Redox flow battery, method for operating the same, and redox flow battery system

Abstract

[Problem] To provide a redox flow battery that can be charged and discharged at a constant voltage, and a method for operating the same. [Solution] The system includes a battery cell to which a positive electrode electrolyte and a negative electrode electrolyte are supplied, an uncharged positive electrode electrolyte tank for storing uncharged positive electrode electrolyte, a charged positive electrode electrolyte tank for storing charged positive electrode electrolyte, an uncharged negative electrode electrolyte tank for storing uncharged negative electrode electrolyte, and a charged negative electrode electrolyte tank for storing charged negative electrode electrolyte. During charging, positive electrode electrolyte is transferred from the uncharged positive electrode electrolyte tank to the charged positive electrode electrolyte tank via the positive electrode electrolyte tank, and negative electrode electrolyte is transferred from the uncharged negative electrode electrolyte tank to the charged negative electrode electrolyte tank via the negative electrode electrolyte tank. During discharging, positive electrode electrolyte is transferred from the charged positive electrode electrolyte tank via the positive electrode electrolyte tank to the uncharged positive electrode electrolyte tank of the positive cell, and negative electrode electrolyte is transferred from the charged negative electrode electrolyte tank to the uncharged negative electrode electrolyte tank via the negative electrode electrolyte tank.

Description

Technical Field

[0001] The present invention relates to a redox flow battery, a method for operating the same, and a redox flow battery system.

Background Art

[0002] Redox flow batteries are used for load leveling of electric power and countermeasures against momentary stoppages, etc., and are attracting attention as new power storage batteries. In particular, redox flow batteries using vanadium salts as active materials are known (see, for example, Patent Document 1).

[0003] The operating principle of the redox flow battery will be described with reference to FIG. 9. The redox flow battery 100 includes a battery cell 110 separated into a positive electrode cell 100A and a negative electrode cell 100B by a separator 101 made of an ion exchange membrane, electrolyte tanks 104A and 104B for storing an electrolyte, circulation pipes 106A and 106B for circulating the electrolyte from the electrolyte tanks 104A and 104B to the battery cell 110, and circulation pumps 105A and 105B connected to the circulation pipes 106A and 106B for circulating the electrolyte.

[0004] The positive electrode cell 100A incorporates a positive electrode 102, and the negative electrode cell 100B incorporates a negative electrode 103. In addition, a positive electrode electrolyte tank 104A for storing a positive electrode electrolyte is connected to the positive electrode cell 100A via a positive electrode electrolyte circulation pipe 106A, and a negative electrode electrolyte tank 104B for storing a negative electrode electrolyte is connected to the negative electrode cell 100B via a negative electrode electrolyte circulation pipe 106B. Circulation pumps 105A and 105B are provided in the circulation pipes 106A and 106B, respectively, and each electrolyte is circulated between the respective tanks and cells via the positive electrode electrolyte circulation pipe 106A and the negative electrode electrolyte circulation pipe 106B.

[0005] An aqueous solution of ions with variable valences such as vanadium ions is used as each electrode electrolyte. While circulating the electrolyte with pumps 105A and 105B, charge and discharge are performed along with the valence change reaction of ions at the positive electrode 102 and the negative electrode 103.

[0006] For example, when using an electrolyte containing vanadium ions, the reactions occurring during charge and discharge at the positive and negative electrodes in the cell are as follows. In reality, V 4+ exists as VO 2+ , and V 5+ is presumed to exist as VO 2+ , and is presumed to exist in a hydrated state or a state where sulfate groups are coordinated, respectively. Positive electrode: V 4+ → V 5+ + e - (Charging) ·V 4+ ← V 5+ + e - (Discharging) Negative electrode: V 3+ + e - → V 2+ (Charging) ·V 3+ + e - ← V 2+ (Discharging)

[0007] Hydrogen ions (H + ) generated at the positive electrode during charging move to the negative electrode side through the separator 101, maintaining the electrical neutrality of the electrolyte. The electric power supplied from a power generation unit (e.g., a power plant, etc.) is stored in the electrolyte tank as a valence change of vanadium ions with different valences. On the other hand, during discharging, the stored electric power can be extracted by a reaction opposite to that during charging and supplied to a load (e.g., a consumer, etc.).

