Electric energy storage system, graphene / carbon nanotube composite material, capacitor, secondary battery, preparation method and application

Abstract

The invention provides an electric energy storage system, a graphene / carbon nanotube composite material, a capacitor, a secondary battery, a preparation method and an application. The electric energy storage system comprises a capacitor, the capacitor comprises a positive plate, the positive plate comprises a graphene / carbon nanotube composite material, the graphene / carbon nanotube composite material comprises a three-dimensional network skeleton, the three-dimensional network skeleton comprises a carbon matrix and doping elements, the carbon matrix is formed by compounding graphene and a carbon nanotube, and the doping elements are doped with the carbon matrix. The doping elements comprise a nitrogen element and a sulfur element, and holes are formed in the surface of the three-dimensional network framework. The electric energy storage system has excellent electrochemical performance, can release high energy density under high power density, and is long in cycle life.

Description

Technical Field

[0001] The present invention relates to the field of electric energy storage technology and secondary batteries, and specifically to electric energy storage systems, graphene / carbon nanotube composite materials, capacitors, secondary batteries, preparation methods and applications, and further to electric energy storage systems, graphene / carbon nanotube composite materials and preparation methods and applications, capacitors and preparation methods, and secondary batteries. Background Art

[0002] As a new type of electrical energy storage device, lithium-ion capacitors are designed with battery-type negative electrode materials with high energy density and capacitor-type positive electrode materials with high power density. The capacitor-type positive electrode mainly relies on the anions in the electrolyte (such as PF6 - ) forms a double layer effect with the cations in the positive electrode to achieve energy conversion and storage; the battery type negative electrode is mainly Li in the electrolyte + Embedded into battery-type negative electrode materials, energy conversion and storage are achieved during repeated lithium insertion / deintercalation processes.

[0003] Lithium-ion capacitors have a wide range of applications in energy storage fields such as portable electronic products, electric vehicles, medical equipment, and aerospace due to their high energy-high power density characteristics. However, current lithium-ion capacitors cannot meet the needs of high-energy, high-power energy storage devices in life. Summary of the invention

[0004] In response to the technical problem that existing electric energy storage devices cannot meet the demand for high-energy, high-power energy storage devices in life, the present application provides an electric energy storage system, a graphene / carbon nanotube composite material, a capacitor, a secondary battery, a preparation method and an application.

[0005] In a first aspect, in some embodiments, an energy storage system is provided, comprising a capacitor, wherein the capacitor comprises a positive electrode plate, wherein the positive electrode plate comprises a graphene / carbon nanotube composite material, wherein the graphene / carbon nanotube composite material comprises a three-dimensional network skeleton, wherein the three-dimensional network skeleton comprises a carbon matrix and doping elements, wherein the carbon matrix is ​​composited by graphene and carbon nanotubes, wherein the doping elements comprise nitrogen and sulfur, and wherein the surface of the three-dimensional network skeleton has holes.

[0006] In some embodiments, the electric energy storage system satisfies one or more of the following features:

[0007] The graphene / carbon nanotube composite material is a nanomaterial;

[0008] The pore size on the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material is 1nm~50nm;

[0009] The pore volume on the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material is 0.3 cm 3 / g~0.5cm 3 / g;

[0010] The specific surface area of ​​the graphene / carbon nanotube composite material is 600 m 2 / g~2300m 2 / g;

[0011] The doping amount of the nitrogen element in the graphene / carbon nanotube composite material is 5wt% to 10wt%;

[0012] The doping amount of the sulfur element in the graphene / carbon nanotube composite material is 1wt% to 3wt%;

[0013] The capacitor is a carbon capacitor;

[0014] The capacitor is a lithium ion capacitor;

[0015] The electrical energy storage system includes at least one of a portable electronic product, an electric vehicle, a medical device, and an aerospace energy storage product.

[0016] In a second aspect, in some embodiments, a graphene / carbon nanotube composite material is provided, wherein the graphene / carbon nanotube composite material includes a three-dimensional network skeleton, wherein the three-dimensional network skeleton includes a carbon matrix and doping elements, wherein the carbon matrix is ​​composited by graphene and carbon nanotubes, wherein the doping elements include nitrogen and sulfur, and wherein the surface of the three-dimensional network skeleton has holes.

[0017] In some embodiments, the graphene / carbon nanotube composite material satisfies one or more of the following characteristics:

[0018] The graphene / carbon nanotube composite material is a nanomaterial;

[0019] The pore size on the surface of the three-dimensional network skeleton is 1nm~50nm;

[0020] The pore volume of the surface of the three-dimensional network skeleton is 0.3 cm 3 / g~0.5cm 3 / g;

[0021] The specific surface area of ​​the graphene / carbon nanotube composite material is 600 m 2 / g~2300m 2 / g;

[0022] The doping amount of the nitrogen element in the graphene / carbon nanotube composite material is 5wt% to 10wt%;

[0023] The doping amount of the sulfur element in the graphene / carbon nanotube composite material is 1wt% to 3wt%;

[0024] The diameter of the carbon nanotubes is 10nm to 20nm;

[0025] The carbon nanotubes have a tube length of 5 μm to 15 μm;

[0026] The carbon nanotubes are multi-walled carbon nanotubes;

[0027] The graphene is multi-layer graphene.

[0028] In a third aspect, in some embodiments, a method for preparing a graphene / carbon nanotube composite material is provided, comprising the following steps:

[0029] Mixing a first dispersion containing graphene oxide, carbon nanotubes and water with potassium hydroxide, etching the graphene oxide and the carbon nanotubes under dispersion conditions, performing solid-liquid separation, and washing to prepare a second dispersion containing etching products;

[0030] The second dispersion is mixed with thiourea to perform a hydrothermal synthesis reaction to prepare a nitrogen-sulfur doped composite material, which is then washed with water, freeze-dried, and heat-treated in an inert atmosphere to obtain the graphene / carbon nanotube composite material.

[0031] In some embodiments, the method for preparing the graphene / carbon nanotube composite material satisfies one or more of the following characteristics:

[0032] In the first dispersion, the mass ratio of the graphene oxide to the carbon nanotubes is 102:(25-51) based on the feed amount;

[0033] In the step of mixing the first dispersion with potassium hydroxide, the ratio of the total mass of the graphene oxide and the carbon nanotubes to the mass of potassium hydroxide is 1:(3-5) based on the feeding amount;

[0034] The step of mixing the first dispersion liquid with potassium hydroxide is achieved by: placing potassium hydroxide in the first dispersion liquid and stirring for 4 hours to 6 hours;

[0035] In the step of mixing the second dispersion with thiourea, the ratio of the total mass of the graphene oxide and the carbon nanotubes in the first dispersion to the mass of the thiourea is (3-5):1, based on the feeding amount;

[0036] The temperature for carrying out the hydrothermal synthesis reaction is 120° C. to 160° C., and the time for carrying out the hydrothermal synthesis reaction is 8 h to 12 h;

[0037] The freeze-drying temperature is -45°C to -20°C, and the freeze-drying time is 24h to 36h;

[0038] The inert atmosphere is a nitrogen atmosphere;

[0039] The temperature of the heat treatment is 700°C to 800°C;

[0040] The heat treatment is performed for 2 to 3 hours.

