CN114927644B - Preparation method of positive electrode material, preparation method of battery and battery - Google Patents
Preparation method of positive electrode material, preparation method of battery and battery Download PDFInfo
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- CN114927644B CN114927644B CN202210577866.3A CN202210577866A CN114927644B CN 114927644 B CN114927644 B CN 114927644B CN 202210577866 A CN202210577866 A CN 202210577866A CN 114927644 B CN114927644 B CN 114927644B
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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
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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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
- H01M4/582—Halogenides
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
A preparation method of a positive electrode material, the positive electrode material, a preparation method of a battery and the battery, wherein the preparation method of the positive electrode material comprises the following steps: dispersing and dissolving cobalt metal organic framework and polyacrylonitrile in N, N-dimethylformamide to form a composite solution; obtaining a polyacrylonitrile nanofiber membrane loaded with the cobalt metal organic framework through an electrostatic spinning means on the composite solution; drying the nanofiber membrane; pre-oxidizing the dried nanofiber membrane; carbonizing the pre-oxidized nanofiber film; reducing the carbonized nanofiber film; and carrying out fluoridation heat treatment on the reduced nanofiber membrane to obtain the anode material. The cathode material (CoF) of the present application 2 -C NF) realizes the improvement of capacity release of cobalt fluoride under low discharge multiplying power and long cycle life of cobalt fluoride under high multiplying power.
Description
Technical Field
The application relates to the technical field of batteries, in particular to a preparation method of a positive electrode material, the positive electrode material, a preparation method of a battery and the battery.
Background
The Ningde era adopts a high-nickel anode and a graphite cathode with a small amount of silicon monoxide added to develop a lithium ion battery sample with specific energy more than or equal to 304Wh/kg, the normal-temperature cycle performance reaches 1500 times, the safety meets the national standard requirement, and mass production is expected to be realized at the end of 2020; the specific energy of the lithium iron phosphate blade battery cell reaches 180Wh/kg, and the specific energy of the system reaches 140Wh/kg. High specific energy batteries are a requisite path in the growing energy demands of today's society, transition metal fluorides (CoF) 2 About 1405 Wh/kg), the high theoretical specific energy density has been of interest in research in the scientific community;
although the transition metal fluoride lithium ion battery has the characteristics of large theoretical specific capacity, low cost, environmental protection and the like, the transition metal fluoride lithium ion battery is characterized by F - Intrinsic defects of poor conductivity/insulation caused by strong electronegativity of (c) and problems of volume change and irreversible phase transition during circulation, serious interface side reactions, etc., have prevented the commercialization process thereof. For the problems, the construction of the metal fluoride-carbon composite positive electrode material can greatly improve the ion/electron conductivity of the metal fluoride-carbon composite positive electrode material, and is favorable for realizing reversible long-cycle of the fluoride positive electrode material, but a common fragile conductive network cannot inhibit volume expansion and relieve the problem of dissolution of intermediate products.
Disclosure of Invention
Object of the application
The application aims to provide a preparation method of a positive electrode material, the positive electrode material, a preparation method of a battery and the battery, so as to solve the problems of poor capacity release, long cycle life, poor intrinsic conductivity of ferrous fluoride and the like of the cobalt fluoride positive electrode material under low multiplying power, and relieve the volume expansion effect and the active substance dissolution effect of the cobalt fluoride positive electrode material in the charging and discharging processes.
(II) technical scheme
The first aspect of the present application provides a method for preparing a positive electrode material, comprising: dispersing and dissolving cobalt metal organic framework and polyacrylonitrile in N, N-dimethylformamide to form a composite solution; obtaining a polyacrylonitrile nanofiber membrane loaded with the cobalt metal organic framework through an electrostatic spinning means on the composite solution; drying the nanofiber membrane; pre-oxidizing the dried nanofiber membrane; carbonizing the pre-oxidized nanofiber film; reducing the carbonized nanofiber film; and carrying out fluoridation heat treatment on the reduced nanofiber membrane to obtain the anode material.
Optionally, before the cobalt metal organic framework and the polyacrylonitrile are dispersed and dissolved in the N, N-dimethylformamide to form a composite solution, the method further comprises: slowly adding a cobalt source and an organic ligand into an anhydrous methanol solution according to a preset proportion, and stirring and mixing; standing at room temperature overnight, centrifuging to obtain precipitate; and drying in a constant temperature box at 60 ℃ for 6 hours, and collecting to obtain the cobalt metal organic frame.
