All-vanadium redox flow battery system and non-stop capacity recovery device

Abstract

The utility model discloses an all-vanadium redox flow battery system and a non-stop capacity recovery device, and belongs to the field of redox flow batteries. The bypass pipeline is added on the basis of an existing all-vanadium redox flow battery system, a non-stop capacity recovery device for controlling the improved all-vanadium redox flow battery system is designed in a matched mode, and the capacity recovery capacity of the improved all-vanadium redox flow battery system is improved by setting battery system charging, an electrolyte temperature threshold value interval and a discharging energy threshold value and controlling a positive and negative pole loop and a liquid return bypass. And transferring the one-pole electrolyte with the high electrolyte liquid level into the one-pole electrolyte with the low electrolyte liquid level, so that the volume of the two-pole electrolyte is recovered to the initial state. According to the invention, adjustment can be rapidly completed in the process of not stopping the pump and charging and discharging, and capacity recovery is realized.

Description

Technical Field

[0001] The present application relates to a liquid flow battery system, belonging to the field of liquid flow batteries, and in particular to an all-vanadium liquid flow battery system and a non-stop capacity recovery device. Background Art

[0002] All-vanadium redox flow battery technology is gaining acceptance in the energy storage market due to its outstanding safety, power-capacity decoupling, deep charge and discharge capabilities, and environmental friendliness. In particular, its power-capacity decoupling makes it ideal for long-term energy storage, making it one of the most promising energy storage technologies.

[0003] During long-term, multi-cycle operation, the discharge capacity of a battery decreases as the number of cycles increases. Although all-vanadium redox flow batteries offer the advantage of 100% online capacity recovery, this requires oxidation or reduction of excess ions in one of the battery storage tanks after the battery system is fully charged and shut down. This is typically accomplished by adding a reducing or oxidizing agent, or even replacing a portion of the high- or low-valent electrolyte, to balance the ions at the positive and negative electrodes and achieve capacity recovery.

[0004] This solution has three drawbacks: First, the system must be charged to a very high SOC and then shut down before operation. If a reducing agent or oxidizing agent is added, it must be fully reacted with the ions in the solution before the system can be restarted. If the reaction product is a gaseous substance, the electrolyte will be filled with bubbles, which will enter the piping system and pose a significant threat to the operation of the pump and battery stack. Second, if the system is stagnant at an excessively high SOC for a long time, a large amount of pentavalent vanadium ions in the positive electrode will be retained in the electrode. Due to their strong oxidizing properties, they will greatly increase the possibility of corrosion and damage to the battery materials. Third, shutdown means the entire station is out of service, which is detrimental to the stable operation of the power grid. If capacity recovery is too frequent, it will inevitably have a negative impact on the application of energy storage power stations. Utility Model Content

[0005] The present application provides an all-vanadium liquid flow battery system and a non-stop capacity recovery device, which can complete capacity recovery online without stopping the pump of the liquid flow battery system and without stopping the charging and discharging process.

[0006] According to one aspect of the present application, an all-vanadium redox flow battery system is provided, comprising: a battery stack, a positive electrode electrolyte storage tank, and a negative electrode electrolyte storage tank; the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank respectively store positive electrode electrolyte and negative electrode electrolyte;

[0007] The positive electrode electrolyte storage tank is connected to the positive electrode pipeline of the battery stack through the positive electrode liquid supply main line, and then connected back to the positive electrode electrolyte storage tank through the positive electrode return line. The positive electrode liquid supply main line and the positive electrode return line are respectively provided with a positive electrode circulation pump and a positive electrode loop main valve; the negative electrode electrolyte storage tank is connected to the negative electrode pipeline of the battery stack through the negative electrode liquid supply main line, and then connected back to the negative electrode electrolyte storage tank through the negative electrode return line. The negative electrode liquid supply main line and the negative electrode return line are respectively provided with a negative electrode circulation pump and a negative electrode loop main valve;

[0008] A first bypass line is provided in front of the main valve of the positive electrode circuit, the first bypass line connects the positive electrode return liquid line and the negative electrode electrolyte storage tank, and a positive electrode to negative electrode return liquid bypass valve is provided on the first bypass line; a second bypass line is provided in front of the main valve of the negative electrode circuit, the second bypass line connects the negative electrode return liquid line and the positive electrode electrolyte storage tank, and a negative electrode to positive electrode return liquid bypass valve is provided on the first bypass line.

[0009] Optionally, a flow sensor, a pressure sensor and a temperature sensor are further provided on the positive electrode liquid supply main path.

