Preparation method of temperature response type supercapacitor

Abstract

The invention belongs to the technical field of temperature-sensitive materials and new energy safety, and relates to a preparation method of a temperature response type supercapacitor. According to the invention, a temperature response type supercapacitor is assembled by a unique in-situ preparation scheme, normal operation at normal temperature can be ensured under the condition of not additionally adding an electrolyte and a diaphragm, and a function of inhibiting thermal runaway can be played when the temperature rises based on spontaneous intelligent phase transformation in a temperature rising process. When the working temperature of the super capacitor is abnormally and continuously increased, the temperature-sensitive electrolyte can spontaneously adjust the charging and discharging rate by responding to the temperature change, so that the protection function is realized when thermal runaway occurs, and the method is an active protection strategy.

Description

Technical Field

[0001] The invention belongs to the field of temperature-sensitive materials and new energy safety technology, and relates to a method for preparing a temperature-responsive supercapacitor. Background Art

[0002] Supercapacitors are a new type of energy storage device that stores and releases charge by physical adsorption / desorption or redox reaction of ions on the electrode surface during the charging and discharging process. It has the advantages of high power density, fast charging and discharging rate, wide operating temperature range and long cycle life, and is widely used in the fields of electricity, railways, smart grids, special heavy-duty vehicles, etc., with significant application value and market potential. However, supercapacitors generate a lot of heat due to their large power output and fast current flow, and the heat dissipates slowly, especially during ultra-fast charging and discharging, which may cause safety problems such as fire and explosion. Therefore, good control of thermal runaway is crucial.

[0003] The measures to prevent thermal runaway are mainly to introduce flame retardants into existing electrolytes, or to fundamentally suppress the occurrence of thermal runaway by preparing gel and solid electrolytes. In addition, physical devices such as safety vents, thermal fuses and thermal detection systems are widely used to release heat in advance when the heat accumulates to a certain extent. The CN220421417U patent reported that the current of the load is detected by a sensor and the information is fed back to the controller. When the controller determines that the load current exceeds the safety limit, the controller immediately cuts off the circuit to ensure the safety protection of the capacitor; CN117238678A has produced an over-temperature self-protection supercapacitor, which is characterized in that the memory spring is designed to shrink in an overheating environment to avoid overheating and spontaneous combustion of the supercapacitor. These protection methods to solve the problem of thermal runaway are passive, and the thermal protection provided is one-time. Therefore, building an intelligent and active temperature-sensitive control strategy can more effectively suppress the occurrence of thermal runaway.

[0004] Thermoresponsive polymers are polymers that respond to changes in temperature. When the temperature changes, the visual or mechanical properties of the polymer will respond accordingly. When the temperature is lower than its phase transition temperature, the hydrophilic groups in the thermosensitive electrolyte form hydrogen bonds with water molecules, and the polymer becomes hydrophilic; when the temperature is higher than its phase transition temperature, the hydrophilic groups in the polymer collapse to form chains with a spherical conformation, which is difficult to interact with water molecules, resulting in the polymer being hydrophobic, thereby achieving a reversible thermal response function. This polymer is widely used in self-healing materials, switch memory devices, and its own biocompatibility has also developed its potential as a targeted drug transport, tissue engineering and other medical fields. At present, thermoresponsive polymers are gradually attracting attention in the field of electrochemical energy storage. Electrolytes prepared from temperature-responsive polymers have the ability to dynamically adjust the electrochemical properties of energy storage devices. Summary of the invention

[0005] In order to solve the problem of thermal runaway, the present invention provides a method for preparing a temperature-responsive supercapacitor. The supercapacitor assembled with a gel thermosensitive electrolyte obtained by in-situ polymerization can operate normally without adding additional diaphragms and electrolytes, and can effectively achieve overheating self-protection at high temperatures. This overheating protection behavior is fast and can dynamically adjust the electrochemical performance of the supercapacitor multiple times following the change of temperature.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for preparing a temperature-responsive supercapacitor, comprising the following steps:

[0008] Step 1: Mix and dissolve activated carbon (AC), polyvinylidene fluoride (PVDF), and conductive agent (Super P) in N-methylpyrrolidone (NMP) solvent, grind evenly to obtain slurry, and coat the slurry on carbon-coated aluminum foil and place it in an oven for drying to obtain an electrode sheet;

[0009] Step 2: Mix the thermosensitive polymer monomer and the saline solution, heat and mix them evenly to obtain a solution A;

[0010] Step 3: Add a photoinitiator, a crosslinking agent and a hydrophilic monomer to solution A or add only a photoinitiator to solution A, heat and stir to obtain a uniform polymer solution B;

[0011] Step 4: Add the polymer solution B dropwise into a battery shell equipped with an electrode sheet until the solution completely covers the electrode sheet, and cure it under ultraviolet curing lamp at room temperature to obtain a gel thermosensitive electrolyte;

[0012] Step 5: Place another electrode sheet on the gel thermosensitive electrolyte, then add a gasket and spring to assemble a supercapacitor;

[0013] Further, the mass ratio of AC, PVDF, and Super P in step 1 is (7-8):1:(1-2);

[0014] Further, the thermosensitive polymer monomer in step 2 is isopropyl acrylamide (NIPAAm) or N-vinyl caprolactam (NVCL);

[0015] The saline solution in step 2 is a mixed solution of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) and deionized water. The concentration of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) in the saline solution is 0.5-4M, and the saline solution is used as a solvent.

[0016] Furthermore, in steps 2 and 3, the mass ratio of the thermosensitive monomer, the photoinitiator, the crosslinking agent, the saline solution and the hydrophilic monomer is (85-97.5):(0.5-3):(0-2):(2-5):(0-10); the heating and stirring temperature is 50-60°C, and the stirring time is 20-60 minutes.

[0017] The photoinitiator prepared in each step 3 may be 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959), 1-hydroxycyclohexylphenyl ketone (Irgacure 184), 2-hydroxy-2-methyl-1-phenylpropane-1-one (Irgacure 369) or bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Irgacure 819);

[0018] In step 3, a cross-linking agent may be added to change the cross-linking mode of the gel electrolyte. The cross-linking agent may be polyethylene glycol diacrylate (PEGDA) or polyethylene glycol dimethacrylate (PEGDMA).

[0019] In step 3, other hydrophilic monomers can be added. Hydrophilic monomers can form more hydrogen bonds between molecules when they react with water. In order to break these hydrogen bonds, more thermal energy is required, thereby achieving a higher phase transition temperature. The hydrophilic monomers that can be used in each preparation are acrylamide (AM) or N-vinylpyrrolidone (NVP).

[0020] Furthermore, the volume of the solution added each time in step 4 needs to completely cover the electrode sheet to ensure the normal operation of the capacitor. The wavelength range of the ultraviolet curing lamp is 254-365nm, and the illumination time under the ultraviolet curing lamp is 20-60 minutes.

[0021] Furthermore, the shell model used for the supercapacitor assembled in step 5 is a CR-2032 button battery shell.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) In the present invention, a temperature-responsive high-safety supercapacitor is assembled by a unique in-situ preparation scheme, which can ensure normal operation at room temperature without adding additional electrolytes and diaphragms. Based on the spontaneous intelligent phase transition during the temperature increase process, it can play a role in suppressing the occurrence of thermal runaway when the temperature increases.

