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

Abstract

The present application 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, the present application 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 sites and the organic ligands connected by strong coordination bonds can effectively slow down the volume expansion effect of the material, and the potential catalytic effect of the metal elements can promote the graphitization degree 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.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy storage materials, and particularly relates to a carbon-containing metal oxide negative material, a preparation method thereof and a lithium ion capacitor. BACKGROUND

[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 from people.

[0003] The lithium ion capacitor is a new type of electrochemical energy storage technology, which combines the high energy density of lithium ion batteries and the high power density of supercapacitors. The positive and negative electrode materials directly determine the comprehensive performance of the device. Under normal circumstances, the positive active material of the lithium ion capacitor uses the porous carbon material (such as activated carbon, mesoporous carbon, carbon aerogel, graphene, etc.) of the double-layer capacitor, and the negative active material uses the negative carbon material (such as graphite, soft carbon, hard carbon, lithium-containing oxides such as lithium titanate, transition metal oxides, alloy materials, etc.) of the lithium ion battery. Among the negative electrode materials, graphite dominates in the market due to its excellent cycle performance, but its theoretical specific capacity is only 372 mAh / g, and it has a serious voltage hysteresis problem. Soft carbon, hard carbon and other materials have low cost and low working potential, but they also have low capacity, serious voltage hysteresis and other problems. Lithium-containing oxides such as lithium titanate have high structural stability and high safety, but their theoretical specific capacity is low and the voltage platform is high, which limits their large-scale application in lithium ion capacitors. Alloy materials have a high theoretical specific capacity, but their structural stability is poor and their cycle stability is poor. Transition metal oxides usually have high theoretical specific capacity, moderate voltage platform, low cost, and environmental friendliness, but their electrical conductivity is low, the volume change is serious, and the cycle life is poor. SUMMARY

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

[0005] The present application provides a preparation method of a carbon-containing metal oxide negative material, comprising the following steps:

[0006] S1) annealing a metal organic framework material in a protective atmosphere by stepwise heating to obtain a metal-containing porous carbon nanobox;

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

[0008] Preferably, the metal organic framework material is selected from zeolitic imidazolate 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 is of 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 step S1) of temperature ramping is specifically as follows: temperature ramping to a first temperature at a first temperature ramping rate, holding at the first temperature, then temperature ramping to a second temperature at a second temperature ramping rate, and annealing treatment.

[0014] The first temperature ramping rate and the second temperature ramping rate are each independently selected from 1-5 ℃ / min.

[0015] The first temperature is 150-300 ℃.

[0016] The holding time at the first temperature is 20-40 min.

[0017] The second temperature is 400-600 ℃.

[0018] The annealing treatment time is 0.5-2 h.

[0019] Preferably, the temperature of the step S2) of calcination is 300-500 ℃, and the calcination time is 2-10 h.

[0020] The present application also provides a carbon-containing metal oxide negative electrode material prepared by the above preparation method, which 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%-5%.

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

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

[0023] Preferably, the lithium ion capacitor further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode material, and the positive electrode material is selected from one or more of onion carbon, carbon nanotube, biomass carbon, graphene, activated carbon, carbide-derived carbon, mesoporous carbon, carbon aerogel and template carbon.

[0024] The application provides a preparation method of a carbon-containing metal oxide negative electrode material, comprising the following steps: S1) annealing a metal organic framework material in a protective atmosphere through stepwise heating to obtain a metal-containing porous carbon nanobox; and S2) calcining the metal-containing porous carbon nanobox in an oxidation atmosphere to obtain the carbon-containing metal oxide negative electrode material. Compared with the prior art, the application 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 sites and the organic ligands connected through strong coordination bonds can effectively slow down the volume expansion effect of the material, and the potential catalytic effect of the metal elements can promote the graphitization degree 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 DRAWINGS

[0025] Figure 1 A transmission electron microscope image of the ZIF-67 polyhedron obtained in Example 1 of the application;

[0026] Figure 2 A scanning electron microscope image of the cobalt / porous carbon nanobox obtained in Example 1 and Comparative Example 2 of the application;

[0027] Figure 3 A transmission electron microscope image of 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 of the application;

[0028] Figure 4 An XRD pattern of 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 of the application;

[0029] Figure 5 A thermogravimetric curve of 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 of the application;

