A method for preparing a carbon-based lithium-ion supercapacitor

Abstract

The present invention relates to a method for preparing a carbon-based lithium ion supercapacitor, which includes the following steps: mixing polyacrylonitrile, cobalt acetate tetrahydrate and graphene oxide in an N,N-dimethylformamide solution to obtain a precursor solution; subjecting the precursor solution to electrostatic spinning, pre-oxidation and carbonization treatment to obtain a negative electrode material; subjecting the negative electrode material, a polypropylene microporous membrane and a lithium sheet to pre-lithium embedding treatment to obtain a negative electrode sheet; coating activated carbon, a conductive additive and a binder on a current collector to obtain a positive electrode sheet; using the negative electrode sheet as a first negative electrode, the positive electrode sheet as a first positive electrode, a lithium salt solution as an electrolyte, and separating the first negative electrode from the first positive electrode by a diaphragm to obtain a carbon-based lithium ion supercapacitor. The raw material composition of the carbon-based lithium ion supercapacitor prepared by the present invention is simple, and while simplifying the steps, the theoretical capacity and cycle stability of energy storage of the carbon-based lithium ion supercapacitor can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of supercapacitors, and in particular to a method for preparing a carbon-based lithium-ion supercapacitor. Background Art

[0002] With the continuous advancement of science and technology, traditional lithium-ion batteries or supercapacitors can no longer meet the higher-level needs of modern economic society for energy storage devices. In this case, lithium-ion supercapacitors that combine the advantages of lithium-ion batteries and supercapacitors have come into being. Lithium-ion capacitors are a new type of hybrid electrochemical energy storage device between lithium-ion batteries and double-layer supercapacitors. They have the characteristics of high power density and long life of double-layer supercapacitors and high energy density of lithium-ion batteries. They have good application prospects in fields such as backup power supplies and mobile communications, and have therefore received widespread attention from scholars from all walks of life. The structure of this device is generally that the positive electrode uses double-layer supercapacitor materials and / or lithium-ion battery positive electrode materials, and the negative electrode uses carbon-based lithium-ion electrode materials.

[0003] There are still many problems to be solved in the existing lithium-ion supercapacitors. Among them, the most urgent problem is that the energy density cannot be further improved due to the low specific capacity of the electrode material. Most of the electrode materials need to go through steps such as batching, coating and rolling. The preparation process is cumbersome and consumes a lot of manpower and material resources. Therefore, it is necessary to improve the preparation method of carbon-based lithium-ion supercapacitors and simplify the preparation steps.

[0004] The Chinese patent with publication number CN105355872A discloses a method for preparing a carbon-based lithium-ion electrode material. The method firstly adds polyacrylonitrile and transition metal nitrate into a dimethylformamide solvent at a mass ratio of 1:1 to prepare a precursor solution; then electrospins the precursor solution using an electrostatic spinning apparatus to prepare a protofilament fiber; then pre-oxidizes and stabilizes the protofilament fiber and performs carbonization treatment in sequence to prepare a carbon-based lithium-ion electrode material. Although the above-mentioned carbon-based lithium-ion electrode material improves the specific capacity by combining transition metal particles with carbon fibers, the transition metal oxides are easy to agglomerate, so that their active sites cannot be fully exposed, and the active sites of the electrode material obtained by carbonization are limited, which seriously affects the cycle stability of its energy storage.

[0005] At present, the preparation process of traditional carbon-based lithium-ion supercapacitors is complicated and the specific capacity is low. There is an urgent need to improve the preparation method of a carbon-based lithium-ion supercapacitor. While simplifying the steps, a carbon-based composite electrode material with uniformly distributed transition metal particles and carbon fibers is prepared, and through further matching with supercapacitor activated carbon and process optimization, a lithium-ion supercapacitor with better energy storage performance is obtained. Summary of the invention

[0006] The problem to be solved by the present invention is to provide a method for preparing a carbon-based lithium-ion supercapacitor in view of the above-mentioned deficiencies in the prior art, which has the advantages of simple steps and is conducive to improving the energy storage performance of the carbon-based lithium-ion supercapacitor.

[0007] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a carbon-based lithium-ion supercapacitor comprises the following steps: uniformly mixing polyacrylonitrile, cobalt acetate tetrahydrate and graphene oxide in an N,N-dimethylformamide solution to obtain a precursor solution; subjecting the precursor solution to electrostatic spinning, pre-oxidation and carbonization treatment to obtain a negative electrode material; subjecting the negative electrode material, a polypropylene microporous membrane and a lithium sheet to lithium pre-embedding treatment to obtain a negative electrode sheet; coating a mixed activated carbon, a conductive additive and a binder on a current collector to obtain a positive electrode sheet; using the negative electrode sheet as a first negative electrode, using the positive electrode sheet as a first positive electrode, using a lithium salt solution as an electrolyte, and separating the first negative electrode from the first positive electrode by a diaphragm, and then stamping and sealing to obtain the carbon-based lithium-ion supercapacitor.

