CN115000343B - Preparation method of flexible double-layer self-supporting electrode - Google Patents
Preparation method of flexible double-layer self-supporting electrode Download PDFInfo
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- CN115000343B CN115000343B CN202210602473.3A CN202210602473A CN115000343B CN 115000343 B CN115000343 B CN 115000343B CN 202210602473 A CN202210602473 A CN 202210602473A CN 115000343 B CN115000343 B CN 115000343B
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- 238000002360 preparation method Methods 0.000 title abstract description 7
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims abstract description 111
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims abstract description 68
- 238000010041 electrostatic spinning Methods 0.000 claims abstract description 55
- 238000000034 method Methods 0.000 claims abstract description 41
- 239000000758 substrate Substances 0.000 claims abstract description 39
- 235000006408 oxalic acid Nutrition 0.000 claims abstract description 37
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims abstract description 36
- UNTBPXHCXVWYOI-UHFFFAOYSA-O azanium;oxido(dioxo)vanadium Chemical compound [NH4+].[O-][V](=O)=O UNTBPXHCXVWYOI-UHFFFAOYSA-O 0.000 claims abstract description 34
- 239000002131 composite material Substances 0.000 claims abstract description 28
- 238000007590 electrostatic spraying Methods 0.000 claims abstract description 25
- 229920002239 polyacrylonitrile Polymers 0.000 claims abstract description 25
- 239000004372 Polyvinyl alcohol Substances 0.000 claims abstract description 24
- 229920002451 polyvinyl alcohol Polymers 0.000 claims abstract description 24
- 230000008569 process Effects 0.000 claims abstract description 22
- 238000001035 drying Methods 0.000 claims abstract description 20
- 238000003756 stirring Methods 0.000 claims abstract description 19
- 229910012949 LiV2O4 Inorganic materials 0.000 claims abstract description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 13
- 239000008367 deionised water Substances 0.000 claims abstract description 12
- 229910021641 deionized water Inorganic materials 0.000 claims abstract description 12
- 238000001354 calcination Methods 0.000 claims abstract description 11
- 238000005303 weighing Methods 0.000 claims abstract description 7
- 239000000243 solution Substances 0.000 claims description 90
- 238000009987 spinning Methods 0.000 claims description 48
- 239000004744 fabric Substances 0.000 claims description 34
- 239000000463 material Substances 0.000 claims description 25
- 239000000835 fiber Substances 0.000 claims description 22
- 238000005245 sintering Methods 0.000 claims description 17
- 238000010438 heat treatment Methods 0.000 claims description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 12
- 239000011259 mixed solution Substances 0.000 claims description 10
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 6
- 239000012456 homogeneous solution Substances 0.000 claims description 5
- 238000001523 electrospinning Methods 0.000 claims description 2
- 239000007772 electrode material Substances 0.000 abstract description 13
- 239000002121 nanofiber Substances 0.000 abstract description 8
- 239000002086 nanomaterial Substances 0.000 abstract description 8
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- 239000002243 precursor Substances 0.000 abstract description 7
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- 230000001070 adhesive effect Effects 0.000 abstract description 3
- 238000011049 filling Methods 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 85
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 15
- 229910001416 lithium ion Inorganic materials 0.000 description 15
- 238000005507 spraying Methods 0.000 description 12
- 238000012360 testing method Methods 0.000 description 12
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- 239000011888 foil Substances 0.000 description 10
- 229920000642 polymer Polymers 0.000 description 9
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 8
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
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- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 2
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 2
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- 239000000843 powder Substances 0.000 description 2
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910013872 LiPF Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- 101150058243 Lipf gene Proteins 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
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- 238000002441 X-ray diffraction Methods 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/0007—Electro-spinning
-
- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
- D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
- D04H1/72—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged
- D04H1/728—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged by electro-spinning
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
- H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The application relates to a preparation method of a flexible double-layer self-supporting electrode. The simple electrostatic spinning and electrostatic spraying process is utilized, and the basal layer is Li 3 VO 4 C electrospun nanofiber with a top layer of Li 3 VO 4 ‑LiV 2 O 4 And (C) double-needle blending composite nano material. And dissolving polyacrylonitrile, lithium nitrate, ammonium metavanadate and oxalic acid in N, N-dimethylformamide, and stirring to form a uniform blue-black solution, thereby obtaining a solution A. Simultaneously weighing polyvinyl alcohol, dissolving in deionized water, stirring until the polyvinyl alcohol is clear, then adding lithium nitrate, ammonium metavanadate and oxalic acid, and stirring until a uniform blue uniform solution is formed, and taking the solution as a solution B; firstly, filling the solution A into a syringe to carry out electrostatic spinning to serve as a self-supporting substrate layer, immediately transferring the precursor solution B into the syringe after the electrostatic spinning is finished, carrying out double-needle blending with the solution A on the substrate layer, and drying and calcining after the completion of the double-needle blending to obtain the flexible double-layer composite material. The application solves the problems of poor flexibility, unstable performance, using adhesive and the like of the self-supporting electrode material.
Description
Technical Field
The application belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of a flexible double-layer self-supporting electrode.
