CN113454815A - Negative electrode composite material, negative electrode, electrochemical device, and electronic device - Google Patents
Negative electrode composite material, negative electrode, electrochemical device, and electronic device Download PDFInfo
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- CN113454815A CN113454815A CN202080011389.3A CN202080011389A CN113454815A CN 113454815 A CN113454815 A CN 113454815A CN 202080011389 A CN202080011389 A CN 202080011389A CN 113454815 A CN113454815 A CN 113454815A
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- 239000002131 composite material Substances 0.000 title claims abstract description 109
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 112
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 112
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims abstract description 106
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 74
- 239000002041 carbon nanotube Substances 0.000 claims abstract description 68
- 229910021393 carbon nanotube Inorganic materials 0.000 claims abstract description 68
- 229910003481 amorphous carbon Inorganic materials 0.000 claims abstract description 61
- 239000000243 solution Substances 0.000 claims description 46
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- YHWCPXVTRSHPNY-UHFFFAOYSA-N butan-1-olate;titanium(4+) Chemical compound [Ti+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] YHWCPXVTRSHPNY-UHFFFAOYSA-N 0.000 claims description 11
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- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
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- -1 lithium cobaltate Chemical class 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
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Images
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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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- 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
- D01D5/0061—Electro-spinning characterised by the electro-spinning apparatus
- D01D5/0069—Electro-spinning characterised by the electro-spinning apparatus characterised by the spinning section, e.g. capillary tube, protrusion or pin
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- 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
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- 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
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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
- H01M4/131—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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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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
The application belongs to the technical field of secondary batteries and provides a negative electrode composite material, a negative electrode, an electronic chemical device and an electronic device, wherein the negative electrode composite material comprises fibrous self-supporting amorphous carbon, and lithium titanate and carbon nano tubes are arranged on the fibrous self-supporting amorphous carbon. The cathode composite material provided by the application has the advantages of good conductivity, excellent rate performance and self-supporting property, can be directly used as a cathode of a secondary battery (such as a lithium ion battery), and gets rid of dependence on a cathode current collector. The present application also provides an electrochemical device and an electronic device.
Description
[ technical field ] A method for producing a semiconductor device
The application belongs to the technical field of secondary batteries, and particularly relates to a flexible self-supporting cathode composite material capable of being directly used as a cathode, and an electrochemical device and an electronic device containing the cathode composite material.
[ background of the invention ]
With the development of the energy storage market, secondary batteries such as lithium ion batteries are receiving more and more attention from researchers and enterprises as key energy storage and conversion components, and the development cycle life is long (>10000 cycles), good rate capability (>3C) The novel lithium ion electrode material with low cost is a key link for research and development of the lithium ion battery. The lithium titanate has long application as the cathode material of the lithium ion battery, the ultrahigh safety performance (the lithium desorption platform is 1.5V, no lithium precipitation occurs), and the overlong cycle life (>1000 cycles) and ultra-small volume change during charge and discharge (no SEI film formation, substantially no volume change in the unit cell) are significant and are referred to as "zero strain" materials. However, lithium titanate has poor electron conductivity, and the electron conductivity thereof is about 10 at room temperature-13S/cm, which is almost an insulator, greatly limits the electrochemical performance of lithium titanate as an electrode material of a lithium ion battery.
The method of coating the carbon layer on the surface of the material can simply and effectively improve the conductivity of the material, and is a method which is used for modifying lithium titanate more frequently at present. The existing method only carries out simple carbon coating, on one hand, the coating uniformity has larger challenges, on the other hand, the coating is mostly hard carbon or soft carbon, the improvement range of the conductivity is still insufficient, and the coating cannot be effectively applied to secondary batteries, so that a new cathode material needs to be developed.
[ summary of the invention ]
In view of the problems of poor conductivity and rate capability of lithium titanate and the like in the prior art, the application provides a self-supporting flexible negative electrode composite material and a preparation method thereof.
Specifically, a first aspect of the present application provides an anode composite for a secondary battery, comprising fibrous self-supporting amorphous carbon having lithium titanate and carbon nanotubes thereon.
In the present application, the meaning of having lithium titanate and carbon nanotubes on fibrous self-supporting amorphous carbon means that fibrous self-supporting amorphous carbon is distributed between and/or at least partially comprised by lithium titanate and carbon nanotubes in the amorphous carbon. More specifically, lithium titanate and carbon nanotubes are mainly contained in amorphous carbon, but the case where there are dispersed lithium titanate and carbon nanotubes between carbon amorphous carbon is not excluded, that is, lithium titanate and carbon nanotubes and carbon amorphous carbon are not embedded in each other although they are in contact.
In the present application, self-supporting amorphous carbon refers to a carbon material having both good conductivity and support, which can be directly used as an anode of a secondary battery without an additional current collector and binder. Microscopically, amorphous carbon is fibrous and has good shape retention properties, and does not collapse due to external forces. The negative electrode composite material composed of the self-supporting amorphous carbon, the lithium titanate and the carbon nano tube has good pressure bearing performance and good flexibility, so that the negative electrode composite material is very suitable for being directly used as a negative electrode of a secondary battery.
In some embodiments of the present application, the fibrous, self-supporting amorphous carbon has a diameter of 200nm to 600 nm.
The method for forming fibrous self-supporting amorphous carbon can be various, such as gel method or freeze-drying method. In one embodiment herein, the fibrous self-supporting amorphous carbon is obtained by calcining a polymer under vacuum or an inert atmosphere.