[0009] By adopting the above technical scheme, the carbonized negative electrode material is mainly composed of carbon nanofibers, cobalt oxide and graphene oxide. The carbon nanofibers have a unique three-dimensional porous structure, a high specific surface area and excellent mechanical properties, while the graphene oxide is distributed from the edge of the sheet to the center in a hydrophilic to hydrophobic property. The graphene oxide is wrapped on the surface of the carbon nanofiber, which can not only improve the conductivity and promote the rapid transmission of electrons, but also promote the dispersion of cobalt oxide in N,N-dimethylformamide solution, inhibit the agglomeration of cobalt oxide itself, so that the cobalt oxide can be evenly compounded on the graphene oxide / carbon nanofiber, so that the active edge of the cobalt oxide is more fully exposed, and then after pre-lithium embedding treatment, the cycle stability of the energy storage of the negative electrode plate can be improved; in addition, the activated carbon and the conductive additive can be cured on the current collector through the binder to give full play to their supercapacitor performance and achieve the improvement of energy storage performance; in this process, the raw material composition of the preparation of the carbon-based lithium-ion supercapacitor is simple, the preparation time is short, and while simplifying the steps, the theoretical capacity and cycle stability of the energy storage of the carbon-based lithium-ion supercapacitor can be improved.

[0010] Furthermore, in the process of preparing the precursor solution, the mass concentration ratio of polyacrylonitrile, cobalt acetate tetrahydrate and graphene oxide is 1000: (230.0-240.0): (0.6-0.8). Preferably, the mass concentration ratio of polyacrylonitrile, cobalt acetate tetrahydrate and graphene oxide is 1000: 236.3: 0.7, and the electrochemical performance of the negative electrode sheet prepared under this ratio is the best.

[0011] Preferably, the process of preparing the precursor solution includes first adding polyacrylonitrile to the N,N-dimethylformamide solution, keeping the solution in a constant temperature water bath at 55-65°C until the polyacrylonitrile is fully dissolved, then adding cobalt acetate tetrahydrate, continuing to stir until fully dissolved, then adding graphene oxide, continuing to stir for 10-15 hours, and then ultrasonicating for 25-35 minutes to obtain the precursor solution. The ultrasonic step is mainly to fully disperse the graphene oxide, thereby promoting the cobalt oxide to be evenly compounded on the graphene oxide / carbon nanofibers, so that the active edge of the cobalt oxide is more fully exposed, thereby ensuring the cycle stability of the negative electrode energy storage.

[0012] Furthermore, the process of preparing the negative electrode material includes firstly performing electrostatic spinning on the precursor solution using an electrospinning apparatus, collecting it with a collector, drying it, pressing it into sheets, obtaining a spinning disc, and then placing the spinning disc into a pre-oxidation device, heating it uniformly to 220-230°C at a rate of 2.5-3.5°C / min, pre-oxidizing it for 5.5-6.5h to obtain a pre-oxidized disc, and then transferring the pre-oxidized disc to a carbonization device, heating it uniformly to 645-665°C at a rate of 4.5-5.5°C / min under a nitrogen protective atmosphere, and carbonizing it for 1.5-2.5h to obtain the negative electrode material. The pre-oxidation process is carried out in a muffle furnace so that the cobalt acetate tetrahydrate can be oxidatively dehydrated and preliminarily composited with graphene oxide / carbon base. The carbonization process is carried out in a tubular furnace so that polyacrylonitrile can be fully converted into carbon nanofibers. The cobalt acetate tetrahydrate after oxidative dehydration can be dehydrogenated and more closely combined with graphene oxide / carbon nanofibers, thereby obtaining better electrochemical performance.

[0013] Preferably, in the electrospinning process, the distance between the discharge port of the electrospinning instrument and the collector is controlled to be 12-18 cm, the injection rate of the electrospinning instrument is 9-11 μL / min, and the voltage is 14-16 kV. The spinning nozzle at the discharge port of the electrospinning instrument is made of stainless steel, with an inner diameter of 0.6 mm, and the sampling volume is 3 mL at a time.

