Description: FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005
(See Section 10 and Rule 13)

COMPLETE SPECIFICATION

TITLE OF THE INVENTION
“MORPHOLOGICAL EVOLUTION OF CARNATION FLOWER LIKE CU2COSNS4 BATTERY TYPE ELECTRODES AND PREPARATION METHODS THERE OF”

The following specification particularly describes the invention and the manner in which it is to be performed:-
 
MORPHOLOGICAL EVOLUTION OF CARNATION FLOWER LIKE CU2COSNS4 BATTERY TYPE ELECTRODES AND PREPARATION METHODS THERE OF
FIELD OF INVENTION
The present invention relates to the field of supercapacitors. More specifically, the field of invention relates to a method of synthesizing a carnation flower like morphology like a battery electrode material, thereby fabricating a supercapacitor.

BACKGROUND

In this burgeoning neo-civilized world, research on clean and renewable energy sources is being considered due to the dramatic increase in global energy requirement and environmental impact of conventional energy supplies. Since these new energy sources are intermediate there is a need to easily store electrical energy. Supercapacitors are unique in that they have the best energy storage efficiency and hence, the device reliability depends largely on fundamental components configuration. Composite materials are designed to achieve functional capabilities beyond the limits of each property such as energy density and lifetime. The production of new materials is essential to develop and improve power transmission and storage systems to meet the extreme energy needs of the growing low carbon economy. Mesoporous materials have the potential to store high charges in energy storage owing to extensive surface area and pores. Due to this reason, basic properties such as material stability, specific capacitance, energy, strength, and longevity are thus improved.
A suitable electrode and its properties or active material is most important to increase the efficiency and performances of the supercapacitors. Recently, several synthetic routes such as thermodynamic (capping agent, structure directing agent, temperature, etc.) and kinetic factors (concentration of reactants, reduction rate, reaction time, etc.) is focused to produce shape-controlled metal nanostructures. Now a days, the development of Cu2MSnS4 (M = Ni2+; Co2+; Fe2+; Mn2+; Ca2+; Mg2+), a new quaternary compound with similar structure and properties to Cu2ZnSnS4 are eye-catching all the research interest in the energy field due to its excellent physical properties, optical band gab between 1.3 eV to 1.5 eV, highly abundance, affordable and non-toxicity.
In these, quaternary compounds of Cu2CoSnS4 are a promising candidate for SCs because of outstanding properties like elevated specific capacity, improved electrical conductivity, variable oxidation conditions, good physical and mechanical properties, and high cyclic stability due to its mixed metal additives. In general, Ruthenium dioxides are a standard electrode material in supercapacitor applications. Though, RuO2 is considered crucial for practical applications because of lofty reversibility, high value specific capacitance and very long cycle life, superior pseudocapacitive performances, but there are limitations in supercapacitor applications due to their low availability and high cost.
Thus, in light of the foregoing examination, there is a long-felt need for a method of manufacturing quaternary compounds of Cu2CoSnS4 with better electrochemical properties, thereby serving as a better alternative material in supercapacitor based energy storing devices.

