Zinc-bromine flow battery electrode structure and zinc-bromine flow battery

Abstract

The invention belongs to the technical field of flow battery energy storage, and particularly relates to a zinc-bromine flow battery electrode structure and a zinc-bromine flow battery. The electrode is a flat-plate-shaped carbon felt electrode, and one or more than two through holes are formed in the carbon felt electrode in the direction parallel to the surface of a flat plate and serve as electrolyte flow channels; and the cross sectional area of the electrolyte runner in the flowing direction of the electrolyte and perpendicular to the surface of the flat plate is gradually reduced. According to the electrode provided by the invention, the electrolyte flow channel is arranged in the electrode, so that the flow resistance of the electrolyte can be effectively reduced, and the mass transfer in the electrode is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of flow battery energy storage technology, and specifically relates to a zinc-bromine flow battery structure and electrode structure. Background Technology

[0002] Zinc-bromine flow batteries are a low-cost, high-safety flow battery energy storage technology with high energy density. Because the negative electrode of a zinc-bromine flow battery involves the deposition and dissolution reaction of zinc, zinc dendrites inevitably form. If these dendrites develop, they can cause short circuits and battery failure, or even, in severe cases, conduct electricity between the positive and negative electrodes, leading to excessive localized current, generating significant heat, and potentially causing a fire and other safety issues. Furthermore, because the electrolyte flows within the electrodes, there is a decreasing concentration gradient of active material from the inlet to the outlet. At the outlet, the concentration of active material is lower, causing concentration polarization and reducing the uniformity of zinc deposition. Therefore, for zinc-bromine flow batteries, avoiding the effects of zinc dendrite formation and controlling concentration polarization to achieve more uniform zinc deposition are key to improving battery performance. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide an electrode structure for a zinc-bromine flow battery.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A zinc-bromine flow battery electrode structure is characterized in that: the electrode is a flat carbon felt electrode, and through holes are provided inside the carbon felt electrode in a direction parallel to the surface of the flat plate to serve as electrolyte channels; the cross-sectional area of ​​the electrolyte channels gradually decreases along the direction of electrolyte flow and perpendicular to the surface of the flat plate.

[0006] The number of through holes is one or two or more, preferably four or more. Each electrolyte channel is evenly arranged inside the carbon felt electrode. When the number of through holes is three or more, the spacing between two adjacent electrolyte channels is the same.

[0007] The electrode is a rectangular plate with through holes between the opposite side walls of the rectangular plate. The center line or axis of the through holes is perpendicular to the opposite side walls where the opening of the through holes is located. The cross-section of the electrolyte flow channel is one or more of the following: circular, rectangular, or trapezoidal.

[0008] The centerline or axis of the electrolyte flow channel is aligned with half the height of the carbon felt thickness (i.e., the centerline or axis of the electrolyte flow channel is parallel to the surface of the carbon felt), or the centerline or axis of the electrolyte flow channel forms an angle greater than 0 to 5 degrees (preferably 1 to 5 degrees) with the surface of the flat plate. Along the direction of electrolyte flow, the distance between the electrolyte flow channel and the upper surface of the carbon felt (i.e., the surface closer to the diaphragm) gradually increases; and the centerlines or axes of two or more through holes are parallel to each other.

[0009] The sum of the areas of the inlet cross-section of the electrolyte flow channel is 5%-15% (preferably 8%-12%) of the area of ​​the side surface of the cuboid carbon felt on which it is located; the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 50%-90% (preferably 50%-80%).

[0010] The area of ​​each through hole is 0.1%-3% (preferably 0.5%-2%) of the area of ​​the side surface of the cuboid carbon felt it belongs to;

[0011] The upper and lower ends of the electrolyte flow channel inlet section are 2-4 mm (preferably 2-3 mm) away from the upper and lower surfaces of the carbon felt electrode, respectively.

[0012] The negative electrode adopts the aforementioned electrode structure. The electrode is placed in the central cavity of the annular electrode frame of the battery negative electrode. The central cavity of the negative electrode frame is connected to the inlet and outlet channels of the negative electrode electrolyte. When the battery is running, the negative electrode electrolyte flows in from the inlet channel of the negative electrode frame, flows through the electrode, undergoes an electrochemical reaction in the electrode, and then flows out of the negative electrode frame through the outlet channel of the negative electrode frame.

