Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
  • H01G11/28—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features arranged or disposed on a current collector; Layers or phases between electrodes and current collectors, e.g. adhesives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/30—Electrodes characterised by their material
  • H01G11/32—Carbon-based
  • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/30—Electrodes characterised by their material
  • H01G11/32—Carbon-based
  • H01G11/38—Carbon pastes or blends; Binders or additives therein
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
  • H01G11/86—Processes for the manufacture of hybrid or EDL capacitors, or components thereof specially adapted for electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

• compositions for energy storage devices and methods of use are “Compositions for energy storage devices and methods of use”.
• This disclosure relates to electrically conductive compositions.
• One or more embodiments may regard, for example, electrically conductive compositions suitable to be used in energy storage devices, preferably in electrochemical double layer capacitors.
• Electrochemical double layer capacitors are energy storage devices also known as ultracapacitors or supercapacitors (SCs).
• SCs store and release energy in second/sub- second timescales, which means they can complement or even replace batteries (typically operating over minute/hour timescales) for high-power (> 10000 W/kg) applications.
• applications include regenerative breaking in electric and hybrid electric vehicles, short-term energy storage in consumer electronics and communication systems, or burst-mode power delivery.
• SCs can provide superior lifetime (-millions of cycles) compared to that of batteries (several hundred cycles). Indeed, the latter suffer intercalation-alloying induced stresses that can cause material swelling and subsequent electrode failure.
• recent research aimed to increase the energy density of SCs ( ⁇ 10 Wh/kg for commercial SCs), since the latter is still significantly inferior to that of batteries (30-70 Wh/kg for Ni-Cd, 50-120 Wh/kg for Ni-MH batteries, 150-270 Wh/kg for Li-ion batteries).
• electrodes for SCs are made of commercially available nanoporous carbon-structures displaying a balanced micro (pore size between 0.2-2 nm)/mesoporosity (pore size 2-10 nm).
• Document US 2018/0201740 Al discloses electrode slurries containing halogenated graphene nanoplatelets.
• Document US 2014/030590 Al discloses an electrode for an energy storage device comprising a self-supporting layer of a mixture of graphene sheets and spacer particles and/or binder particles.
• Document US 2017/0170466 Al discloses electrodes of power devices comprising a coating wherein the active material layer includes a composite in particulate form, graphene and a binder.
• the industrial implementation of “green” solvent-based processing of SC electrodes reduces the human health/environmental impact of the SC production, currently based on hard-to-dispose fluorine (F)-containing binders (e.g., poly(vinylidene difluoride) -PVDF- and polytetrafluoroethylene -PTFE-) and often using hazardous, teratogen, irritating and/or toxic solvents/dispersants (e.g., N-Methyl-2- pyrrolidone -NMP-).
• F hard-to-dispose fluorine
• F hard-to-dispose fluorine
• binders e.g., poly(vinylidene difluoride) -PVDF- and polytetrafluoroethylene -PTFE-
• hazardous, teratogen, irritating and/or toxic solvents/dispersants e.g., N-Methyl-2- pyrrolidone -NMP-
• NMP shall not be used in mixtures at a concentration equal or greater than 0.3%, unless operational conditions ensure exposure of workers below the Derived No-Effect Levels -DNELs- of 4.8 mg/kg per day for dermal exposure and 14.4 mg/m 3 for exposure by inhalation.
• “green” solvent-based SC manufacturing also eliminates the costs associated with the use and recycling of the organic solvents and related binders. For example, NMP is more expensive than water (> 1 US$/kg vs.
• compositions for providing electrically conductive covering layers on a substrate of an energy storage device which are endowed with an optimal trade-off between mechanical stability and electrochemical performance, capable of efficiently operating in a large operating temperature window and attainable through cost-effective, sustainable and environmentally friendly methods.
• the present disclosure provides a composition for providing electrically conductive covering layers on a substrate of an energy storage device, the composition comprising: a) an electrically conductive material comprising at least one allotrope of carbon, wherein said at least one allotrope of carbon comprises pristine graphene flakes, said pristine graphene flakes having an atomic content of oxygen equal to or lower than 5%, preferably equal to or lower than 2%, b) a binding agent comprising a polymeric material, c) an environmentally friendly solvent having a boiling point equal to or lower than 150°C.
• the pristine graphene flakes may be present in an amount between 1% and 100% by weight (w/w) of to the electrically conductive material weight.
• the pristine graphene flakes are non-oxidized graphene flakes displaying a defect-free flat morphology of their basal planes including structural defects of the sp 2 structure.
• Said flakes have an atomic content of oxygen, measured by X-ray photoelectron spectroscopy, equal to or lower than 5%, preferably equal to or lower than 2%.
• the defect-free flat morphology is assessed by the absence of a linear correlation (R 2 ⁇ 0.5) in the plot of the ratio between the intensity of the D and G peak of their Raman spectra versus the full width half maximum of the G peak (ID/I(G) vs. FWHM(G) plot).
• the ratio between the intensities of the D and G peaks (I(D)/I(G)) of the pristine flakes Raman spectra is comprised between 0.1 and 2.0, preferably between 0.1 and 1.2.
• the environmentally friendly solvent may be selected in the group consisting of water, alcohols, mixtures thereof.
