is substantially free of any material other than carbon. For example, in some embodiments, the active layer is at least about 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, 99.999% or more by weight elemental carbon. Despite this, the matrix 110 is operated in combination with the carbonaceous material 108 to maintain the structural integrity of the active layer 106 without, for example, flaking, delaminating, pulverizing, etc.

Substantially any<u style="Single">Non</u>It has been found that using an active layer free of carbon impurities enhances the performance of the active layer in the presence of high voltage differentials, high temperatures, or both. Without wishing to be bound by theory, it is believed that the absence of impurities prevents the occurrence of undesired chemical side reactions that are promoted under other high temperature or high voltage conditions.

As noted above, in some embodiments, a carbon nanotube matrix 110 provides a structural framework for an active layer 106, with the carbonaceous material 108 filling the spaces between the CNTs 112 of the matrix 110. In some embodiments, electrostatic forces (e.g., van der Waals forces) between the CNTs 112 within the matrix 110 and between the matrix 112 and other carbonaceous materials 108 provide substantially all of the binding forces that maintain the structural integrity of the layer.

In some embodiments, the CNTs 112 can include single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), or multi-walled nanotubes (MWNTs), or a mixture thereof. Although a matrix 110 of individual CNTs 112 is shown, in some embodiments, the matrix includes interconnected bundles, clusters, or aggregates of CNTs. For example, in some embodiments where the CNTs are initially formed vertically aligned, the matrix is composed of at least a portion of brush-like bundles of aligned CNTs.

To provide some background for the teachings herein, reference is first made to U.S. Patent No. 7,897,209, entitled "Apparatus and Method for Producing Aligned Carbon Nanotube Aggregates." The aforementioned patent ("the '209 patent") teaches a process for producing aligned carbon nanotube aggregates. Thus, the teachings of the '209 patent, which is one example of a technique for producing CNTs in the form of aligned carbon nanotube aggregates, can be used to collect the CNTs referred to herein. Advantageously, the teachings of the '209 patent can be used to obtain long CNTs with high purity. In other embodiments, other suitable methods known in the art for producing CNTs can be used.

In some embodiments, the active layer 106 can then be formed. A first solution (also referred to herein as a slurry) is provided that includes a solvent and a dispersion of carbon nanotubes, e.g., vertically aligned carbon nanotubes. A second solution (also referred to herein as a slurry) is provided that includes a solvent that includes carbon dispersed in the solvent. The carbon additive includes at least one form of material that is substantially carbon. Exemplary forms of the carbon additive include at least one of, e.g., activated carbon, carbon powder, carbon fiber, rayon, graphene, aerogel, nanohorns, carbon nanotubes, and the like. While in some embodiments, the carbon additive is formed substantially of carbon, it is recognized that in alternative embodiments, the carbon additive may include at least some impurities, e.g., additives included by design.

In some embodiments, forming the first and/or second solution includes introducing mechanical energy to mix the solvent and the carbon material, for example using an ultrasonic disintegrator (sometimes referred to as a sonifier) or other suitable mixing device (e.g., a high shear mixer). In some embodiments, the mechanical energy introduced into the mixture per kilogram of mixture is at least 0.4 kWh/kg, 0.5 kWh/kg, 0.6 kWh/kg, 0.7 kWh/kg, 0.8 kWh/kg, 0.9 kWh/kg, 1.0 kWh/kg, or more. For example, the mechanical energy introduced into the mixture per kilogram of mixture is in the range of 0.4 kWh/kg to 1.0 kWh/kg, or any sub-range therein, such as, for example, 0.4 kWh/kg to 0.6 kWh/kg.

In some embodiments, the solvent used comprises an anhydrous solvent, for example, the solvent comprises at least one of ethanol, methanol, isopropyl alcohol, dimethylsulfoxide, dimethylformamide, acetone, acetonitrile, and the like.

As described above, the two solutions are subjected to "sonication" (a physical effect achieved by an ultrasonic field). For the first solution, sonication is generally performed for a period of time suitable to loosen, fluff, and otherwise analyze the carbon nanotubes. For the second solution, sonication is generally performed for a period of time suitable to ensure good dispersion or mixing of the carbon additive within the solvent. In some embodiments, other techniques for imparting mechanical energy to the mixture are used in addition to or instead of sonication, such as physical mixing using stirring or impellers.

