A hydrolysis-resistant schiff base hydrogel electrolyte for supercapacitor which can be quickly gelled and a preparation method and application thereof

Abstract

The present application belongs to the field of gel electrolyte, and discloses a hydrolysis-resistant Schiff base hydrogel electrolyte for supercapacitors, and a preparation method and application thereof. The present application utilizes the natural dissociation of polyallylamine hydrochloride in aqueous solution, and does not need to adjust the pH value, so that free amino groups can be released under acidic conditions to occur condensation reaction with glutaraldehyde, and a three-dimensional network crosslinked by Schiff base structure is obtained. The preparation method is simple, does not need organic solvent, and the reaction is controllable, and the gelation can be completed at room temperature in a short time. The obtained hydrogel electrolyte overcomes the defect that the traditional Schiff base structure is easy to hydrolyze under acidic conditions, and has excellent chemical stability. The solid-state supercapacitor assembled by using the in-situ forming capacity effectively solves the problem of poor contact between the electrode and the electrolyte, improves the conductivity, specific capacitance and energy density of the device, and has wide application prospect in the field of flexible energy storage devices.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and in particular to a hydrogel that can be rapidly gelled in situ for use in the preparation of electrolyte supercapacitors. Technical Background

[0002] Hydrogels, as elastic materials composed of a three-dimensional network of polymers and a large number of water molecules, have shown undeniable value in fields such as biomedicine, flexible electronics, and environmental engineering due to their hydrophilic network structure and tunable physicochemical properties. Their research promotes interdisciplinary innovation and provides new material pathways for solving cross-disciplinary technical problems.

[0003] However, the preparation process of traditional hydrogels is cumbersome and time-consuming, often relying on heating or photocatalysis, and the long gelation time leads to high time and economic costs, severely restricting their widespread application in rapid on-site deployment, wearable devices, and biomedicine. Although hydrogel electrolytes ingeniously combine the structural integrity of solids with the efficient ion transport capabilities of liquids, becoming a core component of flexible energy storage devices, the inherent trade-off between mechanical properties and ionic conductivity, as well as the instability of electrode-electrolyte interface contact, still urgently need to be addressed. Currently, relevant patents have disclosed research progress on related technologies to address these issues. For example, Chinese patent CN118256006A reports the hydrolysis of dealkalized lignin (DL) in an alkaline environment to generate catechol groups, which promote the formation of various free radicals and jointly promote the rapid polymerization of vinyl monomers (AM / HEA) to form a hydrogel. The fastest gelation speed can reach 4 minutes. After the addition of aluminum chloride, it has good mechanical properties, antifreeze properties, and electrical conductivity. The supercapacitor assembled with it has excellent low-temperature stability. Chinese patent CN116914246A reports the uniform mixing of lithium salt, organic solvent, and additives composed of polymer monomers and initiators in an inert argon atmosphere to obtain a liquid wide-temperature-range electrolyte. The electrolyte can be polymerized in situ inside the battery by simply raising the temperature, changing from a liquid state to a gel state. Unlike traditional hydrogels, this method uses organic solvents as the dispersion medium, resulting in lithium batteries with wide operating temperature ranges, good safety performance, electrochemical performance, compatibility, and low cost. CN111261425A reports the preparation of an antifreeze hydrogel solid electrolyte using methacryloyl ethyl sulfobetaine (SBMA), hydroxyethyl methacrylate (HEMA), and propylene trioxyethyltrimethylammonium chloride (DAC) as monomers, 4-8 mol / L lithium salt solution as solvent, and the addition of N,N-methylenebisacrylamide (MBA, 0.4-0.8% of total monomer weight) and an initiator (0.8-1.2% of total monomer weight). Due to the addition of a certain amount of lithium salt, this hydrogel electrolyte and antifreeze electrode can be used to prepare supercapacitors, which still exhibit good flexibility and a high conductivity of 30 mS / cm at -25℃, and retain 82% of the capacitance after 7000 low-temperature cycles.CN113402651A reports a method for preparing poly(methacrylamide-co-acrylic acid) hydrogels by heating and polymerization of methacrylamide and acrylic acid monomers. The hydrogels are then immersed in 1-10 mol / L solutions of sodium chloride, potassium chloride, or lithium chloride until swelling equilibrium is reached, thus preparing a poly(methacrylamide-co-acrylic acid) hydrogel electrolyte. This hydrogel electrolyte can be used to prepare flexible supercapacitors. The hydrogel electrolyte is free of chemical crosslinking agents, making it safe and environmentally friendly. It exhibits high strength (tensile breaking stress 0.3-0.4 MPa), high tensile strength (elongation at break 670-1180%), self-healing properties, and a conductivity of 1.9-2.8 S / m. The flexible supercapacitors are stretchable and bendable, require no diaphragm, have a simple process, and an energy density of 40-170 μWh / cm². 2 Power density 45000-150000 μW / cm³ 2 .

