A pH-sensitive imidazolyl polyion film modified graphite paper and a preparation method and application thereof

Abstract

The application belongs to the technical field of electrochemistry, and discloses an imidazole-based polyionic thin film modified graphite paper with pH sensitivity, and a preparation method and application thereof. The modified graphite paper is coated with an imidazole-based polyionic liquid and a polyacid compound dissolved in a solvent to obtain a mixed solution, which is subjected to in-situ electrostatic covalent cross-linking reaction at 100-400 DEG C. The application generates a porous ionic liquid thin film interface on the surface of the graphite paper through in-situ electrostatic covalent cross-linking, and the pH-sensitive response characteristics of the ionic liquid thin film interface significantly inhibit the I2 positive electrode loss and zinc metal corrosion reaction, and significantly improve the cycle life and electrochemical performance of the flexible zinc-iodine battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemistry, and in particular relates to a graphite paper modified with an imidazole-based polyion film sensitive to pH, and a preparation method and application thereof. BACKGROUND

[0002] At present, the global industry is developing rapidly, and lithium-ion batteries are widely used in portable electronic devices and energy storage devices due to their high energy density and long service life. At the same time, with the development of electric vehicles and flexible electronics, higher requirements are put forward for the comprehensive performance of batteries. Further reducing the amount of non-active materials in the battery and achieving high utilization of the battery are important directions for future battery development. Flexible graphite paper, also known as expanded graphite, expanded graphite, and combustible graphite, is a semiconductor material that is light in weight, reasonably priced, and easy to produce. Due to its excellent physical and chemical properties such as low density and high chemical stability, graphite paper material is widely studied for use as a current collector in batteries. China has abundant graphite resources, and the development and application of flexible graphite materials have great economic and practical significance. At present, when graphite paper material is used as a negative active material or an electrode additive material, due to the presence of many active sites such as surface area defects, it is prone to irreversible reactions with electrolyte, resulting in a generally low first coulombic efficiency, which cannot be practically applied in batteries. This is also a problem that needs to be solved in the research of graphite paper active materials today. Graphite paper as a current collector in the direction of new energy is a relatively advanced development direction, and due to the strong hydrophobicity of the surface of traditional graphite paper, there are often many difficulties in its use in this direction.

[0003] Zinc-iodine secondary batteries have high capacity ratio, and zinc and iodine elements are abundant, environmentally friendly, and low in manufacturing cost, and safe in post-processing. However, iodine will spontaneously dissociate under alkaline electrolyte conditions, lose activity, and cause capacity decay, and will also undergo "shuttle effect" under concentration difference conditions. In addition, iodine has poor electrical conductivity and poor thermal stability, which inhibits its development. Therefore, how to overcome the defects of zinc-iodine batteries and obtain zinc-iodine batteries with good use performance is a problem that needs to be solved in the field. Patent CN113036144A discloses a zinc-iodine battery positive electrode composite material, a preparation method and application thereof, a doped porous carbon derived from a covalent organic framework compound is compounded with active iodine to form a zinc-iodine battery positive electrode material with excellent electrochemical performance, and the doped porous carbon can well bind the polyiodide anions formed by iodine in the cycle to inhibit the shuttle effect of polyiodide anions, but the capacity retention rate is not high and the cycle capacity retention rate is prone to decay. In patent CN113725414B, an anion exchange material is used as a host to load iodine to limit the free diffusion of intermediate products generated by iodine during charging and discharging, thereby avoiding serious self-discharge behavior and rapid capacity decay of the battery, and greatly improving the electrochemical performance of the prepared battery, but the iodine loading capacity is low and the cycle capacity retention rate can only reach 85%.

[0004] Therefore, zinc-iodine battery is one of the most promising candidates in the field of future electrical energy storage, and the electrochemical performance of graphite paper meets the requirements of the market mainstream. Therefore, surface modification of graphite paper current collector, introduction of hydrophilic functional groups, inhibition of shuttle effect of polyiodide anions, increase of iodine utilization rate, and maintenance of excellent electrochemical performance are the key technical problems to be solved in the application field at present. SUMMARY

[0005] The primary purpose of the present application is to provide a graphite paper modified with a pH-sensitive imidazole-based polyion film.

[0006] Another purpose of the present application is to provide a preparation method of the above-mentioned graphite paper modified with a pH-sensitive imidazole-based polyion film. The method uses a simple process of doctor blade coating to construct an imidazole-based polyion liquid interface layer on the surface of the graphite paper. The prepared graphite paper can not only meet the demand for electrical conductivity, but also effectively inhibit the shuttle effect of polyiodide anions in zinc-iodine batteries and improve the transmission rate of zinc ions, and is light in weight, which is conducive to improving the energy density of the battery.

