Vanadium flow battery and method for maintaining balance of positive and negative electrolytes of vanadium flow battery

Abstract

The present application belongs to the field of electrochemistry, and particularly relates to a vanadium flow battery and a method for keeping the positive and negative electrolyte of the vanadium flow battery balanced. The vanadium flow battery comprises a positive electrolyte tank and a negative electrolyte tank, a balance pipeline is arranged between the two tanks, and the two tanks are also connected through an overflow pipeline. The overflow pipeline is located at a predetermined threshold height above the positive or negative electrolyte level to achieve that, during the charging and discharging process, the positive electrolyte level exceeding the predetermined threshold height overflows into the negative electrolyte tank, or the negative electrolyte level exceeding the predetermined threshold height overflows into the positive electrolyte tank. During the charging and discharging, if the electrolyte level of either side is higher than the specified threshold, it will automatically flow to the other side through the overflow pipeline, so as to realize the automatic adjustment of the liquid level at any time. When needed, the quick liquid level balance between the positive electrolyte tank and the negative electrolyte tank can be realized by opening the balance pipeline, and the partial ion concentration difference and the partial charge capacity can be restored.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a vanadium redox flow battery and a method for maintaining the balance of the positive and negative electrolytes in a vanadium redox flow battery. Background Technology

[0002] In vanadium redox flow batteries, during charge-discharge cycles, vanadium and hydrogen ions cross the membrane in the positive and negative electrode electrolytes, increasing the vanadium ion concentration on one side of the electrolyte. Due to osmotic pressure, water molecules cross the membrane to the side with higher ion concentrations, increasing the total volume of the electrolyte on that side, and vice versa on the other side. This results in a decrease in overall capacity (the total storable capacity drops to the capacity that the electrolyte on the side with fewer ions can store). Furthermore, if left unchecked, excessively high electrolyte levels on one side of the positive or negative electrode chamber can cause electrolyte to overflow from the top of the electrolyte tank (i.e., electrolyte overflow), leading to an accident.

[0003] Chinese patent application CN102055000A discloses a method for maintaining the same electrolyte level between positive and negative electrodes using a balancing tube. However, this patent relies on the principle of communicating vessels to achieve level balance, and the balancing tube can be continuously opened online. Therefore, it requires a very thin and long tube with a length-to-diameter ratio of not less than 10 (because the electrolyte inside the tube is a conductor; if the length-to-diameter ratio is less than 10, the resistance of the electrolyte inside the tube will be too low, resulting in excessive current and circuit losses, which may even lead to short circuits and damage). Furthermore, in this invention, when the vanadium ion concentration deviation is too large, it is difficult to complete the mixing process quickly using such a thin balancing tube, thus requiring the use of other mixing tubes. Therefore, the tube design of this invention is more complex and involves circuit losses.

[0004] To address the above problems, this invention is proposed. Summary of the Invention

[0005] This invention mainly discloses a method for adjusting the liquid volume of positive and negative electrode electrolytes online, and the storage capacity of positive and negative electrode electrolytes can be restored according to the usage status.

[0006] The first aspect of the present invention provides a vanadium redox flow battery, the vanadium redox flow battery comprising: a positive electrolyte tank 1 containing a positive electrolyte and a negative electrolyte tank 2 containing a negative electrolyte;

[0007] A balance pipe 3 is provided between the positive electrode electrolyte tank 1 and the negative electrode electrolyte tank 2 to achieve the connection between the positive electrode electrolyte and the negative electrode electrolyte;

[0008] A valve is installed on the balancing pipeline 3;

[0009] The positive electrode electrolyte tank 1 and the negative electrode electrolyte tank 2 are also connected by an overflow pipe 4. The overflow pipe 4 is arranged parallel to the liquid surfaces of the positive electrode electrolyte tank 1 and the negative electrode electrolyte tank 2. The overflow pipe 4 is located at a predetermined threshold height above the liquid level of the positive electrode electrolyte or the liquid level of the negative electrode electrolyte to achieve the following:

[0010] During the charging and discharging process of the vanadium redox flow battery, if the level of the positive electrolyte in the positive electrolyte tank 1 exceeds the predetermined threshold height, it will overflow into the negative electrolyte tank 2, or if the level of the negative electrolyte in the negative electrolyte tank 2 exceeds the predetermined threshold height, it will overflow into the positive electrolyte tank 1.

