“HIGH PERFORMANCE COMPOSITE ANODE MATERIAL FOR ENERGY STORAGE DEVICES AND DEVICE THEREOF”

FIELD OF INVENTION:

The present invention relates to a composition for energy storage devices comprising the anodic composite of nickel cobalt sulphide (NCS) of general formula NixCoySz and carbon based material of high surface area and molten imidazolium salt as electrolyte of general formula (I). The molten salt electrolyte is operable at varying proportion of the anodic composite and at varying temperature range. The composition of the present invention is stable and improves the capacitance and cyclic stability of energy storage devices.

BACKGROUND & PRIOR ART:

Supercapacitors are well known for their high capacitance values than capacitors, thereby bridging the gap between capacitors and rechargeable batteries. Supercapacitors may be of three types, namely Electric Double Layer Capacitors (EDLCs) in which charge transfer takes place non-faradaically, pseudocapacitors in which charge transfer takes place faradaically and hybrid supercapacitors which combines both of the above supercapacitors. The current invention is applicable to all types of supercapacitors, however it may have particular applications in hybrid supercapacitors.

Pseudocapacitors are charge storage devices that store the charge by means of faradaic current, that is the current generated due to reduction/oxidation process, intercalation process or electrosorption process between an electrolyte and the electrode. Due to this phenomenon, pseudocapacitors achieve higher charge densities than other supercapacitors.

The electrode of pseudocapacitors may be made of conducting polymers or transition metal oxides. Transition metal sulfides have also been studied recently because of their superior capacitive properties to corresponding transition metal oxides such as high mechanical and thermal stability, high electrical conductivity and rich redox reactions [Ref: Enhanced cycle stability of a NiCo2S4 nanostructured electrode for supercapacitors fabricated by the alternate-dip coating method , by Kang et.al., Published in collaboration with the Royal Society of Chemistry, DOI: 10. l098/rsos.180506] Recently, N1C02S4 (NCS) as a material for electrode is driving research in the fields of pseudocapacitors, and supercapacitors in general. Predecessor of NCS is N1C02O4. In NCS, oxygen is replaced by usual sulphur. The incorporation of sulphur in the NCS create more flexible structure with the elongation of chemical bonds; thus making electron transport easier in this tuned structure, which also contributes to the enhancement of the electrochemical performances. NCS as a material for electrode has gained attention due to its rich redox reactions and intrinsically high conductivity.

There have been published reports of using NCS as electrode material in aqueous electrolyte.

However, the use of aqueous electrolyte limits the operating voltage. Similarly, the NCS as electrode material in the pseudocapacitor is shown to give a maximum specific capacitance of 437 F g-l in a KOH electrolyte at a current density of 1 A g ^_1 [Pu, T; Cui, F.; Chu, S.; Wang, T.; Sheng, E.; Wang, Z. Preparation and electrochemical characterization of hollow hexagonal N1C02S4 nanoplates as pseudocapacitor materials. ACS Sustain. Chem. Eng. 2014, 2, 809-815]

Pseudocapacitance is generally dependent upon the chemical affinity of electrode materials to the ions adsorbed on the electrode surface as well as on the structure and dimension of the electrode pores.

Electrolytes have been identified as one of the most influential component in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors (EDLS), pseudocapacitors and hybrid supercapacitors. The electrolytes are classified in to several categories, including aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes.

US6535373B1 discloses non-aqueous electrolyte for use in batteries and electrical capacitors for use at low temperature. The said electrolyte contains a nitrile solvent and the combination of an imidazolium salt of the formula:

Wherein R, R2, R3, R4, and R5 are alkyl groups having 1-3 carbon atoms and X is a member of the group consisting of tetrafluorob orate, triflate, and hexafluorophosphate hexafluoroarsenate and at least two tetraalkylammonium salts in a nitrile solvent. The tetraalkylammonium salts comprises tetraethylammonium tetrafluorob orate and methyltriethylammonium tetrafluorob orate. EP0984471 disclose tetrafluorob orate and hexafluorophosphate of imadazolium derivatives as electrolyte for electric double layer capacitors.

US5965054 discloses non-aqueous electrolytes for electrical storage devices utilizing salts consisting of alkyl substituted, cyclic delocalized aromatic cations and their perfluoro derivatives with alkyl carbonate solvents.

