Carbon-containing metal oxide negative electrode material, preparation method thereof and lithium ion capacitor

Abstract

The invention belongs to the technical field of energy storage materials, and particularly relates to a carbon-containing metal oxide negative electrode material, a preparation method thereof and a lithium ion capacitor. Compared with the prior art, a metal organic framework material with a nano structure is innovatively used as a precursor, and a metal oxide material with a nano structure is formed through heat treatment and is used as the negative electrode material of the lithium ion capacitor. Wherein the confinement effect between a metal site and an organic ligand which are connected through a strong coordination bond can effectively slow down the volume expansion effect of the material, and the potential catalytic action of metal elements can promote the graphitization degree of surrounding carbon, so that the electronic conductivity and the surface roughness of a negative electrode are further enhanced; and the energy density of the lithium ion capacitor is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage materials, and in particular relates to a carbon-containing metal oxide negative electrode material, a preparation method thereof, and a lithium ion capacitor. Background Art

[0002] The development of energy storage materials is the core of promoting the development of energy storage technology and directly determines the comprehensive performance of electrochemical energy storage devices. Therefore, the exploration of energy storage materials has received widespread attention.

[0003] Lithium-ion capacitors (LICs) are a novel electrochemical energy storage technology that combines the high energy density of LIBs with the high power density of supercapacitors. The materials used for the positive and negative electrodes directly determine the overall performance of the device. Typically, the positive electrode active material of LICs utilizes porous carbon materials used in double-layer capacitors (e.g., activated carbon, mesoporous carbon, carbon aerogel, and graphene), while the negative electrode active material utilizes carbon materials used in lithium-ion batteries (e.g., graphite, soft carbon, hard carbon, lithium-containing oxides such as lithium titanate, transition metal oxides, and alloy-based materials). Among negative electrode materials, graphite dominates the commercial market due to its excellent cycling performance, but its theoretical specific capacity is only 372 mAh / g and suffers from severe voltage hysteresis. Soft and hard carbons are low-cost and have low operating potentials, but they also suffer from low capacity and severe voltage hysteresis. Lithium-containing oxides such as lithium titanate offer high structural stability and safety, but their low theoretical specific capacity and high voltage plateau limit their large-scale application in LICs. Alloy-based materials offer high theoretical specific capacity but suffer from poor structural stability and cycling stability. Transition metal oxides generally have advantages such as high theoretical specific capacity, moderate voltage platform, low cost, and environmental friendliness, but they have low electrical conductivity, severe volume changes, and poor cycle life. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a carbon-containing metal oxide negative electrode material with high specific capacity, conductivity and structural stability, a preparation method thereof and a lithium ion capacitor.

[0005] The present invention provides a method for preparing a carbon-containing metal oxide negative electrode material, comprising the following steps:

[0006] S1) annealing the metal organic framework material in a protective atmosphere by step-wise temperature increase to obtain a metal-containing porous carbon nanotube;

[0007] S2) calcining the metal-containing porous carbon nanotube in an oxidizing atmosphere to obtain a carbon-containing metal oxide negative electrode material.

[0008] Preferably, the metal organic framework material is selected from zeolite imidazole metal organic framework materials;

[0009] The metal ions in the metal organic framework material are selected from one or more of transition metal ions, p metal ions, alkaline earth metal ions, actinide metal ions and lanthanide metal ions.

[0010] Preferably, the metal organic framework material has a cubic structure;

[0011] The particle size of the metal organic framework material is 100-600 nm.

[0012] Preferably, the metal organic framework material is selected from ZIF-67(Co).

[0013] Preferably, the stepwise heating in step S1) is specifically as follows: heating to a first temperature at a first heating rate and keeping the temperature, and then heating to a second temperature at a second heating rate and performing annealing;

[0014] The first heating rate and the second heating rate are each independently selected from 1 to 5°C / min;

[0015] The first temperature is 150° C. to 300° C.;

[0016] The holding time at the first temperature is 20 to 40 minutes;

[0017] The second temperature is 400° C. to 600° C.;

[0018] The annealing treatment time is 0.5 to 2 hours.

[0019] Preferably, the calcination temperature in step S2) is 300° C. to 500° C.; and the calcination time is 2 to 10 hours.

[0020] The present invention also provides a carbon-containing metal oxide negative electrode material prepared by the above preparation method, wherein the carbon-containing metal oxide negative electrode material comprises a metal oxide and a carbon material coated on the surface of the metal oxide; the mass content of the carbon material in the carbon-containing metal oxide negative electrode material is 0.1% to 5%.

