Preparation method and application of a novel zwitterionic monomer and hydrogel electrolyte thereof

Abstract

This invention discloses a novel zwitterionic monomer and its preparation method and application in a hydrogel electrolyte. The zwitterionic monomer includes sulfobetaine urea methacrylate and sulfobetaine urea acrylate. The monomer N-acryloylglycine is copolymerized with the two novel zwitterionic monomers to form zwitterionic polymers. The zwitterionic polymer chains are linked by hydrogen bonds and covalent bonds to form a three-dimensional network. The metal salt is encapsulated in the three-dimensional network to obtain the zwitterionic hydrogel electrolyte. The zwitterionic hydrogel electrolyte exhibits low hysteresis, high conductivity, and maintains toughness and stretchability. The zwitterionic groups on the side chains of the zwitterionic polymer and the loaded metal salt give the elastomer excellent antifreeze and ion transport properties. Under low temperature conditions, the zwitterionic hydrogel electrolyte exhibits excellent mechanical flexibility and ion transport properties.

Description

Technical Field

[0001] This invention belongs to the field of gel electrolyte technology, specifically relating to a novel zwitterionic monomer and its preparation method and application as a hydrogel electrolyte. Background Technology

[0002] Gel polymer electrolytes (GPEs) are key materials that combine the advantages of both solid-state and liquid electrolytes. They typically have a jelly-like or gel-like appearance and are formed by a polymer network (such as PEO, PVDF, etc.) as a solid matrix, encapsulating and locking in a large amount of liquid electrolyte (containing lithium salts, etc.), thus achieving a unique "solid-liquid integration" structure. Compared to traditional liquid electrolytes, their core advantage lies in significantly improved safety. Gel electrolytes effectively avoid the risk of electrolyte leakage and offer better thermal and chemical stability, while also suppressing dendrite growth. Simultaneously, gel electrolytes retain the advantages of liquid electrolytes, such as good interfacial contact and high ionic conductivity, effectively ensuring the battery's charge and discharge efficiency. Compared to pure solid-state electrolytes, gel electrolytes often exhibit superior ion conductivity and lower interfacial impedance at room temperature, and their manufacturing process is relatively close to existing lithium battery processes, making them more feasible for industrialization. Currently, gel electrolytes have become an ideal choice for flexible batteries, wearable electronic devices, and other fields, and provide an important direction for the development of next-generation high-safety lithium batteries (such as one of the solid-state battery technology routes).

[0003] Zwitterionic hydrogel electrolytes are cutting-edge materials that have attracted much attention in the fields of flexible electronics and novel energy storage in recent years. Their core design concept originates from zwitterionic polymers, which are special polymers containing equal amounts of positively and negatively charged separated groups (such as sulfonic acid groups and quaternary ammonium groups) on the same monomer chain segment. Early hydrogel electrolytes were mostly based on single-charged or neutral polymers (such as PVA). Although they possessed flexibility, they generally suffered from insufficient mechanical properties, easy water loss, limited ionic conductivity, and susceptibility to freezing at low temperatures. The introduction of zwitterionic materials provides a completely new path to solve these problems. Due to their strong intramolecular electrostatic interactions, they can "lock" a large number of water molecules through hydrogen bonds to form a highly stable hydration layer, thus giving the hydrogel electrolyte excellent adaptability and freeze resistance. Simultaneously, the presence of zwitterions also improves the ion transport efficiency of the hydrogel electrolyte, and due to their hydrophilic properties, the hydrogel electrolyte exhibits excellent interfacial compatibility and stability, leading to a wide range of applications.