Optionally, the dispersing and dissolving the cobalt metal organic framework and polyacrylonitrile in N, N-dimethylformamide to form a composite solution includes: mixing a cobalt metal organic framework with N, N-dimethylformamide to obtain a mixed solution; carrying out ultrasonic treatment on the mixed solution; and adding polyacrylonitrile into the mixed solution after ultrasonic treatment, and stirring for 24 hours to obtain the composite solution.
Optionally, the cobalt source is Co (NO 3 ) 3 ·6H 2 O or a cobalt salt soluble in water; the organic ligand is 2-methylimidazole; the volume of anhydrous methanol was 200mL.
Optionally, the polyacrylonitrile has a weight average molecular weight of 150000; the mass fraction of the carbonized product of the polyacrylonitrile in the positive electrode material is 57.74-63.73wt%, and the mass of the N, N-dimethylformamide is 10g.
Optionally, the step of obtaining the polyacrylonitrile nanofiber membrane loaded with the cobalt metal organic frame from the composite solution through an electrostatic spinning means comprises the following steps: sucking the complex solution into a 10mL syringe; forming a fiber film from the solution in the injector by an electrostatic spinning means; the electrostatic spinning parameter is set to be 15-22kV, the distance between the injector and the collector is set to be 10-15cm, and the propelling speed is set to be 0.008-0.0012mm/min.
Optionally, the drying treatment of the nanofiber membrane includes: the nanofiber membrane was dried at a temperature of 90 ℃.
Optionally, the pre-oxidizing treatment of the dried nanofiber membrane includes: and (3) pre-oxidizing the dried nanofiber membrane in air at 200-240 ℃.
Optionally, carbonizing the pre-oxidized nanofiber membrane, including: cutting the pre-oxidized nanofiber film into a round film with the diameter of 12mm by a cutting machine; and (3) placing the round film in a tube furnace, and carbonizing at 500-700 ℃ in an N2 atmosphere.
Optionally, the reducing treatment of the carbonized nanofiber membrane includes: placing the carbonized nanofiber film in a tube furnace, and performing Ar/H (argon/hydrogen) treatment on the nanofiber film 2 Reducing in the mixed gas at 600-800 ℃; wherein the Ar/H ratio is 2 H in the mixed gas 2 The volume is 5% of the total volume of the gas.
Optionally, the fluorination heat treatment of the reduced nanofiber membrane to obtain a positive electrode material comprises: placing the reduced nanofiber membrane in a tube furnace, and performing NF (ultra-thin film) 3 /H 2 In the mixed gas, fluorination is carried out at the temperature of 300-350 ℃ to obtain the anode material; wherein the NF 3 /H 2 NF in the mixed gas 3 The volume is 5% of the total volume of the gas.
The second aspect of the application provides a positive electrode material prepared by the preparation method of the positive electrode material provided by the first aspect of the application.
A third aspect of the present application provides a battery manufacturing methodThe preparation method comprises the following steps: the positive electrode material provided by the second aspect of the application is taken as a positive electrode, lithium metal is taken as a negative electrode, and LiPF 6 And (3) dissolving the electrolyte into a mixed liquid of fluoroethylene carbonate and methyl ethyl carbonate to be used as an electrolyte for battery assembly, so as to obtain the fluoride battery.
Optionally, the electrolyte is 1M LiPF 6 A solution prepared by dissolving the mixture of fluoroethylene carbonate and methyl ethyl carbonate in a mixed liquid; wherein the volume ratio of fluoroethylene carbonate to methyl ethyl carbonate is 3:7.
A fourth aspect of the application provides a battery prepared by the method of preparing a fluoride battery as provided in the third aspect of the application.
(III) beneficial effects
The technical scheme of the application has the following beneficial technical effects:
(1) The prepared CoF is caused by the large specific surface area and good limiting effect on cobalt ions of ZIF-67 2 The nano particles have good dispersivity, can effectively inhibit the dissolution of cobalt element, and the organic ligand in ZIF-67 can be pyrolyzed into a conductive carbon layer in situ through heat treatment, and can be CoF 2 Providing a good conductive network;
(2) Preparation of self-supporting flexible CoF by electrostatic spinning means and subsequent heat treatment process 2 -C nanofibers (CoF) 2 -C NF) composite positive electrode can omit conductive agent and adhesive in the preparation of traditional positive electrode plate and is CoF 2 A three-dimensional conductive network frame is built, so that the ion/electron transmission capacity of the three-dimensional conductive network frame is further improved;
(3) The cathode material (CoF) of the present application 2 -C NF) realizes the improvement of capacity release of cobalt fluoride under low discharge multiplying power and long cycle life of cobalt fluoride under high multiplying power.