[0011] There is no requirement for the length-to-diameter ratio of the balancing pipe 3. Preferably, the length-to-diameter ratio of the balancing pipe 3 is less than 10. That is, the balancing pipe 3 preferably uses a relatively large pipe to achieve rapid liquid exchange.

[0012] A second aspect of the present invention provides a method for maintaining the electrolyte balance between the positive and negative electrodes of a vanadium redox flow battery, using the vanadium redox flow battery described in any one of the first aspects.

[0013] Preferably, when the valve on the balance pipeline 3 is closed, if the liquid level in the positive electrolyte tank 1 or the negative electrolyte tank 2 is higher than a predetermined threshold height, the positive electrolyte in the positive electrolyte tank 1 overflows into the negative electrolyte tank 2, or the negative electrolyte in the negative electrolyte tank 2 overflows into the positive electrolyte tank 1.

[0014] Preferably, when the valve on the balancing pipeline 3 is opened, the positive electrolyte in the positive electrolyte tank 1 and the negative electrolyte in the negative electrolyte tank 2 are mixed through the balancing pipeline 3 to achieve the same liquid level.

[0015] In the technical solution of the present invention, when opening the valve on the balance pipeline 3, it is not necessary for the liquid level in the positive electrode electrolyte tank 1 or the negative electrode electrolyte tank 2 to be higher than a predetermined threshold height.

[0016] If deemed necessary, the valve on the balance pipeline 3 can be opened, for example, when the electrolyte concentration deviation between the positive electrolyte tank 1 and the negative electrolyte tank 2 reaches a set value or when the battery system reaches a set cycle period.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. Due to the presence of the overflow pipe 4, during normal charging and discharging operation, if the electrolyte level on either side exceeds the specified threshold, it will automatically flow to the other side through the overflow pipe, achieving automatic level adjustment at any time without worrying about excessive level deviation causing the electrolyte tank to overflow. When needed, the balance pipe 3 can be opened to achieve rapid level balance between the positive and negative electrolyte tanks, restoring part of the ion concentration difference and partial charge capacity.

[0019] 2. Under normal circumstances, the valve of the balance pipe 3 is not open. Moreover, the amount of liquid overflowing from the top overflow pipe 4 is very small. When the liquid falls to the electrolyte tank on the low liquid level side, it is a discontinuous dripping flow. Therefore, the electrolyte in the overflow pipe does not actually form a circuit, and there is no current in the overflow pipe. There is no power loss during the liquid overflow process, and it does not affect the battery efficiency.

[0020] 3. Normally, the balancing pipe 3 is not open, and the electrolytes on both sides do not contact each other. When the valve of the balancing pipe 3 is opened to restore part of the electrolyte capacity, the electrolyte is in a state of low charge. Therefore, the balancing pipe 3 can be relatively thick (the length-to-diameter ratio of the pipe does not need to be greater than 10). There is no need to consider the circuitry for the positive and negative terminals, requiring sufficiently high resistance, resulting in a very long and narrow pipe that would hinder liquid exchange (compare with invention application CN102055000A). The thicker balancing pipe 3 allows for faster liquid exchange, thus enabling partial electrolyte capacity restoration to be completed in a very short time (usually no more than 3 minutes).

[0021] In the invention application CN102055000A, since the valve of the balance tube must be kept open to ensure liquid level balance, the liquid circuit is connected at the same time, resulting in circuit loss and seriously affecting battery efficiency.

[0022] 4. The battery management system controls only one valve and pump, and has only two pipelines, making it relatively simple, reliable, and low-cost. This simple system can achieve basic online balance of a single electrolyte circuit (positive electrode + negative electrode electrolyte tank) and can restore electrolyte capacity. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the vanadium redox flow battery structure according to the first embodiment of the present invention.

[0024] List of reference numerals in the attached diagram:

[0025] 1. Positive electrolyte tank, 2. Negative electrolyte tank, 3. Balance line, 4. Overflow line, D1, stack 1, D2, stack 2, Dn, stack n. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the embodiments.