[0030] Figure 6 An impedance diagram of 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 of the application;

[0031] Figure 7 A rate performance diagram of the negative electrode sheet obtained in Examples 1-2 and Comparative Example 1 of the application;

[0032] Figure 8 CV curve diagram of Co3O4-400 / / AC LIC assembled for the embodiment 1 of the present application;

[0033] Figure 9 Charge-discharge curve diagram of Co3O4-400 / / AC LIC assembled for the embodiment 1 of the present application at different current densities;

[0034] Figure 10 Rate performance diagram of Co3O4-400 / / AC LIC assembled for the embodiment 1 of the present application;

[0035] Figure 11 Cycle performance diagram of Co3O4-400 / / AC LIC assembled for the embodiment 1 of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0037] The present application provides a preparation method of carbon-containing metal oxide negative material, comprising the following steps: S1) annealing a metal organic framework material in a protective atmosphere by stepwise heating to obtain a metal-containing porous carbon nanobox; S2) calcining the metal-containing porous carbon nanobox in an oxidation atmosphere to obtain a carbon-containing metal oxide negative material.

[0038] In the present application, there is no special limitation on the source of all raw materials, which can be purchased on the market.

[0039] In a specific embodiment provided by the present application, the metal organic framework material is preferably a zeolitic imidazolate metal organic framework material.

[0040] In a specific embodiment provided by the present application, 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 an embodiment of the present application, the metal organic framework material is preferably ZIF-67(Co).

[0042] In an embodiment of the present application, the metal organic framework material is preferably cubic structure.

[0043] In an embodiment of the present application, the particle size of the metal organic framework material is preferably 100-600 nm; alternatively, 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 an embodiment of the present application, the particle size of the metal organic framework material is 300 nm.

[0045] In an embodiment of the present application, the metal organic framework material is preferably prepared by emulsion polymerization, specifically: mixing a metal salt, a surfactant and water, adding an imidazole ligand solution, stirring at room temperature to obtain a metal organic framework material; the metal salt is a water-soluble metal salt known to those skilled in the art and is not particularly limited, including but not limited to one or more of nitrate, metal chloride, sulfate, carbonate; the type of metal ion in the metal salt is as described above and will not be repeated here; the surfactant is a surfactant known to those skilled in the art and is not particularly limited, preferably a quaternary ammonium salt surfactant in the present application, more preferably cetyltrimethylammonium 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), again preferably 1:(0.008-0.02), most preferably 1:0.01; the imidazole ligand is an imidazole ligand known to those skilled in the art and is not particularly limited, preferably 2-methylimidazole in the present application; the molar ratio of the metal salt to the imidazole ligand is preferably 1:(50-60), more preferably 1:55; the mixing method is a method known to those skilled in the art and is not particularly limited, preferably ultrasonic mixing in the present application; the stirring reaction time is preferably 10-30 min, more preferably 15-25 min, again preferably 20 min; after the stirring reaction is completed, centrifugation, washing and drying are preferably performed to obtain the metal organic framework material; the washing is preferably performed using ethanol; the drying temperature is preferably 50-70°C, more preferably 55-65°C, again preferably 60°C; the drying time is preferably 10-12 h.

[0046] The metal-organic framework material is annealed by stepwise heating in a protective atmosphere to obtain a metal-containing porous carbon nanobox; the protective atmosphere is a protective atmosphere known to those skilled in the art and is not particularly limited, and in the present application, nitrogen and / or argon are preferred; the stepwise heating preferably specifically refers to heating at a first heating rate to a first temperature for heat preservation, and then heating at a second heating rate to a second temperature for annealing treatment; the first heating rate and the second heating rate are each independently preferably 1-5°C / min, more preferably 2-3°C / min; the first temperature is preferably 150-300°C, more preferably 150-250°C, more preferably 180-220°C, and most preferably 200°C; the heat preservation time at the first temperature is preferably 20-40 min, more preferably 25-35 min, and more preferably 30 min; the second temperature, i.e., the annealing temperature, is preferably 400-600°C, more preferably 450-600°C, more preferably 500-600°C, and most preferably 550-600°C; the annealing time is preferably 0.5-2 h, more preferably 0.8-1.5 h, more preferably 0.8-1.2 h, and most preferably 1 h; after the annealing treatment, natural cooling to room temperature is preferred to obtain the metal-containing porous carbon nanobox. The metal-organic framework precursor is innovatively carbonized at low temperature in a protective atmosphere, so that the carbon content in the product is not lost too much, and the nanoframe structure of the metal-organic framework can be better inherited.