[0013] The electrode structures described above are only used for the negative electrode of the zinc-bromine flow battery, while the positive electrode still adopts the traditional flat carbon felt electrode structure.

[0014] The ring-shaped electrode frame of the negative electrode is rectangular, the cavity in the middle is also rectangular, the electrode is also rectangular, and the electrolyte flows from one side of the electrode to the other side.

[0015] The electrolyte flow direction is the direction of electrolyte flow when it flows through the electrode;

[0016] When the electrode is used in a zinc-bromine flow cell, the electrolyte flows in from one opening end of the through hole and flows out from the other opening end, in the same direction as the electrolyte flow.

[0017] The beneficial effects of this invention are as follows:

[0018] The electrode provided by this invention features an electrolyte flow channel within its interior, effectively reducing electrolyte flow resistance and enhancing mass transfer within the electrode. Furthermore, due to the gradually decreasing channel area design, the electrolyte flow within the electrode is a continuously accelerating process. Therefore, at the electrode outlet, the electrolyte flow rate is faster than at the inlet, resulting in a more abundant supply of active material. This counteracts concentration polarization caused by the decrease in active material concentration, leading to more uniform zinc anode deposition. In addition, because the electrolyte flow channel has minimal flow resistance, the electrolyte flow rate within the channel is faster than at other locations. This facilitates chemical reactions of the active material at the interface between the channel and the carbon felt electrode, directing zinc deposition to the interior of the electrode and reducing the impact of zinc dendrite formation. Moreover, since zinc deposition occurs within the electrode, it effectively suppresses capacity loss caused by zinc shedding, improving battery performance. Attached Figure Description

[0019] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0020] Figure 1 This is a schematic diagram of the zinc-bromine flow battery electrode of the present invention. Wherein, 1 is the electrolyte inlet; 2 is the electrolyte outlet; 3 is the electrolyte channel, disposed inside the carbon felt electrode; and 4 is the carbon felt electrode.

[0021] Figure 2 This is a cross-sectional view of the zinc-bromine flow cell electrode of the present invention along the electrolyte flow direction.

[0022] Figure 3 This is a cross-sectional view of the structure of Example 5. Detailed Implementation

[0023] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0024] This invention relates to an electrode structure for a zinc-bromine flow battery. The electrode is a flat carbon felt electrode with through holes inside the carbon felt electrode arranged in a direction parallel to the surface of the flat plate, serving as electrolyte channels. The cross-sectional area of ​​the electrolyte channels, perpendicular to the surface of the flat plate, gradually decreases along the electrolyte flow direction.

[0025] The number of through holes is one or two or more, preferably four or more. Each electrolyte channel is evenly arranged inside the carbon felt electrode. When the number of through holes is three or more, the spacing between two adjacent electrolyte channels is the same.

[0026] The electrode is a rectangular plate with through holes between the opposite side walls of the rectangular plate. The center line or axis of the through holes is perpendicular to the opposite side walls where the opening of the through holes is located. The cross-section of the electrolyte flow channel is one or more of the following: circular, rectangular, or trapezoidal.

[0027] The centerline or axis of the electrolyte flow channel is aligned with half the height of the carbon felt thickness (i.e., the centerline or axis of the electrolyte flow channel is parallel to the surface of the carbon felt), or the centerline or axis of the electrolyte flow channel forms an angle greater than 0 to 5 degrees (preferably 1 to 5 degrees) with the surface of the flat plate. Along the direction of electrolyte flow, the distance between the electrolyte flow channel and the upper surface of the carbon felt (i.e., the surface closer to the diaphragm) gradually increases; and the centerlines or axes of two or more through holes are parallel to each other.

[0028] The sum of the areas of the inlet cross-section of the electrolyte flow channel is 5%-15% (preferably 8%-12%) of the area of ​​the side surface of the cuboid carbon felt on which it is located; the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 50%-90% (preferably 50%-80%).

[0029] The area of ​​each through hole is 0.1%-3% (preferably 0.5%-2%) of the area of ​​the side surface of the cuboid carbon felt it belongs to;

[0030] The upper and lower ends of the electrolyte flow channel inlet section are 2-4 mm (preferably 2-3 mm) away from the upper and lower surfaces of the carbon felt electrode, respectively.

