WO2022183606A1 - High-performance all-solid-state supercapacitor based on gel polymer electrolyte and preparation method therefor - Google Patents

Abstract

The present invention belongs to the field of energy storage, and relates to a gel polymer electrolyte and a preparation method therefor, and a high-performance all-solid-state supercapacitor based on the gel polymer electrolyte. The supercapacitor comprises electrodes and a gel polymer electrolyte between the electrodes. The flame-retardant gel polymer electrolyte comprises a gel polymer and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). The lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) exists in the gel polymer in the form of ions. The flame retardant gel polymer electrolyte as shown in formula (I) is prepared by grafting an active P-H bond of a flame retardant (DOPO) onto a polymer chain. The gel electrolyte has good ionic conductivity and good flame retardant capability of 4 mS cm-1 at 20°C. The mechanical strength of the gel electrolyte is adjusted in the range of ~28 KPa maximum stress and ~305% maximum strain. The gel-based SC has good low temperature tolerance and can work normally in a temperature range of -20°C to 60°C. The multiple advantages of the gel electrolyte expand its use in ion conductors and energy storage devices, solving the drawbacks of conventional liquid electrolytes due to volatile, flammable and easy leakage.

Description

A high-performance all-solid-state supercapacitor based on gel polymer electrolyte and its preparation method technical field

The invention belongs to the field of energy storage, and relates to a high-performance all-solid-state supercapacitor based on a gel polymer electrolyte and a preparation method thereof. In particular, it relates to a high-performance all-solid-state supercapacitor based on a flame-retardant, high-conductivity and low-temperature-resistant gel polymer electrolyte and a preparation method thereof

Background technique

The development of electric vehicles and portable wearable electronics has created a rapidly growing demand for energy storage devices such as lithium-ion batteries and supercapacitors.

The properties of supercapacitor electrode materials and electrolytes are the decisive factors affecting the performance of supercapacitors. Currently, most electrolytes used in energy storage devices are combinations of organic liquids (organic esters or ethers) and lithium salts. One of the most common choices for organic liquids is a mixture of ethylene carbonate and linear carbonate (diethyl carbonate or dimethyl carbonate). However, when the energy storage device is overcharged or short-circuited, the liquid electrolyte has the disadvantages of poor thermal stability, flammability, and easy leakage, so that the device has safety risks such as combustion and explosion. Solid polymer electrolytes are not flammable, however, solid polymer electrolytes have only ~10 ^-4 -10 ^-6 S cm ^-1 ionic conductivity at room temperature and poor interfacial contact with electrodes (X. Cheng, J. Pan , Y.Zhao, M.Liao, H.Peng, Adv.Energy Mater.8(2017) 1702184), limiting its practical application.

Gel polymer electrolytes have high ionic conductivity and good mechanical properties, however, at subzero temperatures, hydrogel electrolytes lead to a sharp drop in conductivity due to the freezing of water. Gel polymer electrolytes made from organic solvents are more advantageous at low temperatures, but still suffer from burning problems. Wen et al. [D.Xu, J.Su, J.Jin, C.Sun, Y.Ruan, C.Chen, Z.Wen, Adv.Energy Mater.9(2019)1900611] reported the use of nonflammable triphosphate Polyvinylidene fluoride-co-hexafluoropropylene based gel polymer electrolyte with ethyl ester as solvent. However, the introduction of organic phosphate solvents will lead to a decrease in the conductivity of the polymer electrolyte. Additionally, organophosphates tend to form unstable solid-electrolyte-interphase films on the surface of graphite anodes, which can lead to graphite exfoliation and continuous electrolyte decomposition during the first charge. These issues require further research to resolve.

How to make the capacitor work continuously at low temperature and have flame retardancy, high ionic conductivity and good mechanical properties is a difficult problem in the industry.

SUMMARY OF THE INVENTION

In order to solve the problem that the liquid electrolyte in the traditional supercapacitor is volatile, flammable and easy to leak, so that the supercapacitor will not burn and explode in the case of overcharge and short circuit, the present invention provides a gel polymerization-based A high-performance all-solid-state supercapacitor with organic electrolyte and a preparation method thereof, using a flame-retardant gel polymer electrolyte; using the active P-H bond of a flame retardant (DOPO) to graft onto a polymer chain to obtain a flame-retardant gel polymer electrolyte, It is then used to make supercapacitors. During performance testing, we were surprised to find that supercapacitors based on gel polymer electrolytes have multiple advantages such as good flame retardancy, good low temperature tolerance, good flexibility and stability.

