CN110797508B - Preparation method of cabo carbon-based flexible self-supporting positive electrode and application of cabo carbon-based flexible self-supporting positive electrode in lithium-sulfur battery - Google Patents

Preparation method of cabo carbon-based flexible self-supporting positive electrode and application of cabo carbon-based flexible self-supporting positive electrode in lithium-sulfur battery Download PDF

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CN110797508B
CN110797508B CN201910966971.4A CN201910966971A CN110797508B CN 110797508 B CN110797508 B CN 110797508B CN 201910966971 A CN201910966971 A CN 201910966971A CN 110797508 B CN110797508 B CN 110797508B
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CN110797508A (en
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钟美娥
管金貂
周南
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Hunan Agricultural University
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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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • 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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • H01M4/621—Binders
    • 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
    • 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
    • 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 invention belongs to the field of material processing, and particularly discloses a preparation method of a cabo carbon-based flexible self-supporting anode, which comprises the steps of placing cabo in a mixed solution of phosphoric acid and metal salt, and carrying out first-stage heat treatment at the temperature of 260-350 ℃ in an open manner to obtain a precursor; then carrying out second-stage heat treatment on the precursor in a protective atmosphere at 500-1000 ℃ to obtain the porous carbon material which is rich in oxygen-containing functional groups and strong in hydrophilicity; filling sulfur simple substances into a porous carbon material to prepare a lithium-sulfur battery positive active material, then utilizing the mutual reaction and dehydration of oxygen-containing functional groups of the porous carbon at high temperature to generate a self-assembly effect, and preparing the positive active material into a flexible self-supporting positive electrode by a coating-drying-self-stripping method. The invention has simple operation, the anode can bear repeated bending without cracking without a current collector, and can be directly cut into various shapes for preparing batteries, thereby being convenient for the design and assembly of different battery shapes. The preparation of the high-performance lithium-sulfur battery anode material can be realized and the preparation cost of the anode can be reduced at the same time.

Description

Preparation method of cabo carbon-based flexible self-supporting positive electrode and application of cabo carbon-based flexible self-supporting positive electrode in lithium-sulfur battery
The technical field is as follows:
the invention belongs to the field of preparation of lithium-sulfur battery anodes, and particularly relates to a preparation method of a tobacco stalk carbon-based flexible self-supporting anode.
Technical background:
in recent years, lithium sulfur electricityThe cell is receiving attention of researchers because of its high energy density (2500 Wh/kg, 2800 Wh/L), wide source of active substance sulfur, low price and other advantages, and is one of the main research directions of lithium metal batteries at present. However, lithium sulfur batteries, while having many advantages, also face a number of serious challenges. Sulfur and its discharge product Li 2 S 2 And Li 2 S has poor conductivity and is changed from S to Li in the process of charging and discharging 2 The S transformation causes the volume expansion of the electrode material, and the dissolution of long-chain polysulfide in the electrolyte causes a shuttle effect, thereby causing serious active substance loss, low coulombic efficiency and quick capacity attenuation.
In order to solve the technical problem of unsatisfactory electrical properties caused by the problems of polysulfide and the like of a lithium-sulfur battery, the prior art provides more technical ideas which are mainly divided into the research on modification of a positive electrode material, an electrolyte and a diaphragm. The introduction of sulfur into a conductive matrix is currently one of the most promising approaches to improve the electrochemical performance of lithium sulfur batteries in terms of optimization of the cathode material. Conductive substrates mainly studied by researchers are nonpolar carbon materials such as porous carbon, hollow carbon, carbon nanotubes, graphene, bio-based carbon materials and the like; however, during long-term cycling, lithium-sulfur batteries using non-polar carbon materials as hosts have a fast capacity fade and poor cycling stability due to poor physical adsorption between the non-polar materials and the polar polysulfides. The bio-based carbon material adopted by the invention has a unique microstructure comprising macropores, mesopores and micropores, is large in specific surface area and uniform in pore size distribution, contains abundant heteroatoms uniformly distributed such as N, P, S and has good physical and chemical stability compared with a common traditional carbon material, and thus the bio-based carbon material is distinguished from a plurality of carbon materials.
