U.S. patent application number 14/892586 was filed with the patent office on 2016-03-31 for in-situ electrolyte preparation in flow battery.
The applicant listed for this patent is UNITED TECHOLOGIES CORPORATION. Invention is credited to Weina Li, Michael L. Perry.
Application Number | 20160093925 14/892586 |
Document ID | / |
Family ID | 51934292 |
Filed Date | 2016-03-31 |
United States Patent
Application |
20160093925 |
Kind Code |
A1 |
Li; Weina ; et al. |
March 31, 2016 |
IN-SITU ELECTROLYTE PREPARATION IN FLOW BATTERY
Abstract
A method of in-situ electrolyte preparation in a flow battery
includes providing a vanadium-based electrolyte solution having
vanadium ions of predominantly vanadium V.sup.4+ to a first
electrode and a second electrode of at least one cell of a flow
battery. The vanadium V.sup.4+ at the first electrode is converted
to vanadium V.sup.3+ and the vanadium V.sup.4+ at the second
electrode is converted to vanadium V.sup.5+ by providing electrical
energy to the electrodes. A reducing agent is then provided to the
vanadium V.sup.5+ at the second electrode to reduce the V.sup.5+ to
vanadium the V.sup.4+. The vanadium V.sup.3+ at the first electrode
is then converted to vanadium V.sup.2+ and the vanadium V.sup.4+ at
the second electrode is then converted to vanadium V.sup.5+ by
providing electrical energy to the electrodes. A simple method to
produce predominantly vanadium V.sup.4+ electrolyte from a V.sup.5+
source, such as V.sub.2O.sub.5, is also taught.
Inventors: |
Li; Weina; (South
Glastonbury, CT) ; Perry; Michael L.; (Glastonbury,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UNITED TECHOLOGIES CORPORATION |
Hartford |
CT |
US |
|
|
Family ID: |
51934292 |
Appl. No.: |
14/892586 |
Filed: |
May 22, 2013 |
PCT Filed: |
May 22, 2013 |
PCT NO: |
PCT/US13/42174 |
371 Date: |
November 20, 2015 |
Current U.S.
Class: |
429/105 ;
429/188; 429/204 |
Current CPC
Class: |
H01M 8/188 20130101;
H01M 2300/002 20130101; H02J 7/00 20130101; Y02E 60/50 20130101;
H01M 8/20 20130101; H01M 10/0563 20130101; H01M 10/446 20130101;
Y02E 60/10 20130101 |
International
Class: |
H01M 10/44 20060101
H01M010/44; H01M 10/0563 20060101 H01M010/0563; H02J 7/00 20060101
H02J007/00; H01M 8/20 20060101 H01M008/20; H01M 8/18 20060101
H01M008/18 |
Claims
1. A method of in-situ electrolyte preparation in a flow battery,
the method comprising: (a) providing a vanadium-based electrolyte
solution having vanadium ions of predominantly vanadium V.sup.4+ to
a first electrode and a second electrode of at least one cell of a
flow battery, the second electrode being spaced apart from the
first electrode, with an electrolyte separator layer arranged
between the first electrode and the second electrode; (b)
converting the vanadium V.sup.4+ in the vanadium-based electrolyte
solution at the first electrode to vanadium V.sup.3+ and converting
the vanadium V.sup.4+ in the vanadium-based electrolyte solution at
the second electrode to vanadium V.sup.5+ by providing electrical
energy through an electric circuit to the first electrode and the
second electrode; (c) after said step (b), providing a reducing
agent to the vanadium-based electrolyte solution of the second
electrolyte to reduce the vanadium V.sup.5+ to vanadium V.sup.4+;
and (d) after said step (c), converting the vanadium V.sup.3+ of
said step (b) in the vanadium-based electrolyte solution at the
first electrode to vanadium V.sup.2+ and converting the vanadium
V.sup.4+ of said step (c) in the vanadium-based electrolyte
solution at the second electrode to vanadium V.sup.5+ by providing
electrical energy through the electric circuit to the first
electrode and the second electrode.