[0014] Furthermore, the process of preparing the negative electrode sheet includes, in a dry environment filled with argon, first using the negative electrode material as the second negative electrode, the lithium sheet as the second positive electrode, and the lithium salt solution as the electrolyte, and the second negative electrode and the second positive electrode are separated by a polypropylene microporous membrane to form a closed button battery, and then the button battery is discharged and charged 8 to 12 times in a cycle, and the discharge cut-off voltage is controlled to be 0.5 to 1.5V, and then the negative electrode material pre-embedded with lithium is taken out to obtain the negative electrode sheet. This process not only avoids the safety problem caused by the residual lithium metal on the surface of the negative electrode sheet after the pre-embedded lithium of the negative electrode sheet, but also avoids the gradient effect when the negative electrode sheet is pre-embedded with lithium. The pre-embedded lithium efficiency is high, and the electrochemical performance of the obtained negative electrode sheet is better; in addition, the button battery is pre-tested for voltage to obtain the minimum and maximum voltages of charge and discharge, and then the voltage of the button battery is made to reach the endpoint value during the charge and discharge process.

[0015] Furthermore, in the process of preparing the positive electrode sheet, the mass concentration ratio of activated carbon, conductive additive and binder is (7-9):1:1; wherein the conductive additive is carbon black and the binder is polyvinylidene fluoride. Preferably, the mass concentration ratio of activated carbon, conductive additive and binder is 8:1:1.

[0016] Preferably, the process of preparing the positive electrode sheet includes first adding activated carbon, conductive additives and binders to N-methylpyrrolidone solution, and controlling the total amount of activated carbon, conductive additives and binders to the mass ratio of the negative electrode material to (1-10):1, stirring and mixing to obtain the positive electrode material, and then applying the positive electrode material to the surface of the current collector with a scraper, vacuum drying at 75-95°C for 20-30h, pressing and cutting to obtain the positive electrode sheet. Among them, it is best to control the total amount of activated carbon, conductive additives and binders to the mass ratio of the negative electrode material to 10:1, and use aluminum foil as the current collector, so that the electrochemical performance of the positive electrode sheet obtained is the best.

[0017] Specifically, the lithium salt of the lithium salt solution is lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, organic borate lithium, perfluoroalkyl sulfonate lithium, perfluoroalkyl sulfonate acyl methyl lithium, perfluoroalkyl sulfonate imide lithium, lithium bis oxalate borate, lithium difluoro oxalate borate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonyl) imide, organic lithium phosphate or organic lithium aluminate, and the molar concentration of the lithium salt is 0.8 to 1.2 mol / L. Preferably, lithium hexafluorophosphate is used as the lithium salt, and the molar concentration of the lithium salt is 1.0 mol / L.

[0018] Specifically, the solvent of the lithium salt solution is ethylene carbonate, dimethyl carbonate and diethyl carbonate, and the volume ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate is (0.9-1.1): (0.9-1.1): (0.9-1.1). Preferably, the volume ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate is 1:1:1.

[0019] In summary, the beneficial technical effects of the present invention are: the raw material composition for preparing carbon-based lithium-ion supercapacitors is simple, the preparation time is short, and while simplifying the steps, the theoretical capacity of carbon-based lithium-ion supercapacitors and the cycle stability of energy storage can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the explosion structure of the carbon-based lithium-ion supercapacitor according to Example 1 of the present invention;

[0021] Figure 2 is a schematic structural diagram of an electrospinning device for implementing the method of the present invention;

[0022] Figure 3 This is the XRD test diagram of the negative electrode material of Example 2 of the present invention;

[0023] Figure 4 is a SEM image of the negative electrode material of Example 2 of the present invention;

[0024] Figure 5 is an EDS image of the negative electrode material of Example 2 of the present invention;

[0025] Figure 6 is a charge and discharge curve diagram of the carbon-based lithium-ion supercapacitor of Example 2 of the present invention;

[0026] Figure 7 3 is a cycle stability diagram of the carbon-based lithium-ion supercapacitor of Example 2 of the present invention.

[0027] In the figure, 1. negative electrode shell; 2. nickel foam layer; 3. negative electrode plate; 4. diaphragm; 5. positive electrode plate; 6. positive electrode shell. DETAILED DESCRIPTION

[0028] In order to make the technical means, creative features, objectives and functions achieved by the present invention clearer and easier to understand, the present invention is further explained below in conjunction with the accompanying drawings and specific implementation methods. Example

[0029] Embodiment 1: A method for preparing a carbon-based lithium-ion supercapacitor disclosed in the present invention, comprising:

[0030] A process of mixing polyacrylonitrile, cobalt acetate tetrahydrate and graphene oxide in an N,N-dimethylformamide solution to prepare a precursor solution;

[0031] The process of subjecting the precursor solution to electrostatic spinning, pre-oxidation and carbonization treatment to obtain a negative electrode material; the process of subjecting the negative electrode material, polypropylene microporous membrane and lithium sheet to pre-lithium embedding treatment to obtain a negative electrode sheet;

[0032] The process of mixing activated carbon, conductive additives and binders and coating them on a current collector to prepare a positive electrode sheet;

[0033] The negative electrode plate is used as the first negative electrode, the positive electrode plate is used as the first positive electrode, a lithium salt solution is used as the electrolyte, and the first negative electrode and the first positive electrode are separated by a diaphragm, and then stamped and sealed to obtain a carbon-based lithium-ion supercapacitor.