However, the conventional lithium battery manufacturing process has certain limitations. For example, the conductive current collector aluminum foil sheet increases the weight and cost of the electrode while ensuring the conductivity and structural stability of the electrode during the coating process. And the preparation of high-loading thick electrodes has many problems, such as easy crack formation, delamination, lack of flexibility and the like.
In addition, with the advent of smart textiles, portable wearable devices, offer new opportunities for energy storage devices, as well as new challenges. The rise of flexible electronic devices requires that energy storage devices must have the property of being flexible and capable of possessing superior electrochemical properties. However, the bending effect of the manufactured flexible electrode battery is limited by using the traditional battery preparation process, so that the use requirement of the flexible energy storage device is difficult to meet by using the traditional lithium-sulfur battery anode. Therefore, how to design the structure of each part in the battery to improve the whole bending resistance is a research topic of those skilled in the art.
In order to achieve the flexibility and light weight of the lithium-sulfur battery, the prior art also provides a few solutions, such as: a graphene film is adopted as a flexible electrode material; or preparing the electrode material by adopting electrostatic spinning. However, the existing method has complicated preparation process and high price of preparation equipment, and limits the application of the materials to a certain extent.
The invention content is as follows:
in order to overcome the defects in the prior art, the first purpose of the invention is to provide a preparation method of a tobacco stalk carbon-based flexible self-supporting anode based on a brand-new flexible anode construction idea.
The second purpose of the invention is to provide the cabo carbon-based flexible self-supporting anode prepared by the preparation method.
The third purpose of the invention is to provide the application of the cabo carbon-based flexible self-supporting positive electrode in a lithium-sulfur battery and the assembly of the cabo carbon-based flexible self-supporting positive electrode into the lithium-sulfur battery.
A preparation method of a cabo carbon-based flexible self-supporting anode comprises the following steps:
step (1): putting a mixed solution containing tobacco stems, phosphoric acid and metal salt into an open container, and carrying out first-stage heat treatment at a temperature higher than the boiling point of the phosphoric acid to obtain a precursor;
step (2): then carrying out second-stage heat treatment on the precursor in a protective atmosphere at 500-1000 ℃ to obtain a porous carbon material (the contact angle with water within 42ms is lower than 45 ℃) with rich oxygen-containing functional groups and strong hydrophilicity;
and (3): filling a sulfur simple substance into the porous carbon material to prepare a positive active material;
and (4): the flexible self-supporting positive electrode is prepared by the steps of coating a slurry of a positive active material, an adhesive and a conductive agent on the surface of a planar metal carrier, drying, and mutually reacting and dehydrating oxygen-containing functional groups of porous carbon at high temperature to generate a self-assembly effect and automatically peel off.
Different from the construction idea of the conventional flexible positive electrode of the lithium-sulfur battery, the invention provides a flexible self-supporting positive electrode which is obtained by constructing a porous carbon material and a positive electrode composite material with special surface characteristics and further utilizing the unique surface characteristics of the porous carbon material and the positive electrode composite material in a coating (compounding) -drying self-stripping manner.
The invention realizes the complete self-stripping of the active material layer coated on the surface of the planar carrier by a coating-drying self-stripping concept for the first time. It was found that for the successful construction of said flexible self-supporting material by said innovative coating-drying self-peeling concept the first task is to construct a fast super-hydrophilic porous carbon material of specific surface properties. In order to successfully construct the porous carbon material with the special surface characteristics, the inventor finds that the porous carbon material with the dry self-peeling characteristic and the positive electrode active material can be unexpectedly obtained by adopting tobacco stems as raw materials, performing a first stage of heat treatment in a phosphoric acid and metal salt solution system at a temperature which is difficult to unexpectedly exceed the boiling point of phosphoric acid in the industry, and then matching the second stage of heat treatment.
The key points of the invention are as follows: (1) The method firstly proposes that the rapid super-hydrophilic porous carbon material can be obtained through the cooperative control of the preparation conditions; (2): the first discovery shows that the successfully constructed rapid super-hydrophilic porous carbon material can realize self-stripping.
According to the invention, the tobacco stems rich in N, O, S and phosphoric acid are used as a reaction system, metal doping and regulation and control of the first-stage heat treatment temperature are further matched, the interface reaction action of an oxygen-containing atmosphere and a phosphoric acid solution is utilized, and a second-stage high-temperature calcination heat treatment is combined to obtain the rapid super-hydrophilic carbon material which is porous in structure, rich in oxygen-containing functional groups, strong in hydrophilic surface characteristics and metal/heteroatom co-doped.
