The present invention relates to the rechargeable redox energy storage device and more
particularly to zinc-based rechargeable redox static energy storage device having high
energy efficiency, long cyclic life, 100% DOD and high rate charging and discharging
capability.
10 BACKGROUND OF THE INVENTION:
With, continuing depletion of fossil fuels and increasing environmental problems with their
use, technology is shifting towards green and sustainable alternatives for energy
generation, utilization and storage. Use of the green and renewable energy resources like
solar, wind, geothermal, tidal, etc. for power generation is now becoming a promising
15 solution for fulfilling ever-growing energy needs for more devices, technology and
transportation. However, efficiently exploiting such renewable energy sources for energy
needs has many critical challenges as suggested from hurdles of intermittent nature of these
resources and lack of apt facilities to store their energy in suitable energy form. Converting
energy from renewable sources into electrical energy and saving the same for later use is
20 the most convenient and effective way of exploiting them.
Various energy storage devices like batteries etc. are being used since long for electricity
storage purposes and have been improved from time to time. Among existing rechargeable
energy storage devices, lithium-ion energy storage devices dominate the rechargeable
25 energy storage devices market with its application including electronic gadgets (mobile
phones, laptops and smartwatches etc.), automobile sector owing to its high energy density.
However, lithium-ion batteries have their shortcomings, including supply chain issues,
high cost of the materials and assembly line, environmental hazard in the disposal and most
important is the safety of the end product. Review reports titled as “Economic and
30 environmental characterization of an evolving Li-ion battery waste stream” by Xue Wang
et. al. published by Journal of Environmental Management,
-3-
http://dx.doi.org/10.1016/j.jenvman.2014.01.021 and “Emerging non-lithium ion
batteries” by Yanrong Wang et.al. published by Energy Storage Materials journal,
http://dx.doi.org/10.1016/j.ensm.2016.04.001 talks about various shortcomings and
environmental harzards inherent with lithium ion energy storage devices.
5
The other energy storage device chemistries like lead-acid batteries suffer from poor
performance with 300-500 cycle life and 70% coulombic efficiency, which reaches a
maximum of 90% in the special design cases. Review reports like “An Overview of
Lithium-ion Batteries for Electric Vehicles by Xiaopeng Chen, et.al. published by IEEE,
10 DOI:10.1109/ASSCC.2012.6523269”; “Energy analysis of batteries in photovoltaic
systems. Part I: Performance and energy requirements by Carl Johan Rydh et. al. published
by Energy Conservation & Management, doi:10.1016/j.enconman.2004.10.003” and
“Battery Technologies for Grid‑Level Large‑Scale Electrical Energy Storage by Xiayue
Fan, https://doi.org/10.1007/s12209-019-00231-w” though disclose various other energy
15 storage device chemistries like lead-acid batteries however then still present with various
shortcomings which needs answers.
The utilization of lead and sulfuric acid is also an environmental concern (refer review
article “Study on the environmental risk assessment of lead-acid batteries” by Jing Zhang
20 et. al. published Procedia Environmental Sciences, doi: 10.1016/j.proenv.2016.02.103).
Nickel metal hydride batteries suffer from low energy densities, high self-discharge rates,
recycling issues and poor performance at elevated temperatures. The main concern
associated with the nickel-cadmium batteries is the toxicity of the cadmium along with low
energy density and fast discharge rate. (Refer “Nickel-based batteries: materials and
25 chemistry” by P-J. TSAI et. al., DOI : 10.1533/9780857097378.3.309 )
Recently other rechargeable energy storage devices chemistries (Zn2+, Ca2+, Mg2+ and
Na+) which offer safe and promising output have acquired the attention of the researchers.
Among these energy storage devices alternatives, zinc chemistry is very compelling owing
30 to its abundance, low cost, high chemical and physical stability at the room temperature
and elevated temperature conditions, recyclability, eco-friendliness, high safety associated
-4-
with the utilization. Beside this zinc offers high anode capacity, non-toxic nature and low
redox potential with respect to the standard hydrogen electrode (-0.76V). Up until now,
zinc has been utilized in many energy storage devices chemistries like zinc-air batteries,
zinc ion batteries, zinc-manganese dioxide batteries, zinc-bromine and nickel-zinc
5 batteries. Out of these zinc-based batteries, primary zinc-manganese dioxide batteries are
popular due to their low cost and high energy density. Report titled as “Recent Advances
in Aqueous Zinc-Ion Batteries” by Guozhao Fang et. al. has attempted to mention various
recent developments in Zinc-ion based batteries technologies, however there are still
various shortcomings remains which requires answers.
