Preparation method of graphene-cobalt oxide composite material with controllable graphene thickness, electrode preparation method, diaphragm preparation method and battery

Abstract

The present invention relates to the technical field of battery materials, and in particular to a graphene-cobalt oxide composite material preparation method, an electrode preparation method, a diaphragm preparation method and a battery with controllable graphene thickness. Wherein, the graphene-cobalt oxide composite material preparation method includes: putting 50-500nm cobalt oxide into a CVD tube furnace, pumping to a basic pressure of less than or equal to 1Pa; purging the system with a 100sccmAr gas flow, and generating a radio frequency plasma with a power of 40-100W near the upstream of the furnace mouth; when the reaction temperature reaches 400°C-800°C, introducing a 10sccm carbon source gas flow into a quartz tube, and after stabilization, introducing a 5-10sccm nitrogen gas flow to start growth, and growing for 12-60 minutes to obtain a graphene-cobalt oxide composite material. The graphene shell thickness is controllable, the cobalt valence state is variable, and it has dual defects of nitrogen atoms and vacancies, which helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness, an electrode preparation method, a diaphragm preparation method and a battery. Background Art

[0002] At present, the development of new energy and the progress of green science and technology are powerful means to ensure national energy security. As a new generation of multi-electron high-energy secondary batteries, lithium-sulfur batteries have shown great potential application value in the field of high-energy electric devices with a theoretical specific energy of up to 2600Wh / kg and a theoretical specific capacity of 1675mAh / g.

[0003] The elemental sulfur in the positive electrode of lithium-sulfur batteries has the advantages of low toxicity, low cost, little environmental pollution, and abundant reserves. However, the following fatal shortcomings still exist in the charging and discharging process of lithium-sulfur batteries: the extremely poor conductivity of elemental sulfur will seriously hinder the transfer of electrons and affect the discharge depth of the battery; the density difference between elemental sulfur and Li2S during charging and discharging will destroy the electrode structure; the "shuttle effect" caused by soluble polysulfides will also greatly reduce the utilization rate of sulfur.

[0004] How to effectively realize lithium-sulfur batteries with high specific capacity and long cycle life is an urgent problem to be solved.

[0005] In view of this, this application is hereby filed. Summary of the invention

[0006] The first object of the present invention is to provide a method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness, which uses plasma enhanced chemical vapor deposition to in-situ grow nitrogen-doped graphene with controllable thickness on cobalt tetroxide to design a highly active electrocatalyst for lithium-sulfur batteries. In the prepared graphene-cobalt oxide composite material, the constructed electrocatalyst-derived heterogeneous interface tightly connects the highly adsorbed oxide and the conductive graphene, which can achieve rapid adsorption, diffusion, and conversion of polysulfides and accelerate the reaction kinetics during charging and discharging. The thickness of the graphene shell is controllable, the valence state of cobalt is variable, and the design flexibility is greatly improved. At the same time, it also has dual defects of nitrogen atoms and vacancies, which makes it have higher catalytic activity, which helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0007] The second object of the present invention is to provide an electrode preparation method, wherein the prepared electrode can realize the rapid adsorption, diffusion and conversion of polysulfides, accelerate the reaction kinetics during the charge and discharge process, has dual defects of nitrogen atoms and vacancies, has higher catalytic activity, and helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0008] The third object of the present invention is to provide a method for preparing a diaphragm, wherein the prepared diaphragm can realize rapid adsorption, diffusion, and conversion of polysulfides, and accelerate the reaction kinetics during the charge and discharge process, has dual defects of nitrogen atoms and vacancies, has higher catalytic activity, and helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0009] The fourth object of the present invention is to provide a battery that can achieve rapid adsorption, diffusion, and conversion of polysulfides, and accelerate the reaction kinetics during charging and discharging, with longer cycle life and better cycle stability.

[0010] The embodiment of the present invention is achieved as follows:

[0011] A method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness comprises the following steps:

[0012] S1. Place cobalt tetroxide with a particle size of 50-500 nm into a CVD tube furnace and evacuate the furnace until the basic pressure is less than or equal to 1 Pa.

