A liquid flow battery electrolyte storage tank and its application

Abstract

The present invention discloses a device for solving the problem of electrolyte migration in an alkaline zinc-iron flow battery, which is composed of an alkaline zinc-iron flow battery or a battery stack, a piping system, and positive and negative electrolyte storage tanks separated by a diaphragm on the outside. During the operation of the battery or battery stack, under the action of the electric field, the bound water carried by the charge-balancing ions in the electrolyte migrates from the negative electrode of the battery or battery stack to the positive electrode due to electromigration; and under the concentration gradient of the positive and negative electrolyte storage tanks separated by a diaphragm on the outside, the water in the electrolyte migrates from the positive electrode to the negative electrode. Under the combined action of electromigration inside the battery or battery stack and the concentration gradient of the external positive and negative electrolyte storage tanks, the volume of the positive and negative electrolytes is balanced, thereby alleviating or solving the problem of poor cycle stability caused by electrolyte migration during the operation of the alkaline zinc-iron flow battery, improving the reliability of system operation, and promoting the practical application of alkaline zinc-iron flow batteries.

Description

Technical Field

[0001] The present invention relates to a device for solving the problem of electrolyte migration in a liquid flow battery or a battery stack, and in particular to the application of such a device in an alkaline zinc-iron liquid flow battery or a battery stack. Background Art

[0002] Liquid flow battery energy storage technology has the characteristics of high safety, long life and environmental friendliness, and is one of the preferred technologies for large-scale and efficient energy storage. Alkaline zinc-iron liquid flow batteries use abundant zinc and iron as active materials, and have the characteristics of low cost and high open circuit voltage. They have good application prospects in the field of energy storage, especially distributed energy storage. Since the concept of alkaline zinc-iron liquid flow batteries was proposed by GB.Adams et al. in the United States in 1979, compared with the all-vanadium liquid flow batteries and zinc-bromine liquid flow batteries that are currently in the demonstration application stage, alkaline zinc-iron liquid flow batteries have not yet made major breakthroughs. One of the key technical bottlenecks is that during the charging and discharging process of alkaline zinc-iron liquid flow batteries or stacks, the electrolyte is under the combined action of the electric field gradient and the concentration gradient, and the bound water carried by the charge-balancing ions migrates from the negative electrode of the battery or stack to the positive electrode, and this process is irreversible, resulting in serious electrolyte migration, which leads to an imbalance in the volume of the electrolyte in the battery or stack, which in turn leads to a reduction in the stability of the battery or stack, which greatly increases the maintenance cost of the battery or stack.

[0003] Therefore, how to alleviate or solve the problem of water migration in the charging process of alkaline zinc-iron flow batteries or stacks and improve the cycle stability of batteries or stacks is of great significance for breaking through the key technical bottlenecks in the application of alkaline zinc-iron flow batteries and promoting their practical application. Summary of the invention

[0004] In order to solve the above problems, the present invention discloses a device for solving the migration of electrolyte during the operation of alkaline zinc-iron flow batteries, and the device is composed of an alkaline zinc-iron flow battery or a battery stack, a piping system, and positive and negative electrolyte storage tanks separated by a diaphragm on the outside. During the operation of the battery or battery stack, under the action of the electric field, the bound water carried by the charge-balancing ions in the electrolyte migrates from the negative electrode of the battery or battery stack to the positive electrode due to electromigration; and under the concentration gradient of the positive and negative electrolyte storage tanks separated by a diaphragm on the outside, the water in the electrolyte migrates from the positive electrode to the negative electrode. Under the combined action of electromigration inside the battery or battery stack and the concentration gradient of the external positive and negative electrolyte storage tanks, the volume of the positive and negative electrolytes is balanced, thereby alleviating or solving the problem of poor cycle stability caused by electrolyte migration during the operation of the alkaline zinc-iron flow battery, and improving the reliability of system operation.

[0005] In order to alleviate or solve the problem of water migration during the operation of alkaline zinc-iron liquid flow batteries or battery stacks, the present invention relates to a device for solving water migration in alkaline zinc-iron liquid flow batteries or battery stacks, and the technical solution adopted is as follows:

[0006] The device for solving the electrolyte migration of alkaline zinc-iron flow battery is composed of an alkaline zinc-iron flow battery or battery stack, a pipeline system and positive and negative electrolyte storage tanks separated by a diaphragm on the outside;

[0007] The electrolyte storage tank is a hollow tank body, in which a diaphragm is arranged;

[0008] The diaphragm is horizontally arranged in the tank body, and the edges of the diaphragm are tightly connected to the inner wall of the tank body, and the diaphragm divides the cavity in the tank body into two upper and lower chambers that are not connected to each other; or, the diaphragm is vertically arranged in the tank body, and the edges of the diaphragm are tightly connected to the inner wall of the tank body, and the diaphragm divides the cavity in the tank body into two left and right chambers that are not connected to each other; or, the diaphragm is vertically arranged in the tank body, and the left and right side edges and the lower end edge of the diaphragm are tightly connected to the inner wall of the tank body, and the diaphragm divides the cavity in the tank body into two chambers that are connected at the top and unconnected at the middle and lower parts.

