An iron-chromium liquid flow battery stack system

Abstract

The present invention discloses an iron-chromium flow battery stack system, comprising: a cathode electrolyte flowing out of a cathode liquid tank passes through a third valve, a cathode pump, a fourth valve, a cathode liquid path of the stack, and a sixth valve in sequence before returning to the cathode liquid tank; a cathode electrolyte flowing out of a cathode liquid tank passes through a first valve, a cathode pump, a second valve, a cathode liquid path of the stack, and a fifth valve in sequence before returning to the cathode liquid tank; a seventh valve and an eighth valve are both bridged between the positive and negative electrode circulation paths and are closed during charging and discharging of the stack; a first cleaning method for cleaning the stack comprises first closing the positive and negative electrode pumps, then, without charging the stack, opening the second, third, fourth, sixth, seventh, and eighth valves, the cathode pump, and the negative electrode pump, while simultaneously closing the first and fifth valves, so as to clean the entire stack with the cathode electrolyte. The present invention improves the performance and service life of the iron-chromium flow battery stack.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow energy storage, and in particular relates to an iron-chromium liquid flow battery stack system. Background Art

[0002] As the global economy continues to grow, demand for energy is increasing, energy shortages are becoming increasingly severe, and the massive consumption of traditional fossil fuels is causing increasing environmental problems. Renewable energy sources such as wind and solar power are crucial for improving the energy mix, protecting the ecological environment, addressing climate change, and achieving sustainable economic and social development.

[0003] Renewable energy generation from sources like wind and solar power is characterized by instability and discontinuity, necessitating the use of large-scale energy storage technologies, particularly long-duration ones, to improve the quality and reliability of electricity generated from renewable sources. Liquid flow battery technology, a chemical energy storage technology, offers significant advantages in terms of energy density, efficiency, scale, cycle life, and cost. Liquid flow battery technology boasts an energy storage density of 10Wh / kg to 30Wh / kg and an efficiency of 60% to 85%. Furthermore, its power and capacity can be independently designed, offering rapid charge and discharge responses and a wide range of applications. It can be used for peak shaving, valley shifting, backup power, emergency power supply, and other applications, including improving power quality and regulating voltage and frequency.

[0004] As a typical device in electrochemical energy storage technology, iron-chromium flow batteries offer outstanding advantages, including high efficiency, long cycle life, independent design of capacity and power, fast response, high safety, and a cost-effective lifecycle. They are particularly suitable for large-scale energy storage. Multiple iron-chromium flow batteries can be connected in series and assembled to form a higher-level energy storage system unit structure—a battery stack.

[0005] However, during the electrochemical process of the iron-chromium liquid flow battery's electrolyte, elements such as copper and nickel will gradually adhere to / deposit inside the battery stack. As the amount of deposition gradually increases over time, the amount of hydrogen evolution in the iron-chromium liquid flow battery will gradually increase. Hydrogen evolution in the iron-chromium liquid flow battery will cause battery degradation, resulting in insufficient hydrogen ions to reduce trivalent iron during the charge and discharge process, leading to excessively high trivalent iron content, battery capacity degradation, affecting battery performance, and reducing the service life of the battery stack. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides an iron-chromium liquid flow battery stack system.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0008] An iron-chromium flow battery stack system, wherein the positive and negative electrolytes of the iron-chromium flow battery in the system are both mixed solutions of divalent iron ions, trivalent chromium ions, and hydrochloric acid, and after the stack is operated, part of the divalent iron ions is oxidized to trivalent iron ions;

[0009] The system includes: a battery stack, a cathode liquid tank, a cathode liquid tank, a first valve, a second valve, a third valve, a fourth valve, a fifth valve, a sixth valve, a seventh valve, an eighth valve, a cathode pump, and a cathode pump; wherein,

[0010] After the cathode electrolyte flows out of the cathode liquid tank, it passes through the third valve, cathode pump, fourth valve, cathode liquid path of the stack, and sixth valve in sequence before flowing back to the cathode liquid tank, forming a cathode circulation liquid path;

[0011] After the negative electrode electrolyte flows out of the negative electrode liquid tank, it passes through the first valve, the negative electrode pump, the second valve, the negative electrode liquid path of the stack, and the fifth valve in sequence before flowing back to the negative electrode liquid tank to form a negative electrode circulation liquid path;

[0012] The seventh valve and the eighth valve are both bridged between the positive electrode circulating liquid circuit and the negative electrode circulating liquid circuit; one end of the seventh valve is connected to the pipeline between the negative electrode pump and the second valve, and the other end is connected to the pipeline between the positive electrode pump and the fourth valve; one end of the eighth valve is connected to the pipeline between the sixth valve and the positive electrode liquid circuit outlet of the battery stack, and the other end is connected to the pipeline between the fifth valve and the negative electrode liquid circuit outlet of the battery stack;

[0013] When charging and discharging the battery stack, the first valve, the second valve, the third valve, the fourth valve, the fifth valve, the sixth valve, the positive electrode pump, and the negative electrode pump are opened, and the seventh valve and the eighth valve are closed;

[0014] The first cleaning method for cleaning the battery stack includes:

[0015] Turn off the positive and negative pumps;

[0016] Without charging the battery stack, open the second valve, the third valve, the fourth valve, the sixth valve, the seventh valve, the eighth valve, the positive electrode pump and the negative electrode pump, and close the first valve and the fifth valve at the same time to clean the entire battery stack with the positive electrode electrolyte.

