ALKALI METAL VANADATE ELECTRODE MATERIALS FOR ELECTROCHEMICAL SUPERCAPACITOR DEVICES AND ITS PREPARATION THEREOF

Abstract

ABSTRACT ALKALI METAL VANADATE ELECTRODE MATERIALS FOR ELECTROCHEMICAL SUPERCAPACITOR DEVICES AND ITS PREPARATION THEREOF This invention presents alkali metal vanadates as electrode materials for supercapacitors, specifically in asymmetric supercapacitor coin cell devices to enhance electrochemical performance. A synthesis method is provided for creating one-dimensional and layered lithium and potassium vanadate nanostructures through a process of heating, stirring, centrifugation, and washing. XRD and FESEM analyses confirm the successful formation of these structures. The asymmetric supercapacitor device features potassium vanadate cathodes, paired with an asymmetric carbon anode. This potassium vanadate based supercapacitor device demonstrates improved electrochemical properties, delivering an energy density of 51 Wh/kg, a power density of 4127 W/kg, and a specific capacitance of 145 F/g, while achieving around 80% cyclic stability after 5000 cycles within a 1.8 V operating window. [To be published with fig.1]

Specification

Description:CROSS-REFERENCE TO RELATED APPLICATION AND PRIORITY
The present application claims no priority from any of the patent application(s).

FIELD OF THE INVENTION:
[0001] The present invention relates to the application of alkali metal vanadates as electrode material in supercapacitors (SCs), particularly asymmetric supercapacitor coin cell devices for enhancing electrochemical performance. The present work also encompasses the method of fabrication of alkali metal vanadates such as lithium vanadate and potassium vanadate.

