JP2019057700A - Capacitive energy storage device and method for manufacturing the device - Google Patents

Abstract

To provide a capacitive energy storage device which improves energy density and power density.SOLUTION: A capacitive energy storage device 200 includes: at least one sheet of a porous film 201 impregnated with an electrolyte; and pairs 202, 203 of separate electrodes being one or more pairs arranged on a first surface 208 of the porous film with each electrode including a capacitive electrode material subjected to ion communication with the porous film of a lower layer. The electrolyte performs ion communication with a space between the separate electrodes through internal gaps 212 of the porous film.SELECTED DRAWING: Figure 4

Description

  [0001] The present invention relates to capacitive energy storage devices, methods of making capacitive energy storage devices, and the use of porous films to make stacked capacitive energy storage devices. Specifically, the capacitive energy storage device is one of capacitive electrodes formed on the film surface and in ion communication with the electrolyte in the internal pores of the film, with at least one porous film infiltrated with the electrolyte. Or with more pairs.

  [0002] Increasing influence of miniaturized electronic devices in today's life is driving more and more research into the development of miniaturized energy storage systems. Power supply systems often occupy more than 50% of the volume or weight of the device and are typically a large footprint. Batteries have traditionally benefited from relatively high energy densities, but the challenges in scaling down while maintaining low battery power, limited cycle life, and electrochemical performance are high performance as battery replacements. It has led to interest in supercapacitors. These devices offer balanced energy and power density, fast charge / discharge capability (tens of orders of magnitude higher for Faraday elements), long life, maintenance-free operation, and low environmental impact. Supercapacitors are therefore an attractive energy source for many applications, whether alone or integrated with a battery system.

  [0003] Traditional supercapacitors are typically fabricated by coating a metallic current collector foil having a thickness of 100 microns with a porous carbon electrode material. Two such electrodes are then assembled face-to-face with a porous separator in between that provides electrical insulation but allows ionic communication as depicted in FIG. The electrolyte saturates the separator and electrodes, and the device is electrically connected to the external circuit via a current collector. The porous electrode stores charge in the form of ions that are primarily located in the electric double layer of high surface area carbon electrode material. Such devices are therefore known as electric double layer (EDL) supercapacitors.

[0004] In such EDL supercapacitors, the electrode separation is governed by the thickness of the separator, and thus the electrodes are separated by at least 50-100 microns. The relatively long distance traversed by the ions during charging and discharging limits the power density of the device. Further, the surface area of large surface area of the electrode, i.e. the range from spreading across the cross-sectional area therefore mm ² or cm ² of supercapacitor devices are typically, efficient electron transport between the electrodes and an external circuit Force the use of a metal current collector for. Thus, current collectors, separators, and inter-component junctions contribute to device dead volume, increased weight, and reduced flexibility.

  [0005] In an attempt to address these disadvantages, in-plane electrode geometries have been developed to provide micro supercapacitors with improved energy density compared to traditional supercapacitors. In these devices, the insulating substrate is typically patterned with a conductive metal pad of the required electrode geometry, and electrode material is deposited on the pad by electrochemical deposition or other techniques. Is done. An electrolyte layer deposited on the substrate provides ionic communication between the electrodes across the surface, and the metal pads serve as current collectors. While such an approach avoids some of the limitations of traditional electrode-separator-electrode type configurations, the electrode resolution that can be reached is generally insufficient to produce electrode separations in the 1-50 micron range. Therefore, a complicated multi-step process is required for production.

  [0006] In recent years, direct "write" techniques have allowed the fabrication of truly micron scale electrodes with in-plane configurations. In this technique, an insulating graphene oxide layer is coated onto a substrate and a focused beam is used to “write” the electrode to the layer by selectively reducing the graphene oxide to conductive high surface area graphene. Yes. The resulting graphene electrodes are separated by intermediate graphene oxide that can hold the electrolyte reservoir necessary for ionic communication between the electrodes. Thus, both the laser and focused ion beam provide high resolution to the comb electrode as described in El Kady et al, Nature Communications 2013, 4, 1475 and Lobo et al, Advanced Energy Materials 2015, 19, 1500665. Has been used for transcription.

[0007] In the latter study, electrodes with electrode separations as small as 1 micron were fabricated, resulting in capacitance per area greater than 100 mFcm ^-2 and ultrafast cycling response. This superior performance is due to the micron-scale resolution of the electrodes, specifically from the linear diffusion in dynamic control that occurs below the critical electrode dimensions that are believed to be below 50 microns. Due to the switch of ion transport mechanism to radial diffusion.

  [0008] Although this research demonstrated a micro supercapacitor that has a higher energy density than thin-film lithium-ion batteries and combines extremely good power density and cycleability, the direct write technique is a beam reduction technique. There is a challenge to scale up to industrial production because of dependence on. In addition, the direct write technique is a slow process and expensive because the porous GO layer doubles as both an electrode precursor (which is subsequently reduced to form an electrode) and an insulating spacer between the reduced electrodes. The electrode material is used relatively inefficiently. Also, as a result of beam reduction techniques, the substrate is limited to non-porous materials such as silicon wafers. As a result, micro supercapacitors become undesirably stiff and limit their applicability to flexible electronic devices. In addition, electrolyte pools exist only above the plane of the substrate surface, that is, typically as a layer of gel electrolyte on the substrate, increasing the thickness of the device and hence the volumetric power density. And the energy density becomes small.

  [0009] Accordingly, there continues to be a need for improved capacitive energy storage devices and methods of making such devices that have superior energy density and / or power density that address one or more of the above-mentioned drawbacks. Exist.

  [0010] A reference to a patent document or other material in this specification given as prior art refers to the admission that the document or material is known or the information it holds is in any of the claims It must not be accepted as an admission that it was part of a well-known general knowledge as of the priority date of the claim.

El Kady et al., Nature Communications, 2013, 4, 1475 (El Kady et al, Nature Communications 2013, 4, 1475) Robo et al., “Advanced Energy Materials”, 2015, 19, 15000665 (Lobo et al, Advanced Energy Materials 2015, 19, 1500665)

  [0011] The inventors now have a capacitive energy storage device and a device for making the same, wherein the capacitive electrode material applied to the porous film forms multiple pairs of spaced electrodes on the surface of the film Developed a method. The film is generally a film having properties similar to those of a separator in a conventional supercapacitor, and in use for the electrolyte so as to provide ionic communication between the spaced electrodes through the internal pores of the film. It is sufficiently porous to serve as a pool of water. Ion-conducting pathways through the interior of the film-optionally augmented by additional ion-conducting pathways across the film surface and / or by further ion-conducting pathways through the overlying porous film in multilayer stacks Is believed to enhance the electrochemical performance of the device because the ease of electrolyte access to the microelectrode from multiple directions reduces the resistance associated with electrolyte diffusion. Additionally or alternatively, the use of a porous substrate as an electrolyte reservoir allows the thickness of the electrolyte stack on the substrate to be minimized or makes such layers completely absent Make it possible. Thus, the volume of the device is reduced while maintaining satisfactory ionic conductivity between the electrodes. Also, film pores are believed to facilitate the production of high resolution electrodes, which will be described in more detail later.

  [0012] Thus, the invention, according to a first aspect, is a capacitive energy storage device: at least one porous film infiltrated with electrolyte; and on the first surface of the porous film One or more pairs of spaced apart electrodes disposed, each electrode comprising a capacitive electrode material in ionic communication with the underlying porous film, wherein the electrolyte is porous A capacitive energy storage device is provided that provides ionic communication between the separation electrodes through the internal pores of the film.

  [0013] A porous film generally has two opposite surfaces of the film. As used herein, “first surface” and “back surface” of a porous film refer to these opposite surfaces, and are terms used to differentiate between surfaces, Does not imply any difference between the surfaces.

  [0014] The porous film has internal pores that are in communication with at least the first surface, typically in communication with either the first surface or the back surface. The internal pores of the porous material refer to internal voids or pores that are dispersed through the solid substrate. The pores of the porous film are interconnected so that the porous film is permeable to liquid and can therefore be infiltrated with electrolyte. As will be appreciated by those skilled in the art, the internal pores of a porous film are such as pore size, porosity (also known as void fraction, ie the proportion occupied by pores in the total volume), and surface area. Can be characterized by various parameters.

  [0015] In some embodiments, at least 80%, desirably at least 90%, or substantially all of the total electrolyte is infiltrated into the internal pores of the porous film in the capacitive energy storage device. Thus, the space occupied by the discrete layers of electrolyte in the device is kept to a minimum.

  [0016] For use herein, "a pair of spaced electrodes disposed on a first surface of a porous film" is at least partially formed above the continuous surface of the underlying porous film. Thus, it refers to a pair of electrically isolated electrodes having a three-dimensional physical structure protruding from the surface, the electrodes being separated by a portion of the porous film surface in between them. The electrode includes a capacitive electrode material that is in ion communication with the underlying porous film. Capacitive electrode materials are in ionic communication with the underlying porous film when electrolyte ions can move through the porous film surface between the electrode and the internal pores of the underlying porous film portion. Please understand that there is. Although the capacitive electrode material may be in direct contact with and / or bonded or bonded to the surface of the first porous film in a preferred embodiment, the requirement for “ion communication” is non- It should be understood that adhesive abutment engagement, partial penetration of capacitive electrode material into the film internal pores, or other modes of engagement in which ionic communication is suitably provided are not excluded.

  [0017] In some embodiments, the pair of spaced electrodes has an interelectrode separation of less than about 50 microns, desirably less than 30 microns. In this case, the interelectrode separation distance is the minimum distance across the first surface portion of the porous film in the middle of the separation electrodes, and the minimum distance for reliably isolating the electrodes from each other reliably. It is. A narrow interelectrode separation reduces the diffusion length scale for the ions, thereby providing improved time and frequency response and / or improved power density. In some embodiments, the pair of spaced electrodes has an interelectrode separation that is less than the thickness of the porous film. Such a separation is essentially not available in conventional supercapacitor designs where electrodes are placed on either side of the porous separator film.

[0018] In some embodiments, each pair of spaced electrodes, including both the electrodes themselves and the inter-electrode separation zone, the porous about 1 mm ² less than the surface area on the film, for example surface area, such as that 0.5mm less than ² , Covering. In the use here, the interelectrode separation area is an area of the first surface of the porous film in the middle of the separation electrodes, and is an area where the electrodes are surely electrically isolated from each other. Conveniently, with such small electrodes, it is believed that charge transport kinetics are controlled by a radial diffusion mechanism, resulting in improved capacitance and energy density. In addition, such electrodes possess sufficient electrical conductivity and do not require an additional current collector, i.e., a foil or other metal layer covering the in-plane area of the electrode. Thus, in some embodiments, the electrodes of the capacitive energy storage device are electrically connected to adjacent electrodes and / or to external circuitry without a metal current collector.

  [0019] In some embodiments, the pair of spaced electrodes is a comb electrode with each electrode having 2 to 6 fingers, preferably 3 to 5 fingers, such as 4 fingers, for example. It has. Each finger can have a width of less than about 50 microns and a length of less than about 250 microns.

