Flexible three-dimensional hard carbon material and preparation method and application thereof

Abstract

The invention discloses a flexible three-dimensional hard carbon material and a preparation method and application thereof.The method comprises the steps that polyamide acid sol is synthesized in situ, then a nickel net is evenly coated with the polyamide acid sol, and faint yellow polyimide, namely a polyimide-nickel net composite material, is formed through thermal imidization after drying; the composite material is dried after being subjected to a nickel net removing procedure, finally, the flexible three-dimensional hard carbon material is obtained through carbonization, the method is easy to operate and efficient in reaction, the three-dimensional net structure is obtained, and the material has good capacity performance, rate performance and cycling stability.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion battery electrode development, and relates to a flexible three-dimensional hard carbon material and a preparation method and application thereof. Background Art

[0002] As time goes by, the conflict between energy and environment caused by the continuous population growth and accelerated industrialization process is difficult to ignore. Therefore, accelerating the transformation of the global energy system and establishing a new energy system based on renewable energy such as solar energy, wind energy, tidal energy, etc. is the key to solving the above problems. However, these renewable energy sources are unpredictable and dependent on weather and climate conditions, which makes the utilization efficiency of these clean energy very low, greatly limiting their development. Therefore, advanced energy storage devices with low R&D cost, high safety and environmental friendliness have become a hot topic of research.

[0003] Sodium-ion batteries have become a highly anticipated candidate for the next generation of energy storage technology due to their cost-effectiveness, abundant sodium resources and their wide distribution around the world, and have great development potential. However, due to the large radius of sodium ions, negative electrode materials have become an important factor restricting their development. The negative electrode materials of sodium-ion batteries are generally amorphous carbon materials, including hard carbon, soft carbon and composite carbon. Among them, hard carbon materials have excellent sodium storage performance, low sodium insertion potential and high specific capacity. When they are applied to the negative electrode of sodium-ion batteries, they have significant advantages, which indicates that it may replace traditional graphite in the future and become the new favorite of negative electrode materials. However, hard carbon materials still have poor performance in discharge voltage stability and first cycle efficiency. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a flexible three-dimensional hard carbon material and a preparation method and application thereof, thereby solving the technical problems in the prior art that when hard carbon materials are used as negative electrode materials, there are poor discharge voltage stability and poor first cycle efficiency.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a flexible three-dimensional hard carbon material comprises the following steps:

[0007] S1: adding 1,2,4,5-pyromellitic dianhydride to a dispersion of 4,4'-diaminodiphenyl ether, stirring for reaction, and obtaining a polyamic acid sol; coating the polyamic acid on a nickel mesh, and drying under a vacuum environment, and obtaining a polyamic acid-nickel mesh composite material;

[0008] S2: performing thermal imidization treatment on the polyamic acid-nickel mesh composite material to obtain a polyimide-nickel mesh composite material;

[0009] S3: acid-washing the polyimide-nickel mesh composite material to obtain a three-dimensional polyimide;

[0010] S4: heat-treating the three-dimensional polyimide in an inert atmosphere and applying pressure to perform carbonization treatment to obtain the flexible three-dimensional hard carbon material.

[0011] Preferably, in step S1, when drying is performed under a vacuum environment, the vacuum degree is -0.08 to -0.1 MPa.

[0012] Preferably, in step S1, when drying under a vacuum environment, the drying temperature is 80-120° C., and the drying time is 12-18 hours.

[0013] Preferably, in step S3, during the pickling process, the pickling solution is a mixed solution of FeCl3 and HCl; the concentration of FeCl3 in the pickling solution is 1 to 2 mol / L, and the concentration of HCl is 1 to 2 mol / L.

[0014] Preferably, in step S3, during the pickling process, the pickling time is 1 to 3 hours.

[0015] Preferably, in step S4, during the heat treatment, the treatment temperature is 900-1300° C., the treatment time is 1-4 hours, and the pressure is 90-473 Pa.

[0016] A flexible three-dimensional hard carbon material is prepared by the above method.

[0017] A negative electrode material comprises the above-mentioned flexible three-dimensional hard carbon material.

[0018] A sodium ion battery comprises the above-mentioned negative electrode material.

[0019] The application of the above-mentioned flexible three-dimensional hard carbon material in sodium ion batteries.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The present invention discloses a method for preparing a flexible three-dimensional hard carbon material. In the method, firstly, the introduction and removal of the nickel mesh constructs a rich three-dimensional pore structure, which significantly improves the specific surface area and electrochemical active sites of the material; then, by controlling the heat treatment conditions and applying pressure, an optimal balance between the crystallinity and disorder of the material is achieved, thereby optimizing its electrochemical properties. This unique three-dimensional pore structure enables the hard carbon electrode to exhibit excellent performance.

