Zinc sulfide-porous carbon nanofiber composite membrane, preparation method thereof, electrode plate and lithium ion battery

Abstract

The invention provides a zinc sulfide-porous carbon nanofiber composite membrane, a preparation method thereof, an electrode plate and a lithium ion battery, and relates to the technical field of nanostructure materials and batteries. According to the preparation method of the zinc sulfide-porous carbon nanofiber composite membrane, electrostatic spinning and calcination vulcanization processes are combined, and the zinc sulfide-porous carbon nanofiber composite membrane with a special morphology is prepared. The fiber composite membrane has a unique structure that zinc sulfide is uniformly distributed in the lotus-root-like porous carbon nanofibers, and the composite structure provides a good electron transport network and improves the conductivity of the material; due to the coating and confinement effects of the porous carbon nanofibers on the zinc sulfide, the volume expansion effect of the zinc sulfide in the circulation process can be effectively inhibited, the defects of poor conductivity, large volume expansion and the like of the zinc sulfide are overcome, and the circulation stability of the composite membrane is improved. As the fiber composite membrane has mechanical flexibility and self-supporting property, the fiber composite membrane can be directly used as an electrode plate, and the preparation process of the electrode plate is greatly simplified.

Description

Technical Field

[0001] The invention belongs to the technical field of nanostructured materials and batteries, and relates to a zinc sulfide-porous carbon nanofiber composite membrane and a preparation method thereof, an electrode plate and a lithium ion battery. Background Art

[0002] Lithium-ion batteries (LIBs) are an indispensable power source in modern electronic devices and are favored for their high energy density, long life and low maintenance requirements. Lithium-ion batteries are widely used in consumer electronics (such as mobile phones and laptops), electric vehicles, power tools, and energy storage systems. Lithium-ion batteries are composed of a positive electrode, a negative electrode, an electrolyte, a separator, and two current collectors (positive and negative electrodes). During the charge and discharge process, lithium ions move between the positive and negative electrodes and are transmitted through the electrolyte. During discharge, the negative electrode releases lithium ions and the positive electrode receives them, while electrons flow from the negative electrode to the positive electrode through an external circuit to generate current. During charging, the process is reversed, and lithium ions move from the positive electrode to the negative electrode. The graphite anode material of current commercial LIBs can no longer meet the needs of the next generation of LIBs due to its low theoretical capacity. Therefore, one of the important steps to promote the development of the next generation of high-performance LIBs is to find a suitable anode material.

[0003] Metal Organic Frameworks (MOFs) are porous materials with periodic topological structures formed by metal ions (or metal clusters) and organic ligands through coordination bonds. These organic ligands are usually organic molecules containing multiple coordination groups, such as carboxyl groups, nitrogen groups, aromatic rings, etc. Organic ligands form coordination bonds with metal ions through their coordination groups to build a three-dimensional network structure, forming pore structures and channels. This unique structure makes MOFs materials have highly controllable pore size, shape and surface chemical properties, thus giving MOFs materials rich functions and application value. As a member of the MOFs series, ZIF-8 has also been widely studied in the field of energy materials because of its unique porous structure and high specific surface area. However, due to its shortcomings such as insufficient electrical conductivity and poor cycle stability, these factors limit the application of ZIF-8 as a battery material. In order to solve these difficulties, ZIF-8-derived nanomaterials and nanocomposites have been developed. For example, ZIF-8 is loaded onto other functional materials (such as graphene and nanofibers). However, there are usually problems such as uneven dispersion of ZIF-8, easy agglomeration, and difficult to control the morphology. Once it is used as an electrode material in a battery, during the cycle process, the material structure is prone to collapse due to insufficient structural stability, affecting the long-term stability and cycle life of the battery.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] In view of the deficiencies and defects in the prior art, the present invention aims to provide a zinc sulfide-porous carbon nanofiber composite membrane and a preparation method thereof, an electrode plate and a lithium ion battery.

[0006] In order to achieve the above purpose, the following technical solutions are adopted: The first object of the present invention is to provide a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane, comprising the following steps: S1. Electrospinning a slurry formed by mixing ZIF-8, polyacrylonitrile and dimethylformamide to obtain a nanofiber membrane; S2. The nanofiber membrane obtained in step S1 is dried and pre-calcined, and then sulfur powder is added to the pre-calcined nanofiber membrane so that the sulfur powder is evenly distributed on the surface of the nanofiber membrane, and then placed in a protective atmosphere for high-temperature calcination to obtain a zinc sulfide-porous carbon nanofiber composite membrane having a lotus root-like structure; Wherein, the high temperature calcination temperature is 1000-1300°C, the high temperature calcination time is 8-12h, and the protective atmosphere includes at least one of nitrogen or argon; The porous carbon nanofibers in the zinc sulfide-porous carbon nanofiber composite membrane have a lotus root-like structure, and the zinc sulfide is at least partially distributed inside the lotus root-like porous carbon nanofibers.