[0004] The prior art patent document CN202410475479.8 discloses a hydrogel electrolyte, its preparation method, and its application. The specific preparation process is as follows: a composite hydrogel is obtained by polymerizing a gel matrix material and functional monomers, the functional monomers including zwitterionic monomers and acrylamide monomers; a mixed salt solution is prepared by preparing zinc salt and ionizing salt, the ionizing salt including at least one of LiTFSI and LiClO4; the composite hydrogel is immersed in the mixed salt solution to obtain the hydrogel electrolyte; the composite hydrogel is formed by polymerizing a first monomer containing zwitterionic groups. The first monomer has hydrophilic properties and can interact electrostatically with water. The constructed molecular chain network has more bound water that can not be frozen or evaporated, thus giving the hydrogel electrolyte a wider operating temperature range; at the same time, by combining a specific composite hydrogel with a specific ionizing salt, the operating temperature range of the battery is further widened. However, the polymer monomer used in this patent document does not disclose a novel zwitterionic monomer with an imidazole structure on its side chain and a urea group and a sulfobetaine group respectively, and there is no related technical inspiration for the hydrogel electrolyte prepared based on this novel zwitterionic monomer.

[0005] Existing technology, patent document CN202510989083.X, discloses a flexible wearable solid-state zinc battery based on a poly-zwitterionic hydrogel electrolyte and its preparation method. In this flexible wearable solid-state zinc battery, the poly-zwitterionic hydrogel electrolyte is used as the electrolyte, a zinc powder dispersion is coated on a current collector as a flexible negative electrode, and a vanadium-based or manganese-based material dispersion is coated on the current collector as a flexible positive electrode. The poly-zwitterionic hydrogel electrolyte is prepared by copolymerizing zwitterionic monomers, acrylate monomers, lithium salts, and photoinitiators, followed by soaking in a zinc salt solution. Its unique structure endows it with good mechanical properties, high ionic conductivity, and a wide electrochemical window, making it suitable for special environments such as stretching, curling, and bending. However, the polymer monomers used in this patent document do not disclose a novel zwitterionic monomer containing an imidazole structure on its side chain and bearing a urea group and a sulfobetaine group, respectively. Furthermore, the hydrogel electrolyte prepared based on this novel zwitterionic monomer does not offer any related technological inspiration.

[0006] Existing technology, patent document CN202111101768.4 discloses zwitterionic hydrogels, electrolytes, secondary batteries or supercapacitors, and electrical devices. The zwitterionic hydrogel includes a network support and electrolyte salts distributed within the network support. The network support comprises a first polymer network structure and a second polymer network structure. The first polymer network structure is mainly polymerized from zwitterionic monomers, and the second polymer network structure provides support strength to the network support. The second polymer network structure and the first polymer network structure are interwoven. This zwitterionic hydrogel possesses good electrical conductivity. Secondary batteries and supercapacitors formed using this zwitterionic hydrogel as an electrolyte can effectively suppress the formation of byproducts on the metal electrode, thereby improving the performance of the secondary battery and supercapacitor, and consequently, the performance of the electrical device. However, the polymeric monomers used in this patent document do not disclose novel zwitterionic monomers containing imidazole structures on their side chains and bearing a urea group and a sulfobetaine group, respectively. Furthermore, there is no related technical inspiration for preparing hydrogel electrolytes based on these novel zwitterionic monomers.

[0007] To improve the performance of the hydrogel electrolyte, this invention introduces urea and imidazole groups into the newly synthesized zwitterionic monomer structure. The hydrogen bond donor and acceptor in the urea group can form intramolecular and intermolecular hydrogen bonds, solving the problem of poor mechanical properties in zwitterionic gels. The imidazole group can form hydrogen bonds with anionic groups and effectively inhibit the hydration of anionic groups, improving ion transport capacity. Simultaneously, the zwitterionic groups on the chain and the loaded lithium chloride give the elastomer excellent antifreeze properties, exhibiting excellent mechanical flexibility and ion transport performance even at low temperatures. Currently, there are no reports on the two newly synthesized zwitterionic monomers in this invention. Summary of the Invention

