Description:FIELD OF THE INVENTION

The present disclosure relates to the field of zinc based rechargeable battery. More specifically, the present disclosure relates to a novel composition of cathode for high-efficiency zinc based rechargeable battery and a method of preparation of the composition.

BACKGROUND OF THE INVENTION

In recent years, zinc-based batteries have emerged as highly promising alternatives for large-scale rechargeable energy storage devices. Unlike other commonly used metal anodes like lead, cadmium, and rare metals, zinc is non-toxic, abundant, and cost-effective. Since the mid-19th century, various zinc-based batteries, such as alkaline manganese dioxide (MnO2)-zinc, nickel (Ni)-zinc, silver (Ag)-zinc, and zinc-air batteries have been extensively researched as substitutes for toxic lead-based rechargeable batteries. Zinc-based rechargeable batteries offer compelling advantages, including low cost, environmental friendliness, and excellent specific energy. These features have made them popular primary cells for numerous applications. Their widespread use is driven by their ability to provide efficient and cost-effective energy storage solutions while being environmentally benign.
Zinc-based batteries have very high energy densities that could be very useful for a number of applications like grid-storage, cell phones, electric vehicles and others. In the early 1980s, a rechargeable alkaline Zn/MnO2 (RAM) has been developed. Over the past three decades, the improvement of this technology has progressed rapidly. However, even now the rechargeability of battery based on Zn anode remains a significant challenge. Minakshi M., Singh P., Mitchell D. R.G., Issa T. B., and Prince K., Electrochim. Acta, 52, 7007, Year 2007, shows that the capacity of rechargeable alkaline zinc based rechargeable battery dramatically drops to below 50% or even worse at only 40 cycles, meanwhile the efficiency decreases to below 50%.
Although, alkaline cells zinc-anode batteries have dominated the primary battery market since its invention, however, the rechargeable version has met with only limited success. This is in part due to various problems with short cycle life and electrical shorts that can occur with alkaline cells using zinc anodes.
There are prior arts that disclose certain methods to overcome the poor life cycle of zinc based rechargeable battery such as Chinese patent application CN103996854A, discloses an electrochemical hybrid energy storage device comprising a positive electrode made up of activated carbon, conductive carbon along with fine graphite, an anode that adopts zinc ions, an alkaline electrolyte and a diaphragm. This patent application discloses the use of various concentration of alkaline solution as electrolyte and its behaviour on the efficiency of the battery.
Chinese patent application CN114883704A, discloses a button type zinc-air battery wherein a positive electrode shell is coated with an adhesive, diffusion paper is pasted on an air hole at the bottom of the positive electrode shell, then the bottom of the positive electrode shell is coated with a sealant. The positive electrode is disclosed to be made up of activated carbon, conductive carbon, manganese oxide, catalyst; and polytetrafluoroethylene, wherein the polytetrafluoroethylene ventilated membrane, the catalytic layer anode powder, the conductive nickel net and the diaphragm paper are sequentially placed on a roller press and rolled into a positive plate.
The existing prior art indicates that electrodes are prepared using multiple components or complex compositions. However, these complex compositions fail to achieve high efficiency and stable charge-discharge in zinc-based batteries. Further, the conventional process of preparing activated carbons produces the product with high ash content which decreases the efficiency of the zinc based rechargeable battery. In view of the existing technical problems and unsolved issues in prior known literatures, there is a need for a suitable cathode composition and preparation method, which overcomes the technical problem of how to increase efficiency and discharge capacity of existing zinc-based rechargeable batteries.
SUMMARY OF THE INVENTION

The present invention provides a composition of cathode for a zinc based rechargeable battery and a method of preparation of the composition. The present disclosure provides a solution to the technical problem of how to increase efficiency and battery discharge capacity of the existing zinc-based rechargeable batteries. The present invention provides a high efficiency zinc based rechargeable battery that contains a cathode comprising of activated carbon treated with potassium hydroxide along with conductive carbon and polytetrafluoroethylene as a binder, wherein the preparation method of the cathode for zinc based rechargeable battery is simple and convenient, and said cathode can effectively avoid the chemical reaction caused by the contact of zinc. The use of such potassium hydroxide activated carbon as one of the components in the cathode of the zinc based rechargeable battery improves the discharge performance of the battery.

Accordingly, one aspect of the present invention provides a composition of cathode for zinc based rechargeable battery, wherein said composition comprises about 20 to 80 wt % of potassium hydroxide activated carbon (AC-K), about 19 to 79 wt % of conductive carbon (CB), and about 1.0 wt % of polytetrafluoroethylene (PTFE) as a binder.

The use of cathode made from the improved composition in the zinc-based rechargeable battery increases energy efficiency of the zinc-based rechargeable battery above 80%. Further, the percentages of AC-K, CB and PTFE in the improved composition provides synergistic effect, that is the combination of the elements AC-K, CB and PTFE in the improved composition provides more efficiency than the use of each individual element. In addition, the use of cathode made from the improved composition in the zinc-based rechargeable battery provides stable charge (when voltage increases) and discharge (when voltage decreases) behavior with charge capacity of 25 mAh. Further, the improved composition of the cathode results in high current densities during operational cycles of the zinc-based rechargeable batteries as well as prevents dendrite formation and self-discharge of the conventional zinc-based rechargeable batteries.

It is known that the main challenges of the zinc based rechargeable battery include (a) low current densities during cycling, (b) dendrite formation, (c) self-discharge and (e) poor capacity. It is observed that the use of potassium hydroxide activated carbon (AC-K) in specific weight percentage along with conductive carbon (CB) and polytetrafluoroethylene (PTFE) as a binder in specific combination solves the abovementioned problems. It is observed that above specific combination of potassium hydroxide activated carbon, conductive carbon and polytetrafluoroethylene as a composition of cathode used in zinc based rechargeable battery, shows synergistic effect, i.e., above 80% energy efficiency along with stable charge (when voltage increases) and discharge (when voltage decreases) with charge capacity of 25 mAh of the zinc based rechargeable battery.

In an implementation, the potassium hydroxide activated carbon (AC-K) comprises an activated carbon with potassium hydroxide as activating agent in a mass ratio of 1:5.