[0022] Further, in step S1, when drying under vacuum environment, the vacuum degree is -0.08~-0.1MPa, which can make the solvent more volatile. First, this setting can accelerate the volatilization of solvent. The vacuum environment reduces the collision frequency between solvent molecules by reducing the surrounding air pressure, thereby accelerating the diffusion rate of solvent from the coating surface to the surrounding environment. Under higher vacuum degree (such as -0.08~-0.1MPa), the boiling point of solvent will be reduced accordingly, because the boiling point of liquid is inversely proportional to the air pressure, so the solvent is more volatile, which can not only shorten the drying time, but also reduce the thermal damage that may be caused to the material due to long-term high temperature heating. At the same time, this setting improves the coating quality. Drying under vacuum conditions can reduce the influence of oxygen, moisture and other impurities in the air on the coating. Oxygen in the air can cause partial oxidation of polyamic acid, and moisture can cause uneven defects on the coating surface. The vacuum environment avoids these unfavorable factors and is conducive to forming a uniform, dense and defect-free coating, thereby improving the quality and performance of the final product. In addition, environmental pollution can be reduced. In the drying process, the volatilization of the solvent is inevitable. However, drying under a vacuum environment can effectively collect and process the volatilized solvent, reducing pollution to the surrounding environment. At the same time, production efficiency can be improved. Since the solvent volatilization speed is accelerated under a vacuum environment, the coating can quickly reach the required degree of dryness, thereby shortening the production cycle and improving production efficiency. This is particularly important for large-scale industrial production, which can reduce production costs and enhance market competitiveness. In summary, drying under a vacuum environment in step S1 and setting the vacuum degree to -0.08 to -0.1 MPa can effectively accelerate solvent volatilization, improve coating quality, reduce environmental pollution and improve production efficiency.

[0023] Further, in step S1, when drying under a vacuum environment, the drying temperature is 80-120°C, and the drying time is 12-18h. This setting can firstly make the solvent fully volatilize. The selection of the drying temperature (80-120°C) is within the effective range of the boiling point of the solvent, but it will not be too high to cause thermal decomposition or thermal damage to the polyamic acid. This temperature range is conducive to the rapid movement and diffusion of the solvent molecules, and promotes the volatilization of the solvent from the coating. The drying time is 2-18h, so that even at a lower temperature, the solvent molecules can be ensured to have enough time to migrate from the inside of the coating to the surface and volatilize. Long-term drying can ensure that the solvent inside the coating is also fully removed, avoiding the influence of residual solvent on subsequent steps or the performance of the final product. Secondly, this setting can also improve the quality of the coating. The full volatilization of the solvent helps to form a more uniform, dense and defect-free coating. The residual solvent may cause the coating to have problems such as bubbling, cracking or shedding in the subsequent treatment, and sufficient drying can avoid these problems. During the drying process, the interaction between the polyamic acid molecules will also be strengthened, which is conducive to the formation of a more stable coating structure. This has a positive effect on improving the mechanical strength, chemical corrosion resistance and electrochemical properties of the coating. In addition, this setting can improve production efficiency. Although the drying time is relatively long, this is a reasonable setting under the premise of ensuring the quality of the coating. By completing the full drying process at one time, the rework and repair work caused by coating quality problems in subsequent processing can be reduced, thereby improving the overall production efficiency. In summary, when drying under a vacuum environment in step S1, the drying temperature is 80-120°C and the drying time is 12-18h, which can effectively ensure that the solvent is fully volatilized, improve the coating quality and production efficiency.

[0024] Further, in step S3, during the pickling process, the pickling solution is a mixed solution of FeCl3 and HCl; the concentration of FeCl3 in the pickling solution is 1-2 mol / L, and the concentration of HCl is 1-2 mol / L. First, this setting can fully remove the nickel mesh. FeCl3 is a strong oxidant that can accelerate the dissolution of metal nickel under acidic conditions. The addition of HCl not only provides the necessary acidic environment, but also promotes the dissolution and ionization of FeCl3, thereby enhancing the corrosion ability of the pickling solution. The concentrations of FeCl3 and HCl are set within the range of 1-2 mol / L. Although too high a concentration may accelerate the reaction speed, it will also increase the cost and pollution to the environment; while too low a concentration may cause the reaction speed to be too slow, and the nickel mesh cannot be fully removed. Within this concentration range, the pickling solution can penetrate into the tiny pores of the polyimide-nickel mesh composite material, fully contact and react with the surface of the nickel mesh, thereby ensuring the thorough removal of the nickel mesh. At the same time, this setting can reduce the impact on polyimide. Polyimide is a relatively stable material with a certain resistance to general acids, alkalis and solvents. Within the selected concentration range, the mixed solution of FeCl3 and HCl can effectively remove the nickel mesh, but the corrosion effect on polyimide is relatively small. By accurately controlling the concentration and pickling time of the pickling solution, the potential impact on polyimide can be further reduced, and its original structure and performance can be maintained. At the same time, this setting can also improve the formation quality of the three-dimensional pore structure. The full removal of the nickel mesh is a key step in the formation of the three-dimensional pore structure. If the nickel mesh is not completely removed, it will affect the connectivity and distribution uniformity of the pores, thereby reducing the specific surface area and electrochemical active sites of the material. Using a mixed solution of FeCl3 and HCl as the pickling solution and setting a suitable concentration range can ensure the full removal of the nickel mesh and the good formation of the three-dimensional pore structure, providing a strong guarantee for the subsequent steps and the performance of the final product. In summary, in step S3, a mixed solution of FeCl3 and HCl is used as the pickling solution, and the concentrations of FeCl3 and HCl are set in the range of 1 to 2 mol / L, which can effectively ensure that the nickel mesh is fully removed, reduce the impact on polyimide, and improve the formation quality of the three-dimensional pore structure.

