U.S. patent application number 16/146702 was filed with the patent office on 2019-03-28 for gelated ionic liquid film-coated surfaces and uses thereof.
The applicant listed for this patent is Gelion Technologies Pty Ltd. Invention is credited to Max Easton, Thomas Maschmeyer, Antony Ward.
Application Number | 20190097273 16/146702 |
Document ID | / |
Family ID | 53777059 |
Filed Date | 2019-03-28 |
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United States Patent
Application |
20190097273 |
Kind Code |
A1 |
Maschmeyer; Thomas ; et
al. |
March 28, 2019 |
GELATED IONIC LIQUID FILM-COATED SURFACES AND USES THEREOF
Abstract
The invention relates to an assembly comprising a first gelated
ionic liquid film in contact with a first electrically conductive
surface, wherein the first gelated ionic liquid film comprises a
first ionic liquid encapsulated within a gel matrix; and a second
gelated ionic liquid film in contact with a second electrically
conductive surface, wherein the second gelated ionic liquid film
comprises a second ionic liquid encapsulated within a gel matrix;
wherein the first and second gelated ionic liquid films are in
contact with each other. There is also described an electrochemical
cell comprising an assembly according to the invention, and methods
for producing same.
Inventors: |
Maschmeyer; Thomas;
(Lindfield, AU) ; Easton; Max; (Enmore, AU)
; Ward; Antony; (Erskineville, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gelion Technologies Pty Ltd |
Sydney |
|
AU |
|
|
Family ID: |
53777059 |
Appl. No.: |
16/146702 |
Filed: |
September 28, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15116802 |
Aug 4, 2016 |
10122049 |
|
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PCT/AU2015/000062 |
Feb 6, 2015 |
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16146702 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/188 20130101;
H01M 4/388 20130101; H01M 4/663 20130101; H01M 8/20 20130101; H01M
4/661 20130101; Y02E 60/50 20130101; H01M 10/36 20130101; H01M
2300/0085 20130101; H01M 2004/023 20130101; H01M 10/0565 20130101;
H01M 10/365 20130101 |
International
Class: |
H01M 10/36 20100101
H01M010/36; H01M 8/18 20060101 H01M008/18; H01M 4/66 20060101
H01M004/66; H01M 4/38 20060101 H01M004/38 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 6, 2014 |
AU |
2014900359 |
Dec 24, 2014 |
AU |
2014905263 |
Claims
1. An electrochemical cell comprising: a first gelated ionic liquid
film in contact with a first electrically conductive surface,
wherein the first gelated ionic liquid film comprises a first ionic
liquid encapsulated within a first gel matrix; and a second gelated
ionic liquid film in contact with a second electrically conductive
surface, wherein the second gelated ionic liquid film comprises a
second ionic liquid encapsulated within a second gel matrix;
wherein the first and second gelated ionic liquid films are in
contact with each other, and wherein the first gelated ionic liquid
film further comprises a dissolved redox species.
2. The electrochemical cell of claim 1, wherein either or both of:
(i) one or both of the first and second ionic liquid comprises one
or more anions selected from the group consisting of a halogen, a
sulfonylimide, a carboxylate, and a fluorinated phosphate anion;
and (ii) one or both of the first and second ionic liquid comprises
one or more cations selected from the group consisting of an
alkylpyridinium, a dialkylimidazolium, a dialkylpyrrolidinium, a
tetraalkylphosphonium, and a tetraalkylammonium cation.
3. The electrochemical cell of claim 2, wherein the first and
second electrically conductive surfaces are electrodes.
4. The electrochemical cell of claim 3, wherein each electrode
independently comprises one or more of graphite, doped carbon
nanotubes, non-doped carbon nanotubes, doped graphene, non-doped
graphene, a graphene composite, carbon paper, platinum, gold, or
titanium.
5. The electrochemical cell of claim 3, wherein the first
electrically conductive surface is an anode, and the second
electrically conductive surface is a cathode.
6. The electrochemical cell of claim 1, wherein the first and
second gelated ionic liquid films are immiscible when in contact
with each other.
7. The electrochemical cell of claim 1, wherein the first and/or
second gelated ionic liquid film has a thickness of between about
50 .mu.m and about 10 mm.
8. The electrochemical cell of claim 1, wherein the first and/or
second encapsulated ionic liquid comprises at least one of: (i) one
or more anions selected from the group consisting of bromide,
chloride, iodide, bis(trifluoromethyl-sulfonyl)imide,
bis(fluorosulfonyl)imide, acetate, propionate, pentanoate,
hexanoate, hexafluorophosphate, and
tris(pentafluoro)trifluorophosphate; and (ii) one or more cations
selected from the group consisting of 1-butylpyridinium,
1-octylpyridinium, 1-(2-hydroxyethyl)pyridinium,
1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium,
1-pentyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium,
1-(2-methoxyethyl)-3-methylimidazolium,
1-(1-methoxymethyl)-3-methylimidazolium,
1-methyl-3-octylimidazolium, 1-methyl-1-ethylpyrolidinium,
1-methyl-1-butylpyrrolidinium, 1-methyl-1-hexylpyrolidinium,
1-(2-methoxyethyl)-1-methylpyrrolidinium,
1-(1-methoxymethyl)-1-methylpyrrolidinium, tetrabutylphosphonium,
tributyloctylphosphonium, tributyl(2-methoxyethyl)phosphonium,
tributyl-tert-butylphosphonium,
tributyl(1-methoxymethyl)phosphonium, tetraethylammonium,
tetrabutylammonium, tributyloctylammonium,
tributyl(2-methoxyethyl)ammonium,
tributyl(1-methoxymethyl)ammonium, and
tributyl-tert-butylammonium.
9. The electrochemical cell of claim 1, wherein said first and
second gel matrices are formed from a gelating agent selected from
one or more of a hydroxy-substituted organic compound, a
polysaccharide, a dipeptide, a protein, a polymer, a
poly(vinylidene fluoride-co-hexafluoropropylene) polymer, carbon
nanotubes, non-doped or doped graphene, functionalised silica
nanospheres, and a silica sol-gel.
10. The electrochemical cell of claim 1, wherein the dissolved
redox species is selected from the group consisting of: (a) an
acetate, nitrate, sulfate, or triflate salt of Li.sup.+, Mg.sup.2+,
Zn.sup.2+, Cu.sup.+/2+, Fe.sup.2+/3+, Co.sup.2+/3+, Mn.sup.2+, or
Cr.sup.3+; (b) a halogen; (c) an oxygen, permanganate, dichromate,
perchlorate, or halide salt of Li.sup.+, K.sup.+, Ca.sup.2+,
Na.sup.+, or Mg.sup.2+; and (d) a mixture of any two or more of
(a)-(c).
11. The electrochemical cell of claim 1, wherein the second gelated
ionic liquid film further comprises a second dissolved redox
species selected from the group consisting of: (a) an acetate,
nitrate, sulfate, or triflate salt of Li.sup.+, Mg.sup.2+,
Zn.sup.2+, Cu.sup.+/2+, Fe.sup.2+/3+, Co.sup.2+/3+, Mn.sup.2+, or
Cr.sup.3+; (b) a halogen; (c) an oxygen, permanganate, dichromate,
perchlorate, or halide salt of Li.sup.+, K.sup.+, Ca.sup.2+,
Na.sup.+, or Mg.sup.2+; and (d) a mixture of any two or more of
(a)-(c).
12. The electrochemical cell of claim 1, wherein one or more of:
(i) either or both of the first and second gelated ionic liquid
film comprises two or more different ionic liquids; (ii) either or
both of the first and second gelated ionic liquid film comprises
two or more cations and two or more anions that together form a
eutectic mixture; and (iii) either or both of the first and second
gelated ionic liquid film further comprises an electrolyte
salt.
13. The electrochemical cell of claim 1, wherein either or both of
the first and second gelated ionic liquid film further comprises an
electrolyte salt.
14. The electrochemical cell of claim 13, wherein the electrolyte
salt is soluble in at least one of the first ionic liquid and the
second ionic liquid.
15. The electrochemical cell of claim 1, which further comprises: a
third gelated ionic liquid film in contact with a third
electrically conductive surface, wherein the third gelated ionic
liquid film comprises a third ionic liquid encapsulated within a
third gel matrix; and wherein the second and third gelated ionic
liquid films are at least partially in contact with each other.
16. The electrochemical cell of claim 15, wherein at least one of:
the second and third gelated ionic liquid films are immiscible with
each other; and the first and third electrically conductive
surfaces are anodes and the second electrically conductive surface
is a cathode.
17. A method of producing the electrochemical cell of claim 1,
comprising: providing a first gelated ionic liquid film comprising
a first encapsulated ionic liquid in contact with a first
electrically conductive surface; providing a second gelated ionic
liquid film comprising a second encapsulated ionic liquid in
contact with a second electrically conductive surface; and
contacting the first and second gelated ionic liquid films with
each other.
18. The method of claim 17, wherein at least one of said steps of
providing comprises: combining a gelating agent with an ionic
liquid at a suitable temperature to produce a mixture, and allowing
the gelating agent to set and thereby form a gelated ionic liquid
film in which the ionic liquid is encapsulated; and contacting the
mixture or the gelated ionic liquid film with an electrically
conductive surface.
19. The method of claim 18, wherein the mixture is contacted with
the electrically conductive surface prior to allowing the gelating
agent to set.
20. The method of claim 17 further comprising: providing a third
gelated ionic liquid film comprising a third encapsulated ionic
liquid in contact with a third electrically conductive surface; and
contacting the second and third gelated ionic liquid films.
Description
TECHNICAL FIELD
[0001] The present invention relates to the field of reversible
electrochemical energy storage and conversion. More particularly,
the present invention relates to film coated electrically
conductive surfaces, for example electrodes, and battery assemblies
comprising same.
PRIORITY
[0002] The present application claims priority from Australian
provisional patent applications AU 2014900359 and AU 2014905263,
the entire contents of which are incorporated herein by
cross-reference.
BACKGROUND
[0003] Electricity supply in Australia is largely based on remote,
centralised fossil-fuelled power stations. Several factors are
emerging that will change this platform to one of a more
distributed, and potentially intermittent, generation. These
include a desire from governments and consumers to reduce carbon
emissions, increasing costs of conventional fossil-based energy,
and a need to improve network quality and reliability in some
fringe and constrained regions. This growing move to distributed
and intermittent systems requires a concurrent development of
energy storage technology if reliability and quality of supply are
to be maintained. Indeed, grid connected energy storage is now
acknowledged to be a key component of future electricity supply
infrastructure. Various technologies are being considered for grid
and transport storage applications, including lithium-ion
batteries, sodium-sulfur batteries (NGK Japan), flow batteries,
compressed air systems, flywheels, supercapacitors and many more.
Flow batteries have long been considered to be the most suitable
storage technology for utility applications due to their potential
long life, deep discharge characteristics and potentially low
manufacturing cost. Flow batteries differ from other battery
technologies in that the electrolyte is pumped over the electrodes,
which remain electrochemically inert, storing charge through a
change in oxidation state (e.g. vanadium redox) or through an
electrodeposition such as the zinc-bromine battery. Of these, the
zinc-bromine battery offers a solution to most of the problems that
have challenged flow battery systems and is considered a highly
prospective technology.
[0004] A zinc-bromine battery consists of two cells separated by a
permeable membrane through which a zinc bromide/bromine electrolyte
is circulated (see, e.g., FIG. 1). During the charging step, zinc
is electroplated onto the carbon anode, and Br.sub.2 is evolved at
the carbon cathode. A complexing agent in the electrolyte,
N-ethyl-N-methylpyrrolidiniumbromide (MEPBr), is used to reduce the
reactivity and vapour pressure of the elemental Br.sub.2 by
complexing the majority of the Br.sub.2 to MEPBr, forming a
so-called polybromide complex (MEPBr.sub.n). This minimises the
self-discharge of the battery and significantly improves the safety
of the system. This complex is removed from the stacks via the
flowing electrolyte and is stored in an external reservoir. On
discharge, the complex is returned to the battery stacks by the
operation of a valve or a third pump. Zinc is oxidized to zinc ions
on the anodes; the Br.sub.2 is released from the complex and
subsequently reduced to Br.sup.- ions on the cathodes.
[0005] While operational and economic for some applications,
existing zinc-bromine battery technology currently only operates at
15% of the theoretically achievable (based on ZnBr.sub.2
solubility) specific energy due to sub-optimal electrode design,
poor fluid dynamics and the inefficient two-phase fluid,
gravity-separated complexing of Br.sub.2. This limits the battery
to non-transport and low specific energy and energy density
applications. Many of the disadvantages with current zinc-bromine
battery technology relate to problems with efficiently storing
and/or transporting Zn.sup.2+ and Br.sub.2/Br.sup.- in the
electrolyte solution. For example, current battery systems are
limited in their specific energy output by the complexing capacity
of bromine sequestering agents (BSAs) in the electrolyte, and an
ion-selective membrane is needed in current battery systems to
prevent a direct reaction between the zinc electrode and bromine
that would otherwise lead to the battery shorting out.
SUMMARY OF THE INVENTION
[0006] The invention described herein comprises a platform for
battery design based on electrolytes comprising gelated ionic
liquid film systems (GILFS), coated onto stacks of high-surface
area, flexible electrodes, for example, carbon electrodes. This
platform provides a basis to produce low-cost, high-performance
batteries such as, for example, zinc-bromine batteries. The present
invention addresses one or more of the following fundamental
scientific parameters that characterise batteries: [0007] 1. the
speed of the chemical reactions that either store or release
electrons (charge/discharge speed); [0008] 2. the speed with which
ions move inside the battery to compensate for electron flow;
[0009] 3. the selectivity of movement and reactivity of the
electroactive species, to minimise self-discharge; [0010] 4.
chemical stability of electrolyte, electroactive species and
electrode surfaces, to minimise degradation in multiple and deep
cycling; [0011] 5. mechanical stability, to accommodate changes in
volume during charge/discharge.
[0012] Within this context, the present invention provides an
improved approach over existing flow battery systems by replacing
limited efficiency electrolyte/bromine sequestering solutions and
removing the ion-selective membrane, while maintaining the ability
to charge and discharge a battery by preventing the oxidant (e.g.,
bromine) from reacting with the reductant (e.g., zinc). This newly
identified approach utilises films comprising ionic liquids
supported on battery electrodes, or more particularly, gelated
ionic liquid films (GILFs) (`ionogels`). A non-limiting example of
an electrochemical cell according to the present invention is shown
in FIG. 2.
[0013] The battery system of the present invention may involve one
or more of the following innovations over existing systems: [0014]
1. Active to passive--A key disadvantage in the design of current
zinc-bromine batteries is evident in that being able to use the
cheap redox couple is only possible by accepting the significant
drawback of managing bromine in an aqueous medium; this makes the
system complicated, bulky, and slow. In accordance with the present
invention, using a polybromide-forming gelated liquid salt to
manage the bromine without the need to pump solutions can allow the
increase of bromide concentration, and reduce both complexity (no
moving parts) and bulk. The change from active flow in aqueous
media to a non-agitated, non-aqueous ionogel can also reduce costs
while maintaining the favourable electrochemistry of zinc bromide.
Adventitious moisture may not unduly interfere with battery
assembly or operation, further lowering cost and increasing
robustness; [0015] 2. Eliminating internal stress failure
modes--One of the main reasons for failure in conventional
batteries is the internal stresses that arise from charging and
discharging: namely volume changes and temperature fluctuations.
The use of flexible electrodes, e.g., carbon electrodes, in
combination with ionogels as disclosed herein can result in
batteries that are forgiving of these stresses. Such stress
resistance may be enabled through the inherent ability of
viscoelastic gels to expand and contract in volume, while not
reducing diffusion much below that present in the ionic liquid
itself; [0016] 3. Positioning the redox species--Reactive ionogel
electrolytes uniquely direct the flow of electroactive species, for
example, capturing bromine on charge and complexing Zn.sup.2+ on
discharge. This active role of the electrolyte is a major benefit,
since the thin gel, customised for each electrode, may keep these
species close to their respective electrode surface, improving
kinetics and achieving favourable charge/discharge speeds.
Experimental results presented herein are consistent with this
notion; see Examples section); [0017] 4. Eliminating the
membrane--Ionogels with superior binding ability can potentially
avoid the need for a membrane to keep, for example, Br.sub.2 away
from a zinc electrode because it will be captured inside its own
ionogel layer. This innovation may also lead to improved kinetics;
[0018] 5. 3D-printed ionogels--Ionogels can be printable on
surface-activated electrodes with a thickness of at least 50
microns, improving on the 1 micron thicknesses achievable with
ink-jet printing. Importantly, the present invention contemplates
the printing of layers of gels with different characteristics,
leading to a gradation of functionality within the overall set of
films, further improving battery tunability. This may enable the
capacity to shape batteries in 3D, allowing their incorporation
into space- and design-constrained locations in vehicles and
buildings.
[0019] Gelated ionic liquid films (GILFs) according to the present
invention may be synthesised by mixing selected ionic liquids with
gelating agents (e.g., 12-hydroxystearic acid). The gelating agent
can then self-assemble into a 3D scaffold, encapsulating the ionic
liquid (IL) ions. Thin layers of such gels may be applied to
surfaces in the form of a film; thus, although the film comprises a
solid-like gel, it retains the fluid characteristics of a liquid
due to the mobility of IL ions within the scaffold. A film formed
in such a way can be described as a `liquid film`, or a `gelated
ionic liquid film` (GILF).