Background
The global energy shortage and the environmental crisis enable the energy structure to be changed, and the green clean development of energy is promoted to be global consensus. As a clean, sustainable secondary energy source, conversion and storage of electrical energy is important in today's critical period of energy conversion. Lithium ion batteries are used as main electric energy storage technologies respectively, and the development bottleneck of the lithium ion batteries is the improvement of the electrode material performance in the system. At present, the traditional method has complicated procedures when preparing electrode materials, and conductive agents, binders and the like are required to be added, so that active materials on the electrodes are unevenly distributed, and the electron transfer and ion transmission in the electrochemical reaction are seriously affected. Therefore, the development of the self-supporting electrode material without the binder is beneficial to fully exposing the active site of the electrode material and improving the utilization rate of the active component, thereby realizing efficient electric energy conversion and storage. Compared with the traditional preparation method, the electrostatic spinning technology has good development prospect in the field of self-supporting nano material preparation due to the advantages of simple method, low cost, high efficiency, wide application range and the like. The spraying technology makes the sprayed fog drop possess great static charge under the action of high voltage, and the fog drop has strong static performance under the action of certain electric field force, so that the fog drop may be deposited homogeneously on the surface near the position and the liquid fog drop may be used as fiber adhesive to strengthen the mechanical performance of fiber.
With the rapid development of the lithium battery industry and the remarkable increase of the economic benefit thereof, people put higher and higher requirements on the performance of the lithium battery. The superiority or superiority of lithium battery performance depends greatly on the negative electrode material. The negative electrode material forms an active material/inert matrix material structure during intercalation and deintercalation of lithium, wherein the active material reacts with lithium to provide capacity, and the inert matrix material maintains a stable structure to ensure battery life. Therefore, the development of high-capacity anode materials with ultra-long cycle life is a key ring for challenging high-performance lithium batteries, li 3 VO 4 Is considered as an ideal negative electrode material for the next generation of high capacity lithium ion batteries.
Disclosure of Invention
The application provides a preparation method of a flexible double-layer self-supporting electrode. The prepared electrode can bear deformation (bending, folding, twisting, compressing or stretching) within a certain range, the double-layer electrode structure has strong bearing capacity, the advantages of each material are fully exerted, the double-layer electrode structure has excellent mechanical flexibility and firmness, structural collapse caused by volume expansion in the charge and discharge process can be effectively restrained, meanwhile, the active material is used as a working electrode, other conductive agents and binders are not added, further permeation of electrolyte is facilitated, excellent electrochemical performance is shown, and the double-layer electrode structure has potential application value in a lithium ion battery.
In order to achieve the purpose, the application adopts the following technical scheme:
a method of making a flexible bilayer self-supporting electrode, the method comprising the steps of:
(1) Dissolving polyacrylonitrile, lithium nitrate, ammonium metavanadate and oxalic acid in N, N-dimethylformamide, and stirring to form a uniform blue-black uniform solution, wherein the uniform solution is taken as a solution A;
(2) Weighing polyvinyl alcohol, dissolving in deionized water, stirring until the polyvinyl alcohol is clear, then adding lithium nitrate, ammonium metavanadate and oxalic acid, and stirring until a uniform blue solution is formed, thereby obtaining a solution B;
(3) And (3) transferring the uniform solution A obtained in the step (1) into an injector for spinning to obtain a flexible electrode substrate layer, wherein the spinning cloth is easy to peel off from an aluminum foil due to good film forming uniformity after polyacrylonitrile spinning, and simultaneously, the spinning cloth is used as the substrate layer, and spinning/spraying of other components is directly added on the substrate layer, so that the structural stability of the flexible electrode material is improved.
The basal layer is uniform in film formation, lays a foundation for the structural stability of subsequent spinning/spraying, and simultaneously enables the spinning cloth to be easily stripped from the aluminum foil, so that a more complete flexible self-supporting electrode material is conveniently obtained;
(4) Transferring the homogeneous solution A, B obtained in the steps (1) and (2) to an electrostatic spinning injector respectively, wherein the solution A is an electrostatic spinning process, the solution B is an electrostatic spraying process, and spinning on the flexible electrode substrate layer obtained in the step (3) to obtain electrostatic spinning cloth interwoven by two materials;
(5) Drying the electrostatic spinning cloth obtained in the step (4), placing the dried electrostatic spinning cloth in a nitrogen environment, heating for presintering, and calcining to obtain the flexible double-layer self-supporting composite material (the substrate layer is Li) 3 VO 4 Composite material/C with Li as top layer 3 VO 4 -LiV 2 O 4 C double needle blended composite nanomaterial);
preferably, in the step (1), the molar ratio of the lithium nitrate, the oxalic acid and the ammonium metavanadate in the mixed solution is (3-4), the molar ratio of the lithium nitrate, the oxalic acid and the ammonium metavanadate is (3-4), the total mass of the added lithium nitrate, the oxalic acid and the ammonium metavanadate is 0.8-1.2 g, the mass of the N, N-dimethylformamide accounts for 82-86% of the total mass, and the mass of the polyacrylonitrile accounts for 5-7% of the total mass;
preferably, in the step (2), the molar ratio of the lithium nitrate, the oxalic acid and the ammonium metavanadate in the mixed solution is (3-4), the molar ratio of the lithium nitrate, the oxalic acid and the ammonium metavanadate is (5-6.7), the total mass of the added lithium nitrate, the oxalic acid and the ammonium metavanadate is 2.3-3.2 and g, the mass of deionized water accounts for 79-84% of the total mass, and the mass of the polyvinyl alcohol accounts for 2-4% of the total mass.