[0010] Optionally, a flow sensor, a pressure sensor and a temperature sensor are further provided on the negative electrode liquid supply main path.

[0011] According to another aspect of the present application, a non-stop capacity recovery device is provided for controlling the above-mentioned all-vanadium liquid flow battery system, the device comprising:

[0012] Liquid level indicator module, used to monitor the liquid level height in the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank;

[0013] The valve control module is used to control the opening and closing of the positive electrode loop main valve, the positive electrode to negative electrode return liquid bypass valve, the negative electrode loop main valve, and the negative electrode to positive electrode return liquid bypass valve according to the liquid level height data monitored by the liquid level indicator module, so that the electrolyte of the electrode with a higher liquid level is transferred to the electrolyte of the electrode with a lower electrolyte level; wherein, the opening and closing of the positive electrode loop main valve and the positive electrode to negative electrode return liquid bypass valve are used to control the liquid flowing out of the battery stack and flowing back through the positive electrode return liquid pipeline. The positive electrode electrolyte is refluxed to the positive electrode electrolyte storage tank or the negative electrode electrolyte storage tank alone, or refluxed to the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank at the same time; the opening and closing of the negative electrode loop main valve and the negative electrode to positive electrode return liquid bypass valve are used to make the negative electrode electrolyte flowing out of the battery stack and flowing back through the negative electrode return liquid pipeline refluxed to the negative electrode electrolyte storage tank or the positive electrode electrolyte storage tank alone, or refluxed to the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank at the same time.

[0014] Optionally, the valve control module meets the following conditions before performing a control operation:

[0015] (1) The vanadium liquid flow battery system is in a charging state, and the soc range is [0-65];

[0016] (2) The temperature of the positive and negative electrolytes is 3-15°C lower than the shutdown protection temperature set by the system;

[0017] (3) The discharge energy is not less than 70% of the rated energy.

[0018] Preferably, the soc interval is [0-45].

[0019] Preferably, the shutdown protection temperature set by the system is 5-10°C.

[0020] Preferably, the discharge energy is not less than 85% of the rated energy.

[0021] Optionally, the valve control module is further provided with a capacity recovery condition: the volume of the electrolyte at both electrodes is restored to the initial liquid level height of the electrolyte when the system is initially running, so that the volume of the electrolyte at both electrodes is restored to the initial state, and the deviation between the volume of the electrolyte at each electrode after recovery and the volume of the electrolyte when the system is initially running is ≤10%.

[0022] Preferably, the deviation between the volume of the electrolyte of each electrode after recovery and the volume of the electrolyte when the system is initially running is ≤5%.

[0023] The beneficial effects of this application include: the all-vanadium redox flow battery system and non-stop capacity recovery device provided herein can rapidly complete adjustment and achieve capacity recovery by selecting the appropriate adjustment timing without disrupting the normal operation of the battery system. Compared to existing methods of adding oxidizing or reducing agents after shutdown or removing the accumulated reactants, this is faster and simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a PID diagram of an all-vanadium redox flow battery system in one embodiment of the present application;

[0025] Figure 2 A graph showing the relationship between discharge energy and cycle number in a test stack for a non-stop capacity recovery method of an all-vanadium redox flow battery system in one embodiment of the present application;

[0026] Figure 3 This is a graph showing the relationship between efficiency and cycle number for a test stack using a method for non-stop capacity recovery of an all-vanadium liquid flow battery system in one embodiment of the present application.

[0027] List of components and reference numerals: 1. Cell stack; 2. Positive electrode electrolyte storage tank; 3. Negative electrode electrolyte storage tank; 4. Positive electrode circulation pump; 5. Negative electrode circulation pump; 6. Positive electrode loop main valve; 7 Positive electrode to negative electrode return liquid bypass valve; 8. Negative electrode loop main valve; 9. Negative electrode to positive electrode return liquid bypass valve. DETAILED DESCRIPTION

[0028] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0029] All-vanadium flow battery systems inevitably experience capacity fade during multi-cycle testing. This is primarily due to the migration of substances involved in the battery reaction in the positive or negative electrolyte through the ion-conducting membrane, resulting in an imbalance in the amount of reactants in the positive and negative electrolytes. The migration of reactants is accompanied by the migration of water, causing the electrolyte level in one electrode's electrolyte storage tank to rise and the electrolyte level in the other electrode's electrolyte storage tank to fall. As the amount of migration increases, the difference in the liquid level in the electrolyte storage tanks of the two electrodes becomes larger and larger, and the capacity fade becomes more and more severe. Generally speaking, the migration of reactants in the electrolyte will result in excess reactants at one electrode that have not reacted completely after each charge and discharge cycle. After multiple charge and discharge cycles, the excess reactants accumulate, causing the total amount of reactants available for reaction at both electrodes to continue to decrease.