[0020] By varying the choice of IL cations and anions in the gel,
GILFs may be made that naturally do not mix (i.e., immiscible
gelated IL films). It is also possible to design ILs, and by
extension gels comprising the ILs, which are able to immobilise
halides such as bromine, and/or which are very inefficient at
accepting cations, e.g., Zn.sup.2+. In isolation, or in
combination, such films may be supported on or applied to an
electrode surface, where it would be possible, for example, to
confine Zn.sup.2+ ions to one film and Br.sub.2 to another
film.
[0021] Batteries according to the present invention may comprise
one or more electrochemical cells, the cells comprising at least an
anode, a cathode, and one or more electrolytes. During battery
discharge, the anode, which often comprises elemental metal, is
oxidised to produce metal cations. The reduction reaction at the
cathode depends on the species being reduced.
[0022] For example, the oxidation reaction at the anode during
battery discharge may be represented by the forward direction of
Equation 1:
M.sub.(s)M.sup.n++ne.sup.- Equation 1
[0023] The reduction reaction at the cathode during battery
discharge may be represented by the forward direction of Equation
2:
R+ne.sup.-R.sup.n- Equation 2
[0024] As outlined above, gels encapsulating certain ionic liquids
may be applied to surfaces, for example, electrode surfaces. When
applied to the surface of an anode or cathode, the gel can form a
solid-like coating on the electrode, but retain the fluid
characteristics of a liquid due to the mobility of IL ions within
it.
[0025] One advantage of applying films comprising gels
encapsulating certain ionic liquids directly onto the electrode
surface is that the IL can be specifically selected to have certain
sequestering properties depending on which electrode it is to be
applied (e.g., the anode or cathode), and also depending on the
nature of the oxidising or reducing chemical species at that
electrode. For example, the IL in the film coating the cathode may
be chosen such that it is able to immobilise the oxidant, R, near
the surface of the cathode by using, for example, an R-sequestering
IL in the film. Further, the IL in the film coating the cathode may
be particularly inefficient at storing M.sup.n+ cations produced at
the anode. Meanwhile, the IL in the film coating the anode may be
particularly inefficient at storing the oxidant, R, and instead
sequester M.sup.n+ cations produced at the anode. In this way, the
cathode and anode films can be specifically tailored to the
chemical reactions occurring at the respective electrode
surfaces.
[0026] Another advantage of applying films comprising gels
encapsulating certain ILs directly onto the electrode surfaces is
that the IL film on the cathode(s) can be engineered to be
immiscible with the IL film on the anode(s). One benefit of
mutually immiscible films is that the film coated anode(s) and
cathode(s) can be alternately stacked to form a battery of
adjustable voltage. However, once the cathode and anode gel films
are in partial or complete contact with each other, their mutual
immiscibility will prevent them intermixing. Thus, any sequestered
redox reaction products can be effectively confined within one gel
film, even though the films are in contact. Further, because the
gels comprise IL ions (and optionally added electrolyte species)
with a liquid-like mobility, a second benefit is that the films
also effectively act as an electrolyte, allowing ion migration
between the electrodes and hence maintenance of charge neutrality.
This removes the need for large volumes of liquid electrolyte and
any associated transport and storage problems.
[0027] Conceivably, any suitable combination of redox-active
species and corresponding IL films could be used to construct such
a battery. For example, the anode could comprise any redox-active
metal, e.g., Li, Mg, Zn, Cu, Fe, Co, Mn, Cr, etc. and the oxidant
could be any suitable oxidant, for example, a halogen (e.g., Cl,
Br, I), oxygen, permanganate, dichromate, perchlorate, etc. One
suitable battery system for which the IL films could be used is a
zinc-bromine battery, particularly in view of the corrosive and
dense nature of Br.sub.2 formed during battery charging and the
aforementioned disadvantages associated with storage and transport
of bromine in the electrolyte. An example of the redox process and
associated IL films for a zinc-bromine battery is provided
below.
[0028] The reduction reaction at the cathode during zinc-bromine
battery discharge is represented by the forward direction in
Equation 3:
Br.sub.2+2e.sup.-2Br.sup.- Equation 3
[0029] Therefore, a liquid film coating the cathode should be able
to immobilise Br.sub.2 near the surface of the cathode (by using,
e.g., a bromine-sequestering IL in the film), and the liquid film
can allow Br.sup.- ion mobility. Simultaneously, the liquid film
coating the cathode can be immiscible with the film coating the
anode, and as an added optional precaution, be inefficient at
storing cations, e.g., Zn.sup.2+.
[0030] The oxidation reaction at the anode during zinc-bromine
battery discharge is represented by the forward direction in
Equation 4:
Zn.sub.(s)Zn.sup.2++2e.sup.- Equation 4
[0031] Therefore, the film coating the anode may allow Zn.sup.2+
ion mobility and be immiscible with the film coating the cathode,
and as an added precaution, be inefficient at immobilising halides,
e.g., Br.sub.2.
[0032] As outlined above, liquid-film-coated electrodes of the
present invention could be used in a zinc-bromine battery without
the need for a liquid electrolyte or an ion-selective membrane.
During charging and discharging, Br.sup.- ions can travel from one
film into the other for electrolyte and charge balance, while the
Br.sub.2 remains separate from the Zn metal in the cathode film.
Other proxy ions (as discussed above) could also perform the charge
balancing role. The Zn.sup.2+ can also be engineered to remain in
its own film to help speed up charging. In this way, liquid-film
coated electrodes can be used to run the reversible electroplating
of zinc and concurrent generation of bromine from bromide (charging
the battery) when applying external power and the same system can
be used to release stored power oxidising zinc metal to Zn.sup.2+
and by reducing bromine to bromide.
[0033] The IL films of the present invention act as filters for
electron transfer to and from the electrode underneath. Therefore,
whenever an event can be linked to a change in charge (distribution
or net) within the film, a potential will change or a current will
flow that can be detected. In the case of ion-selective events, it
means that the invention will enable a variety of sensor
applications.
[0034] According to a first aspect of the present invention there
is provided an assembly comprising a first gelated ionic liquid
film in contact with a first electrically conductive surface,
wherein the first gelated ionic liquid film comprises an ionic
liquid encapsulated within a gel matrix.
[0035] The assembly according to the first aspect above may
comprise a second gelated ionic liquid film in contact with a
second electrically conductive surface, wherein the second gelated
ionic liquid film comprises an ionic liquid encapsulated within a
gel matrix; and wherein the first and second liquid films are in
contact with each other.
[0036] According to a second aspect of the present invention there
is provided an assembly comprising: a first gelated ionic liquid
film in contact with a first electrically conductive surface,
wherein the first gelated ionic liquid film comprises a first ionic
liquid encapsulated within a gel matrix; and a second gelated ionic
liquid film in contact with a second electrically conductive
surface, wherein the second gelated ionic liquid film comprises a
second ionic liquid encapsulated within a gel matrix; wherein the
first and second gelated ionic liquid films are in contact with
each other.
[0037] The following options may be used in conjunction with the
first or second aspects either alone or in any suitable
combination.
[0038] The ionic liquid, e.g., the first and/or second ionic
liquid, may comprise one or more anions selected from the group
consisting of a halogen, a sulfonylimide, a carboxylate, and a
fluorinated phosphate anion. The ionic liquid, e.g., the first
and/or second ionic liquid, may comprise one or more cations
selected from the group consisting of an alkylpyridinium, a
dialkylimidazolium, a dialkylpyrrolidinium, a
tetraalkylphosphonium, and a tetraalkylammonium cation. The first
and/or second gelated ionic liquid film may further comprise an
electrolyte salt. The electrolyte salt may be soluble in the ionic
liquid. When in contact with each other, the first and second
gelated ionic liquid films may be immiscible.
[0039] The first electrically conductive surface may be an
electrode. The second electrically conductive surface may be an
electrode. Each electrode may independently comprise any one or
more of graphite (carbon), carbon nanotubes (doped or non-doped),
graphene (doped or non-doped), a graphene composite, carbon paper,
platinum, gold, or titanium. For example, the first electrically
conductive surface may be an anode, and the second electrically
conductive surface may be a cathode. The anode and/or the cathode
may comprise any one or more of graphite (carbon), carbon nanotubes
(doped or non-doped), graphene (doped or non-doped), a graphene
composite, carbon paper, platinum, gold, or titanium. The first
gelated ionic liquid film may have a thickness of between about 50
.mu.m and about 10 mm. The second gelated ionic liquid film may
have a thickness of between about 50 .mu.m and about 10 mm.
[0040] The encapsulated ionic liquid, e.g., the encapsulated first
and/or second ionic liquid, may comprise one or more anions
selected the group consisting of bromide, chloride, iodide,
bis(trifluoromethyl-sulfonyl)imide (NTf.sub.2),
bis(fluorosulfonyl)imide, acetate, propionate, pentanoate,
hexanoate, hexafluorophosphate, and
tris(pentafluoro)trifluorophosphate. The encapsulated ionic liquid,
e.g., the encapsulated first and/or second ionic liquid, may
comprise one or more cations selected from the group consisting of
1-butylpyridinium, 1-octylpyridinium, 1-(2-hydroxyethyl)pyridinium,
1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium,
1-pentyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium,
1-methyl-3-octylimidazolium,
1-(2-methoxyethyl)-3-methylimidazolium,
1-(1-methoxymethyl)-3-methylimidazolium,
1-methyl-1-ethylpyrolidinium, 1-methyl-1-butylpyrrolidinium,
1-methyl-1-hexylpyrolidinium,
1-(2-methoxyethyl)-1-methylpyrrolidinium,
1-(1-methoxymethyl)-1-methylpyrrolidinium, tetrabutylphosphonium,
tributyloctylphosphonium, tributyl(2-methoxyethyl)phosphonium,
tributyl-tert-butylphosphonium,
tributyl(1-methoxymethyl)phosphonium, tetraethylammonium,
tetrabutylammonium, tributyloctylammonium,
tributyl(2-methoxyethyl)ammonium,
tributyl(1-methoxymethyl)ammonium, and
tributyl-tert-butylammonium.
[0041] The first and/or second gel matrix may be formed from a
gelating agent selected from any one or more of a
hydroxy-substituted organic compound, a polysaccharide, a
dipeptide, a protein, a polymer, carbon nanotubes, non-doped or
doped graphene, functionalised silica nanospheres, and a silica
sol-gel. Where the gelating agent is a polymer, the polymer may be
poly(vinylidene fluoride-co-hexafluoropropylene). The first and/or
second gelated ionic liquid film may further comprise an additional
dissolved redox species. The additional dissolved redox species may
be selected from the group consisting of: an acetate, nitrate,
sulfate, or triflate salt of Li.sup.+, Mg.sup.2+, Zn.sup.2+,
Cu.sup.+/2+, Fe.sup.2+/3+, Co.sup.2+/3+, Mn.sup.2+, or Cr.sup.3+; a
halogen (e.g., Cl.sub.2, Br.sub.2, I.sub.2); an oxygen,
permanganate, dichromate, perchlorate, or halide salt of Li.sup.+,
K.sup.+, Ca.sup.2+, Na.sup.+, or Mg.sup.2+; and a mixture of any
two or more of these. The first and/or second gelated ionic liquid
film may comprise two or more different ionic liquids. The first
and/or second ionic liquid may comprise two or more cations and two
or more anions that together form a eutectic mixture.
[0042] The first and/or second gelated ionic liquid film may be
formed by printing the ionic liquid and the gelating agent onto the
electrically conductive surface. This may allow for layers of
different and to some extent `gradated` gel compositions to be
superimposed that allow for fine-tuning within one gel domain,
which in turn may provide control over the diffusion of
electro-active species. As well as eliminating the need for an
explicit membrane and improving charge and discharge speeds, the
tolerance of the system to temperature variation can be engineered
more readily, since cross-membrane diffusion is eliminated as a
limiting parameter.
[0043] According to a third aspect of the present invention there
is provided an electrochemical cell comprising the assembly of the
first or second aspect above.
[0044] According to a fourth aspect of the present invention there
is provided the assembly of the first or second aspect above which
is an electrochemical cell.
[0045] According to a fifth aspect of the present invention there
is provided an electrochemical cell comprising a first gelated
ionic liquid film in contact with a first electrically conductive
surface, wherein the first gelated ionic liquid film comprises a
first ionic liquid encapsulated within a gel matrix; and a second
gelated ionic liquid film in contact with a second electrically
conductive surface, wherein the second gelated ionic liquid film
comprises a second ionic liquid encapsulated within a gel matrix;
and wherein the first and second liquid films are at least
partially in contact.
[0046] The following options may be used in conjunction with the
third, fourth or fifth aspect either alone or in any suitable
combination.
[0047] The first and second gelated ionic liquid films at least
partially in contact may be immiscible with each other. The first
electrically conductive surface may be an anode and the second
electrically conductive surface may be a cathode. The first and/or
second ionic liquid may comprise one or more anions selected from
the group consisting of a halogen, a sulfonylimide, a carboxylate,
and a fluorinated phosphate anion. The first and/or second ionic
liquid may comprise one or more cations selected from the group
consisting of an alkylpyridinium, a dialkylimidazolium, a
dialkylpyrrolidinium, a tetraalkylphosphonium, and a
tetraalkylammonium cation. The first and/or second ionic liquid may
comprise two or more cations and two or more anions that together
form a eutectic mixture. The first and/or second gelated ionic
liquid film may further comprise an electrolyte salt. The first
and/or second gelated ionic liquid film may have a thickness of
between about 50 .mu.m and about 10 mm.
[0048] The assembly or electrochemical cell may further comprise a
third gelated ionic liquid film in contact with a third
electrically conductive surface, wherein the third gelated ionic
liquid film comprises a third ionic liquid encapsulated within a
gel matrix; and wherein the second and third gelated ionic liquid
films are at least partially in contact. The second and third
gelated ionic liquid films at least partially in contact may be
immiscible with each other.
[0049] The first and third electrically conductive surfaces may be
anodes and the second electrically conductive surface may be a
cathode. The anodes and/or the cathode may comprise any one or more
of graphite (carbon), carbon nanotubes (doped or non-doped),
graphene (doped or non-doped), a graphene composite, carbon paper,
platinum, gold, or titanium.
[0050] The first gelated ionic liquid film may be formed by
printing the ionic liquid and a gelating agent onto the first
electrically conductive surface.
[0051] According to a sixth aspect of the present invention there
is provided a method of producing an assembly according to the
first aspect above comprising combining a gelating agent with an
ionic liquid at a suitable temperature to produce a mixture, and
allowing the gelating agent to set and thereby form a first gelated
ionic liquid film in which the ionic liquid is encapsulated; and
contacting the mixture or the first gelated ionic liquid film with
a first electrically conductive surface.
[0052] The method according to the sixth aspect above may further
comprise providing a second gelated ionic liquid film comprising a
second encapsulated ionic liquid and in contact with a second
electrically conductive surface; and contacting the first and
second gelated ionic liquid films. The first electrically
conductive surface may be an anode and the second electrically
conductive surface may be a cathode.
[0053] According to a seventh aspect of the present invention there
is provided a method of producing an assembly according to the
second or fourth aspect above or an electrochemical cell according
to the third or fifth aspect above comprising: [0054] providing a
first gelated ionic liquid film comprising a first encapsulated
ionic liquid in contact with a first electrically conductive
surface; and [0055] providing a second gelated ionic liquid film
comprising a second encapsulated ionic liquid in contact with a
second electrically conductive surface; and
[0056] contacting the first and second gelated ionic liquid
films.
[0057] The following options may be used in conjunction with the
sixth or seventh aspect above either alone or in any suitable
combination.
[0058] The step of providing may comprise combining a gelating
agent with an ionic liquid at a suitable temperature to produce a
mixture, and allowing the gelating agent to set and thereby form a
gelated ionic liquid film in which the ionic liquid is
encapsulated; and contacting the mixture or the gelated ionic
liquid film with an electrically conductive surface.
[0059] The mixture may be contacted with the electrically
conductive surface, e.g., the first and/or second electrically
conductive surface prior to allowing the gelating agent to set.
Contacting the mixture or the gelated ionic liquid film with the
electrically conductive surface may be effected by printing the
mixture onto the electrically conductive surface, e.g., onto the
first and/or second electrically conductive surface. The first
electrically conductive surface may be an anode and the second
electrically conductive surface may be a cathode.
[0060] The method may further comprise providing a third gelated
ionic liquid film comprising a third encapsulated ionic liquid and
in contact with a third electrically conductive surface; and
contacting the second and third gelated ionic liquid films. The
third electrically conductive surface may be an anode.
[0061] Any one or more of the first, second and/or third ionic
liquids may comprise: (a) one or more anions selected from the
group consisting of bromide, chloride, iodide,
bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide,
acetate, propionate, pentanoate, hexanoate, hexafluorophosphate,
and tris(pentafluoro)trifluorophosphate; and/or (b) one or more
cations selected from the group consisting of 1-butylpyridinium,
1-octylpyridinium, 1-(2-hydroxyethyl)pyridinium,
1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium,
1-pentyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium,
1-(2-methoxyethyl)-3-methylimidazolium,
1-(1-methoxymethyl)-3-methylimidazolium,
1-methyl-3-octylimidazolium, 1-methyl-1-ethylpyrolidinium,
1-methyl-1-butylpyrrolidinium, 1-methyl-1-hexylpyrolidinium,
1-(2-methoxyethyl)-1-methylpyrrolidinium,
1-(1-methoxymethyl)-1-methylpyrrolidinium, tetrabutylphosphonium,
tributyloctylphosphonium, tributyl(2-methoxyethyl)phosphonium,
tributyl-tert-butylphosphonium,
tributyl(1-methoxymethyl)phosphonium, tetraethylammonium,
tetrabutylammonium, tributyloctylammonium,
tributyl(2-methoxyethyl)ammonium,
tributyl(1-methoxymethyl)ammonium, and
tributyl-tert-butylammonium.
