The present invention relates to a method of fabricating flexible solid-state
supercapacitor device on a single Tollable Nafion sheet, which can be folded and
twisted without destroying the structural integrity of the device.
BACKGROUND OF THE INVENTION
However, realization of high-performance supercapacitor devices for flexible
electronics would require consideration of electrochemical, mechanical, and
interfacial properties of the main components such as electrode, separator,
electrolyte, and supporting substrate [1]. For example, active electrode material
needs to have high surface area and electrical conductivity. On the other hand,
electrolyte should be made of flexible solid-state materials. In addition, the
assembly of the components should have high mechanical integrity.
Very recently, Hu et al, [2] prepared a flexible solid-state supercapacitor device.
The electrodes of the supercapacitor device were made of porous and absorbent
cotton paper coated with single wall carbon nanotubes (SWCNTs). To assemble
the supercapacitor cell, two SWCNTs-coated cotton electrodes were immersed
into PVA/ H3PO4 electrolyte. After 10 min, the electrodes were taken out and
assembled together face-to-face to achieve a solid-state flexible supercapacitor
device.
Almost similar approach is used by Yuan et al. [3] to fabricate the flexible solid-
state supercapacitors based on carbon nanoparticles (CNPs)/ MnO2 nanorods
(15 nm) hybrid structure. Two strips of the carbon fabric coated with CNPs/ MnO2
were immersed into the PVA/ H3PO4 solution for 3 min, then taken out and
assembled together with a separator (NKK TF40, 40 nM) to make the final device.
The as-fabricated supercapacitor was light weight and highly flexible and can be
folded and twisted without destroying the structural integrity of the device. In

addition to this, there was no change in electrochemical performance of the
fabricated supercapacitor for different bending angles.
To reduce the weight and increase the flexibility of the device, Andres et al. [4]
fabricated a paper based supercapacitor device. Paper based supercapacitors
were prepared by stacking a paper between two graphene-gold nanoparticles
composite as electrodes and soaking these in an aqueous electrolyte of KOH.
The supercapacitors with a graphene-gold nanoparticle composite as an
electrodes showed a specific capacitance of up to 100 F/g and an energy density
of 1.27 Wh/kg. The observed results indicate that, the paper can be used as an
ion permeable separator in the middle of the supercapacitor.
In most of the fabricated devices, the supercapacitors are made of a polymer
electrolyte layer sandwiched between two flexible nanowires/nanoparticles/
nanotubes based electrodes. The total mass and volume of the supercapacitors
are relatively high because the electrode active materials are also integrated with
some elements such as heavy metal current collectors, binders, bulky
encapsulation packing etc.
In this context, a simplified device structure (less bulky) and low-cost method to
fabricated flexible solid-state supercapacitor device is greatly desired for the
applications, which require thin and light-weight components. To overcome the
problem of bulkiness, Hu et al. [5] prepared flexible paper-based supercapacitors
by coating conductive SWCNTs suspension on both sides of a piece of printing
paper pre-treated by poly vinylidenee fluoride (PVDF). In the fabricated device,
the SWCNTs films behave as both the electrodes and the current collectors and
paper as both the substrate and separator. The SWCNTs coated paper and the
electrolyte (1M LiPF6 in EC and DMC) were encapsulated in a coffee-bag cell to
obtain a supercapacitor. The fabricated device exhibits the specific capacitance
of up to 33 F/g. Such a light weight paper-based supercapacitor could fit wherein
space is inaccessible to the current rigid and bulky energy storage devices.

