CN112768255A

CN112768255A - Anti-freezing zwitterion hydrogel electrolyte and application thereof

Info

Publication number: CN112768255A
Application number: CN202011419388.0A
Authority: CN
Inventors: 刘利彬; 杨健波; 班青; 盖利刚; 李梅
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2020-12-06
Filing date: 2020-12-06
Publication date: 2021-05-07
Anticipated expiration: 2040-12-06
Also published as: CN112768255B

Abstract

The invention belongs to the field of supercapacitors, and relates to a novel zwitterionic polymer hydrogel electrolyte and application thereof. The electrolyte is a polySH electrolyte, a LiCl-bonded poly (SBMA-HEA) electrolyte, Li⁺Carrying out jump migration through zwitterionic groups on polymer chains; in Raman spectrum, -SO₃ ^‑Wherein S-O stretching vibration is 1044cm^‑1～1054cm^‑1，‑N⁺(CH₃)₂CH in (1)₃The stretching vibration is 2953cm^‑1～2957cm^‑1. The addition of LiCl greatly influences the water molecule and polymer structure in an electrolyte system, so that the polySH electrolyte has good frost resistance and high ionic conductivity at low temperature. The polySH electrolyte may even be stretched to 325% strain and compressed to 75% strain at-40 ℃.

Description

Anti-freezing zwitterion hydrogel electrolyte and application thereof

Technical Field

The invention belongs to the field of supercapacitors, and relates to a novel zwitterionic polymer hydrogel electrolyte and application thereof.

Background

With the increasing global energy demand, higher requirements are put on the development of efficient energy storage devices. As a novel energy storage device, the super capacitor is widely concerned by people due to high charging and discharging speed and long service life.

The electrolyte comprises liquid electrolyte and solid electrolyte, and is an indispensable component of the super capacitor. The solid electrolyte mainly comprises inorganic solid electrolyte and polymer solid electrolyte, and the electrolytes can improve the safety of the device to a certain extent, but the inorganic solid electrolyte (including oxide and sulfide) has high conductivity (up to 10 percent)^-3S cm^-1) But the interface resistance between the electrode and the electrode is large, and the electrode is fragile, difficult to process and difficult to scale at present; polymer solid electrolytes overcome the limitations of inorganic solid electrolytes, but have low room temperature ionic conductivity (10)^-4～10-6S cm^-1). The hydrogel solid electrolyte is used as a quasi-solid electrolyte, the property of the quasi-solid electrolyte is between that of liquid and solid electrolyte, the ionic conductivity can be greatly improved, and the quasi-solid electrolyte has wider application space. However, when the freezing point of the hydrogel type solid electrolyte is lower than zero degree, the freezing of water causes the electrolyte to become hard and brittle, and the ionic conductivity to be reduced or even not conductive, which all limit the application of the hydrogel solid electrolyte in low temperature environments (such as deep sea, aerospace field).

Hydrogel capacitors have poor resistance to low temperature environments, limiting their application. Therefore, achieving low-temperature anti-freezing performance and improving ionic conductivity of the hydrogel electrolyte are important challenges for expanding the application range of the hydrogel electrolyte. The addition of organic liquids to hydrogels is one method to obtain antifreeze hydrogels. Common organic liquids include ethylene glycol, glycerol, dimethyl sulfoxide, and the like. In these binary/ternary systems, the interaction of the organic liquid with water molecules is believed to be the primary reason for inhibiting the formation of the ice crystal lattice. However, these hydrogels are either not electrically conductive or have low electrical conductivity due to the presence of organic liquids. In addition, the volatility and high pyrophoricity of organic liquids pose a serious safety hazard to organic hydrogel electrolytes.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a zwitterionic polymer hydrogel electrolyte and application thereof. The zwitterionic polymer hydrogel electrolyte not only has good antifreezing performance, but also has higher conductivity, especially high conductivity at low temperature.

The invention provides a zwitterion antifreezing hydrogel electrolyte which is characterized by being a polySH electrolyte.

The polySH electrolyte is poly (SBMA-HEA) electrolyte in the presence of LiCl, Li⁺Carrying out jump migration through zwitterionic groups on polymer chains; in Raman spectrum, -SO₃ ^-Wherein S-O stretching vibration is 1044cm^-1～1054cm^-1，-N⁺(CH₃)₂CH in (1)₃The stretching vibration is 2953cm^-1～2957cm^-1。

The addition of LiCl firstly breaks the charge balance between zwitterions in the original hydrogel system, so that Li⁺and-SO₃ ^-Binding and carrying out jumping migration by taking the binding site as a binding site, and in addition, Li⁺Can form Li by interaction with water molecules as a strong hydrated ion⁺(H₂O) n structure. This is advantageous in improving the ionic conductivity and freezing resistance of the hydrogel electrolyte.

The chain segment structure of the polySH electrolyte is as follows:

li + is subjected to jumping migration through zwitterion groups on a polymer chain, so that the ionic conductivity is improved; in Raman spectrum, -SO₃ ^-Wherein S-O stretching vibration is 1044cm^-1～1054cm^-1，-N+(CH₃)₂CH in (1)₃The stretching vibration is 2953cm^-1～2957cm^-1Indicating the presence of zwitterionic groups and providing sites for Li + migration; DSC demonstration with H₂O forms a Li⁺(H₂The O) n solvation structure improves the antifreezing property of the hydrogel electrolyte, and has 325 percent of tensile quantity at the temperature of minus 40 ℃; has excellent ionic conductivity at low temperature, and can be applied to ionic conductors and energy storage devices.