2. The method as recited in claim 1, wherein the reducing agent
includes an acid.
3. The method as recited in claim 1, wherein the reducing agent
includes oxalic acid.
4. The method as recited in claim 1, wherein the reducing agent
includes formic acid.
5. The method as recited in claim 1, wherein the reducing agent
includes an alcohol.
6. The method as recited in claim 1, wherein the vanadium ions of
said step (a) have a concentration of 90% or greater of the
vanadium V.sup.4+.
7. The method as recited in claim 1, wherein the vanadium ions of
said step (a) have a concentration of 95% or greater of vanadium
V.sup.4+.
8. The method as recited in claim 1, wherein the vanadium-based
electrolyte solution includes sulfuric acid.
9. The method as recited in claim 1, wherein equal parts of the
vanadium-based electrolyte solution in said step (a) are provided
to the first electrode and the second electrode.
10. The method as recited in claim 9, wherein the concentration of
the vanadium V.sup.2+ of said step (d) in the vanadium-based
electrolyte solution at the first electrode is equal to the
concentration of the vanadium V.sup.5+ of said step (d) in the
vanadium-based electrolyte solution at the second electrode within
+/-5%.
11. The method as recited in claim 1, further comprising preparing
the vanadium-based electrolyte solution having vanadium ions of
predominantly vanadium V.sup.4+ of said step (a) by: (i) providing
a first solution and a second solution, at least one of the first
solution and the second solution including vanadium V.sup.5+, at
least one of the first solution and the second solution including a
reducing agent, and a ratio of moles of the reducing agent to moles
of vanadium V.sup.5+ is 2:1 or greater; and (ii) combining the
first solution and the second solution, the reducing agent reducing
the vanadium V.sup.5+ to the vanadium V.sup.4+.
12. A method of preparing a vanadium-based electrolyte solution
having vanadium ions of predominantly V.sup.4+, the method
comprising: (a) providing a first solution and a second solution,
at least one of the first solution and the second solution
including vanadium V.sup.5+, at least one of the first solution and
the second solution including a reducing agent, and a ratio of
moles of the reducing agent to moles of vanadium V.sup.5+ is 2:1 or
greater; and (b) combining the first solution and the second
solution, the reducing agent reducing the vanadium V.sup.5+ to
vanadium V.sup.4+.
13. The method as recited in claim 12, wherein the first solution
includes the reducing agent and the second solution includes an
acid.
14. The method as recited in claim 13, wherein the reducing agent
includes oxalic acid and the acid of the second solution includes
sulfuric acid.
15. The method as recited in claim 13, wherein the reducing agent
includes formic acid and the acid of the second solution includes
sulfuric acid.
16. The method as recited in claim 13, wherein the reducing agent
includes an alcohol and the acid of the second solution includes
sulfuric acid.
17. The method as recited in claim 12, wherein the first solution
of said step (a) includes the reducing agent and the vanadium
V.sup.5+.
18. The method as recited in claim 12, further comprising providing
the at least one of the first solution and the second solution
including vanadium V.sup.5+ using V.sub.2O.sub.5 powder.
19. A flow battery comprising: at least one cell including a first
electrode, a second electrode spaced apart from the first electrode
and an electrolyte separator layer arranged between the first
electrode and the second electrode; a supply/storage system
external of the at least one cell, the supply/storage system
including first and second vessels fluidly connected with the at
least one cell; and first and second fluid electrolytes in,
respectively, the first and second vessels, each of the first and
second fluid electrolytes having vanadium ions of predominantly
vanadium V.sup.4+, the first and second fluid electrolytes having
substantially equivalent amounts of vanadium ions of predominantly
vanadium V.sup.4+.
20. The flow battery as recited in claim 19, wherein the battery is
initially charged to a fully charged state by two separate
electrochemical charging steps with the addition of a reducing
fluid to one of the electrolytes in between the two charging steps.
Description
BACKGROUND
[0001] Flow batteries, also known as redox flow batteries or redox
flow cells, are designed to convert electrical energy into chemical
energy that can be stored and later released when there is demand.