[0041] In a fourth aspect, in some embodiments, there is provided the use of the graphene / carbon nanotube composite material or the graphene / carbon nanotube composite material obtained by the preparation method in preparing an electrode sheet in a capacitor or a secondary battery; wherein the electrode sheet is a positive electrode sheet or a negative electrode sheet.

[0042] In a fifth aspect, in some embodiments, a capacitor is provided, comprising a positive electrode sheet and a negative electrode sheet,

[0043] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, a first conductive agent and a first binder, and the positive electrode active material comprises at least one of the graphene / carbon nanotube composite material and the graphene / carbon nanotube composite material obtained by the preparation method;

[0044] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a second conductive agent and a second binder; the negative electrode active material comprises a negative electrode composite material pre-embedded with lithium, and the negative electrode composite material in the negative electrode composite material pre-embedded with lithium satisfies one or more of the following characteristics:

[0045] Including the graphene / carbon nanotube composite material;

[0046] A graphene / carbon nanotube composite material obtained by the preparation method;

[0047] It comprises a three-dimensional carbon skeleton, which is composited by graphene and carbon nanotubes, and has holes on the surface of the three-dimensional carbon skeleton.

[0048] In some embodiments, the capacitor satisfies one or more of the following characteristics:

[0049] The capacitor is a carbon capacitor;

[0050] The capacitor is a lithium ion capacitor;

[0051] The capacitor is a carbon-based lithium-ion capacitor;

[0052] In the capacitor, the mass ratio of the positive electrode active material, the first conductive agent and the first binder is (78-82):(9-11):(9-11);

[0053] In the capacitor, the mass ratio of the negative electrode active material, the second conductive agent and the second binder is (78-82):(9-11):(9-11);

[0054] In the capacitor, the positive electrode current collector is aluminum foil;

[0055] In the capacitor, the negative electrode current collector is copper foil;

[0056] In the capacitor, the mass ratio of the negative electrode active material to the positive electrode active material is 1:(3-4).

[0057] In a sixth aspect, in some embodiments, a method for preparing a capacitor is provided, comprising assembling a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator to prepare a capacitor; wherein:

[0058] Using at least one of the graphene / carbon nanotube composite material and the graphene / carbon nanotube composite material prepared by the preparation method as a positive electrode active material to prepare a positive electrode sheet;

[0059] One or more of the following composite materials are used as the negative electrode composite material to prepare the negative electrode sheet:

[0060] The graphene / carbon nanotube composite material;

[0061] The graphene / carbon nanotube composite material obtained by the preparation method;

[0062] A composite material comprising a three-dimensional carbon skeleton, wherein the three-dimensional carbon skeleton is composited with graphene and carbon nanotubes, and the surface of the three-dimensional carbon skeleton has holes;

[0063] The steps of preparing the positive electrode sheet include: mixing the positive electrode active material, the first conductive agent and a glue solution containing a first binder to prepare a first colloid; coating the first colloid on at least one side surface of the positive electrode current collector, and drying to prepare the positive electrode sheet;

[0064] The steps of preparing the negative electrode sheet include: mixing the negative electrode composite material, a second conductive agent and a glue solution containing a second binder to prepare a second colloid; coating the second colloid on at least one side surface of the negative electrode current collector, drying, and preparing a lithium-embedded electrode sheet; electrochemically pre-embed lithium in the lithium-embedded electrode sheet to prepare the negative electrode sheet; the step of electrochemically pre-embed lithium includes: cycling the lithium-embedded electrode sheet with a lithium sheet for 5 to 10 times at a current density of 0.2 A / g in an electrochemical window of 0.01 V to 3 V.

[0065] In a seventh aspect, in some embodiments, a secondary battery is provided, comprising a positive electrode sheet and a negative electrode sheet,

[0066] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, a first conductive agent and a first binder, and the positive electrode active material comprises at least one of the graphene / carbon nanotube composite material and the graphene / carbon nanotube composite material obtained by the preparation method;

[0067] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a second conductive agent and a second binder; the negative electrode active material comprises a negative electrode composite material pre-embedded with lithium, and the negative electrode composite material in the negative electrode composite material pre-embedded with lithium satisfies one or more of the following characteristics:

[0068] Including the graphene / carbon nanotube composite material;

[0069] A graphene / carbon nanotube composite material obtained by the preparation method;

[0070] It comprises a three-dimensional carbon skeleton, which is composited by graphene and carbon nanotubes, and has holes on the surface of the three-dimensional carbon skeleton.

[0071] The above-mentioned electric energy storage system includes a high-performance capacitor, the positive electrode of the capacitor includes a graphene / carbon nanotube composite material, and the graphene / carbon nanotube composite material includes a three-dimensional network skeleton composed of graphene and carbon nanotubes. The composite skeleton assembled from two-dimensional sheet graphene and one-dimensional carbon nanotubes can maintain a stable three-dimensional network skeleton structure by utilizing hydrogen bonds, functional group forces and conjugated π bonds, and the local current density is reduced, and the polarization is reduced, so that the graphene / carbon nanotube composite material has ultra-high rate characteristics. Furthermore, the three-dimensional network skeleton is also doped with nitrogen and sulfur elements, and the surface of the three-dimensional network skeleton has holes and increases defects. The material has a high specific surface area, so that the graphene / carbon nanotube composite material, the positive electrode and the capacitor can have a high specific capacitance.

[0072] Furthermore, the negative electrode of the capacitor includes a three-dimensional carbon skeleton or a three-dimensional network skeleton, and after pre-embedded lithium, has high specific capacity and high initial efficiency. The capacitor assembled from the above-mentioned positive electrode with high specific capacitance and the negative electrode with high rate performance can have significantly improved rate and cycle performance, which can provide new design ideas for the industry pain points of low specific capacitance of the positive electrode of the lithium ion capacitor and mismatch between the positive electrode and the negative electrode kinetics.

[0073] The preparation method of the graphene / carbon nanotube composite material provided above can use graphene oxide and carbon nanotubes as raw materials, and utilize etching treatment technology, N / S doping technology, hydrothermal synthesis reaction, freeze drying and heat treatment technology, and introduce surface holes through etching, nitrogen and sulfur doping and reduction and deoxygenation treatment to form a three-dimensional network skeleton with surface hole defects and N / S element doping, which can increase the specific surface area of ​​the material, reduce the local current density, reduce polarization, and give the material ultra-high rate performance. In addition, after reduction and deoxygenation treatment, a large number of oxygen-containing groups can be eliminated, which is beneficial to further the specific capacitance of the material. The method is simple and easy to achieve industrial-scale production.

[0074] The electric energy storage system including the aforementioned graphene / carbon nanotube composite material, the positive electrode sheet and the capacitor has excellent electrochemical performance, can release a large energy density at a high power density, and has a long cycle life. DETAILED DESCRIPTION

[0075] For ease of understanding of the application, the application will be described more fully below with reference to some embodiments and examples. The application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the application more thorough and comprehensive.

[0076] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0077] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0078] In the present application, "multiple", "multiple", "multiple" and the like, unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0079] The terms "combination thereof", "any combination thereof", "any combination thereof" and the like used in this application include all suitable combinations of any two or more of the listed items.

[0080] In this application, the "suitable" mentioned in "suitable combination", "suitable method", "any suitable method", etc. is based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0081] In the present invention, in the "first aspect", "second aspect", "third aspect", "fourth aspect", etc., the terms "first", "second", "third", "fourth", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0082] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0083] In the present application, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges included therein.

