Doped polyaniline, preparation method thereof and zinc-iodine battery

Abstract

The invention belongs to the technical field of zinc-iodine batteries, and particularly relates to doped polyaniline, a preparation method thereof and a zinc-iodine battery. The preparation method comprises the following steps: in an acidic environment, mixing substituted aniline, aniline and an oxidizing agent to obtain a mixed solution, and carrying out oxidative polymerization reaction to obtain doped polyaniline; wherein a substituent group of the substituted aniline is an electron withdrawing group; the number of the substituent group is 1; the molar ratio of the substituted aniline to the aniline is (5-25): 100; the positive electrode material in the zinc-iodine battery prepared from the doped polyaniline has high specific capacity and cycling stability.

Description

Technical Field

[0001] The invention belongs to the technical field of zinc-iodine batteries, and particularly relates to doped polyaniline and a preparation method thereof, and a zinc-iodine battery. Background Art

[0002] The aqueous zinc-iodine battery (AZB) is an electrochemical energy storage device with zinc as the negative electrode, an iodine-based material as the positive electrode, and an aqueous electrolyte. It has attracted widespread attention for its high safety, high energy density, low cost, and environmental friendliness. The active materials for the positive and negative electrodes, iodine and zinc, respectively, are both highly safe and environmentally friendly. Furthermore, the abundance of zinc and iodine in the Earth's crust makes them easily mined or extracted, giving them the potential for large-scale application in energy storage and other fields.

[0003] However, there is iodine dissolution and shuttle effect at the iodine positive electrode, that is, polyiodide ions (I (2n+1) - , n is a positive integer) dissolves in the electrolyte and diffuses to the negative electrode, resulting in a small capacity and a short service life. The current response strategy is to load iodine on porous carbon (such as activated carbon, graphene) or covalent organic frameworks (COFs) and modify the electrolyte, that is, to introduce polyiodide anchoring agents (such as quaternary ammonium salts, MXene). At present, polyaniline has also been used to bind iodine, but the improvement effect is limited and still cannot meet the use requirements of zinc-iodine batteries. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the existing positive electrode material containing polyaniline cannot take into account both specific capacity and cycle stability, thereby providing a doped polyaniline and a preparation method thereof and a zinc-iodine battery.

[0005] To this end, the present invention provides the following technical solutions:

[0006] The first aspect of the present invention provides a method for preparing doped polyaniline, wherein the method comprises the following steps:

[0007] In an acidic environment, substituted aniline, aniline and an oxidant are mixed to obtain a mixed solution, and an oxidative polymerization reaction is carried out to obtain doped polyaniline;

[0008] Wherein, the substituent group of the substituted aniline is an electron-withdrawing group;

[0009] The number of the substituent groups is 1;

[0010] The molar ratio of the substituted aniline to aniline is (5-25):100.

[0011] In the present invention, the substituted aniline and aniline are protonated in an acidic environment, wherein the acidic environment is a conventional acidic environment in the art, typically but not limitedly, an aqueous sulfuric acid solution is added to provide the acidic environment.

[0012] In the present invention, in order to avoid reaction temperature fluctuations, the substituted aniline and aniline are generally first mixed uniformly, and then the oxidant is prepared into a low-concentration aqueous solution (oxidant concentration ≤ 1 mol / L) and the oxidant aqueous solution is added dropwise to the reaction system. The addition time is generally not less than 30 min. The oxidant is a conventional oxidant in the art. Typically, but not limited to, the oxidant includes persulfate (such as ammonium persulfate, potassium persulfate), hydrogen peroxide, ferric chloride, etc.

[0013] In some optional embodiments, the molar ratio of the substituted aniline to aniline is (7.5-15):100.

[0014] In some optional embodiments, the substituted aniline has a structure shown in formula (1);

[0015]

[0016] Wherein, X includes one of -CF3, -NO2, -SO3H, -COOH, -CN, -F, -Cl, -Br, and -I.

[0017] In some optional embodiments, the substitution site of the substituted aniline is the para position or meta position of the amino group.

[0018] In some optional embodiments, based on the mixed solution, the H + The concentration is 0.1-5mol / L.