[0021] Preferably, the carbon-containing metal oxide negative electrode material has a cubic structure; the particle size of the carbon-containing metal oxide negative electrode material is 10 to 40 nm.

[0022] The present invention also provides a lithium ion capacitor, comprising a negative electrode sheet, wherein the negative electrode sheet contains the above-mentioned carbon-containing metal oxide negative electrode material.

[0023] Preferably, it also includes a positive electrode sheet; the positive electrode sheet includes a positive electrode material; the positive electrode material is selected from carbon-based materials; the carbon-based materials are selected from one or more of onion carbon, carbon nanotubes, biochar, graphene, activated carbon, carbide-derived carbon, mesoporous carbon, carbon aerogel and template carbon.

[0024] The present invention provides a method for preparing a carbon-containing metal oxide negative electrode material, comprising the following steps: S1) annealing a metal-organic framework material in a protective atmosphere by step-by-step temperature increase to obtain a metal-containing porous carbon nanobox; S2) calcining the metal-containing porous carbon nanobox in an oxidizing atmosphere to obtain a carbon-containing metal oxide negative electrode material. Compared with the prior art, the present invention innovatively uses a nanostructured metal-organic framework material as a precursor, and forms a nanostructured metal oxide material as a lithium ion capacitor negative electrode material through heat treatment. The confinement effect between the metal site and the organic ligand connected by a strong coordination bond can effectively slow down the volume expansion effect of the material, and the potential catalytic effect of the metal element can promote the degree of graphitization of the surrounding carbon, thereby further enhancing the electronic conductivity and surface roughness of the negative electrode, and improving the energy density of the lithium ion capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 TEM image of the ZIF-67 polyhedron obtained in Example 1 of the present invention;

[0026] Figure 2 The scanning electron microscope images of the cobalt / porous carbon nanotubes obtained in Example 1 and Comparative Example 2 of the present invention are shown;

[0027] Figure 3 Transmission electron micrographs of the Co3O4-300 nanobox obtained in Example 1 of the present invention, the Co3O4-400 nanobox obtained in Example 2, and the Co3O4-500 nanobox obtained in Comparative Example 1;

[0028] Figure 4 XRD patterns of the Co3O4-300 nanobox obtained in Example 1 of the present invention, the Co3O4-400 nanobox obtained in Example 2, and the Co3O4-500 nanobox obtained in Comparative Example 1;

[0029] Figure 5 3. Thermogravimetric curves of the Co3O4-300 nanobox obtained in Example 1 of the present invention, the Co3O4-400 nanobox obtained in Example 2, and the Co3O4-500 nanobox obtained in Comparative Example 1;

[0030] Figure 6 Impedance graphs of the Co3O4-300 nanobox obtained in Example 1 of the present invention, the Co3O4-400 nanobox obtained in Example 2, and the Co3O4-500 nanobox obtained in Comparative Example 1;

[0031] Figure 7 This is a rate performance diagram of the negative electrode sheets obtained in Examples 1 and 2 of the present invention and Comparative Example 1;

[0032] Figure 8 CV curve of Co3O4-400 / / AC LIC assembled in Example 1 of the present invention;

[0033] Figure 9 The charge and discharge curves of Co3O4-400 / / AC LIC assembled in Example 1 of the present invention at different current densities;

[0034] Figure 10 This is the rate performance diagram of Co3O4-400 / / AC LIC assembled in Example 1 of the present invention;

[0035] Figure 11 This is the cycling performance diagram of the Co3O4-400 / / AC LIC assembled in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] The present invention provides a method for preparing a carbon-containing metal oxide negative electrode material, comprising the following steps: S1) annealing a metal-organic framework material in a protective atmosphere by step-by-step temperature increase to obtain a metal-containing porous carbon nanobox; S2) calcining the metal-containing porous carbon nanobox in an oxidizing atmosphere to obtain a carbon-containing metal oxide negative electrode material.

[0038] The present invention has no particular limitation on the sources of all raw materials, and any commercially available raw materials may be used.

[0039] In a specific embodiment provided by the present invention, the metal-organic framework material is preferably a zeolite imidazole metal-organic framework material.