Once one or both of the first and second solutions have been properly sonicated, they are then mixed to provide a combined solution, which is again sonicated. Typically, the combined mixture is sonicated for a period of time suitable to ensure good mixing of the carbon nanotubes with the carbon additive. This second mixing (followed by suitable coating and drying steps as described below) results in the formation of an active layer 106 comprising a matrix 110 of CNTs 112 with the carbon additive providing a carbonaceous material 108 that fills the voids of the matrix 110.

In some embodiments, mechanical energy is introduced into the blended mixture using an ultrasonic disintegrator (sometimes called a sonifier) or other suitable mixing device (e.g., a high shear mixer). In some embodiments, the mechanical energy introduced into the mixture per kilogram of mixture is at least 0.4 kWh/kg, 0.5 kWh/kg, 0.6 kWh/kg, 0.7 kWh/kg, 0.8 kWh/kg, 0.9 kWh/kg, 1.0 kWh/kg, or greater. For example, the mechanical energy introduced into the mixture per kilogram of mixture is in the range of 0.4 kWh/kg to 1.0 kWh/kg, or any subrange therein, such as, for example, 0.4 kWh/kg to 0.6 kWh/kg.

In some embodiments, the combined slurry is wet cast directly onto the adhesive layer 104 or the conductive layer 102 and dried (e.g., by applying heat or vacuum or both) until substantially all of the solvent and other liquids have been removed, thereby forming the active layer 106. In some such embodiments, it may be desirable to protect various portions of the underlying layer (e.g., the underside of the conductive layer 102 when the current collector is subject to two-sided operation) from the solvent, for example, by masking certain areas or providing drainage paths to direct the solvent.

In other embodiments, the mixed slurry is dried elsewhere and then transferred onto the adhesive layer 104 or conductive layer 102 using other suitable techniques (e.g., roll-to-roll layer application) to form the active layer 106. In some embodiments, the wet mixed slurry is placed onto a suitable surface and dried to form the active layer 106. Any material deemed suitable may be used for the surface, but an exemplary material includes PTFE because its properties facilitate its subsequent removal from the surface. In some embodiments, the active layer 106 is formed in a press to provide a layer exhibiting a desired thickness, area, and density.

In some embodiments, the average length of the CNTs 112 forming the matrix 110 is at least 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 7000 μm, 800 μm, 900 μm, 1000 μm, or more. For example, in some embodiments, the average length of the CNTs 112 forming the matrix 110 is in the range of 1 μm to 1000 μm, or any subrange therein, such as, for example, 1 μm to 600 μm. In some embodiments, 50%, 60%, 70%, 80%, 90%, 95%, 99% or more of the CNTs 112 are within 10% of the average length of the CNTs 112 that make up the matrix 110.

In various embodiments, the other carbonaceous materials 108 can include various forms of carbon, including activated carbon, carbon black, graphite, etc. The carbonaceous materials can include carbon particles including, for example, nanotubes, nanorods, sheet graphene, flake, or curved flake morphologies, and/or nanoparticles in morphologies such as cones, rods, spheres (C60 structural molecules), etc.

Applicants have found the unexpected result that active layers of the type herein can provide exemplary performance (e.g., high conductivity, low resistance, high voltage performance, and high energy and power density) even when the mass fraction of CNTs in the layer is fairly low. For example, in some embodiments, the active layer is at least about 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5% or even more elemental carbon by weight in a form other than CNTs (e.g., activated carbon). In particular, in certain applications, including high performance ultracapacitors, active layers 106 that are in the range of 95% to 99% activated carbon (with the remainder CNTs 112) have been shown to exhibit excellent performance.

In some embodiments, the matrix 110 of CNTs 112 forms an interconnected network of highly conductive paths for electrical current (e.g., ionic conduction) through the active layer 106. For example, in some embodiments, the highly conductive junctions occur at the points where the CNTs 112 of the matrix 110 cross each other or are close enough together to allow quantum tunneling of charge carriers (e.g., ions) from one CNT to the next. While the active layer is composed of a relatively low mass percentage of CNTs 112 (e.g., 10 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, or less, e.g., in the range of 0.5 wt% to 10 wt%, or any subrange thereof, e.g., 1 wt% to 5.0 wt%), the interconnected network of highly conductive paths formed in the matrix 110 can provide long conductive paths (e.g., conductive paths on the order of the thickness of the active layer 106) that facilitate electrical current in and through the active layer 106.