[0007] Further, based on the above technical solution of the present invention, in step S1, the mass ratio of ZIF-8, polyacrylonitrile and dimethylformamide is (1-5): (1-5): (10-20); And / or, the molecular weight of the polyacrylonitrile is 50,000-200,000.

[0008] Further, on the basis of the above technical solution of the present invention, in step S1, the electrospinning adopts at least one of the following process parameters: The voltage of electrospinning is 10-25 kV; and / or, The injection rate of the syringe is 0.05-0.5mL / h.

[0009] Further, on the basis of the above technical solution of the present invention, in step S1, the preparation method of ZIF-8 comprises the following steps: Providing a mixed solution A formed by zinc nitrate hexahydrate and methanol, and a mixed solution B formed by 2-methylimidazole and methanol; The mixed solution A and the mixed solution B are mixed and reacted, the obtained reaction product is subjected to solid-liquid separation, and the separated solid product is washed and dried to obtain ZIF-8.

[0010] Further, based on the above technical solution of the present invention, the molar concentration of zinc nitrate hexahydrate in the mixed solution A is 0.4-0.6 mol / L; And / or, the molar concentration of 2-methylimidazole in the mixed solution B is 4.0-5.0 mol / L; And / or, the molar ratio of zinc nitrate hexahydrate in the mixed solution A to 2-methylimidazole in the mixed solution B is (0.4-0.6): (4.0-5.0).

[0011] Further, on the basis of the above technical solution of the present invention, in step S2, the drying is vacuum drying, the drying temperature is 60-120° C., and the drying time is 8-24 hours; and / or, in step S2, placing the nanofiber membrane in a graphite plate fixture and pre-calcining it in a muffle furnace; And / or, in step S2, the pre-calcination temperature is 200-400°C, and the pre-calcination time is 2-6h.

[0012] Furthermore, based on the above technical solution of the present invention, in step S2, the mass ratio of sulfur powder to nanofiber membrane is (8-10):1.

[0013] The second object of the present invention is to provide a zinc sulfide-porous carbon nanofiber composite membrane, which is prepared by the preparation method of the zinc sulfide-porous carbon nanofiber composite membrane provided by the first object of the present invention; The porous carbon nanofibers in the zinc sulfide-porous carbon nanofiber composite membrane have a lotus root-like structure, zinc sulfide is at least partially distributed inside the lotus root-like porous carbon nanofibers, and the zinc sulfide-porous carbon nanofiber composite membrane is a flexible self-supporting material.

[0014] The third object of the present invention is to provide an electrode plate, which is made by using the zinc sulfide-porous carbon nanofiber composite membrane prepared by the preparation method provided by the first object of the present invention or the zinc sulfide-porous carbon nanofiber composite membrane provided by the second object of the present invention; The electrode plate is a flexible self-supporting electrode plate.

[0015] The fourth object of the present invention is to provide a lithium-ion battery, comprising the electrode plate provided by the third object of the present invention.

[0016] Compared with the prior art, the technical solution of the present invention has at least the following technical effects: (1) The present invention provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane. The method combines electrospinning with calcination vulcanization technology to successfully prepare a zinc sulfide-porous carbon nanofiber composite membrane with a special lotus root-like structure.

[0017] (2) The present invention provides a zinc sulfide-porous carbon nanofiber composite membrane, which has a unique structure in which zinc sulfide is uniformly distributed inside the lotus root-like porous carbon nanofibers. The composite structure provides a good electron transmission network and improves the conductivity of the material. Moreover, due to the coating and confinement of the porous carbon nanofibers on zinc sulfide, its volume expansion effect during the cycle can be effectively suppressed, and the defects of zinc sulfide such as poor conductivity and large volume expansion can be improved, so that the cycle stability of the composite membrane can be improved. In addition, the composite membrane also has a high specific surface area and rich pore structure, which can provide more adsorption and storage sites for lithium ions and significantly improve the specific capacity of the material. A large specific surface area is conducive to shortening the lithium ion transmission path and improving the diffusion and transmission rate of lithium ions. In addition, it also increases the contact area between the material and the electrolyte, which is conducive to the rapid diffusion and transmission of lithium ions in the electrolyte.

