WO2023062656A1

WO2023062656A1 - High density carbon electrodes for ultra capacitors

Info

Publication number: WO2023062656A1
Application number: PCT/IN2022/050927
Authority: WO
Inventors: Robin George; Hemant CHARAYA
Original assignee: Log 9 Materials Scientific Private Limited
Priority date: 2021-10-17
Filing date: 2022-10-17
Publication date: 2023-04-20

Abstract

The embodiments herein disclose a coating slurry composition to fabricate high-dense carbon electrodes for EDLC (Electric Double Layer Capacitor) application and process of preparation thereof. The high-density carbon electrodes employ a quaternary system of carbon or carbonaceous material, that imparts high volumetric capacitance, low ESR values and high-power density to the EDLC device. The quaternary system of carbon or carbonaceous material comprises of a high-density activated carbon, a low density activated carbon, graphene nanoplatelets and low-surface area conductive carbon.

Description

HIGH DENSITY CARBON ELECTRODES FOR ULTRA CAPACITORS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the priority of the Indian Provisional Patent Application (PPA) with serial number 202141017849, filed on April 17, 2021, with the title "HIGH DENSITY CARBON ELECTRODES FOR ULTRACAPACITORS". The priority of the application was postdated by 6 months to October 17^th, 2021. The contents of abovementioned PPA are included in entirety as reference herein.

BACKGROUND

Technical field

[0002] The embodiments herein generally related to energy storage devices. The embodiments herein are particularly related to fabrication of high-density carbon electrodes for Electric Double Layer Supercapacitors (EDLCs). The embodiments herein are more particularly related to the fabrication of EDLCs to achieve a low Equivalent Series Resistance (ESR), high-power density and high volumetric capacitance.

Description of the Related art

[0003] In the path towards global electrification, supercapacitors or ultracapacitors have a significant role to play. Their tendency to provide burst of energy, which is a well- documented limitation of chemical batteries, is suited for applications that require a large amount of energy in quick time such as wind turbines, fork-lifts, and grid power supply during peak power demand. Further, they can be combined with Lithium-ion (Li-ion) battery packs in electric vehicles to support peak current demand during acceleration and to harness energy. The energy produced is harnessed during regenerative braking, thereby preventing a high- current load on Li-ion batteries. The prevention of a high-current load on Li-ion batteries enhances the cycle life of the battery pack and pushing the overall efficiency of a system to a higher value.

[0004] Based on the mechanism of storing energy, supercapacitors can be divided into two categories: Electric Double Layer Capacitors (EDLCs) and Pseudo-capacitors. Pseudocapacitors, like chemical batteries, store energy through redox reactions i.e., chemical species undergoing oxidation or reduction at the electrodes. In contrast, EDLCs, which are most commonly used, store energy by physical adsorption of oppositely charged ions in the two electrodes. Since there is no chemical reaction involved in charge storage mechanism in EDLCs, they get charged and discharged at an extremely high rate and thereby have high power density.

[0005] Electric Double Layer Capacitors (EDLCs) have a symmetric configuration where both the electrodes are composed of a carbon material with high surface area to impart a high specific capacity to the electrodes. The performance of the EDLC is majorly governed by the physical and chemical nature of the carbon material used for the electrodes.

[0006] Furthermore, for the pseudo capacitor, the price of a metal oxide material (in particular, ruthenium oxide) is expensive, and that the material is not environmentally friendly at the time of disposal, -thereby causing environmental pollution. On the contrary, the EDLC is made of an eco-friendly carbon material having excellent stability. For instance, the carbon material that is used for making electrodes includes carbon nanofiber (CNF) and activated carbon nanofiber (ACNF) which are manufactured by carbonization of polymers such as activated carbon powder (ACP), carbon nanotube (CNT), graphite, vapor grown carbon fiber (VGCF), and carbon aerogel, polyacrylonitrile (PAN) and polyvinylidene fluoride (PVdF). In addition, carbon black (CB) may be added in the EDLC capacitor in addition to the carbon material. [0007] Besides, the EDLC is composed of a current collector, two electrodes, an electrolyte, and a separator. Due to the separator, the electrolyte is fdled between the two electrodes that are electrically separated from each other. The current collector plays a role of charging or discharging electric charges in the electrodes effectively. The electrodes that are made of activated carbon that is used as an electrode material for the EDLC are porous and have a wide specific surface area.

[0008] Furthermore, the capacitance of the EDLC is highly dependent on structure and physical properties of the activated carbon electrodes, which requires the following characteristics: a large specific surface area having a low internal resistance of a material, and a high density of a carbon material, and so forth. For example, in the case of the electrodes of the EDLC, the polyacrylonitrile (PAN) is base activated to thereby obtain activated carbon nanofiber (ACNF) having a high specific surface area of 1500-3000 m²/g or so. However, because of low density of the activated carbon nanofiber (ACNF), equivalent series resistance (ESR) increases, and the capacitance between the electrodes of the EDLC is lower than that between electrodes of an EDLC made of active carbon powder (ACP). As described above, if the density of the electrode active material is low, resistance generally increases and capacitance decreases.

[0009] Specifically, if a content of the conductive material increases, resistance of the electrodes will decrease due to high electrical conductivity of the conductive material. However, when the conductive material is compared with an active material such as activated carbon, the former has a lower specific surface area than that of the latter. Accordingly, capacitance of the EDLC is also reduced. In addition, if a content of an active material having high-density increases, capacitance increases. However, because the electrical conductivity of the active material is not high like that of the conductive material, resistance increases. [0010] Thus, if the density of each electrode becomes low, the active material and the conductive material do not contact efficiently. As a result, the equivalent series resistance (ESR) increases and thus, the capacitance decreases. In this case, if a relative content of the conductive material is heightened, the equivalent series resistance (ESR), resistance may be lowered. However, since an amount of an electric double layer to be formed is small due to a low surface area value (not more than 1000 m²/g) of a general conductive material, the EDLC has low capacitance of 10 F/g or less.

