I/We Claim:
1. An energy storage device comprising an array of an electrochemical cell, the
electrochemical cell comprising:
a. MnO2 as a cathode;
b. activated carbon as an anode;
c. an electrolyte; and
d. optionally, a separator,
wherein MnO2 is in crystalline α form; and the device operates at a
voltage between 0 to 12.6 V.
2. The device as claimed in claim 1, wherein the cell further comprises a current collector selected from graphite, nickel foam, stainless steel, carbon cloth, or
combinations thereof; an additive selected from acetylene black,
polyvinylidene fluoride (PVDF), carbon black, super P, carbon nanofibers,
carbon nanotubes, graphite, polytetrafluoroethylene (PTFE), or
combinations thereof; and a connector.
3. The device as claimed in claim 1, wherein the electrolyte is selected from
Na2SO4, H2SO4, K2SO4, NaOH, KOH, or combinations thereof; and the
separator is selected from nylon fibre mesh, cellulose film, or combinations
thereof.
4. The device as claimed in claim 1, wherein the device has capacitance in a range of 154 to 172F and has columbic efficiency in a range of 97 to 99%.
5. The device as claimed in claim 1, wherein the device is stable up to 10000
charge/discharge cycles.
6. The device as claimed in claim 1, wherein the electrochemical cell is
fabricated as a full-cell or as a half-cell.
7. A process for assembling the energy storage device as claimed in claims 1
and 6, the process comprising:
a. coating MnO2 on a first current collector to obtain a cathode plate;
b. coating an activated carbon on a second current collector to obtain an
anode plate;
c. arranging one or more cathode plates and one or more anode plates
alternatively in parallel in the presence of a separator;
d. connecting the cathode plates and anode plates using a connector to
obtain a chamber;
e. filling the chamber with an electrolyte to obtain the electrochemical cell as full cell; and
f. assembling two or more full cell in series to obtain the energy storage
device;
wherein the device operates at a voltage between 0 to 12.6V.
8. The process as claimed in claim 7, wherein coating MnO2 on a first current collector and coating the activated carbon on a second current collector are
carried out by a process selected from spray coating, screen-printing, roll-to-
roll printing, or ink-jet printing.
9. The process as claimed in claim 7, wherein the first current collector and the
second current collector are independently selected from graphite, nicke foam, stainless steel, or carbon cloth; and the connector is nickel grip.
10. A process for assembling the energy storage device as claimed in claims 1
and 6, the process comprising:
a. mixing MnO2 with a first additive in the presence of a first solvent to
form a cathode slurry;
b. mixing activated carbon with a second additive in the presence of a
second solvent to form an anode slurry;
c. coating the cathode slurry on a first current collector followed by
drying to obtain a cathode active electrode;
d. coating the anode slurry on a second current collector followed by drying to obtain an anode active electrode; and
e. immersing the cathode active electrode in an electrolyte to obtain a
cathode half-cell; and the anode active electrode in the electrolyte to
obtain an anode half-cell;
f. arranging the cathode half-cell, the anode half-cell with a reference
electrode and a counter electrode in the electrolyte to obtain the
electrochemical half-cell,
wherein the cathode half-cell operates at a voltage between -0.4V to 0.85V;
and the anode half-cell operates at a voltage between -1.68V to -0.68V.
11. The process as claimed in claim 10, wherein the first additive and the second
additive are independently selected from acetylene black, polyvinylidene
fluoride (PVDF), carbon black, super P, carbon nanofibers, carbon
nanotubes, graphite, or polytetrafluoroethylene (PTFE); and the first solvent
and the second solvent is dimethyl formamide.
12. The process as claimed in claim 10, wherein the first current collector and
the second current collector are independently selected from graphite, nickel
foam, stainless steel, or carbon cloth.
13. The process as claimed in claim 10, wherein mixing the solvent with the
cathode is carried out in a weight ratio range of 1:100 to 1:250.
14. The process as claimed in claim 10, wherein the reference electrode is
Hg/Hg2SO4 electrode; and the counter electrode is Pt electrode.
15. The process as claimed in claim 10, wherein the device has specific
capacitance in a range of 180 to 200 F/g for the anode half-cell and 60 to 70
F/g for the cathode half-cell.
16. A method for preparing MnO2 as claimed in claim 1, the method comprising:
a. mixing KMnO4 and MnSO4 in a mole ratio of 1:10 to obtain a first
mixture;
b. stirring and centrifuging the first mixture followed by drying at a
temperature in a range of 70 to 90°C to obtain a second mixture;
c. annealing the second mixture at a temperature in a range of 280 to
320°C for time period in a range of 2 to 4 hours to obtain MnO2,
wherein stirring the first mixture is carried out for a time period in a
range of 1 hour to 24 hours; and MnO2 is in α crystalline form with
lattice parameters of 0.965nm0.985nm; 0.965nm0.985nm; 0.275nm0.295nm,