A fluorinated acrylamide-based hydrogel electrolyte and its preparation method

Abstract

The present invention discloses a fluorinated acrylamide-based hydrogel electrolyte, comprising a three-dimensional network skeleton formed by cross-linking copolymerization of acrylamide and potassium allyl trifluoroborate; water molecules and sulfate ions are also bonded to the three-dimensional network skeleton. The present invention also discloses a method for preparing the above-mentioned fluorinated acrylamide-based hydrogel electrolyte, comprising the following steps: (1) dissolving acrylamide in a ZnSO4 electrolyte, adding potassium allyl trifluoroborate and a cross-linking agent N,N-methylenebisacrylamide thereto, and ultrasonically stirring to obtain a solution A; (2) adding an initiator to the ZnSO4 electrolyte to obtain a solution B; adding solution B to solution A to form a uniform polymer precursor mixture; and (3) injecting the polymer precursor mixture into a mold and allowing it to stand at no more than 80 degrees Celsius to obtain a fluorinated acrylamide-based hydrogel electrolyte.

Description

Technical Field

[0001] The present invention relates to a fluorinated acrylamide-based hydrogel electrolyte and also relates to a preparation method of the hydrogel electrolyte. Background Art

[0002] The development of flexible wearable electronic devices has triggered a demand for batteries with flexibility, safety, and high electrochemical performance. Compared with rigid batteries with liquid electrolytes, solid-state batteries are more conducive to the design and processing of high flexibility, high wear resistance, and leakage resistance. For the past few decades, lithium-ion batteries (LIBs) have dominated energy storage devices due to their high energy density. However, their application in flexible energy storage devices is very challenging. In recent years, aqueous zinc-ion batteries (ZIBs) have emerged as a promising energy storage device. Due to their low cost, high safety, and environmental friendliness, aqueous ZIBs are expected to replace LIBs for large-scale application in flexible electronic devices. Quasi-solid-state batteries consist of four parts: a positive electrode, a negative electrode (zinc metal), a quasi-solid electrolyte, and a current collector. The gel electrolyte, as a quasi-solid electrolyte, is sandwiched between the positive and negative electrodes and has a significant impact on the performance of the entire battery.

[0003] Currently, various gel electrolytes have been studied and applied to ZIBs. However, gel electrolytes have low ion concentrations and are easily hindered by ion migration, resulting in limited ionic conductivity. Furthermore, gel electrolytes are easily pierced by zinc dendrites, leading to failure and short circuits. As a result, the performance of quasi-solid-state zinc-ion batteries still cannot match that of rigid batteries using liquid electrolytes. Whether gel electrolytes can effectively suppress zinc dendrites during the reaction process, while also ensuring that the gel electrolytes possess good flexibility, mechanical strength, and high ionic conductivity, remain major challenges in aqueous zinc-ion batteries. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a fluorinated acrylamide-based hydrogel electrolyte for use in aqueous zinc-ion batteries. The hydrogel electrolyte has high ionic conductivity and mechanical strength, and can effectively inhibit the growth of zinc dendrites during battery use, thereby significantly improving the battery's cycle stability. Another purpose of the present invention is to provide a method for preparing the above-mentioned hydrogel electrolyte.

[0005] Technical Solution: The fluorinated acrylamide-based hydrogel electrolyte of the present invention comprises a three-dimensional network skeleton formed by cross-linking copolymerization of acrylamide and potassium allyl trifluoroborate; wherein water molecules and sulfate ions are also bonded to the three-dimensional network skeleton; the structure of the fluorinated acrylamide-based hydrogel polymer electrolyte is:

[0006]

[0007] The preparation method of the fluorinated acrylamide-based hydrogel electrolyte comprises the following steps:

[0008] (1) dissolving acrylamide in ZnSO4 electrolyte, adding potassium allyl trifluoroborate and cross-linking agent N,N-methylenebisacrylamide, and stirring with ultrasonic waves to obtain solution A;

[0009] (2) adding an initiator to a ZnSO4 electrolyte to obtain solution B; adding solution B to solution A to form a uniform polymer precursor mixture;

[0010] (3) The polymer precursor mixture is injected into a mold and allowed to stand at a temperature not higher than 80 degrees Celsius to obtain a fluorinated acrylamide-based hydrogel electrolyte.

[0011] Wherein, in step (1), the concentration of ZnSO4 electrolyte is 2 mol / L.

[0012] Wherein, in step (1), the mass ratio of potassium allyl trifluoroborate to acrylamide is 0.0002-0.01:1.

[0013] Wherein, in step (1), the mass volume ratio of acrylamide to ZnSO4 electrolyte is 1g:3mL.

[0014] Wherein, in step (1), the amount of the cross-linking agent added is 0.1% of the mass of acrylamide.

[0015] Wherein, in step (2), the initiator is ammonium persulfate or potassium persulfate; the amount of the initiator added is 0.5% of the mass of acrylamide.

[0016] Wherein, in step (2), the mass volume ratio of acrylamide to ZnSO4 electrolyte is 1 mg:0.3 mL.

[0017] Wherein, in step (3), the standing time is 3 to 20 minutes.