[0027] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the field or according to the product instructions. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0028] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” to another element, it can be directly connected to the other element, or there may be an intermediate element. Furthermore, the term “connected” as used herein can include wireless connections.

[0029] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. The terms "inner," "upper," "lower," etc., indicate the orientation or state relationship based on the orientation or state relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "equipped with" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0031] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0032] A vanadium redox flow battery, the vanadium redox flow battery comprising: a positive electrolyte tank 1 containing a positive electrolyte and a negative electrolyte tank 2 containing a negative electrolyte;

[0033] A balance pipe 3 is provided between the positive electrode electrolyte tank 1 and the negative electrode electrolyte tank 2 to achieve the connection between the positive electrode electrolyte and the negative electrode electrolyte;

[0034] A valve is installed on the balancing pipeline 3;

[0035] The positive electrode electrolyte tank 1 and the negative electrode electrolyte tank 2 are also connected by an overflow pipe 4. The overflow pipe 4 is arranged parallel to the liquid surfaces of the positive electrode electrolyte tank 1 and the negative electrode electrolyte tank 2. The overflow pipe 4 is located at a predetermined threshold height above the liquid level of the positive electrode electrolyte or the liquid level of the negative electrode electrolyte to achieve the following:

[0036] During the charging and discharging process of the vanadium redox flow battery, if the level of the positive electrolyte in the positive electrolyte tank 1 exceeds the predetermined threshold height, it will overflow into the negative electrolyte tank 2, or if the level of the negative electrolyte in the negative electrolyte tank 2 exceeds the predetermined threshold height, it will overflow into the positive electrolyte tank 1.

[0037] There is no requirement for the length-to-diameter ratio of the balancing pipe 3. Preferably, the length-to-diameter ratio of the balancing pipe 3 is less than 10, for example, less than 9, less than 8, less than 7, less than 6, less than 5, etc. That is, the balancing pipe 3 preferably uses a relatively thick pipe to achieve rapid liquid exchange.

[0038] The predetermined threshold height is A. A is 2% to 10% of the original liquid level of the positive electrode electrolyte, preferably 5%.

[0039] When the vanadium redox flow battery is started, the level of the positive electrode electrolyte is equal to the level of the negative electrode electrolyte.

[0040] Preferably, no valve is installed on the overflow pipe 4. The length-to-diameter ratio of the overflow pipe 4 is not required, but is preferably 1 to 10, for example, 3 to 5, depending on the operating conditions.

[0041] Preferably, a pump is installed on the balancing pipeline 3.

[0042] Preferably, the connection between the balance pipeline 3 and the positive electrolyte tank 1 is located in the middle or bottom of the positive electrolyte tank 1.

[0043] Preferably, the connection between the balance pipeline 3 and the negative electrode electrolyte tank 2 is located in the middle or bottom of the negative electrode electrolyte tank 2.

[0044] The balancing pipeline 3 can be arranged parallel to the liquid surfaces of the positive electrolyte tank 1 and the negative electrolyte tank 2, or at a certain angle to the liquid surfaces of the positive electrolyte tank 1 and the negative electrolyte tank 2.

[0045] A method for maintaining electrolyte balance between the positive and negative electrodes of a vanadium redox flow battery, using the vanadium redox flow battery described in any of the above claims.

[0046] Preferably, when the valve on the balance pipeline 3 is closed, if the liquid level in the positive electrolyte tank 1 or the negative electrolyte tank 2 is higher than a predetermined threshold height, the positive electrolyte in the positive electrolyte tank 1 overflows into the negative electrolyte tank 2, or the negative electrolyte in the negative electrolyte tank 2 overflows into the positive electrolyte tank 1.

[0047] Preferably, by opening the valve on the balancing pipeline 3, the positive electrolyte in the positive electrolyte tank 1 and the negative electrolyte in the negative electrolyte tank 2 are mixed through the balancing pipeline 3 to achieve the same liquid level.