The present invention provides a flame-retardant gel polymer electrolyte, comprising a gel polymer having the following formula (I) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI):

m:n:q=(1～10):(0～1):(0.0002～0.0006);

Among them, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) exists in the gel polymer represented by formula (I) in the form of ions.

The stress of the gel polymer electrolyte is 9.9KPa~28.3KPa, and the strain is 305%~232%. Preferably, the electrolyte has a conductivity of 1.4-4 mS cm ^-1 . Under 1% strain, the elastic and loss moduli of the gel polymer electrolyte gradually increased with the increase of shear rate in the range of 0.1-100 rad s ^-1 .

m:n:q=(1~10):1:(0.0002~0.0006). More preferably, m:n:q=(2～10):1:(0.0002～0.0006). More preferably, m:n:q=(4～10):1:(0.0002～0.0006).

For the gel polymer electrolyte, the F 1s peaks attributed to -CF, CF ₂ and -CF ₃ are located at 688.3, 689.1, and 690 eV, respectively, and the peaks attributed to -CF ₂ , -CF ₃ C 1s are located at 290.9 and 293.4 eV, respectively.

Raman spectrum showed that the original DOPO did not show any peak at 1445cm-1; after the polymerization, the P-C stretching vibration peak appeared at 1445cm-1, and the peak of P-H bond at 2400cm-1 disappeared.

The gel polymer electrolyte, FTIR spectrum and Raman spectrum, in the wavelength range of 1000-1200cm ^-1 , after adding LiTFSI, a new peak appeared at 1142cm _- ^1- SO2 peak, TFSI ^- in anion The SNS peak of the gel polymer electrolyte is 741-749 cm ^-1 ; the Raman spectrum of the gel polymer electrolyte has a PC stretching vibration peak at 1445 cm ^-1 .

The present invention also provides the preparation method of the flame retardant gel polymer electrolyte, comprising the following steps:

1) Add hexafluorobutyl acrylate (HFBA) and hydroxyethyl methacrylate (HEMA) to the solvent;

2) adding the flame retardant, polyethylene glycol diacrylate (PEGDA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to the solution formed in step 1) under stirring;

3) After adding the initiator, transfer the solution to the mold. The resulting gel polymer electrolyte was obtained after polymerization at 50-80°C for 10-14 hours.

Preferably, in step 1), the solvent is an organic solvent; more preferably, the solvent is DMF, acetonitrile or DMSO. The amount of solvent is 50%-75% by weight, based on the total weight of monomer and solvent.

Preferably, in step 1), the molar ratio of HFBA and HEMA is greater than 2:1; the ratio can be very high or even close to infinity, such as the case where the molar ratio of HFBA and HEMA is 1:0; more preferably, the molar ratio of HFBA and HEMA is 1:0. The molar ratio is (2-10):1. More preferably, the molar ratio of HFBA and HEMA is 4-10:1. More preferably, the molar ratio of HFBA and HEMA is 6:1-8:1. More preferably, the molar ratio of HFBA to HEMA is 8:1.

Preferably, in step 2), the LiTFSI concentration is 0.5-3 mol L ^-1 . More preferably, the LiTFSI concentration is 1˜2.5 mol L ⁻¹ . More preferably, the LiTFSI concentration is 1˜2 mol L ⁻¹ .

In step 2), the flame retardant is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxidation (DOPO), and the addition amount of the flame retardant is 1- 3 wt%; the total mass of HFBA and HEMA is the total mass of the monomers. Preferably, the added amount of the flame retardant is 1.5% by weight of the total mass of the monomers.

Preferably, the amount of polyethylene glycol diacrylate (PEGDA) added is 1.4-1.6 wt % of the total mass of the monomers; in step 2), the amount of polyethylene glycol diacrylate (PEGDA) added is a single 1.5Wt% by weight of the total mass of the body. The role of polyethylene glycol diacrylate (PEGDA) is to provide mechanical properties, and the role of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is to provide conductive ions.

Preferably, in step 3), the initiator is 2,2-azobisisobutyronitrile (AIBN), and the addition amount of the initiator is 1-3% of the total mass of the monomer; preferably, the addition of the initiator The amount is 2% of the total mass of the monomers.

The present invention also provides a supercapacitor, comprising electrodes and a gel polymer electrolyte between the electrodes; the gel polymer electrolyte is the gel polymer electrolyte described above.

The preparation method of the capacitor comprises the following steps:

1) Mix activated carbon (YP-50F), acetylene black and polyvinylidene fluoride (PVDF) into an organic solvent to form a uniform slurry.

2) The slurry is evenly coated on the carbon cloth, and dried in a vacuum oven at 70-90° C. for 20-28 hours to obtain an electrode. The active material content on each electrode is about 2-2.5 mg.