[0004] However, the preparation methods described in existing literature are often quite complex. For example, the method described in Chinese patent CN116914246A requires external heating to prepare hydrogels with the target properties, which is time-consuming. Patent CN113402651A requires a heating step to prepare the hydrogel, followed by soaking to improve its properties, a cumbersome process that wastes time and resources. Due to time and operational limitations in practical applications, these problems severely restrict the further promotion of hydrogels. Among the many types of hydrogel electrolytes, Schiff base hydrogels have received widespread attention in recent years. Schiff base hydrogels are constructed through the condensation reaction of amino and aldehyde groups, with their crosslinking points consisting of dynamically reversible imine bonds (C=N). This reaction has a low activation energy, mild reaction conditions, and the dynamically reversible nature of the imine bonds endows the hydrogel with good self-healing ability and injectability. Furthermore, by introducing specific components such as chitosan derivatives, these hydrogels also exhibit good antibacterial properties, biocompatibility, and stimuli responsiveness, attracting widespread attention in the biomedical and flexible electronics fields. Existing technologies, such as the *Formation d'hydrogels et réticulation chimique de polymères (chitosane et PAH)*, report methods for preparing hydrogels using glutaraldehyde crosslinked with polyallylamine hydrochloride (PAH) or chitosan. However, these conventional methods typically suffer from the following problems: Since polyallylamine hydrochloride is acidic, existing techniques usually require the addition of alkaline adjusters such as sodium hydroxide (NaOH) to neutralize or alkaline the pH, releasing sufficient amino groups to initiate nucleophilic addition reactions. This step not only increases operational complexity but also introduces additional impurity ions. Some systems require the introduction of organic solvents, which does not conform to green chemistry principles. More critically, the traditional Schiff base structure (imine bond) is highly susceptible to reverse hydrolysis in acidic environments, leading to hydrogel structure disintegration, insufficient chemical stability, and limiting its application in acidic electrolytes or complex environments. Furthermore, because the pH needs to be pre-adjusted or multiple components need to be mixed, the reaction rate is difficult to control precisely, making it difficult to directly use as an electrolyte to achieve in-situ gelation inside the supercapacitor. This results in poor contact at the electrode-electrolyte interface, which limits the electrochemical performance of the device.

[0005] Therefore, how to avoid the pH adjustment step, directly achieve rapid crosslinking of PAH and glutaraldehyde under pure aqueous phase and acidic conditions, and obtain a hydrogel electrolyte that is resistant to acid hydrolysis, has high conductivity, and can be formed in situ is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the technical problems in the background art, this invention provides a hydrolysis-resistant Schiff base hydrogel electrolyte for supercapacitors that can be rapidly gelled, along with its preparation method. This method requires operation at room temperature and achieves rapid gelation without any external stimulation; simultaneously, it ensures that the hydrogel avoids the easy hydrolysis of imine bonds under acidic conditions, thereby improving its chemical stability and broadening its application range under harsh conditions.

[0007] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0008] A method for preparing Schiff base hydrogel electrolyte without external stimulation is proposed. This method involves crosslinking polyamine hydrochloride with aldehyde compounds and directly performing aldehyde-amine condensation under acidic conditions, which rapidly forms a three-dimensional network through the Schiff base structure, thereby simply and efficiently preparing the target hydrogel.

[0009] The main reactants used in this invention include: polyallylamine hydrochloride (PAH), 25% glutaraldehyde aqueous solution, and lithium salt.

[0010] Its raw material composition, in parts by mass, mainly includes:

[0011] Polyallylamine hydrochloride: 4-10 parts by weight;

[0012] Deionized water: 15-30 parts by weight;

[0013] 25% glutaraldehyde aqueous solution: 1.5-3.5 parts by weight;

[0014] Lithium salt: 0-7 parts by weight.

[0015] The weight-average molecular weight of polyallylamine hydrochloride is 3,000-20,000, and its molecular formula is (C3H7N). n .xHCl is an off-white powder that is readily soluble in water;

[0016] Among them, glutaraldehyde is used as a crosslinking agent in a 25% aqueous solution with the molecular formula C5H8O2.

[0017] Among them, lithium salts such as lithium chloride (LiCl) and lithium tetrafluoroborate (LiBF4) are used as electrolyte lithium salts, with lithium tetrafluoroborate being preferred.

[0018] In a first aspect, the present invention provides a method for preparing a Schiff base hydrogel electrolyte based on a polyallylamine hydrochloride-glutaraldehyde system. This hydrogel can rapidly gel at room temperature under acidic conditions. The method includes the following steps:

[0019] S1: Dissolve polyallylamine hydrochloride (PAH) in deionized water to prepare a homogeneous PAH solution.

[0020] S2: Add lithium salt to the PAH solution to adjust the lithium ion concentration in the system to 0 M ~ 1.5 M.

[0021] S3: Add 25% glutaraldehyde aqueous solution as a crosslinking agent to the above solution, stir evenly (about 30 s), pour into a mold, and seal at room temperature for several minutes (<15 min) to carry out crosslinking to obtain PAH. x -GA y -Li z Hydrogel electrolyte, where x is the mass fraction of PAH, y is the mass fraction of 25% glutaraldehyde aqueous solution, and z is the molar concentration of lithium ions in the system.