[0009] The diaphragm is arranged transversely in the tank body, and a supporting screen plate for supporting the diaphragm is arranged below the diaphragm.

[0010] The diaphragm is an ion exchange membrane (such as sulfonated polyetheretherketone, perfluorosulfonic acid ion exchange membrane, sulfonated polysulfone ion exchange membrane, etc.) or a porous ion conduction membrane (such as polyolefin porous ion conduction membrane, polysulfone-based porous ion conduction membrane, polyethersulfone-based porous ion conduction membrane, etc.).

[0011] The two chambers in the tank body are respectively filled with positive electrode electrolyte and negative electrode electrolyte.

[0012] The storage tank is used in an alkaline zinc-iron liquid flow battery.

[0013] The positive electrode electrolyte is a mixed aqueous solution of ferrocyanide and a strong base, and the negative electrode electrolyte is a mixed aqueous solution of zinc salt or / and zinc oxide and a strong base. The concentration of the strong base in the positive and negative electrode electrolytes in the aqueous solution is 0.001-10 mol / L, and the active substance in the positive electrode electrolyte is ferrocyanide (Fe(CN)6 3- ) or ferrocyanide (Fe(CN)6 4- ) one or two of the above, the active material in the negative electrode electrolyte is Zn(OH)4 2- ; The concentration of active substances in the positive and negative electrolytes is 0.001 to 3 mol / L; The strong base is one or more of sodium hydroxide, potassium hydroxide or lithium hydroxide; The total ions of the negative electrolyte (Na + , K + OH - 、Zn(OH)4 2- ) concentration is higher than the total ion (Na + , K + OH - 、Fe(CN)64- 、Fe(CN)6 3- ) concentration, higher than 0.1~1mol / L.

[0014] The storage tank is used as a common storage tank for positive and negative electrode electrolytes, and the positive electrode electrolyte and the negative electrode electrolyte are respectively filled in two chambers in the tank body; it is used to alleviate or solve the problem of electrolyte migration in alkaline zinc-iron flow batteries or battery stacks.

[0015] The diaphragm may be the same as the diaphragm used in the alkaline zinc-iron flow battery or battery stack, or may be different.

[0016] The storage tank is used as a common storage tank for positive and negative electrode electrolytes, and is used to alleviate or solve the problem of electrolyte migration in alkaline zinc-iron flow batteries or battery stacks.

[0017] The alkaline zinc-iron flow battery comprises an alkaline zinc-iron flow battery or a battery stack and any of the storage tanks.

[0018] The total ion concentration of the negative electrode electrolyte is higher than the total ion concentration of the positive electrode electrolyte;

[0019] The diaphragm may be the same as or different from the diaphragm used in the alkaline zinc-iron flow battery or battery stack.

[0020] During the operation of the battery or stack, under the action of the electric field, the bound water carried by the charge-balancing ions in the electrolyte migrates from the negative electrode of the battery or stack to the positive electrode due to electromigration; and the water in the electrolyte migrates from the positive electrode to the negative electrode under the concentration gradient of the positive and negative electrolyte storage tanks separated by the diaphragm outside. Under the combined effect of electromigration inside the battery or stack and the concentration gradient of the external positive and negative electrolyte storage tanks, the volume of the positive and negative electrolytes is balanced, thereby alleviating or solving the problem of poor cycle stability caused by electrolyte migration during the operation of the alkaline zinc-iron flow battery, improving the reliability of the system operation, and promoting the practical application of the alkaline zinc-iron flow battery.