[0018] (3) The present invention also provides an electrode plate, which is made of the zinc sulfide-porous carbon nanofiber composite membrane provided by the present invention, and the electrode plate is a flexible self-supporting electrode plate; because the zinc sulfide-porous carbon nanofiber composite membrane has mechanical flexibility and self-supporting properties, it itself is a membrane structure, and because it also has good electrical conductivity, it can be directly (or only needs to be cut into the size of the electrode plate) used as an electrode plate (working electrode) of a battery, without the introduction of conductive agents, adhesives, etc., and without the need for coating and other processes, which greatly simplifies the electrode plate preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a SEM image of the zinc sulfide-porous carbon nanofiber composite membrane prepared in Example 1 of the present invention; Figure 2 This is a graph showing the electrochemical performance of a button cell assembled from the zinc sulfide-porous carbon nanofiber composite membrane of Example 1 of the present invention at a current density of 0.2 mA / g. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0021] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0022] According to a first aspect of the present invention, there is provided a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane, comprising the following steps: S1. Electrospinning a slurry formed by mixing ZIF-8, polyacrylonitrile and dimethylformamide to obtain a nanofiber membrane; S2. The nanofiber membrane obtained in step S1 is dried and pre-calcined, and then sulfur powder is added to the pre-calcined nanofiber membrane and the sulfur powder is evenly distributed on the surface of the nanofiber membrane. The nanofiber membrane is then placed in a protective atmosphere for high-temperature calcination to obtain a zinc sulfide-porous carbon nanofiber composite membrane (lotus root-like porous carbon @ZnS) having a lotus root-like structure.

[0023] Specifically, step S1 of the present invention mainly prepares the nanofiber membrane containing ZIF-8 through an electrospinning process.

[0024] Step S2 mainly involves first drying the nanofiber membrane containing ZIF-8 to remove residual solvents and obtain a fiber membrane with a stable structure, and then continuing to pre-calcine after drying. Pre-calcination can optimize the fiber morphology, making it more uniform, dense and stable, which is beneficial to subsequent carbonization treatment; at the same time, it can further remove organic impurities and residual solvents in the fiber.

[0025] The pre-calcined nanofiber membrane and sulfur powder are subjected to a high-temperature calcination and sulfurization process, and ZIF-8 is gasified at high temperature to form pores in the carbon nanofibers to prepare porous carbon nanofibers with a special lotus root-like morphology. The zinc in ZIF-8 reacts with the sulfur powder to form zinc sulfide (ZnS), and at least part of the zinc sulfide is evenly distributed inside the pores of the lotus root-shaped porous carbon nanofibers, thereby forming a zinc sulfide-porous carbon nanofiber composite membrane.

[0026] The lotus root-shaped zinc sulfide-porous carbon nanofiber composite membrane has the advantages of high specific surface area, controllable pore structure, excellent mechanical flexibility, excellent conductivity and chemical stability. These characteristics are of great significance for improving battery performance. And because it has a certain self-supporting toughness, it can be directly used as a lithium battery negative working electrode and exhibits good lithium storage performance.

[0027] Through the preparation method provided by the present invention, the controllable preparation of zinc sulfide-porous carbon nanofiber composite membrane with unique morphology can be achieved.

[0028] The raw materials and composition of the slurry used for electrospinning in step S1 are further defined.

[0029] ZIF-8 is composed of zinc ions ( ) and 2-methylimidazole ( ) are combined by coordination bonds and have a unique porous structure and a high specific surface area. The source of ZIF-8 is not specifically limited and can be made by yourself or purchased.

[0030] As an optional implementation of the technical solution of the present invention, in step S1, the preparation method of ZIF-8 comprises the following steps: Providing a mixed solution A formed by zinc nitrate hexahydrate and methanol, and a mixed solution B formed by 2-methylimidazole and methanol; The mixed solution A and the mixed solution B are mixed and reacted, the obtained reaction product is subjected to solid-liquid separation, and the separated solid product is washed and dried to obtain ZIF-8.

[0031] As an optional embodiment of the technical solution of the present invention, the molar concentration of zinc nitrate hexahydrate in the mixed solution A is 0.4-0.6 mol / L, for example, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L or 0.6 mol / L, etc., preferably 0.5 mol / L; and / or, the molar concentration of 2-methylimidazole in the mixed solution B is 4.0-5.0 mol / L, for example, 4.0 mol / L, 4.2 mol / L, 4.5 mol / L, 4.8 mol / L or 5.0 mol / L, etc., preferably 4.5 mol / L; And / or, the molar ratio of zinc nitrate hexahydrate in the mixed solution A to 2-methylimidazole in the mixed solution B is (0.4-0.6):(4.0-5.0), preferably 0.4:4.5.

[0032] As an optional implementation of the technical solution of the present invention, in step S1, the molecular weight of polyacrylonitrile is 50,000-200,000, for example, 50,000, 60,000, 80,000, 100,000, 120,000, 150,000, 180,000 or 200,000, preferably 85,000.

[0033] As an optional implementation of the technical solution of the present invention, in step S1, the mass ratio of ZIF-8, polyacrylonitrile and dimethylformamide is (1-5): (1-5): (10-20), for example, 1:1:10, 1:2:10, 1:5:10, 1:5:15, 1:5:20, 2:1:10, 2:2:10, 2:2:20, 2:5:10, 2:5:15, 2:5:20, 5:1:10, 5:1:10, 5:2:10, 5:5:10, 5:5:15 or 5:5:20, preferably 2:2:20; By further limiting the mass ratio of ZIF-8, polyacrylonitrile and dimethylformamide, the viscosity of the spinning slurry is moderate, and uniform fibers can be spun subsequently.