In pseudocapacitive reactions the cyclic stability, the working potential and the overall performance of the capacitor is generally reduced due to the non-ideal electrochemical reversibility resulting from the interactions between the electrolyte ions and the electrode materials. In view of the same, it is the objective of the present invention to provide a composition for the energy storage device comprising nickel cobalt sulphide (NCS) of general formula NixCoySz and carbon based material of high surface area along with molten salt electrolyte which will ameliorate the disadvantages of the aqueous electrolyte as well as improve upon the cycling stability and power density of the electrode material consequently improving the energy storage capacity of the energy storage device.

SUMMARY OF INVENTION:

These and other modifications in the energy storage devices are provided in the present invention that has advantages over the conventional energy storage devices.

Accordingly, the present invention provides the composition for energy storage device comprising;

i. nickel-cobalt-sulphide (NCS) of formula NixCoySz wherein‘x’ is 1,2;‘y’ is 1,2,4;‘z’ is 4,8; wherein y>x; and

ii. High surface area activated carbon or reduced Graphene Oxide (rGO) or graphitic Carbon Nitride@mesoporous carbon (g-CN@mc) in the ratio ranging between 1-50% (NCS) : 50-99% (carbon based material);

iii. an electrolyte of molten imidazolium salt of general formula 1(1)

X

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen or alkyl groups having 1 to 6 carbon atoms, ‘X’ represents an anion of the group tetrafluoroborate(BF4), triflate(OtF), bis(trifluoromethylsulfonyl)imide(TFSI), hexafluorophosphate(PF ₆ ) or bis(Fluorosulfonyl)imide(FSI); wherein the said composition improves the capacitance and cyclic stability of the energy storage device.

In an aspect, the composition of the present invention further comprises the conductive additives selected from a group consisting of various forms of graphenes, single walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks, graphite in an amount ranging from 0. l-5%w/w. In a preferred aspect, the nickel cobalt sulphide (NCS) of general formula NixCoySz wherein is 1,2;‘y’ is 1,2,4;‘z’ is 4,8 and wherein y>x is in an amount ranging from l-30%w/w. Preferably, the NCS is N1C02S4.

The carbon based material has surface area of atleast l000m ² /g, which improves upon the mobility of the ions and increases the charge density. The carbon based material in the anodic composite is present in an amount ranging from 1-50% w/w.

In an aspect of the present composition, N1C02S4 (NCS) to carbon based material is preferably in the ratio 1 : 4, most preferably 1 :2.

The molten salt electrolyte of the present invention is chemically and electrochemically stable and is compatible to the anodic material of NCS and carbon of the present invention and is operable at varying proportion of the anodic material and at temperature ranging from (-)20°C to (+)80°C.

In yet another aspect, the present invention provides the composition for energy storage device comprising;

i. NiCo2S4(NCS) and carbon based material selected from high surface area activated carbon or reduced graphene oxide (rGO) or functionalized carbon nitride (g-CN) in the ratio ranging between 1-50% (NCS) : 50-99% (carbon based material) as anode composite; with

ii. an electrolyte of molten imidazolium salt of general formula I,

x

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen or alkyl groups having 1 to 6 carbon atoms,‘X’ represents an anion of the group tetrafluoroborate, triflate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate or bis(Fluorosulfonyl)imide;

wherein the said composition improves the capacitance and cyclic stability of the energy storage device.

The composition further comprises conductive additives selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks, graphite in an amount ranging from 0. l-5%w/w.

In another aspect, the present invention provides a process for preparation of the anodic composite of the composition comprising the steps of;

i. preparing NCS of formula NixCoySz wherein‘x’ is 1,2;‘y’ is 1,2,4 and‘z’ is 4,8; wherein y>x, by solvothermal process;

ii. preparing high surface area carbon by two-step pyrolysis with conductive additives and in presence of activating agent; and

iii. forming the composite of NCS and high surface area carbon by pulverizing the respective components of step (i) and step (ii) in suitable ratio. In an aspect, the molar concentration of the precursors depend on the x:y ratio of NixCoySz wherein is 1,2;‘y’ is 1,2,4 and wherein y>x.