[0019] In the present invention, the oxidative polymerization reaction time refers to the time from the completion of the addition of the oxidant to the end of the oxidative polymerization reaction. The conditions of the oxidative polymerization reaction are controlled according to actual conditions. In principle, the lower the temperature, the longer the reaction time. For example, a reaction time of 48 hours at 0°C is similar to a reaction time of 12 hours at 10°C.

[0020] In some optional embodiments, the conditions of the oxidative polymerization reaction include: reaction temperature of -15°C to 60°C, and reaction time of 12-48 hours.

[0021] In some optional embodiments, the doped polyaniline is also subjected to an alkali treatment and an acid treatment step. Alkali treatment can remove impurities, and then acid treatment is performed to make protonation controllable, further ensuring that the doped polyaniline carries a large amount of positive charge. Before the doped polyaniline is subjected to alkali treatment, a washing liquid is also used to clean the doped polyaniline. The washing liquid includes water (deionized water) and ethanol. The washing can remove unreacted substituted aniline, aniline and excess oxidant; the alkali treatment uses the alkali to prepare a solution. The alkali is a conventional reagent in the art. Typically, the alkali includes at least one of sodium hydroxide and potassium hydroxide. The specific amount is selected according to the actual situation. Generally, the alkali is greatly excessive. Typically, the ratio of the total molar amount of substituted aniline to the total molar amount of aniline to the molar amount of the alkali is 1:10-15; the temperature of the alkali treatment is room temperature, and the time The method comprises the steps of: drying the product after alkali treatment and collecting the solid, and drying the solid by vacuum drying at a temperature of 80-100° C. for 10-12 h; in the acid treatment step, the acid used is a conventional acid in the art, typically but not limited to, the acid includes at least one of hydroiodic acid, hydrobromic acid, and hydrochloric acid, and may further be hydroiodic acid; the specific amount is selected according to the actual situation, generally the acid is greatly excessive, typically but not limited to, the ratio of the total molar amount of substituted aniline to the molar amount of aniline to the acid is 1:10-15; the temperature of the acid treatment is room temperature, and the time is 1-4 h.

[0022] In some optional embodiments, the ratio of the substituted aniline to the total molar amount of aniline and the molar amount of the oxidant is 1:1.1-1.5.

[0023] The second aspect of the present invention protects a doped polyaniline prepared by the above-mentioned preparation method.

[0024] A third aspect of the present invention provides a zinc-iodine battery, wherein the zinc-iodine battery comprises a positive electrode, and the positive electrode comprises the aforementioned doped polyaniline.

[0025] In the present invention, the zinc-iodine battery preparation method includes:

[0026] Preparation of the positive electrode: doped polyaniline (or polyaniline), conductive agent (carbon black) and binder (PVDF) are mixed evenly in a mass ratio of 8:1:1. The mixed material is placed in a mold for tableting (the inner diameter of the mold is 10 mm and the pressure is 2.5 tons). The mold is demoulded and the unit area mass of the electrode sheet is 15 mg / cm 2 .

[0027] Zinc-iodine battery assembly: The positive electrode, separator, and zinc foil are sequentially placed into a 2032-size button cell, and an electrolyte (100 μL) is added. The concentration of zinc iodide in the electrolyte is 0.5-1 mol / L, the concentration of zinc sulfate is 2-2.2 mol / L, and the concentration of tetraethylammonium bromide is 0.15-0.18 wt%. The solvent is deionized water, and the separator is glass fiber to obtain a battery.

[0028] The technical solution of the present invention has the following advantages:

[0029] 1. The present invention provides a method for preparing doped polyaniline, wherein the preparation method comprises the following steps: in an acidic environment, mixing substituted aniline, aniline, and an oxidant to obtain a mixed solution, and performing an oxidative polymerization reaction to obtain the doped polyaniline; wherein the substituent group of the substituted aniline is an electron-withdrawing group; the number of the substituent group is 1; and the molar ratio of the substituted aniline to the aniline is (5-25):100; the electron-withdrawing group in the substituted aniline enhances the electronegativity of the doped polyaniline, reduces the electron cloud density of the benzene ring, and the doped polyaniline carries a positive charge after protonation in an acidic environment. The electron-withdrawing group stabilizes the positive charge on the doped polyaniline chain through a conjugation effect, and the positive charge binds iodine through electrostatic action, thereby avoiding or alleviating the decrease in battery positive electrode cycle stability and specific capacity due to iodine dissolution at the iodine positive electrode, and avoiding the shuttle effect that causes the iodine reduction product to not completely return to the positive electrode, thereby decreasing battery cycle performance; the doped polyaniline relies on the redox restriction of nitrogen atoms to limit I3 - Or other polyiodide ions, when all are aniline, the mass proportion of nitrogen atoms is 14 / 91; as the amount of substituted aniline increases, the ratio of 14 / 91 will decrease, and the relative content of active sites will decrease. When the molar ratio of substituted aniline to aniline is appropriate, the restriction ability of doped polyaniline on polyiodide ions will be enhanced, the specific capacity will be improved, the effect of the decrease in specific capacity caused by the decrease in nitrogen content will be offset, and the overall increase will be ensured; the positive electrode material in the zinc-iodine battery prepared by doping polyaniline of the present invention can take into account both specific capacity and cycle stability; when the molar ratio of substituted aniline to aniline is too low, the electronegativity of the doped polyaniline is limited, the iodine binding is limited, and thus the cycle performance is limited. When the molar ratio of substituted aniline to aniline is too high, the proportion of substituents that do not provide positive charge in the polymer increases, and the specific capacity of the prepared zinc-iodine battery electrode decreases.

[0030] 2. The specific molar amount of substituted aniline and aniline in the present invention can further take into account the specific capacity and cycle stability of the zinc-iodine battery positive electrode material.

[0031] 3. The specific type of substituted aniline in the present invention can further take into account the specific capacity and cycle stability of the zinc-iodine battery positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 1 is the infrared spectrum of Example 1 and Comparative Example 1;

[0034] Figure 2 Specific capacity-voltage curves of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0035] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application text are intended to cover non-exclusive inclusions.

[0037] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values ​​and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter can be, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0040] In the description of the embodiments of the present application, the term "at least one" refers to one or more than two (including two).

[0041] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0042] Example 1

[0043] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0044] S1, 20 mmol of aniline, 2 mmol of p-trifluoromethylaniline and 50 mL of 5°C aqueous sulfuric acid solution (concentration of 0.2 mol / L) were mixed and stirred until completely dissolved; 50 mL of 5°C ammonium persulfate solution (molar amount of ammonium persulfate was 33 mmol) was added dropwise, the ratio of the total molar amount of p-trifluoromethylaniline to the total molar amount of aniline and the molar amount of ammonium persulfate was 1:1.5, the addition time was 30 min, the system temperature was maintained at 5°C, and after the addition was completed, an oxidative polymerization reaction was carried out at 5°C for 24 h to obtain doped polyaniline;

[0045] S2, after filtering the product, collecting the solid obtained in step S1, washing the solid with deionized water and ethanol, and treating the solid with an alkali solution having a concentration of 1 mol / L sodium hydroxide, wherein the ratio of the total molar amount of substituted aniline to the total molar amount of aniline to the molar amount of sodium hydroxide is 1:10; the alkali treatment time is 1 hour, filtering the product after the alkali treatment, collecting the solid, and vacuum drying at 80° C. for 12 hours, and acid-treating the dried solid with a 1 mol / L hydroiodic acid solution, wherein the ratio of the total molar amount of substituted aniline to the total molar amount of aniline to the molar amount of hydroiodic acid is 1:10; wherein the acid treatment time is 2 hours, filtering the acid-treated product again, collecting the solid, washing the solid with deionized water and ethanol, and vacuum drying at 80° C. for 12 hours;

[0046] The infrared spectrum of doped polyaniline is as follows Figure 1 As shown, Figure 1 The infrared spectra of Example 1 and Comparative Example 1 are shown in FIG. 1 . Compared with Comparative Example 1, the 694 cm -1 、744cm -1 The intensity of this pair of peaks is weakened, indicating that the number of monosubstituted benzene rings has decreased. The peaks at 806 cm-1 of Example 1 are -1 Position peak (due to 820cm -1 The strong peak near the bottom (shown as a shoulder on the graph) shows an increase in the structure of para-substituted structures. The corresponding change here shows that trifluoromethylaniline is polymerized as a monomer. The peak at 1066 cm in Example 1 -1 The extra single peak at represents the fluorine-carbon bond, proving the existence of trifluoromethyl on polyaniline.

