Composite electrode structure and zinc-bromine flow battery

Abstract

The utility model belongs to the technical field of flow battery energy storage, and particularly relates to a composite electrode structure and a zinc-bromine flow battery. The electrode comprises two carbon felts which are arranged in a laminated mode and a zinc sheet located between the two carbon felts, or more than two zinc sheets which are arranged between the two carbon felts in a laminated mode and are separated by the carbon felts. And a through hole is formed in the zinc sheet. The zinc sheet is placed in the middle of the negative electrode carbon felt, zinc can be induced to preferentially deposit on the zinc sheet in the charging process of the zinc-bromine flow battery, a deposition interface of the zinc is regulated to the interior of the carbon felt and is far away from a diaphragm, and the influence of zinc dendrites can be effectively inhibited.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of flow battery energy storage, especially relates to a zinc-bromine flow battery structure. BACKGROUND

[0002] Zinc-bromine flow battery is a kind of low-cost, high-safety flow battery energy storage technology, and has higher energy density.The negative electrode is the deposition and dissolution reaction of zinc, and is converted into zinc element deposition on the electrode from zinc ion when charging, and is converted into zinc ion when discharging, and is free in electrolyte.Zinc-bromine flow battery belongs to deposition battery, so the deposition capacity of negative electrode zinc restricts the performance and cycle stability of battery.If the deposited zinc is excessive, zinc dendrite will be generated, the zinc dendrite will pierce diaphragm, and battery short circuit failure will be caused, so how to inhibit the generation of zinc dendrite is the key to develop zinc-bromine flow battery technology. CONTENT OF UTILITY MODEL

[0003] To solve the above technical problem, the utility model aims at providing a zinc-bromine flow battery electrode structure.

[0004] To achieve the above object, the utility model adopts the following technical scheme:

[0005] The electrode includes two pieces of carbon felt arranged in layers and one piece of zinc sheet located between the two pieces of carbon felt, or two or more pieces of zinc sheets separated by carbon felt arranged in layers between the two pieces of carbon felt; a through hole is provided on the zinc sheet.The zinc sheet and the carbon felt are alternately and sequentially stacked, and the zinc sheet is placed between the two pieces of carbon felt or two or more pieces of zinc sheets separated by one piece of carbon felt arranged in layers between the two pieces of carbon felt.The number of carbon felt in the composite electrode is between 2 and 4 pieces, the number of zinc sheet is between 1 and 3 pieces, the number of carbon felt is equal to the number of zinc sheet, and the zinc sheet and the carbon felt are alternately and sequentially stacked.A through hole is provided on the zinc sheet, the diameter of the through hole is between 5mm and 20mm, and the opening rate of the surface of the zinc sheet is between 20% and 50%.The thickness of the carbon felt is between 2mm and 5mm, and the thickness of the zinc sheet is between 0.5mm and 2mm.The negative electrode adopts any one of the composite electrode structures, the composite electrode is placed in the middle cavity of the battery annular electrode frame, an inlet and outlet flow channel is provided on the electrode frame, the electrolyte flows into the composite electrode in the middle cavity from the inlet flow channel, and then flows out of the electrode frame through the outlet flow channel.When assembling the battery, the thickness of the composite electrode is 110%-125% of the thickness of the electrode frame (the thickness of the composite electrode in the embodiment and the comparative example is 115% of the thickness of the electrode frame), and after assembling the battery, the composite electrode is compressed to be consistent with the thickness of the electrode frame;The porosity of the carbon felt of the composite electrode before compression is between 0.85 and 0.9, and the porosity of the carbon felt of the composite electrode after compression is between 0.4 and 0.5.

[0006] The composite electrode is used as a negative electrode of a zinc-bromine flow battery, and cannot be used as a positive electrode, and the positive electrode still uses a traditional flat carbon felt electrode structure.