The nickel precursor for step (i) is selected from nickel salts such as nitrates, chlorides, acetates, sulfates, nitrites, oxides, carbonates, oxalates or persulfates in molar concentration of 5-50mM; the cobalt precursors are selected from the salts such as nitrates, chlorides, acetates, sulfates, nitrites, oxides, carbonates, oxalates or persulfates in molar concentration of 5-50mM; the sulphur source is selected from a group consisting of thiourea, sodium sulphides, mercaptopropionic acid, sulphur, thiosulphates, sulphites, L-cysteine or sodium diethyldithiocarbamate (na- DTC) thereof.

The solvent for step (i) is selected from polar or non-polar, protic or aprotic solvents such as ethanol, water, ethylene glycol, polyethylene glycol, DMF, DMSO and such like or mixtures thereof.

The temperature for solvothermal process of step (i) is maintained between l00°C- 200°C.

The carbon precursor in step (ii) is selected from a group consisting of cellulose, lignin, carbohydrates such as glucose, starch, galactose, fructose or lactose, microcrystalline cellulose or cellulose acetate.

The two-step pyrolysis is carried out in presence of activating agent selected from a group consisting of inorganic salts, hydroxides, acids such as KOH, ZnCb, FeCb, MgCb, CaCb, H3PO3 and such like.

The conductive additives selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks or graphite.

The ratio of the carbon precursor(Z): additive (m): activating agent (n) in step (ii) of the process is 1-3 :0.1-0.3 : 1-3. The two step pyrolysis includes (a) the step of calcination at a temperature in the range of 400-500°C for 1-3 hours to obtain raw carbon and (b) pyrolysis of raw carbon at a temperature in the range of 750-950°C for 2-5 hours to obtain high surface area carbon.

The NCS and high surface area (HAS)carbon obtained in step (i) and step (ii) of the process were further pulverized together through various processes consisting of sonication, ball milling, grinding, or shear mixing to form the anodic composite.

The energy storage device of the present invention can be symmetric or asymmetric energy storage devices such as EDLC, supercapacitors or pseudocapacitors.

In yet another aspect, the present invention provides energy storage device with improved cyclic stability and capacitance comprising;

(i) an anode coated with anodic composite of NixCoySz wherein‘x’ is 1,2;‘y’ is 1,2,4 and‘z’ is 4,8; wherein y>x and carbon based material selected from high surface area activated carbon or reduced graphene oxide (rGO) or functionalized carbon nitride (g-CN) in the ratio ranging between l-50%:50-99%;

(ii) a cathode coated with carbonaceous material selected from mesoporous carbon or activated carbon;

(iii) a separator; and

(iv) an electrolyte of molten imidazolium salt of general formula (I)

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen, alkyl groups having 1 to 6 carbon atoms,‘X’ represents an anion of the group tetrafluoroborate, triflate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate or bis(Fluorosulfonyl)imide.

In an aspect, the anodic composite and cathodic material further comprises conductive additives selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks, graphite in an amount ranging from 0. l-5%w/w.

The anode electrodes of the symmetric or asymmetric energy storage device are composed of composite of NixCoySz wherein‘x’ is 1,2;‘y’ is 1,2,4 and‘z’ is 4,8; wherein y>x and carbon based material selected from high surface area activated carbon or reduced graphene oxide (rGO) or functionalized carbon nitride (g-CN) in the ratio 1-50% to 50-99%; preferably in the ratio 1 :4; most preferably in the ratio 1 :2.

The molten salt electrolyte of general formula (I) is compatible with the anodic composite of the present invention, reduces the degradation of the anodic composite as compared to the aqueous electrolyte thereby increases the energy density at wider temperature range, widens the potential window and provides high capacitance of the device.

The composition of the present invention and the device thereof exhibit excellent specific capacitance and cyclic stability. DESCRIPTION OF FIGURES

Fig 1A depicts the specific capacitance of the composition and device thereof

Fig IB depicts the Peak power test of the composition and device thereof

Fig 2 depicts the cyclic stability of the composition and device thereof

Fig 3 depicts the Electrochemical Impedance Spectroscopy (EIS) of the composition and device thereof. Fig 4 depicts the Open circuit potential of the composition and device thereof post charging in Open Circuit voltage test (OCV)

Fig 5 depicts the coulombic efficiency of the composition and device thereof during charge and discharge at constant current.

