U.S. patent application number 10/512155 was filed with the patent office on 2005-07-28 for method for operating redox flow battery and redox flow battery cell stack.
Invention is credited to Kumamoto, Takahiro, Tokuda, Nobuyuki.
Application Number | 20050164075 10/512155 |
Document ID | / |
Family ID | 29267359 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050164075 |
Kind Code |
A1 |
Kumamoto, Takahiro ; et
al. |
July 28, 2005 |
Method for operating redox flow battery and redox flow battery cell
stack
Abstract
The invention provides an operating method of a redox flow
battery capable of grasping a charging state of the battery more
reliably to stabilize an output capacity of the battery. The method
is for operating the redox flow battery comprising a cell stack 1
comprising a plurality of cells. A selected cell(s) in the cell
stack 1, to and from which positive electrode electrolyte and
negative electrode electrolyte are supplied and discharged and
which is/are not normally connected to a DC/AC converter 225,
is/are in the form of an auxiliary cell 2 used for measuring a
charging rate of the electrolyte. Also, a stop of charge of a main
cell 3 and a stop of discharge of the main cell 3 are controlled
with reference to a circuit voltage obtained from the auxiliary
cell 2. Since the auxiliary cell 2 is integrally incorporated in
the cell stack 1, the charging state of the battery can be grasped
reliably without stopping the charge/discharge operation of the
main cell 3. Also, since the stop of charge of the main cell 3 and
the stop of discharge of the same are controlled with reference to
the measured circuit voltage, the output capacity can be
stabilized.
Inventors: |
Kumamoto, Takahiro; (Osaka,
JP) ; Tokuda, Nobuyuki; (Osaka, JP) |
Correspondence
Address: |
McDermott Will & Emery
600 13th Street N W
Washington
DC
20005-3096
US
|
Family ID: |
29267359 |
Appl. No.: |
10/512155 |
Filed: |
October 22, 2004 |
PCT Filed: |
April 21, 2003 |
PCT NO: |
PCT/JP03/05060 |
Current U.S.
Class: |
429/50 ;
429/105 |
Current CPC
Class: |
H01M 8/2455 20130101;
H01M 8/249 20130101; H01M 8/04186 20130101; Y02E 60/50 20130101;
H01M 2250/40 20130101; H01M 8/20 20130101; Y02E 60/528 20130101;
H01M 8/188 20130101; Y02E 60/56 20130101 |
Class at
Publication: |
429/050 ;
429/105 |
International
Class: |
H01M 010/44; H01M
008/20 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2002 |
JP |
2002-120165 |
Claims
1. An operating method of a redox flow battery comprising a cell
stack comprising a plurality of cells, wherein at least a part of
the cells in the cell stack to and from which positive electrode
electrolyte and negative electrode electrolyte are supplied and
discharged and which is not normally connected to a DC/AC converter
is in the form of an auxiliary cell used for measuring a charging
rate of the electrolyte, and wherein at least either of a stop of
charge of the battery and a stop of discharge of the battery is
controlled with reference to a circuit voltage obtained from the
auxiliary cell.
2. An operating method of a redox flow battery comprising a cell
stack comprising a plurality of cells, wherein at least a part of
the cells in the cell stack to and from which positive electrode
electrolyte and negative electrode electrolyte are supplied and
discharged and which is not normally connected to a DC/AC converter
is in the form of an auxiliary cell used for measuring a charging
rate of the electrolyte, and wherein the auxiliary cell is charged
or discharged with reference to a circuit voltage obtained from the
auxiliary cell, to change a charging rate of the electrolyte.
3. A cell stack of a redox flow battery, the cell stack comprising
a plurality of cells, wherein a main cell, to and from which
positive electrode electrolyte and negative electrode electrolyte
are supplied and discharged and which is connected to a DC/AC
converter, and an auxiliary cell for measuring a charging rate of
the electrolyte, which is connected to the main cell in such a
manner as to share the electrolytes with the main cell and is not
normally connected to a DC/AC converter, are integrally combined
with each other.
Description
TECHNICAL FIELD
[0001] The present invention relates to an operating method of a
redox flow battery and to a cell stack of the same. More
particularly, the present invention relates to an operating method
of a redox flow battery capable of constantly grasping the state of
charge to stabilize an output capacity most suitably, and to a cell
stack of the redox flow battery most suitable for this operating
method.