• the alcohols may be selected in the group consisting of ethanol (ethyl alcohol), 1-propanol (propan- l-ol or 1-propyl alcohol or n-propanol), 2-propanol (propan-2-ol or isopropyl alcohol or isopropanol), 1 -butanol (n-butanol or n-butyl alcohol), 2-butanol (sec -butanol or 2-butyl alcohol), 2-methyl- 1 -propanol, 2- methyl-2-propanol (tert-butanol or 2-methylpropan-2-ol), 1-pentanol (pentan-l-ol), 2-pentanol (pentan-2-ol or sec-amyl alcohol), 3 -methyl- 1 -butanol (3-methylbutan- l-ol or isoamyl alcohol or isopentyl alcohol), 2,2-dimethyl- 1 -propanol (2,2- dimethylpropan
• the polymeric material may comprise at least one fluorine-free polymer preferably selected in the group consisting of carboxymethyl cellulose (CMC) and derivatives, preferably sodium carboxymethyl cellulose (Na-CMC), natural cellulose (NC), alginate, polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB).
• CMC carboxymethyl cellulose
• Na-CMC sodium carboxymethyl cellulose
• NC natural cellulose
• PVP polyvinylpyrrolidone
• PVB polyvinyl butyral
• the binding agent may be contained in the composition in an amount comprised between 1% by weight (w/w) and 30% by weight, preferably between 5% and 10% by weight compared to the total weight of the electrically conductive material plus the binding agent.
• the electrically conductive material may further comprise at least one additional allotrope of carbon selected in the group consisting of activated carbon, carbon nanotubes, carbide-derived carbons, carbon black, preferably activated carbon (AC).
• activated carbon selected in the group consisting of activated carbon, carbon nanotubes, carbide-derived carbons, carbon black, preferably activated carbon (AC).
• the disclosure also provides a method for producing the composition.
• the method comprises the steps of:
• an environmentally friendly solvent having a boiling point equal to or lower than 150°C, preferably selected in the group consisting of water, alcohols, mixtures thereof: i) an electrically conductive material comprising at least one allotrope of carbon, wherein said at least one allotrope of carbon comprises pristine graphene flakes having an atomic content of oxygen equal to or lower than 5%, preferably equal to or lower than 2%, ii) a binding agent comprising a polymeric material, to obtain a dispersion,
• the disclosure further provides a method to produce electrically conductive covering layers on a substrate of an energy storage device, wherein the substrate is preferably the surface of a SC electrode.
• Figure 1 shows in a) the comparison between the Raman spectra of the graphite and the pristine graphene flakes produced by wet jet milling exfoliation, b) the plot of I(D)/I(G) vs. FWHM(G) and c) the statistical analysis of I(D)/I(G).
• Figure 2 shows the Ragone plot of representative SCs based on electrodes spray-coated with the compositions according to the present disclosure at room temperature (25°C), in comparison to the Ragone plot of the SC based on spray- coated electrodes using sole ACs as electrically conductive active materials.
• the Ragone plot of SCs produced by conventional casting deposition (i.e., doctor blading deposition) of an electrode material slurry adopting conventional F- containing binders (i.e., PVDF) and expensive toxic organic solvent (i.e., NMP) are also shown, both for electrode covering layers with graphene flakes and without graphene flakes.
• Figure 3 shows the Ragone plots of the SCs based on the spray-coated electrodes obtained according to the present disclosure at temperature of -40°C, 0°C, 50°C and 100°C in comparison to the Ragone plots of the SC based on spray- coated electrodes using sole ACs as electrically conductive active materials at the same operating temperature.
• Figure 4 shows the distribution of the I(D)/I(G) ratios for pristine graphene flakes disclosed in the instant application and for halogenated pristine graphene flakes known in the art.
• Figure 5 shows a TEM image of representative pristine flakes disclosed in the instant application (left panel) in comparison with an image of fluorinated graphene flakes known in the art (right panel).
• the present disclosure relates to the field of compositions suitable to be used in energy storage devices, particularly to be applied on supercapacitor (SC) electrodes.
• SC supercapacitor
• the present disclosure provides a composition for providing electrically conductive covering layers on a substrate of an energy storage device, the composition comprising: a) an electrically conductive material comprising at least one allotrope of carbon, wherein said at least one allotrope of carbon comprises pristine graphene flakes, said pristine graphene flakes being graphene flakes having an atomic content of oxygen equal to or lower than 5%, preferably equal to or lower than 2%, b) a binding agent comprising a polymeric material, c) an environmentally friendly solvent having a boiling point equal to or lower than 150°C.
• the pristine graphene flakes may be produced through graphite exfoliation without exploiting the chemical oxidation- aided graphite exfoliation (e.g., modified Hummer’s methods) followed by thermal reduction (e.g., material annealing at temperature > 700 °C) and/or activation processes (e.g., KOH activation).
• chemical oxidation- aided graphite exfoliation e.g., modified Hummer’s methods
• thermal reduction e.g., material annealing at temperature > 700 °C
• activation processes e.g., KOH activation
• the pristine graphene flakes are two-dimensional flakes that preserve the crystallinity of the basal planes of the native graphite layers.