[0013] S2. Purge the system with 100 sccm of Ar gas flow and generate RF plasma at a power of 40-100 W upstream near the furnace mouth.

[0014] S3. When the reaction temperature reaches 400°C to 800°C, a carbon source gas flow of 10 sccm is introduced into the quartz tube. After stabilization, a nitrogen gas flow of 5 to 10 sccm is continuously introduced to start growth. The growth time is 12 to 60 minutes to obtain a graphene-cobalt oxide composite material.

[0015] Furthermore, the carbon source gas flow includes at least one of a methane gas flow and a propylene gas flow.

[0016] A method for preparing an electrode comprises the following steps:

[0017] D1. Take 0.5 g of LA133 stock solution with a solid content of 15%, add 1.375 g of deionized water, and stir for 2 h to obtain LA133 diluted solution.

[0018] D2. Active material sulfur and conductive carbon black Super P were mixed in a mass ratio of 3:1 to prepare an S / C mixture, and the S / C mixture was melted at 155° C. for 8 hours to obtain a molten sulfur product.

[0019] D3, adding LA133 diluent and the graphene-cobalt oxide composite material prepared by the above-mentioned graphene-cobalt oxide composite material preparation method with controllable graphene thickness to the molten sulfur product, and adding conductive carbon black Super P again, mixing to obtain a positive electrode slurry. Among them, the mass ratio of the molten sulfur product, LA133 diluent, the conductive carbon black Super P added again and the graphene-cobalt oxide composite material is 8:1:0.5:0.5.

[0020] D4, coating the positive electrode slurry on the surface of the aluminum foil and performing vacuum drying to obtain an electrode, wherein the coating thickness of the positive electrode slurry is 100 μm.

[0021] A method for preparing a diaphragm comprises the following steps:

[0022] F1. Take the graphene-cobalt oxide composite material, conductive carbon black Super P and solid PVDF powder prepared by the above-mentioned graphene thickness controllable graphene thickness preparation method, add N-methyl pyrrolidone and disperse for 2 hours to obtain a diaphragm slurry. Among them, the mass ratio of graphene-cobalt oxide composite material, conductive carbon black Super P, solid PVDF powder and N-methyl pyrrolidone is 21:6:3:120.

[0023] F2, coating the diaphragm slurry on the surface of Celgrad-2500 diaphragm, and vacuum drying to obtain a diaphragm. The thickness of the wet film formed by the diaphragm slurry on the surface of Celgrad-2500 diaphragm is 100 μm.

[0024] Furthermore, the diaphragm slurry is stirred and dispersed by a stirring device. The stirring device includes: a mounting seat, a movable seat and a stirring cup.

[0025] One end of the mounting seat is provided with a mounting cavity. Along the depth direction of the mounting cavity, the movable seat is slidably matched in the mounting cavity. The bottom of the stirring cup is accommodated and fixedly matched with the mouth of the mounting cavity, and the mouth of the stirring cup is detachably matched with a cover body.

[0026] A baffle is arranged inside the mixing cup, the baffle is arranged perpendicular to the axis of the mixing cup, the outer peripheral edge of the baffle is fitted with the inner wall of the mixing cup, and the baffle and the mixing cup are slidably sealed.

[0027] The movable seat is fixedly mounted with a reference sleeve, which is arranged along the depth direction of the mounting cavity and penetrates the bottom of the stirring cup and the baffle. Along the axial direction of the reference sleeve, the stirring cup and the baffle are both slidably sealed with the reference sleeve.

[0028] The movable seat has an inner cavity. The movable seat is also equipped with a stirring shaft, which is rotatably accommodated in the reference sleeve, with one end of the stirring shaft extending to the inner cavity and the other end extending outside the reference sleeve. Along the axial direction of the stirring shaft, the stirring shaft is fixedly matched with the movable seat.

[0029] The stirring shaft has an expanded diameter section, the outer diameter of the expanded diameter section is the same as the outer diameter of the reference sleeve, and the end surface of the expanded diameter section is in contact with the end surface of the reference sleeve away from the movable seat.