  [0020] In some embodiments, the electrode has an out-of-plane thickness between about 25 nm and about 1 micron. In the use here, the out-of-plane thickness refers to the distance at which the electrode protrudes from the first surface of the porous film.

  [0021] In some embodiments, multiple pairs of spaced electrodes are disposed in electrical connection in series and / or in parallel on the first surface of the porous film. Depending on the energy and power requirements for any particular application, it can vary widely, including multiple parallel electrode pairs, multiple electrode pairs in series, a block of parallel connected electrode pairs, etc. Various electrode pair configurations can be provided on the porous film. As will be appreciated by those skilled in the art, the total capacitance of the parallel electrode pairs increases as the sum of the capacitances of the individual electrode pairs. In contrast, a series combination of electrode pairs reduces the total capacitance, but the applied voltage increases linearly with the number of electrode pairs. Since the energy density of the capacitor is directly proportional to the square of the applied voltage, the energy density of the device increases linearly with an increase in the number of electrode pairs connected in series.

[0022] Also, efficient utilization of the surface area of the porous substrate maximizes the number of spaced electrode pairs within a given area of the first surface of the substrate, thereby minimizing unused space between the electrode pairs. It will be understood that this is provided by In some embodiments, more than 10 electrode pairs per cm ² surface, desirably more than 50 electrode pairs, such as more than 80 electrode pairs, are disposed on the first surface of the porous film. . In this scheme, the dead volume in the device is reduced and the energy density and power density per unit device volume is maximized.

  [0023] In some embodiments, multiple pairs of spaced electrodes are electrically connected by a conductive linkage on the first surface of the porous film, the conductive linkage also comprising a capacitive electrode material. In these and other embodiments, pairs of remote electrodes or multiple pairs of electrically connected remote electrodes are provided with electrical contacts for electrical connection to an external circuit, and the electrical contacts are also capacitive. Electrode material. Such an embodiment advantageously provides an expanded network of electrically connected electrode pairs configured for connection to external circuitry, typically in a single printing step, with a single Application of a conductive material (or its reducible precursor) simplifies device fabrication by allowing it to be fabricated on a porous film. The length of the conductive linkage between the electrode pairs should be kept to a minimum to minimize voltage drops across the linkage so that the power performance of the device is not compromised. In this regard, in other embodiments, the conductive linkage between a pair of electrodes on the same porous film or an electrical contact for connection to an external circuit comprises other conductive materials, including metals. It should be understood that it is possible. This may be suitable, for example, to reduce the internal resistance of the energy storage device.

  [0024] In some embodiments, a plurality of porous films are stacked and one or more pairs of spaced apart electrodes disposed on a first surface of the first porous film are For example, they are stacked so as to abut and engage with the back surface of the second porous film stacked above the first porous film. It is preferred that the contact provide ionic communication between the electrode and the back surface. When a plurality of porous films are stacked in this manner, the separation electrode of the first film is sandwiched between two porous films each infiltrated with an electrolyte, and the two porous films Ion communication. Therefore, the electrolyte can provide an ion communication path between the separated electrodes through the internal pores of both the first porous film and the second porous film. The electrode is effectively surrounded on all sides by a reservoir of electrolyte contained within the first and second porous films, so that the electrochemical performance is further reduced while minimizing the dead volume of the capacitive energy storage device. Strengthened. In addition, especially when the porous film is a flexible membrane, adjacent porous films are intimately fitted around the sandwiched electrodes so that the films can be stacked with substantially no gap between the films. Can be weighted. Thus, at least 90%, desirably substantially all of the total electrolyte in the device can be infiltrated into the internal pores of the stacked porous film. The volumetric energy density and power density of the device is thus increased.

  [0025] Two or more porous films may be stacked. Those skilled in the art will appreciate that when more than two porous films are stacked, each porous film having both upper and lower adjacent films in the stack is placed on its first surface. One or more pairs of spaced apart electrodes may be defined as the first porous film in that it is in contact with the upper surface of the adjacent film on its upper side. It may also be defined as a second porous film in that the surface is in contact with one or more pairs of adjacent electrodes of the underlying film below it.

  [0026] In some embodiments in which a plurality of porous films are stacked, at least one of the separation electrodes disposed on the first surface of the first porous film is via a conductive path. , Electrically connected to at least one of the separation electrodes disposed on the first surface of the second porous film. In this manner, the energy storage device can comprise a three-dimensional extension network spanning the stack thickness of electrode pairs connected in series and / or in parallel.

  [0027] In some embodiments, the conductive path comprises a conductive material in an opening that extends through the thickness of the second porous film. The conductive material thereby penetrates through the second porous film and is typically in electrical communication with the electrical contacts of the connected electrodes on the first and second porous films. The conductive material may comprise a curable resin comprising a dispersed metal, preferably a silver filled epoxy.

  [0028] The at least one porous film is typically a polymeric porous film, desirably a flexible polymeric membrane, and thus in flexible electronics applications for capacitive energy storage devices. Open up the possibility of use. The thickness of the porous film can be less than 100 microns, desirably less than 50 microns, and most desirably less than 30 microns. In general, the volumetric energy density and power density of the device is increased by reducing the film thickness.

  [0029] In some embodiments, the flexible polymer membrane comprises a porous material suitable for use as a separator in an electrochemical device such as a conventional supercapacitor or lithium ion battery. In addition to pores, such materials are generally sufficiently chemically stable to avoid degradation in the presence of acid or alkaline electrolytes and are able to withstand sudden increases in temperature during operation. It is sufficiently thermally stable. The flexible polymer film may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl chloride, nylon, and polyethylene terephthalate. In certain preferred embodiments, the flexible polymer membrane comprises polyvinylidene fluoride.

  [0030] In some embodiments, the capacitive electrode material comprises at least one selected from the group consisting of a carbon-based electrode material or a pseudo-capacitive electrode material. In some embodiments, the capacitive electrode material comprises a carbon-based electrode material such as reduced graphene oxide, graphene, exfoliated graphite, porous carbon, and activated carbon. It is particularly preferred that the electrode comprises reduced graphene oxide as a capacitive electrode material, advantageously formed from graphene oxide and subsequently reduced on the porous film surface. As described in more detail later, the capacitive electrode material is generally printed on a porous film.

[0031] In some embodiments, the electrolyte is a gel electrolyte and is optionally strongly acidic or strongly basic such as cross-linked polyvinyl alcohol, typically KOH, H ₂ SO ₄ , or H ₃ PO ₄ . In combination with an electrolyte salt. In another example, a polyethylene oxide based gel electrolyte may be suitable. Gel electrolytes are currently preferred because of their ability to provide an energy storage device that is entirely solid but flexible and the potential to provide a supplemental ion-conducting pathway between electrodes across the film surface. However, it is also envisioned to use liquid electrolytes that are at least partially retained within the pores of the porous film, including aqueous, non-aqueous, and ionic liquid electrolytes.

  [0032] As described herein, a particularly advantageous embodiment of a capacitive energy storage device according to the invention has a stacked configuration. Such devices were connected in series and / or in parallel, the microscale size of the electrode pair, the availability of multiple ion-conducting pathways between the electrodes through the internal pores of the upper and lower porous films Due to the feasibility to create a wide variety of three-dimensional extended networks across the thickness of the stack of electrode pairs and the absence of volume-filling components such as a thick electrolyte layer overlying the current collector or electrode Can have one or more of a high energy density, a high power density, and a fast cycling response.

  [0033] Thus, according to a further aspect, the invention is a stacked capacitive energy storage device comprising: a first porous film; disposed on a first surface of a first porous film One or more pairs of spaced electrodes, each electrode comprising a capacitive electrode material in ionic communication with the underlying first porous film; above the first porous film; A second porous film stacked on the first porous film, wherein one or more pairs of spaced apart electrodes disposed on the first surface of the first porous film are the second porous film A stacked capacitive energy storage device comprising: a second porous film stacked to contact the back surface of the first electrode; and an electrolyte in the internal pores of the first and second porous films. providing.

  [0034] Each of the first and second porous films has a first surface and a back surface. When stacked, the back surface of the second porous film faces the first surface of the first porous film and is typically in direct contact with the first surface.

  [0035] In some embodiments, the capacitive electrode material is in ionic communication with the back surface of the second porous film. Thus, in use, the electrolyte provides ionic communication between the separation electrodes through the internal pores of both the first porous film and the second porous film.

  [0036] In some embodiments, the stacked capacitive energy storage device is further one or more pairs of spaced electrodes disposed on the first surface of the second porous film. Each electrode includes a pair of spaced apart electrodes, each of which includes a capacitive electrode material in ionic communication with the underlying second porous film.

  [0037] In some such embodiments, at least one of the separation electrodes disposed on the first surface of the first porous film has a second porous path through the conductive path. It is electrically connected to at least one of the spaced electrodes disposed on the first surface of the film.

  [0038] It is understood that other optional or advantageous features described herein for the capacitive energy storage device embodiments of the invention may also be characteristic of the stacked capacitive energy storage device embodiments. I want. Such features include the nature of the porous film, the composition and geometry of the electrode pair on the first surface of the film, the composition of the electrolyte, and the surface of the film stacked on or adjacent to the same surface. An electrical connection between the upper electrode pair is included.

  [0039] The capacitive energy storage device of the present invention is provided by a method developed by the inventors for making a device. Inventive methods, including formation at high resolution, form spaced electrodes on the surface of the porous film such that ionic communication between the electrodes is provided at least partially through the internal pores of the porous film. To provide that.

  [0040] Thus, according to a further aspect, the invention provides a method of making a capacitive energy storage device, the method comprising: applying a capacitive electrode material or precursor to a first surface of a porous film. Forming one or more pairs of spaced electrodes disposed on the first surface; and infiltrating the porous film with an electrolyte, wherein the electrolyte is porous between the spaced electrodes Ionic communication is provided through the internal pores of the film.

  [0041] In some embodiments, an ink comprising a capacitive electrode material or precursor is printed onto the first surface. Film pores are believed to facilitate the fabrication of microscale electrodes in these preferred embodiments. While not wishing to be bound by any theory, when applied, a continuous phase of ink is rapidly drawn into the pores of the film, thereby reducing very small dimensions and narrow interelectrode distances. It is believed that ink diffusion and coalescence will be prevented even when the electrodes they have are printed.

  [0042] In some embodiments, the ink is printed onto the first surface by gravure printing or flexographic gravure printing, preferably gravure printing. The inventors have surprisingly discovered that using such printing techniques, electrodes having micron scale features can be printed onto the surface of porous films conventionally used as separators. Thereby, excellent resolution and reproducibility can be obtained when an ink of suitable viscosity with dispersed electrode material or precursor is employed. Furthermore, without wishing to be bound by any theory, gravure printing causes shear-induced alignment of the electrode material or precursor that forms the electrode, thereby favoring ions within the electrode during the cycle of the energy storage device. It is believed that conductivity will be provided.

  [0043] The viscosity of the ink must be in an appropriate range to allow gravure or flexographic gravure printing and to limit or avoid penetration of capacitive electrode materials or precursors into the porous film. Don't be. Thus, the ink can have a viscosity between about 25 Pas and about 100 Pas when printed on the first surface. It should be understood that the appropriate concentration of capacitive electrode material or precursor in the ink for printing the electrode of the invention will depend on the nature of the material and the carrier fluid. In one embodiment, the ink had a concentration between about 1% and 5% by weight of the capacitive electrode material or precursor, such as a concentration of approximately 3% by weight.