BRIEF DESCRIPTION OF THE DRAWINGS
This invention is illustrated in the accompanying drawings, throughout which, like reference letters indicate corresponding parts in the various figures.
The embodiments herein will be better understood from the following description with reference to the drawings, in which:
FIG. 1 illustrates a method of synthesis of quaternary Cu2CoSnS4.
FIG. 2 illustrates a method of preparing an electrode, in accordance with an embodiment of the invention.
FIG. 3 illustrates a method of fabricating an asymmetric solid-state supercapacitor, in accordance with an embodiment of the invention.
Fig. 3 illustrates a method of manufacturing an improved quaternary chalcogenide material, in accordance with an embodiment of the invention.
FIG. 4A the crystallographic image of Cu2CoSnS4, in accordance with an embodiment of the invention.
FIG. 4B illustrates the XRD patterns of Cu2CoSnS4 at different variation of time (CCTS-0, 12, 18, 24 h), in accordance with an embodiment of the invention.
FIG. 4C illustrates the Raman spectra of Cu2CoSnS4 at different variation of time (CCTS-0, 12, 18, 24 h), in accordance with an embodiment of the invention.
FIG. 4D illustrates the FTIR of Cu2CoSnS4 at different variation of time (CCTS-0, 12, 18, 24 h), in accordance with an embodiment of the invention.
FIG. 4E illustrates the photoluminescence spectra of Cu2CoSnS4 at different variation of time (CCTS-0, 12, 18, 24 h), in accordance with an embodiment of the invention.
FIG. 5A-5C illustrates the solvothermal tailored FE-SEM images of Cu2CoSnS4 CCTS-0h with increasing magnifications, in accordance with an embodiment of the invention.
FIG. 5D-5F illustrates the solvothermal tailored FE-SEM images of Cu2CoSnS4 CCTS-12h with increasing magnifications, in accordance with an embodiment of the invention.
FIG. 5G-5I illustrates the solvothermal tailored FE-SEM images of Cu2CoSnS4 CCTS-18h with increasing magnifications, in accordance with an embodiment of the invention.
FIG. 5J-5L illustrates the solvothermal tailored FE-SEM images of Cu2CoSnS4 CCTS-24h with increasing magnifications, in accordance with an embodiment of the invention.
FIG. 6A-6C illustrates the HR-TEM micrographs of CCTS-18 h with increasing magnifications, in accordance with an embodiment of the invention.
FIG. 6D illustrates the SAED pattern of CCTS-18 h with increasing magnifications, in accordance with an embodiment of the invention.
FIG. 7A-7E illustrates the XPS of Cu2CoSnS4-18 h, in accordance with an embodiment of the invention.
FIG. 8A shows the N2 adsorption–desorption isotherm of the carnation flower like Cu2CoSnS4, in accordance with an embodiment of the invention.
. FIG. 8B shows the pore size distribution curve of the carnation flower like Cu2CoSnS4, in accordance with an embodiment of the invention.
FIG. 9A illustrates the three-electrode setup with instrument, in accordance with an embodiment of the invention.
FIG. 9B illustrates the CV profiles of CCTS-0 h, in accordance with an embodiment of the invention.
FIG. 9C illustrates the CV profiles of CCTS-12 h, in accordance with an embodiment of the invention.
FIG. 9D illustrates the CV profiles of CCTS-18 h, in accordance with an embodiment of the invention.
FIG. 9E illustrates the CV profiles of CCTS-24 h, in accordance with an embodiment of the invention.
FIG. 9F illustrates the CV profiles of different electrodes at 50mV/s, in accordance with an embodiment of the invention.
FIG. 9G illustrates the specific capacity value from CV profile, in accordance with an embodiment of the invention.
FIG. 10A illustrates the Reciprocal specific capacity plots (q-1 ) vs square root of scan rate (v1/2 ) of CCTS-0h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10B illustrates the Plots of specific capacity (q) vs reciprocal of square root of scan rate (v-1/2) of CCTS-0h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10C illustrates the Reciprocal specific capacity plots (q-1 ) vs square root of scan rate (v1/2 ) of CCTS-12h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10D illustrates the Plots of specific capacity (q) vs reciprocal of square root of scan rate (v-1/2) of CCTS-12h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10E illustrates the Reciprocal specific capacity plots (q-1 ) vs square root of scan rate (v1/2 ) of CCTS-18h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10F illustrates the Plots of specific capacity (q) vs reciprocal of square root of scan rate (v-1/2) of CCTS-18h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10G illustrates the Reciprocal specific capacity plots (q-1) vs square root of scan rate (v1/2) of CCTS-24h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10H illustrates the Plots of specific capacity (q) vs reciprocal of square root of scan rate (v-1/2) of CCTS-24h using the Trasatti method, in accordance with an embodiment of the invention.
FIG. 10I illustrates the bar chart displays the capacitance contribution from electrical double layer capacitance (EDLC) and pseudocapacitance (PC), in accordance with an embodiment of the invention.
FIG. 11A illustrates the GCD profile of CCTS-0h, in accordance with an embodiment of the invention.
FIG. 11B illustrates the GCD profile of CCTS-12h, in accordance with an embodiment of the invention.
FIG. 11C illustrates the GCD profile of CCTS-18h, in accordance with an embodiment of the invention.
FIG. 11D illustrates the GCD profile of CCTS-24h, in accordance with an embodiment of the invention.
FIG. 11E illustrates the specific capacity variations of CCTS-0h, CCTS-12h, CCTS-18h, and CCTS-24h, in accordance with an embodiment of the invention.
FIG. 11F illustrates the capacitive retention of CCTS-18h, in accordance with an embodiment of the invention.
FIG. 11G illustrates the Nyquist plot of EIS spectra, in accordance with an embodiment of the invention.
FIG. 11H illustrates the Bode plots of the phase angle vs frequency spectra of the prepared electrodes, in accordance with an embodiment of the invention.
FIG. 11I illustrates the Bode plots of the modulus vs frequency spectra of the prepared electrodes, in accordance with an embodiment of the invention.
FIG. 12 A illustrates the Schematic illustration of ASSC, in accordance with an embodiment of the invention.
FIG. 12B illustrates the comparative graph of CCTS-18h and activated carbon, in accordance with an embodiment of the invention.
FIG. 12C illustrates the CV curves of ASSC, in accordance with an embodiment of the invention.
FIG. 12D illustrates the GCD curves of ASSC, in accordance with an embodiment of the invention.
FIG. 12E illustrates the discharge curves of ASSC, in accordance with an embodiment of the invention.
FIG. 13A illustrates the capacitive retention and coulombic efficiency of ASSC, in accordance with an embodiment of the invention.
FIG. 13B illustrates the Ragone plot of ASSC, in accordance with an embodiment of the invention.
FIG. 14A illustrates the working model of Pouch type of ASSC, in accordance with an embodiment of the invention.
FIG. 14B illustrates the photograph of an assembled wristwatch-like coin-cell ASSCs, in accordance with an embodiment of the invention.