Drawings
FIG. 1 is a flow chart of a method for preparing a positive electrode material according to an embodiment of the present application;
FIG. 2 is an electronic image of a ZIF-67-PAN nanofiber membrane provided in one embodiment of the present application
FIG. 3 is a Scanning Electron Microscope (SEM) image of a positive electrode material according to an embodiment of the present application
Figure 4 is an X-ray diffraction (XRD) pattern of a positive electrode material provided in an embodiment of the present application,
FIG. 5 is a thermogravimetric analysis (TGA) of a positive electrode material according to an embodiment of the present application based on different carbonization temperatures;
FIG. 6 is a graph showing the low magnification (200mA.g) of the positive electrode material based on different carbonization temperatures according to an embodiment of the present application -1 ) A long-cycle electrochemical performance map;
FIG. 7 is a graph of the rate capability of a positive electrode material according to an embodiment of the present application;
FIG. 8 is a graph of the positive electrode material at 300 mA.g according to an embodiment of the present application -1 And 500 mA.g -1 Long cycle electrochemical performance at current density.
Detailed Description
The objects, technical solutions and advantages of the present application will become more apparent by the following detailed description of the present application with reference to the accompanying drawings. It should be understood that the description is only illustrative and is not intended to limit the scope of the application. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the present application.
It will be apparent that the described embodiments are some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In addition, the technical features of the different embodiments of the present application described below may be combined with each other as long as they do not collide with each other.
First embodiment
Referring to fig. 1, the present embodiment provides a method for preparing a positive electrode material, including: dispersing and dissolving cobalt metal organic frame (ZIF-67) and Polyacrylonitrile (PAN) in N, N-Dimethylformamide (DMF) to form a composite solution; passing the composite solution through static electricitySpinning means to obtain a polyacrylonitrile nanofiber membrane loaded with the cobalt metal organic framework; drying the nanofiber membrane; pre-oxidizing the dried nanofiber membrane; carbonizing the pre-oxidized nanofiber film; reducing the carbonized nanofiber film; and carrying out fluoridation heat treatment on the reduced nanofiber membrane to obtain the anode material. Wherein the positive electrode material is CoF 2 C nanofibers (CoF for short) 2 -C NF)。
The positive electrode material (CoF) prepared by the preparation method of the present embodiment 2 -C NF) realizes the improvement of capacity release of cobalt fluoride under low discharge multiplying power and long cycle life of cobalt fluoride under high multiplying power. It is understood that the discharge rate refers to the current value required by the battery to discharge its rated capacity for a prescribed period of time, which is equal in data value to a multiple of the battery's rated capacity, generally indicated by the letter C. Thereby improving the adhesiveness of the active substance (cobalt fluoride) and the conductive substrate (the conductive substrate refers to a multidimensional conductive network constructed by carbonizing together the organic ligand in ZIF-67 and PAN nanofibers), and having high repeatability, low cost and environmental friendliness.
The NF of the application refers to Nano fiber.
The prepared CoF is caused by the large specific surface area and good limiting effect on cobalt ions of ZIF-67 2 The nano particles have good dispersivity, can effectively inhibit the dissolution of cobalt element, and the organic ligand in ZIF-67 can be pyrolyzed into a conductive carbon layer in situ through heat treatment, and can be CoF 2 Providing a good conductive network;
preparation of self-supporting flexible CoF by electrostatic spinning means and subsequent heat treatment process 2 -C nanofibers (CoF) 2 -C NF) composite positive electrode can omit conductive agent and adhesive in the preparation of traditional positive electrode plate and is CoF 2 A three-dimensional conductive network frame is built, so that the ion/electron transmission capacity of the three-dimensional conductive network frame is further improved;
in some embodiments, a method for preparing a positive electrode material is provided, the method for preparing a battery positive electrode material comprising:
s100, mixing a mixed solution formed by mixing ZIF-67 in DMF and PAN to form a composite solution.