For example, in some embodiments, the matrix 110 includes one or more structures of interconnected CNTs, the structures having an overall length along one or more dimensions that is greater than 2, 3, 4, 5, 10, 20, 50, 100, 500, 1000, 10000, or more times the average length of the constituent CNTs that make up the structure. For example, in some embodiments, the matrix 110 includes one or more structures of interconnected CNTs, the structures having an overall length that is 2 to 10000 times (or any subrange thereof) the average length of the constituent CNTs that make up the structure. For example, in some embodiments, the matrix 110 can include highly conductive paths having lengths of 100 μm, 500 μm, 1000 μm, 10000 μm, or more, such as in the range of 100 μm-10000 μm, and any subrange thereof.

As used herein, the term "highly conductive path" should be understood as a path formed by interconnected CNTs that has a higher electrical conductivity than that of other carbonaceous material 108 (e.g., activated carbon) that surrounds the matrix 110 of CNTs 112.

Without wishing to be bound by theory, in some embodiments, the matrix 110 can be characterized as a conductive interconnected network of CNTs that exhibits connectivity above a percolation threshold. The percolation threshold is a mathematical concept related to percolation theory, which is a form of long-range connectivity in a random organization. Below the threshold, so-called "giant" connected components of the order of the system size do not exist, while above it, giant components of the order of the system size exist.

In some embodiments, the percolation threshold is determined by measuring the conductivity of the layer while increasing the mass fraction of CNTs 112 in the active layer 106, holding all other properties of the layer constant. In some such cases, the threshold is identified as the mass fraction at which the conductivity of the layer shows a sharp increase and/or a greater mass fraction at which the conductivity of the layer increases only slowly with increasing addition of further CNTs. Such behavior indicates that a threshold is crossed that is required for the formation of an interconnected CNT structure that provides a conductive path with a length on the order of magnitude of the active layer 106.

Returning to FIG. 1 , in some embodiments, one or both of the active layer 106 and the adhesion layer 104 are treated by applying heat to remove impurities (e.g., functional groups on the CNTs, and e.g., moisture, oxides, halides, etc.). For example, in some embodiments, one or both of the layers can be heated to at least 100° C., 150° C., 200° C., 250° C., 300° C., 350° C., 400° C., 450° C., 500° C., or higher for at least 1 minute, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 12 hours, 24 hours, or more. For example, in some embodiments, the layers are treated to reduce the moisture in the layers to less than 1000 ppm, 500 ppm, 100 ppm, 10 ppm, 1 ppm, 0.1 ppm, or less.

Returning to FIG. 1 , in some embodiments, adhesion layer 104 is formed with carbon nanotubes. For example, in some embodiments, adhesion layer 104 is at least about 50%, 75%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, 99.999% CNTs by weight. In some embodiments, the CNTs are grown directly on conductive layer 102 using chemical vapor deposition techniques, such as those described in U.S. Patent Publication No. 20150210548, published July 30, 2015, entitled In-Line Production of Carbon Nanotubes. In some embodiments, the CNTs are transferred onto the conductive layer 102 using a wet or dry transfer process, for example of the type described in U.S. Patent Publication No. 20150279578, entitled "High Power and High Energy Electrodes Using Carbon Nanotubes," published Oct. 1, 2015. In some embodiments, the adhesion layer 104 adheres to the upper active layer 106 using substantially only electrostatic forces (e.g., van der Waals attractions) between the CNTs of the adhesion layer 104 and the carbon material and CNTs of the active layer 106.

In some embodiments, the CNTs of the adhesion layer 104 can include single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), or multi-walled nanotubes (MWNTs), or a mixture thereof. In some embodiments, the CNTs are vertically aligned. In one particular embodiment, the CNTs of the adhesion layer 104 are primarily or entirely SWNTs and/or DWNTs, while the CNTs of the active layer 106 are primarily or entirely MWNTs. For example, in some embodiments, the CNTs of the adhesion layer 104 are at least 75%, at least 90%, at least 95%, at least 99% or more SWNTs or at least 75%, at least 90%, at least 95%, at least 99% or even more DWNTs. In some embodiments, the CNTs of the active layer 106 are at least 75%, at least 90%, at least 95%, at least 99% or more MWNTs.

In some embodiments, adhesion layer 104 is formed by applying pressure to a layer of carbonaceous material. In some embodiments, this compression process alters the structure of adhesion layer 104 in a manner that promotes adhesion to active layer 106. For example, in some embodiments, pressure is applied to a layer comprising a vertically aligned array of CNTs or a collection of vertically aligned CNTs, thereby deforming or breaking the CNTs.

