An ion-conducting membrane with dynamically adjustable structure, its preparation method and application

Abstract

The present invention discloses an ion-conducting membrane with dynamically adjustable structure, its preparation method and application, belonging to the technical field of flow batteries. By immersing the organic polymer resin gel coating scraped on a glass plate in a transition metal ion reaction solution for a certain time, after coordinating with metal ions in the reaction solution, a dense layer with wavy stripes is formed, and the unreacted gel layer undergoes nonsolvent phase inversion in a poor solvent to form a sponge-like pore support layer, obtaining an ion-conducting membrane with dynamically adjustable structure. Applying it to a flow battery effectively alleviates the irreconcilable contradiction between ion selectivity and ion conductivity, and achieves high Coulomb efficiency and high voltage efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of flow batteries, and particularly relates to an ion-conducting membrane with dynamically adjustable structure, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing proportion of renewable energy in the global energy structure, people's attention to it has been increasing. However, due to the discontinuity and instability of renewable energy, it is necessary to rely on large-scale energy storage devices to achieve its stable use and meet the urgent social demand for renewable energy. Among them, flow batteries are a typical type of large-scale energy storage device, which have high safety, long service life, and the capacity and power can be separately regulated. And different types of flow batteries can meet the needs of grid connection and distributed energy storage respectively, so it can accelerate the process of renewable energy entering people's lives.

[0003] The separator is a key component in the structure of a flow battery. On the one hand, it blocks the contact between the positive and negative active materials, and on the other hand, it needs to conduct carriers to complete the entire battery circuit. However, for the separator, the selectivity for active materials and the conductivity often restrict each other, and it is difficult to achieve both high ion conductivity and ion selectivity simultaneously. Research and development of ion-conducting membranes with high ion conductivity and high ion selectivity have become an important topic that needs to be studied urgently. Summary of the Invention

[0004] In view of this, the present invention aims to provide an ion-conducting membrane with dynamically adjustable different functional layers, a preparation method thereof, and an application thereof. The ion-conducting membrane has a dense layer with wave stripes and a sponge-like porous layer; by regulating the thicknesses of the dense layer and the porous layer, the ion selectivity and ion conductivity can be regulated. When it is used in a flow battery, high ion selectivity and high ion conductivity, that is, high Coulomb efficiency and high voltage efficiency, can be achieved.

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

[0006] The present invention provides a preparation method of an ion-conducting membrane with dynamically adjustable structure. The ion-conducting membrane is prepared by a coordination phase inversion method. During the coordination phase inversion reaction process, the organic polymer resin gel coating scraped on the glass plate is immersed in the reaction solution for a certain time, and after coordinating with the metal ions in the reaction solution, a dense layer with wave stripes is formed, and the unreacted gel layer undergoes non-solvent phase inversion in a poor solvent to form a sponge-like porous layer.

[0007] Furthermore, the preparation method mainly includes the following steps:

[0008] (1) Dissolve the organic polymer resin in an organic solvent and stir at room temperature for 24 to 48 h to obtain a casting solution, and the concentration of the organic polymer resin is 10 to 30 wt%.

[0009] (2) Dissolve a transition metal salt or its hydrate in an organic solvent to obtain a reaction solution of the transition metal salt, and the concentration of the reaction solution of the transition metal salt is 1 mol / L -1 ~3 mol / L -1 ;

[0010] (3) Knife-coat the casting solution obtained in step (1) on a flat plate, and then quickly immerse it in the reaction solution of the transition metal salt obtained in step (2) for a phase inversion reaction for 20 s to 2.5 min to obtain a gel coating; the knife-coating thickness of the casting solution is 100~300 μm;

[0011] (4) Transfer the gel coating obtained in step (3) to a poor solvent of the organic polymer resin for curing to obtain an ion conductive membrane.

[0012] Further, the organic solvent in steps (1) and (2) is N-methylpyrrolidone.

[0013] Further, the organic polymer resin in step (1) is a nitrogen-containing heterocyclic polymer, preferably polybenzimidazole; the concentration of the organic polymer resin is 15~20 wt%.