• the pristine graphene flakes may comprise a single layer or a number of graphene layers of less than 150. More preferably, the two dimensional flakes are single layer graphene flakes or flakes with a number of graphene layer equal to or lower than 5. These flakes are also referred to “single-/few-layer graphene (SLG/FLG)”.
• These flakes are non-oxidized flakes. They have an atomic content of oxygen equal to or lower than 5%, preferably lower than 2%, more preferably lower than 1%, as measured by X-ray photoelectron spectroscopy.
• the atomic content of oxygen of the pristine graphene flakes herein disclosed resembles the one of the starting graphite, commercially available with different chemical purity grades.
• the starting graphite used to produce the flakes is preferably selected with an atomic content of oxygen measured by x-ray photoelectron spectroscopy lower than 5%, preferably lower than 2%, more preferably lower than 1%.
• the pristine graphene flakes are free of defects on their basal plane. This property is assessed by the absence of a linear correlation (R 2 ⁇ 0.5) in the plot of the ratio between the intensity of the D and G Raman peaks against the full width half maximum of G Raman peak, which is extrapolated by the statistical analysis of Raman spectroscopy measurements of samples comprising different flakes. In such condition (i.e., absence of defective basal planes), I(D)/I(G) varies inversely with the crystal size.
• the ratio between the intensities of the D and G peaks (I(D)/I(G)) of the pristine flakes Raman spectra is comprised between 0.1 and 2.0, preferably between 0.1 and 1.2.
• the flakes exhibit superior electrical conductivity compared to graphite/graphene oxides and derivatives, as a result of a defect-free flat morphology of their basal planes. They show a graphite-like long range order of the sp 2 lattice (contrary to the highly wrinkled defective (reduced) graphene oxides), as well as high surface area (mandatory for the realization of high-capacitance SC electrode) due to their nanometric thickness.
• the ultra-low friction/super-lubricating properties of graphene flakes are drastically deteriorated by both chemical functionalization groups (including oxygen functionalities in (reduced) graphene oxides) and defective sp 3 domains of defective graphene flakes, in which polar and/or charged moieties adhere via friction-enhancing hydrogen bonds.
• the pristine flakes having the features herein disclosed may be obtained by evaporation and freeze-drying of a dispersion of flakes produced by wet-jet milling exfoliation of graphite, as disclosed in document WO2017/089987A1.
• the thickness of the flakes is comprised between about 0.3 nm and 40 nm (values measured by atomic force microscopy measurements).
• the majority of the flakes have thicknesses between 0.3 nm and 2 nm.
• the statistical distribution of the thickness of the flakes obeys a log-normal distribution with the maximum peaking at value inferior to 1.8 nm.
• the two-dimensional flakes in the sample are mainly single layer graphene flakes or flakes with a number of graphene layer equal to or lower than 5 (i.e., SLG/FLG).
• the atomic content of oxygen of the pristine, non-oxidized graphene flakes is lower than 2%.
• Figure 1 illustrates the Raman spectroscopy analysis for the pristine graphene flakes.
• the Raman spectrum of the flakes is compared to that of the starting graphite.
• the Raman spectrum of the flakes exhibits an increase of the D peak compared to those of native graphite, because of the decrease of the crystal size of the flakes compared to starting graphite.
• the plot of I(D)/I(G) vs. FWHM(G) does not show a linear correlation (R 2 ⁇ 0.3), which means that the exfoliation process did not induce in-plane defects into the flakes.
• I(D)/I(G) ranges between 0.1 and 1.2 for the flakes, indicating the presence of flakes with lateral dimension larger than those of the flakes produced by ultrasonication-assisted liquid phase exfoliation, whose I(D)/I(G) can be higher than 1.2.
• the statistical distribution of the lateral dimension of the flakes obeys a log-normal distribution with the maximum peaking at ca. 460 nm, which is higher than those shown by graphene flakes produced by ultrasonication-assisted liquid phase exfoliation ( ⁇ 350 nm).
• the pristine graphene flakes boost the mechanical stability of the SC electrodes based on solely AC thanks to the high Young’s module of graphene flakes ( ⁇ in the order of 1 TPa for single layer graphene flakes).
• the graphene flakes enhance the electrochemical performance, in terms of rate capability (i.e., specific energy density at high specific power density), of the AC -based SC electrodes. More specifically, the electrolyte nanotribology on graphene flakes is effective to overcome electrolyte confinement issues in micropores (pore size ⁇ 2 nm). In fact, as the electrolyte confinement increases, the translational entropy available to the electrolyte molecules decreases until it is thermodynamically favorable for it to condense to an ordered phase, displaying a solid-like behavior even at temperature in which the bulk is a fluid.
• the fluidity of the electrolyte in a porous film is supposed to be limited by the nanoconfinement effects provided by the irregular surface of the AC particles, while the flat surface of graphene flakes can effectively squeeze out the interfacial region providing fluid-like conditions similar to the solely solvent.
• the graphene flakes intrinsically acts as “slide” for electrolyte ions, accelerating the electrolyte transport compared to covering layers comprising AC in form of films.
• the “slide like behavior” of the graphene flakes agrees with the ultra-low nanoscale frictional properties previously reported for FLG films, which behave similarly to super- lubricating highly oriented pyrolytic graphite (HOPG) films (friction coefficient ⁇ 0.01).
• the binding agent of the compositions comprises a polymeric material.