[0011] In contrast, if a content of the active material such as the activated carbon powder or activated carbon nanofiber is heightened, initial capacitance may increase up to 300 F/g due to the high specific surface area (not more than 3000 m²/g). However, if content of the conductive material is lowered, the electrical conductivity reduces. As a result, capacitance is greatly reduced at a fast-scanning speed of 500 mV/s or at a high current value of 100 mA/s.

[0012] In general, a carbon material with properties such as high surface area, low intrinsic resistance, high purity, and high compressibility is considered ideal for application in supercapacitor electrodes. However, these properties are interrelated with one another and achieving one of these properties usually impact the other properties in a negative manner. For example, to increase the specific capacity of the carbon material, the carbon material is activated through a steam or treated in alkaline environment to introduce pores. Although, this activation process generates higher surface area and a large number of pores to store ions or charges, the activation process also generates wide range of undesired functional groups on the surface of the carbon material. These undesired functional groups compromise with the purity of the carbon material and result in reduction in the capacitance retention of the EDLC. Similarly, smaller particle size of the carbon material, due to its high compressibility, is used to prepare highly dense carbon electrodes to increase its volumetric capacitance, butthat comes at the expense of high contact resistance of the two electrodes, which will increase the ESR value and reduce the power density of the device. For high performance EDLCs, therefore it is imperative to achieve a balance between the properties listed above.

[0013] Thus, it is desired to address the above-mentioned disadvantages or other shortcomings or at least provide a useful alternative. Hence, there is a need for a fabrication of a carbon electrodes from a quaternary system of carbonaceous materials. Moreover, there is need for fabricating carbon electrodes with high packing density for Electric Double Layer Capacitors (EDLCs). Further, there is a need for an improved high density carbon electrodes for ultracapacitors and its manufacturing method that uses four different types of carbon materials or quaternary system of carbonaceous materials, to enhance a power density and a volumetric capacitance of the EDLC and substantially reduce the ESR value. Still further, there is need to fabricate the carbon electrodes with a high volumetric capacitance.

[0014] The above-mentioned shortcomings, disadvantages and problems are addressed herein, and which will be understood by reading and studying the following specification.

OBJECTIVES OF THE EMBODIMENTS HEREIN

[0015] The primary object of the embodiments herein is to provide carbon electrodes with high packing density for Electric Double Layer Capacitors (EDLCs).

[0016] Another object of the embodiments herein is to provide carbon electrodes with high volumetric capacitance for Electric Double Layer Capacitors (EDLCs).

[0017] Yet another object of the embodiments herein is to fabricate the carbon electrodes from a quaternary system of carbonaceous materials.

[0018] Yet another object of the embodiments herein is to fabricate the carbon electrodes from the quaternary system of carbon/carbonaceous material such that the carbonaceous materials are a low-density activated carbon, a high-density activated carbon, a conductive carbon agent and graphene nanoplatelets. [0019] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the specific density of the low-density activated carbon is in the range of 0. 10 g/cm³ to 0.30 g/cm³.

[0020] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the surface area of the low-density activated carbon is in the range of 2000-2500 m²/g.

[0021] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the ratio of micro to meso-porous volume of the low-density activated carbon is in the range of 0.7 to 1.

[0022] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the micro-porous volume of the low-density activated carbon is in the range of 0.4 cm³/g to 0.9 cm³/g.

[0023] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the meso-porous volume of the low-density activated carbon is in the range of 0.4 cm³/g to 0.9 cm³/g.

[0024] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the average pore diameter of the low-density activated carbon is 2.1 nm.

[0025] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes such that the particle size of the low-density activated carbon is in the range of 3-8 micron.

[0026] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the specific capacitance of the low-density activated carbon is in the range of 18 to 19 F/g. [0027] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the specific density of the high-density activated carbon is in the range of 0.5g/cm³ to 0.9g/cm³.

[0028] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the surface area of the high-density activated carbon is in the range of 1300-1800 m²/g.

[0029] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes wherein the ratio of micro porous volume to meso-porous volume of the high-density activated carbon is in the range of 0.1 to 0.3.

[0030] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes such that the micro- porous volume of the high-density activated carbon is in the range of 0.4 cm³/g to 0.9 cm³/g.

[0031] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes such that the meso- porous volume of the high-density activated carbon is in the range of 0. 1 cm³/g to 0.3 cm³/g.

[0032] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the average pore diameter of the high-density activated carbon is 1.56 nm.

[0033] Yet another object of the embodiments herein is to use the quaternary system of carbon/carbonaceous material for fabricating the carbon electrodes where the specific capacitance of the high-density activated carbon is in the range of 16 to 18 F/g.

[0034] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes such that the particle size of the high-density activated carbon is in the range of 5-10 micron. [0035] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes such that the density of functional groups of both low-density and high-density activated carbon is less than 10 meq/g.

[0036] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes such that the particle size of a high-density active material is larger than that of low-density activated carbon.

[0037] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes such that the graphene nanoplatelets are added to the high density activated carbon to enhance the packing density of the carbon electrodes.

[0038] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes comprising the graphene nanoplatelets, which is highly conductive in nature and helps to decrease the ESR of the carbon electrodes.

[0039] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes where the number of atomic layers in the graphene nanoplatelets ranges between 5 to 15.

[0040] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the atomic carbon percentage of the graphene nanoplatelets is more than 99%.

[0041] Yet another objective of the present invention is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the average particle size of the graphene nanoplatelets is in the range of 0.3pm to 1 pm. [0042] Yet another object of the embodiments is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the surface area of the graphene nanoplatelets is in the range of 50 m²/g to 300 m²/g.

[0043] Yet another object of the embodiments is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the particle density of the graphene nanoplatelets is 1.8 g/cm³.

[0044] Yet another object of the embodiments herein to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the graphene nanoplatelets helps to decrease the amount of solvent required for achieving desired viscosity of the coating slurry.

[0045] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the surface area of a low-surface area conductive carbon is in the range of 30 to 100 m²/g.

[0046] Yet another object of the present invention is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the particle size of the low-surface area conductive carbon ranges between 5 nm to 80 nm.

[0047] Yet another object of the embodiments is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the particle density of the low-surface area conductive carbon is 1.6 g/cm³.