[0031] The negative electrode adopts the above-described electrode structure. The electrode is placed in the central cavity of the annular electrode frame of the battery negative electrode. The central cavity of the negative electrode frame is connected to the inlet and outlet channels of the negative electrode electrolyte. When the battery is running, the negative electrode electrolyte flows in from the inlet channel of the negative electrode frame, flows through the electrode, undergoes an electrochemical reaction in the electrode, and then flows out of the negative electrode frame through the outlet channel of the negative electrode frame.

[0032] The electrode structures described above are only used for the negative electrode of the zinc-bromine flow battery, while the positive electrode still adopts the traditional flat carbon felt electrode structure.

[0033] The ring-shaped electrode frame of the negative electrode is rectangular, the cavity in the middle is also rectangular, the electrode is also rectangular, and the electrolyte flows from one side of the electrode to the other side.

[0034] The electrolyte flow direction is the direction of electrolyte flow when it flows through the electrode;

[0035] When the electrode is used in a zinc-bromine flow battery, the electrolyte flows in from one opening and out from the other, in the same direction as the electrolyte flow. The reaction conditions for the following comparative examples and embodiments are as follows:

[0036] The electrolyte consisted of an aqueous solution of 2 mol / L zinc bromide, 3 mol / L potassium chloride, and 0.4 mol / L MEP complexing agent. The membrane was a commercially available Daramic porous membrane; the rectangular negative and positive carbon felt electrodes had areas of 800 cm². 2 .

[0037] Comparative Example 1

[0038] Comparative Example 1 uses a conventional electrode structure to assemble a zinc-bromine flow battery. The specific parameters of the battery stack are as follows:

[0039] Electrode area: 800 cm² 2 The positive and negative electrodes adopt a traditional electrode structure: flat carbon felt electrodes (a single piece of carbon felt without through holes between the opposite walls).

[0040] Electrode thickness: 8mm;

[0041] Number of fuel cell stack sections: 20;

[0042] Current density: 40 mA / cm 2 Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0043] Battery cycle performance: Coulombic efficiency 87.2%, voltage efficiency 82.9%, energy efficiency 72.3%;

[0044] Comparative Example 1 used a traditional electrode structure to assemble a zinc-bromine flow battery. Because zinc formed on the surface of the carbon felt electrode, the effects of zinc dendrite formation and zinc shedding were significant, resulting in low battery performance. Comparative Example 2...

[0045] Comparative Example 2 uses the electrode structure provided by this invention, wherein the cross-sectional area of ​​the electrolyte flow channel of the negative electrode is circular, the axis of the electrolyte flow channel is parallel to the surface of the carbon felt, and the spacing between two adjacent electrolyte flow channels is the same. The sum of the areas of the inlet cross-section of the electrolyte flow channel is 10% of the area of ​​the side surface of the cuboid carbon felt on which it is located, and the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 100%; the area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt on which it is located; the upper and lower ends of the inlet cross-section of the electrolyte flow channel are 5 mm away from the upper and lower surfaces of the carbon felt electrode, respectively; the positive electrode adopts a traditional electrode structure of a flat carbon felt electrode (a whole piece of carbon felt without through holes between the opposite walls); the specific parameters of the stack are as follows:

[0046] Electrode area: 800 cm² 2 ;

[0047] Electrode thickness: 12mm;

[0048] Number of fuel cell stack sections: 20;

[0049] Current density: 40 mA / cm 2Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0050] Battery cycle performance: coulombic efficiency 88.1%, voltage efficiency 83.2%, energy efficiency 73.3%; Comparative Example 2 used the electrode provided by this invention, but because its inlet cross-section was too far from the carbon felt surface and the electrolyte flow channel cross-sectional area was too small, the flow rate in the electrolyte flow channel was insufficient, which was not enough to change the deposition site of zinc on the carbon felt electrode, so the performance improvement was not significant.