BACKGROUND OF INVENTION
[0002] Rechargeable electrochemical energy storage devices, such as electrochemical supercapacitors and metal-ion batteries, are essential for large-scale energy storage and portable electronic applications due to their high applicability, material abundance, long life cycle, favorable energy and power density, and environmental friendliness. Recent technological advancements in this field have primarily focused on enhancing the energy storage capacity of electrode materials. The electrode material is a key component that determines the performance of these devices in practical applications. As a result, the design, development, and optimization of electrode materials for energy storage applications continue to be a major area of focus.
[0003] Transition metal oxide materials are the well-known class of electrode materials because of their low cost, high charge storage capacity, simple charge storage mechanism, multifarious oxidation states, and variety of nanostructured morphologies. Among various transition metal oxides, vanadium pentoxide (V2O5) stands out as a prominent cathode material for supercapacitors and metal-ion battery applications. This is attributed to its low cost, high theoretical specific capacitance (2000 F g−1), multiple oxidation states (V2+, V3+, V4+, and V5+) and layered crystal structure. [P. Hu, et al., Vanadium oxide: phase diagrams, structures, synthesis, and applications, Chem. Rev. 123 (2023) 4353-4415].
[0004] However, in practical application, vanadium oxide electrode material displays several limitations in terms of poor electrochemical and structural stability, low charge-discharge capacity, and poor lifespan performance while employed in energy storage applications. This eliminates these shortcomings, inserting the metal cations in between the interlayers of the vanadium oxide is the best strategy. This strategy improves the mechanical, chemical and electrochemical properties of the resultant vanadium-incorporated metal oxide or metal vanadate nanostructure.
[0005] The metal vanadate compounds are generally found in the format of MxVyOz, in which M represents metal cation for example Li, Bi, Ni, Co, Cu, Na, K, etc. Metal vanadate materials possess considerable potential for energy storage applications because they are electrochemically stable with efficient redox activity and layered crystal structures having large d-spacings [D. Xia et al., Transition metal vanadates electrodes in lithium-ion batteries: a holistic review, Energy Storage Mater. 35 (2021) 169-191; G. Yao et al., Nanostructured transition metal vanadates as electrodes for pseudo-supercapacitors: a review, J. Nanoparticle Res. 23 (2021)]. The multiple oxidation states of individual metal and vanadium components from metal vanadate materials allow multi-electron redox reactions during electrolyte ion intercalation/ deintercalation.
[0006] In metal vanadates, alkali metals like highly effective lithium and earth-abundant potassium are promising candidates for the preparation of alkali metal vanadates due to their favourable ionic properties. Potassium, with its smaller hydrated ionic radius and low desolvation energy, can serve as a precharge carrier and improve ion diffusion length during electrochemical processes. Meanwhile, lithium's small ionic radius and high electrochemical potential make it an excellent choice for enhancing the charge storage and diffusion capabilities of metal vanadates in energy storage applications. [Vedpathak, Amol, et al. "Facile synthesis of KV3O8 nanobelts for solid-state supercapacitors." Journal of Power Sources 621 (2024): 235315; Shinde, Tanuja, et al. "1D Layered LiVO3 Nanorods Synthesized by Ultrasonic‐Assisted Chemical Route for Supercapacitor Applications." Energy Technology 12.3 (2024): 2301056]
[0007] IN208960 (1659/CAL/1998) discloses a process of preparation of nanosized metal vanadate particles. The process involves the mixing of vanadyl formate with metal nitrate salt, fuel and polyvinyl alcohol to prepare a homogeneous mixture. This mixture was further subjected to evaporation and calcination processes to obtain the final nanosized metal vanadate product.
[0008] IN437948 (201811022066) belongs to the method of synthesis of lithium vanadate of graphene oxide (Li3VO4-GO) anode material for lithium-ion batteries. The invention presented involves mixing V2O5, GO and LiOH powders separately with ethylene glycol: water solvent and performing hydrothermal treatment at 140 - 170oC for 3 - 5 h to obtain the mesoporous Li3VO4-GO material.
[0009] IN231662 (524/DEL/2001) invention discloses a novel process for the preparation of lithium cobalt vanadate (LiCoVO4) material for secondary lithium-ion cells. This compound is synthesized by mixing oxides of cobalt (Co3O4) and vanadium (V2O5) with lithium hydroxide (LiOH) by solid-state reaction. The process involves heating (200 - 800oC) processes for removing glycerol binder and calcination of the final product.
[0010] IN243456 (964/DEL/2002) invention discloses a process for the synthesis of lithium nickel magnesium vanadate (LiNi0.5Mg0.5VO4) material for secondary lithium-ion cells. The LiNi0.5Mg0.5VO4 product was developed by solid-state reaction using uniform mixing of oxides of nickel, magnesium and vanadium with lithium carbonate or lithium hydroxide or lithium oxide or lithium nitrate in glycerol and heated in between 500 - 800oC.
[0011] CN102320658A invention describes a method for synthesizing alkaline earth metal vanadate micro/nanomaterials by adopting a hydrothermal/solvothermal method. The method is characterized by taking ammonium metavanadate and alkaline earth metal salt as raw materials, one or more of sodium hydroxide, potassium hydroxide, hydrochloric acid and nitric acid as a system pH value regulator and one or arbitrary combination of two or more of distilled water, methanol, ethanol and acetone as a solvent, and applying a one-step hydrothermal/solvothermal synthesis method to controllably prepare the alkaline earth metal vanadate micro/nanomaterials.
[0012] CN107482169A invention relates to the preparation method for lithium cobalt vanadate (LiCoVO4) and its lithium-ion battery application. The preparation method of the LiCoVO4 comprises the uniform mixing of LiOH, Co(CH3CO2)2·4H2O and NH4VO3. After homogenous mixing the resultant suspension was subjected to hydrothermal reaction at 160-220 ℃ for 18-24 h to obtain the LiCoVO4. The preparation method can control the morphology of LiCoVO4 with smaller and uniform particle sizes and is beneficial to the diffusion of lithium ions.
[0013] Vedpathak, Amol, et al. have disclosed an ultrasonic-assisted chemical route to prepare Na2V6O16 nanobelts in an article titled "One-dimensional layered sodium vanadate nanobelts: a potential aspirant for high-performance supercapacitor applications" in ACS Applied Energy Materials (2023): 4693-4703. These Na2V6O16 nanobelts are used as an electrode material for supercapacitor applications, which exhibit a specific capacitance of 455 F g-1 at 0.5 A g-1. An asymmetric coin cell supercapacitor device of activated carbon // Na2V6O16 nanobelts is also fabricated. This fabricated device delivers a high energy density of 42.4 W h kg-1 and a high power density of 4.3 kW h kg-1, along with 80% capacity retention after 5000 cycles.