Preferably, the spinning conditions in the steps (3) and (4) are as follows: the voltage is 16-20kV, the time is 4-6 hours, the temperature is 40-60 ℃, the humidity is 20-30%, and the distance is 20-30cm.
Preferably, the step (3) is single-needle electrostatic spinning, the obtained spinning cloth is used as a substrate layer, the step (4) is double-needle mixed electrostatic spinning and electrostatic spraying, and the substrate layer obtained in the step (3) is directly used as a receiving device, wherein the solution A is electrostatic spinning, and the solution B is electrostatic spraying;
preferably, in step (5), the drying temperature is 60-80 ℃ and the drying is carried out for 10-12 hours.
Preferably, the pre-sintering temperature in the step (5) is 200-300 ℃, the heating speed is 1-3 ℃/min, the pre-sintering time is 2-5 hours, and the pre-sintering is performed at 500-800 ℃ for 5-8 hours at the heating speed of 3-5 ℃/min.
The application forms fiber by stretching polymer solution in strong electric field, and simultaneously utilizes double-needle blending to prepare Li with Y-shaped fiber interweaving 3 VO 4 -LiV 2 O 4 The flexible double-layer self-supporting composite material is prepared by simple electrostatic spinning and electrostatic spraying for the first time, and the substrate layer is Li 3 VO 4 The composite material is integrally in a fiber network shape, a large number of ultrafine nano particles are inlaid on the surface of the composite material, and the top layer is Li 3 VO 4 -LiV 2 O 4 The double needle blended composite nano material presents a Y-shaped extension fiber cross passage, provides a convenient lithium ion transmission channel, and obviously enhances the diffusion of lithium ions in the composite material. Through electrostatic spinning and electrostatic spraying, the double-layer electrode with a more stable design structure is designed, and the self-supporting double-layer fiber composite material is directly used as a negative electrode of a lithium ion battery, so that a convenient lithium ion transmission channel can be provided, excellent electrochemical performance is displayed, and the self-supporting double-layer fiber composite material has a good application prospect.
The principle is as follows: (1) The high viscosity of the Polyacrylonitrile (PAN) solution has good adsorption effect and can effectively adsorb Li + 、VO 2+ The PAN nanofiber membrane is uniformly dispersed in a microscopic scale, and meanwhile, the electrostatic spinning PAN nanofiber membrane has a random orientation structure and enough mechanical strength; (2) The water-based high polymer polyvinyl alcohol (PVA) is used as an adhesive in the electrostatic spraying process, and a plurality of nanofibers are adhered to form fiber branch passages, so that the diffusion and the transfer of lithium ions are facilitated; (3) Oxalic acid is used for providing an acidic environment, so that the formation of a uniform solution is promoted, and simultaneously, the uniform solution is used as a cross-linking agent to carry out a cross-linking reaction with polyvinyl alcohol. Polyacrylonitrile is used as a linear template, and R-OOC-COO-R and Li are used as the template + 、VO 2+ By combining oxalic acid as an effective bridge for connecting the two polymers, and presintering at a low temperature of 200-300 ℃, the linear macromolecular chains of polyacrylonitrile are converted into heat-resistant trapezoid structures, and polyvinyl alcohol is subjected to dehydrogenation reaction to generate conjugated C=C bonds at the same time, so that a stable carbon skeleton is formed. The crosslinking reaction enhances the rigidity of the chain, thereby affecting the thermal stability of the polymer; (4) Due to the synergistic effect of the graded nano fibers and the hydrophilic polymer matrix, a porous fiber layer with a layered structure is constructed, and the synergistic effect of the micro/nano structures and the excellent hydrophilicity of the hydrated polymer matrix lead the connection network of the nano fibers to form an ultrathin and highly porous barrier, thereby being beneficial to the contact and permeation of electrolyte; (5) The mixed nanofiber membrane of multiple components can provide a synergistic effect of the multiple components to improve overall performance; (6) The double-layer electrode has more structural advantages than the single-layer electrode, and the double-layer electrode is made of different materials, fully exerts the advantages of the materials and has excellent propertiesAnd the material shows excellent comprehensive electrochemical performance as a lithium ion battery cathode.
Compared with the prior art, the application has the beneficial effects that:
(1) The manufacturing cost is low, the method is green and pollution-free, and is environment-friendly;
(2) The synthesis process is simple, electrostatic spinning and electrostatic spraying can be simultaneously carried out without additional high-temperature environment, and the repeatability is high;
(3) The prepared flexible double-layer self-supporting composite material has the double-morphology of a fiber network and the cross of Y-shaped extension fibers, has the characteristics of strong bearing capacity and stable structure, can bear the volume expansion caused by charge and discharge, and the self-supporting electrode is beneficial to the contact and permeation of electrolyte and has high capacity and excellent cycle stability.