In some embodiments, the adhesion layer is formed by casting a wet slurry of CNTs (with or without additional carbon) mixed in a solvent onto the conductive layer 102. In various embodiments, similar techniques are used to form the active layer 106 from the wet slurry to those described above.

In some embodiments, mechanical energy is introduced into the wet slurry using an ultrasonic disintegrator (sometimes referred to as a sonifier) or other suitable mixing device (e.g., a high shear mixer). In some embodiments, the mechanical energy introduced into the mixture per kilogram of mixture is at least 0.4 kWh/kg, 0.5 kWh/kg, 0.6 kWh/kg, 0.7 kWh/kg, 0.8 kWh/kg, 0.9 kWh/kg, 1.0 kWh/kg, or greater. For example, the mechanical energy introduced into the mixture per kilogram of mixture is in the range of 0.4 kWh/kg to 1.0 kWh/kg, or any subrange therein, such as, for example, 0.4 kWh/kg to 0.6 kWh/kg.

In some embodiments, the percentage of solid carbon in the wet slurry is less than 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1% or less by weight, such as in the range of 0.1% to 10% by weight or any subrange such as, for example, 0.1% to 2% by weight.

In various embodiments, the conductive layer 102 is made of a suitable conductive material, such as, for example, a metal foil (e.g., aluminum foil). In some embodiments, the surface of the conductive layer 102 is roughened, patterned, or otherwise textured, for example, to promote adhesion to the adhesion layer 104 and to promote good electrical conductivity from the active layer 106. For example, in some embodiments, the conductive layer is, for example, etched (mechanically or chemically). In some embodiments, the conductive layer 102 has a thickness in the range of 1 μm to 1000 μm, or any subrange thereof, for example, 5 μm to 50 μm.

In some embodiments, the conductive layer 102 includes a nanostructured surface. For example, as described in International Patent Publication No. 2016/057983, published April 14, 2016, entitled "Nanostructured Electrodes in Energy Storage Devices," the conductive layer has a top surface that includes nanoscale features, such as whiskers (e.g., carbide whiskers), that promote adhesion to the adhesion layer 104 and promote good electrical conductivity from the active layer 106. An exemplary current collector is a commercially available current collector from Toyo Aluminum Co., Ltd., under the trade name TOYAL-CARBO.

In some embodiments, one or both of the active layer 106 and the adhesion layer 104 are treated by applying heat and/or vacuum to remove impurities (e.g., impurities such as CNT functional groups, moisture, oxides, halides, etc.).

In some embodiments, one or both of the active layer 106 and adhesion layer 104 are compressed, e.g., to break some of the constituent CNTs or other carbonaceous materials, to increase the surface area of each layer. In some embodiments, this compression process increases one or more of the adhesion between the layers, the ion transport rate within the layers, and the surface area of the layers. In various embodiments, compression can be applied before or after each layer is applied and formed into the electrode 100.

In some embodiments, the adhesion layer 104 may be eliminated such that the active layer 106 is disposed directly on the conductive layer 102 .

3, in some embodiments, the electrode 100 may be double-sided, with an adhesion layer 104 and an active layer 106 formed on each of two opposing major surfaces of the conductive layer 102. In some embodiments, the adhesion layer 104 may be omitted on one or both sides of the two-sided electrode 100.

With reference to FIG. 4, an exemplary embodiment of a method 200 for making the active layer 106 of the electrode 100 is described. In step 201, CNTs are dispersed in a solvent to form a dispersion of CNTs. In some embodiments, the dispersion can be formed using any of the techniques described in U.S. Patent Publication No. 20150279578, entitled "High Power and High Energy Electrodes Using Carbon Nanotubes," published October 1, 2015, including agitation, sonication, or a combination of the two. In various embodiments, any suitable solvent can be used, including, for example, ethanol, methanol, isopropyl alcohol, dimethylsulfoxide, dimethylformamide, acetone, acetonitrile, and the like. In general, it is advantageous to choose a solvent that will be substantially eliminated in the drying step 204 described below, for example, using heat and/or vacuum drying techniques.

In some embodiments, the mixture of CNTs and solvent is passed through a filter, such as an array of microchannels (e.g., having channels with diameters on the order of the radius of the CNTs), to help physically separate the CNTs and facilitate dispersion.