[0034] As an optional implementation of the technical solution of the present invention, in step S1, the electrospinning adopts at least one of the following process parameters: The voltage of electrospinning is 10-25 kV, such as 10 kV, 12 kV, 15 kV, 18 kV, 20 kV, 22 kV, 25 kV, etc., preferably 18 kV; and / or, The injection speed of the syringe is 0.05-0.5 mL / h, such as 0.05 mL / h, 0.1 mL / h, 0.2 mL / h, 0.3 mL / h, 0.4 mL / h or 0.5 mL / h, preferably 0.1 mL / h.

[0035] As an optional implementation of the technical solution of the present invention, in step S2, drying is vacuum drying, the drying temperature is 60-120°C, for example, 60°C, 80°C, 100°C or 120°C, preferably 80°C, and the drying time is 8-24h, for example, 8h, 10h, 12h, 16h, 18h, 20h or 24h, etc., preferably 12h; and / or, in step S2, placing the nanofiber membrane in a graphite plate fixture and pre-calcining it in a muffle furnace; And / or, in step S2, the pre-calcination temperature is 200-400°C, for example, 200°C, 220°C, 250°C, 280°C, 300°C, 320°C, 350°C, 380°C or 400°C, etc., preferably 200°C, the pre-calcination time is 2-6h, for example, 2h, 4h, 5h or 6h, etc., preferably 2h; the pre-calcination atmosphere is air.

[0036] As an optional implementation of the technical solution of the present invention, in step S2, the mass ratio of sulfur powder to nanofiber membrane is (8-10): 1, for example, 8: 1, 9: 1 or 10: 1, etc., preferably 10: 1. Excess sulfur powder is used mainly to ensure that there is enough sulfur source to react with zinc in ZIF-8 to form sulfide.

[0037] As an optional implementation scheme of the technical solution of the present invention, in step S2, the temperature of high-temperature calcination is 1000-1300°C, for example, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C or 1300°C, and the high-temperature calcination time is 8-12h, for example, 8h, 9h, 10h or 12h, and preferably 10h.

[0038] And / or, in step S2, the protective atmosphere includes at least one of nitrogen or argon.

[0039] The inventors have determined the optimal calcination process (such as calcination temperature, calcination time, etc.) conditions through a large number of experimental optimizations, so that the prepared zinc sulfide-porous carbon nanofiber composite membrane has a unique microscopic morphology, as well as good mechanical flexibility and conductivity, thereby achieving better electrochemical performance of the electrode plate made therefrom.

[0040] According to a second aspect of the present invention, there is also provided a zinc sulfide-porous carbon nanofiber composite membrane, which is prepared by the method for preparing the zinc sulfide-porous carbon nanofiber composite membrane provided by the first aspect of the present invention; The porous carbon nanofibers in the zinc sulfide-porous carbon nanofiber composite membrane have a lotus root-like structure, zinc sulfide is at least partially distributed inside the lotus root-like porous carbon nanofibers, and the zinc sulfide-porous carbon nanofiber composite membrane is a flexible self-supporting material.

[0041] The zinc sulfide-porous carbon nanofiber composite film prepared by the present invention has a unique structure in which zinc sulfide is uniformly distributed inside the lotus-shaped porous carbon nanofiber. The composite structure provides a good electron transmission network and improves the electrical conductivity of the material; and due to the coating and confinement of the porous carbon nanofiber on zinc sulfide, the volume expansion effect thereof during the cycle can be effectively suppressed, and the defects of zinc sulfide such as poor electrical conductivity and large volume expansion are improved, so that the cycle stability of the composite film can be improved. In addition, the composite film also has a high specific surface area and a rich pore structure, which can provide more adsorption and storage sites for lithium ions, and can significantly improve the specific capacity of the material. A large specific surface area is conducive to shortening the lithium ion transmission path, improving the diffusion and transmission rate of lithium ions, and also increases the contact area between the material and the electrolyte, which is conducive to the rapid diffusion and transmission of lithium ions in the electrolyte.

[0042] According to a third aspect of the present invention, there is also provided an electrode plate, which is made of the zinc sulfide-porous carbon nanofiber composite membrane prepared by the preparation method provided by the first aspect of the present invention and the zinc sulfide-porous carbon nanofiber composite membrane provided by the second aspect of the present invention; The electrode plate is a flexible self-supporting electrode plate.

[0043] The zinc sulfide-porous carbon nanofiber composite membrane provided by the present invention has mechanical flexibility and self-supporting properties. It is a membrane structure itself. At the same time, since it also has good electrical conductivity, it can be directly used as an electrode plate (working electrode) of a battery (or only needs to be cut into the size of a plate) without the introduction of conductive agents, adhesives, etc., and there is no need to perform coating and other processes, which greatly simplifies the plate preparation process.

[0044] According to a fourth aspect of the present invention, there is also provided a lithium-ion battery, comprising the electrode plate provided by the third aspect of the present invention.