Preferably, the LiCl content in the zwitter-ion antifreezing hydrogel electrolyte is 1-7mol L^-1(ii) a Li ion and H₂O forms a Li⁺(H₂O)_nA solvated structure. Preferably, the LiCl content in the zwitter-ion antifreezing hydrogel electrolyte is 3-7mol L^-1. More preferably, the content of LiCl in the zwitter-ion antifreezing hydrogel electrolyte is 5-7mol L^-1。

Preferably, the conductivity of the polySH electrolyte is 114-147 mS cm at room temperature^-1。

Preferably, the storage modulus G' of the polySH electrolyte is greater than the loss modulus G ".

Preferably, the electrolyte has a freezable water content of less than 10% (polySH-5, polySH-7); preferably, the freezable water content of the electrolyte is zero (polySH-7).

Preferably, the electrolyte has a water molecule diffusion coefficient of 11.21 x 10 or less^-6cm²s^-1. Preferably, the electrolyte has a water molecule diffusion coefficient of 1.02 x 10 or less^-6cm²s^-1

At the temperature of minus 40 ℃, the low-temperature conductivity of the electrolyte is 11-13 mS cm^-1. The electrolyte can be stretched to a strain of 300-350% at-40 ℃. The compressibility curve of the electrolyte when compressed to 75% strain is similar to that at room temperature.

The polySH-7 electrolyte has a similar transport effect to the metal mesh wire.

The invention also provides a preparation method of the hydrogel electrolyte, which is characterized in that in the presence of LiCl salt, SBMA and HEA are used for preparing the zwitterionic polySH electrolyte by adopting a one-pot random polymerization method; comprises the following steps:

1) dissolving LiCl in a first solvent to prepare a solution with a concentration of 1-7mol L^-1In LiCl solution.

2) SBMA and HEA were dissolved in LiCl solution, initiator AIBA was added after stirring, followed by stirring in an ice bath for 1.5 h. The mol ratio of SBMA to HEA is 1 (3-5).

3) And (3) after the solution is completely dissolved, performing ultrasonic treatment for 8-15 min to remove bubbles, then injecting the solution into a mold, sealing, and polymerizing for 8-16h in an environment at 30-50 ℃. .

Preferably, in the step 1), the preparation concentration is 5-7mol L^-1In LiCl solution.

Preferably, in the step 2), the molar ratio of SBMA to HEA is 1: 4.

Preferably, the stirring of step 2) is performed in an ice bath.

Preferably, in the step 2), the addition amount of the initiator is 0.5-2 wt% of the total mass of the monomers. More preferably, in the step 2), the amount of the initiator added is 1 wt% based on the total mass of the monomers.

Preferably, the solution is stirred in an ice bath for 1h, then the initiator AIBA is added, and then the solution is stirred in an ice bath for 1.5 h.

Preferably, the ultrasound in step 3) is performed for 10min to remove bubbles.

Preferably, the polymerization in the sealed environment in the step 3) is that the seal is placed in an environment at 38 ℃ for polymerization for 12 hours.

The hydrogel obtained by polymerization is abbreviated as polySH-x, wherein x is the molar concentration of LiCl.

Use of the zwitterionic polymer hydrogel electrolyte for a temperature responsive material. The application of the zwitterionic polymer hydrogel electrolyte as an energy storage device electrolyte. Use of a zwitterionic polymer hydrogel electrolyte for ionic conductors at low temperatures. Use of a zwitterionic polymer hydrogel electrolyte for a strain responsive material.

Advantageous effects

The present invention introduces zwitterions into the polymer network to build up an antifreeze hydrogel electrolyte (polySH). The addition of LiCl greatly influences the water molecule and polymer structure in an electrolyte system, so that the polySH electrolyte has good frost resistance and high ionic conductivity at low temperature. Electrostatic interaction between the zwitterion and the salt ion makes the salt in the system easy to dissociate, so that the number of free ions in the system is increased. In addition, the zwitterion group can provide a migration channel for separated positive ions and negative ions under the action of an applied electric field, so that the conductivity is improved, and the zwitterion group has the thickness of 12.6mS cm at the temperature of-40 DEG C^-1High ionic conductivity. In the prior art, the conductivity and the freezing resistance are in a pair of contradiction, and the method for improving the freezing resistance usually reduces the conductivity; the method of the invention can simultaneously improve the frost resistance and the conductivity of the product, and breaks through the limitation of the prior art and the prejudice of the prior art.

The antifreezing hydrogel electrolyte (polySH) obtained by the invention has antifreezing performance, and the added LiCl destroys hydrogen bonds between water molecules and is combined with H₂O forms a Li⁺(H₂O) n solvated structures; the freezable water content of the electrolyte is less than 10%.

The polySH electrolyte can be stretched to 325% strain and compressed to 75% strain even at-40 ℃, which makes the polySH electrolyte have certain applications in the field of ion conductors and responsive materials. These findings suggest that the use of zwitterions may be a viable strategy for making highly conductive antifreeze solid electrolytes.

In the presence of LiCl salt, a hydrogel electrolyte of an anti-freeze polymer (polySH) was prepared by random copolymerization of zwitterionic monomer (SBMA) and 2-hydroxyethyl acrylate (HEA) (fig. 1 a). The one-pot method provides convenience for large-scale application of the hydrogel electrolyte. Throughout the system, the anionic and cationic groups on the zwitterionic chains facilitate the dissociation of the lithium metal salts and provide channels for ion migration. And the high-concentration LiCl greatly reduces the freezing point of the hydrogel polymer and ensures the excellent antifreezing property of the electrolyte.

