Screen-printed microsupercapacitors enabled by hexagonal boron nitride ionogel electrolytes

Abstract

This invention relates to a screen printable electrolyte ink and a device including a microsupercapacitor that is fully printed with the ink. The ink comprises an ionic liquid; and a solid matrix material mixed with the ionic liquid in at least one solvent.

Description

[0001] SCREEN-PRINTED MICROSUPERCAPACITORS ENABLED BY HEXAGONAL BORON NITRIDE IONOGEL ELECTROLYTES

[0002] STATEMENT AS TO RIGHTS UNDER FEDERALLY-SPONSORED RESEARCH

[0003] This invention was made with government support under grant number 70NANB19H005 awarded by the National Institute of Standards and Technology, and CMMI-2037026 and DGE- 1842165 awarded by the National Science Foundation. The government has certain rights in the invention.

[0004] CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0005] This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 530,099, filed August 1, 2023.

[0006] This application is a continuation in part application of U.S. Patent Application Serial No. 17 / 798,618, filed August 10, 2022, which is a U.S. national stage entry of PCT Patent Application No. PCT / US2021 / 015375, filed January 28, 2021, which itself claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 975,282, filed February 12, 2020.

[0007] This application is also a continuation in part application of U.S. Patent Application Serial No. 18 / 246,197, filed March 22, 2023, which is a U.S. national stage entry of PCT Patent Application No. PCT / US2021 / 052307, filed September 28, 2021, which itself claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 085,240, filed September 30, 2020.

[0008] This application is also a continuation in part application of U.S. Patent Application Serial No. 17 / 968,180, filed October 18, 2022.

[0009] This application is also a continuation in part application of PCT Patent Application No. PCT / US2023 / 064361, filed March 15, 2023, which itself claims priority to and the benefit of U.S. Provisional Application Nos. 63 / 324,311, filed March 28, 2022, and 63 / 327,854, filed April 6, 2022.

[0010] Each of the above-identified applications is incorporated herein in its entirety by reference.

[0011] FIELD OF THE INVENTION

[0012] The present invention relates generally to materials for electronic devices, and more particularly to screen printable electrolyte inks which enable fully printed microsupercapacitors and applications of the same. BACKGROUND OF THE INVENTION

[0013] The background description provided herein is for the purpose of generally presenting the context of the invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the invention.

[0014] The rising demand for portable electronics is driving the need for innovative on-chip energy storage solutions. For example, the expanding Internet of Things (loT) requires widespread, self- powered sensor networks that are robust in diverse environmental conditions. For remote and autonomous operation, these devices rely on compact, integrated power sources. Microsupercapacitors (MSCs) are promising power sources for distributed sensor networks due to their exceptionally long cycle lives coupled with rapid energy delivery and uptake. Additionally, the MSC planar device architecture is easily integrated with all components of a wireless sensor, allowing for streamlined manufacturing directly on a single substrate.

[0015] Supercapacitors store energy via the formation of an electrochemical double layer at the electrode-electrolyte interface. Since the ion adsorption and desorption process is rapid and fully reversible, supercapacitors possess higher power densities and significantly longer cycle lives compared to batteries. Because the strengths of supercapacitors complement the relatively high energy densities of batteries, these two technologies are often used in tandem as a comprehensive energy storage solution. Moreover, the rapid charging capabilities of supercapacitors make them ideal to be integrated with remote energy harvesters or wireless charging coils.

[0016] Planar MSCs include both positive and negative electrodes on a single substrate, often in an interdigitated electrode geometry. This architecture is attractive for on-chip integrated energy storage because the power source can be fabricated alongside other device components instead of as a bulky addition. Conventional microfabrication techniques (e g., photolithography) can be used to pattern interdigitated electrodes with exceptionally small features. However, these techniques are not generally compatible with flexible or wearable devices, nor are they well-poised for industrial manufacturing due to the necessity of clean room processing and toxic chemicals. Similarly, other labscale fabrication techniques that are typically employed in thin-fdm energy storage research, such as physical and chemical vapor deposition, spin-coating, and spray-coating, are absent from industrial energy storage manufacturing due to their low throughput. Therefore, the on-chip energy storage sector stands to benefit greatly from alternative scalable fabrication methods.

[0017] Due to their low waste and rapid deposition of electronic materials, additive manufacturing methods hold significant promise in this context. Among additive manufacturing options, screen printing is particularly desirable due to its high throughput and proven utility for electronics manufacturing such as printed circuit boards. During screen printing, a viscous ink is pushed through a pre-patterned mesh screen using a squeegee and deposited onto a substrate. Unlike related deposition methods (e g., blade coating), screen printing can form complex patterns at the microscale. In addition, multi-step screen printing enables layer-by-layer deposition of each electrically active component for streamlined fabrication of integrated planar microdevices with high reproducibility.

[0018] Among printed electronic materials, graphene is particularly attractive as a supercapacitor electrode material because of its large specific surface area, high electrical conductivity, exceptional theoretical capacitance, and robust mechanical properties. Furthermore, graphene nanoplatelets can be scalability produced and dispersed in various solvents via liquid phase exfoliation. For these reasons, graphene is widely used as a printable electrode material in thin-film transistors and energy storage devices. On the other hand, relatively little effort has been focused on printable solid-state electrolytes. While some examples exist, a large-scale, high-throughput printed solid-state electrolyte has not yet been established for MSCs. For example, while inkjet-printed MSC arrays have been produced using graphene interdigitated electrodes and polymer electrolytes, the manufacturing scalability of this approach is limited by the inherently low throughput of drop-on-demand methods like inkjet printing. Furthermore, these inkjet-printed MSC arrays require 20 total printing passes to achieve the optimal electrolyte print thicknesses due to the low ink deposition volume. In contrast, contact printing methods like screen printing have throughputs that are orders of magnitude higher than drop-on- demand methods. Meanwhile, other attempts to employ additive manufacturing methods for supercapacitors have not printed every component including the current collector and electrolyte, limiting their ultimate scalability. Therefore, the development of suitable inks for high-throughput, multi-step additive manufacturing remains an unmet critical need for MSCs.

[0019] SUMMARY OF THE INVENTION

[0020] In view of the foregoing, one of the objectives of this invention is to provide screen-printable ionogel electrolytes, and its applications.

[0021] In one aspect, the invention relates to a printable ionogel ink, comprising an ionic liquid and a solid matrix material, wherein the solid matrix material is mixed with the ionic liquid in at least one solvent.

[0022] In one embodiment, the printable ionogel ink has a viscosity that is tuned to be compatible with high-throughput screen printing by varying the concentration of the solid matrix material in the at least one solvent.

[0023] In one embodiment, the viscosity is about 76 Pa- s at the shear rate of 10 s'1.

[0024] In one embodiment, a ratio of the solid matrix material :the ionic liquid:the at least one solvent is about 1 :2:2 by mass.

[0025] In one embodiment, the printable ionogel ink is devoid of additives that disrupt ion conduction in an electrolyte film.

[0026] In one embodiment, the printable ionogel ink has an ionic conductivity of about 5 mS cm'1and a storage modulus of about 4 MPa at room temperature.

[0027] In one embodiment, the ionic liquid comprises l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ammonium, imidazolium, pyrrolidinium, pyridinium, piperidinium, phosphonium, sulfonium-based ionic liquids, or a combination of them.

[0028] In one embodiment, the at least one solvent comprises a single solvent including ethyl lactate, cyclohexanone, terpineol, ethylene glycol, ethanol, isopropanol, or butanone.

[0029] In one embodiment, the solid matrix material comprises boron nitride nanosheets (BNNS), borocarbonitrides (BCN), oxide nanosheets, layered perovskites, hydroxide nanosheets including hydrotalcite-like layered double hydroxides, natural clays including bentonites and montmorillonites, or a combination of them.

[0030] In one embodiment, the BNNS comprises hexagonal boron nitride (hBN) nanoplatelets that are obtained from bulk hBN by scalable solution exfoliation.

[0031] In one embodiment, each exfoliated hBN nanoplatelet is coated with a thin amorphous carbon coating.