As an example, a flow battery may be used with a renewable energy
system, such as a wind-powered system, to store energy that exceeds
consumer demand and later release that energy when there is greater
demand.
[0002] A typical flow battery includes a redox flow cell that has a
negative electrode and a positive electrode separated by an
electrolyte layer, which may include a separator, such as an
ion-exchange membrane. A negative fluid electrolyte (sometimes
referred to as the anolyte) is delivered to the negative electrode
and a positive fluid electrolyte (sometimes referred to as the
catholyte) is delivered to the positive electrode to drive
electrochemically reversible redox reactions. Upon charging, the
electrical energy supplied causes a chemical reduction reaction in
one electrolyte and an oxidation reaction in the other electrolyte.
The separator prevents the electrolytes from freely and rapidly
mixing but permits selected ions to pass through to complete the
redox reactions. Upon discharge, the chemical energy contained in
the liquid electrolytes is released in the reverse reactions and
electrical energy can be drawn from the electrodes. Flow batteries
are distinguished from other electrochemical devices by, inter
alia, the use of externally-supplied, fluid electrolyte solutions
that include reactants that participate in reversible
electrochemical reactions.
SUMMARY
[0003] Disclosed is a method of in-situ electrolyte preparation in
a flow battery includes providing a vanadium-based electrolyte
solution having vanadium ions of predominantly vanadium V.sup.4+ to
a first electrode and a second electrode of at least one cell of a
flow battery. The vanadium V.sup.4+ at the first electrode is
converted to vanadium V.sup.3+ and the vanadium V.sup.4+ at the
second electrode is converted to vanadium V.sup.5+ by providing
electrical energy to the electrodes. A reducing agent is then
provided to the vanadium V.sup.5+ at the second electrode to reduce
the V.sup.5+ to vanadium V.sup.4+. The vanadium V.sup.3+ at the
first electrode is then converted to vanadium V.sup.2+ and the
vanadium V.sup.4+ at the second electrode is then converted to
vanadium V.sup.5+ by providing electrical energy to the
electrodes.
[0004] Also disclosed is a method of preparing a vanadium-based
electrolyte solution having vanadium ions of predominantly
V.sup.4+. The method includes providing a first solution and a
second solution. At least one of the solution and the second
solution includes vanadium V.sup.5+. At least one of the first
solution and the second solution includes a reducing agent, and a
ratio of moles of the reducing agent to moles of the vanadium
V.sup.5+ is 2:1 or greater. The first solution and the second
solution are then combined. The reducing agent reduces the V.sup.5+
to V.sup.4+.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The various features and advantages of the present
disclosure will become apparent to those skilled in the art from
the following detailed description. The drawings that accompany the
detailed description can be briefly described as follows.
[0006] FIG. 1 illustrates an example flow battery.
[0007] FIG. 2 illustrates an example method of in-situ electrolyte
preparation in a flow battery.
[0008] FIG. 3 illustrates an example method of preparing a
vanadium-based electrolyte solution having vanadium ions of
predominantly V.sup.4+.
DETAILED DESCRIPTION
[0009] FIG. 1 schematically shows portions of an example flow
battery 20 that can be used for selectively storing and discharging
electrical energy. As an example, the flow battery 20 can be used
to convert electrical energy generated in a renewable energy system
to chemical energy that is stored until a later time when there is
greater demand, at which time the flow battery 20 then converts the
chemical energy back into electrical energy. The flow battery 20
can supply the electric energy to an electric grid, for
example.
[0010] The flow battery 20 includes a fluid electrolyte 22 that has
an electrochemically active specie 24 which, under charge and
discharge conditions, functions in a redox pair with regard to an
additional fluid electrolyte 26 that has an electrochemically
active specie 28. In this example, the electrochemically active
species 24/28 are based on vanadium and the fluid electrolytes
22/26 are thus vanadium-based electrolyte solutions. The fluid
electrolytes 22/26 are contained in a supply/storage system 30 that
includes first and second vessels 32/34 and pumps 35.