[0022] Preferably, in step S3, the amount of the crosslinking agent 25% glutaraldehyde aqueous solution added is 5% to 15% of the total mass of the system.

[0023] Secondly, the present invention provides PAH prepared by the aforementioned method. x -GA y -Li z Application of hydrogel electrolytes in the construction of supercapacitor devices.

[0024] The application method is as follows: prepare electrode sheets containing active materials (such as activated carbon), place two electrode sheets in a mold and maintain a certain distance (such as 4 mm); directly inject the electrolyte precursor solution that has been mixed evenly but has not yet gelled in step S3 into the space between the two electrodes, and allow it to gel in situ at room temperature to form a solid supercapacitor with a sandwich structure.

[0025] The specific application methods are as follows:

[0026] Activated carbon (AC), conductive carbon black, and polyvinylidene fluoride (PVDF) were added sequentially to N-methylpyrrolidone (NMP) and dispersed in an ultrasonic cleaner for 30 minutes to obtain a uniform electrode slurry. The slurry was then uniformly coated onto 1 cm × 1 cm high-purity graphite paper using a pipette and subsequently dried in a 90°C vacuum oven for 9 hours to obtain the AC electrode. The mass of active material loaded on each electrode was recorded. Two AC electrodes with identical active material loadings were selected and placed in a self-made 4 mm thick mold, ensuring complete alignment of the upper and lower electrodes, with the distance between them equal to the mold thickness (4 mm). Then, ungelled PAH was injected. x -GA y -Li z Hydrogel electrolytes achieve in-situ gelation within minutes, forming solid-state supercapacitors with a sandwich structure.

[0027] The amount of each component added to the electrode slurry is as follows: the mass ratio of activated carbon, conductive carbon black and polyvinylidene fluoride is 1:8:1.

[0028] Preferably, the amount of each component added to the electrode slurry is: 100 mg of activated carbon, 800 mg of conductive carbon black, 100 mg of polyvinylidene fluoride, and 30 ml of N-methylpyrrolidone.

[0029] Compared with the prior art, the advantages of the present invention are as follows:

[0030] (1) This invention develops a simple and universal method that does not require pH adjustment, utilizing glutaraldehyde to rapidly crosslink polyallylamine hydrochloride under acidic conditions to achieve rapid gelation of Schiff base hydrogel electrolytes. The numerous amino groups on the side chains of polyallylamine hydrochloride, after protonation, enhance its water solubility and make the solution acidic (pH≈3). After dissolving in water, the free amino groups released by the dissociation of the side-chain amino hydrochloride can react rapidly with glutaraldehyde to form a multi-linked structure, thereby achieving network stability under acidic conditions.

[0031] (2) The gelation time of the present invention can be controlled by adjusting the mass ratio of PAH to GA, the lithium ion concentration, or the pH value. The prepared hydrogel electrolyte can be prepared within 4 minutes at room temperature without any external stimulation. After introducing lithium ions, the conductivity of the hydrogel electrolyte can reach 6.80 S / m. -1 It possesses excellent ion transport performance.

[0032] (3) The rapid gelation system based on the Schiff base reaction has the ability to be formed in situ and is suitable for a variety of applications. For example, the conductivity of a supercapacitor assembled by in-situ gelation is higher than that of a device prepared in situ, which is 2.30 S·m. -1 Increased to 6.80 S·m -1 The specific capacitance is 79.2 F·g -1 Increased to 120.8 F·g -1 The energy density is 5.56 Wh·kg -1 Increased to 8.33 Wh·kg -1 This indicates that its electrochemical performance has been improved. Attached Figure Description

[0033] The invention will now be further described with reference to the accompanying drawings.

[0034] Figure 1 It is PAH x -GA y -Li z Infrared spectra of hydrogel electrolytes and their raw materials.

[0035] Figure 2These are the curves showing the change of G' over time during the gelation process of Examples 1(a), 2(b), 3(c), 4(d), 8(e), and 10(f).

[0036] Figure 3 This is a diagram showing the soaking of Example 2 in an aqueous solution with pH=3.

[0037] Figure 4 These are the oscillation time scan test results of Examples 1, 2, 3, 4, 5, and 6.

[0038] Figure 5 The electrochemical performance of the electrolyte-assembled SC is shown in the figures: (a) CV curves of Example 7 at different cycling rates, (b) GCD curves of Example 7 at different current densities, and (c) GCD curves of Example 7 at different gel times and Comparative Example 1 at 40 mV s. -1 The CV curves at different circulation rates, (d) are from Example 7 at different gel times and Comparative Example 1 at 0.2 A g. -1 The GCD curves at current density, (e), (f), and (g) are the EIS plots of Examples 1, 7, 8, 9, 10, and Comparative Example 1, respectively, and at 40 mV s. -1 CV curves at various cyclic speeds, and at 0.2 A g. -1 The GCD curve (h) at current density is the cycle performance graph of Example 7. Detailed Implementation

[0039] The following embodiments are further illustrations of the present invention, but the present invention is not limited thereto.