BACKGROUND ART
[0002] In general, redox flow batteries are used for load leveling
or for countermeasure to voltage sag (momentary drop in voltage).
FIG. 3 shows an explanatory view showing an operating principle of
a redox flow secondary battery. This battery has a cell 100 which
is separated into a positive electrode cell 100A and a negative
electrode cell 100B by a membrane 103 of an ion-exchange membrane.
A positive electrode 104 and a negative electrode 105 are contained
in the positive electrode cell 100A and the negative electrode cell
100B, respectively. A positive electrode tank 101 for feeding and
discharging positive electrode electrolyte to and from the positive
electrode cell 100A is connected to the positive electrode cell
100A through conduit pipes 106, 107. Similarly, a negative
electrode tank 102 for feeding and discharging negative electrode
electrolyte to and from the negative electrode cell 100B is
connected to the negative electrode cell 100B through conduit pipes
109, 110. Aqueous solution containing ions that change in valence,
such as vanadium ion, is used for the respective electrolytes and
is circulated by using pumps 108, 111, to charge or discharge with
an ionic valence change reaction on the positive and negative
electrodes 104, 105. For example, when the electrolyte containing
the vanadium ions is used, the following reactions occur in the
cell during the charge or discharge of electricity:
[0003] Positive electrode: V.sup.4+.fwdarw.V.sup.5++e.sup.-
(Charge) V.sup.4+.rarw.V.sup.5++e.sup.- (Discharge)
[0004] Negative electrode: V.sup.3++e.sup.-.fwdarw.V.sup.2+
(Charge) V.sup.3++e.sup.-.rarw.V.sup.2+ (Discharge)
[0005] FIG. 4 is a schematic block diagram of a cell stack used for
the battery. A structure comprising a plurality of sub-stacks 201
stacked in layers, each comprising a plurality of cells stacked in
layers, what is called a cell stack 200, is used for battery
described above. Each cell has the positive electrode 104 made of
carbon felt and the negative electrode 105 made of carbon felt
which are arranged at both sides of the membrane 103. Cell frames
210 are arranged at the outside of the positive electrode 104 and
at the outside of the negative electrode 105, respectively. Each
cell frame 210 comprises a bipolar plate 211 made of a plastic
carbon and a frame 212 surrounding the bipolar plate.
[0006] The frame 212 has a plurality of holes, which are called
manifolds, formed therein. Each cell frame has e.g. eight manifolds
in total, four in a lower side thereof and four in an upper side
thereof. Two of the four manifolds in the lower side of the cell
frame are used for supplying positive electrode electrolyte, and
the remaining two are used for supplying negative electrode
electrolyte. Two of the four manifolds in the upper side of the
cell frame are used for discharging the positive electrode
electrolyte, and the remaining two are used for discharging the
negative electrode electrolyte. The manifolds are formed into flow
channels for the electrolytes to pass through by stacking a number
of cells in layers and in turn are connected to circuit pipes 106,
107, 109, 110 in FIG. 3. The electrolytes are supplied and
discharged in each of the sub-stacks 201. As shown in FIG. 2,
electrolyte supplying pipes 220, 221 for supplying the positive
electrode electrolyte and the negative electrode electrolyte and
electrolyte discharging pipes 222, 223 for discharging the positive
electrode electrolyte and the negative electrode electrolyte are
connected to each of the sub-stacks 201.
[0007] The sub-stacks 201 are electrically interconnected through
conductive plates 224, such as copper plates, interposed between
adjacent sub-stacks. Each sub-stack 201 has electrical terminals
(not shown) provided on a side thereof different from the sides on
which the electrolyte supplying pipes 220, 221 and the electrolyte
discharging pipes 222, 223 are provided. The entirety of the cell
stack 200 is usually connected to a DC/AC converter 225 through the
electrical terminals.
[0008] For the load leveling, this redox flow battery is commonly
operated to stop charging and discharging based on an upper limit
and a lower limit of a predetermined distribution voltage. The stop
of charging and the stop of discharging are both determined with
reference to the distribution voltage (a voltage of the cell when
the battery is in operation). Also, the charging state (charging
rate) of the electrolyte in the cell is commonly grasped with
reference to a circuit voltage (a voltage of the cell when the
battery is in non-operation).
