CN104916456B - A kind of high-energy density super capacitor and preparation method thereof - Google Patents

Abstract

The invention discloses a high energy density supercapacitor and a preparation method thereof, belonging to the field of electrochemical energy storage. By introducing metal lithium electrodes in the supercapacitor assembly process to control the electrochemical state of the electrode material, charge injection into the electrode material is achieved, thereby obtaining positive and negative electrode materials with electrochemical potential adjustment, so that the working potential window of the positive and negative electrodes in the supercapacitor can be obtained. The optimization realizes the simultaneous increase of the working voltage and specific capacity of the device, thereby increasing the energy density of the supercapacitor. At the same time, the obtained capacitor can stabilize the potential window through the electrochemical activation process of the metal lithium electrode, so that it has an ultra-long cycle life. The invention has the advantages of simple technological process, compatibility with the existing technological process, and remarkable effect on improving device performance, and thus has great application prospects.

Description

A kind of high energy density supercapacitor and preparation method thereof

technical field

The invention relates to the technical field of supercapacitors for electrochemical energy storage, in particular to a high energy density supercapacitor and a preparation method thereof.

Background technique

Supercapacitors, also known as electrochemical capacitors, rely on the adsorption of double-layer ions on the electrode surface or redox reactions to store charges, and their performance is between that of physical capacitors and secondary batteries. Supercapacitors not only have an energy density much higher than that of physical capacitors, they can charge and discharge within seconds, can charge and discharge with high power/current, have a cycle life of tens of thousands of times, and have a charge and discharge efficiency close to 100%. It can be used in the environment (-40 ~ 70 ℃) and has high safety and long-term maintenance-free characteristics, which are incomparable to secondary batteries. These superior properties make supercapacitors expected to be widely used in consumer electronics, electric vehicles, smart grids, energy generation systems, aerospace, and military. However, the wide application of supercapacitors is still limited by their low energy density. On the premise of maintaining the advantages of supercapacitors, how to further increase their energy density and make it close to the level of secondary batteries is an urgent problem to be solved.

The energy density E of a supercapacitor is proportional to the square of the specific capacitance C and the operating voltage U: E=1/2CU ² , therefore, the improvement of the energy density of a supercapacitor can be achieved by increasing the specific capacitance or operating voltage. The specific capacitance of a supercapacitor depends on the electrode material, so the current main research work is focused on obtaining high-performance electrode materials. Another direction of research is to develop electrolytes in the high-voltage window to increase the working voltage of supercapacitors. At present, the application of ionic liquid electrolytes can increase the working voltage of supercapacitors to above 3.5V.

Great progress has been made in the research of electrode materials and electrolytes. However, the common problem is that after the electrode materials and electrolytes are assembled into devices, the available voltage window of the electrolyte and the high specific capacity of the electrode materials are not fully utilized. Because after being assembled into a supercapacitor, the potential window of the positive and negative electrode materials is restricted and cannot work under the optimized potential window. The specific capacitance of the electrode material is also affected by the working potential window of the electrode, especially for the pseudocapacitive electrode materials that store charges by reversible redox reactions such as metal oxides, conductive polymers, and carbon materials containing functional groups, the electrodes under different potential windows The specific capacitance of the material varies greatly. When the electrode material is composed of a device, its working potential window is often only half of the potential window of the three-electrode test. Therefore, the electrochemical performance of the electrode material cannot be fully exerted, resulting in a great decrease in the specific capacitance of the device. .

In order to solve the problem that the high specific capacity of the material and the available voltage window of the electrolyte cannot be fully utilized after being assembled into a device, two methods are currently used: mass matching and asymmetric capacitors. Through the quality matching of the positive and negative electrode materials, it is ensured that one of the electrode materials is in excess relative to the other, so that the positive and negative electrodes can reach the upper and lower limits of the available voltage window of the electrolyte at the same time. However, mass matching can only increase the working voltage of supercapacitors, but cannot increase the specific capacity of supercapacitors. Asymmetric capacitors are supercapacitors assembled using carbon materials with different pore structures or different types of electrode materials as positive and negative electrodes respectively. Carbon materials with different pore sizes are used as positive and negative electrodes to match the adsorbed anions and cations to increase specific capacitance. , so as to increase the energy density of the supercapacitor, it is necessary to carry out a large number of experiments in order to meet the positive and negative electrode material pore structure materials to achieve matching. Asymmetric capacitors based on different energy storage mechanisms still have the problem of matching the performance of the positive and negative electrodes. In addition, the cycle life and high-current charge and discharge performance of the assembled device are greatly affected by the material electrodes that undergo pseudocapacitive reactions, which are symmetrical with carbon-based capacitors. Type capacitors compared to the gap is very obvious. Only when the capacity of the positive and negative electrodes is the same, and the working voltage can reach the maximum available voltage window of the electrolyte, can the energy density of the supercapacitor reach its maximum. Based on this, we proposed a related concept to maximize the energy density of supercapacitors by adjusting the working potential windows of the positive and negative electrodes respectively (see patent application 201310093023.7). However, how to simplify the phase-related design and develop supercapacitor devices with practical value still needs further research.