  [0044] In some embodiments, the inventive method further comprises providing an ink for printing on the first surface. Providing the ink may comprise concentrating the capacitive electrode material or the precursor dispersion to increase its viscosity. In a preferred method, the capacitive electrode material or precursor is dispersed in the aqueous continuous phase of the dispersion, the dispersion being: i) to absorb water from the aqueous continuous phase into the water-absorbing solid. Contacting the dispersion with a water-absorbing solid, such as a bead of superabsorbent polymer; and ii) subsequently separating the dispersion from the water-absorbing solid. The inventors can conveniently prepare concentrated graphene oxide inks with the appropriate viscosity for gravure printing in this manner, thereby reducing the problem of directly preparing concentrated graphene oxide dispersions or diluted dispersions. It has been discovered that the problem of concentration by volatilization of the aqueous phase can be avoided.

[0045] In some embodiments, the separation electrode formed by applying a capacitive electrode material or precursor according to the method of the invention has an electrode separation distance of less than about 50 microns, desirably less than 30 microns. . Moreover, each pair of spaced electrodes thus formed, including both the electrodes themselves and the interelectrode distance areas, will cover a surface area of less than 1 mm ² on the porous film.

  [0046] In some embodiments, applying the capacitive electrode material or precursor comprises forming multiple pairs of spaced apart electrodes disposed on the first surface of the porous film; Multiple pairs of remote electrodes are connected in series and / or in parallel by a linkage comprising capacitive electrode material or precursor. In some embodiments, applying the capacitive electrode material or precursor further comprises forming an electrical contact for electrical connection to an external circuit, the electrical contact also being a capacitive electrode. With materials. The electrode, linkage, and electrical contact can be printed on the first surface in the same printing step.

  [0047] In some embodiments where an electrode precursor material, such as, for example, graphene oxide, is applied to form an electrode, the method further includes a capacitive electrode material on the first surface of the porous film or It has a step to reduce the precursor and increase its conductivity. The capacitive electrode material or precursor may be reduced by any suitable technique, including chemical, thermal, photothermal, and beam reduction techniques. In some embodiments, the capacitive electrode material or precursor is reduced by exposure to a chemical reducing agent such as hydroiodic acid.

  [0048] In some embodiments, the method further comprises stacking a plurality of porous films, wherein one of the separation electrodes disposed on the first surface of the first porous film. Including one or more pairs stacked to contact a back surface of a second porous film stacked above the first porous film, for example, by abutting engagement. Yes. It is preferred that the contact provide ionic communication between the electrode and the back surface.

  [0049] In some such embodiments, the method further comprises at least one of the spaced electrodes disposed on the first surface of the first porous film via a conductive path, Electrically connecting to at least one of the spaced electrodes disposed on the first surface of the second porous film. The step of electrically connecting the electrodes is conducted through the second porous film, for example, by placing a conductive material into an opening extending through the thickness of the second porous film. Creating a path. The conductive material may be printed, drop cast, or injected onto the first surface of the second film and / or into the opening of the second film. In some embodiments, the conductive material is a curable resin comprising a dispersed metal, preferably a resin that can be cured at room temperature, and preferably comprises a silver-filled epoxy. Once the curable resin has penetrated through the thickness of the second porous film, the resin may be cured to adhere the first porous film to the second porous film.

  [0050] Thus, the inventive method provides an industrially scalable step-by-step method for making stacked multi-layer energy storage devices using readily available microfabrication techniques. Specifically, the device can be fabricated by stacking a second porous film on top of the first porous film, and a separate electrode disposed on the second porous film. The electrical contact of at least one of the electrodes is placed in proper vertical alignment with the electrical contact of at least one of the spaced electrodes disposed on the first porous film. A curable resin comprising a dispersed metal is then placed into the opening of the second porous film that passes through or is adjacent to the electrical contact of the electrode on the second porous film. In order to ensure that a sufficiently conductive connection is made to the electrical contact partner, it is optional to place a curable resin further on the area of the second porous film adjacent to the opening. The opening, which may be a hole of less than 1 mm in diameter, for example about 0.8 mm, is formed in the second porous film either before or after the step of forming the electrode and electrical contacts thereon. It can be made, but preferably later. The conductive resin penetrates through the openings and contacts the electrical contacts of the electrodes on the first porous film. The resin is then cured to create a permanent electrical connection between the electrodes of adjacent layers of the stack and to bond the layers together. Once all the necessary electrical connections between the first porous film electrode and the second porous film electrode have been made in this manner, the third porous film can be attached as described herein. The second porous film can be stacked and electrically connected. In this manner, multi-layer stacks with two, three, four, five, or more layers can be made.

  [0051] Prior to the stacking step, the porous film is optionally saturated with electrolyte, but in some preferred embodiments, the plurality of porous films are after the stacking step of the porous film. In general, it is further infiltrated with electrolyte only after the step of establishing electrical connections between layers within the stack as described herein. It is an advantage of the present invention that, as a result of the permeable nature of the stack film, the stacked and electrically connected capacitive energy storage device can be infiltrated with electrolyte after fabrication. Conceivable.

[0052] In some embodiments, a porous film or a plurality of stacked porous films are infiltrated with a low viscosity curable electrolyte to allow penetration into the device. The curable electrolyte can have a viscosity below about 10 Pas, desirably below about 1 Pas when infiltrated into the film. In such embodiments, the method further comprises curing the low viscosity curable electrolyte to produce a gel electrolyte once the film or films are properly infiltrated. In some embodiments, the low viscosity curable electrolyte is a combination of crosslinkable polyvinyl alcohol, typically with a strongly acidic or strongly basic electrolyte salt such as KOH, H ₂ SO ₄ , or H ₃ PO ₄ . I have. Such a curable electrolyte can be gelled by heat treatment or at room temperature.

  [0053] In some embodiments, the porous film to which the capacitive electrode material or precursor is applied is a polymeric porous film, preferably a flexible polymeric membrane. The flexible polymer membrane may comprise a porous film suitable for use as a separator in an electrochemical device such as a conventional supercapacitor or lithium ion battery. The flexible polymer film may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl chloride, nylon, and polyethylene terephthalate. In certain preferred embodiments, the flexible polymer membrane comprises polyvinylidene fluoride.

  [0054] In some embodiments, the capacitive electrode material or precursor is at least one selected from the group consisting of a carbon-based electrode material, a pseudo-capacitive electrode material, or a precursor of either of these. It has. In some embodiments, the capacitive electrode material or precursor comprises graphene oxide.

  [0055] In such embodiments, the method comprises reducing the capacitive electrode material or precursor on the first surface of the porous film to increase its conductivity. In embodiments where graphene oxide is applied to the first surface of the porous film to form an electrode, the graphene oxide is reduced, for example, by chemical reduction to produce conductive reduced graphene oxide.

[0056] According to a further aspect, the invention provides a capacitive energy storage device made by the method of any of the embodiments disclosed herein.
[0057] As disclosed herein, a particularly advantageous application of the inventive electrode-functionalized porous film is the fabrication of stacked multi-layer energy storage devices.

  [0058] Thus, according to a further aspect, the invention is the use of a plurality of porous films, each porous film being disposed on a first surface of the porous film, Providing the use of a plurality of porous films to make a capacitive energy storage device comprising one or more pairs of spaced electrodes comprising a capacitive electrode material in ionic communication; The use comprises the following: one or more pairs of spaced apart electrodes disposed on a first surface of a first porous film are stacked above the first porous film. Stacking a plurality of porous films in contact with the back surface of two porous films; and infiltrating the porous films with an electrolyte. During charging and discharging of the capacitive energy storage device thus produced, the electrolyte provides ionic communication between the spaced electrodes via the internal pores of the porous film.

  [0059] Contact may be, for example, via abutting engagement. It is preferred that the contact provide ionic communication between the electrode disposed on the first surface of the first porous film and the back surface of the second porous film. During charging and discharging of the capacitive energy storage device thus fabricated, the electrolyte provides ionic communication between the spaced electrodes through the internal pores of the first and second porous films.

  [0060] In some embodiments, the use further comprises connecting at least one of the separation electrodes disposed on the first surface of the first porous film via the conductive path to the second Electrically connecting to at least one of the spaced electrodes disposed on the first surface of the porous film. In some such embodiments, electrically connecting the electrodes to each other comprises conducting material into an opening that extends through the thickness of the second porous film to create a conductive path. The stage of installing. In some embodiments, after the steps of stacking the porous films and electrically connecting the electrodes together, the porous films are infiltrated with an electrolyte.

  [0061] The terms “comprise”, “comprises”, and “comprising” are described in the specification (including claims). Are used to describe one or more other features, individual entities, steps, or specified features, individual entities, steps, or components. It should be construed as not excluding the existence of components or groups of them.

  [0062] As used herein, the terms "first", "second", "third", etc. related to various features of the disclosed embodiments are arbitrarily assigned and It is merely intended to distinguish between two or more such features that may be incorporated into embodiments. The terms themselves do not dictate any particular orientation or sequence order. In addition, the presence of the “first” feature does not imply that the “second” feature exists, and the presence of the “second” feature has the “first” feature. Please understand that it is not implied.

[0063] Further aspects of the invention appear in the detailed description of the invention that follows.
[0064] Embodiments of the invention will now be described by way of example only in connection with the accompanying drawings.