[0084] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0085] In the present application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0086] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the invention purpose and / or technical solution of this application, the cited documents involved in this application are cited with all contents and all purposes. When the cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When the cited documents are involved in this application, the examples and preferred methods of the cited relevant technical features can also be incorporated into this application as references, but are limited to the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be modified adaptively according to the description of this application.

[0087] In a specific embodiment, an electric energy storage system is provided, including a capacitor, wherein the capacitor includes a positive electrode plate, the positive electrode plate includes a graphene / carbon nanotube composite material, the graphene / carbon nanotube composite material includes a three-dimensional network skeleton, the three-dimensional network skeleton includes a carbon matrix and doping elements, the carbon matrix is ​​composited by graphene and carbon nanotubes, the doping elements include nitrogen and sulfur, and the surface of the three-dimensional network skeleton has holes.

[0088] In a specific embodiment, the graphene / carbon nanotube composite material in the electric energy storage system is a nanomaterial.

[0089] In a specific embodiment, the pore size on the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material in the electric energy storage system is 1nm~50nm, for example, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm or a range selected from any two of the foregoing values.

[0090] In a specific embodiment, the pore volume of the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material in the electric energy storage system is 0.3 cm 3 / g~0.5cm 3 / g, for example, 0.3 cm 3 / g,0.4cm 3 / g,0.5cm 3 / g or a range selected from any two of the aforementioned values.

[0091] In a specific embodiment, the specific surface area of ​​the graphene / carbon nanotube composite material in the electric energy storage system is 600m 2 / g~2300m 2 / g, for example, 600m 2 / g,700m 2 / g,800m2 / g,900m 2 / g,1000m 2 / g,1100m 2 / g,1200m 2 / g,1300m 2 / g,1400m 2 / g,1500m 2 / g,1600m 2 / g,1700m 2 / g,1800m 2 / g,1900m 2 / g,2000m 2 / g,2100m 2 / g,2200m 2 / g,2300m 2 / g or a range selected from any two of the aforementioned values.

[0092] In a specific embodiment, the doping amount of the nitrogen element in the graphene / carbon nanotube composite material in the electric energy storage system is 5wt%~10wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% or a range selected from any two of the foregoing values.

[0093] In a specific embodiment, the doping amount of the sulfur element in the graphene / carbon nanotube composite material in the electric energy storage system is 1wt%~3wt%, for example, 1wt%, 2wt%, 3wt% or a range selected from any two of the foregoing values.

[0094] In a specific implementation, the capacitor in the electric energy storage system is a carbon-based capacitor.

[0095] In a specific implementation, the capacitor in the electric energy storage system is a lithium-ion capacitor.

[0096] In a specific embodiment, the electrical energy storage system includes at least one of a portable electronic product, an electric vehicle, a medical device, and an aerospace energy storage product.

[0097] In a specific embodiment, a graphene / carbon nanotube composite material is provided, wherein the graphene / carbon nanotube composite material includes a three-dimensional network skeleton, wherein the three-dimensional network skeleton includes a carbon matrix and doping elements, wherein the carbon matrix is ​​composited by graphene and carbon nanotubes, wherein the doping elements include nitrogen and sulfur, and wherein the surface of the three-dimensional network skeleton has holes.

[0098] In a specific embodiment, the graphene / carbon nanotube composite material is a nanomaterial.

[0099] In a specific embodiment, the pore size on the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material is 1nm~50nm, for example, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm or a range selected from any two of the foregoing values.

[0100] In a specific embodiment, the pore volume of the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material is 0.3 cm 3 / g~0.5cm 3 / g, for example, 0.3 cm 3 / g,0.4cm 3 / g,0.5cm 3 / g or a range selected from any two of the aforementioned values.

[0101] In a specific embodiment, the specific surface area of ​​the graphene / carbon nanotube composite material is 600 m 2 / g~2300m 2 / g, for example, 600m 2 / g,700m 2 / g,800m 2 / g,900m 2 / g,1000m 2 / g,1100m 2 / g,1200m 2 / g,1300m 2 / g,1400m 2 / g,1500m 2 / g,1600m 2 / g,1700m 2 / g,1800m 2 / g,1900m 2 / g,2000m 2 / g,2100m 2 / g,2200m 2 / g,2300m 2 / g or a range selected from any two of the aforementioned values.

[0102] In a specific embodiment, the doping amount of the nitrogen element in the graphene / carbon nanotube composite material is 5wt%~10wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% or a range selected from any two of the foregoing values.

[0103] In a specific embodiment, the doping amount of the sulfur element in the graphene / carbon nanotube composite material is 1wt%~3wt%, for example, 1wt%, 2wt%, 3wt% or a range selected from any two of the foregoing values.

[0104] In a specific embodiment, the diameter of the carbon nanotubes in the graphene / carbon nanotube composite material is 10 nm to 20 nm, for example, 10 nm, 15 nm, 20 nm or a range selected from any two of the foregoing values.

[0105] In a specific embodiment, the carbon nanotubes in the graphene / carbon nanotube composite material have a tube length of 5 μm to 15 μm, for example, 5 μm, 10 μm, 15 μm or a range selected from any two of the foregoing values.

[0106] In a specific embodiment, the carbon nanotubes in the graphene / carbon nanotube composite material are multi-walled carbon nanotubes.

[0107] In a specific embodiment, the graphene in the graphene / carbon nanotube composite material is multilayer graphene.

[0108] The provided graphene / carbon nanotube composite material, graphene and carbon nanotubes are interwoven to form a three-dimensional conductive network, which is modified by adding defects, N, S dual doping and eliminating oxygen-containing groups. The provided graphene / carbon nanotube composite material is applied to positive electrode materials, has a higher specific capacitance, and can increase the energy density of lithium ion capacitors.

[0109] In a specific embodiment, a method for preparing a graphene / carbon nanotube composite material is provided, comprising the following steps:

[0110] S100: mixing a first dispersion liquid containing graphene oxide, carbon nanotubes and water with potassium hydroxide, and etching the graphene oxide and the carbon nanotubes under dispersion conditions;

[0111] S200: solid-liquid separation, washing, and preparing a second dispersion containing the etching product;

[0112] S300: mixing the second dispersion with thiourea;

[0113] S400: performing a hydrothermal synthesis reaction to prepare a nitrogen-sulfur doped composite material;

[0114] S500: washing with water, freeze drying, and heat treating in an inert atmosphere to obtain the graphene / carbon nanotube composite material.

[0115] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, in step S100, in the first dispersion, based on the amount of feed, the mass ratio of the graphene oxide to the carbon nanotubes is 102:(25~51), for example, 102:25, 102:30, 102:35, 102:40, 102:45, 102:50, 102:51 or a range selected from any two of the foregoing ratios.

[0116] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, in step S100, in the step of mixing the first dispersion with potassium hydroxide, the ratio of the total mass of the graphene oxide and the carbon nanotubes to the mass of potassium hydroxide is 1:(3~5) based on the feeding amount, for example, 1:3, 1:4, 1:5 or a range selected from any two of the foregoing ratios.

[0117] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, in step S100, the step of mixing the first dispersion with potassium hydroxide is achieved by placing potassium hydroxide in the first dispersion and stirring for 4h to 6h, for example, 4h, 5h, 6h.