[0040] In a specific embodiment provided by the present invention, the metal ions in the metal-organic framework material are preferably one or more of transition metal ions, p metal ions, alkaline earth metal ions, actinide metal ions and lanthanide metal ions; the transition metal ions include but are not limited to one or more of Zn ions, Cu ions, Fe ions, Co ions and Ni ions; the p metal ions include but are not limited to Ga ions and / or In ions; the alkaline earth metal ions include but are not limited to Sr ions and / or Ba ions; the actinide metal ions include but are not limited to U ions and / or Th ions.

[0041] In a specific embodiment provided by the present invention, the metal organic framework material is preferably ZIF-67(Co).

[0042] In a specific embodiment provided by the present invention, the metal organic framework material preferably has a cubic structure.

[0043] In a specific embodiment provided by the present invention, the particle size of the metal organic framework material is preferably 100-600 nm; optionally, the particle size of the metal organic framework material is 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm or a range between any two of the above values.

[0044] In a specific embodiment provided by the present invention, the particle size of the metal organic framework material is 300 nm.

[0045] In a specific embodiment provided by the present invention, the metal organic framework material is preferably prepared by emulsion polymerization, specifically: a metal salt, a surfactant and water are mixed, an imidazole ligand solution is added, and the reaction is stirred at room temperature to obtain a metal organic framework material; the metal salt is a water-soluble metal salt well known to those skilled in the art, and there is no special restriction, including but not limited to one or more of nitrates, metal chlorides, sulfates, and carbonates; the type of metal ions in the metal salt is the same as described above and will not be repeated here; the surfactant is a surfactant well known to those skilled in the art, and there is no special restriction. In the present invention, it is preferably a quaternary ammonium salt surfactant, more preferably hexadecyltrimethylammonium bromide; the molar ratio of the metal salt to the surfactant is preferably 1: (0.001-0.1), more preferably 1: (0.005-0.05), More preferably, it is 1:(0.008~0.02), and most preferably, it is 1:0.01; the imidazole ligand is any imidazole ligand well known to those skilled in the art, and in the present invention, it is preferably 2-methylimidazole; the molar ratio of the metal salt to the imidazole ligand is preferably 1:(50~60), and more preferably 1:55; the mixing method is any method well known to those skilled in the art, and there is no special limitation, and in the present invention, it is preferably ultrasonic mixing; the stirring reaction time is preferably 10~30min, more preferably 15~25min, and more preferably 20min; after the stirring reaction is completed, it is preferably centrifuged, washed, and dried to obtain a metal organic framework material; the washing is preferably carried out with ethanol; the drying temperature is preferably 50℃~70℃, more preferably 55℃~65℃, and more preferably 60℃; the drying time is preferably 10~12h.

[0046] The metal organic framework material is annealed by step-wise heating in a protective atmosphere to obtain a metal-containing porous carbon nanobox; the protective atmosphere can be any protective atmosphere well known to those skilled in the art and is not particularly limited. In the present invention, nitrogen and / or argon are preferably used; the step-wise heating is preferably as follows: heating to a first temperature at a first heating rate and holding the temperature, and then heating to a second temperature at a second heating rate and annealing; the first heating rate and the second heating rate are each independently preferably 1 to 5°C / min, more preferably 2 to 3°C / min; the first temperature is preferably 150°C to 300°C, more preferably 150°C to 250°C , more preferably 180℃~220℃, most preferably 200℃; the holding time at the first temperature is preferably 20~40min, more preferably 25~35min, more preferably 30min; the second temperature, i.e., the annealing temperature, is preferably 400℃~600℃, more preferably 450℃~600℃, more preferably 500℃~600℃, most preferably 550℃~600℃; the annealing time is preferably 0.5~2h, more preferably 0.8~1.5h, more preferably 0.8~1.2h, most preferably 1h; after the annealing treatment is completed, it is preferably naturally cooled to room temperature to obtain a metal-containing porous carbon nanobox. The present invention innovatively carbonizes the metal-organic framework precursor at a low temperature under a protective atmosphere, so that the carbon content in the product is not lost too much and can better inherit the nanoframework structure of the metal-organic framework.

[0047] The metal-containing porous carbon nanobox is calcined in an oxidizing atmosphere to obtain a carbon-containing metal oxide negative electrode material; the oxidizing atmosphere is any oxidizing atmosphere familiar to those skilled in the art and is not particularly limited. In the present invention, it is preferably air; the calcination temperature is preferably 300°C to 500°C, more preferably 300°C to 400°C, and more preferably 350°C to 400°C; the calcination time is preferably 2 to 10 hours, more preferably 4 to 8 hours, more preferably 5 to 7 hours, and most preferably 7 hours.