[0048] Yet another object of the embodiments is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, where the conductivity of the low-surface area conductive carbon is 25 S/m.

[0049] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, such that the ratio of high- density to low density activated carbon in the electrodes is in the range of 0.1 to 9. [0050] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, such that the ratio of graphene nanoplatelets to conductive carbon in the electrodes is in the range of 0.5 to 5.

[0051] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, such that the ratio of the activated carbon to additive loadings in the electrodes is in the range of 7: 1 to 10: 1.

[0052] Yet another object of the embodiments herein is to use the quaternary carbon/carbonaceous material for fabricating the carbon electrodes, such that the ratio of the carbonaceous material to binder material is in the range of 8 to 16.

[0053] These and other objects and advantages of the embodiments herein will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY

[0054] The following details present a simplified summary of the embodiments herein to provide a basic understanding of the several aspects of the embodiments herein. This summary is not an extensive overview of the embodiments herein. It is not intended to identify key/critical elements of the embodiments herein or to delineate the scope of the embodiments herein. Its sole purpose is to present the concepts of the embodiments herein in a simplified form as a prelude to the more detailed description that is presented later.

[0055] The other objects and advantages of the embodiments herein will become readily apparent from the following description taken in conjunction with the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

[0056] The various embodiments herein provide, a coating slurry composition to fabricate high density carbon electrodes for ultracapacitor. High density carbon electrodes enhance the power density and the volumetric capacitance of the ultracapacitors and substantially reduce the ESR value. Thus, achieving high density in final electrodes is highly desirable for EDLC (Electric Double Layer Capacitor) type of ultracapacitors. Here, high density in carbon electrodes are fabricated by using quaternary system of carbon or carbonaceous materials.

[0057] According to one embodiment herein, a process for preparation of coating slurry for fabricating high density carbon electrodes in an ultracapacitor is provided. The process comprises dissolving carboxymethyl cellulose binder in a solvent at 70°C under continuous stirring for one hour to obtain a binder solution. Then, separately dry mixing conductive carbon agents (CA) and active materials (AM), in a planetary mixer at 600 RPM for 30 minutes. The conductive carbon agents comprise graphene nanoplatelets and low- surface area conductive carbon. The active materials comprise low-density activated carbon and high-density activated carbon. The conductive carbon agents and active materials together constitute quaternary system of carbon or carbonaceous materials. The process further comprises adding dry mixed conductive carbon agents (CA) to the obtained binder solution and mixing at 200 RPM for 10 minutes and followed by 600 RPM for 30 minutes to obtain a CA-binder solution. Furthermore, the process includes adding active materials batch 1 to the obtained CA-binder solution and mixing at 600 RPM for 30 minutes. Further adding active materials batch 2 to the obtained solution and mixing it at 600 RPM for 30 minutes. Furthermore, the process includes adding active materials batch 3 to the obtained solution and mixing it at 600 RPM for 10 minutes to obtain an AM-CA binder solution. The process further includes adding a co-solvent to the obtained AM-CA binder solution and mixing it at 1000 RPM for 30 minutes. Finally, adding styrene-butadiene rubber (SBR) binder to the obtained solution and mixing it at 400 RPM for 15 minutes, and performing de-gassing at 400 RPM for 15 minutes to obtain the high-density carbon electrodes for ultracapacitor.

[0058] According to one embodiment herein, a coating slurry composition for fabricating high density carbon electrodes in an ultracapacitor is provided. The coating slurry composition comprises a quaternary system of carbon or carbonaceous material, a binder, a solvent, a current collector, and a co-solvent. The quaternary system of carbon or carbonaceous material comprises a low-density activated carbon, a high-density activated carbon, a graphene nanoplatelets and a low-surface area conductive carbon. The low-density activated carbon and the high-density activated carbon comprises active materials, and the graphene nanoplatelets and the low-surface area conductive carbon comprises conductive agents. Thus, the quaternary system of carbon or carbonaceous materials are combined to achieve high power density and high volumetric capacitance, and substantially reduce the ESR (Equivalent Series Resistance) values of the ultracapacitor.

[0059] According to one embodiment herein, the low-density activated carbon is a low-dense, highly porous carbon with large number of micropores and mesopores. The large number of micropores ensures high gravimetric capacitance and high mesopores helps in maintaining capacitive behavior even at higher currents, especially during charging cycles. The gravimetric capacitance is also known as specific capacitance, which is the value corresponding to the energy in the carbon electrodes, Furthermore, the mesopore channels function as electrolyte reservoir from where, the ions can migrate to access the micropores in the low-density carbon and return during the discharging cycle.

[0060] According to one embodiment herein, the low-density activated carbon comprises high density of oxygen functional groups, which causes detrimental effect on the cycle life of the ultracapacitors. Hence, it is important to pretreat the low-density activated carbon to bring down the density of the oxygen functional group by pre-treatment process. The pre-treatment process involves subjecting the low-density activated carbon to high temperature or expose it to microwaves in an inert or reducing atmosphere.

[0061] According to one embodiment herein, the high-density activated carbon is high- dense and less porous, having high microporosity and low meso-porosity. The low mesoporosity in the high-density activated carbon imparts less liquid to solid ratio (1/s ratio) of the coating slurry, for a specific viscosity, thereby allowing higher mass loading of active material at lower coating thicknesses and higher mass loading per unit area of the current collector, also the intrinsic resistance of the high-density activated carbon is low, which helps in establishing a good conductive network across the carbon electrodes thereby improving the ESR value and power density of the ultracapacitor. Furthermore, the high micro porosity provides large specific surface area, large ultra-micropore volume (Vp < 10) and good compatibility. The ultracapacitor comprises EDLC (Electric Double Layer Capacitor).