[0014] Shinde, Tanuja et al. have disclosed an ultrasonic-assisted chemical route using V2O5 as the starting material to prepare LiVO3 nanorods in an article in the journal Energy Technol. 2024, 12, 2301056. Also disclosed is the LiVO3 // AC asymmetric coin cell supercapacitor device fabricated with LiVO3 as the cathode shows an excellent energy density of 25.4 Wh kg-1 at a power density of 228.5 W kg-1 along with superior cyclic stability of ~80% after 5000 cycles and wide operating voltage window of 1.6 V.

[0015] Vedpathak, Amol, et al. have disclosed the synthesis of KV3O8 nanobelts for solid-state supercapacitors in an article in the journal Journal of Power Sources 621 (2024) 235315. Described herein is an ultrasonic-assisted chemical method for synthesizing potassium vanadate (KV3O8) nanobelt as cathode material for asymmetric supercapacitor application. Also disclosed is the AC//KV3O8 solid-state asymmetric supercapacitor device, which demonstrates excellent electrochemical performance in terms of high-rate capability, specific capacitance, operating voltage (1.8 V), and energy density (51 Wh kg− 1).
[0016] To address the limitations and shortcomings of vanadium oxide in practical application, we have successfully developed lithium and potassium vanadate materials by converting bulk vanadium pentoxide (V2O5) into the MxVyOz phase through a combination of ultrasonication, heating, and stirring processes. This synthesis approach effectively facilitates the incorporation of lithium and potassium into the vanadate structure, enabling the formation of new materials with enhanced electrochemical properties. Along with this, we have successfully developed their asymmetric supercapacitor coin cell devices by employing developed LiVO3 nanorods and KV3O8 nanobelts as cathodes and activated carbon as anode.
OBJECTIVES OF THE INVENTION
[0013] A primary objective of the present invention is to develop a supercapacitor device having enhanced electrochemical performance
[0014] Another objective of the invention is to develop an asymmetric supercapacitor coin cell device having alkali metal vanadate as a cathode to provide better energy density, power density and cyclic stability/long life cycle.
[0017] Yet another object of the present invention is to provide an environmentally friendly, scalable, and cost-effective method for the preparation of one-dimensional alkali metal vanadate nanomaterials.
SUMMARY OF THE INVENTION:
[0018] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the "Detailed description section". This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0019] The invention also includes the development of asymmetric supercapacitor devices using the synthesized LiVO3 nanorods and KV3O8 nanobelts materials as cathodes (101), paired with commercial activated carbon as the anode. These devices (100) were assembled in coin cell configurations (CR2032), where the electrodes were prepared by coating the active materials on carbon paper or stainless steel foil. The electrodes were combined with 1 M Li2SO4 or 0.5 M K2SO4 aqueous electrolyte solutions for the lithium and potassium vanadate-based devices, respectively. The device structure allows efficient charge storage through electrostatic adsorption and desorption, as confirmed by cyclic voltammetry and galvanostatic charge-discharge tests.
[0020] The LiVO3 // AC and KV3O8 // AC devices (100) exhibit impressive electrochemical performance. The lithium-based device delivers a maximum energy density of 25.4 Wh kg−1 and a power density of 3657 W kg−1, while the potassium-based device achieves a higher energy density of 51 Wh kg−1 and a power density of 4127 W kg−1. Both devices show excellent cyclic stability, with capacity retention of 79% and 89% after 5000 cycles, respectively. These characteristics highlight the potential of the synthesized materials for practical supercapacitor applications.
DESCRIPTION OF THE DRAWINGS:
The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments provided in the disclosure and, together with the description, serve to explain the inventive principles.
Figure 1 illustrates the field emission scanning electron microscopic (FESEM) images of (a) LiVO3 nanorods and (b) KV3O8 nanobelts.
Figure 2 illustrates the XRD patterns of commercial vanadium precursor, LiVO3 nanorods and KV3O8 nanobelts.
Figure 3 illustrates the schematic for the order of materials for the fabrication of supercapacitor device
Figure 4 illustrates the cyclic voltammetry graphs of (a) LiVO3 // AC and (b) KV3O8 // AC coin cell supercapacitor devices
Figure 5 illustrates the galvanostatic charging-discharging graphs of (a) LiVO3 // AC and (b) KV3O8 // AC coin cell supercapacitor devices
Figure 6 illustrates the cyclic stability graphs of (a) LiVO3 vanadate // AC and (b) KV3O8 // AC coin cell supercapacitor devices.
DETAILED DESCRIPTION OF THE INVENTION:
[0021] Some embodiments of the present invention, illustrating all its features, may now be discussed in detail. The words "comprising "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open-ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items or meant to be limited to only the listed item or items. It must also be noted that the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise, although any methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, wherein the exemplary methods are described. The disclosed embodiments are merely exemplary of the disclosure of the present invention, which may be embodied in various forms.