[0034] Reference Figure 1 , is a carbon-based lithium-ion supercapacitor prepared by the method of the present invention, comprising a negative electrode shell 1, a nickel foam layer 2, a negative electrode sheet 3, a diaphragm 4, a positive electrode sheet 5 and a positive electrode shell 6 stacked in sequence from top to bottom. The negative electrode shell 1 is covered on the positive electrode shell 6, and a closed space is formed between the two to accommodate the nickel foam layer 2, the negative electrode sheet 3, the diaphragm 4, the positive electrode sheet 5 and the electrolyte.

[0035] Embodiment 2: A method for preparing a carbon-based lithium-ion supercapacitor disclosed in the present invention, which is different from Embodiment 1 in that it comprises the following steps:

[0036] S1: preparing an electrolyte, mixing ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1 to obtain an organic solvent, and then adding lithium hexafluorophosphate as a lithium salt to the organic solvent to obtain a 1.0 mol / L lithium salt solution;

[0037] S2: Prepare the precursor solution. First, add 1 g of polyacrylonitrile to 10 mL of N,N-dimethylformamide solution, and place in a constant temperature water bath at 50 °C until the polyacrylonitrile is fully dissolved. Then, add 0.2363 g of cobalt acetate tetrahydrate and continue stirring until it is fully dissolved. Then, add 0.7 mg of graphene oxide and continue stirring for 12 h, followed by ultrasonication for 30 min to obtain a precursor solution.

[0038] S3 electrospinning, first use Figure 2 The electrospinning apparatus shown electrospins the precursor solution and collects the solution using aluminum foil as a collector. During the electrospinning process, the distance between the discharge port of the electrospinning apparatus and the collector is controlled to be 15 cm, the injection rate of the electrospinning apparatus is 10 μL / min, the voltage is 15 kV, and the solution is dried and pressed to obtain a spinning disc; wherein, the spinning nozzle at the discharge port of the electrospinning apparatus is made of stainless steel, with an inner diameter of 0.6 mm, a sampling volume of 3 mL at a time, and the spinning nozzle is connected to a high-voltage DC power supply to obtain the above voltage;

[0039] S4 pre-oxidation and carbonization: the spinning disc is placed in a pre-oxidation device, and the temperature is uniformly increased to 225°C at a rate of 3.0°C / min, and then pre-oxidized for 6.0 hours to obtain a pre-oxidized disc. The pre-oxidized disc is then transferred to a carbonization device, and in a nitrogen protective atmosphere, the temperature is uniformly increased to 650°C at a rate of 5.0°C / min, and then carbonized for 2.0 hours to obtain a negative electrode material.

[0040] S5 pre-embeds lithium. In a dry environment filled with argon, the negative electrode material is first used as the second negative electrode, the lithium sheet is used as the second positive electrode, and the lithium salt solution is used as the electrolyte. The second negative electrode and the second positive electrode are separated by a polypropylene microporous membrane to form a closed button battery. The button battery is then discharged and charged 10 times in a cycle, and the discharge cut-off voltage is controlled to be 1.0V. Then, the negative electrode material pre-embedded with lithium is taken out to obtain a negative electrode sheet.

[0041] Prior to this, the highest and lowest voltages of the negative electrode material need to be tested. The voltage of the negative electrode material in this embodiment is between 0.01 and 3 V. During charging and discharging, the button battery is first discharged to 0.01 V and then charged to 3 V, and this cycle is repeated 10 times.

[0042] S6 prepares the positive electrode sheet, firstly adds activated carbon, conductive additive and binder into N-methylpyrrolidone solution, and controls the total amount of activated carbon, conductive additive and binder to the mass ratio of negative electrode material to 10:1, stirs and mixes to obtain positive electrode material, and then uses a scraper to coat the positive electrode material on the surface of the current collector, vacuum dries at 80°C for 20-30h, presses and cuts to obtain positive electrode sheet; the mass concentration ratio of activated carbon, conductive additive and binder is 8:1:1; wherein, the conductive additive is carbon black, the binder is polyvinylidene fluoride, and the current collector is aluminum foil;

[0043] S7 uses the negative electrode plate as the first negative electrode, the positive electrode plate as the first positive electrode, and a lithium salt solution as the electrolyte. The first negative electrode and the first positive electrode are separated by a diaphragm, and then stamped and sealed to obtain a carbon-based lithium-ion supercapacitor.