Electrolysis using the antifreeze hydrogel of the present inventionThe polySH electrolyte prepared from the electrolyte (polySH) has excellent low-temperature conductivity and is very suitable for being applied to energy storage equipment. The specific capacitance of the super capacitor assembled by using the activated carbon as an electrode is 178mF cm at 60 DEG C^-2And a specific capacitance of 134mF cm at-30 DEG C^-2A wide operating temperature range is represented. The good antifreezing property of the capacitor enables the capacitor to maintain 95.5% of the initial value even if the capacitor is placed at-30 ℃ for 30 days. The retention rates of the specific capacitance after 10000 cycles are 81% and 71% of the initial capacitance, respectively, so that the capacitor has the capability of operating for a long time at a low temperature. In addition, the flexibility and adhesion of the hydrogel electrolyte enable the supercapacitor not to be structurally damaged in practical application, and the specific capacitance of the supercapacitor can still be maintained at 78.5 percent even after 500 times of twisting.

Drawings

FIG. 1: (a) schematic diagram of polySH hydrogel electrolyte and its network structure.

FIG. 2: (a) DFT calculations of the interaction of different components in the polySH electrolyte. (b) MSD of salt ions in the polySH electrolyte.

FIG. 3: (a) ionic conductivity of polySH, polyHEA and PVA electrolytes. (b) Viscoelastic properties of polySH electrolytes of different LiCl contents. -SO in polySH electrolytes of different salt concentrations₃ ^-(c) and-N⁺(CH₃)₂(d) The raman spectrum of (a).

FIG. 4: (a) raman spectra of water in different polySH electrolytes. (b) DSC results for polySH electrolytes at different LiCl concentrations. (c) MSD of water in different polySH electrolytes. (d) The electrochemical stability windows of the various electrolytes were determined by the LSV method.

FIG. 5: (a) ionic conductivity of the polySH electrolyte at different temperatures.

FIG. 6: the tensile (a) and compressive (b) stress-strain curves of the polySH-7 electrolyte at different temperatures.

FIG. 7: (a) photograph of a polySH-7 electrolyte circuit connected to an LED lamp. (b) The electrical resistance of the polySH-7 electrolyte responds at different temperatures. (c) The electrical resistance response of the polySH-7 electrolyte at-40 ℃ for a continuous stretch release cycle.

FIG. 8: photographs of the polySH-7 electrolyte in the network circuit were taken at normal and low temperatures (-20 ℃).

FIG. 9: (a) EIS spectra and (b) adhesion tests of polySH-7 based capacitors and PVA based capacitors.

FIG. 10: CV curves of the polySH-based supercapacitor at different temperatures.

FIG. 11: GCD curves of polySH-based supercapacitors at different temperatures.

FIG. 12: electrochemical performance of polySH supercapacitors at different temperatures: (a) the scanning rate is 100mV s^-1CV curve of time. (b) The current density was 1mA cm^-2GCD curve of time. (c) EIS spectra of the polySH-based supercapacitors at different temperatures. (d) Area specific capacitance of the polySH-based supercapacitor calculated from the GCD curve.

FIG. 13: the capacity retention of the poySH group capacitor at different temperatures.

FIG. 14: the polySH-based supercapacitors lit small lamp photographs in a freeze-thaw state.

FIG. 15: (a) capacity retention of the polySH-based supercapacitor after 10 freeze-thaw cycles. (b) Capacity retention of the supercapacitor after 30 days of freezing at-30 ℃. (c) Cycling stability of the polySH-based supercapacitors after 10,000 cycles at different temperatures.

FIG. 16: (a) CV curve of polySH-based supercapacitors at 360 ° twist. (b) The supercapacitor capacitance remains the case after 500 twist cycles. (c) The super capacitor lights up a photograph of the LED lamp in the distorted state.

FIG. 17: CV curves of the polySH-based supercapacitor in the heavy-duty state (a) and the perforated state (b). (c) GCD curves of two supercapacitors in series and in parallel.

Detailed Description

Methacryloylethyl Sulfobetaine (SBMA), hydroxyethyl acrylate (HEA), azobisisobutyramidine hydrochloride (AIBA), lithium chloride (LiCl) were purchased from alatin. Polyvinyl alcohol 1799(PVA), polyvinylidene fluoride (PVDF), methyl pyrrolidone (NMP) were purchased from michelin. Carbon cloth is available from taiwan carbon energy company. Activated Carbon (AC) is commercially available from clony, japan. Carbon black is commercially available from alfa aesar.

Name interpretation:

SBMA: methacryloylethyl sulfobetaine;

HEA: hydroxyethyl acrylate;

poly SH: poly (SBMA-HEA) electrolyte;

polyHEA electrolyte: a poly (HEA) electrolyte;

AC: activated carbon;

PVDF: polyvinylidene fluoride;

AIBA: azodiisobutyamidine hydrochloride;

PVA electrolyte: polyvinyl alcohol 1799 electrolyte; PVA-1799 represents polyvinyl alcohol having a degree of polymerization of 1700 and a degree of alcoholysis of 99%.

Electrochemical testing

The ionic conductivity was measured by Electrochemical Impedance Spectroscopy (EIS) using an electrochemical workstation (CHI 660E). The polySH electrolyte was first placed between two steel plates, then the electrolyte was stabilized at different temperatures for 5h, and then subjected to EIS testing. Three measurements were made for each sample to reduce errors. Ionic conductivity (σ, mS cm)^-1) The following formula is used to obtain:

here, R is the resistance (Ω), and S is the contact area (cm) of the electrolyte²) And L is the thickness (cm) of the test electrolyte.