In the invention, the tobacco stems as raw materials are one of the keys for successfully preparing the porous carbon material with the characteristic surface characteristics.
According to the technical scheme, the tobacco stems are dried in advance and then crushed into powder.
Preferably, the tobacco stem drying temperature is 60-105 deg.C, the drying time is 12-24h, and the particle size of the pulverized powder is 100-200 mesh.
According to the preparation method, the metal salt is innovatively added into the system, and the good solution modification characteristic of the metal salt is utilized, and the carbon raw material, the acid type and the control of the first-stage heat treatment temperature are matched, so that the special surface characteristic and the in-situ doping modified porous carbon material can be obtained, and the high-electrical-property anode can be obtained.
Preferably, the metal salt is a raw material containing at least one metal salt of manganese, iron, nickel and cobalt; preferably permanganate; more preferably KMnO 4 . The addition of the preferred potassium permanganate is beneficial to promoting the oxidation of the tobacco stems in the first stage of heat treatment, is also beneficial to regulating and controlling surface functional groups and is beneficial to obtaining the anode with high electrical properties.
Preferably, the mass ratio of the tobacco stems to the metal salt is 1 g: 0.01-0.1 g.
Phosphoric acid as a starting material is another key to successfully producing porous carbon materials with the characteristic surface characteristics.
Preferably, the mixed solution contains 50 to 85 mass percent of phosphoric acid; more preferably 75 to 85%; most preferably 85%.
In the mixed liquid, the volume ratio of solid to liquid is 1 g: 2-5 mL. The solid part of the solid-liquid volume ratio refers to the weight of the tobacco stems and the metal salt, and the volume of the liquid part refers to the solution of phosphoric acid.
In the actual preparation process, the tobacco stems and the metal salt can be dispersed in the phosphoric acid solution and mixed to obtain the mixed solution. The mass percentage of the phosphoric acid solution is 50-85%; more preferably 75 to 85%; most preferably 85%. The total weight of the tobacco stems and the metal salt and the solid-liquid volume ratio of the phosphoric acid solution are 1 g: 2-5 mL.
The invention creatively carries out the first-stage heat treatment in an open reaction vessel under the temperature coordination which is difficult to be expected in the industry, and through the oxygen-containing atmosphere and the interface action of the phosphoric acid solution, the material is endowed with richer surface active groups and special surface characteristics, and moreover, the invention is also beneficial to the second-stage heat treatment to obtain the metal/heteroatom-codoped carbon material, thereby being beneficial to improving the electrochemical performance of the subsequent preparation material.
In the present invention, the first stage heat treatment temperature is performed in an open reaction vessel, which is understood to mean that the first stage heat treatment is performed in an oxygen-containing atmosphere such as air.
The inventor researches and discovers that in order to further improve the electrical properties of a subsequently prepared positive active material, besides the material type of the step (1), the heat treatment temperature needs to be further strictly controlled.
Preferably, the temperature of the first stage heat treatment is 260-350 ℃. The research finds that the combination of other parameters helps to obtain a flexible and self-supporting positive electrode obtained by a coating-self-stripping technology in a preferable temperature range, and also helps to improve the performance of a subsequently prepared positive electrode active material.
Further preferably, the temperature of the first stage heat treatment is 280 to 300 ℃.
Preferably, the treatment time of the first stage heat treatment is 5-24 h; more preferably 5 to 10 hours.
And obtaining a precursor after the first-stage heat treatment is finished. According to the invention, the carbon material is subjected to second-stage heat treatment, and the carbon material with the metal/heteroatom co-doping characteristic is formed by controlling the temperature in the second-stage heat treatment process, so that the electrochemical performance of the material is effectively improved.
The second stage heat treatment is preferably carried out in a tube furnace.
The protective atmosphere may be nitrogen or an inert gas.
The flow rate of the protective atmosphere is 0.1-1L/min.
Preferably, the temperature of the second stage heat treatment is 600 to 800 ℃. Under the conditions of metal doping, phosphoric acid activation and first-stage heat treatment, the electrical properties of the prepared material can be further improved by further controlling the temperature at the optimal temperature.
The temperature rise rate of the second stage heat treatment is 5-20 ℃/min; preferably 10 to 12 ℃/min.