SUMMARY OF THE INVENTION
The present invention discloses a method of synthesis of quaternary Cu2CoSnS4. The method includes treating copper (II) chloride dehydrate, cobalt (II) chloride hexahydrate, and tin (IV) chloride pentahydrate with deionized water to form a first solution. Thiourea is blended and citric acid is appended to the first solution to form a second solution. The second solution is stirred continuously at a predetermined constant temperature and sonicated. Further, the second solution is processed in an autoclave at 160 °C for 12 to 24 hours.
In various embodiments, the predetermined constant temperature is in a range 80°C. In various embodiments, the method further comprises centrifuging using ethanol, methanol, and deionized water, and drying in vacuum furnace at 80°C for 12 h. The size of the Cu2CoSnS4 crystals prepared by the method is in a range 25 to 30 nm.
The invention in various embodiments, discloses a method of preparing an electrode. The method includes preparing a composition comprising quaternary Cu2CoSnS4 catalyst, activated carbon, acetylene black and polyvinylidene fluoride (PVDF) in the ratio 70:20:5:5 wt%. The composition is mixed with N-methyl pyrrolidinone (NMP) solvent to obtain working material slurry. The working material slurry is coated uniformly on Ni foam substrate and the coating is heated in an oven at 80°C for 12 h.
In various embodiments, the specific capacity of the electrode prepared by the method is in a range 36.18 - 65.55 mAh/g. In various embodiments, the method comprises employing the electrode as working electrode, Pt wire as counter electrode and Ag/AgCl as reference electrode for supercapacitor applications. The capacitive retention over 5000 cycles is 77.67 at 5 A/g.
In an aspect, a method of fabricating an asymmetric solid-state supercapacitor is described. The method includes preparing a first electrode by first synthesising quaternary Cu2CoSnS4 as working material comprising. Synthesising quaternary Cu2CoSnS4 includes treating copper (II) chloride dehydrate, cobalt (II) chloride hexahydrate, and tin (IV) chloride pentahydrate with deionized water to form a first solution. The first solution is blended with thiourea and citric acid to form a second solution. The second solution is stirred continuously at a predetermined constant temperature and sonicated. In various embodiments, the second solution is processed in an autoclave at 160 °C for 12 to 24 hours. The working material slurry thus prepared is uniformly coated on Ni foam substrate; and the coating is heated in an oven at 80°C for 12 h. As a second step, a second electrode is prepared.
The method includes coating activated carbon black on Ni foam substrate and heating the coating in an oven at 80°C for 12 h. As a third step electrolyte separator is prepared. The method include blending KOH and deionised water with polyvinyl alcohol (PVA) and sustaining at 80°C for 2h to obtain gel electrolyte and pouring the electrolyte as a thin sheet and extracting pieces of required size. In various embodiments to fabricate the supercapacitor the first electrode is placed as anode, the second electrode as cathode and the separator between the anode and the cathode.
In various embodiments the energy density of the supercapacitor fabricated by the method is 131.90 W h/kg and power density is 749.98 W/kg at 1 A/g.
DETAILED DESCRIPTION
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and/or detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The present invention discloses a method of synthesis of quaternary Cu2CoSnS4 by varying the thermodynamic and kinetic factors. This forms 3D hierarchical carnation flower like morphology. The synthesized Cu2CoSnS4 shows exceptional performance and improve energy storage ability through the petal like arrangements. In addition, a method of preparing an electrode is disclosed. The method comprises employing the electrode as working electrode, Pt wire as counter electrode and Ag/AgCl as reference electrode for supercapacitor applications. Further, a method of fabricating an asymmetric solid-state supercapacitor is described.
The present invention discloses a method of synthesis of quaternary Cu2CoSnS4 100 as shown in FIG. 1. The method in block 101 includes treating copper (II) chloride dehydrate, cobalt (II) chloride hexahydrate, and tin (IV) chloride pentahydrate with deionized water to form a first solution. The first solution is greenish brown solution which is stirred for 30 min. In block 103 Thiourea is blended and citric acid is appended to the first solution to form a second solution. In various embodiments, in block 105 the second solution is stirred continuously at a predetermined constant temperature and sonicated. The second solution is CCTS-0h.
Further in block 107 the second solution is processed in an autoclave at 160 °C for 12 to 24 hours. In one embodiment the Cu2CoSnS4 that is formed by heating for 12 hours is CCTS-12h. In a second embodiment the Cu2CoSnS4 that is formed by heating for 18 hours is CCTS-12h. In a third embodiment the Cu2CoSnS4 that is formed at heating for 24 hours is CCTS-24h. In various embodiments, the method is a solvothermal process. The solvothermal method is optimal for monitoring and tailoring control over size, shape, and morphological effects. The prepared Cu2CoSnS4 has hierarchical carnation flower like morphology.
The wet-chemical synthetic strategy using water and organic solvent as the medium of solvothermal route is adapted to synthesis the quaternary metal sulfide Cu2CoSnS4. The method offers a good reproducibility, a good performance and the ability to store more charges at lower costs for energy storage applications. In various embodiments, the method further comprises centrifuging using ethanol, methanol, and deionized water, and drying in vacuum furnace at 80°C for 12 h. The size of the Cu2CoSnS4 crystals prepared by the method is in a range 25 to 30 nm.
In various embodiments, the invention discloses a method of preparing an electrode 200 as shown in FIG. 2. The electrode is an anode. The method 200 in block 201 includes preparing a composition of the working material slurry that includes combining quaternary Cu2CoSnS4 catalyst, activated carbon, acetylene black and polyvinylidene fluoride (PVDF) in the ratio 70:20:5:5 wt%. In block 203, the composition 203 is mixed with N-methyl pyrrolidinone (NMP) solvent in an agate mortar to obtain working material slurry. In block 205, the working material slurry is coated uniformly on Ni foam substrate and in block 207, the coating is heated in an oven at 80°C for 12 h.
The carnation flower like microstructure of the electroactive material gives enormous surface area for the electrode surface which provides excellent spacing/intercalation of charges for the electrode material. In various embodiments, the specific capacity of the electrode prepared by the method is in a range 36.18 - 65.55 mAh/g. In various embodiments, the method comprises employing the electrode as working electrode, Pt wire as counter electrode and Ag/AgCl as reference electrode for supercapacitor applications. The capacitive retention over 5000 cycles is 77.67 at 5 A/g.
In various embodiments, a method of fabricating an asymmetric solid-state supercapacitor 300 is described as shown in FIG. 3. The method may be considered as having 3 major steps. As step 1 a first electrode is prepared, a second electrode is prepared as step 2, an electrolyte separator is prepared in step 3 and the prepared electrodes and the separator are assembled to form a supercapacitor. In block 301, the method includes preparing a first electrode by first synthesising quaternary Cu2CoSnS4 as working material. Synthesising quaternary Cu2CoSnS4 includes treating copper (II) chloride dehydrate, cobalt (II) chloride hexahydrate, and tin (IV) chloride pentahydrate with deionized water to form a first solution. The first solution is blended with thiourea and citric acid to form a second solution. The second solution is stirred continuously at a predetermined constant temperature of 80oC and sonicated. In various embodiments, the second solution is processed in an autoclave at 160 °C for 12 to 24 hours. The working material slurry thus prepared is uniformly coated on Ni foam substrate; and the coating is heated in an oven at 80°C for 12 h.
In block 303, as a second step, a second electrode is prepared. The method includes coating activated carbon black on Ni foam substrate and heating the coating in an oven at 80°C for 12 h. In block 305, as a third step electrolyte separator is prepared. The method include blending KOH and deionised water with polyvinyl alcohol (PVA) and sustaining at 80°C for 2h to obtain gel electrolyte and pouring the electrolyte as a thin sheet and extracting pieces of required size. In various embodiments in block 307, to fabricate the supercapacitor the first electrode is placed as anode, the second electrode as cathode and the separator is placed between the anode and the cathode.
In various embodiments the energy density of the supercapacitor fabricated by the method is 131.90 W h/kg and power density is 749.98 W/kg at 1 A/g.
Examples:
Example. 1: Synthesis of carnation flower-like Cu2CoSnS4 micro flowers preparation
The wet-chemical synthetic strategy using water and organic solvent as the medium of solvothermal route was adapted to synthesis the quaternary metal sulfide Cu2CoSnS4 at different times and to study its morphological variations. First, timeless products (0 h) were treated with 3 mM copper (II) chloride dehydrate, 1 mM cobalt (II) chloride hexahydrate, 1 mM tin (IV) chloride pentahydrate in 80 mL deionized water. A greenish brown solution appeared and was stirred for 30 min. Then, 4 mM thiourea was blended and small amount of citric acid was appended to this solution and continuously stirred at 80°C constant temperature and then sonicated more than 1 h. This solution was named as CCTS-0h and it was not fixed to autoclave.

