Zinc-bromine double-flow battery performance recovery method

Abstract

The invention relates to a zinc-bromine double-flow battery performance recovery method, and belongs to the field of flow batteries. After the zinc-bromine double-flow battery is continuously charged and discharged for a period of time, under the condition that the performance of the battery is greatly reduced, an external circuit of the battery is reversely connected (namely positive and negative electrodes for charging and discharging of the battery are exchanged). The original positive electrode of the battery is subjected to a negative electrode electrochemical reaction, and the negative electrode is subjected to a positive electrode electrochemical reaction. And after several cycles of reverse connection charging and discharging, normal charging and discharging are recovered (i.e., after the reverse connection charging and discharging recover the battery performance, the positive electrode and the negative electrode are exchanged, and the original charging and discharging mode of the battery is recovered. And after the battery is charged and discharged, the performance can be recovered. The method is simple to operate, low in cost and obvious in effect, the cycle stability of the battery is remarkably improved, and the service life of the zinc-bromine double-flow battery is effectively prolonged.

Description

Technical Field

[0001] The invention relates to a method for recovering the performance of a zinc-bromine double-flow battery. Background Art

[0002] Zinc-bromine dual-liquid flow energy storage battery is a new type of low-cost, high-efficiency, environmentally friendly liquid flow energy storage battery with the advantages of high energy density and current efficiency, simple and easy operation, long service life and low cost. It is mainly used in power grid peak regulation, wind power, solar power and other renewable energy power generation, electric vehicles and other fields.

[0003] For zinc-bromine flow batteries, the zinc dendrites generated by the negative electrode during charging are difficult to control. During the long-term charge and discharge cycle of the battery, a large amount of zinc will accumulate in the negative electrode. The accumulated zinc will grow into the micropores of the porous diaphragm, blocking the diaphragm and affecting the battery performance. This will eventually lead to a decrease in the performance of the battery stack and make it unable to operate. The above problems are the main reasons for the poor cycle stability of zinc-bromine batteries. Summary of the invention

[0004] The present invention generates bromine element inside the original negative electrode of the battery by periodically reversely connecting the positive and negative electrodes of the zinc-bromine liquid flow battery for charging and discharging, and uses the generated bromine element to oxidize the zinc element accumulated on the original negative electrode and in the micropores near the negative electrode side of the diaphragm, thereby restoring the battery performance.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] 1) During the battery charging process, the positive and negative poles of the battery external circuit are periodically reversed (i.e., the original positive pole becomes the negative pole, and the original negative pole becomes the positive pole). The periodic connection means that after the battery is continuously charged and discharged for a period of time, the battery performance decays, and the battery coulomb efficiency decays by 5-10% (preferably 8% to 9%), the positive and negative poles of the battery are reversed, that is, the positive electrode channel line of the external circuit is connected to the negative electrode of the battery, and the negative electrode channel line of the external circuit is connected to the positive electrode of the battery.

[0007] 2) After the reverse connection, the battery is charged and discharged. During the charging process, the original positive electrode of the battery undergoes an electrochemical reaction of the negative electrode, that is, the zinc ions gain electrons and become zinc elements; the original negative electrode of the battery undergoes an electrochemical reaction of the positive electrode, that is, the bromide ions lose electrons and become bromine molecules. The battery is charged and discharged using the above method, and the charging capacity is 20% to 40% (preferably 30% to 35%) of the maximum capacity of the battery, and the number of charge and discharge times is 3 to 5 times (preferably 4 to 5 times).

[0008] 3) After completing 2), mix the positive and negative electrolytes to the initial state, and reverse the positive and negative poles of the battery external circuit to the initial state, that is, the positive and negative poles when the battery is operating normally, and then charge and discharge normally.

[0009] Beneficial effects of the present invention:

[0010] The present invention is directed to a zinc-bromine dual-flow battery. During a normal charge and discharge cycle, a large amount of zinc will accumulate at the negative electrode, and the accumulated zinc will grow into the micropores of the porous diaphragm, blocking the diaphragm and affecting the battery performance.

[0011] During the normal operation of the battery, the present invention periodically reverses the positive and negative electrodes of the battery to allow the positive and negative electrodes in the battery to produce opposite electrochemical reactions. This method is used to generate a large amount of bromine in the negative electrode of the battery, and the generated bromine is used to oxidize the zinc accumulated on the original negative electrode and in the micropores near the negative electrode side of the diaphragm, thereby restoring the battery performance. This improves the stability of the battery stack performance and ultimately extends the life of the battery stack.