DETAILED DESCRIPTION OF INVENTION:

The present inventors found that though metal oxides work well with the ionic liquids, however, have low cycling stability and energy storage capacity. After extensive research to improve upon the faradaic reactions, the present invention provides anodic composition of nickel cobalt sulphide (NCS) and carbon based material which is not only compatible with the molten salt electrolyte i.e. imidazolium based ionic liquids (ILs) but is stable for several cycles of charge /discharge without any degradation and has profound influence on widening the potential window and enhancing the capacitance.

Accordingly, the present invention relates to the composition for energy storage device comprising; i. nickel-cobalt-sulphide(NCS) of formula NixCoySz wherein‘x’ is 1,2;‘y’ is 1,2,4;‘z’ is 4,8 and wherein y>x; and

ii. carbon based material selected from high surface area activated carbon or reduced graphene oxide (rGO) or functionalized carbon nitride (g-CN) in the ratio ranging between 1-50% (NCS) : 50-99% (carbon based material)as anode material; together with

iii. an electrolyte of molten imidazolium salt of general formula I,

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen, alkyl groups having 1 to 6 carbon atoms,‘X’ represents an anion of the group tetrafluoroborate, triflate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate or bis(Fluorosulfonyl)imide;

wherein the said composition improves the capacitance and cyclic stability of the energy storage device.

The composition of the present invention further comprises the conductive additives selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks, graphite in an amount ranging from 0.l-5%w/w.

The carbon based material in the present composite has surface area of at least l000m ² /g, which improves upon the mobility of the ions and increases the charge density. The carbon based material in the anodic composite is present in an amount ranging from 1-50% w/w.

The nickel cobalt sulphide (NCS) of general formula NixCoySz wherein‘x’ is 1,2; ‘y’ is 1,2,4;‘z’ is 4,8 and wherein y>x is preferably N1C02S4 present in an amount ranging from l-50%w/w.

In an embodiment of the present invention, the ratio of N1C02S4 (NCS):carbon is preferably in the ratio of 1 :4; most preferably in the ratio 1 :2. The electrolyte of general formula (I) is selected from the group consisting of 1- Ethyl-3-methylimidazolium tetrafluoroborate (C2MiMBF4), l-n-Butyl-3- methylimidazolium tetrafluoroborate (C4MiMBF4), 1 -Ethyl-3 -methylimidazolium bis(trifluoromethylsulfonyl)imide (C2MiMTFSI) or l-Butyl-3- methylimidazolium bis(trifluoromethanesulfonyl (C4MiMTFSI). In an embodiment, the molten imidazolium salt electrolyte of formula (I) of the present invention is solvent free thereby reducing the safety problems associated with the use of volatile and flammable organic solvents at high temperature. Further, the molten imidazolium salt electrolyte of formula (I) is compatible to the anodic material consisting of NCS and Carbon, thereby reducing the degradation of the electrode during charging and discharging and increasing the overall stability of the electrode coated with said anodic material. Further, they are used so that there is ionic/electrical connection between the anode/cathode. The molten salt electrolyte of general formula (I) is operable at varying proportion of the anodic material and at temperature ranging from (-)20°C to (+)80°C.

In another embodiment, the present invention discloses the composition for energy storage device comprising;

i. NiCo2S ₄ (NCS) and carbon based material selected from high surface area activated carbon or reduced graphene oxide (rGO) or functionalized carbon nitride (g-CN) in the ratio ranging between 1-50% (NCS) : 50-99% (carbon based material) together with

ii. an electrolyte of molten imidazolium salt of general formula I,

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen, alkyl groups having 1 to 6 carbon atoms,‘X’ represents an anion of the group tetrafluoroborate, triflate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate or bis(Fluorosulfonyl)imide;

wherein the said composition improves the capacitance and cyclic stability of the energy storage device. The composition further comprises conductive additives selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks, graphite in an amount ranging from 0. l-5%w/w.

The carbon based material has surface area of at least l000m ² /g, preferably in the range of l000m ² /g -l800m ² /g which improves upon the mobility of the ions and increases the charge density which is present in an amount ranging from 1-50% w/w.

The electrolyte of general formula (I) is selected from the group consisting of 1- Ethyl-3-methylimidazolium tetrafluorob orate (C2MiMBF4), l-n-Butyl-3- methylimidazolium tetrafluorob orate (C4MiMBF4), 1 -Ethyl-3 -methylimidazolium bis(trifluoromethylsulfonyl)imide (C2MiMTFSI) or l-Butyl-3- methylimidazolium bis(trifluoromethanesulfonyl (C4MiMTFSI).