[0025] Further, in step S3, during the pickling process, the pickling time is 1 to 3 hours. This setting can first achieve full removal of the nickel mesh. The length of the pickling time directly affects the thoroughness of the nickel mesh removal. Too short a pickling time may not allow the pickling solution to fully penetrate into the interior of the polyimide-nickel mesh composite material, resulting in incomplete removal of the nickel mesh. Setting a pickling time of 1 to 3 hours can ensure that the pickling solution is in full contact with the surface of the nickel mesh and reacts, thereby completely removing the nickel mesh. Secondly, the choice of pickling time needs to find a balance between removal efficiency and production cost. Although too long a pickling time can ensure the complete removal of the nickel mesh, it will increase production costs and energy consumption. A pickling time of 1 to 3 hours can both ensure removal efficiency and control production costs within a reasonable range. At the same time, this setting can also reduce the potential impact on polyimide. In the pickling process, in addition to removing the nickel mesh, the impact on polyimide also needs to be considered. Too long a pickling time may increase the corrosion of the pickling solution on the polyimide, thereby affecting its structure and performance. Setting a suitable pickling time (1 to 3 hours) can minimize the potential impact on the polyimide while ensuring the removal of the nickel mesh. In addition, a reasonable pickling time setting can also help reduce the generation and discharge of waste liquid. Too long a pickling time will increase the amount of waste liquid and the difficulty of handling, while an appropriate pickling time can reduce the impact on the environment while ensuring the removal effect. In summary, setting the pickling time to 1 to 3 hours in step S3 can effectively ensure that the nickel mesh is fully removed, reduce the potential impact on polyimide, and achieve environmental friendliness.

[0026] Further, in step S4, in the heat treatment, the treatment temperature is 900-1300°C, and the treatment time is 1-4h; the pressure is 90-473Pa, which can fully carbonize the material, and the pressure can cause microscopic changes in the carbon layer. In the temperature range of 900-1300°C, the organic matter in the material can be fully decomposed to carbonize the polyimide. First, the process can optimize the microstructure. At high temperatures, the movement of atoms and molecules in the material intensifies, which is conducive to the growth of grains and the occurrence of recrystallization processes. These processes can eliminate internal defects in the material, such as pores and cracks, and improve the density and strength of the material. At the same time, during the carbonization process, high temperature can promote the chemical reaction between the carbon source and the material matrix to form a more stable and uniform carbonized layer. Secondly, the treatment time is 1-4 hours, and the carbonization reaction can be carried out step by step until it reaches a state of equilibrium, which can ensure that the carbonization process is fully carried out. Again, the pressure of 90 to 473 Pa can promote microscopic changes in the carbon layer. Heat treatment in a vacuum or low-pressure environment can reduce the frequency of collisions between gas molecules and the surface of the material, thereby reducing the destructive effect on the carbonized layer. At the same time, the low-pressure environment also helps to promote changes in the microstructure of the carbon layer, such as grain growth and orientation adjustment. These changes can further improve the performance of the carbonized layer. Furthermore, the low-pressure environment can also reduce the contamination of the material by impurities such as oxygen and moisture in the air. These impurities will affect the composition and properties of the carbonized layer. Therefore, heat treatment in a low-pressure environment helps to obtain a purer and more stable carbonized layer. In summary, the heat treatment temperature, time, pressure and other parameters set in step S4 can fully carbonize the material and effectively regulate the microstructure of the carbon layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A schematic diagram of a process for preparing a flexible three-dimensional hard carbon material in the present invention;

[0029] Figure 2 This is a SEM image of a slightly compressed hard carbon electrode obtained by carbonization at 1100° C. prepared in Example 2 of the present invention;

[0030] Figure 3 XRD diagram of the flexible three-dimensional hard carbon electrode prepared in Examples 1-3 of the present invention;

[0031] Figure 4The Raman images of the slightly compressed hard carbon electrodes prepared at different carbonization temperatures in Examples 1 to 3 of the present invention;

[0032] Figure 5 This is a TEM image of the slightly pressed hard carbon electrode prepared in Inventive Example 2;

[0033] Figure 6 The charge and discharge curve of the flexible three-dimensional hard carbon electrode prepared in Example 2 of the present invention;

[0034] Figure 7 The rate curves of the flexible three-dimensional hard carbon electrodes prepared in Example 2 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0036] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0037] Herein, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0038] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0039] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0040] like Figure 1 As shown, the present invention provides a method for preparing a flexible three-dimensional hard carbon material for a negative electrode of a sodium ion battery, comprising the following steps:

[0041] S1: adding 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) to a dispersion of 4,4'-diaminodiphenyl ether in multiple times, stirring for reaction, and the stirring time after each addition is 30 minutes, to obtain a polyamic acid sol; coating the polyamic acid on a nickel mesh, and drying at a temperature of 80 to 120° C. for 12 to 18 hours in a vacuum environment with a vacuum degree of -0.08 to -0.1 MPa, to obtain a polyamic acid-nickel mesh composite material;

[0042] The preparation process of the dispersion of 4,4'-diaminodiphenyl ether here is to dissolve 3g of 4,4'-diaminodiphenyl ether (ODA) in 37.8ml of N,N-dimethylformamide (DMF), and ultrasonicate for 5 minutes to fully dissolve the diamine to obtain a dispersion of the diamine; in addition, during the addition of 1,2,4,5-pyromellitic dianhydride (PMDA), keep stirring with external shear force.

[0043] S2: performing thermal imidization treatment on the polyamic acid-nickel mesh composite material to obtain a polyimide-nickel mesh composite material;

[0044] Here, the polyamic acid-nickel mesh composite material is transferred to a precision high-temperature oven or a muffle furnace, treated at 100°C, 200°C, and 300°C for 1 h, and treated at 350°C for 30 min, and then cooled naturally to complete the thermal imidization process to obtain a polyimide-nickel mesh composite material;

[0045] S3: acid-washing the polyimide-nickel mesh composite material to obtain a three-dimensional polyimide;

[0046] Wherein, during the pickling process, the pickling solution is a mixed solution of FeCl3 and HCl; the concentration of FeCl3 in the pickling solution is 1-2 mol / L, the concentration of HCl is 1-2 mol / L, and the pickling time is 1-3 h.

[0047] In addition, after the pickling, deionized water and anhydrous ethanol were used for further soaking to remove FeCl3 and HCl, and the material after the nickel mesh was removed was placed in an oven and dried at 60°C for 12 hours in an air atmosphere.

[0048] S4: heat-treating the three-dimensional polyimide in an inert atmosphere and applying pressure to perform carbonization treatment to obtain the flexible three-dimensional hard carbon material.

[0049] The heat treatment temperature is 900-1300° C., the treatment time is 1-4 hours, and the pressure is 90-473 Pa.

[0050] In addition, the present invention also discloses a flexible three-dimensional hard carbon material prepared by the above method, a negative electrode material comprising the above flexible three-dimensional hard carbon material, and a sodium ion battery comprising the negative electrode material.

[0051] The flexible three-dimensional hard carbon material is a three-dimensional network structure. In the preparation process of the flexible three-dimensional hard carbon material, the diamine is dissolved in an organic solvent at low temperature, and then the dianhydride is added in batches to polymerize in situ into a polyamic acid sol, and then the polyamic acid sol is evenly coated on a nickel mesh, and after drying, it is thermally imidized to form a light yellow polyimide, that is, a polyimide-nickel mesh composite material, and the composite material is dried after the nickel mesh removal process, and finally carbonized to obtain a flexible three-dimensional hard carbon material. The method is simple to operate and has high reaction efficiency. The flexible hard carbon material prepared by the present invention has excellent comprehensive sodium storage performance, including capacity performance, rate performance and cycle stability, and provides a research basis and technical support for promoting the commercialization of sodium ion batteries in the field of energy storage. The introduction of the nickel mesh in the present invention constructs a rich pore structure. Secondly, the appropriate carbonization temperature and micro-pressure treatment make the material have appropriate crystallinity and disorder. This unique structure enables the hard carbon electrode to show excellent performance. In addition, the preparation method is simple and easy to operate, which is of great significance for promoting the practical process of three-dimensional hard carbon electrodes and provides a solid research foundation for the commercialization of sodium ion batteries in the field of energy storage.

[0052] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0053] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0054] Example 1

[0055] (1) Preparation of diamine dispersion

[0056] In an ice-water bath, 3 g of 4,4'-diaminodiphenyl ether (ODA) was added to 37.8 ml of N,N-dimethylformamide (DMF) solvent, and ultrasonicated for 5 min to obtain a diamine dispersion.

[0057] (2) Preparation of polyamic acid sol

[0058] In an ice-water bath, 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) was added to the diamine dispersion in four portions, and shear force was applied and stirred for 2 hours to obtain a polyamic acid sol with a solid content of 15 wt%.

[0059] (3) Preparation of polyamic acid-nickel mesh composite material

[0060] The polyamic acid sol was evenly scraped onto the nickel mesh using a glass slide and a disposable syringe, and dried at 80° C. in a vacuum environment for 12 h.

[0061] (4) Preparation of polyimide-nickel mesh composite material

[0062] The polyamic acid-nickel mesh composite material is treated in a precision high temperature oven or a muffle furnace at 100° C., 200° C., and 300° C. for 1 hour respectively, treated at 350° C. for 30 minutes, and then naturally cooled to obtain a polyimide-nickel mesh composite material.