[0012] The present invention is to reverse the external circuit of the battery (i.e., swap the positive and negative poles of the battery for charging and discharging) when the battery performance has declined significantly after the zinc-bromine dual-flow battery has been continuously charged and discharged for a period of time. The original positive pole of the battery is allowed to undergo an electrochemical reaction of the negative pole, and the negative pole is allowed to undergo an electrochemical reaction of the positive pole. After several cycles of reverse charging and discharging, normal charging and discharging are resumed (i.e., after the reverse charging and discharging restores the battery performance, the positive and negative poles are swapped to restore the original charging and discharging mode of the battery). After the above charging and discharging, the performance of the battery can be restored. The method is simple to operate, low in cost, and effective in effect. It significantly improves the cycle stability of the battery and effectively increases the life of the zinc-bromine dual-flow battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a diagram of a long-life zinc-bromine dual-flow battery device. DETAILED DESCRIPTION

[0014] A zinc-bromine double-flow battery performance recovery method, the zinc-bromine double-flow battery comprises a battery stack consisting of a single battery or two or more batteries connected in series, a positive electrode electrolyte storage tank, and a negative electrode electrolyte storage tank, the positive electrode electrolyte in the positive electrode electrolyte storage tank circulates in the chamber where the positive electrode of the zinc-bromine double-flow battery is located, and the negative electrode electrolyte in the negative electrode electrolyte storage tank circulates in the chamber where the negative electrode of the zinc-bromine double-flow battery is located;

[0015] 1) After the battery is continuously charged and discharged for a period of time, the battery performance decays. When the battery coulomb efficiency decays by 5-10% (preferably 8% to 9%), the positive and negative electrodes of the battery are reversed, that is, the positive electrode channel line of the external circuit is connected to the negative electrode of the battery, and the negative electrode channel line of the external circuit is connected to the positive electrode of the battery.

[0016] 2) After the reverse connection, the battery is charged and discharged. During the charging process, the original positive electrode of the battery undergoes an electrochemical reaction of the negative electrode, that is, the zinc ions gain electrons and become zinc elements; the original negative electrode of the battery undergoes an electrochemical reaction of the positive electrode, that is, the bromide ions lose electrons and become bromine molecules. The battery is charged and discharged using the above method, and the charging capacity is 20% to 40% (preferably 30% to 35%) of the maximum capacity of the battery, and the number of charge and discharge times is 3 to 5 times (preferably 4 to 5 times).

[0017] 3) After completing 2), the positive and negative electrolytes are mixed and then separated to restore the positive and negative electrolytes to their initial state, and the positive and negative poles of the battery external circuit are reversed to the initial state, that is, the positive and negative poles of the battery during normal operation, and normal charging and discharging is sufficient. The positive and negative electrolytes of the zinc-bromine dual-flow battery are both neutral aqueous solutions containing zinc and bromide ions. The zinc and bromine raw materials are zinc bromide. The zinc ion concentration in the positive and negative electrolytes of the battery is the same, and the supporting electrolyte KCl concentration is the same. The zinc ion concentration in the electrolyte is: 2-4mol / L, and the KCl concentration is 2-5mol / L.

[0018] A single cell includes a positive electrode current collector, a positive electrode frame, a positive electrode, a separator, a negative electrode, a negative electrode frame, and a negative electrode current collector stacked in sequence; a positive terminal plate and a negative terminal plate are provided at the two ends of the battery stack or at the two ends of a single cell respectively; the positive electrode electrolyte is sealed in a closed cavity surrounded by the positive electrode frame, the positive electrode current collector, and the battery separator as the positive electrode cavity; the negative electrode electrolyte is sealed in a closed cavity surrounded by the negative electrode frame, the negative electrode current collector, and the battery separator as the negative electrode cavity. The electrolyte in the electrolyte storage tank of the zinc-bromine dual-flow battery flows in the positive and negative electrode cavities respectively through pumps.

[0019] A porous ion-conducting membrane made of PE is installed between the positive and negative carbon felts of a single cell to physically separate the positive and negative carbon felts. The thickness of the membrane is 800-1000um (preferably 900-1000um), and in the present invention, it is 950um.