[0051] Comparative Example 3

[0052] Comparative Example 3 uses the electrode structure provided by this invention, wherein the cross-sectional area of ​​the electrolyte flow channel of the negative electrode is circular, the axis of the electrolyte flow channel is parallel to the surface of the carbon felt, and the spacing between two adjacent electrolyte flow channels is the same. The sum of the areas of the inlet cross-section of the electrolyte flow channel is 10% of the area of ​​the side surface of the cuboid carbon felt on which it is located, and the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 100%; the area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt on which it is located; the upper and lower ends of the inlet cross-section of the electrolyte flow channel are 1 mm away from the upper and lower surfaces of the carbon felt electrode, respectively; the positive electrode adopts a traditional electrode structure of a flat carbon felt electrode (a whole piece of carbon felt without through holes between the opposite walls); the specific parameters of the stack are as follows:

[0053] Electrode area: 800 cm² 2 ;

[0054] Electrode thickness: 4mm;

[0055] Number of fuel cell stack sections: 20;

[0056] Current density: 40 mA / cm 2 Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0057] Battery cycle performance: Coulombic efficiency 87.5%, voltage efficiency 79.3%, energy efficiency 69.4%;

[0058] In Comparative Example 3, the distance between the inlet cross-section of the electrolyte flow channel and the surface of the carbon felt electrode was reduced to 1 mm. Due to the excessively large electrolyte flow cross-section and the reduced volume of the carbon felt, the number of deposition sites for zinc deposition was reduced. This not only failed to inhibit the formation of zinc dendrites, but also exacerbated the formation of zinc dendrites due to the limited number of zinc deposition sites, resulting in poor battery performance.

[0059] Comparative Example 4

[0060] Comparative Example 4 uses the electrode structure provided by this invention, wherein the cross-sectional area of ​​the electrolyte channel of the negative electrode is circular, the axis of the electrolyte channel is parallel to the surface of the carbon felt, and the spacing between two adjacent electrolyte channels is the same. The sum of the areas of the inlet cross-section of the electrolyte channel is 10% of the area of ​​the side surface of the cuboid carbon felt on which it is located, and the ratio of the outlet area of ​​the electrolyte channel to the inlet area of ​​the electrolyte channel is 30%; the area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt on which it is located; the upper and lower ends of the inlet cross-section of the electrolyte channel are 2 mm away from the upper and lower surfaces of the carbon felt electrode, respectively; the positive electrode adopts a traditional electrode structure of a flat carbon felt electrode (a whole piece of carbon felt without through holes between the opposite walls); the specific parameters of the stack are as follows:

[0061] Electrode area: 800 cm² 2 ;

[0062] Electrode thickness: 5mm;

[0063] Number of fuel cell stack sections: 20;

[0064] Current density: 40 mA / cm 2 Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0065] Battery cycle performance: Coulombic efficiency 87.1%, voltage efficiency 81.3%, energy efficiency 70.8%;

[0066] In Comparative Example 4, the inlet and outlet cross-sectional areas of the electrolyte flow channel were too low, resulting in excessive resistance at the flow end. This led to poor electrolyte flow within the flow channel, greater reaction polarization at the electrode end, and lower battery performance.

[0067] Example 1

[0068] Example 1 uses the electrode structure provided by this invention, wherein the cross-sectional area of ​​the electrolyte flow channel of the negative electrode is circular, the axis of the electrolyte flow channel is parallel to the surface of the carbon felt, and the spacing between two adjacent electrolyte flow channels is the same. The sum of the areas of the inlet cross-section of the electrolyte flow channel is 10% of the area of ​​the side surface of the cuboid carbon felt on which it is located, and the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 80%. The area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt on which it is located. The upper and lower ends of the inlet cross-section of the electrolyte flow channel are 2 mm away from the upper and lower surfaces of the carbon felt electrode, respectively. The positive electrode adopts a traditional electrode structure of a flat carbon felt electrode (a whole piece of carbon felt without through holes between the opposite walls). The specific parameters of the stack are as follows:

[0069] Electrode area: 800 cm² 2 ;

[0070] Electrode thickness: 8mm;

[0071] Number of fuel cell stack sections: 20;

[0072] Current density: 40 mA / cm 2 Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0073] Battery cycle performance: Coulombic efficiency 93.6%, voltage efficiency 84.3%, energy efficiency 78.9%;