[0008] In a redox flow battery, the state of charge (SOC) of the electrolyte is determined by the ratio of ion valences in the electrolyte. For example, in the case of a vanadium-based redox flow battery, in the positive electrode electrolyte, for vanadium ions (V 4+ and V 5+ ) in the positive electrode electrolyte, V 5+The ratio in the negative electrode electrolyte is represented by the ratio of vanadium ions (V 2+ and V 3+ ) in V 2+ . During charging, the battery reaction is such that at the positive electrode in the battery cell, V 4+ is oxidized to V 5+ , and at the negative electrode, V 3+ is reduced to V 2+ . The battery reaction during discharging is the reverse of that during charging.

[0009] In a vanadium redox flow battery, a full charge voltage (charge completion voltage, charge end voltage) and a final discharge voltage are preset from the viewpoints of deterioration suppression, charging efficiency, etc. During normal operation of the battery, charging and discharging are performed within the charge-discharge possible range from the final discharge state (for example, state of charge: 20%) to full charge (for example, state of charge: 80%). Here, the full charge voltage is the voltage set to stop charging from the power system, and the final discharge voltage is the voltage set to stop discharging to the power system.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] However, in a conventional redox flow battery, the electrolyte is circulated between the electrolyte tank and the battery cell, that is, the electrolyte supplied to the battery cell and the electrolyte discharged from the battery cell are put into the same electrolyte tank.

[0012] For this reason, the state of charge (SOC) changes during charging and discharging. Even when the load is constant, the charging voltage and the discharging voltage change, and additional equipment is required to match the upper and lower limit voltages. Also, there was a problem that for loads that are sensitive to changes in the output from the redox flow battery, it was difficult to use.

[0013] In the present invention, in view of such a current situation, an object is to provide a redox flow battery capable of charging and discharging at a constant voltage, a method for operating the same, and a redox flow battery system.

Means for Solving the Problems

[0014] The present invention has been invented to solve the problems in the prior art as described above, and the present invention includes, for example, the following aspects.