10
The performance of the rechargeable zinc energy storage devices is dependent on the
chemical nature of the salts, their concentration being used, electrolytes and the materials
used as electrodes. Ionic liquids which usually composed of bulky asymmetric organic
cations and organic/inorganic anions are another kinds of solvents which are being
15 explored for possible solutions to the limitations present with the existing electrolytes used
in zinc-based rechargeable energy storage devices. Even eutectic solvent-based electrolytes
popularly known as Deep Eutectic Solvent (DES) based electrolytes are also being
experimented upon as a possible replacement for existing electrolytes. However, the
limitations present within ionic liquids and even eutectic based solvent electrolytes limit
20 their utilization as electrolytes for zinc-based rechargeable energy storage devices. The
morphology of zinc deposits depends upon the constituent ions of the ionic liquids.
Problems like cost, viscosity, toxicity, etc. which limits the utilization of the existing
electrolytes as a suitable electrolyte. The technology regarding usage of ionic liquids or
eutectic solvent-based electrolytes as the electrolytes for zinc-based rechargeable energy
25 storage devices is at a very nascent stage, and there is much to be explored.
Electrodes have a great impact on the efficiency and life of the energy storage devices.
Further, the surface area of electrodes available to reaction plays a vital role in the
performance of the energy storage devices. Hence, more suitable electrode materials with
30 high surface area, physical, chemical & structural stability is always desired, which
increases overall performance and life of the energy storage devices.
-5-
Many efforts have been made in past to obtain efficient secondary zinc manganese dioxide
batteries. However, the secondary zinc energy storage devices have their issues related to
zinc dendrite formation, reaction irreversibility leading to poor performance, lower
capacity and limited cyclic life. Hence although zinc energy storage devices offer
5 recyclability, cost-effective options and ease of manufacturing (different composition
shapes, sizes) and alternative solutions for large scale off-grid energy storage applications
and mobility substitute for public transportation over lithium-ion or lead-acid energy
storage devices it cannot achieve the desired outcome with the existing chemistries which
are being utilized in zinc-based energy storage devices.
10
Further, most of the existing Zinc based redox energy storage devices works on redox flow
battery technology. The electrolyte for energy storage device requires to be stored in
storage tanks and are pumped so that very large volumes of the electrolytes can be
circulated through the device on separate sides of a membrane acting as separator. The
15 energy storage device when charged chemical potential energy generated is stored in the
electrolyte storage tank. The existing, Zn based flow energy storage device have problems
with dendrite growth particularly as operating current density is increased during charging
(deposition).
20 Patent application US 20180277864 A1 though claims to solve to an extent problem with
dendrite growth the circulation of liquid electrolytes is somewhat cumbersome and does
restrict the use of zinc redox flow batteries in mobile applications, effectively confining
them to large fixed installations. The use large equipment and requirement of storing
electrolyte in storage tanks and pumping it during charging/discharging makes the whole
25 arrangement very costly.
Due to limitations present with the existing Zinc redox flow energy storage devices,
attempts have been made to develop zinc redox battery with non-flow electrolyte.
US5591538A discloses a Zinc- Bromine redox battery with non-flow electrolyte, however,
30 its application is very limited. Bromine is known for its inherent highly corrosive nature
which limits its widescale application as redox couple. The corrosive nature leads to poor
-6-
energy efficiency of the battery and also require special leak proof arrangement to prevent
any escape of bromine in any form outside the battery.
There is need for exploring new possibilities as well as scope of improvement in the
5 existing technology regarding the materials used, designs involved in the manufacturing
the device to overcome the problems present in the existing zinc based rechargeable redox
static energy storage devices and may increase the overall performance of the energy
storage device and decreases manufacturing costs.
10 SUMMARY OF THE INVENTION
The present invention proposes a zinc based rechargeable redox static energy storage
device which has answers to the limitations of the existing zinc based rechargeable redox
static energy storage devices and has desired improved characteristics as mentioned above
over the existing ones.
15
The zinc based rechargeable redox static energy storage device according to present
invention comprising a cathode pre-infused with an eutectic electrolyte in ratio ranging
between 0.5-1.5:2-5; an anode pre-infused with the eutectic electrolyte in ratio ranging
between 0.5-1.5:2-5; wherein the cathode is connected to a current collector; wherein
20 anode is connected to a current collector; a separator separating the cathode and anode so
that the ion exchange carries in between the cathode and anode through ionic permeability.