[0022] It may be understood by all readers of this written description that the example embodiments described herein and claimed hereafter may be suitably practised in the absence of any recited feature, element, or step that is or is not, specifically disclosed herein. For instance, references in this written description to "one embodiment," "an embodiment," "an exemplary embodiment," and the like, indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. The disclosed embodiments are merely exemplary of various forms or combinations.
[0023] The present work was undertaken with a view to meet the intermittent upcoming demands for advanced portable electronics and electric vehicles. Supercapacitors are a progressively promising class of energy storage devices in terms of safety, low-cost and scalable fabrication, compact designs, ease of handling, lightweight, and high performance. The present invention, therefore discloses, a metal vanadate-based asymmetric supercapacitor coin cell device, which is a portable supercapacitor having enhanced electrochemical performance.
[0024] In an embodiment of the present disclosure is described method of preparation of alkali metal vanadates- LiVO3, Li2V6O13, KV3O8 and K2V6O16. Disclosed herein is a method for preparing lithium and potassium vanadate cathode (101) materials for electrochemical supercapacitors. The material developed herein possesses one-dimensional morphologies (such as nanobelts, nanorods, etc.), a layered crystal structure, a high charge storage capacity, and a long life cycle. In another embodiment is described as an asymmetric supercapacitor coin cell device employing lithium vanadate or potassium vanadate as a cathode (101).
[0021] The following examples describe specific embodiments of the present invention and demonstrate the procedures for the preparation of 1) LiVO3 nanorods, 2) KV3O8 nanobelts, 3) fabrication of asymmetric solid-state supercapacitor coin cell device (KV3O8 // AC).
1. Preparation of electrodes:
1.1 Example 1: Preparation of LiVO3 nanorods
[0022] Vanadium pentoxide (V2O5) powder (0.5g) was mixed in 50 mL double distilled water at room temperature with constant stirring and ultrasonication for 30 minutes. The ultrasonicated solution was transferred to a conical flask and stirred at 1000 rpm for 1 h at room temperature (~28°C). 1 M solution of lithium salt such as Li2SO4 or LiCl or LiNO3 prepared in 50 ml double distilled water was slowly added to the V2O5 solution. Then, the temperature of the resultant solution was gradually increased to 60°C. This solution was maintained at 60°C with continuous stirring at 1000 rpm for 48 h (until the colour of the solution turned to red brick colour ) confirming the stabilization and formation of a precipitate i.e. LiVO3 nanorods. The precipitate was collected after centrifugation and washed several times with double distilled water and ethanol to remove unreacted lithium species. The final product was obtained by drying the resultant residue in a vacuum oven at 80 °C for 24 hours.
1.2 Example 2: Preparation of KV3O8 nanobelts
[0023] Vanadium pentoxide (V2O5) powder (0.5g) was mixed in double distilled water (50 mL) and ultrasonicated using a probe sonicator for 30 min. Then, 0.5 M K2SO4 or KCl or KNO3 solution (prepared in a separate beaker) was slowly added to the above-prepared V2O5 solution under constant stirring conditions. Here, the concentration of K2SO4 is relatively higher than the V2O5, ensuring that there is a sufficient amount of K+ ions available to fully react with the vanadium species. This excess of K2SO4 helps to drive the reaction to completion, promoting the formation of the KV3O8 nanobelts. After the complete addition of K2SO4 solution, the reaction temperature was gradually increased to 60°C and kept constant at 60°C with 1000 rpm speed for 48 hours (until the colour of the solution turned to red brick colour). The mixture turned into a sponge-like suspension with a red brick colour, indicating the completion of the reaction and the formation of nanobelts. Finally, the product was centrifuged with double distilled water and dried in a vacuum oven at 80°C for 24 hours.
1.3 Example 3: Fabrication of asymmetric supercapacitor coin cell device
[0024] The asymmetric supercapacitor coin cell device was fabricated using commercially available CR2032 coin cell positive and negative cases. The cases comprise 0.5 mm stainless steel spacers and springs. lithium vanadate or potassium vanadate (i.e. LiVO3 / KV3O8) cathode (101) and commercial activated carbon (AC) anode (102) were prepared using the Doctor's blade technique over a carbon paper current collector having a diameter of 16 mm. Aqueous electrolyte solutions i.e. 1 M Li2SO4 or 1 M KCl were used to fabricate LiVO3 // AC and KV3O8 // AC coin cell devices, respectively. The amount of active material was decided using the charge balance equation having the formula:
m_+/m_- =Q_-/Q_+ =(C_- V_-)/(C_+ V_+ )