[0063] (5) Nickel removal net

[0064] The polyimide-nickel mesh composite material was placed in a glass dish, and appropriate amounts of FeCl3 and HCl were added to soak for 1 h to remove the nickel mesh. The above operation was repeated three times, and deionized water and anhydrous ethanol were used for further soaking to remove FeCl3 and HCl.

[0065] (6) Heat treatment

[0066] The material after the nickel mesh is removed is placed in an oven, dried at 60°C for 12 hours in an air atmosphere, and then moved to an argon atmosphere tubular furnace for carbonization treatment at a temperature of 900°C while applying micro pressure to obtain a flexible three-dimensional hard carbon electrode material.

[0067] Example 2

[0068] (1) Preparation of diamine dispersion

[0069] In an ice-water bath, 3 g of 4,4'-diaminodiphenyl ether (ODA) was added to 37.8 ml of N,N-dimethylformamide (DMF) solvent, and ultrasonicated for 5 min to obtain a diamine dispersion.

[0070] (2) Preparation of polyamic acid sol

[0071] In an ice-water bath, 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) was added to the diamine dispersion in four portions, and shear force was applied and stirred for 2 hours to obtain a polyamic acid sol with a solid content of 15 wt%.

[0072] (3) Preparation of polyamic acid-nickel mesh composite material

[0073] The polyamic acid sol was evenly scraped onto the nickel mesh using a glass slide and a disposable syringe, and dried at 80° C. in a vacuum environment for 12 h.

[0074] (4) Preparation of polyimide-nickel mesh composite material

[0075] The polyamic acid-nickel mesh composite material is treated in a precision high temperature oven or a muffle furnace at 100° C., 200° C., and 300° C. for 1 hour respectively, treated at 350° C. for 30 minutes, and then naturally cooled to obtain a polyimide-nickel mesh composite material.

[0076] (5) Nickel removal net

[0077] The polyimide-nickel mesh composite material was placed in a glass dish, and appropriate amounts of FeCl3 and HCl were added to soak for 1 h to remove the nickel mesh. The above operation was repeated three times, and deionized water and anhydrous ethanol were used for further soaking to remove FeCl3 and HCl.

[0078] (6) Heat treatment

[0079] The material after the nickel mesh is removed is placed in an oven, dried at 60°C for 12 hours in an air atmosphere, and then moved to an argon atmosphere tubular furnace for carbonization treatment at a temperature of 1100°C while applying micro pressure to obtain a flexible three-dimensional hard carbon electrode material.

[0080] Figure 2 This is a SEM image of the micro-pressed hard carbon electrode obtained by carbonization at 1100°C prepared in Example 2 of the present invention. The results show that the hard carbon material obtained by carbonization retains the three-dimensional network structure of the template, which is composed of micron-sized macropores that are interlaced and bridged, and the surface of the material is relatively smooth.

[0081] Example 3

[0082] (1) Preparation of diamine dispersion

[0083] In an ice-water bath, 3 g of 4,4'-diaminodiphenyl ether (ODA) was added to 37.8 ml of N,N-dimethylformamide (DMF) solvent, and ultrasonicated for 5 min to obtain a diamine dispersion.

[0084] (2) Preparation of polyamic acid sol

[0085] In an ice-water bath, 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) was added to the diamine dispersion in four portions, and shear force was applied and stirred for 2 hours to obtain a polyamic acid sol with a solid content of 15 wt%.

[0086] (3) Preparation of polyamic acid-nickel mesh composite material

[0087] The polyamic acid sol was evenly scraped onto the nickel mesh using a glass slide and a disposable syringe, and dried at 80° C. in a vacuum environment for 12 h.

[0088] (4) Preparation of polyimide-nickel mesh composite material

[0089] The polyamic acid-nickel mesh composite material is treated in a precision high temperature oven or a muffle furnace at 100° C., 200° C., and 300° C. for 1 hour respectively, treated at 350° C. for 30 minutes, and then naturally cooled to obtain a polyimide-nickel mesh composite material.

[0090] (5) Nickel removal net

[0091] The polyimide-nickel mesh composite material was placed in a glass dish, and appropriate amounts of FeCl3 and HCl were added to soak for 1 h to remove the nickel mesh. The above operation was repeated three times, and deionized water and anhydrous ethanol were used for further soaking to remove FeCl3 and HCl.

[0092] (6) Heat treatment

[0093] The material after the nickel mesh is removed is placed in an oven, dried at 60°C for 12 hours in an air atmosphere, and then moved to an argon atmosphere tubular furnace for carbonization treatment at a temperature of 1300°C while applying micro pressure to obtain a flexible three-dimensional hard carbon electrode material.

[0094] Figure 4 The Raman images of the slightly compressed hard carbon electrodes prepared at different carbonization temperatures in Examples 1 to 3 of the present invention. D / I G It is an important parameter to measure the degree of graphitization in the structure of the prepared carbon material. By calculation, the I D / I G The values ​​are 0.88, 0.92 and 0.97 respectively. This indicates that the hard carbon material obtained under micro-pressure has a high degree of disorder, and as the carbonization temperature increases, the degree of disorder of the porous carbon material increases, and more defects will exist in the material. These defects provide more active sites for the electrochemical reaction, which is conducive to Na + store.