The ZIF-67 can be obtained by slowly adding cobalt salt and 2-methylimidazole into anhydrous methanol solution, and reacting. The cobalt salt may be cobalt nitrate. Wherein, the mixed solution of ZIF-67 dissolved in DMF is mixed with PAN to form a composite solution. Wherein the cobalt source and the organic ligand are Co (NO 3 ) 3 ·6H 2 O (and other cobalt salts soluble in water) and 2-methylimidazole in a molar ratio of 1:5.875.
And S200, carrying out electrostatic spinning on the composite solution to obtain the PAN nanofiber membrane loaded with ZIF-67.
And carrying out electrostatic spinning on the composite solution to realize that the ZIF-67 is wrapped by the PAN fibers and uniformly distributed on the PAN fibers, thereby obtaining the PAN nanofiber film loaded with the ZIF-67.
S300, drying the PAN nanofiber membrane loaded with the ZIF-67;
s400, performing pre-oxidation treatment on the dried nanofiber membrane;
s500, drying and pre-oxidizing the PAN nanofiber membrane loaded with ZIF-67, and carbonizing.
Specifically, cutting the pre-oxidized nanofiber film into a round film with the diameter of 12mm by a cutting machine; placing the round film in a tube furnace, and adding N to the round film 2 Carbonizing at 500-700 deg.c in atmosphere. Wherein temperatures below this range result in low carbonization and thus low product conductivity, and above this temperature will increase energy consumption.
After carbonization treatment, a multi-dimensional conductive network formed by carbon formed by carbonizing ZIF-67 organic ligand and carbon formed by carbonizing PAN is obtained, and the prepared material is Co 3 O 4 -C NF。
S600 to Co 3 O 4 -subjecting the C NF membrane to a reduction treatment.
After reduction treatment, the cobalt-carbon nanofiber film is obtained, cobalt nano particles are attached to carbon fibers, and the prepared material is Co-C NF.
S700, carrying out fluorination treatment on the Co-C NF film to obtain a positive electrode material CoF 2 -C NF。
After fluorination treatment, a cobalt fluoride-carbon nanofiber film is obtained, cobalt nanoparticles are attached to carbon fibers, and the prepared material is CoF 2 -C NF。
Referring to figure 2 of the drawings, the ZIF-67-PAN nanofiber membrane is in a membrane shape under an electronic image, has certain mechanical properties and is quite complete;
the final product CoF is described in conjunction with FIG. 3 of the drawings 2 the-C nanofiber film is necklace-shaped, and is formed by in-situ CoF after ZIF-67 carbonization 2 Uniformly distributing @ C in carbon fiber obtained by PAN carbonization, wherein the carbon fiber is in a three-dimensional conductive network shape, and on one hand, a carbon layer coated in situ can be used for CoF 2 The nano particles inhibit the occurrence of interfacial side reactions and prevent electrode results from being damaged due to volume expansion in the circulating process; on the other hand, the carbon fiber and the in-situ coated carbon layer jointly construct a conductive network to further promote CoF 2 Electrochemical performance of-C.
Referring specifically to FIGS. 6 and 7, at 200mA.g -1 Is still close to 500 mAh.g after 100 cycles at a current density of (2) -1 Is released by the capacity of the control CoF 2 450 mAh.g after 100 cycles of NCF-500 -1 And CoF 2 390 mAh.g after 100 cycles of NCF-700 -1 Is released. In the rate performance test, coF 2 NCF-600 at 8A.g -1 Can be charged and discharged normally under the current density of (2), and other comparison samples can not be charged and discharged under the current density.
In the embodiment of the application, on one hand, the prepared CoF is caused by the large specific surface area of the ZIF-67 and the good limiting effect on cobalt ions 2 The nano particles have good dispersivity, can effectively inhibit the dissolution of cobalt element, and the organic ligand in ZIF-67 can be pyrolyzed into a conductive carbon layer in situ through heat treatment, and can be CoF 2 Providing good electrical conductivitySimultaneously preparing self-supporting flexible CoF by electrostatic spinning means and subsequent heat treatment process 2 -C nanofibers (CoF) 2 -C NF) composite positive electrode can omit conductive agent and adhesive in the preparation of traditional positive electrode plate and is CoF 2 A three-dimensional conductive network frame is built, and the ion/electron transmission capacity of the three-dimensional conductive network frame is further improved. On the other hand, the positive electrode material (CoF 2 -C NF) realizes the improvement of capacity release of cobalt fluoride under low discharge multiplying power and long cycle life of cobalt fluoride under high multiplying power. It is understood that the discharge rate refers to the current value required by the battery to discharge its rated capacity for a prescribed period of time, which is equal in data value to a multiple of the battery's rated capacity, generally indicated by the letter C. Thereby improving the adhesiveness of the active substance (cobalt fluoride) and the conductive substrate (the conductive substrate refers to a multidimensional conductive network constructed by carbonizing together the organic ligand in ZIF-67 and PAN nanofibers), and having high repeatability, low cost and environmental friendliness.