[0065] Schematic depiction of a conventional supercapacitor configuration reported in the prior art. [0066] FIG. 6 is a schematic depiction in plan view of a pair of spaced electrodes printed on a porous film, according to an embodiment of the invention. [0067] FIG. 3 depicts a side cutaway view of the porous film and printed electrode of FIG. 2, taken through the AB cross section indicated in FIG. [0068] FIG. 4 is a schematic depiction in a side cutaway view of a single layer capacitive energy storage device made by infiltrating the porous film of FIG. 3 with an electrolyte according to an embodiment of the invention. [0069] FIG. 6 is a schematic depiction in plan view of a single layer capacitive energy storage device comprising a comb-type spaced electrode, according to an embodiment of the invention. [0070] FIG. 6 is a schematic depiction in perspective view of a single layer capacitive energy storage device comprising multiple pairs of comb-shaped electrodes connected in parallel and in series, according to an embodiment of the invention. [0071] FIG. 6 is a schematic depiction in side cutaway view of two porous films positioned to stack, according to an embodiment of the invention, with the lower film printed onto the porous film surface. It has a pair of remote electrodes. [0072] The porous film of FIG. 7 is depicted in a side cutaway view, stacked so that the spaced apart electrodes are sandwiched between the films. [0073] FIG. 9 is a schematic depiction in a side cutaway view of a dual layer stacked capacitive energy storage device made by infiltrating the porous film of FIG. 8 with an electrolyte according to an embodiment of the invention. [0074] FIG. 9 is a schematic depiction in perspective view of two porous films positioned for stacking, according to an embodiment of the invention, wherein both films are a plurality of comb-shaped electrodes connected in parallel and in series. A pair of conductive epoxies are dispensed to make electrical connections between electrode arrays on two films. [0075] According to an embodiment of the invention, the separate electrodes of the lower film are stacked so as to be sandwiched between the porous film surfaces, and the electrode array on the two films is connected to the conductive epoxy electrical connection. FIG. 10 is a perspective view of the porous film of FIG. 10 stacked in a state of being electrically connected to each other, and is further stacked on the first and second porous films. 3 depicts a third porous film positioned on the surface. [0076] According to an embodiment of the present invention, the lower two film separation electrodes are stacked so as to be sandwiched between the porous film surfaces, and the electrode array on the three films is made into a conductive epoxy. The three porous films of FIG. 11 stacked in an electrically connected state via an electrical connection are depicted in a perspective view. [0077] In a multi-layer stacked capacitive energy storage device comprising an array of electrically connected electrode pairs connected in parallel and in series across the thickness of the stack, according to an embodiment of the invention. It is a schematic drawing in a perspective view. [0078] FIG. 14 is a side perspective view of the multilayer stacked capacitive energy storage device of FIG. [0079] FIG. 6 is a representation of a plate design used to make a plate for printing a separation electrode on a porous film surface according to the method of Example 1. [0080] FIG. 3 is a photograph of a plate used to print a separation electrode onto a porous film surface according to the method of Example 1. [0081] Fig. 2 is a photograph of a porous PVDF film produced by the method of Example 1 and having a graphene oxide electrode printed on the surface. [0082] An array of comb-shaped electrodes printed on the surface of a porous PVDF film according to the method of Example 1 (a) in parallel and (b) connected in series via graphene oxide linkages. A set of pictures. [0083] FIG. 2 is an optical microscope image of a printed comb electrode pair on a PVDF film made by the method of Example 1. [0084] FIG. 2 is an optical microscopic image of a printed electrode pair having a zigzag configuration on a PVDF film, made by the method of Example 1. [0085] FIG. 6 depicts a graph of point-to-point electrical resistivity of a printed graphene oxide electrode after reduction by a plurality of different reduction procedures. [0086] FIG. 6 is a photograph of a porous PVDF film having a hydroiodic acid reduced graphene oxide electrode made by the method of Example 1. [0087] In a graph of the electrochemical response in the first cycle of a single layer capacitive energy storage device made by the method of Example 1, measured by cyclic voltammetry in Example 2. is there. [0089] FIG. 9 is a graph of the electrochemical response over the first 20 cycles of a single layer capacitive energy storage device made by the method of Example 1 as measured by cyclic voltammetry in Example 2. [0090] FIG. 6 is a Nyquist plot of a single layer capacitive energy storage device as measured by electrochemical impedance spectroscopy in Example 2. [0090-1] is a graph of open circuit potential measurement of a stacked energy storage device prepared in Example 4 with electrolyte infiltrated through the pores of the entire stack, prepared in Example 5. Contrast with a stack type device with an electrolyte layer on top. [0090-2] Electricity for 100 cycles (0 V to 0.5 V at a scan rate of 10 mV / s) of the energy storage device stacked, electrically connected and infiltrated with electrolyte of Example 4 It is a graph of a chemical response. [0090-3] is a Nyquist plot of the stacked energy storage device of Example 4. [0091] FIG. 6 is a schematic depiction of a plurality of different spaced electrodes that are fabricated and characterized by the method of Example 3;

  [0092] The present invention relates to capacitive energy storage devices, methods of making capacitive energy storage devices, and the use of porous films to make stacked capacitive energy storage devices. The capacitive energy storage device of the invention comprises at least one porous film infiltrated with an electrolyte and one or more pairs of spaced apart electrodes disposed on a first surface of the porous film. I have. Each electrode includes a capacitive electrode material that is in ion communication with the underlying porous film. In use, such as when charging or discharging a device through an external circuit, the electrolyte provides ionic communication between the spaced electrodes through the internal pores of the porous film.

Porous film
[0093] The capacitive energy storage device comprises at least one porous film. The thickness of the porous film can be less than 100 microns, desirably less than 50 microns, and most desirably less than 30 microns.

  [0094] The porous film is typically a polymeric porous film and can comprise at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl chloride, nylon, and polyethylene terephthalate. In certain preferred embodiments, the flexible polymeric membrane comprises or consists essentially of polyvinylidene fluoride.

  [0095] The pore size of the porous film can be between 0.1 microns and 0.5 microns, desirably between 0.1 microns and 0.3 microns, such as approximately 0.2 microns. . The pore size of the porous film can be measured using liquid or gas absorption methods, such as according to American Society for Testing and Materials (ASTM) D-2873.

Capacitive electrode material
[0096] The remote electrode on the surface of the porous film comprises a capacitive electrode material. The capacitive electrode material can include either or both of a carbon-based electrode material and a pseudo-capacitive electrode material. It should be understood that carbon-based electrode materials that typically have both a high surface area (eg, between about 100 m ² / g and 2500 m ² / g) and high conductivity are energy storages that are primarily conductive electrode materials. It is particularly suitable for electric double-layer capacitors (EDLC devices) caused by charge separation in a Helmholtz double layer at the interface between the surface and the electrolyte. In comparison, pseudocapacitive materials store energy through a process of rapid reversible redox or intercalation with electrolyte ions occurring at the surface of the electrode material.

  [0097] The capacitive electrode material can comprise a carbon-based electrode material, such as reduced graphene oxide, graphene, exfoliated graphite, porous carbon, and / or activated carbon. Electrodes comprising reduced graphene oxide as a capacitive electrode material are particularly suitable because they can be conveniently formed from graphene oxide and subsequently reduced on the porous film surface. Suitable pseudocapacitive electrode materials include conductive polymers, transition metal oxides, and metal nanoparticles. It is envisioned that the isolated electrode of the invention can include both a carbon-based electrode material such as reduced graphene oxide and a pseudocapacitive material.

Electrolytes
[0098] A capacitive energy storage device includes an electrolyte infiltrated into the internal pores of the porous film. The electrolyte may be a liquid electrolyte containing an ionic liquid or an electrolyte comprising an organic solvent and a suitable soluble salt.

[0099] The electrolyte can be a gel electrolyte, for example, an electrolyte comprising a basic polymer such as cross-linked polyvinyl alcohol or polyethylene oxide. Such an electrolyte would be particularly suitable for flexible capacitive energy storage devices. The gel electrolyte may comprise a strongly acidic or strongly basic electrolyte salt, such as KOH, H ₂ SO ₄ , or H ₃ PO ₄ .

  [0100] The invention also relates to a method for making a capacitive energy storage device. The method comprises applying a capacitive electrode material or precursor to the first surface of the porous film to form one or more pairs of spaced electrodes disposed on the first surface. The porous film is infiltrated with an electrolyte so that ionic communication is provided between the spaced electrodes through the internal pores of the porous film.

Print electrodes
[0101] The capacitive electrode material or precursor may be applied to the first surface by any suitable method capable of forming an electrode. In a preferred embodiment, the capacitive electrode material or precursor is applied by printing an ink comprising the capacitive electrode material or precursor onto the porous film surface.

  [0102] The ink may be printed onto the first surface by an intaglio printing technique such as gravure printing. As will be appreciated by those skilled in the art, gravure (or rotogravure) printing refers to engraved printed surfaces, etched printed surfaces, or otherwise finely structured printed surfaces such as printed sheets, A printing method in which ink is applied to a gravure cylinder or a roller-mounted shim. Excess ink is generally wiped from the printing surface, which is then contacted with the substrate. This is typically accomplished by feeding a flexible substrate around the applicator roller and thus rolling it into contact with the printing surface. The ink in the printing surface recess is then transferred to the substrate.

  [0103] Gravure printing, and related techniques such as flexographic gravure, are particularly suitable for printing microstructures at high resolution because they allow the use of viscous inks that do not easily coalesce on the porous film surface. . In contrast, techniques such as ink jet printing using low viscosity jettable inks may be suitable for making larger electrodes in accordance with the present invention, but the radial diffusive ion transport mechanism is favorably dominated. It would be less suitable or unsuitable for making a fine resolution electrode structure. Also, without wishing to be bound by any theory, it is believed that gravure printing produces a favorable shear-induced alignment of the electrode material or precursor in the electrode structure.

  [0104] The viscosity of the ink is suitable to allow the formation of a high resolution electrode structure by gravure printing and to limit or avoid penetration of capacitive electrode materials or precursors into the porous film. It must be in the proper range. Suitable ink viscosities include viscosities between about 25 Pa s and about 100 Pa s.

  [0105] Inks with such viscosities may in some cases simply disperse a suitable capacitive electrode material or precursor in the carrier fluid at the required concentration, or evaporate the carrier fluid from the diluted dispersion. It may not be easy to get by simply doing it. The inventors have made a sufficiently viscous aqueous ink for gravure printing of microelectrodes by contacting a diluted aqueous dispersion of capacitive electrode material or precursor with a water-absorbing solid such as a super-absorbent polymer bead. I found out that I can offer. The water-absorbing solid can absorb water from the aqueous continuous phase and be separated from the remaining concentrated viscous dispersion.

[0106] Gravure printing of electrodes with a suitable viscosity graphene oxide-containing ink prepared in this manner allows electrodes having a line width of approximately 50 microns and porous with an electrode separation of less than 30 microns. An electrode pair covering a surface area of less than 1 mm ² on the film can be made.

  [0107] Electrodes having a wide variety of geometries can be printed according to the invention. Suitable electrode pair geometries include comb, pad (rectangular), concentric, zigzag, L-shaped, and maze-type geometries, as depicted in FIG.

  [0108] It is to be understood that gravure printing of microelectrodes according to the invention involves further processing via web processing, ie a continuous web of flexible porous film from a feed roll to a further via a printing station. Conveniently it can be modified to scale up for and / or by feeding onto a take-up roll.

Reduce electrode
[0109] In the method of the invention, either the capacitive electrode material or its precursor can be applied to the first surface to form an electrode, optionally further providing a linkage between the electrode pair and the electrical contact. Can be formed. For use herein, a precursor of a capacitive electrode material is a substance that can be converted to a conductive capacitive electrode material on a porous film substrate by appropriate chemical conversion. Thus, when the precursor is applied to the porous film surface, for example, by printing an ink with the precursor on the porous film surface, the method of the invention applies the precursor material on the porous film surface to a capacitive electrode. Including converting to material.

  [0110] In a preferred embodiment, the precursor material is reduced to form a capacitive electrode material. The precursor may be reduced by any suitable technique, including chemical, thermal, photothermal, or beam methods. Suitable reduction methods for making various capacitive electrode materials from their precursors have been reported and are available to those skilled in the art.

  [0111] Graphene oxide is a particularly preferred capacitive electrode material precursor because it is believed that it can be more easily dispersed in aqueous inks than reduced high surface area carbon materials such as graphene. Therefore, it is possible to print the isolated electrode of the invention using graphene oxide-based ink, and then reduce the printed graphene oxide in the printed electrode to form reduced graphene oxide. Reduced graphene oxide has a high surface area and electrical conductivity suitable for use in capacitive energy storage devices according to the present invention. Graphene oxide can be reduced on the surface of the porous film by methods including chemical, thermal, photothermal, and beam reduction techniques. For example, graphene oxide printed electrodes can be reduced by exposure to a chemical reducing agent such as hydrazine or hydroiodic acid.