[0007] The utility model has the beneficial effect as follows:

[0008] Placing zinc sheets in the middle of the negative carbon felt can induce the zinc-bromine flow battery to preferentially deposit zinc on the zinc sheets during the charging process, and regulate the deposition interface of zinc to the inside of the carbon felt, away from the separator, which can effectively inhibit the influence of zinc dendrites. In addition, the deposition of zinc is induced inside the carbon felt, and during the reaction process, the elemental zinc is protected by the extrusion stress of the carbon felt, which can effectively prevent the zinc from falling off and enhance the reliability of the stack, thereby improving the performance of the stack. In addition, the zinc sheets must be provided with a porous structure so as not to affect the mass transfer of the battery, but the porosity should not be too large, which will reduce the specific surface area of the zinc sheets and the deposition sites of zinc. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the embodiments of the utility model, the following will briefly introduce the drawings involved in the embodiments.

[0010] Figure 1 The figure is a schematic diagram of the zinc-bromine flow battery electrode of the utility model. DETAILED DESCRIPTION

[0011] The utility model will be described in detail below in combination with the embodiments, but the implementation of the utility model is not limited thereto, and obviously, the embodiments described below are only some embodiments of the utility model, and for those skilled in the art, other similar embodiments can be obtained without creative labor, which fall within the protection scope of the utility model.

[0012] The utility model discloses a zinc bromine liquid flow battery composite electrode structure, the electrode includes two carbon felt of laminated arrangement and the zinc piece of 1 piece between two carbon felts, or the more than 2 pieces of zinc piece of spacing between two carbon felts of carbon felt spacing between two carbon felts is laminated arrangement, and the through -hole of vertical zinc piece surface is provided on the zinc piece. Among them, zinc piece and carbon felt are alternately laminated and placed in turn, and the zinc piece is placed between two carbon felts, or the more than 2 pieces of zinc piece of spacing between two carbon felts of carbon felt spacing between two carbon felts is laminated arrangement. The number of carbon felt of composite electrode is between 2-4 pieces, and the number of zinc piece is between 1-3 pieces, and the number of carbon felt-number of zinc piece=1, and zinc piece and carbon felt are alternately laminated and placed in turn. The through -hole of vertical zinc piece surface is provided on the zinc piece, and the diameter of through -hole is between 5mm-20mm, and the opening rate of zinc piece surface is between 20% to 50%. The thickness of carbon felt is between 2mm-5mm, and the thickness of zinc piece is between 0.5mm-2mm. The negative pole adopts any one of the composite electrode structures, and the composite electrode is placed in the middle cavity of the battery annular electrode frame, and the length and width of the electrode are matched with the middle cavity region in the annular electrode frame, and the inlet and outlet flow channels are arranged on the electrode frame, and the electrolyte flows into the composite electrode in the middle cavity from the inlet flow channel, and then flows out of the electrode frame through the outlet flow channel. When assembling the battery, the thickness of the composite electrode is 110%-125% of the thickness of the electrode frame, and after assembling the battery, the composite electrode is compressed to be consistent with the thickness of the electrode frame, and the porosity of the carbon felt of the composite electrode before compression is between 0.85-0.9, and the porosity of the carbon felt of the composite electrode after compression is between 0.4-0.5.

[0013] Any one of the above electrode structures is only used for the negative pole of the zinc bromine liquid flow battery, and the positive pole still adopts the traditional electrode structure single flat carbon felt electrode. The positive electrode is placed in the middle cavity of the battery annular electrode frame, and the length and width of the carbon felt electrode used are matched with the middle cavity region in the annular electrode frame, and the inlet and outlet flow channels are arranged on the electrode frame, and the electrolyte flows into the electrode in the middle cavity from the inlet flow channel, and then flows out of the electrode frame through the outlet flow channel. The porosity of the carbon felt electrode is 0.9, and the porosity of the carbon felt electrode after compression is 0.5. The thickness of carbon felt is 5mm.