[0015] [1] Two or more battery cells including a positive electrode cell to which a positive electrode electrolyte is supplied and a negative electrode cell to which a negative electrode electrolyte is supplied, and Three or more positive electrode electrolyte tanks for storing the positive electrode electrolyte, Three or more negative electrode electrolyte tanks for storing the negative electrode electrolyte, Piping connecting the battery cell, the positive electrode electrolyte tank, and the negative electrode electrolyte tank, A redox flow battery system including tank switching means provided in the piping path for switching the flow paths of the positive electrode electrolyte and the negative electrode electrolyte, wherein The input / output ends of each battery cell are connected in parallel, The three or more positive electrode electrolyte tanks include one uncharged positive electrode electrolyte tank for storing an uncharged positive electrode electrolyte, one charged positive electrode electrolyte tank for storing a charged positive electrode electrolyte, and one or more intermediate positive electrode electrolyte tanks, Each of the intermediate positive electrode electrolyte tanks is connected to the positive electrode cells of two battery cells among the plurality of battery cells, The intermediate positive electrode electrolyte tank As the uncharged positive electrode electrolyte tank of one battery cell and operates while As the charged positive electrode electrolyte tank of the other battery cell, operating , The three or more negative electrode electrolyte tanks include one uncharged negative electrode electrolyte tank for storing an uncharged negative electrode electrolyte, one charged negative electrode electrolyte tank for storing a charged negative electrode electrolyte, and one or more intermediate negative electrode electrolyte tanks, The intermediate negative electrode electrolyte tanks are respectively connected to the negative electrode cells of two of the plurality of battery cells. The intermediate negative electrode electrolyte tank The uncharged negative electrode electrolyte tank of one battery cell operates while and the charged negative electrode electrolyte tank of the other battery cell operating , During charging of the redox flow battery system, The tank switching means is switched so that the positive electrode electrolyte is moved from the one uncharged positive electrode electrolyte tank to the one charged positive electrode electrolyte tank through the positive electrode cells of each battery cell and each intermediate positive electrode electrolyte tank connected between the battery cells, and The tank switching means is switched so that the negative electrode electrolyte is moved from the one uncharged negative electrode electrolyte tank to the one charged negative electrode electrolyte tank through the negative electrode cells of each battery cell and each intermediate negative electrode electrolyte tank connected between the battery cells, and Charging is performed such that the SOC (State of Charge) of the positive electrode electrolyte moved from the one uncharged positive electrode electrolyte tank to the one charged positive electrode electrolyte tank and the SOC of the negative electrode electrolyte moved from the one uncharged negative electrode electrolyte tank to the one charged negative electrode electrolyte tank are fully charged in the most downstream is connected to the positive electrode electrolyte tank and the negative electrode electrolyte tank battery cell, During discharging of the redox flow battery system, The tank switching means is switched so that the positive electrode electrolyte is moved from the one charged positive electrode electrolyte tank, through the positive electrode cells of the respective battery cells and the respective intermediate positive electrode electrolyte tanks connected between the respective battery cells, to the one uncharged positive electrode electrolyte tank, and the tank switching means is switched so that the negative electrode electrolyte is moved from the one charged negative electrode electrolyte tank, through the negative electrode cells of the respective battery cells and the respective intermediate negative electrode electrolyte tanks connected between the respective battery cells, to the one uncharged negative electrode electrolyte tank, such that the one charged positive electrode electrolyte tank, the one uncharged positive electrode electrolyte tank, the negative electrode cells of the respective battery cells, the respective intermediate negative electrode electrolyte tanks connected between the respective battery cells, and the one uncharged negative electrode electrolyte tank are connected in series, and the SOC of the positive electrode electrolyte moved from the one charged positive electrode electrolyte tank to the one uncharged positive electrode electrolyte tank and the SOC of the negative electrode electrolyte moved from the one charged negative electrode electrolyte tank to the one uncharged negative electrode electrolyte tank are each is connected to the positive electrode electrolyte tank and the negative electrode electrolyte tank configured to perform discharging so as to reach the end of discharge in the most downstream battery cell. A redox flow battery system is provided.

[0016] [2] The redox flow battery according to item [1], further comprising control means for controlling the switching of the tank switching means system. [Advantages of the Invention]

[0019] According to the present invention, the SOC of the electrolyte during charge and discharge can be kept constant, and charge and discharge can be performed at a constant voltage. [Brief Description of the Drawings]

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments (examples) of the present invention will be described in more detail with reference to the drawings. The drawings used in the following description may show, for the sake of clarity, the characteristic parts enlarged for convenience, and the dimensional ratios of each component may be different from the actual ones. Also, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto.

[0022] Figure 1 is a schematic diagram for explaining the configuration of the redox flow battery in this embodiment. As shown in FIG. 1, the redox flow battery 10 includes a battery cell 20 separated into a positive electrode cell 10A and a negative electrode cell 10B by a separator 11 made of an ion exchange membrane, electrolyte tanks 14A1, 14A2, 14B1, 14B2 for storing an electrolyte, pipes 16A1, 16A2, 16B1, 16B2 for moving the electrolyte between the electrolyte tanks 14A1, 14A2, 14B1, 14B2 and the battery cell 20, and pumps 15A, 15B connected to the pipes 16A1, 16A2, 16B1, 16B2 for circulating the electrolyte. A positive electrode 12 is built into the positive electrode cell 10A, and a negative electrode 13 is built into the negative electrode cell 10B. As the battery cell 20 in the present invention, a known configuration can be adopted.