[0007] Still another purpose of the present application is to provide the application of the above-mentioned graphite paper modified with a pH-sensitive imidazole-based polyion film. Zinc-iodine batteries are easily prepared by using an electrochemical double deposition strategy to achieve high surface energy density and fast kinetics. At the same time, they also have the function of switchable polarity, which can tolerate the confusion of positive and negative electrodes.

[0008] To solve the above problems, the technical scheme adopted by the present application is:

[0009] A graphite paper modified with a pH-sensitive imidazole-based polyion film, wherein the modified graphite paper is prepared by coating an imidazole-based polyion liquid and a polyacid compound dissolved in a solvent to obtain a mixed solution, and then performing in-situ electrostatic covalent cross-linking reaction at 100-400 DEG C.

[0010] Preferably, the imidazole-based ionic liquid is one or more of poly-1-cyano-3-vinylimidazole dicyanamide, 1-benzyl-3-methyl imidazolium bromide, or 1-carboxy-3-vinylimidazole bromide.

[0011] Preferably, the mass ratio of imidazole-based ionic liquid to polyacid compound is (0.5-1.5):1.

[0012] Preferably, the solvent is dimethyl sulfoxide, dimethyl formamide, or tetrahydrofuran.

[0013] Preferably, the polyacid compound is polyacrylic acid, polymethacrylic acid, or poly(2-ethyl acrylic acid).

[0014] Preferably, the thickness of the modified graphite paper is 0.155-0.25 mm, the thickness of the graphite paper in the imidazolium-based polyionic film modified graphite paper is 0.15-0.2 mm, and the thickness of the imidazolium-based polyionic film is 5-50 μm.

[0015] The preparation method of the imidazolium-based polyionic film modified graphite paper with pH sensitivity comprises the following specific steps:

[0016] S1. Dissolve the imidazolium-based ionic liquid in a solvent, add a polyacid compound and stir to obtain a mixed solution;

[0017] S2. Place the graphite paper on a coating machine, drop the mixed solution on the surface of the graphite paper, and let it stand for reaction, then vacuum dry, soak in ammonia water, wash with water, dry, and then place the coated graphite paper in a tube furnace, pass in inert gas argon, and anneal at 100-400℃ for 2-4h to obtain the imidazolium-based polyionic film modified graphite paper with pH sensitivity.

[0018] Preferably, the standing reaction time in step S2 is 1-2h, and the vacuum drying time is 10-20min.

[0019] Preferably, the concentration of the ammonia water in step S2 is 0.2-0.5% w / w.

[0020] The imidazolium-based polyionic film modified graphite paper with pH sensitivity is applied in a zinc-iodine battery.

[0021] The imidazolium-based polyionic film modified graphite paper of the present application is a polyimidazolium-based ionic liquid interface modified graphite paper, and the coating layer is prepared by first electrostatic crosslinking of the imidazolium-based ionic liquid and the polyacid compound, and then covalent crosslinking. The imidazolium-based polyionic film modified graphite paper is stable in electrolyte solution and can work in a wider environmental window. As the positive and negative electrode current collector material of the zinc-iodine battery, the imidazolium-based polyionic film modified graphite paper solves the problem of uneven coating of electrode materials caused by poor hydrophilicity of graphite paper through modification of the conductive polymer on the surface of the graphite paper.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The present application realizes the adsorption of polyiodide on the positive electrode side film interface and the exclusion of polyiodide on the negative electrode side film interface during the discharge process by in-situ electrostatic covalent crosslinking of a porous ionic liquid film interface on the surface of the graphite paper, based on the characteristics that the pH of the positive electrode environment is lower than that of the negative electrode environment in the zinc-iodine battery, thereby significantly inhibiting the I2 positive electrode loss and zinc metal corrosion reaction, and significantly improving the cycle life and electrochemical performance of the flexible zinc-iodine battery.

[0024] 2. The present application builds an imidazolium-based ionic liquid interface on the graphite paper, which mainly realizes the adsorption of ions through a large number of functional groups in the molecules. Its adsorption characteristics are: ① pH sensitive; ② high efficiency. During the discharge process, due to the dynamic regulation of the interface functional groups, the pH gradually decreases from the negative electrode interface to the positive electrode interface. In a lower pH environment, the positive electrode side adsorbs polyiodide negative ions, effectively inhibiting the shuttle effect.

[0025] 3. The imidazolium-based ionic liquid interface constructed in the present application has a porous surface structure, so it has a higher specific area (1500-2600 m 2 / g), thereby realizing a faster electron transmission rate.