[0009] The conventional redox flow battery has the following
problems, however.
[0010] (1) When the stop of charging and discharging is determined
with reference to the distribution voltage, variations in charging
rate of the cell may be caused.
[0011] Operating conditions of the battery vary depending on
changes in battery resistance caused by degradation of the battery,
variation in the environment, such as temperature variation, and
the like. For example, generally speaking, the higher the
temperature is, the more effectively the battery can charge and
discharge. When the stop of charging and the stop of discharging
are determined with reference to the distribution voltage, the
variations in operating condition may cause variations in charging
rate of the cell, i.e., variations in output capacity of the cell
(kWh), at the stop of charging and discharging.
[0012] (2) It is difficult for the conventional redox flow battery
to constantly grasp the charging rate of the cell.
[0013] Measurement of the circuit voltage requires the halt of the
operation of the battery. Consequently, trying to grasp the
charging state (charging rate) of the cell constantly with
reference to the circuit voltage as usual requires the continuous
halt of the operation of the battery. Hence, this is not a
realistic way. As is known in recent years, the redox flow battery
is often combined with a wind power generation system or a solar
power generation system, to provide a stabilized output capacity.
In this combination, the charging rate of the cell cannot be
changed properly without grasping the charging rate of the
electrolytic and, as a result, the battery may fail to charge and
discharge electricity sufficiently. Accordingly, grasping the
charging rate of the cell constantly is being desired.
[0014] It is a primary object of the invention to provide an
operating method of a redox flow battery capable of grasping a
charging rate of the battery further reliably to stabilize an
output capacity of the battery, and provide a cell stack optimum
for this operating method.
DISCLOSURE OF THE INVENTION
[0015] The present invention accomplishes the above-said object by
provision of an auxiliary cell, integrally incorporated in a cell
stack, for monitoring a circuit voltage.
[0016] The present invention is directed to an operating method of
a redox flow battery comprising a cell stack comprising a plurality
of cells. At least a part of the cells in the cell stack to and
from which positive electrode electrolyte and negative electrode
electrolyte are supplied and discharged and which is not normally
connected to a DC/AC converter is in the form of an auxiliary cell
used for measuring a charging rate of the electrolyte. Also, at
least either of a stop of charge of the battery and a stop of
discharge of the battery is controlled in accordance to a circuit
voltage obtained from the auxiliary cell.
[0017] In the present invention, a selected cell(s) of the cells in
the cell stack which are constructed to share the electrolyte with
each other is/are in the form of an auxiliary cell used for
measuring a charging rate. This auxiliary cell serves as a cell
which does not normally charge and discharge, but works to simply
put the electrolyte in circulation through the cell stack. The
remaining cells serve as the cells (main cell) used for charging
and discharging electricity. The stop of charge of the main cell
and the stop of discharge of the main cell can be made when the
circuit voltage measured from the auxiliary cell reaches a certain
value. The provision of this auxiliary cell enables the circuit
voltage to be monitored and measured substantially constantly
without any need to stop the charge/discharge operation of the
battery as usual. When the circuit voltage measured is used for
signals to stop charging and signals to stop discharging, the
battery can be used in substantially the same charging state, thus
ensuring the stabilized output capacity of the battery.
[0018] It may be conceivable that in the conventional redox flow
battery, a cell stack designed specifically for monitoring is added
to the cell stack for charging and discharging electricity.
However, the addition of the cell stack designed specifically for
monitoring results in enlargement of the equipment and leads to
cost increase. In contrast to this, in the present invention, since
a part of the cell stack for charging and discharging electricity
is in the form of the auxiliary cell of a unitary construction, no
special equipment is needed for the monitoring, providing not only
the advantage in productivity but also reduction in scale of the
equipment and in cost.
[0019] Also, the present invention provides an operating method
wherein at least a part of the cells in the cell stack which is not
normally connected to a DC/AC converter is in the form of an
auxiliary cell, as is the case with the above, and the auxiliary
cell is charged or discharged in accordance to the circuit voltage
obtained from the auxiliary cell, to change a charging rate of the
electrolyte.