3) The supercapacitor can be assembled by sandwiching the gel polymer electrolyte between the two electrodes.

Preferably, in step 1), the mass percentage of activated carbon is 60-90%, the mass percentage of acetylene black is 5-30%, and the mass percentage of polyvinylidene fluoride is 5-10%. More preferably, the mass percentage of activated carbon is 70-85%, the mass percentage of acetylene black is 10-20%, and the mass percentage of polyvinylidene fluoride is 5-10%.

Preferably, in step 1), the organic solvent is not particularly limited, and can be an organic solvent commonly used in the art, such as N-methylpyrrolidone (NMP) acetonitrile, N,N-dimethylformamide (DMF) and the like. . Preferably, the organic solvent is N-methylpyrrolidone (NMP).

Preferably, in step 2), drying in a vacuum oven at 75-85°C for 22-26 hours to obtain an electrode

The present invention has at least the following beneficial effects:

In the present invention, in the presence of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and DOPO, a novel novel preparation is prepared through the copolymerization reaction of hexafluorobutyl acrylate (HFBA) and hydroxyethyl methacrylate (HEMA). Flame retardant gel polymer electrolyte (Figure 1). The synthesized gel polymer electrolyte has good mechanical properties (maximum stress ~28 KPa, maximum strain ~305%), good electrical conductivity (4 mS cm ^-1 at 20°C) and good flame retardancy. The mass specific capacitance of the electrode of the poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based supercapacitor can still maintain 76% after 8000 cycles.

The assembled gel-electrolyte-based supercapacitor has good low-temperature tolerance and can operate at temperatures from -20 to 60 °C, and the gel polymer electrolyte shows no change in surface morphology in the range of -20 to 60 °C. , it can still maintain a high conductivity in the range of -20 to 60 °C, and can be charged and discharged normally after being assembled into a supercapacitor. The mechanical properties at -50°C for 24 hours did not change much, and the electrical conductivity at -40°C was 0.1 mS cm ^-1 .

The application range of supercapacitors based on gel electrolyte will be further expanded to various occasions such as flame retardant and low temperature. Supercapacitors can be used in various working conditions, expanding the application scope of supercapacitors. The gel-based supercapacitors exhibit good electrochemical performance and remain substantially unchanged over multiple bending cycles.

Description of drawings

Figure 1 is a schematic diagram of the preparation of the gel polymer electrolyte.

Figure 2 shows the F 1s spectra of poly(HFBA ₈ -co-HEMA ₁ ) electrolytes with salt concentrations of 0, 1, 2, and 3 mol L ^-1 , respectively.

Figure 3 shows the C 1s XPS spectra of poly(HFBA ₈ -co-HEMA ₁ ) electrolytes with salt concentrations of 0, 1, 2, and 3 mol L ^-1 , respectively.

Figure 4 is a Raman spectrum of poly(HFBA ₈ -co-HEMA ₁ ) electrolytes with different salt concentrations in the range of 600-800 cm ⁻¹ .

Figure 5 shows the CV curves of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based SCs in different voltage ranges with a scan rate of 50 mV s ^-1 .

Figure 6 shows the CV curves of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based SCs at different scan rates.

Figure 7 shows the CV curves of SCs assembled from liquid electrolyte and poly(HFBA ₈ -co-HEMA ₁ ) electrolyte.

Figure 8 shows the charge-discharge curves of SCs assembled from liquid electrolyte and poly(HFBA ₈ -co-HEMA ₁ ) electrolyte.

Figure 9 is the EIS spectrum of SC assembled from liquid electrolyte and poly(HFBA ₈ -co-HEMA ₁ ) electrolyte.

Figure 10 shows the specific capacitances of electrodes of supercapacitors assembled from liquid electrolyte and poly(HFBA ₈ -co-HEMA ₁ ) electrolyte at different current densities.

Figure 11 shows the cycling stability of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based supercapacitors at a current density of 1.25 A g ^-1 .

Figure 12 shows the CV curves of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based SCs at different bending angles.

Figure 13 shows the GCD curves of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based SCs at different bending angles.

Figure 14 shows the electrode specific capacity retention of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte after 500 bends at a bending angle of 180° (bending radius r=0.25 cm).

Figure 15 is the GCD and CV curves of SCs in series and parallel states.

Figure 16 shows the stretching and twisting changes of the organogel electrolyte at 25°C and -50°C.

Figure 17 shows the ionic conductivity of the poly(HFBA8-co-HEMA1) electrolyte in the temperature range of -40°C to 65°C.

Figure 18 shows the CV curves of poly(HFBA8-co-HEMA1) electrolyte-based SCs at different temperatures.