[0044] Embodiment 3: A method for preparing a carbon-based lithium-ion supercapacitor disclosed in the present invention, which is different from Embodiment 1 in that it comprises the following steps:

[0045] S1: preparing an electrolyte, stirring and mixing ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 0.9:1:1 to obtain an organic solvent, and then adding lithium hexafluorophosphate as a lithium salt to the organic solvent to obtain a 0.8 mol / L lithium salt solution;

[0046] S2: Prepare the precursor solution. First, add 1 g of polyacrylonitrile to 10 mL of N,N-dimethylformamide solution, and place in a constant temperature water bath at 55°C until the polyacrylonitrile is fully dissolved. Then, add 0.2300 g of cobalt acetate tetrahydrate and continue stirring until it is fully dissolved. Then, add 0.6 mg of graphene oxide and continue stirring for 10 h. Then, ultrasonicate for 25 min to obtain a precursor solution.

[0047] S3 electrospinning, first use an electrospinning apparatus to electrospin the precursor solution, and use aluminum foil as a collector to collect it. During the electrospinning process, the distance between the discharge port of the electrospinning apparatus and the collector is controlled to be 12 cm, the injection rate of the electrospinning apparatus is 9 μL / min, the voltage is 14 kV, and the spinning disc is dried and pressed to obtain a spinning disc; wherein, the spinning nozzle at the discharge port of the electrospinning apparatus is made of stainless steel, with an inner diameter of 0.6 mm, a sampling volume of 3 mL, and the spinning nozzle is connected to a high-voltage DC power supply to obtain the above voltage;

[0048] S4 pre-oxidation and carbonization: the spinning disc is placed in a pre-oxidation device, and the temperature is uniformly increased to 220°C at a rate of 2.5°C / min, and then pre-oxidized for 5.5 hours to obtain a pre-oxidized disc. The pre-oxidized disc is then transferred to a carbonization device, and in a nitrogen protective atmosphere, the temperature is uniformly increased to 645°C at a rate of 4.5°C / min, and then carbonized for 1.5 hours to obtain a negative electrode material.

[0049] S5 pre-embeds lithium. In a dry environment filled with argon, the negative electrode material is first used as the second negative electrode, the lithium sheet is used as the second positive electrode, and the lithium salt solution is used as the electrolyte. The second negative electrode and the second positive electrode are separated by a polypropylene microporous membrane to form a closed button battery. The button battery is then discharged and charged 8 times in a cycle, and the discharge cut-off voltage is controlled to be 0.5V. Then, the negative electrode material pre-embedded with lithium is taken out to obtain a negative electrode sheet.

[0050] S6 prepares the positive electrode sheet, firstly adds activated carbon, conductive additive and binder into N-methylpyrrolidone solution, and controls the total amount of activated carbon, conductive additive and binder to the mass ratio of negative electrode material to 1:1, stirs and mixes to obtain positive electrode material, and then uses a scraper to coat the positive electrode material on the surface of the current collector, vacuum dries at 95°C for 20-30h, presses and cuts to obtain positive electrode sheet; the mass concentration ratio of activated carbon, conductive additive and binder is 7:1:1; wherein, the conductive additive is carbon black, the binder is polyvinylidene fluoride, and the current collector is aluminum foil;

[0051] S7 uses the negative electrode plate as the first negative electrode, the positive electrode plate as the first positive electrode, and a lithium salt solution as the electrolyte. The first negative electrode and the first positive electrode are separated by a diaphragm, and then stamped and sealed to obtain a carbon-based lithium-ion supercapacitor.

[0052] Embodiment 4: A method for preparing a carbon-based lithium-ion supercapacitor disclosed in the present invention is different from Embodiment 1 in that it comprises the following steps:

[0053] S1: preparing an electrolyte by stirring and mixing ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:0.9:1.1 to obtain an organic solvent, and then adding lithium hexafluorophosphate as a lithium salt to the organic solvent to obtain a 1.2 mol / L lithium salt solution;

[0054] S2: Prepare the precursor solution. First, add 1 g of polyacrylonitrile to 10 mL of N,N-dimethylformamide solution, and place in a constant temperature water bath at 65°C until the polyacrylonitrile is fully dissolved. Then, add 0.2400 g of cobalt acetate tetrahydrate and continue stirring until it is fully dissolved. Then, add 0.8 mg of graphene oxide and continue stirring for 15 h. Then, ultrasonicate for 35 min to obtain the precursor solution.