[0045] In view of the above advantages of the electrode plate, the lithium-ion battery containing the electrode plate has the same advantages.

[0046] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0047] Example 1 This embodiment provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane, comprising the following steps: S1. Dissolve Zn(NO3)2·6H2O (0.05 mol) and 2-methylimidazole (0.45 mol) in 1000 mL of methanol to form solution A and solution B respectively; Then, solution A was poured into solution B, and the reaction was carried out at room temperature for 24 h. The reaction solution was centrifuged, and the obtained solid product was washed and vacuum dried to obtain ZIF-8; S2. 2 g ZIF-8, 2 g polyacrylonitrile (molecular weight 85,000) and 20 g dimethylformamide were mixed and stirred for 12 h to obtain an electrospinning slurry; the slurry was transferred to a syringe and electrospun at a voltage of 18 KV and an injection speed of 0.1 mL / h to obtain a nanofiber membrane; S3. The fiber membrane obtained by spinning was vacuum dried at 80 ° C for 12 h, and then the fiber membrane was placed in a graphite plate fixture and pre-calcined in a muffle furnace under air atmosphere. The pre-calcination temperature was 200 ° C and the pre-calcination time was 2 h. After the pre-calcination was completed, it was cooled to room temperature; Excess sulfur powder was added to the pre-calcined nanofiber membrane (the mass ratio of sulfur powder to nanofiber membrane was 10:1) and the sulfur powder was evenly distributed on the surface of the nanofiber membrane. It was then placed in a tubular furnace and calcined at high temperature under a nitrogen atmosphere at a temperature of 1200°C for 10 hours to obtain a zinc sulfide-porous carbon nanofiber composite membrane (thickness of 60-80 μm).

[0048] Example 2 This embodiment provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane. Except for adjusting the temperature of high-temperature calcination in step S3 from 1200° C. to 1100° C., the remaining steps and process parameters are the same as those in Example 1.

[0049] Example 3 This embodiment provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane. Except for adjusting the temperature of high-temperature calcination in step S3 from 1200° C. to 1300° C., the remaining steps and process parameters are the same as those in Example 1.

[0050] Example 4 This embodiment provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane. Except for adjusting the mass of ZIF-8 in step S2 of embodiment 1 from 2 g to 4 g, the remaining steps and process parameters are the same as those of embodiment 1.

[0051] Example 5 This embodiment provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane. Except that the mass ratio of sulfur powder and nanofiber membrane in step S3 of embodiment 1 is adjusted from 10:1 to 6:1, the remaining steps and process parameters are the same as those of embodiment 1.

[0052] Example 6 This embodiment provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane, comprising the following steps: S1. Dissolve Zn(NO3)2·6H2O (0.05 mol) and 2-methylimidazole (0.45 mol) in 1000 mL of methanol to form solution A and solution B respectively; Then, solution A was poured into solution B, and the reaction was carried out at room temperature for 24 h. The reaction solution was centrifuged, and the obtained solid product was washed and vacuum dried to obtain ZIF-8; S2. 5 g ZIF-8, 5 g polyacrylonitrile and 20 g dimethylformamide were mixed and stirred for 12 h to obtain an electrospinning slurry; the slurry was transferred to a syringe and electrospun at a voltage of 20 KV and an injection speed of 0.15 mL / h to obtain a nanofiber membrane; S3. The spun fiber membrane was vacuum dried at 100 ° C for 10 h, and then the fiber membrane was placed in a graphite plate fixture and pre-calcined in a muffle furnace under air atmosphere. The pre-calcination temperature was 350 ° C and the pre-calcination time was 2 h. After the pre-calcination was completed, it was cooled to room temperature; Excess sulfur powder was added to the pre-calcined nanofiber membrane (the mass ratio of sulfur powder to nanofiber membrane was 8:1) and the sulfur powder was evenly distributed on the surface of the nanofiber membrane. It was then placed in a tubular furnace and calcined at high temperature under a nitrogen atmosphere at a temperature of 1000°C for 12 hours to obtain a zinc sulfide-porous carbon nanofiber composite membrane (thickness 60-90 μm).

[0053] Comparative Example 1 This comparative example provides a method for preparing a zinc sulfide-carbon composite material, comprising the following steps: S1. Zn(NO3)2·6H2O (0.05 mol) and 2-methylimidazole (0.45 mol) were dissolved in 1000 mL of methanol to form solution A and solution B. Solution A was then poured into solution B and reacted at room temperature for 24 h. The reaction solution was centrifuged, and the obtained solid product was washed and vacuum dried to obtain ZIF-8.

[0054] Sulfur powder with a mass ratio of 10:1 was mixed with ZIF-8, placed in a tubular furnace, and calcined at high temperature in a nitrogen atmosphere at a temperature of 1200°C for 10 hours to obtain a derivative material of ZIF-8, namely zinc sulfide-carbon composite material (abbreviated as ZnS@C).