[0030] The stirring shaft and the reference sleeve are rotatably sealed. A driver is arranged in the inner cavity, and the driver is matched with the stirring shaft in transmission.

[0031] The stirring shaft has an axial through hole, which is coaxially arranged with the stirring shaft. A core is arranged in the axial through hole, which slides in the axial through hole, and a first linear driver is installed in the inner cavity, which drives in cooperation with the core.

[0032] The outer wall of the expanded diameter section is provided with a first groove and a second groove arranged at intervals, and the first groove and the second groove both extend continuously in a ring shape along the circumference of the expanded diameter section. The first groove is located at an end of the expanded diameter section away from the reference sleeve, and the first groove penetrates to the end wall of the expanded diameter section. The second groove is located at an end of the expanded diameter section close to the reference sleeve.

[0033] The hole wall of the axial through hole is provided with a first cavity and a second cavity. The first groove is provided with a first notch connected to the first cavity at one end close to the second groove, and the second groove is provided with a second notch connected to the second cavity at one end close to the first groove.

[0034] The first groove contains a first stirring rod, one end of which is hinged to one end of the first groove close to the second groove. The hinge shaft of the first stirring rod has a first rack arranged along its circumference, and the first rack extends into the first cavity through the first notch.

[0035] The second groove contains a second stirring rod, one end of which is hinged to one end of the second groove close to the first groove. The hinge shaft of the second stirring rod has a second rack arranged along its circumference, and the second rack extends into the second cavity through the second notch.

[0036] The first cavity is provided with a first transmission gear unit, and the second cavity is provided with a second transmission gear unit. The side wall of the core body has a toothed portion arranged along its axial direction, and the toothed portion is matched with the first rack through the first transmission gear unit, and the toothed portion is matched with the second rack through the second transmission gear unit.

[0037] The length of the first stirring rod is greater than the length of the first groove, the length of the second stirring rod is adapted to the length of the second groove, the thickness of the first stirring rod is adapted to the depth of the first groove, and the thickness of the second stirring rod is adapted to the depth of the second groove.

[0038] A second linear driver is arranged at the bottom of the installation cavity, and the second linear driver cooperates with the movable seat in transmission to drive the movable seat to move along the depth direction of the installation cavity.

[0039] A control rod is fixedly connected to one side of the baffle away from the cup mouth of the stirring cup. The control rod passes through the bottom, the movable seat and the mounting seat of the stirring cup. The outer end of the control rod is in transmission cooperation with the third linear drive.

[0040] Furthermore, in the stirring device, the first stirring rod has a protrusion on one side close to the core body, and when the first stirring rod is received in the first groove, the end of the protrusion fits with the end of the stirring shaft, and the protrusion fits with the side wall of the core body.

[0041] Furthermore, the stirring device further comprises: a base and a bracket. The bracket is mounted on the base.

[0042] The mounting seat is provided with rotating shafts on both sides, the mounting seat is rotatably matched with the bracket through the rotating shafts, and the rotating shafts are driven by a servo motor.

[0043] A battery comprises: at least one of a graphene-cobalt oxide composite material prepared by the above-mentioned method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness, an electrode prepared by the above-mentioned method for preparing an electrode, and a diaphragm prepared by the above-mentioned method for preparing a diaphragm.

[0044] The beneficial effects of the technical solution of the embodiment of the present invention include:

[0045] Compared with the wet chemical method, the method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness provided in an embodiment of the present invention has higher cleanliness and controllability, and can ensure the cleanliness, tight connection and compatibility of the components of the heterojunction surface of graphene-cobalt oxide, thereby giving the catalyst higher activity.

[0046] During the reaction, N2 is selected as the carrier gas to achieve N-doping of graphene. The use of plasma can cause intrinsic defects in graphene. The carbon active species with reducing ability generated during the reaction can regulate the valence state of cobalt in cobalt oxide, thereby enriching the composition of the catalyst.