Contents of the invention

The purpose of the present invention is to provide a high energy density supercapacitor and its preparation method, by redesigning the structure of the supercapacitor to realize a new method of changing the electrode state of the electrode material, adding metal lithium electrodes to the positive and negative electrode materials of the supercapacitor The initial electrochemical potential is regulated, and the potential adjustment can be realized during the service of the supercapacitor. The present invention is based on the conventional supercapacitor production process, through the electrochemical pretreatment process, the assembled supercapacitor can work in the optimal potential window, and the working voltage and specific capacity of the device are improved, thereby extremely The energy density of the capacitor device is greatly improved.

Technical scheme of the present invention is as follows:

A method for preparing a high-energy-density supercapacitor. The method first assembles a positive electrode, a negative electrode and a diaphragm according to a conventional capacitor process, supplemented by a metal lithium electrode, injects an electrolyte, and then assembles a supercapacitor with a three-electrode system; The pretreatment process realizes the injection of charges into the positive and negative electrodes, so that the initial electrochemical potential of the positive and negative electrodes can be adjusted to a specific potential (ie E'ov) at the same time, thereby preparing a high energy density supercapacitor.

The process of injecting charges into the positive and negative electrodes respectively through the pretreatment process is:

At the same time, conduct constant current charge and discharge tests on the positive electrode and the negative electrode relative to the lithium electrode in the maximum voltage range available for the electrolyte at the same current value, and obtain the intersection point E'ov of the constant current discharge curve of the positive electrode and the constant current charge curve of the negative electrode, and finally The positive and negative electrodes are simultaneously charged and discharged to E'ov by constant current or constant voltage.

The method enables the positive and negative electrodes in the final assembled supercapacitor to make maximum use of the available maximum voltage range of the electrolyte in the later service process. Corresponding to different electrode materials and electrolytes, the same method can be used for regulation.

The prepared high-energy-density supercapacitor can be electrochemically activated by metal lithium electrodes during service, so that it has a long cycle life. Carry out constant current charge and discharge tests at the same current value within the maximum voltage range available for the electrolyte, and obtain the intersection point E''ov of the constant current discharge curve of the positive electrode and the constant current charge curve of the negative electrode. Finally, the positive and negative electrodes are simultaneously charged and discharged to E''ov by constant current or constant voltage, and the positive and negative electrodes after potential modulation are obtained. Thereby realizing its long cycle use.

The production of electrode sheets (electrodes) in the high energy density supercapacitor is a conventional process, that is, active electrode materials, binders and conductive agents are prepared by batching, coating, sheeting and slicing.

The electrode material can be a carbon material (such as activated carbon, template carbon, activated carbon fiber, carbon aerosol, carbon nanotubes, graphene, cracked carbon, graphite, etc.), metal oxides (such as ruthenium oxide, manganese oxide, nickel oxide, Vanadium oxide, tin oxide, cobalt oxide, iron oxide, etc.) or metal hydroxide materials (nickel hydroxide, cobalt hydroxide, iron hydroxide, etc.) and conductive polymer materials (polypyrrole, polythiophene, polyaniline, polypara Benzene, polyacene, etc.) in one or more composite materials (such as ruthenium oxide/graphene, polyaniline/carbon nanotubes, polyaniline/manganese oxide, etc., polypyrrole/manganese oxide/graphene, etc.).

The electrolyte can be an aqueous electrolyte (such as sulfuric acid aqueous solution, potassium hydroxide aqueous solution, and neutral aqueous solutions of lithium salts, potassium salts, and sodium salts, etc.), an organic electrolyte (such as perchlorate, tetrafluoroborate, solution of hexafluorophosphate or trifluoromethylsulfonate in organic solvents) or various ionic liquids, etc.; the organic solvents are propylene carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, carbonic acid Methyl propyl ester, dimethyl carbonate, diethyl carbonate, dimethylformamide, sulfolane, acetonitrile, 1,3-dioxolane, 1,2-dimethoxyethane, and 1,4-butane One or more of lactones, etc.