[0008] The technical problem solved by this invention is to provide a novel zwitterionic monomer and its preparation method and application for a hydrogel electrolyte. Two novel zwitterionic monomers are used to prepare hydrogel electrolytes. Since the prepared zwitterionic polymer hydrogels are typically soft and brittle due to their superhydrophilicity, urea units that can form strong hydrogen bonds are added to the molecular structure design to improve the overall toughness of the hydrogel electrolyte. This invention is the first to synthesize two novel zwitterionic monomers with imidazole structures on their side chains and each containing one urea group and one sulfobetaine group, and their structures were characterized. To easily distinguish between the two structurally similar monomers, the monomer sulfobetaine urea methacrylate with a methyl double bond is named SBUVMA1, and the hydrogel electrolyte obtained by copolymerizing it with another common monomer, N-acryloylglycine (NAGA), is named PNSB1-x, where x is the molar ratio of NAGA to SBUVMA1. The sulfobetaine urea methacrylate without a methyl double bond is named SBUVMA2, and the hydrogel electrolyte obtained by copolymerizing it with NAGA is named PNSB1-x. The hydrogel electrolyte obtained by bulk copolymerization was named PNSB2-x, where x is the molar ratio of NAGA to SBUVMA2. By adjusting the ratio of zwitterionic monomers and NAGA as well as the concentration of salt ions, a series of hydrogel electrolytes with different mechanical strengths and conductivity were finally prepared. The obtained zwitterionic hydrogel electrolytes exhibited low hysteresis, high conductivity, and maintained toughness and stretchability. The zwitterionic groups on the polymer side chains and the loaded lithium chloride gave the elastomer excellent antifreeze and ion transport properties. Even at low temperatures, the hydrogel electrolytes exhibited excellent mechanical flexibility and ion transport properties.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a novel zwitterionic monomer comprising sulfobetaine urea methacrylate (monomer 1) and sulfobetaine urea acrylate (monomer 2), with corresponding structural formulas as follows: .

[0010] The specific preparation steps of the novel zwitterionic monomer described in this invention are as follows: Step S1, attaching an imidazole group to the monomer isocyanate acrylate or isocyanate methacrylate: the monomer isocyanate acrylate or isocyanate methacrylate is reacted with 2-(1H-imidazol-1-yl)ethylamine in DMF as a solvent via a nucleophilic addition reaction to obtain an intermediate containing a substituted urea group and an imidazole group. Step S2, synthesizing zwitterionic monomers from intermediates containing substituted urea and imidazole groups: The intermediates containing substituted urea and imidazole groups are reacted with 1,3-propanesulfonic acid lactone in water-DMF as solvent through a ring-opening affinity substitution reaction to obtain imidazole sulfonic acid zwitterionic monomers.

[0011] A zwitterionic hydrogel electrolyte is obtained by copolymerizing N-acryloylglycamide with two novel zwitterionic monomers to form zwitterionic polymers. The zwitterionic polymer chains are linked by hydrogen bonds and covalent bonds to form a three-dimensional network. A metal salt is encapsulated in the three-dimensional network to obtain the zwitterionic hydrogel electrolyte. The zwitterionic hydrogel electrolyte exhibits low hysteresis, high conductivity, and maintains toughness and stretchability. The zwitterionic groups on the side chains of the zwitterionic polymers and the loaded metal salt give the elastomer excellent antifreeze and ion transport properties. Under low temperature conditions, the zwitterionic hydrogel electrolyte exhibits excellent mechanical flexibility and ion transport properties.

[0012] Furthermore, the zwitterionic hydrogel electrolyte has zwitterionic polymer chains with zwitterionic structures, which promote the transport of metal salt cations in the three-dimensional network of the hydrogel through induction, thereby improving the performance of the zwitterionic hydrogel electrolyte. At the same time, the imidazole ions of the zwitterionic polymer form hydrogen bonds with the metal salt anions, which can effectively inhibit the hydration of the metal salt anions, thereby improving the transport capacity of metal salt cations. The urea groups of the zwitterionic polymer are used to increase the mechanical strength of the zwitterionic hydrogel electrolyte.

[0013] Further specified: the cation in the metal salt is Zn. 2+ Mg 2+ Li 1+ or Fe 3+ One or more of the following; the anion in the metal salt is SO4. 2- Cl - ,ClO 4- or HPO4 2- One or more of them.

