Multi-network anti-freezing hydrogel electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a multi-network anti-freezing hydrogel electrolyte, a preparation method thereof and application of the multi-network anti-freezing hydrogel electrolyte in an electrochemical device. The hydrogel is prepared by using polyvinyl alcohol (PVA) and polyacrylamide (PAM) to form a basic network skeleton, introducing phytic acid, ethylene glycol and lithium / zinc bimetal salt (Li2SO4 / ZnSO4), and carrying out thermal initiation polymerization and freeze thawing. The hydrogel prepared by the invention has a multiple physical cross-linked network formed by polymer molecular chain entanglement, hydrogen-bond interaction among functional groups and metal coordinate bonds constructed between phosphate groups and divalent metal ions, so that the hydrogel electrolyte has excellent mechanical properties. Due to introduction of ethylene glycol, formation of ice crystals is effectively inhibited, and the hydrogel is endowed with excellent anti-freezing performance; the high-concentration Li < + > and Zn < 2 + > ensure the high ionic conductivity. The supercapacitor assembled by using the hydrogel electrolyte shows relatively high specific capacitance and good capacitance retention rate under bending and freezing conditions, and has good electrochemical properties and safety performance.

Description

Technical Field

[0001] This invention relates to the field of hydrogel electrolyte preparation, specifically to a method for preparing an antifreeze hydrogel electrolyte with good mechanical properties and high ionic conductivity, and its application in electrochemical energy storage devices. Background Technology

[0002] In today's context of increasing emphasis on environmental sustainability and green environmental protection, flexible energy storage devices have become a research hotspot due to their environmental friendliness and high safety. Hydrogel electrolytes, as a crucial component of flexible energy storage devices, significantly impact the overall performance of the device. However, traditional hydrogel electrolytes, due to the presence of a large amount of free water, inevitably freeze below zero degrees Celsius, leading to reduced ionic conductivity, loss of hydrogel flexibility, and thus limiting the functionality of the constructed supercapacitor. This situation severely hinders their application in cold climates.

[0003] Currently, there are three main methods to solve this problem: (1) Using salt compounds as solvents to prevent water freezing. Only high concentrations of salt can show significant antifreeze effects, but this will lead to ion aggregation, affecting the mechanical stability of the polymer skeleton in low-temperature environments, and may also cause corrosion damage to the device. (2) Adding organic solvents to inhibit ice crystal formation, such as ethylene glycol (EG) and glycerol (Gly). The abundant hydroxyl groups in organic molecules can form competitive hydrogen bonds with water molecules, thereby inhibiting the formation of ice crystals and lowering the freezing point. However, excessive addition of organic solvents will significantly reduce ionic conductivity, affecting practical applications. (3) Introducing ionic liquids (ILs) into hydrogels can not only give hydrogels antifreeze properties, but also improve the ionic conductivity of hydrogels. However, ILs often exhibit high viscosity in low-temperature environments, and their molecular structure lacks flexible segments, resulting in poor compressibility and stretchability of the modified hydrogels. Therefore, developing a new type of hydrogel electrolyte that can synergistically balance antifreeze and high ionic conductivity is a technical problem that urgently needs to be solved in this field.

[0004] This invention conceives of a multi-component synergistic strategy. This strategy utilizes the functional combination of Li₂SO₄ / ZnSO₄ dual salts, ethylene glycol, and phytic acid to successfully prepare hydrogel electrolytes with excellent mechanical properties, low-temperature stability, and high ionic conductivity by leveraging the synergistic interactions between the components. Summary of the Invention

[0005] This invention addresses the shortcomings of traditional hydrogel electrolyte technologies by developing a multi-network antifreeze hydrogel electrolyte, its preparation method, and its applications. Existing antifreeze strategies struggle to simultaneously achieve low-temperature stability, excellent mechanical properties, and high ionic conductivity. This invention aims to solve the problems of traditional hydrogel electrolytes, such as easy freezing at low temperatures, loss of flexibility, and a sharp drop in ionic conductivity.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical method:

[0007] In a first aspect, the present invention provides a multi-network antifreeze hydrogel electrolyte. The raw materials of the hydrogel electrolyte include polyvinyl alcohol, phytic acid, ethylene glycol, lithium sulfate, zinc sulfate, acrylamide, an initiator, and a crosslinking agent; characterized in that the antifreeze hydrogel electrolyte possesses a multi-network physical crosslinking structure formed by polymer molecular chain entanglement, hydrogen bonding between functional groups, and metal coordination bonds between phosphate groups and divalent metal ions.