The 1:5 ratio of the activated carbon with the potassium hydroxide in the AC-K produces have ash content of less than or equal to 0.11% of total weight of the activated carbon after combustion. Moreover, the use of the potassium hydroxide activated carbon (AC-K) in the improved composition as one of the components of cathode along with conductive carbon (CB) and polytetrafluoroethylene (PTFE) provides a solution to the technical problem of poor efficiency of the zinc based rechargeable battery by reducing the ash content.

In an implementation, the potassium hydroxide activated carbon (AC-K) is present in an amount of 65.5 wt % of the total weight of the composition along with 33.5 wt % of conductive carbon and 1.0 wt % of polytetrafluoroethylene (PTFE) of the total weight of the composition.

The percentages of AC-K, CB and PTFE in 65.5 wt %, 33.5 wt % and 1.0% respectively in the improved composition of the cathode increases efficiency of the zin-based rechargeable battery above 89%. Further, such improved composition provides stable charge (when voltage increases) and discharge (when voltage decreases) with charge capacity of 25 mAh of the zinc based rechargeable battery.

In another aspect, the present disclosure provides a method for preparation of composition of a cathode comprising potassium hydroxide activated carbon (AC-K). The method comprising steps of pyrolyzing charcoal with potassium hydroxide at 700oC to 800oC to obtain pyrolyzed product, cooling and washing the pyrolyzed product with 2M hydrochloric acid and distilled water to obtain a first wet mass. In addition, the method comprises steps of stirring the first wet mass with concentrated hydrochloric acid and distilled water taken in the ratio of 1:1 to obtain second wet mass and washing the second wet mass with distilled water and drying to obtain potassium hydroxide activated carbon (AC-K). Moreover, the method comprising mixing the 20 – 80 wt% of the AC-K with 19 to 79 wt % of conductive carbon (CB), and 1.0 wt % of polytetrafluoroethylene (PTFE) to form a composition of the cathode for the zinc based rechargeable battery.

The method reduces the ash content of the activated carbon less than 0.11% of the total weight of the activated carbon, which increases efficiency of the conventional zinc-based rechargeable battery above 80%. In addition, the use of composition produced by the improved method in the cathode of the conventional zinc-based rechargeable batteries provides stable charge (when voltage increases) and discharge (when voltage decreases) behavior with charge capacity of 25 mAh. Further, the composition of the cathode produced by the improved method results in high current densities during operational cycles of the zinc-based rechargeable batteries as well as prevents dendrite formation and self-discharge of the conventional zinc-based rechargeable batteries.

In an implementation, the pyrolyzing of charcoal is carried out for 3-5 hour at a ramp rate of 5?/min.

In an implementation, the cooling of pyrolyzed product is performed to bring the temperature to room temperature.

In an implementation, the stirring of first wet mass with 1:1 ratio of concentrated hydrochloric acid and water is carried out at about 150 ? for 3-5 hours.

In an implementation, the cathode prepared by process of the present invention is shaped in the form selected from fullerene, carbon nanotube, sheet, graphene, carbon fibre, and carbon foam.

The present invention will now be described in detail with reference to the accompanying drawings. These and other features, aspects and advantages of the present drawings will become better understood when the following detailed description is read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 65.5 wt % of AC-K, 33.5 wt % of CB and 1 wt % PTFE, in accordance with an embodiment of the present disclosure;
FIG. 2 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 20 wt % of AC-K, 79 wt % of CB and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure;
FIG. 3 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 40 wt % of AC-K, 59 wt % of CB and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure;
FIG. 4 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 80 wt % of AC-K, 19 wt % of CB and 1 wt % of PTFE; in accordance with an embodiment of the present disclosure;
FIG. 5 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 90 wt % of AC-K, 9 wt % of CB and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure;
FIG. 6 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 99 wt % of AC-K and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure;
FIG. 7 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 99 wt % of CB and 1 wt % of PTFE; in accordance with an embodiment of the present disclosure;
FIG. 8 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 65.5 wt % of ZnCl2 activated carbon, 33.5 wt % of CB and 1 wt % of PTFE; in accordance with an embodiment of the present disclosure;
FIG. 9 is a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 65.5 wt % of AC-K, 33.5 wt % of Graphite and 1 wt % of PTFE; in accordance with an embodiment of the present disclosure;
FIG. 10A is a diagram illustrating charge-discharge profile of a zinc based rechargeable battery with cathode comprising AC-K; in accordance with an embodiment of the present disclosure;
FIG. 10B is a diagram illustrating charge-discharge profile of zinc based rechargeable battery with cathode comprising inactivated carbon; in accordance with an embodiment of the present disclosure;
FIG. 11 is a diagram illustrating a flow chart of a method of preparing a composition of cathode comprising potassium hydroxide activated carbon (AC-K), in accordance with an embodiment of the present disclosure;
FIG. 12 is a diagram illustrating a flowchart of a method of preparing AC-K isolated with ash content of as less as 0.11%, in accordance with an embodiment of the present disclosure; and
FIG. 13 is a diagram illustrating flow chart of a method of determining the ash in potassium hydroxide activated carbon, in accordance with an embodiment of the present disclosure.

For the purpose of better understanding of the invention, reference will now be made to the embodiments or implementations. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further application of the scope of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Reference throughout this specification to “one aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment/implementation is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “one embodiment”, “another embodiment” and similar language throughout this specification, may but not necessarily, all refer to the same embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the disclosure provide a composition of cathode for high-efficiency zinc based rechargeable battery and a method of preparation of the composition, wherein said composition comprises potassium hydroxide activated carbon (AC-K) in specific amounts along with other components such as specific amounts of conductive carbon (CB) and polytetrafluoroethylene (PTFE).

In one example, the prior art literature provides zinc-based rechargeable battery containing a cathode which comprises of multiple components or are made by tedious and complex processes. Prior art teaches to prepare the cathode by using graphite and/or anode powder as catalyst as one of the part of the composition of the cathode. Several experimentations were performed using graphite or zinc chloride as one of the major components of the composition. The zinc-based rechargeable battery containing cathodes of said compositions are observed to be less efficient, and hence are not suitable for the zinc based rechargeable battery.