Similarly, to understand the morphological effect, the different time has been varied as 12 h, 18 h and 24 h to form a CCTS-12 h, CCTS-18 h and CCTS-24 h samples, respectively. After that, these three products were individually poured into stainless steel 80 mL autoclave at 160 °C. All samples were centrifuged employing ethanol, methanol, and deionized water, washed well, and dried in vacuum furnace overnight at 80°C for 12 h. Then, all obtained black color powders were characterized. The simplest form of reactants and the products overall chemical reaction of the materials formation is described below in Eqn. 1. The coefficient number of each compound varies with respect to the reaction stoichiometry calculations.
〖2CUCl〗_2+〖CoCl〗_2+〖SnCl〗_4+〖4SC(〖NH〗_2)〗_2 □(+ 9H_2 O→┴ ) 〖Cu〗_2 〖CoSnS〗_4+〖8NH〗_4 Cl+〖4CO〗_2+H_2 O+〖Cl〗_2-------------- (1)
The crystallinity effects of Cu2CoSnS4 were studied using the primarily XRD analysis for different time varying samples (CCTS-0h, CCTS-12h, CCTS-18h and CCTS-24h). The crystallographic image of the Cu2CoSnS4 structure has been drawn using VESTA software as shown in FIG. 4A. There was no other secondary phase formation observed in the synthesized samples. FIG. 4B explored XRD results of Cu2CoSnS4 samples. All diffraction peaks are coincided with JCPDS 26-0513 corresponding to the stannite phase of the Cu2CoSnS4. The diffraction peaks noted at 28.30°, 33.42°, 37.27°, 47.41°, 56.47°, 57.36°, 69.84° and 76.65° are as of the diffraction planes of (112), (004), (202), (204), (312), (215), (400) and (332) respectively for Cu2CoSnS4 phase.

The mean crystallite size of prepared particles measured using Debye-Scherer’s formula and the values are around 25 to 30 nm ranges for the high intensity peak. As we conferred in the introductory part that these Cu2CoSnS4 phases are useful because they have high conductivity in energy storage applications. The phase purity has been further studied by Raman analysis in wavenumber of 200 to 2000 cm-1 (FIG. 4C). The bands at 260, 470 and 1431 cm-1 matched well with the band positions of previous reports. The low intense peak at 260 cm-1is responsible to the Cu2CoSnS4 compound. The predominant peak was appeared at 470 cm-1 which is corresponding to S anions A1 symmetric molecular vibration mode and band at 1431 cm-1 explored the C=C bonds. Vibration spectroscopy provides structural information on the quality and quantity analysis. FIG. 4D shows the FT-IR responses of the prepared CCTS materials displayed in different bands at 617, 1113, 1404, 1633, 2927 and 3478 cm-1. Generally, sulfur-based materials revealed fixed absorbances at 1404, 1113, and 617 cm-1. The peak typically presents at 3478 cm-1 answerable for the water and thiourea complex, in addition to the peaks 1113 and 1633 cm-1 are liable for the metal–thiourea complexes. The stretching and bending vibrations of oxygen is responsible for the bands around 900-1600 cm-1.

Additional weak bands found at 963 and 683 cm-1 cause resonance interactions between the sulfide vibration modes in the prepared samples. 617 cm-1 belongs to the Co-S band. Specific absorption at 2927 cm-1 is assigned as S-H thiol functional group. Photoluminescence is used to study the optical behaviours of the synthesized materials. The room temperature assisted photoluminescence spectra exhibited well-resolved peaks at 299, 369, 417, 484, 544 nm (4.17, 3.37, 2.97, 2.56, 2.28 eV). The band existed at 484 nm may have been photogenerated electrons and holes recombination and band located at 417 nm may have arisen from 3d9 4s1 ↔ 3d10 transition of Cu+ ion. The band observed at 369 nm is ascribing due to the Co2+ ion in the tetrahedral coordination with Sulphur (FIG. 4E) and definitely confirms the addition of Cu-Co-Sn-S.

