A zinc-bromine flow battery structure that inhibits self-discharge

Abstract

The application belongs to the technical field of liquid flow battery energy storage, and particularly relates to a zinc-bromine liquid flow battery, which is a battery pack composed of two or more single batteries in series from top to bottom (both liquid paths and electric paths are in series). The single battery mainly comprises annular negative electrode frames with through holes for accommodating electrodes, separators and annular positive electrode frames with through holes for accommodating electrodes, which are sequentially stacked; and a negative electrode arranged in the through hole in the middle of the annular negative electrode frame and a positive electrode arranged in the through hole in the middle of the annular positive electrode frame. In the zinc-bromine liquid flow battery, the liquid guide plates at both ends are provided with a certain inclination angle. When the battery is parked, the positive and negative electrolytes in the positive and negative electrodes can flow out of the battery stack from the carbon felt electrode through the outlet flow channel due to gravity, so that the liquid storage amount of the carbon felt electrode is reduced, the water corrosion of zinc on the negative side is reduced, and the self-discharge of the zinc-bromine liquid flow battery is inhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of liquid flow battery energy storage, and particularly relates to a zinc-bromine liquid flow battery. BACKGROUND

[0002] The zinc-bromine liquid flow battery is a low-cost, high-safety liquid flow battery energy storage technology with high energy density. The feature of the zinc-bromine liquid flow battery is that the negative electrode is zinc deposition and dissolution, and zinc ions are converted into zinc element and deposited on the carbon felt electrode during charging. Since the zinc-bromine liquid flow battery uses a porous separator, bromine molecules generated at the positive electrode can pass through the separator to cause self-discharge reaction of the battery, reducing the battery capacity. After being fully charged, the negative electrode of the zinc-bromine liquid flow battery is zinc element, which can cause hydrolysis reaction with the electrolyte if soaked in the electrolyte for a long time, resulting in water corrosion of the zinc element and reduction of the battery capacity. Meanwhile, since a large amount of bromine molecules exist at the positive electrode, the bromine molecules can pass through the separator and cause self-discharge reaction with the zinc at the negative electrode during storage, further reducing the battery capacity. Therefore, the storage performance of the zinc-bromine liquid flow battery is an important problem for improving its application prospect. SUMMARY

[0003] To solve the above technical problems, the application aims to provide a zinc-bromine liquid flow battery structure.

[0004] To achieve the above-mentioned purposes, the application adopts the following technical solutions:

[0005] A zinc-bromine liquid flow battery structure for inhibiting self-discharge is formed by stacking two or more single batteries in series from top to bottom (both liquid and electric circuits are in series). The single battery mainly comprises a ring-shaped negative electrode frame with a through hole for accommodating an electrode in the middle, a separator, and a ring-shaped positive electrode frame with a through hole for accommodating an electrode in the middle; and a negative electrode placed in the through hole in the middle of the ring-shaped negative electrode frame and a positive electrode placed in the through hole in the middle of the ring-shaped positive electrode frame.

[0006] Through holes serving as a negative electrolyte inlet common flow channel, a negative electrolyte outlet common flow channel, a positive electrolyte inlet common flow channel, and a positive electrolyte outlet common flow channel are respectively arranged on the negative electrode frame and the positive electrode frame. On the surface A of the negative electrode frame close to the separator, recesses serving as a negative electrolyte inlet flow channel (on the left side) and a negative electrolyte outlet flow channel (on the right side) are respectively arranged on the opposite sides of the rectangular through hole (i.e. the left and right sides of the surface A).

[0007] On the surface B of the positive electrode frame close to the separator, recesses serving as a positive electrolyte inlet flow channel (on the left side) and a positive electrolyte outlet flow channel (on the right side) are respectively arranged on the opposite sides of the rectangular through hole (i.e. the left and right sides of the surface B).

[0008] The negative electrode frame and the positive electrode frame are respectively provided with through holes as common flow channels of negative electrolyte inlet, negative electrolyte outlet, positive electrolyte inlet and positive electrolyte outlet;

[0009] The common flow channel of negative electrolyte inlet is connected with the electrolyte inlet flow channel of the negative electrode frame, and the common flow channel of negative electrolyte outlet is connected with the electrolyte outlet flow channel of the negative electrode frame; the common flow channel of positive electrolyte inlet is connected with the electrolyte inlet flow channel of the positive electrode frame, and the common flow channel of positive electrolyte outlet is connected with the electrolyte outlet flow channel of the positive electrode frame.