Advantage of the present invention and beneficial effect are as follows:

1. The design composition of the supercapacitor of the present invention is except that the positive and negative electrode materials of the general supercapacitor are made into the positive and negative electrode sheets and the electrolyte, and a metal lithium electrode is added to form a supercapacitor with a three-electrode system; then through the pretreatment process The charge is injected into the positive and negative electrodes respectively, so that the initial electrochemical potential of the positive and negative electrodes can be adjusted to a specific potential (ie E'ov) at the same time, thereby greatly improving the energy density of the device.

Compared with the previous method of maximizing the energy density of supercapacitors (Chinese invention patent 201310093023.7), this invention adopts a new electrochemical potential regulation method, which greatly simplifies the operation process. The design of the three-electrode system is fully compatible with the existing assembly process, and a supercapacitor device with practical value can be obtained. At the same time, the obtained capacitor can stabilize the potential window through the electrochemical activation process of the metal lithium electrode during the service process, so that it has an ultra-long cycle life.

2. The method for realizing a high-energy-density supercapacitor proposed by the present invention has universal applicability. The present invention directly optimizes the working potential window of the positive and negative electrodes by regulating the electrochemical potential of the positive and negative electrodes, so it solves the root cause that the specific capacity of the electrode material and the available voltage window of the electrolyte in the existing supercapacitor cannot be fully controlled. The problem of utilization is applicable to any electrolyte system and any electrode material.

3. The method for realizing a high-energy-density supercapacitor proposed by the present invention can give full play to the performance of the electrode material and the electrolyte, and can simultaneously improve the specific capacity and working voltage of the supercapacitor, thereby greatly improving the energy density of the existing supercapacitor , to expand the application field of supercapacitors.

4. The present invention does not require the positive and negative electrodes to be completely matched (same quality, same specific capacity), and the scope of application is wider.

5. The method for maximizing the energy density of a supercapacitor proposed by the present invention has a simple process, strong repeatability in different batches, and easy large-scale scale-up production.

6. The introduction of lithium electrodes into supercapacitors in the present invention can effectively solve the problems of lithium source and coulombic efficiency of electrode materials, and greatly broaden the applicable range of electrode materials.

7. The supercapacitor device design proposed by the present invention has high practical value.

8. The design of the supercapacitor device proposed by the present invention can realize potential adjustment during the service process of the supercapacitor, so that it has an ultra-long cycle life.

Description of drawings

Figure 1 is a comparison of the production process of conventional supercapacitors and the present invention; in the figure: (a) is the process flow of conventional supercapacitors; (b) is the process flow of the present invention.

Figure 2 is a schematic diagram of the assembly method and modulation principle of the supercapacitor device of the present invention; in the figure: (a) is a schematic diagram of the assembly method of the supercapacitor device of the present invention; (b) is a schematic diagram of the principle of the present invention (the height of the shaded part in the figure represents The electrode potentials of the positive and negative electrodes, E _0v , E _0v ' are the initial electrochemical potentials of the positive and negative electrodes and the electrochemical potentials of the positive and negative electrodes after modulation).

Fig. 3 is a schematic diagram of a specific control method of the supercapacitor device of the present invention.

Fig. 4 is a comparison of the electrochemical performance of the supercapacitor formed before and after the potential regulation of the graphene electrode in Example 1 of the present invention.

Fig. 5 is a comparison of the electrochemical performance of the supercapacitor formed before and after the potential regulation of the graphene electrode in Example 1 of the present invention and the reactivation after cycle.

FIG. 6 is a comparison of the electrochemical performance of the supercapacitor before and after the potential regulation of the multi-walled carbon nanotube electrode in Example 2 of the present invention.

Fig. 7 is a comparison of the electrochemical performance of the supercapacitor formed before and after the potential regulation of the single-walled carbon nanotube electrode in Example 3 of the present invention.

Fig. 8 is a power-energy density curve of a supercapacitor assembled with electrode materials before and after potential modulation in Examples 1-3 of the present invention.

Detailed ways

The present invention is described below in conjunction with embodiment:

The conventional supercapacitor production process is shown in Figure 1(a). On the basis of the conventional supercapacitor production process, the present invention introduces a lithium electrode while adding a step of regulating the initial electrochemical potential of the electrode material, so that the assembled supercapacitor Both the positive and negative electrodes in the capacitor can work in the optimal potential window, which can increase the working voltage and specific capacity of the device at the same time, thereby maximizing the energy density of the device, as shown in Figure 2(a)-(b).