Drawings
FIG. 1 optical photographs of sample precursors prepared after spinning of example 1: (a) a substrate layer, (b) a top layer;
figure 2 XRD pattern of sample prepared in example 1: (a) Base layer Li 3 VO 4 C, (b) Top layer Li 3 VO 4 -LiV 2 O 4 /C；
Fig. 3 SEM image of the sample prepared in example 1: (a) Base layer Li 3 VO 4 C, (b, C) top layer Li 3 VO 4 -LiV 2 O 4 /C；
Fig. 4 optical photographs of samples prepared in example 1: (a) folding 90 ° and (b) cutting into 14 mm electrode sheets;
fig. 5 top three charge and discharge curves and cycle performance graphs for samples prepared in example 1: (a) A charge-discharge curve of the previous three times, (b) a cycle performance diagram;
FIG. 6 is an optical photograph of the sample prepared in example 2;
fig. 7 top three charge and discharge curves and cycle performance graphs for samples prepared in example 2: (a) A charge-discharge curve of the previous three times, (b) a cycle performance diagram;
FIG. 8 is an optical photograph of the sample prepared in example 3;
fig. 9 top three charge and discharge curves and cycle performance graphs for samples prepared in example 3: (a) A charge-discharge curve of the previous three times, (b) a cycle performance diagram;
FIG. 10 is an optical photograph of a sample precursor fiber membrane prepared in example 4;
FIG. 11 is a photograph of the sample prepared in example 5 (a) in the form of a whole sheet and (b) broken up after pressing with forceps; (a) The whole optical photo is sheet-shaped, (b) the image is broken after being pressed by forceps;
fig. 12 top three charge and discharge curves and cycle performance graphs for samples prepared in example 5: (a) A charge-discharge curve of the previous three times, (b) a cycle performance diagram;
FIG. 13 is an optical photograph of the sample prepared in example 6;
fig. 14 top three charge and discharge curves and cycle performance graphs for the samples prepared in example 6: (a) A charge-discharge curve of the previous three times, (b) a cycle performance diagram;
FIG. 15 is an optical photograph of the sample precursor solution prepared in example 7.
Detailed Description
Example 1
Accurately weighing 0.65 g polyacrylonitrile, 3.75 mmol lithium nitrate, 1.25 mmol ammonium metavanadate and 3.75 mmol oxalic acid according to stoichiometric amount, dissolving in 10 mL N, N-dimethylformamide, and stirring to form a uniform blue-black colloid solution, wherein the uniform blue-black colloid solution is taken as a solution A; simultaneously, 0.5. 0.5 g polyvinyl alcohol is weighed and dissolved in 15 mL deionized water, stirred until the solution is clear, then 7.5 mmol of lithium nitrate, 2.5 mmol of ammonium metavanadate and 12.5 mmol of oxalic acid are added, stirred until a uniform blue uniform solution is formed, the solution is taken as a solution B, the obtained uniform solution A is transferred to a syringe, and spinning is carried out for 4 hours under the conditions of 20-kV voltage and 40 ℃ temperature, and the solution A is taken as a flexible electrode substrate layer. Respectively transferring the homogeneous solutions A, B into electrostatic spinning injectors, wherein the solution A is an electrostatic spinning process, the solution B is an electrostatic spraying process, directly spinning on the substrate layer for 4 hours under the same condition to obtain layered electrostatic spinning cloth interwoven by two materials, and rapidly transferring the precursor materials after spinningDrying in a blowing drying oven at 80deg.C for 12 hr to obtain a smooth fiber membrane as the base layer (figure 1 a), forming a rough surface (figure 1 b) with double needle electrostatic spinning and electrostatic spraying as the top layer, pre-sintering at 250deg.C in nitrogen environment for 3 hr, calcining at 600deg.C for 6 hr to obtain a flexible double-layer composite material, and analyzing by XRD spectrum with Li as the base layer 3 VO 4 C, the diffraction peak obtained and Li 3 VO 4 (PDF # 38-1247) corresponds well (FIG. 2 a). The top layer is Li 3 VO 4 -LiV 2 O 4 C, the diffraction peaks obtained are respectively compared with Li 3 VO 4 （PDF#38-1247），LiV 2 O 4 (PDF # 38-0260) corresponds well (FIG. 2 b), and as can be seen from SEM images, the composite base layer and top layer both present a fibrous network-like structure (FIGS. 3a, b), base layer Li 3 VO 4 The fiber surface of/C has a uniform distribution of a plurality of ultra-small nanoparticles (inset in FIG. 3 a), top layer Li 3 VO 4 -LiV 2 O 4 The fiber surface of/C is smooth with special "Y" shaped extending fiber crossover nodes (fig. 3C), the layered structure ensuring efficient impregnation of the electrolyte.
The carbonized composite material, namely the flexible double-layer composite nanofiber membrane, can still keep the structural integrity after being folded to 90 degrees, has no fracture and breakage, can bear a certain range of deformation (figure 4 a), and is manufactured into a battery according to the following method: cutting into electrode plates with diameter of 14 mm with a slicer, with smooth and burr-free fracture and flat surface (FIG. 4 b), using metal lithium plate as counter electrode, celgard film as diaphragm, dissolving LiPF 6 （1 mmol L -1 ) Ec+dmc+dec (volume ratio of 1:1:1) solution as electrolyte, and assembling into a CR2025 type battery in a glove box protected by argon. And standing for 8 hours after the battery is assembled, and then carrying out constant-current charge and discharge test by using a CT2001 battery test system, wherein the test voltage is 3-0.01V. Fig. 5 is a graph of the charge and discharge curves and cycle performance of the prepared lithium ion battery negative electrode in the first three cycles. Specific capacities of initial charge and discharge are 611.2 mAh g respectively -1 And 806.7 mAh g -1 After 20 times of circulation, the charge and discharge capacity are 509.3 mAh g respectively -1 And 512.7 mAh g -1 Exhibits excellent electrochemical properties.
