PH response type intelligent hydrogel interface layer and application

Abstract

The invention discloses a pH response type intelligent hydrogel interface layer and application. The pH response type intelligent hydrogel interface layer is hydrogel. The pH response type intelligent hydrogel interface layer has a micropore or nanopore network structure, the micropore network structure is naturally formed by crosslinking and stacking polymer chains in the polymerization process, and the pore diameter of micropores or nanopores ranges from several nanometers to hundreds of nanometers. The preparation method comprises the following steps: a) dissolving a hydrophilic main monomer, a functional monomer containing a nitrogen-containing heterocyclic group sensitive to pH, a cross-linking agent and an initiator in a solvent to form a gel precursor solution; b) coating the gel precursor solution on the surface of a metal negative electrode substrate; and c) initiating a polymerization reaction through heating or illumination, and forming a gel interface layer on the surface of the negative electrode to obtain the intelligent protective metal negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel technology, specifically relating to a pH-responsive smart hydrogel interface layer and its application. Background Technology

[0002] Aqueous zinc-ion batteries have shown great potential in next-generation large-scale energy storage due to their high safety, low cost, and environmental friendliness. However, their practical application is limited by the inherent instability of the zinc metal anode. During charge and discharge, the zinc anode faces two major challenges: 1) Uncontrolled growth of zinc dendrites may puncture the separator, causing a short circuit in the battery; 2) Severe interfacial side reactions, mainly hydrogen evolution reaction (HER) and corrosion, consume active materials and electrolyte, and generate insulating byproducts (such as basic zinc sulfate), leading to rapid degradation of battery performance.

[0003] Existing technologies typically employ a strategy of constructing an artificial interfacial protective layer (AIL) on the surface of the zinc anode. For example, by coating a layer of hydrogel with a porous structure and zinc-loving groups, the zinc ion flow can be homogenized to some extent, inhibiting dendrite growth. Most hydrogel interfacial layers in existing technologies (such as gels composed of acrylic acid, acrylamide, or their derivatives) are "static." Their physicochemical properties remain largely unchanged during battery operation, primarily serving as physical barriers and passive current conduction.

[0004] However, the battery interface is a dynamic and complex environment. Especially during the hydrogen evolution reaction, protons (H+) are consumed. + ) and generate hydroxide ions (OH-) - This leads to a sharp increase in the local pH value near the negative electrode / electrolyte interface. This increase in pH exacerbates the formation of basic salt byproducts, further deteriorating the interfacial environment. Existing static interfacial layers cannot detect and actively respond to this harmful pH change, thus significantly reducing their protective effect and failing to fundamentally prevent the long-term degradation of battery performance.

[0005] Therefore, there is an urgent need to develop an "intelligent" interface protection technology that can sense changes in interface conditions and make proactive and beneficial responses in order to achieve deeper and more lasting stability for the metal anode. Summary of the Invention

[0006] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a pH-responsive smart hydrogel interface layer and its application, which can sense the local pH increase at the interface caused by side reactions in real time, and actively adjust the ion transport environment by changing its own structure or chemical properties, thereby suppressing side reactions and dendrite growth, and significantly improving the cycle stability and reversibility of the metal anode.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A pH-responsive smart hydrogel interface layer is a hydrogel that is applied to the surface of the metal anode in an aqueous battery during the preparation of a smart protective metal anode. The physicochemical properties of the hydrogel are responsive to changes in the local pH value at the interface between the metal anode and the electrolyte.

[0008] The pH-responsive smart hydrogel interface layer has a microporous or nanoporous network structure, which is naturally formed by the cross-linking and stacking of polymer chains during polymerization. The pore sizes of the micropores or nanopores range from a few nanometers to several hundred nanometers. This porous structure provides physical channels for electrolyte wetting and ion transport.

[0009] Furthermore, when polyhedral oligomeric silsesquioxanes (POSS) are introduced as crosslinking agents, due to the difference in hydrophobicity between them and the hydrophilic host monomer, nanoscale microphase separation structures can be formed in the polymer matrix, further constructing a hierarchical and non-uniform pore network, which is beneficial for controlling the ion flux distribution.

[0010] A method for preparing a smart protective metal anode includes the following steps: Step a): Dissolve the hydrophilic host monomer, the functional monomer containing a nitrogen-containing heterocyclic group that is sensitive to pH, the crosslinking agent and the initiator in a solvent to form a gel precursor solution; Step b): Coat the gel precursor solution onto the surface of the metal anode substrate; Step c): A polymerization reaction is initiated by heating or light to form a gel interface layer on the surface of the negative electrode, thereby preparing a smart protective metal negative electrode.

