Preparation method of hydrogel electrolyte based on nanometer confinement and application of hydrogel electrolyte to ultralow-temperature zinc ion battery

Abstract

The invention discloses a preparation method of a hydrogel electrolyte based on nanometer confinement and application of the hydrogel electrolyte to an ultralow-temperature zinc ion battery. The method comprises the following steps: gradually adding a polymer monomer, N, N '-methylene bisacrylamide and an initiator into an aqueous dispersion of uniform nanospheres, and carrying out stirring and ultrasonic treatment until a uniform and clear state is achieved; adjusting the pH value, adding zinc salt, fully stirring, and then carrying out vacuum treatment to remove bubbles; and injecting the obtained mixed solution into a mold, and initiating until the mixed solution is completely gelatinized. According to the hydrogel electrolyte prepared by the invention, side reactions in a battery circulation process are effectively reduced; compared with traditional hydrogel, the hydrogel electrolyte has the advantages that the mechanical property is obviously improved, the maximum elongation exceeds 3100%, and the maximum tensile strength exceeds 0.92 MPa; the electrolyte prepared by the preparation method disclosed by the invention still shows the ionic conductivity of 3.05 mS / cm at the temperature of 40 DEG C below zero.

Description

Technical Field

[0001] The invention relates to a preparation method of a nano-confined hydrogel electrolyte and an application of the same in an ultra-low temperature zinc ion battery, and belongs to the field of composite materials. Background Art

[0002] Lithium-ion batteries face problems such as safety and material shortages, while aqueous batteries are expected to become an alternative to lithium-ion batteries due to their advantages such as low cost, inherent safety, environmental protection and simple process. Among them, aqueous zinc-ion batteries have attracted much attention due to their high theoretical volume capacity, low standard redox potential, non-toxicity, low cost and high abundance. However, when zinc foil is directly used as the negative electrode of aqueous zinc-ion batteries, rough and irregular zinc dendrites are easily formed, resulting in short circuits. In addition, the electrolyte of aqueous zinc-ion batteries also undergoes water decomposition reactions, resulting in electrolyte consumption and reduced battery efficiency. In order to overcome the above problems, hydrogels are usually used as zinc-ion battery electrolytes, which can not only effectively inhibit dendrite growth, but also alleviate the problem of battery electrolyte decomposition.

[0003] The water in the hydrogel electrolyte can be divided into free water and bound water. Among them, free water will cause the mechanical properties of the hydrogel to decrease, such as toughness, interfacial adsorption, etc. At low temperatures, this part of water will also freeze, resulting in a decrease in the electrolyte ion conductivity. At the same time, due to its high activity, free water will also trigger side reactions on the zinc negative electrode. Bound water refers to water in the hydrogel that is bound to hydrophilic groups and salts. The activity of this part of water is lower than that of free water, and it is not easy to freeze at low temperatures. At present, there are many methods to reduce the activity of free water in hydrogels, but these studies are confined to reducing the proportion of active water by increasing the content of hydrophilic groups and zinc salts, thereby improving the electrochemical stability and mechanical properties of the hydrogel electrolyte, but it will also lead to slow kinetics and decreased ionic conductivity. Summary of the invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing a high-performance hydrogel electrolyte based on nano-confinement and its application in ultra-low temperature zinc ion batteries.

[0005] Technical solution: To solve the above technical problems, the present invention provides a method for preparing a nano-confined hydrogel electrolyte, comprising the following steps:

[0006] (1) gradually adding polymer monomers, crosslinking agents and initiators into a uniform aqueous dispersion of nanospheres, and stirring and ultrasonically treating the dispersion until a uniform and clear state is achieved;

[0007] (2) adjusting the pH of the mixed solution obtained in step (1), adding zinc salt during stirring, and then vacuum treating to remove bubbles;

[0008] (3) Inject the mixed solution obtained in step (2) into a mold and initiate the process until it is completely gelled.