[0047] In general, the method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness provided in an embodiment of the present invention uses plasma enhanced chemical vapor deposition to in-situ grow nitrogen-doped graphene with controllable thickness on cobalt tetroxide to design a highly active electrocatalyst for lithium-sulfur batteries. In the prepared graphene-cobalt oxide composite material, the constructed electrocatalyst-derived heterogeneous interface tightly connects the highly adsorbed oxide and the conductive graphene, which can achieve rapid adsorption, diffusion, and conversion of polysulfides and accelerate the reaction kinetics during charging and discharging. The thickness of the graphene shell is controllable, the valence state of cobalt is variable, and the design flexibility is greatly improved. At the same time, it also has dual defects of nitrogen atoms and vacancies, which makes it have higher catalytic activity, which helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0048] The electrode prepared by the electrode preparation method provided in the embodiment of the present invention can realize the rapid adsorption, diffusion and conversion of polysulfides, and accelerate the reaction kinetics during the charge and discharge process. It has dual defects of nitrogen atoms and vacancies, has higher catalytic activity, and helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0049] The diaphragm prepared by the diaphragm preparation method provided in the embodiment of the present invention can realize the rapid adsorption, diffusion and conversion of polysulfides and accelerate the reaction kinetics during the charge and discharge process. It has dual defects of nitrogen atoms and vacancies and has higher catalytic activity, which helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0050] The battery provided by the embodiment of the present invention can achieve rapid adsorption, diffusion and conversion of polysulfides and accelerate the reaction kinetics during the charge and discharge process, thereby having a longer cycle life and good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] 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.

[0052] Figure 1 This is a microstructure diagram of the graphene-cobalt oxide composite material prepared in Experimental Example 1;

[0053] Figure 2 This is a microstructure diagram of the graphene-cobalt oxide composite material prepared in Experimental Example 2;

[0054] Figure 3 It is a schematic diagram of the overall structure of the stirring device;

[0055] Figure 4 This is a schematic diagram of the coordination between the mounting base, the movable base and the mixing cup (before mixing begins);

[0056] Figure 5 This is a schematic diagram of the coordination of the mounting base, the movable base and the mixing cup (when mixing begins);

[0057] Figure 6 This is a schematic diagram of the coordination between the mounting base, the movable base and the mixing cup (when discharging materials);

[0058] Figure 7 for Figure 4 A schematic diagram of the structure of the expanded diameter section of the middle stirring shaft;

[0059] Figure 8 for Figure 5 A schematic diagram of the structure of the expanded diameter section of the middle stirring shaft;

[0060] Fig. 9 for Figure 6 A schematic diagram of the structure of the mouth of the mixing cup;

[0061] Fig.10 for Figure 7 Schematic diagram of the transmission coordination of the first stirring rod and the second stirring rod.

[0062] Description of reference numerals:

[0063] Mounting seat 100; movable seat 200; reference sleeve 210; stirring shaft 220; expansion section 230; first groove 231; second groove 232; first cavity 233; second cavity 234; first notch 235; second notch 236; first stirring rod 240; first rack 241; first transmission gear unit 242; protrusion 243; second stirring rod 250; second rack 251; second transmission gear unit 252; core 260; stirring cup 300; cover 310; baffle 320; control rod 330; driver 410; first linear driver 420; second linear driver 430; third linear driver 440; base 500; bracket 510. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0065] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0066] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0067] The terms “first”, “second”, etc. are only used for distinguishing descriptions and should not be understood as indicating or implying relative importance.

[0068] In addition, the terms "parallel", "vertical", etc. do not mean that the components must be absolutely parallel or vertical, but can be slightly tilted. For example, "parallel" only means that its direction is more parallel than "vertical", and does not mean that the structure must be completely parallel, but can be slightly tilted.

[0069] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0070] In order to solve the defects existing in the prior art, the present invention provides a method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness, which comprises the following steps:

[0071] S1. Place cobalt oxide with a particle size of 50-500 nm into a CVD tube furnace, and evacuate the furnace until the basic pressure is less than or equal to 1 Pa. Optionally, the basic pressure may be evacuated to 1 Pa during evacuation.

