Preparation method and application of flexible self-supporting lithium-sulfur battery interlayer material

Abstract

The application relates to the technical field of lithium-sulfur batteries, in particular to a preparation method and application of a flexible self-supporting lithium-sulfur battery interlayer material, and a preparation method of the flexible self-supporting lithium-sulfur battery interlayer material. A three-dimensional porous network structure composed of a self-supporting carbon nanofiber modified by a Co / CoSe2 heterostructure and in-situ grown carbon nanotubes is obtained through electrostatic spinning and in-situ selenization. The application realizes chemical anchoring and catalytic conversion of lithium polysulfide by combining a high-conductivity high-specific-surface-area material with a heterostructure, so that the prepared lithium-sulfur battery has good electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium-sulfur batteries, in particular to a preparation method and application of a flexible self-supporting lithium-sulfur battery interlayer material. BACKGROUND

[0002] A lithium-sulfur battery uses metallic lithium as the negative electrode and elemental sulfur as the positive electrode, and its theoretical energy density is as high as 2600 Wh / kg, which is much higher than that of traditional lithium-ion batteries, making it have great application potential in the fields of electric vehicles, portable electronic devices and large-scale energy storage systems. From the perspective of resources, sulfur is abundant in the earth's crust, low in price and environmentally friendly, which provides cost advantages and resource guarantees for large-scale production of lithium-sulfur batteries.

[0003] However, lithium-sulfur batteries face many challenges in actual development. For example, during charging and discharging, the sulfur in the positive electrode undergoes complex multi-step electrochemical reactions, producing lithium polysulfide intermediates that are easily soluble in the electrolyte. These lithium polysulfides are prone to diffusion inside the battery, causing the so-called "shuttle effect", which not only causes loss of active materials, but also causes the battery self-discharge phenomenon to intensify, thereby reducing the coulombic efficiency and cycle life of the battery. In addition, the volume change of sulfur during charging and discharging is large, which can damage the integrity of the electrode structure, thereby affecting the performance and stability of the battery.

[0004] Research has found that the introduction of a functional interlayer in a lithium-sulfur battery can improve the electrochemical performance of the lithium-sulfur battery, and can effectively block the migration of polysulfides, thereby improving the utilization of sulfur. Carbon-based interlayers are of interest due to their high electrical conductivity and physical barrier to polysulfides, but such carbon-based materials do not have outstanding adsorption capacity for polysulfides. For this reason, researchers have used polar materials to modify carbon-based materials, such as metal oxides, metal sulfides, metal nitrides and transition metals, but the modification of carbon-based materials to improve the electrochemical performance of lithium-sulfur batteries is still not ideal.

[0005] Therefore, it is of great significance to develop an interlayer material that can effectively improve the electrochemical performance of lithium-sulfur batteries for the development of lithium-sulfur batteries. SUMMARY

[0006] In order to improve the electrochemical performance of lithium-sulfur batteries, the application provides a preparation method and application of a flexible self-supporting lithium-sulfur battery interlayer material.

[0007] In a first aspect, the application provides a preparation method of a flexible self-supporting lithium-sulfur battery interlayer material, which adopts the following technical scheme:

[0008] A preparation method of a flexible self-supporting lithium-sulfur battery interlayer material, a three-dimensional porous network structure composed of a self-supporting carbon nanofiber modified by a Co / CoSe2 heterostructure obtained by electrospinning and in-situ selenization and an in-situ grown carbon nanotube.

[0009] By adopting the technical scheme, the Co / CoSe2 heterostructure serves as a chemical adsorption carrier and an electrocatalyst, the shuttle effect is inhibited through chemical anchoring, and the redox kinetics of LiPSs is accelerated through catalysis; the CNF-CNT three-dimensional porous conductive network obtained through electrospinning has a physical blocking effect on the shuttle of polysulfides. Therefore, the combination of the high-conductivity and high-specific-surface-area material and the heterostructure realizes chemical anchoring and catalytic conversion of lithium polysulfides, so that the prepared lithium-sulfur battery has good electrochemical performance; meanwhile, the preparation method is simple, low in cost and friendly to the environment, and has good application prospects.