Where, m_+ and m_- are the respective mass loadings, C_+ and C_- are respective specific capacitance (in C g-1), V_+ and V_- signify the negative and the positive electrode potential window, respectively. Whatman paper separator with 16 mm diameter was used as separator (103). The order of materials is represented in Figure 3. Finally, all the components were crimped between the CR2032 positive and negative cases to assemble the LiVO3 // AC and KV3O8 // AC coin cell supercapacitor devices (100).
2. Physicochemical characterizations:
2.1 Field emission scanning electron microscope (FESEM):
[0025] FESEM techniques were used to study the morphological characteristics of the prepared lithium and potassium vanadate nanomaterials. The FESEM technique produces high-magnification images that provide visual insights into the surface morphology of the nanomaterials. Figure 1 presents the high-resolution FESEM micrographs of the LiVO3 and KV3O8 nanomaterials. The LiVO3 exhibits a nanorod-like morphology while the KV3O8 exhibits a nanobelts-like morphology. Both the nanorods and nanobelts are self-assembled and uniformly distributed in random directions. The calculated width and length of the LiVO3 nanorods and KV3O8 nanobelts range between 50-80 nm and 1-2 μm, respectively.
2.2 X-ray diffraction (XRD):
[0026] The phase and crystal structure of the LiVO3 nanorods and KV3O8 nanobelts were studied using X-ray diffraction and shown in Figure 2. The XRD analysis reveals that both the LiVO3 nanorods and KV3O8 nanobelts samples exhibit a monoclinic crystalline phase (JCPDS card no. for LiVO3 = 40-0027 and KV3O8 = 86-2495). Both the XRD patterns display broad and intense peaks indicating lower crystallinity and smaller crystallite size. Additionally, in both the XRD patterns a sharp and intense peak at 11.2° for KV3O8 nanobelts and 12° for LiVO3 nanorods samples was observed, which corresponds to the well-ordered (001) layered structure with large d-spacing.
3. Electrochemical Analysis:
[0027] To evaluate the practical applicability of the LiVO3 nanorods and KV3O8 nanobelts, the aqueous asymmetric supercapacitor coin cell devices were fabricated using activated carbon (AC) as an anode (102) and the LiVO3 nanorods or KV3O8 nanobelts as a cathode (101) with 1 M Li2SO4 and 1 M KCl as electrolyte solutions, respectively. After fabrication, the performance of the fabricated asymmetric supercapacitor coin cell devices was studied using Cyclic voltammetry, Galvanostatic charging-discharging and cyclic stability measurements.
3.1 Cyclic voltammetry (CV) analysis:
[0028] Figures 4 (a, b) shows CV profiles of the LiVO3 // AC and KV3O8 // AC coin cell supercapacitor devices (100), conducted at various scan rates. Both the coin cell supercapacitor devices showed typical capacitive behaviour with oval-shaped CV curves, offering good capacitive behaviour and fast charge-discharge capability. The LiVO3 // AC device (100) can operate within a voltage window of 1.6 V, while the KV3O8 // AC coin cell supercapacitor device (100) can operate within a voltage window of 1.6 V without indication of the water electrolysis processes.
3.2 Galvanostatic charging-discharging (GCD) analysis:
[0029] The GCD measurements of the LiVO3 // AC and KV3O8 // AC coin cell supercapacitor devices (100) are presented in Figures 5 (a, b), respectively, performed for different current densities ranging. All the GCD curves work perfectly within the operating voltage range of 0 - 1.6 V and 0 - 1.8 V with symmetric charging-discharging curves. Both devices show very long charging and discharging times, indicating their high charge storage capacity. From the GCD measurement, the specific capacitance, energy and power density values of the LiVO3 // AC and KV3O8 // AC coin cell supercapacitor devices (100) were calculated using the following formulae:
Specific capacitance: Ability of capacitor to store electrical energy per unit mass or volume.
C= (I × ∆t)/(m×∆V)
Where, C is the specific capacitance of the supercapacitor device in Farad per gram (F/g), I is the current in ampere (A), Δt is the discharge time in sec, m is the mass of electrode material in gram (g) and ΔV is the voltage window (V).
Energy density (E, Wh kg-1): The amount of energy stored per unit of mass, length, area, or volume.
E= 1/2 ×〖CV〗^2/3.2
Where, C is the capacitance in Farad (F), and V is the operating window in voltage (V).
Power density (P, W kg-1): The amount of power released per unit of mass, length, area, or volume.
P= E/∆t×3600
Where, E is the energy density in Wh kg-1, and Δt is the discharge time in sec.
The LiVO3 // AC and KV3O8 // AC coin cell devices deliver the highest energy density values of 25.4 and 51 Wh kg-1 and power density values of 3657 and 4127 W kg-1, respectively. The calculated specific capacitance, energy and power density values of LiVO3 // AC and KV3O8 // AC supercapacitor coin cell devices (100) are displayed in Table 1.
Table 1: Specific capacitance, Energy density and power density values of LiVO3 // AC and KV3O8 // AC devices (100)
Current density
(A g-1) Specific capacitance
(F g-1) Energy density
(Wh kg−1) Power density
(W kg−1)
LiVO3 // AC KV3O8 // AC LiVO3 // AC KV3O8 // AC LiVO3 // AC KV3O8 // AC
0.5 - 145.19 - 51.62 - 128.99
1 71.60 107.34 25.46 38.16 228.57 257.99
2 57.78 71.83 20.54 25.541 457.14 515.99
4 40.57 41.90 14.42 14.89 914.28 1031.99
8 23.14 18.86 8.22 6.70 1828.57 2063.99
16 3.42 12.69 1.21 4.51 3657.14 3657.14