To know the external morphology, chemical composition, and crystal structure of the sample with direct visualization SEM analysis is the best technique. The carnation flower like morphological images of the prepared Cu2CoSnS4 with different reaction time variations of the samples carried out by FE-SEM at different magnification levels 5, 1 µm and 500 nm FIG. 5A-FIG. 5L. The higher magnified 5 µm levels temperature varied images show the close resembles of flower like morphologies. Expect without the temperature all the samples exhibited the perfect flower morphology of the samples. This significantly improves the material surface contact amid electrolyte and the electrode due to the wider and thinner petals of the 18 h time variation, which increases the supercapacitor performance.

FIG. 6A-FIG. 6D explored high magnification TEM images of obtained product. TEM images in FIG. 6A and FIG. 6B explored as-prepared Cu2CoSnS4 has a 3D carnation flower-like structure with two-dimensional ~40-nm-thick petals. The HR-TEM images was obtained to further look at the structure of the CCTS-18 h. FIG. 6C clearly reveals the lattice fringes (0.31 nm) reliable with (111) plane of the Cu2CoSnS4. The obvious diffraction ring in SAED substantiates polycrystalline CCTS-18 h (FIG. 6D). Cu2CoSnS4 materials, which are designed to contribute to carrier separation and electron transport performance, exhibit a stable microstructure. The diffraction rings estimated from the inside to the outside connected to the tetragonal phase of Cu2CoSnS4 with the respective lattice planes of (112), (004), (202), (204), (312), (400) and (332), which are reliable with the XRD results.

FIG. 7A demonstrates the high resolution XPS scanning survey spectra of the synthesized CCTS-18 h which shows all the consistent elements of Cu, Co, Sn and S for Cu2CoSnS4. The core level Cu2p spectra having two splits Cu2p3/2 (931.71 eV) and Cu2p1/2 (951.61 eV) as displayed in FIG. 7B. The split difference noticed to be 19.9 eV which responsible for the Cu1+ state as previously reported. FIG. 7C explored core level spectra of the Co2p species which has two splits at 777.96 eV and 793.08 eV for Co2p3/2 and Co2p1/2. The difference of the splits calculated to 15.12 eV confirms with the reported Co2+ state. The binding energy at 486.82 eV (Sn3d5/2) and 495.29 eV (Sn3d3/2) is responsible for the core level spectra of Sn3d as visible in FIG. 7D. The 8.47 eV peak difference is indicating presence of Sn4+. The fitted core level spectra detected at binding energy of 160.20 eV and 165.44 eV is matching to S2p3/2 and S2p1/2 respectively due to the S-2 species (FIG. 7E).

The quality of the synthesized carnation flower like Cu2CoSnS4 was exemplified by N2 physisorption experiments. The large pores in the carnation flower-shaped structure are formed due to inter nanopetals spaces while small pores may be attributed due to nanopetals. BET and BJH method was used to learn specific surface area and porosity of Cu2CoSnS4. FIG. 8A explored N2 adsorption/desorption curves of type-IV isotherm with a H3 hysteresis loop, representing the mesoporous nature of the Cu2CoSnS4 samples and FIG. 8B denotes the pore size distribution curve. The BET specific surface area (m2/g), cumulative pore volume (cc/g) and average pore diameter (nm) has been calculated from BJH desorption isotherm as tabulated in Table 1. The mesoporous leads to offer high surface area and high porosity which paves the way for promoting shorter diffusion paths for charge transports and providing richer electroactive sites for improving the electrochemical performances of the potential use of Cu2CoSnS4 materials in supercapacitor applications.

Table 1:BJH desorption summary
Sample BET Specific Surface area (m2/g) Cumulative poer volume (cc/g) Mean pre diameter (mm)
CCTS-0 h 93.902 0.395 15.158
CCTS-18 h 105.663 0.244 7.181

The structure and surface morphology of the materials have a major role on electrochemical performances. The carnation flower like microstructure of the electroactive material gives enormous surface area for the electrode surface which provides excellent spacing/intercalation of charges for the electrode material. The different time variation (CCTS-0 h, CCTS-12 h, CCTS-18 h and CCTS-24 h) of synthesized materials change the surface morphology and electrochemical performances. Electrochemical studies have been performed on all electrodes designed to evaluate the influence of temperature on electrochemical performance. Metal sulfides are generally considered to be good candidates for saving more charges on electrode/electrolyte interface and electrode surface. Cyclic voltammetry (CV) is general method to study reduction and oxidation processes associated with electroactive species and provides an excellent algorithm for classifying charge storage systems. Electrochemical dual-layer capacitive materials typically show a rectangular CV shape, while pseudocapacitive material shows quasi-rectangular CVs, whereas battery type electrode gives a pair of oxidation and reduction curves.

Example. 2: Electrode preparations
The electrochemistry measurements were performed using Bio-logic SP-150 Potentiostat at ambient temperature. The working material slurry was prepared using CCTS catalyst, activated carbon, acetylene black and PVDF of 70:20:5:5 wt% respectively by manual mixing in 20 drops NMP (N-methyl pyrrolidinone) solvent in an agate mortar. Ni foam sheets were pre-cleaned with 1 M HCl in 100 mL of DI water using ultrasonication for 15 min to eliminate the NiOx surface, and then cleaned several times. Thereafter, the obtained slurry was uniformly coated on selective 1×1 cm2 area of Ni foam using Art painting brush size 4. Then, all the coated electrodes placed in oven at 80°C for 12 h. The before and after catalyst coating the Ni foam substrate weight was measured properly for mass balancing and error bar calculations. The active mass coated was optimized cautiously within 2 mg. The CCTS catalyst (1×1 cm2 area coated Ni foam) as working, Pt wire as counter, and Ag/AgCl as employed reference electrode for supercapacitor applications in 3 electrode configurations. 2 M of KOH employed as alkaline electrolyte for the electrochemical measurements. In this three-electrode configuration, prepared electrode materials specific capacity in terms of C/g and mAh/g was estimated.
Specific capacity from CV: Cs=∫ (I×dv)/(2×s×∆V×m )C/g -------------------- (2)
Specific capacitance from GCD: Cs=(I×∆t)/(m )C/g -------------------- (3)
Specific capacity from CV: C= (∫I×dv)/(2×3.6×m×ν ) (mAh/g) -------------------- (4)
Specific capacity from GCD: Cs=(I×∆t)/(3.6×m ) (mAh/g) -------------------- (5)
Where ‘I×dv’signifies area under the CV curve, ‘I’ - discharge current (A), ‘∆t’- discharge time (s), dv implies applied potential window (V), ‘ν’ means scan rate (mV/s), and ‘m’ represents active materials mass (mg) coated on the electrodes surface.