The electrolyte linear voltammetry curve (LSV) is obtained by testing in a range of-1.2-1.3V by taking Ag/AgCl as a reference electrode. The electrochemical performance of the capacitor was measured on a CHI660E electrochemical workstation with a two-electrode system. Cyclic Voltammetry (CV) was obtained over different scan ranges in the voltage range 0-1V. Electrochemical Impedance Spectroscopy (EIS) was measured by 10mV in the range of 0.01Hz to 100 kHz. Charge-discharge cycles (GCD) were measured in the range of 0-1V using different current densities. Cycling stability 10000 cycles in GCD. Before testing, the device of the super capacitor is respectively placed at different temperatures and is stabilized for 5h_sp(mF cm^-2) Obtained by GCD calculation, calculation formulaComprises the following steps:

where I is the applied current (mA), Δ t is the discharge time (S), S_deviceIs the total area (cm) of the capacitor electrode²) And Δ V represents a discharge voltage (V).

Mechanical Property test

Tensile testing was performed using a universal testing instrument (Hensgrand, WDW-02, China). The electrolyte sample is a cylinder with a diameter of 5mm and a length of 40mm, and the strain rate is 100mm min^-1. The compression test adopts a cylindrical sample with the diameter of 10mm and the height of 15mm, the compression strain is 75 percent, and the compression speed is 10mm min^-1. All samples were stable at low temperature for 24 hours prior to low temperature testing.

The T-peel test was carried out at room temperature with a tensile speed of 100mm min-1 using a universal tester. One electrode of the supercapacitor was fixed, and the other electrode was peeled off to cover an area of 4mm × 65 mm.

Rheological measurements an ARES-G2 rheometer was used with parallel plates 25mm in diameter. First, using an angular frequency of 10rad s^-1Dynamic strain scanning in the range of 0.1-100% determines the linear viscoelastic region. Frequency sweep between 0.1-100rad s^-1Is carried out in the frequency range of (1%) with a constant strain.

Other characterizations

The Raman spectra were recorded using a LabRAM tHR800 Raman spectrometer (HORIBA JY, France) with a laser excitation wavelength of 532 nm. Differential scanning calorimetry (D-supercapacitor) using a TAQ-10D supercapacitor instrument at a temperature ranging from-80 deg.C to 50 deg.C and a heating rate of 10 deg.C for min^-1The mass of each sample is 5-10 mg.

Example 1

Preparation of PolySH hydrogel electrolyte

Zwitterionic polySH electrolytes were prepared using a one-pot random polymerization process using SBMA and HEA in the presence of LiCl salt. First, LiCl was dissolved in deionized water(8ml), 3mol L of^-1In LiCl solution. Then 0.75g of SBMA and 1.25g of HEA (total mass 2g, molar ratio 1:4) were dissolved in 8ml of LiCl solution, the solution was stirred in an ice bath for 1h, then 0.02g of initiator AIBA (corresponding to 1% by weight of the total mass of the monomers) was added, followed by stirring in an ice bath for 1.5 h. After the solution is completely dissolved, the solution is subjected to ultrasonic treatment for 10min to remove bubbles, and then the precursor solution is injected into a mold, sealed and placed in an environment at 38 ℃ for polymerization for 12 h. The hydrogel obtained by polymerization is abbreviated as polySH-3, wherein 3 is the molar concentration of LiCl.

Assembled super capacitor

Preparing an activated carbon electrode: activated carbon AC, conductive carbon black and PVDF (mass ratio 8:1:1) were dispersed in NMP to prepare a uniform dispersion slurry. And coating the slurry on carbon cloth, placing the carbon cloth in a vacuum oven at 180 ℃ for 24 hours, and drying to obtain the AC electrode. The loading of active material on each electrode was about 2.5mg cm^-2.

Assembling the super capacitor: two AC electrodes with the same load area (0.5cm multiplied by 1.2cm) are taken and respectively covered on two sides of the electrolyte to form a sandwich structure to prepare the super capacitor. And then, one drop of the polySH electrolyte precursor solution is respectively dropped on the electrodes at both sides of the supercapacitor to wet the electrodes, thereby bonding the electrodes and the electrolyte more firmly. The total thickness of the prepared supercapacitor was about 1mm, and the thickness of the polySH electrolyte was 0.4 mm. The prepared capacitors were sealed with tape to prevent moisture evaporation prior to electrochemical testing.

Example 2

The procedure is otherwise the same as in example 1, except that the LiCl concentration in the hydrogel is varied. Zwitterionic polySH electrolytes were prepared using a one-pot random polymerization process using SBMA and HEA in the presence of LiCl salt. First, LiCl was dissolved in deionized water (8ml) to prepare 7mol L^-1In LiCl solution. Then 0.75g of SBMA and 1.25g of HEA (total mass 2g, molar ratio 1:4) were dissolved in 8ml of LiCl solution, the solution was stirred in an ice bath for 1h, then 0.02g of initiator AIBA (corresponding to 1% by weight of the total mass of the monomers) was added, followed by stirring in an ice bath for 1.5 h. Sonicating for 10min after the solution was completely dissolved to remove bubbles, then injecting the precursor solutionAnd sealing the mold and polymerizing for 12h in an environment at 38 ℃. The hydrogel obtained by polymerization is abbreviated as polySH-7, wherein 7 is the molar concentration of LiCl.

Different amounts of LiCl were dissolved in deionized water (8ml) to prepare 1-7mol L of different concentrations^-1The polymerized hydrogel is abbreviated as polySH-x, wherein x is the molar concentration of LiCl.

Comparative examples 1 to 2

For comparison, we also prepared a polyHEA electrolyte and a PVA electrolyte, the preparation method being the same as in example 1. The polyHEA electrolyte is obtained by polymerization using only the HEA monomer, and the preparation method thereof is the same as the above-described preparation method of the polySH electrolyte. The polyHEA-based supercapacitor uses polyHEA as an electrolyte and is prepared in the same manner as a polySH electrolyte supercapacitor. The PVA-based supercapacitor uses PVA as an electrolyte and is prepared by the same method as a polySH electrolyte supercapacitor.