[0062] Any one or more of the first, second and/or third gelated
ionic liquid films may further comprise an electrolyte salt. The
first and/or second and/or third ionic liquid may comprise two or
more cations and two or more anions that together form a eutectic
mixture.
[0063] In one embodiment, the method according to the seventh
aspect above comprises:
[0064] providing a first gelated ionic liquid film comprising a
first encapsulated ionic liquid in contact with a first
electrically conductive surface, wherein said providing comprises
combining a first gelating agent with a first ionic liquid at a
suitable temperature to produce a first mixture, and allowing the
gelating agent to set and thereby form a first gelated ionic liquid
film in which the ionic liquid is encapsulated; and contacting the
mixture or the gelated ionic liquid film with a first electrically
conductive surface; and
[0065] providing a second gelated ionic liquid film comprising a
second encapsulated ionic liquid in contact with a second
electrically conductive surface, wherein said providing comprises
combining a second gelating agent with a second ionic liquid at a
suitable temperature to produce a second mixture, and allowing the
gelating agent to set and thereby form a second gelated ionic
liquid film in which the ionic liquid is encapsulated; and
contacting the mixture or the gelated ionic liquid film with a
second electrically conductive surface; and
[0066] contacting the first and second gelated ionic liquid
films.
[0067] In another embodiment, the method according to the seventh
aspect above comprises:
[0068] providing a first gelated ionic liquid film comprising a
first encapsulated ionic liquid in contact with a first
electrically conductive surface, wherein said providing comprises
combining a first gelating agent with a first ionic liquid at a
suitable temperature to produce a first mixture, contacting the
mixture with the first electrically conductive surface prior to
allowing the gelating agent to set, and allowing the gelating agent
to set, thereby forming the first gelated ionic liquid film in
which the ionic liquid is encapsulated;
[0069] providing a second gelated ionic liquid film comprising a
second encapsulated ionic liquid in contact with a second
electrically conductive surface, wherein said providing comprises
combining a second gelating agent with a second ionic liquid at a
suitable temperature to produce a second mixture, contacting the
mixture with the second electrically conductive surface prior to
allowing the gelating agent to set, and allowing the gelating agent
to set, thereby forming the second gelated ionic liquid film in
which the ionic liquid is encapsulated; and
[0070] contacting the first and second gelated ionic liquid
films.
[0071] In yet another embodiment, the method according to the
seventh aspect above comprises:
[0072] providing a first gelated ionic liquid film comprising a
first encapsulated ionic liquid in contact with a first
electrically conductive surface, wherein the first electrically
conductive surface is an anode, wherein said providing comprises
combining a first gelating agent with a first ionic liquid at a
suitable temperature to produce a first mixture, contacting the
mixture with the first electrically conductive surface prior to
allowing the gelating agent to set, wherein said contacting is
effected by printing the mixture onto the first electrically
conductive surface, and allowing the gelating agent to set, thereby
forming the first gelated ionic liquid film in which the first
ionic liquid is encapsulated;
[0073] providing a second gelated ionic liquid film comprising a
second encapsulated ionic liquid in contact with a second
electrically conductive surface, wherein the second electrically
conductive surface is a cathode, wherein said providing comprises
combining a second gelating agent with a second ionic liquid at a
suitable temperature to produce a second mixture, contacting the
mixture with the second electrically conductive surface prior to
allowing the gelating agent to set, wherein said contacting is
effected by printing the mixture onto the second electrically
conductive surface, and allowing the gelating agent to set, thereby
forming the second gelated ionic liquid film in which the second
ionic liquid is encapsulated; and
[0074] contacting the first and second gelated ionic liquid
films.
BRIEF DESCRIPTION OF FIGURES
[0075] Preferred embodiments of the present invention will now be
described, by way of example only, with reference to the
accompanying figures wherein:
[0076] FIG. 1 provides a schematic illustration of the existing
flow cell battery technology, and in particular, the large tanks
required to carry the electrolyte and redox species.
[0077] FIG. 2 provides an example of an electrochemical cell
according to the present invention. Key: 10: anode, e.g., a redox
active metal, transition metal, or group I or II metal, e.g., Li,
Mg, Zn, Cu, Fe, Co, Mn, Cr, or graphite (carbon), nanotubes
(carbon), or any non-reactive metal, e.g., platinum, gold, etc.;
15=gelated ionic liquid film in contact with the anode, comprising
any suitable ionic liquid and additional dissolved redox species,
e.g., an M.sup.n+ ion, e.g., Li.sup.+, Mg.sup.2+, Zn.sup.2+,
Cu.sup.+/2+, Fe.sup.2+/3+, Co.sup.2+/3+, Mn.sup.2+, Cr.sup.3+,
etc.; 25: cathode, e.g., graphite (carbon), nanotubes (carbon), or
any non-reactive metal, e.g., platinum, gold, etc.; 20: gelated
ionic liquid film in contact with the cathode, comprising any
suitable ionic liquid and additional dissolved redox species, e.g.,
Cl.sub.2 and/or Cl.sup.-; Br.sub.2 and/or Br.sup.-; I.sub.2 and/or
I.sup.-; MnO.sub.4.sup.- and/or Mn.sup.2+; CrO.sub.4.sup.2- and/or
Cr.sub.2O.sub.7.sup.2-; etc; 30: load or power source.
[0078] FIG. 3 provides Raman spectral data for C.sub.2MPyrBr in 10%
MeOH:MeCN with added Br.sub.2. Labelled features: a) signal from
background, b) symmetric tribromide stretch (160 cm.sup.-1), c)
overlapping asymmetric stretch from Br.sub.3.sup.- (197 cm.sup.-1)
and Br.sub.3.sup.- (208 cm.sup.-1), d) symmetric pentabromide
stretch (256 cm.sup.-1).
[0079] FIGS. 4A-4C illustrate the efficiency of polybromide
formation (ratio of Br.sub.5.sup.-:Br.sub.3.sup.- symmetric Raman
stretches) by varying ionic liquid cations with increasing
additions of bromine; (4A) ethyl-substituted cations, (4B)
butyl-substituted, (4C) hexyl or octyl substituted. Dashed lines
are a visual guide only.
[0080] FIGS. 5A-5B show (5A) studied cations ordered towards their
preference towards the formation of the higher polybromide; and
(5B) influence of the IL cation's alkyl-chain length on polybromide
forming efficiency.
[0081] FIG. 6 demonstrates observed trends for bromine
sequestration performance with ionic binding energies.
[0082] FIG. 7 shows the chemical shift of the C2 proton of
C.sub.2MPyrBr as a function of concentration in 10%
MeOD:CD.sub.3CN.
[0083] FIG. 8 shows a `zinc-side` electrode comprising
[C.sub.8Py]NTf.sub.2 ionic liquid gelated with 20 wt. % PVdF-HFP
with 10 wt. % dissolved Zn(NO.sub.3).sub.2.6H.sub.2O as a zinc
source on a carbon paper electrode with a geometric surface area of
4 cm.sup.2, attached to a potentiostat by silver wire.
[0084] FIG. 9 shows a `bromide-side` electrode comprising a
[P.sub.8,4,4,4]Br ionic liquid gelated with 20 wt % PVdF-HFP
containing dissolved 8.8 wt % ZnBr.sub.2 as a bromine source on a
carbon paper electrode with a geometric surface area of 4 cm.sup.2,
attached to a potentiostat by silver wire.
[0085] FIG. 10 shows the results of a four scan two-electrode
cyclic voltammetry (CV) experiment, with the bromine-side electrode
in FIG. 9 set as the working electrode and the zinc-side electrode
in FIG. 8 as the counter and pseudo-reference electrode.
[0086] FIG. 11 shows the charge/time plots for the test cell used
in FIG. 10, and demonstrates that a 50% charge (equivalent to 16 C)
was achieved after 35 minutes (left). It also shows a model
discharge curve achieved by setting a potential of 0 V across the
test battery (right), demonstrating that less than 1 C passed after
18 minutes of `discharge` time, roughly equivalent to a 6% return
of electroactive species.
[0087] FIG. 12 shows a `zinc-side` electrode comprising
[C.sub.8Py]NTf.sub.2 ionic liquid gelated with 20 wt. % PVdF-HFP
with 10 wt. % dissolved Zn(NO.sub.3).sub.2.6H.sub.2O as a zinc
source on a carbon paper electrode with a geometric surface area of
4 cm.sup.2, attached to a potentiostat by silver wire, after the
50% charge shown in FIG. 11.
[0088] FIG. 13 shows a `bromide-side` electrode comprising a
[P.sub.8,4,4,4]Br ionic liquid gelated with 20 wt % PVdF-HFP
containing dissolved 8.8 wt % ZnBr.sub.2 as a bromine source on a
carbon paper electrode with a geometric surface area of 4 cm.sup.2,
attached to a potentiostat by silver wire, after the 50% charge
shown in FIG. 11.
[0089] FIG. 14 shows two half-cell electrodes (the `bromine
electrode` and the `zinc electrode`), each comprising a gelated
ionic liquid gel (comprising [OMIM]NTf.sub.2 and [OMIM]Br in
PVdF-HFP solution as described in Example 8) in contact with a
titanium mesh electrode, encased in a Teflon.RTM. die designed and
manufactured at the University of Sydney.
[0090] FIG. 15 shows the two half-cells in FIG. 14 pushed together
such that the ionic liquid gel in one half cell is in contact with
the ionic liquid gel of the other half cell. The two half cells are
sealed together and connected to an external circuit, allowing for
electrochemical analysis using an eDAQ potentiostat.
[0091] FIGS. 16A-16D show (16A) Pre-cycling voltammograms, (16B)
post-cycling voltammograms, (16C) 20 min charge cycles, and (16D)
20 min discharge cycles for Cell 1 in Table 2.
[0092] FIGS. 17A-17D show (17A) Pre-cycling voltammograms, (17B)
post-cycling voltammograms, (17C) 20 min charge cycles, and (17D)
20 min discharge cycles for Cell 2 in Table 2.
[0093] FIGS. 18A-18D show (18A) Pre-cycling voltammograms, (18B)
post-cycling voltammograms, (18C) 20 min charge cycles, and (18D)
20 min discharge cycles for Cell 3 in Table 2.
[0094] FIGS. 19A-19D show (19A) Pre-cycling voltammograms, (19B)
post-cycling voltammograms, (19C) 20 min charge cycles, and (19D)
20 min discharge cycles for Cell 4 in Table 2.
[0095] FIGS. 20A-20D show (20A) Pre-cycling voltammograms, (20B)
post-cycling voltammograms, (20C) 20 min charge cycles, and (20D)
20 min discharge cycles for Cell 5 in Table 2.
[0096] FIGS. 21A-21D show (21A) Pre-cycling voltammograms, (21B)
post-cycling voltammograms, (21C) 20 min charge cycles, and (21D)
20 min discharge cycles for Cell 6 in Table 2.
[0097] FIG. 22 shows charge/time plots for Cell 2 in Table 2 after
a 20 minute charge (top) and 20 minute discharge (bottom),
demonstrating that 58% of the total battery charge is regained upon
discharge.
DEFINITIONS
[0098] As used in this application, the singular form "a", "an" and
"the" include plural references unless the context clearly dictates
otherwise. For example, the phrase "additional dissolved redox
species" includes one additional dissolved redox species and also
includes two or more additional dissolved redox species.
[0099] As used herein, the term "comprising" means "including."
Variations of the word "comprising", such as "comprise" and
"comprises," have correspondingly varied meanings. Thus, for
example, a gelated ionic liquid film "comprising" an ionic liquid
encapsulated within a gel matrix may consist exclusively of that
ionic liquid encapsulated within a gel matrix or may include one or
more additional components (e.g. additional dissolved redox
species, electrolyte species, etc.).
[0100] It will be understood that use the term "about" herein in
reference to a recited numerical value includes the recited
numerical value and numerical values within plus or minus ten
percent of the recited value.
[0101] It will be understood that use of the term "between" herein
when referring to a range of numerical values encompasses the
numerical values at each endpoint of the range. For example, a
temperature of between 80.degree. C. and 150.degree. C. is
inclusive of a temperature of 80.degree. C. and a temperature
150.degree. C.
[0102] The terms `gelated ionic liquid` and `ionogel` are used
interchangeably herein to denote an ionic liquid encapsulated
within a gel matrix, and where it is apparent from the context that
the ionogel is in the form of a layer or film, the terms `gelated
ionic liquid film` and `ionogel` are also used interchangeably.
[0103] Any description of prior art documents herein, or statements
herein derived from or based on those documents, is not an
admission that the documents or derived statements are part of the
common general knowledge of the relevant art.
[0104] For the purposes of description, all documents referred to
herein are hereby incorporated by reference in their entirety
unless otherwise stated.
DETAILED DESCRIPTION
[0105] The present invention relates to assemblies comprising
gelated ionic liquid films in contact with electrically conductive
surfaces, for example electrodes, where the solid-like properties
of the gels enable the films to be physically immobilised on the
conductive surfaces whilst the liquid-like properties of the
encapsulated ionic liquids within the films enables movement of
charge carrying species. Such assemblies are suited to a variety of
applications, for example, formation of electrolytic cells. The
assemblies according to the invention are particularly suited as
alternatives to flow battery systems.
Gelated Ionic Liquid Film
[0106] The present invention provides an assembly that, for
example, is suitable for use in electrochemical cells (e.g.,
batteries). The assembly may comprise a gelated ionic liquid film
in contact with an electrically conductive surface. The gelated
ionic liquid film may comprise an ionic liquid encapsulated within
a gel matrix.
Gelating Agent/Gel Matrix
[0107] Encapsulation of an ionic liquid within a gel matrix may be
achieved using any suitable technique. For example, an ionic liquid
may be added to a pre-assembled gel matrix such that the ionic
liquid then becomes encapsulated within the matrix. Alternatively,
a gel matrix precursor or gelating agent may be combined with an
ionic liquid such that the resultant gel matrix forms in or around
the ionic liquid and thereby encapsulates it.
[0108] Non-limiting examples of pre-assembled gel matrices include
silica sol-gels, which may be prepared by acid catalysed
polymerisation of any suitable trialkoxysilane (e.g.,
trimethoxysilane or triethoxysilane) in any suitable templating
ionic liquid. Methods of synthesising silica sol-gels with known
structural properties, e.g., pore size and volume, particle size,
surface area, etc. are known in the art (e.g., Menyen, V.; Cool, P.
Vansant, E. F. "Verified Syntheses of mesoporous materials"
Micropor. Mesopor. Mater. 2009, 125, 170-223), as are suitable
templating ionic liquids (e.g., Antionetti, M.; Kuang, D.; Smarsly,
B.; Zhou, Y. "Ionic liquids for the convenient synthesis of
functional nanoparticles and other inorganic nanostructures" Angew.
Chem. Int. Ed. 2004, 43, 4988-4992; Trewyn, B. G.; Whitman, C. M.;
Lin, V. S.-Y. "Morphological control of room-temperature ionic
liquid templated mesoporous silica nanoparticles for controlled
relaes of antibacterial agents" Nano Lett. 2004, 4, 2139-2143;
Wang, T.; Kaper, H.; Antionetti, M.; Smarsly, B. "Templating
behaviour of a long-chain ionic liquid in the hydrothermal
synthesis of mesoporous silica" Langmuir 2007, 23, 1489-1495; Yuen,
A. K. L.; Heinroth, F.; Ward, A. J.; Masters, A. F.; Maschmeyer, T.
"Novel bis(methylimidazolium)-alkane bolaamphiphiles as templates
for supermicroporous and mesoporous silicas" Micropor. Mesopor.
Mater. 2012, 148, 62-72). The templating ionic liquid may be any
suitable ionic liquid, e.g., it may be an ionic liquid as described
herein in the section entitled `Ionic Liquids`. The templating
ionic liquid may be the ionic liquid encapsulated within the gel
matrix, or the templating ionic liquid may be replaced by an ionic
liquid as described herein in the section entitled `Ionic Liquids`
using methods known in the art, e.g., calcining the sol-gel to
remove the template ionic liquid followed by introduction of a
different ionic liquid by, e.g., incipient wetness methods.
[0109] Non-limiting examples of gel matrix precursors or gelating
agents that may be combined with an ionic liquid to form an ionic
liquid encapsulated within a gel matrix may include any substance
capable of forming a 3D network stabilised by one or more
intermolecular forces, including, but not limited to, ion-dipole
interactions, dipole-dipole interactions, and dispersion forces,
e.g., hydrogen bonding, .pi.-.pi. stacking interactions, or any
combinations thereof, either alone or in combination with one or
more ionic liquids. Suitable gel matrix precursors or gelating
agents may therefore include hydroxy-substituted organic compounds,
polysaccharides, dipeptides, proteins, polymers, carbon nanotubes
and functionalised silica nanospheres, and optionally any of the
preceding substances when combined with an ionic liquid as
described in the section entitled `Ionic liquids`. The gel matrix
precursors or gelating agents may be liquid in pure form, or they
may be solid.
[0110] For example, the gel matrix precursor or gelating agent may
be a substance capable of forming a 3D hydrogen-bonded network
either alone or in combination with one or more ionic liquids.