[0010] The copper plate, the liquid guide plate and the end plate are respectively arranged at the upper and lower ends of the battery pack and are away from the battery pack;

[0011] The end plate is a rectangular flat plate with parallel upper and lower surfaces, and the surfaces are arranged parallel to the horizontal plane.

[0012] The copper plate is a rectangular flat plate with parallel upper and lower surfaces, and the surfaces are arranged parallel to the horizontal plane.

[0013] The zinc-bromine flow battery has the following characteristics:

[0014] The liquid guide plate is a wedge-shaped hexahedron, one side surface of which close to the end plate is a plane parallel to the horizontal plane, and the opposite side surface C close to the copper plate is a plane with a certain inclination angle with the horizontal plane; the left and right side surfaces of the wedge-shaped hexahedron are mutually parallel rectangular surfaces with the same shape and size, and the front and rear side surfaces of the wedge-shaped hexahedron are mutually parallel right-angled trapezoidal surfaces with the same shape and size.

[0015] The horizontal plane position D of the one end (left end) of the surface C of the liquid guide plate close to the negative electrolyte inlet flow channel and the positive electrolyte inlet flow channel is higher than (above) the horizontal plane position E of the other end (right end) of the surface C of the liquid guide plate close to the negative electrolyte outlet flow channel and the positive electrolyte outlet flow channel.

[0016] The inclination angle between the surface C of the liquid guide plate close to the copper plate and the horizontal plane is 10-30 degrees.

[0017] In the assembly of the zinc-bromine flow battery, the surface of the liquid guide plate parallel to the horizontal plane at the two ends of the battery pack is tightly attached to the end plate, and the surface of the liquid guide plate with the inclination angle is tightly attached to the copper plate.

[0018] After the assembly of the zinc-bromine flow battery is completed, the direction from the inlet flow channel of the negative electrode frame to the outlet flow channel of the negative electrode frame has a downward inclination angle, and the direction from the inlet flow channel of the positive electrode frame to the outlet flow channel of the positive electrode frame has a downward inclination angle.

[0019] The bipolar plate is arranged between adjacent single cells, and the monopolar plate is arranged at the upper and lower ends of the battery pack.

[0020] The present application has the following beneficial effects relative to the prior art:

[0021] The present application sets a certain inclination angle to the liquid guide plate at both ends of the zinc-bromine flow battery, so that the inlet flow channel to the outlet flow channel of the negative electrode frame and the positive electrode frame has a certain inclination angle after the battery is assembled. When the battery is parked, the positive and negative electrolytes in the positive and negative electrodes can flow out of the stack from the carbon felt electrode through the outlet flow channel due to gravity, reducing the liquid storage amount of the carbon felt electrode, reducing the water corrosion of zinc on the negative side, and inhibiting the self-discharge of the zinc-bromine flow battery; on the positive side, the bromine concentration in the carbon felt electrode is reduced, the bromine molecule penetration during battery storage is reduced, and the self-discharge of the battery is further inhibited. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application, the drawings involved in the embodiments will be briefly introduced below.

[0023] Figure 1 It is a side view of the liquid guide plate of the present application.

[0024] Figure 2 It is a top view of the liquid guide plate of the present application.

[0025] Figure 3 It is a top view of the copper plate of the present application.

[0026] Figure 4 It is the structure of the zinc-bromine flow battery of the present application. Among them, 1 is the end plate of the battery, 2 is the liquid guide plate of the battery, 3 is the copper plate of the battery, 4 is the single cell of the present application, wherein the negative electrode frame, the separator and the positive electrode frame are sequentially arranged, 5 is the bipolar plate, and each two single cells are connected in series through the bipolar plate and are sequentially stacked. DETAILED DESCRIPTION

[0027] The present application will be described in detail below in conjunction with the embodiments, but the implementation of the present application is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present application, and for those skilled in the art, other similar embodiments obtained without creative labor fall within the protection scope of the present application.