The present invention provides a composition of cathode which includes specific combination of components including potassium hydroxide activated carbon (AC-K), conductive carbon (CB) and polytetrafluoroethylene (PTFE). It is observed that a particular combination of components plays important role on the overall efficiency of the zinc-based rechargeable battery. In the present disclosure, several experiments were conducted wherein various combinations were analysed. It is observed that when conductive carbon (CB) is not used in the cathode, the zinc-based rechargeable battery shows low efficiency of 60%. Although charging is observed to be stable, zinc-based rechargeable battery shows unstable discharging with poor discharge capacity and high resistance (charging overpotential) with charge capacity lesser than 25 mAh. Similarly, when potassium hydroxide activated carbon (AC-K) is not used, the efficiency is observed to fall drastically.

In yet another example, the prior art teaches to prepare various kinds of activated carbons. Various processes for preparation of potassium hydroxide activated carbons are known from the literature, however they produce the desired product with high ash content which decreases the efficiency of the zinc based rechargeable battery. There are certain literatures that teach the process of preparing activated carbons; however such activation of carbon via physical or chemical methods produces activated carbons having ash content of as high as 1.5 wt % of total weight of the activated carbon.

To overcome at least the technical problems discussed in the above examples and increase performance of the zinc based rechargeable battery, in one aspect of the present invention, an improved composition of cathode is provided for high-performance of zinc based rechargeable battery.

Accordingly, there is provided a composition of cathode for zinc based rechargeable battery, wherein said composition includes of about 20 to 80 wt % of potassium hydroxide activated carbon (AC-K), about 19 to 79 wt % of conductive carbon (CB), and about 1.0 wt % of polytetrafluoroethylene (PTFE) as a binder.

The activated carbons are known to be highly porous and activation of the activated carbon with potassium hydroxide further results in enhancing the specific surface area and inducing high porosities. The conductive carbon (CB) used in the composition of the cathode of the present disclosure is a powder including finely ground carbon additives and is used to improve the conductivity and performance of zinc based rechargeable battery. The use of conductive carbon (CB) in the amount of 19 to 79 wt % along with the amount of 20 to 80 wt % of potassium hydroxide activated carbon (AC-K) and 1.0 wt% of polytetrafluoroethylene (PTFE) improves the energy efficiency of the zinc-based rechargeable battery by about 80-89%. The polytetrafluoroethylene (PTFE) component of cathode of the present disclosure is used as a binder that improves the electrochemical performance of the cathode in the zinc based rechargeable battery. The PTFE is electrochemically stable, chemically inert and corresponding use as binder provides stability to the cathode of zinc based rechargeable battery resulting into excellent performance of the battery as a whole.

In a specific implementation, the present disclosure provides a composition of the cathode in the zinc-based rechargeable battery, in accordance with a different embodiment of the present disclosure. The composition includes the potassium hydroxide activated carbon (AC-K) present in an amount of 65.5 wt % of the total weight of the composition along with 33.5 wt % of conductive carbon and 1.0 wt % of polytetrafluoroethylene (PTFE) of the total weight of the composition. This implementation of the composition manifests further synergetic effects, i.e., 89% energy efficiency of the zinc-based rechargeable battery. In contrast, by replacing conductive carbon with graphite keeping all other components same with similar weight percentages, it is observed that battery shows low efficiency of 48%. Although charging is stable however, the zinc-based rechargeable battery shows unstable discharging with poor discharge capacity and high resistance (charging overpotential) wherein, the charge capacity is observed to be lesser than 25 mAh.

In another example, when potassium hydroxide activated carbon (AC-K) is not used as part of the composition, the zinc-based rechargeable battery shows low energy efficiency of 55%. The prior art teaches several compositions of the cathode; however the known compositions of cathode are either complex or do not provide sufficiently good results. The cathodes with agents other than potassium hydroxide activated carbon (AC-K) were analyzed such as cathodes containing 65.5 wt % of ZnCl2 activated carbon, 33.5 wt % of conductive carbon (CB) and 1 wt % of polytetrafluoroethylene (PTFE) of the total weight of the composition. Herein, it is observed that battery containing cathode comprising zinc chloride activated carbon instead of potassium hydroxide activated carbon with similar weight percentages, shows low efficiency of 57%. The above illustrations, clearly indicates the impact of the amounts of specific combination of components used in the cathode of zinc based rechargeable battery.

The main challenges of the zinc based rechargeable battery include (a) low current densities during cycling, (b) dendrite formation, (c) self-discharge and (e) poor capacity. The use of potassium hydroxide activated carbon (AC-K) in specific weight percentages in a particular combination with other components, especially specific weight percentages of conductive carbon also known as conductive black and is referred as CB, has dealt and solved the above mentioned problems. During experimentation, a more surprising effect was found that works specifically at a specific and optimized weight percentages of the potassium hydroxide activated carbon (AC-K), conductive carbon (CB) and polytetrafluoroethylene (PTFE). Surprisingly, an enhanced technical effect is obtained when the potassium hydroxide activated carbon (AC-K) is present in an amount of 65.5 wt % of the total weight of the composition along with specific amounts of 33.5 wt % of conductive carbon (CB) of the total weight of the composition and 1.0 wt % of polytetrafluoroethylene (PTFE) of the total weight of the composition. It is observed that above specific combination containing cathode provides 89% efficiency along with stable charge (when voltage increases) and discharge (when voltage decreases) with charge capacity of 25 mAh of the zinc based rechargeable battery.

In accordance with an embodiment, the AC-K includes an activated carbon with potassium hydroxide as activating agent in a mass ratio of 1:5. The said ratio of activated carbon with potassium hydroxide provides potassium hydroxide activated carbon with ash content of less than equal to 0.11% of total weight of the activated carbon.

Generally, the zinc based rechargeable battery contains anode that adopts zinc ions, an alkaline electrolyte solution and a membrane or filter along with the cathode. As discussed above, the present disclosure provides specific composition of cathodic electrode by mixing potassium hydroxide activated carbon (AC-K), conductive carbon (CB) and polytetrafluoroethylene (PTFE). the potassium hydroxide activated carbon includes ash content equals to or less than 0.15 wt % of the total amount of activated carbon. The prior art provides various chemical and physical method for preparing activated carbons, however the activated carbons produced by the conventional methods includes the ash content which is as high as 1.5 wt %, which decreases the efficiency of the zinc based rechargeable battery.