Non-limiting examples of such gelating agents may therefore include
hydroxy-substituted organic compounds. Any suitable organic
compound may be used, for example, the organic compound may be a
carboxylic acid, e.g., a long chain (C.sub.13-C.sub.21) carboxylic
or fatty acid. The fatty acid C.sub.13-C.sub.21 chain may be
saturated or may be unsaturated, and/or may be linear, branched, or
cyclic. The fatty acid may be aromatic. The fatty acid may comprise
any other suitable functional groups, but preferably comprises one
or more hydroxyl groups. Non-limiting examples of suitable
hydroxy-substituted organic compound gelating agents may therefore
include mono, di or trihydroxy-substituted fatty acids, e.g.,
hydroxypalmitic acid, hydroxystearic acid, hydroxyarachidic acid,
e.g., 12-hydroxystearic acid. In accordance with the present
invention, the hydroxy-substituted organic compounds described
above may be combined with an ionic liquid as described in the
section entitled `Ionic Liquids` to form an ionic liquid
encapsulated within a gel matrix using methods known in the art
(e.g., Voss, B. A.; Bara, J. E.; Gin, D. L.; Noble, R. D.
"Physically gelled ionic liquids: solid membrane materials with
liquid like CO.sub.2 gas transport" Chem. Mater. 2009, 21,
3027-3029).
[0111] Other non-limiting examples of suitable gelating agents
include polysaccharides. Any suitable polysaccharides may be
chosen, e.g., polysaccharides comprising galactose monomers or
their derivatives, or sorbitol monomers or their derivatives, e.g.,
agarose gel, 3,4-dimethyl-2,4-O-methyl-benzylidene-D-sorbitol and
its derivatives, and guar gum. In accordance with the present
invention, the polysaccharides described above may be combined with
an ionic liquid as described in the section entitled `Ionic
Liquids` to form an ionic liquid encapsulated within a gel matrix
using methods known in the art (e.g., Sun, S.; Song, J.; Feng, R.;
Shan, Z. "Ionic liquid gel electrolytes for quasi-solid-state
dye-sensitized solar cells" Electrochim. Acta 2012, 69, 51-55;
Mohmeyer, N.; Wang, P.; Schmidt, H.-W.; Zakeeruddin, S. M.`
Gratzel, M. "Quasi-solid-state dye sensitized solar cells with
1,3:2,4-di-O-benzylidene-D-sorbitol derivatives as low molecular
weight organic gelators" J. Mater. Chem. 2004, 14, 1905-1909).
[0112] Further non-limiting examples of suitable gelating agents
include dipeptides. Any suitable dipeptides may be chosen, e.g.,
dipeptides comprising phenylalanine or its derivatives, leucine or
its derivatives, or asparagine or its derivatives, e.g.,
N-carbobenzyloxy-L-isoleucylamino-octadecane, and
cyclo(L-.beta.-3,7-dimethyloctylasparaginyl-L-phenylalanyine).
Suitable gelating agents may also include proteins, such as
collagen or its derivatives, a non-limiting example of which
includes gelatin. In accordance with the present invention, the
dipeptides and/or proteins described above may be combined with an
ionic liquid as described in the section entitled `Ionic Liquids`
to form an ionic liquid encapsulated within a gel matrix using
methods known in the art (Hanabusa, K.; Fukui, H.; Suzuki, M.;
Shirai, H. "Specialist Gelator for Ionic Liquids" Langmuir 2005,
10383-10390; Smith, N. W.; Knowles, J.; Albright, J. G.; Dzyuba, S.
V. "Ionic liquid-assisted gelation of an organic solvent" J. Mol.
Liquids 2010, 157, 83-87; Kubo, W.; Kambe, S.; Nakade, S.;
Kitamura, T.; Hanabusa, K.; Wada, Y.; Yanagida, S.
"Photocurrent-Determining Processes in Quasi-Solid-State
Dye-Sensitized Solar Cells Using Ionic Gel Electrolytes" J. Phys.
Chem. B 2003, 107, 4374-4381; Hanabusa, K.; Hiratsuka, K.; Kimura,
M.; Shirai, H. "Easy Preparation and Useful Character of Organogel
Electrolytes Based on Low Molecular Weight Gelator" Chem. Mater.
1999, 11, 649-655; Voss, B. A.; Noble, R. D.; Gin, D. L. "Ionic
Liquid Gel-Based Containment and Decontamination Coating for
Blister Agent-Contacted Substrates" Chem. Mater. 2012, 24,
1174-1180).
[0113] Further non-limiting examples of suitable gelating agents
include amides. Any suitable amides may be chosen, e.g., amides
comprising one or more alkanoylaminophenyl groups, e.g.,
bis(4-octanoylaminophenyl)ether, and
bis(4-octanoylaminophenyl)-methane. In accordance with the present
invention, the amides described above may be combined with an ionic
liquid as described in the section entitled `Ionic Liquids` to form
an ionic liquid encapsulated within a gel matrix using methods
known in the art (e.g., Tan, L.; Dong, X.; Wang, H.; Yang, Y. "Gels
of ionic liquid [C.sub.4mim]PF.sub.6 formed by self-assembly of
gelators and their electrochemical properties" Electrochem. Commun.
2009, 11, 933-936).
[0114] Still further non-limiting examples of suitable gelating
agents may include polymers. Any suitable polymers may be chosen,
e.g., polymers or copolymers comprising ethylene oxide, methyl
methacylate, sulfonated tetrafluoroethylene, fluorinated
vinylidene, and/or fluorinated propylene, e.g., poly(ethylene
oxide), poly(methyl methacrylate), sulfonated tetrafluoroethylenes
(Nafion.RTM.), or poly(vinylidene fluoride-co-hexafluoropropylene)
(PVdF-HFP). In accordance with the present invention, the polymers
described above may be combined with an ionic liquid as described
in the section entitled `Ionic Liquids` to form an ionic liquid
encapsulated within a gel matrix using methods known in the art
(e.g., Hong, S. U.; Park, D.; Ko, Y.; Baek, I. "Polymer-ionic
liquid gels for enhanced gas transport" Chem. Commun. 2009,
7227-7229; Yoon, J.; Kang, D.; Won, J.; Park, J.-Y.; Kang, Y. S.
"Dye-sensitized solar cells using ion-gel electrolytes for
long-term stability" J. Power Sources 2012, 210, 395-401; Delaney,
J. Y. J.; Liberski, A. R.; Perelaer, J.; Schubert, U. S. "A
Practical Approach to the Development of Inkjet Printable
Functional Ionogels--Bendable, Foldable, Transparent, and
Conductive Electrode Materials" Macromol. Rapid. Commun. 2010, 31,
1970-1976).
[0115] Additional non-limiting examples of suitable gelating agents
may include carbon nanotubes and graphenes (doped and non-doped),
functionalised silica nanospheres, and silica sol-gels. For
example, silica nanospheres may be functionalised with any suitable
functional groups, e.g., silanol groups or propylamine groups. In
accordance with the present invention, the carbon nanotubes,
graphenes (doped and non-doped), or functionalised silica
nanospheres may be combined with an ionic liquid as described in
the section entitled `Ionic Liquids` to form an ionic liquid
encapsulated within a gel matrix using methods known in the art
(Carbon nanotubes: e.g., Fukushima, T.; Kosaka, A.; Ishimura, Y.;
Yamamoto, T.; Takigawa, T.; Ishii, N.; Aida, T. Science 2003, 300,
2072-2074; non-doped graphene: Zhu, Jixin; Yang, Dan; Yin, Zongyou;
et al., Small, 2014, 10(17), 3480-3498; doped graphene: Wang,
Xuewan; Sun, Gengzhi; Routh, Parimal; et al., Chemical Society
Reviews, 2014, 43(20), 7067-7098; unfunctionalised silica
nanosphere (i.e., silanol groups): e.g., Wang, P.; Zakeeruddin, S.
M.; Comte, P.; Exnar, I.; Gratzel, M. J. Am. Chem. Soc. 2003, 125,
1166-1167; Stathatos, E.; Lianos, P.; Zakeeruddin, S. M.; Liska,
P.; Gratzel, M. Chem. Mater. 2003, 15, 1825-1829; Berginc, M.; Ho
evar, M.; Opara Kra ovec, U.; Hinsch, A.; Sastrawan, R.; Topi , M.
Thin Solid Films 2008, 516, 4645-4650; Shimano, S.; Zhou, H.;
Honma, I. Chem. Mater. 2007, 19, 5216-5221; silica nanospheres
functionalised with amines: e.g., Fang, Y.; Zhang, J.; Zhou, X.;
Lin, Y.; Fang, S. Electrochim. Acta 2012, 68, 235-239; silica
nanospheres functionalised with carboxylic acids: e.g., Fang, Y.;
Zhang, D.; Zhou, X.; Lin, Y.; Fang, S. Electrochem. Commun. 2012,
16, 10-13; silica nanospheres functionalised with polymers: e.g.,
Ueno, K.; Hata, K.; Katakabe, T.; Kondoh, M.; Watanabe, M. J. Phys.
Chem. B 2008, 112, 9013-9019; Ueno, K.; Imaizumi, S.; Hata, K.;
Watanabe, M. Langmuir 2009, 25, 825-831; Ueno, K.; Inaba, A.; Sano,
Y.; Kondoh, M.; Watanabe, M. Chem. Commun. 2009, 3603-3605; Ueno,
K.; Inaba, A.; Ueki, T.; Kondoh, M.; Watanabe, M. Langmuir 2010,
26, 18031-18038; Ueno, K.; Sano, Y.; Inaba, A.; Kondoh, M.;
Watanabe, M. J. Phys. Chem. B 2010, 114, 13095-13103). Silica
sol-gels may be prepared by acid catalysed polymerisation of any
suitable trialkoxysilane (e.g., trimethoxysilane or
triethoxysilane) in any suitable ionic liquid as described herein
in the section entitled `Ionic Liquids`.
[0116] It will be understood that the gel matrix encapsulating an
ionic liquid may comprise one gelating agent, or may comprise a
mixture of any two or more gelating agents as described herein.
Ionic Liquids
[0117] An ionic liquid encapsulated within a gel matrix according
to the present invention may be any suitable ionic liquid. For
example, the ionic liquid may comprise any suitable anion, e.g., an
anion selected from the group consisting of a halogen, an organic
anion or an inorganic anion. Non-limiting examples of suitable
halogen anions include bromide, chloride, and iodide. Non-limiting
examples of suitable organic anions include sulfonylimides and
carboxylates, e.g., bis(trifluoromethylsulfonyl)imide,
bis(fluorosulfonyl)imide, acetate, propionate, pentanoate,
hexanoate. Non-limiting examples of suitable inorganic anions
include fluorinated phosphates, e.g., hexafluorophosphate,
tris(pentafluoro)trifluorophosphate.
[0118] The ionic liquid may additionally comprise any suitable
cation, e.g., a cation selected from the group consisting of
alkyl-substituted heterocyclics, alkyl-substituted phosphonium
cations and alkyl-substituted ammonium cations, where the alkyl
group may be any unsaturated, saturated, linear, branched, cyclic
non-aromatic, or aromatic C.sub.1 to C.sub.12 alkyl group or any
unsaturated, saturated, linear, branched, cyclic non-aromatic, or
aromatic optionally substituted C.sub.1 to C.sub.12 alkyl group,
e.g., an ether substituted C.sub.1 to C.sub.12 alkyl group.
Non-limiting examples of suitable alkyl-substituted heterocyclics
cations include: alkylpyridinium cations, e.g., 1-butylpyridinium,
1-octylpyridinium and 1-(2-hydroxyethyl)pyridinium;
dialkylimidazolium cations, e.g., 1-ethyl-3-methylimidazolium,
1-butyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium,
1-hexyl-3-methylimidazolium,
1-(2-methoxyethyl)-3-methylimidazolium,
1-methyl-3-octylimidazolium, and
1-(1-methoxymethyl)-3-methylimidazolium; and dialkylpyrrolidinium
cations, e.g., 1-methyl-1-ethylpyrolidinium,
1-methyl-1-butylpyrrolidinium, 1-methyl-1-hexylpyrolidinium,
1-(2-methoxyethyl)-1-methylpyrrolidinium and
1-(1-methoxymethyl)-1-methylpyrrolidinium. Non-limiting examples of
suitable alkyl-substituted phosphonium cations include:
tetraalkylphosphonium cations, e.g., tetrabutylphosphonium,
tributyloctylphosphonium, tributyl(2-methoxyethyl)phosphonium,
tributyl-tert-butylphosphonium and
tributyl(1-methoxymethyl)phosphonium; and tetraalkylammonium
cations, e.g., tetraethylammonium, tetrabutylammonium,
tributyloctylammonium, tributyl(2-methoxyethyl)ammonium,
tributyl(1-methoxymethyl)ammonium and
tributyl-tert-butylammonium.
[0119] The ionic liquid encapsulated within a gel matrix according
to the present invention may be tailored to the electrically
conductive surface with which it will be in contact, e.g., where
the electrically conductive surface is an active electrode, the
ionic liquid encapsulated within the gel matrix may be chosen for
its ion transport capacity, and where the electrically conductive
surface is an inert electrode, the ionic liquid encapsulated within
the gel matrix may be chosen for its ability to chemically interact
with the species evolved from the electrically conductive
surface.
[0120] Suitable and non-limiting classes of ionic liquids
applicable for encapsulation in a gel in contact with an inert
electrode may be selected from the group consisting of
alkyl-substituted heterocyclic halides, alkyl-substituted
phosphonium halides and alkyl-substituted ammonium halides. For
example, the halide may be bromide. Non-limiting examples of such
ionic liquids include: 1-butylpyridinium bromide, 1-octylpyridinium
bromide, 1-(2-hydroxyethyl)pyridinium bromide,
1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium
bromide, 1-pentyl-3-methylimidazolium bromide,
1-hexyl-3-methylimidazolium bromide,
1-(2-methoxyethyl)-3-methylimidazolium bromide,
1-(1-methoxymethyl)-3-methylimidazolium bromide,
1-methyl-3-octylimidazolium bromide, 1-methyl-1-ethylpyrolidinium
bromide, 1-methyl-1-butylpyrrolidinium bromide,
1-methyl-1-hexylpyrolidinium bromide,
1-(2-methoxyethyl)-1-methylpyrrolidinium bromide,
1-(1-methoxymethyl)-1-methylpyrrolidinium bromide,
tetrabutylphosphonium bromide, tributyloctylphosphonium bromide,
tributyl(2-methoxyethyl)phosphonium bromide,
tributyl-tert-butylphosphonium bromide,
tributyl(1-methoxymethyl)phosphonium bromide, tetraethylammonium
bromide, tetrabutylammonium bromide, tributyloctylammonium bromide,
tributyl(2-methoxyethyl)ammonium bromide,
tributyl(1-methoxymethyl)ammonium bromide and
tributyl-tert-butylammonium bromide.
[0121] By way of non-limiting example, when the chemical reaction
at the inert electrode is represented by Equation 5:
X.sub.2+2e.sup.-2X.sup.- Equation 5
where X is a halogen (e.g., Cl, Br or I) or any other suitable
oxidant, the ionic liquid encapsulated within the gel matrix in
contact with the inert electrode may be able to immobilise X.sub.2
near the surface of the electrode through interactions between the
ionic liquid and the X.sub.2 molecules. Hence, ionic liquids likely
to be particularly suitable for encapsulation in a gel in contact
with an inert electrode may include alkyl-substituted heterocyclic
cations with X.sup.- anions, alkyl-substituted phosphonium cations
with X.sup.- anions and alkyl-substituted ammonium cations with
X.sup.- anions. Without being be bound by theory, the presence of
X.sup.- anions in the ionic liquid may act as a "seed" for the
formation of polyhalide species, e.g., when X is Br, polybromide
species, which may in turn assist with immobilising the X.sub.2
molecules in the ionic liquid encapsulated within the gel matrix.
Further, these classes of cations may possess a shielded localised
point charge and consequently have a high binding energy for the
ion pair and a low dimerization energy for the anion-cation
pair.
[0122] Classes of ionic liquids likely to be particularly suitable
for encapsulation in a gel in contact with an active electrode may
be selected from the group consisting of alkyl-substituted
heterocyclic cations, alkyl-substituted phosphonium cations, and
alkyl-substituted ammonium cations with anions including
bis(trifluoromethylsulfonyl)-imide, bis(fluorosulfonyl)imide,
hexafluoro-phosphate, tris(pentafluoro)trifluorophosphate, acetate,
propionate, pentanoate and hexanoate.
[0123] For example, where the chemical reaction at the active
electrode is represented by Equation 1, where M is any suitable
metal, e.g., Li, Mg, Zn, Cu, Fe, Co, Mn, Cr, etc., the ionic liquid
encapsulated within the gel matrix in contact with the active
electrode may be able to facilitate movement of M.sup.n+ ions.
[0124] It will be understood that ionic liquids suitable for
encapsulation in a gel in contact with an active electrode may be
equally suitable for encapsulation in a gel in contact with an
inert electrode if, for example, the gel further comprises
additional dissolved redox species capable of being oxidised or
reduced at the inert electrode.
[0125] It will also be understood that the gel matrix encapsulating
an ionic liquid may comprise one ionic liquid, or may comprise a
mixture of two or more different ionic liquids as described herein.