[0055] S3 electrospinning, first use an electrospinning apparatus to electrospin the precursor solution, and use aluminum foil as a collector to collect it. During the electrospinning process, the distance between the discharge port of the electrospinning apparatus and the collector is controlled to be 18 cm, the injection rate of the electrospinning apparatus is 11 μL / min, the voltage is 16 kV, and the spinning disc is dried and pressed to obtain a spinning disc; wherein, the spinning nozzle at the discharge port of the electrospinning apparatus is made of stainless steel, with an inner diameter of 0.6 mm, a sampling volume of 3 mL, and the spinning nozzle is connected to a high-voltage DC power supply to obtain the above voltage;

[0056] S4 pre-oxidation and carbonization: put the spinning disc into the pre-oxidation equipment, heat it to 220-230°C at a constant speed of 3.5°C / min, and pre-oxidize it for 6.5h to obtain a pre-oxidized disc. Then transfer the pre-oxidized disc to the carbonization equipment, heat it to 665°C at a constant speed of 5.5°C / min under a nitrogen atmosphere, and carbonize it for 2.5h to obtain the negative electrode material.

[0057] S5 pre-embeds lithium. In a dry environment filled with argon, the negative electrode material is first used as the second negative electrode, the lithium sheet is used as the second positive electrode, and the lithium salt solution is used as the electrolyte. The second negative electrode and the second positive electrode are separated by a polypropylene microporous membrane to form a closed button battery. The button battery is then discharged and charged 12 times in a cycle, and the discharge cut-off voltage is controlled to be 1.5V. Then, the negative electrode material pre-embedded with lithium is taken out to obtain a negative electrode sheet.

[0058] S6 prepares the positive electrode sheet, firstly adds activated carbon, conductive additive and binder into N-methylpyrrolidone solution, and controls the total amount of activated carbon, conductive additive and binder to the mass ratio of negative electrode material to 8:1, stirs and mixes to obtain positive electrode material, and then uses a scraper to coat the positive electrode material on the surface of the current collector, vacuum dries at 75°C for 20-30h, presses and cuts to obtain positive electrode sheet; the mass concentration ratio of activated carbon, conductive additive and binder is 9:1:1; wherein, the conductive additive is carbon black, the binder is polyvinylidene fluoride, and the current collector is aluminum foil;

[0059] S7 uses the negative electrode plate as the first negative electrode, the positive electrode plate as the first positive electrode, and a lithium salt solution as the electrolyte. The first negative electrode and the first positive electrode are separated by a diaphragm, and then stamped and sealed to obtain a carbon-based lithium-ion supercapacitor.

[0060] Embodiment 5: A method for preparing a carbon-based lithium-ion supercapacitor disclosed in the present invention is different from Embodiment 1 in that it comprises the following steps:

[0061] S1: preparing an electrolyte, stirring and mixing ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1 to obtain an organic solvent, and then adding lithium hexafluorophosphate as a lithium salt to the organic solvent to obtain a 1.1 mol / L lithium salt solution;

[0062] S2: Prepare the precursor solution. First, add 1 g of polyacrylonitrile to 10 mL of N,N-dimethylformamide solution, keep in a constant temperature water bath at 58°C until the polyacrylonitrile is fully dissolved, then add 0.2358 g of cobalt acetate tetrahydrate, continue stirring until fully dissolved, then add 0.7 mg of graphene oxide, continue stirring for 13 h, and then ultrasonicate for 28 min to obtain a precursor solution.

[0063] S3 electrospinning, first use an electrospinning apparatus to electrospin the precursor solution, and use aluminum foil as a collector to collect it. During the electrospinning process, the distance between the discharge port of the electrospinning apparatus and the collector is controlled to be 12-18 cm, the injection rate of the electrospinning apparatus is 10 μL / min, the voltage is 15 kV, and the spinning disc is dried and pressed to obtain a spinning disc; wherein, the spinning nozzle at the discharge port of the electrospinning apparatus is made of stainless steel, with an inner diameter of 0.6 mm, a sampling volume of 3 mL, and the spinning nozzle is connected to a high-voltage DC power supply to obtain the above voltage;

[0064] S4 pre-oxidation and carbonization: the spinning disc is placed in a pre-oxidation device, and the temperature is uniformly increased to 225°C at a rate of 3.0°C / min, and then pre-oxidized for 6.0 hours to obtain a pre-oxidized disc. The pre-oxidized disc is then transferred to a carbonization device, and in a nitrogen protective atmosphere, the temperature is uniformly increased to 660°C at a rate of 5.0°C / min, and then carbonized for 2.0 hours to obtain a negative electrode material.

[0065] S5 pre-embeds lithium. In a dry environment filled with argon, the negative electrode material is first used as the second negative electrode, the lithium sheet is used as the second positive electrode, and the lithium salt solution is used as the electrolyte. The second negative electrode and the second positive electrode are separated by a polypropylene microporous membrane to form a closed button battery. The button battery is then discharged and charged 11 times in a cycle, and the discharge cut-off voltage is controlled to be 1.0V. Then, the negative electrode material pre-embedded with lithium is taken out to obtain a negative electrode sheet.