Figure 19 shows the GCD curves of poly(HFBA8-co-HEMA1) electrolyte-based SCs at different temperatures.

Figure 20 shows the EIS spectra of poly(HFBA8-co-HEMA1) electrolyte-based SCs at different temperatures.

Detailed ways

The following examples further illustrate the present invention, but the present invention is not limited thereto.

Experimental Materials

Hexafluorobutyl acrylate (HFBA) was purchased from Harbin Xuejia Fluorosilicone Chemical Co., Ltd. Hydroxyethyl methacrylate (HEMA), 9,10-dihydro-9-oxa-10-phosphinophenanthrene 10 (oxy) (DOPO), polyethylene glycol diacrylate (PEGDA, Mn=1000), 2 , 2-azobisisobutyronitrile (AIBN) and lithium bistrifluoromethanesulfonimide (LiTFSI) were purchased from Aladdin. N,N-Dimethylformamide (DMF) was purchased from Sinopharm Group. Activated carbon (YP-50F) was provided by Kuraray, Japan. Acetylene black was purchased from Hefei Kejing. Polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) were purchased from McLean, and carbon cloth was purchased from Taiwan Carbon Energy.

Mechanical test

Tensile measurements were tested using a universal testing machine (Hensgrand, WDW-02, China). Gel polymer electrolytes with a width of 1 cm and a thickness of 1 mm were tested at a tensile speed of 100 mm min ^-1 . The formula for calculating tensile stress is σ=F/S, where F is the tensile force and S is the cross-sectional area. Tensile strain (ε) is defined as ε=(ll ₀ )/l ₀ ×100%, where l ₀ is the original length and l is the length after stretching.

Rheological tests were performed at 25°C using an ARES-G2 rheometer with a 25mm diameter plate. The linear viscoelastic region was determined by dynamic strain sweeps at a shear rate of 10 rad s, ranging from ^0.1–100 %. Frequency sweeps were performed at 1% strain at shear rates of 0.1-100 rad s ^-1 .

Conductivity Test

The resistance is to sandwich the gel polymer electrolyte between two stainless steels, and use the electrochemical workstation CHI 760E (Shanghai Chenhua Co., Ltd.) in the temperature range of -40 ~ 65 ℃, and in the frequency range of 0.1 ~ 1MHz. Obtained by signal detection, the amplitude is 5mV. Before measurement, the sample was first stabilized at a certain temperature for 30 minutes. The ionic conductivity (σ) is calculated as σ=L/RS, where R is the resistance, S is the cross-sectional area of the gel polymer electrolyte, and L is the thickness of the gel polymer electrolyte.

Electrochemical testing

The voltage window was measured with a three-electrode system using an electrochemical workstation CHI 760E. A silver chloride electrode was used as the reference electrode, a platinum wire was used as the counter electrode, and the prepared electrode was used as the working electrode. The sweep speed is 10mV s ^-1 and the range is 0-2V. The electrochemical performance of the supercapacitor was tested in a two-electrode system. Cyclic voltammetry (CV) was performed at scan rates of 50-1000 mV s ⁻¹ . The charge-discharge test (GCD) is in the voltage range of 0-1.6V with different current densities. Calculate the capacity of one electrode based on the charge-discharge test. The calculation formula is C _electrode =4IΔt/mΔV, where I is the discharge current, Δt is the discharge time, m is the mass of active material in both electrodes, and ΔV is the voltage window.

representation

Fourier transform infrared spectroscopy (FTIR) was measured with an infrared spectrometer (Shimadzu Affinity-1S, Japan) in the range of 4000-400 cm ⁻¹ . Raman spectra were detected with a laser confocal Raman spectrometer (RenishawinVia). X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB 250 (Thermo Fisher Scientific, USA) using a monochromatic Al-Kα X-ray source at 100 W. Thermogravimetric analysis (TGA) was performed on an SDT Q600 (TA, USA) in a N2 atmosphere at a heating rate of 10°C min ⁻¹ . Scanning Electron Microscopy (SEM) images were obtained by Scanning Electron Microscopy (Hitachi Regulus 8220). Energy dispersive X-ray spectroscopy (EDX) was obtained by an energy spectrometer (Xflash 6160).

Name explanation: SC, the full name is Supercapacitor, the Chinese name is supercapacitor.