[0010] In one specific implementable scheme, the following steps are included:

[0011] (1) polyacrylonitrile (PAN) and cobalt acetate are dissolved in N, N-dimethylformamide (DMF) to prepare a spinning solution, the spinning solution is electrospun and dried to obtain a fiber membrane;

[0012] (2) dimethylimidazole is dissolved in a methanol solution, stirred until the solution is clear, the fiber membrane is added, and after washing with deionized water and ethanol, the intermediate is dried to obtain an intermediate; the intermediate is pre-oxidized, carbonized and selenized to obtain a three-dimensional porous conductive interlayer material Co / CoSe2@CNF-CNT.

[0013] By adopting the technical scheme, the Co / CoSe2@CNF-CNT interlayer material prepared by the electrospinning process and the in-situ selenization method can not only be used as a second current collector to enhance conductivity and reduce interface impedance, but also can increase specific surface area and provide more active sites. The CNF-CNT three-dimensional porous conductive network in the Co / CoSe2@CNF-CNT interlayer material has a good physical blocking effect on polysulfides, and the Co / CoSe2 heterostructure catalyst can promote physical adsorption of polysulfides, accelerate catalytic conversion of polysulfides, promote deposition of Li2S and improve redox kinetics.

[0014] In addition, in the preparation method of the composite material, the CNT is formed because Co has high catalytic activity and can promote in-situ growth of CNT, and is not obtained by deposition through a CVD method, so the preparation method is simple, high in yield, low in cost, good in repeatability, friendly to the environment and has good application prospects, and has great significance for development of lithium-sulfur batteries.

[0015] In one specific embodiment, in the step (1), the mass molar ratio of polyacrylonitrile and cobalt acetate is 1 g: (1-3) mmol; the mass volume ratio of polyacrylonitrile and N, N-dimethylformamide is 1 g: (5-15) ml.

[0016] By adopting the above technical solution, the polyacrylonitrile and cobalt acetate are dissolved in N, N-dimethylformamide to form a spinning solution, and the spinning solution is electrospun to obtain a fiber membrane (CH3COO)2Co@PAN; by optimizing the addition amount of the three, the loading rate of polyacrylonitrile on the catalyst cobalt acetate is higher, and the stability of the formed (CH3COO)2Co@PAN is better.

[0017] In one specific embodiment, in the step (1), the electrospinning parameters are as follows: the temperature is 25-35℃, the relative humidity is 40-50%, the positive high voltage is set to 10-20kV, the negative high voltage is set to -1--3kV, the receiver is a stainless steel plate, the distance between the needle and the stainless steel plate is 14-16cm, and the advancing speed is 0.7-0.8mL h -1 .

[0018] By adopting the above technical solution, in the electrospinning process, the solvent evaporation rate and the sensitivity of the solution to humidity are greatly affected by the environmental temperature and humidity. In normal indoor air, higher relative humidity can cause the fiber diameter to decrease. Air is mainly composed of water vapor, nitrogen, oxygen and carbon dioxide. These molecules can interact or react with electrospinning materials. The influence of humidity on fiber diameter depends on the interaction between the solution and the surrounding water vapor. Temperature changes the average diameter of nanofibers through two opposite effects: increasing the evaporation rate of the solvent and reducing the viscosity of the solution. As the temperature increases, the diameter of the fiber decreases. However, both the two mechanisms of solvent evaporation increase and solution viscosity decrease lead to the decrease of the average fiber diameter.

[0019] The spinning voltage ranges from 10kV to 20kV, the prepared nanofibers are continuous and smooth, and as the spinning voltage increases, the diameter of the nanofibers decreases; when the spinning voltage is low, it is difficult to overcome the surface tension of the spinning solution due to the small electric field force, which hinders the stretching and splitting of the spinning solution, so that the diameter of the formed nanofibers is large; as the spinning voltage gradually increases, the electric field strength becomes larger and larger, and the polymer solution jet is more prone to stretching and splitting, forming nanofibers with smaller diameters. When the spinning voltage is too large, the electric field strength is too large, which causes the jet flow of the spinning solution to increase and the jet velocity to accelerate, which is not conducive to the stretching and splitting of the jet flow, thus making the fiber diameter larger and the uniformity worse, leading to the formation of beaded or beaded nanofibers. Therefore, by controlling the voltage during spinning, nanofibers with appropriate diameters can be obtained.