[0055] Comparative Example 2 This comparative example provides a method for preparing a carbon nanofiber membrane, comprising the following steps: S1. 2 g PAN and 20 g DMF were mixed and stirred for 12 h to obtain an electrospinning slurry; the slurry was transferred to a syringe and electrospun at a voltage of 18 KV and an injection speed of 0.1 mL / h to obtain a fiber membrane; S2. The fiber membrane obtained by spinning was vacuum dried at 80°C for 12 h, and then the fiber membrane was placed in a graphite plate fixture and pre-calcined in a muffle furnace under air atmosphere. The pre-calcination temperature was 200°C and the pre-calcination time was 2 h. After the pre-calcination was completed, it was cooled to room temperature; The pre-calcined fiber membrane is placed in a tubular furnace for high-temperature calcination in a nitrogen atmosphere. The high-temperature calcination temperature is 1200° C. and the calcination time is 10 h, and finally a carbon nanofiber membrane is obtained.

[0056] Comparative Example 3 This comparative example provides a method for preparing a zinc sulfide-porous carbon nanofiber composite membrane. Except that no pre-calcination is performed in step S3, the remaining steps and process parameters are the same as those in Example 1.

[0057] The step S3 of this comparative example specifically comprises the following steps: S3. The spun fiber membrane was dried under vacuum at 80°C for 12h; Excess sulfur powder was added to the dried nanofiber membrane (the mass ratio of sulfur powder to nanofiber membrane was 10:1) and the sulfur powder was evenly distributed on the surface of the nanofiber membrane. It was then placed in a tubular furnace and calcined at high temperature under a nitrogen atmosphere at a temperature of 1200°C for 10 hours to obtain a zinc sulfide-porous carbon nanofiber composite membrane.

[0058] Comparative Example 4 This comparative example provides a method for preparing a porous carbon nanofiber membrane. Except that sulfur powder is not added in step S3, the remaining steps and process parameters are the same as those in Example 1.

[0059] The step S3 of this comparative example specifically comprises the following steps: S3. The fiber membrane obtained by spinning was vacuum dried at 80°C for 12h, and then the fiber membrane was placed in a graphite plate fixture and pre-calcined in a muffle furnace at a pre-calcination temperature of 200°C for 2h. After the pre-calcination was completed, it was cooled to room temperature; The pre-calcined nanofiber membrane was placed in a tubular furnace and calcined at high temperature in a nitrogen atmosphere at a temperature of 1200° C. for 10 h to obtain a porous carbon nanofiber membrane.

[0060] Comparative Example 5 This comparative example provides a method for preparing a sulfur-carbon nanofiber composite membrane, comprising the following steps: S1. 2 g of polyacrylonitrile and 20 g of dimethylformamide were mixed and stirred for 12 h to obtain an electrospinning slurry; the slurry was transferred to a syringe and electrospun at a voltage of 18 KV and an injection speed of 0.1 mL / h to obtain a nanofiber membrane; S2. The fiber membrane obtained by spinning was vacuum dried at 80°C for 12h, and then the fiber membrane was placed in a graphite plate fixture and pre-calcined in a muffle furnace at a pre-calcination temperature of 200°C for 2h. After the pre-calcination was completed, it was cooled to room temperature; Excess sulfur powder was added to the pre-calcined nanofiber membrane (the mass ratio of sulfur powder to nanofiber membrane was 10:1), and the sulfur powder was evenly distributed on the surface of the nanofiber membrane. It was then placed in a tubular furnace and calcined at high temperature under a nitrogen atmosphere at a temperature of 1200°C for 10 hours to obtain a sulfur-carbon nanofiber composite membrane.

[0061] Comparative Example 6 This comparative example provides a method for preparing a sulfur-carbon nanofiber composite membrane, comprising the following steps: S1. 2 g of polystyrene, 2 g of polyacrylonitrile and 20 g of dimethylformamide were mixed and stirred for 12 h to obtain an electrospinning slurry; the slurry was transferred to a syringe and electrospun at a voltage of 18 KV and an injection speed of 0.1 mL / h to obtain a nanofiber membrane; S2. The fiber membrane obtained by spinning was vacuum dried at 80°C for 12h, and then the fiber membrane was placed in a graphite plate fixture and pre-calcined in a muffle furnace at a pre-calcination temperature of 200°C for 2h. After the pre-calcination was completed, it was cooled to room temperature; Zinc sulfide is added to the pre-calcined nanofiber membrane (the mass ratio of zinc sulfide to nanofiber membrane is 0.5:1), and the zinc sulfide powder is evenly distributed on the surface of the nanofiber membrane. It is then placed in a tubular furnace and calcined at high temperature under a nitrogen atmosphere at a temperature of 600°C for 10 hours to obtain a zinc sulfide-carbon nanofiber composite membrane.

[0062] In order to verify the technical effects that can be achieved by the embodiments and comparative examples of the present invention, the following experimental examples are specially designed.