[0017] Optionally, the system further comprises: a first pre-filter and a second pre-filter;

[0018] The first pre-filter is located at the inlet of the cathode liquid path of the fuel cell stack, and the second pre-filter is located at the inlet of the cathode liquid path of the fuel cell stack.

[0019] Optionally, the system further comprises: a first post-filter and a second post-filter;

[0020] The first post-filter is located at the cathode liquid outlet of the stack, and the second post-filter is located at the cathode liquid outlet of the stack;

[0021] The second cleaning method for cleaning the battery stack includes:

[0022] A trivalent iron solution is injected into the stack from the cathode liquid path inlet and the cathode liquid path inlet of the stack, so as to collect nickel chloride and copper chloride at the cathode liquid path outlet and the cathode liquid path outlet of the stack by using the first post-filter and the second post-filter.

[0023] Optionally, the system further comprises: a first storage tank, a second storage tank, a ninth valve, a tenth valve, an eleventh valve, and a twelfth valve; wherein,

[0024] A first mixed solution of trivalent iron and hydrochloric acid is injected into the first storage tank, and a second mixed solution of water and hydrochloric acid is injected into the second storage tank;

[0025] The ninth valve, the first storage tank, and the tenth valve are sequentially connected through pipelines to form a first branch; the eleventh valve, the second storage tank, and the twelfth valve are sequentially connected through pipelines to form a second branch; wherein one end of the first branch and the second branch are both connected to the pipeline between the fifth valve and the negative electrode liquid outlet of the fuel cell stack, and the other end of the first branch and the second branch are both connected to the pipeline between the first valve and the negative electrode pump;

[0026] The third cleaning method for cleaning the battery stack includes:

[0027] Turn off the positive electrode pump and the negative electrode pump, and close the first valve, the fifth valve, and the sixth valve; at the same time, the second valve, the fourth valve, the seventh valve, and the eighth valve are all in the open state; the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve are all in the closed state;

[0028] Open the ninth valve and the tenth valve and start the anode pump to circulate the first mixed solution along the first liquid path and the second liquid path, respectively; in the first liquid path, after the first mixed solution flows out of the first storage tank, it passes through the tenth valve, the anode pump, the second valve, the anode liquid path of the fuel cell stack, and the ninth valve in sequence before flowing back to the first storage tank; in the second liquid path, after the first mixed solution flows out of the first storage tank, it passes through the tenth valve, the anode pump, the seventh valve, the fourth valve, the cathode liquid path of the fuel cell stack, the eighth valve, and the ninth valve in sequence before flowing back to the first storage tank;

[0029] Close the cathode pump, the ninth valve, and the tenth valve;

[0030] Open the eleventh valve and the twelfth valve and start the negative electrode pump to allow the second mixed solution to circulate along the third liquid path and the fourth liquid path respectively; in the third liquid path, after the second mixed solution flows out of the second storage tank, it passes through the twelfth valve, the negative electrode pump, the second valve, the negative electrode liquid path of the fuel cell stack and the eleventh valve in sequence before flowing back to the second storage tank; in the fourth liquid path, after the second mixed solution flows out of the second storage tank, it passes through the twelfth valve, the negative electrode pump, the seventh valve, the fourth valve, the positive electrode liquid path of the fuel cell stack, the eighth valve and the eleventh valve in sequence before flowing back to the second storage tank.

[0031] Optionally, the stack is cleaned multiple times during charging, and the timing of cleaning is determined according to the open circuit voltage (OCV) of the stack. During the initial cleaning, at least the open circuit voltage (OCV) of the stack is ensured to be above the potential difference of the iron-chromium redox reaction.

[0032] Optionally, the system further comprises: a hydrogen sensor;

[0033] The hydrogen sensor is used to monitor the amount of hydrogen released from the fuel cell stack. When the amount of hydrogen released from the fuel cell stack exceeds a warning value, the fuel cell stack is cleaned.

[0034] Optionally, the filtration pore sizes of the first pre-filter, the second pre-filter, the first post-filter and the second post-filter are all 0.1 μm to 1 μm.

[0035] Optionally, the system further comprises: a remote control terminal; any valve is an electric remote control valve;

[0036] The remote control terminal is used to control the opening and closing of the positive electrode pump, the negative electrode pump and the electric remote control valve.

[0037] Optionally, the volume of the first storage tank is sufficient to at least fill the first liquid path and the second liquid path with liquid;

[0038] The volume of the second storage tank is sufficient to fill at least the third liquid path and the fourth liquid path with liquid.