[0030] The all-vanadium liquid flow battery system proposed in this utility model can achieve capacity recovery without stopping the pump and charging and discharging. It is mainly achieved by transferring the electrolyte of one electrode with a high electrolyte level to the electrolyte of the other electrode with a low electrolyte level, thereby restoring the total amount balance of the electrolyte reactants of the two electrodes and eliminating the accumulation of excess reactants.

[0031] See Figure 1 , which shows an all-vanadium liquid flow battery system, including: a battery stack 1, a positive electrode electrolyte storage tank 2, a negative electrode electrolyte storage tank 3, a positive electrode circulation pump 4, a negative electrode circulation pump 5, a positive electrode loop main valve 6, a negative electrode loop main valve 8, and a positive electrode return liquid pipeline and a negative electrode return liquid pipeline.

[0032] The positive electrode electrolyte storage tank 2 stores positive electrode electrolyte, and the negative electrode electrolyte storage tank 2 stores negative electrode electrolyte. The positive electrode electrolyte is pumped out of the positive electrode electrolyte storage tank 2 by the positive electrode circulation pump 4, flows through the positive electrode liquid supply main line, and flows into the positive electrode pipeline of the battery stack 1. After flowing out of the battery stack 1, it flows back to the positive electrode electrolyte storage tank 2 through the positive electrode return line and the positive electrode loop main valve 6. The negative electrode electrolyte is pumped out of the negative electrode electrolyte storage tank 3 by the negative electrode circulation pump 5, flows through the negative electrode liquid supply main line, and flows into the negative electrode pipeline of the battery stack 1. After flowing out of the battery stack, it flows back to the negative electrode electrolyte storage tank 3 through the negative electrode return line and the negative electrode loop main valve 8. A first bypass line is provided in front of the positive electrode loop main valve 6 for connecting the positive electrode return line and the negative electrode electrolyte storage tank 3. The first bypass line is provided with a positive to negative electrode return bypass valve 7. A second bypass line is provided in front of the negative electrode loop main valve 8 for connecting the negative electrode liquid return line and the positive electrode electrolyte storage tank 2 , and a negative electrode to positive electrode liquid return bypass valve 9 is provided on the second bypass line.

[0033] Through the above-mentioned first bypass pipeline, the positive electrode electrolyte extracted from the positive electrode electrolyte storage tank 2 can flow through the battery stack 1 and then return to the positive electrode electrolyte storage tank 2 or the negative electrode electrolyte storage tank 3 alone, or return to the positive electrode electrolyte storage tank 2 and the negative electrode electrolyte storage tank 3 at the same time.

[0034] Through the above-mentioned second bypass pipeline, the negative electrode electrolyte extracted from the negative electrode electrolyte storage tank 3 can flow through the fuel cell stack 1 and then return to the negative electrode electrolyte storage tank 3 or the positive electrode electrolyte storage tank 2 alone, or return to the positive electrode electrolyte storage tank 2 and the negative electrode electrolyte storage tank 3 at the same time.

[0035] In one embodiment, a flow sensor, a pressure sensor and a temperature sensor are further provided on the positive electrode liquid supply main line.

[0036] In one embodiment, a flow sensor, a pressure sensor and a temperature sensor are further provided on the negative electrode liquid supply main path.

[0037] The present application also provides a non-stop capacity recovery device for controlling the above-mentioned all-vanadium liquid flow battery system, the device comprising:

[0038] Liquid level indicator module, used to monitor the liquid level height in the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank;

[0039] The valve control module is used to control the opening and closing of the positive electrode loop main valve, the positive electrode to negative electrode return liquid bypass valve, the negative electrode loop main valve, and the negative electrode to positive electrode return liquid bypass valve according to the liquid level height data monitored by the liquid level indicator module, so that the electrolyte of the electrode with a higher liquid level is transferred to the electrolyte of the electrode with a lower electrolyte level; wherein, the opening and closing of the positive electrode loop main valve and the positive electrode to negative electrode return liquid bypass valve are used to control the liquid flowing out of the battery stack and flowing back through the positive electrode return liquid pipeline. The positive electrode electrolyte is refluxed to the positive electrode electrolyte storage tank or the negative electrode electrolyte storage tank alone, or refluxed to the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank at the same time; the opening and closing of the negative electrode loop main valve and the negative electrode to positive electrode return liquid bypass valve are used to make the negative electrode electrolyte flowing out of the battery stack and flowing back through the negative electrode return liquid pipeline refluxed to the negative electrode electrolyte storage tank or the positive electrode electrolyte storage tank alone, or refluxed to the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank at the same time.