[0009] Wherein, the polymer monomer in step (1) is one or more of acrylamide, vinyl alcohol or poly (N-hydroxyethyl) acrylamide, and the concentration is 0.2-0.6 g / mL.

[0010] Wherein, the cross-linking agent is N,N'-methylenebisacrylamide.

[0011] The nanospheres are selected from polystyrene nanospheres, polyacrylamide nanospheres and silicon dioxide nanospheres. The nanospheres are uniform in size, between 30 and 50 nm, and the content of the water monodispersed liquid is 30 to 50 wt%. The stirring time is 5 to 10 minutes, and the ultrasonic time is 5 to 20 minutes.

[0012] Wherein, the pH value in step (2) is in the range of 5-9, the zinc salt is one of the zinc salts commonly used in aqueous zinc ion batteries such as zinc perchlorate, zinc sulfate, zinc acetate, zinc chloride, zinc trifluoromethanesulfonate, and zinc bistrifluoromethanesulfonyl imide, and the amount of the zinc salt added is 0.5-3 mol / L of the mixed solution. The stirring time is 5-10 minutes, and the degassing requires being placed in an environment with an air pressure of less than 0.01 MPa for more than 30 minutes.

[0013] Preferably, the initiation time in step (3) varies depending on the initiator selected. Generally, the initiator is photoinitiator 2959, and the initiation method in step (3) is irradiation with ultraviolet light of wavelength 365-395nm for 5-15 minutes. The initiator is ammonium persulfate. The initiation method in step (3) is heat preservation at 60-90 degrees Celsius for 15-45 minutes.

[0014] The present invention also provides a nano-confined hydrogel electrolyte prepared by the method.

[0015] The present invention also provides application of the nano-confined hydrogel electrolyte in preparing an ultra-low temperature aqueous zinc ion battery.

[0016] Due to the boundary effect, the activity of free water in nano-confinement is lower than that of free water in traditional hydrogels, and higher than that of bound water. By introducing a large number of uniformly dispersed nanospheres into the hydrogel, all free water can be fixed in the nano-confinement. This part of "confined water" has high ionic conductivity, high stability, and is not easy to freeze at low temperatures. At the same time, a large number of dispersed nanospheres significantly improve the toughness and interfacial adsorption properties of the hydrogel. The active water regulation strategy based on nano-confinement not only takes into account excellent mechanical and electrochemical properties, but also maintains its unique interfacial adhesion and self-healing functions. It can still work stably in harsh environments such as mechanical deformation, trauma, and low temperature, which helps to improve the reliability of aqueous batteries.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The hydrogel electrolyte prepared by the present invention effectively reduces the occurrence of side reactions during battery cycling; (2) The electrolyte prepared by the present invention has significantly improved mechanical properties compared to traditional hydrogels, with a maximum elongation of more than 3100% and a maximum tensile strength of more than 0.92 MPa; (3) The electrolyte prepared by the present invention still exhibits an ionic conductivity of 3.05 mS / cm at minus 40 degrees Celsius. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The electrochemical impedance spectrum of the hydrogel synthesized in Example 1 at -50 degrees Celsius;

[0019] Figure 2 This is a photo of the hydrogel synthesized in Example 2;

[0020] Figure 3 This is a photo of the hydrogel synthesized in Example 3;

[0021] Figure 4 This is a SEM photo of the freeze-dried hydrogel synthesized in Example 3;

[0022] Figure 5 This is the infrared spectrum of the hydrogel synthesized in Example 3;

[0023] Figure 6 This is the differential scanning calorimetry analysis of the hydrogel synthesized in Example 3;

[0024] Figure 7 is the stress-strain curve of the hydrogel synthesized in Example 3;

[0025] Figure 8 The relationship between the ionic conductivity of the hydrogel synthesized in Example 3 and the temperature;

[0026] Fig. 9 This is a variable current charge and discharge curve diagram of an aqueous secondary zinc ion battery using the hydrogel synthesized in Example 3 as the electrolyte at -40 degrees Celsius;