Example 1 Preparation of Gel Polymer Electrolyte

HFBA (hexafluorobutyl acrylate) and HEMA (hydroxyethyl methacrylate) were added to the DMF solvent in a molar ratio of 6:1 (the mass ratio of monomer to solvent was 4:6). Then, 1% by weight of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxidation (DOPO) with respect to the total mass of the monomers, with respect to the total mass of the monomers, was added with stirring 1.5 wt% polyethylene glycol diacrylate (PEGDA) and 2.5 mol L ^-1 of LiTFSI (4.306 g) were added to the above solution. Finally, after adding the initiator (2% AIBN with respect to the total mass of the monomers), the solution was transferred into the mould. After 12 hours of polymerization at 60°C, the resulting gel polymer electrolyte (abbreviated as poly(HFBAx-co-HEMAy) was obtained.

Example 2-8 Preparation of Gel Polymer Electrolyte

HFBA and HEMA with different molar ratios (1:0, 10:1, 8:1, 6:1, 4:1, 2:1) were added to a 20 mL glass vial. The amount of solvent is between 50%-75%. Then, DOPO (1 wt % relative to the total mass of monomers), PEGDA (1.5 wt % relative to the total mass of monomers) and 0-3 mol L ^-1 of LiTFSI were added to the above solution with stirring. LiTFSI concentrations were controlled at 0.5, 1, 1.5, 2, 2.5, and 3 mol L ^-1 , respectively. Finally, after adding the initiator (2% AIBN with respect to the total mass of the monomers), the solution was transferred into the mould. After polymerization at 50-80°C for 10-14 hours, the resulting gel polymer electrolyte (abbreviated as poly(HFBAx-co-HEMAy), where x and y represent the molar ratio of HFBA and HEMA, respectively. Reaction conditions see Table 1.

Table 1 Preparation parameters of gel polymer electrolytes

In the specific embodiment of the present invention, the solvent, the flame retardant, the initiator, and the polyethylene glycol diacrylate (PEGDA) are based on the total mass of the monomers, which are all weight percentages. The total mass of HFBA and HEMA is the total monomer mass. The amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) added is based on the molar mass of the solvent.

Example 9 Preparation of electrodes and capacitors

Activated carbon (YP-50F), acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 were mixed into N-methylpyrrolidone (NMP) to form a uniform slurry. The slurry was evenly coated on the carbon cloth and dried in a vacuum oven at 80 °C for 24 hours. The active material content on each electrode is about 2.2 mg. The supercapacitor can be assembled by sandwiching the gel polymer electrolyte prepared in Examples 1-6 above between two electrodes.

Examples 10-12 Preparation of electrodes and capacitors

According to the mass percentage of activated carbon is 60-90%, the mass percentage of acetylene black is 5-30%, and the mass percentage of polyvinylidene fluoride is 5-10%, YP-50F, acetylene black and PVDF are mixed into NMP to A homogeneous slurry is formed. The slurry was evenly coated on the carbon cloth and dried in a vacuum oven at 70-90°C for 20-28 hours. The active material content on each electrode is about 2 to 2.5 mg. The supercapacitor can be assembled simply by sandwiching the gel polymer electrolyte between the two electrodes. The reaction conditions are shown in Table 2.

Table 2 Preparation parameters of electrodes and capacitors

	Example 9	Example 10	Example 11	Example 12
YP-50F(%)	80	90	70	60
Acetylene black (%)	10	5	20	30
PVDF ratio (%)	10	5	10	10
solvent	NMP	NMP	NMP	NMP
temperature	80	70	90	85
drying time	twenty four	28	20	26
Active substance content (mg)	2.2	2.4	2.2	2

Results and discussion:

Gel polymer electrolytes were formed by one-step random copolymerization of HFBA and HEMA in the presence of LiTFSI and DOPO (Figure 1).

The interactions between polymer chains and salts were investigated in detail by X-ray photoelectron spectroscopy (XPS). As shown in Fig. 2, when no lithium salt was introduced, three distinct F 1s peaks at 686.9, 687.6 and 688.4 eV were assigned to -CF, _CF2 and _-CF3 , respectively. After the addition of lithium salt at a concentration of 2 mol L ^-1 , these peaks were shifted to higher energy levels by 1.4, 1.5 and 1.6 eV (F 1s peaks were at 688.3, 689.1, 690 eV, respectively), indicating that LiTFSI was completely dissolved in the polymer matrix . However, when the lithium salt concentration was increased from 2 mol L ^-1 to 3 mol L ^-1 , the peaks assigned to -CF, _-CF2 and _-CF3 were shifted to lower binding energy levels by 0.7, 0.6, 0.7 eV (F 1s The peaks are at 687.6, 688.5, and 689.3 eV, respectively), indicating that adding too much lithium salt changes the coordination environment. The C 1s spectrum also showed similar results. As the salt concentration increased from 0 mol L ^-1 to 2 mol L ^-1 , the C 1s spectra assigned to -CF ₂ and -CF ₃ moved from 290.5 and 293 eV to 290.9 and 293.4 eV, respectively. The salt concentration was further increased to 3 mol L ^-1 , and the peaks attributed to -CF ₂ and -CF ₃ were shifted by 0.5, 0.7 eV to the low binding energy level, which indicated that the -CF ₂ and -CF ₃ were not active at high and low salt concentrations. The environment is different (Figure 3). For the obtained gel polymer electrolyte, the F 1s peaks of -CF, CF ₂ and -CF ₃ are located at 688.3, 689.1, and 690 eV, respectively, and the peaks of -CF ₂ and -CF ₃ C 1s are located at 290.9 and 293.4 eV, respectively. , the overall performance of the electrolyte is the best.