[0040] In one embodiment, the valve control module satisfies the following conditions before performing a control operation:

[0041] (1) The vanadium liquid flow battery system is in a charging state, and the soc range is [0-65];

[0042] (2) The temperature of the positive and negative electrolytes is 3-15°C lower than the shutdown protection temperature set by the system;

[0043] (3) The discharge energy is not less than 70% of the rated energy.

[0044] As a preferred implementation, the soc interval is [0-45].

[0045] As a preferred embodiment, the shutdown protection temperature set by the system is 5-10°C.

[0046] As a preferred embodiment, the discharge energy is not less than 85% of the rated energy.

[0047] In one embodiment, the valve control module is further provided with a capacity recovery condition: the volume of the electrolyte at both electrodes is restored to the initial liquid level height of the electrolyte when the system is initially running, so that the volume of the electrolyte at both electrodes is restored to the initial state, and the deviation between the volume of the electrolyte at each electrode after recovery and the volume of the electrolyte when the system is initially running is ≤10%.

[0048] As a preferred embodiment, the deviation between the volume of the electrolyte of each electrode after recovery and the volume of the electrolyte when the system is initially running is ≤5%.

[0049] Example

[0050] Connecting a 60kW all-vanadium flow battery stack Figure 1 A 60kW constant power charge-discharge test was conducted on the battery system in the stack over 1200 cycles. During the actual test, the electrolyte level in the positive electrode electrolyte tank decreased, while the electrolyte level in the negative electrode electrolyte tank increased. After multiple cycles, pentavalent vanadium ions accumulated in the positive electrode. Over long periods of time, the total amount of tetravalent vanadium available for charging in the positive electrode decreased, leading to a decrease in capacity. During the more than 1200 cycles of the stack test, the electrolyte was adjusted a total of seven times using the method proposed in this utility model. Table 1 shows a comparison of the discharge energy before and after adjustment with the rated energy.

[0051] Table 1 Comparison of discharge energy and rated energy before and after adjustment

[0052]

[0053] The system operating conditions during the above 7 adjustments are as follows:

[0054] When the system is charging, the soc range is [15-35];

[0055] The electrolyte is a sulfuric acid system, and the temperature during capacity recovery is between 35.2-36.9°C;

[0056] To ensure the effect of capacity recovery, capacity recovery is performed when the discharge energy is not less than 92% of the rated energy;

[0057] During the capacity recovery operation, the electrolyte of the electrode with a higher electrolyte level is transferred to the electrolyte of the electrode with a lower electrolyte level until the volume of the electrolytes of the two electrodes is restored to the initial electrolyte level when the system is initially operated, so that the volume of the electrolytes of the two electrodes is restored to the initial state. The deviation of the electrolyte volume of each electrode after recovery from the electrolyte volume when the system is initially operated is less than 4%.

[0058] The discharge energy of the test changes with the number of cycles as shown in Figure 2 As shown in the figure, the positions of the 7 adjustment points are marked on the figure. It can be seen that through the online capacity recovery strategy, the capacity recovery effect is very good, and it can basically recover to more than 97% of the rated discharge capacity, and generally recover to 99%. Figure 3 The change of efficiency with the number of cycles is indicated. It can be seen that except for the charge and discharge cycles after the adjustment point, which have a relatively obvious decrease in coulombic efficiency due to the adjustment of the electrolyte, the efficiency of the remaining cycles is very stable. After 1200 cycles, the decrease rate of energy efficiency is less than 2%, indicating that the capacity stability and efficiency stability of the system are well guaranteed by adopting the capacity recovery method proposed in the utility model, and the practicality of this method is very high.