In a preferred embodiment, the ratio of N1C02S4 : carbon based material in the composition is 1 :4; most preferably 1 :2.

In yet another embodiment, the present invention relates to a process for preparation of the anodic composite of the composition comprising the steps of;

i. mixing 5-50mM solution of nickel precursors, 5-50mM solution of cobalt precursor and sulphur source in suitable ratio; heating the mixture at temperature in the range of l00-200°C, cooling at the rate varying between ECmin ¹ to 20°C min ¹ to obtain N1C02S4 of varing morphology;

ii. calcining the mixture of carbon precursor, conductive additives and activating agent in the ratio 1-3 :0.1-0.3 : 1-3 to a temperature in the range of 400- 500°C to obtain raw carbon followed by pyrolysis at 750-950°C under inert flow to obtain carbon of surface area of at least l000m ² /gm;

iii. forming the anode composite of NCS and high surface area carbon by pulverizing the respective components of step (i) and step (ii) in suitable ratio. The nickel precursor for step (i) is selected from nickel salts such as nitrates, chlorides, acetates, sulfates, nitrites, oxides, carbonates, oxalates or persulfates in molar concentration of 5-50mM; the cobalt precursors are selected from the salts such as nitrates, chlorides, acetates, sulfates, nitrites, oxides, carbonates, oxalates or persulfates in molar concentration of 5-50mM; the sulphur source is selected from a group consisting of thiourea, sodium sulphides, mercaptopropionic acid, sulphur, thiosulphates, sulphites, L-cysteine or sodium diethyldithiocarbamate (na- DTC) thereof.

The molar concentration of the precursors depend on the x:y ratio of NixCoyS; wherein x=l,2 ; y=l,2,4 and wherein y>x.

The solvent for step (i) is selected from polar or non-polar, protic or aprotic solvents such as ethanol, water, ethylene glycol, polyethylene glycol, DMF, DMSO and such like or mixtures thereof.

The carbon precursor in step (ii) is selected from a group consisting of cellulose, lignin, carbohydrates, glucose, starch, glucose, galactose, fructose, lactose, microcrystalline cellulose or cellulose acetate.

The conductive additive is selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks or graphite.

The two-step pyrolysis is carried out in presence of activating agent selected from a group consisting of inorganic salts, hydroxides, acids such as KOH, ZnCb, FeCb, MgCb, CaCb, H3PO3 and such like.

The NCS and high surface area (HAS)carbon obtained in step (i) and step (ii) of the process are further pulverized together through various processes consisting of sonication, ball milling, grinding, shear mixing, etc to form the desired composite. The NCS: (HAS) carbon can be varied between NCS: l-50% and Carbon: 50-99%; preferably the ratio is 1 :4; most preferably 1 :2 .

In another preferred embodiment, the present invention discloses the composition for energy storage device comprising;

i. NiCo2S ₄ (NCS) and carbon based material with surface area of l000m ² /gm in the ratio ranging between 1-50% (NCS) : 50-99% (carbon based material) as anode composite; together with

ii. molten imidazolium salt of general formula I,

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen, alkyl groups having 1 to 6 carbon atoms,‘X’ represents an anion of the group tetrafluoroborate, triflate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate or bis(Fluorosulfonyl)imide;

wherein the said composition improves the capacitance and cyclic stability of the energy storage device.

The energy storage device of the present invention can be symmetric or asymmetric energy storage devices such as EDLC, supercapacitors or pseudocapacitors.

In yet another embodiment, the present invention discloses energy storage device with improved cyclic stability and capacitance comprising;

(i) an anode coated with anodic material consisting of NixCoySz wherein‘x’ is 1,2; ‘y’ is 1,2,4;‘z’ is 4,8, wherein y>x; and carbon based material selected from high surface area activated carbon or reduced graphene oxide (rGO) or functionalized carbon nitride (g-CN) in the ratio ranging between 1-50%: 50-99%; (ii) a cathode coated with carbonaceous material selected from mesoporous carbon or activated carbon,

(iii) a separator; and

(iv) an electrolyte of molten imidazolium salt of general formula (I);

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen, alkyl groups having 1 to 6 carbon atoms,‘X’ represents an anion of the group tetrafluoroborate, triflate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate or bis(Fluorosulfonyl)imide.