[0020] By controlling the pushing speed during spinning, not only the production efficiency of nanofibers is effectively controlled, but more importantly, the stability of the needle droplet and the diameter of the fiber are affected; in the process of preparing nanofibers, as the spinning speed increases, due to the incomplete drying of the nanofiber jet during the flight process between the needle tip and the receiver, the diameter of the prepared nanofibers will gradually increase, and even lead to the formation of beaded fibers.

[0021] The distance between the spinning needle and the receiver will affect the electric field strength and the evaporation of the solvent of the spinning solution, thereby affecting the diameter of the nanofiber. If the voltage remains constant, the electric field strength is inversely proportional to the distance. In the electrospinning device, the distance is in the range of 14-16㎝, which can allow the solvent to evaporate for enough flight time to deposit dry fiber bundles; if the distance is too short, the solvent will not evaporate sufficiently, and fused fibers may be formed.

[0022] In a specific implementable embodiment, in step (1), the drying is specifically vacuum drying at 55-65℃ and holding for 10-14h.

[0023] By adopting the above technical solution, vacuum drying is a common means to remove water inside the material. The temperature and time during drying have a crucial impact on the performance of the product. If the drying temperature is too high, the holding time is short, which has a certain impact on the pore size of the fiber membrane; on the contrary, if the drying temperature is too low, the holding time is longer, the water evaporation is not enough, and the subsequent reaction effect is affected.

[0024] In a specific implementable embodiment, in step (2), the molar ratio of dimethyl imidazole to cobalt acetate is 1:2-6.

[0025] By adopting the above technical solution, the N atom in the imidazole structure can coordinate with the metal cobalt ion, affecting the pore size and channel structure of the intermediate layer material. The N atom in the imidazole can also increase the nitrogen content of the intermediate layer material and increase its specific capacitance. Therefore, by optimizing the molar ratio of dimethyl imidazole to cobalt acetate, the obtained intermediate layer material has good chemical stability and can improve the electrochemical performance of lithium-sulfur batteries.

[0026] In a specific implementable embodiment, in step (2), the pre-oxidation is specifically: holding the intermediate at 230℃ in air at a heating rate of 1℃ / min for 2h.

[0027] By adopting the above technical solution, the intermediate is pre-oxidized to remove the oxygen group in PAN, so that the CNFs have stronger mechanical stability.

[0028] In a specific implementable embodiment, in step (2), the carbonization treatment is specifically: heating the material after pre-oxidation treatment to 900℃ in argon for 3h.

[0029] By adopting the above technical scheme, argon is an inert gas, which does not react with most materials including metals; at the same time, it is used at high temperature and does not produce any reaction risk; the use of argon can protect the metal Co from oxidation, ensuring the integrity and quality of the metal Co.

[0030] In one specific implementation, in step (2), the selenium treatment is specifically: adding selenium powder above the material after carbonization treatment, heating to 450 DEG C in argon and keeping for 2h, and then naturally cooling to room temperature.

[0031] By adopting the above technical scheme, the material obtained by directly heating to 450 DEG C and keeping for 2h during the selenium treatment has a smooth surface and uniform and dense particles; by using the method of placing selenium powder above the material and heating for selenium treatment, when the temperature of the selenium source reaches the melting point, the surface selenium powder melts into a liquid and then diffuses to the carbonized layer at the bottom, the reaction between the carbonized layer and the selenium source is a solid-liquid reaction, the reaction first occurs on the contact surface of the carbonized layer and the selenium powder, the reaction interface moves to the preset inner layer with time, until the reaction ends, the chemical reaction at the interface is quickly completed, and the diffusion of selenium elements is controllable; according to the area and thickness of the intermediate layer material, a proper amount of selenium powder is covered on the surface of the carbonized material as a selenium source, thereby greatly saving raw materials and avoiding pollution of selenium vapor.

[0032] In a second aspect, the present application provides a lithium-sulfur battery, which adopts the following technical scheme:

[0033] The lithium-sulfur battery comprises the above-mentioned flexible self-supporting lithium-sulfur battery intermediate layer material.