[0014] The embodiments and comparative examples in the utility model are experimented under the following conditions:

[0015] The electrolyte is the aqueous solution of 2mol / l zinc bromide solution, 3mol / l potassium chloride solution and 0.4mol / l MEP complexing agent. The diaphragm is commercial Daramic porous diaphragm, and the areas of the negative carbon felt electrode and the positive carbon felt electrode are respectively 800cm 2 The zinc piece and the carbon felt electrode used in the utility model are rectangular, and the length and width of the zinc piece and the carbon felt electrode used are matched with the hollow region in the annular electrode frame, that is, the surface shape and size of the zinc piece and the carbon felt electrode are the same.

[0016] Comparative example 1

[0017] Comparative Example 1 uses a traditional electrode structure as the negative electrode to assemble a zinc-bromine flow battery. The electrode is composed of a single carbon felt, which is placed in the central cavity of the battery's annular electrode frame. The length and width of the carbon felt electrode used match the central cavity area inside the annular electrode frame. Inlet and outlet flow channels are provided on the electrode frame. The electrolyte flows from the inlet flow channel into the electrode in the central cavity and then flows out of the electrode frame through the outlet flow channel. The porosity of the carbon felt electrode is 0.9 (before compression, the same below), and the porosity of the carbon felt electrode after compression is 0.5. The specific parameters of the battery stack are as follows:

[0018] Electrode area: 800cm 2 ;

[0019] Positive and negative electrode carbon felt thickness before compression: 5mm;

[0020] Number of battery stacks: 20;

[0021] Current density: 40mA / cm 2 , charging time: 3 hours, discharge cut-off voltage: 16V;

[0022] Battery cycle performance: Coulomb efficiency 86.2%, voltage efficiency 81.9%, energy efficiency 70.6%; the performance of Comparative Example 1 is lower. This is because zinc is deposited on the surface of the carbon felt, zinc dendrites gradually accumulate, and since zinc is generated on the surface, it is easy to fall off after being washed by the electrolyte, resulting in faster degradation of battery performance.

[0023] Comparative Example 2

[0024] Comparative Example 2 uses a composite electrode structure as the negative electrode to assemble a zinc-bromine flow battery. When assembling the battery, the thickness of the composite electrode is 115% of the thickness of the electrode frame, wherein the number of carbon felts is 1, and a zinc sheet is placed on the bottom side of the carbon felt. A through hole is set on the zinc sheet, the through hole diameter is 10mm, the through hole porosity (the percentage of the through hole opening end area to the zinc sheet surface area, the same below) is 30%, the zinc sheet thickness is 1mm, the carbon felt electrode porosity is 0.9, and the porosity of the carbon felt electrode after compression is 0.5. The specific parameters of the battery stack are as follows:

[0025] Electrode area: 800cm 2 ;

[0026] Positive and negative electrode carbon felt thickness before compression: 5mm;

[0027] Number of battery stacks: 20;

[0028] Current density: 40mA / cm 2 , charging time: 3 hours, discharge cut-off voltage: 16V;

[0029] Battery cycle performance: Coulombic efficiency 85.1%, voltage efficiency 77.5%, energy efficiency 65.9%;

[0030] The performance of Comparative Example 2 is even lower. This is because the zinc sheet is placed on the bottom side of the carbon felt, in direct contact with the current collector, and the zinc sheet cannot be compressed. Therefore, the contact resistance between the zinc sheet and the current collector is extremely large, the internal resistance of the battery increases, and the battery efficiency is poor.

[0031] Comparative Example 3

[0032] Comparative Example 3 uses a composite electrode structure as the negative electrode to assemble a zinc-bromine flow battery. When assembling the battery, the thickness of the composite electrode is 115% of the thickness of the electrode frame. Two carbon felt sheets are used, with one zinc sheet placed between them. The zinc sheet is provided with a through-hole with a diameter of 10 mm and a porosity of 80%. The zinc sheet is 1 mm thick, the porosity of the carbon felt electrode is 0.9, and the porosity of the compressed carbon felt electrode is 0.5. The specific parameters of the battery stack are as follows:

[0033] Electrode area: 800cm 2 ;

[0034] Positive and negative electrode carbon felt thickness before compression: 5mm;