Self-supporting amorphous carbon can be obtained by calcining polymers (e.g., polyvinylpyrrolidone, polyacrylonitrile, polyvinyl alcohol) under high temperature conditions. In some embodiments of the present application, the polymer comprises at least one of polyvinylpyrrolidone (PVP), Polyacrylonitrile (PAN), polyvinyl alcohol (PVA). The amorphous carbon layer obtained after calcining polyvinylpyrrolidone (PVP), Polyacrylonitrile (PAN) and polyvinyl alcohol (PVA) has a structure with powerful supporting property, is not easy to crush and has strong toughness. The one-dimensional amorphous carbon layer compounds lithium titanate and the carbon nano tube to obtain the one-dimensional carbon nano fiber. The carbon nano tubes and the one-dimensional carbon nano fibers form a conductive network distributed over the cathode composite material, so that the conductivity of the cathode composite material is greatly improved, and the cathode composite material integrally shows a flexible self-supporting characteristic and can be directly used as a secondary cathode.
In some embodiments of the present application, a mixture of a polymer, lithium titanate and a carbon nanotube is calcined at a high temperature, so that the obtained amorphous carbon is formed by coating lithium titanate and the carbon nanotube inside the amorphous carbon, so as to form an amorphous carbon nanofiber, and finally a sheet-like composite material with a complete structure and good flexibility is formed. The composite material can be directly used as a negative pole piece of a secondary battery after drying, cold pressing and cutting, so that the negative pole composite material is called as a self-supporting flexible negative pole composite material. The self-supporting flexible negative electrode composite material can be directly used as a negative electrode due to self-supporting characteristics of the self-supporting flexible negative electrode composite material, and does not need to use an additional current collector and a negative electrode active material like a traditional negative electrode. The cathode composite material of the application shows great improvement in conductivity and electrochemical performance, and the characteristic of self-supporting flexibility has great potential in the application of flexible batteries. The secondary battery adopting the cathode composite material can realize high-rate discharge and ensure long circulation.
The negative electrode composite material comprises lithium titanate, a carbon nanotube and an amorphous carbon coating layer. The lithium titanate may be a commercially available lithium titanate or a lithium titanate prepared according to the process of the present application. The lithium titanate prepared by the method passes through lithium chloride monohydrate (LiCl. H) in the preparation process2O) and tetrabutyl titanate (C)16H36O4Ti) is reacted, thusThe obtained lithium titanate, the carbon nano tube and the amorphous carbon are mixed more uniformly, and finally the obtained negative electrode composite material has more uniform characteristics.
In some embodiments of the negative electrode composite material of the present application, the mass percentages of the lithium titanate, the carbon nanotube, and the coated amorphous carbon are 40% to 65% to 3% to 10% to 30% to 50% based on the total mass of the lithium titanate, the carbon nanotube, and the amorphous carbon layer. Under the proportion, the lithium titanate and the carbon nano tubes can be uniformly dispersed, the carbon nano tubes are taken as conductive mesh wires by utilizing the excellent conductivity of the carbon nano tubes, and the outer layer is coated with a layer of one-dimensional carbon nano fibers, so that the lithium titanate and the conductive mesh wires can be coated into a whole to form a complete three-dimensional conductive network.
In some embodiments of the negative electrode composites of the present application, the lithium titanate can be a commercial lithium titanate as well as an in situ synthesized lithium titanate of the present application. The lithium titanate is a spinel-structured lithium titanate, and the lithium titanate has a crystallinity of 75% to 100%. The observation shows that the crystallinity of lithium titanate can influence the capacity of the battery cell, and the higher the crystallinity of lithium titanate is, the higher the capacity of the battery cell is. When the crystallinity of lithium titanate substantially reaches more than 80%, the easy influence on the battery cell is limited. When the lithium titanate material is selected, lithium titanate having a crystallinity of 75% to 100% is preferably selected.
In the negative electrode composite material of the present application, the particle diameter of lithium titanate needs to be in a suitable range. Too large a particle diameter of the lithium titanate exceeds the size range of the nano-sized lithium titanate. In addition, in view of cost, the particle diameter of lithium titanate is not suitable to be too small, which results in increased difficulty of production and increased cost. In the present application, the particle diameter of the lithium titanate is 10nm to 200 nm.
In the negative electrode composite material of the present application, the carbon nanotubes may be multi-walled carbon nanotubes, single-walled carbon nanotubes, or a mixture of multi-walled carbon nanotubes and single-walled carbon nanotubes. The multi-wall carbon nano tube has wide sources and lower cost, and is very suitable to be used as the carbon nano tube raw material in the application. In some cases, single-walled carbon nanotubes are employed. The single-walled carbon nanotube has better improvement effect on the performance of the secondary battery due to more excellent conductivity and physicochemical property. In addition, the diameter and length of the carbon nanotube may affect the mixing of the carbon nanotube and lithium titanate, and if the diameter and length of the carbon nanotube are too large or too long, the lithium titanate is not well and uniformly mixed, so that the amorphous carbon is difficult to coat, and the uniformity of the negative electrode composite material is poor. In some embodiments of the present application, the carbon nanotubes have a diameter of 10nm to 70nm and a length of 100nm to 200 nm.
In the application, the one-dimensional amorphous carbon nanofiber is obtained by carbonizing a polymer PVP or PAN in high-temperature vacuum or high-temperature inert atmosphere, the carbon nanofiber obtained after high-temperature calcination has a stable structure and can be used as an excellent coating layer, and the stability of the overall structure of the negative electrode composite material can be maintained in the charging and discharging processes.
The application also provides a negative electrode, which is composed of the negative electrode composite material, and the expansion rate of the negative electrode is 3-5%.