In general, Li ⁺ can be solvated by DMF molecules to form a complex form of [Li(DMF) ₄ ] ⁺ . As shown in Figure 4, with the increase of lithium salt concentration, the peak of free DMF molecules (663 cm ^-1 ) gradually disappeared, while the peak of solvated DMF (676 cm ^-1 ) gradually increased. Indicates the formation of solvent separation ion pairs (SSIPs). In SSIP, the interaction between [Li(DMF) ₄ ] ⁺ solvation sphere and TFSI ^- anion is relatively weak, which is also reflected in the SNS peak of TFSI ^- anion. In 1-2 mol L ^-1 of low salt concentration, the SNS peak hardly changed. However, further increasing the salt concentration to 3 mol L ⁻¹ , the free TFSI ⁻ anions coordinate with Li ⁺ and displace DMF to form [Li(DMF) _x ] ⁺ -[TFSI _y ] ^- contacting ion pair (CIP). Correspondingly, the SNS peak in the TFSI ^- anion shifted from 741 (2 mol L ^-1 ) to 749 cm ^-1 (3 mol L ^-1 ). Due to the presence of [Li(DMF) _x ] ⁺ -[TFSI _y ] ^- clusters, the conductivity of the electrolyte decreases at high salt concentrations. The gel electrolyte with good performance has a peak attributable to SNS in the Raman spectrum between 741-749 cm ^-1 , which ensures the transport of lithium ions in it.

After assembly into SCs, the cyclic voltammetry (CV) curves of poly(HFBA8-co-HEMA1) electrolyte-based SCs exhibited regular rectangles below 1.6 V (Fig. 5). Therefore, the electrochemical performance of the assembled SCs was measured in a voltage window of 0 to 1.6 V. As shown in Fig. 6, the CV curves of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte SCs are regular rectangles at scan rates of 50-200 mV s ^-1 and slightly curved at scan rates of 500-1000 mV s ^-1 tilted state. In order to express the electrochemical performance of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte more intuitively, electrochemical tests were performed on SCs assembled with LiTFSI/DMF liquid electrolyte for comparison. At a scan rate of 100 mV s ^-1 , the CV curves of SCs assembled from both poly(HFBA ₈ -co-HEMA ₁ ) electrolytes and liquid electrolytes showed regular rectangular shapes, while poly(HFBA ₈ -co-HEMA ₁ ) based on The CV curve of the SC of the electrolyte contains a slightly larger area (Fig. 7). By comparing the GCD curves at current densities of 0.2 to 2 A g ^-1 , the charge-discharge curves show an approximately triangular linear behavior, indicating a good electric double layer behavior. At the same current density, the discharge time of poly(HFBA ₈ -co-HEMA ₁ )-based SC was longer than that of liquid electrolyte-based SC (Fig. 8). At 0.5 A g-1 current density, poly(HFBA ₈ The discharge time of the -co-HEMA ₁ )-based SC was 17 s longer than that of the liquid electrolyte-based SC. The EIS spectra of the two SCs were also investigated. As shown in Fig. 9, the interfacial resistance of the poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based SC is smaller than that of the liquid electrolyte-based SC (14.3 VS 14.5 Ω). At a current density of 0.2 A g ^-1 , the specific capacitance of the electrode of SC with poly(HFBA ₈ -co-HEMA ₁ ) electrolyte was 63.8 F g ^-1 , which was higher than that of the electrode of SC with liquid electrolyte (57.7 F g ^-1 ). When the current density increased to 2A g ^-1 , the specific capacitance of the electrode of the SC with poly(HFBA ₈ -co-HEMA ₁ ) electrolyte decreased to 39.5 F g ^-1 , still with a high specific capacitance retention (61.9% ) (Figure 10). In addition, the cycling stability of the poly( _HFBA8 -co- _HEMA1 )-based SC was also measured. It can be seen that after 8000 cycles, the mass specific capacitance can still maintain about 76%, indicating good cycling stability (Figure 11).