Infiltrate the film with electrolyte
[0112] In the method of the invention, the porous film is infiltrated with an electrolyte. In a preferred embodiment, after applying a capacitive electrode material or precursor to form an electrode on the porous film, the porous film is wetted with an electrolyte. However, it is not excluded that the electrode can also be formed on a porous film that is already wetted with an electrolyte or one or more components thereof or precursors thereof.

  [0113] The electrolyte is at least partially infiltrated into the internal pores of the porous film or films. As such, it is generally preferred that a low viscosity liquid electrolyte or precursor mixture be infiltrated into the porous film, thereby allowing permeation into the film. Thus, infiltration can be achieved by applying a liquid phase electrolyte such as an ionic liquid electrolyte or an organic solvent electrolyte directly into the porous film, for example, by applying the electrolyte to the surface of the porous film. Where gel electrolytes are preferred, low viscosity electrolyte precursors may be used to enable infiltration into the internal pores of the film, followed by gelling the precursor to produce the electrolyte. Good. The low viscosity electrolyte precursor may comprise a crosslinkable polymer such as polyvinyl alcohol in an aqueous mixture that also contains electrolyte ions. In that case, the gel electrolyte is produced by crosslinking the polymer.

Exemplary embodiments
[0114] FIG. 1 schematically depicts a prior art supercapacitor 100 comprising metal current collector foils 101 and 102 connected to an external circuit. Current collector foils 101 and 102 are covered with high surface area conductive carbon electrodes 103 and 104. An intervening porous separator 105 provides electrical insulation between the electrodes, while an electrolyte 106 saturating the separator 105 and electrodes 103 and 104 provides ionic communication between the electrodes during charging and discharging. To do. The separation between the electrodes (denoted as d _{s in} FIG. 1) is greater than the thickness of the separator and is therefore typically greater than 50 microns. In addition, the electrode can only be reached from a single direction during device charging and discharging, i.e., an ion-conducting path (indicated by arrow 106) extending directly between electrodes 103 and 104 through separator 106. ) Can only be reached through. In addition, the relatively large size of the electrodes 103 and 104 forces the use of current collector foils 101 and 102 to avoid unacceptable internal electrode resistance.

[0115] Certain embodiments of the present invention will now be described with particular reference to FIGS. FIG. 2 schematically depicts in plan view a fracture surface of a capacitive energy storage device 200 comprising a porous PVDF film 201 and a pair of spaced apart electrodes 202 and 203. Electrodes 202 and 203, the shape is rectangular, and has a distance of less than 30 microns (labeled _{d s} in Figure 2). Electrodes 202 and 203 are connected to electrical contact pads 204 and 205 via linkages 206 and 207, respectively, which can be used for electrical connection to external circuitry, for example, via attached wires. The electrodes, linkages, and contact pads are generated by printing an ink comprising graphene oxide onto the porous film 201 and then chemically reducing the graphene oxide, as described in more detail below. Graphene oxide.

[0116] FIG. 3 schematically depicts a capacitive energy storage device 200 taken through the A-B cross section indicated in FIG. 2 in a side view. Porous film 201, have a first surface 208 and back surface 209, and has approximately 50 micron thickness (shown as _{t s} in Figure 3). Electrodes 202 and 203 are disposed directly on the first surface 208 without interposing the metal current collector layer has out-of-plane thickness of approximately 50nm to (t _e and display). As depicted in FIGS. 3 and 4, a polyvinyl alcohol / KOH electrolyte 210 is applied as a low viscosity aqueous mixture from the dispenser 211 to the porous film 201, thereby filling the internal pores 212 of the porous film 201. , Optionally further forming a layer 213 overlying the first surface of the porous film. The electrolyte 210 is then gelled by heat treatment to provide the gel electrolyte in the internal pores of the film 201 and in the layer 213.

  [0117] The high surface area reduced graphene oxide of the electrodes 202 and 203 is in direct contact with the underlying portion of the first surface 208 of the porous film 201 and thus in ionic communication with the first surface 208. In use, when a potential is applied across the separation electrodes 202 and 203 to charge the energy storage device, or when the device is discharged through an external circuit, the electrolyte in the internal pores is shown by the arrow 214 in FIG. Provides a path for ion communication between the electrodes as depicted in FIG. Optionally, an augmented path for ionic communication is also provided through layer 213 above first surface 2018 as depicted by arrow 215. Nonetheless, the internal pore 212 serves as the primary reservoir for the electrolyte 210, and in particular provides an ion transport path through multiple directions between the capacitive reduced graphene oxide materials of the electrodes 202 and 203.

[0118] From this, a schematic plan view of a fracture surface of a capacitive energy storage device 300 comprising a porous PVDF film 301 infiltrated with an electrolyte (not shown) and a pair of spaced electrodes 302 and 303 is shown. Another embodiment of the invention will be described with reference to FIG. The electrodes 302 and 303 include reduced graphene oxide, which is printed directly on the surface of the porous film as graphene oxide and chemically reduced there. The plurality of electrodes integrally form a pair of comb-shaped electrodes, and each electrode has four fingers. Fingers has a 100 microns wide (FIG. 5 on the display and _{w f)} and 900 microns long (shown in Figure 5 and _{L f).} The separation between the electrodes (designated as d _{s in} FIG. 5), ie the shortest distance between adjacent fingers, is approximately 30-50 microns. Pair of spaced apart electrodes 302 and an electrode itself and the inter-electrode separation zone 303, about which is calculated as the product of (respectively shown in Figure 5 as w _e and L _e) electrode to width and the electrode-to-length covering the surface area on the porous film of less than 1 mm ^2.

  [0119] Another embodiment of the invention will now be described with reference to FIG. 6 depicting a capacitive energy storage device 400. A plurality of pairs of spaced electrodes 402 and 403 (shown as 402a / 403a to 402d / 403d in FIG. 6) are disposed on the first surface 408 of the porous PVDF film 401. The film 401 is infiltrated with an electrolyte (not shown). Electrodes 402 and 403 comprise reduced graphene oxide, reduced graphene oxide printed directly on the surface of the porous film as graphene oxide and chemically reduced therein, in ionic communication with surface 408. ing.

  [0120] Capacitive energy storage device 400 comprises parallel electrode pairs (ie, 402a / 403a in parallel with 402b / 403b and 402c / 403c in parallel with 402d / 403d). Capacitive energy storage device 400 also includes electrode pairs connected in series (ie, a combination of 402a / 403a and 402b / 403b is connected in series with a combination of 402c / 403c and 402d / 403d). ing. The array of electrode pairs is electrically connected by a printed linkage of reduced graphene oxide 406 on the first surface 408 of the porous film 401. The array of electrically connected electrode pairs is further provided with electrical contact pads 404 and 405, respectively, made of graphene oxide, which is also printed and reduced. The array of electrodes can be electrically connected to external circuitry via wires 416 and 417 attached to contact pads 404 and 405, respectively.

  [0121] Although the capacitive energy storage device 400 is depicted with two blocks of two parallel-connected electrode pairs connected in series, a wide variety of electrode configurations can also be provided according to the invention. It will be understood that.

  [0122] Another embodiment of the invention will now be described with reference to FIGS. FIG. 7 depicts in side view a first porous PVDF film 501a having a pair of spaced electrodes 502 and 503 disposed directly on the first surface 508a. Electrodes 502 and 503 can be connected to an external circuit via contact pads (not shown) having attached wires. As depicted in FIGS. 7 and 8, the second porous PVDF film 501b is then overlying the first porous film 501a, and the electrodes 502 and 503 are the back surface 509b of the second porous film 501b. Are stacked so as to abut and engage with each other. Since the first porous film and the second porous film are both flexible membranes, the films 501a and 501b fit closely around the electrodes 502 and 503 so that the surfaces 508a and 509b are in contact, At most, a slight gap 519 remains around the electrode.

  [0123] As depicted in FIGS. 8 and 9, a polyvinyl alcohol / KOH electrolyte 510 is then applied as a low viscosity aqueous mixture from a dispenser 511 to the stacked porous film 501a and film 501b, This fills the internal pores 512a of the porous film 501a and the internal pores 512b (and the gap 519 if present) of the porous film 201b. The electrolyte 210 is then gelled by heat treatment to provide the gel electrolyte within the internal pores of both films 501a and 501b. Thus, a stacked capacitive energy storage device 500 is depicted in FIG.

  [0124] The high surface area reduced graphene oxide of the electrodes 502 and 503 is in direct contact with the first surface 208a of the porous film 501a and the back surface 509b of the second porous film 501b, and thus in ionic communication. In use, when a potential is applied across the separation electrodes 502 and 503 to charge the energy storage device, or when the device is discharged via an external circuit, the electrolyte in the internal pores of both films 9 provides a path for ion communication between the electrodes, as depicted by arrows 514a and 514b. Electrodes 502 and 503 are effectively surrounded on all sides by a reservoir of electrolyte contained substantially entirely within the internal pores of the first porous film 501a and the second porous film 501b. , Thereby providing an ion transport path through multiple directions between the capacitive reduced graphene oxide materials of electrodes 502 and 503, while avoiding dead volume in the device occupied by the electrolyte layer .

  [0125] Another embodiment of the invention will now be described with reference to FIGS. FIG. 10 depicts a first porous PVDF film 601a and a second porous PVDF film 601b, each of which is a plurality of spaced electrodes 602 and 603 disposed on the first surfaces 608a and 608b. A pair (including 602a / 603a and 602b / 603b, respectively). Electrodes 602 and 603 comprise reduced graphene oxide and are connected via conductive linkages 606a and 606b, as described herein with reference to FIG. 6, and electrical contact pads 604a and 605a and 604b and 605b are provided respectively. The contact pad 604a can be electrically connected to an external circuit through an attached wire 616.

  [0126] As depicted in FIGS. 10 and 11, the second porous PVDF film 601b is described in more detail above the first porous film 601a, now in connection with FIG. As shown, the electrodes 602a and 603a are stacked so as to abut and engage with the back surface 609b of the second porous film 601b. The films are stacked so that the contact pads 605b are aligned vertically with the contact pads 605a. A conductive silver particle filled epoxy resin 618 dispensed from dispenser 619 is then placed into opening 620b and onto the adjacent area of contact pad 605b. The opening 620b is a hole that penetrates the entire thickness of the contact pad 605b and the second porous film 601b. With the films stacked, the conductive epoxy 618 penetrates through the openings 620b and contacts the contact pads 605a on the first porous film 601a. The epoxy 618 is then cured to create a permanent electrical connection 621a-621b between the contact pads 605a and 605b and permanently bond the porous films 601a and 601b together.