[0021] Beneficial results of the present invention:

[0022] 1. The device can alleviate or solve the electrolyte migration problem caused by the bound water carried by the charge-balancing ions passing through the membrane material during the operation of the alkaline zinc-iron flow battery or the stack through the positive and negative electrode electrolyte concentration gradient in the positive and negative electrode storage tanks separated by the diaphragm;

[0023] 2. The device only requires one storage tank outside, which is separated by a diaphragm to ensure the mixing of positive and negative electrolytes. The structure is relatively simple and has strong operability and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of a traditional alkaline zinc-iron flow battery;

[0025] Figure 2 A schematic diagram of a device for solving electrolyte migration in alkaline zinc-iron flow batteries according to the present invention;

[0026] Figure 3 Comparison of the volume changes of positive and negative electrolytes in the traditional alkaline zinc-iron flow battery and the device for solving the electrolyte migration of the alkaline zinc-iron flow battery disclosed in this patent under the same operating conditions; 1- Changes in the volume of positive electrolyte during the operation of the traditional alkaline zinc-iron flow battery; 2- Changes in the volume of negative electrolyte during the operation of the traditional alkaline zinc-iron flow battery; 3- Using Figure 2 Changes in the volume of the cathode electrolyte in the alkaline zinc-iron flow battery assembled with the device under the same operating conditions; 4- Figure 2 Changes in the volume of the negative electrode electrolyte of the device-assembled alkaline zinc-iron flow battery under the same operating conditions.

[0027] Figure 4 Cycling performance test of traditional alkaline zinc-iron flow battery.

[0028] Figure 5 use Figure 2 The battery cycle performance test of the alkaline zinc-iron flow battery assembled in the device under the same operating conditions;

[0029] In the figure: 1-positive electrode liquid storage tank; 2-negative electrode liquid storage tank; 3-diaphragm; 4-load; 5-pump; 6-positive electrode half-cell; 7-negative electrode half-cell; 8-diaphragm. DETAILED DESCRIPTION

[0030] The following examples are provided to further illustrate the present invention, but are not intended to limit the scope of the present invention.

[0031] Comparative Example 1

[0032] The comparative example of the present invention is Figure 1 Traditional alkaline zinc-iron flow battery. A densely structured polybenzimidazole ion-conducting membrane is used as the separator, and the positive electrode electrolyte is 0.5 molL -1 Na4Fe(CN)6+0.5molL -1 KOH+0.5molL -1 K4Fe(CN)6+0.5molL -1 NaOH solution, total ion concentration is 7 molL -1 ; The negative electrode electrolyte is 0.6 molL -1 Na2Zn(OH)4+3.8molL - 1 NaOH solution, total ion concentration is 9.4 molL -1 ; The volume of positive and negative electrolyte is 80mL each; The effective area of ​​the battery is 48cm 2, using constant current charge and discharge mode, at 80mA cm -2 The battery was charged for 25 min under the current density condition, and the battery discharge process was cut off with voltage, 80 mA cm -2 Discharge to 0.1V under the current density condition. Figure 3 The changes in the volume of the positive and negative electrolytes show that during the operation of the battery, the negative electrolyte continuously migrates to the positive electrode, resulting in a continuous increase in the volume of the positive electrolyte. At the 57th cycle, the volume of the positive electrolyte has increased to 117 mL, and the volume of the negative electrolyte has dropped to 43 mL. As the battery cycle progresses, due to the migration of the electrolyte, the volume of the positive electrolyte gradually increases, the concentration of active substances gradually decreases, the concentration polarization of the battery is large at the end of charging, and the battery efficiency begins to gradually decrease ( Figure 4 ).

[0033] Example 1

[0034] use Figure 2 The device assembles an alkaline zinc-iron flow battery, with a densely structured polybenzimidazole ion-conducting membrane as a diaphragm between the positive and negative electrode storage tanks inside and outside the battery. The diaphragm is vertically arranged in the tank body, and the edges of the diaphragm are tightly connected to the inner wall of the tank body. The diaphragm divides the cavity in the tank body into two unconnected chambers on the left and right. The positive electrode electrolyte and the negative electrode electrolyte are respectively filled in the two chambers in the tank body. The positive electrode electrolyte is 0.5 molL -1 Na4Fe(CN)6+0.5molL -1 KOH+0.5molL -1 K4Fe(CN)6+0.5molL -1 NaOH solution, total ion concentration is 7 molL -1 ; The negative electrode electrolyte is 0.6 molL -1 Na2Zn(OH)4+3.8molL -1 NaOH solution, total ion concentration is 9.4 molL -1 ; The volume of positive and negative electrolyte is 80mL each; The effective area of ​​the battery is 48cm 2 , using constant current charge and discharge mode, at 80mA cm -2 The battery was charged for 25 min under the current density condition, and the battery discharge process was cut off with voltage, 80 mA cm -2 Discharge to 0.1V under the current density condition. Figure 3It can be seen from the changes in the volume of the positive and negative electrolytes that during the operation of the battery, due to the concentration gradient in the positive and negative electrolytes in the external storage tank, water migrates from the low-concentration positive electrode to the high-concentration negative electrode, thereby alleviating the problem of water migration carried by the charge-balancing ions inside the battery being faster than the water migration caused by the concentration gradient and then the electrolyte migration. At the 245th cycle, the volume of the positive electrolyte was only 87.5mL, and the volume of the negative electrolyte remained at 72.5mL; and as the battery cycle progresses, since the volume of the positive and negative electrolytes remains stable, the use of Figure 2 The device assembled alkaline zinc-iron flow battery operated continuously and stably for more than 280 cycles and its performance remained stable ( Figure 5 ), the cycle stability is significantly improved compared with the traditional alkaline zinc-iron flow battery.