[0020] Example 1

[0021] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 120mAh / cm 2The initial coulombic efficiency of the battery is 93%. When the battery runs for 53 cycles (after a period of charge and discharge, the same below), the coulombic efficiency of the battery stack decays to 85%. At the end of the 53rd discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 40 mAh / cm 2 . Charge and discharge in this way for 5 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the battery stack performance is restored to the initial value.

[0022] The battery performance is shown in Table 1.

[0023] Example 2

[0024] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 120mAh / cm 2 The initial coulombic efficiency of the battery is 94%. When the battery runs for 66 cycles, the coulombic efficiency of the battery stack decays to 85%. At the end of the 66th discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 2 . Charge and discharge in this way 4 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the battery stack performance is restored to about the initial value.

[0025] The battery performance is shown in Table 1.

[0026] Example 3

[0027] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 140mAh / cm 2 The initial coulombic efficiency of the battery is 94%. When the battery runs for 48 cycles, the coulombic efficiency of the battery stack decays to 85%. At the end of the 48th discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 2 . Charge and discharge in this way for 5 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the battery stack performance is restored to about the initial value.

[0028] The battery performance is shown in Table 1.

[0029] Example 4

[0030] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 140mAh / cm 2 The initial coulombic efficiency of the battery is 93%. When the battery runs for 51 cycles, the coulombic efficiency of the battery stack decays to 85%. At the end of the 51st discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 2 . Charge and discharge in this way for 5 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the battery stack performance is restored to the initial value.

[0031] The battery performance is shown in Table 1.

[0032] Example 5

[0033] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 200mAh / cm 2 The initial coulombic efficiency of the battery is 91%. When the battery runs for 41 cycles, the coulombic efficiency of the battery stack decays to 82%. At the end of the 41st discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of , and the charging capacity is 60mAh / cm 2 . Charge and discharge in this way for 5 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the battery stack performance is restored to about the initial value.

[0034] The battery performance is shown in Table 1.

[0035] Comparative Example 1

[0036] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 120mAh / cm 2 The initial coulombic efficiency of the battery is 94%. When the battery runs for 81 cycles, the coulombic efficiency of the battery stack decays to 80%. At the end of the 81st discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 2. Charge and discharge in this way for 5 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the performance of the battery stack is too low and cannot be restored to the initial state.

[0037] The battery performance is shown in Table 1.

[0038] Comparative Example 2

[0039] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 120mAh / cm 2 The initial coulombic efficiency of the battery is 94%. When the battery runs for 56 cycles, the coulombic efficiency of the battery stack decays to 85%. At the end of the 56th discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 2 . Charge and discharge in this way for 5 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the performance of the battery stack is too low and cannot be restored to the initial state.

[0040] The battery performance is shown in Table 1.

[0041] Comparative Example 3

[0042] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 140mAh / cm2 The initial coulombic efficiency of the battery is 92%. When the battery runs for 44 cycles, the coulombic efficiency of the battery stack decays to 83%. At the end of the 44th discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of , and the charging capacity is 70mAh / cm 2 . Charge and discharge in this way for 5 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the performance of the battery stack is too low and cannot be restored to the initial state.

[0043] The battery performance is shown in Table 1.

[0044] Comparative Example 4

[0045] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 140mAh / cm 2 The initial coulombic efficiency of the battery is 93%. When the battery runs for 49 cycles, the coulombic efficiency of the battery stack decays to 85%. At the end of the 49th discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 2 . Charge and discharge once in this way. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the performance of the battery stack is too low and cannot be restored to the initial state.

[0046] The battery performance is shown in Table 1.

[0047] Comparative Example 5

[0048] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 140mAh / cm 2 The initial coulombic efficiency of the battery is 93%. When the battery runs for 47 cycles, the coulombic efficiency of the battery stack decays to 84%. At the end of the 47th discharge of the battery, the positive and negative electrode channel wires of the battery are reversed, and the charge and discharge current density is 40mA / cm 2 The battery is reverse charged under the conditions of 2 . Charge and discharge in this way 10 times. After the above operations are completed, the battery external channel line is reversed, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. At this time, the battery stack is charged and discharged normally, and the performance of the battery stack is too low and cannot be restored to the initial state.

[0049] The battery performance is shown in Table 1.