Preferably, the time of the second heat treatment is 2 to 5 hours.
In the present invention, after the second heat treatment, the obtained product is washed and dried to obtain the porous carbon material. According to the preparation method, the porous carbon material which is rich in special oxygen-containing functional groups and has strong hydrophilicity can be obtained, and the strong hydrophilicity means that the contact angle is smaller when the contact time with water is the same; when complete infiltration occurs, the time required is shorter and is significantly less than that of porous carbon materials with similar material contact angles.
The inventor researches and discovers that the rapid super-strong hydrophilic porous carbon material with the contact angle of less than 45 degrees with water within 42ms can be successfully constructed by the innovative preparation method, and further discovers that the material can unexpectedly realize self-peeling.
Preferably, the contact angle of the porous carbon material with water within 42ms is lower than 30 degrees. It was found that the carbon material having a fast low contact angle further unexpectedly achieves self-exfoliation, and not only contributes to improvement of electrochemical properties.
The washing treatment is preferably water washing, or acid washing followed by water washing to neutrality.
For example, the product of the second stage heat treatment is naturally cooled, taken out and dispersed in deionized water for ultrasonic treatment for 10-30min, and then is shaken for 5-12h, washed to be neutral by the deionized water, and then dried and sieved to obtain the porous biological carbon, wherein the drying temperature is 60-100 ℃, and the mesh number of the sieve is 400 meshes.
Preferably, the porous carbon material and sublimed sulfur are mixed and then placed in a closed container, and are treated at 155-160 ℃ in advance, and then are treated at 195-200 ℃ to prepare the positive electrode active material of the lithium-sulfur battery. Under the two-stage treatment, the performance of the prepared cathode material is further improved.
Preferably, the positive electrode active material, the conductive agent and the adhesive are slurried with a solvent and combined on the surface of the positive electrode current collector, the slurry solidified after drying is naturally separated from the surface of the current collector in a whole block, and the slurry is cut into regular flexible self-supporting positive electrode sheets and assembled into the lithium-sulfur battery.
The conductive agent can adopt any conductive material obtained by a person skilled in the lithium-sulfur battery field, and preferably the conductive agent is at least one of acetylene black, super P and Ketjen black.
The adhesive is PVDF;
the weight ratio of the positive electrode active material, the adhesive and the conductive agent is 8-9: 0.25 to 1:0.75 to 1.
The proportion of the positive electrode active material, the binder and the conductive agent can be adjusted according to the use requirement of the lithium-sulfur battery.
The slurry method may be any conventional method, for example, a slurry is prepared by dispersing a binder with a dispersant, adding a positive electrode active material and a conductive agent, and mixing them. The dispersant may be any solvent that can dissolve the binder.
The slurry of the invention can be loaded on the surface of a plane carrier by a coating method.
Preferably, the planar support is a planar metal foil with a smooth surface, such as an aluminum foil.
In the invention, the slurry can be coated on the surface of a planar carrier to form a positive electrode material layer on the surface, and then drying treatment is carried out to remove the solvent in the positive electrode material, so that the self-stripping with the planar carrier in the drying process is realized by virtue of the special surface property of the oxygen-containing functional group abundant on the surface of the material, and the positive electrode is obtained.
The invention discloses a preparation method of a preferred cabo carbon-based flexible self-supporting anode, which comprises the following steps:
(1) Drying tobacco stems and then crushing the dried tobacco stems into powder; putting tobacco stem powder with a certain mass into a reaction vessel, adding a small amount of potassium permanganate, adding a phosphoric acid solution with a certain volume mass fraction of 85%, putting the mixture into an air-blast drying oven, pre-carbonizing the mixture for 5-10 hours at a temperature higher than the boiling point of phosphoric acid (preferably 260-350 ℃) to obtain a precursor, and adjusting the addition amount of the phosphoric acid, so as to regulate and control the specific surface area of a subsequently prepared material.
(2) Directly transferring the precursor into a tubular furnace, and sintering for 2-5h at 600-800 ℃ in a nitrogen atmosphere;
(3) Naturally cooling the product, taking out the product, washing the product to be neutral, drying and sieving the product to obtain the porous biological carbon;
(4) Reacting the prepared porous biological carbon with sublimed sulfur by a physical melting method to obtain a carbon-sulfur composite material; and then the carbon-sulfur composite material is subjected to size mixing and smear cutting to prepare a flexible self-supporting positive plate, and finally the flexible self-supporting positive plate is assembled into a button battery in a glove box to detect the electrochemical performance of the button battery.