[0024] (2) The temperature-responsive high-safety supercapacitor of the present invention has a thermal response function. When the operating temperature of the supercapacitor increases abnormally, the temperature-sensitive electrolyte can spontaneously adjust the charge and discharge rate by responding to the temperature change, thereby realizing the protection function when thermal runaway occurs. This is an active protection strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the infrared spectrum of the PNVCL thermosensitive polymer synthesized in Example 1;

[0026] Figure 2 is a charge and discharge curve diagram of a supercapacitor assembled with a gel temperature-sensitive electrolyte at 30° C. in Example 2;

[0027] Figure 3 is a charge and discharge curve diagram of a supercapacitor assembled with a gel temperature-sensitive electrolyte at 70° C. in Example 2;

[0028] Figure 4 is a graph showing the change in impedance (EIS) of a supercapacitor assembled with a gel thermosensitive electrolyte as a function of temperature in Example 3;

[0029] Figure 5 This is a graph showing the cyclic voltammetry (CV) curve of the supercapacitor assembled with the gel thermosensitive electrolyte in Example 4 as a function of temperature. DETAILED DESCRIPTION

[0030] The following further describes the implementation of the present invention in conjunction with specific embodiments and drawings;

[0031] Example 1

[0032] Step 1: Mix AC, PVDF, and Super P in a ratio of 8:1:1 and dissolve them in NMP. Grind them in a mortar until they are uniform and free of particles. Use a scraper to coat the slurry on a carbon-coated aluminum foil and dry it in an oven to obtain an electrode sheet.

[0033] Step 2: Mix 2 g of NVCL monomer and 2 mL of 0.5 M NaTFSI saline, heat at 50 °C and stir evenly.

[0034] Step 3: Add 0.01 g of Irgacure 819 photoinitiator to the uniformly mixed solution and stir with a magnetic stirrer at 50° C. for 20 minutes.

[0035] Step 4: Add the uniformly mixed polymer solution dropwise into the battery shell containing the electrode sheets, ensuring that the electrode sheets in each battery shell are completely covered by the polymer solution, and cure the mixture under room temperature with a 254 nm ultraviolet curing lamp for 20 minutes to obtain a gel thermosensitive electrolyte;

[0036] Step 5: Place another electrode sheet on the gel thermosensitive electrolyte, then add a gasket and assemble the springs into a supercapacitor, which is then assembled into a supercapacitor with the electrolyte on a 2032 button battery mold using a sealing machine.

[0037] The gel thermosensitive electrolyte is transparent at ambient temperature. Due to the effect of the hydrophobic chain, the polymer gradually precipitates, causing the solution to become opaque. As the temperature rises, at a certain temperature, the growing internal energy will destroy the hydrogen bonds. Water molecules are released, producing polar polymer conformations, causing the system to change from colorless to milky white, verifying the thermosensitive properties of the electrolyte.

[0038] The infrared spectrum characterization of PNVCL polymer is shown in the figure Figure 1 As shown, the strongest characteristic peak in the spectrum is at 1620 cm -1 The wavelength appears, which comes from the C=O stretching vibration in PNVCL; the CN stretching vibration peak of the polymer is at 1477cm -1 and was detected at 2924cm -1 The aliphatic CH stretches are all retained in the NVCL monomer, thus indicating the successful polymerization of PNVCL.

[0039] Example 2

[0040] Step 1: Mix AC, PVDF, and Super P in a ratio of 7:2:1 and dissolve them in NMP. Grind them in a mortar until they are uniform and free of particles. Use a scraper to coat the slurry on a carbon-coated aluminum foil and dry it in an oven to obtain an electrode sheet.

[0041] Step 2: Mix 1.5 g NIPAAm monomer and 2.5 mL 0.5 M NaTFSI saline, heat at 55 °C and stir evenly.

[0042] Step 3: Add 0.035 g Irgacure 184 photoinitiator, 0.015 g PEGDMA crosslinker, and 0.045 g NVP monomer solution to the uniformly mixed solution, and stir with a magnetic stirrer at 60° C. for 30 minutes.