FIG. 9A shows the arrangement of three electrode system in an electrolytic cell with photograph image of the electrochemical potentiostat Biologic SP-150. FIG. 9A-9E shows the CV curves at 10-100 mV/s for CCTS-0 h, CCTS-12 h, CCTS-18 h and CCTS-24 h electrodes. All the curves show the oxidation and reduction pair and clearly demonstrates surface redox reaction is dominant than the EDLC. The CV profiles undoubtedly show battery type behavior and possible faradaic redox mechanisms are proposed as follows:
Cu2CoSnS4 + 9 OH− 2 Cu(OH)2 + Co(SOH) + Sn(OH)4 + 3S---------(9)

The CV curves of Cu2CoSnS4 exhibits active redox pairs of Cu+/Cu2+, Co2+/Co3+ and Sn2+/Sn4+ working with the support of OH anions in the alkaline medium of definite potential window. The specific capacity was computed employing formula in Eqn. 2 and 4. At low 10 mV/s scan rates, the prepared CCTS-0 h, CCTS-12 h, CCTS-18 h and CCTS-24 h electrodes delivers 36.18, 67.91, 73.26 and 65.55 mAh/g specific capacities, respectively and calculated values are shown in Fig. 6(f). Compared to the temperature aided electrodes, the CCTS-18 h electrode performed better and offers higher electrochemical performances than other electrodes. The lower the scan rate the more time it takes for the OH- ions to intercalate to the electrode/electrolyte interface, thus increasing the specific capacity. At high scan rate, however, less time is available to intercalate with the OH- ions as a result of a decrease in specific capacity.
Trasatti method is the characteristic feature that helps in categorization of the intrinsic charge storage kinetics of the electrode materials. The method involves calculating approximately the contributions of ‘inner’ (diffusion-controlled) and ‘outer’ (surface-controlled) surfaces to total charge (𝑞𝑇 = 𝑞𝑖 + 𝑞o) evaluated using cyclic voltammetry curves. The basis of the technique is charged species (ions) on inner surfaces is diffusion-controlled route, and electrode outer surface is non-diffusion-controlled process which is independent of the scan rate. The detailed calculations of the charge storage process using Trasatti method is clearly discussed in our previous work “Superiorsupercapacitive performance of Cu2MnSnS4 asymmetric devices”, M. Isacfranklin et. al, Nanoscale Advances, 2021, 3, 486-498. Plotting the reciprocal of specific capacity (q-1) vs square root of scan rates (v1/2) and q vs v-1/2 give linear correlation which would take an account the semi-infinite diffusion of the ions. Owing to the electrode internal resistance and deviation from the semi-infinite ion diffusion from this linear relationship, the data points deviated at high scan rates. FIG. 10A, 10C, 10E and 10G represents linear fit of q−1vs. ν1/2 and FIG. 10B, 10D, 10F and 10H displayed the linear fit of q vs. ν−1/2. Trasatti analysis revealed that the maximum capacity for CCTS-18 and from EDLC (capacitive) and pseudocapacitive (diffusive) contributions are 10.06 % and 89.94 % which is quite higher than the other electrodes as shown in FIG. 10I.

The galvanostatic charge discharge study was carried out for different current density 0.5, 1, 2, 3 and 5 A/g values for all the electrodes (FIG. 11A-11D). The GCD clearly revealed and confirmed the behaviour of this material based on battery type electrodes. The specific capacity for each discharge curve was calculated using Eqn. 3. The values are 52.01, 129.72, 132.08 and 65.97 mAh/g at 0.5 A/g for CCTS-0 h, CCTS-12 h, CCTS-18 h and CCTS-24 h electrodes, respectively. All the remaining values are pictorially represented in the bar graph FIG. 11E. High specific capacities can be achieved at low current densities because of its low ohmic drops so that the internally active sites of the electrolyte can easily reach the electrode holes. At higher current densities, the specific capacity values decrease as the rate of redox reaction is lower. The stability of the best performed CCTS-18 electrode studied at 5 A/g, and retained capacitance of 77.67 % for 5000 charge discharge cycles (FIG. 11F).