[0062] According to one embodiment herein, the graphene nanoplatelets provide high density, and comprises individual graphite layers, which slide over one another and impart high compressibility to the high-density carbon electrodes. The individual graphite layers further allows the high-density carbon electrodes to withstand large compressive forces at high compaction during calendaring process without the formation of any stress cracks at the interface of the current collector and the high-density carbon electrodes. The calendaring process is used for smoothing and compressing the quaternary carbon materials during fabrication process, by passing a single continuous carbon sheet through a number of pairs of heated rolls. The rolls in combination are called calendars. Furthermore, the graphene nanoplatelets possess high conductivity, to further reduce the charge transfer resistance of the high-density electrodes and reduces the amount of conductive carbon required to form a conductive network. In addition, the graphene nanoplatelets helps to increase the loading of active materials in the high-density carbon electrodes.

[0063] According to one embodiment herein, the low-surface area conductive carbon helps to achieve desired ESR (Equivalent Series Resistance) values, and also helps to decrease the solvent amount in the coating slurry and thereby improving density of the high-density carbon electrodes.

[0064] According to one embodiment herein, the low-density activated carbon has a specific density in the range of 0. 10 g/cm³ to 0.30 g/cm³ and surface area in the range of 2000 to 2500 m²/g. Furthermore, the microporous volume of the low-density activated carbon is in the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume in the range of 0.4 cm³/g to 0.9 cm³/g.

[0065] According to one embodiment herein, the high-density activated carbon has a specific density in the range of 0.50 g/cm³ to 0.90 g/cm³ and surface area in the range of 1300 to 1800 m²/g. Moreover, the high-density activated carbon has a high microporous and low mesoporous volume and the ratio of meso to micro porous volume ranges between O.lto 0.3. The microporous volume of the high-density activated carbon is the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume is in the range of 0. 1 cm³/g to 0.3 cm³/g.

[0066] According to one embodiment herein, the particle size of the low-density activated carbon ranges from 3 to 8 micron and the particle size of the high-density activated carbon is in the range of 5 to 10 micron. The particle size of high-density activated carbon is always higher than the particle size of low-density activated carbon. Furthermore, the density of functional groups of both low-density and high-density activated carbons is less than 10 meq/g.

[0067] According to one embodiment herein, the graphene nanoplatelets are added to the high-density carbon electrodes to improve the packing density, decreasing the ESR, and enhancing the volumetric capacitance of the EDLC ultracapacitor. The number of atomic layers of the graphene nanoplatelets is in the range of 5 to 15 and the average size is in the range of 0.3 pm to 1 pm. Furthermore, the graphene nanoplatelets have high purity with atomic carbon percentage of more than 99% and a surface area of 50 m²/g to 300 m²/g. The particle density of the graphene nanoplatelets is 1.8 g/cm³. Moreover, the graphene nanoplatelets also decreases the amount of the solvent required to achieve desired viscosity of the coating slurry.

[0068] According to one embodiment herein, the surface area of the low-surface area conductive carbon is in the range of 30 to 100 m²/g and the particle size of the low surface area conductive carbon is in the range of 5 nm to 80 nm. The particle density of the low-surface area conductive carbon is 1.6 g/cm³ and the conductivity is 25 S/m. Furthermore, the ratio of the high-density to low density activated carbon in the electrodes is in the range of 0. 1 to 9 and the ratio of graphene nanoplatelets to low surface area conductive carbon in the electrodes is in the range of 0.5 and 5. In addition, the ratio of the activated carbon to additive loadings in the electrodes is in the range of 7: 1 to 10: 1, additive loadings is the ratio of additives to the active material in the slurry. Furthermore, the ratio of the quaternary carbonaceous material to binder material is in the range of 8 to 16.

[0069] According to one embodiment herein, the binder comprises carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR).

[0070] According to an embodiment herein, the solvent comprises deionization (DI) water, the current collector comprises etched aluminium foil and the co-solvent comprises n- octanol. Furthermore, the ratio of active materials to conductive carbon to binder includes 87:8:5. Besides, the ratio of active materials include 75:25 and the ratio of conductive carbon includes 50:50.

[0071] According to one embodiment herein, a process for preparation of coating slurry for fabricating high density carbon electrodes in an ultracapacitor is provided. The process comprises dissolving carboxymethyl cellulose binder in a solvent at 70°C under continuous stirring for one hour. Then, separately dry mixing conductive agent and active materials, in the planetary mixer at 600 RPM for 30 minutes. The process further comprises adding active materials to the carboxymethyl cellulose binder solution and mixing at 200 RPM for 10 minutes and followed by 600 RPM for 30 minutes. Furthermore, the process includes adding active materials batch 1 and batch 2 separately and mixing it at 600 RPM for 30 minutes. Furthermore, the process includes adding of active materials batch 3 and mixing it at 600 RPM for 10 minutes. The process further includes adding a co-solvent and mixing it at 1000 RPM for 30 minutes. Finally, adding styrene -butadiene rubber (SBR) binder and mixing it at 400 RPM for 15 minutes, and performing de-gassing at 400 RPM for 15 minutes.

[0072] According to one embodiment herein, the solvent comprises deionization (DI) water, the conductive agent comprises low-surface area conductive carbon and graphene nanoplatelets. Furthermore, the active materials comprises low-density activated carbon and high-density activated carbon. The co-solvent comprises n-octanol. The active materials and conductive agent together form a quaternary system of carbon or carbonaceous material and the quaternary system of carbon or carbonaceous material is combined to achieve high power density and high volumetric capacitance, and substantially reduce the ESR (Equivalent Series Resistance) values of the ultracapacitor. Besides, ratio of active materials to conductive carbon to binder includes 87:8:5. The ratio of active materials include 75:25 and the ratio of conductive carbon includes 50:50.

[0073] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating the preferred embodiments and numerous specific details thereof, are given by way of an illustration and not of a limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The other objects, features, and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:

[0075] FIG. 1 illustrates a flowchart of a process for preparation of coating slurry for fabricating high density carbon electrodes in an ultracapacitor, according to an embodiment herein.

[0076] FIG.2 illustrates a Scanning Electron Microscope (SEM) image of the low- density activated carbon, according to an embodiment herein.

[0077] FIG. 3 illustrates a Scanning Electron Microscope (SEM) image of high-density activated carbon, according to an embodiment herein.

[0078] FIG. 4 illustrates a a Scanning Electron Microscope (SEM) images of graphene nanoplatelets, according to an embodiment herein.