[0095] Comparative Example 1

[0096] (1) Preparation of diamine dispersion

[0097] In an ice-water bath, 3 g of 4,4'-diaminodiphenyl ether (ODA) was added to 37.8 ml of N,N-dimethylformamide (DMF) solvent, and ultrasonicated for 5 min to obtain a diamine dispersion.

[0098] (2) Preparation of polyamic acid sol

[0099] In an ice-water bath, 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) was added to the diamine dispersion in four portions, and shear force was applied and stirred for 2 hours to obtain a polyamic acid sol with a solid content of 15 wt%.

[0100] (3) Preparation of polyamic acid-nickel mesh composite material

[0101] The polyamic acid sol was evenly scraped onto the nickel mesh using a glass slide and a disposable syringe, and dried at 80° C. in a vacuum environment for 12 h.

[0102] (4) Preparation of polyimide-nickel mesh composite material

[0103] The polyamic acid-nickel mesh composite material is treated in a precision high temperature oven or a muffle furnace at 100° C., 200° C., and 300° C. for 1 hour respectively, treated at 350° C. for 30 minutes, and then naturally cooled to obtain a polyimide-nickel mesh composite material.

[0104] (5) Nickel removal net

[0105] The polyimide-nickel mesh composite material was placed in a glass dish, and appropriate amounts of FeCl3 and HCl were added to soak for 1 h to remove the nickel mesh. The above operation was repeated three times, and deionized water and anhydrous ethanol were used for further soaking to remove FeCl3 and HCl.

[0106] (6) Heat treatment

[0107] The material after the nickel mesh is removed is placed in an oven, dried at 60°C for 12 h in an air atmosphere, and then moved to an argon atmosphere tubular furnace for treatment at a carbonization temperature of 900°C to obtain a flexible three-dimensional hard carbon electrode material.

[0108] That is, the difference between this comparative example and Example 1 is that pressure is applied during the heat treatment.

[0109] Comparative Example 2

[0110] (1) Preparation of diamine dispersion

[0111] In an ice-water bath, 3 g of 4,4'-diaminodiphenyl ether (ODA) was added to 37.8 ml of N,N-dimethylformamide (DMF) solvent, and ultrasonicated for 5 min to obtain a diamine dispersion.

[0112] (2) Preparation of polyamic acid sol

[0113] In an ice-water bath, 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) was added to the diamine dispersion in four portions, and shear force was applied and stirred for 2 hours to obtain a polyamic acid sol with a solid content of 15 wt%.

[0114] (3) Preparation of polyamic acid-nickel mesh composite material

[0115] The polyamic acid sol was evenly scraped onto the nickel mesh using a glass slide and a disposable syringe, and dried at 80° C. in a vacuum environment for 12 h.

[0116] (4) Preparation of polyimide-nickel mesh composite material

[0117] The polyamic acid-nickel mesh composite material is treated in a precision high temperature oven or a muffle furnace at 100° C., 200° C., and 300° C. for 1 hour respectively, treated at 350° C. for 30 minutes, and then naturally cooled to obtain a polyimide-nickel mesh composite material.

[0118] (5) Nickel removal net

[0119] The polyimide-nickel mesh composite material was placed in a glass dish, and appropriate amounts of FeCl3 and HCl were added to soak for 1 h to remove the nickel mesh. The above operation was repeated three times, and deionized water and anhydrous ethanol were used for further soaking to remove FeCl3 and HCl.

[0120] (6) Heat treatment

[0121] The material after the nickel mesh is removed is placed in an oven, dried at 60°C for 12 h in an air atmosphere, and then moved to an argon atmosphere tubular furnace for treatment at a carbonization temperature of 1100°C to obtain a flexible three-dimensional hard carbon electrode material.

[0122] That is, the difference between this comparative example and Example 1 is that pressure is applied during the heat treatment.

[0123] Comparative Example 3

[0124] (1) Preparation of diamine dispersion

[0125] In an ice-water bath, 3 g of 4,4'-diaminodiphenyl ether (ODA) was added to 37.8 ml of N,N-dimethylformamide (DMF) solvent, and ultrasonicated for 5 min to obtain a diamine dispersion.

[0126] (2) Preparation of polyamic acid sol

[0127] In an ice-water bath, 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) was added to the diamine dispersion in four portions, and shear force was applied and stirred for 2 hours to obtain a polyamic acid sol with a solid content of 15 wt%.

[0128] (3) Preparation of polyamic acid-nickel mesh composite material

[0129] The polyamic acid sol was evenly scraped onto the nickel mesh using a glass slide and a disposable syringe, and dried at 80° C. in a vacuum environment for 12 h.