[0028] The zinc-bromine flow battery structure of the embodiment of the present application is a battery pack composed of two or more single batteries stacked in series from top to bottom (both liquid path and electric circuit are in series). The single battery mainly comprises annular negative electrode frame with through hole for accommodating electrode, diaphragm and annular positive electrode frame with through hole for accommodating electrode, which are stacked in sequence; and negative electrode accommodated in the through hole of the annular negative electrode frame and positive electrode accommodated in the through hole of the annular positive electrode frame; the negative electrode frame and the positive electrode frame are respectively provided with through holes as common flow channels of negative electrolyte inlet, common flow channels of negative electrolyte outlet, common flow channels of positive electrolyte inlet and common flow channels of positive electrolyte outlet; the side surface A of the negative electrode frame close to the diaphragm is respectively provided with recesses as negative electrolyte inlet flow channel (on the left side) and negative electrolyte outlet flow channel (on the right side) on the opposite sides of the rectangular through hole (i.e. the left and right sides of the surface A); the side surface B of the positive electrode frame close to the diaphragm is respectively provided with recesses as positive electrolyte inlet flow channel (on the left side) and positive electrolyte outlet flow channel (on the right side) on the opposite sides of the rectangular through hole (i.e. the left and right sides of the surface B); the negative electrode frame and the positive electrode frame are respectively provided with through holes as common flow channels of negative electrolyte inlet, common flow channels of negative electrolyte outlet, common flow channels of positive electrolyte inlet and common flow channels of positive electrolyte outlet; the common flow channels of negative electrolyte inlet are connected with the electrolyte inlet flow channels of the negative electrode frame, and the common flow channels of negative electrolyte outlet are connected with the electrolyte outlet flow channels of the negative electrode frame; the common flow channels of positive electrolyte inlet are connected with the electrolyte inlet flow channels of the positive electrode frame, and the common flow channels of positive electrolyte outlet are connected with the electrolyte outlet flow channels of the positive electrode frame; copper plates, liquid guide plates and end plates are respectively arranged at the upper and lower ends of the battery pack and away from the battery pack; the end plates are rectangular flat plates with parallel upper and lower surfaces, and the surfaces are arranged parallel to the horizontal plane; the copper plates are rectangular flat plates with parallel upper and lower surfaces, and the surfaces are arranged parallel to the horizontal plane; the liquid guide plates are wedge-shaped hexahedrons, the side surface close to the end plate is a plane parallel to the horizontal plane, and the opposite side surface close to the copper plate C is a plane with a certain inclination angle with the horizontal plane; the left and right side surfaces of the wedge-shaped hexahedron are parallel to each other and rectangular with the same size, and the front and back side surfaces of the wedge-shaped hexahedron are parallel to each other and right-angled trapezoids with the same size; and the horizontal plane position D of the left end of the surface C of the liquid guide plate close to the negative electrolyte inlet flow channel and the positive electrolyte inlet flow channel is higher than (above E) the horizontal plane position E of the right end of the surface C of the liquid guide plate close to the negative electrolyte outlet flow channel and the positive electrolyte outlet flow channel. The inclination angle between the surface C of the liquid guide plate close to the copper plate and the horizontal plane is 10-30 degrees.The liquid flow battery is assembled with the liquid guide plates at both ends of the battery pack closely attached to the surface parallel to the horizontal plane and the end plate, and the liquid guide plates closely attached to the copper plate with the surface having an inclined angle with the horizontal plane; the liquid flow battery is assembled and completed with the downward inclined inclined angle from the inlet flow channel of the negative electrode frame to the outlet flow channel of the negative electrode frame; and the downward inclined inclined angle from the inlet flow channel of the positive electrode frame to the outlet flow channel of the positive electrode frame. The bipolar plates are arranged between adjacent single cells, and the monopolar plates are arranged at the upper and lower ends of the battery pack.

[0029] The electrolyte is a 2 mol / l zinc bromide solution, a 3 mol / l potassium chloride solution and a 0.4 mol / l MEP complexing agent aqueous solution. The separator is a commercial Daramic porous separator; the negative carbon felt electrode and the positive carbon felt electrode have an area of 800 cm 2

[0030] Comparative Example 1

[0031] Comparative Example 1 adopts a traditional structure to assemble a zinc bromine liquid flow battery pack. The battery liquid guide plate is a horizontal structure without an inclined angle. The specific electrode size, the number of battery stacks and the charging and discharging system are as follows:

[0032] The electrode area is 800 cm 2 ;

[0033] The number of battery stacks (single cell number) is 10 stacks;

[0034] The current density is 40 mA / cm 2 , the charging time is 3 hours, the discharging cut-off voltage is 8V, and the standing time is 24 hours;

[0035] The battery cycle performance is: coulomb efficiency 91.3%, voltage efficiency 83.3%, and energy efficiency 76.1%;

[0036] The battery standing performance is: coulomb efficiency 75.4%, voltage efficiency 70.3%, and energy efficiency 53.0%;