[0079] FIG. 5 illustrates a Scanning Electron Microscope (SEM) image of the low- surface area conductive carbon, according to an embodiment herein.

[0080] Although the specific features of the embodiments herein are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all the other features in accordance with the embodiments herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS HEREIN

[0081] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.

[0082] The various embodiments herein provide, a coating slurry composition to fabricate high density carbon electrodes for ultracapacitor. High density carbon electrodes enhance the power density and the volumetric capacitance of the ultracapacitors and substantially reduce the ESR value. Thus, achieving high density in electrodes is highly desirable for EDLC (Electric Double Layer Capacitor) type of ultracapacitors. Here, high density in carbon electrodes is achieved by using quaternary system of carbon or carbonaceous materials.

[0083] According to one embodiment herein, a process for preparation of coating slurry for fabricating high density carbon electrodes in an ultracapacitor is provided. The process comprises dissolving carboxymethyl cellulose binder in a solvent at 70°C under continuous stirring for one hour to obtain a binder solution. Then, separately dry mixing conductive carbon agents (CA) and active materials (AM), in a planetary mixer at 600 RPM for 30 minutes. The conductive carbon agents comprise graphene nanoplatelets and low- surface area conductive carbon. The active materials comprise low-density activated carbon and high-density activated carbon. The conductive carbon agents and active materials together constitute quaternary system of carbon or carbonaceous materials. The process further comprises adding dry mixed conductive carbon agents (CA) to the obtained binder solution and mixing at 200 RPM for 10 minutes and followed by 600 RPM for 30 minutes to obtain a CA-binder solution. Furthermore, the process includes adding active materials batch 1 to the obtained CA-binder solution and mixing at 600 RPM for 30 minutes. Further adding active materials batch 2 to the obtained solution and mixing it at 600 RPM for 30 minutes. Furthermore, the process includes adding active materials batch 3 to the obtained solution and mixing it at 600 RPM for 10 minutes to obtain an AM-CA binder solution. The process further includes adding a co-solvent to the obtained AM-CA binder solution and mixing it at 1000 RPM for 30 minutes. Finally, adding styrene-butadiene rubber (SBR) binder to the obtained solution and mixing it at 400 RPM for 15 minutes, and performing de-gassing at 400 RPM for 15 minutes to obtain the high-density carbon electrodes for ultracapacitor.

[0084] According to an example embodiment herein, a coating slurry composition for fabricating high density carbon electrodes in an ultracapacitor is provided. The coating slurry composition comprises a quaternary system of carbon or carbonaceous material, a binder, a solvent, a current collector, and a co-solvent. The quaternary system of carbon or carbonaceous material comprises a low-density activated carbon, a high-density activated carbon, a graphene nanoplatelets and a low-surface area conductive carbon. The low-density activated carbon and the high-density activated carbon constitute active materials, and the graphene nanoplatelets and the low-surface area conductive carbon constitute conductive agents. Thus, the quaternary system of carbon or carbonaceous materials are combined to achieve high power density and high volumetric capacitance, and substantially low ESR (Equivalent Series Resistance) values.

[0085] According to one embodiment herein, the low-density activated carbon is a low-dense, highly porous carbon with large number of micropores and mesopores. The large number of micropores ensures high gravimetric capacitance and high mesopores helps in maintaining capacitive behavior even at higher currents, especially during charging cycles. Furthermore, a plurality of mesopore channels function as an electrolyte reservoir from where the ions migrate to access the micropores in the low-density carbon and return during a discharging cycle. [0086] According to one embodiment herein, wherein the low-density activated carbon comprises high density of oxygen functional groups, which causes detrimental effect on a life cycle of the ultracapacitors. Hence, it is important to pretreat the low-density activated carbon to bring down the density of the oxygen functional groups by pre-treatment process. The pretreatment process involves subjecting the low-density activated carbon to an elevated temperature or expose it to microwaves in an inert or a reducing atmosphere.

[0087] According to an example embodiment herein, the high-density activated carbon is high in density and less porous, having high microporosity, and low meso-porosity. The low meso-porosity in the high-density activated carbon imparts less liquid to solid ratio (1/s ratio) of the coating slurry, for a specific viscosity, thereby allowing higher mass loading of the active material at lower coating thicknesses and higher mass loading per unit area of the current collector, also the intrinsic resistance of the high-density activated carbon is low, which helps in establishing a good conductive network across the carbon electrodes thereby improving the ESR value and power density of the ultracapacitor. Furthermore, the high micro porosity provides large specific surface area, large ultra-micropore volume (Vp < 10) and good compatibility.

[0088] According to one embodiment herein, the graphene nanoplatelets provide high density, and comprises individual graphite layers, which slide over one another and impart high compressibility to the high-density carbon electrodes. The individual graphite layers further allows the high-density carbon electrodes to withstand large compressive forces at high compaction during the calendaring process, without the formation of any stress cracks at the interface of the current collector and the high-density carbon electrodes. Furthermore, the graphene nanoplatelets possess high conductivity, which further reduces the charge transfer resistance of the high-density electrodes and the amount of conductive carbon required to form a conductive network. In addition, the graphene nanoplatelets helps to increase the loading of active materials in the high-density carbon electrodes.

[0089] According to one embodiment herein, the low-surface area conductive carbon helps to achieve desired ESR (Equivalent Series Resistance) values, and also helps to decrease the solvent amount in the coating slurry, thereby improving density of the high-density carbon electrodes.

[0090] According to one embodiment herein, the low-density activated carbon has a specific density in the range of 0. 10 g/cm³ to 0.30 g/cm³ and surface area in the range of 2000 to 2500 m²/g. Furthermore, the microporous volume of the low-density activated carbon is in the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume in the range of 0.4 cm³/g to 0.9 cm³/g.

[0091] According to one embodiment herein, the high-density activated carbon has a specific density in the range of 0.50 g/cm³ to 0.90 g/cm³ and surface area in the range of 1300 to 1800 m²/g. Moreover, the high-density activated carbon has a high microporous and low mesoporous volume and the ratio of mesa to micro porous volume ranges between 0. 1 to 0.3. The microporous volume of the high-density activated carbon is the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume is in the range of 0. 1 cm³/g to 0.3 cm³/g.