The PVA electrolyte was obtained by dissolving in a high temperature water bath 2g PVA in 8ml LiCl solution (1-7mol L)^-1) Then the mixture is placed in a water bath at 85 ℃ to be stirred, and a PVA electrolyte is obtained after the PVA is completely dissolved.

Analysis of results

As shown in FIG. 1, the anionic and cationic groups present on SBMA are simultaneously with Li⁺And Cl^-The binding site facilitates the dissociation of the lithium salt. To verify this hypothesis, Density Functional Theory (DFT) calculations were performed on the system. Figure 2a shows the optimal configuration of SBMA fragments using LiCl salt. Before addition of the lithium salt, the anions and cations on SBMA will interact with the cations and anions on other SBMAs due to electrostatic effects (ESBMA-SBMA: -4.025Kcal mol)^-1) An internal salt is formed to maintain the neutrality of the system. After addition of LiCl, the reaction mixture is reacted with-N⁺(CH₃)₂SO₃ ^-Comparison of-SO₃ ^-Li⁺The binding energy of (1) is lower (-18.15Kcal mol)^-1) Description of-SO₃ ^-More inclined to Li⁺Bonding (fig. 2 a). Thus, the introduction of amphoteric groups does promote the dissociation of LiCl and is Li⁺Provides site support. By molecular dynamicsThe method studies the ion transport mechanism in the polySH electrolyte. It is generally believed that, for polymer electrolytes, Li⁺Can migrate hopping by successive complexation and dissociation with polar groups such as O, S, N on the polymer chain. As shown in FIG. 2b, in the polySH and polyHEA electrolytes, Li⁺And Cl^-Mean Square Displacement (MSD) of (a) is linear with time interval. In polySH electrolytes, Li⁺And Cl^-The slope of (a) is greater than that of the polyHEA electrolyte, indicating a faster diffusion rate in the polyelectrolytes, which is facilitated by the presence of zwitterionic groups in SBMA, providing a channel for ion migration. Taking SO into account₃ ^-And Li⁺Lower binding energy and Li⁺Faster diffusion rate, Li⁺Should be transported in SO₃ ^-The position of the group undergoes successive complexation and decomposition (FIG. 1 e). More importantly, in high concentrations of LiCl, Li ions can react with H₂The O molecules combine to form Li⁺(H₂O)_nAnd (5) structure. Therefore, the migration of Li ions should also be in conjunction with Li⁺(H₂O)_nThe solvating structure is relevant, which also contributes to the antifreeze properties of the polySH, which have been verified by Raman, Differential Scanning Calorimetry (DSC) and molecular modeling.

The ionic conductivity of the polySH electrolyte was determined at room temperature at various salt concentrations. For comparison, we also measured the conductivity of the polyHEA and the conventional PVA electrolyte. As shown in fig. 3a (see table 1 for specific data), at a certain salt concentration, the conductivity of the polySH electrolyte was higher than that of the polyHEA. As the salt concentration increases, the conductivity of the polySH electrolyte also increases. When the LiCl concentration reaches about 5mol L^-1When a threshold is observed, indicating anions and cations with Li⁺And Cl^-The binding of (c) is saturated. The conductivity of the polySH electrolyte is 146mS cm at room temperature^-1It is stated that the introduction of the amphoteric group is indeed Li⁺Provides a migration channel, greatly improves Li⁺The migration rate of (2). In addition, compared to conventional PVA electrolytes, the polySH electrolyte has higher conductivity, indicating that the polySH electrolyte has potential for application to energy storage devices.

TABLE 1 Ionic conductivity electrolytes of polySH, polyHEA and PVA electrolytes

The addition of salts also changes the rheological properties of the polySH electrolyte. First at 10rad s^-1The linear viscoelastic region of the polySH electrolyte was measured in the range of 0.1 to 100% under strain. All subsequent viscoelasticity tests were performed at a strain of 1% to ensure the effectiveness of linear viscoelasticity and sufficient sensitivity. As shown in fig. 3b, the storage modulus G' of each polySH electrolyte is greater than the loss modulus G ", indicating that the electrolyte is primarily elastically deformed, exhibiting solid state behavior. As previously described, in the absence of LiCl, electrostatic interactions between anions and cations on the SBMA chains can increase the degree of crosslinking of the network to some extent, thereby giving the highest modulus to the polySH-0 hydrogel. The modulus of the polySH electrolyte gradually decreases as the salt concentration increases. The change in the mechanical modulus of the electrolyte indicates that LiCl disrupts the interaction between the cationic and anionic groups, reducing the crosslink density of the polymer network. To further understand the interaction of ionic groups on the polymer chains with salt ions, we performed raman spectroscopy studies on the polySH electrolyte. As the salt concentration increases from polySH-0 to polySH-7, -SO3^-The S ═ O stretching vibration in the (C) is respectively from 1044cm^-1Gradually changing to 1054cm^-1，-N⁺(CH₃)₂CH in (1)₃The stretching vibration is respectively from 2953cm^-1Gradually changes to 2957cm^-1(FIGS. 3c,3 d). The change in these peaks indicates that the electrostatic balance between the original anion and cation in the zwitterion is disrupted and a new electrostatic balance between the anion and cation occurs.