[0026] 4. The zinc-iodine battery of the present application uses imidazolium-based polyion film modified graphite paper as the positive and negative electrode current collector, which is light in mass, greatly reduces the proportion of non-active materials in the battery, and improves the energy density of the battery; and the graphite paper has excellent electrochemical corrosion resistance and will not undergo the corrosion and oxidation behaviors commonly seen in metal current collectors. The spacing between the two adjacent interdigital structures on the graphite paper electrode modified with different imidazolium-based polyion films does not change, and the connectivity between the electrodes is good, and the preparation process will not cause short circuit or open circuit, and the interdigital structure profile is clear. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the zinc-iodine battery assembled by the imidazolium-based polyion film modified graphite paper of the present application.

[0028] Figure 2 is a surface scanning electron microscope photo of the imidazolium-based polyion film modified graphite paper prepared in Example 1.

[0029] Figure 3 is the contact angle of the imidazolium-based polyion film modified graphite paper prepared in Example 1.

[0030] Figure 4 is the electrochemical performance diagram of the zinc-iodine battery assembled by the imidazolium-based polyion film modified graphite paper prepared in Example 1.

[0031] Figure 5 is a scanning electron microscope photo of the imidazolium-based polyion film modified graphite paper prepared in Example 1 after 200 cycles.

[0032] Figure 6 is the ultraviolet test of the electrolyte during the charging process of the zinc-iodine battery assembled by the imidazolium-based polyion film modified graphite paper prepared in Example 1.

[0033] Figure 7 is a surface scanning electron microscope photo of the untreated graphite paper of Comparative Example 1.

[0034] Figure 8 This is the contact angle of the untreated graphite paper in Comparative Example 1.

[0035] Figure 9 This is a graph showing the electrochemical performance of a zinc-iodine battery assembled with untreated graphite paper, as shown in Comparative Example 1.

[0036] Figure 10 This is a UV test of the electrolyte during the charging process of a zinc-iodine battery assembled with untreated graphite paper, as shown in Comparative Example 1. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0038] Example 1

[0039] 1. Weigh 10.0 g of 1-vinylimidazolium and 12.6 g of bromoacetonitrile and dissolve them in 70 mL of acetone. Stir at room temperature for 24 h to precipitate a white or light yellow powder. Filter the precipitate, wash it three times with 70 mL of diethyl ether, and then dry it under vacuum at room temperature for 12 h to obtain 1-cyano-3-vinylimidazolium bromide monomer.

[0040] 2. Dissolve 20 g of 1-cyano-3-vinylimidazolium bromide monomer and 0.4 g of azobisisobutyronitrile in 200 mL of dimethyl sulfoxide. Deoxygenate three times using a freeze-pump-thaw process, and finally purge with nitrogen. Then place the reaction mixture in an oil bath at 75 °C for 24 h. When cooled to room temperature, add the reaction mixture dropwise to excess tetrahydrofuran. Filter off the precipitate to obtain poly(1-cyano-3-vinylimidazolium bromide), wash with excess ethanol, and dry under vacuum at 60 °C.

[0041] 3. Slowly add sodium dicyandiamide solution (0.917 g sodium dicyandiamide dissolved in 30 mL of water) dropwise to poly(1-cyano-3-vinylimidazolium) bromide solution (2 g poly(1-cyano-3-vinylimidazolium) bromide dissolved in 60 mL of water). The resulting poly(1-cyano-3-vinylimidazolium) precipitates in water, is filtered, and dried to constant weight to obtain poly(1-cyano-3-vinylimidazolium) powder.

[0042] 4. Dissolve 4.5g of poly(1-cyano-3-vinylimidazolium dicyandiamide) and 3g of polyacrylic acid in 50mL of dimethyl sulfoxide and stir overnight to prepare a homogeneous and transparent ionic liquid mixture.

[0043] 5. Place the graphite paper on a coating machine, drop the prepared ionic liquid mixture onto the graphite paper surface, and coat it. Place it in a vacuum oven at 80℃ for 10 minutes to allow the solution to evaporate. Then immerse it in 0.2% w / w ammonia water for 2 hours. Finally, wash it with water and dry it in a vacuum oven for 2 hours. Finally, anneal it in a tube furnace at 200℃ for 2 hours after purging with argon gas. After the in-situ electrostatic covalent crosslinking reaction, graphite paper modified with an imidazole-based polyion exchange film is obtained. The thickness of the imidazole-based polyion exchange film is 5–50 μm, and it exhibits pH sensitivity.