Beneficially as compared to conventional approaches, the present disclosure provides a method for preparing potassium hydroxide activated carbon (AC-K). The method provides the activated carbon with ash content as less as 0.11 wt % of total amount of the activated carbon. The method includes steps of activating powdered charcoal/ carbon with potassium hydroxide as the activating agent, pyrolyzing the powdered charcoal/ carbon to obtain a pyrolyzed product and washing the pyrolyzed product thoroughly with 2 M hydrochloric acid and distilled water. Further, the method includes stirring the pyrolyzed product in 1:1 ratio of concentrated hydrochloric acid and distilled water, and filtering and washing with water to reduce the ash content from 3% to 0.11%..

Accordingly, in another implementation of the invention, the present disclosure provides a method for preparation of composition of the cathode in a zinc based rechargeable battery. comprising the steps of:
a) pyrolyzing charcoal with potassium hydroxide at 700oC to 800oC to obtain a pyrolyzed product;
b) cooling and washing the pyrolyzed product with 2M hydrochloric acid and distilled water to obtain a first wet mass;
c) stirring the first wet mass with concentrated hydrochloric acid and distilled water taken in the ratio of 1:1 to obtain a second wet mass; and
d) washing the second wet mass with distilled water and drying to obtain potassium hydroxide activated carbon (AC-K); and
e) mixing the 20 – 80 wt% of the AC-K with 19 to 79 wt % of conductive carbon (CB), and 1.0 wt % of polytetrafluoroethylene (PTFE) to form a composition of the cathode for the zinc based rechargeable battery.

In an implementation, the pyrolyzing of charcoal is carried out for 3-5 hour at a ramp rate of 5?/min to get pyrolyzed product which is then cooled to bring the reaction temperature to room temperature. The washing of pyrolyzed product with 2M hydrochloric acid and distilled water helps in removing potassium metal and unreacted potassium hydroxide from the carbon. The washing of pyrolyzed product with 2M hydrochloric acid and distilled water provides a first wet mass, which after washing with 1:1 concentrated hydrochloric acid and distilled water provides a second wet mass. Herein, the washing of the first wet mass with 1:1 concentrated hydrochloric acid and distilled water helps in removal of the acid soluble ash content from carbon. The second wet mass on drying provides potassium hydroxide activated carbon (AC-K) which contains ash content of as less as 0.11%.

The activation of carbon results into enhancing the specific surface area and inducing high porosities. Higher the surface area and pore volume, stable the behaviour of the battery during numerous cycles. A proper surface area not only ensures the stability towards degradation, but also improves columbic efficiency. Use of such activated carbon in cathode effects overall efficiency of the battery. From experimental results, it is observed that in case the potassium hydroxide activated carbon is used in the amounts of 66.5 wt % of the total weight of the composition along with other components, the battery shows a higher energy efficiency of 89% with coulombic efficiency of 94%.

Some additional advantages of the cathode of the present invention are: a) cost-effective, energy-efficient and scalable process in cathode production; b) eco-friendly and non-toxic cathode composition; c) non-flammable cathode composition; d) suitable for zinc based rechargeable battery which are not prone to overheating and are applicable for a range varying from electric vehicles to grid storage; and e) the cathodic composition of the present invention can also be used for energy storage, carbon capture, H2 storage, sensing, and drug delivery.

In an implementation, the cathode is shaped in the form selected from fullerene, carbon nanotube, sheet, graphene, carbon fiber, and carbon foam.

In a preferred implementation, when the cathode composition includes 65.5 wt % of potassium hydroxide activated carbon, 33.5 wt % of conductive carbon and 1 wt % of polytetrafluoroethylene, the said cathode in a surprising effect, provides stability to the zinc-based rechargeable battery and the zinc-based rechargeable battery in turn shows high energy efficiency of 89% at C/5 rate (i.e. at a 5 hour charging rate) and coulombic efficiency of 94% was achieved.

The present disclosure will now be described in detail with reference to examples.

EXAMPLES
Example 1: Method of preparation of potassium hydroxide activated carbon
1g of commercially available charcoal was grounded with 5g of potassium hydroxide in a mortar and pestle. The powdered mixture was then transferred to an alumina crucible and inserted into a tube furnace. Thereafter, the compound was pyrolyzed at 750 ? for 1 hour at a ramp rate of 5 ?/ min in an inert atmosphere. After cooling down to room temperature, the pyrolyzed product was taken out from the furnace and washed thoroughly with 500 mL of 2 M hydrochloric acid followed by distilled water to remove potassium metal and unreacted potassium hydroxide from the carbon. After this step, the sample was again stirred in a mixture of 100 mL of 1:1 concentrated hydrochloric acid and distilled water for 5 hours at about 150 ? to remove the acid soluble ash content from carbon. Finally, it was washed with copious amounts of distilled water to remove the acid and then dried at 100 ? for 24 hours to obtain the final product.

Example 2: General Process for the preparation of cathode electrode sheets
A solvent consisting of 8-12 mL of 80% de-ionized water and 20% isopropanol was taken and polytetrafluoroethylene (PTFE) was added to it and stirred. Thereafter, a mixture of potassium hydroxide activated carbon (AC-K) and conductive carbon (CB) was added to the solvent. It was then dried at 100 ? for about 1 hour and then mixed with approx. 3 mL of isopropanol per gram of solid mixture and then roller pressed to obtain a thickness of 2 mm.

Table 1: Various compositions containing mixture of potassium hydroxide activated carbon (AC-K), conductive carbon (CB) and polytetrafluoroethylene (PTFE)

Example Number AC-K: CB: PTFE (in wt %) AC-K (g) CB (g) PTFE (µL)
2a 65.5:33.5:1 1 0.511 15
2b 40:59:1 0.678 1 17
2c 20:79:1 0.253 1 13

Example 3: Preparation method of ZnCl2 activated carbon
1g of commercially available charcoal was mixed with 5g of ZnCl2. The powdered mixture was then transferred to an alumina crucible and inserted into a tube furnace. Thereafter, the sample was pyrolyzed at 950 ? for 1 hour at a ramp rate of 5?/ min in an inert atmosphere. After cooling down to room temperature, the pyrolyzed compound was taken out from the furnace and stirred in a mixture of 100 mL of 1:1 concentrated hydrochloric acid and distilled water for 5 hours at 150 ? to remove the acid soluble ash content from carbon. Zinc boils off at about 900 ?, therefore acid washing step is not required. Finally, it was washed with copious amounts of distilled water to remove the acid and then dried at 100 ? for about 24 hours to obtain the final product.

