Carbon dot modified low-temperature-resistant hydrogel solid electrolyte membrane and preparation method thereof

Abstract

The invention discloses a carbon dot modified low-temperature-resistant hydrogel solid electrolyte membrane and a preparation method thereof, and the preparation method specifically comprises the following steps: synthesis of S001 carbon dots, reaction of citric acid and 3-aminobenzene sulfonic acid in N, N-dimethylformamide, high-pressure heating after adding ethidene diamine, ethanol precipitation, dialysis and freeze drying to obtain CD powder; and S002 preparation of the PAM-CD hydrogel solid electrolyte membrane: mixing and stirring acrylamide, ammonium persulfate, N, N '-methylene bisacrylamide and CD powder, pouring the mixture into a mold for crosslinking, then soaking the mixture in a zinc trifluoromethanesulfonate solution, and finally naturally drying the mixture to obtain the PAM-CD hydrogel solid electrolyte membrane. The carbon dots CD break the hydrogen-bond interaction among water molecules in the hydrogel through surface functional groups, so that the ionic conductivity and the mechanical strength of the hydrogel are enhanced, and the low-temperature resistance, the relatively high ionic conductivity and the mechanical durability of the solid electrolyte membrane are further realized; the zinc ion battery assembled by using the hydrogel solid electrolyte membrane shows excellent cycling stability at low temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogel preparation, and particularly relates to a carbon dot modified low-temperature resistant hydrogel solid electrolyte membrane and a preparation method thereof. Background Art

[0002] Zinc ion aqueous solution batteries based on hydrogel electrolytes have attracted extensive attention in next-generation flexible and wearable devices due to their inherent safety, mechanical flexibility, and high stability at the electrode-electrolyte interface. In particular, compared with traditional liquid electrolytes, hydrogel electrolytes have also been proven to be more effective in suppressing Zn dendrites and side reactions caused by the interaction between Zn2+ and functional groups in the hydrogel. However, due to the relatively high freezing point of water, the use of traditional hydrogel electrolytes will inevitably freeze below zero degrees. This will greatly reduce the mechanical properties and ionic conductivity of the polymer gel, resulting in a decline in cycle stability and even short circuit.

[0003] Currently, two main strategies of high-concentration salts and organic additives have been proven to obtain anti-freezing hydrogel electrolytes to achieve batteries with low-temperature performance. However, there are the following problems: Although high-concentration salts can inhibit the freezing of hydrogels at low temperatures, they are expensive, have poor electrolyte wettability, and serious salt precipitation at low temperatures. Crucially, the use of high-concentration salts in batteries will reduce the mechanical durability of the hydrogel. For organic additives, during the coordination process, the radius of the Zn2+ solvation structure increases, which will reduce the ionic conductivity of the battery, especially at low temperatures, and the ionic conductivity decreases significantly. Summary of the Invention

[0004] Embodiments of the present application solve the problems of poor low-temperature resistance and low ionic conductivity of traditional hydrogel electrolytes in the prior art by providing a carbon dot modified low-temperature resistant hydrogel solid electrolyte membrane and a preparation method thereof. Through the introduction of carbon dots CD, the low-temperature resistance performance and relatively high ionic conductivity of the hydrogel electrolyte are achieved.

[0005] Embodiments of the present application provide a preparation method of a carbon dot modified low-temperature resistant hydrogel solid electrolyte membrane, which is characterized by including the following steps:

[0006] S001 Synthesis of carbon dots: Through the reaction of citric acid and 3-aminobenzenesulfonic acid in N,N-dimethylformamide, after adding ethylenediamine, high-pressure heating is carried out, and then ethanol precipitation, dialysis, and freeze-drying are performed to obtain CD powder;

[0007] S002 Preparation of PAM-CD hydrogel: Mix acrylamide, ammonium persulfate, N,N'-methylenebisacrylamide, and a certain amount of CD powder and stir, pour it into a mold for crosslinking, then soak it in a zinc trifluoromethanesulfonate solution, and finally naturally dry to obtain a PAM-CD hydrogel solid electrolyte membrane.