3.3 Cyclic Stability:
[0030] Figures 6 (a, b) show the cyclic stability measurements of the fabricated metal vanadate // AC supercapacitor devices for 5000 CV cycles at different current densities. The LiVO3 // AC and KV3O8 // AC coin cell supercapacitor devices (100) show excellent cyclic stability of 79% and 89% after 5000 cycles, respectively.
A comparative study of metal vanadate-based supercapacitor devices and their electrochemical performances reported in the literature are displayed in Table 2.
Table 2: A comparative study of metal vanadate-based supercapacitor devices and their electrochemical performances reported in the literature
Electrode material Preparation method Three electrode system Supercapacitor device Ref
Electrolyte Specific capacitance Cyclic Stability (%) Voltage window (V) Max. Energy density
(Wh kg−1) Max. Power density
(W kg−1) Cyclic Stability (%)
LiNiVO4 Ball Milling 1 M LiOH 212 F g−1
at 0.5 A g−1 99 % after 1000 cyc - - - - H. Hareendrakrishnakumar et. al.
Hydrothermal 456 F g−1
at 0.5 A g−1 99.6 % after 1000 cyc
LiV3O8 Rheological Phase Reaction 1 M LiNO3 120 F g−1
at 1 A g−1 78.6 % after 2000 cycles 1 V 36 Wh kg−1 0.25 W kg−1 77 % after 150 cycles Pavithra et al.
Na2V6O16 Chemical route 1 M Na2SO4 455 F g−1
at 0.5 A g−1 90 % after 5000 cycles 1.6 V 42 Wh kg−1 4300 W kg−1 80 % after 5000 cycles Vedpathak et. al.
KxV2O5 Hydrothermal 1 M Na2SO4 - - 0.8 V 2.9 Wh kg−1 4 W kg−1 72 % after 25000 cycles R. Manikandanet et al.
LiVO3 Ultrasonic-assisted Chemical route 1 M Li2SO4 426 F g−1
at 0.5 A g−1 78.6 % after 2000 cycles 1.6 V 25 Wh kg−1 3600 W kg−1 80 % after 5000 cycles This work
KV3O8 Ultrasonic-assisted Chemical route 0.5 M K2SO4 677 F g−1
at 0.5 A g−1 89 % after 5000 cycles 1.8 V 51 Wh kg−1 4127 W kg−1 90 % after 5000 cycles
In summary, H. Hareendrakrishnakumar et. al. prepared the LiNiVO4 phase using the ball milling and hydrothermal method. These methods are expensive and require sophisticated equipment to produce nanoparticles. (H. Hareendrakrishnakumar, R. Chulliyote, M.G. Joseph, Effect of crystallite size on the intercalation pseudocapacitance of lithium nickel vanadate in aqueous electrolyte, Journal of Solid State Electrochemistry 22 (2018) 1-9). Similarly, R. Manikandanet et al. reported a hydrothermal method to produce the KxV2O5 phase. The device fabricated in this study showed a very less operating voltage of 0.8 V, while in our case it is double with high energy and power density values. (R. Manikandan, C.J. Raj, M. Rajesh, B.C. Kim, S. Park, K.H. Yu, Vanadium Pentoxide with H2O, K+, and Na+ Spacer between Layered Nanostructures for High‐Performance Symmetric Electrochemical Capacitors, Advanced Materials Interfaces 5(12) (2018) 1800041). Pavithra et al. used the rheological phase reaction method, influenced by Poly (Vinylpyrrolidone) (PVP) to synthesize LiV3O8. The method likely provides control over particle size and morphology. The results of this study showed poor specific capacitance of 120 F g−1 at 1 A g−1 and poor cyclic stability of 77 % after 150 cycles. These comparative results highlight that our invented method to produce lithium and potassium vanadate has the potential to fabricate high-performing supercapacitor devices with very low cost and high scalability.
Although the disclosure has been described concerning the above embodiments, it will be apparent to one of ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the disclosure. Accordingly, the scope provided in the disclosure is defined by the attached claims. , Claims:WE CLAIM:
1. An asymmetric supercapacitor coin cell device (100) with enhanced charge transfer kinetics, the coin cell device (100) comprising:
a) a cathode (101) essentially consisting of an alkali metal vanadate, the said metal
vanadate being potassium vanadate (KV3O8); and
b) an anode (102) essentially consisting of activated carbon;
characterized in that the KV3O8 is in the form of nanobelts and wherein, the the asymmetric supercapacitor coin cell device (100) at a current density of 0.5 Ag-1
i) delivers an energy density of 51 W h kg-1;
ii) delivers a power density of 4127 W kg−1 ; and
iii) exibits specific capacitance of 145 F/g.;
while maintaining a cyclic stability of about 80% after 5000 cycles over an operating voltage window of 1.8 V

