A method of suppressing water transport in zinc-iron flow batteries by electric field modification of the separator

Abstract

This invention relates to the field of flow battery technology and discloses a method for suppressing water migration in zinc-iron flow batteries by modifying the separator using an electric field. The technical solution includes the following steps: S1, preparing a sulfonated polyether ether ketone (SPEEK) membrane of a certain area; S2, sandwiching the SPEEK membrane between two insulating rubber sheets to prevent damage to the metal electrodes, placing the two metal electrodes on the outside of the two insulating rubber sheets respectively; S3, applying voltage to the electrodes on both sides of the separator using a capacitor, so that the SPEEK membrane wrapped in the insulating rubber sheets is in an electric field space. In this invention, the SPEEK membrane can achieve orientation control of its ordered phase morphology under the action of an electric field. The main chain skeleton of SPEEK is arranged in a regular and orderly manner. A high-intensity electric field is more conducive to achieving the orientation of hydrophobic channels in the SPEEK membrane, which can effectively alleviate water migration. SPEEK membranes with oriented structures were prepared by applying electric fields of different intensities perpendicular to the membrane surface. This invention can effectively improve the water migration problem in alkaline zinc-iron flow batteries. Furthermore, the preparation process of this invention is simple to operate and has significant effects.

Description

Technical Field

[0001] This invention relates to an application of electric field-modified diaphragm to suppress water migration in zinc-iron flow batteries, belonging to the field of alkaline flow battery technology. Background Technology

[0002] With the increasing depletion of fossil fuels, the development and utilization of renewable energy sources such as wind and solar power have become a focus of attention for countries worldwide. However, the discontinuous and unstable nature of wind and solar power, influenced by weather and other factors, can impact the power grid during grid connection, affecting power quality and grid stability. Flow batteries can address this issue. In particular, emerging aqueous zinc-based flow batteries (ZFBs) have attracted widespread interest from researchers in recent years due to their high energy density, long cycle life, safety, and environmental friendliness. However, severe irreversible water migration occurs in the electrolyte at both the positive and negative electrodes during charge-discharge cycles, leading to an imbalance in electrolyte volume within the battery or stack. This, in turn, reduces battery or stack stability and significantly increases maintenance costs. Therefore, developing more convenient and effective strategies to suppress water migration in zinc-iron flow batteries remains a challenge. Summary of the Invention

[0003] This invention addresses the shortcomings and defects of existing technologies by providing a method for suppressing water migration in zinc-iron flow batteries through electric field modification of the diaphragm. This method can effectively improve the water migration problem in alkaline zinc-iron flow batteries and increase their lifespan.

[0004] The objective of this invention can be achieved through the following technical solutions.

[0005] A method for suppressing water migration in zinc-iron redox flow batteries by modifying the diaphragm with an electric field, the technical solution of which is as follows:

[0006] A type of separator modified by an electric field, the SPEEK membrane, can achieve orientation control of its ordered phase morphology under the action of an electric field. The main chain backbone of the SPEEK membrane is arranged in a regular and orderly manner, and a high-intensity electric field is more conducive to the orientation of hydrophilic channels in the SPEEK membrane. SPEEK membranes with oriented structures were prepared by applying electric fields of different intensities perpendicular to the membrane surface.

[0007] Step 1: Use a screw clamping device to apply a certain clamping force to fix the SPEEK membrane between two pieces of insulating rubber. Apply different electric fields of different intensities and apply them for different times under the same electric field intensity to obtain membranes with different modification effects. Mark the positive and negative effects of the electric field on the membrane.

[0008] Step 2: Assemble the battery using the modified separator. During assembly, the separator on the positive electrode side (marked with the electric field) is placed on the same side as the negative electrode side of the battery, and the separator on the negative electrode side (marked with the electric field) is placed on the same side as the positive electrode side of the battery. After battery assembly, electrolyte is introduced and the water migration data of the positive and negative electrodes are recorded.

[0009] The clamping force of the clamping device is 5-10N.

[0010] The thickness of the insulating rubber is 2 to 20 mm.

[0011] The diaphragm marking is achieved by spraying the same color as the positive electrode clamp on the edge of the diaphragm on the positive electrode side and the same color as the negative electrode clamp on the edge of the diaphragm on the negative electrode side, with a spraying width of 1-2 mm.

[0012] The modified diaphragm has an electric field strength of 100–800 V·cm. -1 .

[0013] The modified diaphragm is subjected to an electric field for 4 to 12 hours.

[0014] The thickness of the diaphragm is 40–120 μm.

[0015] The electrolyte is divided into a positive electrode electrolyte and a negative electrode electrolyte.

[0016] The positive electrode electrolyte is an alkaline solution of ferricyanide, with a total concentration of ferricyanide complex of 0.1–3 mol·L⁻¹. -1 ;

[0017] The negative electrode electrolyte is an alkaline solution of zincate ions, with a zincate ion concentration of 0.05–3 mol·L⁻¹. -1 .