[0130] (4) Preparation of polyimide-nickel mesh composite material

[0131] The polyamic acid-nickel mesh composite material is treated in a precision high temperature oven or a muffle furnace at 100° C., 200° C., and 300° C. for 1 hour respectively, treated at 350° C. for 30 minutes, and then naturally cooled to obtain a polyimide-nickel mesh composite material.

[0132] (5) Nickel removal net

[0133] The polyimide-nickel mesh composite material was placed in a glass dish, and appropriate amounts of FeCl3 and HCl were added to soak for 1 h to remove the nickel mesh. The above operation was repeated three times, and deionized water and anhydrous ethanol were used for further soaking to remove FeCl3 and HCl.

[0134] (6) Heat treatment

[0135] The material after the nickel mesh is removed is placed in an oven, dried at 60°C for 12 h in an air atmosphere, and then moved to an argon atmosphere tubular furnace for treatment at a carbonization temperature of 1300°C to obtain a flexible three-dimensional hard carbon electrode material.

[0136] That is, the difference between this comparative example and Example 1 is that pressure is applied during the heat treatment.

[0137] Figure 3 XRD images of the flexible three-dimensional hard carbon electrodes prepared in Examples 1 to 3 of the present invention. The results show that the increase in carbonization temperature and the introduction of micro-pressure will cause the (002) diffraction peak of the hard carbon material to slightly shift to a low angle, thereby improving the crystallinity of the material. This structural transformation is conducive to improving the structural stability of the material, thereby improving its cycle stability.

[0138] Table 1 shows the electrochemical properties of the flexible three-dimensional hard carbon electrodes prepared in Examples 1 to 3 of the present invention and Comparative Examples 1 to 3.

[0139]

[0140] Table 1 shows the electrochemical properties of the flexible three-dimensional hard carbon electrodes prepared in Examples 1 to 3 of the present invention and Comparative Examples 1 to 3. The results show that sample 2 (micro-pressed hard carbon electrode obtained by carbonization at 1100°C) has the best sodium storage performance, with a charge capacity of 298.1 mAh g -1 , the discharge capacity is 365.2mAh g -1 , ICE is 81.6%.

[0141] Figure 5 This is a TEM image of the flexible three-dimensional hard carbon electrode prepared in Example 2 of the present invention. It can be seen from the figure that the prepared carbon material is a disordered carbon structure.

[0142] Figure 6The charge and discharge curve of the flexible three-dimensional hard carbon electrode prepared in Example 2 of the present invention can reflect that the electrode material has good sodium storage performance, and its charge specific capacity is 298.1 mAh g -1 , the discharge capacity is 365.2mAh g -1 , ICE is 81.6%.

[0143] Figure 7 The rate curves of the flexible three-dimensional hard carbon electrode prepared in Example 2 of the present invention and Comparative Example 1 can reflect that the electrode material has good rate performance. -1 At a current density of 210.4 mAh g -1 capacity.

[0144] Example 4

[0145] A method for preparing a flexible three-dimensional hard carbon material for a negative electrode of a sodium ion battery comprises the following steps:

[0146] S1: adding 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) to a dispersion of 4,4'-diaminodiphenyl ether in five times, stirring for reaction, and stirring for 30 min after each addition, to obtain a polyamic acid sol; coating the polyamic acid on a nickel mesh, and drying at 80° C. for 18 h in a vacuum environment with a vacuum degree of -0.08 MPa, to obtain a polyamic acid-nickel mesh composite material;

[0147] S2: transferring the polyamic acid-nickel mesh composite material to a precision high-temperature oven or muffle furnace, treating at 100°C, 200°C, 300°C for 1 hour, and 350°C for 30 minutes, and then cooling naturally to complete the thermal imidization process to obtain a polyimide-nickel mesh composite material;

[0148] S3: placing the polyimide-nickel mesh composite material in a mixed solution of FeCl3 and HCl for pickling for 1 hour, wherein the concentration of FeCl3 in the mixed solution is 2 mol / L, and the concentration of HCl is 2 mol / L, and then further soaking in deionized water and anhydrous ethanol to remove FeCl3 and HCl, and placing the material after removing the nickel mesh in an oven, and drying it at 60° C. for 12 hours in an air atmosphere to obtain a three-dimensional polyimide;

[0149] S4: placing the three-dimensional polyimide in an inert atmosphere, heat treating it at 900° C. for 4 hours, and applying a micro-pressure of 90 Pa for carbonization treatment to obtain the flexible three-dimensional hard carbon material.