[0040] PolyPAH prepared in the following examples x -GA y -Li z The hydrogel underwent the following performance tests using the methods described below:

[0041] 1.1. Rheological property testing

[0042] Dynamic oscillation test: Using an MCR301 rotational rheometer, in 25 mm plate mode with a plate gap of 1000 μm, the dynamic oscillation test was performed by time scanning at a frequency of 1 Hz and a strain of 1% to obtain data on elastic modulus and viscous modulus. The corresponding test temperature was set to 25 ℃.

[0043] 1.2. Gel time

[0044] The prepared solution is added dropwise to the rotational rheometer apparatus, and the gel time is measured using the oscillation mode of the rotational rheometer. The intersection of the elastic modulus G' and the viscous modulus G'' is the gel time. Near the gel point, G' and G'' intersect, which is a hallmark feature of the transition from liquid to solid. In other words, the gel time point can be considered when the elastic modulus and viscous modulus are equal.

[0045] 1.3. Measurement of the conductivity of hydrogel electrolytes

[0046] The ionic conductivity of the hydrogel electrolyte was measured by electrochemical impedance spectroscopy (EIS) in a CHI660E electrochemical workstation. First, the hydrogel electrolyte was filled into a self-made electrode mold containing active material and stabilized at 25 °C for 12 hours. Then, impedance was measured at the corresponding temperature. Three measurements were performed for each sample to minimize error. Ionic conductivity (σ, Sm) -1 It is calculated using the following formula.

[0047]

[0048] Where R is the resistance (Ω) and S is the contact area of ​​the electrolyte (m²). 2 L is the thickness (m) of the sample to be tested.

[0049] 1.4. Electrochemical performance testing of SC devices

[0050] Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) were measured using a dual-electrode system on a CHI660E workstation. Cyclic stability was measured using 5000 cycles of GCD. The specific capacitance of a single electrode (C0) was calculated based on the discharge profiles of the GCD. sp , F g -1 The calculation formula is as follows:

[0051]

[0052] Furthermore, the energy density (E, Wh kg) of sc can be calculated based on the specific capacitance. -1 The calculation formula is as follows:

[0053]

[0054] Where I is the discharge current (mA). is the discharge time (s), m is the amount of active material on the capacitor electrode (mg), and This indicates the discharge voltage (V).

[0055] The present invention will be further described in detail below with reference to the embodiments:

[0056] Raw material source: Polyallylamine hydrochloride (PAH) with a weight average molecular weight of 15,000-18,000, sourced from Shanghai Titan Technology Co., Ltd.

[0057] Example 1:

[0058] Solution preparation: Dissolve 4 parts by mass of polyallylamine hydrochloride powder in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to ensure complete dissolution. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, PAH is prepared after several minutes. 16 -GA6-Li0 hydrogel.

[0059] Performance test results

[0060] PAH prepared in Example 1 16 The GA6-Li0 hydrogel had a gelation time of 260.7 s and a storage modulus of 413.4 Pa, as measured by oscillation testing on a rotational rheometer.

[0061] Example 2:

[0062] Solution preparation: Dissolve 5 parts by mass of polyallylamine hydrochloride powder in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to ensure complete dissolution. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, PAH is prepared after several minutes. 20 -GA6-Li0 hydrogel.

[0063] Performance test results

[0064] PAH prepared in Example 2 20 The GA6-Li0 hydrogel had a gelation time of 291.3 s and a storage modulus of 1555.0 Pa, as measured by oscillation testing on a rotational rheometer.

[0065] Example 3:

[0066] Solution preparation: Dissolve 6 parts by mass of polyallylamine hydrochloride powder in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to ensure complete dissolution. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, PAH is prepared after several minutes. 23 -GA6-Li0 hydrogel.

[0067] Performance test results

[0068] PAH prepared in Example 3 23 The GA6-Li0 hydrogel had a gelation time of 163.7 s and a storage modulus of 626.7 Pa, as measured by oscillation testing on a rotational rheometer.

[0069] Example 4:

[0070] Solution preparation: Dissolve 7 parts by mass of polyallylamine hydrochloride powder in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to ensure complete dissolution. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, PAH is prepared after several minutes. 26 -GA6-Li0 hydrogel.

[0071] Performance test results

[0072] PAH prepared in Example 4 26 The GA6-Li0 hydrogel had a gelation time of 127.1 s and a storage modulus of 582.5 Pa, as measured by oscillation testing on a rotational rheometer.

[0073] Example 5:

[0074] Solution preparation: Dissolve 5 parts by mass of polyallylamine hydrochloride powder in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to ensure complete dissolution. While stirring, add 2.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, PAH is prepared after several minutes. 20 -GA 10 -Li0 hydrogel.