For example, the gel matrix in contact with a first electrode
(e.g., anode) may encapsulate one ionic liquid, or may encapsulate
a mixture of two or more different ionic liquids as described
herein, and/or the gel matrix in contact with a second electrode
(e.g., cathode) may encapsulate one ionic liquid, or may
encapsulate a mixture of two or more different ionic liquids as
described herein. One or more of the encapsulated ionic liquid(s)
in the gel matrix in contact with the first electrode may be
different to the one or more encapsulated ionic liquid(s) in the
gel matrix in contact with the second electrode. Where a mixture of
two different ionic liquids (designated as `A` and `B`) is used,
where each of `A` and `B` is an ionic liquid as described in this
section entitled `Ionic Liquids` and `A` and `B` are different, the
proportion by weight of ionic liquid `A` in the gel matrix may be
between about 0.1 wt. % and about 50 wt. %, and the proportion by
weight of ionic liquid `B` in the gel matrix may be between about
50 wt. % and about 99.9 wt. %. For example, the gel matrix may
comprise an ionic liquid mixture comprising about 50 wt. % ionic
liquid `A` and about 50 wt. % ionic liquid `B`, or may comprise an
ionic liquid mixture comprising about 40 wt. % ionic liquid `A` and
about 60 wt. % ionic liquid `B`, or may comprise an ionic liquid
mixture comprising about 30 wt. % ionic liquid `A` and about 70 wt.
% ionic liquid `B`, or may comprise an ionic liquid mixture
comprising about 20 wt. % ionic liquid `A` and about 80 wt. % ionic
liquid `B`, or may comprise an ionic liquid mixture comprising
about 1 wt. % ionic liquid `A` and about 99 wt. % ionic liquid `B`,
or may comprise an ionic liquid mixture comprising about 40 wt. %
ionic liquid `A` and about 60 wt. % ionic liquid B'. In one
embodiment, ionic liquid `A` is a dialkylimidazolium halide, e.g.,
1-methyl-3-octylimidazolium bromide, and ionic liquid `B` is a
dialkylimidazolium sulfonylimide, e.g., 1-methyl-3-octylimidazolium
bis(trifluoromethylsulfonyl)imide. Accordingly, the gel matrix in
contact with an electrode (e.g., inert or active electrode) may
comprise a mixture of about 50 wt. % [OMIM]NTf.sub.2
(octylimidazolium bis(trifluoromethylsulfonyl)imide) and 50 wt. %
[OMIM]Br (1-methyl-3-octylimidazolium bromide).
[0126] Ionic liquids particularly suitable for encapsulation within
a gel in contact with an inert electrode, e.g., in contact with an
inert anode and/or an inert cathode, may be selected from the group
consisting of 1-methyl-3-octylimidazolium bromide (abbreviated to
[OMIM]Br), 1-methyl-3-octylimidazolium
bis(trifluoromethylsulfonyl)imide (abbreviated to [OMIM]NTf.sub.2),
and mixtures thereof as described above.
[0127] In one embodiment, where two or more ionic liquids are
encapsulated within the same gel matrix, the resultant mixture of
ionic liquids may be a eutectic mixture.
Bromine Sequestering Ionic Liquids
[0128] As described above, the ionic liquid encapsulated within the
gel matrix may be chosen for its ability to chemically interact
with the species evolved from the electrically conductive surface.
In one embodiment, the ionic liquid may be chosen for its ability
to sequester, or bind, bond or otherwise chemically immobilise,
certain species evolved from the electrically conductive surface.
For example, the species may be a halide, e.g., bromine (Br.sub.2),
and the sequestering of the halide, e.g., bromine (Br.sub.2) may be
achieved through formation of polyhalide species, e.g.,
polybromides. Ionic liquids chosen in accordance with the present
invention, and more particularly those chosen for encapsulation
within a gelated ionic liquid film in contact with a cathode, may
therefore be capable of facilitating formation of polyhalides,
e.g., polybromides. Non-limiting examples of suitable ionic
liquids, and non-limiting methods for screening other ionic liquids
for suitability for this purpose, are outlined in Example 1.
[0129] For example, ionic liquids capable of facilitating the
formation of polyhalides, e.g., polybromides, may include
alkyl-substituted heterocyclic halides, alkyl-substituted
phosphonium halides and alkyl-substituted ammonium halides. For
example, where the halide is bromide, non-limiting examples ionic
liquids capable of facilitating the formation of polybromides may
include: 1-butylpyridinium bromide, 1-octylpyridinium bromide,
1-(2-hydroxyethyl)pyridinium bromide, 1-ethyl-3-methylimidazolium
bromide, 1-butyl-3-methylimidazolium bromide,
1-pentyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium
bromide, 1-(2-methoxyethyl)-3-methylimidazolium bromide,
1-(1-methoxymethyl)-3-methylimidazolium bromide,
1-methyl-3-octylimidazolium bromide, 1-methyl-1-ethylpyrolidinium
bromide, 1-methyl-1-butylpyrrolidinium bromide,
1-methyl-1-hexylpyrolidinium bromide,
1-(2-methoxyethyl)-1-methylpyrrolidinium bromide,
1-(1-methoxymethyl)-1-methylpyrrolidinium bromide,
tetrabutylphosphonium bromide, tributyloctylphosphonium bromide,
tributyl(2-methoxyethyl)phosphonium bromide,
tributyl-tert-butylphosphonium bromide,
tributyl(1-methoxymethyl)phosphonium bromide, tetraethylammonium
bromide, tetrabutylammonium bromide, tributyloctylammonium bromide,
tributyl(2-methoxyethyl)ammonium bromide,
tributyl(1-methoxymethyl)ammonium bromide and
tributyl-tert-butylammonium bromide. Without being be bound by
theory, the presence of Br.sup.- anions in these ionic liquids may
act as a "seed" for the formation of polybromide species, and the
cations in these ionic liquids may possess a shielded localised
point charge and consequently have a high binding energy for the
ion pair and a low dimerization energy for the anion-cation
pair.
Gelated Ionic Liquids
[0130] The gel matrix encapsulating an ionic liquid may comprise
any suitable proportion by mass of gel matrix precursor/gelating
agent relative to the mass of ionic liquid. For example, the gel
matrix encapsulating an ionic liquid may comprise from about 1 wt %
to about 30 wt % gel matrix precursor, gelating agent, or
pre-assembled gel matrix, e.g. the gel matrix may comprise from
about 1 wt % to about 10 wt %, or from about 10 wt % to about 20 wt
%, or from about 20 wt % to about 30 wt % gel matrix precursor,
gelating agent, or pre-assembled gel matrix. The proportion by mass
of gel matrix precursor/gelating agent or pre-assembled gel matrix
relative to the mass of ionic liquid may be measured prior to
formation of the gel, and therefore these values may vary in the
final gel or gelated ionic liquid film product.
[0131] The gel matrix encapsulating an ionic liquid may further
comprise any suitable electrolyte salt. The electrolyte salt may
include, for example, halogen ions and group I or II metal ions,
e.g., sodium chloride. The electrolyte salt may be soluble in the
ionic liquid encapsulated in the gel matrix. The electrolyte salt
may be added to the gelating agent and ionic liquid during
synthesis of the gel matrix, or may be passively diffused into the
gel matrix once it has formed. The proportion by mass of
electrolyte salt in the gel matrix may be from 0 wt % to about 20
wt %, e.g., the proportion by mass of electrolyte salt in the gel
matrix may be between 0 wt % and about 5 wt %, or between about 5
wt % and about 10 wt %, or between about 10 wt % and about 20 wt %,
e.g., may be 0 wt %, about 5 wt %, about 10 wt %, about 15 wt % or
about 20 wt %.
[0132] The gel matrix encapsulating an ionic liquid or gelated
ionic liquid film may further comprise any suitable additional
dissolved redox species. The additional dissolved redox species in
the gel matrix or gelated ionic liquid film may be chosen according
to the electrically conductive surface with which the gel matrix or
film will be in contact. For example, where the chemical reaction
at the active electrode is represented by Equation 1, where M is
any suitable metal, e.g., a redox active metal, transition metal,
or group I or II metal, e.g., Li, Mg, Zn, Cu, Fe, Co, Mn, Cr, etc.,
the additional dissolved redox species may be an M.sup.n+ ion,
e.g., Li.sup.+, Mg.sup.2+, Zn.sup.2+, Cu.sup.+/2+, Fe.sup.2+/3+,
CO.sup.2+/3+, Mn.sup.2+, Cr.sup.3+, etc. In another non-limiting
example, where the chemical reaction at the inert electrode is also
represented by Equation 1, where M is any suitable metal, e.g., a
redox active metal, transition metal, or group I or II metal, e.g.,
Li, Mg, Zn, Cu, Fe, Co, Mn, Cr, etc., the additional dissolved
redox species may be an M.sup.n+ ion, e.g., Li.sup.+, Mg.sup.2+,
Zn.sup.2+, Cu.sup.+/2+, Fe.sup.2+/3+, Co.sup.2+/3+, Mn.sup.2+,
Cr.sup.3+, etc. The additional dissolved redox species may be
present in the gel matrix and/or ionic liquid encapsulated therein
and/or in the resultant gelated ionic liquid film in any suitable
concentration. The additional dissolved redox species may have any
suitable counter-ion, e.g., an inorganic counter-ion, e.g.,
acetate, nitrate, or sulfate, or an organic counter-ion, e.g.,
triflate (trifluoromethanesulfonate). In one embodiment, the
additional dissolved redox species is Zn(OTf).sub.2. Where the
chemical reaction at the inert electrode is represented by Equation
2, where R is any suitable oxidant, for example, a halogen (e.g.,
Cl.sub.2, Br.sub.2, I.sub.2), oxygen, permanganate, dichromate,
perchlorate, etc. and R.sup.n- is the reduced form of R, the
additional dissolved redox species in the gel matrix may be R
and/or may be R.sup.n- species, e.g., the additional dissolved
redox species in the gel matrix may be Cl.sub.2 and/or Cl.sup.-;
Br.sub.2 and/or Br.sup.-; I.sub.2 and/or I.sup.-; MnO.sub.4 and/or
Mn.sup.2+; CrO.sub.4.sup.2- and/or Cr.sub.2O.sub.7.sup.2-; etc.
Where the additional dissolved redox species in the gel matrix is
R.sup.n-, the R.sup.n- may have any suitable counter-ion. For
example, the counter-ion may be a metal cation, e.g., a metal
cation with a large negative standard reduction potential, e.g.,
Li.sup.+, K.sup.+, Ca.sup.2+, Na.sup.+, or Mg.sup.2+. Accordingly,
in one embodiment, the additional dissolved redox species is
LiBr.
[0133] The gel matrix encapsulating an ionic liquid and/or gelated
ionic liquid film may comprise one additional dissolved redox
species as described above or may comprise a mixture of two or more
additional dissolved redox species as described above. For example,
the additional dissolved redox species in the gel matrix may
comprise R species (e.g., Br.sub.2) and may also comprise R.sup.n-
species (e.g., in the form of dissolved LiBr), and may optionally
further comprise an M.sup.n+ ion, e.g., Li.sup.+, Mg.sup.2+,
Zn.sup.2+, Cu.sup.+/2+, Fe.sup.2+/3+, Co.sup.2+/3+, Mn.sup.2+ or
Cr.sup.3+ having any suitable counter-ion, e.g., acetate, nitrate,
sulfate, or triflate (trifluoromethanesulfonate).
[0134] The additional dissolved redox species may be present in the
gel matrix and/or ionic liquid encapsulated therein and/or in the
gelated ionic liquid film in any suitable concentration. The
proportion by mass of each additional dissolved redox species in
the gel matrix or film may be from 0 wt % to about 20 wt %, e.g.,
the proportion by mass of the additional dissolved redox species in
the gel matrix or film may be between 0 wt % and about 5 wt %, or
between about 5 wt % and about 10 wt %, or between about 10 wt %
and about 20 wt %, e.g., the proportion by mass of the additional
dissolved redox species in the gel matrix or film may be 0 wt %,
about 1 wt %, about 2 wt %, about 3 wt %, about 4 wt %, about 5 wt
%, about 6 wt %, about 7 wt %, about 8 wt %, about 9 wt %, about 10
wt %, about 15 wt % or about 20 wt %.
[0135] The additional dissolved redox species described in this
section may be added to the gelating agent and ionic liquid during
synthesis of the gel matrix, or may be passively diffused into the
gel matrix once it has formed.
[0136] The gel and/or gelated ionic liquid films may further
comprise a solvent. For example, if a solvent has been used to
dissolve, swell or suspend the gelating agent, the gel and/or
gelated ionic liquid films may contain residual or trace amounts of
this solvent. If the gel and/or gelated ionic liquid film is
allowed to set under standard laboratory conditions, the residual
solvent amount in the gel or gelated ionic liquid film may be
between about 0 wt % and about 25 wt %, e.g., between about 0 wt %
and about 5 wt %, between about 5 wt % and about 10 wt %, between
about 10 wt % and about 15 wt %, or between about 15 wt % and about
25 wt %. Any suitable solvent may be used. For example, the solvent
may be an organic solvent, e.g., an organic solvent having a
suitably wide electrochemical window so as not to interfere with
the electrochemical processes of the electrochemical cell. For
example, the solvent may be acetone or it may be acetonitrile.
[0137] The gel may be thermally stable up to any suitable
temperature, e.g., it may be stable up to at least about
150.degree. C., at least about 160.degree. C., or at least about
180.degree. C. The gel may have any suitable electrochemical
stability, e.g., it may have an electrochemical stability that is
greater than the electrochemical window of the redox couple, e.g.,
the M/M.sup.n+ and R/R.sup.n- redox couple, e.g., Zn/Zn.sup.2+ and
Br.sub.2/Br.sup.- (-0.83 V for Zn/Zn.sup.2+ and 1.07 V for
Br.sub.2/Br.sup.-).
[0138] Non-limiting examples of gelated ionic liquids made in
accordance with the present invention are given in Example 2.
Non-limiting examples of gelated ionic liquids made in accordance
with the present invention comprising additional dissolved redox
species are given in Example 3, Example 4 and Example 8.
Gelated Ionic Liquid Films (GILFs)
[0139] A gelated ionic liquid film in accordance with the present
invention comprises an ionic liquid encapsulated within a gel
matrix. The gel matrix may be as described in the section entitled
`Gelating agent/Gel matrix`. The encapsulated ionic liquid may be
as described in the section entitled `Ionic liquids`. The gelated
ionic liquid films may comprise other species, e.g., electrolyte
salts and/or other aqueous redox species and/or may have certain
physical and/or chemical properties as described in the section
entitled `Gelated ionic liquids`.
[0140] It will be understood by persons skilled in the art that the
gel matrix encapsulating an ionic liquid may be formed into a film,
thereby becoming a gelated ionic liquid film, using any suitable
film-forming technique.
Assembly
Electrically Conductive Surface
[0141] An assembly as described herein may comprise a gelated ionic
liquid film in contact with an electrically conductive surface. The
contacting may be effected, for example, by printing the mixture
onto the electrically conductive surface. The electrically
conductive surface may conduct electricity. The electrically
conductive surface may be an electrode, e.g., an anode or a
cathode. The anode and/or cathode may be inert, e.g., it may be
graphite (carbon), nanotubes (carbon), graphene composite (carbon),
or any non-reactive metal, e.g., platinum, gold, titanium, or
mixtures thereof etc. Preferably, the cathode is inert. The anode
or cathode may alternatively be active (i.e., reactive), e.g., it
may be any suitable reactive metal e.g., a transition metal
including Fe, Zn, Ni, Cu, Mn, etc. The anode and cathode may be
made from the same material. For example, in one embodiment, both
the anode and the cathode comprise or consist of graphite (carbon),
e.g., carbon paper, or a graphene composite. In another embodiment,
both the anode and the cathode comprise or consist of titanium,
e.g., titanium mesh. The terms `anode` and `cathode` as used in
this section and elsewhere in the description and claims refer to
the anode (i.e., site of oxidation) and cathode (i.e., site of
reduction) when a complete circuit comprising the anode and cathode
is operating in a spontaneous direction (i.e., during discharge),
unless the context indicates otherwise.
Contact conditions
[0142] An assembly in accordance with the present invention
comprising a gelated ionic liquid film in contact with an
electrically conductive surface may be manufactured using any
suitable method. For example, the gelated ionic liquid film may be
contacted with the electrically conductive surface by application
of an ionic liquid encapsulated within a gel matrix onto the
electrically conductive surface using film forming techniques known
in the art, including spreading, evaporative drying, dip coating,
etc. The ionic liquid encapsulated within a gel matrix may be
formed into a film prior to contacting with the electrically
conductive surface. Alternatively, the ionic liquid encapsulated
within a gel matrix may form into a film once applied to the
electrically conductive surface, e.g., the ionic liquid
encapsulated within a gel matrix may be applied to the electrically
conductive surface using any of the preceding film forming
techniques whilst it is melted, e.g., at a temperature of between
about 80.degree. C. and about 150.degree. C., and then allowed to
set on the electrically conductive surface to form a gelated ionic
liquid film thereon. The film may be applied to one side and/or
face of the electrically conductive surface, or may be applied to
all sides and/or faces of the electrically conductive surface.
[0143] The contact between the gelated ionic liquid film and the
electrically conductive surface may be strengthened by attractive
interactions between the film and the surface.