[0039] Optionally, in the first mixed solution, the concentration of trivalent iron is 0.2 mol / L to 3 mol / L, and the concentration of hydrochloric acid is 0.5 mol / L to 3 mol / L;

[0040] In the second mixed solution, the concentration of hydrochloric acid is 0.5 mol / L to 3 mol / L.

[0041] Optionally, the situation of not charging the battery stack includes: discharging the battery stack, or leaving the battery stack stationary with a charging device turned off.

[0042] In the iron-chromium flow battery stack system provided by the present invention, when the stack is charged and discharged, the first valve, the second valve, the third valve, the fourth valve, the fifth valve, the sixth valve, the positive electrode pump and the negative electrode pump are opened, and the seventh valve and the eighth valve are closed; after the positive electrode electrolyte flows out of the positive electrode liquid tank, it passes through the third valve, the positive electrode pump, the fourth valve, the positive electrode liquid path of the stack, and the sixth valve in sequence before flowing back to the positive electrode liquid tank to form a positive electrode circulating liquid path; after the negative electrode electrolyte flows out of the negative electrode liquid tank, it passes through the first valve, the negative electrode pump, the second valve, the negative electrode liquid path of the stack, and the fifth valve in sequence before flowing back to the negative electrode liquid tank to form a negative electrode circulating liquid path; based on the above structure, it can The stack is cleaned using the first cleaning method. During cleaning, the positive and negative electrode pumps are first shut down. Then, without charging the stack, the second, third, fourth, sixth, seventh, and eighth valves, as well as the positive and negative electrode pumps, are opened, while the first and fifth valves are closed. This allows the positive electrolyte to flow from the positive electrode tank, pass through the third valve and the positive electrode pump, and then split into two paths. One path passes through the fourth valve, the positive electrode path of the stack, and the sixth valve before returning to the positive electrode tank. The other path passes through the seventh valve, the second valve, the negative electrode path of the stack, the eighth valve, and the sixth valve before returning to the positive electrode tank. Because the positive and negative electrolytes in the chromium flow battery in this system are both mixed solutions of divalent iron ions, trivalent chromium ions, and hydrochloric acid, some of the divalent iron ions are oxidized to trivalent iron ions during stack operation. Therefore, after the trivalent iron ions and hydrochloric acid in the positive electrode electrolyte flow into the battery stack, there are enough hydrogen ions. The trivalent iron ions can dissolve the metallic copper and nickel inside the battery stack into ionic compounds such as nickel chloride and copper chloride. In particular, after the positive electrode electrolyte enters the negative electrode, it can replenish hydrogen ions for the negative electrode with severe hydrogen evolution, thereby using the positive electrode electrolyte to clean the entire battery stack.

[0043] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic structural diagram of an iron-chromium flow battery stack system provided by an embodiment of the present invention;

[0045] Figure 2 is based on Figure 1 The schematic diagram of the positive electrode circulating fluid path and the negative electrode circulating fluid path when the system is charging and discharging the battery stack;

[0046] Figure 3 is based on Figure 1 A schematic diagram of the circulation of the positive electrode electrolyte when the system shown cleans the battery stack according to the first cleaning method;

[0047] Figure 4 This is a structural diagram of another iron-chromium flow battery stack system provided by an embodiment of the present invention;

[0048] Figure 5 This is a structural diagram of another iron-chromium flow battery stack system provided by an embodiment of the present invention;

[0049] Figure 6 is based on Figure 5 A schematic diagram of a circulating liquid path of the first mixed solution when the system is cleaning the battery stack according to the third cleaning method;

[0050] Figure 7 is based on Figure 5 A schematic diagram of another circulating liquid path of the first mixed solution when the system is cleaning the stack according to the third cleaning method;

[0051] Figure 8 is based on Figure 5 A schematic diagram of a circulating liquid path of the second mixed solution when the system is cleaning the battery stack according to the third cleaning method;

[0052] Figure 9 is based on Figure 5 A schematic diagram of another circulating liquid path of the second mixed solution when the system is cleaning the fuel cell stack according to the third cleaning method;

[0053] Figure 10 This is a structural schematic diagram of another iron-chromium liquid flow battery stack system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0055] To improve the performance and service life of an iron-chromium flow battery stack, an embodiment of the present invention provides an iron-chromium flow battery stack system. The positive and negative electrolytes of the iron-chromium flow battery in this system are both mixed solutions of divalent iron ions, trivalent chromium ions, and hydrochloric acid, wherein the content of hydrochloric acid is not high, such as less than 0.1 mol / L. It is understood that after the stack is in operation, some of the divalent iron ions in the mixed solution are oxidized to trivalent iron ions.

[0056] It should be noted that the components of the positive electrode electrolyte in the existing iron-chromium flow battery are mainly iron ions, and the components of the negative electrode electrolyte are mainly chromium ions, which are different from the electrolytes in the embodiments of the present invention. The main reason why the electrolytes in the existing iron-chromium flow battery and the embodiments of the present invention are different is that: the existing iron-chromium flow battery usually uses an ion exchange membrane, which has small pores and cannot be penetrated by iron and chromium ions; the iron-chromium flow battery in the embodiment of the present invention uses a porous membrane, which allows iron and chromium ions to penetrate each other. Although the energy density is less than half of that of the stack using an ion conductive membrane, the cost can be reduced by a hundred times compared to the traditional ion exchange membrane. The iron-chromium flow battery stack system provided in the embodiment of the present invention is constructed based on this iron-chromium flow battery using a porous membrane.