[0150] Example 5

[0151] A method for preparing a flexible three-dimensional hard carbon material for a negative electrode of a sodium ion battery comprises the following steps:

[0152] S1: adding 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) to a dispersion of 4,4'-diaminodiphenyl ether in five times, stirring for reaction, and the stirring time after each addition is 30 minutes, to obtain a polyamic acid sol; coating the polyamic acid on a nickel mesh, and drying at a temperature of 120° C. for 12 hours in a vacuum environment with a vacuum degree of -0.1 MPa, to obtain a polyamic acid-nickel mesh composite material;

[0153] S2: transferring the polyamic acid-nickel mesh composite material to a precision high-temperature oven or muffle furnace, treating at 100°C, 200°C, 300°C for 1 hour, and 350°C for 30 minutes, and then cooling naturally to complete the thermal imidization process to obtain a polyimide-nickel mesh composite material;

[0154] S3: placing the polyimide-nickel mesh composite material in a mixed solution of FeCl3 and HCl for pickling for 3 hours, wherein the concentration of FeCl3 in the mixed solution is 1 mol / L, and the concentration of HCl is 1 mol / L, and then further soaking in deionized water and anhydrous ethanol to remove FeCl3 and HCl, and placing the material after removing the nickel mesh in an oven, and drying it at 60° C. for 12 hours in an air atmosphere to obtain a three-dimensional polyimide;

[0155] S4: placing the three-dimensional polyimide in an inert atmosphere, heat treating it at 1300° C. for 1 h, and applying a micro-pressure of 473 Pa for carbonization treatment to obtain the flexible three-dimensional hard carbon material.

[0156] Example 6

[0157] A method for preparing a flexible three-dimensional hard carbon material for a negative electrode of a sodium ion battery comprises the following steps:

[0158] S1: adding 3.28 g of 1,2,4,5-pyromellitic dianhydride (PMDA) to a dispersion of 4,4'-diaminodiphenyl ether in five times, stirring for reaction, and the stirring time after each addition is 30 minutes, to obtain a polyamic acid sol; coating the polyamic acid on a nickel mesh, and drying at a temperature of 100° C. for 15 hours under a vacuum environment with a vacuum degree of -0.09 MPa, to obtain a polyamic acid-nickel mesh composite material;

[0159] S2: transferring the polyamic acid-nickel mesh composite material to a precision high-temperature oven or muffle furnace, treating at 100°C, 200°C, 300°C for 1 hour, and 350°C for 30 minutes, and then cooling naturally to complete the thermal imidization process to obtain a polyimide-nickel mesh composite material;

[0160] S3: placing the polyimide-nickel mesh composite material in a mixed solution of FeCl3 and HCl for pickling for 2 hours, wherein the concentration of FeCl3 in the mixed solution is 1.5 mol / L, and the concentration of HCl is 1.5 mol / L, and then further soaking in deionized water and anhydrous ethanol to remove FeCl3 and HCl, and placing the material after removing the nickel mesh in an oven, and drying it at 60° C. for 12 hours in an air atmosphere to obtain a three-dimensional polyimide;

[0161] S4: placing the three-dimensional polyimide under an inert atmosphere, heat-treating it at 1100° C. for 3 h, and applying a micro-pressure of 200 Pa for carbonization treatment to obtain the flexible three-dimensional hard carbon material.

[0162] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a flexible three-dimensional hard carbon material, It is characterized in that The following steps are involved: S1: adding 1,2,4,5-pyromellitic dianhydride to a dispersion of 4,4'-diaminodiphenyl ether, stirring for reaction, and obtaining a polyamic acid sol; coating the polyamic acid on a nickel mesh, and drying under a vacuum environment, and obtaining a polyamic acid-nickel mesh composite material; S2: performing thermal imidization treatment on the polyamic acid-nickel mesh composite material to obtain a polyimide-nickel mesh composite material; S3: acid-washing the polyimide-nickel mesh composite material to obtain a three-dimensional polyimide; S4: heat-treating the three-dimensional polyimide in an inert atmosphere and applying pressure to perform carbonization treatment to obtain the flexible three-dimensional hard carbon material.

2. A method for preparing a flexible three-dimensional hard carbon material according to claim 1, It is characterized in that In step S1, when drying is performed under a vacuum environment, the vacuum degree is -0.08 to -0.1 MPa.

3. A method for preparing a flexible three-dimensional hard carbon material according to claim 1, It is characterized in that In step S1, when drying under vacuum environment, the drying temperature is 80-120° C. and the drying time is 12-18 hours.

4. The method for preparing a flexible three-dimensional hard carbon material according to claim 1, It is characterized in that In step S3, during the pickling process, the pickling liquid is FeCl 3 and HCl mixed solution; FeCl 3 The concentration of is 1~2mol / L, and the concentration of HCl is 1~2mol / L.

5. The method for preparing a flexible three-dimensional hard carbon material according to claim 1, It is characterized in that In step S3, during the pickling process, the pickling time is 1 to 3 hours.

6. The method for preparing a flexible three-dimensional hard carbon material according to claim 1, It is characterized in that In step S4, during the heat treatment, the treatment temperature is 900-1300° C., the treatment time is 1-4 hours; and the pressure is 90-473 Pa.

7. A flexible three-dimensional hard carbon material, It is characterized in that It is prepared by the method according to any one of claims 1 to 6.

8. A negative electrode material, It is characterized in that It comprises a flexible three-dimensional hard carbon material as described in claim 7.

9. A sodium ion battery, It is characterized in that The negative electrode material according to claim 8 is included.

10. Use of the flexible three-dimensional hard carbon material described in claim 8 in sodium ion batteries.

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