[0118] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, in step S300, in the step of mixing the second dispersion with thiourea, the ratio of the total mass of the graphene oxide and the carbon nanotubes in the first dispersion to the mass of thiourea is (3~5):1, for example, 3:1, 4:1, 5:1 or a range selected from any two of the foregoing ratios.

[0119] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, in step S400, the temperature for the hydrothermal synthesis reaction is 120°C to 160°C, for example, 120°C, 130°C, 140°C, 150°C, 160°C or a range selected from any two of the foregoing numerical values; the time for the hydrothermal synthesis reaction is 8h to 12h, for example, 8h, 9h, 10h, 11h, 12h or a range selected from any two of the foregoing numerical values.

[0120] The hydrothermal method is used to prepare the three-dimensional graphene / carbon nanotube macroscopic body, which can eliminate the oxygen-containing functional groups of graphene oxide and carbon nanotubes, which is beneficial to improving the material's specific capacitance. The two-dimensional graphene sheets and one-dimensional carbon nanotubes are assembled into a macroscopic three-dimensional structure using hydrogen bonds, functional group forces and conjugated π bonds. The obtained graphene / carbon nanotube composite material is used as a positive electrode material, which can increase the specific capacitance of the positive electrode material.

[0121] In a specific embodiment, the preparation method of the graphene / carbon nanotube composite material, the freeze-drying temperature is -45°C to -20°C, for example, -45°C, -40°C, -35°C, -30°C, -25°C, -20°C or a range selected from any two of the foregoing numerical values, and the freeze-drying time is 24h to 36h, for example, 24h, 25h, 26h, 27h, 28h, 29h, 30h, 31h, 32h, 33h, 34h, 35h, 36h or a range selected from any two of the foregoing numerical values.

[0122] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, the inert atmosphere is a nitrogen atmosphere.

[0123] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, the temperature for the heat treatment is 700°C to 800°C.

[0124] In a specific embodiment, in the method for preparing the graphene / carbon nanotube composite material, the heat treatment is performed for 2 hours to 3 hours.

[0125] The preparation method provided adopts freeze-drying technology and heat treatment technology to realize the preparation of three-dimensional nanomaterials, which has the following advantages: (1) maintaining the three-dimensional structure of graphene / carbon nanotubes, increasing the specific surface area of ​​the material, reducing the local current density, reducing polarization, and making the material have ultra-high rate characteristics; (2) eliminating residual oxygen-containing groups in the material and increasing the specific capacitance of the material.

[0126] In a specific embodiment, there is provided an application of the graphene / carbon nanotube composite material or the graphene / carbon nanotube composite material obtained by the preparation method in preparing an electrode sheet in a capacitor or a secondary battery; wherein the electrode sheet is a positive electrode sheet or a negative electrode sheet.

[0127] In a specific embodiment, a capacitor is provided, comprising a positive electrode sheet and a negative electrode sheet.

[0128] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, a first conductive agent and a first binder, and the positive electrode active material comprises at least one of the graphene / carbon nanotube composite material and the graphene / carbon nanotube composite material obtained by the preparation method;

[0129] In a specific embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, a second conductive agent and a second binder; the negative electrode active material includes a negative electrode composite material pre-embedded with lithium.

[0130] In a specific embodiment, the negative electrode composite material in the pre-lithium embedded negative electrode composite material used in the capacitor includes the graphene / carbon nanotube composite material.

[0131] In a specific embodiment, the negative electrode composite material in the pre-lithium embedded negative electrode composite material used in the capacitor includes the graphene / carbon nanotube composite material obtained by the preparation method.

[0132] In a specific embodiment, the negative electrode composite material in the pre-lithium embedded negative electrode composite material used in the capacitor includes a three-dimensional carbon skeleton, the three-dimensional carbon skeleton is composited by graphene and carbon nanotubes, and the surface of the three-dimensional carbon skeleton has holes.

[0133] In a specific embodiment, the preparation method of the negative electrode composite material in the negative electrode composite material pre-embedded with lithium used in the capacitor can be prepared by the steps including the aforementioned S100, S200, S300, S400 and S500. Specifically, in the method for preparing the negative electrode composite material, the step S300 may be included or excluded, that is, nitrogen and sulfur doping may be included or excluded.

[0134] In a specific embodiment, the capacitor is a carbon-based capacitor.

[0135] In a specific embodiment, the capacitor is a lithium ion capacitor.

[0136] In a specific embodiment, the capacitor is a carbon-based lithium-ion capacitor.

[0137] In a specific embodiment, the capacitor further comprises a separator and an electrolyte between the positive electrode and the negative electrode.

[0138] In a specific embodiment, the separator can be one of a polyethylene microporous membrane, a polypropylene microporous membrane, a polyethylene polypropylene composite membrane, an inorganic ceramic membrane, a cellulose separator and a non-woven fabric separator.

[0139] In a specific embodiment, the electrolyte is an electrolyte prepared by a lithium ion electrolyte salt and a non-aqueous organic solvent; the lithium ion electrolyte salt in the electrolyte is at least one of lithium perchlorate LiClO4, lithium tetrafluoroborate LiBF4, lithium hexafluorophosphate LiPF6, lithium trifluoromethanesulfonate LiCF3SO3, and lithium hexafluoroarsenate LiAsF6; the non-aqueous organic solvent in the electrolyte is, for example, one or more of dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, ethylene sulfite, propylene sulfite, butylene carbonate, γ-butyrolactone, methyl vinyl carbonate, methyl propyl carbonate, ethyl acetate or acetonitrile.

[0140] In some embodiments of the capacitor, the positive electrode is mainly based on the anions in the electrolyte (such as PF6 - ) forms a double layer effect with the cations in the positive electrode to achieve energy conversion and storage; the negative electrode is mainly Li in the electrolyte + Embedded into the negative electrode active material, energy conversion and storage are achieved during repeated lithium insertion / delithiation.

[0141] In a specific embodiment, in the capacitor, the mass ratio of the positive electrode active material, the first conductive agent and the first binder is (78~82):(9~11):(9~11), for example, 78:9:9, 78:11:11, 80:10:10, 80:9:11, 82:9:10, 82:11:11 or a range selected from any two of the foregoing ratios.

[0142] In a specific embodiment, in the capacitor, the mass ratio of the negative electrode active material, the second conductive agent and the second binder is (78~82):(9~11):(9~11), for example, 78:9:9, 78:11:11, 80:10:10, 80:9:11, 82:9:10, 82:11:11 or a range selected from any two of the foregoing ratios.

[0143] In a specific embodiment, the first conductive agent and the second conductive agent are independently one or more of acetylene black, conductive carbon black and carbon nanotubes.

[0144] In a specific embodiment, the first binder and the second binder are independently polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE).

[0145] In a specific embodiment, in the capacitor, the positive electrode current collector is aluminum foil.

[0146] In a specific embodiment, in the capacitor, the negative electrode current collector is copper foil.

[0147] In a specific embodiment, in the capacitor, the mass ratio of the negative electrode active material to the positive electrode active material is 1:(3-4).

[0148] In a specific embodiment, a method for preparing a capacitor is provided, comprising assembling a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator to prepare a capacitor.

[0149] In a specific embodiment, at least one of the graphene / carbon nanotube composite material and the graphene / carbon nanotube composite material prepared by the preparation method is used as a positive electrode active material to prepare a positive electrode sheet.