[0048] This invention innovatively uses nanostructured metal-organic frameworks as precursors, and through heat treatment, forms nanostructured metal oxide materials as the negative electrode material for lithium-ion capacitors. The confinement effect between the metal sites and organic ligands, connected by strong coordination bonds, effectively mitigates the volume expansion of the material. Furthermore, the potential catalytic effect of the metal elements promotes the graphitization of the surrounding carbon, further enhancing the electronic conductivity and surface roughness of the negative electrode, and improving the energy density of the lithium-ion capacitor.

[0049] The present invention also provides a carbon-containing metal oxide negative electrode material prepared by the above preparation method, wherein the carbon-containing metal oxide negative electrode material comprises a metal oxide and a carbon material coated on the surface of the metal oxide; the mass content of the carbon material in the carbon-containing metal oxide negative electrode material is 0.1% to 5%.

[0050] In a specific embodiment provided by the present invention, the metal oxide is preferably one or more of a transition metal oxide, a p-metal oxide, an alkaline earth metal oxide, an actinide metal oxide and a lanthanide metal oxide; the transition metal element in the transition metal oxide includes but is not limited to one or more of Zn, Cu, Fe, Co and Ni; the p-metal element in the p-metal oxide includes but is not limited to Ga and / or In; the alkaline earth metal element in the alkaline earth metal oxide includes but is not limited to Sr and / or Ba; the actinide metal element in the actinide metal oxide includes but is not limited to U and / or Th.

[0051] In a specific embodiment provided by the present invention, the metal oxide is preferably cobalt oxide, more preferably tricobalt tetroxide.

[0052] In a specific embodiment provided by the present invention, the mass content of the carbon material in the carbon-containing metal oxide negative electrode material is preferably 1% to 5%, more preferably 1.5% to 4.5%, more preferably 1.9% to 4.2%, more preferably 1.93% to 3.5%, more preferably 1.93% to 3%, more preferably 1.93% to 2.5%, and most preferably 1.93% to 2%.

[0053] In a specific embodiment provided by the present invention, the carbon-containing metal oxide negative electrode material has a cubic structure.

[0054] In a specific embodiment provided by the present invention, the particle size of the carbon-containing metal oxide negative electrode material is preferably 10 to 40 nm, more preferably 10 to 30 nm, further preferably 15 to 30 nm, and further preferably 17 to 26 nm.

[0055] The present invention also provides a lithium ion capacitor, comprising a negative electrode sheet, wherein the negative electrode sheet comprises the above-mentioned carbon-containing metal oxide negative electrode material.

[0056] In a specific embodiment provided by the present invention, the lithium ion capacitor is preferably a lithium ion capacitor with high energy / power output.

[0057] In a specific embodiment provided by the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer attached to at least one surface of the negative electrode current collector; the negative electrode active layer includes the above-mentioned carbon-containing metal oxide negative electrode material; the negative electrode current collector can be a negative electrode current collector well known to those skilled in the art, and there is no special limitation. In the present invention, it is preferably aluminum foil, carbon-coated aluminum foil, copper foil or carbon-coated copper foil; the mass of the carbon-containing metal oxide negative electrode material is preferably 65% to 90% of the mass of the negative electrode active layer, more preferably 65% to 85%, more preferably 68% to 80%, more preferably 68% to 75%, and most preferably 70%.

[0058] In a specific embodiment provided by the present invention, the negative electrode active layer further includes a negative electrode conductive agent and a negative electrode binder; the negative electrode conductive agent is a negative electrode conductive agent well known to those skilled in the art, and there is no special limitation. In the present invention, it is preferably one or more of graphene, carbon nanotubes, Ketjen black, onion carbon, carbon black, acetylene black, KS series carbon particles and carbon fibers; the mass of the negative electrode conductive agent is preferably 5% to 20% of the mass of the negative electrode active layer, more preferably 10% to 20%, more preferably 15% to 20%, and most preferably 18% to 20%; the negative electrode binder is a negative electrode binder well known to those skilled in the art, and there is no special limitation. In the present invention, it is preferably one or more of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, polymethyl methacrylate, hydrogenated nitrile rubber, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile and sodium alginate; the mass of the negative electrode binder is preferably 5% to 15% of the mass of the negative electrode active layer, more preferably 8% to 12%, and more preferably 10%.