[0020] In the invention as previously mentioned, the stop of charge
of the main cell and the stop of discharge of the main cell are
controlled with reference to the circuit voltage measured from the
auxiliary cell, and the auxiliary cell is solely used for measuring
the circuit voltage substantially constantly. In contrast to this,
in this invention, when the circuit voltage measured from the
auxiliary cell is in a constant level, the auxiliary cell is
brought to a halt to monitoring and is temporally used for charging
and discharging electricity, in addition to being used for
measuring the circuit voltage. This operating method is optimum for
combination of the redox flow battery with a wind generation system
or a solar photovoltaic system and also is optimum for any battery
operation that may provide an unstable output capacity, including a
demand control. In this operating method, the charging rate of the
main cell which is usually operated to recharge and discharge can
be surely grasped by the auxiliary cell. In addition to this, even
when the charging rate of the main cell is decreased or increased
excessively, the main cell can be allowed to charge and discharge
continuously by putting the auxiliary cell into operation to charge
and discharge. This can produce a stabilized output capacity.
[0021] For charging and discharging the auxiliary cell, a power
source can be additionally attached to the auxiliary cell.
[0022] For this operating method of the present invention, the
following cell stack is preferably used. The present invention
provides a cell stack of a redox flow battery comprising a
plurality of cells, the cell stack including the combination of a
main cell and an auxiliary cell being integrally combined with each
other as given below:
[0023] The main cell to and from which positive electrode
electrolyte and negative electrode electrolyte are supplied and
discharged and which is connected to a DC/AC converter; and
[0024] The auxiliary cell for measuring a charging rate of the
electrolyte, which is connected to the main cell in such a manner
as to share the electrolytes with the main cell and is not normally
connected to the DC/AC converter.
[0025] The auxiliary cell can be formed to have the same
construction as the sub-stack forming the main cell and can be
formed by stacking a plurality of cells in layers. A smaller number
of auxiliary cell than the number of cells forming the sub-stack is
preferably used in that reduction in scale of facilities as well as
in cost can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a diagrammatic illustration of a cell stack of the
present invention.
[0027] FIG. 2 is a diagrammatic illustration of a conventional cell
stack.
[0028] FIG. 3 is an explanatory view of an operating principle of
the redox flow battery.
[0029] FIG. 4 is a diagrammatic illustration of the construction of
the cell stack used for the redox flow battery.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] In the following, an embodiment of the present invention
will be explained.
TEST EXAMPLE 1
[0031] A redox flow battery of AC170 kW.times.8 hrs. was produced
and the changes of the battery capacity with variation of
temperature was monitored. For the test, the redox flow battery
system as shown in FIGS. 3 and 4 was fabricated. Taken as the test
sample No. 1-1 was a redox flow battery using the cell stack 1
comprising a total of five sets of cells, namely, four sets of
sub-stacks 201 (main cell 3), each comprising twenty-five cells
stacked in layers, not shown, and one set of auxiliary cell 2
comprising the same cell 1, as shown in FIG. 1. Taken as the test
sample No. 1-2 was a redox flow battery using the cell stack 200
comprising four sets of sub-stacks 201 and having no auxiliary cell
(the cell stack comprising the main cell only), as shown in FIG. 2.
The operating conditions for the test are shown below. The test
results are shown in TABLE 1.
[0032] Test Sample No. 1-1: The circuit voltage is constantly
measured by the auxiliary cell so that the stop of charge of the
main cell and the stop of discharge of the same are controlled with
reference to the circuit voltage as constantly measured by the
auxiliary cell. The battery is recharged till a circuit voltage of
1.46V/cell and is discharged till a circuit voltage of
1.33V/cell.
[0033] Test Sample No. 1-2: The distribution voltage is constantly
measured so that the stop of charge of the main cell and the stop
of discharge of the same are controlled with reference to the
distribution voltage. The battery is operated with a charging
voltage of 1.55V/cell and a discharging voltage of 1V/cell.
1TABLE 1 Temperature Test Sample No. 1-1 Test Sample No. 1-2
25.degree. C. 8 hours 6.4 hours 35.degree. C. 8 hours 8 hours
[0034] As shown in TABLE 1, both of the test samples exhibited a
rated discharging output capacity of 8 hours at a relatively high
temperature of 35.degree. C. However, the test sample No. 1-2
wherein the stop of charge and discharge of the main cell was
controlled with reference to the distribution voltage exhibited
only a capacity lower than the rated discharging output capacity at
a relatively low temperature of 25.degree. C. In contrast to this,
the test sample No. 1-1 wherein the stop of charge and discharge of
the main cell was controlled with reference to the circuit voltage
exhibited the rated discharging output capacity of 8 hours at the
relatively low temperature of 25.degree. C.