A second aspect of the present application provides a method of preparing the anode composite material as described above, specifically comprising the steps of:
(1) adding a polymer and a carbon nano tube into an organic solvent, and stirring at room temperature until the polymer and the carbon nano tube are completely dissolved in a polymerization manner to obtain a solution A; the polymer is one or more of polyvinylpyrrolidone, polyacrylonitrile and polyvinyl alcohol, and the organic solvent is selected from ethanol, N-Dimethylformamide (DMF) or a mixed solvent consisting of ethanol and N, N-dimethylformamide;
(2) mixing lithium titanate and glacial acetic acid, and stirring until the mixture is clear to obtain a solution B;
(3) adding the solution B into the solution A, and stirring at normal temperature to obtain a mixed solution C;
(4) preparing the mixed solution C into a nanofiber membrane through electrostatic spinning, and performing vacuum drying and pre-oxidation treatment on the obtained nanofiber membrane; and after the pre-oxidation treatment is finished, carbonizing the nano fiber film subjected to the pre-oxidation treatment under the vacuum or inert atmosphere condition to obtain the negative electrode composite material.
According to the method, a precursor solution (namely, a mixed solution C) of the cathode composite material is prepared by adopting an electrostatic spinning method, and the spinning precursor solution is injected into an injector connected with a blunt metal needle head by the mixed solution C for electrostatic spinning. And after the electrostatic spinning is finished, putting the nanofiber membrane collected on the receiving device into a vacuum drying oven for complete drying. And then, placing the dried nanofiber membrane in a muffle furnace for preoxidation for a certain time, and finally carbonizing at high temperature for a certain time under the vacuum or inert atmosphere condition of a tubular furnace to obtain the fibrous self-supporting flexible negative electrode composite material.
In some embodiments of the methods described herein, in step (2), the lithium titanate is added in an amount of 4 to 25 times the mass of the carbon nanotubes.
In some embodiments of the methods described herein, glacial acetic acid is used in an amount of 75L to 85L per mole of tetrabutyltitanate in step (2).
In some embodiments of the methods described herein, in step (3), the mixed solution C is stirred at room temperature for 8 to 20 hours. Stirring times of less than 8 hours may result in uneven material dispersion, which may negatively affect the uniformity of the subsequently obtained negative electrode composite material. The stirring time exceeding 20 hours is not necessary, and the production cost is also increased.
In some embodiments of the methods described herein, in step (4), the pre-oxidation treatment is performed at a temperature of 200 ℃ to 280 ℃; the time of the pre-oxidation treatment may be 1 hour to 3 hours. The pre-oxidation treatment is carried out in the presence of oxygen, and is a process for converting an oxidizable component in the polymer into an oxide. The pre-oxidation operation may include: and (3) placing the spinning obtained in the previous step in a muffle furnace, and carrying out low-temperature pre-oxidation treatment in the air or oxygen atmosphere. In addition, the temperature rise rate is 1 to 10 ℃/min during the pre-oxidation treatment. The temperature rise rate is not too fast, and the structure of the carbon nanofiber formed in the subsequent carbonization process is prevented from being damaged.
In some embodiments of the methods described herein, the lithium titanate is a commercial lithium titanate. In this case, the amount of carbon nanotubes added is 3.6 to 40% by mass of lithium titanate.
In some embodiments of the methods described herein, in step (4), the high temperature carbonization is performed in a vacuum or an inert atmosphere; the high-temperature carbonization temperature is 650 ℃ to 900 ℃, and the heat preservation time is 5 hours to 15 hours; the heating rate is 1 to 10 ℃/min. In the high-temperature carbonization process, the inert gas atmosphere is an argon atmosphere, a nitrogen atmosphere, or a mixed inert gas atmosphere of a combination of argon and nitrogen. The temperature of high-temperature carbonization is between 650 ℃ and 900 ℃. The carbonization of the nanofiber membrane cannot be realized at a low temperature, and the unnecessary cost increase is caused by a high temperature, and more importantly, the brittleness of the negative electrode composite material obtained after carbonization is increased due to a high temperature, so that the negative electrode composite material is not favorable for being used as a negative electrode material.
In the process of the present application, the lithium titanate may be a commercial lithium titanate, or may be synthesized by the process of the present application. In this case, the method of the present application comprises the steps of:
(1) adding polymer and carbon nanotube into organic solvent, stirring at room temperature until the polymer is completely dissolved, and adding lithium chloride monohydrate (LiCl. H)2O) to obtain a solution A; wherein the polymer comprises at least one of polyvinylpyrrolidone, polyacrylonitrile and polyvinyl alcohol; the organic solvent is selected from ethanol and/or N, N-dimethylformamide;
(2) mixing tetrabutyl titanate (C)16H36O4Ti) and glacial acetic acid are mixed and stirred until the mixture is clear, and a solution B is obtained;
(3) adding the solution B into the solution A to obtain a mixed solution C, and stirring the mixed solution C at normal temperature;
(4) preparing the mixed solution C into a nanofiber membrane through electrostatic spinning, carrying out vacuum drying on the obtained nanofiber membrane, and then carrying out pre-oxidation treatment; and carbonizing the nano fiber film subjected to the pre-oxidation treatment under the vacuum or inert atmosphere condition to obtain the negative electrode composite material.
In some embodiments of the methods described herein, in step (1), the mass fraction of polymer in solution a is from 30% to 50%; the mass fraction of lithium chloride monohydrate in the solution A is 3-6%.
In some embodiments of the methods described herein, the mass of the carbon nanotubes is 7% to 46% of the mass of the lithium chloride monohydrate.
In some embodiments of the methods described herein, the molar ratio of tetrabutyltitanate to lithium chloride monohydrate is from 1: 1 to 10: 9.
By limiting the mass fraction of the polymer in the solution a, the mass content of the carbon nanotubes and the molar ratio of tetrabutyl titanate to lithium chloride monohydrate, the solubility of lithium chloride and tetrabutyl titanate in the solvent can be in a proper range, and the problem that the solubility of the materials is too high to be beneficial to the dispersion of the materials is avoided.
In the present application, the anode composite directly constitutes an anode of a secondary battery, and the expansion rate of the anode is 3% to 5%.