[0043] Step 4: Add the uniformly mixed polymer solution dropwise into the battery shell containing the electrode sheets, ensuring that the electrode sheets in each battery shell are completely covered by the polymer solution, and cure the mixture under room temperature with a 365nm ultraviolet curing lamp for 30 minutes to obtain a gel thermosensitive electrolyte;

[0044] Step 5: Place another electrode sheet on the gel thermosensitive electrolyte, then add a gasket and shrapnel to assemble into a supercapacitor, and assemble it with the electrolyte on a 2032 button battery mold through a sealing machine to form a supercapacitor, and perform a cyclic charge and discharge test.

[0045] The supercapacitor assembled with the temperature-sensitive electrolyte was subjected to cyclic charge and discharge tests at different temperatures. The test curves at 30°C and 70°C are as follows: Figure 2 and 3As shown. At 30°C, the supercapacitor assembled with the thermosensitive electrolyte operates normally and exhibits good cyclic charge and discharge capabilities. When the temperature rises, the electrochemical activity decreases due to the transition of the polymer from hydrophilic to hydrophobic, and the reduction of ion migration. When the solution lacks ions, it is difficult to maintain the input current density, and the voltage quickly switches between the maximum and minimum allowable ranges, resulting in a shortened charge and discharge time. This verifies the protective function of the thermosensitive electrolyte in the supercapacitor at high temperatures.

[0046] Example 3

[0047] Step 1: Mix AC, PVDF, and Super P in a ratio of 8:1:1 and dissolve them in NMP. Grind them in a mortar until they are uniform and free of particles. Use a scraper to coat the slurry on a carbon-coated aluminum foil and dry it in an oven to obtain an electrode sheet.

[0048] Step 2: Mix 1.5 g NIPAAm monomer and 3 mL 2 M NaTFSI saline, heat at 60 °C and stir evenly.

[0049] Step 3: Add 0.045 g Irgacure 369 photoinitiator, 0.015 g PEGDA crosslinker, and 0.075 g AM monomer powder to the uniformly mixed solution, and stir with a magnetic stirrer at 55° C. for 40 minutes.

[0050] Step 4: Add the uniformly mixed polymer solution dropwise into the battery shell containing the electrode sheets, ensuring that the electrode sheets in each battery shell are completely covered by the polymer solution, and cure the mixture under room temperature with a 365nm ultraviolet curing lamp for 40 minutes to obtain a gel thermosensitive electrolyte;

[0051] Step 5: Place another electrode sheet on the gel thermosensitive electrolyte, then add a gasket and shrapnel to assemble into a supercapacitor, and assemble it with the electrolyte on a 2032 button battery mold through a sealing machine to form a supercapacitor, and perform electrochemical impedance spectroscopy.

[0052] The impedance test of supercapacitors assembled with gel thermosensitive electrolyte at different temperatures is as follows: Figure 4 As shown in the figure, after the temperature rises to reach LCST, the transition of the polymer from hydrophilic to hydrophobic causes the curling of the polymer molecular chain, thereby increasing the internal resistance and ion transfer impedance. The fitting calculation of the Nquist diagram shows that as the temperature gradually increases, Rct increases significantly from 156.4Ω to 331.2Ω, indicating that the phase change of the gel electrolyte destroys its ionic conductivity and electrochemical response, and exerts its temperature response function.

[0053] Example 4

[0054] Step 1: Mix AC, PVDF, and Super P in a ratio of 8:1:1 and dissolve them in NMP. Grind them in a mortar until they are uniform and free of particles. Use a scraper to coat the slurry on a carbon-coated aluminum foil and dry it in an oven to obtain an electrode sheet.

[0055] Step 2: Mix 1.5 g NIPAAm monomer and 2.5 mL 4 M NaTFSI saline, heat at 50 °C and stir evenly.

[0056] Step 3: Add 0.053 g of Irgacure 2959 photoinitiator, 0.035 g of PEGDA crosslinker, and 0.176 g of AM monomer powder to the uniformly mixed solution, and stir with a magnetic stirrer at 50° C. for 60 minutes.