[0074] Example 1 uses the electrode structure provided by this invention. Because an electrolyte flow channel is provided inside the carbon felt, when the electrolyte flows into the electrode, it preferentially flows from the electrolyte flow channel with lower flow resistance. During the electrochemical reaction, zinc preferentially deposits in the area with higher flow rate, that is, at the electrolyte flow channel. Therefore, the zinc deposition site is adjusted from the interface between the carbon felt and the separator to the interior of the carbon felt, suppressing the influence of zinc dendrite formation. Moreover, since elemental zinc is generated inside the carbon felt, the zinc shedding phenomenon caused by the electrolyte scouring due to elemental zinc being generated on the surface of the carbon felt is effectively suppressed, further improving battery performance and reliability.

[0075] Example 2

[0076] Example 2 uses the electrode structure provided by this invention, wherein the cross-sectional area of ​​the electrolyte flow channel of the negative electrode is circular, the axis of the electrolyte flow channel is parallel to the surface of the carbon felt, and the spacing between two adjacent electrolyte flow channels is the same. The sum of the areas of the inlet cross-section of the electrolyte flow channel is 10% of the area of ​​the side surface of the cuboid carbon felt on which it is located, and the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 80%; the area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt on which it is located; the upper and lower ends of the inlet cross-section of the electrolyte flow channel are 3 mm away from the upper and lower surfaces of the carbon felt electrode, respectively; the positive electrode adopts a traditional electrode structure of flat carbon felt electrode (a whole piece of carbon felt without through holes between the opposite walls); the specific parameters of the stack are as follows:

[0077] Electrode area: 800 cm² 2 ;

[0078] Electrode thickness: 10mm;

[0079] Number of fuel cell stack sections: 20;

[0080] Current density: 40 mA / cm 2 Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0081] Battery cycle performance: Coulombic efficiency 94.4%, voltage efficiency 83.3%, energy efficiency 78.6%;

[0082] In Example 2, the distance between the inlet cross-section of the electrolyte flow channel and the surface of the carbon felt was increased to 3 mm. Since the reaction interface was further away from the membrane surface, the electrochemical polarization of the battery was increased compared to Example 1, resulting in a decrease in the battery's voltage efficiency. However, also because the reaction interface was further away from the membrane, the zinc dendrite effect and zinc shedding were further suppressed, and the coulombic efficiency of the battery was improved. The overall energy efficiency was not much different from that of the battery in Example 1.

[0083] Example 3

[0084] Example 3 uses the electrode structure provided by this invention, wherein the cross-sectional area of ​​the electrolyte channel of the negative electrode is circular, the axis of the electrolyte channel is parallel to the surface of the carbon felt, and the spacing between two adjacent electrolyte channels is the same. The sum of the areas of the inlet cross-section of the electrolyte channel is 10% of the area of ​​the side surface of the cuboid carbon felt on which it is located, and the ratio of the outlet area of ​​the electrolyte channel to the inlet area of ​​the electrolyte channel is 50%. The area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt on which it is located. The upper and lower ends of the inlet cross-section of the electrolyte channel are 2 mm away from the upper and lower surfaces of the carbon felt electrode, respectively. The positive electrode adopts a traditional electrode structure of a flat carbon felt electrode (a whole piece of carbon felt without through holes between the opposite walls). The specific parameters of the stack are as follows:

[0085] Electrode area: 800 cm² 2 ;

[0086] Electrode thickness: 8mm;

[0087] Number of fuel cell stack sections: 20;

[0088] Current density: 40 mA / cm 2 Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0089] Battery cycle performance: Coulombic efficiency 95.9%, voltage efficiency 86.6%, energy efficiency 83.0%;

[0090] Compared to Example 1, Example 3 reduces the outlet cross-sectional area while keeping the inlet cross-sectional area unchanged. This means that the contraction angle of the electrolyte flow channel is larger, and the acceleration effect of the electrolyte in the flow channel is more obvious. Therefore, near the electrode outlet, due to the increased electrolyte flow rate, the active material is replenished more promptly, and the battery polarization is smaller, thus further improving the battery performance.