The added LiCl not only interacts with the polySH polymer chains but also influences the structure of the solvent water in the system. The most intuitive manifestation of this effect is the lowering of the freezing point of the electrolyte. As shown in FIG. 4a, Raman spectra show H at different LiCl concentrations₂The stretching vibration of O-H in O is changed. 3230cm^-1Is a water moleculeThe peak of the inter-hydrogen bonds gradually decreased, and accordingly, 3420cm^-1The asymmetric expansion band becomes gradually sharp along with the increase of LiCl concentration, and the corresponding peak value is shifted to a certain extent. These changes indicate that the added LiCl breaks the hydrogen bonds between water molecules and reacts with H₂O forms a Li⁺(H₂O) n solvated structures. It is believed that the water state in hydrophilic polymer hydrogels can be divided into at least two broad categories, non-freezable binding water and freezable water. Non-frozen water, which is produced due to the interaction of water with other components in the system, does not exhibit a phase change in calorimetric analysis. The DSC method can measure the relative content of water in different states, and provides a tool for quantitative analysis of the frozen state of the polySH electrolyte. As can be seen from FIG. 4b, in the absence of LiCl, polySH-0 has similar melting properties to pure water, with a melting peak near 0 ℃ indicating that a large amount of freezable water is contained in the polySH-0 hydrogel. After introduction of LiCl, the melting peak of water in the polySH electrolyte begins to shift towards sub-zero temperatures as the LiCl concentration increases. The calculation formula of the content of the freezable water in the polySH electrolyte is as follows:

in the formula, W_fIs the freezable water content, Δ H, in the electrolyte_mIs the enthalpy of fusion of freezable water in the electrolyte, obtained by integrating the DSC melting peak, Δ H_m ⁰Is the melting enthalpy, Δ H, of pure water_m ⁰＝333.5J g^-1。W_H2OIs the relative content of water in the electrolyte, W_H2O＝m_H2O/m_total. The freezable water content of the polySH-0 hydrogel was calculated to be 80.5%. The freezable water content of the polySH-5 electrolyte gradually dropped to 8.2%. Interestingly, no melting peak was found in the thermogram of polySH-7, indicating that almost no freezable water was present in the polySH-7 electrolyte in the temperature range of-80 to 50 ℃. These data indicate that the higher the LiCl concentration, the lower the amount of freezable water in the electrolyte. In summary, the addition of LiCl did destroy the water freezing processEspecially, the effect of reducing the freezing point of the hydrogel electrolyte is more obvious when LiCl is used at high concentration. The freezable water content of the high-salt-concentration electrolyte is less than 10% (polySH-5, polySH-7); preferably, the freezable water content of the electrolyte is zero (polySH-7).

The water molecule diffusion coefficient of the electrolyte is shown in table 2. To further study Li⁺Interaction of H2O, we performed MSD simulations of several electrolytes at room temperature to understand the diffusion properties of water molecules. As shown in fig. 4c, MSD is linear with time interval. The slope of the curve decreases with increasing LiCl concentration, indicating that diffusion of water molecules is more limited at high LiCl concentrations. The diffusion coefficient of water molecules was calculated from MSD, and a high diffusion coefficient of 19.08X 10-5cm was observed for water molecules due to the absence of LiCl in polySH-0²s^-1. With increasing LiCl concentration, the water molecule diffusion coefficient of polySH-7 gradually decreases to 0.4X 10^-5cm²s^-1And is only 2.1% of polySH-0. Proves Li in the electrolyte⁺(H₂O)_nThe formation of a solvating structure and the reduction of the content of the freezable water enable the polySH electrolyte to have good antifreezing performance. The state of water in the polymer hydrogel is also reflected in the electrochemical stability window of the electrolyte. As shown in FIG. 4d, the electrochemical window of the polySH electrolyte measured by Linear Sweep Voltammetry (LSV) widened from 2.0V for polySH-0 to 2.2V for polySH-7 with increasing LiCl concentration. Li⁺And H₂The binding of the O molecule reduces the activity of the water molecule, thereby inhibiting the decomposition of the water molecule under high pressure.

TABLE 2 diffusion coefficients of water molecules in polySH electrolytes with different salt concentrations

The addition of LiCl greatly influences the water molecule and polymer structure in an electrolyte system, so that the polySH electrolyte has good frost resistance and high ionic conductivity at low temperature. FIG. 5 shows the conductivities of the polySH electrolytes at different temperaturesThe trend of change of (c). It can be seen that the curve is divided into two ranges: an above-zero temperature and a below-zero temperature. At above-zero temperatures, the conductivity of all electrolytes slowly decreases with decreasing temperature because all electrolytes are in a non-frozen state at this time. Within the subzero temperature range, the conductivity of the polySH-1 and polySH-3 electrolytes decreases faster, while the conductivity of the polySH-5 and polySH-7 electrolytes decreases less. In addition, in the temperature range below zero degree, the ion conductivity and the absolute temperature reciprocal are in a linear relation, and the conductivity of the electrolyte obeys the arrhenius law. The activation energy of each electrolyte in the subzero temperature range was calculated, and the activation energy of the electrolyte decreased as the salt concentration increased. For example, the activation energy of polySH-1 is from 33.5kJ mol^-19.5kJ mol down to polySH-7^-1. The activation energy is an energy barrier that ion migration must overcome, and the smaller the activation energy, the easier ion migration. Thus, the conductivity of polySH-1 increases from 0.11mS cm-1 to 12.6mS cm^-1. The high-concentration LiCl improves the antifreezing property of the electrolyte, so that the low-temperature conductivity of the electrolyte can reach 12.6mS cm at the temperature of minus 40 DEG C^-1. More importantly, the polySH-7 electrolyte can still maintain good flexibility at-40 ℃. The polySH-7 electrolyte can be stretched to a strain of 325%, slightly above the strain at room temperature (FIG. 6 a). Meanwhile, the compressibility curve of the electrolyte was similar to that at room temperature when compressed to 75% strain (fig. 6b), indicating that the polySH-7 electrolyte maintained good mechanical properties and stability at low temperature. At the temperature of minus 40 ℃, the low-temperature conductivity of the electrolyte is 11-13 mS cm^-1. The electrolyte can be stretched to a strain of 300-350% at-40 ℃. The compressibility curve of the electrolyte when compressed to 75% strain is similar to that at room temperature.