[0035] Number of battery stacks: 20;

[0036] Current density: 40mA / cm 2 , charging time: 3 hours, discharge cut-off voltage: 16V;

[0037] Battery cycle performance: Coulombic efficiency 88.1%, voltage efficiency 79.3%, energy efficiency 69.8%;

[0038] The battery performance of Comparative Example 3 is improved compared with Comparative Examples 1 and 2, but it is still not ideal. This is because the porosity of the zinc sheet is too large, resulting in a large reduction in the deposition sites of zinc on the zinc sheet. When there is insufficient space for zinc deposition on the zinc sheet, zinc is still deposited on the surface of the carbon felt, resulting in zinc dendrites and zinc shedding.

[0039] Comparative Example 4

[0040] Comparative Example 4 uses a composite electrode structure as the negative electrode to assemble a zinc-bromine flow battery. During battery assembly, the composite electrode thickness is 115% of the electrode frame thickness. Two carbon felt sheets are used, with a zinc sheet placed between them. The zinc sheet is provided with a through-hole with a diameter of 10 mm and a porosity of 5%. The zinc sheet is 1 mm thick, the carbon felt electrode has a porosity of 0.9, and the compressed carbon felt electrode has a porosity of 0.5. The specific parameters of the battery stack are as follows:

[0041] Electrode area: 800cm 2 ;

[0042] Positive and negative electrode carbon felt thickness before compression: 5mm;

[0043] Number of battery stacks: 20;

[0044] Current density: 40mA / cm 2 , charging time: 3 hours, discharge cut-off voltage: 16V;

[0045] Battery cycle performance: Coulombic efficiency 76.1%, voltage efficiency 72.3%, energy efficiency 55.0%;

[0046] The battery performance of Comparative Example 4 is the worst. This is because the porosity of the zinc sheet is too low, which affects the normal mass transfer of the battery. The internal resistance of the battery is extremely large, so the efficiency is low.

[0047] Comparative Example 5

[0048] Comparative Example 5 uses a composite electrode structure as the negative electrode to assemble a zinc-bromine flow battery. When assembling the battery, the thickness of the composite electrode is 115% of the thickness of the electrode frame. The number of carbon felt sheets is 5, and the zinc sheet is placed between two carbon felt sheets, resulting in a total of 4 zinc sheets. The zinc sheets are provided with through holes with a diameter of 10 mm and a porosity of 30%. The zinc sheet thickness is 1 mm, the porosity of the carbon felt electrode is 0.9, and the porosity of the compressed carbon felt electrode is 0.5. The specific parameters of the battery stack are as follows:

[0049] Electrode area: 800cm 2 ;

[0050] Positive and negative electrode carbon felt thickness before compression: 5mm;

[0051] Number of battery stacks: 20;

[0052] Current density: 40mA / cm 2 , charging time: 3 hours, discharge cut-off voltage: 16V;

[0053] Battery cycle performance: Coulombic efficiency 80.5%, voltage efficiency 77.2%, energy efficiency 62.1%;

[0054] In Comparative Example 5, the amount of carbon felt and zinc sheet in the composite electrode is increased, resulting in an increase in the thickness of the composite electrode, an increase in the internal resistance of the battery, and a lower battery performance.

[0055] Example 1

[0056] The embodiment 1 uses the composite electrode structure provided by the utility model as a negative electrode to assemble a zinc-bromine flow battery. When assembling the battery, the thickness of the composite electrode is 115% of the thickness of the electrode frame, the number of carbon felt is 2, the zinc sheet is placed in the middle of the two pieces of carbon felt, a through hole is arranged on the zinc sheet, the diameter of the through hole is 10mm, the porosity of the through hole is 30%, the thickness of the zinc sheet is 1mm, the porosity of the carbon felt electrode is 0.9, and the porosity of the compressed carbon felt electrode is 0.5. The specific parameters of the electric pile are as follows:

[0057] The electrode area is 800cm 2 ;

[0058] The thickness of the positive electrode and the negative electrode carbon felt before compression is 5mm.