[0050] Comparative Example 6

[0051] The battery electrolyte is 2mol / LZnBr 2 +3mol / LKCl+0.8M MEP (nitrogen bromide-ethylmethylpyrrolidine), the single cells in the stack are the positive electrode current collector (bipolar plate 1000cm 2 ), a positive electrode frame with carbon felt placed in the middle through hole, a separator, a negative electrode frame with carbon felt placed in the middle through hole, a negative current collector (bipolar plate 1000cm 2 ), and the cells are stacked one by one in this way. The number of cells in the battery stack is 20. The charge and discharge current density is 40 mA / cm 2 The maximum charge capacity is 120mAh / cm 2 The initial coulombic efficiency of the battery is 94%. When the battery runs for 62 cycles, the coulombic efficiency of the battery stack decays to 85%. At the end of the 62nd discharge of the battery, the positive and negative electrolytes are mixed and then separated to restore to the initial charge and discharge state. After that, the battery stack is charged and discharged normally, and the performance of the battery stack is too low to be restored to the initial state.

[0052] The battery performance is shown in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] It can be seen from the experimental results of comparative example 1 that when the battery performance decreases a lot (the battery coulomb efficiency decays by more than 10%), the method of reverse charging and discharging the battery to restore the performance has almost no effect. Because when the zinc in the negative electrode of the battery accumulates to a certain extent, the zinc dendrites have completely grown into the diaphragm, blocking all the micropores in the diaphragm. At this time, the bromine element generated by the reverse charging method at the negative electrode of the battery cannot completely oxidize the zinc in the diaphragm, because the zinc element in the middle part of the diaphragm micropores accumulates too much. At this time, the bromine molecules in the negative electrode are difficult to move to the center of the diaphragm micropores by molecular diffusion. The zinc element in this part is difficult to be oxidized, which causes the diaphragm micropores to be always blocked, causing the battery to fail to operate normally. Even if reverse charging is used, the battery performance cannot be restored.

[0057] It can be seen from the experimental results of Comparative Example 2 that when the reverse charging capacity is too low (the charging capacity is less than 20% of the maximum charging capacity of the battery), the method of reverse charging and discharging the battery to restore the performance has almost no effect. Because in the reverse charging process, too low a capacity will lead to insufficient generation of bromine molecules in the negative electrode, and too low a bromine molecule amount cannot completely oxidize the zinc element accumulated in the micropores on the negative electrode and in the diaphragm near the negative electrode, so that the diaphragm is still blocked by zinc element, resulting in the battery not being able to operate normally. Even if reverse charging is used, the battery performance still cannot be restored.

[0058] It can be seen from the experimental results of Comparative Example 3 that when the reverse charging capacity is too high (the charging capacity is higher than 40% of the maximum charging capacity of the battery), the reverse charging and discharging method cannot be used to restore the battery performance. Because the reverse charging capacity that is too high will cause the zinc element generated in the positive electrode to accumulate, although the zinc element on the electrode in the negative electrode and in the micropores of the diaphragm are oxidized and removed by bromine molecules, too much zinc element accumulates in the positive electrode, and a part of the zinc element grows into the micropores on the side of the diaphragm close to the positive electrode. When the battery resumes normal charging, because of the excessive accumulation of zinc in the positive electrode, the battery cannot operate normally after just being restored, and it needs to be activated for 3-5 cycles to operate normally, which increases the recovery step and wastes more time. Therefore, it is considered that it is not within the experimental conditions protected by this patent.

[0059] It can be seen from the experimental results of Comparative Example 4 that when the number of reverse charging is too small (less than 3 times), the reverse charging and discharging method cannot be used to restore the battery performance. When the number of reverse charging is too small, the bromine element generated at the negative electrode cannot completely oxidize the accumulated zinc, and the diaphragm is still blocked. Similar to Comparative Example 2, even if reverse charging is used, the battery performance cannot be restored.

[0060] It can be seen from the experimental results of Comparative Example 5 that when the number of reverse charging is too many (the number of reverse charging is greater than 5 times), the battery performance is restored by the reverse charging and discharging method. After the battery is just restored, the performance cannot return to the initial state. Too many reverse charging times will lead to excessive accumulation of zinc in the positive electrode. The reason is the same as that of Comparative Example 3, which increases the recovery step and wastes more time. Therefore, it is considered that it is not within the experimental conditions protected by this patent.