[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 an oxidizing atmosphere known to those skilled in the art and is not particularly limited, and in the present application, air is preferred; the calcination temperature is preferably 300-500°C, more preferably 300-400°C, and more preferably 350-400°C; the calcination time is preferably 2-10 h, more preferably 4-8 h, more preferably 5-7 h, and most preferably 7 h.

[0048] The present application innovatively uses a nanostructured metal-organic framework material as a precursor to form a nanostructured metal oxide material as a lithium ion capacitor negative electrode material by heat treatment. The confinement effect between the metal sites and the organic ligands connected by strong coordination bonds can effectively slow down the volume expansion effect of the material, and the potential catalytic effect of the metal elements can promote the graphitization degree 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.

[0049] The application further provides the carbon-containing metal oxide negative electrode material prepared by the preparation method.

[0050] In a specific embodiment of the application, the metal oxide is preferably one or more of transition metal oxides, p-metal oxides, alkaline earth metal oxides, actinide oxides and lanthanide oxides; the transition metal elements in the transition metal oxides include, but are not limited to, one or more of Zn, Cu, Fe, Co and Ni; the p-metal elements in the p-metal oxides include, but are not limited to, Ga and / or In; the alkaline earth metal elements in the alkaline earth metal oxides include, but are not limited to, Sr and / or Ba; and the actinide elements in the actinide oxides include, but are not limited to, U and / or Th.

[0051] In a specific embodiment of the application, the metal oxide is preferably cobalt oxide, and more preferably tricobalt tetroxide.

[0052] In a specific embodiment of the application, 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%, further preferably 1.9% to 4.2%, further preferably 1.93% to 3.5%, further preferably 1.93% to 3%, further preferably 1.93% to 2.5%, and most preferably 1.93% to 2%.

[0053] In a specific embodiment of the application, the carbon-containing metal oxide negative electrode material has a cubic structure.

[0054] In a specific embodiment of the application, 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 application further provides a lithium ion capacitor comprising a negative electrode sheet, wherein the negative electrode sheet comprises the carbon-containing metal oxide negative electrode material.

[0056] In a specific embodiment of the application, the lithium ion capacitor is preferably a lithium ion capacitor with high energy / power output.

[0057] In one embodiment of the present application, the negative electrode sheet comprises 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 comprises the carbon-containing metal oxide negative electrode material described above; the negative electrode current collector can be any known to those skilled in the art without special restrictions, and is preferably an aluminum foil, a carbon-coated aluminum foil, a copper foil, or a carbon-coated copper foil in the present application; the mass of the carbon-containing metal oxide negative electrode material is preferably 65% to 90%, more preferably 65% to 85%, even more preferably 68% to 80%, still more preferably 68% to 75%, and most preferably 70% of the mass of the negative electrode active layer.

[0058] In one embodiment of the present application, the negative electrode active layer further comprises a negative electrode conductive agent and a negative electrode binder; the negative electrode conductive agent can be any known to those skilled in the art without special restrictions, and is preferably one or more of graphene, carbon nanotubes, Ketjen black, onion carbon, carbon black, acetylene black, KS series carbon microparticles, and carbon fibers in the present application; the mass of the negative electrode conductive agent is preferably 5% to 20%, more preferably 10% to 20%, even more preferably 15% to 20%, and most preferably 18% to 20% of the mass of the negative electrode active layer; the negative electrode binder can be any known to those skilled in the art without special restrictions, and 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 in the present application; the mass of the negative electrode binder is preferably 5% to 15%, more preferably 8% to 12%, and even more preferably 10% of the mass of the negative electrode active layer.

[0059] In one embodiment of the present application, the negative electrode sheet is preferably prepared by 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, a negative electrode conductive agent, and part of a negative electrode binder to form a secondary dry mixture; stirring and mixing the secondary dry mixture with part of a solvent, then stirring and dispersing the remaining negative electrode binder, and continuing to stir and mix the remaining solvent to obtain a negative electrode slurry; coating the negative electrode slurry on the surface of a negative electrode current collector to form a negative electrode sheet; and the solvent includes, but is not limited to, one or more of deionized water, acetonitrile, N-methyl pyrrolidone, N,N-dimethylacetamide, and acetone.