A third aspect of the present application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is composed of the negative electrode composite material described herein.
Specifically, in the present application, the electrochemical device may be a lithium ion battery, a sodium ion battery, a magnesium ion battery. When the electrochemical device may be a lithium ion battery, the lithium ion battery includes: a positive electrode, a negative electrode, and an electrolyte. The positive electrode material may be a lithium-containing compound such as lithium cobaltate, lithium manganate, lithium iron phosphate, or the like. The negative electrode material is the negative electrode composite material described in the first aspect of the present application, or the negative electrode material is the negative electrode composite material prepared by the method described in the second aspect of the present application. The electrolyte can be ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate, dimethyl carbonate and the like.
The cathode composite material provided by the application has the advantages of good conductivity, excellent rate performance and self-supporting characteristic, and can be directly used as a cathode of a lithium ion battery, so that the dependence on a cathode current collector is eliminated.
[ description of the drawings ]
FIG. 1 is a schematic view of an electrospinning apparatus;
fig. 2 shows a schematic view of a circular sheet made of the negative electrode composite obtained in example 1;
fig. 3 shows a schematic view of a circular sheet made of the negative electrode composite obtained in example 1 after being bent;
FIG. 4 is a part of a Scanning Electron Micrograph (SEM) of a circular sheet made of the negative electrode composite obtained in example 1; in the figure, lithium titanate particles are positioned on the surface of a hollow or non-hollow amorphous carbon fiber tube to form spurs or positioned inside the amorphous carbon fiber tube;
FIG. 5 is a part of a scanning electron micrograph of a circular sheet made of the negative electrode composite obtained in example 1; in the figure, the carbon nanotube is partially contained in the fibrous amorphous carbon, and a part of the carbon nanotube is exposed to the outside of the amorphous carbon;
fig. 6 is an X-ray diffraction (XRD) pattern of the negative electrode composite obtained in example 1 and comparative examples 1 and 2;
FIG. 7 is a graph comparing rate performance of negative electrode composites obtained in example 1 and comparative examples 1 and 2 used as negative electrodes of lithium ion batteries;
fig. 8 is a graph comparing the cycle performance of the negative electrode composite obtained in example 1 and comparative examples 1 and 2 as a negative electrode of a lithium ion battery.
[ detailed description ] embodiments
For the purpose of making the purpose and advantages of the present application more apparent, the present application will be described in further detail with reference to the accompanying drawings.
Calculating the relative crystallinity of lithium titanate: the relative crystallinity (hereinafter, crystallinity is synonymous with relative crystallinity) is represented by the ratio of the (111) plane intensity in the XRD pattern of the material in each example or comparative example to the (111) plane intensity in the standard XRD pattern of lithium titanate.
Preparing a battery: the negative electrode composite material obtained in the application is used as a negative electrode plate after being dried, cold-pressed and cut into pieces, the metal lithium piece is used as a counter electrode, and 1M LiPF is added6Dissolved in solvents such as Ethylene Carbonate (EC) and dimethyl carbonate (DMC), and used as electrolyte to assemble 2032 button cell.
And (3) testing cycle and rate performance: the cycle test is a charge-discharge cycle test of the battery at a current density of 1C (175 mAh/g), a voltage range of 1.0V to 2.5V, and a cycle test temperature of 25 ℃. The rate performance is the battery capacity obtained by performing 10 charge and discharge cycles on the battery at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 10C respectively and testing.
Example 1
The method comprises the following steps: 0.5g Polyacrylonitrile (PAN), 0.2g polyvinylpyrrolidone (PVP) and 15mg multiwall carbon nanotubes were added to 10mL DMF and stirred until the polymer was well dissolved.
Step two: 2.25mmol of LiCl. H2And O is added into the solution obtained in the step one, and the mixture is continuously stirred until the mixture is dissolved, so that a solution A is obtained.
Step three: 2.5mmol of tetrabutyl titanate (C)16H36O4Ti) and 200 μ L glacial acetic acid and stirred until a clear solution B is obtained.
Step four: slowly adding the solution B into the solution A, stirring for 12 hours at normal temperature to obtain a mixed solution C, and taking the mixed solution C as an electrostatic spinning precursor solution.
Step five: and (3) injecting the mixed solution C into an injector connected with a blunt metal needle to perform an electrostatic spinning experiment, wherein the schematic diagram of the electrostatic spinning experiment device is shown in figure 1. And collecting the nanofiber membrane after electrostatic spinning is finished, and then carrying out vacuum drying.
Step six: the dried nanofiber membrane was pre-oxidized in a muffle furnace at 230 ℃ for 2 hours.
Step seven: carbonizing the pre-oxidized nanofiber membrane at 800 ℃ under a vacuum condition, and preserving heat for 10 hours to obtain the lithium titanate composite carbon nanotube one-dimensional nanofiber (LTO/CNT-V)0)。
FIG. 2 shows the negative electrode composite material LTO/CNT-V prepared by the present embodiment0Schematic of the circular wafer of (1). Fig. 3 is a schematic view of a circular sheet after being bent. As can be seen from FIG. 3, the round sheet made of the negative electrode composite material has a good self-supporting flexible structure, is high in toughness, is not easy to break when being bent, can be directly used as an electrode, and can get rid of the constraint of a current collector and remove the manufacturing process of a pole pieceThe process is favorable for increasing the specific energy density of the battery and shortening the manufacturing period of the battery.
Fig. 4 is a part of a scanning electron micrograph of the negative electrode composite material of the present application. As can be seen in fig. 4, the fibrous amorphous carbon has lighter colored dots thereon. The light-colored dots are lithium titanate particles. The lithium titanate particles are positioned on the surface of the hollow or non-hollow amorphous carbon fiber tube to form the spurs or positioned inside the amorphous carbon fiber tube and are dispersed light-color granular objects under a scanning electron microscope.