[0023] The charged electrolyte is stored in the electrolyte tanks 14A1 and 14B1, while the discharged electrolyte, i.e., the uncharged electrolyte, is stored in the electrolyte tanks 14A2 and 14B2. Hereinafter, the electrolyte tanks 14A1 and 14B1 are also referred to as "charged positive electrode electrolyte tanks 14A1 and charged negative electrode electrolyte tanks 14B1", and the electrolyte tanks 14A2 and 14B2 are also referred to as "uncharged positive electrode electrolyte tanks 14A2 and uncharged negative electrode electrolyte tanks 14B2". Further, the charged positive electrode electrolyte tanks 14A1 and charged negative electrode electrolyte tanks 14B1 are collectively referred to as "charged electrolyte tanks 14A1 and 14B1", and the uncharged positive electrode electrolyte tanks 14A2 and uncharged negative electrode electrolyte tanks 14B2 are collectively referred to as "uncharged electrolyte tanks 14A2 and 14B2".

[0024] The battery cell 20 is connected to a power generation unit (e.g., a power plant) or a load (e.g., a consumer) via an AC / DC converter and a power line, and stores the power supplied from the power generation unit and supplies power to the load.

[0025] In the redox flow battery 10 of the present embodiment, tank switching means 17A1a, 17A1b, 17A2a, 17A2b, 17B1a, 17B1b, 17B2a, 17B2b for switching the connection between the battery cell 20 and the electrolyte tanks 14A1, 14A2, 14B1, 14B2 are provided in the pipes 16A1, 16A2, 16B1, 16B2, respectively.

[0026] The tank switching means 17A1a, 17A1b, 17A2a, 17A2b, 17B1a, 17B1b, 17B2a, 17B2b are connected to control means (not shown). As will be described later, the control means is configured to switch the path from the electrolyte tanks 14A1, 14A2, 14B1, 14B2 to the battery cell 20 by controlling the tank switching means 17A1a, 17A1b, 17A2a, 17A2b, 17B1a, 17B1b, 17B2a, 17B2b.

[0027] In this embodiment, as the tank switching means 17A1a, 17A1b, 17A2a, 17A2b, 17B1a, 17B1b, 17B2a, 17B2b, an electromagnetic valve (two-way electromagnetic valve) whose opening and closing operation is controlled by an electrical signal from the control means is used, but it is not limited thereto. For example, a three-way electromagnetic valve or the like can be used to configure the path to be switched. Also, a manual valve can be used as the tank switching means 17A1a, 17A1b, 17A2a, 17A2b, 17B1a, 17B1b, 17B2a, 17B2b to switch the path manually without using the control means.

[0028] In the redox flow battery 10 configured as described above, the opening and closing control of the tank switching means 17A1a, 17A1b, 17A2a, 17A2b, 17B1a, 17B1b, 17B2a, 17B2b is performed by the control means as follows, and the battery is operated while the flow path of the electrolyte is switched.

[0029] (1) During charging During charging, as shown in FIG. 2, the tank switching means 17A1a, 17A2b, 17B1a, 17B2b are opened, and the tank switching means 17A2a, 17A1b, 17B2a, 17B1b are closed, so that the positive electrolyte is moved from the uncharged positive electrolyte tank 14A2 to the charged positive electrolyte tank 14A1 via the positive electrode cell 10A, and the negative electrolyte is moved from the uncharged negative electrolyte tank 14B2 to the charged negative electrolyte tank 14B1 via the negative electrode cell 10B.

[0030] (2) After charging and before discharging (1) When the charging of (1) is completed and the SOC of the charged positive electrode electrolyte tank 14A1 is further improved, and until the start of discharging, as shown in FIG. 3, the tank switching means 17A1a, 17A1b, 17B1a, 17B1b are opened and the tank switching means 17A2a, 17A2b, 17B2a, 17B2b are closed, so that the positive electrode electrolyte is circulated between the charged positive electrode electrolyte tank 14A1 and the positive electrode cell 10A, and the negative electrode electrolyte may be circulated between the charged negative electrode electrolyte tank 14B1 and the negative electrode cell 10B. When charging is completed, the tank switching means 17A1a, 17A1b, 17B1a, 17B1b may be closed and the pumps 15A, 15B may be stopped to stop the circulation of the positive electrode electrolyte and the negative electrode electrolyte.