[0060] In one embodiment of the present application, the lithium ion capacitor further comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode material; the positive electrode material is preferably a carbon-based material; and the carbon-based material is preferably one or more of onion carbon, carbon nanotubes, biomass carbon, graphene, activated carbon, carbide-derived carbon, mesoporous carbon, carbon aerogel, and templated carbon.

[0061] In one specific embodiment provided by the present application, the positive electrode sheet comprises 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 comprises the positive electrode material described above; the positive electrode current collector can be any positive electrode current collector known to those skilled in the art without special limitation, and in the present application, aluminum foil, carbon-coated aluminum foil, copper foil or carbon-coated copper foil is preferred; 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%, even more preferably 68% to 80%, still more preferably 68% to 75%, and most preferably 70%.

[0062] In one specific embodiment provided by the present application, the positive electrode active layer further comprises a positive electrode conductive agent and a positive electrode binder; the positive electrode conductive agent can be any positive electrode conductive agent known to those skilled in the art without special limitation, and in the present application, one or more of graphene, carbon nanotubes, Ketjen black, onion carbon, carbon black, acetylene black, KS series carbon microparticles and carbon fibers is preferred; the mass of the positive electrode conductive agent is preferably 5% to 20% of the mass of the positive electrode active layer, more preferably 10% to 20%, even more preferably 15% to 20%, and most preferably 18% to 20%; the positive electrode binder can be any positive electrode binder known to those skilled in the art without special limitation, and in the present application, one or more of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, polymethyl methacrylate, hydrogenated nitrile rubber, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile and sodium alginate is preferred; 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 even more preferably 10%.

[0063] In one specific embodiment provided by the present application, the positive electrode sheet is preferably prepared by the following method: mixing the positive electrode material in a mixer to form a primary dry mixture; mixing the primary dry mixture, the positive electrode conductive agent and part of the positive electrode binder to form a secondary dry mixture; stirring and mixing the secondary dry mixture with part of the solvent, then stirring and dispersing the remaining positive electrode binder, and continuing to stir and mix the remaining solvent to obtain a positive electrode slurry; coating the positive electrode slurry 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-methyl pyrrolidone, dimethylformamide and dimethyl sulfoxide.

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

[0065] In a specific embodiment provided by the present application, the lithium ion capacitor comprises an electric core, a shell and an electrolyte; the electric core and the electrolyte are arranged in the shell; the electric core is formed by stacking or winding the negative electrode sheet, the separator and the positive electrode sheet in sequence; the shell comprises, but is not limited to, an aluminum plastic film, a steel shell or an aluminum shell, etc.; the electrolyte comprises a lithium salt, a solvent and an additive; the lithium salt is well known to those skilled in the art and is not particularly limited, including but not limited to one or more of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium trifluoroacetate; the solvent is well known to those skilled in the art and is not particularly limited, including but not limited to one or more of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), perfluoropolyether and fluoroether; the additive is well known to those skilled in the art and is not particularly limited, including but not limited to one or more of vinylene carbonate, 1,3-propane sultone, vinyl ethylene carbonate, ethylene sulfate, propylene sultone, butanedinitrile, methyl vinyl sulfate, vinyl sulfite, methylene methane disulfonate, tris(trimethylsilyl)phosphine, triethyl phosphate, hexafluorocyclotriphosphazene, 1,4-dicyano-2-butene, cyclobutane sulfone and methyl ethyl sulfone.

[0066] In a specific embodiment provided by the present application, the lithium ion capacitor is prepared by the following method: assembling a lithium ion capacitor electric core in the form of stacking or winding the negative electrode sheet, the separator and the positive electrode sheet in sequence, then placing the electric core in the shell, injecting the electrolyte, completing pre-lithiation, sealing, and forming the lithium ion capacitor.

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

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

[0069] Example 1

[0070] 1.1 Preparation of zeolitic imidazolate framework (ZIF-67) polyhedron

[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, which was injected into 140 mL of a deionized water solution containing 2-methylimidazole (9.08 g) and stirred at room temperature for 20 min. The obtained purple suspension was centrifuged multiple times, washed with ethanol, and the purple sample was collected and dried at 60°C for 12 h.