[0018] The alkaline zinc-iron flow battery is a flow battery in which Fe(II) / Fe(III) is used as the active material for the positive electrode electrolyte and Zn(II) / Zn is used as the active material for the negative electrode electrolyte. The positive and negative electrolytes circulate between the positive electrode and the separator, and between the negative electrode and the separator, respectively.

[0019] Furthermore, the electric field strength is preferably 400–600 V·cm. -1 .

[0020] The beneficial technical effects of this invention are as follows: Under the action of an electric field, the orientation of the SPEEK membrane, with its ordered phase morphology, can be controlled. The main chain framework of SPEEK is arranged in a regular and orderly manner. A high-intensity electric field is more conducive to the orientation of hydrophobic channels in the SPEEK membrane, effectively mitigating water migration. By applying electric fields of different intensities perpendicular to the membrane surface, SPEEK membranes with oriented structures were prepared. This invention can effectively improve the water migration problem in alkaline zinc-iron flow batteries. Furthermore, the preparation process of this invention is simple to operate and has significant effects. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the electric field modified diaphragm device of the present invention.

[0022] Figure 2 This is a comparison of electrolyte migration in an alkaline zinc-iron flow battery between Example 2 and Comparative Example 1 of the present invention.

[0023] Figure 3 To compare the electrolyte migration in zinc-iron flow batteries with diaphragm assembly under the same electric field strength but different modification times.

[0024] Figure labels: 1-Positive electrode of electric field; 2-Negative electrode of electric field; 3-Insulating rubber; 4-Insulating rubber; 5-Diaphragm. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and do not limit the scope of the invention.

[0026] Comparative Example 1:

[0027] Assemble a zinc-iron flow battery, wherein the electrode is an activated carbon felt with an electrode area of ​​25 cm². 2 The current collector is a graphite plate, the diaphragm is a modified SPEEK membrane, and the current density is 80 mA cm⁻¹. -2 The volumes of the positive and negative electrode electrolytes are both 80 mL. The concentration of zincate ions in the negative electrode electrolyte is 0.4 mol / L. -1 The alkali concentration is 3 mol NaOH, and the concentration of ferrocyanide ions at the positive electrode is 0.8 mol L. -1 The alkali concentration was 3 mol KOH. After 40 cycles of operation, the volume of the positive electrode electrolyte became 137 mL, and the volume of the negative electrode electrolyte became 23 mL. The electrolyte migration was approximately 68.67%. The average migration rate per cycle was 1.7%.

[0028] Example 1:

[0029] Modification of the SPEEK ion exchange membrane: The SPEEK membrane is sandwiched between two pieces of insulating rubber to prevent damage to the metal electrodes. The two metal electrodes are placed on the outside of the two insulating rubber sheets respectively. An 800V cm⁻¹ voltage is applied. -1 The membrane was modified by an electric field for 4 hours.

[0030] Assemble a zinc-iron flow battery, wherein the electrode is an activated carbon felt with an electrode area of ​​25 cm². 2 The current collector is a graphite plate, the diaphragm is a modified SPEEK membrane, and the current density is 80 mA cm⁻¹.-2 The volumes of the positive and negative electrode electrolytes are both 80 mL. The concentration of zincate ions in the negative electrode electrolyte is 0.4 mol / L. -1 The alkali concentration is 3 mol NaOH, and the concentration of ferrocyanide ions at the positive electrode is 0.8 mol L / L. -1 The alkali concentration was 3 mol KOH. After 40 cycles, the assembled zinc-iron flow battery had an electrolyte volume of 81 mL at the positive electrode and 79 mL at the negative electrode. The electrolyte mobility was 1.2%, and the average cycle mobility was 0.015%. The electric field altered the orientation of the hydrophobic channels in the SPEEK film, effectively mitigating water migration.

[0031] Example 2:

[0032] Modification of the SPEEK ion exchange membrane: The SPEEK membrane is sandwiched between two insulating rubber sheets to prevent damage to the metal electrodes. The two metal electrodes are placed on the outside of the two insulating rubber sheets respectively. A 400V cm⁻¹ voltage is applied. -1 The membrane was modified by an electric field for 4 hours.

[0033] Assemble a zinc-iron flow battery, wherein the electrode is an activated carbon felt with an electrode area of ​​25 cm². 2 The current collector is a graphite plate, the diaphragm is a modified SPEEK membrane, and the current density is 80 mA cm⁻¹. -2 The volumes of the positive and negative electrode electrolytes are both 80 mL. The concentration of zincate ions in the negative electrode electrolyte is 0.4 mol / L. -1 The alkali concentration is 3 mol NaOH, and the concentration of ferrocyanide ions at the positive electrode is 0.8 mol L. -1 The alkali concentration was 3 mol KOH. After 40 cycles, the assembled zinc-iron flow battery had a positive electrode electrolyte volume of 115 mL and a negative electrode electrolyte volume of 45 mL. The electrolyte mobility was 43.75%, and the average cycle mobility was 1.09%.