In some embodiments, in step S200, electrospinning the composite solution to obtain a PAN nanofiber membrane loaded with ZIF-67 comprises:
s210, sucking the composite solution by using a needle tube;
s220, spinning under the condition that the voltage is 15-22kV, the distance between the injector and the collector is 10-15cm, and the propelling speed is 0.008-0.0012mm/min. If the PAN film is lower than the voltage range of 15-22kV, the electrostatic repulsive force acts little, so that the solution is in a liquid drop shape instead of fiber, and if the electrostatic repulsive force is too large, the fiber flies in disorder, and the product distribution is uneven.
In the embodiment, under the 15-22kV voltage, the distance between the injector and the collector is set to be 10-15cm, the propelling speed is set to be 0.008-0.0012mm/min, and in a product (ZIF-67-PAN NF) obtained after electrostatic spinning, the particle size of the ZIF-67 is uniformly distributed in the range of 50-100 nm, and under the electrostatic spinning parameter range, the beading phenomenon caused by too high moisture in the air can be effectively avoided, and a complete and compact nanofiber film with excellent mechanical properties can be formed.
Further, in step S300, the PAN nanofiber membrane loaded with ZIF-67 is subjected to a drying process, which includes:
the electrospun film was dried at 90 ℃.
In the embodiment of the application, DMF solvent can be completely volatilized under the drying condition of 90 ℃, and the pre-oxidation phenomenon of PAN nanofiber at high temperature is avoided.
Further, in step S400, the pre-oxidation treatment for the electrospun film includes:
and (3) pre-oxidizing the dried electrostatic spinning film in air at the temperature of 200-240 ℃. Under the condition of ensuring that the organic components in the product are not carbonized, the pre-oxidation can be carried out at the temperature of 200-240 ℃, and if the temperature is too low, the pre-oxidation effect is not achieved.
In other embodiments, in step S500, during carbonization of the electrospun nanofiber film after pre-oxidation, the method includes:
the heat treatment is carried out for 2 hours in Ar atmosphere at 500-700 ℃, and the temperature range can ensure that the organic ligand and PAN in ZIF-67 are completely carbonized, has good conductivity, and prevents structural collapse and energy consumption caused by excessive temperature.
In step S600, the reduction treatment of the carbonized tricobalt tetraoxide carbon nanofiber film includes:
Ar/H at 600-800 deg.C 2 (wherein H 2 The volume fraction is 5 vol%) is subjected to reduction treatment for 2 hours in an atmosphere, and the temperature range can ensure that the cobaltosic oxide is completely reduced into the elemental cobalt, and prevent incomplete reduction caused by the excessively low temperature and structural damage and energy consumption caused by the excessively high temperature.
In step S700, the fluorination treatment of the cobalt carbon nanofiber thin film after the reduction treatment includes:
Ar/NF at 300-320 DEG C 3 (wherein NF 3 The volume fraction is 5 vol%) is subjected to fluorination treatment for 2h in the atmosphere, the temperature range can ensure that the cobalt simple substance is fluorinated into cobalt fluoride, and the cobalt simple substance cannot be fluorinated into cobalt fluoride due to the excessively low temperature is preventedAnd an excessive temperature causes the carbon to be fluorinated to form fluorinated carbon, so that the electron conductivity is lowered.
In this example, ZIF-67 and PAN (Poly Acrylo Nitrile is abbreviated as PAN, which is a compound obtained by free radical polymerization of acrylonitrile monomer and is white or yellowish opaque powder) were used as cobalt source and precursor of polymer fiber in electrospinning, respectively.
Preferably, as shown in FIG. 5, (in FIG. 5, conditional CoF 2 NCF-500, 600 and 700 can be understood as: PAN nanofiber film loaded with ZIF-67 prepared by electrostatic spinning is pre-oxidized and carbonized at 500 ℃, 600 ℃ and 700 ℃ respectively to obtain a product), and carbonized at 600 ℃ to obtain CoF 2 NCF-600 has optimal electrochemical performance. As shown in FIG. 8, the lithium ion battery assembled by the positive electrode according to the method is 200 mA.g -1 Is still close to 500 mAh.g after 100 cycles at a current density of (2) -1 Is significantly higher than CoF 2 450 mAh.g after 100 cycles of NCF-500 -1 And CoF 2 390 mAh.g after 100 cycles of NCF-700 -1 Is released.