[0011] In step a): The molar ratio of each reactant is as follows: the molar ratio of the hydrophilic host monomer to the functional monomer containing a nitrogen-containing heterocyclic group that is sensitive to pH is 10:1 to 1:5; this ratio ensures that the gel has both a good ion conduction basis and sufficient pH response sites.

[0012] The molar amount of the crosslinking agent accounts for 0.1% to 5% of the total molar amount of the monomers (the sum of the hydrophilic host monomer and the functional monomers containing nitrogen-containing heterocyclic groups that are sensitive to pH); the molar amount of the initiator accounts for 0.5% to 3% of the total molar amount of the monomers (the sum of the hydrophilic host monomer and the functional monomers containing nitrogen-containing heterocyclic groups that are sensitive to pH). Too little crosslinking agent will lead to difficulties in gel formation and poor mechanical strength; too much crosslinking agent will result in an overly dense network, hindering ion transport.

[0013] The solvent is selected from one or a mixture of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), water, and ethanol, preferably DMF, because it has good solubility for all components.

[0014] In step b): The thickness of the wet film formed by coating the gel precursor solution onto the surface of the metal anode substrate is controlled between 20 micrometers and 200 micrometers. The thickness of the final cured gel interface layer dry film is preferably between 5 micrometers and 50 micrometers. If the thickness is too thin, the protective effect is limited; if the thickness is too thick, it will significantly increase the ion transport impedance.

[0015] In step c): When heating is used to initiate polymerization, the heating temperature is 50°C to 90°C, preferably 60°C to 80°C; the heating time is 30 minutes to 3 hours, preferably 1 hour to 2 hours.

[0016] When photo-initiated polymerization is used, ultraviolet light with a wavelength of 254 nm to 400 nm is used, preferably 365 nm; the light intensity is 10 mW / cm² to 100 mW / cm²; and the irradiation time is 5 minutes to 30 minutes.

[0017] When the local pH value at the interface increases, the nitrogen-containing heterocyclic group undergoes deprotonation, thereby triggering at least one of the following responses: (1): Enhance the coordination ability of the hydrogel for metal cations; (2): Change the swelling degree or network pore size of the hydrogel.

[0018] The nitrogen-containing heterocyclic group is selected from one or more of the following: pyridine ring, imidazole ring, pyrimidine ring, purine ring, or quinoline ring.

[0019] The functional monomer containing a pH-sensitive nitrogen-containing heterocyclic group is formed by linking the nitrogen-containing heterocyclic group with a polymerizable functional group (such as vinyl group); When the nitrogen-containing heterocyclic group is a pyridine ring, the functional monomer is 4-vinylpyridine; When the nitrogen-containing heterocyclic group is an imidazole ring, the functional monomer can be 1-vinylimidazole.

[0020] The hydrophilic host monomer is selected from one or more of acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, or hydroxyethyl acrylate.

[0021] The crosslinking agent is a polyhedral oligomeric silsesquioxane (POSS) with a cage-like structure, and the POSS has one or more polymerizable functional groups.

[0022] A smart protective metal anode includes a metal anode substrate and a pH-responsive smart interface layer as described above, which is in-situ polymerized and solidified on the surface of the metal anode substrate.

[0023] The pH-responsive smart hydrogel interface and metal anode are applied to aqueous metal-ion batteries.

[0024] The beneficial effects of this invention are: This invention is the first to achieve an intelligent response of the interface layer to local pH changes. It is not a passive "shield," but an "intelligent system" that can actively counteract interface deterioration, achieving a leap from "static protection" to "dynamic self-regulation."

[0025] This invention achieves both the mitigation of concentration polarization (enhanced coordination) and the inhibition of side reactions (structural contraction) through pH response, with diverse and efficient mechanisms of action.

[0026] The negative feedback regulation mechanism of this invention can maintain interface stability for a long time, fundamentally suppress the accumulation of zinc dendrites and by-products, and enable the metal anode to maintain high reversibility under harsh conditions (high current density, long cycle).

[0027] This invention utilizes the synergistic effect of two mechanisms—triggered reaction (deprotonation) and network contraction (physical effect)—to form a highly efficient negative feedback regulatory closed loop: side reaction → pH increase → gel response (enhanced coordination + structural contraction) → suppression of side reaction & homogenization of ion flow → interface stabilization → pH decrease. This dynamic adaptive process maintains the interface in a healthy state, thereby fundamentally inhibiting the accumulation of dendrites and byproducts.

[0028] This invention is not only applicable to zinc anodes, but can also be extended to the protection of other aqueous metal anodes (such as magnesium, calcium, aluminum, etc.) by adjusting the type of pH-responsive monomer and pKa value. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings.