[0059] The number of electric pile nodes is 20 nodes.

[0060] The current density is 40mA / cm 2 , the charging time is 3 hours, and the discharge cutoff voltage is 16V.

[0061] The battery cycle performance is that the coulomb efficiency is 93.2%, the voltage efficiency is 85.3%, and the energy efficiency is 79.5%.

[0062] The number of operations when the energy efficiency of the electric pile decays by 5% is 402 cycles.

[0063] The embodiment 1 uses the composite electrode structure provided by the utility model, the deposition site of the zinc sheet is regulated to the inside of the carbon felt, the influence of zinc dendrite is eliminated, and the problem of zinc falling is improved because the generated zinc is in the inside of the carbon felt, so the battery performance is greatly improved, and the cycle performance is good.

[0064] Embodiment 2

[0065] The embodiment 2 uses the composite electrode structure provided by the utility model as a negative electrode to assemble a zinc-bromine flow battery. When assembling the battery, the thickness of the composite electrode is 115% of the thickness of the electrode frame, the number of carbon felt is 2, the zinc sheet is placed in the middle of the two pieces of carbon felt, a through hole is arranged on the zinc sheet, the diameter of the through hole is 10mm, the porosity of the through hole is 50%, the thickness of the zinc sheet is 1mm, the porosity of the carbon felt electrode is 0.9, and the porosity of the compressed carbon felt electrode is 0.5. The specific parameters of the electric pile are as follows:

[0066] The electrode area is 800cm 2 ;

[0067] The thickness of the positive electrode and the negative electrode carbon felt before compression is 5mm.

[0068] The number of electric pile nodes is 20 nodes.

[0069] The current density is 40mA / cm 2, Charging time: 3 hours, Discharge cut-off voltage: 32V;

[0070] Battery cycle performance: Coulombic efficiency 94.4%, voltage efficiency 86.3%, energy efficiency 81.5%;

[0071] Number of cycles when stack energy efficiency decays by 5%: 502 cycles

[0072] Example 2 adopts the composite electrode structure provided by the present invention. Compared with Example 1, this example further improves the porosity of the zinc sheet, improves mass transfer, and has sufficient zinc deposition sites, further improving battery performance.

[0073] Example 3

[0074] Example 3 uses the composite electrode structure provided by the present invention as the negative electrode to assemble a zinc-bromine flow battery. When assembling the battery, the thickness of the composite electrode is 115% of the thickness of the electrode frame. There are four carbon felt sheets, with a zinc sheet placed between every two sheets, for a total of three sheets. The zinc sheets are provided with through holes with a diameter of 10 mm and a porosity of 30%. The zinc sheet is 1 mm thick, the porosity of the carbon felt electrode is 0.9, and the porosity of the compressed carbon felt electrode is 0.5. The specific parameters of the battery stack are as follows:

[0075] Electrode area: 800cm 2 ;

[0076] Positive and negative electrode carbon felt thickness before compression: 5mm;

[0077] Number of battery stacks: 20;

[0078] Current density: 40mA / cm 2 , Charging time: 3 hours, Discharge cut-off voltage: 32V;

[0079] Battery cycle performance: Coulombic efficiency 95.8%, voltage efficiency 86.6%, energy efficiency 83.0%;

[0080] Number of cycles when stack energy efficiency decays by 5%: 651 cycles

[0081] Example 3 increases the number of carbon felt and zinc sheets. It can be seen that due to the increase in the number of zinc sheets, the number of zinc deposition sites increases, the deposition uniformity is improved, and the battery performance is improved. Moreover, since zinc can be produced on multiple zinc sheets at the same time, the amount of zinc material generated at the same position is reduced, further suppressing the influence of zinc dendrites. Moreover, due to the reduction in the amount of zinc material at the same position, the extrusion stress between the zinc and carbon felt electrodes is stronger, which better suppresses the problem of zinc shedding.