In some embodiments, in step 500, carbonizing the PAN nanofiber membrane loaded with ZIF-67 comprises:
carbonizing the nanofiber film at 500-700 ℃ in Ar gas atmosphere, wherein the talking treatment time is 120min.
Specifically, the nanofiber membrane was heat-treated for 120min while maintaining the temperature at 600 ℃.
In the above examples, under this condition, it was possible to ensure complete carbonization of the organic ligand and PAN in ZIF-67, have good electrical conductivity, and prevent structural collapse and energy consumption due to excessive temperature.
ZIF-67 is a cobalt-containing metal organic framework, has a regular morphology and a stable organic framework and has a large specific surface area, and the content of the ZIF-67-loaded PAN nanofiber membrane is 88.9wt%. The weight average molecular weight of polyacrylonitrile was 150000, and the mass of polyacrylonitrile was 11.1% of the mass of the PAN nanofiber membrane loaded with ZIF-67.
On the one hand, the ZIF-67 has large specific surface area and good limiting effect on cobalt ions, so that the prepared CoF 2 The nano particles have good dispersivity, can effectively inhibit the dissolution of cobalt element, and the organic ligand in ZIF-67 can be pyrolyzed into a conductive carbon layer in situ through heat treatment, and can be CoF 2 Provides a good electrical conduction network, on the other hand, the composite material (CoF 2 -C NF) realizes the improvement of capacity release of cobalt fluoride under low discharge multiplying power and long cycle life of cobalt fluoride under high multiplying power.
Further, the self-supporting flexible CoF is prepared by an electrostatic spinning means and a subsequent heat treatment process 2 -C nanofibers (CoF) 2 -C NF) composite positive electrode can omit conductive agent and adhesive in the preparation of traditional positive electrode plate and is CoF 2 A three-dimensional conductive network frame is built, and the ion/electron transmission capacity of the three-dimensional conductive network frame is further improved.
In a specific embodiment, a preparation method of a fluoride battery composite positive electrode material is provided, and the specific flow is as follows:
(1) Slowly adding cobalt nitrate and 2-methylimidazole into an anhydrous methanol solution according to a certain proportion, standing for reaction overnight, centrifuging to obtain precipitate, drying and collecting to obtain ZIF-67; wherein, a certain proportion can be 1:1.
(2) Adding ZIF-67 and PAN into 10g of DMF solution according to the mass fraction of ZIF-67 to 80wt% of PAN, uniformly stirring and ultrasonically mixing;
(3) Collecting the solution in the step (2) by using a syringe, and preparing the solution into a Co-MOF-PAN nanofiber film by using an electrostatic spinning means;
(4) Pre-oxidizing the ZIF67-PAN nanofiber membrane in the step (3) in an air atmosphere;
(5) Carbonizing the ZIF-67-PAN nanofiber film subjected to the pre-oxidation treatment in the step (4) at 500-700 ℃ in Ar gas atmosphere to prepare Co 3 O 4 -a C nanofiber film;
(6) Co in step (5) 3 O 4 -C nanofiber filmIn Ar/H 2 Reducing at 600-800 deg.c in atmosphere to prepare Co-C nanometer fiber film
(7) The Co-C nanofiber membrane in the step (6) is subjected to Ar/NF 3 Fluorination treatment at 300-350 deg.c in atmosphere to prepare CoF 2 -a C nanofiber film.
Taking 2.28g of cobalt nitrate and 3.856g of 2-methylimidazole as raw materials, dissolving in 200mL of methanol solution, after reaction for overnight, collecting precipitate by centrifugation, drying in a 60 ℃ incubator for 6 hours, pre-oxidizing at 200-240 ℃ for 2 hours, carbonizing at 500-700 ℃ in Ar atmosphere and Ar/H at 600-800 ℃ respectively 2 Reducing in mixed gas and Ar/NF at 300-350 DEG C 3 And (3) carrying out fluorination treatment in the mixed gas. Wherein drying in an oven at 60 ℃ ensures complete drying and a faster drying rate, and oxidation of the product may occur if drying is performed at too high a temperature. The carbonization temperature is 600-800 ℃, the reduction effect cannot be realized below 600 ℃, and the mechanical properties of the product can be damaged above 800 ℃. The fluorination temperature is 300-350 ℃, the fluorination effect cannot be achieved below 300 ℃, and the fluorination temperature is higher than 350 ℃ to cause partial carbon in the product to be fluorinated, so that the overall conductivity is reduced.