[0044] The prepared imidazole-based polyion exchange membrane-modified graphite paper was assembled into a coin cell. A zinc-iodine battery was obtained by adding a mixed electrolyte of 2.0 mol / L ZnSO4 and 0.5 mol / L 1-methyl-3-propylimidazolium iodide. Constant current charge-discharge tests were performed using the Xinwei Electrochemical Working System CT-4008-10V50mA-164.

[0045] Figure 1 This is a schematic diagram of a zinc-iodine battery assembled using graphite paper modified with an imidazole-based polyionomer thin film, according to the present invention. Figure 1 It is known that during the discharge process, the pH value at the positive electrode interface is lower than that at the negative electrode. Furthermore, the triazine ring structure on the positive electrode side of the graphite paper modified with imidazole-based polyionomer film plays a role in adsorbing polyiodide anions, reducing their shuttle effect in the electrolyte. Meanwhile, in the polycation-anion coordination mechanism on the negative electrode side of the imidazole-based polyionomer film-modified graphite paper, the anions on the coordination orbitals play a secondary diffusion role on the cations, achieving Zn... 2+ Rapid internal migration reduces polarization voltage, thereby suppressing dendrite growth and hydrogen evolution side reactions, significantly improving the cycle life and safety of zinc-iodine batteries. Figure 2 These are scanning electron microscope (SEM) images of the graphite paper prepared in Example 1. From... Figure 2 It can be seen that the graphite paper modified with imidazole-based polyion exchange films has a dense porous structure. Figure 3 The contact angle of the graphite paper prepared in Example 1 is... Figure 3 It can be seen that a significantly reduced contact angle is beneficial for the graphite paper to be fully wetted by the electrolyte. Figure 4 The image shows the electrochemical performance of the zinc-iodine battery assembled in Example 1. It can be seen that the assembled zinc-iodine battery has excellent cycle stability and long cycle life. Figure 5 These are scanning electron microscope (SEM) images of the negative electrode side of graphite paper modified with imidazole-based polyionomer thin films after 200 cycles. Figure 5 It can be seen that the morphology of the graphite paper remains good after cycling, and the distribution of each element is uniform. Figure 6 This is the result of the ultraviolet test of the electrolyte during the charging process in this embodiment, from... Figure 6 It can be seen that the zinc-iodine battery assembled with graphite paper modified with imidazole-based polyion exchange membrane can suppress I3 in the electrolyte.- shuttle effect.

[0046] Example 2

[0047] The difference between Example 2 and Example 1 is that in Step 4, 1-benzyl-3- methylimidazolium bromide and poly(acrylic acid) with a mass ratio of 1:1 were dissolved in dimethylformamide and stirred for 10 h to prepare a homogeneous mixed solution. The graphite paper was placed on a coating machine, and the prepared mixed solution was added dropwise onto the surface of the graphite paper. After standing for 1 h, coating was performed, and the solution was allowed to volatilize in a vacuum oven at 80°C for 10 min. Then, the graphite paper was immersed in 0.2% w / w ammonia water for 2 h. After washing with water and drying in a vacuum oven for 2 h, the graphite paper was annealed in a tube furnace under argon at 200°C for 2 h to cause in-situ electrostatic covalent crosslinking, thereby preparing the imidazole-based polyionic film-modified graphite paper.

[0048] Example 3

[0049] The difference between Example 3 and Example 1 is that in Step 4, 1-carboxyl-3- vinylimidazolium bromide and poly(2-ethyl acrylic acid) with a mass ratio of 1:1 were dissolved in dimethylformamide and stirred for 10 h to prepare a homogeneous mixed solution. The graphite paper was placed on a coating machine, and the mixed solution was added dropwise onto the surface of the graphite paper. After standing for 1 h, coating was performed, and the solution was allowed to volatilize in a vacuum oven at 80°C for 10 min. Then, the graphite paper was immersed in 0.2% w / w ammonia water for 2 h. After washing with water and drying in a vacuum oven for 2 h, the graphite paper was annealed in a tube furnace under argon at 200°C for 2 h to cause in-situ electrostatic covalent crosslinking, thereby preparing the imidazole-based polyionic film-modified graphite paper.

[0050] Comparative Example 1

[0051] Figure 7 is a surface scanning electron microscope image of the untreated graphite paper of Comparative Example 1. It can be seen from Figure 7 that the morphology of the graphite paper is smooth, and the specific surface area is very small. Figure 8 is the contact angle of the untreated graphite paper of Comparative Example 1, and the hydrophobic graphite paper is not conducive to the infiltration of the electrolyte. Figure 9 is the electrochemical performance diagram of the zinc-iodine battery assembled by the untreated graphite paper of Comparative Example 1, and the test condition is a current density of 0.1 mA cm -2 . It can be seen from Figure 9 that the battery assembled by the untreated graphite paper has poor cycle stability and a short service life. Figure 10 is the ultraviolet test of the electrolyte during the charging process of the zinc- iodine battery assembled by the untreated graphite paper of Comparative Example 1. It can be seen from Figure 10 that the content of I3 - in the electrolyte during the charging process of the untreated graphite paper increases significantly, indicating that the untreated graphite paper cannot inhibit the shuttle of I3 - , thereby causing capacity attenuation.