[0063] Experimental Example 1 The morphology of the zinc sulfide-porous carbon nanofiber composite membrane prepared in Example 1 was detected. Figure 1 shown.

[0064] Depend on Figure 1 It can be seen that the fiber composite membrane prepared by the preparation method of the present invention has wrinkles on the surface, with a diameter between 200-300nm, and a uniform porous lotus root-like structure is formed inside due to the gasification of some zinc ions, and there are no obvious agglomerated metal particles on the surface. And from the SEM image of the fiber end, the pore size is similar, and the pores are evenly distributed, which infers that zinc sulfide should be evenly distributed inside the fiber.

[0065] Experimental Example 2 For the zinc sulfide-porous carbon nanofiber composite membranes prepared in Examples 1-6 and the fiber membranes or composite membranes prepared in Comparative Examples 2-6, the composite membranes or fiber membranes were directly cut into circular pole pieces with a diameter of 14 mm by a cutter, and then the circular pole pieces were respectively assembled with lithium sheets, separators, electrolytes (1M LiPF6, EC: DMC: DEC (1:1:1)), springs, gaskets and positive and negative electrode shells into button batteries.

[0066] The composite material obtained in Comparative Example 1 was used as a negative electrode active material. A mixture of the negative electrode active material, PVDF and Super P (the mass ratio of the negative electrode active material, PVDF and Super P was 80:10:10) was dissolved in N-methylpyrrolidone (NMP) to obtain a uniform slurry. The slurry was uniformly coated on a copper foil, and after drying, the electrode sheet was cut into a disc with a diameter of 14 mm. The load density of the disc was about 1.2 mg / cm 2 The above-mentioned pole piece, lithium sheet, separator, electrolyte (1MLiPF6, EC: DMC: DEC (1:1:1)), spring piece, gasket and positive and negative electrode shells are assembled into a button battery.

[0067] The button cells prepared in each embodiment and comparative example were subjected to constant current charge and discharge tests using the NEWARE BTS-5V battery test system, with a voltage range of 0.01 ~ 3V and a current density of 0.2A / g and 2 A / g. The specific steps are as follows: first stand for 5 minutes, and charge the battery at a current of 0.2A / g (or 2A / g) until the cut-off voltage is reached. Stand for 10 minutes, and discharge at a constant current of 0.2A / g (or 2A / g) until the cut-off voltage is reached. Repeat the above charging and discharging steps and perform multiple cycle tests. The relevant performance is shown in Table 1.

[0068] Table 1 Combination Figure 2 As can be seen from the data in Table 1, the zinc sulfide-porous carbon nanofiber composite membranes prepared in Examples 1-6 of the present invention can be directly used as electrode sheets and have good lithium storage performance. At a current density of 0.2 A / g, after 100 cycles, their specific capacity is >690 mAh / g.

[0069] Comparative Examples 1-6 of the present invention are all comparative experiments of Example 1. Specifically, compared with Example 1, which adds sulfur powder to the pre-calcined nanofiber membrane for sulfurization and high-temperature calcination, Comparative Example 1 directly mixes sulfur powder with ZIF-8 and then performs sulfurization and high-temperature calcination. Since Comparative Example 1 does not perform electrostatic spinning to form a film, the prepared zinc sulfide-carbon composite material does not exist in the form of a film. Therefore, when it is used as a negative electrode active material, it needs to be used in combination with a conductive agent and a binder, and a conventional coating process can be used to form an electrode plate. And from the data in Table 1, it can be seen that the electrical performance of the battery prepared by Comparative Example 1 is greatly reduced compared with Example 1.

[0070] Compared with Example 1, in Comparative Example 2, ZIF-8 and sulfur powder were not added at the same time during the preparation of the fiber composite membrane, in Comparative Example 4, sulfur powder was not added during the preparation of the fiber composite membrane, and in Comparative Example 5, ZIF-8 was not added during the preparation of the fiber composite membrane. As can be seen from the data in Table 1, the electrical performance data of the battery prepared in Comparative Example 2 has decreased significantly, which is mainly because the fiber composite membrane material obtained in Comparative Example 2 is a pure carbon nanofiber material, so its capacity is significantly lower than the carbon nanofiber and transition metal sulfide composite material in Example 1. The electrical performance data of the batteries prepared in Comparative Examples 4 and 5 also decreased to a certain extent, but the degree of decrease was not as good as that in Comparative Example 2, which is mainly because Comparative Example 4 forms a composite material of carbon nanofiber and zinc oxide, and Comparative Example 5 obtains sulfur-doped carbon nanofibers, and the composite of transition metal compounds and the doping of miscellaneous elements are helpful to improve the lithium storage capacity of carbon nanofibers.