The cathode comprises a carbon material – binder composition in weight ratio maintained
between 80-99.9:0.1-20; the anode comprises a carbon material –Zinc material- binder
25 composition, in weight ratio maintained between 80-90:10-15.9:0.1-10; wherein the carbon
material is selected alone or in combination from a group consisting of conductive carbon
black, graphite, carbon particles, carbon nanoparticles, woven or non-woven carbon cloth,
carbon felt, carbon paper, carbon rod, and combination thereof; wherein the binder is
selected from a group consisting of PTFE, PVDF, SBR, CMC, PVA; wherein the zinc
30 material is selected from a group consisting of Zinc powder, Zinc Dust, Zinc foil; wherein
the eutectic electrolyte comprises one or more inorganic transition metal salt(s) of zinc
-7-
selected from a group consisting of Zinc Chloride, Zinc Acetate, Zinc Methanesulfonate,
Zinc Sulphate, Zinc triflate; one or more salt(s) of metal(s) selected from a group consisting
of manganese, nickel, titanium and copper metal with sulphate anions, methane sulfonate
anions, halides anions including chloride, bromide, organic salts of transition metal ions
5 with anions like acetate, oxalates, formates, phosphinates, lactate, malate, citrate, benzoate,
ascorbate; one or more Metal hydroxide(s) selected from a group consisting of sodium
hydroxide, potassium hydroxide, aluminum hydroxide, zinc hydroxide, calcium hydroxide,
cesium hydroxide, magnesium hydroxide, iron hydroxide; wherein one or more inorganic
transition metal salt(s) of zinc, one or more salt(s) of metal(s) and one or more Metal
10 hydroxide(s) in molar concentration range 0.1-3: 0.1-3: 0.05-1 are mixed to a eutectic
solvent comprising one or more derivative(s) of methanesulfonic acid selected from its
salts with various metal ions selected from a group consisting of manganese, zinc, cerium,
nickel, titanium, copper, sodium, potassium and calcium ; one or more ammonium salt(s)
having general formula NH4X, where X can be selected from a group consisting of
15 chloride, methanesulfonate, acetate, sulphate, triflate, trimethanesulfonate; one or more
hydrogen bond donor(s) selected from a group consisting of urea, thiourea, glycerol, oxalic
acid, acetic acid, ethylene glycol, acetamide, benzamide, adipic acid, benzoic acid, citric
acid ; wherein the molar ratio of derivative(s) of methanesulfonic acid, ammonium salt(s)
and hydrogen bond donor(s) is in the range 0.5-3: 2-7: 8-13.
20
The current collector is selected from a group consisting of titanium, and carbon material;
and the current collector is selected from a group consisting of titanium, carbon material
and zinc material.
25 The separator used is selected from material selected from a group consisting of micro
porous PVC, micro porous poly propylene, absorptive glass matt, cellulose filter paper.
The thickness ratio of the anode and cathode ranges in between 2-10:1-5. The zinc based
rechargeable redox static energy storage device as disclosed in the present invention has C
rating ranging between 0.2-5 and cycle life ranging between 3000 to 10000.
30
BRIEF DESCRIPTION OF DRAWINGS
-8-
Figure 1 is exploded view of one embodiment according to present invention.
Figure 2 shows a scan rate of 5 mV/s, the cyclic voltammetry curve of test device. At a
possible range of 1-2.2V, a pair of well-defined peaks could be seen. The ratio of oxidation
5 and reduction is ~1 indicating highly reversible reaction.
Figure 3 shows XRD pattern of cathode of test devices A and B at 100% and 0% state of
charge respectively after removing carbon peaks. At 0% SOC there are no obvious peaks
except for titanium current collector peaks while at 100% SOC there are Manganese
10 Dioxide peaks.
Figure 4 shows Galvanostatic charge-discharge profile of test device. Two voltage plateaus
at around 1.5 V and 1.4 V represents charging and discharging process, respectively.
15 Figure 5 shows cycling of the test device at a constant current, the test device's chargedischarge behavior. Both profiles show a steady increase in discharge capacity as the cycle
life increases.
Figure 6 shows Galvanostatic charge-discharge profile of test device at constant voltage
20 1.7 V charge - constant current discharge (CV-CC) condition.
Figure 7 shows Galvanostatic charge-discharge profile of test device at different current
rate, i.e, C/7, C/4, 1C, 5C. High columbic efficiency and low polarization is observed
throughout the current range.
25
Figure 8 shows the cycle performance - Coulombic efficiency and discharge capacity of
prepared test device in different temperature of 15 C (Lower Dot) and 30 C (Upper Dot).
Figure 9 shows Cycle life, Coulombic efficiency of the Zinc Redox battery test device at
30 3C rate. The Zinc Redox battery exhibits excellent cycling stability. Close to 95% of the
maximum discharge capacity is maintained after prolong cycling.
-9-
Figure 10 shows Cycle life, Coulombic efficiency of the Zinc Redox battery test device at
5C rate. The Zinc Redox battery exhibits excellent cycling stability, even at high rates.
DETAILED DESCRIPTION OF THE INVENTION:
5 The present invention discloses a zinc based rechargeable redox static energy storage
device (1) which works on redox principle. The components used in the preparation of the
device (1) are eco-friendly, non-toxic and non-flammable. The device, according to the
present invention, is recyclable.
10 I. DEFINITIONS
For purposes of interpreting the specification and appended claims, the following terms
shall be given the meaning set forth below:
The term “redox” shall refer to chemical reaction in which oxidation and reduction changes
can occur by losing and gaining electrons for example Mn2+ 15 ion is oxidized to manganese
dioxide, Manganese dioxide is reduced to Mn2+ ion.
The term “static energy storage device” shall mean an energy storage device with
physically non-flowing or non-moving electrolyte or cathode or anode materials.