The kinetic mechanism of electrode/electrolyte interface of CCTS-0 h, 12 h, 18 h and 24 h electrodes were evaluated through the Nyquist diagram in FIG. 11G, the inset photograph is the equivalent electrical circuit for fitting Nyquist plots. An equivalent circuit has a semicircle part which corresponds to the resistor-capacitor at a series connection of solution resistance. The high frequency region is responsible for trapping/de-trapping transfer of charge carriers, whereas the medium and low frequency semicircle regions correspond to the charge transfer of the surface-active sites. The diameter of semicircle in Nyquist diagram explains charge transfer resistance (Rct), which is primarily a function of the ion shift between electrode and electrolyte. The Rct values are 2.704, 2.607, 2.206 and 2.647 Ω for CCTS-0 h, 12 h, 18 h and 24 h electrodes respectively. The intercept with real axis communicates to equivalent series resistance (Rs), and is consequential from intrinsic resistance of electrode material and electrolyte. The lowest solution resistance and the charge transfer resistance of CCTS-18 electrodes indicate rapid ion/electron transfer kinetics during the redox reaction process and could be able to provide high conductivity to improve the specific capacity. Table 2 explains the fitted parameter values of Nyquist plots. Bode plots are the second most important form of EIS analysis, which contains important information related to the frequency used, i.e., changes in capacitance, resistance, and ion diffusion of the electrodes. From Bode plots (FIG. 11H and 11I) that the CCTS-18 h electrode revealed better electrical/ionic resistance with smaller value of equivalent series resistance (ESR) at high-frequency range than other electrodes. In addition, all electrodes deviated from 90° angle from phase angle versus frequency curve, which ensures battery-type behavior.
Table 2 Nyquist plot Z fit analysis
Parameter Equivalent circuit: R1+C2/(R3+W3+C3)
CCTS-0 h CCTS-12 h CCTS-18 h CCTS-24 h Unit
R1=Rs 1.053 1.004 1.0054 1.023 Ohm
C2 0.205 0.273 0.373 0.224 F
R3=Rct 2.704 2.607 2.206 2.647 Ohm
S3 9.867 10.74 13.99 10.05 Ohm s(-1/2)
C3 0.1967 0.2418 0.5392 0.2234 F

Example. 3: Fabrication of asymmetric solid-state supercapacitor (ASSC)
ASSC was accumulated employing Cu2CoSnS4 and activated as a cathode and anode materials, respectively. The PVA/KOH gel separator placed amid negative and positive electrode. The Ni-foam substrate is act as a current collector in two electrode arrangements. 2 M KOH (3.36 g) was blended in 30 mL deionized water with 3g polyvinyl alcohol (PVA) and sustained at 80°C for 2h to construct gel electrolytes. The semisolid gel is then poured as a homogeneous transparent very thin layer onto Overhead Projector Sheet (OHP) sheet and cooled naturally in the environment. After a while, this sheet is extracted, and piece of required size was used as a separator. A two-electrode system was constructed of Cu2CoSnS4-18 h (2 mg) and Activated carbon (5 mg) coated Ni-foam as positive and negative electrode respectively and an electrolyte separator made of PVA/KOH gel polymer. A sandwiched type ASSC device was made as positive electrode, separator and negative electrode and is used for electrochemical measurements. In accordance with Q- = Q+, the following formula was used to charge balance between the two-working electrodes Cu2CoSnS4-18 h and activated carbon.
m^+/m^- = (C_(sp+) × 〖∆V〗^+)/(C_(sp-) × 〖∆V〗^- )-------------------- (6)
For testing the practical use, two electrode measurements were used to examine the electrochemistry properties of ASSC device. All the characterizations were done at room temperature conditions. Further, the Cu2CoSnS4-18 h//AC ASSC device energy density (E) and power density (P) was computed:
E = (Csp×∆V^2)/(2 × 3.6)-------------------- (7)
P = (3600 × E )/∆t-------------------- (8)
To check the practical applicability, an asymmetric solid-state supercapacitor (ASSC) device was built with CCTS-18 h as +ive and activated carbon as -ive electrode. FIG. 12A shows a description of assembled ASSC device (CCTS-18//AC) with applied power source. The structure of the ASSC device and the comparative CV curves of the negative (-1 to 0 V) and positive electrode (0 to 0.5 V) were illustrated in FIG. 12B. FIG. 12C revealed CV profile of two electrode measurements for 0-1.5 V potential ranges by different scan rates from 10 to 100 mV/s. The active mass is 2 mg in three electrode and 7 mg in two electrode configurations (2 mg and 5 mg in both positive and negative electrodes respectively in two electrode configurations). Exposure to CV curves similar to all scan rates ensures good reversibility and quick charge-discharge capability of the ASSC device. The charge discharge profile and discharge profile with diverse current densities of ASSC device is illustrated in the FIG. 12D and FIG. 12E. Although current density has been amplified from 1 to 25 A/g, at higher current density its discharge time is very close to the charge time, which indicates good columbic efficiency and good electrochemical reversibility of the device. Capacitive retention of the ASSC device has been verified with 78% retention and 97.98% columbic efficiency in 20000 charge discharge cycles as displayed in FIG. 13A. Capacitive parameters of energy and power density from GCD plot of CCTS-18//AC in two electrode configurations with other reported values are summarized in Table 3. Based on these values, the Ragone plot displayed the comparison graph of power density against energy density as show in FIG. 13B.

Table 3: Capacitive parameters from GCD plot in two electrode
Potential window (V) Current (A) Discharge time
(s) Specific capacitance (F/g)
Energy density
(Wh/kg) Power density
(W/kg)

1.5
1 633.14 422.09 131.90 749.98
2 270.63 360.84 112.76 1499.97
3 163.55 327.10 102.21 2249.81
4 113.37 302.32 94.48 3000.15
5 83.97 279.90 87.47 3750.05
6 65.39 261.56 81.74 4500.14
10 27.21 181.40 56.69 7500.33
15 12.00 120.00 37.50 11250.00
20 5.64 75.20 23.50 15000.00
25 3.08 51.33 16.04 18758.05