• the polymeric material may comprise at least one fluorine -free polymer.
• the at least one fluorine-free polymer has the advantage that it may be better processable in the environmentally friendly solvent.
• the at least one fluorine-free polymer may be selected in the group consisting of carboxymethyl cellulose (CMC) and derivatives, preferably sodium carboxymethyl cellulose (Na-CMC), natural cellulose (NC), alginate, polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB).
• the at least one polymer is sodium carboxymethyl cellulose (Na- CMC).
• the binding agent may be contained in the composition in an amount comprised between 1% by weight (w/w) and 30% by weight, preferably between 5% and 10% by weight with respect to the total weight of the electrically conductive material plus the binding agent.
• said binding agent is capable of inhibit the sedimentation/aggregation of graphitic flakes (especially non-polar graphene flakes) in the selected environmentally friendly solvent and provide physio/electro/chemical properties of the covering layers in form of films, comparable or superior to those obtained by conventional fluorine-containing polymers.
• compositions herein disclosed allow achieving covering layers, preferably in form of film, endowed with mechanical stability without impeding wettability, ion mobility in the electrode pores and electron conduction.
• the binding agent comprising a polymeric material preferably comprising at least one fluorine-free polymer may be used for organic electrolytes or ionic liquids that are typically adopted in commercial SCs and high-voltage SCs, respectively, due to their low-cost ( ⁇ 2 US$/kg) and their surfactant properties impeding active material sedimentation.
• the at least one polymer for example Na-CMC
• the carboxylic groups of Na-CMC adsorbed onto the graphite surface dissociate and stabilize the graphene- based inks.
• the solvent contained in the composition herein disclosed is an environmentally friendly solvent having a boiling point equal to or lower than 150°C.
• environmentally friendly solvent refers to a solvent that do not exert adverse effects to the environment and to the health of living organisms.
• the environmentally friendly solvent having a boiling point equal to or lower than 150°C may be selected in the group consisting of water, alcohols, mixtures thereof.
• the alcohols may be selected in the group consisting of ethanol (ethyl alcohol), 1-propanol (propan- l-ol or 1-propyl alcohol or n-propanol), 2- propanol (propan-2-ol or isopropyl alcohol or isopropanol), 1 -butanol (n-butanol or n-butyl alcohol), 2-butanol (sec -butanol or 2-butyl alcohol), 2-methyl- 1 -propanol, 2-methyl-2-propanol (tert-butanol or 2-methylpropan-2-ol), 1-pentanol (pentan-1- ol), 2-pentanol (pentan-2-ol or sec-amyl alcohol), 3 -methyl- 1 -butanol (3- methylbutan-l-o
• the environmentally friendly solvents may comprise water and ethanol (a biosolvent derived from the processing of agricultural crops).
• the solvent may be present in the composition herein disclosed in an amount comprised between 70% and 99.5% by weight (w/w) compared to the total weight of the composition.
• the amount of solvent is preferably chosen dependently by the solvent composition to result in a composition viscosity ⁇ 50 mPa s.
• the solvent may be present in the composition in an amount comprised between 10% and 70% by weight (w/w) compared to the total weight of the composition.
• Lower amount of solvent for example comprised between 10% and 70% by weight (w/w) can be obtained by drying the dispersion at temperature inferior to the temperature degrading chemically the component of the compositions (for example, the binding agents).
• the products with less than 70% w/w of solid contents compared to the total weight of the composition could result in slurries, which can be deposited by casting method.
• the solvent may comprise water in an amount comprised between 10% and 90% by weight with respect to the total amount of the solvent.
• each of them may have a boiling point comprised between 50°C and 150°C.
• the boiling point of the solvent used in the composition (equal or lower than 150°C), allow avoiding high-temperature processes (> 100°C) for its removal during and/or after the composition deposition.
• the solvent suitable to be used in the compositions herein disclosed comprises a mixture of water and ethanol, preferably in a 1: 1 volume ratio (vol/vol).
• the solvent herein disclosed preferably comprising a mixture of water and ethanol, favours the dispersion and stabilization (i.e., impeding material sedimentation) of the electrically conductive material contained in the composition.
• an “environmentally friendly” solvent reduces the environmental and human health impacts of electrode film production.
• NMP organic solvent
• environmentally friendly solvents preferably water-based solvents
• the use of “green” solvents intrinsically reduce the costs associated to the actions ensuring hazardous organic solvents exposure within the operational condition limits and costs associated to both drying and recovery of the hazardous organic solvents.
• the equilibrium pressure of NMP is 35-times lower than that of water (in agreement with the lower boiling point of NMP (203°C) compared to that of water (100°C)), potentially requiring relevant drying costs impacting on the overall SC production costs.
• the recovery of NMP solvent via condensation and/or distillation is also necessary to prevent toxic/irritating solvent release into the environment, thus introducing additional cost compared to “environmentally friendly” solvent processing.
• the at least one allotrope of carbon consists of pristine graphene flakes having an atomic content of oxygen equal to or lower than 5%, preferably equal to or lower than 2%.
• the composition may comprise as active electrically conductive material at least one further allotrope of carbon selected in the group consisting of activated carbon (AC), carbon nanotubes, carbide-derived carbons, carbon black.