[0047] Example 2

[0048] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0049] The process was carried out in the same manner as in Example 1, except that the amount of p-trifluoromethylaniline used was 1 mmol.

[0050] Example 3

[0051] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0052] The process was carried out in the same manner as in Example 1, except that the amount of p-trifluoromethylaniline used was 5 mmol.

[0053] Example 4

[0054] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0055] The same method as in Example 1 was used, except that p-trifluoromethylaniline was replaced with an equimolar amount of m-trifluoromethylaniline.

[0056] Example 5

[0057] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0058] The method of Example 1 was followed, except that p-trifluoromethylaniline was replaced with an equimolar amount of p-nitroaniline.

[0059] Example 6

[0060] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0061] The same method as in Example 1 was used, except that p-trifluoromethylaniline was replaced with an equimolar amount of p-aminobenzenesulfonic acid.

[0062] Example 7

[0063] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0064] The method of Example 1 was followed, except that p-trifluoromethylaniline was replaced with an equimolar amount of 4-fluoroaniline.

[0065] Example 8

[0066] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0067] The method of Example 7 was followed, except that the amount of 4-fluoroaniline used was 1 mmol.

[0068] Example 9

[0069] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0070] The method of Example 7 was followed, except that the amount of 4-fluoroaniline used was 5 mmol.

[0071] Example 10

[0072] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0073] The same method as in Example 1 was used, except that p-trifluoromethylaniline was replaced with an equimolar amount of 4-chloroaniline.

[0074] Example 11

[0075] This embodiment provides a doped polyaniline, and the preparation method includes the following steps:

[0076] The method of Example 1 was followed, except that p-trifluoromethylaniline was replaced with an equimolar amount of o-trifluoromethylaniline.

[0077] Comparative Example 1

[0078] This comparative example provides a polyaniline, and the preparation method comprises the following steps:

[0079] The method of Example 1 was followed, except that “20 mmol of aniline, 2 mmol of p-trifluoromethylaniline” was changed to “22 mmol of aniline”.

[0080] Comparative Example 2

[0081] This comparative example provides a doped polyaniline, the preparation method of which comprises the following steps:

[0082] The method of Example 1 was followed, except that the amount of aniline used was 20 mmol and the amount of p-trifluoromethylaniline used was 0.5 mmol.

[0083] Comparative Example 3

[0084] This comparative example provides a doped polyaniline, the preparation method of which comprises the following steps:

[0085] The method of Example 1 was followed, except that the amount of aniline used was 20 mmol and the amount of p-trifluoromethylaniline used was 8 mmol.

[0086] Comparative Example 4

[0087] This comparative example provides a doped polyaniline, the preparation method of which comprises the following steps:

[0088] The method of Example 1 was followed except that p-trifluoromethylaniline was replaced with an equal molar amount of 2,4,6-trichloroaniline. Test Case

[0089] Preparation of the positive electrode: The doped polyaniline or polyaniline prepared in the example and the comparative example, the conductive agent (carbon black) and the binder (PVDF) were mixed uniformly in a mass ratio of 8:1:1. The mixed material was placed into a mold for tableting (the mold inner diameter was 10 mm and the pressure was 2.5 tons) and then demolded. The unit area mass of the electrode sheet was 15 mg / cm 2 .

[0090] Zinc-iodine battery assembly: The positive electrode, separator, and zinc foil were sequentially placed into a 2032-size button cell, and an electrolyte (100 μL) was added. The concentration of zinc iodide in the electrolyte was 0.8 mol / L, the concentration of zinc sulfate was 2 mol / L, and the concentration of tetraethylammonium bromide was 0.15 wt%. The solvent was deionized water, and the separator was glass fiber to obtain a battery.

[0091] The specific capacity test method of zinc-iodine battery is as follows: current (A) = current density (here 0.2A / g) × positive electrode mass (g). After charging to 1.4V according to the calculated current, discharge to 0.6V with the same current; specific capacity = average discharge capacity of the 10th-20th cycle / positive electrode mass.