In the step (4), the mass ratio of the porous carbon material to the sublimed sulfur is 3:7, uniformly mixing, placing in a closed reaction vessel, reacting for 12h at 155 ℃, and reacting for 3h at 200 ℃ to obtain the carbon-sulfur composite material. Mixing a carbon-sulfur composite material, acetylene black and polyvinylidene fluoride according to a certain proportion, placing the mixture into a closed reaction vessel, stirring the mixture for 5 to 12 hours by taking N, N-dimethyl pyrrolidone as a solvent to prepare slurry, coating the slurry on an aluminum foil, drying the aluminum foil at the temperature of between 50 and 60 ℃, naturally separating the whole cured slurry from the surface of a current collector after drying treatment, cutting the current collector into a regular flexible self-supporting positive plate, and preparing the button battery in a glove box.
The invention also provides a cabo carbon-based flexible self-supporting anode prepared by the preparation method.
The invention also provides a lithium-sulfur battery which is assembled with the tobacco stalk carbon-based flexible self-supporting anode.
Advantageous effects
The invention provides a novel idea for constructing and obtaining a flexible self-supporting anode through a coating-drying self-stripping idea, and researches show that a mixed solution system of tobacco stems, phosphoric acid and metal salt is matched with the special two-stage heat treatment process, so that a rapid super-hydrophilic porous carbon material with special surface characteristics and an anode active material can be successfully constructed, and the flexible self-supporting anode can be successfully constructed through the innovative idea.
Compared with the traditional lithium battery preparation process method, the method can avoid using expensive metal current collectors, graphene, carbon nanotubes and the like, and solves a plurality of defects of weight, thickness, preparation cost and the like of the positive electrode.
According to the technical scheme, the preparation of the flexible self-supporting anode can be realized, the lithium-sulfur battery anode material with good electrochemical performance can be obtained, the preparation cost and the weight of the anode are reduced, and the preparation method has wide market application prospect. The method is simple and easy to operate, and the prepared flexible self-supporting anode not only can reduce the production cost of the battery, but also has higher battery capacity and better cycling stability.
Description of the drawings:
fig. 1 is a photograph of a flexible self-supporting positive electrode sheet prepared in example 1.
Fig. 2 is a photograph of the flexible self-supporting positive electrode sheet prepared in example 1.
Fig. 3 is a graph showing different-rate charge and discharge curves of the carbon-sulfur composite material prepared in example 1.
Fig. 4 is a graph showing different-rate charge and discharge curves of the carbon-sulfur composite material prepared in example 2.
Fig. 5 is a graph showing different-rate charge and discharge curves of the carbon-sulfur composite material prepared in example 3.
Fig. 6 is a graph showing different-rate charge and discharge curves of the carbon-sulfur composite material prepared in comparative example 1.
Fig. 7 is a graph showing different-rate charge and discharge curves of the carbon-sulfur composite material prepared in comparative example 2.
Fig. 8 is a graph showing different-rate charge and discharge curves of the carbon-sulfur composite material prepared in comparative example 3.
FIG. 9 is an infrared spectrum of the carbon materials prepared in example 1, comparative example 1 and comparative example 2.
Fig. 10 is an infrared spectrum of the carbon-sulfur composite materials prepared in example 1, comparative example 1, and comparative example 2.
Fig. 11 is a contact angle test chart of the carbon materials prepared in example 1, example 2, example 3, comparative example 1, comparative example 2, and comparative example 3.
The specific implementation mode is as follows:
the invention will now be further described by way of the following examples, which are not intended to limit the scope of the invention in any way. It will be understood by those skilled in the art that equivalent substitutions and corresponding modifications of the technical features of the present disclosure can be made within the scope of the present disclosure.
The tobacco stems of the following cases are dried at the temperature of 60-105 ℃ for 12-24h, and the granularity of the crushed tobacco stems is 100-200 meshes.