Example 4: Method for the preparation of composition comprising 66.5 wt % of Zinc chloride activated carbon, 33.5 wt % of conductive carbon (CB) and 1.0 wt % of polytetrafluoroethylene (PTFE)
A solvent consisting of 8-12 mL of 80% de-ionized water and 20% isopropanol was taken and 15 µL of polytetrafluoroethylene (PTFE) was added to it and stirred. Thereafter, a mixture 1g of ZnCl2 activated carbon and 0.511 g of conductive carbon was added to the solvent. It was then dried at 100 ? for about 1 hour and then mixed with approx. 3 mL isopropanol per gram of solid mixture and then roller pressed to obtain a thickness of 2 mm.

Example 5: Process for the preparation of composition comprising 66.5 wt % of potassium hydroxide activated carbon (AC-K), 33.5 wt % of graphite and 1.0 wt % of polytetrafluoroethylene (PTFE)
A solvent consisting of 8-12 mL of 80% de-ionized water and 20% isopropanol was taken and 15 µL of polytetrafluoroethylene (PTFE) was added to it and stirred. Thereafter, a mixture 1g of potassium hydroxide activated carbon (AC-K) and 0.511 g of graphite was added to the solvent. It was then dried at 100 ? for about 1 hour and then mixed with approx. 3 mL isopropanol per gram of solid mixture and then roller pressed to obtain a thickness of 2 mm.

Example 6: Procedure for the removal of ash
An empty crucible was kept inside a muffle furnace at 650 ? for 1 hour. After this, the crucible was kept inside a desiccator and allowed to cool to room temperature. The crucible was then weighed which was equal to 165.435g. After this, a measured weight of dried potassium hydroxide activated carbon (AC-K) was placed in the empty crucible and weighed again which was equals to 168.327g. The crucible containing dried potassium hydroxide activated carbon (AC-K) was placed inside the muffle furnace at 650 ? for about 12 hours. Taken out the crucible from muffle furnace and kept inside a desiccator and allowed to cool to room temperature. After cooling down the above crucible, the crucible and ash content was weighed which was equal to 165.438g.
Herein, the percentage of ash content is given by [(165.438-165.435)/(168.327-165.435)]]*100 = 0.1%

RESULTS
Now, referring to FIG. 1, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 65.5 wt % of AC-K, 33.5 wt % of CB and 1 wt % PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, there is shown a zinc-based rechargeable battery 104 having a cathode 102. Further, there is shown a graphical representation 106 indicating the performance of the zinc-based rechargeable battery 104 due to the above mentioned specific composition of the AC-K, CB and PTFE. The graphical representation shows an energy efficiency of the the zinc-based rechargeable battery 104containing the cathode 102 including composition of Example 2 in zinc based rechargeable battery. In this case, the composition of the cathode 102 specified in Example 2a was 65.5 wt % of potassium hydroxide activated carbon (AC-K), 33.5 wt % of conductive carbon (CB) and 1 wt % of polytetrafluoroethylene (PTFE). Herein, the zinc-based rechargeable battery battery 104 showed 89% of efficiency and stable charge (when voltage increases) and discharge (when voltage decreases) with charge capacity of 25 mAh. The cathode 102 was used for the zinc based rechargeable battery 104 wherein said zinc based rechargeable battery 104 finds application for energy storage and can be used, for example, in electric vehicles, home appliances, grid storage, etc. The cathode 102 is a part of the zinc based rechargeable battery 104. It is to be understood that the zinc based rechargeable battery 104 includes various other components, like anode, electrolyte etc, not shown for the sake of brevity.

In an implementation, the cathode 102 manifested steady coulombic efficiency of greater than equal to 94%, throughout the cycles indicating efficient participation of the redox couples within the applied voltage range.

Referring to FIG. 2, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 20 wt % of AC-K, 79 wt % of CB and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 2, there is shown the zinc-based rechargeable battery 104 having a cathode 102A. Further, there is shown a graphical representation 108 indicating the performance of the zinc-based rechargeable battery 104 due to the above mentioned specific composition of the AC-K, CB and PTFE. The graphical representation shows an energy efficiency of battery 104 containing cathode 102A comprising composition of Example 2 in zinc based rechargeable battery 104. In such a case, the composition of the cathode 102A specified in Example 2, was 20 wt % of potassium hydroxide activated carbon (AC-K), 79 wt % of conductive carbon (CB) and 1 wt % of polytetrafluoroethylene (PTFE). Herein, the zinc based rechargeable battery 104 showed 82% efficiency and stable charge (when voltage increases) and discharge (when voltage decreases) with charge capacity of 25 mAh. The cathode 102A is used for the zinc based rechargeable battery 104. From experimental data, it is observed that reduction in amount of potassium hydroxide activated carbon and/or increase in weight percentage of conductive carbon, affects the efficiency of the zinc-based rechargeable battery 104 wherein, when potassium hydroxide activated carbon was reduced from 66.5 to 20 wt %, and conductive carbon was increased from 33.5 to 79 wt %, the efficiency is observed to decline by 6%.

Referring to FIG. 3, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 40 wt % of AC-K, 59 wt % of CB and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 3, there is shown the zinc-based rechargeable battery 104 having a cathode 102B. Further, there is shown a graphical representation 110 indicating the performance of the zinc-based rechargeable battery 104 due to the above-mentioned specific composition of the AC-K, CB and PTFE. The graphical representation 110 shows an energy efficiency of battery 104 containing cathode 102B including composition of Example 2 in the zinc based rechargeable battery 104. In this case, the composition of the cathode specified in Example 2 was 40 wt % of potassium hydroxide activated carbon (AC-K), 59 wt % of conductive carbon (CB) and 1 wt % of polytetrafluoroethylene (PTFE). Herein, the zinc based rechargeable battery 104 showed 85% efficiency and stable charge (when voltage increases) and discharge (when voltage decreases) with charge capacity of 25 mAh when the cathode 102B is used for the zinc based rechargeable battery 104. It is observed that a slight increase in amount of potassium hydroxide activated carbon from 20 wt % to 40 wt %, and decrease in amount of conductive carbon from 79 to 59 wt %, increases the efficiency of battery by 3%.