In some embodiments, the CNT dispersion can be formed without added surfactants, for example, to avoid the presence of impurities from these surfactants upon completion of method 200.

In step 202, the CNT dispersion is mixed with a carbonaceous material (e.g., activated carbon) to form a slurry. In some embodiments, the slurry can be formed using any of the techniques described in U.S. Patent Publication No. 20150279578, published October 1, 2015, including stirring, sonication, or a combination of the two. In some embodiments, the slurry has a percentage of solid carbon less than 20%, 15%, 10%, 5%, 2%, 1% or even less by weight, such as in the range of 1% to 20% by weight, or any subrange thereof, such as 4% to 6%. The mass ratio of CNTs to other carbonaceous materials in the slurry is less than or equal to 1:5, 1:10, 1:15, 1:20, 1:50, 1:100, in the range of 1:10 to 1:20, or any subrange thereof.

In step 203, the slurry is applied to the adhesive layer 104, or to the conductive layer 102 of the electrode 100 if the adhesive layer 104 has been removed. In some embodiments, the slurry is formed into a sheet and coated onto the electrode. For example, in some embodiments, the slurry is applied by a slot die to control the thickness of the applied layer. In other embodiments, the slurry is applied to the conductive layer 102 and then leveled to the desired thickness using, for example, a doctor blade.

In some embodiments, the slurry is compressed (e.g., with a calendaring device) before or after it is applied to the electrode 100. In some embodiments, the slurry is partially or completely dried (e.g., by applying heat, vacuum, or a combination thereof) during this step 203.

In step 204, if the slurry was not dried or was only partially dried during step 203, the slurry to be applied to the electrode is thoroughly dried (e.g., by applying heat, vacuum, or a combination thereof). In some embodiments, substantially all of the solvent (and other non-carbonaceous materials, such as, for example, dispersion materials) is removed from the active layer 106. In some embodiments, if impurities remain after the drying step, and an additional step of heating the layer (e.g., baking or annealing) is performed. For example, in some embodiments, one or both of the active layer 106 and the adhesion layer 104 are treated by applying heat to remove impurities (e.g., functional groups of the CNTs, and impurities such as, for example, moisture, oxides, halides, etc.).

With reference to FIG. 5, an exemplary embodiment of a method 300 for making the adhesion layer 104 of the electrode 100 is described. In step 301, CNTs are dispersed in a solvent to form a dispersion of CNTs. In some embodiments, the dispersion can be formed using any of the techniques described in U.S. Patent Publication No. 20150279578, published October 1, 2015, including stirring, sonication, or a combination of the two. In various embodiments, any suitable solvent can be used, including organic solvents such as isopropyl alcohol, acetonitrile, propylene carbonate, and the like. In general, it is advantageous to choose a solvent that will be substantially eliminated in the drying step 304 described below.

In some embodiments, the mixture of CNTs and solvent is passed through a filter, such as an array of microchannels (e.g., having channels with diameters on the order of the radius of the CNTs), to help physically separate the CNTs and facilitate dispersion.

In some embodiments, the CNT dispersion can be formed without added surfactants, for example, to avoid the presence of impurities from these surfactants upon completion of method 300.

In step 302, the CNT dispersion is optionally mixed with additional carbonaceous material (e.g., activated carbon) to form a slurry. In some embodiments, the additional carbonaceous material is omitted, such that the slurry is comprised of CNTs dispersed in a solvent. In some embodiments, the slurry has a percent solids of less than 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, 0.5 wt%, 0.1 wt%, or less, in the range of 0.1 to 5 wt%, or any sub-range therebetween.

In step 303, the slurry is applied to the conductive layer 102 of the electrode 100. In some embodiments, the slurry is coated onto the electrode. For example, in some embodiments, the slurry is applied by a slot die to control the thickness of the applied layer. In other embodiments, the slurry is applied to the conductive layer 102 and then leveled to a desired thickness using, for example, a doctor blade.

In some embodiments, the slurry is compressed (e.g., with a calendaring device) before or after it is applied to the electrode 100. In some embodiments, the slurry is partially or completely dried (e.g., by applying heat, vacuum, or a combination thereof) during this step 303.