[0034] Example 3:

[0035] Modification of the SPEEK ion exchange membrane: The SPEEK membrane is sandwiched between two insulating rubber sheets to prevent damage to the metal electrodes. The two metal electrodes are placed on the outside of the two insulating rubber sheets respectively. A 400V cm⁻¹ voltage is applied. -1 The membrane was modified by an electric field for 5 hours.

[0036] Assemble a zinc-iron flow battery, wherein the electrode is an activated carbon felt with an electrode area of ​​25 cm². 2 The current collector is a graphite plate, the diaphragm is a modified SPEEK membrane, and the current density is 80 mA cm⁻¹. -2 The volumes of the positive and negative electrode electrolytes are both 80 mL. The concentration of zincate ions in the negative electrode electrolyte is 0.4 mol / L.-1 The alkali concentration is 3 mol NaOH, and the concentration of ferrocyanide ions at the positive electrode is 0.8 mol L. -1 The alkali concentration was 3 mol KOH. After 40 cycles, the assembled zinc-iron flow battery had a positive electrode electrolyte volume of 103 mL and a negative electrode electrolyte volume of 57 mL. The electrolyte mobility was 28.75%, and the average cycle mobility was 0.72%.

[0037] Example 4:

[0038] Modification of the SPEEK ion exchange membrane: The SPEEK membrane is sandwiched between two insulating rubber sheets to prevent damage to the metal electrodes. The two metal electrodes are placed on the outside of the two insulating rubber sheets respectively. A 400V cm⁻¹ voltage is applied. -1 The membrane was modified by an electric field for 6 hours.

[0039] Assemble a zinc-iron flow battery, wherein the electrode is an activated carbon felt with an electrode area of ​​25 cm². 2 The current collector is a graphite plate, the diaphragm is a modified SPEEK membrane, and the current density is 80 mA cm⁻¹. -2 The volumes of the positive and negative electrode electrolytes are both 80 mL. The concentration of zincate ions in the negative electrode electrolyte is 0.4 mol / L. -1 The alkali concentration is 3M NaOH, and the concentration of ferrocyanide ions at the positive electrode is 0.8 mol / L. -1 The alkali concentration was 3M KOH. After 40 cycles, the assembled zinc-iron flow battery had a positive electrode electrolyte volume of 94 mL and a negative electrode electrolyte volume of 66 mL. The electrolyte mobility was 17.5%, and the average cycle mobility was 0.43%.

[0040] Compared with the modified membrane, the battery assembled with the modified SPEEK membrane showed a significant inhibitory effect on electrolyte water migration, and the longer it was subjected to an electric field, the more obvious the inhibitory effect on water migration became.

Claims

1. A method for suppressing water migration in a zinc-iron flow battery by modifying the diaphragm with an electric field, characterized in that, Includes the following steps: S1, Use a screw clamping device to apply a certain clamping force to fix the SPEEK film between two insulating rubber pads; S2, Apply electric fields of different intensities to the diaphragm and apply them for different times under the same electric field intensity to obtain diaphragms with different modification effects, and mark the positive and negative effects of the electric field on the diaphragm; S3. Assemble the battery using the modified separator. During assembly, the separator on the positive electrode side of the marking electric field is placed on the same side as the negative electrode side of the battery, and the separator on the negative electrode side of the marking electric field is placed on the same side as the positive electrode side of the battery. After battery assembly, electrolyte is introduced and the water migration data of the positive and negative electrodes are recorded.

2. The clamping device according to claim 1, characterized in that, Clamping force 5-10N.

3. The insulating rubber according to claim 1, characterized in that, The thickness is 0.5 to 10 mm.

4. The diaphragm marking according to claim 1, characterized in that, The edge of the diaphragm on the positive electrode side of the electric field is sprayed with the same color as the positive electrode clip, and the edge of the diaphragm on the negative electrode side of the electric field is sprayed with the same color as the negative electrode clip.

5. The diaphragm marking according to claim 4, wherein the width of the spray coating on the diaphragm edge is 1-2 mm.

6. The diaphragm-modified electric field according to claim 1, characterized in that, Electric field strength 100–500 V·cm -1 .

7. The duration of electric field application for the diaphragm modification according to claim 1, characterized in that, The duration of action is 4–12 hours.

8. The diaphragm according to claim 1, characterized in that: The membrane thickness is 40–110 μm.

9. The electrolyte according to claim 1, characterized in that: The electrolyte consists of a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte is an alkaline solution of ferricyanide, and the total concentration of the ferricyanide complex is 0.1-3 mol·L⁻¹. -1 The negative electrode electrolyte is an alkaline solution of zincate ions, with a zincate ion concentration of 0.05-3 mol·L⁻¹. -1 .

10. An alkaline zinc-iron flow battery assembled with a modified separator according to any one of claims 1 to 9; characterized in that: The alkaline zinc-iron flow battery is a flow battery in which Fe(II) / Fe(III) is used as the active material for the positive electrode electrolyte and Zn(II) / Zn is used as the active material for the negative electrode electrolyte. The positive and negative electrolytes circulate between the positive electrode and the separator, and between the negative electrode and the separator, respectively.

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