The polySH electrolyte has good conductivity and flexibility at low temperature, so that the polySH electrolyte can be used as a low-temperature conductor. After connecting the polySH-7 to the LED lamp circuit, the LED lamp can be lit at a low temperature, with a brightness comparable to that at room temperature (fig. 7 a). polySH electrolytes may also be used as temperature responsive materials due to changes in conductivity at different temperatures. As shown in FIG. 7b, the polySH-7 electrolyte was sealed and placed at a temperature ranging from-40 ℃ to 40 ℃ and the change in resistance was recorded. We have found that the resistance of the polySH-7 electrolyte changes significantly when the temperature changes, and remains stable when the temperature remains constant. After completing one high-low temperature cycle, the resistance of the polySH-7 electrolyte can still be restored to the original state, and excellent resistance reversibility is shown. Unlike most reported strain sensors with operating temperatures above 0 ℃, the polySH-7 electrolyte can be released by stretching at-40 ℃ at a constant rate, with a corresponding uniform resistance change and with a good symmetry shape (fig. 7 c). The resistance change remains stable even over several consecutive stretch-release cycles, which is of great significance for low temperature strain sensor applications. To further verify the stability of the polySH electrolyte in conductor applications, we connected the polySH-7 electrolyte into a wire mesh for network signaling. As shown in fig. 8a, after connecting to the network circuit, the computer can successfully recognize the network signal and stably operate. In the network delay test, it was found that the network delay was maintained at a low level of 24ms with less fluctuation. More importantly, when the measured polySH-7 electrolyte was placed in a low temperature environment (-20 ℃) (FIG. 8b), the computer still worked normally, and the network delay was reduced by only 1ms compared to room temperature (25 ms). The polySH-7 electrolyte has almost the same transmission effect as a metal mesh wire and is a good signal transmission material.

TABLE 3 rate of change of resistance of polySH-7 electrolyte at different temperatures

Temperature (. degree.C.)	40	20	0	-20	-40
						Rate of change of resistance	0	0.7	2.0	5.6	19.5

Our polySH electrolyte was also assembled into a solid supercapacitor, using activated carbon electrodes to evaluate electrochemical performance. The charged groups and polar groups in the zwitterions enable the electrolyte to be tightly combined with the electrodes, damage to the structure of the supercapacitor is reduced, and the electrochemical performance of the supercapacitor at low temperature is effectively improved. For comparison, we first performed an EIS diagram of a supercapacitor assembled with a polySH electrolyte and a PVA electrolyte at room temperature (fig. 9 a). It can be seen that the polySH-based capacitor has a smaller interfacial resistance ratio PVA-based capacitor (1.8vs 6.8 Ω). Adhesion tests on both capacitors showed that the adhesion of the polysaccharide electrolyte was higher than that of the PVA electrolyte (85N m)^-1vs 42N m^-1) (FIG. 9 b). This indicates that the zwitterion does contribute to improving the adhesion between the electrolyte and the electrode, which is of great significance in reducing the interfacial resistance and improving the electrochemical performance of the supercapacitor. The CV curves of the polySH group capacitors at various temperatures were further investigated in the voltage range of 0-1V. As shown in FIG. 10, the scan rate for the solid supercapacitor was 1000mV s^-1And the scanning rate is far higher than that of other AC electrode solid supercapacitors. As shown in fig. 11, the GCD curves at different temperatures also have regular inverted triangles with smaller voltage drops. 100mV s in the range of-40 ℃ to 40 DEG C^-1The CV curve of (a) is shown in FIG. 12 a. At 60 ℃, the CV curve maintains a rectangular shape similar to room temperature. Due to the unique water-retaining property of the zwitterionic hydrogel, the super capacitor has good performance at high temperature. CV curve with decreasing temperaturePresenting a tendency to gradually deform. Furthermore, the GCD curve is in the shape of a regular inverted triangle with a small voltage drop (0.1V) only at-30 deg.C (FIG. 12 b). The EIS curves at different temperatures reflect the mobility of the ions. It can be seen that the EIS curves are almost parallel to the imaginary axis in the low frequency region, indicating that the polySH electrolyte has good ion diffusion behavior (fig. 12 c). At 25 c, the supercapacitor had a series resistance of 6.3 Ω, and this value increased to 12.2 Ω at-30 c and decreased to 5.9 Ω at 60 c. The change in temperature affects the diffusion rate of the electrolyte ions and thus the electrochemical performance of the supercapacitor. It is noteworthy that the supercapacitors also exhibited a small interfacial resistance, only 1.8 Ω at 25 ℃, indicating adequate contact between the electrodes and the electrolyte and a faster rate of charge transfer.

