A method of inhibiting water crossover or permeation across a membrane of a zinc-iron flow battery

Abstract

This invention belongs to the field of flow battery electrolyte technology and discloses a method for inhibiting water migration or permeation across the membrane in a zinc-iron flow battery. The positive electrode electrolyte of the zinc-iron flow battery is composed of sodium ferrocyanide and an alkali metal hydroxide, and the negative electrode electrolyte is composed of zinc oxide and an alkali metal hydroxide. Both the positive and negative electrode electrolytes are magnetically stirred until completely dissolved in a water bath at a temperature of 20-80°C. Then, equal volumes of the positive and negative electrode electrolytes are placed in the zinc-iron flow battery, with a separator separating the positive and negative electrodes. This invention is simple, has widely available and low-cost resources, and features high safety and good stability, making it applicable to the field of flow battery electrolytes.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology for flow batteries, and specifically relates to a method for inhibiting water migration or permeation across the membrane in zinc-iron flow batteries. Background Technology

[0002] Against the backdrop of the current energy transition goals of "peak carbon and carbon neutrality," my country's energy industry has seen both positive developments and challenges. Among these, developing energy storage has become a crucial pathway to achieving these dual carbon goals. Flow battery energy storage offers advantages such as flexible design, freely adjustable power and capacity, and safety and environmental friendliness. Zinc-iron flow batteries, as a highly promising chemical energy storage method, also possess advantages such as low cost and suitability for large-scale energy storage. Currently used zinc-iron flow batteries mostly employ alkaline Fe(CN)6... 2- / Zn(OH) 2- The system solution has an inconsistent osmotic pressure between the positive and negative electrodes, causing the positive electrode to migrate to the negative electrode to a large extent. This easily leads to the precipitation of positive electrode active material, which seriously affects the long-term stability and performance of the zinc-iron flow battery.

[0003] Currently, the main method for suppressing ion migration in zinc-iron battery systems is to add additives to the side with lower osmotic pressure. Chinese patent CN209016196U proposes an organic additive based on salt cavern, but this additive is only effective at low charge density (10 mA / cm²). 2 While methods to reduce battery degradation can be implemented, they fail to meet practical application requirements. Chinese patent CN111200146A proposes using additives such as small-molecule sugars and alcohols, but this increases the demand for high-concentration solutions, making solubility a difficult problem to solve. Chinese patent CN109509901A proposes using symmetrical electrolytes to suppress electrolyte migration, but the excess active material Zn(OH) at the positive electrode... 2- and the excess active material Fe(CN)6 at the negative electrode 2- This increases system costs, and migration still affects battery performance to some extent during actual use. Therefore, balancing the osmotic pressure of the zinc-iron electrolyte to suppress migration in zinc-iron flow batteries is a crucial issue that urgently needs to be addressed to effectively reduce the rapid capacity decay of zinc-iron batteries.

[0004] In the field of flow battery electrolytes, to ensure a high energy density in the battery system, the concentration of active materials needs to be maximized under certain conditions. Adding further additives beyond this point makes them difficult to dissolve. Therefore, for high-performance zinc-iron flow batteries, a method is needed to effectively suppress zinc-iron flow battery migration and improve system stability. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for suppressing water migration or permeation across the membrane in zinc-iron flow batteries. It utilizes the characteristic that the positive and negative electrolytes of the zinc-iron system have different osmotic pressures on both sides of the membrane, and the principle that they will permeate each other on both sides of the membrane. During long-term circulation, the osmotic pressure of the electrolytes on both sides of the membrane will tend to reach equilibrium. After equilibrium is reached, the positive and negative electrolytes will hardly migrate anymore. The electrolyte concentration at which the osmotic pressure reaches equilibrium can be deduced from the remaining volume of the electrolyte after migration.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: a method for suppressing water transmembrane migration or permeation in a zinc-iron flow battery, wherein the positive electrode electrolyte of the zinc-iron flow battery is composed of sodium ferrocyanide and alkali metal hydroxide, and the negative electrode electrolyte is composed of zinc oxide and alkali metal hydroxide; the positive and negative electrode electrolytes are each magnetically stirred at a water bath temperature of 20-80℃ until completely dissolved; then, equal volumes of positive and negative electrode electrolytes are placed in the zinc-iron flow battery, with a membrane separating the positive and negative electrodes; the flow rate of the positive and negative electrode electrolytes is in the range of 30-60 mL / min; the concentration of ferrocyanide ions in the positive electrode electrolyte is 0.01-1.5 mol / L; the concentration of potassium hydroxide in the positive electrode electrolyte is 0.1-3 mol / L; the concentration of zinc ions in the negative electrode electrolyte is 0.01-2.5 mol / L; and the concentration of sodium hydroxide in the negative electrode electrolyte is 0.01-6.0 mol / L.