[0048] A schematic diagram of the vanadium redox flow battery structure shown in the first embodiment of the present invention is as follows: Figure 1 As shown. The positive electrolyte tank 1 and negative electrolyte tank 2 are connected to each battery stack (stack 1 to stack n) in a conventional manner. The bottoms of the positive electrolyte tank 1 and negative electrolyte tank 2 are connected by a balancing pipe 3 with a valve and a pump. The tops of the positive electrolyte tank 1 and negative electrolyte tank 2 are directly connected by an overflow pipe 4 at a position approximately 5% above the original electrolyte level. During battery charging and discharging, the liquid inside the positive electrolyte tank 1 and negative electrolyte tank 2 will shift. When it reaches 5%, an overflow occurs, and the excess electrolyte on one side returns to the other side.

[0049] After multiple cycles, when the electrolyte (system) capacity is found to have decreased to a certain value (e.g., the total capacity has decreased to 90%), and the SOC is low (e.g., below 10%) (judgment method: reference battery OCV < 1.33), open the valve and pump on the balance pipeline 3 to exchange half of the liquid in the positive electrode electrolyte tank 1 and the negative electrode electrolyte tank 2, and the electrolyte capacity can be partially restored.

[0050] When a serious problem occurs in the system, charging and discharging can be stopped, and another mixing pipeline can be opened to continuously exchange the electrolyte (i.e., a special use of vanadium batteries, the mixing recovery system). A reference battery is used to detect whether the mixing is complete until the reference battery voltage returns to 0 and the electrolyte is restored to 3.5 valence.

Claims

1. A method for maintaining electrolyte balance at the positive and negative electrodes of a vanadium redox flow battery, characterized in that, Use vanadium redox flow batteries; The vanadium redox flow battery includes: a positive electrolyte tank (1) containing a positive electrolyte and a negative electrolyte tank (2) containing a negative electrolyte; A balance pipeline (3) is provided between the positive electrode electrolyte tank (1) and the negative electrode electrolyte tank (2) to achieve the connection between the positive electrode electrolyte and the negative electrode electrolyte; The balancing pipeline (3) is equipped with a valve; The positive electrode electrolyte tank (1) and the negative electrode electrolyte tank (2) are also connected by an overflow pipe (4). The overflow pipe (4) is arranged parallel to the liquid surfaces of the positive electrode electrolyte tank (1) and the negative electrode electrolyte tank (2). The overflow pipe (4) is located at a predetermined threshold height above the liquid level of the positive electrode electrolyte or at a predetermined threshold height above the liquid level of the negative electrode electrolyte to achieve the following: During the charging and discharging process of the vanadium redox flow battery, if the level of the positive electrolyte in the positive electrolyte tank (1) exceeds the predetermined threshold height, it will overflow into the negative electrolyte tank (2), or if the level of the negative electrolyte in the negative electrolyte tank (2) exceeds the predetermined threshold height, it will overflow into the positive electrolyte tank (1). The length-to-diameter ratio of the balancing pipeline (3) is less than 10; No valve was installed on the overflow pipe (4); During the charging and discharging process of the vanadium redox flow battery, the valve on the balance pipeline (3) is closed. When the liquid level in the positive electrolyte tank (1) or the negative electrolyte tank (2) is higher than a predetermined threshold height, the positive electrolyte in the positive electrolyte tank (1) overflows into the negative electrolyte tank (2), or the negative electrolyte in the negative electrolyte tank (2) overflows into the positive electrolyte tank (1). After multiple cycles, when the electrolyte capacity is found to have decreased to a certain value, the valve on the balance pipeline (3) is opened, and the positive electrolyte in the positive electrolyte tank (1) and the negative electrolyte in the negative electrolyte tank (2) are mixed through the balance pipeline (3) to achieve the same liquid level.

2. The method for maintaining electrolyte balance between the positive and negative electrodes of a vanadium redox flow battery according to claim 1, characterized in that, The balancing pipeline (3) may or may not have a pump installed.

3. The method for maintaining electrolyte balance between the positive and negative electrodes of a vanadium redox flow battery according to claim 1, characterized in that, The connection between the balance pipeline (3) and the positive electrolyte tank (1) is located in the middle or bottom of the positive electrolyte tank (1); The connection between the balance pipeline (3) and the negative electrode electrolyte tank (2) is located in the middle or bottom of the negative electrode electrolyte tank (2).

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