In step 304, if the slurry was not dried or was only partially dried during step 203, the slurry to be applied to the electrode is thoroughly dried (e.g., by applying heat, vacuum, or a combination thereof). In some embodiments, substantially all of the solvent (and other non-carbonaceous materials, such as, for example, dispersion materials) is removed from the active layer 106. In some embodiments, if impurities remain after the drying step, an additional step of heating the layer (e.g., baking or annealing) is performed. For example, in some embodiments, one or both of the active layer 106 and the adhesion layer 104 are treated by applying heat to remove impurities (e.g., functional groups of the CNTs, and impurities such as, for example, moisture, oxides, halides, etc.).

In some embodiments, the method 300 for forming the adhesion layer 104 and the method 200 for forming the active layer 106 are performed in sequence such that the adhesion layer 104 is subsequently formed followed by the overlying active layer 106. In some embodiments, the foregoing methods can be repeated to form a two-sided electrode, for example of the type described herein.

Advantageously, in some embodiments, the method 300 of forming the adhesion layer 104 and/or the method 200 of forming the active layer 106 can be performed as a roll-to-roll process to enable mass production of electrode sheets, e.g., tens of meters or more in length.

6 illustrates an exemplary mixing apparatus 400 for performing the method 300 of forming the adhesion layer 104 and/or the method 200 of forming the active layer 106. For simplicity, the apparatus 400 is described for use in forming the active layer 106 using the method 200. However, as will be apparent to one of ordinary skill in the art, the apparatus 400 can be readily adapted to perform the method 300 of forming the adhesion layer 104.

Apparatus 400 includes a mixing vessel 401. The mixing vessel receives a slurry comprised of a solvent, carbon nanotubes, and (optionally) additional carbonaceous material of the type described above. In some embodiments, this slurry (or components thereof) is first formed in mixing vessel 401. In other embodiments, the slurry is transferred to mixing vessel 401 after being formed elsewhere.

In some embodiments, the mixing vessel 401 includes one or more mechanisms for mixing the slurry, such as, for example, an impeller or a high shear mixer. In some embodiments, a mixing mechanism is provided that can agitate the slurry at a controlled rate, for example, up to 1000 revolutions per minute (RPM) or more. In some embodiments, the mixing vessel can include one or more devices for imparting mechanical energy to the slurry, such as, for example, an ultrasonic disintegrator, a mixer (e.g., a high shear mixer), a homogenizer, or other suitable devices known in the art. In some embodiments, the mixing vessel is temperature controlled using one or more heating and/or cooling elements, such as, for example, electric heaters, tubes for circulating cooling water, or other such devices known in the art.

The slurry in the mixing vessel 401 is circulated through a flow line 402, such as a pipe or tube, using a pump 403. The pump 403 can be of any suitable form, such as a peristaltic pump. A flow meter 404 is provided for measuring the flow rate of the slurry through the flow line 402. A filter 405 is provided for filtering the slurry flowing through the flow line 402, for example to remove agglomerates of solid material having a size greater than a desired threshold.

In some embodiments, for example when mixing vessel 401 does not include a sonicator, an in-line sonicator 406 is provided for ultrasonic disintegration of the slurry flowing through flow line 402. For example, in some embodiments, a flow through sonicator such as a Branson Digital SFX-450 Sonicator available from Thomas Scientific, 1654 High Hill Road, Swedesboro, NJ 08085, USA, is used.

In some embodiments, a temperature control device 407 , such as a heat exchanger arranged in a sleeve disposed around flow line 402 , is provided to control the temperature of the slurry flowing through flow line 402 .

In some embodiments, a valve 408 is provided that is selectively controlled to direct a first portion of the slurry flowing through flow line 402 to be recirculated back to mixing vessel 401, while a second portion can be output externally, such as to coating apparatus 500. In some embodiments, a sensor 409, such as a pressure sensor or a flow sensor, is provided to sense one or more aspects of the slurry output.

In various embodiments, any or all of the elements of the apparatus 400 are operatively connected to one or more computing devices to provide automated monitoring and/or control of the blending apparatus 400. For example, the sonicator 406 includes digital controls to control its operating parameters, such as power and duty cycle.

In various embodiments, the coating apparatus 500 is of any suitable type known in the art. For example, FIG. 7A shows an exemplary embodiment of a coating apparatus 500 featuring a slot die 501 that distributes a slurry received from a source, such as a mixer 400, through a distribution channel 502 onto a substrate 503 (e.g., a conductive layer 102, either bare or already coated with an adhesive layer 104) moving across a roller 504. By setting the height of the slot die above the substrate 503 on the roller 504 and controlling the flow rate and pressure of the slurry in the channel 502, the thickness and density of the applied coating can be controlled. In some embodiments, the channel 502 may include one or more reservoirs to help ensure a constant flow of the slurry to provide a uniform coating during operation.