Example 2
In this example, only the solution a in example 1 was used for spinning, and then a material was obtained under the same sintering conditions, and the obtained material was entirely in the form of a fiber film with surface wrinkles (fig. 6), was cut into electrode sheets with a diameter of 14 mm by a microtome, and had smooth and burr-free fracture (illustration in fig. 6), and was fabricated into a battery according to the method of example 1. Specific capacities of the first charge and discharge are 309.9 mAh g respectively -1 And 581.7 mAh g -1 (FIG. 7 a) has obvious charge and discharge plateau, and after 20 cycles, the charge and discharge capacities are 315.4 mAhg respectively -1 And 316.1 mAh g -1 (FIG. 7 b), electrochemical performance is poor.
Example 3
In this example, only the solution B in example 1 was used for spraying, and the solution concentration was low, so that the solution could not be stretched into fibers in an electric field, and therefore the process was an electrostatic spraying process, and then a material was obtained under the same sintering condition, and the obtained material was powder (fig. 8), and a self-supporting battery product could not be realized, and the material was made into a battery according to the following method: mixing the prepared sample with acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, preparing slurry by using N-methyl pyrrolidone as a solvent, coating the slurry on copper foil with the thickness of 10 mu m, drying the slurry at 60 ℃ for 10 hours, cutting the slurry into wafers with the diameter of 14 and mm, and drying the wafers at 120 ℃ in vacuum for 12 hours. The metal lithium sheet is used as a counter electrode, the Celgard membrane is used as a diaphragm, and the LiPF is dissolved 6 (1 mmol/L) of EC+DMC+DEC (volume ratio of 1:1:1) solution was used as an electrolyte, and a CR2025 type battery was assembled in a glove box under argon protection. And standing for 8 hours after the battery is assembled, and then carrying out constant-current charge and discharge test by using a CT2001 battery test system, wherein the test voltage is 3-0.01V. Fig. 9 is a graph of the charge and discharge curves and cycle performance of the prepared lithium ion battery negative electrode in the first three cycles. Specific capacities of initial charge and discharge are 329.2 mAh g respectively -1 And 664.2 mAh g -1 After 20 times of circulation, the charge and discharge capacity are 278.2 mAh g respectively -1 And 280.5 mAh g -1 The electrochemical performance is poor.
Example 4
In this example, the solution B in example 1 was used alone for spraying, and the substrate layer was sprayed at a voltage of 20kV and a temperature of 40 ℃ for 4 hours. And then directly spinning on the basal layer for 4 hours under the same condition by using the solution A to obtain layered electrostatic spinning cloth interwoven by two materials, rapidly transferring the precursor material to a blast drying oven at 80 ℃ to dry for 12 hours after spinning, wherein the basal layer of the precursor material is a yellow surface formed by electrostatic spraying, the top layer is a smooth fiber film (figure 10 a), and the fiber film is peeled off from the aluminum foil by using tweezers, so that the two layers are obviously separated from each other (figure 10 b), and a good double-layer bonding state cannot be achieved, so that it is inferred that a double-layer self-supporting electrode cannot be obtained, and a flexible self-supporting battery product cannot be realized.
Example 5
In the embodiment, only the solution A and the solution B in the embodiment 1 are adopted for double-needle blending, then the material is obtained under the same sintering condition, the obtained material cannot be completely peeled off from the aluminum foil, the peeled part is in a sheet shape after sintering (fig. 11 a), the brittleness is strong, the self-supporting battery product cannot be realized after being pressed and broken (fig. 11B), the material is manufactured into a battery according to the method of the embodiment 3, the battery is left for 8 hours after being assembled, and then a constant-current charge and discharge test is carried out by using a CT2001 battery test system, wherein the test voltage is 3-0.01V. Fig. 12 is a graph of the charge and discharge curves and cycle performance of the prepared lithium ion battery negative electrode in the first three cycles. Specific capacities of initial charge and discharge are 570.1 mAh g respectively -1 And 752.1 mAh g -1 After 20 times of circulation, the charge and discharge capacity are 466.9 mAh g respectively -1 And 471.6 mAh g -1 And shows good electrochemical performance.
Example 6
In this example, the high polymer polyacrylonitrile used in example 1 was merely changed to polyvinylpyrrolidone (PVP), double-needle blending was performed using the solution A and the solution B, and then a material was obtained under the same sintering conditions, the obtained material was a powder (FIG. 13), a self-supporting battery product could not be realized, the material was fabricated into a battery according to the method of example 3, and the battery was left to stand after the completion of the battery assemblyAnd (3) after 8 hours, carrying out constant-current charge and discharge test by using a CT2001 battery test system, wherein the test voltage is 3-0.01V. Fig. 14 is a graph of the charge and discharge curves and cycle performance of the prepared lithium ion battery negative electrode for the first three cycles. Specific capacities of initial charge and discharge are 404.8 mAh g respectively -1 And 752.1 mAh g -1 After 20 times of circulation, the charge and discharge capacity are 372.3 mAh g respectively -1 And 375.5 mAh g -1 And shows good electrochemical performance.