[0091] Example 4

[0092] Example 4 uses the electrode structure provided by this invention, wherein the cross-sectional area of ​​the electrolyte flow channel of the negative electrode is trapezoidal, with the long side of the trapezoid closer to the diaphragm side and the short side closer to the current collector side, the length of the short side being half the length of the long side. The axis of the electrolyte flow channel is aligned with half the height of the carbon felt thickness, and the spacing between two adjacent electrolyte flow channels is the same. The sum of the areas of the electrolyte flow channel inlet cross-section is 10% of the area of ​​the side surface of the cuboid carbon felt, and the ratio of the electrolyte flow channel outlet area to the electrolyte flow channel inlet area is 50%; the area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt; the upper and lower ends of the electrolyte flow channel inlet cross-section are 2 mm from the upper and lower surfaces of the carbon felt electrode, respectively; the positive electrode uses a traditional electrode structure, a flat carbon felt electrode (a whole piece of carbon felt without through holes between opposite walls); the specific parameters of the stack are as follows:

[0093] Electrode area: 800 cm² 2 ;

[0094] Electrode thickness: 8mm;

[0095] Number of fuel cell stack sections: 20;

[0096] Current density: 40 mA / cm 2 Charging time: 4 hours; Discharge cut-off voltage: 16V.

[0097] Battery cycle performance: Coulombic efficiency 96.3%, voltage efficiency 86.9%, energy efficiency 83.7%;

[0098] In Example 4, the cross-section of the electrolyte flow channel was replaced with an inverted trapezoid, with the long side of the trapezoid closer to the separator and the short side closer to the current collector. Therefore, the concentration of active material in the electrolyte flow channel was distributed in two ways: there was more active material near the separator and less near the current collector. As a result, the electrochemical reaction occurred more near the separator. This not only induced the zinc deposition sites to be inside the carbon felt, but also controlled the electrochemical reaction to be as close to the separator as possible, reducing ohmic polarization and electrochemical polarization, and improving battery performance.

[0099] Example 5

[0100] Example 5 uses the electrode structure provided by the present invention, wherein the cross-sectional area of ​​the electrolyte flow channel of the negative electrode is trapezoidal, wherein the long side of the trapezoid is close to the diaphragm side, the short side of the trapezoid is close to the current collector side, and the length of the short side is half of the long side. The central axis of the electrolyte flow channel forms an angle of 2 degrees with the horizontal surface. Along the electrolyte flow direction, the distance between the electrolyte flow channel and the upper surface of the carbon felt (that is, the surface close to the diaphragm side) increases, and the spacing between two adjacent electrolyte flow channels is the same. The sum of the areas of the inlet cross-section of the electrolyte flow channel is 10% of the area of ​​the side surface of the cuboid carbon felt on which it is located, and the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 50%; the area of ​​each through hole is 2% of the area of ​​the side surface of the cuboid carbon felt on which it is located; the upper and lower ends of the inlet cross-section of the electrolyte flow channel are 2 mm away from the upper and lower surfaces of the carbon felt electrode, as shown in Figure (3); the positive electrode adopts the traditional electrode structure of a flat carbon felt electrode (a whole piece of carbon felt without through holes between the opposite walls); the specific parameters of the stack are as follows:

[0101] Electrode area: 800 cm² 2 ;

[0102] Electrode thickness: 8mm;

[0103] Number of fuel cell stack sections: 20;

[0104] Current density: 40 mA / cm 2 Charging time: 3 hours; Discharge cut-off voltage: 16V.

[0105] Battery cycle performance: Coulombic efficiency 97.2%, voltage efficiency 86.6%, energy efficiency 84.2%;

[0106] In Example 5, the central axis of the electrolyte flow channel is positioned at a certain angle to the surface of the carbon felt. That is, along the direction of electrolyte flow, the flow channel is further away from the separator. Compared with Examples 1 to 4, since the end of the electrolyte flow is further away from the separator, in the area where zinc dendrites are more likely to form (at the end of the flow, due to the lower concentration of active material, zinc dendrites are more likely to form), the zinc deposition sites are further moved away from the separator, which more effectively suppresses the influence of zinc dendrite formation and improves battery reliability. Furthermore, since the flow channel is not parallel to the surface of the carbon felt, the distance between the flow channel and the surface of the carbon felt at the electrolyte inlet is still within the range described in this invention (2-4 mm). Therefore, the polarization of the battery will not be too large, ensuring battery performance.

