Title of Invention

AN IMPROVED NORMAL CUM SUPER CAPACITOR

Abstract

Title An improved normal cum super capacitor. An improved normal cum super capacitor characterized by two presoaked carbon electrode are separated by glass mat separator, the said electrode and separator are sandwiched and fixed inside a protective coversuch as herein described, the presoaking of the said electrode is done by an electrolyte consist aqueous moisture of alkali metal carbonate and amino guanidine bicarbonate at a mol ratio in the range of 0.2 to 33.

Full Text

This present invention relates to "An improved carbon / alkali carbonate and aminoguanidinc bicarbonate electrolyte / carbon cloctricaldcuble layer normal cum super capacitor". Hitherto it has been propsed to use high area carbon, as the electrode and an electrolyte solution containing aqueous (such as water) or non-aqueous solvents (such as ethylene and/or propylene carbonate, y-butyro lactone) and electrolytes (such as LiClO4, MgClO4, NaClO4, KC1O4, quarternary ammonium salts such as tetra alkyl and/or aryl salts) and some insulator (such as PVC based or otherwise) as separators in electrical double layer normal and super capacitors. This is open to the following objections that: 1. The aqueous electrolyte solution based capacitors could give only 1.25V or less voltage window and hence low power output. 2. Only capacitors containing non-aqueous solvents were able to give a larger voltage window and hence larger power output and capacity. But these components have to be used in a perfectly pure and moisture free conditions and they are quite costly. 3. The electrolytes that can be used with non aqueous solvents arc also costly and only salts of very high purity can be used in capacitor electrolytes. 4. Purification of non-aqueous solvents for capacitors is a tedious time consuming process and it adds on to the ultimate cost of the product. The main object of the present invention is to provide "An improved carbon / alkali carbonate and amino guanidine bicarbonate electrolyte / carbon electrical double layer normal cum super capacitor" which obviates the drawbacks as detailed above. Accordingly the present invention provides an improved normal cum super capacitor characterized by two presoaked carbon electrode are separated by glass mat separator, the said electrode and separator are sandwiched and fixed inside a protective coversuch as herein described, the presoaking of the said electrode is done by an electrolyte consist aqueous moisture of alkali metal carbonate and amino guanidine bicarbonate at a mol ratio in the range of 0.2 to 33. In an embodiment of the present invention is the use of an aqueous alkali carbonate solution as the capacitor electrolyte which has not been done hitherto. IN another embodiment of the present invention is the use of amino guanidine bicarbonate in the electrolyte to increase the capacity of the capacitor which is also not attempted hitherto. In yet another embodiment of the present invention is that decomposition of water is carefully prevented (while charging with higher currents) and the value of the cell voltage realized is 2.5 to 2.7 or slightly higher. In another embodiment of the invention is that the carbon source may be taken in the form of fibre, powder, felt and plates. The electrode may be made up of carbon, activated carbon or graphite. The separator may be selected from asbestos, polypropylene, PVC, any micro porous material or any other material which may be capable of conducting ions. The molecular ratio of alkali metal carbonate and amino guanidine bicarbonate is in the range of 0.2 to 33. When this system is charged with 2 mA/cm2 to 150 mA/cm2 of direct current, it attains an OCV of 2 to 2.7 V or slightly greater within a short time of 3 minutes or less. In fact 85% of OCV is reached before the first 2 minutes. In the same way 70-80% of the total capacity of the above .apacitor is discharged within a very short time of 1 to 2 minutes provided the resistance (loa.d) for discharge is ahnost the same as that used for charging. Thus the charging and discharging processes are very quick. In fact the discharge can be made to occur upto 95% within one minute or even less, giving rise to the provision of high wattage in a flash. In fact a number of super capacitors can be packed in series and parallel to give rise to capacitor banks for use in places where high voltage and high current are required, that is in circuits which are fast responding. The purpose of adding aminoguanidine bicarbonate is to avoid decomposition of water and to increase the capacity sivice it is strongly and preferentially adsorbed over carbon by replacing more than one water molecule of aminoguanidine bicarbonate. The pseudocapacitance at carbon/electrolyte interface is generated due to the K+ ion intercalation due to strong adsorption of aminoguanidine bicarbonate. However the potential window (voltage) of the capacitor is less than that in" the presence of aminoguanidine bicarbonate since aminoguanidine bicarbonate adsorption feduces K+ intercalation lo some extent. During charging, one electrode behaves as cathode and the other as anode. At the cathode K+ ions arc intercalated giving rise to intercalation pseudocapacitance. At the anode not much of interesting reactions excepting the formation of adsorbed oxygen atoms occur. During the reverse cycles the former i\+ ion intercalated cathode becomes now the anode thereby giving rise to anodic removal or deintercalation of intercalated K+ ions. The two reactions arc K+ + e + 8C ->• KCB (cathodic) .. (1) KCB -> K+ + e + 8C (anodic) .. (2) K" + Off -» KOH .. (3) The equation (3) gives rise to the formation of a very thin layer of KOH very near the anode thereby increasing the overvoltage for oxygen evolution at the anode. During the second cycle the former anode becomes cathode giving rise to K+ intercalation, inspite of the presence of KOH film. Through this film water molecules are prevented from reaching the intercalated cathode where hydrogen evolution overvoltage is raised. The same happens at the other electrode where oxygen overvoltage is raised. In the successive cycles the enhanced voltage window of the cell is maintained above the thermoneutral voltage of water. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of,the present invention. The following typical examples are given to illustrate the invention. Example 1 Average characteristics of a single cell as capacitor based on actual experimental results. System: C/K2CO3 (l.OM) + aminoguanidinc bicarbonate (0.3 - 0.5M)/C A single cell is defined as a cell with 2 electrodes which act as positive and negativ eterminals during charging and discharging cycles. Anode: Graphite or Carbon Cathode: Graphite or Carbon Dimension of the anode and cathode Thickness Diameter Shape of cell and capacitor Electrolyte solution Separator Current used for charging Charging time Resistance used for discharging Voltage after charging OCV Weight of a single capacitor Capacitance of a single capacitor Voltage window i Power of single capacitor Sp. capacitance of a single capacitor Sp. power of a single capacitor Actual number of cycles 3 mm 1.8cm Small cylinder or just like a pencil torch cell l.0M K2CO3 containing 0.3 to 0.5M aminoguanidine bicarbonate asbestos/glass mat soaked in the above electrolyte solution 14mA about 3 minutes 2.2xl03ohm 3.173V 1.1653 gm 0.84,66 F 2.6533 V 37.1 mW 0.7265 F/g 31.8mW/g 1500 (extendable to 104 cycles) Example 2 Average characteristics of a big capacitor containing 10 cells in series or parallel based on experimental single cell characteristics System: C/lv2CO3 (l.OM) + aminoguanidine bicarbonate (0.3 - 0.5M)/C (Table Removed) Example - 4 Characteristics of Carbon Capacitors (Table Removed) * By using higher area electrodes specific energy can be improved to 106 J/Kg. So also the specific power Based on the above examples 1 to 4 the following observations can be made to highlight the novelty of the present invention. 1. The novelty of the above capacitor is lhat the single capacitor of C/aqu.K2CO2/C gives 2.5 to 2.7V or higher even in the presence of an aqueous electrolyte, thereby proving that non aqueous solvents are not necessary. This is for the first time achieved in the capacitor field as a whole. 2. Use of aminoguanidine bicarbonate is to enhance the capacity by the increase of adsorption of pseudo capacitance and by removing a number of water molecule; by aminoguanidine bicarbonate molecules. This is also a real novelty. 3. All the ingredients are available in India. Hence the capacitor as a whole may be highy cost effective coupled with performance characteristics. 4. Capacitor bank made use of above carbon capacitors can be further improved to attain very high specific energy (J/kg) (of 106 J/kg for use in higher velocity guns or in electric vehicles). 5. Using these capacitors low current, medium current and large current capacitor bank can be fabricated which find use in different areas as the case may be. The main advantages of the present invention are: 1. This is an aqueous electrolyte capacitor with mixed electrolyte containing K2CO3 or NaaCO3 (1.0 M) and aminoguanidine bicarbonate (0.3 to 0.5M). The electrodes are made of graphite or active carbon or carbon paper or carbon fibre that are commercially available. 2. When combined in series and/or parallel these capacitors start showing supercapacitor behaviour. In fact even in the single cell form, the capacitor fabricated as per this patent will exhibit the characteristics of a super capacitor when high area carbon is used in the place of graphite. For example with Indian active carbon of specific area 300 m2/gm we can get a minimum capacity of 8.46F for the electrodes of dimensions given in example 1 for a single cell. 3. Majority of the components for this type of capacitor are available in India. 4. Since the components are not costl;, the capacitor system as a whole is quite competitive in cost. 5. Even though the electrolyte is based on an aqueous medium this electrolyte can be charged to a voltage greater than 3.0 V and its voltage window also is quite high. This is achieved through the use of aminoguanidine bicarbonate and K+ intercalation whereby super capacity behaviour is exhibited by the system due to the generation of pseudocapacitance. 6. The life of the capacitor is expected to be higher since the decomposition of water in the electrolyte in this capacitor is reduced to a greater extent by the addition of aminoguanidine bicarbonate which gets preferentially adsorbed over the cathode during charging and desorbed during anodic cycle. The use of new aqueous electrolyte namely K2CO3/Na2CO3 in combination with aminoguanidine bicarbonate in the aqueous medium with graphite, active carbon, carbon paper, cabon fibre or carbon felt as electrodes and some electronically insulating but ionically conducting microporous materials such as poly propylene, asbestos, PVC etc., capable of absorbing large volume of electrolyte solution as separators in a ncwry fabricated capacitor of the following structure: C/K2CO.3 or Na:CO3 + aminoguanidine bicarbonate / C. We Claim: 1. An improved normal cum super capacitor characterized by two presoaked carbon electrode are separated by glass mat separator, the said electrode and separator are sandwiched and fixed inside a protective coversuch as herein described, the presoaking of the said electrode is done by an electrolyte consist aqueous moisture of alkali metal carbonate and amino guanidine bicarbonate at a mol ratio in the range of 0.2 to 33. 2. An improved normal cup super capacitor as claimed in claim T wherein carbon electrodes used is selected from carbon, activated carbon or graphite. 3. An improved normal cum super capacitor as claimed in claims 1-2 wherein the source of carbon is selected from fibre, powder, felt and plates. 4. An improved normal cup super capacitor as claimed in claims 1-3 wherein the separator used is selected from asbestos, polypropylene, PVC, any micro porous material. 5. An improved normal cum super capacitor substantially herein described with reference to the examples.

Documents:

1491-del-1999-abstract.pdf

1491-del-1999-claims.pdf

1491-del-1999-correspondence-others.pdf

1491-del-1999-correspondence-po.pdf

1491-del-1999-description (complete).pdf

1491-del-1999-form-1.pdf

1491-del-1999-form-19.pdf

1491-del-1999-form-2.pdf