FIG. 7B shows an exemplary embodiment of a coating apparatus 500 featuring a doctor blade 601 that levels slurry received from a source such as a mixing apparatus 400 that is applied by one or more applicators 602 (one shown) on a substrate 603 (e.g., a conductive layer 102 that is bare or already coated with an adhesive layer 104) moving across a roller 604. The direction of movement of the substrate 603 is indicated by a thick black arrow. By setting the height of the doctor blade 601 above the substrate 603 on the roller 604 and controlling the flow rate and pressure of the slurry by the applicator 602, the thickness and density of the applied coating can be controlled. Although a single doctor blade 601 is shown, multiple blades can be used, for example a first blade to set a rough thickness of the coating and a second blade positioned downward from the first blade to provide a finely smooth coating.

Further disclosed herein are capacitors incorporating electrodes that provide users with improved performance over a wide temperature range. Such ultracapacitors include an energy storage cell and an electrolyte system hermetically sealed in a housing, the cell electrically coupled to a positive contact and a negative contact, and the ultracapacitor is configured to operate at a temperature range of about -100°C to about 300°C or greater, or any subrange therein, such as, for example, -40°C to 200°C, -40°C to 250°C, -40°C to 300°C, 0°C to 200°C, 0°C to 250°C, 0°C to 300°C, etc. In some embodiments, such ultracapacitors can operate at voltages of 1.0V, 2.0V, 3.0V, 3.2V, 3.5V, 4.0V or greater with a life span of greater than 1000 hours.

As shown in Figures 8A and 8B, exemplary embodiments of a capacitor are shown. In each case, the capacitor is an ultracapacitor 10. The difference between Figures 8A and 8B is the inclusion of a separator in the exemplary ultracapacitor 10 of Figure 8A. The concepts disclosed herein generally apply equally to any exemplary ultracapacitor 10. Certain electrolytes of certain embodiments are suitable for constructing an exemplary ultracapacitor 10 without a separator. Unless otherwise stated, the discussion herein applies equally to any ultracapacitor 10 with or without a separator.

A typical ultracapacitor 10 is an electric double layer capacitor (EDLC). An EDLC includes at least one set of electrodes 3 (which may simply be referred to as negative electrodes 3 and positive electrodes 3 for purposes of reference herein). When assembled into an ultracapacitor 10, each of the electrodes 3 (each of which is an electrode 100 of the type shown in FIG. 1 above) will have a double layer of charge at the electrolyte interface. In some embodiments, multiple electrodes 3 are included (e.g., in some embodiments, at least two sets of electrodes 3 are included). However, for purposes of discussion, only one set of electrodes 3 is shown. As a convention herein, it will be assumed that at least one of the electrodes 3 employs a carbon-based energy storage medium 1 (e.g., active layer 106 of electrode 100 shown in FIG. 1 ) and that each of the electrodes includes a carbon-based energy storage medium 1. It should be noted that electrolytic capacitors differ from ultracapacitors because metal electrodes differ greatly (at least by an order of magnitude) in surface area.

Each of the electrodes 3 includes a respective current collector 2 (also referred to as a current collector), which is the conductive layer 102 of the electrode 100 shown in FIG. 1. In some embodiments, the electrodes 3 are separated by a separator 5. Generally, the separator 5 is a thin structural material (usually a sheet) used to separate the negative electrode 3 from the positive electrode 3. The separator 5 also serves to separate the set of electrodes 3. Once assembled, the electrodes 3 and the separator 5 provide a storage cell 12. Note that in some embodiments, the carbon-based energy storage medium 1 is not included in one or both of the electrodes 3. That is, in some embodiments, each electrode 3 consists only of the current collector 2. The material used to provide the current collector 2 can be roughened, anodized, etc., to increase its surface area. In these embodiments, the current collector 2 serves alone as the electrode 3. With this in mind, however, as used herein, the term "electrode 3" generally refers to the combination of the energy storage medium 1 and the current collector 2 (which is not limiting for at least the reasons discussed above).