Example 7
In this example, only oxalic acid was not added to the solution A, B in example 1, at this time, the solution A, B could not be sufficiently dissolved in a neutral environment, and delamination occurred after standing (fig. 15), and the electrostatic spinning process could not be completed due to the non-uniformity of the solution, so it was inferred that a double-layer self-supporting electrode could not be obtained, and a flexible self-supporting battery product could not be realized.
Example 8
In this example, only the solution a in example 1 was not added with the polymer polyacrylonitrile, and was electrospun at the same voltage and injection speed, at this time, the solution a could not be drawn into filaments in the electric field, and the solution was easy to drop from the needle, and the electrospinning process could not be completed, so it was inferred that a double-layer self-supporting electrode could not be obtained, and a flexible self-supporting battery product could not be realized.
Example 9
In this embodiment, only the solution B in example 1 was not added with the polymer polyvinyl alcohol, and was electrostatically sprayed at the same voltage and injection speed, at this time, the solution B could not be atomized in the electric field, and the solution was dropped from the needle during the spraying, and the electrostatic spraying process could not be completed, so it was inferred that a double-layer self-supporting electrode could not be obtained, and a flexible self-supporting battery product could not be realized.
Example 10
This example only doubles the high polymer content of the solution A, B of example 1, namely: 1.3 g polyacrylonitrile is added to the solution A, 1.0 g polyvinyl alcohol is added to the solution B, and electrostatic spinning/spraying is performed under the same voltage and injection speed, at this time, the concentration of the solution A is too high, a needle is easy to block, and the electrostatic spinning process cannot be completed, so that it is inferred that a double-layer self-supporting electrode cannot be obtained, and a flexible self-supporting battery product cannot be realized.
Example 11
A method of making a flexible bilayer self-supporting electrode, the method comprising the steps of:
(1) Dissolving polyacrylonitrile, lithium nitrate, ammonium metavanadate and oxalic acid in N, N-dimethylformamide, and stirring to form a uniform blue-black uniform solution, wherein the uniform solution is taken as a solution A;
(2) Weighing polyvinyl alcohol, dissolving in deionized water, stirring until the polyvinyl alcohol is clear, then adding lithium nitrate, ammonium metavanadate and oxalic acid, and stirring until a uniform blue solution is formed, thereby obtaining a solution B;
(3) And (3) transferring the uniform solution A obtained in the step (1) into an injector for spinning to obtain a flexible electrode substrate layer, wherein the spinning cloth is easy to peel off from an aluminum foil due to good film forming uniformity after polyacrylonitrile spinning, and simultaneously, the spinning cloth is used as the substrate layer, and spinning/spraying of other components is directly added on the substrate layer, so that the structural stability of the flexible electrode material is improved.
The basal layer is uniform in film formation, lays a foundation for the structural stability of subsequent spinning/spraying, and simultaneously enables the spinning cloth to be easily stripped from the aluminum foil, so that a more complete flexible self-supporting electrode material is conveniently obtained;
(4) Transferring the homogeneous solution A, B obtained in the steps (1) and (2) to an electrostatic spinning injector respectively, wherein the solution A is an electrostatic spinning process, the solution B is an electrostatic spraying process, and spinning on the flexible electrode substrate layer obtained in the step (3) to obtain electrostatic spinning cloth interwoven by two materials;
(5) Drying the electrostatic spinning cloth obtained in the step (4), placing the dried electrostatic spinning cloth in a nitrogen environment, heating for presintering, and calcining to obtain the flexible double-layer self-supporting composite material (the substrate layer is Li) 3 VO 4 Composite material/C with Li as top layer 3 VO 4 -LiV 2 O 4 C double needle blended composite nanomaterial);
preferably, in the step (1), the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution is 3:3:1, the total mass of the added lithium nitrate, oxalic acid and ammonium metavanadate is 0.9 g, the mass of N, N-dimethylformamide accounts for 86.1% of the total mass, and the mass of polyacrylonitrile accounts for 5.9% of the total mass;
preferably, in the step (2), the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution is 3:5:1, the total mass of the added lithium nitrate, oxalic acid and ammonium metavanadate is 2.4 and g, the mass of deionized water accounts for 83.9% of the total mass, and the mass of polyvinyl alcohol accounts for 2.8% of the total mass.
Preferably, the spinning conditions in the steps (3) and (4) are as follows: the voltage was 16kV, the time was 4 hours, the temperature was 40 ℃, the humidity was 20%, and the distance was 20cm.
Preferably, the step (3) is single-needle electrostatic spinning, the obtained spinning cloth is used as a substrate layer, the step (4) is double-needle mixed electrostatic spinning and electrostatic spraying, and the substrate layer obtained in the step (3) is directly used as a receiving device, wherein the solution A is electrostatic spinning, and the solution B is electrostatic spraying;
preferably, in step (5), the drying temperature is 60℃and the drying is carried out for 10 hours.
Preferably, the pre-sintering temperature in the step (5) is 200 ℃, the heating rate is 1 ℃/min, the pre-sintering time is 2 hours, and the calcination is performed at 500 ℃ for 5 hours at the heating rate of 3 ℃/min.