[0057] like Figure 1 As shown, the iron-chromium liquid flow battery stack system provided by the embodiment of the present invention includes: a stack, a cathode liquid tank, a cathode liquid tank, a first valve 1, a second valve 2, a third valve 3, a fourth valve 4, a fifth valve 5, a sixth valve 6, a seventh valve 7, an eighth valve 8, a cathode pump 14 and a cathode pump 13, and also includes pipelines between them. Figure 1 In the subsequent figures, the positive electrode liquid tanks are marked with a positive sign "+" and the negative electrode liquid tanks are marked with a negative sign "-".

[0058] Among them, such as Figure 2 As shown by the dotted lines in the figure, when the stack is charging or discharging, the first valve 1, second valve 2, third valve 3, fourth valve 4, fifth valve 5, sixth valve 6, positive electrode pump 14, and negative electrode pump 13 are open, and the seventh valve 7 and eighth valve 8 are closed. After the positive electrode electrolyte flows out of the positive electrode liquid tank, it passes through the third valve 3, positive electrode pump 14, fourth valve 4, the positive electrode liquid path of the stack, and the sixth valve 6 in sequence before returning to the positive electrode liquid tank, forming a positive electrode circulation path. After the negative electrode electrolyte flows out of the negative electrode liquid tank, it passes through the first valve 1, negative electrode pump 13, second valve 2, the negative electrode liquid path of the stack, and the fifth valve 5 in sequence before returning to the negative electrode liquid tank, forming a negative electrode circulation path.

[0059] The seventh valve 7 and the eighth valve 8 are both bridged between the positive electrode circulating liquid circuit and the negative electrode circulating liquid circuit; wherein, one end of the seventh valve 7 is connected to the pipeline between the negative electrode pump 13 and the second valve 2, and the other end is connected to the pipeline between the positive electrode pump 14 and the fourth valve 4; one end of the eighth valve 8 is connected to the pipeline between the sixth valve 6 and the positive electrode liquid circuit outlet of the fuel cell stack, and the other end is connected to the pipeline between the fifth valve 5 and the negative electrode liquid circuit outlet of the fuel cell stack.

[0060] based on Figure 1 The structure of the system shown in FIG. 1 can be used to clean the battery stack during normal charging and discharging of the battery stack using a first cleaning method, including:

[0061] (1) Turn off the positive electrode pump 14 and the negative electrode pump 13;

[0062] (2) Without charging the battery stack, open the second valve 2, the third valve 3, the fourth valve 4, the sixth valve 6, the seventh valve 7, the eighth valve 8, the positive electrode pump 14 and the negative electrode pump 13, and close the first valve 1 and the fifth valve 5 at the same time to clean the entire battery stack with the positive electrode electrolyte.

[0063] Situations where the stack is not charged include discharging the stack, for example, at maximum current, or leaving the stack idle with the charging equipment turned off. The actual charging equipment includes a power supply, a power converter, and a power conversion system (PCS). Simply turning off the power converter and PCS is sufficient.

[0064] like Figure 3 As shown by the dotted line in , when the first cleaning method is used to clean the battery stack, the positive electrode electrolyte flows out of the positive electrode liquid tank, passes through the third valve 3 and the positive electrode pump 14, and is divided into two liquid paths. One liquid path passes through the fourth valve 4, the positive electrode liquid path of the battery stack, and the sixth valve 6 before flowing back to the positive electrode tank. The other liquid path passes through the seventh valve 7, the second valve 2, the negative electrode liquid path of the battery stack, the eighth valve 8, and the sixth valve 6 in sequence before also flowing back to the positive electrode tank.

[0065] Because both the positive and negative electrolytes are mixed solutions of divalent iron ions, trivalent chromium ions, and hydrochloric acid, some of the divalent iron ions are oxidized to trivalent iron ions. Therefore, after the trivalent iron ions and hydrochloric acid in the positive electrolyte flow into the stack, there are sufficient hydrogen ions. The trivalent iron ions can then dissolve the metallic copper and nickel inside the stack into ionic compounds such as nickel chloride and copper chloride. In particular, after the positive electrolyte enters the negative electrode, it can replenish hydrogen ions for the negative electrode, which is severely affected by hydrogen evolution, thereby using the positive electrolyte to clean the entire stack.

[0066] It should be noted that the above-mentioned first cleaning method is not applicable to existing common battery stacks with different compositions of positive electrode electrolyte and negative electrode electrolyte, because the positive electrode electrolyte and negative electrode electrolyte will be converted into each other during the cleaning process, resulting in the scrapping of such battery stacks.