[0031] (3) During discharging During discharging, as shown in FIG. 4, the tank switching means 17A2a, 17A1b, 17B2a, 17B1b are opened and the tank switching means 17A1a, 17A2b, 17B1a, 17B2b are closed, so that the positive electrode electrolyte is moved from the charged positive electrode electrolyte tank 14A1 through the positive electrode cell 10A to the uncharged positive electrode electrolyte tank 14A2, and the negative electrode electrolyte is moved from the charged negative electrode electrolyte tank 14B1 through the negative electrode cell 10B to the uncharged negative electrode electrolyte tank 14B2.

[0032] (4) During discharging and before charging When the discharge of (3) is completed and the SOC of the uncharged positive electrode electrolyte tank 14A2 is then decreased, and until charging is started, as shown in FIG. 5, the tank switching means 17A2a, 17A2b, 17B2a, 17B2b are opened and the tank switching means 17A1a, 17A1b, 17B1a, 17B1b are closed, whereby the positive electrode electrolyte is circulated between the uncharged positive electrode electrolyte tank 14A2 and the positive electrode cell 10A, and the negative electrode electrolyte may be circulated between the uncharged negative electrode electrolyte tank 14B2 and the negative electrode cell 10B. Note that at the end of discharge, the tank switching means 17A2a, 17A2b, 17B2a, 17B2b may be closed and the pumps 15A, 15B may be stopped to stop the circulation of the positive electrode electrolyte and the negative electrode electrolyte.

[0033] By configuring in this way, during charging and discharging, the electrolyte supplied to the battery cell 20 and the electrolyte discharged from the battery cell 20 can keep the SOC of the electrolyte supplied to the battery cell 20 constant without being mixed in the electrolyte tank.

[0034] Also, in a conventional redox flow battery, since the electrolyte is circulated between the electrolyte tank and the battery cell, the amount of electrolyte sent in one charge or discharge is several times or more (usually not less than the amount of electrolyte in the electrolyte tank) the amount of electrolyte required for charging or discharging. In comparison with this, in the present embodiment, the amount of electrolyte sent in one charge or discharge is equal to the amount of electrolyte required for charging or discharging (at most the amount of electrolyte in the electrolyte tank), and since the flow rate of the electrolyte can be decreased, the power consumption of the pumps 15A, 15B can be reduced.

[0035] Note that from the viewpoints of deterioration suppression, charging efficiency, etc., it is preferable to maintain the SOC of the electrolyte such that when the open-circuit voltage of the battery cell 20 with the electrolyte is measured, it is below the full charge voltage during charging and above the end-of-discharge voltage during discharging.

[0036] In addition, if the SOC of the electrolytic solution discharged from the battery cell 20 during charging is sufficiently low and the open-circuit voltage of the battery cell 20 is sufficiently lower than the full-charge voltage, further charging may be performed while circulating the electrolytic solution between the fully charged electrolytic solution tanks 14A1 and 14B1 and the positive electrode cell 10A and the negative electrode cell 10B.

[0037] Also, if the SOC of the electrolytic solution discharged from the battery cell 20 during discharging is sufficiently high and the open-circuit voltage of the battery cell 20 is sufficiently higher than the end-discharge voltage, further discharging may be performed while circulating the electrolytic solution between the uncharged electrolytic solution tanks 14A2 and 14B2 and the positive electrode cell 10A and the negative electrode cell 10B.

[0038] Note that by circulating the electrolytic solution in this way for charging or discharging, it becomes easy to adjust the SOC of the electrolytic solution. Therefore, not only can the SOC during the same cycle period (i.e., the period from one charge to one discharge) be kept constant, but also the SOC of each cycle can be kept constant.

[0039] It should be noted that as in this embodiment, it is preferable to provide the uncharged electrolytic solution tanks 14A2 and 14B2 and the fully charged electrolytic solution tanks 14A1 and 14B1 for the positive electrode cell 10A and the negative electrode cell 10B, respectively. However, only one electrolytic solution tank connected to either the positive electrode cell 10A or the negative electrode cell 10B may be provided, and the electrolytic solution may be circulated in the same manner as in a conventional redox flow battery.