[0031] A pH-responsive smart hydrogel interface layer is provided, which covers the surface of a metal anode; the hydrogel is prepared by in-situ polymerization of the following components: Hydrophilic host monomer (component A): at least one hydrophilic vinyl monomer containing acidic or polar groups, used to construct the gel network framework and provide basic ion conduction capabilities.

[0032] pH-responsive functional monomer (component B): at least one vinyl monomer containing a nitrogen-containing heterocyclic group that is sensitive to pH, serving as the core unit for intelligent response.

[0033] Crosslinking agent (component C): at least one multifunctional crosslinking agent used to crosslink polymer chains into a three-dimensional network structure.

[0034] When the battery is operating normally, the interface pH is low, and the pH-responsive groups (component B) are in a protonated or inactive state. When side reactions such as hydrogen evolution occur, causing a local increase in the interface pH, the pH-responsive groups undergo deprotonation or conformational changes. This change triggers one or more of the following synergistic effects: Enhanced Zn 2+ Coordination ability: The deprotonated nitrogen-containing group (such as the nitrogen atom of pyridine or imidazole) becomes a stronger Lewis base, which can more effectively coordinate with Zn. 2+ Coordination occurs. This creates "ion enrichment centers" in regions with low zinc ion concentrations, actively attracting and immobilizing Zn. 2+ It effectively alleviates concentration polarization and promotes uniform deposition.

[0035] Self-regulation of gel network structure: Changes in the protonation state alter the electrostatic interactions or solvation between polymer chains, leading to changes in the swelling degree of the gel (e.g., shrinkage). The shrinkage of the gel network can reduce its pore size and make its structure more compact, thereby physically restricting the penetration of water molecules to the negative electrode surface and inhibiting the hydrogen evolution side reaction at its source.

[0036] This negative feedback regulation mechanism of "pH increase → gel response → suppression of side reactions / homogenization of ion flow → interface stabilization" gives the interface layer an unprecedented adaptive stabilization capability.

[0037] The hydrophilic host monomer (component A) is selected from one or more of acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), and N-isopropylacrylamide (NIPAM).

[0038] The pH-responsive functional monomer (component B) is selected from vinyl monomers containing pyridine, imidazole, pyrimidine, or quinoline rings, preferably 4-vinylpyridine (4VP) or 1-vinylimidazolium (VIM). The pKa values ​​of these groups enable them to have a sensitive response within the typical pH range (pH 7-10) of an aqueous battery interface.

[0039] The crosslinking agent (component C) is a multifunctional cage-type polyhedral oligomeric silsesquioxane (POSS), such as methacryloxypropyl cage-type POSS (MP-POSS). The introduction of POSS not only plays a crosslinking role, but its nanocage structure also provides a nanoconfining effect to promote Zn...2+ Desolvation, its hydrophobic core helps to repel water molecules, forming a synergistic enhancement effect with pH response function.

[0040] A method for preparing the above-mentioned pH-responsive smart hydrogel interface-protected metal anode includes the following steps: Components A, B, and C, along with a free radical initiator (such as azobisisobutyronitrile AIBN), are dissolved in an organic solvent (such as DMF) and mixed thoroughly to obtain a gel precursor solution.

[0041] The metal negative electrode substrate (such as zinc foil) is pretreated to be clean.

[0042] The obtained gel precursor solution was uniformly coated on the surface of the metal anode substrate.

[0043] The polymerization reaction is initiated by heating or ultraviolet light, which causes the precursor solution to solidify in situ on the negative electrode surface to form a hydrogel interface layer.

[0044] The negative electrode with the gel layer is immersed in the target electrolyte for solvent exchange to obtain the final intelligent protective metal negative electrode.

[0045] An aqueous electrochemical energy storage device comprising the aforementioned intelligent protective metal negative electrode, particularly an aqueous zinc-ion battery.

[0046] A typical structure of the aqueous electrochemical energy storage device includes: One positive pole; A negative electrode, wherein the negative electrode is the intelligent protective metal negative electrode of the present invention; A porous membrane positioned between the positive and negative electrodes; And the aqueous electrolyte that permeates the entire device.

[0047] In one specific embodiment, the device is a button cell, the structure of which consists of, in sequence, a negative electrode shell, a gasket, a smart protective zinc negative electrode, a glass fiber diaphragm impregnated with electrolyte, an α-MnO2 positive electrode, and a positive electrode shell, and is assembled by sealing using a press.