Fig. 5 is another part of an electron micrograph of the negative electrode composite material of the present application. As can be seen from fig. 5, the carbon nanotubes in the figure are partially contained in the fibrous amorphous carbon, and some of them are exposed to the outside of the amorphous carbon.
Fig. 6 is an XRD spectrum of the negative electrode composite material, the top is an XRD spectrum of the negative electrode composite material in the present application, which is consistent with a standard spectrum of lithium titanate, and indicates that the main material of the negative electrode composite material is lithium titanate.
In FIG. 7, the top is LTO/CNT-V0The multiplying power performance diagram of the cathode composite material directly used as the lithium ion battery pole piece can be seen, and LTO/CNT-V0The cathode composite material is directly used as a pole piece, the effect is excellent, the rate capability is greatly improved, and the reversible capacity of 78mAh/g is still available under the condition of 10C ultrahigh rate.
In FIG. 8, the top is LTO/CNT-V in this example0The negative electrode composite material is directly used as a cycle chart of a lithium ion battery pole piece, and the battery in the embodiment still maintains reversible capacity of 140mAh/g after being cycled for 500 cycles under the current of 1C.
In the embodiment, the mass ratio of the lithium titanate to the carbon nanotube to the amorphous carbon is 52: 8: 40, wherein the particle size of the lithium titanate is about 50nm (the particle size refers to the average particle size of particles, and is measured by a conventional particle distribution tester), the smaller particle size is favorable for ion transmission, the carbon nanotube plays a role of a conductive mesh wire, and the amorphous carbon after high-temperature carbonization mainly plays a role in constructing a conductive network and stabilizing the overall structure of the negative electrode composite material. The negative electrode composite material in the present example has greater electron conductivity and superior rate capability, relative to the case of no carbon nanotube in comparative example 1, and neither carbon nanotube nor amorphous carbon in comparative examples 2 and 5.
Example 2
In this example, the carbonization temperature was increased to 900 ℃ on the basis that the other conditions were kept consistent with example 1. The increase in temperature causes further carbonization of the shaped carbon, the amorphous carbon proportion is slightly reduced (from 40% to 39%), the conductivity is further increased, and the thickness is slightly reduced; meanwhile, the high temperature can promote the lithium titanate crystal to grow (about 50nm to about 55nm), which is not beneficial to keeping the overall stability and lithium ion transmission of the cathode composite material.
Example 3
In this embodiment, on the basis that other conditions are consistent with those in embodiment 1, the carbonization temperature is increased to 1000 ℃, the conductivity of the amorphous carbon is increased when the temperature is increased, but the quality is not changed any more, and the lithium titanate crystal grows up due to an excessively high temperature, so that the amorphous carbon may not coat the lithium titanate crystal well, the overall stability of the negative electrode composite material is deteriorated, and the process cost is increased significantly.
Example 4
In this example, the carbonization yield of the polymer was slightly decreased in the argon atmosphere, and the porosity was slightly increased (about 30% to about 32%) with the flow of the atmosphere, and the increased porosity consumed more electrolyte than in the vacuum condition, while the other conditions were kept the same as in example 1, except that the high-temperature carbonization condition was changed from vacuum to argon atmosphere.
Example 5
In this example, the carbonization temperature was lowered to 650 ℃ under otherwise the same conditions as in example 1. At the temperature, the lithium titanate crystal form cannot be completely molded, the crystallization degree is low (41%), the structure is unstable, the particle size is small, the difficulty coefficient in the lithium titanate lithium intercalation and deintercalation process is large, and the capacity cannot be fully exerted. The carbonization degree of the polymer at a lower temperature is low, the conductivity cannot be effectively improved, the function of a conductive network cannot be realized, and the formed disordered layer structure (the disordered layer structure refers to a structure after the polymer is carbonized at a low temperature) can influence the transmission of lithium ions and electrons, so that the rate capability of the battery is further deteriorated.
Example 6
In this example, the amounts of lithium chloride monohydrate and tetrabutyl titanate used were increased while keeping the other conditions consistent with example 1. The use amounts of the lithium salt and the titanium salt are increased, so that the mass percentage of lithium titanate in the negative electrode composite material in the embodiment is increased, and the load of the active material lithium titanate is improved. The proper increase of the lithium titanate load, the carbon nano tube or the amorphous carbon in the specified range does not cause great loss of the conductivity of the whole negative electrode composite material, and simultaneously, the flexibility is maintained so as to be directly used as a negative electrode plate, and the multiplying power and the cycle performance of the battery are not obviously deteriorated. As the lithium titanate content increases, the gram capacity of the negative electrode composite material at a small current slightly increases, the energy density increases, but the power density decreases.
Example 7
In this example, the amount of carbon nanotubes used was reduced (from 15mg to 10mg) while keeping the other conditions consistent with example 1. The using amount of the carbon nano tube is reduced, the effective contact between the lithium titanate and the carbon nano tube is reduced, and partial area electron transfer needs to depend on the lithium titanate (the self conductivity of the lithium titanate is only 10)-13S/cm), the electron conductivity is somewhat lowered, but the rate performance of the entire battery is slightly deteriorated but not much affected. Because the mass percentage of the amorphous carbon is increased, the overall stability of the negative electrode composite material is improved, and the cycling stability of the battery is enhanced.
Example 8
In this example, the amount of polymer used was reduced to 60% of that in example 1, while keeping the other conditions in agreement with example 1. After the usage amount of the polymer is reduced, the content of amorphous carbon in the negative electrode composite material after high-temperature carbonization is greatly reduced, so that the amorphous carbon cannot effectively coat lithium titanate and carbon nanotubes, the negative electrode composite material cannot maintain stable toughness, and cannot be directly used as an electrode material of a lithium ion battery.