[0075] Performance test results

[0076] PAH prepared in Example 5 20 -GA 10 The Li0 hydrogel was gelled in an oscillation test using a rotational rheometer, with a gelation time of 106.5 s and a storage modulus of 509.4 Pa.

[0077] Example 6:

[0078] Solution preparation: Dissolve 5 parts by mass of polyallylamine hydrochloride powder in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to ensure complete dissolution. While stirring, add 3.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, PAH is prepared after several minutes. 20 -GA 14 -Li0 hydrogel.

[0079] Performance test results

[0080] PAH prepared in Example 6 20 -GA 14 The Li0 hydrogel, when subjected to oscillation testing on a rotational rheometer, had a gelation time of 84.3 s and a storage modulus of 7850.2 Pa.

[0081] Example 7:

[0082] Assembly of the supercapacitor mold: 800 mg of activated carbon (AC), 100 mg of conductive carbon black, and 100 mg of polyvinylidene fluoride (PVDF) were added sequentially to 30 ml of N-methylpyrrolidone (NMP) and dispersed in an ultrasonic cleaner for 30 min to obtain a uniform dispersion. The dispersion was evenly spread on 1 cm * 1 cm high-purity graphite paper using a pipette and placed in a vacuum oven at 90 °C for 9 h to obtain the AC electrode. The mass of the active material on each electrode was recorded. Two AC electrodes with the same mass of loaded active material were placed in a self-made 4 mm thick mold, with the top and bottom completely aligned, and the distance between the two AC electrodes was 4 mm of the mold thickness.

[0083] Solution preparation and supercapacitor assembly: Dissolve 5 parts by mass of polyallylamine hydrochloride powder and 2.2 parts by mass of lithium tetrafluoroborate in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to dissolve it completely. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution and quickly drop it into a 4 mm supercapacitor mold. After sealing, prepare the in-situ formed supercapacitor within a few minutes.

[0084] Performance test results

[0085] PAH prepared in Example 7 20 -GA6-Li 1.0 The hydrogel had a gelation time of 573.3 s and a storage modulus of 1566.0 Pa. The conductivity of the assembled supercapacitor was 6.80 ± 0.40 S m. -1 At a current density of 0.2 A g -1 It showed 120.8 F g -1 Specific capacitance and 8.33 Wh kg -1 Energy density.

[0086] Example 8:

[0087] The supercapacitor mold was assembled in the same manner as in Example 7.

[0088] Solution preparation and supercapacitor assembly: Dissolve 5 parts by mass of polyallylamine hydrochloride powder and 1.1 parts by mass of lithium tetrafluoroborate in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to dissolve it completely. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution and quickly drop it into a 4 mm supercapacitor mold. After sealing, prepare the in-situ formed supercapacitor within a few minutes.

[0089] Performance test results

[0090] PAH prepared in Example 8 20 -GA6-Li 0.5 The hydrogel, with a gelation time of 424.7 s and a storage modulus of 1513.0 Pa measured by oscillation testing on a rotational rheometer, was used. The assembled supercapacitor had a conductivity of 4.15 ± 0.24 S / m. -1 At a current density of 0.2 A g -1 It showed a value of 94.4 F g. -1 Specific capacitance and 6.67 Wh kg -1 Energy density.

[0091] Example 9:

[0092] The supercapacitor mold was assembled in the same manner as in Example 7.

[0093] Solution preparation and supercapacitor assembly: Dissolve 5 parts by mass of polyallylamine hydrochloride powder and 0.2 parts by mass of lithium tetrafluoroborate in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to dissolve it completely. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution and quickly drop it into a 4 mm supercapacitor mold. After sealing, prepare the in-situ formed supercapacitor within a few minutes.

[0094] Performance test results

[0095] PAH prepared in Example 9 20 -GA6-Li 0.1 The hydrogel had a gelation time of 347.2 s and a storage modulus of 1642.0 Pa. The assembled supercapacitor had a conductivity of 4.72 ± 0.28 S / m. -1 At a current density of 0.2 A g -1 It showed 76.8 F g -1 Specific capacitance and 5.33 Wh kg -1 Energy density.

[0096] Example 10:

[0097] The supercapacitor mold was assembled in the same manner as in Example 7.

[0098] Solution preparation and supercapacitor assembly: Dissolve 5 parts by mass of polyallylamine hydrochloride powder and 3.3 parts by mass of lithium tetrafluoroborate in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to dissolve it completely. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution and quickly drop it into a 4 mm supercapacitor mold. After sealing, prepare the in-situ formed supercapacitor within a few minutes.

[0099] Performance test results

[0100] PAH prepared in Example 10 20 -GA6-Li 1.5 The hydrogel, with a gelation time of 739.8 s and a storage modulus of 1453.0 Pa measured by oscillation testing on a rotational rheometer, was used. The assembled supercapacitor had a conductivity of 5.86 ± 0.35 S / m. -1 At a current density of 0.2 A g -1 It showed 121.6 F g -1 Specific capacitance and 8.47 Wh kg -1 Energy density.