[0034] By adopting the above technical scheme, the flexible self-supporting lithium-sulfur battery intermediate layer material prepared by the present application can be used as an auxiliary channel for ion conduction, which not only can adjust the ion transmission path, adsorb the electrolyte additives exuded from the positive electrode, ensure that they can be reused during the battery working process, thereby reducing the loss of additives, and at the same time, the material as the intermediate layer does not affect the normal migration of Li + .

[0035] In summary, the present application has at least one of the following beneficial technical effects:

[0036] 1. A three-dimensional porous network structure of self-supporting carbon nanofiber modified by Co / CoSe2 heterostructure and in-situ grown carbon nanotube as an intermediate layer material (Co / CoSe2@CNF-CNT) for lithium-sulfur batteries is prepared by electrospinning process and in-situ selenization; the Co / CoSe2 heterostructure acts as a chemical adsorption carrier and an electrocatalyst, inhibits the shuttle effect through chemical anchoring, and accelerates the redox kinetics of LiPSs through catalysis; the three-dimensional porous conductive network of CNF-CNT obtained by electrospinning has a physical blocking effect on the shuttle of polysulfides, thereby improving the electrochemical performance of lithium-sulfur batteries.

[0037] 2. The flexible self-supporting lithium-sulfur battery intermediate layer material of the application has a simple preparation method, low cost, and is environmentally friendly, and has good application prospects;

[0038] 3. The material obtained by directly heating to 450°C for 2h during selenization not only has a smooth surface, uniform and dense particles, but also can cover an appropriate amount of selenium powder as a selenium source on the surface of the carbonized material according to the area and thickness of the intermediate layer material, thereby greatly saving raw materials and avoiding pollution by selenium vapor. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 SEM morphology of the flexible self-supporting lithium-sulfur battery intermediate layer material prepared in Example 1.

[0040] Figure 2 XRD curve of the flexible self-supporting lithium-sulfur battery intermediate layer material prepared in Example 1.

[0041] Figure 3 Elemental distribution mapping of the flexible self-supporting lithium-sulfur battery intermediate layer material prepared in Example 1.

[0042] Figure 4 SEM morphology of the flexible self-supporting lithium-sulfur battery intermediate layer material prepared in Comparative Example 1.

[0043] Figure 5 XRD curve of the flexible self-supporting lithium-sulfur battery intermediate layer material prepared in Comparative Example 1.

[0044] Figure 6 XRD curve of the flexible self-supporting lithium-sulfur battery intermediate layer material prepared in Comparative Example 2.

[0045] Figure 7 Cycling performance test results of the batteries assembled based on the prepared flexible self-supporting lithium-sulfur battery intermediate layer materials in Example 1 and Comparative Examples 1 and 2 at a current density of 0.5A / g. DETAILED DESCRIPTION

[0046] The following will be described through examples and drawingsFigures 1-7 The present application is further described in detail. Embodiment

[0047] Embodiment 1

[0048] The present embodiment discloses a method for preparing a flexible self-supporting lithium-sulfur battery interlayer material, comprising the following steps:

[0049] (1) 0.5 g of polyacrylonitrile (PAN, Mw=150000) and 0.249 g of cobalt acetate ((CH3COO)2Co·4H2O) were weighed and added to 5 ml of N, N-dimethylformamide (DMF), stirred at room temperature for 12 h until completely dissolved as a spinning solution; the spinning solution was electrospun and dried to obtain a fiber membrane; the electrospinning parameters were as follows: the temperature was controlled at 30°C, the humidity was controlled at 45%, the positive high voltage was set at 15 kV, the negative high voltage was set at -2 kV, the receiver was a stainless steel flat plate, the distance between the needle and the receiving flat plate was 15 cm, and the advancing speed was 0.75 ml / h; the drying was carried out in a vacuum drying oven at 60°C, and the holding time was 12 h;

[0050] (2) 0.328 g of dimethylimidazole was dissolved in 50 ml of methanol solution, stirred until the solution was clear, and the above fiber membrane was soaked in the clear solution for 12 h, washed with deionized water and ethanol, and dried in an oven at 60°C to obtain an intermediate;