[0008] Secondly, the present invention provides a method for preparing the aforementioned multi-network antifreeze hydrogel electrolyte. The method includes the following steps:

[0009] Step (1): Add polyvinyl alcohol (PVA) to deionized water and stir to dissolve it in a constant temperature water bath at 80-90℃ to obtain a PVA solution;

[0010] Step (2): Add phytic acid solution, ethylene glycol (EG), lithium sulfate (Li2SO4) and zinc sulfate (ZnSO4) mixed solution to the PVA solution in step (1), and stir to dissolve in a constant temperature water bath at 80-90℃ to obtain solution A;

[0011] Step (3): Mix acrylamide (AM), initiator ammonium persulfate (APS), crosslinking agent N,N'-methylenebisacrylamide (MBA) and deionized water at room temperature to obtain solution B;

[0012] Step (4): Solution A is cooled in a cold water bath and then mixed with solution B, and stirred.

[0013] Step (5): Transfer the mixed solution to a mold, carry out a thermally initiated polymerization reaction at 60-75℃, then cool to room temperature, freeze at -20 to -10℃ for 6-12 hours, and finally thaw for 3-6 hours to room temperature to obtain the antifreeze hydrogel electrolyte.

[0014] The mass fraction of the polyvinyl alcohol (PVA) solution in step (1) is 8-13%.

[0015] In step (2), a phytic acid aqueous solution with a mass fraction of 50% is added, which is 3-4 times the mass of PVA.

[0016] In step (2), ethylene glycol (EG) with a mass of 3-4 times that of PVA is added.

[0017] In step (2), the total concentration of lithium ions and zinc ions in the mixed solution of lithium sulfate (Li2SO4) and zinc sulfate (ZnSO4) is 1.0 mol / L to 4.0 mol / L, and the molar ratio of zinc ions to lithium ions is 1:1 to 1:4.

[0018] In step (3), the acrylamide (AM) monomer is dissolved in water to prepare a solution with a mass fraction of 20-25%. The initiator ammonium persulfate (APS) accounts for 0.5-1.5% of the mass of the acrylamide (AM) monomer, and the crosslinking agent N,N'-methylenebisacrylamide (MBA) accounts for 0.1-0.5% of the mass of the acrylamide (AM) monomer.

[0019] In step (4), the temperature of the cold water bath is controlled at 5-18℃.

[0020] Thirdly, the present invention provides a supercapacitor. The supercapacitor includes electrodes and the aforementioned multi-network antifreeze hydrogel electrolyte.

[0021] The electrode includes a current collector and an active material layer, wherein the active material layer comprises activated carbon, conductive carbon black and polyvinylidene fluoride binder.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The antifreeze hydrogel electrolyte prepared in this invention is constructed by a multi-component synergistic system of phytic acid, ethylene glycol and bimetallic salt (Li2SO4 / ZnSO4). Phytic acid and ethylene glycol molecules synergistically disrupt the hydrogen bond network of water molecules, significantly reducing the freezing point, while maintaining extremely high ionic conductivity under the synergistic effect of bimetallic ions.

[0024] The hydrogel prepared by this invention possesses excellent mechanical properties, and the system exhibits polymer chain entanglement, multiple hydrogen bonds (between PVA / PAM / phytic acid), and Zn... 2+ Phytic acid coordination bonds together form a dynamic and reversible multi-crosslinked network, giving the hydrogel high strength and high toughness.

[0025] The hydrogel prepared by this invention has wide temperature range stability and safety. The supercapacitor assembled based on this hydrogel electrolyte can maintain high specific capacitance and capacitance retention rate under environments such as torsion, bending, impact and low temperature (such as -20℃), showing excellent environmental adaptability, electrochemical stability and safety in use.

[0026] The hydrogel prepared by this invention has wide temperature range stability and safety. The supercapacitor assembled based on this hydrogel electrolyte can maintain high specific capacitance and capacitance retention rate under environments such as torsion, bending, impact and low temperature (such as -20℃), showing excellent environmental adaptability, electrochemical stability and safety in use. Attached Figure Description

[0027] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below.

[0028] Figure 1 This is a schematic diagram illustrating the preparation of antifreeze hydrogel electrolytes and the assembly of supercapacitors.

[0029] Figure 2 The tensile stress-strain curves of the multi-network antifreeze hydrogel electrolytes prepared in Examples 1, 2, 3 and Comparative Examples 1 and 2 are shown. The tensile strength of hydrogel S1 is 148 kPa and the elongation at break is 450%, indicating its excellent mechanical strength and ductility.