[0101] Example 11:

[0102] The supercapacitor mold was assembled in the same manner as in Example 7.

[0103] Solution preparation and supercapacitor assembly: Dissolve 5 parts by mass of polyallylamine hydrochloride powder and 1 part by mass of lithium chloride in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to dissolve it completely. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution and quickly drop it into a 4 mm supercapacitor mold. After sealing, prepare the in-situ formed supercapacitor within a few minutes.

[0104] Performance test results

[0105] PAH prepared in Example 11 20 -GA6-LiCl 1.0 The hydrogel, with a gelation time of 621.3 s and a storage modulus of 1573.0 Pa measured by oscillation testing on a rotational rheometer, produced a supercapacitor with a conductivity of 5.12 ± 0.32 S m. -1 At a current density of 0.2 A g -1 It showed 105.3 F g. -1 Specific capacitance and 7.31 Wh kg -1 Energy density.

[0106] Comparative Example 1:

[0107] Using the same formulation as in Example 7 (PAH) 20 -GA6-Li 1.0 )

[0108] The difference between Comparative Example 1 and Example 7 is that PAH was used... 20 -GA6-Li 1.0The hydrogel was directly molded in a 4 mm polytetrafluoroethylene mold. After gelation, it was removed and simply stacked with AC electrodes to assemble a supercapacitor.

[0109] Performance test results

[0110] The supercapacitor assembled in Comparative Example 1 has a conductivity of 2.30 ± 0.14 S m. -1 At a current density of 0.2 A g -1 It showed 79.2 F g at that time. -1 Specific capacitance and 5.56 Wh kg -1 Energy density.

[0111] As can be seen from Comparative Example 1, compared with traditional simple stacked supercapacitors, in-situ molded supercapacitors have higher conductivity, specific capacitance and energy density.

[0112] Comparative Example 2:

[0113] Comparative Example 2 compared to Example 1: 5 parts by mass of chitosan hydrochloride were used to replace PAH, and the other conditions were the same as in Example 1.

[0114] Solution preparation: Dissolve 5 parts by mass of chitosan hydrochloride powder in 20 parts by mass of deionized water. Stir the prepared chitosan hydrochloride solution with a glass rod until fully dissolved. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, CSH is prepared after several minutes. 20 -GA6-Li0 hydrogel.

[0115] Performance test results

[0116] CSH prepared in Comparative Example 2 20 -GA6-Li0 hydrogel, the gelation time measured in the oscillation test of rotational rheometer was 30.2 s. However, the viscosity of the gel precursor liquid of CSH aqueous solution is extremely high, which makes it impossible to disperse and adhere evenly in the electrode sheet when assembling supercapacitors. The dispersion of crosslinking agent also becomes extremely difficult, which significantly limits the performance release of supercapacitors.

[0117] Comparative Example 3:

[0118] Solution preparation: Dissolve 0.2 parts by mass of chitosan hydrochloride powder in 20 parts by mass of deionized water. Stir the prepared chitosan hydrochloride solution with a glass rod until it is fully dissolved. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution. After sealing, hydrogel still cannot be formed after one day.

[0119] Performance test results

[0120] The CSH1-GA6-Li0 aqueous solution prepared in Comparative Example 3 has a viscosity similar to that of PAH in Example 2. 20 The viscosity of the GA6-Li0 aqueous solution is comparable, but it cannot form a gel within 24 hours.

[0121] Compared with Example 2, Comparative Example 2 and Comparative Example 3, it can be seen that traditional chitosan hydrochloride cannot achieve rapid gelation; while the polyallylamine hydrochloride (PAH) selected in this invention can be uniformly dispersed at low viscosity and then rapidly crosslinked into a gel.

[0122] Comparative Example 4:

[0123] Same as Example 2, but before adding the crosslinking agent, the pH of the PAH solution was adjusted to 7 (neutral) using NaOH.

[0124] Solution preparation: Dissolve 5 parts by mass of polyallylamine hydrochloride powder in 20 parts by mass of deionized water. Place the prepared polyallylamine solution on a magnetic stirrer to dissolve it completely. Add an appropriate amount of sodium hydroxide to adjust the pH to 7. While stirring, add 1.5 parts by mass of 25% glutaraldehyde aqueous solution. Localized, uneven gels will form in the solution and precipitate.

[0125] Performance test results

[0126] PAH prepared in Comparative Example 4 with a pH of 7 20 The reaction rate between the GA6-Li0 aqueous solution and the glutaraldehyde aqueous solution is too fast. Before the glutaraldehyde can fully diffuse in the aqueous solution, small, uneven gels are formed. It is necessary to dilute the 25% glutaraldehyde aqueous solution and then add it to the PAH aqueous solution for uniform cross-linking, which makes the experimental procedure cumbersome.