  [0127] It should be understood that the openings 620b may be formed either before or after the step of printing the contact pads 605b on the first surface 608b, and further the porous film 601b is made porous. It may be formed either before or after the stage of stacking on the film 601a. Similarly, it should be understood that the opening 620b does not necessarily extend straight through the contact pad 605b, for example, it extends over the surface 608b onto the contact pad 605b when epoxy 618 is applied. It may be positioned adjacent to the contact pad 605b. Also, the contact pads 605b and 605a need not be the same size and need not be perfectly vertically aligned. As will be appreciated by those skilled in the art, contact pads 605a and 605b and opening 620b may be configured differently, provided that an appropriate electrical connection between the contact pads can be provided.

  [0128] Other means that electrically connect contact pads 605a and 605b and do not rely on openings formed in the film are considered to be within the invention. For example, a sufficiently low viscosity conductive material may be applied to the first surface 608b on and / or adjacent to the contact pad 605b and the internal pores of the porous film 601b to make an electrical connection. May be allowed to pass through to contact the contact pad 605a. As another alternative, the electrical connection may be provided via a metal wire or clip that extends around the edge of the porous film 601b.

  [0129] As depicted in FIGS. 11 and 12, a third porous PVDF film 601c having a plurality of pairs of electrodes comprising 602c / 603c disposed on the first surface 608c is then The electrodes 602b and 603b are stacked on the second porous film 601b so as to abut and engage with the back surface 609c of the third porous film 601c. Then, conductive connections 621b-621c between contact pads 604c and 604b are made by infiltrating conductive epoxy resin 618 through openings 620c. The contact pad 605c can be electrically connected to an external circuit through an attached wire 617.

  [0130] Polyvinyl alcohol / KOH electrolyte 610 is then applied to porous films 601a, 601b, and 601c stacked from dispenser 611 as a low viscosity aqueous mixture, as depicted in FIGS. , Thereby infiltrating the entire stack including the internal pores 612 of all three porous films. The electrolyte 610 is then gelled by heat treatment to provide the gel electrolyte within the internal pores of the films 601a, 601b, and 601c. Thus, a stacked capacitive energy storage device 600 is depicted in FIG.

  [0131] FIG. 14 depicts a side perspective view of a capacitive energy storage device 600 that includes stacked porous films 601a, 601b, and 601c and electrode pairs 602 and 603 on each film; The electrode pairs 602a / 603a and 602b / 603b are sandwiched between the films 601a and 601b and between the films 601b and 601c, respectively. Cured conductive epoxy electrical connections 621a-621b penetrate the thickness of film 601b, thus electrically connecting contact pads 605b and 605a as described herein. Similarly, electrical connections 621b-621c penetrate the thickness of film 601c, thus connecting contact pads 604c and 604b to the electrical body. Gelled electrolyte 610 is infiltrated throughout the stack and is primarily located within the internal pores 612 of each of the porous films 601a, 601b, and 601c. The entire electrochemical storage device is isolated in a Kapton polyimide pouch 621 with only wires 616 and 617 protruding for connection to external circuitry. . It is noteworthy that the stacked device 600 is flexible because it is constructed from multiple layers of flexible polymer membranes and wrapped entirely in a flexible pouch.

  [0132] The high surface area reduced graphene oxide of the paired electrodes 602a / 603a is sandwiched between the porous films 601a and 601b and thus in ionic communication with both porous films, while the paired electrodes The reduced graphene oxide of 602b / 603b is sandwiched between the porous films 601b and 601c, and thus is in ionic communication with both porous films. In use, when a potential is applied across a connected array of electrode pairs extending across all three layers of the stack to charge device 600, or device 600 (via wires 616 and 617). When discharged through an external circuit, the electrolyte in the internal pores of the porous film provides a path for ionic communication between the electrode pair.

  [0133] FIGS. 13 and 14 depict a stacked capacitive energy storage device 600 having three layers of porous films and electrodes, but with multiple layers comprising four layers, five layers, or even more. It will be appreciated that the layer stack can be made by the same methodology. The device 600 is depicted as having only one electrical connection between adjacent layers, but the multi-layer stack is also designed to have multiple electrical connections between electrodes in adjacent layers. You can also. For example, pairs of electrodes on adjacent layers may be connected in parallel by electrically connecting one electrode of each pair to a corresponding electrode on the adjacent layer side.

  [0134] The invention will now be described in connection with the following examples. It should be understood that the examples are illustrative of the invention described herein and are not intended to limit the invention described herein.

material
[0135] Large flake natural graphite was obtained from Strategic Energy Resources Pty Ltd. From the company. Potassium hydroxide (KOH), polyvinyl alcohol (PVA), acetonitrile, hydroiodic acid, acetic acid, sulfuric acid, potassium persulfate, phosphorous pentoxide, potassium permanganate, ammonia (NH ₄ OH), and hydrazine were added to Sigma Aldrich. Purchased from the company and used without any further purification. A cross-linked polyacrylic acid copolymer-based hydrogel bead having the ability to absorb water up to 90 times its own weight is obtained from Demi Co Ltd. From China (China). Flexible and porous PVDF membranes (˜50 micron thick and 0.2 micron pore size) were obtained from mdi Technologies Pty Ltd. From India (India). A non-porous cellulose acetate sheet (Nobo Universal's transparency sheet) was obtained from an office supply retailer. Electrically conductive epoxies were made from Japanese AgIC Inc. AGIC is at least a registered trademark of AGIC Co., Ltd. in Japan, and AgIC is at least a registered trademark of Elephantec Co., Ltd. (former name: AgIC Co., Ltd.). Is a separate corporation, and this description seems to indicate the latter). A Kapton polyimide sheet was purchased from Dupont.

Example 1. Preparation of single layer capacitive energy storage device 1a) Synthesis of graphene oxide
[0136] Graphene oxide (GO) was synthesized using a modified Hamers method. For synthesis, large flake graphite, sulfuric acid, potassium persulfate, phosphorus pentoxide, and potassium permanganate were used. The synthesized GO was exfoliated in reverse osmosis purified water by ultrasonic treatment for 1 hour (UP-100 ultrasonic treatment apparatus), and then centrifuged to remove unexfoliated crystals of GO.

1b) Preparation of GO ink
[0137] A dispersion in which GO was dispersed in water at a GO concentration of 0.25 mg / ml was prepared as described above. To a 1 liter dispersion sample, 10 g of superabsorbent polymer (SAP) beads were added. After 1 hour, the saturated bead was separated from the remaining dispersion, washed with water and dried at 50 ° C. for reuse. The concentrated dispersion after bead removal had a volume of 10 ml with a GO concentration of 30 mg / ml. The viscosity of the ink was 25 Pas.

1c) Gravure printing of graphene oxide microelectrodes
[0138] The GO ink was printed on flexible porous polyvinylidene fluoride (PVDF) film using a gravure printing device (Labratester 180 from nsm Norbert Schlafli Machinen, Switzerland). A plate was designed having comb electrodes of various sizes and comprising an array of interconnected electrode patterns in various combinations of series and parallel configurations. The plate surface was etched with a laser procured from Norbert Schlafli AG, Switzerland. An example of plate design is depicted in FIG. 15 and a photograph of the etched plate is depicted in FIG.

  [0139] GO ink was applied to the plate surface. Next, the flexible PVDF film wound around the coating roller was brought into rolling contact with the flat plate surface, and the separation electrode was printed on the surface of the PVDF film. The printed electrode was dried within a few minutes under atmospheric conditions.

  [0140] An example of a porous PVDF film having spaced comb GO electrodes disposed on the surface is depicted in FIGS. In FIG. 17, a wide variety of combinations of series and / or parallel electrode pairs are produced in the printing process, including parallel multiple electrode pairs, serial multiple electrode pairs, and blocks with parallel connected electrode pairs connected in series. You will see that. The spaced electrode pairs in the array are connected by graphene oxide linkages on the surface of the PVDF film, and each connected array of spaced electrode pairs further has two square graphene oxide contact pads.

[0141] FIG. 18 (a) shows an enlarged view of an array of four pairs of comb-shaped spaced apart electrodes 4 connected in parallel, and FIG. 18 (b) shows a comb-shaped spaced apart electrode 4 connected in series. An enlarged view of the paired array can be seen. Each pair of electrodes has two comb electrodes, each electrode having four fingers having a width of approximately 90 microns and a length of approximately 890 microns. The out-of-plane thickness of the electrode was approximately 50 nm. The electrode separation distance, that is, the separation distance between the fingers of the comb electrode, is approximately 100 microns. Each pair of comb electrodes, including both electrodes and interelectrode separation areas, covers a surface area of approximately 9 mm ² on the porous PVDF film surface. The graphene oxide contact pads are 2 mm × 2 mm square to facilitate electrical connection to external circuitry.

[0142] Thus, printed electrode pairs with various different dimensions were made. FIG. 19 shows an optical microscope image of the printed comb electrode pair on the PVDF film. The finger width of each electrode is approximately 100 microns and the electrode separation is approximately 40 microns. The electrode pair covers a surface area of less than 2 mm ^{2 on the} surface of the porous PVDF film.

[0143] FIG. 20 depicts an optical microscope image of a pair of printed electrodes on a PVDF film, where the electrodes have a zigzag configuration. The electrode separation is approximately 30 microns, and the electrode pair covers a surface area of less than 0.25 mm ^{2 on the} surface of the porous PVDF film. The printed electrical linkage connecting the electrodes to the electrical contact pads has a line width of approximately 30 microns. Thus, for example, it is believed that a comb electrode having a finger width of less than about 30 microns and an electrode separation of less than about 30 microns can be made by the present method.

  [0144] Various different arrays of electrode pair combinations depicted in FIG. 17 were made on a substrate for research purposes, and in commercial implementations, the configuration of printed electrodes on a porous substrate is It will be understood that it will be made according to energy storage requirements and from the perspective of minimizing unused space on the film surface.

1d) Reduction of the microelectrode
[0145] Use multiple chemical reduction methodologies to reduce printed GO microelectrodes on porous PVDF films with the aim of maximizing conductivity and thereby minimizing resistance-related losses in printed supercapacitors did.

[0146] In a first reduction procedure (hydrazine and ammonia solution reduction), a PVDF film with printed GO microelectrodes was placed in 0.15 ml hydrazine (80 wt%) and 1.05 ml NH ₄ OH (0. 28% by weight) and 300 ml of water and heated at 95 ° C. for 1 hour under a water-cooled condenser. After 1 hour, the film was thoroughly washed with water and methanol and dried in a vacuum oven at 145 ° C. for 1 hour.

  [0147] In a second reduction procedure (hydrazine gas phase reduction), a PVDF film with printed GO microelectrodes was placed on the wall of a 100 ml beaker using Kapton tape. 1 ml of hydrazine (80% by weight) was added to the beaker, which was then covered with parafilm and heated at 100 ° C. for 16 hours. Subsequently, the film was thoroughly washed with water and methanol and dried in a vacuum oven at 145 ° C. for 1 hour.

  [0148] In a third reduction procedure (thermal reduction), a PVDF film with a printed GO microelectrode was heated at 150 ° C. (below the melting temperature of the PVDF substrate 170 ° C.) for 6 hours under vacuum.

  [0149] In the fourth reduction procedure (hydrazine solution reduction), a PVDF film equipped with a printed GO microelectrode is immersed in a mixed solution of 1 ml of hydrazine (80% by weight) and 100 ml of water, followed by water-cooled condensation. Heated under a vessel at 100 ° C. for 24 hours. Subsequently, the film was thoroughly washed with water and methanol and dried in a vacuum oven at 145 ° C. for 1 hour.