To further improve the capacitance of paper based supercapacitors, Li et al. [6]
also fabricated the capacitor on single sheet of paper using carbon nanotubes-
graphene composites. The fabricated device exhibits the specific capacitance of
up to 100 F/g, which is significantly higher than those devices, which are
fabricated by Hu et al. [5] using SWCNTs. The great advantage of carbon
nanotubes-graphene composites is that graphene can make the contribution for
good conductivity in plane of nano-structures and high surface area for the
charge storage. However, the important role of SWCNTs in the composite is to
connect all the structures of network, and thus enhance the performance of
composite supercapacitors.
However, the flexibility of paper based supercapacitors is not very good and
easily broken under harsh conditions and also cannot withstand the temperature
of more than 100°C, which limits their wide spread applications in the area of
flexible electronics. In addition to this, use of carbon nanotubes (CNTs) in paper
based supercapacitors also limits the flexibility of the devices, because the
folding of the paper based supercapacitor device increases the internal
resistance of the CNTs film leading to lower performance of the supercapacitors.
In most of the known paper based supercapacitors, the paper is treated with poly
vinylidene fluoride PVDF or other polymers to prevent the short circuit. The
treated paper functions as an electrolyte membrane and separator without
allowing the CNTs to short the device. However, thin coating on the paper leads
to inefficient infiltration of electrolyte ions into CNTs surface and as a result, there
is a reduction in capacitance of the fabricated device. In this context, a simplified
device structure is required, where use of paper and polymer coating could be
avoided and the fabricated device have enough flexibility that can be folded and
twisted without degrading the electrochemical properties. In view of this, the
present inventors recognized that proton conducting membrane could be a
solution to fabricate the flexible and foldable supercapacitors.

OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a method of
fabricating flexible solid-state supercapacitor device on a single reliable Nation
sheet, which can be folded and twisted without destroying the structural integrity
of the device.
Another object of the present invention is to propose a method of fabricating
flexible solid-state supercapacitor device on a single reliable Nafion sheet, which
can be folded and twisted without destroying the structural integrity of the device,
which exhibits that a single sheet of Nafion can be used as a supercapacitor.
A still another object of the present invention to propose a method of fabricating
flexible solid-state supercapacitor device on a single reliable Nafion sheet, which
can be folded and twisted without destroying the structural integrity of the device,
in which the supercapacitor can be fabricated by spraying of CNPs over flexible
Nafion sheet.
Yet another object of the present invention is to propose a method of fabricating
flexible solid-state supercapacitor device on a single reliable Nafion sheet, which
can be folded and twisted without destroying the structural integrity of the device,
in which the electrode materials are grown directly over the flexible solid state
electrolyte to facilitate the effective charge collection and transport.
SUMMARY OF THE INVENTION
Present invention, discloses a method of fabricating flexible solid-state
supercapacitors on roll-able Nafion sheet, which can be folded and twisted
without destroying the structural integrity and degrading the electrochemical
properties. In the fabricated device, the electrode material can be grown directly
over the flexible solid state electrolyte to facilitate the effective charge collection

and transport. The CNPs films behave as both the electrodes and the current
collectors and Nation sheet as both the electrolyte and separator.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - A schematic diagram of the spray deposition system used to
fabricate the flexible and foldable solid-state supercapacitors over the
single sheet of Nafion using CNPs ink.
Figure 2 - Image of flexible Nafion sheet of size 10 cm x 10 cm coated with
CNPs film is shown in Fig. 2 (a), CNPs films behave as both the
electrodes and the current collectors. Photograph of the Nafion sheet
after bending, showing its flexibility is shown in Fig. 2 (b), [Inset
shows the final assembled device of size 2 cm x 2 cm].
Figure 3 - Scanning electron microscopic (SEM) image of CNPs films coated
over the Nafion membrane by spraying of CNPs ink at the spray rate
of 1ml /min.
Figure 4 - Cyclic Voltammetry (CV) of flexible Nafion based supercapacitor at
scan rate of 10 mV/sec.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention disclosed the fabrication of flexible solid-
state supercapacitors on roll-able Nafion sheet, which can be folded and twisted
without destroying the structural integrity and degrading the electrochemical
properties. In the fabricated device CNPs film grown directly over the Nafion
sheet to facilitate the effective charge collection and transport. The CNPs films
behave as both the electrodes and the current collectors and Nafion sheet as
both the electrolyte and separator, which increase the flexibility and reduce the