[0008] Preferably, the mass ratio of the CD powder in the step S002 to acrylamide is 3:100.

[0009] Preferably, the cut-off molecular weight of the dialysis bag for dialysis in the step S001 is 3500.

[0010] Preferably, in the step S002, specifically, the solution after adding the CD powder and stirring evenly is poured into a mold and crosslinked in an oven at 60 °C for 2 h, and then cooled and soaked in a 2 zinc trifluoromethanesulfonate solution for 12 h.

[0011] The embodiment of the present invention also provides a carbon dot-modified low-temperature-resistant hydrogel solid electrolyte membrane, and the hydrogel solid electrolyte membrane is prepared by the above preparation method.

[0012] One technical solution provided in the embodiment of the present application has at least the following technical effects:

[0013] 1. Since carbon dots CD are introduced into the preparation process of the polyacrylamide (PAM)-based hydrogel solid electrolyte membrane, the carbon dots CD break the hydrogen bond between water molecules in the hydrogel through surface functional groups, enhance the ionic conductivity and mechanical strength of the hydrogel. Therefore, the problems of poor low-temperature resistance and low ionic conductivity of traditional hydrogel electrolytes in the prior art are effectively solved, and the low-temperature resistance performance and high ionic conductivity of the hydrogel electrolyte are realized.

[0014] 2. The carbon dots CD in the embodiment of the present invention serve as covalent connection points of the PAM molecular chain, improving the breaking strength and mechanical durability of the hydrogel.

[0015] 3. The introduction of the carbon dots CD in the embodiment of the present invention adjusts the solvation structure of zinc ions, improving the ionic conductivity. Description of the Drawings

[0016] Figure 1 It is a comparison chart of the low-temperature resistance test results of the PAM hydrogel solid electrolyte membrane in Example 1 and the PAM-CA-2 hydrogel solid electrolyte membrane in Example 3 of the present application at -30 °C;

[0017] Figure 2 It is a SEM diagram of the PAM hydrogel solid electrolyte membrane in Example 1 and the PAM-CA-2 hydrogel solid electrolyte membrane in Example 3 of the present application;

[0018] Figure 3 It is a diagram of the pore size and porosity results of the PAM hydrogel solid electrolyte membrane in Example 1 and the PAM-CA-2 hydrogel solid electrolyte membrane in Example 3 of the present application;

[0019] Figure 4This is the mechanical property diagram of the PAM hydrogel solid electrolyte membrane in Example 1 of this application and the PAM-CA hydrogel solid electrolyte membranes in Examples 2 to 4.

[0020] Figure 5 This is the ionic conductivity of the PAM hydrogel solid electrolyte membrane in Example 1 of this application and the PAM-CA hydrogel solid electrolyte membranes in Examples 2 to 4 at different temperatures.

[0021] Figure 6 This is the cycle stability of the battery assembled with the PAM-CD-2 solid electrolyte membrane in Example 3 of this application. Detailed implementation manners

[0022] In the embodiments of this application, by providing a carbon dot-modified low-temperature-resistant hydrogel solid electrolyte membrane and its preparation method, the problems of poor low-temperature resistance and low ionic conductivity of traditional hydrogel solid electrolyte membranes in the prior art are solved. Through the introduction of carbon dots CD, the low-temperature resistance performance and relatively high ionic conductivity of the hydrogel solid electrolyte membrane are achieved.

[0023] The technical solutions in the embodiments of this application to solve the above problems of poor low-temperature resistance and low ionic conductivity are generally as follows:

[0024] Carbon dots CD are synthesized by a solvothermal synthesis method. Citric acid and 3-aminobenzenesulfonic acid are used as carbon sources and sulfur sources, and are dissolved in N,N-dimethylformamide (DMF). DMF, as a high-boiling-point polar solvent, can promote the uniform dispersion of carbon precursors and the stability of high-temperature reactions. The introduction of ethylenediamine provides amino groups, and amide bonds are formed through the condensation reaction of amino groups and carboxyl groups. At the same time, as a nitrogen dopant and surface passivator, it regulates the fluorescence properties of carbon dots. The polyacrylamide (PAM)-based hydrogel electrolyte is prepared by a chemical cross-linking and ion doping preparation method. Carbon dots CD are added during the preparation process, and the ionic conductivity and mechanical strength of the hydrogel are enhanced through surface functional groups (such as sulfonic acid groups, amino groups). Furthermore, the low-temperature resistance performance and relatively high ionic conductivity of the carbon dot CD-modified hydrogel solid electrolyte membrane are achieved.