[0032] In one embodiment, the high-surface-area nanostructured hBN matrix of the ionogel increases interactions with the ionic liquid and leads to an exceptionally high mechanical modulus at sufficiently low hBN loadings that preserve high ionic conductivity.

[0033] In one embodiment, oxide nanosheets comprises AI2O3, TiO2(anatase and rutile), ZrO2, Nb2O5, HfO2, CaCu3Ti40i2, Pb(Zr,Ti)O3, (Pb,La)(Zr,Ti)O3, SiO2, A12O3, HfSiO4, ZrO2, HfO2, Ta2O5, La2O3, LaA103, Nb2Os, BaTiO3, SrTiO3, Ta2Os, or a combination of them.

[0034] In one embodiment, the printable ionogel ink is stable in extreme conditions including at high temperatures up to 180 °C

[0035] In another aspect, the invention relates to a device, comprising one or more components formed of the ionogel ink as disclosed above.

[0036] In one embodiment, the device is one or more batteries, one or more supercapacitors, one or more transistors, one or more neuromorphic computing devices, one or more flexible electronics, one or more printed electronics, or any combination of them.

[0037] In one embodiment, the one or more supercapacitors include one or more all -screen -printed microsupercapacitors (MSCs).

[0038] In one embodiment, each microsupercapacitor includes at least one screen-printed graphene interdigitated electrode and an ionogel electrolyte screen-printed of the printable ionogel ink.

[0039] In one embodiment, the screen-printed graphene interdigitated electrodes include a high- quality percolating network of graphene flakes with an electrical conductivity of 4* 104S m’1.

[0040] In one embodiment, the ionogel electrolyte is screen printed on top of the graphene interdigitated electrodes and dried at a temperature for a period of time to remove residual solvent.

[0041] In one embodiment, the microsupercapacitor is electrochemically characterized using cyclic voltammetry (CV) and galvanostatic measurements, wherein rectangular cyclic voltammograms absent of redox peaks along with triangular galvanostatic charge-discharge curves indicate ideal electrochemical double layer behavior even at high discharge rates.

[0042] In one embodiment, the microsupercapacitor has a capacitance retention of 91.9% after 10,000 charge-discharge cycles.

[0043] In one embodiment, the active material loading is adjusted by increasing the number of printed graphene layers, leading to larger capacitance values.

[0044] In one embodiment, each graphene printed layer is about 690 nm and increases linearly as additional layers are deposited via screen printing.

[0045] In one embodiment, an areal capacitance of 0.14 mF cm’2is achieved with a single graphene print layer, and 0.92 mF cm’2is achieved with ten print layers (an electrode thickness of ~7.5 pm).

[0046] In one embodiment, the interdigitated electrode geometry is utilized so that ions penetrate laterally into the graphene fdm, enabling low-barrier access to the space between individual graphene sheets, thus effectively increasing the electroactive surface area.

[0047] In one embodiment, the microsupercapacitor is flexible and bendable.

[0048] In one embodiment, the microsupercapacitor maintains full capacitance after flexing the MSCs to a 1.5 mm bending radius.

[0049] In one embodiment, the mechanical resilience is enabled by the highly flexible graphene electrodes and the gel-like behavior of the hBN electrolyte.

[0050] In one embodiment, the at least one solvent is selected to result in crack-free screen-printed fdms after its thermal removal, whereby an uninterrupted ion diffusion path throughout the entire device leads to excellent electrochemical performance in addition to reinforcing high mechanical integrity and flexibility.

[0051] In one embodiment, the interdigitated electrode architecture of the microsupercapacitor further eliminates the risk of leakage or device shorting.

[0052] In one embodiment, the individual MSCs are integrated to form series and / or parallel device arrays.

[0053] In one embodiment, the integrated device configurations include two devices in series (2S), two devices in parallel (2P), and a 2SX2P array of devices.

[0054] In one embodiment, the two devices connected in series expand the operating voltage window, while the two devices connected in parallel result in increased discharge current.

[0055] In one embodiment, a 10SxlOPdevice array maintains excellent electrochemical performance, displaying rectangular cyclic voltammograms and triangular galvanostatic curves in the extended 10 V voltage window.

[0056] In one embodiment, the screen-printed MSC arrays maintain excellent cyclability up to 180 °C with improved power density due to the increased ionic conductivity and decreased viscosity of the hBN ionogel electrolyte at elevated temperatures.

[0057] In one embodiment, the reduced electrolyte viscosity allows the electrolyte ions to more easily penetrate the graphene fdm and access the nanostructured surface of the electrodes. In one embodiment, the devices retain 93.6% capacitance after 1000 charge-discharge cycles at

[0058] 180 °C.

[0059] In one embodiment, the IOS* 1 OP array displays excellent cycling behavior at elevated temperatures, including increased capacitance and a power output of 2.6 mW at 180 °C.

[0060] In yet another aspect, the invention relates to a method for forming a printable ionogel ink. The method comprises providing an ionic liquid and a solid matrix material; and mixing the solid matrix material with the ionic liquid in at least one solvent to form the printable ionogel ink.

[0061] In one embodiment, the method further comprises varying the concentration of the solid matrix material and the ionic liquid with the at least one solvent so as to tune a viscosity of the printable ionogel ink that is compatible with high-throughput screen printing.

[0062] In one embodiment, the viscosity is about 25-100 Pa s at the shear rate of 10 s’1.

[0063] In one embodiment, a ratio of the solid matrix materiakthe ionic liquid:the at least one solvent is about 1:2:2 by mass.

[0064] In one embodiment, the printable ionogel ink is devoid of additives that disrupt ion conduction in an electrolyte film.

[0065] In one embodiment, the printable ionogel ink has an ionic conductivity of about 5 mS cm’1and a storage modulus of about 4 MPa at room temperature.

[0066] In one embodiment, the ionic liquid comprises l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ammonium, imidazolium, pyrrolidinium, pyridinium, piperidinium, phosphonium, sulfonium-based ionic liquids, or a combination of them.

[0067] In one embodiment, the at least one solvent comprises a single solvent including ethyl lactate, cyclohexanone, terpineol, ethylene glycol, ethanol, isopropanol, or butanone.

[0068] In one embodiment, the solid matrix material comprises boron nitride nanosheets (BNNS), borocarbonitrides (BCN), oxide nanosheets, layered perovskites, hydroxide nanosheets including hydrotalcite-like layered double hydroxides, natural clays including bentonites and montmorillonites, or a combination of them.

[0069] In one embodiment, the hBN nanoplatelets are obtained from bulk hBN by scalable solution exfoliation.

[0070] In one embodiment, each exfoliated hBN nanoplatelet is coated with a thin amorphous carbon coating.

[0071] In one embodiment, the high-surface-area nanostructured hBN matrix of the ionogel increases interactions with the ionic liquid and leads to an exceptionally high mechanical modulus at sufficiently low hBN loadings that preserve high ionic conductivity.

[0072] In one embodiment, the hBN nanoplatelets are obtained by shear-mixing bulk hBN microparticles in ethanol with ethyl cellulose (EC) acting as a dispersing agent to form a shear-mixed dispersion; separating the exfoliated hBN nanoplatelets and EC from the shear-mixed dispersion by centrifuge-assisted sedimentation and flocculation; and collecting hBN / EC solids; and heating the collected hBN / EC solids at a temperature for a period of time to decompose the EC, thereby volatilizing most of the EC, but also leaving behind a thin amorphous carbon coating on the surface of each of the exfoliated hBN nanoplatelets, which contributes to enhanced interactions between the hBN nanoplatelets and the ionic liquids for stronger solidification of the ionogel ink.

[0073] In one embodiment, the EC decomposition temperature is about 300-500 °C, and the period of time is for about 2-4 hours.

[0074] In one embodiment, the oxide nanosheets comprises AI2O3, TiO2(anatase and rutile), ZrO2, Nb2O5, HfO2, CaCu3Ti40i2, Pb(Zr,Ti)O3, (Pb,La)(Zr,Ti)O3, SiO2, A12O3, HfSiO4, ZrO2, HfO2, Ta2O5, La2O3, LaA103, Nb2Os, BaTiO3, SrTiO3, Ta2Os, or a combination of them.