Example 12
A method of making a flexible bilayer self-supporting electrode, the method comprising the steps of:
(1) Dissolving polyacrylonitrile, lithium nitrate, ammonium metavanadate and oxalic acid in N, N-dimethylformamide, and stirring to form a uniform blue-black uniform solution, wherein the uniform solution is taken as a solution A;
(2) Weighing polyvinyl alcohol, dissolving in deionized water, stirring until the polyvinyl alcohol is clear, then adding lithium nitrate, ammonium metavanadate and oxalic acid, and stirring until a uniform blue solution is formed, thereby obtaining a solution B;
(3) And (3) transferring the uniform solution A obtained in the step (1) into an injector for spinning to obtain a flexible electrode substrate layer, wherein the spinning cloth is easy to peel off from an aluminum foil due to good film forming uniformity after polyacrylonitrile spinning, and simultaneously, the spinning cloth is used as the substrate layer, and spinning/spraying of other components is directly added on the substrate layer, so that the structural stability of the flexible electrode material is improved.
The basal layer is uniform in film formation, lays a foundation for the structural stability of subsequent spinning/spraying, and simultaneously enables the spinning cloth to be easily stripped from the aluminum foil, so that a more complete flexible self-supporting electrode material is conveniently obtained;
(4) Transferring the homogeneous solution A, B obtained in the steps (1) and (2) to an electrostatic spinning injector respectively, wherein the solution A is an electrostatic spinning process, the solution B is an electrostatic spraying process, and spinning on the flexible electrode substrate layer obtained in the step (3) to obtain electrostatic spinning cloth interwoven by two materials;
(5) Drying the electrostatic spinning cloth obtained in the step (4), placing the dried electrostatic spinning cloth in a nitrogen environment, heating for presintering, and calcining to obtain the flexible double-layer self-supporting composite material (the substrate layer is Li) 3 VO 4 Composite material/C with Li as top layer 3 VO 4 -LiV 2 O 4 C double needle blended composite nanomaterial);
preferably, in the step (1), the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution is 4:4:1.3, the total mass of the added lithium nitrate, oxalic acid and ammonium metavanadate is 1.2 g, the mass of N, N-dimethylformamide accounts for 82.8% of the total mass, and the mass of polyacrylonitrile accounts for 7.2% of the total mass;
preferably, in the step (2), the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution is 4:6.7:1.3, the total mass of the added lithium nitrate, oxalic acid and ammonium metavanadate is 3.2 and g, the mass of deionized water is 79.6% of the total mass, and the mass of polyvinyl alcohol is 3.6% of the total mass.
Preferably, the spinning conditions in the steps (3) and (4) are as follows: the voltage was 20kV, the time was 6 hours, the temperature was 60℃and the humidity was 30%, the distance was 30cm.
Preferably, the step (3) is single-needle electrostatic spinning, the obtained spinning cloth is used as a substrate layer, the step (4) is double-needle mixed electrostatic spinning and electrostatic spraying, and the substrate layer obtained in the step (3) is directly used as a receiving device, wherein the solution A is electrostatic spinning, and the solution B is electrostatic spraying;
preferably, in step (5), the drying temperature is 80℃and the drying is carried out for 12 hours.
Preferably, the pre-sintering temperature in the step (5) is 300 ℃, the heating rate is 3 ℃/min, the pre-sintering time is 5 hours, and the calcination is performed at 800 ℃ for 8 hours at the heating rate of 5 ℃/min.
Example 13
A method of making a flexible bilayer self-supporting electrode, the method comprising the steps of:
(1) Dissolving polyacrylonitrile, lithium nitrate, ammonium metavanadate and oxalic acid in N, N-dimethylformamide, and stirring to form a uniform blue-black uniform solution, wherein the uniform solution is taken as a solution A;
(2) Weighing polyvinyl alcohol, dissolving in deionized water, stirring until the polyvinyl alcohol is clear, then adding lithium nitrate, ammonium metavanadate and oxalic acid, and stirring until a uniform blue solution is formed, thereby obtaining a solution B;
(3) And (3) transferring the uniform solution A obtained in the step (1) into an injector for spinning to obtain a flexible electrode substrate layer, wherein the spinning cloth is easy to peel off from an aluminum foil due to good film forming uniformity after polyacrylonitrile spinning, and simultaneously, the spinning cloth is used as the substrate layer, and spinning/spraying of other components is directly added on the substrate layer, so that the structural stability of the flexible electrode material is improved.