[0035] It can be seen from the test results that the method of the
present invention wherein the circuit voltage is measured by the
auxiliary cell, so that the stop of charge of the main cell and the
stop of discharge of the same is controlled with reference to the
circuit voltage as measured by the auxiliary cell can provide a
stabilized output capacity of free of influence from the
temperature and the like. In addition, since the auxiliary cell is
integrally combined with the cell stack, for the measurement of the
circuit voltage, the circuit voltage can be measured by the
auxiliary cell without any need to stop the charge/discharge
operation of the main cell.
TEST EXAMPLE 2
[0036] A redox flow battery of AC170 kW.times.6 hrs. was produced.
When the charging rate of the main cell decreased, the auxiliary
cell was charged. The basic configuration of the battery used in
this example was the same as that of the redox flow battery taken
as the test sample No. 1-1 used in the Test Example 1. The test was
carried out in the following manner. When the circuit voltage as
measured by the auxiliary cell reached 1.35V/cell, a direct-current
power source additionally provided on the auxiliary cell was turned
on to start the charging and discharging operation of the auxiliary
cell.
[0037] It was found from the test results that when about 100 kWh
was charged by the auxiliary cell in a constant current operation,
the decreased charging rate of the main cell could be increased by
the auxiliary cell, so that the main cell could keep on discharging
to an extent corresponding to the electricity charged by the
auxiliary cell. Then, the output capacity was nearly 6.5 hours. For
comparison, the auxiliary cell was not charged even when the
circuit voltage reached 1.35V/cell. In this case, the output
capacity was 6 hours, coming to the end of the discharge of
electricity.
[0038] It can be seen from the test results that the auxiliary cell
can be used not only for measuring the circuit voltage constantly,
but also for additionally supporting the charge of the main cell,
as occasion demands. The application of the auxiliary cell to the
charge of electricity can produce an increased output capacity.
TEST EXAMPLE 3
[0039] Combination of the redox flow battery (AC170 kW.times.6
hrs.) produced in Test Example 2 with a wind generator was
produced. When reduction occurred in charging rate of the main
cell, a total output of the wind generator plus the redox flow
battery was decreased. This test was carried out in the following
manner. When the circuit voltage as measured by the auxiliary cell
reached 1.37V/cell, the total output was decreased and the
operation was continued until the circuit voltage reached
1.35V/cell. The specification of the wind generator used is given
below.
[0040] (Specification of Wind Generator)
[0041] Type: Dielectric generator
[0042] Rated output: 275 kW
[0043] Rated voltage: 400V
[0044] Rated speed: 1,500 rpm
[0045] It was found from the test results that the charging rate of
the main cell could be increased by decreasing the total output,
whereby the main cell could keep on discharging. Then, the output
capacity was nearly 1,120 kWh. For comparison, the total output was
not decreased even when the circuit voltage reached 1.37V/cell. In
this case, the output capacity was 1,020 kWh.
[0046] In Examples 2 and 3, the ways of increasing the charging
rate of the main cell were examined. When the charging rate of the
main cell increased so excessively that the main cell could not
charge any more, the charging rate of the main cell could be
reduced by using the above-mentioned ways in reverse, such as, for
example, discharging electricity from the auxiliary cell or
increasing the total output.
[0047] Capabilities of Exploitation in Industry
[0048] As mentioned above, in the cell stack of the redox flow
battery of the present invention, since the auxiliary cell is
integrally combined with the cell stack, there can be provided the
advantageous result that the circuit voltage can be measured
substantially constantly by the auxiliary cell, without stopping
the charge/discharge operation of the main cell. Also, in the
operating method of the present invention, since the stop of charge
of the main cell and the stop of discharge of the same are
controlled with reference to the circuit voltage obtained by the
measurement, the output capacity can be stabilized further. Hence,
the operating method of the present invention can realize the
stabilization of the output capacity even in an irregular
operation, such as a power generation by wind and a demand
control.
* * * * *