20
The term “solvent” shall refer to a liquid medium capable of dissolving other substance(s).
The “eutectic electrolyte” shall refer to an electrolyte solution that comprises ions, but does
not use water as the solvent. It generally contains eutectic solvent and ions, atoms or
25 molecules that have lost or gained electrons, and is electrically conductive.
The term “carbon material” shall refer to carbon-containing material or carbon-containing
compound having at least 98% carbon. Examples includes but not limited to conductive
carbon black, carbon particles, carbon nanoparticles, woven or non-woven carbon cloth,
30 carbon felt, carbon paper, carbon rod, and combination thereof.
-10-
The binder shall refer to a substance that holds two or more materials together. Examples
includes but not limited to PTFE, PVDF, SBR, CMC, PVA.
The zinc material shall refer to various form of zinc metal. Examples includes but not
5 limited to Zinc powder, Zinc Dust, Zinc foil.
The term “separator” shall refer to a permeable membrane between anode and cathode and
allows ion exchange between the electrodes without short circuiting the device. Examples
includes but not limited to micro porous PVC, micro porous poly propylene, absorptive
10 glass matt, cellulose filter paper.
The term “current collectors” shall refer to material used for carrying out conduction of
electron through electrodes.
15 When referring to the concentration of components or ingredients for electrolytes, Mols
shall be based on the total volume of the electrolyte.
II. DESCRIPTION
Reference is hereby made in detail to various embodiments according to present invention,
20 examples of which are illustrated in the accompanying drawings and described below. It
will be understood that invention according to present description is not intended to be
limited to those exemplary embodiments. The present invention is intended to cover
various alternatives, modifications, equivalents and other embodiments, which may be
included within the spirit and scope of the invention as defined by the claims.
25
The zinc based rechargeable redox static energy storage device according to present
invention comprising a cathode pre-infused with an eutectic electrolyte in ratio ranging
between 0.5-1.5:2-5; an anode pre-infused with the eutectic electrolyte in ratio ranging
30 between 0.5-1.5:2-5; wherein the cathode is connected to a current collector; wherein
-11-
anode is connected to a current collector; a separator separating the cathode and anode so
that the ion exchange carries in between the cathode and anode through ionic permeability.
In formation of cathode (2), carbon material is homogenously mixed with the binder in the
weight ratio ranging between 80-99.9:0.1-20. The carbon material – binder composition is
5 infused with eutectic electrolyte in wt. ratio ranging between 0.5-1.5:2-5 forming a claykind paste. The paste is shaped to be used as cathode (2). The cathode (2) so prepared is
termed as “cathode pre-infused with the eutectic electrolyte”.
In formation of anode (3), carbon material is homogenously mixed with Zinc material and
10 the binder in weight ratio ranging between 80-90:10-15.9:0.1-10. The carbon material -
Zinc material – binder composition is infused with eutectic electrolyte in wt. ratio ranging
between 0.5-1.5:2-5 forming a clay-kind paste. Alternatively, anode (3) is formed by
homogenously mixing carbon material with the binder. The carbon material – binder
composition is infused with eutectic electrolyte in wt. ratio ranging between 0.5-1.5:2-5
15 forming a clay-kind paste. Instead of homogenously mixing zinc material to carbon
material – binder composition, it is used in from of zinc foil in proportionate weight ratio
maintaining carbon material - Zinc material – binder weight ratio ranging between 80-
90:10-15.9:0.1-10. The paste is shaped with zinc foil ranging to be used as anode (3).
carbon material - Zinc material – binder composition is shaped to be used as anode (3). The
20 anode (3) so prepared is termed as “anode pre-infused with the eutectic electrolyte”.
The carbon material used is selected from a group consisting of conductive carbon black,
carbon particles, carbon nanoparticles, woven or non-woven carbon cloth, carbon felt,
carbon paper, carbon rod, and combination thereof.
25
The binder used is selected from a group consisting of PTFE, PVDF, SBR, CMC, PVA.
The zinc material used is selected from a group consisting of Zinc powder, Zinc Dust, Zinc
foil.