[0075] In one embodiment, the printable ionogel ink is stable in extreme conditions including at high temperatures up to 180 °C.

[0076] These and other aspects of the present invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure.

[0077] BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The accompanying drawings illustrate one or more embodiments of the invention and together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment.

[0079] FIG. 1 shows an exfoliated hBN ionogel screen-printable ink according to embodiments of the invention. Panel a: Scanning electron microscopy (SEM) image of exfoliated hBN nanoplatelets. Panel b: Photograph of the hBN ionogel screen-printable ink. Panel c: Ionic conductivity as a function of temperature for the hBN ionogel. The dashed line is a Vogel-Fulcher-Tammann (VFT) model fit. Panel d: Temperature dependence of the storage and loss moduli of the hBN ionogel. Panel e: Therm ogravimetric analysis of the hBN ionogel screen-printable ink, which indicates that the ink composition is 1 :2:2 of hBN:EMIM-TFSI:ethyl lactate by mass. Panel f: Viscosity as a function of shear rate of the hBN ionogel ink and a PVA-H3PO4 gel. Panel g: Photograph of a screen-printed ionogel feature on a flexible polyimide substrate. Panels h-i: SEM images of the printed hBN ionogel at two different magnifications.

[0080] FIG. 2 shows electrochemical performance of the fully-printed microsupercapacitor device according to embodiments of the invention. Panel a: Left: photograph of the graphene interdigitated electrodes; Right: completed device with the hBN ionogel printed on top of the graphene interdigitated electrodes. Panels b-c: Cyclic voltammograms of a single microsupercapacitor device at low and high scan rates. Panel d: Galvanostatic charge-discharge curves for a single microsupercapacitor device. Panel e: Capacitance as a function of cycle number for a single microsupercapacitor device. Inset: Cyclic voltammograms at cycle 1 and cycle 10,000. Panel f: Cyclic voltammograms for microsupercapacitor devices printed with 1, 2, 5, and 10 layers of graphene (scan rate: 50 mV / s). Panel g: Rate capability of microsupercapacitor devices printed with 1, 2, 5, and 10 layers of graphene. Panel h: Cyclic voltammograms of a single microsupercapacitor device during bending (bending radius: 1.5 mm; scan rate: 50 mV / s). Panel i: Photographs of a microsupercapacitor device during bending tests.

[0081] FIG. 3 shows microsupercapacitor device integration according to embodiments of the invention. Panel a: Photograph of small-scale integrated device configurations: two devices in series (2S), two devices in parallel (2P), and a 2x2 array of devices (2Sx2P). Panel b: Cyclic voltammograms of various microsupercapacitor device configurations (scan rate: 100 mV / s). Panel c: Galvanostatic charge-discharge curves of various microsupercapacitor device configurations (applied current: 10 pA). Panel d: Top: photograph of a lOSx lOP array of screen printed graphene interdigitated electrodes before the hBN ionogel was printed; Bottom: photograph of a fully-printed 10Sx 10P microsupercapacitor array including the hBN ionogel printed on top of the graphene interdigitated electrodes. Panel e: Cyclic voltammograms of the 10Sx10P microsupercapacitor array. Panel f: Galvanostatic charge-discharge curves of the 10Sx10P microsupercapacitor array. Panel g: Photographs of the lOSx lOP microsupercapacitor array while being flexed around a 2.5 cm bending radius. Panel h: Cyclic voltammograms of the 10Sx10P microsupercapacitor array, showing indistinguishable performance while in the bent and flat orientations (scan rate: 2 V / s).

[0082] FIG. 4 shows high-temperature operation of screen-printed microsupercapacitors according to embodiments of the invention. Panel a: Cyclic voltammograms of a single microsupercapacitor device at elevated operating temperatures (scan rate: 1 V / s). Panel b: Capacitance retention as a function of cycle number for a single microsupercapacitor device operating at 180 °C (scan rate: 1 V / s). Inset: Cyclic voltammograms at cycle 1 and cycle 1000. Panel c: Cyclic voltammograms of a 10Sx10P array of microsupercapacitor devices at elevated operating temperatures (scan rate: 10 V / s). Panel d: Output power as a function of operating temperature of the IOS* 1 OP microsupercapacitor array. Panel e: Comparative photographs of microsupercapacitor devices based on the hBN ionogel electrolyte and a PVA-H3PO4 polymer gel electrolyte after exposure to elevated temperatures.

[0083] FIG. 5 shows screen-printed graphene electrodes according to embodiments of the invention. Panel a: Thermogravimetric analysis of the graphene screen-printable ink. Panel b: Viscosity as a function of shear rate for the graphene screen-printable ink, showing shear thinning behavior. Panel c: Optical micrograph of the screen-printed graphene interdigitated electrodes. Panel d: Scanning electron micrograph of the graphene electrode surface.

[0084] FIG. 6 shows mesh screens used for screen printing according to embodiments of the invention. Photographs of patterned mesh screens used for printing (panel a) the graphene electrodes and (panel b) the hexagonal boron nitride (hBN) ionogel electrolyte.

[0085] FIG. 7 shows graphene thickness as a function of number of screen-printed layers on a polyimide substrate according to embodiments of the invention. The thickness was determined by laser confocal microscopy.

[0086] FIG. 8 shows cyclic voltammograms of a single microsupercapacitor (MSC) device at operating temperatures up to 200 °C, according to embodiments of the invention.

[0087] FIG. 9 shows cyclic voltammograms of a single MSC device before and after a high- temperature soak at 300 °C for 20 min, according to embodiments of the invention.

[0088] FIG. 10 shows a photograph of the high-temperature testing setup according to embodiments of the invention. MSCs were cycled while on a hot plate at elevated temperatures. Extended leads were painted with silver paint so the potentiostat probes could be connected to the device away from the hot plate.

[0089] DETAILED DESCRIPTION OF THE INVENTION

[0090] The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

[0091] The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. Certain terms that are used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the invention. For convenience, certain terms may be highlighted, for example using italics and / or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term is the same, in the same context, whether or not it is highlighted. It will be appreciated that same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

[0092] It will be understood that, as used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates otherwise. Also, it will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0093] It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the invention.

[0094] Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element’s relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending of the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.

[0095] It will be further understood that the terms “comprises” and / or “comprising,” or “includes” and / or “including” or “has” and / or “having”, or “carry” and / or “carrying,” or “contain” and / or “containing,” or “involve” and / or “involving, and the like are to be open-ended, i.e., to mean including but not limited to. When used in this disclosure, they specify the presence of stated features, regions, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / or groups thereof.

[0096] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0097] As used in this disclosure, “around”, “about”, “approximately” or “substantially” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about”, “approximately” or “substantially” can be inferred if not expressly stated.

[0098] As used in this disclosure, the phrase “at least one of A, B, and C” should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. Embodiments of the invention are illustrated in detail hereinafter with reference to accompanying drawings. The description below is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. The broad teachings of the invention can be implemented in a variety of forms. Therefore, while this invention includes particular examples, the true scope of the invention should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the invention.

[0099] Motivated by the need for easily-manufactured, compact energy storage for applications in harsh environments, the proposed technology involves fully screen-printed, high-temperature microsupercapacitor arrays. The key innovation is the development of a hexagonal boron nitride (hBN) ionogel electrolyte ink that can be rapidly patterned via screen printing. Unlike incumbent polymer-based electrolytes, the use of a nonflammable, nonvolatile ionic liquid and a thermally stable hBN matrix enables electrochemical cycling up to 180 °C. These elevated operating temperatures enable microsupercapacitor-powered remote devices that can be deployed in harsh, high-temperature environments, thus significantly expanding the application space for microsupercapacitors. Furthermore, the hBN ionogel electrolyte ink rheology has been optimized for high-throughput screen printing, enabling precise electrolyte deposition onto large-area (-100 cm2), graphene-based electrode arrays within seconds for fully printed and high-temperature energy storage devices.

[0100] In one aspect, the invention relates to a printable ionogel ink, comprising an ionic liquid and a solid matrix material, wherein the solid matrix material is mixed with the ionic liquid in at least one solvent.