The anodic composite and the cathode material of the present invention further comprises the conductive additives selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks, graphite in an amount ranging from 0.1- 5%w/w.

The carbon based material in the composition of the present invention has a surface area of at least l000m ² /gm. In another embodiment, the present invention discloses pseudocapacitor with improved cyclic stability and capacitance comprising;

(i) an anode coated with N1C02S4 (NCS) and carbon based material selected from of high surface area activated carbon or reduced graphene oxide (rGO) or functionalized carbon nitride (g-CN) in the ratio ranging between 1-50% (NCS) : 50-99% (carbon based material)

(ii) a cathode coated with carbonaceous material selected from mesoporous carbon or activated carbon, (iii) a separator; and

(iv) molten imidazolium salt of general formula I,

wherein Rl, R2, R3, R4 and R5 independently represent hydrogen, alkyl groups having 1 to 6 carbon atoms,‘X’ represents an anion of the group tetrafluoroborate, triflate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate or bis(Fluorosulfonyl)imide.

The anodic composite of the present invention can be formed into an anodic electrode for energy storage device. Accordingly, the process for preparation of the anodic electrodes for energy storage devices comprises;

(i) mixing N1C02S4, high surface carbon based material in fixed proportions , conductive additives , with 5-l0%w/w of carboxymethyl cellulose/ styrene- butadiene rubber (CMC/SBR) binder in water to obtain a slurry;

(ii) coating the slurry of step (i) on to the current collector at 2-4mg/cm ² loading; and

(iii) drying the electrode to remove any trace moisture.

The anodic composite is in the form of powder with a particle size of 25um, which is slurried with a binder and coated on to the electrode (current collector) and dried. The film thickness can vary in the range of lOOum to 250um.

The carbonaceous material can also be assembled to cathodic electrode by a process which comprises;

(i) mixing the carbon based material and the additives in fixed proportions with 5- l0%w/w of carboxymethyl cellulose/ styrene-butadiene rubber (CMC/SBR) binder in water to obtain a slurry; (ii) coating the slurry of step (ii) on to the current collectors at 2-4mg/cm ² loading; and

(iii) drying the electrode to remove any trace moisture. The conductive additives selected from a group consisting of various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks, graphite in an amount ranging from 0. l-5%w/w.

The ratio of the components used for anodic and cathodic electrodes is given below:

The final electrodes have a loading of 2.5mg of active material in anode and 3.75 mg of active material in cathode summing to a total of 6.25mg of active material in the cell.

The cell is constructed by utilizing the said anodic and cathodic electrodes and a microfibre glass separator and the electrodes are dipped into the molten imidazolium salt of formula (I). The cell was allowed to sit for about 12 hours before any electrochemical tests were carried out to allow the electrolyte to fully soak into and wet the electrodes. The electrochemical measurements were carried out on a potentiostat/galvanostat at room temperature(~25C). Soaking the separator ensures that the pores of the separator are completely filled with the electrolyte to allow for proper ion conduction.

The composition of the present invention exhibit constant current discharge under various current density. At high current density of 5A/g the specific capacitance of about l30-l33F/g is obtained, at 0.8A/g the specific capacitance exceeds l95F/g (Fig 1A), although the specific capacitance can range significantly depending on the loading of the material, the particle size of the anode material and the film thickness of the electrode.

The composition of the present invention has high power capability even at high current density of 5A/g (Fig IB) without degradation. The composition of the present invention is stable and can be used for about lOOOcycles which is an indication of the enhanced performance of the composition at the high charge/discharge rates for which they are usually adapted (Fig 2). The“Electrochemical Impedance Spectroscopy” (EIS) disclose that the energy storage device with the composition of the present invention show decrease resistance to the small AC current perturbation indicating the high power capability of the device due to high conductance of both the electrolyte and the increased electronic conductivity of the current collectors (Fig 3).

The composition of the present invention is stable with coulombic efficiency of about 95% as shown in Fig 5.

The composition of the present invention is useful as energy supply/ capture devices for wide range of electrical and electronic devices.