[0030] Figure 3 The bar charts show the ionic conductivity of the antifreeze hydrogel electrolytes prepared in Examples 1, 2, and 3, and Comparative Examples 1 and 2 at room temperature, demonstrating the effect of different zinc-lithium molar ratios on the ionic conductivity of the materials and proving the effectiveness of the synergistic effect of the two salts. Hydrogel S1 has a conductivity of 140 mS / cm at 25°C and 85 mS / cm at -20°C.

[0031] Figure 4 The bar chart shows the ionic conductivity of the antifreeze hydrogel electrolyte prepared in Example 1 at different temperatures, demonstrating that the electrolyte maintains high ionic conductivity over a wide temperature range, especially at low temperatures, and possesses excellent antifreeze properties.

[0032] Figure 5 The cyclic voltammetry (CV) curves of the supercapacitor assembled based on the hydrogel electrolyte of Example 1 after being twisted and restored exhibit a certain rectangular shape, demonstrating the excellent electrochemical stability and flexibility of the device under mechanical deformation.

[0033] Figure 6 The constant current charge-discharge (GCD) test curves of the supercapacitor assembled based on the hydrogel electrolyte of Example 1 at different temperatures are used to demonstrate the reliability of the device under extreme environments. Detailed Implementation Plan

[0034] The technical solution and effects of the present invention will be further described below with reference to the embodiments. However, the specific methods, formulas and descriptions used are not intended to limit the present invention.

[0035] Example 1

[0036] 1. Preparation of antifreeze hydrogel electrolytes

[0037] (1) Add 1.36g of polyvinyl alcohol (PVA) to 10g of deionized water and stir in a 90℃ constant temperature water bath for 20min until dissolved to obtain a PVA solution with a mass fraction of 12%;

[0038] (2) Add 6.0g of 50% phytic acid solution, 5.7g of ethylene glycol (EG), and 2.5ml of a mixed solution of lithium sulfate (Li2SO4) and zinc sulfate (ZnSO4) with a total concentration of 4mol / L to the PVA solution in step (1). 2+ With Li + The molar ratio of the two components is 1:3. Stir the mixture in a 90℃ constant temperature water bath for 20 minutes until it is completely dissolved to obtain a clear and transparent solution A.

[0039] (3) Weigh 3.2g acrylamide (AM), 0.038g initiator ammonium persulfate (APS), 0.01g crosslinking agent N,N'-methylenebisacrylamide (MBA) and 10g deionized water at room temperature and stir for 10 minutes until completely dissolved to obtain solution B;

[0040] (4) Solution A is cooled in a 10°C cold water bath for 10 minutes and then mixed with solution B and stirred until homogeneous;

[0041] (5) The mixed solution is injected into the mold and then placed in a 70°C drying oven for 3 hours. After that, it is cooled to room temperature, frozen at -20°C for 12 hours, and finally thawed for 5 hours to room temperature. After the reaction is completed, a flexible multi-network antifreeze hydrogel electrolyte is obtained, which is denoted as S1.

[0042] 2. Assembly of supercapacitor devices

[0043] The active material is activated carbon, the conductive agent is conductive carbon black, and the binder is polytetrafluoroethylene emulsion, which are mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone is added and ground into a uniform slurry. The slurry is coated on a nickel foam current collector and dried under vacuum at 80°C for 12 hours to obtain the electrode sheet.

[0044] The antifreeze gel electrolyte and active electrode material prepared in step 1 are assembled into a sandwich-shaped supercapacitor with a symmetrical structure.

[0045] Example 2

[0046] The preparation steps are similar to those of the antifreeze hydrogel electrolyte in Example 1. The difference is that Zn in step (2) is used in... 2+ With Li + The molar ratio of 1:3 was replaced with a molar ratio of 2:2 to obtain an antifreeze hydrogel, denoted as S2.

[0047] The preparation steps of the supercapacitor device in Example 1 are basically the same, except that the antifreeze gel electrolyte used in Example 2 is the antifreeze gel electrolyte synthesized in this example.

[0048] Example 3

[0049] The preparation steps are similar to those of the antifreeze hydrogel electrolyte in Example 1. The difference is that Zn in step (2) is used in... 2+ With Li + The molar ratio of 1:3 was replaced with a molar ratio of 3:1 to obtain an antifreeze hydrogel, denoted as S3.

[0050] The preparation steps of the supercapacitor device in Example 1 are basically the same, except that the antifreeze gel electrolyte used in Example 2 is the antifreeze gel electrolyte synthesized in this example.