[0059] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. An all-vanadium liquid flow battery system, characterized in that: The system comprises: a battery stack (1), a positive electrode electrolyte storage tank (2), and a negative electrode electrolyte storage tank (3); the positive electrode electrolyte storage tank (2) and the negative electrode electrolyte storage tank (3) respectively store positive electrode electrolyte and negative electrode electrolyte; The positive electrode electrolyte storage tank (2) is connected to the positive electrode pipeline of the stack (1) through the positive electrode liquid supply main line, and then connected back to the positive electrode electrolyte storage tank (2) through the positive electrode liquid return line. The positive electrode liquid supply main line and the positive electrode liquid return line are respectively provided with a positive electrode circulation pump (4) and a positive electrode loop main valve (6); the negative electrode electrolyte storage tank (3) is connected to the negative electrode pipeline of the stack (1) through the negative electrode liquid supply main line, and then connected back to the negative electrode electrolyte storage tank (3) through the negative electrode liquid return line. The negative electrode liquid supply main line and the negative electrode liquid return line are respectively provided with a negative electrode circulation pump (5) and a negative electrode loop main valve (8); A first bypass line is provided in front of the positive electrode loop main valve (6), the first bypass line is connected to the positive electrode return line and the negative electrode electrolyte storage tank (3), and a positive electrode to negative electrode return line bypass valve (7) is provided on the first bypass line; a second bypass line is provided in front of the negative electrode loop main valve (8), the second bypass line is connected to the negative electrode return line and the positive electrode electrolyte storage tank (2), and a negative electrode to positive electrode return line bypass valve (9) is provided on the second bypass line.

2. The all-vanadium liquid flow battery system according to claim 1, characterized in that: The positive electrode liquid supply main path is also provided with a flow sensor, a pressure sensor and a temperature sensor.

3. The all-vanadium liquid flow battery system according to claim 1, characterized in that: The negative electrode liquid supply main path is also provided with a flow sensor, a pressure sensor and a temperature sensor.

4. A non-stop capacity recovery device for controlling the all-vanadium liquid flow battery system according to any one of claims 1 to 3, characterized in that: The device includes: Liquid level indicator module, used to monitor the liquid level height in the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank; The valve control module is used to control the opening and closing of the positive electrode loop main valve (6), the positive electrode to negative electrode return liquid bypass valve (7), the negative electrode loop main valve (8), and the negative electrode to positive electrode return liquid bypass valve (9) according to the liquid level height data monitored by the liquid level indication module, so that the electrolyte of one electrode with a higher liquid level is transferred to the electrolyte of one electrode with a lower electrolyte level; wherein the opening and closing of the positive electrode loop main valve (6) and the positive electrode to negative electrode return liquid bypass valve (7) is used to control the positive electrode electrolyte flowing out of the battery stack (1) and flowing back through the positive electrode return liquid pipeline. , refluxes to the positive electrode electrolyte storage tank (2) or the negative electrode electrolyte storage tank (3) alone, or refluxes to the positive electrode electrolyte storage tank (2) and the negative electrode electrolyte storage tank (3) simultaneously; the opening and closing of the negative electrode loop main valve (8) and the negative electrode to positive electrode return liquid bypass valve (9) are used to make the negative electrode electrolyte flowing out of the battery stack (1) and flowing back through the negative electrode return liquid pipeline reflux to the negative electrode electrolyte storage tank (3) or the positive electrode electrolyte storage tank (2) alone, or reflux to the positive electrode electrolyte storage tank (2) and the negative electrode electrolyte storage tank (3) simultaneously.

5. The non-stop capacity recovery device according to claim 4, characterized in that: The valve control module meets the following conditions before performing control operations: (1) The vanadium liquid flow battery system is in a charging state, and the soc range is [0-65]; (2) The temperature of the positive and negative electrolytes is 3-15°C lower than the shutdown protection temperature set by the system; (3) The discharge energy is not less than 70% of the rated energy.

6. The non-stop capacity recovery device according to claim 5, characterized in that: The soc interval is [0-45].

7. The non-stop capacity recovery device according to claim 5, characterized in that: The shutdown protection temperature set by the system is 5-10°C.

8. The non-stop capacity recovery device according to claim 5, characterized in that: The discharge energy is not less than 85% of the rated energy.

9. The non-stop capacity recovery device according to claim 5, characterized in that: The valve control module is also provided with a capacity recovery condition: the volume of the electrolyte at both electrodes is restored to the initial liquid level height of the electrolyte when the system is initially running, so that the volume of the electrolyte at both electrodes is restored to the initial state, and the deviation between the volume of the electrolyte at each electrode after recovery and the volume of the electrolyte when the system is initially running is ≤10%.

10. The non-stop capacity recovery device according to claim 9, characterized in that: The deviation of the electrolyte volume of each electrode after recovery from the electrolyte volume when the system is initially running is ≤5%.

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