[0051] (3) The above intermediate was placed in a tube furnace, heated at a rate of 1°C / min in air at 230°C for 2 h to remove the oxygen groups in PAN and make the CNFs have stronger mechanical stability; after pretreatment, the material was heated to 900°C in argon for 3 h to obtain Co@CNF-CNT; Co@CNF-CNT was placed in the middle of the tube furnace, excess selenium powder was placed upstream of the furnace, and then the tube furnace was heated to 450°C at a rate of 5°C / min in argon for 2 h, and the sample was naturally cooled to room temperature to obtain the desired flexible self-supporting lithium-sulfur battery interlayer material Co / CoSe2@CNF-CNT.

[0052] As Figure 1 SEM image of the flexible self-supporting lithium-sulfur battery interlayer material Co / CoSe2@CNF-CNT, the carbon nanotubes in the Co / CoSe2@CNF-CNT interlayer material grow uniformly on the surface of the CNF, forming a three-dimensional porous conductive network.

[0053] As Figure 2 XRD image of the flexible self-supporting lithium-sulfur battery interlayer material Co / CoSe2@CNF-CNT, which proves the successful synthesis of Co / CoSe2@CNF-CNT.

[0054] As Figure 3 Elemental mapping of the flexible self-supporting lithium-sulfur battery interlayer material Co / CoSe2@CNF-CNT, illustrating the uniform distribution of Co and Se elements on the surface of CNFs.

[0055] The present embodiment also discloses a lithium-sulfur battery comprising the above flexible self-supporting lithium-sulfur battery interlayer material.

[0056] The preparation method of the lithium-sulfur battery of the present embodiment comprises the following steps:

[0057] (1) After 6 g of sulfur sublimation, 3 g of Ketjen black and 1 g of polyvinylidene fluoride were thoroughly ground and mixed, N-methyl pyrrolidone (NMP) was added to grind into a uniform slurry, and then the slurry was coated on a carbon-coated aluminum foil. After vacuum drying at 45°C for 24h, cut into a 12mm diameter disc for standby, the sulfur loading of each electrode is 1.1mg;

[0058] (2) The above cut electrode is used as the positive electrode, lithium metal sheet as the negative electrode, commercial Celgard2500 separator and cut flexible self-supporting lithium-sulfur battery interlayer material Co / CoSe2@CNF-CNT as the intermediate layer, assembled into CR-2032 type button cell with a diameter of 16mm.

[0059] Example 2

[0060] The present embodiment is basically the same as Example 1, the difference is that in the preparation method of the flexible self-supporting lithium-sulfur battery interlayer material, step (1): 0.5g of polyacrylonitrile (PAN, Mw=150000) and 0.125g of cobalt acetate ((CH3COO)2Co·4H2O) are added to 2.5ml of N,N-dimethylformamide (DMF), stirred at room temperature for 12h until completely dissolved, as a spinning solution; After electrospinning the spinning solution, dry the fiber membrane; The electrospinning parameters are as follows: temperature control at 25°C, humidity control at 40%, positive high voltage set to 10kV, negative high voltage set to -1kV, receiver is stainless steel plate, the distance between needle and receiving plate is 14cm, the advancing speed is 0.7ml / h; Drying is carried out in a vacuum drying oven at 55°C, and the holding time is 10h.

[0061] Example 3

[0062] This example is basically the same as Example 1, except that the preparation method of the flexible self-supporting lithium-sulfur battery interlayer material is different in step (1): 0.5 g of polyacrylonitrile (PAN, Mw=150000) and 0.374 g of cobalt acetate ((CH3COO)2Co·4H2O) are weighed into 7.5 ml of N,N-dimethylformamide (DMF) and stirred at room temperature for 12 h until completely dissolved as a spinning solution; the spinning solution is electrospun and dried to obtain a fiber membrane; the electrospinning parameters are as follows: the temperature is controlled at 35°C, the humidity is controlled at 50%, the positive high voltage is set at 20 kV, the negative high voltage is set at -3 kV, the receiver is a stainless steel flat plate, the distance between the needle and the receiving flat plate is 16 cm, and the advancing speed is 0.8 ml / h; drying is carried out in a vacuum drying oven at 65°C, and the holding time is 14 h.