[0150] In a specific embodiment, the steps of preparing the positive electrode sheet include: mixing the positive electrode active material, the first conductive agent and a glue solution containing a first binder to prepare a first colloid; coating the first colloid on at least one side surface of the positive electrode collector, and drying to prepare the positive electrode sheet.

[0151] In a specific embodiment, the graphene / carbon nanotube composite material is used as the negative electrode composite material to prepare a negative electrode sheet. Specifically, the graphene / carbon nanotube composite material includes a three-dimensional network skeleton, the three-dimensional network skeleton includes a carbon matrix and a doping element, the carbon matrix is ​​composited by graphene and carbon nanotubes, the doping element includes nitrogen and sulfur, and the surface of the three-dimensional network skeleton has holes.

[0152] In a specific embodiment, the graphene / carbon nanotube composite material obtained by the preparation method is used as a negative electrode composite material to prepare a negative electrode sheet.

[0153] In a specific embodiment, the negative electrode composite material used to prepare the negative electrode sheet includes a three-dimensional carbon skeleton, the three-dimensional carbon skeleton is composited by graphene and carbon nanotubes, and the surface of the three-dimensional carbon skeleton has holes.

[0154] In a specific embodiment, the method for preparing the negative electrode composite material comprises the following steps:

[0155] S100: mixing a first dispersion liquid containing graphene oxide, carbon nanotubes and water with potassium hydroxide, and etching the graphene oxide and the carbon nanotubes under dispersion conditions;

[0156] S200: solid-liquid separation, washing, and preparing a second dispersion containing the etching product;

[0157] S300: mixing the second dispersion with thiourea;

[0158] S400: performing a hydrothermal synthesis reaction to prepare a nitrogen-sulfur doped composite material;

[0159] S500: washing with water, freeze drying, and heat treating in an inert atmosphere to obtain a graphene / carbon nanotube composite material. The obtained graphene / carbon nanotube composite material can be used as a negative electrode composite material.

[0160] In a specific embodiment, the method for preparing the negative electrode composite material comprises the following steps:

[0161] S100: mixing a first dispersion liquid containing graphene oxide, carbon nanotubes and water with potassium hydroxide, and etching the graphene oxide and the carbon nanotubes under dispersion conditions;

[0162] S200: solid-liquid separation, washing, and preparing a second dispersion containing the etching product;

[0163] S400: performing a hydrothermal synthesis reaction;

[0164] S500: washing with water, freeze drying, and heat treating in an inert atmosphere to obtain a graphene / carbon nanotube composite material. The obtained graphene / carbon nanotube composite material can be used as a negative electrode composite material.

[0165] In a specific embodiment, the steps of preparing the negative electrode sheet include:

[0166] The negative electrode composite material, the second conductive agent and the glue containing the second binder are mixed to prepare a second colloid; the second colloid is coated on at least one side surface of the negative electrode current collector, and dried to prepare a lithium-embedded electrode sheet; the lithium-embedded electrode sheet is electrochemically pre-embedded with lithium to prepare the negative electrode sheet; the step of electrochemical pre-embedded lithium includes: cycling the lithium-embedded electrode sheet with a lithium sheet for 5 to 10 times at a current density of 0.2 A / g in an electrochemical window of 0.01 V to 3 V.

[0167] It is well known to those skilled in the art that a capacitor comprises a separator and an electrolyte between a positive electrode and a negative electrode.

[0168] In a specific embodiment, the separator can be one of a polyethylene microporous membrane, a polypropylene microporous membrane, a polyethylene polypropylene composite membrane, an inorganic ceramic membrane, a cellulose separator and a non-woven fabric separator.

[0169] In a specific embodiment, the electrolyte is an electrolyte prepared by a lithium ion electrolyte salt and a non-aqueous organic solvent; the lithium ion electrolyte salt in the electrolyte is at least one of lithium perchlorate LiClO4, lithium tetrafluoroborate LiBF4, lithium hexafluorophosphate LiPF6, lithium trifluoromethanesulfonate LiCF3SO3, and lithium hexafluoroarsenate LiAsF6; the non-aqueous organic solvent in the electrolyte is, for example, one or more of dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, ethylene sulfite, propylene sulfite, butylene carbonate, γ-butyrolactone, methyl vinyl carbonate, methyl propyl carbonate, ethyl acetate or acetonitrile.

[0170] In a specific embodiment, an electric energy storage system is provided, which includes at least one of the graphene / carbon nanotube composite material, the graphene / carbon nanotube composite material obtained by the preparation method, the capacitor, and the capacitor prepared by the preparation method.

[0171] In a specific embodiment, a secondary battery is provided, comprising a positive electrode sheet and a negative electrode sheet.

[0172] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, a first conductive agent and a first binder, and the positive electrode active material comprises at least one of the graphene / carbon nanotube composite material and the graphene / carbon nanotube composite material obtained by the preparation method;

[0173] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a second conductive agent and a second binder; and the negative electrode active material comprises a negative electrode composite material pre-embedded with lithium.

[0174] In a specific embodiment, the negative electrode composite material in the pre-lithium embedded negative electrode composite material used in the secondary battery includes the graphene / carbon nanotube composite material.

[0175] In a specific embodiment, the negative electrode composite material in the pre-lithium embedded negative electrode composite material used in the secondary battery includes the graphene / carbon nanotube composite material obtained by the preparation method.

[0176] In a specific embodiment, the negative electrode composite material in the pre-lithium embedded negative electrode composite material used in the secondary battery includes a three-dimensional carbon skeleton, the three-dimensional carbon skeleton is composited by graphene and carbon nanotubes, and the surface of the three-dimensional carbon skeleton has holes.

[0177] The provided graphene / carbon nanotube composite material has high specific capacity when applied to positive electrode materials, high rate performance when applied to negative electrode materials, and high reaction rate. The capacitor prepared therefrom can balance the difference between positive and negative electrode dynamics and has high energy density.

[0178] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0179] The provided capacitor has the following advantages: (1) the positive electrode material used includes graphene and carbon nanotubes interwoven to form a three-dimensional conductive network, and the specific capacitance is improved by increasing defects, N, S dual doping and eliminating oxygen-containing groups, thereby increasing the energy density of the lithium ion capacitor; (2) the negative electrode material used includes graphene and carbon nanotubes interwoven to form a three-dimensional conductive network structure, thereby improving the conductivity of the negative electrode material and shortening the kinetic gap with the capacitive positive electrode; (3) the lithium ion capacitor is assembled according to the mass ratio of positive to negative electrode 1: (3~4), so that the negative electrode material has capacity redundancy. This design can effectively reduce the current density on the surface of the negative electrode material during the charging and discharging process, reduce polarization, avoid significant expansion and contraction of the volume of the negative electrode material, and the positive electrode and the negative electrode are kinetically matched, which significantly improves the energy density, rate and cycle performance of the lithium ion capacitor; (4) both the positive and negative electrode materials are graphene and carbon nanotubes, and this design can effectively reduce the cost of the lithium ion capacitor. The capacitor provided can achieve a high rate discharge of 5A / g, a charge-discharge cycle life of 2A / g of more than 10,000 times, and a coulombic efficiency of more than 99% in the 1,000th cycle. The preparation method of the lithium ion capacitor is simple and easy to realize industrial-scale production. The lithium ion capacitor can also be used as a button battery and can be used as a reference battery for analyzing the electrochemical properties of capacitor samples. The present invention also provides a preparation method and an assembly method of the above-mentioned high-performance lithium ion capacitor electrode material, wherein a hydrothermal method is used to realize the preparation of a three-dimensional macroscopic graphene / carbon nanotube body, which has the following advantages: (1) the oxygen-containing functional groups of graphene oxide and carbon nanotubes can be eliminated to increase the specific capacitance of the positive electrode material; (2) the two-dimensional sheet graphene and the one-dimensional carbon nanotubes are assembled into a macroscopic three-dimensional structure by using hydrogen bonds, functional group forces and conjugated π bonds.