[0007] Furthermore, the concentration of ferrocyanide ions in the positive electrode electrolyte is 0.1-0.8 mol / L.

[0008] Furthermore, the concentration of ferrocyanide ions in the positive electrode electrolyte is 0.5-0.7 mol / L.

[0009] Furthermore, the concentration of potassium hydroxide in the positive electrode electrolyte is 1.5-2.5 mol / L.

[0010] Furthermore, the zinc ion concentration of the negative electrode electrolyte is 0.05-0.5 mol / L.

[0011] Furthermore, the zinc ion concentration of the negative electrode electrolyte is 0.1-0.25 mol / L.

[0012] Furthermore, the concentration of sodium hydroxide in the negative electrode electrolyte is 3.5-5.0 mol / L.

[0013] Furthermore, the magnetic pump model is Xinxishan MP-10RN.

[0014] After the zinc-iron flow battery is made, the magnetic pumps of the positive and negative electrodes are started to begin the migration experiment. The volume of the positive and negative electrolytes is recorded every 5 hours until the volume of the positive and negative electrolytes remains unchanged in at least 3 records. Then the recording is stopped, and the remaining volume of the positive and negative electrolytes is recorded.

[0015] The volume of the electrolyte must meet two conditions: first, it must be sufficient for electrolyte circulation in the battery after the magnetic pump is working; second, it must still be sufficient for electrolyte circulation in the battery after the self-migration experiment ends.

[0016] The advantages of this invention compared to existing technologies are: by optimizing electrolyte concentration and volume, the assembled battery can achieve an efficiency of 1-120 mA / cm². 2 It operates stably within the specified current density, and the problem of positive electrode electrolyte precipitation caused by the migration of positive and negative electrode electrolytes is solved. At the same time, the overall battery efficiency is improved, demonstrating excellent battery performance.

[0017] This invention provides a method for suppressing water migration across the membrane in zinc-iron flow batteries. The electrolyte prepared by this method, when applied to zinc-iron flow batteries, can effectively suppress the problem of electrolyte migration across the membrane between the positive and negative electrodes, thereby reducing the problem of large-scale migration between electrolytes, improving battery performance, reducing the risk of positive electrode electrolyte precipitation, and achieving long-term stable cycling of zinc-iron flow batteries.

[0018] The method of this invention is simple, has a wide range of low-cost sources, and features high safety and good stability. It can be applied to the field of flow battery electrolytes. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 This is a graph showing the volume change of the positive and negative electrolytes in Embodiment 2 of the present invention;

[0021] Figure 2 This is a graph showing the volume change of the positive and negative electrolytes in Embodiment 3 of the present invention. Detailed Implementation

[0022] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0023] The battery assembly uses Liaoyang Jingu graphite felt as the reaction electrode, with an effective working area of ​​48 cm². 2 Nafion 212 is used as the diaphragm, impregnated hard graphite plate is used as the manifold, and silicone gasket is used as the seal.

[0024] Battery performance testing conditions: at room temperature and 40 mA / cm 2 Under the conditions of charging and discharging, the charging and discharging voltage range is 1-2.1V. A resting step of 30s is performed at the end of charging and discharging.

[0025] Example 1

[0026] The zinc-iron system consists of a positive electrode electrolyte of 0.50M Fe(CN)6. 2- +1.50M KOH and negative electrode electrolyte 0.25M Zn 2+ The electrolyte system consists of 5.00M NaOH, with each electrolyte having a volume of 100mL. This electrolyte system was tested for charge and discharge in a battery system, and the battery test results are shown in Table 1.

[0027] Example 2

[0028] The zinc-iron system consists of a positive electrode electrolyte of 0.50M Fe(CN)6. 2- +1.50M KOH and negative electrode electrolyte 0.25M Zn 2+ The electrolyte is composed of +5.00M NaOH. 100mL of each electrolyte is added to the battery system. Without charging or discharging, the magnetic pump is started. The volume of the positive and negative electrolytes is recorded every 5 hours. After 90 hours, the magnetic pump is stopped. The volume changes of the positive and negative electrolytes are shown below. Figure 1 As shown.