[0061] From the experimental results of Comparative Example 6, it can be seen that when the performance of the battery stack decreases (CE decreases by 9%), the battery stack performance cannot be restored to the initial state by only mixing the positive and negative electrolytes instead of using the reverse charging method. The reason is that the zinc element accumulated in the negative electrode cannot be completely removed, the reason is the same as that of Comparative Examples 2 and 4.

Claims

1. A zinc-bromine dual flow battery performance recovery method, wherein the zinc-bromine dual flow battery comprises a battery stack consisting of a single battery or two or more batteries connected in series, a positive electrode electrolyte storage tank, and a negative electrode electrolyte storage tank, wherein the positive electrode electrolyte in the positive electrode electrolyte storage tank circulates in the chamber where the positive electrode of the zinc-bromine dual flow battery is located, and the negative electrode electrolyte in the negative electrode electrolyte storage tank circulates in the chamber where the negative electrode of the zinc-bromine dual flow battery is located, characterized in that: 1) During the battery charging process, the positive and negative poles of the battery external circuit are periodically reversed (i.e., the original positive pole is used as the negative pole, and the original negative pole is used as the positive pole). The periodic connection means that when the battery performance decays after a period of continuous charging and discharging, and the battery coulomb efficiency decays by 5-10% (preferably 8% to 9%), the positive and negative poles of the battery are reversed, that is, the positive pole channel line of the external circuit is connected to the negative pole of the battery, and the negative pole channel line of the external circuit is connected to the positive pole of the battery; 2) After the reverse connection, the battery is charged and discharged. During the charging process, the original positive electrode of the battery undergoes an electrochemical reaction of the negative electrode, that is, the zinc ions gain electrons and become zinc elemental substances; the original negative electrode of the battery undergoes an electrochemical reaction of the positive electrode, that is, the bromide ions lose electrons and become bromine molecules; the battery is charged and discharged using the above method, the charging capacity is 20% to 40% (preferably 30% to 35%) of the maximum capacity of the battery, and the number of charge and discharge times is 3 to 5 times (preferably 4 to 5 times); 3) After completing the process of step 2), the positive and negative electrolytes are mixed and then separated to restore the positive and negative electrolytes to their initial states, and the positive and negative electrodes of the battery external circuit are reversed to their initial states, that is, the positive and negative electrodes of the battery during normal operation (that is, the positive electrode channel line of the external circuit is connected to the positive electrode of the battery, and the negative electrode channel line of the external circuit is connected to the negative electrode of the battery), and normal charging and discharging can be performed.

2. The recovery method according to claim 1, characterized in that: A porous ion-conducting membrane made of PE is installed between the positive and negative electrodes of the single cell, and the thickness of the membrane is 800 to 1000 um (preferably 900 to 1000 um).

3. The recovery method according to claim 1, characterized in that: The positive and negative electrolytes of the zinc-bromine dual-flow battery are both neutral aqueous solutions containing zinc and bromide ions. The zinc and bromine raw materials are zinc bromide. The zinc ion concentration in the positive and negative electrolytes of the battery is the same, and the supporting electrolyte KCl concentration is the same. The zinc ion concentration in the electrolyte is: 2-4mol / L, and the KCl concentration is 2-5mol / L.

4. The recovery method according to claim 1 or 2, characterized in that: The single cell includes a positive electrode collector, a positive electrode frame, a positive electrode, a separator, a negative electrode, a negative electrode frame, and a negative electrode collector stacked in sequence; the two ends of the battery stack, or the two ends of a single cell in the case of a single cell, are respectively provided with a positive terminal plate and a negative terminal plate; the positive electrode is accommodated in a through hole in the middle of the positive electrode frame, and the positive electrode electrolyte in the single cell is sealed in a closed cavity surrounded by the positive electrode frame, the positive electrode collector and the battery separator, serving as a positive electrode cavity; the negative electrode is accommodated in a through hole in the middle of the negative electrode frame, and the negative electrode electrolyte in the single cell is sealed in a closed cavity surrounded by the negative electrode frame, the negative electrode collector and the battery separator, serving as a negative electrode cavity.

5. The recovery method according to any one of claims 1 to 4, characterized in that: The electrolyte in the electrolyte storage tank of the zinc-bromine dual-flow battery flows in the positive and negative electrode cavities respectively through pumps, and an ion exchange membrane is arranged between the positive and negative electrodes.

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