Example 1
Drying tobacco stems, crushing the tobacco stems into powder, putting 3g of tobacco stem powder into a crucible, adding 0.1g of potassium permanganate, 10mL of phosphoric acid with the mass fraction of 85% and 10mL of water, stirring until the mixture is uniformly mixed into a paste, putting the paste into a forced air drying oven, pre-carbonizing for 5 hours at the open temperature of 280 ℃ to obtain a precursor, directly transferring the precursor into a tubular furnace, heating to 700 ℃ at the heating rate of 10 ℃/min under the nitrogen atmosphere with the flow of 0.1L/min, carrying out heat preservation sintering for 2 hours at the temperature, naturally cooling the sintered product, taking out, dispersing in deionized water, carrying out ultrasonic treatment for 15 minutes, carrying out suction filtration and washing with the deionized water until the product is neutral, and drying and sieving the solid product to obtain the porous biochar. Mixing porous biochar with sublimed sulfur according to the mass ratio of 3:7, uniformly mixing, placing in a weighing bottle, reacting for 12 hours at 155 ℃, and reacting for 3 hours at 200 ℃ to obtain the carbon-sulfur composite material. The material was measured by infrared measurement, and as shown in fig. 10, the produced carbon material contained abundant hydrophilic groups (C = O, -OH), etc.; the contact angle data is shown in FIG. 11; as can be seen from fig. 11, the carbon material prepared in example 1 has a contact angle of only 15 ° when it is contacted with water for 42ms, and has a remarkably strong hydrophilic property. And oxygen-containing functional groups rich on the surface of the material can react with each other and dehydrate under the high-temperature heating to generate self-assembly action, so that the slurry is self-stripped from the surface of the carrier after being coated and dried to form the self-supporting material). Mixing a carbon-sulfur composite material, acetylene black and polyvinylidene fluoride according to a mass ratio of 8; after drying for 12h, the sheet was cut into regular flexible self-supporting positive plates as shown in fig. 2, and button cells were prepared in a glove box.
The discharge data is shown in figure 3.
Example 2
Drying tobacco stems, crushing the tobacco stems into powder, putting 3g of tobacco stem powder into a crucible, adding 0.1g of potassium permanganate, 10mL of phosphoric acid with the mass fraction of 85% and 10mL of water, stirring until the mixture is uniformly mixed into a paste, putting the paste into a forced air drying oven, pre-carbonizing for 5 hours at the open temperature and the temperature of 260 ℃ to obtain a precursor, directly transferring the precursor into a tubular furnace, heating to 700 ℃ at the heating rate of 10 ℃/min under the nitrogen atmosphere with the flow of 0.1L/min, carrying out heat preservation sintering for 2 hours at the temperature, naturally cooling the sintered product, taking out the sintered product, dispersing the sintered product in deionized water, carrying out ultrasonic treatment for 15 minutes, carrying out suction filtration and washing with the deionized water until the product is neutral, and drying and sieving the solid product to obtain porous biochar (the contact angle of 42ms is 22.5 degrees). Mixing porous biological carbon and sublimed sulfur according to the mass ratio of 3:7, uniformly mixing, placing in a weighing bottle, reacting for 12h at 155 ℃, reacting for 3h at 200 ℃ to obtain a carbon-sulfur composite material, mixing the carbon-sulfur composite material, acetylene black and polyvinylidene fluoride in a weighing bottle according to a mass ratio of 8.
The discharge data is shown in figure 4.
Example 3
Drying tobacco stems, crushing the tobacco stems into powder, putting 3g of tobacco stem powder into a crucible, adding 0.1g of potassium permanganate, 12mL of phosphoric acid with the mass fraction of 85% and 10mL of water, stirring the mixture until the mixture is uniformly mixed into slurry, putting the slurry into a forced air drying oven, pre-carbonizing the slurry for 5 hours at the condition of opening and 280 ℃ to obtain a precursor, directly transferring the precursor into a tubular furnace, heating the precursor to 700 ℃ at the heating rate of 10 ℃/min under the nitrogen atmosphere with the flow of 0.1L/min, carrying out heat preservation sintering for 2 hours at the temperature, naturally cooling the sintered product, taking out the sintered product, dispersing the sintered product in deionized water, carrying out ultrasonic treatment for 15 minutes, carrying out suction filtration and washing with the deionized water until the product is neutral, and drying and sieving the solid product to obtain porous biochar (the contact angle of 42ms is 25.4 degrees). Mixing porous biological carbon and sublimed sulfur according to the mass ratio of 3:7, uniformly mixing, placing in a weighing bottle, reacting for 12h at 155 ℃, reacting for 3h at 200 ℃ to obtain a carbon-sulfur composite material, mixing the carbon-sulfur composite material, acetylene black and polyvinylidene fluoride in a weighing bottle according to a mass ratio of 8.