The step of adjusting the initial electrochemical potential (the process of charge injection into the positive and negative electrodes) is performed after the supercapacitor device is assembled (as shown in Figure 1(b)).

Example 1

The process of regulating the supercapacitor system with graphene as electrode material (oxygen content 6.5at%, specific surface area 412m ² /g) and LiPF ₆ ethylene carbonate/dimethyl carbonate solution as electrolyte is as follows:

Graphene materials are used to make electrode sheets, and the ethylene carbonate/dimethyl carbonate solution of LiPF ₆ is used as the electrolyte (the concentration of LiPF ₆ is 1mol/L, and the volume ratio of ethylene carbonate and dimethyl carbonate is 1:1) , At the same time as positive and negative electrodes and lithium foil electrodes assembled into a supercapacitor device. The upper limit of the available potential window of the electrolyte is between 4.3V and 0.001V vs. Li, so that the positive and negative electrodes are charged and discharged at a constant current of 175mA/g with respect to the lithium electrode for 20 cycles respectively. Obtain the intersection point E'ov of the discharge curve of the positive electrode and the charge curve of the negative electrode. Then simultaneously charge (discharge) the positive and negative electrodes to E'ov constant voltage for 12h. The modulated supercapacitor device is obtained, as shown in Figure 3.

Figure 4(a) shows the comparison of the device voltage and specific capacity of the graphene supercapacitor before and after potential regulation at a current density of 875mA/g. The device before regulation is represented by GSC, and the device after regulation is represented by TGSC. It can be seen that the voltage of the supercapacitor device and the specific capacity of the device after potential regulation have been greatly improved. Figure 4(b) shows the cycle performance test of the graphene device after potential regulation under the condition of 875mA/g current density. It can be seen that the supercapacitor after potential regulation maintains good cycle stability.

Figure 5(a) shows the comparison of the electrochemical performance before and after the electrochemical activation of the regulated supercapacitor. It can be seen that under the condition of 875mA/g current density, the graphene supercapacitor (TGSCreactivation) after electrochemical activation can regain Comparable specific capacity to TGSC. Through electrochemical activation, an ultra-long cycle life is obtained.

Figure 5(b) is a comparison of the rate performance of supercapacitors before and after potential modulation and electrochemical activation at different current densities. It can be seen that graphene can exert higher energy storage in supercapacitors after potential modulation performance. At the same time, it can be seen that the electrochemical activation of the modulated supercapacitor during service can regain good energy storage performance.

Example 2

Multi-walled carbon nanotubes (diameter<2nm, length 5-15μm, specific surface area 500-700m ² /g, oxygen content 4.5at%) were made into electrode sheets, and LiPF ₆ ethylene carbonate/dimethyl carbonate solution As an electrolyte (in which the concentration of LiPF ₆ is 1mol/L, the volume ratio of ethylene carbonate to dimethyl carbonate is 1:1), it is also used as positive and negative electrodes and lithium foil electrodes to assemble supercapacitor devices. The upper limit of the available potential window of the electrolyte is between 4.3V and 0.001V vs. Li, so that the positive and negative electrodes are charged and discharged at a constant current of 175mA/g with respect to the lithium electrode for 20 cycles respectively. Obtain the intersection point E'ov of the discharge curve of the positive electrode and the charge curve of the negative electrode. At the same time, charge (discharge) the positive and negative electrodes to E'ov constant voltage for 12h. A modulated supercapacitor device is obtained.

Figure 6(a) shows the constant current charge and discharge curves of the multi-walled carbon nanotube supercapacitor after potential regulation at different rates. It can be seen that the multi-wall carbon nanotube supercapacitor after potential regulation has the same Can work very stably.

Figure 6(b) is a comparison of the capacitance rate performance of multi-walled carbon nanotubes in supercapacitors before and after potential modulation at different current densities. It can be seen that multi-walled carbon nanotubes in supercapacitors after potential modulation can play Higher energy storage performance.

Example 3

Single-walled carbon nanotubes (diameter<10nm, length 5-15μm, specific surface area 250-300m ² /g, oxygen content 6.5at%) were made into electrode sheets, and LiPF ₆ ethylene carbonate/dimethyl carbonate solution As an electrolyte (in which the concentration of LiPF ₆ is 1mol/L, the volume ratio of ethylene carbonate to dimethyl carbonate is 1:1), it is also used as positive and negative electrodes and lithium foil electrodes to assemble supercapacitor devices. The upper limit of the available potential window of the electrolyte is between 4.3V and 0.001V vs. Li, so that the positive and negative electrodes are charged and discharged at a constant current of 175mA/g with respect to the lithium electrode for 20 cycles respectively. Obtain the intersection point E'ov of the discharge curve of the positive electrode and the charge curve of the negative electrode. At the same time, charge (discharge) the positive and negative electrodes to E'ov constant voltage for 12h. A modulated supercapacitor device is obtained.