[0027] Fig.10 This is a constant current charge and discharge curve diagram of an aqueous secondary zinc ion battery using the hydrogel synthesized in Example 3 as the electrolyte at -40 degrees Celsius;

[0028] Fig.11 This is a SEM photograph of the zinc negative electrode surface of an aqueous secondary zinc ion battery using the hydrogel synthesized in Example 3 as an electrolyte after 5000 cycles at -40 degrees Celsius;

[0029] Fig.12This is a constant current charge and discharge curve of an aqueous secondary zinc ion battery using the hydrogel synthesized in Example 1 as the electrolyte at -40 degrees Celsius. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0031] Example 1

[0032] (1) Weigh 0.3 g of commercial grade N-hydroxyethyl acrylamide and 6.5 mg of commercial grade photoinitiator 2959, add 0.065 mL of 5 g / L crosslinker N,N'-methylenebisacrylamide aqueous solution to 1 mL of 50 wt% silica nanosphere (30 nm, Zhichuan Technology) aqueous monodisperse solution, stir for 5 minutes, and ultrasonicate for 10 minutes;

[0033] (2) Add 0.05 mL of pH 7.2 buffer (MP036 TEN, ISE Biotech), add 0.745 g of commercial grade zinc perchlorate hexahydrate (Z109396, Aladdin), stir for 10 minutes, and vacuum remove bubbles for 30 minutes;

[0034] (3) The solution obtained in step (2) was injected into a glass mold and induced under ultraviolet light with a wavelength of 365 nm for 5 minutes to obtain a hydrogel electrolyte. The electrochemical impedance spectroscopy at -50 degrees Celsius is as follows: Figure 1 shown.

[0035] Example 2

[0036] (1) Weigh 0.3 g of commercial acrylamide and 6.5 mg of commercial photoinitiator 2959, add 0.065 mL of 5 g / L N,N'-methylenebisacrylamide aqueous solution to 1 mL of 30 wt% polystyrene nanospheres (60 nm, Zhichuan Technology) aqueous monodisperse solution, stir for 5 minutes, and ultrasonicate for 10 minutes;

[0037] (2) Add 0.05 mL of pH 6.86 buffer (BS011, Ise Biotech), add 0.574 g of commercial grade zinc sulfate heptahydrate, stir for 10 minutes, and vacuum remove bubbles for 30 minutes;

[0038] (3) The solution obtained in step (2) was injected into a glass mold and kept warm at 70 degrees Celsius for 30 minutes to obtain a hydrogel electrolyte ( Figure 2 ).

[0039] Example 3

[0040] (1) Weigh 0.3 g of commercial acrylamide and 6.5 mg of commercial photoinitiator 2959, add 0.065 mL of 5 g / L N,N'-methylenebisacrylamide aqueous solution to 1 mL of 30 wt% polystyrene nanosphere (60 nm) aqueous monodisperse solution, stir for 5 minutes, and ultrasonicate for 10 minutes;

[0041] (2) Add 0.05 mL of pH 7.2 buffer, add 0.745 g of commercial grade zinc perchlorate hexahydrate, stir for 10 minutes, and vacuum remove bubbles for 30 minutes;

[0042] (3) The solution obtained in step (2) was injected into a glass mold and induced under ultraviolet light with a wavelength of 365 nm for 15 minutes to obtain a hydrogel electrolyte ( Figure 3 ). Its appearance is like Figure 4 As shown, the infrared spectrum is Figure 5 As shown in (where PAM is a polyacrylamide control sample prepared under the same conditions, 30PS-PAM is a nano-confined hydrogel prepared from a 30wt% concentration of PS microsphere aqueous dispersion as a raw material), differential scanning calorimetry analysis is as follows Figure 6 As shown. Among them, Figure 6 The PAM in the figure is a polyacrylamide control sample prepared under the same conditions. 10PS-PAM, 20PS-PAM, and 30PS-PAM are nano-confined hydrogels prepared under the same conditions as this example using 10wt%, 20wt%, and 30wt% of PS microsphere aqueous dispersion as raw materials. Figure 7 As shown, the low temperature ionic conductivity is Figure 8 shown.