[0063] Comparative Example

[0064] Comparative Example 1

[0065] This comparative example discloses a preparation method of a flexible self-supporting lithium-sulfur battery interlayer material, comprising the following steps:

[0066] (1) 0.5 g of polyacrylonitrile (PAN, Mw=150000) and 0.249 g of cobalt acetate ((CH3COO)2Co·4H2O) are weighed into 5 ml of N,N-dimethylformamide (DMF) and stirred at room temperature for 12 h until completely dissolved as a spinning solution; the spinning solution is electrospun and dried to obtain a fiber membrane; the electrospinning parameters are as follows: the temperature is controlled at 30°C, the humidity is controlled at 45%, the positive high voltage is set at 15 kV, the negative high voltage is set at -2 kV, the receiver is a stainless steel flat plate, the distance between the needle and the receiving flat plate is 15 cm, and the advancing speed is 0.75 ml / h; drying is carried out in a vacuum drying oven at 60°C, and the holding time is 12 h;

[0067] (2) 0.328 g of dimethylimidazole is dissolved in 50 ml of methanol solution, stirred until the solution is clear, and the above fiber membrane is soaked in the clear solution for 12 h, washed with deionized water and ethanol, and dried in an oven at 60°C to obtain an intermediate;

[0068] (3) The above intermediate is placed in a tube furnace and heated at 230°C at a heating rate of 1°C / min for 2 h in air to remove the oxygen groups in PAN and make the CNFs have stronger mechanical stability; after pretreatment, the material is heated to 900°C in argon for 3 h to obtain the desired lithium-sulfur battery interlayer material Co@CNF-CNT.

[0069] As Figure 4SEM image of the lithium-sulfur battery interlayer material Co@CNF-CNT, the morphology of the Co@CNF-CNT interlayer material is similar to that of the Co / CoSe2@CNF-CNT interlayer material, and carbon nanotubes are uniformly grown on the surface of CNF to form a three-dimensional porous conductive network.

[0070] As Figure 5 XRD image of the lithium-sulfur battery interlayer material Co@CNF-CNT, proving the successful synthesis of Co@CNF-CNT.

[0071] Comparative Example 2

[0072] The present comparative example discloses a preparation method of a flexible self-supporting lithium-sulfur battery interlayer material, comprising the following steps:

[0073] (1) 0.5 g of polyacrylonitrile (PAN, Mw=150000) and 0.249 g of cobalt acetate ((CH3COO)2Co·4H2O) were weighed into 5 ml of N,N-dimethylformamide (DMF) and stirred at room temperature for 12 h until completely dissolved as a spinning solution; the spinning solution was electrospun and dried to obtain a fiber membrane; the electrospinning parameters are as follows: the temperature is controlled at 30°C, the humidity is controlled at 45%, the positive high voltage is set at 15 kV, the negative high voltage is set at -2 kV, the receiver is a stainless steel flat plate, the distance between the needle and the receiving flat plate is 15 cm, and the advancing speed is 0.75 ml / h; drying is carried out in a vacuum drying oven at 60°C, and the holding time is 12 h;

[0074] (2) 0.328 g of dimethylimidazole was dissolved in 50 ml of methanol solution, stirred until the solution was clear, and the above fiber membrane was soaked in the clear solution for 12 h, washed with deionized water and ethanol, and then dried in an oven at 60°C to obtain an intermediate;

[0075] (3) The above intermediate was placed in a tube furnace, heated at a rate of 1°C / min in air at 230°C for 2 h to remove the oxygen groups in PAN and make the CNFs have stronger mechanical stability; after pretreatment, the material was heated to 900°C in argon for 3 h to obtain Co@CNF-CNT; Co@CNF-CNT was placed in the middle of the tube furnace, excess selenium powder was placed in the upstream of the furnace, and then the tube furnace was heated to 450°C at a heating rate of 5°C / min in argon for 6 h, and the sample was naturally cooled to room temperature to obtain the desired flexible self-supporting lithium-sulfur battery interlayer material CoSe2@CNF-CNT.