30
-12-
The eutectic electrolyte comprises one or more inorganic transition metal salt(s) of zinc
selected from a group consisting of Zinc Chloride, Zinc Acetate, Zinc Methanesulfonate,
Zinc Sulphate, Zinc triflate ; one or more salt(s) of metal(s) selected from a group
consisting of manganese, nickel titanium and copper metal with sulphate anions, methane
5 sulfonate anions, halides anions including chloride, bromide, organic salts of transition
metal ions with anions like acetate, oxalates, formates, phosphinates, lactate, malate,
citrate, benzoate, ascorbate ; one or more Metal hydroxide(s) selected from a group
consisting of sodium hydroxide, potassium hydroxide, aluminum hydroxide, zinc
hydroxide, calcium hydroxide, cesium hydroxide, magnesium hydroxide, iron hydroxide ;
10 wherein one or more inorganic transition metal salt(s) of zinc, one or more salt(s) of
metal(s) and one or more Metal hydroxide(s) in molar concentration range 0.1-3: 0.1-
3:0.05-1 are mixed to a eutectic solvent comprising one or more derivative(s) of
methanesulfonic acid selected from its salts with various metal ions selected from group
consisting of manganese, zinc, cerium, nickel, titanium, copper, sodium, potassium and
15 calcium ; one or more ammonium salt(s) having general formula NH4X, where X can be
selected from a group chloride, methanesulfonate, acetate, sulphate, triflate,
trimethanesulfonate ; one or more hydrogen bond donor(s) selected from a group consisting
of urea, thiourea, glycerol, oxalic acid, acetic acid, ethylene glycol, acetamide, benzamide,
adipic acid, benzoic acid, citric acid ; wherein the molar ratio of derivative(s) of methane
20 sulfonic acid, ammonium salt(s) and hydrogen bond donor(s) is in the range 0.5-3: 2-7: 8-
13.
In order to prepare the eutectic solvent one or more derivative(s) of methanesulfonic acid
selected from its salts with various metal ions selected from a group consisting of
25 manganese, zinc, cerium, nickel, titanium, copper, sodium, potassium and calcium; one or
more ammonium salt(s) having general formula NH4X, where X can be selected from a
group consisting of chloride, methanesulfonate, acetate, sulphate, triflate,
trimethanesulfonate ; one or more hydrogen bond donor(s) selected from a group consisting
of urea, thiourea, glycerol, oxalic acid, acetic acid, ethylene glycol, acetamide, benzamide,
30 adipic acid, benzoic acid, citric acid; wherein the molar ratio of derivative(s) of
methanesulfonic acid, ammonium salt(s) and hydrogen bond donor(s) in the range 0.5-3:
-13-
2-7: 8-13 are mixed. Upon proper mixing, the mixture starts converting into a liquid
eutectic solvent at ambient temperature and pressure. To ensure the proper mixing of the
components and to speed up the process, this mixture may be uniformly heated at a
temperature upto 60°C. One or more inorganic transition metal salt(s) of zinc selected from
5 a group consisting of Zinc Chloride, Zinc Acetate, Zinc Methanesulfonate, Zinc Sulphate,
Zinc triflate ; one or more salt(s) of metal(s) selected from a group consisting of manganese,
nickel, titanium and copper metal with sulphate anions, methane sulfonate anions, halides
anions including chloride, bromide, organic salts of transition metal ions with anions like
acetate, oxalates, formates, phosphinates, lactate, malate, citrate, benzoate, ascorbate ; one
10 or more Metal hydroxide(s) selected from a group consisting of sodium hydroxide,
potassium hydroxide, aluminum hydroxide, zinc hydroxide, calcium hydroxide, cesium
hydroxide, magnesium hydroxide, iron hydroxide; wherein one or more inorganic
transition metal salt(s) of zinc, one or more salt(s) of metal(s) and one or more Metal
hydroxide(s) in molar concentration range 0.1-3: 0.1-3:0.05-1 are added to the eutectic
15 solvent and are continuously mixed until they are completely dissolved in the eutectic
solvent resulting into eutectic electrolyte.
For assembling a zinc based rechargeable redox static energy storage device (1) according
to the present invention, the cathode (2) pre-infused with eutectic electrolyte and the anode
20 (3) pre-infused with eutectic electrolyte are arranged with a separator between them which
allows ion exchange between cathode (2) and anode (3). The cathode (2) is connected with
a current collector (5) selected from a group consisting of titanium and carbon material.
The anode (2) is connected with a current collector (6) selected from a group consisting of
titanium, carbon material, zinc material.
25
The thickness ratio of the cathode (2) versus anode (3) ranges between 2-10:1-5.
The separator (4) used is selected from a group consisting of micro porous PVC, micro
porous poly propylene, absorptive glass matt, cellulose filter paper.
30
-14-
The current collector (5) is selected from a group consisting of titanium and carbon
material, wherein carbon material wherein carbon material is selected from the group
consisting graphite, woven or non-woven carbon cloth, carbon felt, carbon paper, carbon
rod.
5
The redox reaction on the cathode side (2) involves manganese ionic species dissolved in
the eutectic electrolyte which electro deposits manganese oxide during charging and
dissolves back to eutectic electrolyte during discharging.
10 The redox reaction on the anode side (3) involves Zinc ionic species dissolved in eutectic
electrolyte which electro deposits zinc metal during charging and dissolves back to eutectic
electrolyte during discharging.
The cathode (2) pre-infused with eutectic electrolyte and the anode (3) pre-infused with
15 eutectic electrolyte omits requirement of storing electrolyte in storage tanks and pumping
them into the device (1). Further, pre-infusing the electrodes (2, 3) with electrolyte in the
device (1) according to the present invention omits the requirement of keeping the device
(1) idle, which earlier was a requirement for uniform soaking of electrolyte in electrodes
in the existing devices. The high efficiency, long cyclic life, 100% DOD and high rate
20 charging and discharging capability, simple yet effective and economical design and use
of nontoxic and non-corrosive constituents ensures safe and widescale applications of the
device according to the present invention.