[0101] In one embodiment, the printable ionogel ink has a viscosity that is tuned to be compatible with high-throughput screen printing by varying the concentration of the solid matrix material in one or more solvents.

[0102] In one embodiment, the viscosity is about 76 Pa s at the shear rate of 10 s’1.

[0103] In one embodiment, a ratio of the solid matrix material :the ionic liquid:the at least one solvent is about 1 :2:2 by mass.

[0104] In one embodiment, the printable ionogel ink is devoid of additives that disrupt ion conduction in an electrolyte film.

[0105] In one embodiment, the printable ionogel ink has an ionic conductivity of about 5 mS cm'1and a storage modulus of about 4 MPa at room temperature.

[0106] In one embodiment, the ionic liquid comprises l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ammonium, imidazolium, pyrrolidinium, pyridinium, piperidinium, phosphonium, sulfonium-based ionic liquids, or a combination of them.

[0107] In one embodiment, one or more solvents comprises a single solvent including ethyl lactate, cyclohexanone, terpineol, ethylene glycol, ethanol, isopropanol, or butanone.

[0108] In one embodiment, the solid matrix material comprises boron nitride nanosheets (BNNS), borocarbonitrides (BCN), oxide nanosheets, layered perovskites, hydroxide nanosheets including hydrotalcite-like layered double hydroxides, natural clays including bentonites and montmorillonites, or a combination of them.

[0109] In one embodiment, the BNNS comprises hexagonal boron nitride (hBN) nanoplatelets that are obtained from bulk hBN by scalable solution exfoliation.

[0110] In one embodiment, each exfoliated hBN nanoplatelet is coated with a thin amorphous carbon coating.

[0111] In one embodiment, the high-surface-area nanostructured hBN matrix of the ionogel increases interactions with the ionic liquid and leads to an exceptionally high mechanical modulus at sufficiently low hBN loadings that preserve high ionic conductivity.

[0112] In one embodiment, oxide nanosheets comprises A12O3, TiO2(anatase and rutile), ZrO2, Nb2O5, HfO2, CaCu3Ti40i2, Pb(Zr,Ti)O3, (Pb,La)(Zr,Ti)O3, SiO2, A12O3, HfSiCU, ZrO2, HfO2, Ta2O5, La2O3, LaA103, Nb2Os, BaTiO3, SrTiO3, Ta2Os, or a combination of them.

[0113] In one embodiment, the printable ionogel ink is stable in extreme conditions including at high temperatures up to 180 °C

[0114] In another aspect, the invention relates to a device, comprising one or more components formed of the ionogel ink as disclosed above.

[0115] In one embodiment, the device is one or more batteries, one or more supercapacitors, one or more transistors, one or more neuromorphic computing devices, one or more flexible electronics, one or more printed electronics, or any combination of them.

[0116] In one embodiment, the one or more supercapacitors include one or more all-screen-printed microsupercapacitors (MSCs). In one embodiment, each microsupercapacitor includes at least one screen-printed graphene interdigitated electrode and an ionogel electrolyte screen-printed of the printable ionogel ink.

[0117] In one embodiment, the screen-printed graphene interdigitated electrodes include a high- quality percolating network of graphene flakes with an electrical conductivity of 4* 104S m’1.

[0118] In one embodiment, the ionogel electrolyte is screen printed on top of the graphene interdigitated electrodes and dried at a temperature for a period of time to remove residual solvent.

[0119] In one embodiment, the microsupercapacitor is electrochemically characterized using cyclic voltammetry (CV) and galvanostatic measurements, wherein rectangular cyclic voltammograms absent of redox peaks along with triangular galvanostatic charge-discharge curves indicate ideal electrochemical double layer behavior even at high discharge rates.

[0120] In one embodiment, the microsupercapacitor has a capacitance retention of 91.9% after 10,000 charge-discharge cycles.

[0121] In one embodiment, the active material loading is adjusted by increasing the number of printed graphene layers, leading to larger capacitance values.

[0122] In one embodiment, each graphene printed layer is about 690 nm and increases linearly as additional layers are deposited via screen printing.

[0123] In one embodiment, an areal capacitance of 0.14 mF cm’2is achieved with a single graphene print layer, and 0.92 mF cm’2is achieved with ten print layers (an electrode thickness of ~7.5 pm).

[0124] In one embodiment, the interdigitated electrode geometry is utilized so that ions penetrate laterally into the graphene film, enabling low-barrier access to the space between individual graphene sheets, thus effectively increasing the electroactive surface area.

[0125] In one embodiment, the microsupercapacitor is flexible and bendable.

[0126] In one embodiment, the microsupercapacitor maintains full capacitance after flexing the MSCs to a 1.5 mm bending radius.

[0127] In one embodiment, the mechanical resilience is enabled by the highly flexible graphene electrodes and the gel-like behavior of the hBN electrolyte.

[0128] In one embodiment, one or more solvents is selected to result in crack-free screen-printed films after its thermal removal, whereby an uninterrupted ion diffusion path throughout the entire device leads to excellent electrochemical performance in addition to reinforcing high mechanical integrity and flexibility.

[0129] In one embodiment, the interdigitated electrode architecture of the microsupercapacitor further eliminates the risk of leakage or device shorting.

[0130] In one embodiment, the individual MSCs are integrated to form series and / or parallel device arrays.

[0131] In one embodiment, the integrated device configurations include two devices in series (2S), two devices in parallel (2P), and a 2SX2P array of devices.

[0132] In one embodiment, the two devices connected in series expand the operating voltage window, while the two devices connected in parallel result in increased discharge current.

[0133] In one embodiment, a 10Sx10P device array maintains excellent electrochemical performance, displaying rectangular cyclic voltammograms and triangular galvanostatic curves in the extended 10 V voltage window.

[0134] In one embodiment, the screen-printed MSC arrays maintain excellent cyclability up to 180 °C with improved power density due to the increased ionic conductivity of the hBN ionogel electrolyte at elevated temperatures.

[0135] In one embodiment, the viscosity of the electrolyte decreases at elevated temperatures, and the ionic conductivity increases and leads to improved capacitance.

[0136] In one embodiment, the reduced electrolyte viscosity allows the electrolyte ions to more easily penetrate the graphene film and access the nanostructured surface of the electrodes.

[0137] In one embodiment, the devices retain 93.6% capacitance after 1000 charge-discharge cycles at 180 °C.

[0138] In one embodiment, the 10Sx10P array displays excellent cycling behavior at elevated temperatures, including increased capacitance and a power output of 2.6 mW at 180 °C.

[0139] In one embodiment, the method further comprises varying the concentration of the solid matrix material and the ionic liquid with the at least one solvent so as to tune a viscosity of the printable ionogel ink that is compatible with high-throughput screen printing.

[0140] In one embodiment, the viscosity is about 25-100 Pa s at the shear rate of 10 s'1.

[0141] In one embodiment, a ratio of the solid matrix material :the ionic liquid:the at least one solvent is about 1:2:2 by mass.

[0142] In one embodiment, the printable ionogel ink is devoid of additives that disrupt ion conduction in an electrolyte film.

[0143] In one embodiment, the printable ionogel ink has an ionic conductivity of about 5 mS cm'1and a storage modulus of about 4 MPa at room temperature. In one embodiment, the ionic liquid comprises l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ammonium, imidazolium, pyrrolidinium, pyridinium, piperidinium, phosphonium, sulfonium-based ionic liquids, or a combination of them.

[0144] In one embodiment, the at least one solvent comprises a single solvent including ethyl lactate, cyclohexanone, terpineol, ethylene glycol, ethanol, isopropanol, or butanone.

[0145] In one embodiment, the solid matrix material comprises boron nitride nanosheets (BNNS), borocarbonitrides (BCN), oxide nanosheets, layered perovskites, hydroxide nanosheets including hydrotalcite-like layered double hydroxides, natural clays including bentonites and montmorillonites, or a combination of them.

[0146] In one embodiment, the hBN nanoplatelets are obtained from bulk hBN by scalable solution exfoliation.

[0147] In one embodiment, each exfoliated hBN nanoplatelet is coated with a thin amorphous carbon coating.

