阅读说明：本技术 一种烟梗碳基柔性自支撑正极的制备方法及其在锂硫电池中的应用 (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 ) 是由 钟美娥 管金貂 周南 于 2019-10-12 设计创作，主要内容包括：本发明属于材料加工领域,具体公开了一种烟梗碳基柔性自支撑正极的制备方法,将烟梗置于磷酸和金属盐的混合溶液中,在敞口、260-350℃的温度下进行第一段热处理,得前驱体；再将前驱体在保护性气氛、500-1000℃下进行第二段热处理,获得具有丰富含氧官能团的、强亲水性的多孔碳材料；向多孔碳材料中填充硫单质,制得锂硫电池正极活性材料,再利用多孔碳的含氧官能团在高温下相互反应脱水发生自组装作用,通过涂覆-干燥-自剥离方法将正极活性材料制成柔性自支撑正极。本发明操作简单,正极无需集流体,能承受反复弯曲且不破裂,可直接裁剪成各种形状用于制备电池,便于不同电池外形设计和组装。可同时实现高性能锂硫电池正极材料制备和降低正极制备成本。(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 opening and 350 ℃ plus material, so as to obtain a precursor; then carrying out second-stage heat treatment on the precursor in a protective atmosphere at the temperature of 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.)

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 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 the temperature of 500-1000 ℃ to obtain a strong hydrophilic porous carbon material with a contact angle with water lower than 45 ℃ within 42 ms;

and (3): filling a sulfur simple substance into the porous carbon material to prepare a positive 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 tobacco stalk carbon-based flexible self-supporting anode according to claim 1, wherein in the mixed solution, the mass fraction of phosphoric acid is 50-85%, and the solid-liquid volume ratio is preferably 1 g: 2-5 mL.

3. The preparation method of the cabo carbon-based flexible self-supporting positive electrode according to claim 1, wherein the metal salt is at least one metal salt raw material selected from manganese, iron, nickel and cobalt; preferably a permanganate salt.

4. The preparation method of the tobacco stalk carbon-based flexible self-supporting anode according to claim 3, wherein the mass ratio of the tobacco stalk to the metal salt is 1 g: 0.01-0.1 g.

5. The preparation method of the cabo carbon-based flexible self-supporting anode according to any one of claims 1 to 4, wherein the temperature of the first stage of the heat treatment process is 260-350 ℃.

6. The preparation method of the tobacco stem carbon-based flexible self-supporting anode according to claim 1, characterized in that after the second stage of heat treatment, the obtained product is washed and dried to obtain the porous carbon material;

the washing process is preferably water washing, or acid washing and then water washing to neutrality.

7. The preparation method of the cabo carbon-based flexible self-supporting positive electrode according to claim 1, wherein the positive electrode active material is prepared by mixing a porous carbon material and sublimed sulfur, placing the mixture in a closed container, treating the mixture at 155-160 ℃ in advance, and then treating the mixture at 195-200 ℃.

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 active material to the adhesive to the conductive agent is 8-9: 0.25-1: 0.75 to 1.

9. A cabo carbon-based flexible self-supporting positive electrode prepared by the preparation method of any one of claims 1 to 8.

10. A lithium sulfur battery equipped with the cabo carbon based flexible self-supporting positive electrode of claim 9.

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 batteries have attracted attention from researchers because of their advantages, such as high energy density (2500Wh/kg, 2800Wh/L), wide sulfur source as an active material, and low cost, and are one of the major research directions in lithium metal batteries today. However, lithium sulfur batteries, while having many advantages, also face a number of serious challenges. Sulfur and its discharge product Li₂S₂And Li₂S has poor conductivity and is changed from S to Li in the process of charging and discharging₂The 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 such as N, P, S which are uniformly distributed compared with the common traditional carbon material, and has good physical and chemical stability, so that the bio-based carbon material is unique in a plurality of carbon materials.

However, the conventional lithium battery preparation 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 the high-loading thick electrode has a plurality of 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 be flexible and possess 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 overall bending resistance is the subject of research by 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 the temperature of 500-1000 ℃ to obtain a porous carbon material (the contact angle between the porous carbon material and 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 drying 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 be unexpected in the industry and is higher than the boiling point of phosphoric acid, and matching with 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, N, O, S-rich tobacco stems 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 oxygen-containing atmosphere and phosphoric acid solution is utilized, and the second-stage high-temperature calcination heat treatment is combined to obtain the rapid super-hydrophilic carbon material which has a porous structure, is rich in oxygen-containing functional groups, has strong hydrophilic surface characteristics and is co-doped with metal/heteroatoms.

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 stems are dried at the temperature of 60-105 ℃ for 12-24h, and the particle size of the pulverized powder is 100-200 meshes.

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 a permanganate salt; more preferably KMnO₄. 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 mass fraction of the phosphoric acid in the mixed solution is 50-85%; even more preferably 75-85%; 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 a phosphoric acid solution and mixed to obtain the mixed solution. The phosphoric acid solution is 50-85% by mass; even more preferably 75-85%; 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 280-300 ℃.

Preferably, the treatment time of the first stage of heat treatment is 5-24 h; further 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 stage heat treatment is 2-5 h.

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 fast low contact angle carbon material further unexpectedly achieves self-exfoliation, and not only contributes to improved electrochemical performance.

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 the 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 lithium-sulfur battery positive electrode active material. 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 active material to the adhesive to the conductive agent is 8-9: 0.25-1: 0.75 to 1.

The proportion of the positive electrode active material, the adhesive 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 is soluble in the adhesive 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 ℃), and adjusting the addition of phosphoric acid, thereby regulating and controlling the specific surface area of the subsequent preparation material.

(2) Directly transferring the precursor into a tubular furnace, and sintering for 2-5h at the temperature of 600-800 ℃ in the 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 cell 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 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 has the advantages that expensive metal current collectors, graphene, carbon nanotubes and the like are not used, and the defects of positive electrode weight, thickness, preparation cost and the like are overcome.

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 in the following cases are dried at the temperature of 60-105 ℃ for 12-24h, and the particle size of the crushed tobacco stems is 100-200 meshes.