Area specific capacitance values at different current densities were calculated from the GCD curve (fig. 12 d). At 25 ℃, the specific capacitance of the super capacitor is 1mA cm^-2At a time of 171mF cm^-2At 5mA cm^-2At a time of 152mF cm^-2And the voltage is weakened by only 11%, thus the good multiplying power performance of the super capacitor is illustrated. As shown in FIG. 13 for capacity retention at different temperatures, the area specific capacitance changed to 178mF cm when the temperature was increased to 60 ℃ or decreased to-30 ℃^-2And 134mF cm^-2Approximately 104% and 78% at 25 ℃, indicating good electrochemical performance at extreme temperatures. As shown in fig. 14, an "QLU" type LED bulb (operating voltage 2.5V) can be illuminated in series by three super capacitors. After being frozen for 24 hours at low temperature, the super capacitor can still work normally. After the super capacitor is unfrozen, the brightness of the LED bulb is not obviously changed compared with the initial state. This indicates that low temperatures do not cause irreversible damage to the supercapacitor. To further confirm the antifreeze performance of the supercapacitor, the electrochemical performance of the supercapacitor was measured at 25 ℃ and-30 ℃ several times. As shown in fig. 15a, the specific capacitance can still be restored to the original level after thawing at room temperature. The capacitance of the supercapacitor was the same as at room temperature even after 10 freeze-thaw cycles (fig. 10 a). More importantly, when the supercapacitor is placed at a low temperature of-30 ℃ for more than 30 days, the capacitance of the supercapacitor only drops to 95.5% of the original capacitance (fig. 15 b). For circulation at different temperaturesThe ring stability was tested. As shown in FIG. 15c, after 10000 cycles, the capacity retention of the supercapacitor at-30 ℃, 25 ℃ and 60 ℃ was 71%, 81% and 76.4%, respectively. This excellent cycling performance indicates that the polySH-based supercapacitor can operate at low and high temperatures for long periods of time.

The solid-state super capacitor has good flexibility besides anti-freezing performance, can avoid structural damage in practical application, and prolongs the service life. As shown in fig. 16a, the CV curve shows almost the same capacitance behavior as the initial state after twisting the polySH-based supercapacitor by 360 °. The capacity retention of the supercapacitor was 78.5% even after 500 twist cycles (fig. 16 b). After the supercapacitor was connected to the circuit, there was no significant change in the brightness of the LED lamp before and after twisting the supercapacitor (fig. 16c), indicating that large deformations did not affect the electrochemical performance. This is not only due to the flexibility of the entire supercapacitor, but also due to the good adhesion between the electrodes and the electrolyte, so that the supercapacitor can maintain structural integrity in the face of deformations. When loaded 4000 times its own weight, the capacitance of the polySH-based supercapacitor increased slightly, probably due to the shortened ion transport path in the electrolyte under high load (fig. 17 a). The good mechanical properties of the polySH electrolyte enable the supercapacitor to avoid short circuits during heavy loading. In addition, when our supercapacitor was punctured by sharps, the supercapacitor still worked properly and remained capacitively stable (fig. 17 b). In practical applications, higher voltages and higher energy densities can be achieved by connecting multiple supercapacitors in series and parallel. In our work, two supercapacitors in series showed a voltage window of 2.0V compared to a single supercapacitor, and when connected in parallel, the discharge time increased almost 2 times (fig. 17 c). Therefore, the antifreezing property and good mechanical strength of the polySH electrolyte expand the application field of the energy storage device.

Claims

1. The zwitterion antifreezing hydrogel electrolyte is characterized in that the electrolyte is a polySH electrolyte;

the polySH electrolysisA poly (SBMA-HEA) electrolyte in the presence of LiCl, Li⁺Carrying out jump migration through zwitterionic groups on polymer chains; in Raman spectrum, -SO₃ ^-Wherein S-O stretching vibration is 1044cm^-1～1054cm^-1，-N⁺(CH₃)₂CH in (1)₃The stretching vibration is 2953cm^-1～2957cm^-1。

2. The zwitterionic antifreeze hydrogel electrolyte of claim 1, wherein said zwitterionic antifreeze hydrogel electrolyte comprises LiCl in an amount of from 1 to 7mol L^-1(ii) a Li ion and H₂O forms a Li⁺(H₂O)_nA solvated structure. Preferably, the LiCl content in the zwitter-ion antifreezing hydrogel electrolyte is 3-7mol L^-1. More preferably, the content of LiCl in the zwitter-ion antifreezing hydrogel electrolyte is 5-7mol L^-1。

3. The zwitterionic antifreeze hydrogel electrolyte of claim 1, wherein the conductivity of the polySH electrolyte is 114-147 mS cm at room temperature^-1。

4. The zwitterionic antifreeze hydrogel electrolyte of claim 1,

the freezable water content of the electrolyte is less than 10%.

5. The zwitterionic antifreeze hydrogel electrolyte of claim 1, wherein said electrolyte has a water molecule diffusion coefficient of 11.21 x 10 or less^-6cm² s^-1. Preferably, the electrolyte has a water molecule diffusion coefficient of 1.02 x 10 or less^-6cm² s^-1。

6. The zwitterionic antifreeze hydrogel electrolyte of claim 1,

at-40 ℃, the electrolyteThe low-temperature conductivity of the conductive material is 11-13 mS cm^-1(ii) a The electrolyte can be stretched to a strain of 300-350% at-40 ℃.

7. The method for preparing a hydrogel electrolyte as claimed in any one of claims 1 to 6, wherein the zwitterionic type polySH electrolyte is prepared using a one-pot random polymerization method using SBMA and HEA in the presence of LiCl salt; comprises the following steps:

8. The method for preparing a hydrogel electrolyte according to claim 7, wherein the concentration of the prepared hydrogel electrolyte in the step 1) is 5 to 7mol L^-1In LiCl solution.

9. The method for preparing a hydrogel electrolyte according to claim 7, wherein the amount of the initiator added in step 2) is 0.5 to 2 wt% based on the total mass of the monomers.

The polymerization in the sealed environment in the step 3) is carried out by sealing and placing in an environment at 38 ℃ for polymerization for 12 h.

10. Use of the zwitterionic polymer hydrogel electrolyte of any one of claims 1-6 in a temperature responsive material, an energy storage device electrolyte, an ionic conductor at low temperature, or a strain responsive material.