  [0150] In a fifth reduction procedure (hydroiodide reduction), a PVDF film with printed GO microelectrodes was placed on the wall of a 300 ml beaker using Kapton tape. 2 ml of hydroiodic acid (55 wt%) and 5 ml of acetic acid were added to the beaker. The beaker was covered with parafilm and heated at 40 ° C. for 16 hours. Subsequently, the film was washed thoroughly with water and methanol and dried under atmospheric conditions.

  [0151] Wire the Precision B2900 series Precision Source / Major Unit with a 5 micron tip tungsten probe through the EmCal Genelyte probe station. Used to perform a two point conductivity measurement. The probe was placed 1 mm apart on a 2 mm × 2 mm contact pad of the electrode. Measurements were taken by changing the applied voltage between 0V and 1V. The scanning speed used for the measurement was 0.8 V / s, and the measured value was taken every 0.008 V.

  [0152] The resistivity of the printed graphene oxide after reduction according to one of the first to fifth reduction procedures is shown in FIG. The highest resistivity was observed in the case of thermally reduced and printed GO (10 kΩm), which was equivalent to the resistivity of GO at the time of printing. The lowest resistivity (approximately 20 Ωm) has been observed in the case of hydroiodic acid reduction and therefore it was used in subsequent electrochemical characterization studies.

  [0153] FIG. 22 depicts a porous PVDF film with multiple pairs of comb-shaped reduced graphene oxide electrodes disposed on the film surface. The clear color change of graphene oxide from brown (unreduced) to black (reduced) was obvious. The reduction process did not degrade the printed configuration of the electrode.

1e) Cell assembly and electrolyte infiltration
[0154] A thin line of wax (generally having a width in the range of 1 mm-1.5 mm) was deposited on the porous film between the printed and reduced electrode and the electrode contact pad. This locally penetrated the holes in the film and closed the holes prior to solidifying the contact pads, thus isolating the contact pads from the electrolyte. An electrolyte mixture was prepared by adding polyvinyl alcohol (PVA, 1 g) to deionized (DI) water (10 ml) and the mixture was heated at 90 ° C. with constant stirring. When the PVA / water solution became clear, KOH (10 ml of 6M solution) was added dropwise until a homogeneous solution was achieved. Subsequently, the electrolyte mixture was cooled to room temperature. The porous film was then infiltrated with a low viscosity PVA / KOH electrolyte mixture qualitatively having the same viscosity as glycerin and therefore estimated to be about 1 Pas. Infiltration was performed by drop casting the electrolyte onto the porous film until saturation; the uncured electrolyte mixture was visibly in the film until a visible electrolyte layer was formed on the surface. Absorbed. Once the film was infiltrated with the electrolyte premix, the electrode / electrolyte assembly was allowed to stand at room temperature for 24 hours to promote electrolyte gelation within the film pores. The cell was then sealed in a Kapton sheet pouch. A small alligator clip with metal wire attached is sandwiched between the pair of comb-like reduced graphene oxide electrodes on the surface of a porous PVDF film or the electrical contact pad side of a plurality of electrically connected arrays In addition, the electrochemical response of various devices was measured.

Example 2 Electrochemical evaluation of single layer capacitive energy storage devices
[0155] The electrochemical response of the capacitive energy storage device made by the method of Example 1 was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using Biologic's VSP potentiostat. It was attached.

  [0156] In order to ensure stable electrochemical conditions, open circuit potential measurements were performed for 1 hour before each electrochemical test. A stable electrochemical condition was considered if a variation of less than 10 mV of open circuit potential persisted over a period of 1000 seconds. The CV test was performed at a scanning speed of 10 mV / s between 0 V and 0.5 V, and was repeated for approximately 100 cycles. The EIS test was performed by applying a sinusoidal potential wave at an open circuit potential with an amplitude of 10 mV. The impedance response was measured over a frequency between 1 MHz and 10 mHz and 6 points were recorded per decade of frequency.

[0157] CV response of a single pair of printed and reduced comb electrodes (4 fingers, finger width approximately 90 microns, finger length approximately 890 microns, out-of-plane thickness approximately 50 nm, electrode separation distance approximately 100 microns) Is approximately rectangular, suggesting ideal capacitive behavior and low internal resistivity, as depicted in FIG. The energy storage capacity of the device increased slightly over the first 20 cycles, as depicted in FIG. 24, and then remained substantially unchanged over an additional 80 cycles. The specific capacitance of the single electrode to capacitive energy storage device was calculated to be approximately 3 mF / cm ² and further demonstrated a high cyclability of 10 mV / s.

[0158] Consistent with the CV response, the Nyquist plot of the single electrode pair device also shows excellent capacitive behavior, as shown in FIG. The equivalent series resistance was calculated to be 8 Ωcm ² .

Example 3 Comparative example
[0159] Graphene oxide ink prepared according to the procedure of Example 1a) -1b) was printed onto a flexible polymer film according to the procedure of Example 1c). As described in Example 1, a high resolution spaced electrode pair with well-defined features of less than about 30 microns could be printed onto the porous PVDF film. In contrast, non-porous cellulose acetate films were unsuccessfully printed on comb electrodes. The ink coalesces on the surface, causing a complete loss of the printed depiction. Accordingly, it has been determined that the uptake of aqueous phase ink into the pores of the PVDF film being printed contributes to the high resolution of the electrode features realized.

Example 4 Preparation of stacked capacitive energy storage devices 4a) Multi-layer stacking and electrical connection
[0160] Three porous PVDF films, each having a pair of comb-shaped reduced graphene oxide electrodes, were prepared by the method of Examples 1a) -1d). The electrode pair comprised four finger electrodes having a finger width of approximately 90 microns, a finger length of approximately 1800 microns, an out-of-plane thickness of approximately 50 nm, and an interelectrode separation of approximately 200 microns. Each electrode was connected to a reduced graphene oxide contact pad (2 mm × 2 mm) on the film surface. Between each electrode and contact pad, a wax coating was deposited as described in Example 1e). A precision hole puncher with a diameter of 0.8 mm was then used to create a precision hole with a diameter of 0.8 mm through each layer of electrical contact pads and the underlying film.

  [0161] The three layers were then stacked directly on top of each other with the holes in each layer aligned vertically. Next, a highly conductive epoxy adhesive containing silver nanoparticles and having a paste-like consistency was used to pre-stack the electrical contacts of the electrode using a syringe with a 0.5 mm needle opening. Through the holes, the epoxy was brought into contact with the electrical contact pads of each layer. After deposition, the epoxy adhesive was cured at room temperature for 24 hours. The establishment of electrical connections through the three substrate layers was verified using a digital multimeter. As a result of the electrical connection, the electrode pairs on each layer were electrically connected in parallel.

4b) Cell assembly and electrolyte infiltration
[0162] An electrolyte mixture was prepared by mixing polyvinyl alcohol (PVA, 3 g) in deionized water (30 ml) and adding H ₂ SO ₄ (98%, 3 g) dropwise. The mixture (8.33 wt% PVA) was heated to 85 ° C. with vigorous stirring for 1 hour and allowed to cool to room temperature. The low viscosity electrolyte mixture was then drop cast onto a stack of porous films and subsequently dried under atmospheric conditions for 24 hours. The infiltration of the electrolyte in the three-layer stack was visually observable because the entire stack became transparent. The cell was then sealed in a Kapton sheet pouch. Next, two small crocodile clips with metal wires attached were sandwiched between the stacks, and the electrochemical response of the stack type energy storage device was measured. Each clip was electrically connected to one electrode on each layer via a top layer electrical contact pad and a conductive epoxy connection between layers.

Example 5 FIG. (Comparative example)
[0163] A three-layer stacked device was prepared according to the method of Example 4a.
[0164] An electrolyte mixture was prepared by mixing polyvinyl alcohol (PVA, 3 g) in deionized water (30 ml) and adding H ₂ SO ₄ (98%, 3 g) dropwise. The mixture (8.33 wt% PVA) was heated to 85 ° C. with vigorous stirring for 1 hour, poured as a film into a petri dish and dried at 80 ° C. for 8 hours. The gelled film was then removed from the Petri dish, placed over the top layer of the stack manually and pressed onto the stack through polyimide tape. Thus, the porous film of the stack was placed in ionic communication with the electrode pair on the stack with the electrolyte layer overlying but not infiltrating. The cell was sealed in a kapton sheet pouch as described in Example 4b) and an alligator clip was attached.

Example 6 Electrochemical evaluation of stacked capacitive energy storage devices
[0165] The electrochemical response of stacked capacitive energy storage devices made according to the methods of Example 4 and Example 5 is electrochemical impedance using cyclic voltammetry (CV) and Biologic's VSP potentiostat. Characterized by spectroscopy (EIS).

  [0166] In order to investigate the effect of electrolyte infiltration through the three porous film layers in the stack, an open circuit potential measurement was first performed as described in Example 2. As evident in FIG. 26, the stacked energy storage device (prepared in Example 4) with electrolyte infiltrated through the pores of the entire stack was stable with very low fluctuations (up to 30 mV vs SHE). An open circuit potential was provided. In contrast, large voltage fluctuations (range 600 mV-1.8 V vs SHE) were obtained in the stacked device (prepared in Example 5) with only the electrolyte layer on top. This result demonstrates the importance of electrolyte infiltration into the pores of the porous film of the electrochemical storage device according to the invention.

  [0167] The CV response over 100 cycles (0 V to 0.5 V at a scan rate of 10 mV / s) of the stacked, electrically connected, and electrolyte infiltrated energy storage device of Example 4 It is shown in FIG. The energy storage capacity of the device increased slightly over the first 20 cycles and then remained substantially unchanged over an additional 80 cycles. The CV plot is roughly rectangular, suggesting the capacitive behavior of the stacked device configuration.

  [0168] A Nyquist plot for a stacked energy storage device (Example 4) is shown in FIG. The relatively high resistance (compared to that of the single layer device depicted in FIG. 25) may be due to a conductive epoxy connection established between the electrical contact pads on the three layers.

Example 7 Electrode configuration
[0169] In this example, the electrochemical performance of a plurality of different capacitive microelectrode geometries is examined. Microelectrodes were not made according to the present invention; however, it is believed that learning about the effect of geometry on electrode performance can be used to guide the design of capacitive energy storage devices according to the present invention.

[0170] A continuous graphene oxide layer (0.6 micron thick and having an rms roughness of 2.0 nm ± 0.4 nm) was spin coated onto a silicon wafer. Attach wafer to SEM stub with double-sided carbon tape, put into FEI Helios Nanolab 600 FIB-SEM chamber and pump down to vacuum level below 1x10 ^-3 Pa did. Different electrode designs of reduced graphene oxide were then fabricated using a 1 × 10 ⁻⁴ FIB fluence focused ion beam (FIB) direct writing technique on the graphene oxide layer. FIG. 29 shows electrode pair geometries made in this manner, including (a) comb, (b) pad, (c) concentric circles, (d) zigzag, (e) L-shaped, and (f) maze type. The outline is drawn schematically. Each pair of electrodes had the same interelectrode separation and covered the same surface area on the silicon chip.