Example 9
In this example, the length and diameter of the carbon nanotubes were reduced while keeping the other conditions consistent with example 1. The length and the diameter of the carbon nanotube are reduced (specific numerical values are shown in tables 1 and 2), and the size of the carbon nanotube is closer to that of the lithium titanate in the embodiment, so that the carbon nanotube is beneficial to better dispersion and contact between the carbon nanotube and the lithium titanate; meanwhile, the smaller length and diameter are beneficial to uniformly coating the amorphous carbon, so that the coating thickness is more uniform, and the overall capacity exertion and the rate capability of the negative electrode composite material are improved to a certain extent.
Example 10
In this example, the multi-walled carbon nanotubes were replaced with single-walled carbon nanotubes under otherwise identical conditions as in example 1. The single-walled carbon nanotube has better conductivity than the multi-walled carbon nanotube, so the overall electronic conductivity of the negative electrode composite material in the embodiment is better than that in embodiment 1, and the rate capability is improved, but the single-walled carbon nanotube has high cost, so the single-walled carbon nanotube is not beneficial to large-scale application.
Example 11
The method comprises the following steps: 0.5g Polyacrylonitrile (PAN), 0.2g polyvinylpyrrolidone (PVP) and 15mg multiwall carbon nanotubes were added to 10mL DMF and stirred until the polymer was well dissolved.
Step two: adding 2.5mmol of spinel lithium titanate (the particle size is about 50nm) into the first step, stirring and dispersing to obtain a suspension of lithium titanate, stirring at normal temperature for 12 hours to obtain a mixed solution C, and taking the mixed solution C as an electrostatic spinning precursor suspension.
Step three: the mixed solution is injected into a 10mL syringe connected with a blunt metal needle, a high-voltage direct-current power supply applies 8kV direct-current high voltage between the syringe needle and a receiving device, the solution is pushed at the speed of 0.6mL/h through a syringe pump, the distance between the needle and the receiving device is 15cm, and the experimental process schematic diagram is shown in FIG. 1. And after the end, collecting the nanofiber membrane and performing vacuum drying.
Step four: the dried nanofiber membrane was pre-oxidized in a muffle furnace at 230 ℃ for 2 hours.
Step five: carbonizing the pre-oxidized nanofiber membrane at 800 ℃ under a vacuum condition, and preserving heat for 10 hours to obtain the one-dimensional carbon nanofiber compounded with the lithium titanate and the carbon nano tube.
In this example, since lithium titanate is insoluble in DMF (N, N-dimethylformamide), the uniformity of dispersion of the electrospinning precursor liquid was inferior to the above ten examples, and the cell uniformity was relatively poor.
Example 12
This example exchanged multi-walled carbon nanotubes for single-walled carbon nanotubes under otherwise unchanged conditions as in example 11. The introduction of single-walled carbon nanotubes slightly enhances the rate performance of the battery.
Examples 13 to 15
Examples 13-15 the amounts of PAN and PVP were adjusted based on other conditions remaining consistent with example 1. Example 13 using 0.4g each of PAN and PVP, where PAN gave better structural stability after carbonization and PVP gave superior conductivity after carbonization, with adjustments between the amounts being critical to the final conductivity (especially final flexibility) of the negative electrode composite. Therefore, in example 14, the amount of the two materials is not enough, so that the negative electrode composite material cannot be directly used as a flexible material of a pole piece, which results in a significant reduction in energy density; in example 15, PAN used in a relatively large amount significantly increased the carbon content ratio in the product, and the flexibility of the negative electrode composite material was improved, but the relative content of lithium carbonate as an active material was decreased, and the overall energy density of the negative electrode composite material was also significantly decreased as compared with example 1.
Examples 16 to 19
In examples 16 to 19, the carbonization temperature and the carbonization retention time were experimentally designed while keeping the other conditions in accordance with example 1. The overall influence of properly shortening the carbonization heat preservation time on the cathode composite material under the condition of unchanging temperature cannot be too great. However, if the time is too short, the crystallinity of lithium titanate and the carbonization of the polymer are not completed, and the performance of the negative electrode composite is deteriorated as much as in example 19. However, too long a carbonization time does not significantly improve the performance of the negative electrode composite material, and significantly increases the time and energy costs (e.g., example 18). Therefore, the carbonization temperature and the heat preservation time need to be controlled within a reasonable range, so that the dual benefits of improving the performance and saving the cost are achieved.
Example 20
In this example, while the ratio and particle size of carbon nanotubes were studied to the utmost, PVA was used in place of a portion of PVP, and the lower limit of the diameter was 10nm and the lower limit of the length was 100nm at a minimum content of 3%. The electron conductivity will decrease due to the decrease of the content of the carbon nano-tube, but the decrease of the particle size and the length thereof is beneficial to the contact with the lithium titanate to alleviate the rate capability deterioration to a certain extent.
Comparative example 1
The method comprises the following steps: 0.5g Polyacrylonitrile (PAN), 0.2g polyvinylpyrrolidone (PVP) was added to 10mL DMF and stirred until the polymer was fully dissolved.
Step two: 2.25mmol of LiCl. H2And O is added into the solution obtained in the step one, and the mixture is continuously stirred until the mixture is dissolved, so that a solution A is obtained.
Step three: 2.5mmol of tetrabutyl titanate (C)16H36O4Ti) and 200 μ L glacial acetic acid and stirred until a clear solution B is obtained.
Step four: slowly adding the solution B into the solution A, stirring for 12 hours at normal temperature to obtain a mixed solution C, and taking the mixed solution C as an electrostatic spinning precursor solution.