[0051] Comparative Example 1

[0052] The preparation steps are similar to those of the antifreeze hydrogel electrolyte in Example 1. The difference is that Zn in step (2) is used in... 2+ With Li + The molar ratio of 1:3 was replaced with a molar ratio of 0:4 to obtain an antifreeze hydrogel, denoted as D1.

[0053] The preparation steps of the supercapacitor device in Example 1 are basically the same, except that the antifreeze gel electrolyte used in Example 2 is the antifreeze gel electrolyte synthesized in this example.

[0054] Comparative Example 2

[0055] The preparation steps are similar to those of the antifreeze hydrogel electrolyte in Example 1. The difference is that Zn in step (2) is used in... 2+ With Li + The molar ratio of 1:3 was replaced with a molar ratio of 4:0 to obtain an antifreeze hydrogel, denoted as D2.

[0056] The preparation steps of the supercapacitor device in Example 1 are basically the same, except that the antifreeze gel electrolyte used in Example 2 is the antifreeze gel electrolyte synthesized in this example.

[0057] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention, and all such changes should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims

1. A multi-network antifreeze hydrogel electrolyte, characterized in that, Its raw material composition includes: polyvinyl alcohol (PVA), polyacrylamide (PAM), phytic acid solution, ethylene glycol, lithium sulfate, zinc sulfate, initiator and crosslinking agent; the hydrogel electrolyte contains a multi-layer physical crosslinking network composed of polymer molecular chain entanglement, hydrogen bonds and metal coordination bonds formed by phytic acid phosphate groups and zinc ions.

2. A method for preparing a multi-network antifreeze hydrogel electrolyte for electrochemical devices, characterized in that, Includes the following steps: (1) Add polyvinyl alcohol (PVA) to deionized water and stir to dissolve it in a constant temperature water bath at 80-90℃ to obtain a PVA solution; (2) Add phytic acid solution, ethylene glycol (EG), lithium sulfate (Li2SO4) and zinc sulfate (ZnSO4) mixed solution to the PVA solution in step (1), and stir to dissolve in a constant temperature water bath at 80-90℃ to obtain solution A; (3) Acrylamide (AM), initiator ammonium persulfate (APS), crosslinking agent N,N'-methylenebisacrylamide (MBA) and deionized water are stirred evenly at room temperature to obtain solution B; (4) Solution A is cooled in a cold water bath and then mixed with solution B, and stirred. (5) Transfer the mixed solution to a mold, carry out a thermally initiated polymerization reaction at 60-75°C, cool to room temperature, freeze at -20 to -10°C for 6-12 hours, and finally thaw for 3-6 hours to room temperature to obtain the antifreeze hydrogel electrolyte.

3. The method for preparing a multi-network antifreeze hydrogel electrolyte according to claim 2, characterized in that: The mass fraction of the polyvinyl alcohol (PVA) solution in step (1) is 8-13%.

4. The method for preparing a multi-network antifreeze hydrogel electrolyte according to claim 2, characterized in that: In step (2), add a phytic acid aqueous solution with a mass fraction of 50%, which is 3-4 times the mass of PVA.

5. The method for preparing a multi-network antifreeze hydrogel electrolyte according to claim 2, characterized in that: In step (2), ethylene glycol (EG) with a mass of 3-4 times that of PVA is added.

6. The method for preparing a multi-network antifreeze hydrogel electrolyte according to claim 2, characterized in that: In step (2), the total concentration of lithium ions and zinc ions in the mixed solution of lithium sulfate (Li2SO4) and zinc sulfate (ZnSO4) is 1.0 mol / L to 4.0 mol / L, and the molar ratio of zinc ions to lithium ions is 1:1 to 1:

4.

7. The method for preparing a multi-network antifreeze hydrogel electrolyte according to claim 2, characterized in that: In step (3), the acrylamide (AM) monomer is dissolved in water to prepare a solution with a mass fraction of 20-25%. The initiator ammonium persulfate (APS) accounts for 0.5-1.5% of the mass of the acrylamide (AM) monomer, and the crosslinking agent N,N'-methylenebisacrylamide (MBA) accounts for 0.1-0.5% of the mass of the acrylamide (AM) monomer.

8. The method for preparing a multi-network antifreeze hydrogel electrolyte according to claim 2, characterized in that: In step (4), the temperature of the cold water bath is controlled at 5-18℃.

9. A supercapacitor containing an antifreeze hydrogel electrolyte, characterized in that: The supercapacitor includes electrodes and the antifreeze hydrogel electrolyte as described in claim 1.

10. The supercapacitor according to claim 11, characterized in that: The electrode includes a current collector and an active material layer, wherein the active material layer comprises activated carbon, conductive carbon black and polyvinylidene fluoride binder.

Images