The discharge data is shown in figure 5.
Comparative example 1
Compared with the example 1, the difference is that the pre-carbonization temperature is 250 ℃, and the specific operation is as follows:
drying tobacco stems, crushing the tobacco stems into powder, putting 3g of tobacco stem powder into a crucible, adding 0.1g of potassium permanganate, 10mL of phosphoric acid with the mass fraction of 85% and 10mL of water, stirring until the mixture is uniformly mixed into slurry, putting the slurry into a forced air drying oven, pre-carbonizing for 5 hours at the condition of opening and 250 ℃ to obtain a precursor, directly transferring the precursor into a tubular furnace, heating to 700 ℃ at the heating rate of 10 ℃/min under the nitrogen atmosphere with the flow of 0.1L/min, carrying out heat preservation sintering for 2 hours at the temperature, naturally cooling the sintered product, taking out the sintered product, dispersing the product in deionized water, carrying out ultrasonic treatment for 15 minutes, carrying out suction filtration and washing with deionized water to neutrality, drying and sieving the solid product to obtain porous biochar (the contact angle is up to 105.2 degrees when 42ms is shown in figure 11, and the contact angle is up to 76.5 degrees when the contact reaction is 168 ms). Mixing porous biological carbon and sublimed sulfur according to the mass ratio of 3:7, uniformly mixing, placing in a weighing bottle, reacting for 12h at 155 ℃, further reacting for 3h at 200 ℃ to obtain a carbon-sulfur composite material, mixing the carbon-sulfur composite material, acetylene black and polyvinylidene fluoride according to a mass ratio of 8.
The discharge data is shown in figure 6.
Comparative example 2
Compared with the example 1, the difference is only that the phosphoric acid is replaced by the phytic acid, and the specific difference is as follows:
drying and crushing tobacco stems into powder, putting 3g of tobacco stem powder into a crucible, adding 10mL of phytic acid and 10mL of water, stirring until the mixture is uniformly mixed into paste, putting the paste into a blast drying box, pre-carbonizing the paste at the condition of opening and 280 ℃ for 5 hours to obtain a precursor, directly transferring the precursor into a tubular furnace, heating to 700 ℃ at the heating rate of 10 ℃/min under the nitrogen atmosphere with the flow rate of 0.1L/min, carrying out heat preservation and sintering at the temperature for 2 hours, naturally cooling a sintered product, taking out the sintered product, dispersing the cooled sintered product into deionized water, carrying out ultrasonic treatment for 15 minutes, carrying out suction filtration and washing with deionized water until the temperature is neutral, drying and sieving a solid product to obtain porous biochar (the contact angle is as shown in figure 11, the contact angle is up to 100.5 degrees when 42ms, and is still up to 77.8 degrees when the contact reaction is carried out for 168 ms). Mixing porous biological carbon and sublimed sulfur according to the mass ratio of 3:7, uniformly mixing, placing in a weighing bottle, reacting for 12h at 155 ℃, reacting for 3h at 200 ℃ to obtain a carbon-sulfur composite material, mixing the carbon-sulfur composite material, acetylene black and polyvinylidene fluoride in a mass ratio of 8.
The discharge data is shown in figure 7.
Comparative example 3
Compared with the embodiment 1, the difference is that the used raw material is jute stalks, which is concretely as follows:
drying and crushing jute stalks into powder, putting 3g jute stalk powder into a crucible, adding 0.1g potassium permanganate, 10mL phosphoric acid with the mass fraction of 85% and 10mL water, stirring until the mixture is uniformly mixed into slurry paste, putting the slurry paste into a blast drying box, pre-carbonizing for 5h at the condition of opening and 280 ℃ to obtain a precursor, directly transferring the precursor into a tubular furnace, heating to 700 ℃ at the heating rate of 10 ℃/min under the nitrogen atmosphere with the flow of 0.1L/min, insulating and sintering for 2h at the temperature, naturally cooling the sintered product, taking out, dispersing in deionized water, ultrasonically treating for 15min, suction-filtering and washing with deionized water to neutrality, drying and sieving the solid product to obtain porous biochar (the contact angle is up to 69 degrees when the solid product is dried and sieved, and the contact angle is up to 67.8 degrees when the solid product is in contact reaction for 168 ms). Mixing porous biological carbon and sublimed sulfur according to the mass ratio of 3:7, uniformly mixing, placing in a weighing bottle, reacting for 12h at 155 ℃, reacting for 3h at 200 ℃ to obtain a carbon-sulfur composite material, mixing the carbon-sulfur composite material, acetylene black and polyvinylidene fluoride in a mass ratio of 8.