The basal layer is uniform in film formation, lays a foundation for the structural stability of subsequent spinning/spraying, and simultaneously enables the spinning cloth to be easily stripped from the aluminum foil, so that a more complete flexible self-supporting electrode material is conveniently obtained;
(4) Transferring the homogeneous solution A, B obtained in the steps (1) and (2) to an electrostatic spinning injector respectively, wherein the solution A is an electrostatic spinning process, the solution B is an electrostatic spraying process, and spinning on the flexible electrode substrate layer obtained in the step (3) to obtain electrostatic spinning cloth interwoven by two materials;
(5) Drying the electrostatic spinning cloth obtained in the step (4), placing the dried electrostatic spinning cloth in a nitrogen environment, heating for presintering, and calcining to obtain the flexible double-layer self-supporting composite material (the substrate layer is Li) 3 VO 4 Composite material/C with Li as top layer 3 VO 4 -LiV 2 O 4 C double needle blended composite nanomaterial);
preferably, in the step (1), the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution is 3.5:3.5:1.2, the total mass of the added lithium nitrate, oxalic acid and ammonium metavanadate is 1.0 g, the mass of N, N-dimethylformamide accounts for 84.8% of the total mass, and the mass of polyacrylonitrile accounts for 6.4% of the total mass;
preferably, in the step (2), the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution is 3.5:6.2:1.2, the total mass of the added lithium nitrate, oxalic acid and ammonium metavanadate is 2.8 and g, the mass of deionized water is 81.8% of the total mass, and the mass of polyvinyl alcohol is 3.2% of the total mass.
Preferably, the spinning conditions in the steps (3) and (4) are as follows: the voltage was 18kV, the time was 5 hours, the temperature was 55℃and the humidity was 28%, the distance was 28cm.
Preferably, the step (3) is single-needle electrostatic spinning, the obtained spinning cloth is used as a substrate layer, the step (4) is double-needle mixed electrostatic spinning and electrostatic spraying, and the substrate layer obtained in the step (3) is directly used as a receiving device, wherein the solution A is electrostatic spinning, and the solution B is electrostatic spraying;
preferably, in step (5), the drying temperature is 75℃and the drying is carried out for 11 hours.
Preferably, the pre-sintering temperature in the step (5) is 250 ℃, the heating rate is 2 ℃/min, the pre-sintering time is 4 hours, and the calcination is performed at 700 ℃ for 7 hours at the heating rate of 4 ℃/min.
The above embodiments are merely preferred embodiments of the present application, and should not be construed as limiting the present application, and the embodiments and features of the embodiments of the present application may be arbitrarily combined with each other without collision. The protection scope of the present application is defined by the claims, and the protection scope includes equivalent alternatives to the technical features of the claims. I.e., equivalent replacement modifications within the scope of this application are also within the scope of the application.
Claims (7)
1. A method for preparing a flexible double-layer self-supporting electrode, which is characterized by comprising the following steps:
(1) Dissolving polyacrylonitrile, lithium nitrate, ammonium metavanadate and oxalic acid in N, N-dimethylformamide, and stirring to form a uniform blue-black solution serving as a solution A;
(2) Weighing polyvinyl alcohol, dissolving in deionized water, stirring until the polyvinyl alcohol is clear, then adding lithium nitrate, ammonium metavanadate and oxalic acid, and stirring until a uniform blue uniform solution is formed, thereby taking the solution as a solution B;
(3) Transferring the uniform solution A obtained in the step (1) into an injector, and carrying out electrostatic spinning to obtain a flexible electrode substrate layer;
(4) Transferring the homogeneous solution A, B obtained in the steps (1) and (2) to a double-needle mixed electrostatic spinning and electrostatic spraying in an electrostatic spinning injector respectively, wherein the solution A is an electrostatic spinning process, the solution B is an electrostatic spraying process, and spinning on the flexible electrode substrate layer obtained in the step (3) to obtain electrostatic spinning cloth interwoven by two materials;
(5) Drying the electrostatic spinning cloth obtained in the step (4), placing the dried electrostatic spinning cloth in a nitrogen environment, heating for presintering, and calcining to obtain a flexible double-layer self-supporting composite material, wherein the substrate layer and the top layer of the composite material are of fiber network structures, and the substrate layer is Li 3 VO 4 C, the top layer is Li 3 VO 4 -LiV 2 O 4 /C。
2. The method for preparing the flexible double-layer self-supporting electrode according to claim 1, wherein the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution in the step (1) is (3-4): (3-4): (1-1.3), the mass of N, N-dimethylformamide accounts for 82-86% of the total mass, and the mass of polyacrylonitrile accounts for 5-7% of the total mass.
3. The method for preparing the flexible double-layer self-supporting electrode according to claim 1, wherein in the step (2), the molar ratio of lithium nitrate, oxalic acid and ammonium metavanadate in the mixed solution is (3-4): (5-6.7): (1-1.3), the mass of deionized water is 79-84% of the total mass, and the mass of polyvinyl alcohol is 2-4% of the total mass.
4. The method for preparing a flexible double-layer self-supporting electrode according to claim 1, wherein the spinning conditions in the steps (3) and (4) are as follows: the voltage is 16-20kV, the time is 4-6 hours, the temperature is 40-60 ℃, the humidity is 20-30%, and the distance is 20-30cm.
5. The method of producing a flexible double-layer self-supporting electrode according to claim 1, wherein step (3) is single needle electrospinning, and the resulting woven cloth is used as a base layer.
6. The method for producing a flexible double-layered self-supporting electrode according to claim 1, wherein in the step (5), the drying temperature is 60 to 80 ℃ and the drying is performed for 10 to 12 hours.
7. The method for preparing a flexible double-layer self-supporting electrode according to claim 1, wherein the pre-sintering temperature in the step (5) is 200-300 ℃, the heating rate is 1-3 ℃/min, the pre-sintering time is 2-5 hours, and the calcination is performed at 500-800 ℃ for 5-8 hours at the heating rate of 3-5 ℃/min.
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