[0011] The fluid electrolytes 22/26 are delivered from the first
and second vessels 32/34, using the pumps 35, to at least one cell
36 of the flow battery 20 through respective feed lines 38. The
fluid electrolytes 22/26 are returned from the cell 36 to the
vessels 32/34 via return lines 40. The feed lines 38 and the return
lines 40 connect the vessels 32/34 with first and second electrodes
42/44 of the cell. Multiple cells 36 can be provided as a
stack.
[0012] The cell or cells 36 each include the first electrode 42,
the second electrode 44 spaced apart from the first electrode 42,
and an electrolyte separator layer 46 arranged between the first
electrode 42 and the second electrode 44. For example, the
electrodes 42/44 are porous carbon structures, such as carbon paper
or felt. In general, the cell or cells 36 can include bipolar
plates, manifolds and the like for delivering the fluid
electrolytes 22/26 through flow field channels to the electrodes
42/44. The bipolar plates can be carbon plates, for example. It is
to be understood, however, that other configurations can be used.
For example, the cell or cells 36 can alternatively be configured
for flow-through operation where the fluid electrolytes 22/26 are
pumped directly into the electrodes 42/44 without the use of flow
field channels.
[0013] The electrolyte separator layer 46 can be an ionic-exchange
membrane, an inert micro-porous polymer membrane or an electrically
insulating microporous matrix of a material, such as silicon
carbide (SiC), that prevents the fluid electrolytes 22/26 from
freely and rapidly mixing but permits selected ions to pass through
to complete the redox reactions while electrically isolating the
electrodes 42/44. In this regard, the fluid electrolytes 22/26 are
generally isolated from each other during normal operation of the
flow battery, such as in charge, discharge and shutdown states.
[0014] The fluid electrolytes 22/26 are delivered to the cell 36 to
either convert electrical energy into chemical energy or, in the
reverse reaction, convert chemical energy into electrical energy
that can be discharged. The electrical energy is transmitted to and
from the cell 36 through an electric circuit 48 that is
electrically coupled with the electrodes 42/44.
[0015] In the charge, discharge and shutdown state after charge or
discharge, the vanadium in the first fluid electrolyte 22 has
vanadium ions of V.sup.2+/V.sup.3+ and the vanadium in the second
fluid electrolyte 26 has vanadium ions of V.sup.4+/V.sup.5+ (which
can also be denoted as V(ii)/V(iii) and V(iv)/V(v), although the
valences of the vanadium species with oxidation states of 4 and 5
are not necessarily 4+ and 5+), the concentrations of which depend
upon the charge state of the flow battery 20. In the illustrated
example, however, the flow battery 20 is shown in an in-situ
preparation state, prior to any charging or discharging of the
fluid electrolytes 22/26, for preparing the fluid electrolytes
22/26 from starting materials. In the in-situ preparation state,
the fluid electrolytes 22/26 each have vanadium ions of
predominantly V.sup.4+. The term "predominantly" and variations
thereof used herein with reference to ions of a particular
oxidation state means that the particular oxidation state is the
highest concentration oxidation state among all oxidation states of
the electrochemically active species. In further examples,
equivalent amounts (by volume) or substantially equivalent amounts
of the fluid electrolytes 22/26 are provided to the electrodes
42/44 such that there are also equivalent or substantially
equivalent concentrations of V.sup.4+ at the electrodes 42/44. For
example, the fluid electrolytes 22/26 are provided from the same
source batch or starting material such that, once the starting
material is divided, the fluid electrolytes 22/26 have equivalent
or substantially equivalent concentrations of V.sup.4+. The fluid
electrolytes 22/26 thus also have equivalent or substantially
equivalent amounts (by moles) of V.sup.4+. The term "substantially
equivalent" used herein with reference to amounts or concentrations
means that the amounts or concentrations are within +/-5%.