[0014] Further, the transition metal salt in step (2) includes cobalt chloride, cobalt sulfate, and cobalt nitrate; the concentration of the reaction solution of the transition metal salt is 1.5~3 mol / L -1 .

[0015] Further, the poor solvent in step (4) is one or a mixed solution of two or more of water, ethanol, and isopropanol; the curing temperature is 20~35 °C, and the curing time is 5 min~20 min.

[0016] On the other hand, the present invention provides an ion conductive membrane with dynamically adjustable structure prepared by the above preparation method, and the ion conductive membrane has a spongy porous layer and a dense layer with periodically fluctuating stripes.

[0017] Further, the thickness of the spongy porous layer is 3-25 μm, the distance from the interface between the spongy porous layer and the dense layer to the wave crest is 10-30 μm, and the distance from the wave crest to the wave trough of the dense layer is 1-10 μm.

[0018] The present invention also provides the application of the above ion conductive membrane as a separator of a flow battery, and the flow battery includes an alkaline zinc-iron flow battery, a zinc-bromine flow battery, and a zinc-iodine flow battery.

[0019] Further, the flow battery is an alkaline zinc-iron flow battery, the electrode is an activated carbon felt, the bipolar plate is a graphite plate, the positive electrolyte includes 0.4 mol / L sodium ferrocyanide decahydrate and 3 mol / L potassium hydroxide; the negative electrolyte includes 0.2 mol / L zinc oxide and 3.8 mol / L sodium hydroxide.

[0020] Further, the sponge-like support layer of the ion-conducting membrane faces the positive electrode, and the dense layer faces the negative electrode.

[0021] The beneficial effects of the present invention compared with the prior art are as follows:

[0022] 1. The ion-conducting membrane prepared by the present invention with dynamically adjustable different functional layers has a dense layer with fluctuating stripes and a sponge-like porous layer.

[0023] 2. The ion-conducting membrane prepared by the present invention realizes the thickness ratio of the dense layer and the sponge-like porous layer, as well as the height of the fluctuating stripes of the dense layer (the distance from the wave peak to the wave valley) by regulating multiple technical parameters such as the types and concentrations of organic polymer resins and metal salts, the matching of corresponding organic solvents, and the phase inversion reaction time, and further achieves the optimization of the ion selectivity and conductivity of the membrane. When it is used in a flow battery, both the Coulomb efficiency and the voltage efficiency are as high as over 90%, and high ion selectivity and high ion conductivity can be achieved. By controlling the types and concentrations of organic polymer resins and metal salts, the morphology of the fluctuating stripes of the dense layer can be adjusted. As the distance between the wave peak and the wave valley increases, the specific surface area of the dense layer also increases, further improving the ion conductivity of the membrane. When this type of membrane is applied to a zinc-based flow battery, the dense layer with fluctuating stripes facing the negative electrode can further flatten the zinc deposition morphology, inhibit the growth of zinc dendrites, and significantly improve the cycle stability of the battery. Description of the Drawings

[0024] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments will be briefly introduced below.

[0025] Figure 1 It is the surface morphology of the ion-conducting membranes of Example 1, Example 2, Comparative Example 1 and Comparative Example 8 photographed by an optical microscope.

[0026] Figure 2 It is the cross-sectional morphology of the ion-conducting membranes of Example 1, Example 2, Comparative Example 1 and Comparative Example 8 photographed by a scanning electron microscope.

[0027] Figure 3 It is the cross-sectional morphology of the ion-conducting membranes of Comparative Example 2 and Comparative Example 3 photographed by a scanning electron microscope. Detailed Embodiments

[0028] The present invention will be described in detail below in conjunction with embodiments. However, the implementation manners of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, without creative efforts, obtaining other similar embodiments will fall within the protection scope of the present invention.