[0127] Results and Discussion

[0128] Synthesis of hydrogel electrolytes

[0129] PAH is a long-chain polymer with numerous protonated -NH2 groups on its side groups. After the addition of glutaraldehyde (GA), the -NH3 groups... + The dissociated amino groups rapidly undergo a Schiff base reaction with the -CHO groups in GA, forming a large number of imine bonds (C=N). These dense imine bonds constitute multiple cross-linking points, which in turn promote the construction of a stable three-dimensional network structure between PAH molecular chains, allowing them to maintain a gel state even under acidic conditions.

[0130] The reaction process was characterized by Fourier transform infrared spectroscopy (FTIR). Figure 1 Typically, the characteristic absorption peak of an aldehyde group is located at 1700-1750 cm⁻¹. -1 Within the range. As can be seen from the infrared spectrum, after 12 hours of reaction, it is located at 1750 cm⁻¹.-1 The complete disappearance of the characteristic absorption peak of the aldehyde group indicates that glutaraldehyde has fully participated in the reaction and the cross-linking process is basically complete.

[0131] The gelation rate of this system mainly depends on -NH3. + The relative ratio of PAH groups to -CHO groups. By adjusting the mass fraction of PAH, the number of imine bonds formed in the system can be changed, thereby controlling the gelation rate. Different PAH ratios... x -GA y -Li z Rheological testing of hydrogel electrolytes ( Figure 2 The data shows that PAH 16 -GA6-Li0, PAH 23 -GA6-Li0 and PAH 26 The gel times of the GA6-Li0 hydrogel, measured by rotational rheology, were 260.7 s, 163.7 s, and 127.1 s, respectively. With increasing PAH content, the number of reaction sites in the system increased, promoting the rapid formation of the cross-linked network and thus significantly shortening the gel time. [The text then abruptly shifts to a seemingly unrelated topic: PAH...] 20 -GA6-Li0 hydrogel is immersed in an aqueous solution with pH=3 ( Figure 3 It gradually swells and reaches equilibrium within 4 hours, and shows no signs of dissolution after 72 hours.

[0132] Furthermore, the relationship between the elastic modulus and loss modulus of hydrogels with different ratios was studied. Figure 4 It can be seen that the elastic modulus is closely related to the mass fractions of PAH and GA. When the amount of the crosslinking agent 25% glutaraldehyde aqueous solution is fixed at 6 wt%, PAH... 20 The elastic modulus of the GA6-Li0 hydrogel is 1555.0 Pa, which is higher than that of other PAH-containing hydrogels in the same series, indicating the existence of an optimal PAH concentration range. Too low a concentration leads to a sparse crosslinking network and loose structure, resulting in a low modulus; too high a concentration results in some polymer chains not being effectively crosslinked, making it easy for chain segments to slip, also causing a decrease in modulus. However, when the amount of crosslinking agent is increased (Example 6), the PAH... 20 -GA 14 The elastic modulus of the Li0 hydrogel reached 7850.2 Pa, indicating that appropriately increasing the amount of GA helps to form a denser three-dimensional network, thereby significantly improving the mechanical properties of the hydrogel.

[0133] Preparation and Properties of Supercapacitors Based on In-situ Gel Electrolytes

[0134] To fully utilize the rapid gelation characteristics of this hydrogel system, this invention uses it as an electrolyte and assembles it with a self-made graphite paper electrode to form a supercapacitor, and systematically evaluates its electrochemical performance. Figure 5 Cyclic voltammetry (CV) tests showed that at 40 mV·s -1 Up to 200 mV·s -1 Within the scan rate range, the CV curves all exhibit an approximately rectangular shape, even at 200 mV·s. -1 No significant distortion occurred even at high scan rates, indicating that the device exhibits ideal capacitive behavior and good rate performance. The galvanostatic charge-discharge (GCD) curves all exhibited symmetrical isosceles triangles at different current densities, further confirming its excellent reversibility and capacitive characteristics. At 0.2 A·g -1 At a current density of 120.8 F·g, this supercapacitor achieved 120.8 F·g. -1 Specific capacitance and 8.33 Wh·kg -1 The energy density is high. These excellent electrochemical properties are closely related to their high ionic conductivity, demonstrating the application potential of hydrogel electrolytes in high-efficiency energy storage devices.

[0135] To verify the effect of in-situ gel assembly on improving the electrochemical performance of capacitors, a non-in-situ gel supercapacitor was prepared using the same hydrogel electrolyte as a control. The assembly method for this control device was as follows: after the hydrogel electrolyte was completely gelled, it was simply stacked with an electrode sheet of the same active material to form a sandwich structure. The drawback of this method is that neither the electrode sheet nor the electrolyte surface is ideally flat, with local protrusions or depressions. This results in a large number of micro-gaps remaining at the interface after stacking, severely limiting ion transport efficiency and causing the overall conductivity to drop to 2.03 S·m. -1 .