[0025] To better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the accompanying drawings of the specification and specific implementation manners.

[0026] Example 1

[0027] Synthesis of carbon dots CD:

[0028] 1.728 g of citric acid and 0.7 g of 3-aminobenzenesulfonic acid were mixed in 20 mL of N,N-dimethylformamide and stirred for 30 minutes to be fully dissolved to obtain solution A. Then, 600 μL of ethylenediamine was added, and after stirring evenly, it was poured into the inner liner of an autoclave and heated in an oven at 160 °C for 5 hours. Subsequently, the reactant solution was poured into ethanol, and the brown precipitate was collected by high-speed centrifugation. Then, the precipitate was dissolved in deionized water and dialyzed for 3 days. Among them, the cut-off molecular weight of the dialysis bag was 3500, and the dialysis solution was freeze-dried to obtain carbon dot CD powder.

[0029] Preparation of polyacrylamide PAM-CD hydrogel solid electrolyte membrane:

[0030] 2.5 g of acrylamide was added to 10 mL of water and stirred and mixed for 30 minutes. Then, 15 mg of ammonium persulfate, 3 mg of N,N'-methylenebisacrylamide, and 0% (relative to the mass of acrylamide) of CD powder were added, and it was fully stirred and mixed for 2 h. The above fully stirred and mixed solution was poured into a mold and crosslinked in an oven at 60 °C for 2 h. After cooling, the hydrogel was immersed in a 2 M zinc trifluoromethanesulfonate solution for 12 h, taken out and dried naturally to obtain polyacrylamide hydrogel solid electrolyte membrane PAM.

[0031] Example 2

[0032] In the preparation steps of the polyacrylamide PAM-CD hydrogel electrolyte in Example 1, 0% CD powder (relative to the mass of acrylamide) was changed to 1%, and the rest remained unchanged, to obtain polyacrylamide hydrogel solid electrolyte membrane PAM-CD-1.

[0033] Example 3

[0034] In the preparation steps of the polyacrylamide PAM-CD hydrogel electrolyte in Example 1, 0% CD powder (relative to the mass of acrylamide) was changed to 3%, and the rest remained unchanged, to obtain polyacrylamide hydrogel solid electrolyte membrane PAM-CD-2.

[0035] Example 4

[0036] In the preparation steps of the polyacrylamide PAM-CD hydrogel electrolyte in Example 1, 0% CD powder (relative to the mass of acrylamide) was changed to 5%, and the rest remained unchanged, to obtain polyacrylamide hydrogel solid electrolyte membrane PAM-CD-3.

[0037] Please refer to Figures 1-6 , for the low-temperature resistance experiment of the PAM hydrogel solid electrolyte membrane in Example 1 and the PAM-CA-2 hydrogel solid electrolyte membrane in Example 3, the results are as Figure 1It shows that the PAM hydrogel solid electrolyte membrane has a freezing phenomenon at -30°C, while PAM-CD-2 exhibits good antifreeze properties.

[0038] Figure 2 SEM images of the PAM hydrogel solid electrolyte membrane of Example 1 and the PAM-CA-2 hydrogel solid electrolyte membrane of Example 3. Both the PAM hydrogel solid electrolyte membrane and the PAM-CA-2 hydrogel solid electrolyte membrane have obvious porous structures. The introduction of CD makes the structure of the hydrogel more dense.

[0039] Figure 3 Results of pore size and porosity of the PAM hydrogel solid electrolyte membrane of Example 1 and the PAM-CA-2 hydrogel solid electrolyte membrane of Example 3. Compared with PAM, although the pore size of PAM-CD-2 decreases, its porosity increases, which is beneficial to shortening the conduction path of the ionic solution and promoting rapid ion transport.