Preferably, the added Polyacrylonitrile (PAN) is added according to the mass percentage of PAN accounting for 11.1wt% of the ZIF67-PAN nano film, the pre-oxidation treatment temperature is 240 ℃ and the duration time is 120min, and the carbonization, reduction and fluorination treatment temperatures are 600 ℃, 700 ℃ and 320 ℃ and the duration time is 120min respectively.
In summary, the present application utilizes a metal organic framework and a carbon framework formed by in situ pyrolysis of PAN as an active material (CoF 2 ) Builds a strong and stable conductive network and combines advanced fluorination means to synthesize nano-scale CoF 2 Excellent electrochemical performance is achieved.
The pole piece is manufactured by the manufacturing method, the assembled pole piece is assembled into a battery, the battery is subjected to cyclic charge and discharge performance test at different current densities, and the voltage interval is 1.0-4.0V. Low magnification (200 mA g) -1 ) The cycle chart is shown in fig. 4: after 100 cyclesThe specific discharge capacity of CoF2-NCF-600 is 500mAh/g which is obviously higher than that of CoF 2 450 mAh.g after 100 cycles of NCF-500 -1 And CoF 2 390 mAh.g after 100 cycles of NCF-700 -1 Is released. And has more excellent multiplying power performance than a comparison sample, and is in the range of 8 A.g -1 Can be charged and discharged normally under the current density.
Second embodiment
The present embodiment provides a positive electrode material prepared by the method for preparing a positive electrode material as provided in the first embodiment of the present application.
The same points as the first embodiment are not described in detail in this embodiment.
Third embodiment
The embodiment provides a method for preparing a battery, which comprises the following steps: the positive electrode material provided according to the second embodiment of the present application is used as a positive electrode, lithium metal is used as a negative electrode, and LiPF 6 And (3) dissolving the electrolyte into a mixed liquid of fluoroethylene carbonate and methyl ethyl carbonate to be used as an electrolyte for battery assembly, so as to obtain the fluoride battery.
Optionally, the electrolyte is 1M LiPF 6 A solution prepared by dissolving the mixture of fluoroethylene carbonate and methyl ethyl carbonate in a mixed liquid; wherein the volume ratio of fluoroethylene carbonate to methyl ethyl carbonate is 3:7. This ratio is preferred for fluoride cathode materials, coF 2 The battery performance is best.
Alternatively, the mass ratio of the volume of electrolyte used to assemble the battery to the active material in the positive electrode material is 10uL/mg.
The same points as the second embodiment are not described in detail in this embodiment.
Fourth embodiment
The present embodiment provides a battery prepared by the method for preparing a fluoride battery as provided in the third embodiment of the present application.
The same points as in the third embodiment are not described in detail in this embodiment.
It is to be understood that the above-described embodiments of the present application are merely illustrative of or explanation of the principles of the present application and are in no way limiting of the application. Accordingly, any modification, equivalent replacement, improvement, etc. made without departing from the spirit and scope of the present application should be included in the scope of the present application. Furthermore, the appended claims are intended to cover all such changes and modifications that fall within the scope and boundary of the appended claims, or equivalents of such scope and boundary.