[0067] In addition, in the prior art, the hydrogen evolution reaction on the negative electrode side of the iron-chromium flow battery is severe, and the concentrations of copper and nickel, the hydrogen evolution substances, reach 5mg / L~20mg / L. Catalysts are often required, which makes it difficult to improve the overall efficiency and power density of the stack to a reasonable level. As a key component of the iron-chromium flow battery, the electrolyte is the core material for storing energy in the flow battery. The reaction characteristics of the electrode and electrolyte interface directly affect and determine the performance of the battery. Therefore, the electrolyte largely determines the efficiency and stability of the battery. In the embodiment of the present invention, after the positive electrode electrolyte enters the negative electrode, it can replenish hydrogen ions for the negative electrode with severe hydrogen evolution, improve the reaction characteristics of the electrode and electrolyte interface, and by dissolving the hydrogen evolution substances, reduce the amount of hydrogen evolution during the battery charge and discharge process, increase the hydrogen ion content of the electrolyte for repeated use, reduce battery attenuation, maintain battery capacity, and increase battery service life, thereby improving the overall efficiency and power density of the stack. Moreover, as the stack runs for a long time, the positive and negative electrolytes of the stack are balanced, and the stack life is longer.

[0068] The reaction formula in which trivalent iron ions dissolve metallic nickel into ionic nickel chloride is:

[0069] ;

[0070] The reaction formula for the dissolution of metallic copper by trivalent iron ions into ionic copper chloride is:

[0071] .

[0072] In practical applications, according to Figure 3 After configuring the valves and pumps as shown, the cleaning process can be completed by continuously running the cathode pump 13 for a period of time. For example, assuming the frequency of the cathode pump 13 is 20Hz to 40Hz, the cleaning process can be completed by continuously running it for about 10 minutes. At this point, the stack can be confirmed to be in a healthy state by sending the electrolyte for testing or checking that the hydrogen evolution rate of the stack is less than 5L / min.

[0073] After the stack is cleaned using the first cleaning method, the system is restored to Figure 2 The battery stack can continue to be charged and discharged after the status shown is reached.

[0074] In one embodiment, see Figure 4 As shown, the iron-chromium liquid flow battery stack system provided by the embodiment of the present invention may further include: a first pre-filter 18 and a second pre-filter 16 .

[0075] The first pre-filter 18 is located at the inlet of the cathode liquid path of the fuel cell stack, and the second pre-filter 16 is located at the inlet of the cathode liquid path of the fuel cell stack.

[0076] It is understandable that during the production process of iron-chromium flow batteries, large and harmful impurities such as fossils, organic matter, and metals are inevitably mixed into the electrolyte. These impurities can enter the battery stack along with the electrolyte, causing blockages within the stack, affecting the fluid flow, seriously affecting the operational stability of the stack, and reducing the service life of the stack. Therefore, placing pre-filters at the positive and negative electrode fluid inlets of the stack can effectively prevent impurities from entering the stack, causing blockages in the fluid flow within the stack and affecting the fluid flow of the entire system.

[0077] In one embodiment, see Figure 4 As shown, the iron-chromium liquid flow battery stack system provided in the embodiment of the present invention may further include: a first post-filter 17 and a second post-filter 15 .

[0078] The first post-filter 17 is located at the outlet of the cathode liquid path of the fuel cell stack, and the second post-filter 15 is located at the outlet of the cathode liquid path of the fuel cell stack.

[0079] based on Figure 4 The system shown can also use a second cleaning method to clean the fuel cell stack, including: injecting trivalent iron solution into the fuel cell stack from the positive electrode liquid path inlet and the negative electrode liquid path inlet of the fuel cell stack, and using the first post-filter 17 and the second post-filter 15 to collect nickel chloride and copper chloride at the positive electrode liquid path outlet and the negative electrode liquid path outlet of the fuel cell stack.

[0080] Those skilled in the art are aware that in order to maintain the chemical stability of the ferric solution, the actual ferric solution contains a small amount of hydrochloric acid. Therefore, after the ferric solution is injected into the battery stack from the positive electrode liquid path inlet and the negative electrode liquid path inlet of the battery stack, the chemical reaction produced inside the battery stack is the same as the first cleaning method, that is, the ferric ions dissolve the metallic copper and nickel inside the battery stack into compounds such as nickel chloride and copper chloride in ionic form.

[0081] In practical applications, the second cleaning method can be used to clean the battery stack after the battery stack is charged.

[0082] Preferably, the filtration pore size of the first pre-filter 18, the second pre-filter 16, the first post-filter 17, and the second post-filter 15 can all be 0.1 μm to 1 μm, so as to more effectively filter out impurities such as fossils, organic matter, and metals that may be contained in the electrolyte.

[0083] In one embodiment, Figure 1 Based on the system shown, Figure 5 As shown, the iron-chromium liquid flow battery stack system provided in the embodiment of the present invention may further include: a first storage tank, a second storage tank, a ninth valve 9 , a tenth valve 10 , an eleventh valve 11 and a twelfth valve 12 .