[0040] Figure 4 Mechanical property diagrams of the PAM hydrogel solid electrolyte membrane of Example 1 and the PAM-CA hydrogel solid electrolyte membranes of Examples 2 to 4. 4a is the stress-strain curve of PAM-CD at room temperature (25°C). The introduction of an appropriate amount of CD is beneficial to improving the fracture strength of the PAM-CD hydrogel, while excessive CD will reduce the fracture strength. This is because the interaction between excessive CD and the PAM molecular chain is saturated, making a single CD molecule unable to covalently bind to two molecular chains simultaneously and unable to play the role of a connection point. 4b is the stress-strain curve of PAM and PAM-CD-2 at -30°C. At -30°C, PAM shows obvious brittleness due to being frozen, while the freeze resistance of PAM-CD-3 enables it to still have the characteristics of high strength and high elasticity.

[0041] Figure 5 Ionic conductivities of the PAM hydrogel solid electrolyte membrane of Example 1 and the PAM-CA hydrogel solid electrolyte membranes of Examples 2 to 4 at different temperatures. The introduction of CD can improve the ionic conductivity of the PAM hydrogel solid electrolyte membrane, especially under low-temperature conditions. There are significant differences in the ionic conductivities between the PAM and PAM-CD solid electrolyte membranes.

[0042] Figure 6 Cyclic stability of the battery assembled with the PAM-CD-2 solid electrolyte membrane of Example 3. PAM-CD-2 maintains 93.75% of its capacity after 1500 stable cycles at -30°C and a current density of 3 A / g. The excellent cyclic stability at low temperature is mainly attributed to the good freeze resistance and excellent ionic conductivity of the PAM-CD-3 electrolyte.

[0043] The technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

[0044] 1. Since carbon dots CD are introduced into the preparation process of the polyacrylamide (PAM)-based hydrogel solid electrolyte membrane, the carbon dots CD enhance the ionic conductivity and mechanical strength of the hydrogel through surface functional groups, and the carbon dots CD break the hydrogen bond between water molecules in the hydrogel. Therefore, the problems of poor low-temperature tolerance and low ionic conductivity of traditional hydrogel electrolytes in the prior art are effectively solved, and the low-temperature tolerance performance and high ionic conductivity of the hydrogel electrolyte are realized.

[0045] 2. The carbon dots CD in the embodiments of the present invention serve as covalent connection points of the PAM molecular chains, improving the fracture strength and mechanical durability of the hydrogel.

[0046] 3. The introduction of the carbon dots CD in the embodiments of the present invention adjusts the solvation structure of zinc ions, improving the ionic conductivity.

[0047] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0048] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a carbon dot-modified low-temperature-resistant hydrogel solid electrolyte membrane, characterized in that: The following steps are involved: Synthesis of S001 carbon dots: CD powder was obtained by reacting citric acid and 3-aminobenzenesulfonic acid in N, N-dimethylformamide, adding ethylenediamine and heating under high pressure, and then ethanol precipitation, dialysis and freeze drying. S002 Preparation of PAM-CD hydrogel solid electrolyte membrane: Mix acrylamide, ammonium persulfate, N,N'-methylenebisacrylamide and a certain amount of CD powder, pour them into a mold for cross-linking, then soak them in zinc trifluoromethanesulfonate solution, and finally dry them naturally to obtain the PAM-CD hydrogel solid electrolyte membrane.

2. The preparation method according to claim 1, characterized in that The mass ratio of CD powder to acrylamide in step S002 is 3:

100.

3. The preparation method according to claim 1, characterized in that: The cut-off molecular weight of the dialysis bag in step S001 is 3500.

4. The preparation method according to claim 1, characterized in that: In the step S002, the solution after adding CD powder and stirring evenly is poured into a mold and cross-linked in an oven at 60° C. for 2 h. After cooling, the solution is immersed in a zinc trifluoromethanesulfonate solution for 12 h.

5. A carbon dot-modified low-temperature resistant hydrogel solid electrolyte membrane, characterized in that: The hydrogel solid electrolyte membrane is prepared according to the preparation method according to any one of claims 1 to 4.

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