[0092] Cycling performance test method of zinc-iodine battery: Current (A) = current density (here 1A / g) × positive electrode mass (g), charge to 1.4V according to the calculated current, and then discharge to 0.6V with the same current; Capacity retention rate = discharge capacity at the 1000th cycle / initial capacity (the average discharge capacity of the 11th to 20th cycles is used as the initial capacity) × 100%.

[0093] The specific test data are shown in Table 1;

[0094] Table 1

[0095] Specific capacity (mAh / g) Capacity retention rate (%) Example 1 249.5 89 Example 2 223.6 86 Example 3 237.2 87 Example 4 253.9 82 Example 5 224.3 88 Example 6 231.8 82 Example 7 243.3 88 Example 8 230.8 85 Example 9 229.1 86 Example 10 219.1 82 Example 11 233.8 89 Comparative Example 1 208.2 76 Comparative Example 2 212.0 77 Comparative Example 3 183.0 87 Comparative Example 4 192.0 88

[0096] The batteries prepared in Example 1 and Comparative Example 1 were subjected to constant current charge and discharge tests, with the charge and discharge voltage range being 0.6-1.4V, and the specific capacity-voltage curves were obtained as shown in FIG. Figure 2 As shown in the figure, it can be seen that at the same voltage, the specific capacity of trifluoromethyl substituted polyaniline in the charging process and the discharging process is significantly improved compared with the unsubstituted polyaniline.

[0097] Comparing Example 1 with Comparative Example 3, it can be seen that although Comparative Example 3 has a higher capacity retention rate, the specific capacity is low and cannot meet the needs. The inventors speculate that the reason may be that the proportion of substituents that do not provide positive charge in the polymer increases, the relative content of active sites decreases, and the specific capacity of the prepared zinc-iodine battery electrode decreases.

[0098] Comparison of Example 1 with Comparative Example 4 shows that although Comparative Example 4 has a higher capacity retention rate, the specific capacity is low and cannot meet the requirements. The inventors speculate that the reason may be that the introduction of multiple electron-withdrawing groups (chlorine atoms) significantly reduces the electron cloud density of the benzene ring, making the oxidative polymerization reaction of the aniline monomer more difficult, which may lead to polymer chain breakage or uneven molecular weight distribution, and increase the structural defects of the doped polyaniline formed.

[0099] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing doped polyaniline, characterized in that: The preparation method comprises the following steps: In an acidic environment, substituted aniline, aniline and an oxidant are mixed to obtain a mixed solution, and an oxidative polymerization reaction is carried out to obtain doped polyaniline; Wherein, the substituent group of the substituted aniline is an electron-withdrawing group; The number of the substituent groups is 1; The molar ratio of the substituted aniline to aniline is (5-25):

100.

2. The preparation method according to claim 1, characterized in that The molar ratio of the substituted aniline to aniline is (7.5-15):

100.

3. The preparation method according to claim 1 or 2, characterized in that The substituted aniline has a structure shown in formula (1); Wherein, X includes one of -CF3, -NO2, -SO3H, -COOH, -CN, -F, -Cl, -Br, and -I.

4. The preparation method according to claim 3, characterized in that The substitution site of the substituted aniline is the para position or meta position of the amino group.

5. The preparation method according to any one of claims 1 to 4, characterized in that Based on the mixed solution, the H + The concentration is 0.1-5mol / L.

6. The preparation method according to any one of claims 1 to 5, characterized in that The conditions of the oxidative polymerization reaction include: reaction temperature of -15°C to 60°C, and reaction time of 12-48 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that The doped polyaniline was also subjected to base treatment and acid treatment steps.

8. The preparation method according to any one of claims 1 to 7, characterized in that The ratio of the total molar amount of the substituted aniline to the total molar amount of the aniline to the molar amount of the oxidant is 1:1.1-1.

5.

9. Doped polyaniline prepared by the preparation method according to any one of claims 1 to 8.

10. A zinc-iodine battery, characterized in that: The zinc-iodine battery comprises a positive electrode, and the positive electrode comprises the doped polyaniline according to claim 9.

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