Zinc-based flow battery structure

Abstract

The zinc-based flow battery 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] This invention relates to the field of flow battery technology, and particularly to the field of zinc-based flow batteries. Background Technology

[0002] Renewable energy sources such as wind and solar power are characterized by their discontinuity and instability, which can impact the power grid during grid connection and affect its safe and stable operation. Energy storage technology can ensure the efficient and stable operation of renewable energy generation connected to the grid. Energy storage technology is mainly divided into two categories: physical energy storage and chemical energy storage. Among chemical energy storage technologies, redox flow batteries, suitable for large-scale and high-capacity energy storage, have received widespread attention due to their advantages such as independent battery power and capacity, rapid response, simple structure, and ease of design. Zinc-based flow batteries, in particular, 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, and zinc-nickel flow batteries, etc., in which metallic zinc undergoes a deposition and dissolution reaction at the negative electrode during battery charging and discharging. Due to the solid-phase reaction characteristics of zinc liquid, the capacity of the zinc deposition surface area at the negative electrode of zinc-based flow batteries is generally limited by the zinc deposition space. Furthermore, to obtain higher operating current densities, carbon felt or graphite felt are typically used as electrode materials for both the positive and negative electrodes of zinc-based flow batteries. Since carbon felt can absorb a certain amount of electrolyte, this can lead to zinc corrosion 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 presence of zinc corrosion leads to a decrease in the discharge capacity of zinc-based batteries after storage, affecting the overall efficiency of the battery. Furthermore, the use of electrode materials such as carbon felt and graphite felt further increases the manufacturing cost of zinc-based flow batteries. Patent (CN202211549404.7) improves the areal capacity of zinc-based flow batteries, reduces zinc corrosion, and enhances battery storage performance by employing a cavity structure on the negative electrode side. However, this structure still requires the use of carbon felt on the positive electrode side, and additional support needs to be added to the surface of the negative electrode frame near the separator to reduce the positive electrode contact resistance, both of which increase the battery manufacturing cost. Moreover, when using carbon felt as the electrode in a flow battery, an electrolyte "dead zone" forms on the electrode, where the electrolyte flow rate is very slow, affecting mass transfer during the electrochemical reaction. This results in higher resistance in this area, leading to higher charging voltage and lower discharging voltage, reducing stack performance. Long-term cyclic operation can also cause electrode penetration, leading to stack failure. Summary of the Invention

[0006] This invention proposes a zinc-based flow battery structure that uses cavities for both the positive and negative electrodes. This structure ensures battery surface capacity and shelf performance while reducing the distance between the electrodes, thereby further improving battery performance.

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

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

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

[0010] The carbon powder in the spraying 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 coating slurry is either polyvinylidene fluoride (PVDF) or Nafion solution, preferably Nafion solution.

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

[0013] The carbon powder loading on the surface of the positive electrode is 4-12 mg / cm³. 2 Preferred concentration: 8-10 mg / cm³ 2 Further optimization to 10mg / cm 2 .

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

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

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

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

[0018] The zinc-based flow batteries include zinc-bromine flow batteries, zinc-iron flow batteries, zinc-iodine flow batteries, and zinc-nickel flow batteries.

[0019] To address the issue of limited active sites and significant battery polarization when using graphite plate current collectors as the positive electrode, this invention employs a spraying method to coat the surface of the positive electrode with a certain amount of carbon powder, increasing the number of active sites and improving battery performance. Furthermore, since neither the positive nor negative electrode uses carbon felt electrodes or support mesh, battery manufacturing costs are further reduced. Simultaneously, by polishing the graphite plate of the negative electrode, the surface roughness is increased, improving the adhesion of zinc to the electrode surface and solving the problem of zinc detachment from the negative electrode. The use of a cavity structure reduces the flow resistance of the electrolyte within the stack, eliminating flow "dead zones" and improving the stack's cycle stability.

[0020] The beneficial effects of this invention are:

[0021] 1. By using a cavity structure for both positive and negative electrodes, the battery surface capacity and shelf performance are maintained while the distance between the battery electrodes is reduced, further improving battery performance.

[0022] 2. By using carbon powder spraying 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, which further improves battery performance and reduces the cost of zinc-based flow batteries.

[0023] 3. Neither the positive nor negative electrodes require carbon felt electrodes, reducing the stack volume, further reducing the cost of zinc-based flow batteries, reducing the flow resistance of the electrolyte inside the stack, eliminating the flow "dead zone" inside the stack, and improving the cycle stability of the stack. Attached Figure Description

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

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

[0026] Figure 3 This is a schematic diagram of the hollow annular gasket structure for the positive / negative electrode.

[0027] Among them: 1. Positive electrode plate, 2. Positive electrode current collector, 3. Positive electrode hollow annular gasket, 4. Separator, 5. Negative electrode hollow annular gasket, 6. Negative electrode current collector, 7. Negative electrode plate, 8. Carbon powder layer. Detailed Implementation

[0028] The zinc-based flow battery structures in the following embodiments and Comparative Example 2 include, in sequence, end plates, positive electrode current collectors, separators, negative electrode current collectors, and end plates.

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

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

[0031] Hollow annular gaskets are used to separate the positive current collector from the diaphragm and the diaphragm from the negative current collector.

[0032] The gap between the positive current collector and the diaphragm serves as a chamber for containing the positive electrolyte, and the gap between the diaphragm and the negative current collector serves as a chamber for containing the positive 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 even 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 diaphragm) is 0.5-3 mm, preferably 2-2.5 mm, and even more preferably 2.3-2.5 mm.

[0035] The zinc-based flow battery has a carbon powder layer sprayed onto the surface of the current collector side facing the separator.

[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 between 1:1 and 1.2.

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

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

[0039] The carbon powder loading on the surface of the positive electrode is 4-12 mg / cm³. 2 Preferred concentration: 8-10 mg / cm³ 2 Further optimization is needed at 9-10 mg / cm³. 2 .

[0040] The surface roughness Ra of the negative electrode current collector facing the diaphragm ranges from 60 to 100 μm, preferably 80 to 100 μm, and even more preferably 85 to 90 μm.

[0041] Example 1

[0042] Cyclic performance tests of a zinc-bromine flow battery were conducted using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. A graphite plate was used as the current collector, and both the positive and negative electrodes were cavities. A coating with a loading capacity of 10 mg / cm³ was sprayed onto the surface of the current collector on the positive electrode side. 2 The carbon powder contains expanded graphite in a 1:1 mass ratio with activated carbon. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as the solvent. The positive electrode cavity thickness is 0.5 mm. The surface roughness Ra of the negative electrode current collector before polishing is 10 μm. The surface of the negative electrode current collector near the separator is polished with 40-mesh sandpaper, resulting in a surface roughness Ra of 90 μm for the negative electrode. The negative electrode cavity thickness is 2.5 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm². 2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

[0043] Both the positive and negative electrode sides employ cavities, achieving a battery surface capacity of up to 120mAh / cm². 2 The battery charge / discharge curves are normal. The battery's CE is 98%, VE is 87%, and EE is 85%. Compared to batteries using carbon felt for the positive electrode and a cavity for the negative electrode, the battery performance is improved. This is mainly due to the cavity structure used for both the positive and negative electrodes, which further reduces the electrode spacing and thus reduces battery polarization.

[0044] Comparative Example 1

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

[0046] Cyclic performance tests of a zinc-bromine flow battery were conducted using a 2MZnBr2 + 3MKCl + 0.8MMEP aqueous solution as the positive and negative electrode electrolytes. A graphite plate was used as the current collector. The positive electrode was a carbon felt (placed within the positive electrode frame), and the negative electrode was a hollow negative electrode frame. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator was 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode was 90 μm. The negative electrode cavity thickness was 2.5 mm. The negative electrode frame near the separator had a mesh support made of 0.5 mm thick polyvinyl chloride (PVC) with a total porosity of 50% and a single pore area ratio of 5%. The separator was a PE membrane. The electrolyte flow rate was 60 ml / min, and the current density was 40 mA / cm². 2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the empty region parallel to its surface within the frames of the positive and negative electrodes is 48 cm². 2 .

[0047] When a cavity is used on the negative electrode side, the battery surface capacity can reach 120mAh / cm². 2 The battery charge / discharge curve is normal. Battery CE 97%, VE 85%, EE 82%.

[0048] Comparative Example 2

[0049] Cyclic performance tests of a zinc-bromine flow battery were conducted using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. A graphite plate was used as the current collector, and both the positive and negative electrodes were cavities. A coating with a loading capacity of 10 mg / cm³ was sprayed onto the surface of the current collector on the positive electrode side. 2 The carbon powder contains expanded graphite in a 1:1 mass ratio to activated carbon. PVDF is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as a solvent. The positive electrode cavity thickness is 0.5 mm. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator is 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode is 90 μm, and the negative electrode cavity thickness is 2.5 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm². 2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 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 adhesion between PVDF and the graphite substrate.

[0051] Example 2

[0052] An alkaline zinc-iron flow battery was assembled using a sulfonated polyetheretherketone (SPEEK) ion-conducting membrane. A graphite plate served as the current collector, and both the positive and negative electrodes were cavities. The current collector surface on the positive electrode side of the graphite plate was coated with a coating having a loading capacity of 10 mg / cm³. 2 The carbon powder contains expanded graphite in a 1:1 mass ratio to activated carbon. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as the solvent. The positive electrode cavity is 0.5 mm thick, and the negative electrode is hollow. The surface roughness Ra of the negative electrode current collector is 10 μm. The surface of the negative electrode current collector near the diaphragm is polished with 40-mesh sandpaper. The surface roughness Ra of the negative electrode is 90 μm, and the cavity thickness is 2.5 mm. The electrolyte composition for both positive and negative electrodes is 0.3 mol / L. -1 Na₄Fe(CN)₆ + 0.3 mol L -1 K4Fe(CN)6+ 0.3mol L -1 Na₂Zn(OH)₄ + 2mol L - 1NaOH aqueous solution; positive electrode electrolyte volume 80 mL; negative electrode electrolyte volume 80 mL; battery charging conditions: time cutoff, 40 mA cm⁻¹ -2 Under the current density conditions, the charging time is 30 minutes, the resting time is 120 hours, and then the voltage is cut off, with a current density of 40mA cm. -2 Discharged to 0.1V under the specified current density. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

[0053] When both the positive and negative electrodes use cavities, the battery CE is 92% after being left to stand for 120 hours. This is mainly because the positive and negative electrodes use a cavity structure, which further reduces the distance between the battery electrodes and reduces battery polarization.

[0054] Comparative Example 3

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

[0056] An alkaline zinc-iron flow battery was assembled using a sulfonated polyetheretherketone (SPEEK) ion-conducting membrane. A graphite plate served as the current collector. The positive electrode was a carbon felt (placed within the positive electrode frame), and the negative electrode was a hollow negative electrode frame. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator was 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode was 90 μm. The negative electrode frame near the separator had a mesh support made of 0.5 mm thick polyvinyl chloride (PVC) with a total porosity of 50% and a single pore area ratio of 5%. The electrolyte composition for both positive and negative electrodes was 0.3 mol / L. -1 Na₄Fe(CN)₆ + 0.3 mol L -1 K4Fe(CN)6+ 0.3mol L -1 Na₂Zn(OH)₄ + 2mol L -1 NaOH; positive electrode electrolyte volume 80 mL; negative electrode electrolyte volume 80 mL; battery charging conditions: time cutoff, 40 mA cm⁻¹ -2 Under the current density conditions, the charging time is 30 minutes, the resting time is 120 hours, and then the voltage is cut off, with a current density of 40mA cm. -2 Discharged to 0.1V under the specified current density. The cross-sectional area of ​​the empty region parallel to its surface within the frames of the positive and negative electrodes is 48 cm². 2 .

[0057] When a carbon felt electrode is used on the positive side and the cavity is used on the negative side, the CE of the battery is 90% after being left for 120 hours.

[0058] Example 3

[0059] Cyclic performance tests of a zinc-bromine flow battery were conducted using a 2MZnBr2 + 3MKCl + 0.8MMEP aqueous solution as the positive and negative electrode electrolytes. Graphite plates were used as current collectors, and both the positive and negative electrodes were cavities. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator was 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode was 90 μm. The surface of the graphite plate current collector on the positive electrode side was coated with a coating containing 4 mg / cm³ of precipitate. 2 6mg / cm 2 8mg / cm 2 10mg / cm 2 12mg / cm 2 The carbon powder contains expanded graphite in a 1:1 mass ratio with activated carbon. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as the solvent. The positive electrode cavity thickness is 0.5 mm, and the negative electrode cavity thickness is 2.5 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm². 2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

[0060] The battery performance is as follows:

[0061]

[0062] With the increase of carbon powder loading, both CE and VE of the battery increased. This is mainly due to the further reduction in the inter-electrode spacing and the increase in active sites of electrode reactions as the carbon powder loading increases. When the electrode carbon powder loading reaches 10 mg / cm³, the CE and VE values ​​also increase. 2 At that time, the battery performance reaches its optimal level.

[0063] Example 4

[0064] Cyclic performance tests of a zinc-bromine flow battery were conducted using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. A graphite plate was used as the current collector, and both the positive and negative electrodes were cavities. A coating with a loading capacity of 10 mg / cm³ was sprayed onto the surface of the current collector on the positive electrode side. 2 The carbon powder has an expanded graphite to activated carbon mass ratio of 1:2, 1:1, and 2:1. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as a solvent. The positive electrode cavity thickness is 0.5 mm. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator is 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode is 90 μm, and the negative electrode cavity thickness is 2.5 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm².2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

[0065] The battery performance is as follows:

[0066]

[0067] The battery data shows that the battery performance is optimal when the ratio of expanded graphite to activated carbon is 1:1. This is mainly because the reduction of expanded graphite content reduces the conductivity of carbon materials, and the reduction of activated carbon content reduces the reactive sites of the electrodes.

[0068] Example 5

[0069] Cyclic performance tests of a zinc-bromine flow battery were conducted using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. A graphite plate was used as the current collector, and both the positive and negative electrodes were cavities. A coating with a loading capacity of 10 mg / cm³ was sprayed onto the surface of the current collector on the positive electrode side. 2 The carbon powder contains expanded graphite in a 1:1 mass ratio with activated carbon. Nafion solution is used as a binder, with carbon powder to binder mass ratios of 10:1, 9:1, and 8:1. Isopropanol is used as the solvent. The positive electrode cavity thickness is 0.5 mm. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator is 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode is 90 μm, and the negative electrode cavity thickness is 2.5 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm². 2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

[0070] The battery performance is as follows:

[0071]

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

[0073] Example 6

[0074] Cyclic performance tests of a zinc-bromine flow battery were conducted using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. A graphite plate was used as the current collector, and both the positive and negative electrodes were cavities. A coating with a loading capacity of 10 mg / cm³ was sprayed onto the surface of the current collector on the positive electrode side. 2 The carbon powder contains expanded graphite in a 1:1 mass ratio with activated carbon. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as the solvent. The positive electrode cavity thickness is 0.5 mm. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator is 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode is 60 μm, 70 μm, 80 μm, 90 μm, and 100 μm, respectively. The negative electrode cavity thickness is 2.5 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm². 2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

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

[0076]

[0077] The battery performance data obtained from using negative electrode materials with different roughnesses shows that when using untreated graphite plates as current collectors, the battery surface capacity is 20 mAh / cm². 2 Zinc detachment occurs immediately, leading to a lower battery capacitance (CE). Compared to a current collector battery with a surface roughness Ra of 90 μm, the CE is reduced by 15%. As the surface roughness of the negative electrode increases, the areal capacity increases when zinc detachment occurs during charging, resulting in a higher CE. The battery performance is optimal when the surface roughness Ra is 90 μm. This is mainly because increased surface roughness increases the adhesion of zinc to the electrode surface, resolving the issue of zinc detachment during charging.

[0078] Example 7

[0079] Cyclic performance tests of a zinc-bromine flow battery were conducted using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. A graphite plate was used as the current collector, and both the positive and negative electrodes were cavities. A coating with a loading capacity of 10 mg / cm³ was sprayed onto the surface of the current collector on the positive electrode side. 2The carbon powder contains expanded graphite in a 1:1 mass ratio with activated carbon. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as the solvent. The thicknesses of the positive electrode cavity are 0.5mm, 1mm, 1.5mm, and 2mm. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator is 10µm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode is 90µm, and the negative electrode cavity thickness is 2.5mm. The separator is a PE membrane. The electrolyte flow rate is 60ml / min, and the current density is 40mA / cm³. 2 Charge for 3 hours, then discharge to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

[0080] The battery performance for different thicknesses of the positive electrode cavity is as follows:

[0081]

[0082] As the thickness of the positive electrode cavity increases, the battery resistance (VE) decreases. This is mainly due to the increased spacing between the battery electrodes and the increased internal resistance of the battery as the thickness of the positive electrode cavity increases.

[0083] Example 8

[0084] Cyclic performance tests of a zinc-bromine flow battery were conducted using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. A graphite plate was used as the current collector, and both the positive and negative electrodes were cavities. A coating with a loading capacity of 10 mg / cm³ was sprayed onto the surface of the current collector on the positive electrode side. 2 The carbon powder contains expanded graphite in a 1:1 mass ratio with activated carbon. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as a solvent. The positive electrode cavity thickness is 0.5 mm. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator is 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode is 90 μm. The negative electrode cavity thicknesses are 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, and 3 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the charge / discharge current density is 40 mA / cm². 2 Discharged to 0.1V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 48 cm². 2 .

[0085] The battery performance for different thicknesses of the negative electrode cavity is as follows:

[0086]

[0087]

[0088] As the thickness of the positive electrode cavity increases, the battery's energy density (VE) decreases. This is mainly due to the increased electrode spacing and internal resistance resulting from the increased thickness of the positive electrode cavity. Insufficient electrode frame thickness also limits the capacity of the zinc negative electrode, leading to a lower battery surface capacity.

[0089] Example 9

[0090] A stack of 10 zinc-bromine flow batteries was assembled using an aqueous solution of 2MZnBr2 + 3MKCl + 0.8MMEP as the positive and negative electrode electrolytes. Graphite plates were used as current collectors. Both the positive and negative electrodes were cavities. The surface of the current collector on the positive electrode side of the graphite plate was coated with a coating with a loading capacity of 10 mg / cm³. 2 The carbon powder contains expanded graphite in a 1:1 mass ratio with activated carbon. Nafion solution is used as a binder, with a carbon powder to binder mass ratio of 9:1. Isopropanol is used as the solvent. The positive electrode cavity thickness is 0.5 mm. Before polishing, the surface roughness Ra of the negative electrode current collector near the separator is 10 μm. After polishing with 40-mesh sandpaper, the surface roughness Ra of the negative electrode is 90 μm, and the negative electrode cavity thickness is 2.5 mm. The separator is a PE membrane. The electrolyte flow rate is 60 ml / min, and the current density is 40 mA / cm². 2 Charge for 3 hours, then discharge to 8V. The cross-sectional area of ​​the hollow region of the hollow annular gasket, parallel to its surface, is 1000 cm². 2 .

[0091] The fuel cell stack has an efficiency of CE 98%, VE 87%, and EE 85%. The stack exhibits stable performance after 1000 cycles.

[0092] Comparative Example 4

[0093] The zinc-bromine flow battery includes, in sequence, an end plate, a positive current collector, a positive electrode placed in a positive electrode frame, a separator, a negative electrode placed in a negative electrode frame, a negative current collector, and an end plate;

[0094] A stack of 10 zinc-bromine flow batteries was assembled using a 2MZnBr2 + 3MKCl + 0.8MMEP aqueous solution as the positive and negative electrode electrolytes. Both positive and negative electrode materials were carbon felt, and the separator was a PE membrane. The electrolyte flow rate was 60 ml / min, and the current density was 40 mA / cm². 2 Charge for 3 hours, then discharge to 8V. Electrode area 1000 cm² 2 .

[0095] The stack efficiency is CE 98%, VE 84%, and EE 82%. Internal leakage appeared after 800 cycles of operation. Upon disassembly, electrode penetration was found. This was mainly due to the use of carbon felt electrodes, which created electrolyte "dead zones" on the electrodes. These zones had very slow electrolyte flow rates, affecting mass transfer during the electrochemical reaction, leading to higher resistance and higher charging voltage. Prolonged cycling ultimately caused 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 sequentially, characterized in that: A gap is left between the positive current collector and the diaphragm, and a gap is left between the diaphragm and the negative current collector, so that both the positive and negative sides of the diaphragm are cavity structures, namely positive cavity and negative cavity.

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

3. The zinc-based flow battery structure according to claim 1, characterized in that: 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 even more preferably 0.5-0.8 mm.

4. The zinc-based flow battery structure according to claim 1, characterized in that: The thickness of the negative electrode cavity (the distance between the negative electrode current collector and the diaphragm) is 0.5-3 mm, preferably 2-2.5 mm, and even more preferably 2.3-2.5 mm.

5. The zinc-based flow battery structure according to claim 1, 3, or 4, characterized in that: The zinc-based flow battery has a carbon powder layer sprayed onto the surface of the current collector side facing the separator.

6. The zinc-based flow battery structure according to claim 5, characterized in that: 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 between 1:1 and 1.

2.

7. The zinc-based flow battery structure according to claim 5, characterized in that: The sprayed carbon powder layer also contains a binder, which is one or two of polyvinylidene fluoride (PVDF) or Nafion, preferably Nafion; The mass ratio of carbon powder to binder in the spray coating slurry is between 8:1 and 10:1, preferably between 8.5 and 9:

1.

8. The zinc-based flow battery structure according to claim 5, characterized in that: The carbon powder loading on the surface of the positive electrode is 4-12 mg / cm³. 2 Preferred concentration: 8-10 mg / cm³ 2 Further optimization is needed at 9-10 mg / cm³. 2 .

9. The zinc-based flow battery structure according to claim 1, 3, or 4, characterized in that: The surface roughness Ra of the negative electrode current collector facing the diaphragm ranges from 60 to 100 μm, preferably 80 to 100 μm, and even more preferably 85 to 90 μm.

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