[0082] Example 4

[0083] Example 4 uses the composite electrode structure provided by the present invention as the negative electrode to assemble a zinc-bromine flow battery. During battery assembly, the composite electrode thickness is 115% of the electrode frame thickness. Two carbon felt sheets are used, with a zinc sheet placed between them. A through-hole is provided in the zinc sheet with a diameter of 10 mm and a porosity of 30%. The zinc sheet is 2 mm thick, the carbon felt electrode has a porosity of 0.9, and the porosity of the compressed carbon felt electrode is 0.5. The specific parameters of the battery stack are as follows:

[0084] Electrode area: 800cm 2 ;

[0085] Positive and negative electrode carbon felt thickness before compression: 5mm;

[0086] Number of battery stacks: 20;

[0087] Current density: 40mA / cm 2 , charging time: 4 hours, discharge cut-off voltage: 32V;

[0088] Battery cycle performance: Coulombic efficiency 93.9%, voltage efficiency 84.6%, energy efficiency 79.4%;

[0089] Number of cycles when stack energy efficiency decays by 5%: 421 cycles

[0090] In Example 4, the thickness of the zinc sheet is increased to 2 mm. As the thickness of the zinc sheet increases, the ohmic resistance inside the battery increases, and the battery performance decreases slightly. Therefore, the thickness of the zinc sheet should not be too thick.

[0091] It can be concluded from the comparative examples and the embodiments that the composite electrode proposed in the present invention is used as the negative electrode of the zinc-bromine flow battery, which can effectively regulate the zinc deposition site to the inside of the carbon felt, effectively inhibit the shedding of zinc, and reduce the impact of zinc dendrites, preventing the diaphragm from being penetrated and causing battery short circuit failure, thereby improving battery performance.

Claims

1. A composite electrode structure, characterized in that: The electrode comprises two stacked carbon felts and a zinc sheet located between the two carbon felts, or two or more zinc sheets stacked between the two carbon felts and separated by the carbon felts; A through hole is provided on the zinc sheet.

2. The composite electrode structure according to claim 1, characterized in that: in, The zinc sheets and the carbon felt are stacked alternately in sequence, the zinc sheet is placed between two carbon felt sheets, or two or more zinc sheets are stacked between two carbon felt sheets separated by a piece of carbon felt.

3. The electrode structure according to claim 1, wherein: The number of carbon felts in the composite electrode is between 2 and 4, the number of zinc sheets is between 1 and 3, the number of carbon felts minus the number of zinc sheets = 1, and the zinc sheets and carbon felts are alternately stacked.

4. The composite electrode structure according to any one of claims 1 to 3, characterized in that: The zinc sheet is provided with through holes perpendicular to the surface of the zinc sheet, the diameter of the through holes is between 5mm and 20mm, and the opening rate of the surface of the zinc sheet is between 20% and 50%.

5. The composite electrode structure according to any one of claims 1 to 3, characterized in that: The thickness of the carbon felt is between 2mm and 5mm, the thickness of the zinc sheet is between 0.5mm and 2mm, and the surface shape and size of the zinc sheet and the carbon felt electrodes are the same.

6. A zinc-bromine flow battery, characterized in that: The negative electrode adopts the composite electrode structure described in any one of claims 1 to 5. The composite electrode is placed in the central cavity of the battery ring electrode frame. Inlet and outlet flow channels are provided on the electrode frame. The electrolyte flows from the inlet flow channel into the composite electrode in the central cavity and then flows out of the electrode frame through the outlet flow channel.

7. The zinc-bromine flow battery according to claim 6, characterized in that: When assembling the battery, the thickness of the composite electrode is 110%-125% of the thickness of the electrode frame. After assembling the battery, the composite electrode is compressed to the same thickness as the electrode frame. The porosity of the carbon felt of the composite electrode before compression is between 0.85-0.9, and the porosity of the carbon felt of the composite electrode after compression is between 0.4-0.

5. This composite electrode is used as the negative electrode of the zinc-bromine flow battery and cannot be used as the positive electrode. The positive electrode still uses a flat carbon felt electrode with a traditional electrode structure.

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