[0029] Example 1

[0030] 12 g of polybenzimidazole (PBI) was dissolved in 60 g of N-methylpyrrolidone (NMP), and stirred at room temperature for 24 hours to obtain a 17 wt% casting solution. 35.7 g of cobalt chloride hexahydrate was dissolved in 100 mL of NMP and stirred evenly to obtain solution A with a concentration of 1.5 mol / L. The casting solution was blade-coated on a glass plate with a blade-coating thickness of 200 μm. The glass plate was immersed in solution A for 2 min to obtain a Co gel layer. The glass plate carrying the Co gel layer was placed in water and cured for 10 min to obtain an NMP-Co-PBI ion-conducting membrane with wavy stripes on the surface, named NMP-Co-PBI-2min. By taking SEM images of the membrane cross-section, the distance from the interface of the porous layer with wavy stripes to the wave crest was 16.1 μm, the distance from the wave crest to the wave trough of the dense layer was 7.3 μm, and the thickness of the sponge-like porous layer was 5.9 μm.

[0031] Using the above ion-conducting membrane to assemble an alkaline zinc-iron flow battery, where the electrode was activated carbon felt, the bipolar plate was a graphite plate, and the effective area of the membrane was 9 cm 2 . The volumes of the positive and negative electrolytes were the same, both 250 ml; the positive electrolyte was 0.4 mol / L sodium ferrocyanide decahydrate and 3 mol / L potassium hydroxide; the negative electrolyte was 0.2 mol / L zinc oxide and 3.8 mol / L sodium hydroxide. The obtained alkaline zinc-iron flow battery was subjected to charge-discharge tests at 80 mA / cm -2 , 100 mAh / cm -2 , and the results are shown in Table 2.

[0032] Examples 2 - 6:

[0033] The preparation process of the ion-conducting membrane, the process of assembling it into a battery, and the performance test process were the same as those in Example 1. The differences were the types and concentrations of organic polymer resins, the concentrations of metal salts, the phase inversion time, and the organic solvents. The relevant data are shown in Table 1, and the performance test data of the alkaline zinc-iron flow battery assembled with the ion-conducting membrane are shown in Table 2.

[0034] Comparative Examples 1 - 9

[0035] The preparation process of the ion-conducting membrane, the process of assembling it into a battery, and the performance testing process are the same as those in Example 1. The differences lie in the types and concentrations of organic polymer resins, the concentration of metal salts, the phase inversion time, and the organic solvents. The relevant data are shown in Table 1, and the performance testing data of the alkaline zinc-iron flow battery assembled with the ion-conducting membrane are shown in Table 2.

[0036] Table 1. Preparation process parameters of the ion-conducting membranes in Examples 2-6 and Comparative Examples 1-9

[0037]

[0038]

[0039] Table 2. Performance testing results of the batteries composed of the ion-conducting membranes in Examples 1-6 and Comparative Examples 1-9

[0040]

[0041] From the implementation data of the above Examples 1 to 6, it can be seen that the ion-conducting membrane prepared by the present invention has a dense layer with dynamically adjustable fluctuating stripes and a spongy support layer. By regulating multiple technical parameters such as the types and concentrations of organic polymer resins and metal salts, the matching of corresponding organic solvents, and the phase inversion reaction time, the thickness ratio of the dense layer to the spongy porous layer and the height of the fluctuating stripes of the dense layer (the distance from the wave peak to the wave valley) are realized, thereby optimizing the ion selectivity and conductivity of the membrane. When it is used in a flow battery, high ion selectivity (high Coulomb efficiency) and high ion conductivity (high voltage efficiency) can be achieved, and it has excellent performance in the battery. By controlling the types and concentrations of organic polymer resins and metal salts, the morphology of the fluctuating stripes of the dense layer can be adjusted. By increasing the distance between the wave peak and the wave valley, the specific surface area of the dense layer is increased, further improving the ion conductivity of the membrane. When this type of membrane is applied to a zinc-based flow battery, the dense layer with fluctuating stripes facing the negative electrode can further level the zinc deposition morphology, inhibit zinc dendrites, and improve the cycle stability of the battery.