Our obtained poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-assembled SCs also exhibit good flexibility and mechanical stability. As shown in Fig. 12, 13, when the SC is bent at 60°, 120° and 180°, respectively, the area covered by the CV curve is almost unchanged, and the GCD curve is almost the same, which indicates that the SC has good flexibility during the bending process. can keep the effective working area unchanged. To further demonstrate its flexibility and stability, the SC was bent at a bending angle of 180° for 500 cycles. As shown in Fig. 14, the electrode of the poly( _HFBA8 -co- _HEMA1 ) electrolyte-based SC still had a specific gravity retention rate of 100%, which indicated that the solid SC had good flexibility and stability.

To evaluate the practical performance of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-based SCs, we connected two SCs in series or parallel. As shown in Figure 15, when connected in series, the voltage window becomes twice that of a single SC, reaching a voltage window of 3.2 V. When connected in parallel, the voltage window is unchanged, and the charging and discharging time is twice that of a single SC. Likewise, the area covered by the CV curves of two SCs in series or parallel is almost twice that of a single SC.

More importantly, our poly(HFBA ₈ -co-HEMA ₁ ) electrolyte can maintain good mechanical properties and flexibility at low temperatures. As shown in Figure 16, the original length of the poly(HFBA ₈ -co-HEMA ₁ ) electrolyte is about 2 cm at room temperature. It can be twisted and stretched up to 5 cm without breaking. After standing at -50°C for 24 hours, the state of the poly(HFBA ₈ -co-HEMA ₁ ) electrolyte did not change compared to room temperature, and could be stretched and twisted to a large extent at -50°C. This suggests that the poly(HFBA ₈ -co-HEMA ₁ ) electrolyte can maintain stable mechanical properties and flexibility at low temperatures and has the potential to be used in low-temperature energy storage devices.

The conductivity of the poly(HFBA ₈ -co-HEMA ₁ ) electrolyte was tested in the range of -40°C to 65°C ( FIG. 17 ). As the temperature increased from -40°C to 65°C, the conductivity increased from 0.1 mS cm ^-1 to 11 mS cm ^-1 , indicating that the conductivity of the electrolyte increased gradually with temperature. The higher the temperature, the higher the ion migration rate and the easier the movement of polymer segments, which further promotes the migration of lithium ions. Furthermore, the relationship between the logarithm of the ionic conductivity and the inverse of the absolute temperature (T) follows the simple Arrhenius formula:

σ=σ ⁰ exp(-Ea/RT)

where σ, ^σ0 , Ea and R are the ionic conductivity, exponential factor, activation energy for ion transport and gas constant, respectively. According to the Arrhenius formula, the activation energy of the poly(HFBA ₈ -co-HEMA ₁ ) electrolyte at 5-65° C. is 0.089 eV.

To demonstrate the performance of poly(HFBA ₈ -co-HEMA ₁ ) electrolyte-assembled SCs at different temperatures, CV, GCD and EIS (full name of EIS: AC Impedance Spectroscopy) were performed in the temperature range of -20°C to 60°C. test. As shown in Fig. 18, 19, 20, as the temperature increases from -20 °C to 60 °C, the area covered by the corresponding CV curves gradually becomes larger, and there is no obvious redox reaction. Accordingly, the charging and discharging time gradually increases. At the same time, the resistance gradually decreased from 47Ω to 10.4Ω, and the ion diffusion rate gradually increased. These results suggest that our electrolyte can be used over a wide temperature range.

We incorporated DOPO into the polymer chain to fabricate a series of flame-retardant gel polymer electrolytes, and the resulting gel electrolytes exhibited good electrical conductivity (4 mS cm ^-1 at 20 °C) and good flame retardancy. The mechanical strength of the gel electrolyte can be tuned by changing the monomer ratio and salt concentration. The gel-electrolyte-assembled SC still maintains 76% of the specific gravity capacitance after 8000 cycles with good flexibility and stability. The assembled gel electrolyte SC has good low temperature tolerance and can work at temperatures from -20 to 60 °C. The application range of the gel electrolyte will be further expanded to various occasions such as flame retardant and low temperature, so that the prepared supercapacitor can be used in various working conditions, and the application scope of the supercapacitor is expanded.