[0092] According to one embodiment herein, the particle size of the low-density activated carbon ranges from 3 to 8 micron, and the particle size of the high-density activated carbon is in the range of 5 to 10 micron. The particle size of high-density activated carbon is always higher than the particle size of low-density activated carbon. Furthermore, the density of functional groups of both low-density and high-density activated carbons is less than 10 meq/g.

[0093] According to one embodiment herein, the graphene nanoplatelets are added to the high-density carbon electrodes to improve the packing density, decreasing the ESR, and enhancing the volumetric capacitance of the EDLC ultracapacitor. The number of atomic layers of the graphene nanoplatelets is in the range of 5 to 15 and the average size of each of the layer is in the range of 0.3 pm to 1 pm. Furthermore, the graphene nanoplatelets have high purity with atomic carbon percentage of more than 99% and a surface area of 50 m²/g to 300 m²/g. The particle density of the graphene nanoplatelets is 1.8 g/cm³. Moreover, the graphene nanoplatelets also decreases the amount of the solvent required to achieve desired viscosity of the coating slurry.

[0094] According to one embodiment herein, the surface area of the low-surface area conductive carbon is in the range of 30 to 100 m²/g and the particle size of the low surface area conductive carbon is in the range of 5 nm to 80 nm. The particle density of the low-surface area conductive carbon is 1.6 g/cm³ and the conductivity is 25 S/m. Furthermore, the ratio of the high-density to low density activated carbon in the electrodes is in the range of 0. 1 to 9 and the ratio of graphene nanoplatelets to low surface area conductive carbon in the electrodes is in the range of 0.5 and 5. In addition, the ratio of the activated carbon to additive loadings in the electrodes is in the range of 7: 1 to 10: 1, additive loadings is the ratio of additives to the active material in the slurry. Furthermore, the ratio of the quaternary carbonaceous material to binder material is in the range of 8 to 16.

[0095] According to one embodiment herein, the binder comprises carboxymethyl cellulose (CMC) and styrene -butadiene rubber (SBR). The solvent comprises deionization (DI) water, the current collector comprises etched aluminium foil and the co-solvent comprises n-octanol. Furthermore, the ratio of active materials to conductive carbon to binder includes 87:8:5. Besides, the ratio of active materials i.e., ratio of high conductive carbon to the low conductive carbon is 75:25. The ratio of conductive carbon to the graphene nanoplatelets is

50:50. [0096] According to one embodiment herein, a process for preparation of coating slurry for fabricating high density carbon electrodes in an ultracapacitor is provided. The process comprises dissolving carboxymethyl cellulose binder in a solvent at 70°C under continuous stirring for one hour. Then, separately dry mixing conductive agent and active materials, in the planetary mixer at 600 RPM for 30 minutes. The process further comprises adding active materials to the carboxymethyl cellulose binder solution and mixing at 200 RPM for 10 minutes and followed by 600 RPM for 30 minutes. Furthermore, the process includes adding active materials batch 1 and batch 2 separately and mixing it at 600 RPM for 30 minutes. Furthermore, the process includes adding of active materials batch 3 and mixing it at 600 RPM for 10 minutes. The process further includes adding a co-solvent and mixing it at 1000 RPM for 30 minutes. Finally, adding styrene -butadiene rubber (SBR) binder and mixing it at 400 RPM for 15 minutes, and performing de-gassing at 400 RPM for 15 minutes.

[0097] According to one embodiment herein, the solvent comprises deionization (DI) water, the conductive agent comprises low-surface area conductive carbon and graphene nanoplatelets. Furthermore, the active materials comprises low-density activated carbon and high-density activated carbon. The co-solvent comprises n-octanol. The active materials and conductive agent together form a quaternary system of carbon or carbonaceous material and the quaternary system of carbon or carbonaceous material is combined to achieve high power density and high volumetric capacitance, and substantially reduce the ESR (Equivalent Series Resistance) values of the ultracapacitor. Besides, ratio of active materials to conductive carbon to binder includes 87:8:5. The ratio of active materials include 75:25 and the ratio of conductive carbon includes 50:50.

[0098] FIG. 1 illustrates a flowchart of a process for preparation of coating slurry for fabricating high density carbon electrodes in an ultracapacitor. The process 100 comprises dissolving carboxymethyl cellulose binder in a solvent at 70°C under continuous stirring for one hour at step 102. Then, separately dry mixing conductive agent and active materials, in the planetary mixer at 600 RPM for 30 minutes at step 104. The process 100 further comprises adding active materials to the carboxymethyl cellulose binder solution and mixing at 200 RPM for 10 minutes and followed by 600 RPM for 30 minutes at 106. Furthermore, the process 100 includes adding active materials batch 1 and batch 2 separately and mixing it at 600 RPM for 30 minutes at step 108. Furthermore, the process 100 includes adding of active materials batch 3 and mixing it at 600 RPM for 10 minutes at step 110. The process 100 further includes adding a co-solvent and mixing it at 1000 RPM for 30 minutes at step 112. Finally, adding styrenebutadiene rubber (SBR) binder and mixing it at 400 RPM for 15 minutes, and performing degassing at 400 RPM for 15 minutes at step 114.

[0099] FIG. 2 illustrates a Scanning Electron Microscope (SEM) image of the low- density activated carbon. The low-density activated carbon as illustrated in FIG. 2 is a low- dense, highly porous carbon with large number of micropores and mesopores. The large number of micropores ensures high gravimetric capacitance and high mesopores helps in maintaining capacitive behavior even at higher currents, especially during charging cycles. Furthermore, the mesopore channels function as electrolyte reservoir from where, the ions can migrate to access the micropores in the low-density carbon and return during the discharging cycle. Moreover, the low-density activated carbon has a specific density in the range of 0.10 g/cm³ to 0.30 g/cm³ and surface area in the range of 2000 to 2500 m²/g. Furthermore, the microporous volume of the low-density activated carbon is in the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume in the range of 0.4 cm³/g to 0.9 cm³/g.