[0048] Example 1: 4-Vinylpyridine / acrylamide sulfonic acid copolymer gel protecting zinc anode Preparation of the gel precursor solution: In a clean glass bottle, 1.5 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as the hydrophilic host monomer, 0.5 g of 4-vinylpyridine (4VP) as the pH-responsive functional monomer, 0.06 g of methacryloxypropyl cage-type POSS (MP-POSS) as the crosslinking agent, and 0.02 g of AIBN as the initiator were dissolved together in 8 mL of N,N-dimethylformamide (DMF). The solution was magnetically stirred at room temperature for 15 minutes until all components were completely dissolved, forming a homogeneous and clear precursor solution.

[0049] Preparation of the intelligent negative electrode: A commercial zinc foil with a thickness of 100 micrometers was taken, and its surface was polished with 2000-grit sandpaper. It was then ultrasonically cleaned in acetone and ethanol for 5 minutes each, followed by rinsing with deionized water and drying. The cleaned zinc foil was fixed onto a glass slide, and the precursor solution prepared in step 1 was added dropwise to uniformly cover the zinc foil surface. Subsequently, the sample was placed in a vacuum oven at 70°C and heated for 1 hour to allow in-situ gel polymerization and solidification.

[0050] Activation and Assembly: The zinc anode with the gel layer was immersed in a 2MZnSO4 aqueous solution for 24 hours for solvent exchange and activation. The activated anode was used as the working electrode, with α-MnO2 as the positive electrode, a glass fiber membrane as the separator, and 2MZnSO4 + 0.1MnSO4 as the electrolyte to assemble a CR2032 coin cell.

[0051] Example 2: 1-Vinylimidazol / Acrylic acid copolymer gel protecting zinc anode Preparation of the gel precursor solution: 1.0 g of acrylic acid (AA) as the hydrophilic host monomer, 0.8 g of 1-vinylimidazole (VIM) as the pH-responsive functional monomer, 0.05 g of N,N'-methylenebisacrylamide (MBA) as the crosslinking agent, and 0.02 g of AIBN as the initiator were dissolved in 10 mL of a mixed solvent of deionized water and ethanol (volume ratio 1:1). After stirring evenly, the solution was bubbled with nitrogen for 10 minutes to remove dissolved oxygen.

[0052] Preparation of the intelligent negative electrode: The same zinc foil pretreatment method as in Example 1 was used. The precursor solution obtained in step 1 was coated on the surface of the zinc foil, and then irradiated with a 365nm ultraviolet lamp for 15 minutes to initiate a photopolymerization reaction and form a gel layer.

[0053] Activation and Assembly: The electrode was also activated by immersion in a 2M ZnSO4 aqueous solution for 24 hours. The activated negative electrode and a bare zinc sheet were used as the counter electrode to assemble a symmetrical cell in a 2M ZnSO4 electrolyte for evaluation of its cycle stability.

[0054] Example 3: Synergistic gel protection of zinc anode by dual-monomer and pyridine functionalization Preparation of gel precursor solution: 0.8 g of acrylic acid (AA) and 0.8 g of acrylamide (AM) as amphiphilic host monomers, 0.4 g of 4-vinylpyridine (4VP) as pH-responsive functional monomer, 0.06 g of MP-POSS as crosslinking agent, and 0.02 g of AIBN as initiator were dissolved in 8 mL of DMF and stirred until homogeneous.

[0055] Preparation of the intelligent negative electrode: A gel interface layer was formed on the surface of the pretreated zinc foil using the same thermally initiated polymerization method as in Example 1.

[0056] Activation and Assembly: The electrode was activated by immersion in a 2M ZnSO4 aqueous solution. The activated negative electrode was then assembled with a copper foil as the counter electrode in a 2M ZnSO4 electrolyte to form an asymmetric cell (Zn||Cu) for evaluation of its coulombic efficiency.

[0057] Example 4: Application of pH-responsive gel on magnesium anode of aqueous magnesium battery Preparation of gel precursor solution: 4VP / AMPS / MP-POSS gel precursor solution was prepared using the same formulation and method as in Example 1.

[0058] Preparation of the intelligent negative electrode: Commercial magnesium foil (200 micrometers thick) was mechanically polished and cleaned. The precursor solution obtained in step 1 was coated onto the surface of the magnesium foil and heat-cured at 70°C for 1 hour.

[0059] Activation and Assembly: The magnesium anode with a gel layer was activated by immersing it in an aqueous electrolyte containing 3 mmol (TFSI)₂ for 24 hours. The activated anode and a bare magnesium sheet were then assembled into a symmetrical cell (Mg||Mg) in the same 3 mmol (TFSI)₂ electrolyte to evaluate its performance under high charge density Mg. 2+ Stability under environmental conditions.