[0016] The preparation of vanadium-based fluid electrolytes for
flow batteries can be relatively expensive. For example,
vanadium-based fluid electrolyte can be produced, ex-situ with
respect to a flow battery, from vanadyl sulfate (VOSO.sub.4)
crystals. Vanadyl sulfate is expensive and thus greatly increases
the cost of preparing a vanadium-based fluid electrolyte. As will
be described, the flow battery 20 can be used for the in-situ
preparation of the fluid electrolytes 22/26 from relatively
inexpensive vanadium oxide (V.sub.2O.sub.5) powder.
[0017] FIG. 2 illustrates an example method 50 of in-situ
electrolyte preparation in a flow battery, such as the flow battery
20. As shown, the method 50 generally includes steps 52, 54, 56 and
58. The example method 50 will be described with reference to the
flow battery 20. However, it is to be understood that the method 50
is not limited to the illustrated configuration of the flow battery
20 disclosed herein and may be utilized with other flow batteries
having different configurations. In this example, step 52 includes
providing a vanadium-based electrolyte solution having vanadium
ions of predominantly vanadium V.sup.4+ to the first electrode 42
and the second electrode 44. With reference to FIG. 1, the
vanadium-based electrolyte solution can be provided in the vessels
32/34 and then pumped into the cell 36 to the respective first and
second electrodes 42/44. In one example, the vanadium ions provided
to each of the first electrode 42 and the second electrode 44 has a
concentration of 90% or greater, or alternatively 95% or greater,
of V.sup.4+.
[0018] After providing the vanadium-based electrolyte solution to
the first and second electrodes 42/44, the vanadium V.sup.4+ at the
first electrode 42 and the second electrode 44 are converted,
respectively, to vanadium V.sup.3+ and vanadium V.sup.5+ by
providing electrical energy through the electric circuit 48 to the
first and second electrodes 42/44.
[0019] The electrical energy is then stopped and, at step 56, a
reducing agent is provided into the second fluid electrolyte 26 to
reduce the vanadium V.sup.5+ to vanadium V.sup.4+. In other words,
the charging cycle of the flow battery 20 at step 52 converts the
V.sup.4+ to, respectively, V.sup.3+ and V.sup.5+, while the
reducing agent then converts the V.sup.5+ back to V.sup.4+. At this
tage in the method 50, the vanadium-based electrolyte solution at
the first fluid electrolyte 22 is thus predominantly V.sup.3+ and
the vanadium-based second electrolyte solution at fluid electrolyte
26 is predominantly V.sup.4+.
[0020] At step 58, which represents a second charging cycle,
electrical energy is again provided through the electric circuit 48
to the first and second electrodes 42/44 to convert the V.sup.3+ at
the first electrode 42 to V.sup.2+ and convert the V.sup.4+ at the
second electrode 44 to V.sup.5+. Thus, after step 58, the
vanadium-based electrolyte solution at the first electrode 42 and
the second electrode 44 are in a fully charged state. Moreover,
because equal parts of the vanadium-based electrolyte solution are
provided to the first and second electrodes 42/44 at step 52, the
concentration of the V.sup.2+ at the first electrode 42 is equal to
the concentration of the V.sup.5+ at the second electrode 44 after
step 58. For example, the concentrations are equal within
+/-5%.
[0021] In one example, the reducing agent that is added at step 56
includes an acid. In a further example, the acid is selected from
oxalic acid, formic acid or combinations thereof. Alcohol can
alternatively be used. In one example based upon the use of oxalic
acid, a byproduct of the reaction between the electrolyte and the
oxalic acid is the generation of carbon dioxide, which is not
harmful to the flow battery 20. Thus, the use of oxalic acid
additionally provides the benefit of avoiding the generation of
toxic chemicals or chemicals that would otherwise debit the
performance of the flow battery 20.