[0100] FIG. 3 illustrates a Scanning Electron Microscope (SEM) image of high-density activated carbon. The high-density activated carbon as illustrated in FIG.3, is a high-dense and less porous, having high microporosity and low meso-porosity. The low meso-porosity in the high-density activated carbon imparts less liquid to solid ratio (1/s ratio) of the coating slurry, for a specific viscosity, thereby allowing higher mass loading of active material at lower coating thicknesses and higher mass loading per unit area of the current collector, also the intrinsic resistance of the high-density activated carbon is low, which helps in establishing a good conductive network across the carbon electrodes thereby improving the ESR value and power density of the system. Furthermore, the high-density activated carbon has a specific density in the range of 0.50 g/cm³ to 0.90 g/cm³ and surface area in the range of 1300 to 1800 m²/g. Correspondingly, the high-density activated carbon has a high microporous and low mesoporous volume and the ratio of miso to micro porous volume ranges between O. lto 0.3. Besides, the microporous volume of the high-density activated carbon is the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume is in the range of 0.1 cm³/g to 0.3 cm³/g.

[0101] FIG. 4 illustrates a Scanning Electron Microscope (SEM) image of graphene nanoplatelets. The graphene nanoplatelets as illustrated in FIG. 4, provide high density. The graphene nanoplatelets comprises individual graphite layers about 5 to 15 layers, which slide over one another and impart high compressibility to the high-density carbon electrodes. Furthermore, the individual graphite layers further allows the high-density carbon electrodes to withstand large compressive forces at high compaction during calendaring process without the formation of any stress cracks at the interface of the current collector and the high-density carbon electrodes. Besides, the graphene nanoplatelets possess high conductivity, to further reduce the charge transfer resistance of the high-density electrodes and reduces the amount of conductive carbon required to form a conductive network. The graphene nanoplatelets further helps to increase the loading of active materials in the high-density carbon electrodes. Subsequently, the graphene nanoplatelets are added to the high-density carbon electrodes to improve the packing density, decreasing the ESR, and enhancing the volumetric capacitance of the EDLC ultracapacitor. The number of atomic layers of the graphene nanoplatelets is in the range of 5 to 15 and the average size is in the range of 0.3 pm to 1 pm. In addition, the graphene nanoplatelets have high purity with atomic carbon percentage of more than 99% and a surface area of 50 m²/g to 300 m²/g. The graphene nanoplatelets also decreases the amount of the solvent required to achieve desired viscosity of the coating slurry.

[0102] FIG. 5 illustrates a Scanning Electron Microscope (SEM) image of the low- surface area conductive carbon. The low-surface area conductive carbon as illustrated in FIG. 5, helps to achieve desired ESR (Equivalent Series Resistance) values. The low-surface area conductive carbon further helps to decrease the solvent amount in the coating slurry and thereby improving density of the high-density carbon electrodes. Furthermore, surface area of the low-surface area conductive carbon is in the range of 30 to 100 m²/g and the particle size of the low surface area conductive carbon is in the range of 5 nm to 80 nm.

[0103] Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications.

[0104] The advantages of the embodiments herein, is to provide a coating slurry composition comprising quaternary system of carbon or carbonaceous material to obtain high- density carbon electrodes for EDLC application. The high-density carbon electrodes thus obtained, provides low ESR values, high volumetric capacitance, and high-power density. Similarly, the high-density carbon electrodes allows loading of more active material inside the device and helps improving the form -factor of the same. The primary advantage of the embodiments herein is to provide carbon electrodes with high power density for Electric Double Layer Capacitors (EDLCs). Also, yet another advantage of the embodiment herein is to fabricate the high-density carbon electrodes from a quaternary system of carbon/carbonaceous material such that the carbonaceous materials comprises a low-density activated carbon, a high-density activated carbon, a conductive carbon agent and graphene nanoplatelets. The quaternary carbon/carbonaceous material used for fabricating the carbon electrodes, the particle size of the high-density active material is higher than that of low-density activated carbon. Moreover, the low density activated carbon provides maximum surface area and High density activated carbon helps in compaction and improves conductivity.

[0105] Moreover, the graphene nanoplatelets added to the activated carbon, helps to enhance the packing density of the carbon electrodes. The graphene nanoplatelets are also highly conductive in nature and helps to decrease the ESR values of the high-density carbon electrodes. Therefore, the high-density carbon electrodes of the embodiments herein have higher energy density, longer life compared to existing conventional carbon electrodes. For instance, the energy density of the embodiments herein is in the range of 5 to 6 Wh/kg, compared to 4 to 5 Wh/kg energy density in conventional carbon electrodes for ultracapacitors. Furthermore, the embodiment herein also possess atleast 5% greater life than the existing ones.

[0106] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such as specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.

[0107] It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications. However, all such modifications are deemed to be within the scope of the claims.

Claims

CLAIMS What is claimed is:

1. A coating slurry composition for fabricating high density carbon electrodes in an ultracapacitor comprising: a quaternary system of carbon or carbonaceous material, a binder, a solvent, a current collector and a co-solvent, wherein the quaternary system of carbon or carbonaceous material comprises a low-density activated carbon, a high-density activated carbon, graphene nanoplatelets and a low-surface area conductive carbon, and wherein the low-density activated carbon and the high-density activated carbon constitute active materials, and wherein the graphene nanoplatelets and the low- surface area conductive carbon constitute conductive agents, and wherein the ratio of graphene nanoplatelets and the low-surface area conductive carbon is 50:50.

2. The composition according to Claim 1, wherein the low-density activated carbon is a low-dense, highly porous carbon with a large number of micropores and mesopores.

3. The composition according to Claim 1, wherein the low-density activated carbon comprises high density of oxygen functional groups.

4. The composition according to Claim 1, wherein the high-density activated carbon is high-dense and less porous, having high microporosity and low meso-porosity.