Step five: the mixed solution C is injected into a 10mL syringe connected with a blunt metal needle, a high-voltage direct-current power supply applies 8kV direct-current high voltage between the syringe needle and a receiving device, the solution is pushed at the speed of 0.6mL/h through a syringe pump, the distance between the syringe needle and the receiving device is 15cm, and the experimental process schematic diagram is shown in FIG. 1. And after the end, collecting the nanofiber membrane and performing vacuum drying.
Step six: the dried nanofiber membrane was pre-oxidized in a muffle furnace at 230 ℃ for 2 hours.
Step seven: carbonizing the pre-oxidized nanofiber membrane at 800 ℃ under a vacuum condition, and preserving heatObtaining the lithium titanate composite carbon nano tube one-dimensional nanofiber (LTO-V) in 10 hours0)。
In FIG. 6, the middle curve is LTO-V obtained in the present comparative example0From the XRD pattern, it can be seen that the main material of the negative electrode composite material is also lithium titanate.
In FIG. 7, the middle curve is LTO-V0The cathode composite material is directly used as a rate performance graph of an electrode, and the cathode composite material is also shown to have good effect and obviously improved rate performance when being used as a self-supporting flexible electrode.
Comparative example 2
The method comprises the following steps: 0.5g Polyacrylonitrile (PAN), 0.2g polyvinylpyrrolidone (PVP) was added to 10mL DMF and stirred until the polymer was fully dissolved.
Step two: 2.25mmol of LiCl. H2And O is added into the solution obtained in the step one, and the mixture is continuously stirred until the mixture is dissolved, so that a solution A is obtained.
Step three: 2.5mmol of tetrabutyl titanate (C)16H36O4Ti) and 200 μ L glacial acetic acid and stirred until a clear solution B is obtained.
Step four: slowly adding the solution B into the solution A, stirring for 12 hours at normal temperature to obtain a mixed solution C, and taking the mixed solution C as an electrostatic spinning precursor solution.
Step five: the mixed solution C is injected into a 10mL syringe connected with a blunt metal needle, a high-voltage direct-current power supply applies 8kV direct-current high voltage between the syringe needle and a receiving device, the solution is pushed at the speed of 0.6mL/h through a syringe pump, the distance between the syringe needle and the receiving device is 15cm, and the experimental process schematic diagram is shown in FIG. 1. And after the end, collecting the nanofiber membrane and performing vacuum drying.
Step six: the dried nanofiber membrane was pre-oxidized in a muffle furnace at 230 ℃ for 2 hours.
Step seven: and calcining the pre-oxidized nano fiber membrane at 800 ℃ under the air condition, and preserving the heat for 10 hours to obtain lithium titanate (LTO-air).
In fig. 6, the bottom curve is the XRD pattern of LTO-air obtained in this comparative example, and it can be seen that the phase of the negative electrode composite is lithium titanate.
In fig. 7, the lowest curve is a rate capability graph of the LTO-air electrode, and it is explained that the rate capability is general because lithium titanate itself has poor conductivity.
Comparative examples 3 and 4
The first six steps of the preparation of the negative electrode composites of comparative examples 3 and 4 were kept in accordance with comparative example 1, except that in step seven, the carbonization temperature was increased to 900 ℃ and 1000 ℃, respectively. As the carbonization temperature increases, the conductivity of amorphous carbon becomes better, but the size of lithium titanate also becomes larger. When the temperature is too high, the cost is increased, the performance improving effect is weak, and the lithium titanate particles are too large to adversely affect the performance of the cathode composite material.
Comparative example 5
The method comprises the following steps: 0.5g Polyacrylonitrile (PAN), 0.2g polyvinylpyrrolidone (PVP) was added to 10mL DMF and stirred until the polymer was fully dissolved.
Step two: adding 2.25mmol of commercial nano lithium titanate into the solution obtained in the step one, and continuously stirring until the solution is uniformly dispersed to obtain a suspension (solution A).
Step three, 200 mu L of glacial acetic acid is taken as a solution B.
And step four, slowly adding the solution B into the solution A, stirring for 12 hours at normal temperature to obtain a mixed solution C, and taking the mixed solution C as an electrostatic spinning precursor solution.
Step five: the mixed solution C is injected into a 10mL syringe connected with a blunt metal needle, a high-voltage direct-current power supply applies 8kV direct-current high voltage between the syringe needle and a receiving device, the solution is pushed at the speed of 0.6mL/h through a syringe pump, the distance between the syringe needle and the receiving device is 15cm, and the experimental process schematic diagram is shown in FIG. 1. And after the end, collecting the nanofiber membrane and performing vacuum drying.
Step six: the dried nanofiber membrane was pre-oxidized in a muffle furnace at 230 ℃ for 2 hours.
Step seven: and calcining the pre-oxidized nano fiber membrane at 800 ℃ under the air condition, and preserving the heat for 10 hours to obtain the lithium titanate.
The examples, comparative fabrication process parameters, and the main parameters for preparing the final material are listed in tables 1 and 2.
TABLE 1 relevant experimental parameters for the examples and comparative examples in the present application
TABLE 2 Main parameters of negative electrode composite materials of examples and comparative examples in the present application
The parameters in table 2 were tested as follows:
particle size D of particles obtained by particle distribution testerv90 (90% of the particles have a size smaller than this value).
The crystallinity of lithium titanate is tested by crystal XRD to obtain d(101)Peak intensity, and d in its standard XRD spectrum(101) Sign boardBy contrast, degree of crystallinity ═ d(101)/d(101) Sign board。
Porosity is measured by the true volume V of the material0Calculated from the apparent volume V, the porosity being (V)0-V)/V100%. The porosity can affect the transmission and infiltration of electrolyte in the battery cell, and further affect the performances of the battery cell such as circulation and multiplying power.
The conductivity is measured by measuring the resistance of the material under a certain pressure and calculating the conductivity. The conductivity mainly affects the transmission process of electrons in the material, and further affects the rate performance.