[0084] Among them, a first mixed solution of trivalent iron and hydrochloric acid is injected into the first storage tank, and a second mixed solution of water and hydrochloric acid is injected into the second storage tank; the ninth valve 9, the first storage tank and the tenth valve 10 are connected in sequence through pipelines to form a first branch; the eleventh valve 11, the second storage tank and the twelfth valve 12 are connected in sequence through pipelines to form a second branch; wherein, one end of the first branch and the second branch are both connected to the pipeline between the fifth valve 5 and the negative electrode liquid outlet of the fuel cell stack, and the other end of the first branch and the second branch are both connected to the pipeline between the first valve 1 and the negative electrode pump 13.

[0085] based on Figure 5 The structure of the system shown can also use a third method to clean the battery stack, including:

[0086] (1) Turn off the positive electrode pump 14 and the negative electrode pump 13, and close the first valve 1, the fifth valve 5, and the sixth valve 6; at the same time, the second valve 2, the fourth valve 4, the seventh valve 7, and the eighth valve 8 are all in the open state; the ninth valve 9, the tenth valve 10, the eleventh valve 11, and the twelfth valve 12 are all in the closed state;

[0087] (2) opening the ninth valve 9 and the tenth valve 10 and starting the cathode pump 13 to allow the first mixed solution to circulate along the first liquid path and the second liquid path respectively;

[0088] See also Figure 6 As shown, in the first liquid path, after the first mixed solution flows out of the first storage tank, it passes through the tenth valve 10, the cathode pump 13, the second valve 2, the cathode liquid path of the stack, and the ninth valve 9 and then flows back to the first storage tank; see Figure 7 As shown, in this second liquid path, after the first mixed solution flows out of the first storage tank, it passes through the tenth valve 10, the cathode pump 13, the seventh valve 7, the fourth valve 4, the cathode liquid path of the fuel cell stack, the eighth valve 8, and the ninth valve 9 before returning to the first storage tank. Thus, the first mixed solution, i.e., a mixture of trivalent iron and hydrochloric acid, dissolves the metallic copper and nickel inside the fuel cell stack into ionic compounds such as nickel chloride and cupric chloride.

[0089] In actual application, the first mixed solution enters the fuel cell stack to clean the stack, and the cleaned liquid flows back to the first storage tank. This cycle of cleaning is repeated 1 to 5 times to dissolve the metallic copper and nickel in the fuel cell stack into ionic compounds such as nickel chloride and copper chloride.

[0090] (3) Close the cathode pump 13, the ninth valve 9, and the tenth valve 10;

[0091] (4) Open the eleventh valve 11 and the twelfth valve 12 and start the cathode pump 13 to allow the second mixed solution to circulate along the third liquid path and the fourth liquid path respectively.

[0092] See also Figure 8 As shown, in the third liquid path, after the second mixed solution flows out of the second storage tank, it passes through the twelfth valve 12, the cathode pump 13, the second valve 2, the cathode liquid path of the stack, and the eleventh valve 11 and then flows back to the second storage tank; see Figure 9 As shown, in this fourth liquid path, after the second mixed solution flows out of the second storage tank, it passes through the twelfth valve 12, the cathode pump 13, the seventh valve 7, the fourth valve 4, the cathode liquid path of the fuel cell stack, the eighth valve 8, and the eleventh valve 11 before returning to the second storage tank. Thus, the second mixed solution, i.e., a mixed solution of water and hydrochloric acid, is used to clean out excess trivalent iron ions introduced into the fuel cell stack by the first mixed solution.

[0093] In actual application, the second mixed solution cleans the stack after entering the stack, and the cleaned liquid flows back into the first storage tank. This cycle of cleaning is repeated 1 to 5 times to wash away the trivalent iron introduced by the first mixed solution.

[0094] After the stack is cleaned using the third cleaning method, the cathode pump 13, the eleventh valve 11 and the twelfth valve 12 are closed to interrupt the cleaning; then the first valve 1, the fifth valve 5, the sixth valve 6, the cathode pump 14 and the cathode pump 13 are opened, and the cleaning is continued as follows. Figure 2 The positive electrode circulating fluid path and the positive electrode circulating fluid path shown charge and discharge the battery stack.

[0095] It should be noted that the above-mentioned third cleaning method is also not applicable to existing common fuel cells with different compositions of positive electrode electrolyte and negative electrode electrolyte, because opening the seventh valve 7 and the eighth valve 8 during the cleaning process will cause some of the positive electrode electrolyte and negative electrode electrolyte remaining in the pipeline to mix with each other, affecting the performance of such fuel cells.

[0096] In one embodiment, Figure 4 and Figure 5 The system shown can be combined into Figure 10 When the stack is cleaned using the first cleaning method or the third cleaning method, dissolved compounds such as nickel chloride and copper chloride can also be filtered out by the first post-filter 17 and the second post-filter 15 .

[0097] In actual applications, during the charging process of the battery stack, the first cleaning method or the third cleaning method can be used to clean the battery stack multiple times. The timing of cleaning can be determined according to the open circuit voltage (OCV) of the battery stack. During the first cleaning, at least ensure that the OCV of the battery stack is above the potential difference of the iron-chromium redox reaction.