[0052] The zinc-iodine batteries composed of Example 1 and Comparative Example 1 were compared respectively, and the current density was 0.1 mA cm -2 , the charge-discharge performance test was carried out, and the results are shown in Table 1. Table 1 is the performance of the zinc-iodine batteries prepared by Examples 1-3 and Comparative Example 1. From Table 1, the transverse comparison data of Example 1 and Example 2, Example 3, and Comparative Example 1 prove that the electrochemical performance of the graphite paper modified by the imidazole-based polyion thin film with pH sensitivity is better than that of the untreated graphite paper electrode. The surface coating can improve the coulombic efficiency and cycle life of the zinc-iodine battery by inhibiting the I3 - shuttle effect.

[0053] Table 1 Performance of zinc-iodine batteries assembled by Examples 1-3 and Comparative Example 1

[0054]

[0055] The batteries composed of Examples 1-3 and Comparative Example 1 were compared respectively in the change of pH during the cycle, and the current density was 0.1 mA cm -2 , and the results are shown in Table 2. Table 2 is the change of pH of the zinc-iodine batteries prepared by Examples 1-3 and Comparative Example 1 during the cycle. From Table 2, the imidazole-based ionic liquid coating is sensitive to pH, and in the discharge process, dynamic pH regulation is achieved. The graphite paper modified by the imidazole-based polyion thin film has a large number of functional groups in the molecule, and has a higher adsorption property for polyiodine ions in a lower pH environment.

[0056] Table 2 Performance of zinc-iodine batteries assembled by Examples 1-3 and Comparative Example 1

[0057]

[0058] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A graphite paper modified with a pH-sensitive imidazolium-based polyion thin film, characterized in that, The modified graphite paper is prepared by coating imidazole-based polyionic liquid and polyacid compound dissolved in a solvent to obtain a mixed solution, and then performing in-situ static covalent cross-linking reaction at 100-400 DEG C. The imidazole-based polyionic liquid is poly(1-cyano-3-vinylimidazolium dicyanamide), the mass ratio of the imidazole-based polyionic liquid to the polyacid compound is (0.5-1.5):1, the solvent is dimethyl sulfoxide, dimethyl formamide or tetrahydrofuran, the polyacid compound is poly(acrylic acid), poly(methacrylic acid) or poly(2-ethyl acrylic acid), the thickness of the modified graphite paper is 0.155-0.25 mm, the thickness of the graphite paper in the imidazole-based polyionic film modified graphite paper is 0.15-0.2 mm, and the thickness of the imidazole-based polyionic film is 5-50 μm.

2. The method for preparing pH-sensitive imidazole-based polyionomer film-modified graphite paper according to claim 1, characterized in that, The method comprises the following specific steps: S1. dissolving the imidazole-based polyionic liquid in a solvent, adding the polyacid compound and stirring to obtain a mixed solution; S2. placing the graphite paper on a coating machine, dropping the mixed solution on the surface of the graphite paper, and then performing static reaction, vacuum drying, soaking in ammonia water, washing with water, drying, placing the coated graphite paper in a tube furnace, introducing inert gas argon, and annealing at 100-400 DEG C for 2-4 h to obtain the imidazole-based polyionic film modified graphite paper with pH sensitivity.

3. The method of claim 2, wherein the pH-sensitive imidazolium-based polyion membrane-modified graphite paper is prepared by the steps of: (a) preparing a graphite paper; (b) preparing an imidazolium-based polyion membrane; and (c) coating the imidazolium-based polyion membrane on the graphite paper. The static reaction time in step S2 is 1-2 h, and the vacuum drying time is 10-20 min.

4. The method of claim 2, wherein the pH-sensitive imidazolium-based polyion membrane-modified graphite paper is prepared by the steps of: (a) preparing a graphite paper; (b) preparing an imidazolium-based polyion membrane; and (c) coating the imidazolium-based polyion membrane on the graphite paper. The concentration of the ammonia water in step S2 is 0.2-0.5% w / w.

5. Application of the imidazole-based polyionic film modified graphite paper with pH sensitivity in zinc-iodine batteries according to claim 1.

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