[0014] A method for preparing a zwitterionic hydrogel electrolyte, the specific preparation process of which is as follows: dissolving the zwitterionic monomer sulfobetaine urea methacrylate or sulfobetaine urea acrylate and the monomer N-acryloylglycine in a metal salt solution, adding a photoinitiator, pouring into a mold, and obtaining the zwitterionic hydrogel electrolyte by ultraviolet light initiation polymerization.

[0015] Further specified, the molar ratio of the zwitterionic monomer sulfobetaine urea methacrylate or sulfobetaine urea acrylate to the monomer N-acryloylglycine is 1:2~6; the concentration of the metal salt solution is 0.5~4.0 mol / L.

[0016] Further specifying, the photosensitizer is a water-soluble 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylphenylacetone (1173), 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone (2959), 1-hydroxycyclohexylphenyl ketone (184), or azobisisobutyramidine hydrochloride (V50).

[0017] The application of the zwitterionic hydrogel electrolyte described in this invention in the preparation of secondary batteries or supercapacitors.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. This invention synthesizes two novel zwitterionic monomers. Because they have urea groups, they can establish dynamic hydrogen bond cross-linking sites. At the same time, the imidazole ions can form hydrogen bonds with metal salt anionic groups and effectively inhibit the hydration of metal salt anionic groups. Meanwhile, the sulfonic acid groups can assist positive ion transport through induction, resulting in excellent ionic conductivity.

[0019] 2. The hydrogel electrolyte in this invention has good biocompatibility, and due to the presence of urea groups and amphoteric structures, it also has good adhesion.

[0020] 3. The hydrogel electrolyte of this invention incorporates an imidazole ring, which can effectively inhibit bacterial growth and accelerate ion transport.

[0021] 4. The hydrogel electrolyte in this invention contains zwitterionic structure, which can maintain good performance at low temperature and has a certain degree of antifreeze properties. Attached Figure Description

[0022] Figure 1 The images show the 1H NMR spectra of the two newly synthesized zwitterionic monomers.

[0023] Figure 2 The Fourier transform infrared spectra of the two newly synthesized zwitterionic monomers are shown.

[0024] Figure 3 This is a high-resolution mass spectrum of the newly synthesized zwitterionic monomer (SBUVMA1).

[0025] Figure 4 This is a high-resolution mass spectrum of the newly synthesized zwitterionic monomer (SBUVMA2).

[0026] Figure 5 This is a flowchart illustrating the preparation route of hydrogel electrolytes.

[0027] Figure 6 The conductivity and impedance diagrams for PNSB1 and PNSB2 hydrogel electrolytes are shown.

[0028] Figure 7 The tensile properties of PNSB1 and PNSB2 hydrogel electrolytes are shown in the diagram.

[0029] Figure 8 Thermoelectric properties of PNAGA, PNSB1-4, and PNSB2-5 hydrogel electrolytes at low temperatures were characterized. Detailed Implementation

[0030] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Example 1

[0031] Synthesis of zwitterionic monomers Synthesis of zwitterionic monomers SBUVMA1 and SBUVMA2: The synthesis of zwitterionic monomers involves two steps. Taking the synthesis of SBVIUIA1 monomer as an example: The first step involved attaching an imidazole group to the monomer isocyanate methacrylate: 5 mmol of isocyanate methacrylate was dissolved in 2 mL of anhydrous DMF. 5 mmol of 2-(1H-imidazol-1-yl) dissolved in 3 mL of anhydrous DMF was added to the flask. The mixture was kept at 25 °C under nitrogen gas, and the DMF solution of isocyanate methacrylate was added dropwise. The reaction was allowed to proceed for 5 h. The reaction product was precipitated with 100 mL of acetone, centrifuged, and the supernatant was removed by rotary evaporation. Impurities were then extracted with diethyl ether to obtain an intermediate containing a substituted urea group and an imidazole.

[0032]

[0033] The second step involves synthesizing zwitterionic monomers using intermediates containing substituted urea groups and imidazoles as raw materials: The intermediates containing substituted urea groups and imidazoles prepared above and 5 mmol of 1,3-propanesulfonic acid lactone were dispersed in anhydrous DMF solvent and reacted at room temperature (25°C) for 5 h under nitrogen atmosphere. The reaction solution was precipitated three times with 100 mL of ethyl acetate, and the precipitated product was lyophilized with water to obtain the imidazole sulfonic acid zwitterionic monomer (SBUVMA1).