[0148] In one embodiment, the high-surface-area nanostructured hBN matrix of the ionogel increases interactions with the ionic liquid and leads to an exceptionally high mechanical modulus at sufficiently low hBN loadings that preserve high ionic conductivity.

[0149] In one embodiment, the hBN nanoplatelets are obtained by shear-mixing bulk hBN microparticles in ethanol with ethyl cellulose (EC) acting as a dispersing agent to form a shear-mixed dispersion; separating the exfoliated hBN nanoplatelets and EC from the shear-mixed dispersion by centrifuge-assisted sedimentation and flocculation; and collecting hBN / EC solids; and heating the collected hBN / EC solids at a temperature for a period of time to decompose the EC, thereby volatilizing most of the EC, but also leaving behind a thin amorphous carbon coating on the surface of each of the exfoliated hBN nanoplatelets, which contributes to enhanced interactions between the hBN nanoplatelets and the ionic liquids for stronger solidification of the ionogel ink.

[0150] In one embodiment, the EC decomposition temperature is about 300-500 °C, and the period of time is for about 2-4 hours.

[0151] In one embodiment, the oxide nanosheets comprises AI2O3, TiO2(anatase and rutile), ZrO2, Nb2O5, HfO2, CaCu3Ti40i2, Pb(Zr,Ti)O3, (Pb,La)(Zr,Ti)O3, SiO2, A12O3, HfSiCU, ZrO2, HfO2, Ta2O5, La2O3, LaA103, Nb2Os, BaTiO3, SrTiO3, Ta2Os, or a combination of them.

[0152] In one embodiment, the printable ionogel ink is stable in extreme conditions including at high temperatures up to 180 °C. The invention may find applications in a variety of fields such as, but is not limited to, lithium- ion batteries, supercapacitors, transistors, neuromorphic computing devices, flexible electronics, and printed electronics, high-temperature energy storage, flexible electronics, sensors, internet of things, underground exploration / drilling, electric vehicles, aerospace, autoclave sterilizable biomedical devices, and the like.

[0153] The invention, among other things, has at least the following advantages over the existing technology.

[0154] High-temperature supercapacitors have been limited to non-flexible devices with large form factors. The proposed technology enables thin, flexible, and fully-printed energy storage for deployment in extreme-temperature environments.

[0155] Screen printing is a highly scalable, industrially mature patterning method for electronic materials and is compatible with roll-to-roll processing. We estimate a manufacturing throughput of 10,000 devices / hour via the proposed fabrication scheme. Other printed supercapacitor demonstrations are limited in throughput by deposition of the electrolyte due to: (1) the need to dropcast the electrolyte layer because its rheological properties are incompatible with patterning methods, (2) the inherently slower speed of nozzle-based printing methods like inkjet and aerosoljet printing, (3) the need to print multiple electrolyte layers to achieve optimal film thickness due to inherently thin printed films, and (4) the short shelf life and corrosive nature of polymer-acid gel electrolytes. In contrast, our hBN ionogel ink exhibits excellent rheological properties for screen printing, produces relatively thick films, is shelf-stable for months, and has excellent patterning control.

[0156] The high-temperature capability of our microsupercapacitors is enabled by the use of a nonflammable, nonvolatile ionic liquid as the ion-conducting medium and thermally stable hBN as the matrix material. As a gelling matrix for ionogel electrolytes, hBN possesses several desirable attributes including electrically insulating properties, chemical inertness, thermal stability, and mechanical robustness. In addition, the nanoscale size and large surface area of exfoliated hBN nanoplatelets enable strong immobilization of ionic liquids without significant disruption of ion conduction pathways, yielding hBN ionogel electrolytes with high mechanical strength and ionic conductivity.

[0157] These and other aspects of the present invention are further described below. Without intent to limit the scope of the invention, exemplary instruments, apparatus, methods and their related results according to the embodiments of the present invention are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the invention. Moreover, certain theories are proposed and disclosed herein; however, in no way they, whether they are right or wrong, should limit the scope of the invention so long as the invention is practiced according to the invention without regard for any particular theory or scheme of action.

[0158] EXAMPLE

[0159] FULLY-PRINTED, HIGH-TEMPERATURE MICROSUPERCAPACITOR ARRAYS ENABLED BY A HEXAGONAL BORON NITRIDE IONOGEL ELECTROLYTE

[0160] The proliferation and miniaturization of portable electronics require energy storage devices that are simultaneously compact, flexible, and amenable to scalable manufacturing.

[0161] In this example, we demonstrate mechanically flexible microsupercapacitor arrays via sequential high-speed screen printing of conductive graphene electrodes and a high-temperature hexagonal boron nitride (hBN) ionogel electrolyte. By combining the superlative dielectric properties of two-dimensional hBN with the high ionic conductivity of ionic liquids, the resulting hBN ionogel electrolyte enables microsupercapacitors with exceptional areal capacitances that approach 1 mF cm'2. Unlike incumbent polymer-based electrolytes, the high-temperature stability of the hBN ionogel electrolyte implies that the printed microsupercapacitors can be operated at unprecedentedly high temperatures up to 180 °C. These elevated operating temperatures result in increased power densities that make these printed microsupercapacitors particularly promising for applications in harsh environments such as underground exploration, aviation, and electric vehicles. The combination of enhanced functionality in extreme conditions and high-speed production via scalable additive manufacturing significantly broadens the technological phase space for on-chip energy storage.

[0162] Specifically, we present the inks and methodology for achieving rapid manufacturing of MSCs in which all electrochemically active components are screen printed. The key innovation is a screen- printable ionogel electrolyte includes hexagonal boron nitride (hBN) nanoplatelets and l-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) ionic liquid that is fully compatible with pre-screen-printed graphene interdigitated electrodes. Unlike incumbent polymer- based electrolytes, the hBN ionogel is stable in extreme conditions including at high temperatures up to 180 °C. This stability holds promise for self-powered devices that can be deployed in harsh environments such as underground exploration, aviation, and electric vehicles. In addition to achieving superlative areal capacitances that approach 1 mF cm'2, these MSCs can be directly and rapidly printed in series and parallel configurations to allow full control over the voltage and power outputs that are needed for diverse technological requirements. In this manner, this work represents a significant step forward towards scalable manufacturing of on-chip energy storage, particularly for applications in extreme environments.

[0163] Materials and Methods

[0164] Ionogel Ink Formulation and Characterization: To produce the hBN nanoplatelets, 120 g of hBN powder (1 pm, Sigma-Aldrich), 12 g of ethyl cellulose (4 cp, Sigma-Aldrich), and 1 L of ethanol (200 proof, Decon Labs) were shear mixed for 2 hr at 10230 rpm (L5M-A, Silverson). The resulting dispersion was centrifuged at 4000 rpm for 20 min to remove unexfoliated material. The supernatant was collected and mixed with a 0.04 g / ml solution of aqueous sodium chloride and centrifuged at 7500 rpm for 7 min. The flocculated material was then rinsed, dried, and ground to form a powder. Finally, the resulting powder was baked in a box furnace at 400 °C for 4 hr to remove the ethyl cellulose. To form the hBN ionogel ink, the exfoliated hBN powder was combined with EMIM-TFSI ionic liquid (>98% (HPLC), Sigma- Aldrich) and ethyl lactate (Sigma-Aldrich) in a weight ratio of 1:2:2 and mixed in a centrifugal mixer (ARE-310, Thinky USA) with ceramic ball bearings for 20 min at a maximum speed of 2000 rpm. Thermogravimetric analysis was performed on a Mettler Toledo TGA / DSC 3+, and rheometry measurements were performed on an Anton Paar MCR 302. The viscolelastic properties of the hBN ionogel were measured using an 8 mm parallel plate geometry, a 1 mm gap, a shear strain of 0.1%, and an oscillation frequency range of 0.1 to 100 Hz. Scanning electron microscopy (SEM) images of the hBN nanoplatelets and the hBN ionogel were performed on a Hitachi SU8030 SEM after an osmium layer was deposited. The ionic conductivity (o) of the hBN ionogel was measured using a coin cell configuration (CR2032) in which the ionogel was manually inserted between two stainless steel disks. Equation (1) was used to determine the conductivity: ff = (1) fix?}v 7where t is the thickness and A is the area of the hBN ionogel. R represents the bulk resistance, which was determined by electrochemical impedance spectroscopy (EIS) in a frequency window of 1 MHz to 1 Hz using a potentiostat (VSP, BioLogic). The temperature dependence of the ionic conductivity was determined in an environmental chamber (BTX- 475, Espec) at 20, 40, 60, 80, 100, and 120 °C, sequentially. The experimental data was fitted to the Vogel-Fulcher-Tammann (VFT) model curve according to Equation (2): a = A exp (- ) (2)

[0165] 1~i0 with 4 (the pre-exponential factor) set at 125.51 mS B (the pseudoactivation energy term related to the entropic barrier to ion motion) set at 358.11 I< and To (the ideal glass transition temperature) set at 179.32 K. Laser confocal microscopy thickness and roughness measurements were performed on an Olympus LEXT OLS5000 optical microscope fitted with a *50 objective lens (numerical aperture = 0.95).