[0107] The comparative examples and embodiments lead to the conclusion that assembling a zinc-bromine flow battery using the electrode proposed in this invention can effectively control the zinc deposition sites to the interior of the carbon felt, reducing the impact of zinc dendrite formation. Furthermore, since the electrolyte flow channel accelerates the electrolyte flow, it balances the concentration gradient of active materials from the electrode inlet to the outlet, reducing concentration polarization and improving battery performance.

Claims

1. A zinc-bromine flow battery electrode structure, characterized in that: The electrode is a flat carbon felt electrode, with through holes provided inside the carbon felt electrode in a direction parallel to the surface of the flat plate, serving as electrolyte flow channels; the cross-sectional area of ​​the electrolyte flow channels gradually decreases along the direction of electrolyte flow and perpendicular to the surface of the flat plate.

2. The electrode structure according to claim 1, characterized in that: The number of through holes is one or two or more, preferably four or more. Each electrolyte channel is evenly arranged inside the carbon felt electrode. When the number of through holes is three or more, the spacing between two adjacent electrolyte channels is the same.

3. The electrode structure according to claim 1, characterized in that: The electrode is a rectangular plate with a through hole between the two opposite side walls of the rectangular plate. The center line or axis of the through hole is perpendicular to the two opposite side walls where the opening end of the through hole is located. The cross-section of the electrolyte flow channel is one or more of the following: circular, rectangular, or trapezoidal.

4. The electrode structure according to claim 3, characterized in that: The centerline or axis of the electrolyte flow channel is aligned with half the height of the carbon felt thickness (i.e., the centerline or axis of the electrolyte flow channel is parallel to the carbon felt surface), or the centerline or axis of the electrolyte flow channel forms an angle greater than 0 to 5 degrees (preferably 1 to 5 degrees) with the carbon felt surface. Along the electrolyte flow direction, the distance between the electrolyte flow channel and the upper surface of the carbon felt (i.e., the surface closer to the diaphragm) gradually increases. Furthermore, the centerlines or axes of two or more through holes are parallel to each other.

5. The electrode structure according to any one of claims 1-4, characterized in that: The sum of the areas of the inlet cross-section of the electrolyte flow channel is 5%-15% (preferably 8%-12%) of the area of ​​the side surface of the cuboid carbon felt on which it is located; the ratio of the outlet area of ​​the electrolyte flow channel to the inlet area of ​​the electrolyte flow channel is 50%-90% (preferably 50%-80%).

6. The electrode structure according to any one of claims 1-4, characterized in that: The area of ​​each through hole is 0.1%-3% (preferably 0.5%-2%) of the area of ​​the side surface of the cuboid carbon felt it belongs to; The upper and lower ends of the electrolyte flow channel inlet section are 2-4 mm (preferably 2-3 mm) away from the upper and lower surfaces of the carbon felt electrode, respectively.

7. A zinc-bromine flow battery, characterized in that: The negative electrode adopts the electrode structure described in any one of claims 1-6. The electrode is placed in the central cavity of the annular electrode frame of the battery negative electrode. The central cavity of the negative electrode frame is connected to the inlet and outlet channels of the negative electrode electrolyte. When the battery is running, the negative electrode electrolyte flows in from the inlet channel of the negative electrode frame, flows through the electrode, undergoes an electrochemical reaction in the electrode, and then flows out of the negative electrode frame through the outlet channel of the negative electrode frame.

8. The zinc-bromine flow battery according to claim 7, characterized in that: The electrode structure described in any one of claims 1-6 is used only as the negative electrode of the zinc-bromine flow battery, while the positive electrode still adopts the traditional plate-shaped carbon felt electrode structure.

9. The zinc-bromine flow battery according to claim 8, characterized in that: The ring-shaped electrode frame of the negative electrode is rectangular, the cavity in the middle is also rectangular, the electrode is also rectangular, and the electrolyte flows from one side of the electrode to the other side. The electrolyte flow direction is the direction of electrolyte flow when it flows through the electrode; When the electrode is used in a zinc-bromine flow cell, the electrolyte flows in from one opening end of the through hole and flows out from the other opening end, in the same direction as the electrolyte flow.

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