[0040] FIG. 6 is a schematic diagram for explaining the configuration in an embodiment of the redox flow battery system of the present invention. The redox flow battery system 30 in this embodiment basically includes a plurality of redox flow batteries 10 having the same configuration as the redox flow battery 10 shown in FIGS. 1 to 5. The same components as those in the foregoing embodiments are denoted by the same reference numerals in this embodiment, and detailed descriptions thereof are omitted. Also, the drawings are simplified to clearly show the connection of the pipes and power lines.

[0041] In this embodiment, for a plurality of redox flow batteries, the flow paths of the electrolytes are connected in series to the power lines in parallel. Hereinafter, a case where the redox flow battery system is composed of three redox flow batteries, namely, a redox flow battery 10X, a redox flow battery 10Y, and a redox flow battery 10Z, will be described as an example.

[0042] The redox flow batteries 10X, 10Y, and 10Z all have the same configuration as the redox flow battery 10 shown in FIG. 1. However, the uncharged positive electrode electrolyte tank 14A2 of the redox flow battery 10X is shared as the charged positive electrode electrolyte tank 14A1 of the redox flow battery 10Y, and the uncharged positive electrode electrolyte tank 14A2 of the redox flow battery 10Y is shared as the charged positive electrode electrolyte tank 14A1 of the redox flow battery 10Z. Also, the uncharged negative electrode electrolyte tank 14B2 of the redox flow battery 10X is shared as the charged negative electrode electrolyte tank 14B1 of the redox flow battery 10Y, and the uncharged negative electrode electrolyte tank 14B2 of the redox flow battery 10Y is shared as the charged negative electrode electrolyte tank 14B1 of the redox flow battery 10Z.

[0043] The tanks shared as the uncharged electrolyte tank and the charged electrolyte tank are referred to as intermediate tanks (intermediate positive electrode electrolyte tank 14A3 and intermediate negative electrode electrolyte tank 14B3) in this specification.

[0044] As shown in FIG. 6, in the redox flow battery 10 of this embodiment, the electrolyte after discharge discharged from the redox flow battery 10X is supplied to the redox flow battery 10Y, and the electrolyte after discharge discharged from the redox flow battery 10Y is supplied to the redox flow battery 10Z. On the other hand, the electrolyte after charging discharged from the redox flow battery 10Z is supplied to the redox flow battery 10Y, and the electrolyte after charging discharged from the redox flow battery 10Y is supplied to the redox flow battery 10X.

[0045] That is, by switching the tank switching means provided in each pipe, when charging the redox flow batteries 10X, 10Y, and 10Z, as shown in FIG. 7, from the uncharged positive electrode electrolyte tank 14A2, the positive electrode electrolyte is moved to the charged positive electrode electrolyte tank 14A1 through the intermediate positive electrode electrolyte tank 14A3 and the positive electrode cells 10A of each redox flow battery, and from the uncharged negative electrode electrolyte tank 14B2, the negative electrode electrolyte is moved to the charged negative electrode electrolyte tank 14B1 through the intermediate negative electrode electrolyte tank 14B3 and the negative electrode cells 10B of each redox flow battery.

[0046] On the other hand, when discharging the redox flow batteries 10X, 10Y, and 10Z, as shown in FIG. 8, the positive electrode electrolyte is moved from the charged positive electrode electrolyte tank 14A1 to the uncharged positive electrode electrolyte tank 14A2 through the intermediate positive electrode electrolyte tank 14A3 and the positive electrode cells 10A of each redox flow battery, and the negative electrode electrolyte is moved from the charged negative electrode electrolyte tank 14B1 to the uncharged negative electrode electrolyte tank 14B2 through the intermediate negative electrode electrolyte tank 14B3 and the negative electrode cells 10B of each redox flow battery.

[0047] Also, the input / output terminals (terminals connected to the power line via an AC / DC converter) of the redox flow batteries 10X, 10Y, and 10Z are connected in parallel. By connecting in this way, each of the redox flow batteries 10X, 10Y, and 10Z is connected in parallel to the power generation unit and the load, respectively, and the input / output of the redox flow batteries 10X, 10Y, and 10Z do not affect each other.