[0166] Device Fabrication and Characterization: The graphene screen-printable ink was prepared by mixing graphene-ethyl cellulose composite powder with terpineol at 140 mg / ml using a centrifugal mixer (ARE-310, Thinky USA) and ceramic ball bearings for 60 min at a maximum speed of 2000 rpm. The patterned screen employed 325-mesh stainless steel stretched over a 12x 12 inch aluminum frame (Hary Manufacturing Inc.). The screen printer (886PC DSIV, Hary Manufacturing Inc.) was programmed with the following settings: squeegee and flood plate pressures of 20 psi, speed of 127 mm / s, and snapoff distance of 1016 pm. Following printing on Kapton sheets (0.005 inch thickness), the electrodes were cured in a box furnace at 350 °C for 30 min. The hBN ionogel was printed on top of the graphene electrodes using the same print settings as the graphene ink. Alignment between print layers was achieved through camera recognition of printed fiducial markers. Finally, the devices were placed on a hot plate at 160 °C for 30 min to remove sequestered EL solvent. All electrochemical testing was performed with a potentiostat (VSP, BioLogic). The entire footprint area of the device, including the gaps between electrode fingers, was considered for the area-normalized calculations.

[0167] High-Temperature Characterization: High-temperature device characterization was performed while the devices were sitting on a hot plate at the specified temperature. Extended leads were painted on the substrate using silver paint so that the devices could be attached to the measurement probes away from the hot plate (FIG. 10). The PVA-H3PO4 gel electrolyte was formed by mixing 4.5 g deionized water, 0.5 g H3PO4 (85%, Sigma Aldrich), and 0.3 g PVA (MW 89, GOO- 98, 000, Sigma Aldrich), followed by stirring for 2 hr at 80 °C.

[0168] Results and Discussion

[0169] Screen-Printable Hexagonal Boron Nitride Ionogel Ink: Rapidly-printed, high-temperature microsupercapacitors (MSCs) are enabled by a screen-printable hBN ionogel electrolyte ink (FIG. 1). The electrolyte includes the ionic liquid EMIM-TFSI and a gelling matrix of exfoliated hBN nanoplatelets (panel a of FIG. 1). When combined, a stiff electrolyte gel is formed (panel b of FIG. 1) with an ionic conductivity of ~5 mS cm'1(panel c of FIG. 1) and a storage modulus of ~4 MPa (panel d of FIG. 1) at room temperature. The hBN nanoplatelets are produced via a scalable liquid phase exfoliation process that has been reported previously. The high-surface-area nanostructured hBN matrix of the ionogel increases interactions with the ionic liquid and leads to an exceptionally high mechanical modulus at sufficiently low hBN loadings that preserve high ionic conductivity.

[0170] Screen printing requires highly viscous inks to produce high-resolution, high-fidelity printed features. Thus, it is crucial to choose a compatible solvent that can disperse the hBN ionogel components at high concentrations. Simultaneously, screen-printable inks must exhibit shear thinning, meaning that they become significantly less viscous under applied shear stress from the squeegee but stiffen and retain their shape once the squeegee is removed. Finally, high-boiling point solvents need to be utilized in order to avoid mesh clogging from solvent evaporation between prints. These ink requirements were met through careful formulation of the screen-printable hBN ionogel ink. Specifically, the viscosity of the ink was tuned to be compatible with high-throughput screen printing by varying the concentration of the hBN ionogel components in the non-toxic, high-boiling-point solvent ethyl lactate (EL). The optimized screen-printable ink formulation includes a 1 :2:2 mass ratio of hBN nanoplatelets:EMIM-TFSI ionic liquid:EL (panel e of FIG. 1). This formulation produces a shear- thinning ink with a viscosity of 76 Pa- s at a shear rate of 10 s'1(panel f of FIG. 1). Ultimately, the stiffness imparted by the nanostructured hBN ionogel matrix leads to a viscous ink without the use of additives that could disrupt ion conduction in the electrolyte film. Following ink formulation, the hBN ionogel was deposited using an automated screen printer, resulting in a homogeneous film (panel g of FIG. 1). The relatively low volatility of the EL enabled continuous printing without mesh clogging issues. Scanning electron microscopy (SEM) images of the printed hBN ionogel show that the hBN nanoplatelets are well-distributed within the ionic liquid (panels h-i of FIG. 1). The thickness of the film was measured by laser confocal microscopy and determined to be 14.0 ± 0.3 pm with a root-mean-square roughness of 2.2 pm.

[0171] Currently, gel electrolytes based on polyvinyl alcohol (PVA) and H3PO4 are widely used for graphene-based solid-state supercapacitors However, PVA-H3PO4 gel electrolytes are inherently ill- suited for screen printing since they show limited shear thinning behavior (panel f of FIG. 1) and produce rough, non-uniform films. In addition, the acid component of PVA-H3PO4 gel electrolytes corrodes stainless steel mesh screens when employed continuously for large-scale manufacturing. While there have been rare instances of screen-printable polymer-based MSC electrolytes, these studies have been limited to single device demonstrations and contain no discussion of print quality or scalability. In contrast, our screen-printable hBN ionogel electrolyte enables reliable patterning that routinely produces hundreds of devices. Furthermore, our hBN-ionogel -based MSCs achieve areal capacitances approaching 1 mF cm'2, which meet or exceed the areal capacitance of previously reported graphene MSCs based on polymer electrolytes (Table 1).

[0172] Table 1. Comparison to other reported graphene solid-state microsupercapacitors Microsupercapacitor Device Fabrication and Characterization: FIG. 2 delineates the electrochemical performance of the MSC devices. All electrochemically active components were screen printed, including the graphene interdigitated electrodes and the hBN ionogel electrolyte (panel a of FIG. 2). The screen-printable graphene ink is adapted from a previous formulation and is composed of a composite of graphene nanoplatelets and ethyl cellulose dispersed in terpineol. The composition and rheological properties of the screen-printable graphene ink are described in panels a-b of FIG. 5. The screen-printed graphene interdigitated electrodes have a total geometric area of 0.56 cm2with finger widths of 540 pm and gap widths of 250 pm (panel c of FIG. 5). Following screen printing, the graphene electrodes are cured at 350 °C for 30 min to remove ethyl cellulose. The resulting screen-printed electrodes include a high-quality percolating network of graphene flakes (panel d of FIG. 5) with an electrical conductivity of 4* 104S m'1. Due to the exceptionally high electrical conductivity of the graphene electrodes, no current collector was required, eliminating this common fabrication step. The hBN ionogel was then screen printed on top of the graphene interdigitated electrodes and dried at 160 °C for 30 min to remove residual EL. A photograph of the patterned mesh screens is provided in FIG. 6.