Claims (15)

1. A flame retardant gel polymer electrolyte comprising a gel polymer having the structure of the following formula (I) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI):

   

   m:n:q=(1～10):(0～1):(0.0002～0.0006);

   Among them, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) exists in the gel polymer represented by formula (I) in the form of ions.
2. The flame-retardant organic gel electrolyte according to claim 1, wherein the stress of the gel polymer electrolyte is 9.9KPa-28.3KPa, and the strain is 305%-232%. Preferably, the electrolyte has a conductivity of 1.4-4 mS cm ^-1 . m:n:q=(1~10):1:(0.0002~0.0006). More preferably, m:n:q=(2～10):1:(0.0002～0.0006).
3. The flame-retardant organogel electrolyte according to claim 1, wherein the gel polymer electrolyte has F 1s peaks at 688.3, 689.1, 690 eV and attributable to -CF, CF ₂ and -CF ₃ , respectively. The peaks of -CF ₂ and -CF ₃ C 1s are located at 290.9 and 293.4 eV, respectively.

   Raman spectrum showed that the original DOPO did not show any peak at 1445cm-1; after the polymerization, the P-C stretching vibration peak appeared at 1445cm-1, and the peak of P-H bond at 2400cm-1 disappeared.
4. The flame-retardant gel polymer electrolyte according to claim 1, wherein the gel polymer electrolyte, FTIR spectrum and Raman spectrum, in the wavelength range of 1000-1200cm ^-1 , after adding LiTFSI, in A new peak-SO ₂ peak appeared at 1142cm ^-1 , and the SNS peak in TFSI ^- anion was 741-749cm ^-1 ; the Raman spectrum of the gel polymer electrolyte showed PC stretching at 1445cm ^-1 vibration peak.
5. The preparation method of flame retardant gel polymer electrolyte as claimed in claim 1, comprising the following steps:

   1) Add hexafluorobutyl acrylate (HFBA) and hydroxyethyl methacrylate (HEMA) to the solvent;

   2) adding the flame retardant, polyethylene glycol diacrylate (PEGDA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to the solution formed in step 1) under stirring;

   3) After adding the initiator, transfer the solution to the mold. The resulting gel polymer electrolyte was obtained after polymerization at 50-80°C for 10-14 hours.
6. The method for preparing a flame retardant gel polymer electrolyte according to claim 5, wherein in step 1), the solvent is an organic solvent; more preferably, the solvent is DMF, acetonitrile or DMSO. The amount of solvent is 50%-75% by weight.
7. The preparation method of the flame-retardant gel polymer electrolyte according to claim 5, wherein in step 1), the molar ratio of HFBA and HEMA is greater than 2:1; more preferably, the molar ratio of HFBA and HEMA is ( 2 to 10): 1.
8. The method for preparing a flame retardant gel polymer electrolyte according to claim 5, wherein in step 2), the LiTFSI concentration is 0.5-3 mol L ^-1 . More preferably, the LiTFSI concentration is 1˜2.5 mol L ⁻¹ .

   In step 2), the flame retardant is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxidation (DOPO), and the addition amount of the flame retardant is 1- 3 wt%; the total mass of HFBA and HEMA is the total mass of the monomers.
9. The method for preparing a flame-retardant gel polymer electrolyte according to claim 5, wherein the amount of polyethylene glycol diacrylate (PEGDA) added is 1.4-1.6% by weight of the total monomer mass.
10. The method for preparing a flame retardant gel polymer electrolyte according to claim 1, wherein in step 3), the initiator is 2,2-azobisisobutyronitrile (AIBN), and the amount of the initiator is added. The total mass of the monomer is 1-3%.
11. A supercapacitor, comprising electrodes and a gel polymer electrolyte between the electrodes; the gel polymer electrolyte is the gel polymer electrolyte of claim 1 .
12. The preparation method of the capacitor as claimed in claim 11, comprising the following steps:

    1) Mix activated carbon (YP-50F), acetylene black and polyvinylidene fluoride (PVDF) into an organic solvent to form a uniform slurry.

    2) The slurry is evenly coated on the carbon cloth, and dried in a vacuum oven at 70-90° C. for 20-28 hours to obtain an electrode. The active material content on each electrode is about 2-2.5 mg.

    3) The supercapacitor can be assembled by sandwiching the gel polymer electrolyte between the two electrodes.
13. The preparation method of claim 12, wherein in step 1), the mass percentage of activated carbon is 60-90%, the mass percentage of acetylene black is 5-30%, and the mass percentage of polyvinylidene fluoride is 5% ~10%. More preferably, the mass percentage of activated carbon is 70-85%, the mass percentage of acetylene black is 10-20%, and the mass percentage of polyvinylidene fluoride is 5-10%.
14. The preparation method according to claim 12, wherein in step 1), the organic solvent is N-methylpyrrolidone (NMP) acetonitrile and N,N-dimethylformamide (DMF).
15. The preparation method according to claim 12, wherein in step 2), the electrode is obtained by drying in a vacuum oven at 75-85° C. for 22-26 hours.

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