[0180] The preparation method also includes freeze-drying technology and heat treatment technology, which realizes the preparation of three-dimensional nanomaterials and has the following advantages: (1) maintaining the three-dimensional structure of graphene / carbon nanotubes, increasing the specific surface area of ​​the material, reducing the local current density, reducing polarization, and making the material have ultra-high rate characteristics; (2) eliminating residual oxygen-containing groups in the material and increasing the specific capacitance of the material.

[0181] The preparation method provided by the present invention can realize the preparation of high-performance electrode materials. The preparation method of the electrode material is simple and easy to realize industrial-scale production.

[0182] In summary, the above structure and component design prepares a high specific capacity positive electrode and a high rate negative electrode, effectively solving the industry pain points of low specific capacitance of the capacitive positive electrode of lithium ion capacitors and mismatch between the positive and negative electrode dynamics, thereby significantly improving the rate and cycle performance of lithium ion capacitors. This invention provides a design idea for the development of carbon-based lithium ion capacitors.

[0183] The embodiments of the present application will be described in detail below in conjunction with some examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which the conditions are not specified in the following examples are preferably referred to the guidance given in the present application, and can also be based on the experimental manual or normal conditions in the art, or can also be based on the conditions recommended by the manufacturer, or with reference to experimental methods known in the art.

[0184] Example 1

[0185] A method for preparing a high-performance lithium-ion capacitor comprises the following steps:

[0186] Step 1: Place 102 mg of graphene oxide and 34 mg of carbon nanotubes in deionized water and perform ultrasonic dispersion for 3 h to obtain a first dispersion.

[0187] Step 2: 408 mg of potassium hydroxide is placed in the first dispersion and stirred. After centrifugation and washing with deionized water for 3 times, a second dispersion of etched graphene oxide and carbon nanotubes is obtained.

[0188] Step 3: Add 34 mg of thiourea to the second dispersion and stir to obtain a third dispersion.

[0189] Step 4: Pour the third dispersion into a reaction kettle and subject it to hydrothermal synthesis at 140° C. for 8 h to obtain a black solid.

[0190] Step 5: Wash the black solid with deionized water three times, and then dry it in a freeze dryer at -40°C for 24 h to obtain a macroscopic body.

[0191] Step 6: Heat-treat the macrostructure obtained in step 5 at 800° C. for 2 h in a nitrogen atmosphere to obtain a N-rGO / CNT composite positive electrode material.

[0192] Step 7: Grind the composite material, conductive carbon black and PVDF in a mass ratio of 8:1:1 for 5 hours to obtain a black colloid.

[0193] Step 8: Apply the black colloid obtained in step 7 to the surface of the aluminum foil, dry it at 100° C. for 12 hours, and then cut it to obtain the high-performance lithium-ion capacitor N-rGO / CNT positive electrode sheet.

[0194] Step nine, repeat steps one, two, four, five, and six to obtain rGO / CNT composite materials; repeat steps seven and eight, apply the material on the surface of copper foil to obtain rGO / CNT pole pieces.

[0195] Step 10: Assemble the rGO / CNT electrode obtained in step 9 with lithium metal to form a half-cell, and perform electrochemical pre-lithium embedding in a blue-electric test system to obtain a L-rGO / CNT composite negative electrode.

[0196] Step 11: assemble the L-rGO / CNT composite negative electrode pre-embedded with lithium in step 10 and the N-rGO / CNT composite positive electrode into a lithium ion capacitor according to a mass ratio of active material of 1:3, and perform electrochemical testing.

[0197] The prepared N-rGO / CNT composite cathode material was tested using a Raman spectrometer, and the ID / IG was 1.39, indicating that a large number of defects were created on the surface of the carbon material.

[0198] The prepared N-rGO / CNT composite cathode material was detected by X-ray photoelectron spectroscopy, and the content of N element doped in the N-rGO / CNT composite cathode material was measured to be 4.74wt%, and the content of S element doped in the N-rGO / CNT composite cathode material was 1.07wt%.

[0199] The pore size, pore volume and specific surface area of ​​the N-rGO / CNT composite cathode material were measured by nitrogen adsorption-desorption curve method, and the pore diameter was 2-3 nm and the pore volume was 0.32 cm 3 / g, specific surface area is 639m 2 / g.

[0200] Example 2

[0201] A method for preparing a high-performance lithium-ion capacitor comprises the following steps:

[0202] Step 1: Place 102 mg of graphene oxide and 25 mg of carbon nanotubes in deionized water and perform ultrasonic dispersion for 3 h to obtain a first dispersion.

[0203] Step 2: 381 mg of potassium hydroxide is placed in the first dispersion and stirred. After centrifugation and washing with deionized water three times, a second dispersion of etched graphene oxide and carbon nanotubes is obtained.

[0204] Step 3: Add 31 mg of thiourea to the second dispersion and stir to obtain a third dispersion.

[0205] Step 4: Pour the third dispersion into a reaction kettle and subject it to hydrothermal synthesis at 140° C. for 8 h to obtain a black solid.

[0206] Step 5: Wash the black solid with deionized water three times, and then dry it in a freeze dryer at -40°C for 24 h to obtain a macroscopic body.

[0207] Step 6: Heat-treat the macrostructure obtained in step 5 at 800° C. for 2 h in a nitrogen atmosphere to obtain a N-rGO / CNT composite positive electrode material.

[0208] Step 7: Grind the composite material, conductive carbon black and PVDF in a mass ratio of 8:1:1 for 5 hours to obtain a black colloid.

[0209] Step 8: Apply the black colloid obtained in step 7 to the surface of the aluminum foil, dry it at 100° C. for 12 hours, and then cut it to obtain the high-performance lithium-ion capacitor N-rGO / CNT positive electrode sheet.

[0210] Step nine, repeat steps one, two, four, five, and six to obtain rGO / CNT composite materials; repeat steps seven and eight, apply the material on the surface of copper foil to obtain rGO / CNT pole pieces.

[0211] Step 10: Assemble the rGO / CNT electrode obtained in step 9 with lithium metal to form a half-cell, and perform electrochemical pre-lithium embedding in a blue-electric test system to obtain a L-rGO / CNT composite negative electrode.

[0212] Step 11: assemble the L-rGO / CNT composite negative electrode pre-embedded with lithium in step 10 and the N-rGO / CNT composite positive electrode into a lithium ion capacitor according to a mass ratio of active material of 1:3, and perform electrochemical testing.

[0213] Example 3

[0214] A method for preparing a high-performance lithium-ion capacitor comprises the following steps:

[0215] Step 1: Place 102 mg of graphene oxide and 51 mg of carbon nanotubes in deionized water and perform ultrasonic dispersion for 3 h to obtain a first dispersion.

[0216] Step 2: 459 mg of potassium hydroxide is placed in the first dispersion and stirred. After centrifugation and washing with deionized water for 3 times, a second dispersion of etched graphene oxide and carbon nanotubes is obtained.