[0035] In Example 2-5, the liquid storage tank and the connection relationship are the same as in Example 1, and the differences are shown in the following table:

[0036]

[0037]

[0038]

[0039] The results show that the use of positive and negative electrode electrolyte concentration gradients in external positive and negative electrode storage tanks separated by a diaphragm can effectively alleviate or solve the electrolyte migration problem caused by the bound water carried by charge-balancing ions through the membrane material during the operation of the alkaline zinc-iron flow battery or stack, thereby improving the battery cycle stability; when the total ion concentration of the positive electrode is higher than the total ion concentration of the negative electrode, the external electrolyte concentration gradient will accelerate the migration of the electrolyte from the negative electrode to the positive electrode (Example 5), thereby reducing the battery cycle stability.

[0040] During the operation of the battery or stack, under the action of the electric field, the bound water carried by the charge-balancing ions in the electrolyte migrates from the negative electrode of the battery or stack to the positive electrode due to electromigration; and the water in the electrolyte migrates from the positive electrode to the negative electrode under the concentration gradient of the positive and negative electrolyte storage tanks separated by the diaphragm outside. Under the combined effect of electromigration inside the battery or stack and the concentration gradient of the external positive and negative electrolyte storage tanks, the volume of the positive and negative electrolytes is balanced, thereby alleviating or solving the problem of poor cycle stability caused by electrolyte migration during the operation of the alkaline zinc-iron flow battery, improving the reliability of the system operation, and promoting the practical application of the alkaline zinc-iron flow battery.

Claims

1. A flow battery electrolyte storage tank used in an alkaline zinc-iron flow battery, characterized in that: The electrolyte storage tank is a hollow tank body, in which a diaphragm is arranged; The diaphragm is arranged horizontally in the tank body, and the edges of the diaphragm are tightly connected to the inner wall of the tank body, and the diaphragm divides the cavity in the tank body into two upper and lower chambers that are not connected to each other; or, the diaphragm is arranged vertically in the tank body, and the edges of the diaphragm are tightly connected to the inner wall of the tank body, and the diaphragm divides the cavity in the tank body into two left and right chambers that are not connected to each other; The diaphragm is one or more of an ion exchange membrane or a porous ion conducting membrane; The ion exchange membrane is sulfonated polyetheretherketone; The porous ion conducting membrane is one or more of a polyolefin porous ion conducting membrane and a polyethersulfone-based porous ion conducting membrane; The storage tank is used as a common storage tank for positive and negative electrode electrolytes, and the positive electrode electrolyte and the negative electrode electrolyte are respectively filled in two chambers in the tank body; The positive electrode electrolyte is a mixed aqueous solution of ferrocyanide or ferrocyanide and a strong base, the negative electrode electrolyte is a mixed aqueous solution of zinc salt and / or zinc oxide and a strong base, the concentration of the strong base in the positive and negative electrode electrolytes in the aqueous solution is 0.001-10 mol / L, and the active substance in the positive electrode electrolyte is ferrocyanide Fe(CN)6 3- or ferrocyanide Fe(CN)6 4- One or two of the above, the active substance in the negative electrode electrolyte is Zn(OH)4 2- ; The concentration of active substances in the positive and negative electrolytes is 0.001 to 3 mol / L; the strong base is one or more of sodium hydroxide, potassium hydroxide or lithium hydroxide; the total ion concentration of the negative electrolyte is higher than that of the positive electrolyte, and is higher than 0.1 to 1 mol / L.

2. An alkaline zinc-iron flow battery system, characterized in that: It comprises an alkaline zinc-iron liquid flow battery or an alkaline zinc-iron liquid flow battery stack and the liquid flow battery electrolyte storage tank as claimed in claim 1.

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