[0018] The reaction formula of the cross-linking copolymerization of acrylamide and potassium allyl trifluoroborate is:

[0019]

[0020] The above-mentioned hydrogel electrolyte is applied to a flexible aqueous Zn-MnO2 full battery, wherein the positive electrode material of the Zn-MnO2 full battery is α-phase manganese dioxide.

[0021] The fluorinated acrylamide-based hydrogel electrolyte of the present invention can effectively inhibit the growth of zinc dendrites during the reaction process, and also has good flexibility, mechanical strength and high ionic conductivity, so that the Zn-MnO2 full battery composed of the hydrogel electrolyte, MnO2 positive electrode and zinc negative electrode has stable electrochemical performance.

[0022] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the present invention can effectively solve the problem of severe zinc dendrite growth in the existing aqueous zinc ion battery during the cycle process, which affects the battery cycle stability. The hydrogel electrolyte of the present invention has high ionic conductivity and mechanical strength, and can effectively inhibit the growth of zinc dendrites during the use of the battery, thereby greatly improving the battery's cycle stability performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a digital photo of the hydrogel obtained in Example 1;

[0024] Figure 2 This is the infrared spectrum of the hydrogel obtained in Example 1;

[0025] Figure 3 This is a SEM photo of the freeze-dried hydrogel obtained in Example 1;

[0026] Figure 4 1 is the stress-strain curve of the hydrogels obtained in Examples 1 to 6 and Comparative Example 1;

[0027] Figure 5 Impedance spectra of the stainless steel / / stainless steel batteries obtained in Examples 1 to 6 and Comparative Example 1;

[0028] Figure 6 The Zn symmetric battery test of the hydrogel obtained in Comparative Example 1 (a) and the SEM image of the zinc sheet after cycling (b);

[0029] Figure 7 The Zn symmetric battery test of the hydrogel obtained in Example 1 (a) and the SEM image of the zinc sheet after cycling (b);

[0030] Figure 8 Assemble the Zn-MnO2 full cell for the hydrogel electrolyte of Example 1, and -1 The current density was cycled for 500 cycles. DETAILED DESCRIPTION

[0031] Example 1

[0032] The preparation method of the fluorinated acrylamide-based hydrogel electrolyte of the present invention comprises the following steps:

[0033] (1) Dissolve 1.0 g of acrylamide in 3.0 mL of 2 mol / L ZnSO4 electrolyte, then add 2.0 mg of potassium allyl trifluoroborate and 1.0 mg of cross-linking agent N,N-methylenebisacrylamide in sequence, and dissolve under ultrasonic stirring to obtain solution A;

[0034] (2) adding 5.0 mg of initiator ammonium persulfate to 1.5 mL of 2 mol / L ZnSO4 electrolyte to obtain solution B; adding solution B to solution A to form a uniform polymer precursor mixture;

[0035] (3) The polymer precursor mixture was injected into a polytetrafluoroethylene mold and allowed to stand at 80°C for 15 min to obtain a fluorinated acrylamide-based hydrogel with a thickness of ∼1.5 mm.

[0036] Fluorinated acrylamide-based hydrogel was used as an electrolyte in ss / / ss symmetric cells to calculate the ionic conductivity (ss is a stainless steel sheet), in Zn / / Zn symmetric cells to characterize the inhibitory effect on zinc dendrites, and in aqueous Zn-MnO2 full cells to verify its practicality.

[0037] Example 2

[0038] The preparation method of Example 2 is the same as that of Example 1, except that the amount of potassium allyl trifluoroborate added is adjusted to 0.2 mg, and other parameters remain unchanged.

[0039] Example 3

[0040] The preparation method of Example 3 is the same as that of Example 1, except that the amount of potassium allyl trifluoroborate added is adjusted to 0.5 mg, and other parameters remain unchanged.

[0041] Example 4

[0042] The preparation method of Example 4 is the same as that of Example 1, except that the amount of potassium allyl trifluoroborate added is adjusted to 1.0 mg, and other parameters remain unchanged.

[0043] Example 5

[0044] The preparation method of Example 5 is the same as that of Example 1, except that the amount of potassium allyl trifluoroborate added is adjusted to 5.0 mg, and other parameters remain unchanged.

[0045] Example 6

[0046] The preparation method of Example 6 is the same as that of Example 1, except that the amount of potassium allyl trifluoroborate added is adjusted to 10 mg, and other parameters remain unchanged.

[0047] Comparative Example 1

[0048] The preparation method of Comparative Example 1 is the same as that of Example 1, except that the amount of potassium allyl trifluoroborate added is adjusted to 0 mg, and other parameters remain unchanged.

[0049] Figure 2 This is the infrared spectrum of the hydrogel obtained in Example 1, located at 3458 cm-1 The absorption peak at 2926 cm corresponds to the OH stretching vibration, which appears as a broad peak due to the formation of hydrogen bonds between trifluoroborate and water molecules; –1 、1625cm -1 The wavelengths at 1100 cm correspond to CH stretching vibration and C=O stretching vibration; -1 The position corresponds to the in-plane bending vibration of -NH2 and the stretching vibration of BF bond, indicating that -BF 3- Successful introduction of functional groups.