5. The composition according to Claim 1, wherein the graphene nanoplatelets provide high density, and wherein the graphene nanoplatelets comprises a plurality of graphite layers, that slide over one another to impart high compressibility to the high-density carbon electrodes; and wherein the individual graphite layers further allows the high- density carbon electrodes to withstand large compressive forces at high compaction during calendaring process without the formation of any stress cracks at the interface of the current collector and the high-density carbon electrodes.

28 The composition according to Claim 1, wherein the graphene nanoplatelets possess high conductivity, to further reduce the charge transfer resistance of the high-density electrodes, and to reduce the amount of conductive carbon required to form a conductive network, and wherein the graphene nanoplatelets further helps to increase the loading of active materials in the high-density carbon electrodes. The composition according to Claim 1, wherein the ultracapacitor comprises EDLC (Electric Double Layer Capacitor). The composition according to Claim 1, wherein the low-density activated carbon has a specific density in the range of 0.10 g/cm³ to 0.30 g/cm³ and surface area in the range of 2000 to 2500 m²/g; and wherein the microporous volume of the low-density activated carbon is in the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume in the range of 0.4 cm³/g to 0.9 cm³/g; and wherein the micro to meso-porous volume of the low- density activated carbon is in the range of 0.7 to 1. The composition according to Claim 1, wherein the high-density activated carbon has a specific density in the range of 0.50 g/cm³ to 0.90 g/cm³ and surface area in the range of 1300 to 1800 m²/g; and wherein the high-density activated carbon has a high microporous and low mesoporous volume and the ratio of meso to micro porous volume ranges between O.lto 0.3; and wherein the microporous volume of the high-density activated carbon is the range of 0.4 cm³/g to 0.9 cm³/g and mesoporous volume is in the range of 0.1 cm³/g to 0.3 cm³/g. The composition according to Claim 1, wherein the particle size of the low -density activated carbon ranges from 3 to 8 micron, and wherein the particle size of the high- density activated carbon is in the range of 5 to 10 microns, and wherein the particle size of high-density activated carbon is always higher than the particle size of low-density activated carbon. The composition according to Claim 1, wherein the density of functional groups of both low-density and high-density activated carbons is less than 10 meq/g. The composition according to Claim 1, wherein the graphene nanoplatelets are added to the high-density carbon electrodes to improve the packing density, decreasing the ESR, and enhancing the volumetric capacitance of the EDLC ultracapacitor; and wherein the number of atomic layers of the graphene nanoplatelets is in the range of 5 to 15 and the average size is in the range of 0.3 pm to 1 pm; and wherein the graphene nanoplatelets have high purity with atomic carbon percentage of more than 99% and a surface area of 50 m²/g to 300 m²/g; and wherein the particle density of the graphene nanoplatelets is 1.8 g/cm³; and wherein the graphene nanoplatelets decreases the amount of the solvent required to achieve desired viscosity of the coating slurry. The composition according to Claim 1 , wherein the surface area of the low-surface area conductive carbon is in the range of 30 to 100 m²/g and the particle size of the low surface area conductive carbon is in the range of 5 nm to 80 nm; and wherein the particle density of the low surface area conductive carbon is 1.6 g/cm³; and wherein the conductivity of the low-surface area conductive carbon is 25 S/m. The composition according to Claim 1, wherein the ratio of the high-density to low density activated carbon in the electrodes is in the range of 0. 1 to 9, and wherein the ratio of graphene nanoplatelets to low surface area conductive carbon in the electrodes is in the range of 0.5 and 5, and wherein the ratio of the activated carbon to additive loadings in the electrodes is in the range of 7: 1 to 10: 1, and wherein the ratio of the quaternary carbonaceous material to binder material is in the range of 8 to 16. The composition according to Claim 1, wherein the binder comprises carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR); and wherein the solvent comprises deionization (DI) water; and wherein the current collector comprises etched aluminium foil; and wherein the co-solvent comprises n-octanol. The composition according to Claim 1, wherein the ratio of active materials to conductive carbon to binder includes 87:8:5, and wherein the ratio of active materials include 75:25. A process (500) for preparation of coating slurry for fabricating high density carbon electrodes in an ultracapacitor comprising the steps of: a. dissolving carboxymethyl cellulose binder in a solvent at 70°C under continuous stirring for one hour (502); b. dry mixing of conductive agent in a planetary mixer at 600 RPM for 30 minutes (504); c. dry mixing of active materials in the planetary mixer at 600 RPM for 30 minutes (504); d. adding active materials to the carboxymethyl cellulose binder solution and mixing at 200 RPM for 10 minutes and 600 RPM for 30 minutes (506); e. adding active materials batch 1 and mixing at 600 RPM for 30 minutes (508); f. adding active materials batch 2 and mixing at 600 RPM for 30 minutes (508); g. adding active materials batch 3 and mixing at 600 RPM for 10 minutes (510); h. adding a co-solvent and mixing at 1000 RPM for 30 minutes (512); i. adding styrene-butadiene rubber (SBR) binder and mixing at 400 RPM for 15 minutes and performing de-gassing at 400 RPM for 15 minutes (514); wherein the active materials and conductive agent together form a quaternary system of carbon or carbonaceous material, and wherein the quaternary system of carbon or carbonaceous material is combined to achieve high power density and high volumetric capacitance, and substantially reduce the ESR (Equivalent Series Resistance) values of the ultracapacitor, wherein the ultracapacitor comprises Electric Double Layer Capacitor (EDLC). The process (500) according to Claim 17, wherein the solvent comprises deionization (DI) water, and wherein the conductive agent comprises low-surface area conductive carbon and graphene nanoplatelets, and wherein the active materials comprises low- density activated carbon and high-density activated carbon, and wherein the co-solvent comprises n-octanol. The process (500) according to Claim 17, wherein the ratio of active materials to conductive carbon to binder includes 87:8:5; and wherein the ratio of active materials include 75:25; and wherein the ratio of conductive carbon includes 50:50. The process (500) according to Claim 17, wherein the particle size of the low-density activated carbon ranges from 3 to 8 micron; and wherein the particle size of the high- density activated carbon is in the range of 5 to 10 micron; and wherein the particle size of high-density activated carbon is always higher than the particle size of low-density activated carbon.

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