As can be seen from table 2, the main function of the amorphous carbon is to support lithium titanate and carbon nanotubes, maintain the overall structure to maintain flexibility, and at the same time, the amorphous carbon is also beneficial to improving the conductivity of the material and enhancing the rate capability. The smaller the diameter of the amorphous carbon, the better the overall rate capability of the negative electrode composite material. However, if the diameter of the amorphous carbon is too small, the amorphous carbon cannot support lithium carbonate and carbon nanotubes, and if the diameter of the amorphous carbon is too large, the capacity performance is not good.
The porosity of the negative electrode composite material is mainly influenced by the content and size of amorphous carbon, the porosity further influences the infiltration of electrolyte and the consumption rate of the electrolyte, the electrolyte with the porosity of 25-40% can be well infiltrated to facilitate the transmission of a lithium ion liquid phase, the infiltration of the electrolyte is influenced when the porosity is too small, and the first efficiency of the battery is deteriorated when the porosity is too large.
Similarly, the carbon nanotube mainly plays a role in improving the electrical conductivity of the negative electrode composite material, the smaller the particle size in a certain range is, the more beneficial the electrical conductivity is to improve, but the too small particle size cannot be connected with the lithium titanate particle, the processability is affected, and the specific capacity is reduced; meanwhile, the increase of the ratio of the carbon nano tube in the cathode composite material is beneficial to improving the electronic conductivity and the rate capability, but the increase of the ratio of the carbon nano tube to the capacity is very small, the whole gram capacity of the cathode composite material is reduced, and the ratio of the carbon nano tube to the cathode composite material needs to be controlled to be 3% -10%.
The diameter of lithium titanate particles has obvious influence on the dynamic performance, the smaller-sized nanoparticles are beneficial to solid-phase transmission of lithium ions, but the smaller the particles are, the processing cost and difficulty are obviously increased, the overlarge particles not only influence the lithium ion transmission, but also are not beneficial to the dispersion and the embedding of the particles in amorphous carbon, so that the particle size of the particles needs to be controlled between 10nm and 200nm, and the electrical performance is better exerted. The crystallinity of lithium titanate mainly affects whether the battery capacity can be fully exerted (as in example 5). When the calcination temperature exceeds 750 ℃, the crystallinity of the lithium titanate basically reaches more than 80%, and the influence on the performance of the battery cell is relatively small, so that the description is omitted.
The negative electrode composite material prepared by the method has self-supporting flexibility, can be used as a negative electrode plate, shows great improvement on both conductivity and electrochemical performance, and has great potential in the application of flexible batteries due to the characteristic of the self-supporting flexibility. In addition, the secondary battery adopting the cathode composite material can realize high-rate discharge and ensure long circulation.
The above are only specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily made within the technical scope of the present application should be covered by the scope of the present application.
Claims (11)
1. An anode composite, comprising fibrous self-supporting amorphous carbon having lithium titanate and carbon nanotubes thereon.
2. The anode composite according to claim 1, wherein the fibrous self-supporting amorphous carbon has a diameter of 200nm to 600 nm.
3. The anode composite according to claim 1, wherein the fibrous self-supporting amorphous carbon is obtained by calcining a polymer under vacuum or inert atmosphere, wherein the polymer comprises at least one of polyvinylpyrrolidone, polyacrylonitrile, polyvinyl alcohol.
4. The negative electrode composite material as claimed in claim 1, wherein the mass percentages of lithium titanate, carbon nanotubes and fibrous self-supporting amorphous carbon in the negative electrode composite material are 40 to 65% to 3 to 10% to 30 to 50% based on the total mass of lithium titanate, carbon nanotubes and amorphous carbon.
5. The negative electrode composite of claim 1, wherein the lithium titanate has at least one of the following characteristics: the lithium titanate has a spinel structure; the lithium titanate has a crystallinity of 75% to 100%; the particle diameter of the lithium titanate is 10nm to 200 nm.
6. The negative electrode composite of claim 1, wherein the carbon nanotubes have at least one of the following characteristics: the carbon nanotubes comprise at least one of multi-walled carbon nanotubes or single-walled carbon nanotubes; the diameter of the carbon nano tube is 10nm to 70 nm; the length of the carbon nanotube is 100nm to 200 nm.
7. A preparation method of a negative electrode composite material is characterized by comprising the following steps:
(1) adding a polymer and a carbon nano tube into an organic solvent, and stirring at room temperature until the polymer is completely dissolved to obtain a solution A; wherein the polymer comprises at least one of polyvinylpyrrolidone, polyacrylonitrile and polyvinyl alcohol, and the organic solvent is selected from ethanol and/or N, N-dimethylformamide;
(2) mixing lithium titanate and glacial acetic acid, and stirring until the mixture is clear to obtain a solution B;
(3) adding the solution B into the solution A, and stirring at normal temperature to obtain a mixed solution C;
(4) preparing the mixed solution C into a nanofiber membrane through electrostatic spinning, and performing vacuum drying and pre-oxidation treatment on the obtained nanofiber membrane; and after the pre-oxidation treatment is finished, carbonizing the nano fiber film subjected to the pre-oxidation treatment under the vacuum or inert atmosphere condition to obtain the negative electrode composite material.
8. The method of claim 7, further comprising: in step (1), lithium chloride monohydrate is added after the polymer is completely dissolved, and tetrabutyl titanate is used to replace lithium titanate in step (2).
9. A negative electrode, characterized in that the negative electrode is composed of the negative electrode composite material according to any one of claims 1 to 6, and the negative electrode has an expansion ratio of 3% to 5%.
10. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is composed of the negative electrode composite material according to any one of claims 1 to 6.
11. An electronic device comprising the electrochemical device of claim 10.
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