[0022] FIG. 3 illustrates an example method 60 of preparing the
vanadium-based electrolyte solution having vanadium ions of
predominantly V.sup.4+. As an example, the method 60 can be used to
prepare the vanadium-based electrolyte solution that is used in the
method 50. The method 60 includes steps 62 and 64. At step 62, a
first solution and a second solution are provided. At least one of
the first solution and the second solution includes vanadium
V.sup.5+. In one example, the vanadium V.sup.5+ is the predominant
vanadium ion. At least one of the first solution and the second
solution includes a reducing agent, and a ratio of moles of the
reducing agent to moles of the vanadium V.sup.5+ is 2:1 or
greater.
[0023] At step 64, the first solution and the second solution are
combined. Once combined, the reducing agent reduces the vanadium
V.sup.5+ to vanadium V.sup.4+ and thus results in the production of
the vanadium-based electrolyte solution with vanadium ions of
predominantly V.sup.4+.
[0024] In a further example, the first solution includes the
reducing agent and the second solution includes an acid. In a
further example, the reducing agent includes oxalic acid, formic
acid or a combination thereof, and the acid of the second solution
includes sulfuric acid. The oxalic acid can be provided as oxalic
acid dihydrate, for example. Alternatively, or in addition to the
oxalic acid and formic acid, the reducing agent can include an
alcohol. In one further example, the first solution includes the
reducing agent and the vanadium V.sup.5+.
[0025] The one of the first solution or the second solution that
includes the vanadium V.sup.5+ can be prepared using vanadium oxide
(V.sub.2O.sub.5) powder. For example, the vanadium oxide powder can
be combined with the reducing agent and water (e.g., deionized
water) to form the first solution or can be combined with the acid
of the second solution.
[0026] Equations I and II below illustrate the underlying chemical
reactions of the reduction of the vanadium oxide powder to produce
vanadium V.sup.4+. In Equation I, the reaction product of
VO.sub.2.sup.+ represents the oxidation state of vanadium V.sup.5+.
In Equation II, the reaction product of VO.sup.2+ represents the
oxidation state of vanadium V.sup.4+. The reduction of V.sup.5+to
V.sup.4+ in Equation II is an endothermic reaction. In method 60,
the combining of the first solution and the second solution
provides heat to drive this endothermic reaction. For example, the
dilution of the acid of the second solution is exothermic and thus
provides heat to drive the reduction of V.sup.5+ to V.sup.4+.
Moreover, the use of the noted ratio of 2:1 provides a sufficient
amount of reducing agent to reduce substantially all of the
V.sup.5+ to V.sup.4+. Thus, the resulting vanadium-based
electrolyte solution has predominantly V.sup.4+. In one further
example, step 64 is carried out at room temperature without the
application of external heat. The exothermic reaction of the
dilution of the acid of the second solution can heat the mixture of
the first solution and the second solution to a temperature above
room temperature (approximately 23.degree. C.), such as about
60.degree. C. Furthermore, although the method 60 can also be
carried out in-situ in the flow battery 20, the method 60 can
alternatively be carried out ex-situ, separate from the flow
battery 20, with equal amounts of the resulting electrolyte
solution having vanadium ions of predominantly V.sup.4+
subsequently provided into the first and second electrodes 32/44 of
flow battery 20 for execution of method 50.
V.sub.2O.sub.5(s)+2H.sup.+.fwdarw.2VO.sub.2.sup.++H.sub.2O EQUATION
I:
2VO.sub.2.sup.++H.sub.2C.sub.2O.sub.4+2H.sup.+.fwdarw.2VO.sup.2++2CO.sub-
.2+2H.sub.2O EQUATION II:
[0027] Although a combination of features is shown in the
illustrated examples, not all of them need to be combined to
realize the benefits of various embodiments of this disclosure. In
other words, a system designed according to an embodiment of this
disclosure will not necessarily include all of the features shown
in any one of the Figures or all of the portions schematically
shown in the Figures. Moreover, selected features of one example
embodiment may be combined with selected features of other example
embodiments.
[0028] The preceding description is exemplary rather than limiting
in nature. Variations and modifications to the disclosed examples
may become apparent to those skilled in the art that do not
necessarily depart from the essence of this disclosure. The scope
of legal protection given to this disclosure can only be determined
by studying the following claims.
* * * * *