[0144] An assembly in accordance with the present invention may
also be manufactured by printing a mixture of a gelating agent and
an ionic liquid onto an electrically conductive surface. Any
suitable printing technique may be used; for example, the printing
may be inkjet and/or 3D printing. Where an inkjet/3D printing
technique is used, the mixture of a gelating agent and an ionic
liquid may be printed or deposited onto the electrically conductive
surface. The mixture of a gelating agent and an ionic liquid may be
deposited on the electrically conductive surface by the printer
prior to the mixture setting. In this way, the printer may enable
formation of a gelated ionic liquid film of known or tuneable
thickness on the electrically conductive surface. The printing may
comprise depositing a first layer of a mixture of a gelating agent
and an ionic liquid on an electrically conductive surface, or may
comprise depositing a first and second layer of a mixture of a
gelating agent and an ionic liquid on an electrically conductive
surface, wherein the second layer is deposited over the first layer
and wherein the second layer may comprise the same or different
gelating agent and/or ionic liquid to the first layer. The printing
may further comprise depositing a third, fourth, fifth, or
subsequent layer of a mixture of a gelating agent and an ionic
liquid on the electrically conductive surface such that a desired
thickness and/or number of layers is achieved. The printing may
comprise depositing one or more layer(s) of a mixture of a gelating
agent and an ionic liquid on one side and/or face of the
electrically conductive surface, or may comprise depositing one or
more layer(s) of a mixture of a gelating agent and an ionic liquid
on all sides and/or faces of the electrically conductive
surface.
[0145] The gelated ionic liquid film may have a thickness of from
about 50 .mu.m to about 10 mm, e.g., between about 50 .mu.m and
about 1 mm, or between about 100 .mu.m and about 10 mm, or between
about 100 .mu.m and about 1 mm, or between about 0.5 mm and about 1
mm, or between about 1 mm and about 5 mm, or between about 5 mm and
about 10 mm.
[0146] The gelated ionic liquid film may cover or coat up to 100%
of the surface area of the electrically conductive surface, or up
to about 99%, or up to about 95%, or up to about 90%, about 80%,
about 70%, about 60%, or up to about 50% of the surface area of the
electrically conductive surface. Where the electrically conductive
surface is an electrode, and the electrode comprises two
substantially large surface area faces, the gelated ionic liquid
film may coat up to about 100% of the surface area of either one of
or both of those faces, or up to about 99%, or up to about 95%, or
up to about 90%, about 80%, about 70%, about 60%, or up to about
50% of the surface area of either one of or both of those
faces.
[0147] An assembly in accordance with the present invention and as
described in this section may comprise a first gelated ionic liquid
film in contact with a first electrically conductive surface,
wherein the first gelated ionic liquid film comprises an ionic
liquid encapsulated within a gel matrix. The first gelated ionic
liquid film may comprise a gel matrix as described in the section
entitled `Gelating agent/Gel matrix`, an encapsulated ionic liquid
as described in the section entitled `Ionic liquids`, and
optionally other species, e.g., electrolyte salts and/or additional
dissolved aqueous redox species as described in the section
entitled `Gelated ionic liquids`. The first electrically conductive
surface may be as described in the section entitled `Electrically
conductive surface`, and the first gelated ionic liquid film may be
contacted with the first electrically conductive surface as
described in the section entitled `Contact conditions`.
[0148] The assembly in accordance with the present invention and as
described in this section may further comprise a second gelated
ionic liquid film in contact with a second electrically conductive
surface, wherein the second gelated ionic liquid film comprises an
ionic liquid encapsulated within a gel matrix, and wherein the
first and second liquid films are in contact with each other. When
in contact with each other, the first and second liquid films may
be immiscible. The second gelated ionic liquid film may comprise a
gel matrix as described in the section entitled `Gelating agent/Gel
matrix`, an encapsulated ionic liquid as described in the section
entitled `Ionic liquids`, and optionally other species, e.g.,
electrolyte salts and/or additional dissolved redox species as
described in the section entitled `Gelated ionic liquids`. The
second electrically conductive surface may be as described in the
section entitled `Electrically conductive surface`, and the second
gelated ionic liquid film may be contacted with the second
electrically conductive surface as described in the section
entitled `Contact conditions`. Preferably, the first electrically
conductive surface is an anode, and the second electrically
conductive surface is a cathode. More preferably, the anode is an
inert anode, and the cathode is an inert cathode.
[0149] The assembly in accordance with the present invention and as
described in this section may still further comprise a third
gelated ionic liquid film in contact with a third electrically
conductive surface, wherein the third gelated ionic liquid film
comprises a third ionic liquid encapsulated within a gel matrix;
and wherein the second and third liquid films are at least
partially in contact. When in contact with each other, the second
and third liquid films may be immiscible. The third gelated ionic
liquid film may comprise a gel matrix as described in the section
entitled `Gelating agent/Gel matrix`, an encapsulated ionic liquid
as described in the section entitled `Ionic liquids`, and
optionally other species, e.g., electrolyte salts and/or additional
dissolved redox species as described in the section entitled
`Gelated ionic liquids`. The third electrically conductive surface
may be as described in the section entitled `Electrically
conductive surface`, and the third gelated ionic liquid film may be
contacted with the second electrically conductive surface as
described in the section entitled `Contact conditions`. Preferably,
the third electrically conductive surface is an anode.
[0150] In accordance with the present invention, when the second
and third gelated ionic liquid films are in contact, the first and
third gelated ionic liquid films are not in contact with each
other. Accordingly, in one embodiment, the first gelated ionic
liquid film is in contact with one face or side of the second
gelated ionic liquid film, which is itself in contact with the
second electrically conductive surface, and the third gelated ionic
liquid film is in contact with another (e.g., opposing or parallel)
face or side of the second gelated ionic liquid film.
[0151] The assembly according to the invention may yet further
comprise a fourth gelated ionic liquid film in contact with a
fourth electrically conductive surface, and optionally a fifth
gelated ionic liquid film in contact with a fifth electrically
conductive surface, up to an nth gelated ionic liquid film in
contact with an nth electrically conductive surface, where n is a
positive integer. Preferably, the assembly according to the
invention comprises an even number of gelated ionic liquid films in
contact with electrically conductive surfaces. Accordingly, in one
embodiment, every first electrically conductive surface is an
anode, and every second electrically conductive surface is a
cathode.
Electrochemical Cell
Construction
[0152] The present invention also provides for an electrochemical
cell comprising an assembly as described above in the section
entitled `Assembly`. More particularly, the present invention
provides for an electrochemical cell comprising at least a first
gelated ionic liquid film in contact with a first electrically
conductive surface and a second gelated ionic liquid film in
contact with a second electrically conductive surface, wherein the
first and second gelated ionic liquid films comprise an ionic
liquid encapsulated within a gel matrix, and wherein the first and
second liquid films are in contact with each other.
[0153] The present invention also provides for an electrochemical
cell comprising a first gelated ionic liquid film in contact with a
first electrically conductive surface, wherein the first gelated
ionic liquid film comprises a first ionic liquid encapsulated
within a gel matrix, and a second gelated ionic liquid film in
contact with a second electrically conductive surface, wherein the
second gelated ionic liquid film comprises a second ionic liquid
encapsulated within a gel matrix, wherein the first and second
liquid films are at least partially in contact. The term `partially
in contact` may refer to the liquid films being at least about 30%
overlapping, or at least about 40%, 50%, 60%, 70%, 80%, 90%, 99%,
or up to about 100% overlapping, where the size of the region of
overlap is equal or approximately equal for both films.
[0154] As described above in the section entitled `Assembly`, the
first and/or second gelated ionic liquid film may comprise a gel
matrix as described in the section entitled `Gelating agent/Gel
matrix`, an encapsulated ionic liquid as described in the section
entitled `Ionic liquids`, and optionally other species, e.g.,
electrolyte salts and/or other aqueous redox species as described
in the section entitled `Gelated ionic liquids`. The first and/or
second electrically conductive surfaces may be as described in the
section entitled `Electrically conductive surface`, and the first
and/or second gelated ionic liquid film may be contacted with the
first and/or second electrically conductive surface, respectively,
as described in the section entitled `Contact conditions`.
Preferably, the first electrically conductive surface is an anode,
and the second electrically conductive surface is a cathode. More
preferably, the anode is an active anode, and the cathode is an
inert cathode.
[0155] The electrochemical cell described above may further
comprise a third gelated ionic liquid film in contact with a third
electrically conductive surface, wherein the third gelated ionic
liquid film comprises a third ionic liquid encapsulated within a
gel matrix, and wherein the second and third liquid films are at
least partially in contact. The second and third liquid films may
be immiscible when in contact with each other. The third ionic
liquid film may comprise a gel matrix as described in the section
entitled `Gelating agent/Gel matrix`, an encapsulated ionic liquid
as described in the section entitled `Ionic liquids`, and
optionally other species, e.g., electrolyte salts and/or other
aqueous redox species as described in the section entitled `Gelated
ionic liquids`. The third electrically conductive surface may be as
described in the section entitled `Electrically conductive
surface`, and the third gelated ionic liquid film may be contacted
with the third electrically conductive surface as described in the
section entitled `Contact conditions`. Preferably, the third and
first electrically conductive surfaces are anodes and the second
electrically conductive surface is a cathode. More preferably, the
anodes are inert anodes, and the cathode is an inert cathode.
[0156] As outlined above for the assembly according to the
invention, the electrochemical cell according to the invention may
further comprise a fourth gelated ionic liquid film in contact with
a fourth electrically conductive surface, optionally a fifth
gelated ionic liquid film in contact with a fifth electrically
conductive surface, and optionally up to an nth gelated ionic
liquid film in contact with an nth electrically conductive surface,
where n is a positive integer.
[0157] The electrochemical cell may therefore comprise two or more
assemblies, e.g., two or more alternating anodes and/or cathodes,
wherein each anode and cathode is in contact with its own gelated
ionic liquid film. Preferably, the gelated ionic liquid films in
contact with adjacent anode and cathode surfaces are also in
contact with each other, such that ion transport between the two
gelated ionic liquid films is enabled.
[0158] The ionic liquids encapsulated in the gel matrices of the
gelated ionic liquid films may also alternate, such that the ionic
liquid encapsulated in the gel matrix in contact with the anode has
one composition, and the ionic liquid encapsulated in the gel
matrix in contact with the cathode has a different composition.
Preferably, the ionic liquid encapsulated in the gel matrix in
contact with the anode is immiscible with the ionic liquid
encapsulated in the gel matrix in contact with the cathode, such
that the gelated ionic liquid film in contact with the anode is
immiscible with the gelated ionic liquid film in contact with the
cathode. This may advantageously prevent the gelated ionic liquid
films from intermixing when in contact with each other, whilst
still allowing ion transport between the films. In some
embodiments, mutually miscible ionic liquids are used in the anode
and cathode films where the gel films sufficiently immobilise the
ionic liquids and thus prevent them from intermixing or
substantially intermixing.
[0159] The gelated ionic liquid films may also be immiscible with
each other. In the context of gelated ionic liquid films,
`immiscible` may refer to the gel matrix of one film being
physically distinct or separable from the gel matrix of another
film, even though ion transport may be enabled between the films
when they are in contact with each other. Accordingly, the gel
matrix of one film may be derived from the same gelating agent as
the gel matrix of another film, but by virtue of, e.g., separate
synthesis of the two films, the films may be immiscible when in
contact with each other. For example, the first and second gelated
ionic liquid films may be immiscible when in contact with each
other, and the second and third gelated ionic liquid films may be
immiscible when in contact with each other. The gelated ionic
liquid films may be immiscible with each other when the ionic
liquids encapsulated within the gel matrices are immiscible, or
when the ionic liquids are mutually miscible. Accordingly, in one
embodiment, the first and second (or second and third) gelated
ionic liquid films comprise mutually miscible ionic liquids, but
the films themselves are immiscible when in contact with each
other. In another embodiment, the first and second (or second and
third) gelated ionic liquid films comprise immiscible ionic
liquids, and the films themselves are immiscible when in contact
with each other.
[0160] The assemblies may be connected to an external circuit using
any suitable means, e.g., using any suitable electrically
conductive material of any suitable size or shape. For example, the
external circuit may comprise wires, e.g., metal wires, as a means
to connect to one or more external devices, e.g., devices to
measure current, voltage, and/or resistance, or means to connect to
one or more loads for discharging, or means to connect to one or
more power supplies to enable recharging. The external circuit may
thus include any suitable device(s) to transport and/or moderate
the electrical energy for consumption in an external application.
The external circuitry may be connected to the anode(s) and
cathode(s) using any suitable method, e.g., clamping, welding, or
fixing using adhesives, e.g., epoxy resins, etc. such that electron
flow to or from the anode or cathode through the external circuitry
is enabled.
[0161] In one embodiment, the anodes and cathodes in each assembly
may be flat or substantially flat in shape, for example, flat
square or rectangular sheets or substantially flat square or
rectangular prisms, and the gelated ionic liquid film in contact
with each anode or cathode may cover up to 100% of the available
anode or cathode surface area, or up to 95%, 90%, 85%, 80% or 70%
of the available anode or cathode surface area. The available anode
or cathode surface area may be the total surface area of the anode
or cathode minus the surface area required to connect the anode or
cathode to an external circuit and/or support the anode or cathode
in a stack. For example, the gelated ionic liquid film in contact
with each anode or cathode may cover up to 100% of each of the
substantially flat surfaces of the cathode or anode, optionally
also covering each edge or edge face. The size and shape of each
anode and cathode may be the same or may differ. The % area
coverage of gelated ionic liquid films on each anode or cathode
similarly may be the same or may differ.
[0162] Where the anodes and cathodes in each assembly are
substantially flat in shape, the assemblies may be stacked together
such that the substantially flat surfaces are at least partially in
contact. For example, the stacking arrangement may be such that the
flat or substantially flat surface of the anode is in contact with
the entire flat or substantially flat surface of its adjacent
cathode(s). In one embodiment, the substantially flat surface of
the anode is in partial contact with the substantially flat surface
of its adjacent cathode(s), and the anodes and cathodes in the
stack are staggered such that the anodes extend beyond the contact
area in one direction, and the cathodes extend beyond the contact
area in the opposite direction. The stacked assemblies may be
encased using any suitable encasing structure.
Method of Producing an Assembly
[0163] The present invention also provides for a method of
producing an assembly as described in the preceding sections
comprising providing a first gelated ionic liquid film comprising a
first encapsulated ionic liquid in contact with a first
electrically conductive surface; and providing a second gelated
ionic liquid film comprising a second encapsulated ionic liquid in
contact with a second electrically conductive surface; and
contacting the first and second gelated ionic liquid films. In this
method of producing an assembly, `providing` may comprise combining
a gelating agent (e.g., a liquefied or solid gelating agent) with
an ionic liquid at a suitable temperature to produce a mixture, and
allowing the mixture to set and thereby form a gelated ionic liquid
film in which the ionic liquid is encapsulated, and contacting the
mixture or the gelated ionic liquid film with an electrically
conductive surface. The first and second (and third, fourth, etc.)
gelated ionic liquid films may be provided in this way.
[0164] The gelating agent may be as described in the section
entitled `Gelating agent/gel matrix` and the ionic liquid may be as
described in the section entitled `Ionic liquids`.
[0165] In the above method of producing an assembly, the liquefied
mixture may be contacted with the electrically conductive surface
prior to allowing the liquefied mixture to set. In doing so, a
greater proportion of the available surface area of the
electrically conductive surface may be covered by, and thus
interact with, the liquefied mixture (and thus the resultant
gelated ionic liquid film) relative to if the gelated ionic liquid
film is set prior to contacting it with the electrically conductive
surface. The contacting may, for example, be effected by printing
the mixture onto the first electrically conductive surface.
[0166] Preferably, the first electrically conductive surface is an
anode and the second electrically conductive surface is a
cathode.
[0167] The method above may still further comprise providing a
third gelated ionic liquid film comprising a third encapsulated
ionic liquid and in contact with a third electrically conductive
surface, and contacting the second and third gelated ionic liquid
films. Preferably, the third electrically conductive surface is an
anode.
[0168] As described above, any one or more of the first, second
and/or third ionic liquids may comprise an anion selected from any
one or more of bromide, chloride, iodide,
bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide,
acetate, propionate, pentanoate, hexanoate, hexafluorophosphate,
and tris(pentafluoro)trifluorophosphate and/or a cation selected
from any one or more of 1-butylpyridinium, 1-octylpyridinium,
1-(2-hydroxyethyl)pyridinium, 1-ethyl-3-methylimidazolium,
1-butyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium,
1-hexyl-3-methylimidazolium,
1-(2-methoxyethyl)-3-methylimidazolium,
1-(1-methoxymethyl)-3-methylimidazolium,
1-methyl-3-octylimidazolium, 1-methyl-1-ethylpyrolidinium,
1-methyl-1-butylpyrrolidinium, 1-methyl-1-hexylpyrolidinium,
1-(2-methoxyethyl)-1-methylpyrrolidinium,
1-(1-methoxymethyl)-1-methylpyrrolidinium, tetrabutylphosphonium,
tributyloctylphosphonium, tributyl(2-methoxyethyl)phosphonium,
tributyl-tert-butylphosphonium,
tributyl(1-methoxymethyl)phosphonium, tetraethylammonium,
tetrabutylammonium, tributyloctylammonium,
tributyl(2-methoxyethyl)ammonium,
tributyl(1-methoxymethyl)ammonium, and tributyl-tert-butylammonium
as described in the section entitled `Ionic liquids`. The first,
second and/or third gelated ionic liquid film may optionally
comprise other species, e.g., electrolyte salts and/or other
aqueous redox species as described in the section entitled `Gelated
ionic liquids`. The first, second and/or third electrically
conductive surface may be as described in the section entitled
`Electrically conductive surface`, and the first, second and/or
third gelated ionic liquid film may be contacted with the first,
second and/or third electrically conductive surface, respectively,
as described in the section entitled `Contact conditions`.