[0037] Comparative Example 2

[0038] Comparative Example 2 adopts the above structure to assemble a zinc bromine liquid flow battery pack. The inclined angle of the battery liquid guide plate is 5 degrees. The specific electrode size, the number of battery stacks and the charging and discharging system are as follows:

[0039] The electrode area is 800 cm 2 ;

[0040] The number of battery stacks (single cell number) is 10 stacks;

[0041] The current density is 40 mA / cm 2Charge time: 3 hours, discharge cut-off voltage: 8 V; shelf time: 24 hours

[0042] Battery cycling performance: Coulombic efficiency 90.1%, voltage efficiency 82.3%, energy efficiency 74.2%;

[0043] Battery shelf performance: Coulombic efficiency 77.2%, voltage efficiency 73.4%, energy efficiency 56.7%; Comparative Example 3

[0044] Comparative Example 3

[0045] Electrode area: 800 cm 2 ;

[0046] Stack number (single cell number): 10 stacks;

[0047] Current density: 40 mA / cm 2 , charge time: 3 hours, discharge cut-off voltage: 8 V; shelf time: 24 hours

[0048] Battery cycling performance: Coulombic efficiency 88.3%, voltage efficiency 79.5%, energy efficiency 70.2%;

[0049] Battery shelf performance: Coulombic efficiency 79.4%, voltage efficiency 72.5%, energy efficiency 57.6%;

[0050] Example 1

[0051] Example 1

[0052] Electrode area: 800 cm 2 ;

[0053] Stack number (single cell number): 10 stacks;

[0054] Current density: 40 mA / cm 2 , charge time: 3 hours, discharge cut-off voltage: 8 V; shelf time: 24 hours

[0055] Battery cycling performance: Coulombic efficiency 90.8%, voltage efficiency 82.3%, energy efficiency 74.7%;

[0056] Battery shelf performance: Coulombic efficiency 82.5%, voltage efficiency 74.6%, energy efficiency 61.5%;

[0057] Example 2

[0058] Example 2 uses the above structure to assemble a zinc-bromine flow battery. The liquid guide plate inclination angle of the battery is 25 degrees. The specific electrode size, the number of battery stacks, and the charging and discharging system are as follows:

[0059] Electrode area: 800 cm 2 ;

[0060] Number of battery stacks (number of single cells): 10 stacks;

[0061] Current density: 40 mA / cm 2 , charging time: 3 hours, discharging cut-off voltage: 8 V; resting time: 24 hours;

[0062] Battery cycle performance: coulomb efficiency 92.9%, voltage efficiency 83.8%, and energy efficiency 77.9%;

[0063] Battery resting performance: coulomb efficiency 83.1%, voltage efficiency 76.6%, and energy efficiency 63.6%;

[0064] Comparative Example 1 uses a conventional structure to assemble a zinc-bromine flow battery. It can be seen that the battery resting performance is very low after 3 hours of charging, which is due to the fact that a large amount of electrolyte is stored in the positive and negative carbon felt during the battery resting. At the negative electrode, the electrolyte and zinc undergo water corrosion, resulting in a loss of zinc capacity. At the positive electrode, a large amount of bromine is stored, and the bromine molecules pass through the separator and chemically react with the zinc element of the negative electrode, also consuming active substances and causing a loss of battery capacity. Comparative Example 2 uses the zinc-bromine flow battery structure provided by the present application, but the liquid guide plate inclination angle is smaller, resulting in the fact that the electrolyte cannot completely flow out of the electrode during the battery resting, and a more serious self-discharge occurs. However, compared with Comparative Example 1, the resting performance is higher. Comparative Example 3 uses the zinc-bromine flow battery structure provided by the present application, and the liquid guide plate inclination angle is larger. Although the electrolyte can completely flow out of the electrode during the battery resting, the uniformity of the electrolyte distribution inside the electrode is poor during the normal charging and discharging cycle due to the excessively large inclination angle, resulting in a large battery polarization and a low voltage efficiency, which affects the performance of the battery during normal operation.