Referring to FIG. 4, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 80 wt % of AC-K, 19 wt % of CB and 1 wt % of PTFE; in accordance with an embodiment of the present disclosure. With reference to FIG. 4, there is shown the zinc-based rechargeable battery 104 having a cathode 102C. Further, there is shown a graphical representation 112 indicating the performance of the zinc-based rechargeable battery 104 due to the above-mentioned specific composition of the AC-K, CB and PTFE. Further, the graphical representation 112 shows an energy efficiency of the zinc-based rechargeable battery 104 containing the cathode 102C including the composition of Example 2 in the zinc based rechargeable battery 104. In such case, the composition of the cathode 102C was 80 wt % of potassium hydroxide activated carbon (AC-K), 19 wt % of conductive carbon (CB) and 1 wt % of polytetrafluoroethylene (PTFE). Herein, the zinc based rechargeable battery 104 showed 80% efficiency and stable charge (when voltage increases) and discharge (when voltage decreases) with charge capacity of 25 mAh when cathode 102C is used for the zinc based rechargeable battery 104. Herein, it is observed that increase in amount of potassium hydroxide activated carbon from 66.5 to 80 wt %, and decrease in amount of conductive carbon from 33.5 to 19 wt %, negatively affects the efficiency of battery wherein, the efficiency is observed to decline slightly from 89% to 80%.

Referring to FIG. 5, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 90 wt % of AC-K, 9 wt % of CB and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 4, there is shown the zinc-based rechargeable battery 104 having a cathode 102D. Further, there is shown a graphical representation 114 indicating the performance of the zinc-based rechargeable battery 104 due to the above-mentioned specific composition of the AC-K, CB and PTFE. The graphical representation 114 shows an energy efficiency of the zinc-based rechargeable battery 104 containing cathode 102D comprising composition of Example 2 in zinc based rechargeable battery 104. In this case, the composition of the cathode was 90 wt % of potassium hydroxide activated carbon (AC-K), 9 wt % of conductive carbon (CB) and 1 wt % of polytetrafluoroethylene (PTFE). Herein, the zinc-based rechargeable battery 104 showed 58% efficiency and poor discharge capacity with high resistance (charging overpotential) when the cathode 102D is used in zinc based rechargeable battery 104. Herein, it is observed that further increase in weight percentages of potassium hydroxide activated carbon from 66.5 wt % to 90 wt %, and further decrease in weight percentages of conductive carbon from 33.5 to 9 wt %, drastically reduces the efficiency of battery wherein, the efficiency is observed to decline from 89% to 58%.

In an implementation, the specific weight percentage of components of composition i.e., potassium hydroxide activated carbon and conductive carbon, plays a vital role toward the efficiency of the battery. It is observed that when the weight percentage of potassium hydroxide activated carbon is increased drastically above 70 wt %, along with inverse change in weight percentages of conductive carbon, maintaining overall weight of the composition same, there is negative impact on the overall efficiency of the battery, which drastically decline and hence such compositions are found to be not suitable for use in cathodes of zinc based rechargeable battery. Similarly, it is observed in reverse case scenario, when the weight percentages of potassium hydroxide activated carbon is decreased drastically from 35 wt %, along with inverse change in weight percentages of conductive carbon, maintaining overall weight of the composition same, there is negative impact on the overall efficiency of the battery, which is decreased, and hence such compositions are found to be not suitable for use in cathodes of zinc based rechargeable battery.

Referring to FIG. 6, , there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 99 wt % of AC-K and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 4, there is shown the zinc-based rechargeable battery 104 having a cathode 102E. Further, there is shown a graphical representation 116 indicating the performance of the zinc-based rechargeable battery 104 due to the above-mentioned specific composition of the AC-K, CB and PTFE. The graphical representation shows an energy efficiency of the zinc-based rechargeable battery 104 containing cathode 102E comprising only potassium hydroxide activated carbon (AC-K), and polytetrafluoroethylene (PTFE), wherein potassium hydroxide activated carbon is present in an amount of 99 wt % and polytetrafluoroethylene is present in an amount of 1 wt % of the total amount of the composition. Herein, the zinc-based rechargeable battery 104 showed 60% efficiency. Although, the zinc-based rechargeable battery 104 showed stable charging, there is observed and unstable discharging with poor discharge capacity and high resistance (charging overpotential). Moreover, the charge capacity is observed to be less than 25 mAh when cathode 102E is used in zinc based rechargeable battery 104. Herein, it is observed that not only the weight percentages play a vital role towards the efficiency of the battery, but the specific combination is also equally crucial, showing synergistic effect. Herein, when one of the major components of the composition is removed, i.e., conductive carbon is not added to the composition, the battery shows poor efficiency.

Similarly Referring to FIG. 7, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 99 wt % of AC-K and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 7, there is shown the zinc-based rechargeable battery 104 having a cathode 102F. Further, there is shown a graphical representation 118 indicating the performance of the zinc-based rechargeable battery 104 due to the above-mentioned specific composition of the AC-K, CB and PTFE. The graphical representation shows an energy efficiency of the zinc-based rechargeable battery 104 containing the cathode 102F including only conductive carbon (CB) and polytetrafluoroethylene (PTFE) with no potassium hydroxide activated carbon. Further, the conductive carbon is present in an amount of 99 wt % and polytetrafluoroethylene is present in an amount of 1 wt % of the total amount of the composition. Herein, the zinc-based rechargeable battery 104 showed 55% efficiency. Although, the zinc-based rechargeable battery 104 showed stable charging, there is observed an unstable discharging with poor discharge capacity and high resistance (charging overpotential). Moreover, the charge capacity is observed to be less than 25 mAh when cathode 102F is used in zinc based rechargeable battery 104. Herein, the observation that not only the weight percentages play a vital role towards the efficiency of the battery, but the specific combination is also equally crucial, showing synergistic effect is affirmed. Herein, when one another major component of the composition is removed, i.e., potassium hydroxide activated carbon is not added to the composition, the battery shows poor efficiency.