[0066] S6 prepares the positive electrode sheet, firstly adds activated carbon, conductive additive and binder into N-methylpyrrolidone solution, and controls the total amount of activated carbon, conductive additive and binder to the mass ratio of negative electrode material to 5:1, stirs and mixes to obtain positive electrode material, and then uses a scraper to coat the positive electrode material on the surface of the current collector, vacuum dries at 83°C for 20-30h, presses and cuts to obtain positive electrode sheet; the mass concentration ratio of activated carbon, conductive additive and binder is 8:1:1; wherein, the conductive additive is carbon black, the binder is polyvinylidene fluoride, and the current collector is aluminum foil;

[0067] S7 uses the negative electrode plate as the first negative electrode, the positive electrode plate as the first positive electrode, and a lithium salt solution as the electrolyte. The first negative electrode and the first positive electrode are separated by a diaphragm, and then stamped and sealed to obtain a carbon-based lithium-ion supercapacitor.

[0068] Performance testing

[0069] 1) The negative electrode material obtained in Example 2 was subjected to X-ray diffraction analysis, and the results were as follows: Figure 3 As shown. Figure 3 It can be concluded that the XRD spectrum of the negative electrode material prepared in Example 2 of the present invention corresponds to the diffraction peaks in the standard cards of carbon material and cobalt oxide, which proves the successful synthesis of cobalt oxide material. The synergistic effect of cobalt oxide material and carbon material jointly improves Li + The rapid transfer capability helps to achieve high capacity and cycle stability of the carbon-based lithium-ion supercapacitor prepared by the present invention.

[0070] 2) The negative electrode material obtained in Example 2 was scanned under a scanning electron microscope and subjected to dispersion spectrum analysis. The results are as follows: Figure 4 and Figure 5 As shown. Figure 4 and Figure 5 It can be concluded that the EDC graph shows that the negative electrode material is mainly composed of C, O and Co elements; the SEM graph shows that the cobalt oxide particles can be evenly covered on the carbon nanofibers, and the defect sites generated by the introduction of cobalt oxide and graphene can improve the Li + storage, thereby improving the electrochemical performance of the electrode material.

[0071] 3) The carbon-based lithium-ion supercapacitor obtained in Example 2 was subjected to a charge and discharge test, with a charge and discharge current of 0.5 A / g (active material) and a charge and discharge cut-off voltage of 0-3 V. The results are as follows: Figure 6 As shown. Figure 6 It can be concluded that the charge-discharge specific capacity can reach about 224 mAh / g, indicating that the carbon-based lithium-ion supercapacitor prepared by the method of the present invention has a higher storage capacity.

[0072] 4) The carbon-based lithium-ion supercapacitor obtained in Example 2 was subjected to a cycle stability test, and the cycles were 200, 400, 600, 800, and 1000 times, respectively, with a charge and discharge current of 0.5 A / g (active material). The results are as follows: Figure 7 As shown. Figure 7 It can be concluded that the capacity retention rate of the carbon-based lithium-ion supercapacitor is still about 88.7% after 1,000 cycles, showing good cycle performance.