[0042] However, in the data of Comparative Example 1, Comparative Examples 4-6, and Comparative Example 9, both the voltage efficiency and the energy efficiency are inferior to those in Examples 1-2. This is mainly because after the experimental parameters are changed, an ion-conducting membrane with fluctuating stripes on the surface cannot be obtained. The membrane with a flat surface does not have a high specific surface area, and its ion conductivity is not as good as that of the ion-conducting membrane with surface fluctuating stripes. In the data of Comparative Examples 2-3 and Comparative Example 7, the Coulomb efficiency is inferior to that in Examples 1-2. This is mainly because their pore structures are too large. Although it can allow carriers to pass through the diaphragm smoothly and obtain high ion conductivity, it cannot effectively block the active substances, resulting in cross-contamination of the active substances during the operation of the battery, thus leading to poor ion selectivity and low Coulomb efficiency of the battery.

[0043] The surface morphologies of the ion-conducting membranes of Example 1, Example 2, Comparative Example 1, and Comparative Example 8 are as Figure 1 and Figure 2 shown. The ion-conducting membranes of Example 1, Example 2, and Comparative Example 8 have surface undulating stripes, and the thicknesses of the dense undulating cortex and the sponge-like pore support layer can be dynamically regulated by the reaction time, thereby regulating the ion conductivity and selectivity of the separator. However, Comparative Example 1 does not have surface undulating stripes and has a flat surface.

[0044] The surface morphologies of the ion-conducting membranes of Comparative Example 2 and Comparative Example 3 are as Figure 3 shown. Comparative Example 2 only has overall sponge-like pores, and Comparative Example 3 has a dense layer and a macroporous support layer, both of which cannot achieve high ion selectivity and high ion conductivity.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Application of an ion-conducting membrane with dynamically adjustable structure as a separator for a flow battery, the flow battery including an alkaline zinc-iron flow battery, a zinc-bromine flow battery, and a zinc-iodine flow battery, the ion-conducting membrane having a spongy porous layer and a dense layer with periodically fluctuating stripes; the thickness of the spongy porous layer is 3 - 25 μm, the distance from the interface of the spongy porous layer and the dense layer to the peak is 10 - 30 μm, and the distance from the peak to the valley of the dense layer is 1 - 10 μm; the preparation method of the ion-conducting membrane includes the following steps: (1) Dissolve an organic polymer resin in an organic solvent and stir at room temperature for 24 - 48 h to obtain a casting solution, the concentration of the organic polymer resin being 10 - 30 wt%; (2) Dissolve a transition metal salt or its hydrate in an organic solvent to obtain a transition metal salt reaction solution, and the concentration of the transition metal salt reaction solution is 1.5 mol L -1 ~3 mol L -1 ; (3) Coat the casting solution obtained in step (1) on a flat plate and quickly immerse it in the transition metal salt reaction solution obtained in step (2) for a phase inversion reaction of 20 s - 2.5 min to obtain a gel coating; the coating thickness of the casting solution is 100 - 300 μm; (4) Transfer the gel coating obtained in step (3) to a poor solvent of the organic polymer resin for curing to obtain an ion-conducting membrane.

2. The application according to claim 1, wherein The organic solvent in steps (1) and (2) is N-methylpyrrolidone.

3. The application according to claim 1, wherein The organic polymer resin in step (1) is a nitrogen-containing heterocyclic polymer, including polybenzimidazole; the concentration of the organic polymer resin is 15 - 20 wt%.

4. The application according to claim 1, wherein The transition metal salt in step (2) is cobalt chloride hexahydrate.

5. The application according to claim 1, wherein The poor solvent in step (4) is one or a mixed solution of two or more of water, ethanol, and isopropanol; the curing temperature is 20 - 35 °C and the curing time is 5 min - 20 min.

6. The application according to claim 1, wherein The flow battery is an alkaline zinc-iron flow battery, the electrode is an activated carbon felt, the bipolar plate is a graphite plate, the positive electrolyte includes 0.4 mol / L sodium ferrocyanide decahydrate and 3 mol / L potassium hydroxide; the negative electrolyte includes 0.2 mol / L zinc oxide and 3.8 mol / L sodium hydroxide.

7. The application according to claim 1, wherein The spongy porous layer of the ion-conducting membrane faces the positive electrode and the dense layer faces the negative electrode.

Images