[0072] 1.2 Preparation of cobalt / porous carbon nanobox

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

[0074] 1.3 Preparation of cobalt trioxide (Co304-300) nanoboxes

[0075] The prepared cobalt / porous carbon nanoboxes were heated to 300°C at a heating rate of 5°C / min in a tube furnace air atmosphere, and held for 6 h to obtain Co304-300 nanoboxes.

[0076] 1.4 Preparation of electrode sheets

[0077] The 70 wt.% of the powder active material (Co304-300 nanoboxes), 20 wt.% of the conductive agent (conductive carbon black), and 10 wt.% of the binder polyvinylidene fluoride (PVDF) were mixed uniformly in an N-methyl pyrrolidone (NMP) solvent by grinding, so that the slurry was in a state of no or few particles. Then the mixed slurry was coated on the current collector (carbon-coated copper foil) with a doctor blade, dried at 80°C for 1 h with a blower, and then punched into a circular sheet electrode with a diameter of 8 or 11 mm with a sheet puncher. The cut electrode sheet was first flattened under a powder sheet press with an appropriate pressure, so that the electrode material coating was more dense. Finally, the electrode sheet was vacuum dried at 100°C for 12 h, weighed (the overall weight of the electrode sheet was about 8-10 mg, the area density was 1 mg / cm 2 , and the compacted density was 0.5 g / cm 3 ), and transferred to a glove box for assembly of the button cell.

[0078] 1.5 Assembly of the button lithium ion capacitor

[0079] The assembly process of the lithium ion capacitor mainly included two parts. First, the lithium half-cell assembled with the negative electrode (electrolyte: 1.2 M LiPF6, solvent DEC: DMC: EC = 1:2:2) was cycled at a small current of 0.1 A / g for five times and discharged to 0.01 V, so as to achieve the purpose of activating and pre-lithiating the negative electrode. Second, the pre-lithiated negative electrode was taken out, matched with the YP80F activated carbon positive electrode (containing 80% YP80F, 10% Super C45, 10% PVDF) with an area density of 2 mg / cm 2 and a compacted density of 0.4 g / cm 3 , and assembled into a lithium ion capacitor according to the assembly order of the button cell (the lithium sheet position was replaced by the negative electrode sheet, and the electrode sheet position was replaced by the positive electrode sheet). After sealing, the lithium ion capacitor was left to stand and waited for testing.

[0080] Example 2

[0081] The method steps are the same as in Example 1, except that the holding temperature in the preparation step of the cobalt tetroxide nanobox is 400°C, to obtain Co304-400 nanoboxes.

[0082] Comparative Example 1

[0083] The method steps are the same as in Example 1, except that the holding temperature in the preparation step of the cobalt tetroxide nanobox is 500°C, to obtain Co304-500 nanoboxes.

[0084] Comparative Example 2

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

[0086] The zeolitic imidazolate framework (ZIF-67) polyhedron obtained in Example 1 is analyzed by transmission electron microscopy, and the transmission electron microscopy image thereof is shown in Figure 1 As can be seen from Figure 1 , the ZIF-67 polyhedron presents a cubic structure with an average size of 300nm, the surface is smooth and the interior presents a solid structure.

[0087] The cobalt / porous carbon nanoboxes obtained in Example 1 and Comparative Example 2 are analyzed by scanning electron microscopy, and the scanning electron microscopy images thereof are shown in Figure 2 . Figure 2 a and b are the cobalt / porous carbon nanoboxes obtained by carbonization from 200°C to 600°C in Example 1, and c and d are the cobalt / porous carbon nanoboxes obtained by direct carbonization at 600°C in Comparative Example 2, as can be seen from Figure 2 , the sample morphology of the cobalt / porous carbon nanoboxes obtained by direct carbonization at 600°C is severely damaged compared to the cobalt / porous carbon nanoboxes obtained by carbonization from 200°C to 600°C. The reason is that carbonization at 200°C allows the sample to be kept at low temperature, which plays a very important role in promoting the stability of the material structure.