[0073] In summary, the carbon-based lithium-ion supercapacitor prepared by the method of the present invention has a high theoretical capacity and cycle stability of energy storage. This is because the carbonized negative electrode material is mainly composed of carbon nanofibers, cobalt oxide and graphene oxide. The carbon nanofibers have a unique three-dimensional porous structure, a high specific surface area and excellent mechanical properties, and the graphene oxide is distributed from the edge of the sheet to the center in a hydrophilic to hydrophobic nature. It is wrapped on the surface of the carbon nanofiber, which can not only improve the conductivity and promote the rapid transmission of electrons, but also promote the dispersion of cobalt oxide in N, N-dimethylformamide solution, inhibit the agglomeration of cobalt oxide itself, so that cobalt oxide can be evenly compounded on graphene oxide / carbon nanofibers, so that the active edge of cobalt oxide is more fully exposed, and then after pre-lithium embedding treatment, the cycle stability of energy storage of the negative electrode can be improved; in addition, the activated carbon and the conductive additive can be cured on the current collector through the binder to give full play to its supercapacitor performance and achieve the improvement of energy storage performance.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a carbon-based lithium-ion supercapacitor, characterized in that: include, A process of mixing polyacrylonitrile, cobalt acetate tetrahydrate and graphene oxide in an N,N-dimethylformamide solution to prepare a precursor solution; The precursor solution is subjected to electrostatic spinning, pre-oxidation and carbonization treatment to obtain a negative electrode material; The negative electrode material, the polypropylene microporous membrane and the lithium sheet are subjected to a pre-lithium embedding treatment to prepare a negative electrode sheet; The process of mixing activated carbon, conductive additives and binders and coating them on a current collector to prepare a positive electrode sheet; The negative electrode plate is used as the first negative electrode, the positive electrode plate is used as the first positive electrode, a lithium salt solution is used as the electrolyte, and the first negative electrode and the first positive electrode are separated by a diaphragm, and then stamped and sealed to obtain the carbon-based lithium-ion supercapacitor; In the process of preparing the precursor solution, the mass concentration ratio of polyacrylonitrile, cobalt acetate tetrahydrate and graphene oxide is 1000: (230.0-240.0): (0.6-0.8); The process of preparing the precursor solution includes first adding polyacrylonitrile to N,N-dimethylformamide solution, placing in a constant temperature water bath at 55-65°C until the polyacrylonitrile is fully dissolved, then adding cobalt acetate tetrahydrate, continuing to stir until fully dissolved, then adding graphene oxide, continuing to stir for 10-15 hours, and then ultrasonicating for 25-35 minutes to obtain a precursor solution; The process of preparing the negative electrode material comprises: firstly electrostatically spinning a precursor solution by using an electrostatic spinning apparatus, collecting the precursor solution by using a collector, drying the precursor solution, and pressing the precursor solution into a sheet to obtain a spinning disc; then, the spinning disc is put into a pre-oxidation device, and the pre-oxidation device is pre-oxidized for 5.5 to 6.5 hours after the pre-oxidation disc is uniformly heated to 220 to 230° C. at a rate of 2.5 to 3.5° C. / min to obtain a pre-oxidized disc; then, the pre-oxidized disc is transferred to a carbonization device, and the pre-oxidized disc is carbonized for 1.5 to 2.5 hours after the pre-oxidized disc is uniformly heated to 645 to 665° C. at a rate of 4.5 to 5.5° C. / min under a nitrogen protective atmosphere to obtain a negative electrode material; During the electrospinning process, the distance between the discharge port of the electrospinning apparatus and the collector is controlled to be 12-18 cm, the injection rate of the electrospinning apparatus is 9-11 μL / min, and the voltage is 14-16 kV; The carbonized negative electrode material is mainly composed of carbon nanofibers, cobalt oxide and graphene oxide. The carbon nanofibers have a unique three-dimensional porous structure, and the graphene oxide is distributed from the edge to the center of the sheet in a hydrophilic to hydrophobic property. It is wrapped on the surface of the carbon nanofibers so that the cobalt oxide can be evenly compounded on the graphene oxide / carbon nanofibers, so that the active edge of the cobalt oxide is more fully exposed.

2. The method for preparing a carbon-based lithium-ion supercapacitor according to claim 1, characterized in that: The process of preparing the negative electrode plate comprises: in a dry environment filled with argon, first using the negative electrode material as the second negative electrode, the lithium sheet as the second positive electrode, and the lithium salt solution as the electrolyte, and the second negative electrode and the second positive electrode are separated by a polypropylene microporous membrane to form a closed button battery, and then cyclically discharging and charging the button battery 8 to 12 times, and controlling the discharge cut-off voltage to be 0.5 to 1.5V, and then taking out the pre-embedded lithium negative electrode material to obtain the negative electrode plate.

3. The method for preparing a carbon-based lithium-ion supercapacitor according to claim 1, characterized in that: In the process of preparing the positive electrode sheet, the mass concentration ratio of activated carbon, conductive additive and binder is (7-9):1:1; wherein the conductive additive is carbon black and the binder is polyvinylidene fluoride.

4. The method for preparing a carbon-based lithium-ion supercapacitor according to claim 3, characterized in that: The process for preparing the positive electrode sheet includes: firstly adding activated carbon, a conductive additive and a binder into an N-methylpyrrolidone solution, and controlling the mass ratio of the total amount of the activated carbon, the conductive additive and the binder to the mass of the negative electrode material to be (1-10):1, stirring and mixing to obtain the positive electrode material, and then coating the positive electrode material on the surface of the current collector with a scraper, vacuum drying at 75-95° C. for 20-30 hours, pressing and cutting to obtain the positive electrode sheet.

5. A method for preparing a carbon-based lithium-ion supercapacitor according to any one of claims 1 to 4, characterized in that: The lithium salt of the lithium salt solution is lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, organic lithium borate, lithium perfluoroalkyl sulfonate, lithium perfluoroalkyl sulfonate acyl methyl, lithium perfluoroalkyl sulfonate imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, organic lithium phosphate or organic lithium aluminate, and the molar concentration of the lithium salt is 0.8-1.2 mol / L.

6. A method for preparing a carbon-based lithium-ion supercapacitor according to any one of claims 1 to 4, characterized in that: The solvent of the lithium salt solution is ethylene carbonate, dimethyl carbonate and diethyl carbonate, and the volume ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate is (0.9-1.1): (0.9-1.1): (0.9-1.1).

Images