[0060] Example 5 (Comparative Example): Static gel protection for zinc anode without pH response function Preparation of the gel precursor solution: To verify the necessity of the pH-responsive group, a control group without component B was prepared. 1.5 g of AMPS as the hydrophilic host monomer, 0.06 g of MP-POSS as the crosslinking agent, and 0.02 g of AIBN as the initiator were dissolved together in 8 mL of DMF. Note: No pH-responsive functional monomers were added to this formulation.

[0061] Preparation and assembly of the negative electrode: Using the same steps as in Example 1, a static gel protective layer was prepared on zinc foil and assembled into a full cell under the same conditions as in Example 1.

[0062] Performance Comparison: It is expected that in long-cycle testing, the smart negative electrode full cell in Example 1 will exhibit significantly better capacity retention and lower voltage polarization growth rate than the static negative electrode full cell in this comparative example, thus demonstrating the key role of pH response function in improving the long-term stability of the battery.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pH-responsive smart hydrogel interface layer, characterized in that, The pH-responsive smart hydrogel interface layer is a hydrogel; the pH-responsive smart hydrogel interface layer has a microporous or nanoporous network structure, which is naturally formed by the cross-linking and stacking of polymer chains during the polymerization process, and the pore size of the micropores or nanopores ranges from a few nanometers to several hundred nanometers.

2. The pH-responsive smart hydrogel interface layer according to claim 1 is applied to the preparation of a smart protective metal anode, characterized in that, The preparation method includes the following steps: Step a): Dissolve the hydrophilic host monomer, the functional monomer containing a nitrogen-containing heterocyclic group that is sensitive to pH, the crosslinking agent and the initiator in a solvent to form a gel precursor solution; Step b): Coat the gel precursor solution onto the surface of the metal anode substrate; Step c): A polymerization reaction is initiated by heating or light to form a gel interface layer on the surface of the negative electrode, thereby obtaining a smart protective metal negative electrode.

3. The method for preparing a smart protective metal anode according to claim 2, characterized in that, In step a): The molar ratio of the hydrophilic main monomer to the functional monomer containing a nitrogen-containing heterocyclic group that is sensitive to pH is 10:1 to 1:5; The molar amount of the crosslinking agent is 0.1% to 5% of the total molar amount of the monomers (the sum of the hydrophilic host monomer and the functional monomers containing nitrogen-containing heterocyclic groups that are sensitive to pH); the molar amount of the initiator is 0.5% to 3% of the total molar amount of the monomers (the sum of the hydrophilic host monomer and the functional monomers containing nitrogen-containing heterocyclic groups that are sensitive to pH).

4. The method for preparing a smart protective metal anode according to claim 3, characterized in that, The solvent is selected from one or a mixture of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), water, and ethanol.

5. The method for preparing a smart protective metal anode according to claim 2, characterized in that, In step b): The thickness of the wet film formed by coating the gel precursor solution onto the surface of the metal anode substrate is controlled between 20 micrometers and 200 micrometers.

6. The method for preparing a smart protective metal anode according to claim 2, characterized in that, In step c): When heating is used to initiate polymerization, the heating temperature is 50°C to 90°C and the heating time is 30 minutes to 3 hours. When photo-initiated polymerization is used, ultraviolet light with a wavelength of 254 nm to 400 nm is used, with a light intensity of 10 mW / cm² to 100 mW / cm² and an irradiation time of 5 to 30 minutes.

7. The method for preparing a smart protective metal anode according to claim 2, characterized in that, The nitrogen-containing heterocyclic group is selected from one or more of the following: pyridine ring, imidazole ring, pyrimidine ring, purine ring, or quinoline ring.

8. The method for preparing a smart protective metal anode according to claim 7, characterized in that, The functional monomer containing a pH-sensitive nitrogen-containing heterocyclic group is formed by linking the nitrogen-containing heterocyclic group with a polymerizable functional group (such as vinyl group); When the nitrogen-containing heterocyclic group is a pyridine ring, the functional monomer is 4-vinylpyridine; When the nitrogen-containing heterocyclic group is an imidazole ring, the functional monomer is 1-vinylimidazole.

9. A method for preparing a smart protective metal anode according to claim 2, characterized in that, The hydrophilic host monomer is selected from one or more of acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, or hydroxyethyl acrylate; The crosslinking agent is a polyhedral oligomeric silsesquioxane (POSS) with a cage-like structure, and the POSS has one or more polymerizable functional groups.

10. A smart protective metal anode, comprising a metal anode substrate; a pH-responsive smart hydrogel interface layer as described in claim 1, wherein the pH-responsive smart hydrogel interface layer is polymerized and solidified in situ on the surface of the metal anode substrate.

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