Structure of zinc-based flow battery

Abstract

The utility model relates to a zinc-based flow battery which comprises a positive current collector, a diaphragm and a negative current collector which are sequentially overlapped, a gap is reserved between the positive current collector and the diaphragm, a gap is reserved between the diaphragm and the negative current collector, and the positive side and the negative side of the diaphragm are both of a cavity structure, namely a positive cavity and a negative cavity. While the surface capacity and shelving performance of the battery are ensured, the distance between battery electrodes is reduced, and the performance of the battery is further improved.

Description

Technical Field

[0001] The utility model relates to the technical field of liquid flow batteries, in particular to the field of zinc-based liquid flow batteries. Background Art

[0002] Renewable energy sources such as wind and solar energy are discontinuous and unstable, which can cause impacts on the power grid during the grid connection process, affecting the safe and stable operation of the grid. Energy storage technology can ensure the efficient and stable operation of renewable energy power generation and grid connection. Energy storage technology is mainly divided into two categories: physical energy storage and chemical energy storage. Among chemical energy storage, redox flow batteries, which are suitable for large-scale and large-capacity energy storage, have attracted widespread attention due to their advantages such as independent battery power and capacity, rapid response, simple structure, and easy design. Among them, zinc-based flow batteries have attracted widespread attention due to their high energy density, abundant raw material reserves, and low price. Zinc-based flow batteries mainly include zinc-bromine flow batteries, zinc-iron flow batteries, zinc-iodine flow batteries, zinc-nickel flow batteries, etc., and their negative electrodes undergo deposition and dissolution reactions of metallic zinc during the battery charging and discharging process. Due to the solid-phase reaction characteristics of metallic zinc liquid, the zinc deposition surface capacity of the negative electrode of zinc-based flow batteries is generally limited by the negative electrode zinc deposition space. In addition, in order to obtain a higher operating current density, the positive and negative electrode materials of zinc-based flow batteries generally use carbon felt, graphite felt, etc. as electrode materials. Since carbon felt can absorb a certain amount of electrolyte, this will cause zinc corrosion problems in zinc-based batteries during storage. The zinc corrosion reactions of alkaline and acidic zinc-based flow batteries are as follows:

[0003] Zn-2e ― +4OH ― →ZnO+H2O

[0004]

[0005] The existence of zinc corrosion problems will lead to a decrease in the discharge capacity of zinc-based batteries after they are shelved, affecting the overall efficiency of the battery. In addition, the use of electrode materials such as carbon felt and graphite felt has further increased the manufacturing cost of zinc-based flow batteries. The patent (CN202211549404.7) adopts a cavity structural design on the negative electrode side to increase the surface capacity of zinc-based flow batteries, reduce zinc corrosion, and improve battery shelving performance. However, carbon felt is still required on the positive electrode side of this structure, and it is necessary to add support to the negative electrode frame close to the diaphragm side surface to reduce the positive electrode contact resistance under this structure, which will increase the manufacturing cost of the battery. In addition, when carbon felt is used as a flow battery electrode, an electrolyte "dead zone" will be formed on the electrode, that is, the electrolyte flow rate in this area is very slow, which affects the mass transfer during the electrochemical reaction, resulting in a high resistance in this area, resulting in a high charging voltage and a low discharge voltage in this area, reducing the performance of the battery stack; long-term cyclic operation will also cause electrode penetration, leading to battery stack failure. Utility Model Content

[0006] The utility model proposes a zinc-based liquid flow battery structure, which adopts a cavity structure for both the positive and negative electrodes, thereby reducing the distance between the battery electrodes while ensuring the battery surface capacity and shelf performance, thereby further improving the battery performance.

[0007] The zinc-based liquid flow battery structural assembly includes an end plate, a positive electrode current collector, a separator, a negative electrode current collector, and an end plate stacked in sequence.

[0008] The zinc-based liquid flow battery structure has a cavity structure on both the positive and negative electrode sides.

[0009] A certain amount of carbon powder is sprayed on the surface of the current collector on the positive electrode side of the zinc-based liquid flow battery by spraying.

[0010] The carbon powder in the spray slurry is expanded graphite and activated carbon, wherein the mass ratio of expanded graphite to activated carbon is between 1:2 and 2:1, preferably 1:1.

[0011] The binder in the spray slurry is one of polyvinylidene fluoride (PVDF) or Nafion solution, preferably Nafion solution.

[0012] The mass ratio of carbon powder to binder in the spraying slurry is between 8:1 and 10:1, preferably 9:1.

[0013] The carbon powder loading on the positive electrode surface is 4-12 mg / cm 2 , preferably 8-10 mg / cm 2 , and preferably 10mg / cm 2 .

[0014] The thickness of the positive electrode cavity is 0.5-2 mm, preferably 0.5-1 mm, and more preferably 0.5 mm.

[0015] The thickness of the negative electrode cavity is 0.5-3 mm, preferably 2-2.5 mm, and more preferably 2.5 mm.

[0016] The roughness Ra of the negative electrode current collector is in the range of 60-100 μm, preferably 80-100 μm, and more preferably 90 μm.

[0017] Ra: Arithmetic mean deviation of the profile, the arithmetic mean of the absolute values ​​of the profile deviation within the sampling length.

[0018] The zinc-based liquid flow battery includes zinc-bromine liquid flow battery, zinc-iron liquid flow battery, zinc-iodine liquid flow battery, and zinc-nickel liquid flow battery.

[0019] At the same time, in order to solve the problem of fewer active sites for electrode reactions and greater battery polarization when the positive electrode uses a graphite plate current collector as the electrode, the utility model adopts a spraying method to spray a certain amount of carbon powder on the surface of the positive electrode side electrode to increase the active sites for positive electrode reactions and improve battery performance. In addition, since neither the positive nor the negative electrodes use carbon felt electrodes and support meshes, the manufacturing cost of the battery is further reduced. At the same time, by polishing the negative electrode graphite plate, the surface roughness of the electrode is increased, the adhesion of zinc to the electrode surface is improved, and the problem of negative electrode zinc shedding is solved. By adopting a cavity structure, the flow resistance of the electrolyte inside the battery stack is reduced, the "dead zone" of the flow inside the battery stack is eliminated, and the cycle stability of the battery stack is improved.

[0020] Beneficial effects of the utility model:

[0021] 1. By adopting a cavity structure for both the positive and negative electrodes, the battery surface capacity and shelf performance are guaranteed while reducing the distance between the battery electrodes, further improving the battery performance;

[0022] 2. By spraying carbon powder on the positive electrode side, the use of carbon felt electrodes is avoided. At the same time, there is no need to use a support mesh on the electrode frame to reduce the contact resistance between the carbon felt electrode and the graphite plate, further improving battery performance and reducing the cost of zinc-based liquid flow batteries.

[0023] 3. No carbon felt electrodes are required for both the positive and negative electrodes, which reduces the volume of the battery stack, further reduces the cost of zinc-based liquid flow batteries, reduces the flow resistance of the electrolyte inside the battery stack, eliminates the "dead zone" of flow inside the battery stack, and improves the cycle stability of the battery stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a structural diagram of a zinc-based flow battery.

[0025] Figure 2 Schematic diagram of the positive electrode side graphite plate current collector structure with a carbon powder layer.

[0026] Figure 3 Schematic diagram of the positive / negative electrode hollow ring gasket structure.

[0027] Among them: 1. positive electrode end plate, 2. positive electrode current collector, 3. positive electrode hollow ring gasket, 4. diaphragm, 5. negative electrode hollow ring gasket, 6. negative electrode current collector, 7. negative electrode end plate, 8. carbon powder layer. DETAILED DESCRIPTION

[0028] The zinc-based liquid flow battery structure in the following examples and comparative example 2 includes an end plate, a positive electrode current collector, a separator, a negative electrode current collector, and an end plate stacked in sequence.

[0029] The zinc-based flow battery structure is as follows Figure 1-3As shown, a gap is left between the positive electrode current collector and the separator, and a gap is left between the separator and the negative electrode current collector, so that the positive and negative electrode sides of the separator are both cavity structures, namely the positive electrode cavity and the negative electrode cavity.

[0030] There is no positive electrode in the gap between the positive electrode current collector and the separator, and there is no negative electrode in the gap between the separator and the negative electrode current collector, so that the zinc-based liquid flow battery structure is a zinc-based liquid flow battery structure without positive and negative electrodes;

[0031] The hollow annular gasket is used to separate the positive electrode current collector from the separator and the negative electrode current collector from the separator.

[0032] The gap between the positive electrode current collector and the separator serves as a chamber for accommodating the positive electrode electrolyte, and the gap between the separator and the negative electrode current collector serves as a chamber for accommodating the positive electrode electrolyte.

[0033] The thickness of the positive electrode cavity (the distance between the positive electrode current collector and the separator) is 0.5-2 mm, preferably 0.5-1 mm, and more preferably 0.5-0.8 mm.

[0034] The thickness of the negative electrode cavity (the distance between the negative electrode current collector and the separator) is 0.5-3 mm, preferably 2-2.5 mm, and more preferably 2.3-2.5 mm.

[0035] A carbon powder layer is sprayed on the surface of the current collector on the positive electrode side of the zinc-based liquid flow battery facing the diaphragm.

[0036] The carbon powder is a mixture of expanded graphite and activated carbon, wherein the mass ratio of expanded graphite to activated carbon is between 1:2 and 2:1, preferably 1:1 to 1.2.

[0037] The sprayed carbon powder layer also contains a binder, which is one or both of polyvinylidene fluoride (PVDF) and Nafion, preferably Nafion;

[0038] The mass ratio of carbon powder to binder in the spraying slurry is between 8:1-10:1, preferably 8.5-9:1.

[0039] The carbon powder loading on the positive electrode surface is 4-12 mg / cm 2 , preferably 8-10 mg / cm 2 , and preferably 9-10 mg / cm 2 .

[0040] The surface roughness Ra of the negative electrode current collector facing the separator is in the range of 60-100 μm, preferably 80-100 μm, and more preferably 85-90 μm.

[0041] Example 1

[0042] The cycling performance experiment of zinc-bromine flow battery was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as positive and negative electrolyte. The graphite plate was used as current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, Nafion solution is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5mm, and the surface roughness Ra of the negative electrode current collector before polishing is 10um. The surface of the negative electrode current collector close to the diaphragm is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 90um, and the thickness of the negative electrode cavity is 2.5mm. The diaphragm is a PE film, the electrolyte flow rate is 60ml / min, and the current density is 40mA / cm 2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the hollow ring gasket parallel to its surface is 48cm 2 .

[0043] Both the positive and negative sides use cavities, and the battery surface capacity can reach 120mAh / cm 2 The battery's charge and discharge curves are normal. CE is 98%, VE is 87%, and EE is 85%. Compared to batteries using carbon felt for the positive electrode and a cavity-type negative electrode, battery performance is improved. This is primarily due to the cavity-type structure of both the positive and negative electrodes, which further reduces the inter-electrode distance and reduces polarization.

[0044] Comparative Example 1

[0045] The zinc-bromine flow battery comprises an end plate, a positive electrode current collector, a positive electrode in a positive electrode frame, a separator, a negative electrode frame, a negative electrode current collector, and an end plate stacked in sequence;

[0046] The zinc-bromine flow battery cycle performance experiment was carried out using 2MZnBr2+3MKCl+0.8MMEP aqueous solution as the positive and negative electrolytes. The graphite plate was the current collector, the positive electrode of the battery was carbon felt (placed in the positive electrode frame), the negative electrode was a negative electrode frame with a cavity, and the surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing was 10um. The surface of the negative electrode current collector near the diaphragm side was polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode was 90um, the thickness of the negative electrode cavity was 2.5mm, and the negative electrode frame had a mesh support near the diaphragm side. The mesh support material was polyvinyl chloride with a thickness of 0.5mm, a total porosity of 50%, a single hole area of ​​5%, a PE film, an electrolyte flow rate of 60ml / min, and a current density of 40mA / cm 2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the positive electrode and the negative electrode frame parallel to its surface is 48cm 2 .

[0047] When the cavity is used on the negative electrode side, the battery surface capacity can reach 120mAh / cm 2 The battery charge and discharge curve is normal. Battery CE 97%, VE 85%, EE 82%.

[0048] Comparative Example 2

[0049] The cycling performance experiment of zinc-bromine flow battery was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as positive and negative electrolyte. The graphite plate was used as current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, PVDF is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5mm. The surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10um. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 90um, and the thickness of the negative electrode cavity is 2.5mm. The diaphragm is a PE film, the electrolyte flow rate is 60ml / min, and the current density is 40mA / cm 2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the hollow ring gasket parallel to its surface is 48cm 2 .

[0050] When PVDF is used as a binder, carbon powder may fall off and clog the battery during operation. This is mainly due to the poor bonding between PVDF and the graphite plate substrate.

[0051] Example 2

[0052] Sulfonated polyetheretherketone (SPEEK) ion conductive membrane is assembled into an alkaline zinc-iron flow battery. The graphite plate is the current collector. Both the positive and negative electrodes of the battery are hollow. The surface of the graphite plate current collector on the positive electrode side is sprayed with a 10mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, Nafion solution is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The positive electrode cavity thickness is 0.5mm, the negative electrode is a cavity, the surface roughness Ra of the negative electrode current collector is 10um, the negative electrode current collector is polished with sandpaper near the diaphragm, the sandpaper mesh number is 40, the surface roughness Ra of the negative electrode is 90um, and the cavity thickness is 2.5mm. The positive and negative electrode electrolyte compositions are both 0.3mol L -1 Na4Fe(CN)6+0.3mol L -1 K4Fe(CN)6+0.3mol L -1 Na2Zn(OH)4+2mol L - 1NaOH aqueous solution; positive electrode electrolyte volume 80mL; negative electrode electrolyte volume 80mL; battery charging conditions are time cut-off, at 40mA cm -2 Under the current density condition, the charging time is 30min, the standby time is 120h, and then the voltage is cut off, 40mA cm -2 The cross-sectional area of ​​the hollow region of the hollow annular gasket parallel to its surface is 48 cm 2 .

[0053] When both the positive and negative electrodes adopt cavities, the battery CE is 92% after 120 hours of storage. This is mainly because both the positive and negative electrodes adopt a cavity structure, which further reduces the battery electrode spacing and reduces battery polarization.

[0054] Comparative Example 3

[0055] The zinc-bromine flow battery comprises an end plate, a positive electrode current collector, a positive electrode placed in a positive electrode frame, a separator, a negative electrode frame, a negative electrode current collector, and an end plate, which are stacked in sequence;

[0056] Sulfonated polyetheretherketone (SPEEK) ion conductive membrane is assembled into an alkaline zinc-iron flow battery. The graphite plate is the current collector, the positive electrode of the battery is carbon felt (placed in the positive electrode frame), and the negative electrode is a hollow negative electrode frame. The surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10um. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 90um. The negative electrode frame has a mesh support near the diaphragm side. The mesh support material is polyvinyl chloride with a thickness of 0.5mm, a total porosity of 50%, and a single hole area of ​​5%. The electrolyte composition of the positive and negative electrodes is 0.3molL -1 Na4Fe(CN)6+0.3mol L -1 K4Fe(CN)6+0.3mol L -1 Na2Zn(OH)4+2mol L -1 NaOH; positive electrode electrolyte volume 80mL; negative electrode electrolyte volume 80mL; battery charging conditions are time cutoff, at 40mA cm -2 Under the current density condition, the charging time is 30min, the standby time is 120h, and then the voltage is cut off, 40mA cm -2 The cross-sectional area of ​​the hollow area of ​​the positive electrode and the negative electrode frame parallel to the surface is 48 cm 2 .

[0057] When the positive electrode side uses a carbon felt electrode and the negative electrode side is empty, the battery CE is 90% after 120 hours of storage.

[0058] Example 3

[0059] The zinc-bromine flow battery cycle performance experiment was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as the positive and negative electrolytes. The graphite plate was used as the current collector. The positive and negative electrodes of the battery were both hollow. The surface roughness Ra of the negative electrode current collector near the diaphragm side was 10um before polishing. The surface of the negative electrode current collector near the diaphragm side was polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode was 90um. The surface of the graphite plate current collector on the positive side was sprayed with a loading of 4mg / cm 2 , 6mg / cm 2 , 8mg / cm 2 、10mg / cm 2 , 12mg / cm 2 Carbon powder, with a mass ratio of expanded graphite to activated carbon of 1:1, Nafion solution as a binder, a mass ratio of carbon powder to binder of 9:1, and isopropyl alcohol as a solvent. The positive electrode cavity thickness is 0.5mm, and the negative electrode cavity thickness is 2.5mm. The separator is a PE film, the electrolyte flow rate is 60ml / min, and the current density is 40mA / cm 2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the hollow ring gasket parallel to its surface is 48cm 2 .

[0060] The battery performance is as follows:

[0061]

[0062] With the increase of carbon powder loading, the battery CE and VE both increase. This is mainly because with the increase of carbon powder loading, the battery inter-electrode distance becomes smaller and the electrode reaction active sites increase. When the electrode carbon powder loading reaches 10mg / cm 2 The battery performance reaches its optimum.

[0063] Example 4

[0064] The cycling performance experiment of zinc-bromine flow battery was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as positive and negative electrolyte. The graphite plate was used as current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:2, 1:1, and 2:1 respectively, Nafion solution is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5mm, and the surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10um. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 90um, and the thickness of the negative electrode cavity is 2.5mm. The diaphragm is a PE film, the electrolyte flow rate is 60ml / min, and the current density is 40mA / cm2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the hollow ring gasket parallel to its surface is 48cm 2 .

[0065] The battery performance is as follows:

[0066]

[0067] It can be seen from the battery data that the battery performance is optimal when the ratio of expanded graphite to activated carbon is 1:1. This is mainly because the reduction in expanded graphite content will reduce the conductivity of the carbon material, and the reduction in activated carbon content will reduce the reaction active sites of the electrode.

[0068] Example 5

[0069] The cycling performance experiment of zinc-bromine flow battery was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as positive and negative electrolyte. The graphite plate was used as current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, Nafion solution is used as a binder, the mass ratios of carbon powder to binder are 10:1, 9:1, and 8:1, respectively, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5 mm, and the surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10 μm. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40, the surface roughness Ra of the negative electrode is 90 μm, and the thickness of the negative electrode cavity is 2.5 mm. The diaphragm is a PE film, the electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm 2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the hollow ring gasket parallel to its surface is 48cm 2 .

[0070] The battery performance is as follows:

[0071] Toner to binder ratio CE / % VE / % EE / % 10:1 98 87 85 9:1 98 87 85 8:1 97 84 81

[0072] When the ratio of carbon powder to binder is 10:1 and 9:1, the battery performance is comparable. However, when the ratio is 10:1, carbon powder will fall off during battery operation, affecting the battery cycle stability. Further increasing the binder content will cause a decrease in battery CE and VE, which is mainly due to the decrease in electrode conductivity as the binder content increases.

[0073] Example 6

[0074] The cycling performance experiment of zinc-bromine flow battery was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as positive and negative electrolyte. The graphite plate was used as current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, Nafion solution is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5mm. The surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10um. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 60um, 70um, 80um90um, and 100um respectively. The thickness of the negative electrode cavity is 2.5mm. The diaphragm is a PE film, the electrolyte flow rate is 60ml / min, and the current density is 40mA / cm 2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the hollow ring gasket parallel to its surface is 48cm 2 .

[0075] The battery performance with different roughness of the negative electrode surface is as follows:

[0076]

[0077] From the performance of the battery using different roughness negative electrodes, it can be seen that when the untreated graphite plate is used as the current collector, the battery surface capacity is 20mAh / cm 2 Zinc shedding occurs when the negative electrode is charged, resulting in a low battery CE. Compared to a battery using a current collector with a roughness Ra of 90 μm, the battery CE is reduced by 15%. As the surface roughness of the negative electrode increases, the surface capacity and battery CE increase when zinc shedding occurs during charging. The battery performance is optimal when the negative electrode surface roughness Ra is 90 μm. This is primarily due to the increased adhesion of zinc to the electrode surface, which prevents the shedding of deposited zinc from the electrode surface during charging.

[0078] Example 7

[0079] The cycling performance experiment of zinc-bromine flow battery was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as positive and negative electrolyte. The graphite plate was used as current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10mg / cm 2Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, Nafion solution is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5mm, 1mm, 1.5mm, and 2mm respectively. The surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10um. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 90um, and the thickness of the negative electrode cavity is 2.5mm. The diaphragm is a PE film, the electrolyte flow rate is 60ml / min, and the current density is 40mA / cm 2 , charge for 3h, discharge to 0.1V. The cross-sectional area of ​​the hollow area of ​​the hollow ring gasket parallel to its surface is 48cm 2 The battery performance of different cathode cavity thicknesses is as follows:

[0080]

[0081] As the thickness of the positive electrode cavity increases, the battery VE decreases, which is mainly due to the increase in the thickness of the positive electrode cavity, the increase in the distance between the battery electrodes and the increase in the internal resistance of the battery.

[0082] Example 8

[0083] The cycling performance experiment of zinc-bromine flow battery was carried out with 2MZnBr2+3MKCl+0.8MMEP aqueous solution as positive and negative electrolyte. The graphite plate was used as current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, Nafion solution is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5mm, and the surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10um. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 90um. The thickness of the negative electrode cavity is 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, and 3mm respectively. The diaphragm is a PE film, the electrolyte flow rate is 60ml / min, and the charge and discharge current density is 40mA / cm 2 , discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket parallel to its surface is 48cm 2 .

[0084] The battery performance of different thicknesses of the negative electrode cavity is as follows:

[0085]

[0086]

[0087] As the thickness of the cathode cavity increases, the battery VE decreases. This is mainly due to the increase in the thickness of the cathode cavity, which increases the distance between the battery electrodes and the internal resistance of the battery. A low electrode frame thickness will also limit the surface capacity of the zinc negative electrode and reduce the surface capacity of the battery.

[0088] Example 9

[0089] A 10-cell zinc-bromine flow battery stack was assembled using 2MZnBr2+3MKCl+0.8MMEP aqueous solution as the positive and negative electrolytes. The graphite plate was used as the current collector. Both the positive and negative electrodes of the battery were hollow. The surface of the graphite plate current collector on the positive electrode side was sprayed with a 10 mg / cm 2 Carbon powder, the mass ratio of expanded graphite to activated carbon in the carbon powder is 1:1, Nafion solution is used as a binder, the mass ratio of carbon powder to binder is 9:1, and isopropyl alcohol is used as a solvent. The thickness of the positive electrode cavity is 0.5mm, and the surface roughness Ra of the negative electrode current collector near the diaphragm side before polishing is 10um. The surface of the negative electrode current collector near the diaphragm side is polished with sandpaper with a mesh size of 40. The surface roughness Ra of the negative electrode is 90um, and the thickness of the negative electrode cavity is 2.5mm. The diaphragm is a PE film, the electrolyte flow rate is 60ml / min, and the current density is 40mA / cm 2 , charge for 3h, discharge to 8V. The cross-sectional area of ​​the hollow region of the hollow annular gasket parallel to its surface is 1000cm 2 .

[0090] The stack efficiency is CE 98%, VE 87%, and EE 85%. The stack has maintained stable performance after 1,000 cycles.

[0091] Comparative Example 4

[0092] The zinc-bromine liquid flow battery comprises an end plate, a positive electrode current collector, a positive electrode placed in a positive electrode frame, a separator, a negative electrode placed in a negative electrode frame, a negative electrode current collector, and an end plate, which are stacked in sequence.

[0093] A 10-cell zinc-bromine flow battery stack was assembled using 2MZnBr2+3MKCl+0.8MMEP aqueous solution as the positive and negative electrolytes. The positive and negative electrode materials were carbon felt, the separator was PE film, the electrolyte flow rate was 60ml / min, and the current density was 40mA / cm 2 , charge for 3 hours and discharge to 8V. Electrode area 1000cm 2 The stack efficiency was 98% CE, 84% VE, and 82% EE. After 800 cycles, the stack developed an internal leak. Upon disassembly, the electrodes were found to be penetrated. This was primarily due to the use of carbon felt as electrodes, which creates an electrolyte "dead zone" on the electrodes. This area has a very slow electrolyte flow rate, which affects mass transfer during the electrochemical reaction, resulting in high resistance in this area and a high charging voltage. This long-term cycling can cause electrode penetration.

Claims

1. A zinc-based flow battery structure comprising a positive electrode current collector, a separator, and a negative electrode current collector stacked in sequence, characterized in that: A gap is left between the positive electrode current collector and the separator, and a gap is left between the separator and the negative electrode current collector, so that both the positive and negative electrode sides of the separator have a cavity structure, namely a positive electrode cavity and a negative electrode cavity.

2. The structure of the zinc-based flow battery according to claim 1, characterized in that: There is no positive electrode in the gap between the positive electrode current collector and the separator, and there is no negative electrode in the gap between the separator and the negative electrode current collector, so that the zinc-based liquid flow battery structure is a zinc-based liquid flow battery structure without positive and negative electrodes; The spacing between the positive electrode current collector and the separator and between the separator and the negative electrode current collector are respectively achieved by a hollow annular gasket or a hollow annular electrode frame; The gap between the positive electrode current collector and the separator serves as a chamber for accommodating the positive electrode electrolyte, and the gap between the separator and the negative electrode current collector serves as a chamber for accommodating the positive electrode electrolyte.

3. The structure of the zinc-based flow battery according to claim 1, characterized in that: The thickness of the positive electrode cavity, that is, the distance between the positive electrode current collector and the separator, is 0.5-2 mm.

4. The structure of the zinc-based flow battery according to claim 3, characterized in that: The thickness of the positive electrode cavity, that is, the distance between the positive electrode current collector and the separator, is 0.5-1 mm.

5. The structure of the zinc-based flow battery according to claim 1, characterized in that: The thickness of the negative electrode cavity, that is, the distance between the negative electrode current collector and the separator, is 0.5-3 mm.

6. The structure of the zinc-based flow battery according to claim 5, characterized in that: The thickness of the negative electrode cavity, that is, the distance between the negative electrode current collector and the separator, is 2-2.5 mm.

7. The structure of the zinc-based flow battery according to claim 1, 3 or 5, characterized in that: A carbon powder layer is sprayed on the surface of the current collector on the positive electrode side of the zinc-based liquid flow battery facing the diaphragm.

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