[0076] As Figure 6 SEM image of the flexible self-supporting lithium-sulfur battery interlayer material CoSe2@CNF-CNT, CoSe2 nanoparticles are scattered and distributed on CNF, and the number of carbon nanotubes also decreases.

[0077] Performance test

[0078] Battery assembly: the interlayer materials prepared in Example 1, Comparative Example 1 and Comparative Example 2, respectively, the positive electrode uses the lithium-sulfur battery positive electrode sheet of sublimation sulfur: Ketjen black: polyvinylidene fluoride = 6:3:1, the negative electrode sheet is lithium metal sheet, the separator is commercial Celgard 2500 separator, the electrolyte is 1 M lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) dissolved in ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) with a volume ratio of 1:1, the electrolyte additive is 2wt% LiNO3, and the electrolyte dosage of each battery is 40 μL. All batteries are assembled in a glove box (H2O, O2<0.01 ppm).

[0079] Electrochemical test: the constant current charge and discharge and rate performance test of lithium-sulfur battery is carried out on a new wei battery test system, the voltage window is 1.8-2.7 V, and the charge and discharge test is carried out at a current density of 0.5 A / g.

[0080] As Figure 7 The figure is the cycle performance test result of the battery assembled in Example 1, Comparative Example 1 and Comparative Example 2 based on the prepared flexible self-supporting lithium-sulfur battery interlayer material modified by heterostructure, and it can be seen that the specific capacity and cycle stability of the lithium-sulfur battery assembled by the Co / CoSe2@CNF-CNT interlayer material prepared in the application are better than those of the lithium-sulfur battery assembled by the Co@CNF-CNT interlayer material and the CoSe2@CNF-CNT interlayer material.

[0081] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution according to the needs after reading the present specification, but as long as the scope of the claims of the present application is within the scope of the patent law.

Claims

1. A method of making a flexible self-supporting lithium sulfur battery interlayer material, characterized by, A three-dimensional porous network structure of self-supporting carbon nanofiber modified by Co / CoSe2 heterostructure obtained by electrospinning and in-situ selenization, and carbon nanotube grown in-situ; The preparation of the intermediate layer material comprises the following steps: (1) dissolving polyacrylonitrile (PAN) and cobalt acetate in N, N-dimethylformamide (DMF) to prepare a spinning solution, electrospinning the spinning solution and drying to obtain a fiber membrane; (2) dissolving dimethylimidazole in a methanol solution, stirring until the solution is clear, adding the fiber membrane, washing with deionized water and ethanol, and drying to obtain an intermediate; pre-oxidizing, carbonizing and selenizing the intermediate to obtain a three-dimensional porous conductive intermediate layer material Co / CoSe2@CNF-CNT; In step (2), the pre-oxidation is specifically: heating the intermediate in air at a heating rate of 1℃ / min at 230℃ for 2h; In step (2), the carbonization treatment is specifically: heating the material after pre-oxidation to 900℃ in argon for 3h; In step (2), the selenization treatment is specifically: adding selenium powder above the material after carbonization treatment, heating to 450℃ in argon for 2h, and naturally cooling to room temperature.

2. The method of claim 1, wherein: In step (1), the mass molar ratio of polyacrylonitrile and cobalt acetate is 1g: (1-3) mmol; the mass volume ratio of polyacrylonitrile and N, N-dimethylformamide is 1g: (5-15) ml.

3. The method of claim 1, wherein: In the step (1), the electrospinning parameters are as follows: temperature is 25-35℃, relative humidity is 40-50%, positive high voltage is set to 10-20kV, negative high voltage is set to -1--3kV, the receiver is a stainless steel plate, the distance between the needle and the stainless steel plate is 14-16cm, and the advancing speed is 0.7-0.8mL h -1 .

4. The method of claim 1, wherein: In step (1), the drying is specifically vacuum drying at a temperature of 55-65℃ for 10-14h.

5. The method of claim 1, wherein: In step (2), the molar ratio of dimethylimidazole to cobalt acetate is 1:2-6.

6. A lithium-sulfur battery characterized by: The intermediate layer material prepared by the preparation method of the flexible self-supporting lithium-sulfur battery intermediate layer material of any one of claims 1-5.

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