[0098] For example, the first cleaning method or the third cleaning method may be used to clean the battery stack when the OCV reaches 0.8V, 0.9V, 1V, 1.1V, or 1.15V.

[0099] In practical applications, it is preferred to start cleaning the battery stack using the first or third cleaning method when the battery stack's remaining battery capacity (SOC) is greater than 30%. This is because when the SOC is below 30%, the nickel and copper in the battery stack are still in an ionic state, and there is little metallic nickel and copper deposited inside the stack.

[0100] In one embodiment, the iron-chromium liquid flow battery stack system provided by the embodiment of the present invention may further include: a hydrogen sensor; the hydrogen sensor is used to monitor the amount of hydrogen evolved in the stack; wherein, when the amount of hydrogen evolved in the stack exceeds the warning value, the stack is cleaned.

[0101] In practice, when the amount of hydrogen released from the stack exceeds a warning threshold, the hydrogen sensor triggers an alarm, notifying the operator to clean the stack. The warning threshold can be set based on the stack power. For example, when the stack power is around 100kW, the warning value can be set to 5L / min, or no more. This effectively mitigates the risk of explosion caused by excessive hydrogen release from the iron-chromium flow battery.

[0102] In one implementation, the iron-chromium liquid flow battery stack system provided in an embodiment of the present invention may further include: a remote control terminal; any valve is an electric remote-controlled valve; thereby, the remote control terminal can control the opening and closing of the positive electrode pump 14, the negative electrode pump 13 and these electric remote-controlled valves.

[0103] In addition, the hydrogen sensor can be connected to the remote control end for communication, so that when the hydrogen sensor detects that the amount of hydrogen evolution in the fuel cell stack exceeds the warning value, the remote control end can be notified, so that the remote control end can automatically clean the fuel cell stack by controlling the positive electrode pump 14, the negative electrode pump 13 and the electric remote control valve.

[0104] It is worth mentioning that in the prior art, due to the large amount of hydrogen released from the negative electrode of the stack, in order to prevent the explosion caused by large-scale concentrated emission of hydrogen, it is necessary to install a hydrogen collection / processing device on the stack. In the embodiment of the present invention, only the hydrogen sensor is needed to monitor the hydrogen. Once the amount of hydrogen released exceeds the warning value, the stack is cleaned, thereby intervening / slowing down the further occurrence of hydrogen release. During the cleaning process of the stack, the small amount of hydrogen that has been released can be dispersed and will not be discharged in a large amount and concentrated, and there is no risk of explosion. Therefore, the iron-chromium liquid flow battery stack system provided by the present invention does not need to be equipped with a hydrogen collection / processing device on the stack, thereby saving system construction costs.

[0105] It should be noted that the terms "first," "second," and the like are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present disclosure described herein can be implemented in an order other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure.

[0106] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0107] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the drawings and the disclosed content. In the description of the present invention, the word "comprising" does not exclude other components or steps, "one" or "a" does not exclude multiple situations, and "multiple" means two or more, unless otherwise clearly and specifically limited. In addition, certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0108] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0109] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0110] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0111] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. An iron-chromium liquid flow battery stack system, characterized in that: The positive and negative electrolytes of the iron-chromium flow battery in the system are both mixed solutions of divalent iron ions, trivalent chromium ions, and hydrochloric acid. After the battery stack is in operation, some of the divalent iron ions are oxidized to trivalent iron ions. The system includes: a battery stack, a cathode liquid tank, a cathode liquid tank, a first valve, a second valve, a third valve, a fourth valve, a fifth valve, a sixth valve, a seventh valve, an eighth valve, a cathode pump, and a cathode pump; wherein, After the cathode electrolyte flows out of the cathode liquid tank, it passes through the third valve, cathode pump, fourth valve, cathode liquid path of the stack, and sixth valve in sequence before flowing back to the cathode liquid tank, forming a cathode circulation liquid path; After the negative electrode electrolyte flows out of the negative electrode liquid tank, it passes through the first valve, the negative electrode pump, the second valve, the negative electrode liquid path of the stack, and the fifth valve in sequence before flowing back to the negative electrode liquid tank to form a negative electrode circulation liquid path; The seventh valve and the eighth valve are both bridged between the positive electrode circulating liquid circuit and the negative electrode circulating liquid circuit; one end of the seventh valve is connected to the pipeline between the negative electrode pump and the second valve, and the other end is connected to the pipeline between the positive electrode pump and the fourth valve; one end of the eighth valve is connected to the pipeline between the sixth valve and the positive electrode liquid circuit outlet of the battery stack, and the other end is connected to the pipeline between the fifth valve and the negative electrode liquid circuit outlet of the battery stack; When charging and discharging the battery stack, the first valve, the second valve, the third valve, the fourth valve, the fifth valve, the sixth valve, the positive electrode pump, and the negative electrode pump are opened, and the seventh valve and the eighth valve are closed; The first cleaning method for cleaning the battery stack includes: Turn off the positive and negative pumps; Without charging the battery stack, open the second valve, the third valve, the fourth valve, the sixth valve, the seventh valve, the eighth valve, the positive electrode pump and the negative electrode pump, and close the first valve and the fifth valve at the same time to clean the entire battery stack with the positive electrode electrolyte.