[0065] In Example 1, the zinc-bromine flow battery structure provided by the application can be seen to have a significant improvement in shelf performance compared to the comparative example, which is due to the electrolyte flowing out of the electrode by gravity due to the presence of the inclined angle of the liquid guide plate, inhibiting the zinc corrosion of the negative electrode and the bromine molecule penetration of the positive electrode, and improving the shelf performance of the battery. In Example 2, it can be seen that the shelf performance has been improved to a certain extent after increasing the inclined angle, and the normal charge-discharge cycle performance of the battery has also been improved to a certain extent, which is due to the electrode frame having a certain inclined angle, increasing the electrolyte flow rate, reducing the battery polarization, and improving the voltage efficiency of the battery. At the same time, compared with Comparative Example 3, the inclined angle of Example 2 is not too large, which can ensure the uniformity of the electrolyte flow while increasing the electrolyte flow rate and improving the performance of the battery.

Claims

1. A zinc-bromine flow battery structure for suppressing self-discharge, comprising a battery pack composed of two or more single cells stacked in series from top to bottom, with both the liquid and electrical circuits connected in series. The single cells primarily comprise a sequentially stacked annular negative electrode frame with a central through-hole for accommodating an electrode, a diaphragm, and an annular positive electrode frame with a central through-hole for accommodating an electrode; a negative electrode positioned within the central through-hole of the annular negative electrode frame, and a positive electrode positioned within the central through-hole of the annular positive electrode frame. On the surface A of the negative electrode frame close to the diaphragm, on the two sides opposite to the rectangular through hole, i.e., on the left and right sides of the surface A, there are grooves for the negative electrolyte inlet and outlet on the left and right sides respectively. On the surface B of the positive electrode frame close to the diaphragm, on the two sides opposite to the rectangular through hole, i.e., on the left and right sides of the surface B, there are grooves for the positive electrolyte inlet and outlet on the left and right sides respectively; The negative electrode frame and the positive electrode frame are respectively provided with through holes serving as a common flow channel for the negative electrode electrolyte inlet, a common flow channel for the negative electrode electrolyte outlet, a common flow channel for the positive electrode electrolyte inlet, and a common flow channel for the positive electrode electrolyte outlet; The negative electrode electrolyte inlet common flow channel is connected to the electrolyte inlet flow channel of the negative electrode frame, and the negative electrode electrolyte outlet common flow channel is connected to the electrolyte outlet flow channel of the negative electrode frame; the positive electrode electrolyte inlet common flow channel is connected to the electrolyte inlet flow channel of the positive electrode frame, and the positive electrode electrolyte outlet common flow channel is connected to the electrolyte outlet flow channel of the positive electrode frame; Copper plates, liquid guide plates and end plates are respectively provided at the upper and lower ends of the battery pack in a direction away from the battery pack; The end plate is a rectangular flat plate with parallel upper and lower surfaces, and its surface is arranged parallel to the horizontal plane; The copper plate is a rectangular flat plate with parallel upper and lower surfaces, and its surface is arranged parallel to the horizontal plane; Its characteristics are: The liquid guide plate is a wedge-shaped hexahedron, with a surface on the side close to the end plate being a plane parallel to the horizontal plane, and an opposite surface C on the side close to the copper plate being a plane with a certain inclination angle to the horizontal plane; the left and right surfaces of the wedge-shaped hexahedron are parallel to each other and are rectangular with the same shape and size, and the front and rear surfaces of the wedge-shaped hexahedron are parallel to each other and are right-angled trapezoid with the same shape and size; And the horizontal plane position D of one end of the liquid guide plate surface C close to the negative electrode electrolyte inlet flow channel and the positive electrode electrolyte inlet flow channel, that is, the left end of C is higher than the horizontal plane position E of one end of the liquid guide plate surface C close to the negative electrode electrolyte outlet flow channel and the positive electrode electrolyte outlet flow channel, that is, the right end of C is located, where D is above E; the inclination angle between the surface C of the liquid guide plate close to the copper plate and the horizontal plane is 15 degrees to 25 degrees.

2. The battery structure according to claim 1, characterized in that: When the zinc-bromine flow battery is assembled, the surfaces of the liquid guide plates at both ends of the battery pack that are parallel to the horizontal plane are closely fitted with the end plates, and the planes of the liquid guide plates that are inclined at an angle to the horizontal plane are closely fitted with the copper plates; After the zinc-bromine liquid flow battery is assembled, the direction from the inlet flow channel of the negative electrode frame to the outlet flow channel of the negative electrode frame has a downward inclination angle; the direction from the inlet flow channel of the positive electrode frame to the outlet flow channel of the positive electrode frame has a downward inclination angle.

3. The battery structure according to claim 1, characterized in that: Bipolar plates are provided between adjacent single cells, and monopolar plates are provided at the upper and lower ends of the battery pack.

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