[0059] In a specific embodiment provided by the present invention, the negative electrode sheet is preferably prepared according to the following method: mixing the carbon-containing metal oxide negative electrode material in a mixer to form a primary dry mixture; mixing the primary dry mixture, the negative electrode conductive agent and part of the negative electrode binder to form a secondary dry mixture; stirring and mixing the secondary dry mixture with part of the solvent, and then adding the remaining negative electrode binder and stirring and dispersing, and continuing to add the remaining solvent and stirring and mixing to obtain a negative electrode slurry; coating the negative electrode slurry on the surface of the negative electrode current collector to form a negative electrode sheet; the solvent includes but is not limited to one or more of deionized water, acetonitrile, N-methylpyrrolidone, N,N-dimethylacetamide and acetone.

[0060] In a specific embodiment provided by the present invention, the lithium ion capacitor also includes a positive electrode sheet; the positive electrode sheet includes a positive electrode material; the positive electrode material is preferably a carbon-based material; the carbon-based material is preferably one or more of onion carbon, carbon nanotubes, biochar, graphene, activated carbon, carbide-derived carbon, mesoporous carbon, carbon aerogel and template carbon.

[0061] In a specific embodiment provided by the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer attached to at least one surface of the positive electrode current collector; the positive electrode active layer includes the above-mentioned positive electrode material; the positive electrode current collector can be a positive electrode current collector well known to those skilled in the art, without any special restrictions. In the present invention, it is preferably aluminum foil, carbon-coated aluminum foil, copper foil or carbon-coated copper foil; the mass of the positive electrode material is preferably 65% to 90% of the mass of the positive electrode active layer, more preferably 65% to 85%, more preferably 68% to 80%, more preferably 68% to 75%, and most preferably 70%.

[0062] In a specific embodiment provided by the present invention, the positive electrode active layer further includes a positive electrode conductor and a positive electrode binder; the positive electrode conductor is a positive electrode conductor well known to those skilled in the art, and there is no special limitation. In the present invention, it is preferably one or more of graphene, carbon nanotubes, Ketjen black, onion carbon, carbon black, acetylene black, KS series carbon particles and carbon fibers; the mass of the positive electrode conductor is preferably 5% to 20% of the mass of the positive electrode active layer, more preferably 10% to 20%, more preferably 15% to 20%, and most preferably 18% to 20%; the positive electrode binder is a positive electrode binder well known to those skilled in the art, and there is no special limitation. In the present invention, it is preferably one or more of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, polymethyl methacrylate, hydrogenated nitrile rubber, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile and sodium alginate; the mass of the positive electrode binder is preferably 5% to 15% of the mass of the positive electrode active layer, more preferably 8% to 12%, and more preferably 10%.

[0063] In a specific embodiment provided by the present invention, the positive electrode sheet is preferably prepared according to the following method: the positive electrode material is mixed in a mixer to form a primary dry mixture; the primary dry mixture, the positive electrode conductive agent and a portion of the positive electrode binder are mixed to form a secondary dry mixture; the secondary dry mixture is stirred and mixed with a portion of the solvent, and then the remaining positive electrode binder is added and stirred and dispersed, and the remaining solvent is continued to be added and stirred to obtain a positive electrode slurry; the positive electrode slurry is coated on the surface of the negative electrode current collector to form a positive electrode sheet; the solvent includes but is not limited to one or more of ethanol, acetone, N-methylpyrrolidone, dimethylformamide and dimethyl sulfoxide.

[0064] In a specific embodiment provided by the present invention, the lithium ion capacitor further includes a diaphragm; the diaphragm is arranged between the negative electrode sheet and the positive electrode sheet; the diaphragm includes but is not limited to one or more of a polyethylene microporous membrane, a polypropylene microporous membrane, a composite membrane, an inorganic ceramic membrane and a paper diaphragm.

[0065] In a specific embodiment provided by the present invention, the lithium ion capacitor includes a battery core, a shell and an electrolyte; the battery core and the electrolyte are arranged in the shell; the battery core is formed by stacking or winding a negative electrode sheet, a separator and a positive electrode sheet in sequence; the shell includes but is not limited to an aluminum-plastic film, a steel shell or an aluminum shell; the electrolyte includes a lithium salt, a solvent and an additive; the lithium salt is a lithium salt well known to those skilled in the art, and there is no special restriction, including but not limited to one or more of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bisoxalate borate, lithium tetrafluoroborate, lithium bistrifluoromethanesulfonyl imide, lithium bisfluorosulfonyl imide and lithium trifluoroacetate; the solvent is a solvent well known to those skilled in the art. The additives include but are not limited to one or more of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), perfluoropolyether and fluoroether; the additives are additives well known to those skilled in the art without special restrictions, including but not limited to one or more of vinylene carbonate, 1,3-propane sultone, vinyl ethylene carbonate, ethylene sulfate, propene sultone, succinonitrile, vinyl methyl sulfate, vinyl sulfite, methylene methanedisulfonate, tris(trimethylsilyl)phosphine, triethyl phosphate, hexafluorocyclotriphosphazene, 1,4-dicyano-2-butene, sulfolane and methyl ethyl sulfone.