[0034]

[0035] The synthesis steps of the zwitterionic monomer SBUVMA2 are the same as those of SBUVMA1. The preparation conditions for the above zwitterionic monomers have been preliminarily explored and can guarantee successful synthesis. The synthesized intermediates and monomers were purified by solvent precipitation and then dried, and analyzed using nuclear magnetic resonance (¹H NMR, ¹³C NMR)... Figure 1 Fourier transform infrared spectrometer (FT-IR) Figure 2 High-resolution mass spectrometry (HS-MS) Figure 3 , Figure 4 Characterization techniques such as ) were used to characterize the structure and confirm the molecular weight of intermediates and zwitterionic monomers. Example 2

[0036] Preparation process of zwitterionic hydrogel electrolyte (reference) Figure 5 .

[0037] The molar ratios of NAGA and SBUVMA1 / SBUVMA2 were weighed at 1:2, 1:3, 1:4, 1:5, and 1:6, respectively. A prepolymer solution with a total solids content of 35 wt% was prepared using a 1.0 M lithium chloride aqueous solution. The amount of photoinitiator IR 2959 added was 1 wt%–2 wt% of the prepolymer solution mass. The solution was irradiated for 12 min under a UVGO UV lamp (AC180V–250V, 300W wide wavelength). After the reaction was complete, the solution was immersed in a thermoelectric ionizing solution for 2 h to obtain zwitterionic hydrogel electrolytes. The products with different ratios were labeled PNSB1-2, PNSB1-3, PNSB1-4, PNSB1-5, and PNSB1-6. Example 3

[0038] Preparation of gel thermoelectric materials: Accurately weigh equimolar ratios of redox couple salts (potassium ferricyanide / potassium ferrocyanide) to prepare a 0.5M aqueous solution. Immerse the prepared zwitterionic hydrogel electrolytes made from raw materials in different proportions in the redox couple solution for solvent exchange. Let it stand for about 2 hours to reach an equilibrium state to make it a semi-solid thermoelectric material.

[0039] Thermal battery construction and thermoelectric performance testing: Thermoelectric battery construction: 0.3mm diameter platinum wire was used as the electrode material. Semi-solid thermoelectric materials (PNSB1-4, PNSB2-5, 35wt% NAGA hydrogel material) were fixed at both ends of the positive and negative electrodes with platinum wire. The surface was wrapped with 3M polyacrylate tape to prevent moisture loss and ensure the long-term stability of the hydrogel under different temperatures. Electrochemical performance, including voltage, current, and conductivity, was tested using a CHI 660E thermometer. During voltage and current measurements, the temperature difference across the battery was monitored in real time by thermocouples. A gradient was set every 10K to test the electrochemical performance of the hydrogel between 0℃ and -10℃ to -50℃.

[0040] Depend on Figure 6 It can be seen that the hydrogel with zwitterionic polymer chains has a conductivity that is up to twice as high as that of pure NAGA hydrogel. Furthermore, at the same ratio, PNSB1 hydrogel has a better conductivity than PNSB2 hydrogel, which is presumably because the methyl structure can better regulate the orderly arrangement of polymer chains within the hydrogel. Figure 7 The image shows the tensile properties of the hydrogel electrolyte. Due to the poor toughness of PNAGA hydrogel, the addition of zwitterions significantly improved both the flexibility and tensile properties of the hydrogel.

[0041] Depend on Figure 8It can be seen that, under low-temperature conditions, the Seebeck coefficient of PNSB1-4 is more than twice that of PNSB2-5, reaching a maximum of 2.703 mV·K. -1 Both zwitterionic hydrogel electrolytes exhibit significantly higher Seebeck coefficients than pure NAGA hydrogel, and their performance remains stable at low temperatures. The addition of zwitterions endows the hydrogel electrolytes with excellent antifreeze and water retention properties, while also improving their ion transport capacity and significantly enhancing their thermoelectric properties.