[0043] Application Example 1

[0044] An aqueous secondary zinc ion battery, wherein the electrolyte material is the hydrogel prepared in Example 3, the positive electrode material is polyaniline grown in situ on carbon cloth, and the negative electrode is zinc foil. A hydrogel with a diameter of 12 mm and a thickness of 0.5 mm is prepared using a mold, and assembled with positive and negative electrode materials with a diameter of 10 mm into a 2032 button battery.

[0045] At -40 degrees Celsius, it can stably cycle at a current of 0.5-2A / g ( Fig. 9 ). Under 1A / g conditions, aqueous zinc-ion batteries have a discharge capacity of 75mAh / g and a cycle life of 5000 times ( Fig.10 ), after cycling, the zinc negative electrode is flat and uniform, with no dendrite formation ( Fig.11 ), and its low temperature performance is better than most zinc-ion batteries.

[0046] Application Example 2

[0047] An aqueous secondary zinc ion battery, wherein the electrolyte material is the hydrogel prepared in Example 1, a slurry of VO2, Ketjen black, and polyvinylidene fluoride in a mass ratio of 7:2:1 is coated on an iron foil as a positive electrode material, and a zinc foil is used as a negative electrode. A hydrogel with a diameter of 12 mm and a thickness of 0.5 mm is prepared using a mold, and assembled with positive and negative electrode materials with a diameter of 10 mm to form a 2032 button battery.

[0048] At -40 degrees Celsius, it can cycle stably at 1A / g current, showing a discharge capacity of 84mAh / g ( Fig.12 ), and its low temperature performance is better than most zinc-ion batteries.

Claims

1. A method for preparing a nano-confined hydrogel electrolyte, characterized in that: The steps include: (1) gradually adding polymer monomers, N,N'-methylenebisacrylamide and initiator into a uniform aqueous dispersion of nanospheres, and stirring and ultrasonically treating the dispersion until a uniform and clear state is achieved; the diameter of the nanospheres is 30-60 nm; and the content of the nanospheres in the aqueous dispersion of the nanospheres is 30-50 wt %; (2) adding zinc salt to the pH-adjusted mixed solution obtained in step (1), stirring the mixture sufficiently, and then performing a vacuum treatment to remove bubbles; (3) Inject the mixed solution obtained in step (2) into a mold and initiate the process until it is completely gelled.

2. The preparation method according to claim 1, characterized in that: The polymer monomers in step (1) include one or more of acrylamide, vinyl alcohol or poly (N-hydroxyethyl) acrylamide.

3. The preparation method according to claim 1, characterized in that: The nanospheres in step (1) include polystyrene nanospheres or silicon dioxide nanospheres.

4. The preparation method according to claim 1, characterized in that: The stirring time in step (1) is 5-10 minutes, and the ultrasonic time is 5-20 minutes.

5. The preparation method according to claim 1, characterized in that: The pH value in step (2) is 6.86-7.

2.

6. The preparation method according to claim 1, characterized in that: The zinc salt in step (2) includes zinc salts commonly used in aqueous zinc ion batteries; the zinc salts commonly used in aqueous zinc ion batteries include zinc perchlorate, zinc sulfate, and zinc trifluoromethanesulfonate.

7. The preparation method according to claim 1, characterized in that: The initiation method in step (3) is irradiation with ultraviolet light of wavelength 365-395nm for 5-15 minutes.

8. The method for preparing the nanoconfined hydrogel according to claim 1, characterized in that: When the initiator in step (1) is ammonium persulfate, the initiation method in step (3) is to keep warm at 70 degrees Celsius for 30 minutes.

9. A nanoconfined hydrogel prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the nano-confined hydrogel material according to claim 9 in the preparation of ultra-low temperature aqueous zinc ion batteries.

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