In a preferred embodiment according to the present invention, complete device (1) is
25 prepared in the following manner:
Preparation of eutectic electrolyte:
Eutectic electrolyte is prepared by combining 2 moles of calcium methanesulfonate, 5
moles of ammonium chloride, and 10 moles of ethylene glycol in a rotary round-bottom
30 flask at 60 C in an oil bath and rotating it for about 45 minutes obtain a clear, colorless
eutectic solvent. Then the eutectic solvent is transferred to a glass bottle. The bottle is
-15-
placed on a magnetic stirrer plate. 1 mole of Manganese Chloride, 1 mole of Zinc Chloride
are then weighed and slowly added to the eutectic solvent under continued stirring. The
mixture is stirred until all the salts is dissolved. Then 0.4 Zinc Hydroxide is added to the
mixture and is stirred again resulting into slight pinkish transparent eutectic electrolyte.
5 The eutectic electrolyte is then removed from the stirrer plate and stored in a glass bottle.
Zinc based rechargeable redox static energy storage device (1) preparation
Carbon material - binder composition is prepared by uniform mixing of conductive
acetylene black and a binder solution. In the carbon material - binder composition, the
10 weight ratio of carbon to binder is maintained at 99.1:0.9. Liquid dispersed
Polytetrafluoroethylene (PTFE), a non-sticky fluoropolymer, is used as a binder. Diluted
Isopropyl alcohol (20 vol %) is used as a solvent for the PTFE binder. Conductive carbon,
AB 50 from Polimaxx, is mixed with the PTFE solution to form a homogeneous clay-like
paste in a planetary mixer for 1 hour. Then the clay like paste is laid over the tray and
15 spread across it. This is then followed by vacuum dried at 60 °C for overnight to evaporate
the solvent. The carbon material – binder composition is infused with the eutectic
electrolyte mentioned above in 1:3 weight ratios. Mixing is done in end mill roll for 30
mins resulting into clay like paste. The paste is thereafter used to prepare sheets of
controlled thickness by repeatedly rolling using TOB-SG-100L lab roll press machine. For
20 the cathode (2) thickness of sheet is maintained at 1mm and for the anode (3) the thickness
is 0.5 mm. A thin zinc foil having a thickness of 30 microns is placed over sheet of
thickness 0.5mm forming anode. Individual titanium foil is connected to each of the
electrodes (2, 3) and served as a current collector for both electrodes (2, 3).

25 The electrodes (2, 3) with current collectors are assembled with Celgard 3501, a
polypropylene-based microporous membrane, used as the separator (4) between them.
The resultant embodiment is termed as “Test device (1)”
30 Figure 1 is exploded view of preferred embodiment that is termed as “test device (1)”
-16-
EXPERIMENTATION
TESTING:
Test device (1) is prepared as above and tested using cyclic voltammetry (CV) on a
Biologic VPM3 electrochemical workstation at a scanning rate of 5 mV s-1.
5
Constant Current Charge and Constant Current Discharge procedures are used to test the
test device (1). The test device (1) is also tested at different C rate of C/7, C/4, 1C, 5C.
The test device (1) is tested at voltages ranging from 0.5 to 1.9 volts. The test device (1) is
10 tested using a Neware battery cycler. When the test device (1) is charged, soluble
Manganese ions in the eutectic electrolyte diffuse to the cathode and deposit on the various
forms of conductive carbon black as solid Manganese oxide, while Zinc ions are
electrodeposited on the carbon side of anode. The homogeneous layer of as-deposited
Manganese oxide on the cathode is dissolved back to soluble Manganese ions in the
15 eutectic electrolyte during battery discharge, and the as-deposited Zinc on the anode is
dissolved back to Zinc ions in the eutectic electrolyte.
EXPERIMENT 1
Test device (1)'s cyclic voltammograms is obtained to determine reversibility and stability
20 as a possible use case for Zinc redox batteries. Test device (1) CVs of a device from 1 V
to 2.2 V at a scan rate of 5 mV/s for 1000 cycles. These results reveal that the eutectic
electrolyte has a mainly faradaic reaction and are compatible with galvanic charge
discharge patterns.
25 The above approach is used to prepare test device (1), which are then tested utilizing
constant current procedures.
For Manganese Oxide deposition and dissolution, the CV curve of the test device (1) shows
a comparable oxidation and reduction peak. At a potential range of 0.9-2.2 V, a pair of
30 well-defined peaks can be seen. The electrochemical deposition of Manganese Oxide from
the soluble eutectic electrolyte is assigned to the oxidation peak at 1.7V, whereas the
-17-
dissolution of Manganese Oxide to Mn2+ Ions is attributed to the reduction peak at 1.35V.