[0048] When configured in this way and operating so that the redox flow batteries 10X and 10Y do not discharge until the end of discharge and the redox flow batteries 10Z and 10Y do not charge until full charge, the open circuit voltages of the redox flow battery 10X, the redox flow battery 10Y, and the redox flow battery 10Z will be different. However, since each redox flow battery cell 10X, 10Y, 10Z is supplied with an electrolyte of a certain SOC, charge and discharge can be performed at a constant voltage in each of the redox flow batteries 10X, 10Y, 10Z.

[0049] It is preferable to make the capacities of the redox flow batteries 10X, 10Y, and 10Z the same, because the period during which these three redox flow batteries can be operated simultaneously becomes longer. For example, assuming that the SOC at the end of discharge is S0 and the SOC at full charge is S3, and the SOCs at the points that divide the range from S0 to S3 into three equal parts are S1 and S2 (where S0 < S1 < S2 < S3). In this case, if the redox flow battery 10X is operated in the range from S2 to S3, the redox flow battery 10Y is operated in the range from S1 to S2, and the redox flow battery 10Z is operated in the range from S0 to S1, the capacities of the respective redox flow batteries 10X, 10Y, and 10Z will be substantially the same.

[0050] In addition, in this embodiment, although three redox flow batteries 10X, 10Y, and 10Z are used for explanation, the number of redox flow batteries is not particularly limited and can be appropriately changed according to the required capacity. Specifically, when performing charge and discharge at high power, it is preferable to use a larger number of redox flow batteries, and when charge and discharge at high power is not required, a smaller number may be sufficient.

[0051] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto. In the above embodiments, a vanadium-based electrolyte containing vanadium ions is used as the electrolyte, but it is not limited thereto. For example, a titanium-manganese-based electrolyte, an iron-chromium-based electrolyte, etc. can also be used, and various modifications can be made without departing from the object of the present invention.

Explanation of Reference Numerals

[0052] 10 Redox flow battery 10A Positive electrode cell 10B Negative electrode cell 11 Diaphragm 12 Positive electrode 13 Negative electrode 14A1 Charged positive electrode electrolyte tank 14A2 Uncharged positive electrode electrolyte tank 14B1 Charged negative electrode electrolyte tank 14B2 Uncharged Negative Electrolyte Tank 15A Pump 15B Pump 16A1 Pipe 16A2 Pipe 16B1 Pipe 16B2 Pipe 17A1a Tank Switching Means 17A1b Tank Switching Means 17A2a Tank Switching Means 17A2b Tank Switching Means 17B1a Tank Switching Means 17B1b Tank Switching Means 17B2a Tank Switching Means 17B2b Tank Switching Means 20 Battery Cell 100 Redox Flow Battery 100A Positive Electrode Cell 100B Negative Electrode Cell 101 Diaphragm 102 Positive Electrode 103 Negative Electrode 104A Positive Electrolyte Tank 104B Negative Electrolyte Tank 105A Circulation Pump 105B Circulation Pump 106A Positive Electrolyte Circulation Pipe 106B Negative Electrolyte Circulation Pipe 110 Battery Cell