• AC activated carbon
• carbon nanotubes carbon nanotubes
• carbide-derived carbons carbon black
• the weight percentage (wt%) of the nano structured allotropes of carbon with respect to the total weight of the electrically conductive active material contained in the compositions herein disclosed can vary, as shown in Table 1.
• the composition may comprise as electrically conductive material: pristine graphene flakes in an amount comprised between 1% and 100%, activated carbon (AC) in an amount comprised between 0% and 99%, carbon nanotubes in an amount comprised between 0% and 99%, carbide-derived carbons in an amount comprised between 0% and 99%, acetylene black (carbon black) in an amount comprised between 0% and 99%.
• electrically conductive material pristine graphene flakes in an amount comprised between 1% and 100%, activated carbon (AC) in an amount comprised between 0% and 99%, carbon nanotubes in an amount comprised between 0% and 99%, carbide-derived carbons in an amount comprised between 0% and 99%, acetylene black (carbon black) in an amount comprised between 0% and 99%.
• ACs may be used in combination with graphene flakes due to both their high SS A (> 1000 m 2 /g) and low-cost ( ⁇ 50 US$/kg for SC-grade AC).
• activated carbon may be present in the composition in an amount higher than 0% and lower than or equal to 99% by weight (w/w), preferably between 20% and 90% by weight (w/w) compared to the weight of the electrically conductive material.
• the electrically conductive material may consist of pristine graphene flakes having an atomic content of oxygen equal to or lower than 5%, preferably equal to or lower than 2%.
• the electrically conductive material may consist of pristine graphene flakes having an atomic content of oxygen equal to or lower than 5%, preferably equal to or lower than 2% and activated carbon (AC).
• compositions may be produced by:
• an environmentally friendly solvent having a boiling point equal to or lower than 150°C, preferably selected in the group consisting of water, alcohols, mixtures thereof: i) an electrically conductive material comprising at least one allotrope of carbon, wherein said at least one allotrope of carbon comprises pristine graphene flakes having an atomic content of oxygen equal to or lower than 5%, preferably equal to or lower than 2%, ii) a binding agent comprising a polymeric material, to obtain a dispersion,
• the mixing step may be performed by sonicating the dispersion in a bath sonicator, preferably for a time period of at least 30 minutes.
• compositions herein disclosed allows to produce electrically conductive covering layers on a substrate of an energy storage device in form of film.
• a method for providing electrically conductive layers of covering material on a substrate of an energy storage device in form of film comprises at least one step of depositing the composition onto the substrate.
• the method for providing at least one electrically conductive covering layer on a substrate of an energy storage device comprises the steps of:
• the covering layer in form of film preferably at a temperature comprised between 40°C and 150°C.
• the method may consist of the step of depositing the composition herein disclosed onto the substrate to obtain the covering layer in form of film.
• the depositing step may be carried out by spray coating the composition.
• the spray-coating may be carried out by using a mass loading comprised between 0.01 mg/cm 2 and 1000 mg/cm 2 , preferably between 0.2 mg/cm 2 and 20 mg/cm 2 , more preferably between 1 mg/cm 2 and 10 mg/cm 2 .
• the gas carrier pressure may be comprised between 1 bar and 5 bar, preferably 1 bar.
• the deposition distance may be comprised between 0.2 cm and 100 cm, preferably between 1 and 10 cm.
• the aperture of nozzle may be comprised between 0.1 mm and 10 mm, preferably between 1 mm and 2 mm.
• the temperature of the substrate may be comprised between room temperature (e.g., 20°C or even lower) and 200°C, preferably between 40°C and 150°C, more preferably equal to or lower than 100°C.
• the line deposition velocity may be higher than 0.01 mm/s, preferably comprised between 0.5 mm/s and 500 mm/s, more preferably between 10 mm/s and 50 mm/s.
• the step of heating the covering layer in form of film favors the solvent evaporation.
• the obtained film is a homogeneous film of electrically conductive layers of covering material.
• the heating step may be carried out at a temperature comprised between 40°C and 100°C. A temperature of 50°C may be advantageous to obtain homogeneous films of electrically conductive covering material.
• the substrate may be a surface of a supercapacitor electrode, preferably a surface of a current collector of a supercapacitor electrode.
• the substrate may comprise a material selected in the group consisting of a metal, preferably aluminum (Al), gold (Au), nickel (Ni), stainless steel, a carbon- coated non-electric ally conductive material, preferably plastic, fabric, paper, a graphitic foil, preferably a graphite paper.
• a metal preferably aluminum (Al), gold (Au), nickel (Ni), stainless steel, a carbon- coated non-electric ally conductive material, preferably plastic, fabric, paper, a graphitic foil, preferably a graphite paper.
• said substrate may be a flexible substrate.
• the substrates can be coated by a thin layer ( ⁇ 2 pm) of electrically conductive nanoparticles (e.g., acetylene black) to promote the adhesion and optimal electrical connection between the covering layer comprising the composition herein disclosed and the substrate.
• electrically conductive nanoparticles e.g., acetylene black
• the covering layer in form of film obtained according to the method disclosed above may have a thickness comprised between 0.5 pm and 500 pm.