Claims (10)
1. A method for preparing a positive electrode material, comprising:
dispersing and dissolving cobalt metal organic framework and polyacrylonitrile in N, N-dimethylformamide to form a composite solution; wherein, the cobalt metal organic framework and polyacrylonitrile are dispersed and dissolved in N, N-dimethylformamide to form a composite solution, which comprises the following steps: mixing a cobalt metal organic framework with N, N-dimethylformamide to obtain a mixed solution; carrying out ultrasonic treatment on the mixed solution; adding polyacrylonitrile into the mixed solution after ultrasonic treatment, and stirring for 24 hours to obtain the composite solution;
obtaining a polyacrylonitrile nanofiber membrane loaded with the cobalt metal organic framework through an electrostatic spinning means on the composite solution;
drying the nanofiber membrane;
pre-oxidizing the dried nanofiber membrane;
carbonizing the pre-oxidized nanofiber film; wherein, coF formed in situ after carbonization of the cobalt metal organic framework 2 Uniformly distributing @ C in carbon fibers obtained by carbonizing polyacrylonitrile to form a three-dimensional conductive network, and coating the carbon fibers with a carbon layer pair CoF in situ 2 The nano particles inhibit the occurrence of interface side reaction and prevent electrode result damage caused by volume expansion in the circulation process, and a conductive network is constructed by carbon fibers and an in-situ coated carbon layer;
reducing the carbonized nanofiber film;
performing fluoridation heat treatment on the reduced nanofiber membrane to obtain a positive electrode material; the positive electrode material is necklace-shaped under a scanning electron microscope;
wherein, the pre-oxidation treatment of the dried nanofiber membrane comprises the following steps: pre-oxidizing the dried nanofiber membrane in air at 200-240 ℃;
the carbonization treatment of the pre-oxidized nanofiber membrane comprises the following steps: cutting the pre-oxidized nanofiber film into a round film with the diameter of 12mm by a cutting machine; placing the round film in a tube furnace, and adding N to the round film 2 Carbonizing at 500-700 deg.c in atmosphere;
the reduction treatment of the carbonized nanofiber membrane comprises the following steps: placing the carbonized nanofiber film in a tube furnace, and performing Ar/H (argon/hydrogen) treatment on the nanofiber film 2 Reducing in the mixed gas at 600-800 ℃; wherein the Ar/H ratio is 2 H in the mixed gas 2 The volume is 5% of the total volume of the gas;
the reduced nanofiber membrane is subjected to fluoridation heat treatment to obtain a positive electrode material, which comprises the following steps: placing the reduced nanofiber membrane in a tube furnace, and performing NF (ultra-thin film) 3 /H 2 In the mixed gas, fluorination is carried out at the temperature of 300-350 ℃ to obtain a positive electrode material; wherein the NF 3 /H 2 NF in the mixed gas 3 The volume is 5% of the total volume of the gas.
2. The method of preparing a positive electrode material according to claim 1, further comprising, before dispersing and dissolving the cobalt metal organic framework and polyacrylonitrile in N, N-dimethylformamide to form a composite solution:
slowly adding a cobalt source and an organic ligand into an anhydrous methanol solution according to a preset proportion, and stirring and mixing;
standing at room temperature overnight, centrifuging to obtain precipitate;
drying in an incubator at 60 ℃ for 6h and collecting to obtain the cobalt metal organic frame.
3. The method for producing a positive electrode material according to claim 2, wherein,
the cobalt source is cobalt salt which can be dissolved in water;
the organic ligand is 2-methylimidazole;
the volume of anhydrous methanol was 200mL.
4. The method for producing a positive electrode material according to claim 2, wherein the polyacrylonitrile has a weight average molecular weight of 150000;
the mass fraction of the carbonized product of the polyacrylonitrile in the positive electrode material is 57.74-63.73wt percent, and the mass of the N, N-dimethylformamide is 10g.
5. The method for preparing a positive electrode material according to claim 2, wherein the step of obtaining the polyacrylonitrile nanofiber membrane loaded with the cobalt metal organic framework from the composite solution by means of electrospinning comprises:
sucking the composite solution into a 10mL syringe;
forming a fiber film from the solution in the injector by an electrostatic spinning means;
the electrostatic spinning parameter is set to be 15-22kV, the distance between the injector and the collector is set to be 10-15cm, and the propelling speed is set to be 0.008-0.0012mm/min.
6. The method of producing a positive electrode material according to claim 2, wherein the drying the nanofiber membrane comprises:
the nanofiber membrane was dried at a temperature of 90 ℃.
7. A positive electrode material prepared by the method of any one of claims 1 to 6.
8. A method of making a battery comprising: a positive electrode material according to claim 7, lithium metal as a negative electrode, liPF 6 Dissolved in a mixed liquid of fluoroethylene carbonate and methyl ethyl carbonate as an electrolyteAnd (5) assembling the battery to obtain the fluoride battery.
9. The method for producing a battery according to claim 8, wherein the electrolyte is 1M LiPF 6 A solution prepared by dissolving the mixture of fluoroethylene carbonate and methyl ethyl carbonate in a mixed liquid; wherein the volume ratio of fluoroethylene carbonate to methyl ethyl carbonate is 3:7.
10. A battery prepared by the method of preparing a battery according to claim 8 or 9.
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