[0173] The MSC devices were electrochemically characterized using cyclic voltammetry (CV) and galvanostatic measurements. Rectangular cyclic voltammograms absent of redox peaks (panels b-c of FIG. 2) along with triangular galvanostatic charge-discharge curves (panel d of FIG. 2) indicate ideal electrochemical double layer behavior even at high discharge rates. The MSC devices also display a capacitance retention of 91.9% after 10,000 charge-discharge cycles (panel e of FIG. 2). The active material loading was adjusted by increasing the number of printed graphene layers, leading to larger capacitance values (panels f-g of FIG. 2). Specifically, each graphene printed layer is -690 nm and increases almost linearly as additional layers are deposited via screen printing (FIG. 7). An areal capacitance of 0.14 mF cm’2was achieved with a single graphene print layer and 0.92 mF cm’2is achieved with ten print layers (an electrode thickness of -7.5 pm). Traditional sandwich-structured devices typically do not benefit from higher active material loadings because the counter ions must penetrate deeper into the electrode films. However, an advantage of the interdigitated electrode geometry is that ions penetrate laterally into the graphene film, enabling low-barrier access to the space between individual graphene sheets, thus effectively increasing the electroactive surface area. As shown in Table 1, the capacitance of our hBN ionogel -based MSCs compare favorably with other recent graphene MSC demonstrations, all of which use incumbent polymer-based electrolytes (Table 1).

[0174] Since two-dimensional materials are intrinsically flexible, the screen-printed MSCs can also withstand mechanical flexing. In particular, full capacitance is maintained after flexing the MSCs to a 1.5 mm bending radius panels h-i of FIG. 2). This mechanical resilience is enabled by the highly flexible graphene electrodes and the gel-like behavior of the hBN electrolyte. It is noteworthy that the carefully selected diluent solvent EL results in crack-free screen-printed fdms after its thermal removal. Thus, the uninterrupted ion diffusion path throughout the entire device leads to excellent electrochemical performance in addition to reinforcing high mechanical integrity and flexibility. In contrast to traditional sandwich-structured supercapacitors, the interdigitated electrode architecture of these MSC devices also eliminate the risk of leakage or device shorting.

[0175] Microsupercapacitor Device Integration: In order to meet a wide range of voltage and current requirements, the individual MSCs can be integrated to form series and / or parallel device arrays (FIG. 3). Due to the high electrical conductivity of the screen-printed graphene films, the same graphene ink is used to screen print the conductive interconnects. Various integrated device configurations are shown, including 2 devices in series (2S), 2 devices in parallel (2P), and a 2SX2P array of devices (panel a of FIG. 3). Corresponding cyclic voltammograms and galvanostatic charge-discharge curves show expected outputs - namely, 2 devices connected in series expand the operating voltage window, while 2 devices connected in parallel result in increased discharge current (panels b-c of FIG. 3). Unlike drop-on-demand printing methods, screen printing can rapidly pattern large-area device arrays. For example, 100 devices (10Sx 10P) are patterned with negligible additional effort compared to a single device (panels d and g of FIG. 3). These arrays maintain excellent electrochemical performance, displaying rectangular cyclic voltammograms and triangular galvanostatic curves in the extended 10 V voltage window (panels e-f of FIG. 3). The IOS* 1 OP array also maintains resilience to mechanical flexing, as its performance is unaffected when it is operated under a bending radius of 2.5 cm (panels h-i of FIG. 3).

[0176] Microsupercapacitor High-Temperature Operation’. Unlike polymer-based electrolytes, the hBN ionogel can withstand high temperatures without degradation. The screen-printed device performance at elevated temperatures is summarized in FIG. 4. Cyclic voltammograms of a single device display near-rectangular behavior up to 180 °C (panel a of FIG. 4). Because the viscosity of the electrolyte decreases at elevated temperatures, the ionic conductivity increases and leads to improved capacitance. The reduced electrolyte viscosity also allows the electrolyte ions to more easily penetrate the graphene film and access the nanostructured surface of the electrodes. Cycle life testing shows that the devices retain 93.6% capacitance after 1000 charge-discharge cycles at 180 °C (panel b of FIG. 4). The lOSxlOP array also displays excellent cycling behavior at elevated temperatures, including increased capacitance (panel c of FIG. 4) and a power output of 2.6 mW at 180 °C (panel d of FIG. 4). Some distortion of the cyclic voltammograms and a plateau in the power output begin to occur above 180 °C, likely due to side reactions between the electrolyte and the active material. For these reasons, 180 °C was deemed to be the maximum operating temperature even though the devices were cycled at higher temperatures without issues (FIG. 8). In contrast to common polymer-based electrolytes (e.g., PVA-H3PO4) that begin to degrade at -100 °C and show visible cracking at 180 °C, the hBN ionogel shows no sign of degradation at these temperatures (panel e of FIG. 4) and can continue to be cycled even after exposure to 300 °C (FIG. 9). Consequently, the screen-printed hBN ionogel opens up unprecedented opportunities for on-chip remote power sources in extreme environments.

[0177] Conclusion

[0178] In the exemplary work, we demonstrate fully and rapidly screen-printed MSC arrays based on a high-temperature hBN ionogel electrolyte with robust mechanical properties and state-of-the-art ionic conductivity. Importantly, the device fabrication is entirely based on screen printing, which is a high- throughput additive manufacturing method that is widely used in printed electronics manufacturing. Moreover, this fabrication strategy minimizes waste, making it both scalable and environmentally sustainable. Exceptional areal capacitances approaching 1 mF cm’2are achieved with the combination of screen-printed graphene interdigitated electrodes and the hBN ionogel. By employing hBN as the solid matrix, we entirely replace the polymers that limit high-temperature performance in incumbent gel electrolytes. As a result, the screen-printed MSC arrays maintain excellent cyclability up to 180 °C with improved power density due to the increased ionic conductivity of the hBN ionogel electrolyte at elevated temperatures. Overall, this work establishes an additive manufacturing platform that can support future on-chip energy storage for extreme-environment applications in underground exploration, aviation, and electric vehicles.

[0179] The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.

[0180] The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.

[0181] Some references, which may include patents, patent applications and various publications, are cited and discussed in the description of this invention. The citation and / or discussion of such references is provided merely to clarify the description of the present invention and is not an admission that any such reference is “prior art” to the invention described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.

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Claims

CLAIMSWhat is claimed is:

1. A printable ionogel ink, comprising: an ionic liquid; and a solid matrix material, wherein the solid matrix material is mixed with the ionic liquid in at least one solvent.

2. The printable ionogel ink of claim 1, having a viscosity that is tuned to be compatible with high-throughput screen printing by varying the concentration of the solid matrix material and the ionic liquid with the at least one solvent.

3. The printable ionogel ink of claim 2, wherein the viscosity is about 25-100 Pa s at the shear rate of 10 s'1.

4. The printable ionogel ink of claim 2, wherein a ratio of the solid matrix materiakthe ionic liquid:the at least one solvent is about 1 :2:2 by mass.

5. The printable ionogel ink of claim 2, being devoid of additives that disrupt ion conduction in an electrolyte fdm.

6. The printable ionogel ink of claim 2, having an ionic conductivity of about 5 mS cm'1and a storage modulus of about 4 MPa at room temperature.

7. The printable ionogel ink of claim 1, wherein the ionic liquid comprises l-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ammonium, imidazolium, pyrrolidinium, pyridinium, piperidinium, phosphonium, sulfonium-based ionic liquids, or a combination of them.

8. The printable ionogel ink of claim 1, wherein the at least one solvent comprises a single solvent including ethyl lactate, cyclohexanone, terpineol, ethylene glycol, ethanol,isopropanol, or butanone.

9. The printable ionogel ink of claim 1, wherein the solid matrix material comprises boron nitride nanosheets (BNNS), borocarbonitrides (BCN), oxide nanosheets, layered perovskites, hydroxide nanosheets including hydrotalcite-like layered double hydroxides, natural clays including bentonites and montmorillonites, or a combination of them.

10. The printable ionogel ink of claim 9, wherein the BNNS comprises hexagonal boron nitride (hBN) nanoplatelets that are obtained from bulk hBN by scalable solution exfoliation.

11. The printable ionogel ink of claim 10, wherein each exfoliated hBN nanoplatelet is coated with a thin amorphous carbon coating.

12. The printable ionogel ink of claim 10, wherein the high-surface-area nanostructured hBN matrix of the ionogel increases interactions with the ionic liquid and leads to an exceptionally high mechanical modulus at sufficiently low hBN loadings that preserve high ionic conductivity.