[0050] Figure 3 This is an SEM image of the freeze-dried hydrogel obtained in Example 1, showing its three-dimensional hierarchical pore structure. Hydrogel electrolytes with a multi-level pore structure provide more ion diffusion channels, accelerating ion transport within the material and thus improving the electrolyte's ionic conductivity. Furthermore, the multi-level pore structure allows zinc ions to deposit more evenly on the electrode surface, reducing the formation of zinc dendrites. This improves the battery's cycling stability and safety, thereby increasing its service life.

[0051] The present invention adopts the fluorine-containing monomer potassium allyl trifluoroborate and acrylamide to copolymerize to synthesize the hydrogel electrolyte. 3- The synergistic effect with -CONH2 effectively enhances hydrogen bonds, thereby improving the mechanical strength of the hydrogel electrolyte; 3- The polarity of -CONH2 provides a fast migration channel for zinc ions and guides their uniform deposition, thereby improving ionic conductivity and effectively inhibiting the growth of zinc dendrites during battery cycling.

[0052] pass Figure 4 Compared to Comparative Example 1, the tensile strength of the hydrogels in Examples 1-6 initially increased and then decreased. This is attributed to the fact that when potassium allyl trifluoroborate exceeds a certain concentration, it triggers polymerization, destroying the internal structure of the hydrogel and reducing its mechanical properties. Example 1 exhibits the best mechanical properties, reaching a tensile strength of 163 kPa and an elongation at break of 1344%.

[0053] pass Figure 5 It can be seen that the volume resistance of the hydrogels of Examples 1 to 6 is reduced, and the ionic conductivity is significantly improved. The ionic conductivity of the hydrogel electrolyte of Example 1 is as high as 35.89 mS cm-1 according to the fitting circuit calculation. -1 .

[0054] pass Figure 6 It can be seen that the Zn symmetric battery system short-circuited after 480h of cycling; SEM analysis of the zinc sheet after cycling showed that there were many protruding dendrites. Figure 7It can be seen that the Zn / / Zn symmetrical battery assembled with the hydrogel electrolyte in Example 1 remains stable after cycling for more than 1000 hours without short circuit or voltage polarization, which indicates that the hydrogel electrolyte of the present invention has high cycling stability. SEM analysis shows that the surface of the zinc sheet remains flat after cycling, confirming that the hydrogel electrolyte of the present invention can effectively inhibit the growth of zinc dendrites. Specifically, at 1 mA cm -2 At a current density of , the Zn symmetric battery exhibits a low voltage polarization of less than 100 mV for more than 1000 hours; SEM analysis of the zinc sheets after cycling the Zn / / Zn symmetric battery shows that the hydrogel of the present invention can effectively inhibit the growth of zinc dendrites.

[0055] pass Figure 8 It can be seen that the fluorinated acrylamide-based hydrogel electrolyte prepared in Example 1 has a large reversible capacity when applied to aqueous Zn-MnO2 full batteries. -1 After 500 cycles of charge and discharge at the same current density, the capacity still remains at 188 mAh g -1 The discharge specific capacity shows that the zinc-manganese full battery based on the hydrogel of the present invention has good cycle stability and reversibility.

Claims

1. A fluorinated acrylamide-based hydrogel electrolyte, characterized in that: The invention comprises a three-dimensional network skeleton formed by cross-linking copolymerization of acrylamide and potassium allyl trifluoroborate; water molecules and sulfate ions are also bonded to the three-dimensional network skeleton.

2. The method for preparing the fluorinated acrylamide-based hydrogel electrolyte according to claim 1, characterized in that: The steps include: (1) dissolving acrylamide in ZnSO4 electrolyte, adding potassium allyl trifluoroborate and cross-linking agent N,N-methylenebisacrylamide, and stirring with ultrasonic waves to obtain solution A; (2) adding the initiator to the ZnSO4 electrolyte to obtain solution B; Adding solution B to solution A to form a uniform polymer precursor mixture; (3) The polymer precursor mixture is injected into a mold and allowed to stand at a temperature not higher than 80° C. to obtain a fluorinated acrylamide-based hydrogel electrolyte.

3. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (1), the concentration of the ZnSO4 electrolyte is 2 to 2.5 mol / L.

4. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (1), the mass ratio of potassium allyl trifluoroborate to acrylamide is 0.0002 to 0.01:

1.

5. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (1), the mass volume ratio of acrylamide to ZnSO4 electrolyte is 1g:3-4mL.

6. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (1), the amount of the cross-linking agent added is 0.1 to 0.2% of the mass of the acrylamide.

7. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (2), the initiator is ammonium persulfate or potassium persulfate.

8. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (2), the amount of the initiator added is 0.5 to 0.6% of the mass of acrylamide.

9. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (2), the mass volume ratio of acrylamide to ZnSO4 electrolyte is 1 mg: 0.3-0.5 mL.

10. The method for preparing a fluorinated acrylamide-based hydrogel electrolyte according to claim 2, wherein: In step (3), the standing time is 3 to 20 minutes.

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