The following examples are provided to illustrate the present invention but not to limit the scope of the invention. Example 1: General Method of Preparation of the composite of NiCo2S4 (NCS) + Carbon based material

1(a): Synthesis of NCS

NCS was synthesized through a solvothermal approach. Accordingly, the Nickel precursor was selected from a group consisting of nickel salts like nitrates, chlorides, acetates, sulfates, nitrites, oxides, carbonates, oxalates or persulfates at a molar concentration ranging from 5-50mM. The cobalt precursor was selected from a group consisting of cobalt salts like nitrates, chlorides, acetates, sulfates, nitrites, oxides, carbonates, oxalates or persulfates at a molar concentration ranging from 5-50mM. The sulphur source was provided from a group consisting of thiourea, sodium sulphides, mercaptopropionic acid, sulphur, thiosulphates, sulphites, L-cysteine or Sodium diethyldithiocarbamate(Na-dtc). The molar concentrations for each precursor depended on the‘x’ :‘y’ ratio of NixCoySz (wherein‘x’ is 1,2;‘y’ is 1,2,4 and y>v. The precursors were mixed in a solvent from a group consisting of Ethanol, Water, Ethylene Glycol, Polyethylene Glycol, DMF or DMSO. After mixing via ultrasonication, the mixtures were transferred to a Teflon lined autoclave maintained at temperature in the range of l00-200°C, heating time varying between 3hrs to 48hrs, cooling rates varying between l°C min ¹ to 20°C min ¹ to obtain NCS of varying morphology.

1(b): Synthesis of high surface area activated carbon (HAS carbon) by two- step pyrolysis:

Carbon precursor: Cellulose, lignin, carbohydrates, glucose, starch, glucose, galactose, fructose, lactose, microcrystalline cellulose or cellulose acetate.

Conductive additives: Various forms of graphenes, SWCNTs, MWCNTs, carbon fibres, carbon blacks, lamp blacks, acetylene blacks, furnace blacks or graphites. Activating agent: KOH, ZnCk, FeCb, MgCb, CaCb or H3PO3.

The ratio of carbon (Z) to additive (m)to activating agent (n) was maintained at 1- 3:0. 1 -0.3: 1 -3.

Step 1 : The mixture of the carbon precursor, additive and the activating agent was calcined at a temperature of 450°C for 1-3 hours to obtain raw carbon. Step 2: The raw carbon of step 1 was subjected to pyrolysis at a temperature ranging from 750-950°C under nitrogen or argon flow for 2-5 hours. The obtained carbon was then washed and rinsed repeatedly to obtain final HSA carbon.

1(c): Synthesis of the composite of NCS and carbon

The NCS obtained in 1(a) and the HAS carbon obtained in 1(b) in the ratio varying between 1-50% (NCS) and 50-99% (HAS carbon) were pulverized together through various processes consisting of sonication, ball milling, grinding, shear mixing, etc to form the desired composite.

Example 2: Preparation of the composite of N1C02S4 (NCS) + Carbon based material in the ratio 1:4

2(a): Preparation of N1C02S4

lOmM, 20mmol and 35mmol of nickel nitrate, cobalt nitrate and thiourea respectively were dissolved in ethylene glycol. After complete dissolution the liquid was transferred to a Teflon lined autoclave and kept in an oven for l2hrs at l85°C.

2(b): Preparation of high surface area carbon (HAS carbon)

l8g Cellulose powder, 2g sucrose, 40mg Graphene Oxide, 20g zinc chloride were mixed well in 20ml of water. This slurry/paste was then heated to 425°C for 1 hr to carbonize the materials and dehydrate them. The material was further heated to 700°C to activate the HSAC leading to formation of HSAC with surface area of l000m ² /g.

2(c): Synthesis of the composite:

NCS of example 2(a) and HAS carbon of example 2(b) in the ratio 1 :4 were pulverized together by any of the processes consisting of sonication, ball milling, grinding, or shear mixing to obtain the composite.