[0066] In a specific embodiment provided by the present invention, the lithium ion capacitor is prepared according to the following method: a negative electrode sheet, a separator, and a positive electrode sheet are stacked or wound in sequence to form a lithium ion capacitor cell, and then the cell is placed in a shell, and an electrolyte is injected to complete pre-lithiation and seal to form a lithium ion capacitor.

[0067] To further illustrate the present invention, a carbon-containing metal oxide negative electrode material, a preparation method thereof, and a lithium ion capacitor provided by the present invention are described in detail below with reference to examples.

[0068] The reagents used in the following examples are all commercially available.

[0069] Example 1

[0070] 1.1 Preparation of zeolitic imidazole framework (ZIF-67) polyhedrons

[0071] 0.58 g of cobalt nitrate hexahydrate and 0.01 g of cetyltrimethylammonium bromide (CTAB) were added to 20 mL of deionized water (DIW) and ultrasonically mixed to obtain a pink solution. This solution was then poured into 140 mL of DIW containing 9.08 g of 2-methylimidazole and stirred at room temperature for 20 minutes. The resulting purple suspension was centrifuged multiple times, washed with ethanol, and the purple sample was collected and dried at 60°C for 12 hours.

[0072] 1.2 Preparation of Cobalt / Porous Carbon Nanoboxes

[0073] The ZIF-67 polyhedron was heated to 200°C at a heating rate of 2°C / min in an Ar atmosphere of a tube furnace and annealed for 30 min, then heated to 600°C at a heating rate of 2°C / min and annealed for 1 h, and naturally cooled to room temperature to obtain a cobalt / porous carbon nanobox.

[0074] 1.3 Preparation of Co3O4-300 Nanoboxes

[0075] The prepared cobalt / porous carbon nanobox was heated to 300°C at a heating rate of 5°C / min in an air atmosphere in a tube furnace and kept warm for 6 h to obtain Co3O4-300 nanobox.

[0076] 1.4 Electrode preparation

[0077] 70wt.% of powdered active material (Co3O4-300 nanobox), 20wt.% of conductive agent (conductive carbon black) and 10wt.% of binder polyvinylidene fluoride (PVDF) are mixed evenly by grinding in N-methylpyrrolidone (NMP) solvent, so that the slurry is free of particles or has few particles. The mixed slurry is then coated on the current collector (carbon-coated copper foil) with a scraper, dried with a blower at 80℃ for 1h, and then punched into disc electrodes with a diameter of 8 or 11mm using a punching machine. The cut electrodes are first flattened by applying appropriate pressure under the powder tableting machine to make the electrode material coating more dense. Finally, the electrodes are vacuum dried at 100℃ for 12h and then weighed (the overall weight of the electrodes is about 8-10mg, and the surface density is 1mg / cm 2 , compacted density is 0.5g / cm 3 ), and transferred to the glove box to assemble button batteries.

[0078] 1.5 Assembly of button-type lithium-ion capacitors

[0079] The assembly process of lithium-ion capacitors is mainly divided into two parts. First, the negative electrode is assembled into a lithium half-cell (electrolyte: 1.2M LiPF6, solvent DEC:DMC:EC=1:2:2) and then discharged to 0.01V at a low current of 0.1A / g for five cycles to activate and pre-lithiate the negative electrode. Second, the pre-lithiated negative electrode is removed and matched to the surface density of 2mg / cm 2 , compacted density is 0.4g / cm 3 The YP80F activated carbon positive electrode (containing 80% YP80F, 10% Super C45, and 10% PVDF) was assembled into a lithium-ion capacitor according to the assembly sequence of button batteries (the lithium sheet was replaced with the negative electrode sheet, and the electrode sheet was replaced with the positive electrode sheet). After sealing, it was allowed to stand and wait for testing.