Claims

【Claim 1】 comprising two or more battery cells including a positive electrode cell supplied with a positive electrode electrolyte and a negative electrode cell supplied with a negative electrode electrolyte, three or more positive electrode electrolyte tanks for storing the positive electrode electrolyte, three or more negative electrode electrolyte tanks for storing the negative electrode electrolyte, piping connecting the battery cells, the positive electrode electrolyte tanks, and the negative electrode electrolyte tanks, a redox flow battery system comprising tank switching means provided in the piping path for switching the flow paths of the positive electrode electrolyte and the negative electrode electrolyte, the input / output ends of each battery cell are connected in parallel, the three or more positive electrode electrolyte tanks include one uncharged positive electrode electrolyte tank for storing uncharged positive electrode electrolyte, one charged positive electrode electrolyte tank for storing charged positive electrode electrolyte, and one or more intermediate positive electrode electrolyte tanks, each of the intermediate positive electrode electrolyte tanks is connected to the positive electrode cells of two of the plurality of battery cells, and each intermediate positive electrode electrolyte tank operates as an uncharged positive electrode electrolyte tank for one battery cell and as a charged positive electrode electrolyte tank for the other battery cell, the three or more negative electrode electrolyte tanks include one uncharged negative electrode electrolyte tank for storing uncharged negative electrode electrolyte, one charged negative electrode electrolyte tank for storing charged negative electrode electrolyte, and one or more intermediate negative electrode electrolyte tanks, each of the intermediate negative electrode electrolyte tanks is connected to the negative electrode cells of two of the plurality of battery cells, and each intermediate negative electrode electrolyte tank operates as an uncharged negative electrode electrolyte tank for one battery cell and as a charged negative electrode electrolyte tank for the other battery cell, during charging of the redox flow battery system, the tank switching means is switched so that the positive electrode electrolyte is moved from the one uncharged positive electrode electrolyte tank through the positive electrode cells of each battery cell and each intermediate positive electrode electrolyte tank connected between the battery cells to the one charged positive electrode electrolyte tank, and the one uncharged positive electrode electrolyte tank, the positive electrode cells of each battery cell, each intermediate positive electrode electrolyte tank connected between the battery cells, and the one charged positive electrode electrolyte tank are connected in series, The tank switching means is switched so that the negative electrode electrolyte is moved from the one uncharged negative electrode electrolyte tank to the one charged negative electrode electrolyte tank through the negative electrode cells of the respective battery cells and the respective intermediate negative electrode electrolyte tanks connected between the respective battery cells, and the one uncharged negative electrode electrolyte tank, the negative electrode cells of the respective battery cells, the respective intermediate negative electrode electrolyte tanks connected between the respective battery cells, and the one charged negative electrode electrolyte tank are connected in series. Charging is performed such that the state of charge (SOC) of the positive electrode electrolyte moved from the one uncharged positive electrode electrolyte tank to the one charged positive electrode electrolyte tank and the SOC of the negative electrode electrolyte moved from the one uncharged negative electrode electrolyte tank to the one charged negative electrode electrolyte tank are fully charged in the battery cells connected to the most downstream positive electrode electrolyte tank and negative electrode electrolyte tank, respectively. During discharge of the redox flow battery system, the tank switching means is switched so that the positive electrode electrolyte is moved from the one charged positive electrode electrolyte tank to the one uncharged positive electrode electrolyte tank through the positive electrode cells of the respective battery cells and the respective intermediate positive electrode electrolyte tanks connected between the respective battery cells, and the one charged positive electrode electrolyte tank, the positive electrode cells of the respective battery cells, the respective intermediate positive electrode electrolyte tanks connected between the respective battery cells, and the one uncharged positive electrode electrolyte tank are connected in series, and the tank switching means is switched so that the negative electrode electrolyte is moved from the one charged negative electrode electrolyte tank to the one uncharged negative electrode electrolyte tank through the negative electrode cells of the respective battery cells and the respective intermediate negative electrode electrolyte tanks connected between the respective battery cells, and the one charged negative electrode electrolyte tank, the negative electrode cells of the respective battery cells, the respective intermediate negative electrode electrolyte tanks connected between the respective battery cells, and the one uncharged negative electrode electrolyte tank are connected in series. A redox flow battery system configured to perform discharge such that the SOC of the positive electrode electrolyte moved from the one charged positive electrode electrolyte tank to the one uncharged positive electrode electrolyte tank and the SOC of the negative electrode electrolyte moved from the one charged negative electrode electrolyte tank to the one uncharged negative electrode electrolyte tank are at the end of discharge in the battery cells connected to the most downstream positive electrode electrolyte tank and negative electrode electrolyte tank, respectively. Claim 2 The redox flow battery system according to claim 1, further comprising control means for controlling the switching of the tank switching means.

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