Example 3: Preparation of the Electrodes

a: Preparation of Anode Electrode To the mixture of 23.8% NCS, 47.6% HSAC (in the ratio 1 :2) prepared by the process as exemplified in example 1, was added 4.76% carbon black and 4.76% graphite(conductive additive). The composition was then proportionated to accommodate a typical of 4% CMC and 2% SBR binder to the weight of the active materials. Water was then added to obtain a slurry and coated on to the current collector at approximately 3 mg/cm2 loading to obtain the anode The anode was dried at l20°C under vacuum to remove any trace moisture. b: Preparation of Cathode Electrode

To the mixture of 14.2% graphene (previously synthesized), 4.76% g- CN(previously synthesized) was added 4.76% Carbon Black and 4.76% graphite(conductive additive). The mixture was then proportionated to accommodate a typical of 4% CMC and 2% SBR binder to the weight of the active materials. Water was then added to obtain a slurry and coated on to the current collector at 3 mg/cm2 loading to obtain the cathode. The cathode was dried at l20°C under vacuum to remove any trace moisture.

Example 4: Construction of the cell with two electrode system

Into the molten salt electrolyte, l-ethyl-3-methylimidazolium Tetrafluoroborate, were inserted the anode and cathode electrode of example 3a and 3b respectively. Microfibre glass separator was inserted between the electrodes. The cell was allowed to sit for 12 hours before any electrochemical tests were carried out to allow the electrolyte to fully soak into and wet the electrodes. The electrochemical measurements were then carried out on a potentiostat/galvanostat at room temperature of 25°C.

Example 5: Electrochemical Measurements:

1 Specific Capacitance: The electrochemical properties of the electrode coated with anodic composite together with the electrolyte , such as 1 -ethyl-3 -methylimidazolium Tetrafluorob orate, in the cell disclosed in example 4 was evaluated for its specific capacitance under various current densities as depicted in Fig 1(A) and Table 2 below:

As can be seen from Fig 1 and Table 2 maximum capacitance is attained at 0.8A/g and the high capacitance of 132.69 F/g is retained even at high current density of 5A/g.

Further, high practical power capability of the anodic composite together with the electrolyte was observed by the peak power test as shown in Fig 1(B) and Table 3: Table 3:

(ii) Cyclic Stability:

The composite together with the electrolyte of the present invention was subjected to cyclic voltammetry to determine the stability of the composition. Capacity retention was observed by doing multiple GCD cycles and testing the cyclic voltammetry response of the device at every 500 cycles. A capacity retention of 97% was found even after 1000 cycles as shown in Fig 2 and Table 4 below.

Table 4:

(iii) Electrochemical Impedance Spectroscopy” (EIS)

The composite together with the electrolyte of the present invention show decrease resistance to the small AC current perturbation indicating the high power capability of the device due to high conductance of both the electrolyte and the increased electronic conductivity of the current collectors as shown in Fig 3.

(iv) Open circuit voltage test (OCV):

A no-load open circuit voltage test was done to find the open circuit potential of the device post charging. The device showed an OCV of 2.7V as depicted in Fig 4.

(v): Coulombic Efficiency:

The coulombic efficiency was calculated from the charge discharge graphs.

Coulombic efficiency= Output charge/input Charge

The Charge and Discharge at constant current were compared to find the coulombic efficiency of the device. The device had an initial CE of -90% on the first charge as shown in Fig 5.

Example 5: Comparative study of the energy stored of the present composite vis-a-vis the conventional composite

The energy stored by the composite was calculated by the formula;

Ewh = 0.5 * C * V ² / 3.6 and the result is expressed in wh/kg

Comparative example: Cconv is the capacitance achieved for conventional composite as seen in the cited articles.

Cinv is the capacitance achieved for the current invention.

Cconv = ~l036F/g [In respect to only single NiCo2S4 electrode mass] Cconv =—119 F/g [For fully assembled device with conventional composites]

Cinv = ~l97F/g [For fully assembled device - considering the mass of both the electrodes]

Vconv = 0.6V (KOH electrolyte)

Vinv = 2.7V (Molten Salt Electrolyte, such as 1 -ethyl-3 -methylimidazolium Tetrafluorob orate)

Econv ⁼ 0.5 * 119 * (1.6) ² / 3.6 = 42.3 wh/kg

Emv = 0.5 * 197 * (2.7) ² / 3.6 = 199 wh/kg

It can be seen from this working example that, by utilizing the electrode composite/electrolyte combination of the present invention, a 300% increment in the gravimetric energy stored is realized.

While the present invention has been described in conjunction with a preferred embodiment, one of ordinary skill, after reading the foregoing specification, will be able to effect various changes, substitutions of equivalents, and other alterations to the compositions detailed herein. It is therefore intended that the protection granted by the definitions contained in the appended claims and equivalents thereof.