[0080] Example 2

[0081] The method and steps are the same as those in Example 1, except that the holding temperature in the preparation step of the cobalt trioxide nanobox is 400° C., and a Co 3 O 4 -400 nanobox is obtained.

[0082] Comparative Example 1

[0083] The method and steps are the same as those in Example 1, except that the holding temperature in the preparation step of the cobalt oxide nano-box is 500° C., and a Co 3 O 4 -500 nano-box is obtained.

[0084] Comparative Example 2

[0085] The ZIF-67 polyhedron was heated to 600°C in an Ar atmosphere in a tube furnace at a heating rate of 2°C / min and annealed for 1 h, and then naturally cooled to room temperature to obtain a cobalt / porous carbon nanobox.

[0086] The zeolite imidazole framework (ZIF-67) polyhedron obtained in Example 1 was analyzed using a transmission electron microscope, and its transmission electron microscope image was obtained as shown in FIG. Figure 1 As shown. Figure 1 It can be seen that the ZIF-67 polyhedron presents a cubic structure with an average size of 300 nm, a smooth surface and a solid structure inside.

[0087] The cobalt / porous carbon nanotubes obtained in Example 1 and Comparative Example 2 were analyzed using a scanning electron microscope, and the scanning electron microscope images thereof were as follows: Figure 2 shown. Figure 2 a and b are cobalt / porous carbon nanotubes obtained by carbonization at 200°C to 600°C in Example 1, c and d are cobalt porous carbon nanotubes obtained by carbonization at 600°C in Comparative Example 2. Figure 2 It can be seen that the cobalt / porous carbon nanobox obtained by direct carbonization at 600°C has a more severely damaged morphology than the cobalt / porous carbon nanobox obtained by carbonization from 200°C to 600°C. This is because carbonization at 200°C allows the sample to be kept at a low temperature, which plays a very important role in promoting the stability of the material structure.

[0088] The Co3O4-300 nanometer box obtained in Example 1, the Co3O4-400 nanometer box obtained in Example 2 and the Co3O4-500 nanometer box obtained in Comparative Example 1 were analyzed using a transmission electron microscope, and the transmission electron microscope images thereof were as follows: Figure 3 As shown. Figure 3It can be seen that after low-temperature carbonization treatment in an inert atmosphere at different temperatures and heat treatment in an air atmosphere, the Co nanoparticles are transformed into internal hollow Co3O4 monodisperse nanoparticles through the Kirkendall diffusion effect. The obtained Co3O4-300 and Co3O4-400 products can better maintain the cubic morphology of the ZIF-67 precursor. The average diameters of the monodisperse particles are 17nm and 26nm, respectively. The Co3O4-500 monodisperse particles are uneven in size, with an average diameter of 46nm, and cannot maintain the overall cubic framework structure of the ZIF-67 precursor.

[0089] The Co3O4-300 nanometer box obtained in Example 1, the Co3O4-400 nanometer box obtained in Example 2 and the Co3O4-500 nanometer box obtained in Comparative Example 1 were analyzed by X-ray diffraction, and their XRD patterns were as follows: Figure 4 As shown. Figure 4 It can be seen that the XRD diffraction patterns of the three products perfectly correspond to the PDF#42-1467 card of Co3O4.

[0090] The Co3O4-300 nanobox obtained in Example 1, the Co3O4-400 nanobox obtained in Example 2 and the Co3O4-500 nanobox obtained in Comparative Example 1 were analyzed by thermogravimetric analysis, and the thermogravimetric curves thereof were as follows: Figure 5 As shown. Figure 5 It can be seen that the carbon content in the product can be tested through the thermogravimetric diagram. As the heating temperature evaporates, the final product is Co3O4. The carbon contents in Co3O4-300, Co3O4-400, and Co3O4-500 are measured to be 4.12%, 1.93%, and 1.11%, respectively.

[0091] The impedance of Co3O4-300, Co3O4-400 and Co3O4-500 obtained in Examples 1 and 2 and Comparative Example 1 was tested on an electrochemical workstation, and the impedance diagrams were as follows: Figure 6 shown.

[0092] The rate performance of the negative electrode sheets obtained in Examples 1 to 2 and Comparative Example 1 was tested according to DLT 2080-2020 Supercapacitors for Power Energy Storage and GBT 36276-2023 Lithium-ion Batteries for Power Energy Storage, and the rate performance diagram thereof is shown in FIG. Figure 7 shown.