The oxidation-to-reduction ratio is 1, indicating that the process is highly reversible.
Figure 2 shows a scan rate of 5 mV/s, the cyclic voltammetry curve of a test-device zinc5 based redox battery. At a possible range of 1-2.2V, a pair of well-defined peaks could be
seen. The ratio of oxidation and reduction is ~1 indicating highly reversible reaction.

EXPERIMENT 2
To determine the crystalline structure of the electrodes at 0% state of charge and at 100%
10 state of charge (SOC) is identified by Xray diffraction (XRD, PANalytical) with Cu Kɑ
radiation.
Two identical test devices A and B are prepared using the above method and both are fully
charged.
15
Cathode of test device A is removed from device and is separately tested which is
considered as 100% SOC.
Test device B is fully discharged at a constant current rate and Cathode is removed from
20 test device B and is separately tested which is considered as 0% SOC.
At 100% SOC, the oxidation product is further confirmed by X-ray diffraction (XRD),
which demonstrated a type of beta, gamma Manganese Oxide with the birnessite structure
and belong to the hexagonal crystal system. After discharging to 0% SOC state, the pattern
25 of Manganese Oxide cannot be observed which further confirm the dissolution of
Manganese Oxide.
Figure 3 shows XRD pattern of cathode of both test devices A and B at 100% and 0%,
respectively, state of charge after removing carbon peaks. At 0% SOC there are no obvious
30 peaks except for titanium current collector peaks while at 100% SOC there are Manganese
Dioxide peaks.
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EXPERIMENT 3
To determine Zinc Redox battery performance of a test device (1).
Test device (1) is prepared using the above method and tested using constant current charge
and discharge techniques as described above.
5
Within the range of 0.5 to 1.9V, charge/discharge curves reveal a highly reversible
electrochemical process. Low polarization is shown by the average charge and discharge
voltage plateaus of 1.55 V and 1.4 V, respectively. The coulombic efficiency and energy
efficiency of a highly reversible electrochemical reaction are both approximately >99%
10 and >90%, respectively. Figure 4 shows Galvanostatic charge-discharge profile of
device. Two voltage plateaus at around 1.5 V and 1.4 V represents charging and
discharging process, respectively.
EXPERIMENT 4
15 To determine the effect of constant cycling at lower C rate of C/5.
Test device (1) is prepared using the above method and tested using constant current
techniques as described above.
20 Test device (1) is tested by cycling under a voltage limit of 0.5 to 1.9 V to investigate the
cycling stability at slow C rate of C/5. It shows that the capacity improves after each full
cycle for the first 15 cycles. This indicates there is a more electrolyte utilization over
prolonged cycling period. Figure 5 shows cycling of a test device (1) at a constant current,
the device's charge-discharge behavior. Both profiles show a steady increase in discharge
25 capacity as the cycle life increases.
EXPERIMENT 5
To determine the effect of constant voltage charging on the Zinc Redox battery test device
(1).
30
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Test device (1) is prepared using the above method and tested using constant current
techniques as described above.
During charging at a constant voltage of 1.7 V, soluble Mn2+ ions in the eutectic electrolyte
5 is oxidized to Manganese Oxide deposited evenly on the carbon substrate, while
simultaneous electrodeposition of Zn occurs on the anode. The voltage value of 1.7 V
ensures both a successful electrodeposition reaction and the suppression of any other side
reaction. Even with constant voltage charging methods the test device (1) is stable and has
higher efficiency of 80%. Figure 6 shows Galvanostatic charge-discharge profile of test
10 device (1) at constant voltage 1.7 V charge - constant current discharge (CV-CC)
condition.
EXPERIMENT 6
To determine the effect of C rating on Zinc Redox battery test device (1).
15
Test device (1) is prepared using the above method and tested using constant current charge
and discharge techniques as described above.
Test device (1) is tested by cycling under a different C rating with voltage limit of 0.5 to
20 1.9V to investigate stability of test device (1) under higher load. Even at higher C rate of
5C it shows high energy efficiency of 82% indicating lower internal resistance of the test
device (1).
Figure 7 shows Galvanostatic charge-discharge profile of device at different current rate,
25 i.e, C/7, C/4, 1C, 5C. High columbic efficiency and low polarization is observed throughout
the current range.
EXPERIMENT 7
To determine the effect of temperature on Zinc Redox battery test device (1) capacity.
30
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Test device (1) is prepared using the above method and tested using constant current charge
and discharge techniques as described above.
Test device (1) is tested by cycling under a different temperature rating of 15 °C and 30
5 °C. It is observed that at higher temperature the capacity increases as compared to lower
temperature. Figure 8 shows the cycle performance - Coulombic efficiency and discharge
capacity of prepared device in different temperature of 15°C (Lower Dot) and 30°C (Upper
Dot).
10 EXPERIMENT 8
To determine the effect of prolong cycling at different C rates.