• thickness higher than 10 mhi corresponding to electrode material weight > 1 mg/cm 2
• active electrically conductive material weight has to account for about more than 30% of the total mass of the packaged device. Otherwise, the gravimetric electrochemical performance of the latter drastically decreases (by a factor > 10 for active material mass loading of 1 mg cm 2 ).
• a deposition mask is used during spray coating deposition method in order to deposit patterned electrode electrically conductive covering layer in form of film with spatial resolution superior to those achievable by simple spray coating deposition method.
• the disclosure provides a supercapacitor electrode comprising an electrically conductive covering layer in form of film obtained by the method above disclosed, comprising the step of depositing the composition object of the instant application.
• the final supercapacitors may be obtained by assembling in vertical or planar configuration two identical, preferably spray-coated, electrodes above described.
• a commercial separator is needed to avoid the electrical contact between the electrodes.
• planar configurations the electrode are intrinsically electrically disconnected by the spatial gap between their fingers of the interdigitated electrodes.
• the pristine graphene flakes when the composition is deposited on a substrate of a supercapacitor configured in a vertical configuration the pristine graphene flakes may be preferably present in an amount comprised between 1% and 30% by weight based to total weight of the electrically conductive material weight.
• the composition may comprise as electrically conductive material pristine graphene flakes in combination with at least one further allotrope of carbon selected in the group consisting of activated carbon, carbon nanotubes, carbide-derived carbons, carbon black, preferably activated carbon.
• the at least one further allotrope of carbon, preferably active carbon may be present in the composition in an amount comprised between 70% and 99% by weight compared to total weight of the electrically conductive material weight.
• pristine graphene flakes and activated carbon may be present in the composition in an amount, with respect to the total amount of the electrically conductive material, comprised between 1% and 30% by weight (w/w) and between 70% and 99% by weight (w/w), respectively.
• the at least one further allotrope of carbon, preferably active carbon acts as spacers for impeding graphene flakes restacking with a displacement parallel to the current electrode collectors. Therefore, said spacers facilitate the electrolyte access to the electrode surface, boosting the maximum power density of the SCs.
• spacers favors the full exploitation of the surface area of the graphene flakes, reaching specific surface area of active materials comparable to those of commercially available high-SSA ACs (> 1000 m 2 /g).
• said at least another allotrope of carbon acts as conductive bridges between graphene flakes, thus creating highly electrically conductive carbon-based nanoporous covering layer in form of films, as required for high power operating SC electrodes.
• an electrically conductive component such as those given by acetylene black (carbon black) nanoparticles in commercial -like electrode material formulations, may not be strictly required in the graphene-based electrode material formulation to provide satisfactory low equivalent series resistance -ESR- of the SC electrodes (e.g., ⁇ 10 W per 1 cm 2 of device area).
• the supercapacitor may be configured in a planar configuration and the pristine graphene flakes may be preferably present in the composition in an amount comprised between 20% and 100% by weight compared to the total weight of the electrically conductive material weight.
• solely graphene flakes may be used as electrically conductive active material. The in-plane displacement of graphene flakes is parallel to the electrolyte ions movements during the device charging/discharging.
• planar SCs based on solely graphene flakes may intrinsically facilitate the flow of the electrolyte ions between the graphene flakes in a short diffusion pathway, maximizing the ion accessibility to the SSA of the substrate covering layer in form of films, thus boosting the rate capability of the SCs (i.e., the maximum power density of the SCs).
• the optimized films electrically conductive layers of covering material for both the vertical and planar SC configurations show an optimal balance between the resulting mechanical stability, porosity and wettability of the electrode, otherwise unreachable with commercially available SC active materials, i.e., ACs and typical electrode composition deposition methods (i.e., casting deposition of active material compositions in form of slurry).
• symmetric SCs produced by using electrically conductive covering layers comprising the composition herein disclosed display high specific or gravimetric energy density (> 10 Wh/kg) at high specific power density (> 30 kW/kg).
• the SCs composed by electrodes produced by conventional casting deposition which typically have specific energy density ⁇ 10 Wh/kg at specific power density of 15 kW/kg).
• composition herein disclosed allows improving the rate capability of the SCs compared to commercially available electrode materials.
• rate capability improvement has here been validated in a large operating temperature window (-40/+100°C), as disclosed in the Examples section.
• Example 1 Compositions for supercapacitors
• compositions were formulated by mixing the following components:
• AC - activated carbon
• pristine graphene flakes alone or in combination, as active electrically conductive material
• NA-CMC sodium carboxymethyl cellulose
• Pristine, non-oxidized graphene flakes having an atomic content of oxygen equal to or lower than 5% in form of powder were isolated by drying the single- /few-layer graphene (SLG/FLG) flake dispersion obtained by wet jet milling exfoliation as disclosed in document WO2017/089987A1 and summarized below.
• the wet jet milling exfoliation process exploits a high pressure (between 180 and 250 MPa) to force the passage of the solvent/graphite mixture through perforated disks, with adjustable hole diameters (0.3-0.1 mm, named nozzle), strongly enhancing the effectiveness of the generated shear forces originating the exfoliation of the graphite.
• the shear force generated by the solvent when the sample passed through such a nozzle promoted the graphite exfoliation.
• the sample was cooled down using a chiller.
• the processed sample was then collected in another container.