weight of supercapacitor. An embodiment describes the process adopted for
fabrication of flexible solid-state supercapacitors on single sheet of Nafion.
To fabricate the flexible solid-state supercapacitors over the Nafion sheet, at first
Nafion membrane was treated in a 5 wt. % H2O2 solution for an hour at 353 K
and then washed with Dl water to remove traces of H2O2 from the surface. In
next step, Nafion membrane were transferred to 8 wt. % H2SO4 solution and
treated for an hour at 353 K. To make the final device, the CNPs film was coated
on both sides of the Nafion sheet by spraying the nano-ink, as shown in Fig. 1.
The H2O2 cleaning was used to remove the organic impurities. After this cleaning
stage, membrane was first washed with Dl water to remove traces of H2O2 from
the surface and then heated in H2SO4, to ensure acidification of any remaining
non-protonated sites (i.e. activation of sulphonic acid groups). The conductivity of
Nafion comes from the protons of the sulfonic acid groups. The hydrated -SO3
side chain end groups and the absorbed water provide the media for the
transport of protons. Unlike the other fabrication methods of solid-state
supercapacitors, the processing described in here alleviates the need of re-
immersion of Nafion membrane in an electrolyte solution.
However, according to the present invention the proton conducting membrane
may utilize any of a wide variety of Poly fluorocarbon sulphonic acid-based
membranes, such as Aciplex®, Flemion® and Dow® etc. In addition to this, a poly
(vinyl alcohol) (PVA)/ H3PO4and (PVA)/ H2SO4 based polymer matrix (solid) also
can be used as a both electrolyte and separator to fabricate the flexible
supercapacitors.
To prepare the nano-ink, CNPs (particle size 500 nm) was dispersed in iso-
propanol (IP) with a typical concentration of 0.5 wt %. The as-prepared nano-ink
was then ultrasonically agitated using a probe sonicator with an intensity of 150
W for ~ 120 min. To prepare homogenous and stable solution the nano-ink was

ball-milled. The as prepared nano-ink and stainless balls were loaded in a
stainless container. The ball-to-powder weight ratio was maintained at 15:1 and
milling was carried out at 1200 rpm for 9 hrs. The nano-ink was stable at room
temperature for at least one week.
It is within the scope of this invention that, the nano-ink used for electrodes could
be a combination of carbon based materials, conductive polymers, metal oxides
and many more to enhance the capacitance. Carbon based materials may be
CNTs, activated carbon, carbon fibers, and graphene etc. Conductive polymers
could be polypyrrole (PPy), polyaniline (PANI), polythiophenes and the metal
oxides are RuO2, MnO2, Fe3O4, NiO, IrO2, Co3O4, and Mo03 etc.
To fabricate the flexible and roll-able solid-state supercapacitor, the CNPs based
nano-ink was coated on both sides of the Nafion sheet at a constant spray rate of
1.6 ml /min. The density of CNPs in the deposited film and thickness was
controlled by the number of spraying cycles. In the fabricated device CNPs film
grown directly over the Nafion sheet to facilitate the effective charge collection
and transport. The CNPs films behave as both the electrodes and the current
collectors and Nafion sheet as both the electrolyte and separator, which increase
the flexibility and reduce the weight of supercapacitor.
It is within the scope of this invention that, the CNPs films can be deposited by
variety of techniques: dip-coating, spin coating, doctor blade coating, roller
coating, meyer bar coating, spraying, brushing, screen-printing, contact-printing,
ink-jet printing or other similar printing technology.
Image of flexible Nafion sheet of size 10 cm x 10 cm coated with CNPs film is
shown in Fig. 2 (a), CNPs films behave as both the electrodes and the current
collectors. Photograph of the Nafion sheet after bending, showing its flexibility is
shown in Fig. 2 (b), [Inset shows the final assemble device of size 2 cm x 2 cm].

A typical scanning electron microscopy (SEM) image of spray coated CNPs films
over flexible Nafion sheet is shown in Fig. 3. The coated films is densely packed
with uniform distribution of CNPs. The capacitance of fabricated supercapacitor
depends on the resistivity of CNPs films. Higher is the resistivity lesser is the
capacitance. The resistivity of deposited film could be controlled by number of
spraying cycles and concentration of CNPs in IP solution.
Flexible Nafion based supercapacitor of size 2 cm x 2 cm was tested using cyclic
voltammetry (CV). Figure 3 shows the CV of the fabricated supercapacitor at the
scanning rate of 10 mV/s in the potential range of 0-0.8 V. The CV curve of
Nafion based supercapacitor is close to rectangular shape, this indicates that the
CNPs film has excellent capacitance behaviour with very rapid current response
on voltage with low equivalent series resistance (ESR).
The specific capacitance was obtained from the CV curve according to following
equation, Csp = i/(s * m) F/g, where i is the corresponding current of the voltage
applied (at 0.8 V), s is the potential sweep rate, and m is the total mass of
electrodes (including positive and negative electrodes). The calculated specific
capacitance of the flexible supercapacitor is about 20 F /gm at a scan rate of 10
mV/ s. However, according to the embodiment the capacitance of Nafion based
supercapacitor can be increased further using combination of carbon based
materials, conductive polymers and metal oxides for electrode preparation.
Although the present invention has been described with reference to the
preferred embodiments, thereof, it is intended that the specification and
examples be considered as exemplary only, the true scope and spirit of the
invention being indicated by the following claims:

Literature Reference
1. Y.J. Kang, H. Chung, C.H. Han and W. Kim, Nanotechnology, 23, 065401
(2012).
2. S. Hu, R. Rajamani and Xun Yu, Appl. Phys. Lett. 100,1O4103 (2012).
3. L. Yuan, X. Lu, X. Xiao, T. Zhai, J. Dai, F. Zhang, B. Hu, X. Wang, L.
Gong, J. Chen, C. Hu, Y. Tong, J. Zhou and Z. L. Wang, ACS Nano. 6,
656 (2012).
4. B. Andres, S. Forsberg, A. P. Vilches, R. Zhang, H. Andersson, M.
Hummelgard, J.Backstrom and H.Olin, Nordic Pulp and Paper Research
Journal 27, 485 (2012).
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6. J. Li, X. Cheng, J. Sun, C. Brand, A. Shashurin, M. Reeves and M. Keidar,
J. Appl. Phys. 115,164301 (2014).

WE CLAIM
1. Fabrication of flexible supercapacitor over Nafion sheet comprising the steps
of:-
- treating a Nafion membrane in a 5wt% H2O2 solution for about an hour at
353K;
- washing the treated Nafion membrane with Dl water to remove traces of
H2O2 from the surface;
- treating the washed Nafion membrane for about an hour in a 8wt% H2SO4
solution at 353K; and
- coating both sides of the treated Nafion membrane with carbon
nanoparticles (CNP) base ink at a constant spray rate of 1.6ml/min.

2. The method as claimed in claim 1, wherein an anode and a cathode is
integrated over a single sheet of Nafion.
3. The method as claimed in claim 1, wherein the Nafion membrane acts both
as the electrolyte and separator, and wherein the Nafion membrane is proton-
conducting.
4. The method as claimed in claim 1, wherein the portion conducting membrane
is selected from a group consisting of Nafion, Aciplex®, Flemion®, Dow® and
other similar products.
5. The method as claimed in claim 1, wherein the CNP ink can be coated over
electrolytic paper by variety of techniques, such as, dip-coating, spin coating,

doctor blade coating, roller coating, meyer bar coating, spraying, brushing,
screen-printing, contact-printing, ink-jet printing or other similar printing
technology.
6. The method as claimed in claim 1, wherein the nano-ink was prepared by
dispersing CNPs in iso-propanol (IP) solution.
7. The method as claimed in claim 1, wherein the concentration of the CNPs in
IP may range from 0.5-2 wt %.
8. The method as claimed in any of the preceding claims, wherein the CNP films
acts both as electrodes and current collectors.
9. The method as claimed in claim 6, wherein the CNP ink can be a combination
of carbon based materials conductive polymers, metal oxides and other
similar materials.
10. The method as claimed in claim 9, wherein the carbon based materials can
be CNTs, activated carbon.
11. The method as claimed in claim 9, wherein the conductive polymers can be
polypyrrole (PPy), polyaniline (PANI), and polythiophenes.
12. The method as claimed in claim 9, wherein the metal oxides can be RuO2,
MnO2, Fe3O4, NiO, IrO2, Co3O4, MoO3.
13. The method as claimed in claim 1, wherein the flexible solid-state on roll-able
Nafion sheet has the specific capacitance of about 20F / gm.

14. The method as claimed in claim 13, wherein the specific capacitance can be
further increased using combination of carbon based materials, conductive
polymers and metal oxides.