[0072] S2. Purge the system with 100 sccm of Ar gas flow and generate RF plasma at a power of 40-100 W upstream near the furnace mouth.

[0073] S3. When the reaction temperature reaches 400°C to 800°C, a carbon source gas flow of 10 sccm is introduced into the quartz tube. After stabilization, a nitrogen gas flow of 5 to 10 sccm is continuously introduced to start growth. The growth time is 12 to 60 minutes to obtain a graphene-cobalt oxide composite material.

[0074] The carbon source gas flow includes at least one of a methane gas flow and a propylene gas flow.

[0075] It should be noted that in S3, the reaction temperature is within the range of 400°C to 800°C. The lower the temperature, the thinner the graphene shell layer in the graphene-cobalt oxide composite material. Conversely, the higher the temperature, the thicker the graphene shell layer in the graphene-cobalt oxide composite material.

[0076] In addition, within the growth time of 12 to 60 minutes, the shorter the growth time, the thinner the thickness of the graphene shell layer in the graphene-cobalt oxide composite material. Conversely, the longer the growth time, the thicker the thickness of the graphene shell layer in the graphene-cobalt oxide composite material.

[0077] This achieves control and adjustment of the thickness of the graphene shell layer in the graphene-cobalt oxide composite material.

[0078] The present invention also provides a method for preparing an electrode, which comprises the following steps:

[0079] D1. Take 0.5 g of LA133 stock solution with a solid content of 15%, add 1.375 g of deionized water, and stir for 2 h to obtain LA133 diluted solution.

[0080] D2. Active material sulfur and conductive carbon black Super P were mixed in a mass ratio of 3:1 to prepare an S / C mixture, and the S / C mixture was melted at 155° C. for 8 hours to obtain a molten sulfur product.

[0081] D3, adding LA133 diluent and the graphene-cobalt oxide composite material prepared by the above-mentioned graphene-cobalt oxide composite material preparation method with controllable graphene thickness to the molten sulfur product, and adding conductive carbon black Super P again, mixing to obtain a positive electrode slurry. Among them, the mass ratio of the molten sulfur product, LA133 diluent, the conductive carbon black Super P added again and the graphene-cobalt oxide composite material is 8:1:0.5:0.5.

[0082] D4, coating the positive electrode slurry on the surface of the aluminum foil and vacuum drying to obtain an electrode. The coating thickness of the positive electrode slurry is 100 μm. The prepared electrode is a positive electrode sheet.

[0083] The present invention also provides a method for preparing a diaphragm, which comprises the following steps:

[0084] F1. Take the graphene-cobalt oxide composite material, conductive carbon black Super P and solid PVDF powder prepared by the above-mentioned graphene thickness controllable graphene thickness preparation method, add N-methyl pyrrolidone and disperse for 2 hours to obtain a diaphragm slurry. Among them, the mass ratio of graphene-cobalt oxide composite material, conductive carbon black Super P, solid PVDF powder and N-methyl pyrrolidone is 21:6:3:120.

[0085] F2, coating the diaphragm slurry on the surface of Celgrad-2500 diaphragm, and vacuum drying to obtain a diaphragm. The thickness of the wet film formed by the diaphragm slurry on the surface of Celgrad-2500 diaphragm is 100 μm.

[0086] The present invention also provides a battery, which comprises: a graphene-cobalt oxide composite material prepared by the above-mentioned method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness, an electrode prepared by the above-mentioned electrode preparation method, and at least one of a diaphragm prepared by the above-mentioned diaphragm preparation method.

[0087] The technical solution of this application will be further explained below in conjunction with specific data.

[0088] Experimental Example 1

[0089] Preparation of graphene-cobalt oxide composite material: Cobalt oxide with a particle size of 100 nm was placed in a CVD tube furnace and evacuated to a basic pressure of 1 Pa. The system was purged with an Ar gas flow (100 sccm) and a radio frequency plasma (80W) was generated upstream near the furnace mouth. When the reaction temperature reached 550°C, a methane gas flow (10 sccm) was introduced into the quartz tube. After stabilization, a nitrogen gas flow of 10 sccm was continued to be introduced. The graphene-cobalt oxide composite material was grown in an 80W plasma environment for 15 minutes.