Table 4: Comparison of energy storage properties of Cu2CoSnS4//AC with other reported results
Device materials Electrolyte Working potential (V) Energy density (Wh/Kg) Power density (W/Kg) Capacitive retention (%) @ cycle Ref.
CuCo2S4 on caron textile//AC PVA/KOH
(9:1 ratio) 1.6 17.12 194.4 78.4%@3000 59
CuCo2S4/CNTs-3.2%//AC 2 M KOH 1.6 23.2 402.7 87.5%@10000 60
CuCo2S4@NiCo(OH)2//
CuCo2S4@NiCo(OH)2 3 M KOH 1.5 32 750 92%@2000 61
CuCo2S2/CuCo2O4// graphene 2 M KOH 1.6 33.2 800 73%@10000 62
N-DLCHs//CuCo2S4 6 M KOH 1.6 40.2 799.1 90.89%@5000 63
CuCo2S4/CC//AC/CC PVA/KOH (3g) 1.6 42.9 800 80%@5000 64
CuCo2S4//AC 3 M KOH 1.6 43.65 ⁓800 91.7%@10000 65
CuCo2S4/Ni foam//AC 3 M KOH 1.6 46.1 991.6 70.8%@4000 66
r-NiCo2S4-6 HSs // N/S-AC PVA+KOH 1.6 50.76 800 91.35%@5000 67
CuCo2S4 NRAs//AC PVA+KOH 1.6 56.96 320 88%@5000 68
SnNi2S4//AC 2 M KOH 1.41 64.38 700.3  98.38%@10000 69
CePO4@CuCo2S4//AC 2 M KOH 1.6 80.4 799.5 94.4%@10000 70
MCNSvac//AC 1 M KOH 1.8 85.2 1030 79.1%@10000 71
CuCo2S4 NS//Fe2O3/NG//AC PVA +KOH 1.6 89.6 663 91.5%@10000 72
Cu2CoSnS4//AC PVA +KOH 1.5 131.90 749.98 78%@20000 This application

Photographic assembled pouch type and coin-cell type ASSC are described to evaluate the device for practical applications. FIG. 14A exemplifies the pouch type ASSC supercapacitor device using Ni-foam. The prepared device showed an excellent electrochemical performance after charging at 10 second, the device can operate a mini size 1.5 V electric table fan. This demonstration refers to the best possible use for its practical application in energy storage applications. Lastly in terms of being used for realistic perspective, we have connected a two-coin cell type ASSC device in series fashion to extend the voltage window designed to switch applications. The electrode material in all coin cells has an area of about 1 cm2. The function of coin-cell type ASSCs can be extended to design a wristwatch-like application by considering the compact design as displayed in FIG. 14B. A designed 2 coin-cell type of ASSC connected with the help of Scotch tape.
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 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. 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 modification within the spirit and scope of the embodiments as described herein.
Dated 25th July 2022 Patent Agent for Applicant
S. Priyadarsini IN/PA -1677
, Claims:CLAIM
WE CLAIM:
1. A method of synthesis of quaternary Cu2CoSnS4 comprising:
treating copper (II) chloride dehydrate, cobalt (II) chloride hexahydrate, and tin (IV) chloride pentahydrate with deionized water to form a first solution;
blending thiourea and appending citric acid to the first solution to form a second solution;
stirring the second solution continuously at a predetermined constant temperature and sonicating; and
processing the second solution in an autoclave at 160 °C for 12 to 24 hours.
2. The method as claimed in claim 1, wherein the predetermined constant temperature is in a range 80 °C.
3. The method as claimed in claim 1, wherein the method further comprises centrifuging using ethanol, methanol, and deionized water, and drying in vacuum furnace at 80°C for 12 h.
4. The method as claimed in claim 1, wherein the size of the Cu2CoSnS4 crystals prepared by the method are in a range 25 to 30 nm.
5. A method of preparing an electrode comprising:
preparing a composition comprising quaternary Cu2CoSnS4 catalyst, activated carbon, acetylene black and polyvinylidene fluoride (PVDF) in the ratio 70:20:5:5 wt%;
mixing the composition with N-methyl pyrrolidinone (NMP) solvent to obtain a working material slurry;
coating the working material slurry uniformly on Ni foam substrate; and
heating the coating in an oven at 80°C for 12 h.
6. The method as claimed in claim 5, wherein the specific capacity of the electrode prepared by the method is in a range 36.18 - 65.55 mAh/g.
7. The method as claimed in claim 5, wherein the method comprises employing the electrode as working electrode, Pt wire as counter electrode and Ag/AgCl as reference electrode for supercapacitor applications.
8. The method as claimed in claim 6, wherein the capacitive retention over 5000 cycles is 77.67 at 5 A/g.
9. A method of fabrication of an asymmetric solid-state supercapacitor comprising:
preparing a first electrode comprising
synthesising quaternary Cu2CoSnS4 as working material comprising:
treating copper (II) chloride dehydrate, cobalt (II) chloride hexahydrate, and tin (IV) chloride pentahydrate with deionized water to form a first solution;
blending thiourea and appending citric acid to the first solution to form a second solution;
stirring the second solution continuously at a predetermined constant temperature and sonicating; and
processing the second solution in an autoclave at 160 °C for 12 to 24 hours.
coating the working material slurry uniformly on Ni foam substrate; and
heating the coating in an oven at 80°C for 12 h;
preparing a second electrode comprising coating activated carbon black on Ni foam substrate and heating the coating in an oven at 80°C for 12 h;
preparing electrolyte separator comprising:
blending KOH and deionised water with polyvinyl alcohol (PVA) and sustaining at 80°C for 2h to obtain gel electrolyte;
pouring the electrolyte as a thin sheet and extracting pieces of required size; and
placing the first electrode as anode, the second electrode as cathode and the separator between the anode and the cathode.
10. The method as claimed in claim 9, wherein the energy density of the supercapacitor fabricated by the method is 131.90 W h/kg and power density is 749.98 W/kg at 1 A/g.

Dated 25th July 2022 Patent Agent for Applicant
S. Priyadarsini IN/PA -1677