The discharge data is shown in figure 8.
The test results of each example and comparative example are shown in Table 1
Item Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3
Specific surface area (m) 2 /g) 696 742 832 778 512 728
0.2C(mAh/g) 1087 944 935 738 766 857
1C(mAh/g) 976 881 782 654 671 735
2C(mAh/g) 874 806 666 591 559 625
In conclusion, the flexible positive electrode material capable of being peeled off automatically can be prepared unexpectedly by adopting tobacco stems as a carbon source and cooperating with oxygen-containing atmosphere and temperature for cooperative control, and the material has unexpectedly better electrical properties.

Claims (10)

1. A preparation method of a cabo carbon-based flexible self-supporting anode is characterized by comprising the following steps:
step (1): putting a mixed solution containing tobacco stems, phosphoric acid and metal salt into an open container, and carrying out first-stage heat treatment at the temperature of 260-350 ℃ in an oxygen-containing atmosphere to obtain a precursor; the metal salt is permanganate;
step (2): carrying out second-stage heat treatment on the precursor at 500-1000 ℃ in protective atmosphere to obtain a strong hydrophilic porous carbon material with a contact angle with water of less than 45 ℃ within 42 ms;
and (3): mixing a porous carbon material and sublimed sulfur, placing the mixture in a closed container, processing the mixture at 155 to 160 ℃ in advance, and then processing the mixture at 195 to 200 ℃ to prepare a positive electrode active material;
and (4): the method comprises the steps of coating a slurry of a positive active material, an adhesive and a conductive agent on the surface of a planar metal carrier, drying, and automatically separating the slurry from the surface of the metal carrier by utilizing the self-assembly function of oxygen-containing functional groups of a porous carbon material to obtain the flexible self-supporting positive electrode.
2. The preparation method of the cabo carbon-based flexible self-supporting positive electrode according to claim 1, wherein in the step (1), the cabo and the metal salt are dispersed in a phosphoric acid solution and mixed to obtain the mixed solution; the mass percentage of the phosphoric acid solution is 50 to 85 percent.
3. The preparation method of the cabo carbon-based flexible self-supporting positive electrode as claimed in claim 2, wherein in the step (1), the solid-liquid volume ratio of the total weight of the cabo and the metal salt to the phosphoric acid solution is 1 g: 2-5mL.
4. The preparation method of the cabo carbon-based flexible self-supporting positive electrode as claimed in claim 1, wherein the mass ratio of the cabo to the metal salt is 1 g: 0.01-0.1g.
5. The preparation method of the cabo carbon-based flexible self-supporting positive electrode according to any one of claims 1~4, wherein the temperature of the first stage of heat treatment process is 280-300 ℃.
6. The preparation method of the cabo carbon-based flexible self-supporting positive electrode according to claim 1, wherein after the second-stage heat treatment, the obtained product is washed and dried to obtain the porous carbon material.
7. The preparation method of the cabo carbon-based flexible self-supporting positive electrode according to claim 6, wherein the washing process is water washing, or acid washing and then water washing to neutrality.
8. The preparation method of the cabo carbon-based flexible self-supporting positive electrode according to claim 1, wherein the conductive agent is at least one of acetylene black, super P and Ketjen black;
the adhesive is PVDF;
the weight ratio of the positive electrode active material to the adhesive to the conductive agent is 8~9:0.25 to 1:0.75 to 1.
9. A cabo carbon-based flexible self-supporting anode prepared by the preparation method of any one of claims 1~8.
10. A lithium sulfur battery equipped with the cabo carbon based flexible self-supporting positive electrode of claim 9.
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