• the WJM process was repeated three times adjusting the diameter of the nozzle to 0.2 0.15 and 0.1 mm, respectively, to obtain the final SLG/FLG dispersion.
• the as-obtained SLG/FLG dispersion was dried in a rotary evaporator (Heidolph HEIVAP INDUSTRIAF, FKV Sri, Italy) setting the bath temperature at 80°C and gradually lowering the pressure to 5 mbar, allowing the evaporation of NMP.
• DMSO dimethyl sulfoxide
• Activated carbon was purchased by AB-520, MTI Corp. and used as received.
• the binding agent sodium carboxymethyl cellulose (Na-CMC; 90000 molecular weight), was purchased by Sigma Aldrich and used as received.
• compositions were obtained by dispersing the electrically conductive material (activated carbon, graphene flakes or mixtures comprising activated carbon and graphene flakes) and the polymer sodium carboxymethyl cellulose (Na- CMC) in an aqueous solvent comprising water and ethanol in a volume ratio (v/v) of 1 : 1.
• the obtained dispersions were ultrasonicated in a bath sonicator (Branson® 5800 cleaner, Branson Ultrasonics) for 30 min before their use to homogenize the distribution of the electrically conductive material and the binding agent.
• Table 2 reports the amounts of the composition components produced ad disclosed above.
• compositions “Graphene”, “AC:graphene (50:50)” and “AC:graphene (20:80)” have been preferably used for the realization of SCs in planar configuration.
• composition “AC:graphene (90:10)” has been validated in sandwich-like vertical SC configurations displaying rate capability superior to reference device based on commercially available ACs as active materials.
• an amount of graphene flakes for example of about 10% by weight with respect to the total amount of the electrically conductive material (“AC:graphene (90:10)”) has been shown to be sufficient to achieve the desired results.
• compositions “AC” (comparative composition) and “AC:graphene (90:10)” obtained as disclosed in Example 1 were deposited in form of films onto C-coated Aluminum current collector (En'Safe® 91, Armor) by a manual dual action gravity feed airbrush (FE-180, Fengda) or a custom-built automatized spray coater (Aurel XCEL, Aurel Automation S.p.A.) with: a computer-controlled spray head, movable in the XYZ directions on a heatable stage; a 2 mm orifice diameter nozzle (Nordson EFD) with fluid recirculation, supplied with compressed air.
• a computer-controlled spray head movable in the XYZ directions on a heatable stage
• a 2 mm orifice diameter nozzle Nedson EFD
• the amount of material comprising the composition deposited by each spray coating sequence is calibrated.
• the composition mass loadings between 1 and 20 mg cm 2 were deposited on current collectors by adjusting the amount of sprayed electrode composition. Said mass loadings are comparable to those adopted in commercial-like SCs for large-scale applications), in which active material weight has to account for about more than 30% of the total mass of the packaged device, otherwise the gravimetric performance (i.e., the specific energy density) of the SCs drastically decreases (e.g., by a factor > 10 for active material mass loading of 1 mg cm 2 ).
• the spray-coated layers in form of films were characterized by Brunauer, Emmett and Teller (BET) surface area and sheet resistance (Rsheet) measurements. Specific surface area measurements of the spray-coated films were carried out in Autosorb-iQ (Quantachrome) by Kr physisorption at temperatures of 77 K.
• the SSAs were calculated using the multipoint Brunauer, Emmett and Teller (BET) model, (1) considering equally spaced points in the P/P0 range of 0.009 - 0.075. Po is the vapour pressure of Kr at 77 K, corresponding to 2.63 Torr. (2-5).
• the obtained BET SSAs of spray-coated films are between 40-200 m 2 /g.
• the measured BET SSAs for spray-coated “AC” and “AC:graphene (90:10)” films are between 2000-2700 m 2 /g, depending on the electrode material mass loadings. Such values are superior to those measured for electrode films deposited by conventional casting deposition (i.e., doctor blading deposition) of electrode material (ACs or AC- hybridized graphene flakes) slurries adopting conventional F-containing binders (i.e., PVDF) and expensive and toxic organic solvents (i.e., NMP) (between 1000- 1800 m 2 /g).
• AC particles act as spacers to avoid restacking of graphene flakes enabling the exploitation of the SSA of graphene flakes beyond their mechanical, electrical and tribological properties.
• the lower SSA values of films obtained by composition containing graphene as sole active electrically conductive material compared to the films obtained by composition containing graphene and AC are ascribed to the in-plane displacement of the SLG/FLG flakes, which may impede an efficient gas (and ion) transport along the vertical direction of the film. Therefore, the laminar morphology of the films comprising the composition “Graphene” is preferred for the realization of interdigitated electrodes to be used in planar SC configurations. In fact, in such configuration, the in-plane displacement of graphene flakes is parallel to the electrolyte ions movements during the device charging/discharging. This intrinsically facilitates the flow of the electrolyte ions between the graphene flakes in a short diffusion pathway, maximizing the ion accessibility to the SSA of the electrode films.
• the calculated SSAs for representative slurry-casted films are -1430 m 2 /g for AC, -2120 m 2 /g for “AC:graphene (90:10)”, -1600 m 2 /g for “AC:graphene (80:20)”, -630 m 2 /g for “AC:graphene (50:50)” and -40 m 2 /g for “graphene”.