At least one form of electrolyte 6 is included in the ultracapacitor 10. The electrolyte 6 fills the space between the electrodes 3 and the separator 5. In general, the electrolyte 6 is a material that does not associate with charged ions. A solvent that dissolves the material is suitably included in some embodiments of the electrolyte 6. The electrolyte 6 conducts electricity by ionic transport.

In some embodiments, the electrolyte 6 is in gel or solid form (e.g., a polymer layer impregnated with an ionic liquid). Examples of such electrolytes are provided in International Patent Publication No. WO 2015/102716, published July 9, 2015, entitled "Advanced Electrolytes in High Temperature Energy Storage Devices."

In other embodiments, the electrolyte 6 is in a non-aqueous liquid form, such as an ionic liquid, for example of a type suitable for high temperature applications. Examples of such electrolytes are provided in International Patent Publication No. WO 2015/102716, published July 9, 2015, entitled "Advanced Electrolytes in High Temperature Energy Storage Devices."

In some embodiments, the storage cells 12 are formed in one of a wraparound or prismatic form that is then packaged in a cylindrical or prismatic housing 7. Once the electrolyte 6 is contained, the housing 7 is hermetically sealed. In various embodiments, the package is hermetically sealed by techniques using laser, ultrasonic and/or welding techniques. In addition to providing robust physical protection for the storage cells 12, the housing 7 provides external contacts to provide electrical transmission to respective terminals 8 within the housing 7. Each of the terminals 8 provides electrical access to the energy stored in the energy storage medium 1, typically through electrical leads that are then coupled to the energy storage medium 1.

As discussed herein, "hermetic" refers to a seal whose quality (i.e., leak rate) is defined in units of "atm-cc/second," meaning one cubic centimeter of gas (e.g., helium) per second at atmospheric pressure and temperature. This is equivalent to the unit expression "standard He-cc/sec." It is further recognized that 1 atm-cc/sec is equal to 1.01325 mbar-liter/sec. Generally, the ultracapacitor 10 disclosed herein has a leak rate of approximately 5.0×10^-6It is possible to provide an airtight seal with a leak rate of less than or equal to atm-cc/sec, approximately 5.0×10^-10A leak rate of atm-cc/sec or less may be exhibited, and successful hermetic sealing performance should be judged by the user, designer, or manufacturer, as appropriate, and "hermetic" is considered to imply a standard that is ultimately to be defined by the user, designer, manufacturer, or other interested party.

Leak detection can be accomplished, for example, by the use of a tracer gas. Using a tracer gas, for example helium, for leak testing is advantageous because it is a dry, fast, accurate, and non-destructive method. In one example of this technique, the ultracapacitor 10 is placed in a helium environment. The ultracapacitor 10 is subjected to pressurized helium. The ultracapacitor 10 is then placed in a vacuum chamber connected to a detector (e.g., an atomic absorption unit) that can monitor for the presence of helium. With knowledge of the pressurization time, pressure, and internal volume, the leak rate of the ultracapacitor 10 can be determined.

In some embodiments, at least one lead (also referred to herein as a tab) is electrically coupled to a respective one of the current collectors 2. Multiple leads (depending on the polarity of the ultracapacitor 10) are grouped together and coupled to respective terminals 8. The terminals 8 are then coupled to electrical accesses referred to as "contacts" (e.g., one of the housings 7 and an external electrode (also conventionally referred to herein as a "feedthrough" or "pin")). Suitable exemplary designs are provided in International Patent Publication No. WO 2015/102716, published July 9, 2015, entitled "Advanced Electrolytes in High Temperature Energy Storage Devices."

The various forms of ultracapacitors 10 are coupled together using known techniques, such as by bringing the contacts into electrical contact with one another, for example, by use of at least one mechanical connector, for example, by welding the contacts, etc. Multiple ultracapacitors 10 are electrically connected in at least one of a parallel and a series manner.

As used herein, the symbol "wt. %" means percent by weight. For example, when referring to the weight percent of a solute in a solvent, "wt. %" refers to the proportion of the total mass of the mixture of solute and solvent that is made up of the solute.

The entire contents of each of the above-referenced publications and patent applications are incorporated herein by reference. In the event that any of the cited documents conflict with the present disclosure, the present disclosure shall control.

While the invention has been described with reference to exemplary embodiments, it will be understood that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. For example, in some embodiments, one of the layers described above may include multiple layers therein. In addition, it will be understood that many modifications can be made to adapt a particular device, situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is not intended that the invention be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but the invention will include all embodiments falling within the scope of the appended claims.