In an implementation, the three components of the battery show synergistic effect wherein, removal of even one of the components, pose a negative impact on the overall efficiency of the battery.

Now, Referring to FIG. 8, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 65.5 wt % of ZnCl2 activated carbon, 33.5 wt % of CB and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 8, there is shown the zinc-based rechargeable battery 104 having a cathode 102G. Further, there is shown a graphical representation 120 indicating the performance of the zinc-based rechargeable battery 104 due to the above-mentioned specific composition of the AC-K, CB and PTFE. The graphical representation 120 shows an energy efficiency of zinc-based rechargeable battery 104 containing the cathode 102G including the composition of Example 4 in zinc based rechargeable battery 104. In such case, the composition of the cathode includes 65.5 wt % of ZnCl2 activated carbon instead of potassium hydroxide activated carbon, 33.5 wt % of conductive carbon (CB), and 1 wt % of polytetrafluoroethylene (PTFE). Herein, the zinc based rechargeable battery 104 shows 57% efficiency. Although, the zinc based rechargeable battery 104 shows stable charging, there is observed an unstable discharging with poor discharge capacity and high resistance (charging overpotential). Moreover, the charge capacity is observed to be less than 25 mAh when cathode 102G is used in zinc based rechargeable battery 104. Herein, when one the major component of the composition is replaced by other component, i.e., ZnCl2 activated carbon is used instead of potassium hydroxide activated carbon, the battery shows poor efficiency.

Referring to FIG. 9, there is shown a diagram illustrating the performance of a zinc-based rechargeable battery due to a cathode made of a composition containing 65.5 wt % of AC-K, 33.5 wt % of Graphite and 1 wt % of PTFE, in accordance with an embodiment of the present disclosure. With reference to FIG. 9, there is shown the zinc-based rechargeable battery 104 having a cathode 102H. Further, there is shown a graphical representation 122 indicating the performance of the zinc-based rechargeable battery 104 due to the above-mentioned specific composition of the AC-K, CB and PTFE. The graphical representation 122 shows an energy efficiency of the zinc-based rechargeable battery 104 containing the cathode 102H including the composition of Example 5 in the zinc based rechargeable battery 104. In this case, the composition of the cathode 102H includes 65.5 wt % of potassium hydroxide activated carbon (AC-K), 33.5 wt % of graphite instead of conductive carbon, and 1 wt % of polytetrafluoroethylene (PTFE). Herein, the zinc based rechargeable battery 104showed 48% efficiency. Although, the zinc based rechargeable battery 104 showed stable charging, there is observed and unstable discharging with poor discharge capacity and high resistance (charging overpotential). Moreover, the charge capacity is observed to be less than 25 mAh when cathode 102H is used in zinc based rechargeable battery 104. Herein, it is affirmed that when one the major component of the composition is replaced by other component, i.e., graphite is used instead of conductive carbon, the battery shows poor efficiency.

In an implementation, the three components of the battery show synergistic affect wherein replacing even one of the two components selected from potassium hydroxide activated carbon, and conductive carbon with any other component, keeping polytetrafluoroethylene unchanged pose negative impact on the overall efficiency of the battery.

FIG. 10A is a diagram illustrating charge-discharge profile of a zinc based rechargeable battery with cathode comprising AC-K; in accordance with an embodiment of the present disclosure. Referring to FIG. 10A, it is observed that zinc based rechargeable battery 104 shows better charge-discharge profile 124 when potassium hydroxide activated carbon (AC-K) is used as one of the component in a cathode 102I. Further, the experimentation was performed wherein instead of potassium hydroxide activated carbon, an inactive carbon was used in the cathode 102J. It showed poor charge-discharge profile of the battery (FIG. 10B). This shows that potassium hydroxide activated carbon in itself plays an important role in overall efficiency of the battery.
FIG. 11 is a diagram illustrating a flow chart of a method of preparing a composition of cathode comprising potassium hydroxide activated carbon (AC-K); in accordance with an embodiment of the present disclosure. Referring to FIG. 11, the present invention further provides a method 1100 of preparaing a composition of cathode comprising potassium hydroxide activated carbon (AC-K). As discussed, various processes for preparation of potassium hydroxide activated carbon are known from the literature, however they produce the desired product with high ash content which decreases the efficiency of the zinc based rechargeable battery. In order to solve the technical problems, following steps were performed:
At step 1102, the method 1100 includes pyrolyzing charcoal with potassium hydroxide at 700oC to 800oC to obtain a pyrolyzed product.
At step 1104, the method 1100 includes cooling and washing the pyrolyzed product with 2M hydrochloric acid and distilled water to obtain a first wet mass.

At step 1106, the method 1100 includes stirring the first wet mass with concentrated hydrochloric acid and distilled water taken in the ratio of 1:1 to obtain second wet mass.
At step 1108, the method 1100 includes washing the second wet mass with distilled water and drying to obtain potassium hydroxide activated carbon (AC-K).

At step 1110, the method 1100 includes washing the second wet mass with distilled water to wash off the acid in order to obtain potassium hydroxide activated carbon (AC-K).

At step 1112, the method 1100 includes mixing the 20 – 80 wt% of the AC-K with 19 to 79 wt % of conductive carbon (CB), and 1.0 wt % of polytetrafluoroethylene (PTFE) to form a composition of the cathode for the zinc based rechargeable battery 104

FIG. 12 is a diagram illustrating a flowchart of a method of preparing AC-K isolated with ash content of as less as 0.11%.in accordance with an embodiment of the present disclosure Referring to FIG. 12, the present disclosure further provides a method 1200 of preparing potassium hydroxide activated carbon (AC-K). As discussed, various processes for preparation of potassium hydroxide activated carbon are known from the literature, however they produce the desired product with high ash content which decreases the efficiency of the zinc based rechargeable battery. In order to solve the technical problems, following steps were performed:

At step 1202, the method 1200 includes grounding the charcoal and mixing it with potassium hydroxide in the ratio of 1:5.

At step 1204, the method 1200 includes pyrolyzing the mixture of step 1202 at 700oC to 800oC to obtain pyrolyzed product.