2. An asymmetric supercapacitor coin cell device (100) as claimed in claim 1, wherein the alkali metal vanadate is in the form of nanomaterial selected from the group consisting of LiVO3, Li2V6O13, KV3O8 and K2V6O16.

3. The asymmetric supercapacitor coin cell device (100) as claimed in claim 1, wherein the alkali vanadate electrode is a monoclinic layered structure essentially consisting of alternating layers of vanadium oxide that are connected by alkali metal, which act as a spacer between them.

4. The asymmetric supercapacitor coin cell device (100), as claimed in claim 1, wherein the alkali metal is one-dimensional layered.

5. The asymmetric supercapacitor coin cell device (100) as claimed in claim 1, wherein the potassium vanadate nanobelts have a width of 50-80 nm and a length of 1-2 μm.


6. The asymmetric supercapacitor coin cell device (100) as claimed in claim 1, wherein the lithium vanadate is in the form of lithium nanorods having width of 50-80 nm and length of 1-2 μm.


7. A method of fabricating an assymetric supercapacitor coin cell device (100), the method comprising the steps of:

i) mixing an alkali metal vanadate, activated carbon (conducting agent) and polyvinyl-
difluoride (PVDF as a binder) in a weight ratio of 8:1:1 to get a mixed powder;
ii) adding 1-Methyl-2-pyrrolidinone (as a solvent) to the mixed powder of step i to form
the homogeneous slurry;
iii) pasting the homogeneous slurry obtained in step ii onto the current collector
electrode (carbon paper or stainless steel foil) onto the effective area of 1 cm × 1
cm to obtain a working electrode; and
iv) drying the working electrode at 120°C for 24 h.

8. The method of fabricating an assymetric supercapacitor coin cell device (100) as claimed in claim 7, wherein the alkali metal vanadate is in the form of nanomaterial and is selected from a group consisting of LiVO3, Li2V6O13, KV3O8 and K2V6O16.

9. The method of fabricating an assymetric supercapacitor coin cell device (100) as claimed in claim 9, wherein, 1 M Li2SO4 aqueous electrolyte and whatmann paper separator (103) were used to fabricate the assymetric supercapacitor coin cell device (100).

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