[0217] Step 3: Add 38 mg of thiourea to the second dispersion and stir to obtain a third dispersion.

[0218] Step 4: Pour the third dispersion into a reaction kettle and subject it to hydrothermal synthesis at 140° C. for 8 h to obtain a black solid.

[0219] Step 5: Wash the black solid with deionized water three times, and then dry it in a freeze dryer at -40°C for 24 h to obtain a macroscopic body.

[0220] Step 6: Heat-treat the macrostructure obtained in step 5 at 800° C. for 2 h in a nitrogen atmosphere to obtain a N-rGO / CNT composite positive electrode material.

[0221] Step 7: Grind the composite material, conductive carbon black and PVDF in a mass ratio of 8:1:1 for 5 hours to obtain a black colloid.

[0222] Step 8: Apply the black colloid obtained in step 7 to the surface of the aluminum foil, dry it at 100° C. for 12 hours, and then cut it to obtain the high-performance lithium-ion capacitor N-rGO / CNT positive electrode sheet.

[0223] Step nine, repeat steps one, two, four, five, and six to obtain rGO / CNT composite materials; repeat steps seven and eight, apply the material on the surface of copper foil to obtain rGO / CNT pole pieces.

[0224] Step 10: Assemble the rGO / CNT electrode obtained in step 9 with lithium metal to form a half-cell, and perform electrochemical pre-lithium embedding in a blue-electric test system to obtain a L-rGO / CNT composite negative electrode.

[0225] Step 11: assemble the L-rGO / CNT composite negative electrode pre-embedded with lithium in step 10 and the N-rGO / CNT composite positive electrode into a lithium ion capacitor according to a mass ratio of active material of 1:3, and perform electrochemical testing.

[0226] Comparative Example 1

[0227] Step 2 was not performed, and the other preparation processes were the same as in Example 1.

[0228] That is, steps 1, 3 to 11 are the same as those in Example 1, and graphene and carbon nanotubes are directly hydrothermally synthesized without being etched with potassium hydroxide to prepare N-rGO / CNT and L-rGO / CNT composite negative electrodes, and then lithium ion capacitors are assembled.

[0229] Comparative Example 2

[0230] Step 5 was not performed, and the other preparation processes were the same as in Example 1.

[0231] That is, steps 1 to 4, 6 to 11 are the same as in Example 1, after the black solid is dried in an oven, the positive and negative electrode materials are heat treated to prepare N-rGO / CNT and L-rGO / CNT composite materials, and the composite materials are coated and cut into pieces to obtain the negative electrode sheet.

[0232] Comparative Example 3

[0233] Step 6 was not performed, and the other preparation processes were the same as in Example 1.

[0234] That is, steps 1 to 5 and 7 to 11 are the same as in Example 1, and the materials are not heat treated, and N-rGO / CNT and L-rGO / CNT composite negative electrodes are directly prepared to assemble lithium ion capacitors.

[0235] Test Case

[0236] The positive electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were cut into discs with a diameter of 16 mm (surface density of 3 mg / cm 2, N-rGO / CNT:SP:PVDF mass ratio is 8:1:1), the negative electrode is cut into a disc with a diameter of 16 mm (surface density is 1 mg / cm 2 , N-rGO / CNT:SP:PVDF mass ratio is 8:1:1). Polypropylene Celgard2500 is used as the diaphragm, lithium hexafluorophosphate salt solution (lithium hexafluorophosphate concentration is 1 mol / L, solvent DMC, EMC, EC volume ratio is 1:1:1) is used as the electrolyte, and a CR2025 type button lithium ion capacitor is assembled in a glove box. The water and oxygen concentrations in the glove box are ≤0.1ppm.

[0237] The assembled button-type lithium-ion capacitor was subjected to constant current charge and discharge test using the Blue Electric charge and discharge test system (CT2001A). The electrochemical data obtained are shown in Table 1.

[0238] Table 1

[0239]

[0240] The test results in Table 1 show that the lithium ion capacitors prepared by the technical solution of the present invention in Examples 1 to 3 have excellent electrochemical properties. Thanks to the unique design of the positive electrode material and the negative electrode material, the positive electrode has high specific capacity performance and the negative electrode has high rate performance, so that the two electrode materials with different energy storage mechanisms, the capacitor-type positive electrode and the battery-type negative electrode, have good synergistic effects. The lithium ion capacitor assembled with the positive and negative electrode materials has excellent electrochemical properties: at power densities of 0.3kW / kg and 20kW / kg, it can release a large energy density, the 2A / g charge and discharge cycle life can reach more than 10,000 times, the capacity retention rate can reach more than 86%, and the coulombic efficiency of the 10,000th cycle can reach more than 99%.

[0241] In the preparation process of the lithium ion capacitor of Comparative Example 1, graphene and carbon nanotubes were not etched, resulting in fewer defects, which seriously affected the specific capacitance of the positive electrode material and the transport performance of the negative electrode material for lithium ions, so that the prepared lithium ion capacitor could not achieve the expected performance.

[0242] During the preparation of the positive and negative electrode materials of Comparative Example 2, oven drying was used instead of freeze drying, which destroyed the macroscopic three-dimensional structure of the positive and negative electrode materials and affected the conductivity of the positive and negative electrode materials, resulting in a serious deterioration in the capacity retention rate of the assembled lithium ion capacitor at high power density, affecting the electrochemical properties of the lithium ion capacitor.

[0243] During the preparation process of the positive and negative electrode materials of Comparative Example 3, the macroscopic body was not heat-treated, resulting in a small amount of oxygen-containing groups remaining in the material, which affected the electrochemical properties of the lithium ion capacitor and caused the prepared lithium ion capacitor to fail to achieve the expected effect.

[0244] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0245] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description can be used to interpret the scope of the claims.

Claims

1. An electric energy storage system, characterized in that: The invention comprises a capacitor, wherein the capacitor comprises a positive electrode sheet, the positive electrode sheet comprises a graphene / carbon nanotube composite material, the graphene / carbon nanotube composite material comprises a three-dimensional network skeleton, the three-dimensional network skeleton comprises a carbon matrix and doping elements, the carbon matrix is ​​composited by graphene and carbon nanotubes, the doping elements comprise nitrogen and sulfur, and the surface of the three-dimensional network skeleton has holes.

2. The electric energy storage system according to claim 1, characterized in that: Meet one or more of the following characteristics: The graphene / carbon nanotube composite material is a nanomaterial; The pore size on the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material is 1nm~50nm; The pore volume on the surface of the three-dimensional network skeleton of the graphene / carbon nanotube composite material is 0.3 cm 3 / g~0.5cm 3 / g; The specific surface area of ​​the graphene / carbon nanotube composite material is 600 m 2 / g~2300m 2 / g; The doping amount of the nitrogen element in the graphene / carbon nanotube composite material is 5wt% to 10wt%; The doping amount of the sulfur element in the graphene / carbon nanotube composite material is 1wt% to 3wt%; The capacitor is a carbon capacitor; The capacitor is a lithium ion capacitor; The electrical energy storage system includes at least one of a portable electronic product, an electric vehicle, a medical device, and an aerospace energy storage product.