EXAMPLES
[0169] The present invention will now be described with reference
to specific examples, which should not be construed as in any way
limiting
Example 1: Synthesis and Characterisation of Ionic Liquid
Polybromide Formation
[0170] This example presents the results of a study into a range of
ionic liquid cations capable of forming polybromide species (see
Scheme 1). The bromine sequestering agent (BSA) [C.sub.2MPyr]Br was
used as a model, and the cyclic structure
1-alkyl-1-methylpiperdinium (C.sub.2MPipBr), its aromatic analogue,
1-ethylpyridinium ([C.sub.2Py]Br) and its ethoxy-substituted
analogue, 1-(2-hydroxyethyl)pyridinium ([C.sub.2OHPy]Br) and
alkylammonium bromide salts ([N.sub.n,n,n,n]Br) were studied.
##STR00001##
[0171] (a) Ionic Liquid Synthesis:
[0172] Tetraethyl and tetrabutylammonium bromide were sourced from
Sigma Aldrich. Other ionic liquids were prepared by quaternisation
of the required tertiary amine with the respective bromoalkane
(Sigma Aldrich) as per literature methods (Burrell, A. K., et al.,
The large scale synthesis of pure imidazolium and pyrrolidinium
ionic liquids. Green Chemistry, 2007. 9(5): p. 449-454).
[0173] (b) Polybromide Preparation:
[0174] Most of the studied ionic liquids are white crystalline
powders at room temperature. While all starting compounds are
soluble in aqueous solutions, the resulting polybromide species
form a separate phase. To examine their behavior in solution by
both Raman spectroscopy and .sup.1H NMR, ionic liquids were
dissolved in methanol:acetonitrile (1:10) mixture which was capable
of dissolving all studied ionic liquids and their respective
polybromides at the required concentrations. 1 M solutions of ionic
liquid were prepared prior to sequential volumetric addition of
bromine at Br.sub.2:IL molar ratios of 0.8, 1.0, 1.2, 1.4, 1.6 and
1.8:1.
[0175] (c) Raman Spectroscopy:
[0176] IL-polybromides were sub-sampled in glass capillaries after
each addition of liquid bromine and flame sealed prior to Raman
spectroscopy. Raman spectra were recorded on an inVia Renishaw
spectrometer using a liquid cooled Ge detector. Spectra were
recorded in backscattering mode at room temperature (830 nm, 1%
power, resolution 4 cm.sup.-1).
[0177] At the studied concentrations, spectra indicated the
presence of tri- and pentabromide species. To elucidate the
relative proportions of these, raw spectra were treated by Gaussian
peak fitting. The integrated areas of the peak-fitted signals for
the symmetric stretches of tri- and pentabromide were then used to
rate the ionic liquids in terms of polybromide forming efficiency
(i.e., their preference towards the higher order polybromide).
[0178] (d).sup.1H NMR Dimerisation Experiments:
[0179] Dimerisation experiments were conducted as per adapted
literature methods (Weber, C. C., A. F. Masters, and T. Maschmeyer,
Controlling hydrolysis reaction rates with binary ionic liquid
mixtures by tuning hydrogen-bonding interactions. Journal of
Physical Chemistry B, 2012. 116(6): p. 1858-186; Hunter, C. A., et
al., Substituent effects on cation-.pi. interactions: A
quantitative study. Proceedings of the National Academy of Sciences
of the United States of America, 2002. 99(8): p. 4873-4876).
CD.sub.3CN was added to an NMR tube equipped with a Young's valve,
with 0.1 M and 1 M solutions of the chosen ionic liquid (10% MeOD
in CD.sub.3CN) prepared independently. These stock solutions were
added to the NMR tube sequentially prior to recording of the
.sup.1H NMR spectrum. The chemical shift of the C2 proton of the
ionic liquid at each concentration was recorded and fitted to the
dimerisation isotherm generated previously by Weber, et al.
[0180] (e) Computational Details:
[0181] Standard DFT calculations were carried out with Gaussian 09
(Frisch, M. J., et al., Gaussian 09, Revision C.01, ed. I.
Gaussian. 2009, Wallingford Conn.). Geometries were obtained at the
M05-2X/6-31G(d) level in conjunction with the SMD continuum
solvation model (Zhao, Y., N. E. Schultz, and D. G. Truhlar, J.
Chem. Theory Comput., 2006. 2: p. 364-382; Marenich, A. V., C. J.
Cramer, and D. G. Truhlar, J. Phys. Chem. B 2009. 113: p.
6378-6396). The SMD model, when used in conjunction with the
M05-2X/6-31G(d) method, has been shown to yield free energies of
solvation with an overall mean absolute deviation of just 2.7 kJ
mol.sub.-1 for a diverse set of solutes in a wide range of
non-aqueous solvents (Marenich et al.). The parameters for
acetonitrile were used in conjunction with the SMD model in order
to best reflect the experimental reaction conditions. The
vibrational frequencies of stationary points were inspected to
ensure that they corresponded to minima on the potential energy
surface. Refined single-point energies were obtained with the
MPW-B1K procedure with the 6-311+G(3df,2p) basis set (Zhao, Y. and
D. G. Truhlar, J. Phys. Chem. A 2004. 108: p. 6908-6918).
Scalar-relativistic effects are incorporated into the MPW-B1K
calculations using the second-order Douglas-Kroll-Hess protocol.
The D3BJ dispersion corrections were included in total electronic
energies. In this preliminary investigation, it was find that this
protocol yields binding energies of bromides that are in best
agreement with benchmark values obtained with the high-level W1X-2
procedure (Grimme, S., et al., J. Chem. Phys., 2010. 132(154104):
p. 1-19; Grimme, S., S. Ehrlich, and L. Goerigk, J. Comput. Chem,
2011. 32: p. 1456-1465; Chan, B. and L. Radom, J. Chem. Theory
Comput., 2012. 8: p. 4259-4269). Zero-point vibrational energies
and thermal corrections to enthalpy and entropies at 298 K, derived
from scaled M05-2X/6-31G(d) frequencies, were incorporated into the
total energies (Merrick, J. P., D. Moran, and L. Radom, J. Phys.
Chem. A, 2007. 111: p. 11683-11700). The total MPW-B1K free
energies also include the effect of solvation using the SMD model
and parameters derived for acetonitrile. All relative energies are
reported as solvation-corrected 298 K free energies in kJ
mol.sup.-1.
[0182] Results and Discussion:
[0183] Ionic liquid solutions progressed from a light orange to
deep red with sequential additions of bromine. Raman spectroscopy
of these solutions revealed a pure tribromide species at the 0.8:1
Br.sub.2:IL ratio as signified by the strong symmetric stretch at
160 cm.sup.-1 and the broad asymmetric stretch at 197 cm.sup.-1
(literature, 163 and 198 cm.sup.-1; Chen, X., et al., Raman
Spectroscopic Investigation of Tetraethylammonium Polybromides.
Inorganic Chemistry, 2010. 49(19): p. 8684-8689) With subsequent
additions of bromine, the growth of a pentabromide species
(signified by the broad asymmetric stretch at 208 cm.sup.-1 and the
sharp symmetric stretch at 256 cm.sup.-1: literature; 210 and 253
cm.sup.-1; Chen et al.) was observed eventually for all ionic
liquids. An example Raman spectrum for the [C.sub.2MPyr]Br.sub.n
system is shown in FIG. 3, with peak heights normalised to the
tribromide symmetric peak in order to demonstrate the growth of the
pentabromide anion with increasing bromine concentration. The ratio
of Br.sub.5.sup.-/Br.sub.3.sup.- defines the `Polybromide Forming
Efficiency` and was used to construct FIGS. 4A-C.
[0184] FIGS. 4A-C show the selectivity for the higher bromide
species as a function of the concentration of Br.sub.2. For the
ionic liquid species studied, the aromatic analogues [C.sub.2MIM]Br
and [C.sub.2Py]Br were the most poorly performing cations, while
the tetraalkylammonium and butyl-substituted pyrrolidinium and
pyridinium were the best performing cations. Of moderate
performance were the long (C.sub.6) and short (C.sub.2) chain
pyrrolidinium and pyridinium cations which all gave numerical
values that were remarkably alike.
[0185] In order to determine the efficacy of the polybromide
formation in various ILs, the ratio of the symmetric Br.sub.5.sup.-
to the symmetric Br.sub.3.sup.- stretches in the Raman spectra was
determined, with the rationale being that the better an IL was at
forming and stabilising the higher order polybromide, the more
efficient its action as a sequestering agent. The absorption bands
of even higher order polybromides (Br.sub.7.sup.-, Br.sub.9.sup.-,
etc) appear at wavenumbers so close to each other that it is
difficult to obtain clear ratios of each, and thus other ratios
were not determined. From FIG. 5A, it is clear that certain cation
species have an enhanced ability to form polybromide species. For
example, the cations [C.sub.4MPyr].sup.+ and [N.sub.4444].sup.+
have the greatest ability of the cations studied to form and
stabilise higher order polybromide species in solution, closely
followed by the cations [N.sub.2222].sup.+, [C.sub.4MPip].sup.+,
[N.sub.8884].sup.+, [C.sub.2MPip].sup.+, and [C.sub.2Mpyr].sup.+.
Grouping the various cation types together allows information on
the influence of the length of the alkyl chain on the polybromide
to obtained (FIG. 5B). In every case, the longest chain derivative
performed most poorly, with the butyl derivative the best
performing and the ethyl analogue of intermediate performance.
[0186] These observations allow the conclusion that cations with
less diffuse charges and moderate length of substituted alkyl
chains preferentially form higher order polybromide species. It is
hypothesised that these observations stemmed from a combination of
the relative strength of cation-anion interactions and ion pair
self-assembly in solution. These hypotheses were examined by DFT
calculations of ionic binding energy, and .sup.1H NMR dimerisation
experiments respectively.
[0187] DFT calculations were performed to quantitate the strength
of Q-Br ion pair interactions, which were used here as a proxy to
the polybromide forming efficiency. The calculated binding energy
forms a reasonable correlation with the experimentally observed
efficiency. The condensed phase MPW-B1K free energies of binding
are listed in Table 1 and a plot of these values against the
polybromide forming efficiency is shown in FIG. 6. The ILs that
preferenced the higher order polybromide were generally seen to be
those that exhibited more positive free energy of binding (FIG. 6),
that is, more weakly associated ion pairs.
[0188] This trend is ascribed to the `availability` of the bromide
anion. Ion pairs with more positive binding energies are more
weakly associated ion pairs, and less electronic influence of the
cation over the bromide anion can therefore be expected. This
allows the bromide ion to donate greater influence from its HOMO to
the LUMO of the entering bromine molecules without the competition
present in the ion pairing process. Diffuse charges, such as that
of the pyridinium and imidazolium cations, are undesirable as they
`consume` the charge of the bromide anion, making it less available
for bromine molecules to be sequestered by the bromide salt.
Conversely, positive point charges were calculated to be more
weakly associating, and in turn elicit less influence on the
bromide anion, effectively freeing it up for polybromide
formation.
[0189] The trend of binding energy with performance was generally
reasonable, but the calculations do not fully account for the
relatively lower performance of [C.sub.6MIM]Br and [C.sub.6MPip]Br
in particular. Their behaviour was thus attributed to other
structural effects. It is proposed that this is associated with the
self-assembly of the IL ion pairs in solution.
[0190] In order to explain the "off-trend" behaviours of
[C.sub.6MIM]Br and [C.sub.6MPip]Br, a series of .sup.1H NMR
dilution experiments were performed to follow the dimerisation of
IL ion pairs, and thus quantitate their degree of self-assembly in
solution. The .sup.1H chemical shifts for the respective C2 protons
of the cations were recorded and plotted against species
concentration before fitting to a dimerisation isotherm (an example
is shown in FIG. 7). This procedure allowed the dimerisation
association constant (K.sub.a), Gibbs free energy values
(.DELTA.G.sub.d) and the limiting chemical shifts of the ion pair
and dimer (.delta..sub.ip and .delta..sub.d) to be determined
(Table 1).
TABLE-US-00001 TABLE 1 Summary of Binding Energy Calculations and
.sup.1H NMR Titration Data (at 300K in MeOD:CD.sub.3CN (1:10)).
.DELTA.G.sub.B.E. .DELTA.G.sub.dim .DELTA..delta..sub.2H Compound
(kJ mol.sup.-1) K.sub.a (kJ mol.sup.- (ppm.sup.-1)
[N.sub.2,2,2,2]Br 28.1 4.70 .+-. 0.20 -3.86 0.07 [N.sub.4,4,4,4]Br
37.4 9.71 .+-. 0.46 -5.67 0.09 [N.sub.8,8,8,4]Br 25.6 15.5 .+-.
0.91 -6.84 0.08 [C.sub.2MPyr]Br 21.0 20.6 .+-. 0.72 -7.54 0.14
[C.sub.4MPyr]Br 23.3 8.53 .+-. 1.3 -5.35 0.21 [C.sub.6MPyr]Br 19.6
27.1 .+-. 7.6 -8.23 0.18 [C.sub.2MPip]Br 14.2 20.8 .+-. 1.1 -7.57
0.14 [C.sub.4MPip]Br 19.5 21.0 .+-. 2.3 -7.59 0.17 [C.sub.6MPip]Br
18.2 14.26 .+-. 1.8 -- -- [C.sub.2MIM]Br 16.9 29.9 .+-. 2.32 -- --
[C.sub.4MIM]Br 21.6 -- -- -- [C.sub.6MIM]Br 16.5 24.3 .+-. 3.1 --
-- [C.sub.2Py]Br 11.5 28.6 .+-. 1.0 -8.36 0.14 [C.sub.2OHPy]Br
-10.2 172 .+-. 24 -12.8 1.46
The results in Table 1 demonstrate a high propensity for
dimerisation of cations with aromatic groups or long-alkyl chains,
which is consistent with the previously proposed influence of
.pi.-interactions between monomers, or the increased influence of
intermolecular hydrophobic interactions, respectively. The trend
for ease of dimerisation is inversely proportional to the
polybromide forming efficiency, demonstrating that freely
dissociated ion pairs are more likely to build higher-order
polybromide species. Thus, where the binding energy influence does
not fully explain the compound's performance as a BSA, their
strength of dimerisation may also be a significant factor. This can
be ascribed to a reduced steric availability of the bromide anion
in highly associated ionic liquids, which limits entering bromine
molecules from sequestration by bromide anions.
[0191] In contrast, in the case of the alkylammonium bromide salts,
the dimerization energies decreased with increasing chain-length,
which does not directly correspond with the aforementioned bromine
sequestration behaviour of the order of
tetrabutyl>tetraethyl>trioctylbutyl. While dimerization
behaviour does have some influence over the bromine sequestration
properties of ionic liquids, this experimental observation suggests
that the binding energy of the ion-pair is likely to be the more
dominant influence over the cation's bromine sequestration
behaviour, in particular for the alkylammonium cations.
Example 2: Synthesis of Ionogels Using Polymer Gelation Agents
[0192] General Considerations:
[0193] The following chemicals were used as received: poly(ethylene
oxide) (M.sub.n 1000000; PEO), poly(vinylidene
fluoride-co-hexafluoropropylene) (av. M.sub.w .about.455000,
PVdF-HPF), zinc bromide dehydrate, zinc nitrate hexahydrate,
bromine.
[0194] The following ionic liquids (ILs) were prepared using
standard literature methods: N-octylpyridinium bromide
([C.sub.8Py]Br), N-octylpyridinium
bis(trifluoromethanesulfonyl)imide ([C.sub.8Py]NTf.sub.2),
octyltributylphosphonium bromide ([P.sub.8,4,4,4]Br),
tetrabutylphosphonium bromide ([P.sub.4,4,4,4]Br),
1-butyl-3-methylimidazolium bromide ([BMIM]Br),
1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide
([BMIM]NTf.sub.2), 1-butyl-2,3-dimethylimidazolium bromide
([BDMIM]Br), 1-butyl-2,3-dimethylimidazolium
bis(trifluoromethanesulfonyl)imide ([BDMIM]NTf.sub.2).
[0195] General Method:
[0196] To a solution of the ionic liquid (500 mg) in acetone (4 mL)
was added the desired polymer (50 mg (10 wt. %) or 100 mg (20 wt.
%)). The resultant suspension was heated at 60.degree. C. with
constant agitation until the solution was homogeneous. The
resultant solution was then decanted into a suitable mould and then
placed on a heated surface (.about.50.degree. C.) to allow the
acetone to slowly evaporate over a the course of a couple of hours.
The resultant ionogel was then carefully removed from the mould by
means of forceps.
[0197] Gelation of [C.sub.8Py]NTf.sub.2 with 20 wt. % Poly(Ethylene
Oxide) (PEO):
[0198] The resultant ionogel was obtained as an optically clear gel
and very sticky to the touch, and turned out to be an extremely
viscous liquid, not a self-supporting membrane.
[0199] Gelation of [P.sub.8444]Br with 20 wt. % PEO:
[0200] The resultant ionogel was obtained as a white opaque gel
with good elastic strength. When 10 wt. % of polymer was used there
was insufficient polymer to fully sequester the IL.
[0201] Gelation of Octyltributylphosphonium Phosphonium Bromide
with PEO:
[0202] To a solution of poly(ethylene oxide) (M.sub.n 1000000) (100
mg) in ethyl acetate (10 mL), which had been heated at 60.degree.
C. in order to facilitate dissolution of the polymer, was added
octyltributylphosphonium bromide (500 mg) in ethyl acetate (5 mL).
The resultant solution was heated at 60.degree. C. with constant
agitation until the solution was completely homogeneous. After this
time, the solvent was removed by passing a stream of dry nitrogen
over it. The resultant material is a white viscoelastic
material.