[0029] Without charging or discharging, the volume of the positive electrode electrolyte was reduced from 100 mL to 70 mL, while the volume of the negative electrode electrolyte was increased from 100 mL to 130 mL. Based on the migration results, the optimal electrolytes for equal osmotic pressure across the membrane were recalculated, resulting in a positive electrode electrolyte of 0.7143 M Fe(CN)6. 2- +2.1429M KOH, negative electrode electrolyte is 0.1923M Zn 2+ +3.8462M NaOH.

[0030] Example 3

[0031] The zinc-iron system consists of a positive electrode electrolyte of 0.7143M Fe(CN)6. 2- +2.1429M KOH and negative electrode electrolyte 0.1923M Zn 2+ Composed of +3.8462M NaOH, 100mL of each electrolyte was added to the battery system. The magnetic pump was started without charging or discharging, and the volumes of the positive and negative electrolytes were recorded every 5 hours. After 90 hours, the magnetic pump was stopped. The volume changes of the positive and negative electrolytes are shown below. Figure 2 As shown.

[0032] Example 4

[0033] The zinc-iron system consists of a positive electrode electrolyte of 0.7143M Fe(CN)6. 2- +2.1429M KOH and negative electrode electrolyte 0.1923M Zn 2+The system consists of 3.8462M NaOH, 70mL of positive electrolyte, and 130mL of negative electrolyte to ensure that the total molar amount of active material in the positive and negative electrolytes is equal. The system was tested for charge and discharge in a battery system, and the battery test results are shown in Table 1.

[0034] As can be seen from the results of Examples 2 and 3, the method for inhibiting water migration across the membrane in a zinc-iron flow battery provided by the present invention can effectively reduce the permeation of electrolyte on both sides of the membrane, that is, it plays the role of inhibiting electrolyte migration on both sides of the membrane.

[0035] Table 1 shows a comparison of the battery performance between Examples 1 and 4. The electrolyte volume in Examples 1 and 4 remained unchanged before and after the experiment, indicating that the method for suppressing water migration across the membrane in the zinc-iron electrolyte system provided by this invention can effectively suppress electrolyte migration during battery cycling. Furthermore, when the electrolyte prepared according to this invention is applied to a battery system, the battery stability is significantly improved, enabling long-term stable cycling. Simultaneously, due to the osmotic pressure balance across the membrane, electrolyte migration between the positive and negative electrodes is reduced, resulting in improved coulombic efficiency, reduced membrane polarization resistance, increased voltage efficiency, and enhanced overall battery energy efficiency.

[0036] Table 1

[0037] Example 1 98.9 85.4 84.5 31 Example 4 99.4 86.0 85.5 >500

[0038] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for inhibiting water migration or permeation across the membrane in a zinc-iron flow cell, characterized in that, The positive electrode electrolyte of the zinc-iron flow battery is composed of sodium ferrocyanide and alkali metal hydroxide, and the negative electrode electrolyte is composed of zinc oxide and alkali metal hydroxide. Both the positive and negative electrolytes are magnetically stirred until completely dissolved in a water bath at a temperature of 20-80℃. The concentration of ferrocyanide ions in the positive electrode electrolyte is 0.5-0.7 mol / L; the concentration of potassium hydroxide in the positive electrode electrolyte is 1.5-2.5 mol / L; and the concentration of zinc ions in the negative electrode electrolyte is 0.1-0.25 mol / L. The concentration of sodium hydroxide in the negative electrode electrolyte is 3.5-5.0 mol / L. Then, take the same volume of positive and negative electrode electrolytes and place them in the zinc-iron flow battery. Separate the positive and negative electrodes with a diaphragm. Start the positive and negative electrode magnetic pumps without charging or discharging and circulate them at a flow rate of 30-60 mL / min. Record the volume of positive and negative electrode electrolytes every 5 hours until the volume of positive and negative electrode electrolytes does not change in at least 3 records. Record the remaining volume of positive and negative electrode electrolytes. Based on the remaining volume of electrolytes after migration, back-calculate the electrolyte concentration at which the osmotic pressure reaches equilibrium. Then, charge and discharge the zinc-iron flow battery at the obtained positive and negative electrode electrolyte concentrations.

2. The method for inhibiting water migration or permeation across the membrane in a zinc-iron flow battery according to claim 1, characterized in that, The magnetic pump is model MP-10RN.

Images