[0071] Compared with Example 1, in Comparative Example 6, ZIF-8 is not added during the preparation of the fiber composite membrane, and sulfur powder is directly replaced by a small amount of zinc sulfide. As can be seen from the data in Table 1, the data of Comparative Example 6 is somewhat lower than that of Example 1, which is mainly due to the fact that the mixing method of zinc sulfide and the spun fiber membrane in Comparative Example 6 is physical mixing, which is prone to metal particle agglomeration, affecting the material morphology and structural stability, while in Example 1, zinc sulfide and carbon nanofibers are in-situ composited and evenly dispersed, and its structural stability and cycle performance are better than those of Comparative Example 6.

[0072] The above experiments show that the fiber composite membrane prepared by the preparation method of the present invention not only realizes the uniform compounding of transition metal sulfide and carbon material, improves the conductivity of the material, but also can be directly used as a battery working electrode due to its good flexibility and mechanical properties, showing excellent lithium storage performance.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for preparing a zinc sulfide-porous carbon nanofiber composite membrane, characterized in that: The following steps are involved: S1. Electrospinning a slurry formed by mixing ZIF-8, polyacrylonitrile and dimethylformamide to obtain a nanofiber membrane; S2. The nanofiber membrane obtained in step S1 is dried and pre-calcined, and then sulfur powder is added to the pre-calcined nanofiber membrane so that the sulfur powder is evenly distributed on the surface of the nanofiber membrane, and then placed in a protective atmosphere for high-temperature calcination to obtain a zinc sulfide-porous carbon nanofiber composite membrane having a lotus root-like structure; Wherein, the high temperature calcination temperature is 1000-1300°C, the high temperature calcination time is 8-12h, and the protective atmosphere includes at least one of nitrogen or argon; The porous carbon nanofibers in the zinc sulfide-porous carbon nanofiber composite membrane have a lotus root-like structure, and the zinc sulfide is at least partially distributed inside the lotus root-like porous carbon nanofibers.

2. The method for preparing the zinc sulfide-porous carbon nanofiber composite membrane according to claim 1, characterized in that: In step S1, the mass ratio of ZIF-8, polyacrylonitrile and dimethylformamide is (1-5): (1-5): (10-20); And / or, the molecular weight of the polyacrylonitrile is 50,000-200,000.

3. The method for preparing the zinc sulfide-porous carbon nanofiber composite membrane according to claim 1, characterized in that: In step S1, the electrospinning adopts at least one of the following process parameters: The voltage of electrospinning is 10-25 kV; and / or, The injection rate of the syringe is 0.05-0.5mL / h.

4. The method for preparing the zinc sulfide-porous carbon nanofiber composite membrane according to claim 1, characterized in that: In step S1, the preparation method of ZIF-8 comprises the following steps: Providing a mixed solution A formed by zinc nitrate hexahydrate and methanol, and a mixed solution B formed by 2-methylimidazole and methanol; The mixed solution A and the mixed solution B are mixed and reacted, the obtained reaction product is subjected to solid-liquid separation, and the separated solid product is washed and dried to obtain ZIF-8.

5. The method for preparing the zinc sulfide-porous carbon nanofiber composite membrane according to claim 4, characterized in that: The molar concentration of zinc nitrate hexahydrate in the mixed solution A is 0.4-0.6 mol / L; And / or, the molar concentration of 2-methylimidazole in the mixed solution B is 4.0-5.0 mol / L; And / or, the molar ratio of zinc nitrate hexahydrate in the mixed solution A to 2-methylimidazole in the mixed solution B is (0.4-0.6): (4.0-5.0).

6. The method for preparing the zinc sulfide-porous carbon nanofiber composite membrane according to claim 1, characterized in that: In step S2, the drying is vacuum drying, the drying temperature is 60-120° C., and the drying time is 8-24 h; and / or, in step S2, placing the nanofiber membrane in a graphite plate fixture and pre-calcining it in a muffle furnace; And / or, in step S2, the pre-calcination temperature is 200-400°C, and the pre-calcination time is 2-6h.

7. The method for preparing the zinc sulfide-porous carbon nanofiber composite membrane according to claim 1, characterized in that: In step S2, the mass ratio of sulfur powder to nanofiber membrane is (8-10):

1.

8. A zinc sulfide-porous carbon nanofiber composite membrane, characterized in that: The zinc sulfide-porous carbon nanofiber composite membrane is prepared by the preparation method of any one of claims 1 to 7; The porous carbon nanofibers in the zinc sulfide-porous carbon nanofiber composite membrane have a lotus root-like structure, zinc sulfide is at least partially distributed inside the lotus root-like porous carbon nanofibers, and the zinc sulfide-porous carbon nanofiber composite membrane is a flexible self-supporting material.

9. An electrode plate, characterized in that: Made of the zinc sulfide-porous carbon nanofiber composite membrane prepared by the preparation method according to any one of claims 1 to 7 or the zinc sulfide-porous carbon nanofiber composite membrane according to claim 8; The electrode plate is a flexible self-supporting electrode plate.

10. A lithium ion battery, characterized in that: Including the electrode plate as described in claim 9.

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