Figure 7(a) shows the constant current charge and discharge curves of the single-walled carbon nanotube supercapacitor after potential regulation at different rates. Can work very stably.

Figure 7(b) is a comparison of the capacitance rate performance of single-walled carbon nanotubes in supercapacitors before and after potential modulation at different current densities. It can be seen that single-walled carbon nanotubes in supercapacitors after potential modulation can play Higher energy storage performance.

Figure 8 shows the power-energy density curves of supercapacitors assembled with various electrode materials in the above embodiments before and after potential modulation. The results show that after the electrode potential modulation, the energy density of the supercapacitor is greatly improved, while maintaining the high power characteristics of the supercapacitor.

Claims (6)

1. A preparation method for a high-energy-density supercapacitor, characterized in that: the method first assembles a positive electrode, a negative electrode and a diaphragm, supplemented by a metal lithium electrode, and injects an electrolytic solution into a supercapacitor of a three-electrode system; Then through the pretreatment process, the charge is injected into the positive and negative electrodes respectively, so that the initial electrochemical potential of the positive and negative electrodes is adjusted to a specific potential at the same time, thereby preparing a high energy density supercapacitor; Positive and negative electrodes, the specific process of modulating the initial electrochemical potential of the positive and negative electrodes to a specific potential at the same time is: after installing a supercapacitor with a three-electrode system, simultaneously test the positive and negative electrodes in the maximum voltage range available in the electrolyte relative to the lithium electrode Carry out the constant current charge and discharge test with the same current value, and obtain the intersection point E'ov of the positive electrode constant current discharge curve and the negative electrode constant current charge curve, and finally charge and discharge the positive and negative electrodes at the same time with constant current or constant voltage to E'ov . 2. the preparation method of high energy density supercapacitor according to claim 1, is characterized in that: the making of electrode in described high energy density supercapacitor is conventional technology, is about to active electrode material and binding agent and conducting agent carry out batching , coated, pressed and sliced, and the electrode material is one or more composite materials of carbon materials, metal oxides, metal hydroxide materials and conductive polymer materials. 3. The preparation method of high energy density supercapacitor according to claim 2, characterized in that: the carbon material is activated carbon, template carbon, activated carbon fiber, carbon aerosol, carbon nanotubes, graphene, pyrolysis carbon or graphite The metal oxide is ruthenium oxide, manganese oxide, nickel oxide, vanadium oxide, tin oxide, cobalt oxide or iron oxide; the metal hydroxide material is nickel hydroxide, cobalt hydroxide or iron hydroxide; the The conductive polymer material is polypyrrole, polythiophene, polyaniline, polyparaphenylene or polyacene. 4. the preparation method of high energy density supercapacitor according to claim 1 is characterized in that: described electrolyte is aqueous electrolyte, organic electrolyte or various ionic liquids; Described aqueous electrolyte is sulfuric acid aqueous solution, hydrogen An aqueous solution of potassium oxide or a neutral aqueous solution of lithium salt, potassium salt, and sodium salt; the organic electrolyte is perchlorate, tetrafluoroborate, hexafluorophosphate, or trifluoromethanesulfonate in an organic solvent The solution, the organic solvent is propylene carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, dimethyl carbonate, diethyl carbonate, dimethylformamide, sulfolane, acetonitrile, One or more of 1,3-dioxolane, 1,2-dimethoxyethane and 1,4-butyrolactone. 5. A high energy density supercapacitor prepared by the method according to claim 1. 6. The high-energy-density supercapacitor according to claim 5, characterized in that: the high-energy-density supercapacitor can be electrochemically activated by a metal lithium electrode during service to ensure its cycle life, and the specific process is: The positive and negative electrodes of the supercapacitor in the service process are respectively subjected to constant current charge and discharge tests with the same current value in the maximum voltage range available for the electrolyte with respect to the lithium electrode, and the constant current discharge curve of the positive electrode and the constant current charge curve of the negative electrode are obtained. The intersection point E"ov; finally, the positive and negative electrodes are simultaneously charged and discharged to E"ov by constant current or constant voltage to obtain the positive and negative electrodes after potential modulation, so as to realize its long cycle performance.