[0088] The Co304-300 nanoboxes obtained in Example 1, the Co304-400 nanoboxes obtained in Example 2 and the Co304-500 nanoboxes obtained in Comparative Example 1 are analyzed by transmission electron microscopy, and the transmission electron microscopy images thereof are shown in Figure 3 . Figure 3It can be seen that, after low-temperature carbonization treatment under different temperature inert atmosphere and heat treatment under air atmosphere, Co nanoparticles are converted into internally hollow Co3O4 monodisperse nanoparticles by Kirkendall diffusion effect, and the obtained Co3O4-300 and Co3O4-400 products can better maintain the cubic morphology of the ZIF-67 precursor, and the average diameters of the monodisperse particles are 17 nm and 26 nm, respectively. The Co3O4-500 monodisperse particles are uneven in size, with an average diameter of 46 nm, and cannot maintain the cubic frame structure of the ZIF-67 precursor as a whole.

[0089] 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 X-ray diffraction, and the XRD patterns thereof are shown in Figure 4 Figure 4 It can be seen that the XRD 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 curve thereof is shown in Figure 5 Figure 5 It can be seen that the carbon content in the product can be tested by the thermogravimetric curve, and the final product is Co3O4 after evaporation with heating temperature. The carbon contents in Co3O4-300, Co3O4-400 and Co3O4-500 are 4.12%, 1.93% and 1.11%, respectively.

[0091] The impedance of the Co3O4-300, Co3O4-400 and Co3O4-500 obtained in Examples 1-2 and Comparative Example 1 was tested on an electrochemical workstation, and the impedance diagram thereof is shown in Figure 6

[0092] The rate performance of the negative electrode sheet obtained in Examples 1-2 and Comparative Example 1 was tested according to DLT 2080-2020 supercapacitors for electrical energy storage and GBT 36276-2023 lithium ion batteries for electrical energy storage, and the rate performance diagram thereof is shown in Figure 7

[0093] The Co3O4-400 was used as the negative electrode, and the AC was used as the positive electrode to assemble a lithium ion capacitor (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), and the CV curves at different scan rates of 1-50 mV / s were as follows:​​​​Figure 8 As shown in Figure 8 It can be seen that with the increase of scanning speed, the CV curve is approximately rectangular, and there is no obvious polarization phenomenon, indicating that it has good electrochemical reaction reversibility. Figure 9 The charge-discharge curve of the device with a negative / positive mass ratio of 1:1.5 at different current densities is shown in Figure 9 It can be seen that the curve shows good symmetry triangle, indicating that the device has fast capacitive storage behavior.

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

[0095] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for the preparation of a carbon-containing metal oxide negative material for lithium ion capacitors, characterized in that, The method comprises the following steps: S1) annealing the metal-organic framework material in a protective atmosphere by stepwise heating to obtain a metal-containing porous carbon nanobox; S2) calcining the metal-containing porous carbon nanobox in an oxidation atmosphere to obtain a carbon-metal oxide negative electrode material; The metal-organic framework material has a cubic structure; The particle size of the metal-organic framework material is 100-600 nm; The metal-organic framework material is selected from ZIF-67 (Co); The stepwise heating in step S1) is specifically as follows: heating at a first heating rate to a first temperature for heat preservation, and then heating at a second heating rate to a second temperature for annealing treatment; The first heating rate and the second heating rate are each independently selected from 1-5 ℃ / min; The first temperature is 150-300 ℃; The heat preservation time at the first temperature is 20-40 min; The second temperature is 400-600 ℃; The annealing treatment time is 0.5-2 h; The calcination temperature in step S2) is 300-400 ℃; and the calcination time is 2-10 h.

2. The carbon-containing metal oxide anode material for lithium ion capacitors produced by the production method of claim 1, characterized in that, The carbon-metal oxide negative electrode material comprises a metal oxide and a carbon material coated on the surface of the metal oxide; and the mass content of the carbon material in the carbon-metal oxide negative electrode material is 0.1%-5%.

3. The carbon-containing metal oxide negative electrode material of claim 2, wherein, The carbon-metal oxide negative electrode material has a cubic structure; and the particle size of the carbon-metal oxide negative electrode material is 10-40 nm.

4. A lithium-ion capacitor characterized by comprising: The method further comprises the following steps:

5. The lithium-ion capacitor of claim 4, wherein, The method further comprises the following steps: The positive electrode sheet comprises a positive electrode material; and the positive electrode material is selected from a carbon-based material; and the carbon-based material is selected from one or more of onion carbon, carbon nanotubes, biomass carbon, graphene, activated carbon, carbide-derived carbon, mesoporous carbon, carbon aerogel and template carbon.

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