2. The iron-chromium flow battery stack system according to claim 1, characterized in that: Also includes: a first pre-filter and a second pre-filter; The first pre-filter is located at the inlet of the cathode liquid path of the fuel cell stack, and the second pre-filter is located at the inlet of the cathode liquid path of the fuel cell stack.

3. The iron-chromium flow battery stack system according to claim 2, characterized in that: Also includes: a first post-filter and a second post-filter; The first post-filter is located at the cathode liquid outlet of the stack, and the second post-filter is located at the cathode liquid outlet of the stack; The second cleaning method for cleaning the battery stack includes: A trivalent iron solution is injected into the stack from the cathode liquid path inlet and the cathode liquid path inlet of the stack, so as to collect nickel chloride and copper chloride at the cathode liquid path outlet and the cathode liquid path outlet of the stack by using the first post-filter and the second post-filter.

4. The iron-chromium flow battery stack system according to claim 1, characterized in that: Also includes: The first storage tank, the second storage tank, the ninth valve, the tenth valve, the eleventh valve and the twelfth valve; wherein, A first mixed solution of trivalent iron and hydrochloric acid is injected into the first storage tank, and a second mixed solution of water and hydrochloric acid is injected into the second storage tank; The ninth valve, the first storage tank, and the tenth valve are sequentially connected through pipelines to form a first branch; the eleventh valve, the second storage tank, and the twelfth valve are sequentially connected through pipelines to form a second branch; wherein one end of the first branch and the second branch are both connected to the pipeline between the fifth valve and the negative electrode liquid outlet of the fuel cell stack, and the other end of the first branch and the second branch are both connected to the pipeline between the first valve and the negative electrode pump; The third cleaning method for cleaning the battery stack includes: Turn off the positive electrode pump and the negative electrode pump, and close the first valve, the fifth valve, and the sixth valve; at the same time, the second valve, the fourth valve, the seventh valve, and the eighth valve are all in the open state; the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve are all in the closed state; Open the ninth valve and the tenth valve and start the anode pump to circulate the first mixed solution along the first liquid path and the second liquid path, respectively; in the first liquid path, after the first mixed solution flows out of the first storage tank, it passes through the tenth valve, the anode pump, the second valve, the anode liquid path of the fuel cell stack, and the ninth valve in sequence before flowing back to the first storage tank; in the second liquid path, after the first mixed solution flows out of the first storage tank, it passes through the tenth valve, the anode pump, the seventh valve, the fourth valve, the cathode liquid path of the fuel cell stack, the eighth valve, and the ninth valve in sequence before flowing back to the first storage tank; Close the cathode pump, the ninth valve, and the tenth valve; Open the eleventh valve and the twelfth valve and start the negative electrode pump to allow the second mixed solution to circulate along the third liquid path and the fourth liquid path respectively; in the third liquid path, after the second mixed solution flows out of the second storage tank, it passes through the twelfth valve, the negative electrode pump, the second valve, the negative electrode liquid path of the fuel cell stack and the eleventh valve in sequence before flowing back to the second storage tank; in the fourth liquid path, after the second mixed solution flows out of the second storage tank, it passes through the twelfth valve, the negative electrode pump, the seventh valve, the fourth valve, the positive electrode liquid path of the fuel cell stack, the eighth valve and the eleventh valve in sequence before flowing back to the second storage tank.

5. The iron-chromium flow battery stack system according to claim 1 or 4, characterized in that: Also includes: Hydrogen sensor; The hydrogen sensor is used to monitor the amount of hydrogen released from the fuel cell stack. When the amount of hydrogen released from the fuel cell stack exceeds a warning value, the fuel cell stack is cleaned.

6. The iron-chromium flow battery stack system according to claim 3, characterized in that: The filtration pore sizes of the first pre-filter, the second pre-filter, the first post-filter and the second post-filter are all 0.1 μm to 1 μm.

7. The iron-chromium flow battery stack system according to claim 1 or 4, characterized in that: Also includes: remote control terminal; any valve is an electric remote control valve; The remote control terminal is used to control the opening and closing of the positive electrode pump, the negative electrode pump and the electric remote control valve.

8. The iron-chromium flow battery stack system according to claim 4, characterized in that: The volume of the first storage tank is such that at least the first liquid path and the second liquid path are filled with liquid; The volume of the second storage tank is sufficient to fill at least the third liquid path and the fourth liquid path with liquid.

9. The iron-chromium flow battery stack system according to claim 4, characterized in that: In the first mixed solution, the concentration of trivalent iron is 0.2-3 mol / L, and the concentration of hydrochloric acid is 0.5-3 mol / L; In the second mixed solution, the concentration of hydrochloric acid is 0.5-3 mol / L.

10. The iron-chromium flow battery stack system according to claim 1, characterized in that: The situation where the battery stack is not charged includes: discharging the battery stack, or leaving the battery stack stationary with the charging device turned off.

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