[0042] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A novel zwitterionic monomer, characterized in that... Including sulfobetaine urea methacrylate and sulfobetaine urea acrylate, the corresponding structural formulas are as follows: 。 2. A method for preparing the novel zwitterionic monomer according to claim 1, characterized in that... The specific preparation steps are as follows: Step S1, attaching an imidazole group to the monomer isocyanate acrylate or isocyanate methacrylate: the monomer isocyanate acrylate or isocyanate methacrylate is reacted with 2-(1H-imidazol-1-yl)ethylamine in DMF as a solvent via a nucleophilic addition reaction to obtain an intermediate containing a substituted urea group and an imidazole group. Step S2, synthesizing zwitterionic monomers from intermediates containing substituted urea and imidazole groups: The intermediates containing substituted urea and imidazole groups are reacted with 1,3-propanesulfonic acid lactone in anhydrous DMF as solvent through a ring-opening affinity substitution reaction to obtain imidazole sulfonic acid zwitterionic monomers.

3. A zwitterionic hydrogel electrolyte, characterized in that: The monomer N-acryloylglycine is copolymerized with the two novel zwitterionic monomers described in claim 1 to form zwitterionic polymers. The zwitterionic polymer chains are linked by hydrogen bonds and covalent bonds to form a three-dimensional network. The metal salt is encapsulated in the three-dimensional network to obtain a zwitterionic hydrogel electrolyte. The zwitterionic hydrogel electrolyte exhibits low hysteresis, high conductivity, and maintains toughness and stretchability. The zwitterionic groups on the side chains of the zwitterionic polymer and the loaded metal salt give the elastomer excellent antifreeze and ion transport properties. Under low temperature conditions, the zwitterionic hydrogel electrolyte exhibits excellent mechanical flexibility and ion transport properties.

4. The zwitterionic hydrogel electrolyte according to claim 3, characterized in that: The zwitterionic hydrogel electrolyte has zwitterionic structures on its zwitterionic polymer chains, which promote the transport of metal salt cations in the three-dimensional network of the hydrogel through induction, thereby improving the performance of the zwitterionic hydrogel electrolyte. At the same time, the imidazole ions of the zwitterionic polymer form hydrogen bonds with the metal salt anions, which can effectively inhibit the hydration of the metal salt anions, thereby improving the transport capacity of metal salt cations. The urea groups of the zwitterionic polymer are used to increase the mechanical strength of the zwitterionic hydrogel electrolyte.

5. The zwitterionic hydrogel electrolyte according to claim 3, characterized in that: The cation in the metal salt is Zn. 2+ Mg 2+ Li 1+ or Fe 3+ One or more of the following; the anion in the metal salt is SO4. 2- Cl - ,ClO 4- or HPO4 2- One or more of them.

6. A method for preparing a zwitterionic hydrogel electrolyte according to any one of claims 4 to 6, characterized in that... The specific preparation process is as follows: the zwitterionic monomers sulfobetaine urea methacrylate or sulfobetaine urea acrylate and N-acryloylglycine amide are dissolved in a metal salt solution, a photoinitiator is added, and the mixture is poured into a mold and polymerized by ultraviolet light to obtain a zwitterionic hydrogel electrolyte.

7. The method for preparing the zwitterionic hydrogel electrolyte according to claim 6, characterized in that: The molar ratio of the zwitterionic monomer sulfobetaine urea methacrylate or sulfobetaine urea acrylate to the monomer N-acryloylglycamide is 1:2~6; the concentration of the metal salt solution is 0.5~4.0 mol / L.

8. The method for preparing the zwitterionic hydrogel electrolyte according to claim 6, characterized in that: The photosensitizer is water-soluble 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylphenylacetone, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone, 1-hydroxycyclohexylphenyl ketone, or azobisisobutyramidine hydrochloride.

9. The application of the zwitterionic hydrogel electrolyte according to any one of claims 4 to 6 in the preparation of secondary batteries or supercapacitors.

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