[0093] A lithium ion capacitor was assembled with Co3O4-400 as the negative electrode and AC as the positive electrode (Co3O4-400 / / AC LIC, the mass ratio of the negative electrode to the positive electrode was 1:1.5, the electrolyte was 1.2M LiPF6, and the solvent was DEC:DMC:EC=1:2:2). The CV curves at different scan rates of 1-50mV / s are shown in Figure 2. Figure 8 As shown by Figure 8 It can be seen that with the increase of scan rate, the CV curves are approximately rectangular in shape, with no obvious polarization phenomenon, indicating that it has good electrochemical reaction reversibility. Figure 9 The charge and discharge curves of the device with a negative / positive electrode mass ratio of 1:1.5 at different current densities are shown in Figure 2. Figure 9 It can be seen that the curve presents a well-symmetrical triangle, indicating that the device has fast capacitive storage behavior.

[0094] The rate performance test results of Co3O4-400 / / AC LIC are as follows: Figure 10 As shown by Figure 10 It can be seen that at current densities of 0.1, 0.2, 0.3, 0.5, 0.8, 1, 2, 5, 10, 15, and 20 A / g, based on the total mass of the active material, the specific capacities are 60.18, 51.84, 50.64, 48.81, 47.20, 46.11, 43.21, 39.16, 31.33, 32.89, and 25.06 F / g, respectively. The prepared AC / / Co3O4-400 lithium ion capacitor operates stably in the voltage range of 1.0-4.2 V and can output a power density of up to 33660 W / kg, corresponding to an energy density of 46.75 Wh / kg, and at a high energy density of 124.11 Wh / kg, the output power density is 251.29 W / kg. Figure 11 As shown, the capacity retention rate after 4000 charge and discharge cycles at a current density of 2 A / g is 88.21%.

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-containing metal oxide negative electrode material, characterized in that: The following steps are involved: S1) annealing the metal organic framework material in a protective atmosphere by step-wise temperature increase to obtain a metal-containing porous carbon nanotube; S2) calcining the metal-containing porous carbon nanotube in an oxidizing atmosphere to obtain a carbon-containing metal oxide negative electrode material.

2. The preparation method according to claim 1, characterized in that The metal organic framework material is selected from zeolite imidazole metal organic framework materials; The metal ions in the metal organic framework material are selected from one or more of transition metal ions, p metal ions, alkaline earth metal ions, actinide metal ions and lanthanide metal ions.

3. The preparation method according to claim 1, characterized in that The metal organic framework material has a cubic structure; The particle size of the metal organic framework material is 100-600 nm.

4. The preparation method according to any one of claims 1 to 3, characterized in that The metal organic framework material is selected from ZIF-67(Co).

5. The preparation method according to claim 1, characterized in that The stepwise heating in step S1) is specifically as follows: heating to a first temperature at a first heating rate and holding the temperature, and then heating to a second temperature at a second heating rate and performing annealing; The first heating rate and the second heating rate are each independently selected from 1 to 5°C / min; The first temperature is 150° C. to 300° C.; The holding time at the first temperature is 20 to 40 minutes; The second temperature is 400° C. to 600° C.; The annealing treatment time is 0.5 to 2 hours.

6. The preparation method according to claim 1, characterized in that The calcination temperature in step S2) is 300° C. to 500° C.; and the calcination time is 2 to 10 hours.

7. The carbon-containing metal oxide negative electrode material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The carbon-containing metal oxide negative electrode material comprises a metal oxide and a carbon material coated on the surface of the metal oxide; the mass content of the carbon material in the carbon-containing metal oxide negative electrode material is 0.1% to 5%.

8. The carbon-containing metal oxide negative electrode material according to claim 7, characterized in that: The carbon-containing metal oxide negative electrode material has a cubic structure; the particle size of the carbon-containing metal oxide negative electrode material is 10 to 40 nm.

9. A lithium ion capacitor, characterized in that: The negative electrode comprises a negative electrode sheet, wherein the negative electrode sheet comprises a carbon-containing metal oxide negative electrode material prepared by the preparation method according to any one of claims 1 to 6 or a carbon-containing metal oxide negative electrode material according to claim 7 or 8.

10. The lithium ion capacitor according to claim 9, characterized in that It also includes a positive electrode sheet; the positive electrode sheet includes a positive electrode material; the positive electrode material is selected from carbon-based materials; the carbon-based materials are selected from one or more of onion carbon, carbon nanotubes, biochar, graphene, activated carbon, carbide-derived carbon, mesoporous carbon, carbon aerogel and template carbon.

Images