3. A graphene / carbon nanotube composite material, characterized in that: The graphene / carbon nanotube composite material comprises a three-dimensional network skeleton, the three-dimensional network skeleton comprises a carbon matrix and doping elements, the carbon matrix is ​​composited by graphene and carbon nanotubes, the doping elements comprise nitrogen and sulfur, and the surface of the three-dimensional network skeleton has holes.

4. The graphene / carbon nanotube composite material according to claim 3, characterized in that: Meet one or more of the following characteristics: The graphene / carbon nanotube composite material is a nanomaterial; The pore size on the surface of the three-dimensional network skeleton is 1nm~50nm; The pore volume of the surface of the three-dimensional network skeleton is 0.3 cm 3 / g~0.5cm 3 / g; The specific surface area of ​​the graphene / carbon nanotube composite material is 600 m 2 / g~2300m 2 / g; The doping amount of the nitrogen element in the graphene / carbon nanotube composite material is 5wt% to 10wt%; The doping amount of the sulfur element in the graphene / carbon nanotube composite material is 1wt% to 3wt%; The diameter of the carbon nanotubes is 10nm to 20nm; The carbon nanotubes have a tube length of 5 μm to 15 μm; The carbon nanotubes are multi-walled carbon nanotubes; The graphene is multi-layer graphene.

5. A method for preparing a graphene / carbon nanotube composite material, characterized in that: The following steps are included: Mixing a first dispersion containing graphene oxide, carbon nanotubes and water with potassium hydroxide, etching the graphene oxide and the carbon nanotubes under dispersion conditions, performing solid-liquid separation, and washing to prepare a second dispersion containing etching products; The second dispersion is mixed with thiourea to perform a hydrothermal synthesis reaction to prepare a nitrogen-sulfur doped composite material, which is then washed with water, freeze-dried, and heat-treated in an inert atmosphere to obtain the graphene / carbon nanotube composite material described in claim 3 or 4.

6. The preparation method according to claim 5, characterized in that: Meet one or more of the following characteristics: In the first dispersion, the mass ratio of the graphene oxide to the carbon nanotubes is 102:(25-51) based on the feed amount; In the step of mixing the first dispersion with potassium hydroxide, the ratio of the total mass of the graphene oxide and the carbon nanotubes to the mass of potassium hydroxide is 1:(3-5) based on the feeding amount; The step of mixing the first dispersion liquid with potassium hydroxide is achieved by: placing potassium hydroxide in the first dispersion liquid and stirring for 4 hours to 6 hours; In the step of mixing the second dispersion with thiourea, the ratio of the total mass of the graphene oxide and the carbon nanotubes in the first dispersion to the mass of the thiourea is (3-5):1, based on the feeding amount; The temperature for carrying out the hydrothermal synthesis reaction is 120° C. to 160° C., and the time for carrying out the hydrothermal synthesis reaction is 8 h to 12 h; The freeze-drying temperature is -45°C to -20°C, and the freeze-drying time is 24h to 36h; The inert atmosphere is a nitrogen atmosphere; The temperature of the heat treatment is 700°C to 800°C; The heat treatment is performed for 2 to 3 hours.

7. Use of the graphene / carbon nanotube composite material according to claim 3 or 4 or the graphene / carbon nanotube composite material obtained by the preparation method according to claim 5 or 6 in preparing an electrode sheet for a capacitor or a secondary battery; wherein: The electrode sheet is a positive electrode sheet or a negative electrode sheet.

8. A capacitor, comprising a positive electrode and a negative electrode, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, a first conductive agent and a first binder, the positive electrode active material comprises at least one of the graphene / carbon nanotube composite material according to claim 3 or 4 and the graphene / carbon nanotube composite material obtained by the preparation method according to claim 5 or 6; The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a second conductive agent and a second binder; the negative electrode active material comprises a negative electrode composite material pre-embedded with lithium, and the negative electrode composite material in the negative electrode composite material pre-embedded with lithium satisfies one or more of the following characteristics: A graphene / carbon nanotube composite material comprising the graphene / carbon nanotube composite material according to claim 3 or 4; A graphene / carbon nanotube composite material obtained by the preparation method according to claim 5 or 6; It comprises a three-dimensional carbon skeleton, wherein the three-dimensional carbon skeleton is composited with graphene and carbon nanotubes, and the surface of the three-dimensional carbon skeleton has holes; The capacitor meets one or more of the following characteristics: The capacitor is a carbon capacitor; The capacitor is a lithium ion capacitor; The capacitor is a carbon-based lithium-ion capacitor; In the capacitor, the mass ratio of the positive electrode active material, the first conductive agent and the first binder is (78-82):(9-11):(9-11); In the capacitor, the mass ratio of the negative electrode active material, the second conductive agent and the second binder is (78-82):(9-11):(9-11); In the capacitor, the positive electrode current collector is aluminum foil; In the capacitor, the negative electrode current collector is copper foil; In the capacitor, the mass ratio of the negative electrode active material to the positive electrode active material is 1:(3-4).

9. A method for preparing a capacitor, characterized in that: The method comprises assembling a positive electrode sheet, a negative electrode sheet, an electrolyte and a diaphragm to prepare a capacitor; wherein, At least one of the graphene / carbon nanotube composite material according to claim 3 or 4 and the graphene / carbon nanotube composite material prepared by the preparation method according to claim 5 or 6 is used as a positive electrode active material to prepare a positive electrode sheet; One or more of the following composite materials are used as the negative electrode composite material to prepare the negative electrode sheet: The graphene / carbon nanotube composite material according to claim 3 or 4; The graphene / carbon nanotube composite material obtained by the preparation method according to claim 5 or 6; A composite material comprising a three-dimensional carbon skeleton, wherein the three-dimensional carbon skeleton is composited with graphene and carbon nanotubes, and the surface of the three-dimensional carbon skeleton has holes; The steps of preparing the positive electrode sheet include: mixing the positive electrode active material, the first conductive agent and a glue solution containing a first binder to prepare a first colloid; coating the first colloid on at least one side surface of the positive electrode current collector, and drying to prepare the positive electrode sheet; The steps of preparing the negative electrode sheet include: mixing the negative electrode composite material, a second conductive agent and a glue solution containing a second binder to prepare a second colloid; coating the second colloid on at least one side surface of the negative electrode current collector, drying, and preparing a lithium-embedded electrode sheet; electrochemically pre-embed lithium in the lithium-embedded electrode sheet to prepare the negative electrode sheet; the step of electrochemically pre-embed lithium includes: cycling the lithium-embedded electrode sheet with a lithium sheet for 5 to 10 times at a current density of 0.2 A / g in an electrochemical window of 0.01 V to 3 V.

10. A secondary battery, comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, a first conductive agent and a first binder, the positive electrode active material comprises at least one of the graphene / carbon nanotube composite material according to claim 3 or 4 and the graphene / carbon nanotube composite material obtained by the preparation method according to claim 5 or 6; The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a second conductive agent and a second binder; the negative electrode active material comprises a negative electrode composite material pre-embedded with lithium, and the negative electrode composite material in the negative electrode composite material pre-embedded with lithium satisfies one or more of the following characteristics: A graphene / carbon nanotube composite material comprising the graphene / carbon nanotube composite material according to claim 3 or 4; A graphene / carbon nanotube composite material obtained by the preparation method according to claim 5 or 6; It comprises a three-dimensional carbon skeleton, which is composited by graphene and carbon nanotubes, and has holes on the surface of the three-dimensional carbon skeleton.

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