13. The printable ionogel ink of claim 9, wherein the oxide nanosheets comprises AI2O3, TiCh (anatase and rutile), ZrCh, Nb2Os, HfCh, CaCu3Ti40i2, Pb(Zr,Ti)Os, (Pb,La)(Zr,Ti)O3, SiO2, AI2O3, HfSiO4, ZrO2, HfO2, Ta2O5, La2O3, LaA103, Nb2O5, BaTiCh, SrTiCh, Ta2Os, or a combination of them.

14. The printable ionogel ink of claim 1, being stable in extreme conditions including at high temperatures up to 180 °C15. A device, comprising: one or more components formed of the ionogel ink according to any one of claims 1-14.

16. The device of claim 15, being one or more batteries, one or more supercapacitors, one ormore transistors, one or more neuromorphic computing devices, one or more flexible electronics, one or more printed electronics, or any combination of them.

17. The device of claim 16, wherein the one or more supercapacitors include one or more allscreen-printed microsupercapacitors (MSCs).

18. The device of claim 17, wherein each microsupercapacitor includes at least one screen- printed graphene interdigitated electrode and an ionogel electrolyte screen-printed of the printable ionogel ink.

19. The device of claim 18, wherein the ionogel electrolyte is screen printed on top of graphene interdigitated electrodes and dried at a temperature for a period of time to remove residual solvent.

20. The device of claim 18, wherein the microsupercapacitor is electrochemically characterized using cyclic voltammetry (CV) and galvanostatic measurements, wherein rectangular cyclic voltammograms absent of redox peaks along with triangular galvanostatic charge-discharge curves indicate ideal electrochemical double layer behavior even at high discharge rates.

21. The device of claim 18, wherein the microsupercapacitor has a capacitance retention of 91.9% after 10,000 charge-discharge cycles.

22. The device of claim 18, wherein the active material loading is adjusted by increasing the number of printed graphene layers, leading to larger capacitance values.

23. The device of claim 22, wherein each graphene printed layer is about 690 nm and increases linearly as additional layers are deposited via screen printing.

24. The device of claim 23, wherein an areal capacitance of 0.14 mF cm'2is achieved with a single graphene print layer, and 0.92 mF cm'2is achieved with ten print layers (anelectrode thickness of ~7.5 pm).

25. The device of claim 18, wherein the interdigitated electrode geometry is adapted such that ions penetrate laterally into the graphene film, enabling low-barrier access to the space between individual graphene sheets, thus effectively increasing the electroactive surface area.

26. The device of claim 17, wherein the microsupercapacitor is flexible and bendable.

27. The device of claim 26, wherein the microsupercapacitor maintains full capacitance after flexing the MSCs to a 1.5 mm bending radius.

28. The device of claim 26, wherein the mechanical resilience is enabled by the highly flexible graphene electrodes and the gel-like behavior of the hBN electrolyte.

29. The device of claim 26, wherein the at least one solvent is selected to result in crack-free screen-printed films after its thermal removal, whereby an uninterrupted ion diffusion path throughout the entire device leads to excellent electrochemical performance in addition to reinforcing high mechanical integrity and flexibility.

30. The device of claim 29, wherein the interdigitated electrode architecture of the microsupercapacitor further eliminates the risk of leakage or device shorting.

31. The device of claim 17, wherein the individual MSCs are integrated to form series and / or parallel device arrays.

32. The device of claim 31, wherein the two devices connected in series expand the operating voltage window, while the two devices connected in parallel result in increased discharge current.

33. The device of claim 31, wherein the device array maintains excellent electrochemical performance, displaying rectangular cyclic voltammograms and triangular galvanostaticcurves in the extended 10 V voltage window.

34. The device of claim 31, wherein the screen-printed MSC arrays maintain excellent cyclability up to 180 °C with improved power density due to the increased ionic conductivity of the hBN ionogel electrolyte at elevated temperatures.

35. The device of claim 31, wherein the viscosity of the electrolyte decreases at elevated temperatures, and the ionic conductivity increases and leads to improved capacitance.

36. The device of claim 35, wherein the reduced electrolyte viscosity allows the electrolyte ions to more easily penetrate the graphene film and access the nanostructured surface of the electrodes.

37. The device of claim 31, wherein the devices retain 93.6% capacitance after 1000 chargedischarge cycles at 180 °C.

38. The device of claim 37, wherein the 1 OS x 10P array displays excellent cycling behavior at elevated temperatures, including increased capacitance and a power output of 2.6 mW at 180 °C.

39. A method for forming a printable ionogel ink, comprising: providing an ionic liquid and a solid matrix material; and mixing the solid matrix material with the ionic liquid in at least one solvent to form the printable ionogel ink.

40. The method of claim 30, further comprising: varying the concentration of the solid matrix material and the ionic liquid with the at least one solvent so as to tune a viscosity of the printable ionogel ink that is compatible with high-throughput screen printing.

41. The method of claim 40, wherein the viscosity is about 25-100 Pa s at the shear rate of 10 s'1.

42. The method of claim 40, wherein a ratio of the solid matrix material :the ionic liquid:the at least one solvent is about 1:2:2 by mass.

43. The method of claim 40, wherein the printable ionogel ink is devoid of additives that disrupt ion conduction in an electrolyte film.

44. The method of claim 40, wherein the printable ionogel ink has an ionic conductivity of about 5 mS cm’1and a storage modulus of about 4 MPa at room temperature.

45. The method of claim 39, wherein the ionic liquid comprises 1 -ethyl-3 - methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ammonium, imidazolium, pyrrolidinium, pyridinium, piperidinium, phosphonium, sulfonium-based ionic liquids, or a combination of them.

46. The method of claim 39, wherein the at least one solvent comprises a single solvent including ethyl lactate, cyclohexanone, terpineol, ethylene glycol, ethanol, isopropanol, or butanone.

47. The method of claim 39, wherein the solid matrix material comprises boron nitride nanosheets (BNNS), borocarbonitrides (BCN), oxide nanosheets, layered perovskites, hydroxide nanosheets including hydrotalcite-like layered double hydroxides, natural clays including bentonites and montmorillonites, or a combination of them.

48. The method of claim 47, wherein the BNNS comprises hexagonal boron nitride (hBN) nanoplatelets that are obtained from bulk hBN by scalable solution exfoliation.

49. The method of claim 48, wherein each exfoliated hBN nanoplatelet is coated with a thin amorphous carbon coating.

50. The method of claim 48, wherein the high-surface-area nanostructured hBN matrix of the ionogel increases interactions with the ionic liquid and leads to an exceptionally highmechanical modulus at sufficiently low hBN loadings that preserve high ionic conductivity.

51. The method of claim 48, wherein the hBN nanoplatelets are obtained by shear-mixing bulk hBN microparticles in ethanol with ethyl cellulose (EC) acting as a dispersing agent to form a shear-mixed dispersion; separating the exfoliated hBN nanoplatelets and EC from the shear-mixed dispersion by centrifuge-assisted sedimentation and flocculation; and collecting hBN / EC solids; and heating the collected hBN / EC solids at a temperature for a period of time to decompose the EC, thereby volatilizing most of the EC, but also leaving behind a thin amorphous carbon coating on the surface of each of the exfoliated hBN nanoplatelets, which contributes to enhanced interactions between the hBN nanoplatelets and the ionic liquids for stronger solidification of the ionogel ink.

52. The method of claim 51, wherein the temperature is about 300-500 °C, and the period of time is for about 2-4 hours.

53. The method of claim 47, wherein the oxide nanosheets comprises AI2O3, TiO2(anatase and rutile), ZrO2, Nb2O5, HfO2, CaCu3Ti40i2, Pb(Zr,Ti)O3, (Pb,La)(Zr,Ti)O3, SiO2, A12O3, HfSiO4, ZrO2, HfO2, Ta2Os, La2O3, LaA103, Nb2Os, BaTiO3, SrTiO3, Ta2Os, or a combination of them.

54. The method of claim 39, wherein the printable ionogel ink is stable in extreme conditions including at high temperatures up to 180 °C.

Images