At step 1206, the method 1200 includes cooling and washing the pyrolyzed product with 2M hydrochloric acid and distilled water to wash off the unreacted potassium metal and unreacted potassium hydroxide from pyrolyzed product and to obtain a first wet mass.
At step 1208, the method 1200 includes stirring the first wet mass with concentrated hydrochloric acid and distilled water taken in the ratio of 1:1 to wash off acid soluble ash from the first wet mass and to obtain a second wet mass.

At step 1210, the method 1200 includes washing the second wet mass with distilled water to wash off the acid in order to obtain potassium hydroxide activated carbon (AC-K).

At step 1212, the method 1200 includes drying the potassium hydroxide activated carbon (AC-K) at 100oC for 24h.

At step 1214, the method 1200 includes isolation of dried potassium hydroxide activated carbon (AC-K) which is analysed to contain 0.11 wt% of ash content of the total weight of the activated carbon.

FIG. 13 is a diagram illustrating flow chart of a method of determining the ash in potassium hydroxide activated carbon, in accordance with an embodiment of the present disclosure. Referring to FIG. 13, there is provided a method 1300 of determining the ash in potassium hydroxide activated carbon. There is a set method known in prior art and is followed in present invention to calculate the content of ash present in an activated carbon. An empty crucible is kept inside a muffle furnace at 650 ? for 1 hour. After this, the crucible is kept inside a desiccator and allowed to cool to room temperature. After cooling to room temperature, the method 1300 includes steps of:

At step 1302, the method 1300 includes drying empty crucible in muffle furnace at 650oC for 1 h.

At step 1304, the method 1300 includes cooling the dried empty crucible in desiccator at room temperature.
At step 1306, the method 1300 includes weighing the empty crucible to obtain a mass labeled as “A”.

At step 1308, the method 1300 includes adding weighed amount of dried potassium hydroxide activated carbon (AC-K) to empty crucible of step 1306 and weighing the crucible containing potassium hydroxide activated carbon (AC-K) to obtain a mass labeled as “B”.

At step 1310, the method 1300 includes placing the crucible of step 1308 in muffle furnace at 650oC to burn the activated carbon.

At step 1312, the method 1300 includes cooling the crucible of step 1310 in desiccator at room temperature.

At step 1314 and 1216, the method 1300 includes taking the above crucible of step 1212 containing ash content (left after burning of activated carbon) and weighing to obtain a mass labeled as “C”
Therefore, the percentage of ash content is given by = (C-A)/(B-A) ×100

TABLE 2: Overall synergistic effect of composition of the present invention
Composition (wt %) Efficiency
20 wt % AC-K, 79 wt % CB, 1 wt % PTFE 82%
40 wt % AC-K, 59 wt % CB, 1 wt % PTFE 85%
65.5 wt % AC-K, 35.5 wt % CB, 1 wt % PTFE 89%
80 wt % AC-K, 19 wt % CB, 1 wt % PTFE 80%
90 wt % AC-K, 9 wt % CB, 1 wt % PTFE 58%
99 wt % AC-K, 1 wt % PTFE 60%
99 wt % CB, 1 wt % PTFE 55%
65.5 wt % ZnCl2 activated carbon, 35.5 wt % CB, 1 wt % PTFE 57%
65.5 wt % AC-K, 35.5 wt % Graphite, 1 wt % PTFE 48%

The binder PTFE is required in all compositions to bind other components of the composition.
Exemplary embodiments of the invention have been disclosed. A person of ordinary skill in the art recognizes that modifications fall within the teachings of this application. Any numerical values recited in the above application include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. All possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application. Unless otherwise stated, all ranges include both endpoints and all numbers between the endpoints. The use of “about' or “approximately in connection with a range applies to both ends of the range. Thus, “about 20 to 80” is intended to cover “about 20 to about 80”, inclusive of at least the specified endpoints. , Claims:1. A composition of cathode for zinc based rechargeable battery, wherein said composition comprising of about 20 to 80 wt % of potassium hydroxide activated carbon (AC-K), about 19 to 79 wt % of conductive carbon (CB), and about 1.0 wt % of polytetrafluoroethylene (PTFE) as a binder.

2. The composition as claimed in claim 1, wherein said potassium hydroxide activated carbon (AC-K) comprises an activated carbon with potassium hydroxide as activating agent in a mass ratio of 1:5.

3. The composition as claimed in claim 1, wherein said potassium hydroxide activated carbon (AC-K) is present in an amount of about 20 to 65.5 wt % by total weight of the composition.

4. The composition as claimed in claim 1, wherein said potassium hydroxide activated carbon (AC-K) is present in an amount of 65.5 wt % by total weight of the composition.

5. The composition as claimed in claim 1, wherein said conductive carbon (CB) is present in an amount of about 33.5 to 79 wt % by total weight of the composition.

6. The composition as claimed in claim 1, wherein said conductive carbon (CB) is present in an amount of 33.5 wt % by total weight of the composition.

7. The composition as claimed in claim 1, wherein said cathode is in the shape selected from fullerene, carbon nanotube, sheet, graphene, carbon fiber, and carbon foam.

8. A method (1100) for preparation of composition for a cathode (102) in a zinc-based rechargeable battery (104), the method (1100) comprising the steps of:
pyrolyzing charcoal with potassium hydroxide at a temperature range of 700oC to 800oC to obtain pyrolyzed product;
cooling and washing the pyrolyzed product with 2M hydrochloric acid and distilled water to obtain a first wet mass;
stirring the first wet mass with concentrated hydrochloric acid and distilled water taken in the ratio of 1:1 to obtain second wet mass; and
washing the second wet mass with distilled water and drying to obtain potassium hydroxide activated carbon (AC-K); and
mixing the 20 – 80 wt% of the AC-K with 19 to 79 wt % of conductive carbon (CB), and 1.0 wt % of polytetrafluoroethylene (PTFE) to form a composition of the cathode for the zinc based rechargeable battery.

9. The method as claimed in claim 8, wherein the pyrolyzing is carried out for 3-5 hour at a ramp rate of 5?/min.

10. The method as claimed in claim 8, wherein the cooling of the pyrolyzed product is performed to bring the reaction temperature to room temperature.

11. The method as claimed in claim 8, wherein the potassium hydroxide activated carbon (AC-K) comprises an ash content equal to or less than 0.11% of total weight of the activated carbon.