• the trend of these values observed by changing the graphene flakes content resemble those observed for spray-coated SCs.
• Supercapacitors were fabricated in a symmetric sandwich-like vertical configuration by stacking two identical electrodes. Films obtained by the deposition of the composition “AC:graphene (90:10)”, as well as the composition “AC” as comparative composition, spray-coated onto C-coated A1 current collector were used as electrodes.
• the SCs were assembled in both coin cell (CR2032 cases, springs and spacers purchased from MTI Corp.), by using a compact crimper (MSK-PN110-S, MTI Corp.), or pouch cell-configurations, by packaging electrodes in A1 laminated films (MTI Corp.), and contacting electrodes by A1 Tab (MTI Corp.).
• organic electrolyte e.g., 1 M tetraethylammonium tetrafluoroborate -TEABF4- in acetonitrile (ACN) or propylene carbonate (PC)
• ionic liquid electrolyte e.g., butyl-trimethylammonium bis(trifluoromethyl sulfonyl)imide -[N 1114] [TFSI]-, methyl-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide -[PYR13] [TFSI]- l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide-[EMIM][TFSI]-, l-ethyl-3-methylimidazolium tetrafuoroborate -[EMIM][BF4])-, or mixture of organic (g-Butyrolactone, PC and ACN) and
• binary mixture of g-Butyrolactone (50 wt%) and [EMIM][TFSI] (50 wt%) (g- B uty o 1 ac tonc/[ E I M] [ TFS I J ) were used as electrolyte with high voltage window electrochemical stabilities over a wide temperature range (- 50/+100°C).
• the addition of g-Butyrolactone into [EMIM][TFSI] enhances the ionic conductivity and fluidity of the pure ionic liquid, especially at low temperature(7,8).
• C g (
• E 0.5xC areai x(AV) 2 .
• P E/td.
• the electrochemical measurements were performed at five different temperatures, i.e., -40°C, 0°C, room temperature (25°C), 50°C and 100°C by placing the SCs inside a temperature-controlled chamber.
• Figure 2 shows the Ragone plots obtained at room temperature (25°C) for the SCs based on the electrodes produced according to the disclosed embodiments, adopting an electrode material mass loading of ⁇ 5 mg/cm 2 (excluding the mass of current collectors) and g- B uty ro 1 actonc/[ E I J [TFS I J as electrolyte.
• the Ragone plots obtained room temperature for the SCs based on the electrodes produced through conventional casting deposition (i.e., doctor blading deposition) of electrode material slurries adopting conventional F-containing binders (i.e., PVDF) and, organic solvents (i.e., NMP) are also shown for comparison.
• the SCs are simply named with the name of the electrode film compositions (i.e., “AC” or “AC:graphene (90:10)”).
• AC the electrode film compositions
• AC:graphene (90:10) At specific power density above 1500 W/kg, the spray coated “AC:graphene (90:10)” exhibits a specific energy density higher than that of “AC” (+313% at the specific tested power density of 30000 W/kg), as a consequence of the high electron conductivity of the graphene-based electrode films and the ultrafast electron ion transport enabled by graphene flakes. More in detail, the spray coated “AC:graphene (90:10)” exhibits a specific energy density > 10 Wh/kg at specific power density > 30 kW/kg.
• spray coating-based manufacturing of SCs enable superior electrochemical performance of the SCs compared to those of slurry casted SCs (e.g., specific energy density more than +50% for specific power density > 7500 W/kg), which show specific energy density ⁇ 10 Wh/kg at specific power density of 15 kW/kg.
• Figure 3 shows the Ragone plots obtained at -40°C, 0°C, 50°C and 100°C for the spray-coated “AC” and “AC:graphene (90:10)” compositions previously measured at room temperature.
• AC:graphene (90:10) improves the SC rate capability of the “AC”, validating the increase of the SC rate capability enabled by the use of graphene flakes as electrode material.
• AC:graphene (90:10) exhibits specific energy densities higher than those of “AC” at all the measured specific power density.
• Fluorinated graphene flakes were synthetized according to the disclosure of the prior art document US 2018/0201740 Al.
• the oxygen and fluorine contents measured through X-ray photoelectron spectroscopy and TEM-coupled energy- dispersive X-ray spectroscopy was approximately equal to 2.0 wt% and 3.9 wt%, respectively.
• the structural properties of the fluorinated graphene flakes have been evaluated through Raman spectroscopy measurements, while providing a comparison with the pristine graphene flakes disclosed in the instant application.
• the statistical analysis of the Raman spectra of the fluorinated graphene flakes shows that the ratio between the intensities of the D and G peaks (I(D)/I(G)) is different from the ratio I(D)/I(G) of the pristine graphene flakes contained in the composition of the instant application; specifically, the I(D)/I(G) ratios for the fluorinated graphene flakes are markedly higher than 2.0.
• TEM transmission electron microscopy
• the pristine, non-oxidized, graphene flakes showing a ratio I(D)/I(G) of the Raman spectra comprised between 0.1 and 2.0 simultaneously provide high electrochemically accessible specific surface area (SSA) of the SC electrodes and ultrafast ions transport within the SC electrodes, boosting the specific energy density of the SCs at high specific power density (i.e., the SC rate capability).
• SSA electrochemically accessible specific surface area

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