[0136] As a result, non-in-situ assembled devices at 40 mV·s -1 At the scan rate, a rectangular CV curve could no longer be maintained, and the GCD curve also showed a shorter discharge time, ultimately resulting in a specific capacitance of only 79.2 F·g. -1 The energy density is 5.56 Wh·kg. -1 Compared with supercapacitors assembled in situ using gel, its key electrochemical performance decreased by more than 30%, fully demonstrating the significant advantages of the in-situ gel strategy in improving electrode-electrolyte interface contact and enhancing overall device performance.

[0137] Furthermore, to achieve a supercapacitor with more stable performance, lower cost, and superior overall performance, this invention systematically investigated the effects of different lithium-ion concentrations and gel times on the electrochemical performance of the device. As a crucial conductive carrier in the capacitor, the lithium-ion concentration directly affects its conductivity. However, from the rheological testing of the gel point (… Figure 2(b, e, f) shows that increasing the lithium salt concentration affects the gelation time to some extent, but the system as a whole still exhibits rapid gelation characteristics. Regarding the electrochemical performance of SC ( Figure 5 As shown in the figure, within the range of lithium ion concentration from 0.1 M to 1.5 M, the overall conductivity of the capacitor remains at a high level, and the specific capacitance and energy density increase with increasing concentration, reaching a peak at 1 M. Therefore, this concentration is determined to be the preferred ratio in this invention.

[0138] Further research using this optimized formulation to study the effect of gel time on electrochemical performance can improve the electrochemical performance of SC. Figure 5 In c) and d), it was found that the cross-linking density of the three-dimensional network formed in the early stage of gelation was low, and there was a large amount of free water in the system that could participate in ion transport, which was beneficial to improving the electrochemical performance of the capacitor. As time went on, the performance gradually stabilized after 10 hours, indicating that the network structure was basically mature at this time and the performance entered a plateau period.

[0139] To evaluate the cycle stability and environmental durability of supercapacitors, this invention uses 0.5 Ag at 25°C. -1 The device was subjected to 5000 continuous charge-discharge cycles at a given current density. Figure 5 The results showed that the capacitor maintained a high initial capacitance after 5000 cycles, indicating that it has excellent long-term cycling stability.

[0140] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of them. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a hydrolyzable Schiff base hydrogel electrolyte that can be rapidly gelled, characterized in that, Includes the following steps: The composition of the raw material, by mass, includes: 4-10 parts by mass of polyallylamine hydrochloride; 15-30 parts by weight of deionized water; 1.5-3.5 parts by weight of glutaraldehyde aqueous solution; 0-7 parts by weight of lithium salt; (1) Dissolve polyallylamine hydrochloride in deionized water to prepare a polyallylamine hydrochloride solution; (2) Add lithium salt to the polyallylamine hydrochloride solution and dissolve it, or do not add lithium salt; (3) Add glutaraldehyde aqueous solution to the above solution as a crosslinking agent, mix well, seal and let stand at room temperature. The amino groups released by the dissociation of polyallylamine hydrochloride react with glutaraldehyde under acidic conditions to form the hydrogel electrolyte, which is PAH. x -GA y -Li z Hydrogel electrolyte, where x is the mass fraction of PAH, y is the mass fraction of glutaraldehyde aqueous solution, and z is the molar concentration of lithium ions in the system.

2. The method for preparing the rapidly gelling, hydrolyzable Schiff base hydrogel electrolyte according to claim 1, characterized in that, The polyallylamine hydrochloride has a weight-average molecular weight of 3000-20000 and a molecular formula of (C3H7N). n .xHCl.

3. The method for preparing the rapidly gelling, hydrolysis-resistant Schiff base hydrogel electrolyte according to claim 1, characterized in that, In step (2), the lithium salt is selected from one or more of lithium chloride and lithium tetrafluoroborate; the lithium ion concentration in the system is adjusted to 0 M~1.5 M.

4. The method for preparing the rapidly gelling, hydrolyzable Schiff base hydrogel electrolyte according to claim 1, characterized in that, In step (2), the lithium salt is lithium tetrafluoroborate, and the lithium ion concentration in the system is 1.0 M.

5. The method for preparing the rapidly gelling, hydrolysis-resistant Schiff base hydrogel electrolyte according to claim 1, characterized in that, In step (3), the glutaraldehyde aqueous solution is a glutaraldehyde aqueous solution with a mass fraction of 25%.

6. A Schiff base hydrogel electrolyte prepared by the preparation method according to any one of claims 1-5.

7. The application of the Schiff base hydrogel electrolyte according to claim 6 in supercapacitor devices.

8. The application according to claim 7, characterized in that, The supercapacitor was prepared using an in-situ gel assembly method, and the specific steps are as follows: Two electrode plates loaded with active materials are placed in a mold and kept at a preset distance to form a cavity to accommodate the electrolyte. Inject the electrolyte precursor solution, which is uniformly mixed but not gelled, in step (3) of claim 1, between the two electrode plates; By allowing the electrolyte precursor solution to stand at room temperature, it gels in situ between the electrodes, forming a solid-state supercapacitor.

9. The application according to claim 8, characterized in that, The active materials loaded on the electrode sheet include activated carbon, conductive carbon black, and binder.

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