[0057] Step 4: Add the uniformly mixed polymer solution dropwise into the battery shell containing the electrode sheets, ensuring that the electrode sheets in each battery shell are completely covered by the polymer solution, and cure the mixture under room temperature with a 365nm UV curing lamp for 60 minutes to obtain a gel thermosensitive electrolyte;

[0058] Step 5: Place another electrode sheet on the gel thermosensitive electrolyte, then add a gasket and shrapnel to assemble into a supercapacitor, and assemble it with the electrolyte on a 2032 button battery mold through a sealing machine to form a supercapacitor, and perform a cyclic voltammetry test.

[0059] The cyclic voltammetry test of the supercapacitor assembled with gel electrolyte at different temperatures is shown in the figure Figure 5 As shown in the figure, after the temperature rises to reach the LCST, the transition of the polymer from hydrophilic to hydrophobic causes the curling of the polymer molecular chain to inhibit the migration of conductive ions. The area enclosed by the CV curve decreases with the increase in temperature. The specific capacitance calculation shows that the specific capacitance of the supercapacitor decreases from the initial 115F / g at 30°C to 15F / g at 70°C, thus verifying the protective function of the temperature-sensitive electrolyte in the supercapacitor at high temperatures.

Claims

1. A method for preparing a temperature-responsive supercapacitor, characterized in that: Here are the steps: Step 1: Mix and dissolve activated carbon AC, polyvinylidene fluoride PVDF, and conductive agent Super P in N-methylpyrrolidone NMP solvent, grind evenly to obtain slurry, and coat the slurry on carbon-coated aluminum foil and place it in an oven for drying to obtain an electrode sheet; Step 2: Mix the thermosensitive polymer monomer and the saline solution, heat and mix them evenly to obtain a solution A; Step 3: Add a photoinitiator, a crosslinking agent and a hydrophilic monomer to solution A or add only a photoinitiator to solution A, heat and stir to obtain a uniform polymer solution B; Step 4: Add the polymer solution B dropwise into a battery shell equipped with an electrode sheet until the solution completely covers the electrode sheet, and cure it under ultraviolet curing lamp at room temperature to obtain a gel thermosensitive electrolyte; Step 5: Place another electrode sheet on the gel thermosensitive electrolyte, then add a gasket and spring to assemble the supercapacitor; The mass ratio of AC, PVDF and Super P in step 1 is (7-8):1:(1-2); In steps 2 and 3, the mass ratio of the thermosensitive monomer, the photoinitiator, the crosslinking agent, the saline solution and the hydrophilic monomer is (85-97.5):(0.5-3):(0-2):(2-5):(0-10).

2. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: The temperature-sensitive polymer monomer in step 2 is isopropyl acrylamide or N-vinyl caprolactam.

3. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: The saline solution in step 2 is a mixed solution of sodium bis(trifluoromethanesulfonyl)imide and deionized water, the concentration of sodium bis(trifluoromethanesulfonyl)imide in the saline solution is 0.5-4M, and the saline solution is used as a solvent.

4. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: In steps 2 and 3, the heating and stirring temperature is 50-60° C., and the stirring time is 20-60 minutes.

5. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: The photoinitiator in step 3 is one of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylpropane-1-one or bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

6. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: The cross-linking agent in step 3 is polyethylene glycol diacrylate or polyethylene glycol dimethacrylate.

7. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: The hydrophilic monomer in step 3 is acrylamide or N-vinyl pyrrolidone.

8. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: The volume of solution added each time in step 4 needs to completely cover the electrode sheet to ensure the normal operation of the capacitor. The wavelength range of the ultraviolet curing lamp is 254-365nm, and the illumination time under the ultraviolet curing lamp is 20-60 minutes.

9. The method for preparing a temperature-responsive supercapacitor according to claim 1, characterized in that: The shell model used for the supercapacitor assembled in step 5 is a CR-2032 button battery shell.

Images