[0203] Gelation of [C.sub.8Py]NTf.sub.2 with 10 wt. %
Poly(Vinylidene Fluoride-Co-Hexafluoropropylene) (PVdF-HFP):
[0204] The resultant ionogel was slightly cloudy with low strength,
but still a self-supporting membrane.
[0205] Gelation of [C.sub.8Py]NTf.sub.2 with 20 wt. % PVdF-HFP:
[0206] The resultant ionogel was slightly cloudy with good
strength.
[0207] Gelation of [BMIM]NTf.sub.2 with 20 wt. % PVdF-HFP:
[0208] The resultant ionogel was slightly cloudy with good
strength.
[0209] Gelation of [BDMIM]NTf.sub.2 with 20 wt. % PVdF-HFP:
[0210] The resultant ionogel was slightly cloudy with good
strength.
[0211] Gelation of [C.sub.8Py]Br with 20 wt. % PVdF-HFP:
[0212] The resultant ionogel was cloudy and opaque with good
strength.
[0213] Gelation of [P.sub.8,4,4,4]Br with 20 wt. % PVdF-HFP:
[0214] The resultant ionogel was slightly cloudy with good
strength.
[0215] Gelation of [P.sub.4,4,4,4]Br with 20 wt. % PVdF-HFP:
[0216] The resultant ionogel was slightly cloudy with what appeared
to be crystallised ionic liquid on the surfaces (the IL is a solid
at room temperature). This gel was deliquescent and beads of water
appeared on the surface when standing at room temperature.
[0217] Gelation of [BMIM]Br with 20 wt. % PVdF-HFP:
[0218] The resultant ionogel was cloudy and opaque with good
strength.
Example 3: Incorporation of Zn.sup.2+ into Gels
[0219] General Method:
[0220] To a solution of the ionic liquid (500 mg) in acetone (4 mL)
was added the desired polymer (50 mg (10 wt. %) or 100 mg (20 wt.
%)) and the zinc salt (ZnBr.sub.2 or Zn(NO.sub.3).sub.2). The
resultant suspension was heated at 60.degree. C. with constant
agitation until the solution was homogeneous. The resultant
solution was then decanted into a suitable mould and then placed on
a heated surface (.about.50.degree. C.) to allow the acetone to
slowly evaporate over a the course of a couple of hours. The
resultant ionogel was then carefully removed from the mould by
means of forceps.
[0221] Gelation of [C.sub.8Py]NTf.sub.2 with 10 wt. % PEO and 5 wt.
% ZnBr.sub.2:
[0222] Obtained a clear highly viscous material. No gel formation
observed.
[0223] Gelation of [C.sub.8Py]NTf.sub.2 with 10 wt. % PVdF-HFP and
5 wt. % ZnBr.sub.2:
[0224] Obtained a cloudy ionogel with little strength.
[0225] Gelation of [C.sub.8Py]NTf.sub.2 with 10 wt. % PEO and 5 wt.
% Zn(NO.sub.3).sub.2:
[0226] Obtained a clear highly viscous material. No gel formation
observed.
[0227] Gelation of [C.sub.8Py]NTf.sub.2 with 10 wt. % PVdF-HFP and
5 wt. % Zn(NO.sub.3).sub.2:
[0228] A slightly cloudy gel is obtained with similar strength to
that obtained when using ZnBr.sub.2.
[0229] Gelation of [C.sub.8Py]NTf.sub.2 with 10 wt. % PEO and 10
wt. % Zn(NO.sub.3).sub.2:
[0230] A cloudy gel is obtained which, when being removed, reveals
that much of the IL sits below the plastic layer and has not been
incorporated.
[0231] Gelation of [C.sub.8Py]NTf.sub.2 with 10 wt. % PVdF-HFP and
10 wt. % Zn(NO.sub.3).sub.2:
[0232] A slightly cloudy gel is obtained which appears to be more
fragile than that obtained when using 5 wt. % of the zinc
salts.
Example 4: Treatment of Bromine Sequestering Ionogels with
Br.sub.2
General Method:
[0233] To the respective ionogels (in petri dishes) was added a
hexane solution of Br.sub.2 (17 mL in 2 mL hexane, 10 wt. %). The
petri dish was covered with a watch glass to prevent evaporation
and the solution allowed to stand for .about.5 min before it was
removed. The resultant ionogels were now a bright orange colour and
the hexane solutions were colourless. A small portion of the
ionogel was then removed for characterization by Raman
spectroscopy. This process was repeated up to 3 times for the
following gels: [P.sub.8,4,4,4]Br/20 wt. % PVdF-HFP,
[P.sub.4,4,4,4]Br/20 wt. % PVdF-HFP, [C.sub.8Py]Br/20 wt. %
PVdf-HFP, and [BMIM]Br/20 wt. % PVdF-HFP.
[0234] In the case of the [C.sub.8Py]Br/20 wt. % PVdf-HFP gel a
large amount of the IL/polybromide separates from the polymer
network. This is significantly less pronounced for the
[P.sub.8,4,4,4]Br/20 wt. % PVdF-HFP system. The [BMIM]Br/20 wt. %
PVdF-HFP system showed no IL separation from the polymer network.
For the [P.sub.4,4,4,4]Br/20 wt. % PVdF-HFP after 10 wt. % Br.sub.2
was added, it appears as though the IL has been displaced form the
gel network and crystallised on the surface of the gel.
[0235] Raman spectroscopy of all of the gels after Br.sub.2
addition (up to 30 wt. %) showed the exclusive formation of only
[Br.sub.3].sup.-. No higher order polybromide species were
observed. This is currently believed to be the result of the
nanoconfinement of the IL preventing adequate Br.sub.2 from
diffusing into the pores and, when this occurs, the size of the
pore may then too small to allow the formation of higher order
polybromide species.
Example 5: Assembly of Gelated IL Films on Carbon Paper
Electrodes
[0236] A prototype zinc bromide ionogel battery was assembled from
a `zinc side` electrode and a `bromine side` electrode. The `zinc
side` electrode consisted of a [C.sub.8Py]NTF.sub.2 ionic liquid,
gelated with 20 wt % PVdF-HFP with 10 wt % dissolved
Zn(NO.sub.3).sub.2 as a zinc source (see FIG. 8). The `bromide
side` electrode consisted of a [P.sub.8,4,4,4]Br ionic liquid
gelated with 20 wt % PVdF-HFP containing dissolved 8.8 wt %
ZnBr.sub.2 as a bromine source (see FIG. 9). The gels were formed
around a carbon paper electrode with a geometric surface area of 4
cm.sup.2, attached to the potentiostat by silver wire.
[0237] A test cell of two ionogel electrodes was tested by cyclic
voltammetry and constant potential electrolysis (CPE) to simulate a
charge and discharge cycle.
Example 6: Cyclic Voltammetry (CV) of Assembly in Example 5
[0238] In order to find the potential range to be used in a model
charging step, a two-electrode CV was set up, with the bromine side
as described in Example 5 set as the working electrode and the zinc
side as described in Example 5 as the counter and pseudo-reference
electrode. The results for a four scan CV experiment are shown in
FIG. 10. It is important to note that positive current does not
represent an oxidative process, but a `redox` process. With this
set-up, inputting positive potential `charges` the battery, so that
all events seen in the positive range could be either oxidative or
reductive. The potential on the horizontal axis is thus a relative
potential between each half-cell.
[0239] On the first scan (FIG. 10, black dashed line) only very
small redox processes can be seen in the positive direction. In the
negative direction, a large signal at -3 V (e) can be seen. This is
a result of a strongly sequestering species formed from the
charging step. On the second scan (FIG. 10, grey solid line) three
distinct peaks (a, b and c) are observed in the `charging` phase.
These are currently attributed to zinc deposition and two different
bromide oxidation steps which may result from an ECE mechanism
(bromide and tribromide oxidation) or from oxidation of the
ZnBr.sub.2 and the bromide ionic liquid. On the return sweep,
another signal (d) is seen, and is likely coupled to the redox
process, a.
[0240] For the third and fourth sweeps (FIG. 10, black dot-dashed
line and FIG. 10 black dotted line, respectively), the peak current
of process a is decreased, while that of b and c are increased.
Further tests are required to confirm the sources of these
signals.
Example 7: Battery Charge/Discharge of Assembly in Example 5 by
Constant Potential Electrolysis (CPE)
[0241] Charge/time plots for the test cell described in Example 5
are shown in FIG. 11. For the charging phase, a potential of +3.0 V
was applied as determined from the CVs in the Example 6. For
complete consumption of the zinc nitrate dissolved in the ionogel,
it was calculated that 32 C would have to pass. Thus, a 50% charge
(equivalent to 16 C) was achieved after 35 minutes (see left plot,
FIG. 11) The right plot in FIG. 11 shows a model discharge curve
achieved by setting a potential of 0 V across the test battery. The
current passed in this step was minimal, with less than 1 C passed
after 18 minutes of `discharge` time, roughly equivalent to a 6%
return of electroactive species.
[0242] The electrodes after charge are pictured in FIG. 12 (`zinc
side` electrode) and FIG. 13 (`bromine side` electrode),
demonstrating the generation of a significant amount of
bromine/polybromide (shading in FIG. 13; see arrows) confirming
sequestration of a polybromide species in the ionic liquid gel
layer.
Example 8: Assembly of Gelated IL Films on Titanium Mesh Electrodes
and Battery Formed from Same
[0243] In this example, the following chemicals were used:
Poly(vinylidene difluoride-hexafluoropropylene) (PVdF-HFP)
(Aldrich, M.sub.w .about.455000), zinc triflate (Aldrich), lithium
bromide (Aldrich), bromine (Panreac), 1-methyl-3-octylimidazolium
bromide ([OMIM]Br), and 1-methyl-3-octylimidazolium
bis(trifluoromethanesulfonyl)imide ([OMIM]NTf.sub.2). Titanium mesh
electrodes were purchased form NMT Electrodes (Perth, Australia)
and were cleaned using 6 M HNO.sub.3 and distilled water prior to
use.
[0244] Teflon.RTM. dies were designed and manufactured at the
University of Sydney. These dies were designed such that each
half-cell, comprising a gelated ionic liquid gel in contact with a
titanium mesh electrode, could be prepared separately (see FIG.
14). When the gel had `cured`, the half-cells could then be pushed
together and sealed to allow for electrochemical analysis using an
eDAQ potentiostat (see FIG. 15). The half-cells are described in
this example as either a `zinc electrode` (i.e., the electrode at
which zinc ions are reduced during charge or zinc is oxidised
during discharge) or a `bromine electrode` (i.e., the electrode at
which bromide ions are oxidised during charge or bromine is reduced
during discharge).
[0245] Table 2 shows the composition of the iongels used to prepare
the batteries in this example for testing. The ionogels containing
10 wt. % polymer gelation agent were prepared according to the
following method:
[0246] Poly(vinylidene difluoride-hexafluoropropylene) (PVdF-HFP)
(150 mg) was swelled in CH.sub.3CN (7 mL) at 65.degree. C. until a
clear homogeneous solution was obtained. For the iongel to be used
on the zinc electrode, the PVdF-HFP solution was added to a mixture
of the ionic liquid [OMIM]NTf.sub.2 (1.5 g) and Zn(OTf).sub.2 (150
mg, 10 wt. % based on the IL) in acetonitrile and the mixture was
then heated at 65.degree. C. with constant agitation until the
solution was homogeneous. For the iongel to be used on bromide
electrode, the PVdF-HFP solution was added to a 50:50 mixture of
the ionic liquids [OMIM]NTf.sub.2 (0.75 g) and [OMIM]Br (0.75 g)
and LiBr (71 mg, 4.7 wt. % based on the IL, 2 molar equivalents
based on Zn(OTf).sub.2) in acetonitrile and this was then heated at
65.degree. C. with constant agitation until the solution was
homogeneous. In both cases, the acetonitrile was removed until the
volume of the solution was .about.3 mL. The resultant solutions
were then poured into their respective dies containing a Ti mesh
electrode. The gels were then allowed to set and excess solvent
evaporated at ambient temperature (22-25.degree. C.) for 2 h. After
this time, the two battery half-cells were pushed together such
that the surface of the gel on the zinc electrode was substantially
completely in contact with the surface of the gel on the bromine
electrode and the pushed together cells were secured in place for
testing. The thickness of the gel layer on each titanium mesh
electrode was approximately 3-5 mm. Using this protocol, the
distance between the electrodes was thus 6-10 mm.
[0247] In the case where Br.sub.2 was added to the bromide
electrode ionogel, 0.1 equivalents (based on total Br.sup.-
concentration) was used. This Br.sub.2 was added after removal of
the CH.sub.3CN to .about.3 mL. In the case of any inhomogeneities
formed in the gel after adding the Br.sub.2, the solution was
reheated to 65.degree. C. to re-swell the polymer.
[0248] The electrochemical testing regimen involved the acquisition
of 3 cyclic voltammograms prior to charging, 2 charging-discharging
cycles (20 min for each cycle) and, finally, 3 cyclic
voltammograms. The results of electrochemical testing are given in
Table 3 below for each of Cells 1-6 as described in Table 2 and in
FIGS. 16A-D, 17A-D, 18A-D, 19A-D, 20A-D, and 21A-D.
TABLE-US-00002 TABLE 2 Composition of the ionogels used for various
Zn--Br battery test cells. Br Electrode Cell Zn Electrode Iongel Zn
Source Br Electrode Ionogel Bromide Source Ionogel Additive 1
[OMIM]NTf.sub.2 + 10 10 wt. % 50:50 [OMIM]NTf.sub.2:[OMIM]Br + --
-- wt. % PVdF-HFP Zn(OTf).sub.2 10 wt. % PVdF-HFP 2 [OMIM]NTf.sub.2
+ 10 10 wt. % 50:50 [OMIM]NTf.sub.2:[OMIM]Br + 4.7 wt. % LiBr --
wt. % PVdF-HFP Zn(OTf).sub.2 10 wt. % PVdF-HFP 3 [OMIM]NTf.sub.2 +
10 10 wt. % 50:50 [OMIM]NTf.sub.2:[OMIM]Br + 4.7 wt. % LiBr 3.8 wt.
% Br.sub.2 wt. % PVdF-HFP Zn(OTf).sub.2 10 wt. % PVdF-HFP 4
[OMIM]NTf.sub.2 + 20 10 wt. % 50:50 [OMIM]NTf.sub.2:[OMIM]Br + 4.7
wt. % LiBr -- wt. % PVdF-HFP Zn(OTf).sub.2 20 wt. % PVdF-HFP 5
50:50 [OMIM]NTf.sub.2:[OMIM]Br + 5 wt. % Zn(OTf).sub.2 + 50:50
[OMIM]NTf.sub.2:[OMIM]Br + 2.35 wt. % LiBr + -- 10 wt. % PVdF-HFP
2.35 wt. % LiBr 10 wt. % PVdF-HFP 5 wt. % Zn(OTf).sub.2 6 50:50
[OMIM]NTf.sub.2:[OMIM]Br + 5 wt. % Zn(OTf).sub.2 + 50:50
[OMIM]NTf.sub.2:[OMIM]Br + 2.35 wt. % LiBr + 1.9 wt. % Br.sub.2 10
wt. % PVdF-HFP 2.35 wt. % LiBr 10 wt. % PVdF-HFP 5 wt. %
Zn(OTf).sub.2 in both gels
[0249] Thus, it can be seen from Table 2 that: [0250] Cell 1
contains no additional Br.sup.- species in the bromide electrode
ionogel [0251] Cell 2 contains Br.sup.- in the bromide electrode
ionogel [0252] Cell 3 contains Br.sup.- and Br.sub.2 in the bromide
electrode ionogel [0253] Cell 4 contains additional PVdF-HFP in
both ionogels (20 wt. % compared to 10 wt. %). [0254] Cell 5
contains the same gels on both electrodes (with Zn.sup.2+ and
Br.sup.- additives in both gels) [0255] Cell 6 contains the same
gel on both electrodes plus 1.9 wt. % Br.sub.2 in both gels (this
is identical to the classical flow battery composition).
TABLE-US-00003 [0255] TABLE 3 Electrochemical testing of Cells 1-6
from Table 2. Q @ 20 min Charge Q @ 20 min Discharge CV Peak
Potential (mA) (mA s.sup.-1) (mA s.sup.-1) Cell Pre-charge
Post-charge Cycle 1 Cycle 2 Cycle 1 Cycle 2 1 15.6 @ 3.5 V 5.43 @
2.36 V 3866 3657 (95%) -2316 (60%) -1732 (47%) 2 31.7 @ 3.2 V 9.42
@ 2.87 V 6993 8590 (122%) -4084 (58%) -4666 (54%) 3 19.6 @ 3.4 V
7.82 @ 3.3 V 9234 7763 (84%) -5823 (63%) -3725 (48%) 4 8.36 @ 3.5 V
6.52 @ 3.3 V 3024 3175 (105%) -1606 (53%) -1735 (55%) 5 5.25 @ 3.3
V 3.52 @ 3.5 V 1173 1157 (99%) -6.65 (0.6%) -2.28 (0.2%) 6 16.36 @
3.2 V 5.79 @ 3.3 V 5489 3643 (66%) -22 (0.4%) -26 (0.7%)
[0256] From Table 3, it can be seen that Cell 2 is the best
performing of the batteries. This cell is able to achieve an
increased charging on the second cycle (122% of the first 20 min
charge cycle). In this set-up, the two discharge cycles achieved 58
and 54% discharge in 20 mins (see also FIG. 22).
[0257] In contrast, the batteries with the single gels (5 and 6)
had less favourable discharge characteristics over the 20 min
discharge period, achieving less than 1% in both cases for both
cycles.
* * * * *