Test device (1) is prepared using the above method and tested using constant current
techniques as described above.
15
The device shows good cycling stability at 3C showing 95% capacity retentions even after
1300 cycles. The device with a higher rate capability of 5C shows a stable cycle life up to
3500 cycles. Figure 9 shows Cycle life, Coulombic efficiency of the Zinc Redox battery at
3C rate. The Zinc Redox battery exhibits excellent cycling stability. Close to 95% of the
20 maximum discharge capacity is maintained after prolong cycling. The Zinc Redox battery
exhibits excellent cycling stability, even at high rates. Figure 10 shows Cycle life,
Coulombic efficiency of the Zinc Redox battery at 5C rate. The Zinc Redox battery exhibits
excellent cycling stability, even at high rates.

We Claim:

1. A zinc based rechargeable redox static energy storage device (1) comprising
a cathode (2) pre-infused with an eutectic electrolyte in ratio ranging between 0.5-
1.5:2-5;
an anode (3) pre-infused with the eutectic electrolyte in ratio ranging between 0.5-
1.5:2-5;
wherein the cathode (2) is connected to a current collector (5);
wherein anode (3) is connected to a current collector (6);
a separator (5) separating the cathode (2) and anode (3) so that the ion exchange
carries in between the cathode (2) and anode (3) through ionic permeability.

2. The zinc based rechargeable redox static energy storage device (1) as claimed in
claim 1, wherein the cathode (2) comprises a carbon material – binder composition
in weight ratio maintained between 80-99.9:0.1-20;
the anode (3) comprises a carbon material –Zinc material- binder composition, in
weight ratio maintained between 80-90:10-15.9:0.1-10.
wherein the carbon material is selected alone or in combination from a group
consisting of conductive carbon black, graphite, carbon particles, carbon
nanoparticles, woven or non-woven carbon cloth, carbon felt, carbon paper, carbon
rod, and combination thereof;
wherein the binder is selected from a group consisting of PTFE, PVDF, SBR, CMC,
PVA;
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wherein the zinc material is selected from a group consisting of Zinc powder, Zinc
Dust, Zinc foil;
wherein the eutectic electrolyte comprises
one or more inorganic transition metal salt(s) of zinc selected from a group consisting
of Zinc Chloride, Zinc Acetate, Zinc Methanesulfonate, Zinc Sulphate, Zinc triflate;
one or more salt(s) of metal(s) selected from a group consisting of manganese, nickel,
titanium and copper metal with sulphate anions, methane sulfonate anions, halides
anions including chloride, bromide, organic salts of transition metal ions with anions
like acetate, oxalates, formates, phosphinates, lactate, malate, citrate, benzoate,
ascorbate;
one or more Metal hydroxide(s) selected from a group consisting of sodium
hydroxide, potassium hydroxide, aluminum hydroxide, zinc hydroxide, calcium
hydroxide, cesium hydroxide, magnesium hydroxide, iron hydroxide;
wherein one or more inorganic transition metal salt(s) of zinc, one or more salt(s) of
metal(s) and one or more Metal hydroxide(s) in molar concentration range 0.1-3: 0.1-
3: 0.05-1 are mixed to a eutectic solvent comprising one or more derivative(s) of
methanesulfonic acid selected from its salts with various metal ions selected from a
group consisting of manganese, zinc, cerium, nickel, titanium, copper, sodium,
potassium and calcium ; one or more ammonium salt(s) having general formula
NH4X, where X can be selected from a group consisting of chloride,
methanesulfonate, acetate, sulphate, triflate, trimethanesulfonate; one or more
hydrogen bond donor(s) selected from a group consisting of urea, thiourea, glycerol,
oxalic acid, acetic acid, ethylene glycol, acetamide, benzamide, adipic acid, benzoic
acid, citric acid ; wherein the molar ratio of derivative(s) of methanesulfonic acid,
ammonium salt(s) and hydrogen bond donor(s) is in the range 0.5-3: 2-7: 8-13.
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3. The zinc based rechargeable redox static energy storage device as claimed in any of
the claims 1 or 2 wherein the current collector (5) is selected from a group consisting
of titanium, and carbon material; and the current collector (6) is selected from a group
consisting of titanium, carbon material and zinc material.
4. The zinc based rechargeable redox static energy storage device as claimed in any of
the claims 1 to 3 wherein the separator used is selected from material selected from
a group consisting of micro porous PVC, micro porous poly propylene, absorptive
glass matt, cellulose filter paper.
5. The zinc based rechargeable redox static energy storage device as claimed in any of
the claims 1 to 4, wherein the thickness ratio of the anode and cathode ranges in
between 2-10:1-5.
6. The zinc redox battery as claimed in any of the claims 1 to 5, having C rating 0.2-5.
7. The zinc redox battery as claimed in claim 1 to 6, having cycle ranging between 3000
to 10000.
8. A method of preparing a zinc based rechargeable redox static energy storage device
(1) as claimed in claims 1 to 5.