  [0171] Electrochemical characterization was performed using a probe station with Biologic's VSP potentiostat and Pt probe (5 μm diameter) in reduced sodium contacts in 1 M sodium sulfate. Cyclic voltammetry (CV) was performed at different scan rates for a potential range of 0V-0.5V vs SHE. Electrochemical impedance spectroscopy (EIS) was performed by applying a 10 mV sinusoidal perturbation at an open circuit potential over a frequency range of 10 mHz-1 MHz. CV and EIS measurements were also performed on the Pt probe in contact with the reduced GO to obtain control current, capacitance, and resistance values.

[0172] Table 1 shows the capacitance (calculated as mF / cm ² ) obtained at a low scan rate of 1 mV / s for FIB-reduced graphene oxide electrodes with different geometries for the comb electrode design The normalized value for the obtained capacitance value is shown. It is clear from Table 1 that the geometric shape affects the capacitance value. The maze-type geometry shows the lowest capacitance, whereas the zigzag design shows the highest capacitance. It has been found that the ESR of all these electrodes is equivalent, i.e. within experimental error.

[0173] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such changes and modifications that fall within the spirit and scope of the invention.

Claims (52)

At least one porous film infiltrated with electrolyte;
One or more pairs of spaced electrodes disposed on the first surface of the porous film, each electrode comprising a capacitive electrode material in ion communication with the underlying porous film A pair of
With
The electrolyte provides ionic communication between the spaced electrodes through the internal pores of the porous film;
Capacitive energy storage device.   The capacitive energy storage device of claim 1, wherein the pair of spaced electrodes has an interelectrode separation of less than about 50 microns, desirably less than 30 microns.   The capacitive energy storage device according to claim 1, wherein the pair of separated electrodes has an interelectrode separation distance smaller than a thickness of the porous film. 4. A capacitive energy storage device according to any one of claims 1-3, wherein each pair of spaced electrodes covers a surface area of less than about 1 mm < ² > on the porous film.   The capacitive energy storage device according to any one of claims 1 to 4, wherein the pair of spaced electrodes comprises a comb electrode having 2 to 6 fingers.   The capacitive energy storage device of claim 5, wherein the fingers have a width of less than about 50 microns and a length of less than about 250 microns.   7. A capacitive energy storage device according to any one of the preceding claims, wherein the electrodes are electrically connected to adjacent electrodes and / or external paths without a metal current collector.   The plurality of pairs of the separation electrodes are arranged on the first surface of the porous film and are electrically connected in series and / or in parallel. A capacitive energy storage device according to claim 1.   9. The plurality of pairs of spaced electrodes are electrically connected by a conductive linkage on the first surface of the porous film, the conductive linkage comprising a capacitive electrode material. Capacitive energy storage device.   A plurality of porous films are stacked, and the plurality of porous films includes one or more pairs of the separation electrodes disposed on the first surface of the first porous film. The first to second embodiments, wherein the first and second porous films are stacked in contact with and desirably in ionic communication with a back surface of a second porous film stacked above the first porous film. 10. A capacitive energy storage device according to any one of claims 9 to 10.   At least one of the separation electrodes disposed on the first surface of the first porous film is on the first surface of the second porous film via a conductive path. The capacitive energy storage device of claim 10, wherein the capacitive energy storage device is electrically connected to at least one of the spaced apart electrodes disposed.   The capacitive energy storage device of claim 11, wherein the conductive path comprises a conductive material in an opening extending through the thickness of the second porous film.   13. A capacitive energy storage device according to claim 12, wherein the conductive material comprises a curable resin comprising a dispersed metal, preferably a silver filled epoxy.   14. Capacitive according to any one of the preceding claims, wherein the at least one porous film is a flexible polymer membrane having a thickness of less than 100 microns, desirably less than 50 microns. Energy storage device.   15. The flexible polymer film comprises at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl chloride, nylon, and polyethylene terephthalate, and preferably comprises polyvinylidene fluoride. A capacitive energy storage device according to claim 1.   The capacitive energy according to any one of claims 1 to 15, wherein the capacitive electrode material comprises at least one selected from the group consisting of a carbon-based electrode material and a pseudo-capacitive electrode material. Storage device.   The capacitive energy storage device according to any one of claims 1 to 15, wherein the capacitive electrode material comprises reduced graphene oxide.   The capacitive energy storage device according to claim 1, wherein the capacitive electrode material is printed on the porous film.   The capacitive energy storage device according to any one of claims 1 to 18, wherein the electrolyte is a gel electrolyte.   The capacitive energy storage device of claim 19, wherein the gel electrolyte comprises cross-linked polyvinyl alcohol. A first porous film;
One or more pairs of spaced apart electrodes disposed on a first surface of the first porous film, each electrode being in ion communication with the underlying first porous film A pair of spaced apart electrodes comprising a material;
A second porous film stacked above the first porous film, wherein the first electrode of the separation electrode disposed on the first surface of the first porous film; A second porous film, wherein one or more pairs are stacked in contact with the back surface of the second porous film;
An electrolyte in the internal pores of the first and second porous films;
A stacked capacitive energy storage device comprising:   The stacked capacitive energy storage device of claim 21, wherein the capacitive electrode material is in ion communication with the back surface of the second porous film.   23. A stacked capacitive energy storage device according to claim 22, wherein the electrolyte provides ionic communication between the spaced electrodes through internal pores of the first and second porous films.   One or more pairs of spaced apart electrodes disposed on a first surface of the second porous film, each electrode being in ion communication with the underlying second porous film 24. A stacked capacitive energy storage device according to any one of claims 21 to 23, further comprising a pair of spaced apart electrodes comprising an electrode material.   At least one of the separation electrodes disposed on the first surface of the first porous film is on the first surface of the second porous film via a conductive path. 25. The stacked capacitive energy storage device of claim 24, wherein the stacked capacitive energy storage device is electrically connected to at least one of the spaced apart electrodes disposed. A method of making a capacitive energy storage device comprising:
Applying a capacitive electrode material or precursor to the first surface of the porous film to form one or more pairs of spaced electrodes disposed on the first surface;
Infiltrating the porous film with an electrolyte; and
With
The electrolyte provides ionic communication between the spaced electrodes through the internal pores of the porous film;
Method.   27. The method of claim 26, wherein an ink comprising the capacitive electrode material or the precursor is printed onto the first surface.   28. The method of claim 27, wherein the ink is printed onto the first surface by gravure printing or flexographic gravure printing.   29. A method according to claim 27 or claim 28, wherein the ink has a viscosity between 25 Pas and 100 Pas when printed on the first surface.   The method further comprises providing the ink for printing on the first surface, the providing the ink comprising the step of providing the capacitive electrode material or the precursor to increase its viscosity. 30. A method according to any one of claims 27 to 29, comprising the step of concentrating the dispersion.   The capacitive electrode material or the precursor is dispersed in the aqueous continuous phase of the dispersion, and the step of concentrating the dispersion comprises i) absorbing water from the aqueous continuous phase into the water-absorbing solid. 31. The method of claim 30, comprising contacting the dispersion with a water-absorbing solid to effect, and ii) subsequently separating the dispersion from the water-absorbing solid.   32. A method according to any one of claims 26 to 31 wherein the spaced electrodes have an interelectrode separation of less than about 50 microns, desirably less than 30 microns.   The step of applying the capacitive electrode material or the precursor comprises the step of forming a plurality of pairs of the separation electrodes disposed on the first surface of the porous film, 33. A method according to any one of claims 26 to 32, wherein multiple pairs are connected in series and / or in parallel by a linkage comprising the capacitive electrode material or the precursor.   34. The method of any one of claims 26 to 33, further comprising reducing the capacitive electrode material or the precursor on the first surface of the porous film to enhance its conductivity. The method according to item.   35. The method of claim 34, wherein the capacitive electrode material or the precursor is reduced by exposure to a chemical reducing agent, desirably hydroiodic acid.   Stacking a plurality of porous films, wherein the one or more pairs of spaced-apart electrodes disposed on the first surface of the first porous film are the first porous 36. The method of claim 26, further comprising the step of stacking in contact with the back surface of the second porous film stacked above the porous film, and preferably in ionic communication. The method according to any one of the above.   At least one of the separation electrodes disposed on the first surface of the first porous film via a conductive path is disposed on the first surface of the second porous film. The method of claim 36, further comprising electrically connecting to at least one of the spaced apart electrodes disposed.   The step of electrically connecting the electrodes comprises the step of placing a conductive material into an opening extending through the thickness of the second porous film to create the conductive path. 38. The method of claim 37.   39. A method according to claim 37 or claim 38, wherein the conductive material comprises a curable resin comprising a dispersed metal, desirably a silver filled epoxy.   40. The method of claim 39, wherein the method further comprises the step of curing the curable resin, wherein the step of curing adheres the first porous film to the second porous film.   41. The method of any one of claims 36 to 40, wherein the plurality of porous films are infiltrated with the electrolyte after the step of stacking the porous films.   42. Any of claims 26 to 41, wherein the porous film is infiltrated with a low viscosity curable electrolyte and the method further comprises curing the low viscosity curable electrolyte to form a gel electrolyte. The method according to claim 1.   43. The method of claim 42, wherein the low viscosity curable electrolyte comprises crosslinkable polyvinyl alcohol.   44. A method according to any one of claims 26 to 43, wherein the at least one porous film is a flexible polymeric membrane having a thickness of less than 100 microns, desirably less than 50 microns.   45. The flexible polymer membrane comprises at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl chloride, nylon, and polyethylene terephthalate, and preferably comprises polyvinylidene fluoride. The method described in 1.   46. The capacitive electrode material or the precursor comprises at least one selected from the group consisting of carbon-based electrode materials, pseudo-capacitive electrode materials, and precursors thereof. The method according to any one of the above.   The capacitive electrode material or the precursor comprises graphene oxide, and the method includes reducing the graphene oxide on the first surface of the porous film to produce reduced graphene oxide. 46. A method according to any one of claims 26 to 45, comprising:   48. A capacitive energy storage device made by the method of any one of claims 26 to 47. A plurality of porous films, wherein each porous film is disposed on a first surface of the porous film and includes a capacitive electrode material that is in ion communication with the first surface. Use of a plurality of porous films comprising one or more pairs for making a capacitive energy storage device, the use comprising:
Stacking the porous films, wherein the one or more pairs of spaced electrodes disposed on the first surface of the first porous film are the first porous film; Stacking in contact with the back surface of a second porous film stacked above the film;
Infiltrating the porous film with an electrolyte; and
Equipped with, use.   50. Use according to claim 49, wherein the contact provides ionic communication between the electrode and the back surface.   At least one of the separation electrodes disposed on the first surface of the first porous film via a conductive path is disposed on the first surface of the second porous film. 51. Use according to claim 49 or claim 50, further comprising electrically connecting to at least one of the spaced apart electrodes disposed.   The step of electrically connecting the electrodes comprises the step of placing a conductive material into an opening extending through the thickness of the second porous film to create the conductive path. 52. The use according to claim 51, wherein: