A high face capacity zinc-bromine redox flow battery

Abstract

The application relates to a high surface capacity zinc-bromine double liquid flow battery and belongs to the field of liquid flow batteries. The zinc-bromine double liquid flow battery is provided with a layer of non-conductive, chemically stable and dense plastic fiber between the positive electrode and the diaphragm. In the charging process of the battery, the zinc dendrites of the negative electrode grow along the micropores of the diaphragm to the positive electrode. The zinc dendrites growing to the positive electrode are blocked by the dense plastic fiber and do not contact the positive electrode, so that the short circuit in the battery is avoided. Therefore, the surface capacity of the negative electrode can be increased, and the surface capacity of the battery is further increased. The fiber membrane can be composed of one or several materials of PE, PP and PVC. When the battery is assembled, the fiber membrane is only needed to be placed between the positive electrode and the diaphragm in sequence. The method is simple in operation, low in cost, obvious in effect, significantly improves the surface capacity of the battery and effectively improves the energy density of the zinc-bromine double liquid flow battery.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to a high areal capacity zinc-bromine dual-flow battery. Technical Background

[0002] Zinc-bromine dual-flow energy storage battery is a new type of low-cost, high-efficiency, and environmentally friendly flow energy storage battery. It has advantages such as high energy density and current efficiency, simple and easy-to-operate device, long service life, and low cost. It is mainly used in grid peak shaving, renewable energy power generation such as wind and solar power, electric vehicles and other fields.

[0003] For zinc-bromine flow batteries, because the battery separator uses a porous ion-conducting membrane, during the charging process of elemental zinc at the negative electrode, the zinc dendrites grow along the micropores of the separator and eventually reach the positive electrode. When these zinc dendrites come into contact with the positive electrode, a short circuit occurs, rendering the stack inoperable and resulting in a low cycle life. To avoid short circuits between the positive and negative electrodes and reduce zinc dendrite formation, the battery's charging capacity must be reduced. These issues are the main reasons limiting the relatively low capacity of zinc-bromine batteries. Summary of the Invention

[0004] To address the above technical problems, this invention, taking into account the structural characteristics of a zinc-bromine dual-flow battery, adds a layer of plastic fiber membrane between the positive electrode and the separator to prevent short circuits caused by zinc dendrites from the negative electrode growing through the micropores of the separator to the positive electrode during charging. This prevents zinc dendrites from contacting the positive electrode, avoids short circuits, improves the battery's cycle life, and also increases the battery's charging capacity.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A high-area-capacity zinc-bromine dual-flow battery includes a stack consisting of one or more single cells connected in series, an electrolyte storage tank, and each single cell includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. The electrolyte in the electrolyte storage tank circulates in the chambers containing the positive and negative electrodes of the zinc-bromine dual-flow battery. A plastic fiber membrane is disposed between the positive electrode and the separator, and the plastic fiber membrane is arranged parallel to the positive electrode and the separator. The plastic fiber membrane has a porous structure and a thickness of 0.5 mm to 0.8 mm.

[0007] Based on the above scheme, preferably, the pore size of the plastic fiber membrane is 0.5um to 1.5um, and the porosity is 60% to 95%.

[0008] Based on the above scheme, preferably, in the pore structure of the plastic fiber membrane, macropores of 1µm to 1.5µm account for 70-90% of the total pore volume; and the porosity of the plastic fiber membrane is 70-90%.

[0009] Based on the above scheme, preferably, the material of the plastic fiber film is one of PE, PP, and PVC.

[0010] Based on the above scheme, preferably, the area of ​​the plastic fiber membrane is not less than the area of ​​the battery positive electrode.

[0011] Based on the above scheme, preferably, the diaphragm is a porous membrane with a pore size of 80nm to 120nm and a porosity of 60% to 70%; the diaphragm thickness is 800um to 1000um.

[0012] Based on the above scheme, preferably, the positive and negative electrode electrolytes of the zinc-bromine dual-flow battery are both neutral aqueous solutions containing zinc ions, the zinc and bromine raw materials are zinc bromide, the zinc ion concentrations in the positive and negative electrode electrolytes are the same, and the supporting electrolyte KCl concentrations are the same, the zinc ion concentration in the electrolyte is 2-4 mol / L, and the KCl concentration is 2-5 mol / L.

[0013] As a further explanation, when the zinc-bromine dual-flow battery provided by the present invention is a single cell, its structure is as follows: from the positive electrode side to the negative electrode side, the components are arranged in sequence: positive electrode plate, positive electrode current collector, positive electrode frame, positive electrode, plastic fiber membrane, separator, negative electrode, negative electrode frame, negative electrode current collector, and negative electrode plate; the positive electrode electrolyte is sealed in a closed cavity formed by the positive electrode frame, the positive electrode current collector (graphite plate), and the battery separator; the electrolyte in the electrolyte storage tank of the zinc-bromine dual-flow battery flows in the positive and negative electrode cavities by a pump; and an ion exchange membrane (separator) is provided between the positive and negative electrodes.

[0014] During battery charging, elemental zinc is deposited on the negative electrode substrate. When the deposition amount is large enough, zinc dendrites grow along the micropores of the separator and penetrate the separator to reach the positive electrode side. The zinc dendrites growing on the positive electrode side first contact the plastic fiber membrane. The plastic fiber has water-absorbing, oxidation-resistant, and non-conductive properties. When elemental zinc comes into contact with the plastic fiber, bromine adsorbed in the fiber reacts with the zinc dendrites, causing a redox reaction that consumes the grown zinc. This prevents further growth of zinc dendrites, which could cause a short circuit upon contact with the positive electrode, and also further increases the battery's areal capacity. During battery charging, the slope of the charging curve is observed. When the slope of the charging curve decreases significantly, the charging capacity at this point is the battery's maximum charging capacity. Batteries assembled using this method show a significant increase in capacity, completely solving the problem of low areal capacity in zinc-bromine single-flow batteries and greatly improving battery energy density. This method is simple to operate, low in cost, and has significant effects.

[0015] The beneficial effects of this invention are:

[0016] (1) This invention addresses the problem of limited battery capacity caused by zinc dendrites growing from the negative electrode to the positive electrode through the micropores of the separator during battery charging. The invention employs a plastic fiber membrane with strong oxidation resistance and non-conductivity between the positive electrode and the battery separator to prevent zinc dendrites from directly contacting the positive electrode. Plastic fibers have advantages such as oxidation resistance, density, water absorption, and low cost. The plastic fiber membrane can effectively block zinc dendrites that grow from the negative electrode to the positive electrode, thus avoiding direct contact between the zinc dendrites that grow to the positive electrode and the positive electrode, which would cause a short circuit.

[0017] (2) Unlike zinc-bromine single-flow batteries, in dual-flow batteries, the electrolyte at the positive electrode is always in a flowing state during operation. The electrolyte in the positive electrode cavity of the battery is always flowing. If zinc dendrites grow from the negative electrode to the positive electrode through the separator, the zinc dendrites will first come into contact with the plastic fibers. These zinc dendrites will quickly react with the bromine on the surface of the plastic fibers and be consumed. Therefore, in dual-flow batteries, the plastic fibers installed in the positive electrode can be made as thin as possible.

[0018] (3) In the zinc-bromine dual-flow battery provided by this invention, the elemental bromine adsorbed in the plastic fiber membrane can rapidly oxidize the zinc dendrites that come into contact with the plastic fiber membrane. This protects the battery from short circuits before it reaches its maximum capacity, significantly increasing battery capacity and effectively improving battery energy density while ensuring normal battery operation. This method is low-cost, fast-acting, and simple to operate. It quickly and efficiently solves the problems of low capacity and low energy density in zinc-bromine dual-flow batteries, thus promoting the development of zinc-bromine flow batteries. Attached Figure Description

[0019] Figure 1 The data represents the cycle stability of the zinc-bromine dual-flow battery in Example 1. Detailed Implementation

[0020] The following detailed description, in conjunction with specific embodiments, aims to make the advantages and features of the present invention more readily understood by those skilled in the art. The raw materials used in the following embodiments and comparative examples are all commercially available conventional products. The diaphragm used is a daramic membrane, made of PE material, with a pore size of 80nm–120nm, a porosity of 70%, and a thickness of 900µm.

[0021] Example 1

[0022] The battery electrolyte is 2 mol / L ZnBr2 + 3 mol / L KCl + 0.8 M MEP (N-methyl-N-ethylpyrrolidine salt). The single cell consists of a positive electrode plate and a 6x6 cm positive electrode. 2Graphite plate, positive electrode frame, carbon felt, PE fiber membrane (pore size range 0.5um~1.0um, porosity 85%, thickness 0.8mm), separator, carbon felt, negative electrode frame, negative electrode 6x6cm 2 Graphite plate, negative electrode plate. Electrolyte flows between the positive and negative electrode chambers via a circulation pump. Charge / discharge current density: 40 mA / cm². 2 The maximum charging capacity is 160mAh / cm². 2 Battery performance is shown in Table 1.

[0023] Battery cycle performance such as Figure 1 As shown, the battery exhibited excellent stability during operation, running continuously and stably for 1050 cycles without performance degradation. This data indicates that the zinc dendrites growing through the micropores of the battery separator to the positive electrode were effectively blocked by the PE fiber membrane of the positive electrode and reacted with the elemental bromine in the positive electrode, thus preventing short circuits between the positive and negative electrodes and effectively extending battery life.

[0024] Example 2

[0025] The battery electrolyte is 2 mol / L ZnBr2 + 3 mol / L KCl + 0.8 M MEP. The single cell consists of a positive electrode plate and a 6x6 cm positive electrode. 2 Graphite plate, positive electrode frame, carbon felt, PP fiber membrane (pore size range 1.0um~1.5um, porosity 90%, thickness 0.8mm), separator, carbon felt, negative electrode frame, negative electrode 6x6cm 2 Graphite plate, negative terminal plate. During battery operation, the electrolyte flows between the positive and negative electrode chambers via a circulation pump. Charge / discharge current density: 40 mA / cm². 2 The maximum charging capacity is 160mAh / cm². 2 Battery performance is shown in Table 2.

[0026] As shown in Tables 1-2, by adding the plastic fiber membrane of this invention between the positive electrode and the separator, the maximum charging capacity of the battery can reach 160 mAh / cm². 2 And the performance is almost unaffected (compared to charging conditions with low areal capacity).

[0027] Comparative Example 1

[0028] The battery electrolyte is 2 mol / L ZnBr2 + 3 mol / L KCl + 0.8 M MEP. The single cell consists of a positive electrode plate and a 6x6 cm positive electrode. 2 Graphite plate, positive electrode frame, carbon felt, diaphragm, carbon felt, negative electrode frame, negative electrode 6x6cm 2 Graphite plate, negative terminal plate. During battery operation, the electrolyte flows between the positive and negative electrode chambers via a circulation pump. Charge / discharge current density: 40 mA / cm². 2The maximum charging capacity is 100mAh / cm². 2 Battery performance is shown in Table 3.

[0029] As shown in Table 3 regarding battery performance, without a plastic fiber membrane between the positive electrode and the separator, increasing the battery's charging surface capacity significantly reduces its performance, indicating a damaged battery. This is because zinc dendrites from the negative electrode grow through the separator's micropores to the positive electrode, causing a short circuit. The internal short-circuit current generates high temperatures, burning out the battery.

[0030] Comparative Example 2

[0031] The battery electrolyte is 2 mol / L ZnBr2 + 3 mol / L KCl + 0.8 M MEP. The single cell consists of a positive electrode plate and a 6x6 cm positive electrode. 2 Graphite plate, positive electrode frame, carbon felt, PP fiber membrane (pore size range of 1um to 1.5um, porosity of 90%, thickness of 3mm), separator, carbon felt, negative electrode frame, negative electrode 6x6cm 2 Graphite plate, negative terminal plate. During battery operation, the electrolyte flows between the positive and negative electrode chambers via a circulation pump. Charge / discharge current density: 40 mA / cm². 2 The maximum charging capacity is 160mAh / cm². 2 Battery performance is shown in Table 4.

[0032] As shown in Table 4 regarding battery performance, increasing the thickness of the plastic fiber membrane significantly reduces battery performance. Increasing the thickness of the plastic fiber membrane is equivalent to increasing the distance between the positive and negative electrodes, leading to increased battery polarization and reduced performance. Because the positive electrode capacity of a zinc-bromine dual-flow battery is not limited by the electrolyte volume, and the electrolyte at the positive electrode remains in a flowing state, elemental bromine in the positive electrode reacts more readily with zinc dendrites growing from the negative electrode through the micropores of the separator. Therefore, the plastic fiber membrane added to the positive electrode in a zinc-bromine dual-flow battery can be thinned, avoiding the performance degradation caused by the introduction of the plastic fiber membrane.

[0033] Comparative Example 3 (Single Flow Cell)

[0034] The battery electrolyte is 2 mol / L ZnBr2 + 3 mol / L KCl + 0.8 M MEP. The single cell has a positive electrode plate and a 6x6 cm positive electrode. 2 Graphite plate, positive electrode frame, carbon felt, PE fiber membrane (pore size range 0.1um~0.2um, porosity 85%, thickness 1mm), separator, carbon felt, negative electrode frame, negative electrode 6x6cm 2 Graphite plate, negative terminal plate. The positive electrolyte is sealed within a closed cavity formed by the positive electrode frame, the positive current collector (graphite plate), and the battery separator, and the positive electrolyte does not flow. Charge / discharge current density: 40 mA / cm². 2The maximum charging capacity is 100mAh / cm². 2 Battery performance is shown in Table 5.

[0035] As shown in Table 5, the dual-flow battery outperforms the zinc-bromine single-flow battery with the same battery structure. Because the positive electrode electrolyte volume in the dual-flow battery is sufficiently large, the positive electrode capacity is not limited. Therefore, compared to the zinc-bromine single-flow battery with the same battery structure, the dual-flow battery has a higher capacity. Table 5 also shows that the zinc-bromine single-flow battery assembled using the method of this invention achieves a maximum capacity of 100 mAh / cm³. 2 (Under the premise of stable and normal performance), this capacity is far smaller than that of a dual-flow battery. Zinc-bromine dual-flow batteries have advantages, including higher energy density.

[0036] Table 1. Performance results of the zinc-bromine dual-flow battery in Example 1

[0037]

[0038] Table 2. Performance results of the zinc-bromine dual-flow battery in Example 2

[0039]

[0040]

[0041] Table 3. Performance results of the zinc-bromine dual-flow battery in Comparative Example 1

[0042]

[0043] Table 4. Performance results of the zinc-bromine dual-flow battery in Comparative Example 2

[0044]

[0045] Table 5. Performance results of the zinc-bromine single-liquid-flow battery in Comparative Example 3

[0046]

Claims

1. A high-area-capacity zinc-bromine dual-flow battery, wherein the zinc-bromine dual-flow battery comprises an electrolyte storage tank, a stack consisting of one or more single cells connected in series, each single cell comprising a positive electrode, a negative electrode, and a separator between the positive and negative electrodes, and the electrolyte in the electrolyte storage tank circulates within the chambers containing the positive and negative electrodes of the zinc-bromine dual-flow battery, characterized in that: A plastic fiber membrane is disposed between the positive electrode and the separator, and the plastic fiber membrane is arranged parallel to the positive electrode and the separator; the plastic fiber membrane has a porous structure and a thickness of 0.5 mm to 0.8 mm; The plastic fiber membrane has a pore size of 0.5 μm to 1.5 μm and a porosity of 60% to 95%. In the pore structure of the plastic fiber membrane, macropores of 1µm to 1.5µm account for 70-90% of the total pore volume; the porosity of the plastic fiber membrane is 70-90%. The plastic fiber film is made of one of PE, PP, or PVC. The area of ​​the plastic fiber membrane is not less than the area of ​​the positive electrode of the battery.

2. The zinc-bromine dual-flow battery according to claim 1, characterized in that: The diaphragm is a porous membrane with a pore size of 80nm to 120nm and a porosity of 60% to 70%; the diaphragm thickness is 800um to 1000um.

3. The zinc-bromine dual-flow battery according to claim 1, characterized in that: The zinc-bromine dual-flow battery uses neutral aqueous solutions containing zinc ions in both the positive and negative electrodes. The zinc and bromine raw materials are zinc bromide. The zinc ion concentration in the positive and negative electrode electrolytes is the same, and the supporting electrolyte KCl concentration is the same. The zinc ion concentration in the electrolyte is 2-4 mol / L, and the KCl concentration is 2-5 mol / L.

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