[0090] The microstructure of the graphene-cobalt oxide composite material was photographed by transmission electron microscopy. Figure 1 As shown, it has a thicker graphene shell.

[0091] The graphene-cobalt oxide composite material was prepared into a diaphragm according to the diaphragm preparation method described above, and the diaphragm was applied to a lithium-sulfur battery. The battery was assembled and electrochemically tested. The full battery was subjected to a constant current charge and discharge test and cycled at a rate of 0.2C. The initial discharge capacity of the battery can reach 978.5 mAh g -1 After 100 cycles, the capacity is maintained at 61.14% of the initial specific capacity.

[0092] Experimental Example 2

[0093] Preparation of graphene-cobalt oxide composite material: Cobalt oxide with a particle size of 100 nm was placed in a CVD tube furnace and evacuated to a basic pressure of 1 Pa. The system was purged with an Ar gas flow (100 sccm) and a radio frequency plasma (80W) was generated upstream near the furnace mouth. When the reaction temperature reached 450°C, a methane gas flow (10 sccm) was introduced into the quartz tube. After stabilization, a nitrogen gas flow of 5 sccm was continued to be introduced. The graphene-cobalt oxide composite material was grown in an 80W plasma environment for 15 minutes.

[0094] The microstructure of the graphene-cobalt oxide composite material was photographed by transmission electron microscopy. Figure 2 As shown, compared with Experimental Example 1, it has a thinner graphene shell.

[0095] The graphene-cobalt oxide composite material was prepared into a diaphragm according to the diaphragm preparation method described above, and the diaphragm was applied to a lithium-sulfur battery. The battery was assembled and electrochemically tested. The full battery was subjected to a constant current charge and discharge test and cycled at a rate of 0.2C. The initial discharge capacity of the battery can reach 1063.7 mAh g -1 After 100 cycles, the capacity is maintained at 78.50% of the initial specific capacity.

[0096] It can be seen from this that the method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness provided in an embodiment of the present invention utilizes plasma enhanced chemical vapor deposition to in-situ grow nitrogen-doped graphene with controllable thickness on cobalt oxide to design a highly active electrocatalyst for lithium-sulfur batteries. In the prepared graphene-cobalt oxide composite material, the constructed electrocatalyst-derived heterogeneous interface tightly connects the highly adsorbed oxide and the conductive graphene, which can achieve rapid adsorption, diffusion and conversion of polysulfides. At the same time, the prepared graphene-cobalt oxide composite material can be used to obtain a graphene shell with controllable thickness by changing the reaction temperature and growth time.

[0097] Compared with wet chemical methods, this scheme has higher cleanliness and controllability, and can ensure the cleanliness, tight connection and coordination of components of the graphene-cobalt oxide heterojunction, thereby giving the catalyst higher activity.

[0098] During the reaction, N2 is selected as the carrier gas to achieve N-doping of graphene. The use of plasma can cause intrinsic defects in graphene. The carbon active species with reducing ability generated during the reaction can regulate the valence state of cobalt in cobalt oxide, thereby enriching the composition of the catalyst.

[0099] The thickness of the graphene shell is controllable, the valence state of cobalt is variable, and the design flexibility is greatly improved. At the same time, it also has dual defects of nitrogen atoms and vacancies, which makes it have higher catalytic activity and helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0100] In general, the method for preparing a graphene-cobalt oxide composite material with controllable graphene thickness provided in an embodiment of the present invention uses plasma enhanced chemical vapor deposition to in-situ grow nitrogen-doped graphene with controllable thickness on cobalt tetroxide to design a highly active electrocatalyst for lithium-sulfur batteries. In the prepared graphene-cobalt oxide composite material, the constructed electrocatalyst-derived heterogeneous interface tightly connects the highly adsorbed oxide and the conductive graphene, which can achieve rapid adsorption, diffusion, and conversion of polysulfides and accelerate the reaction kinetics during charging and discharging. The thickness of the graphene shell is controllable, the valence state of cobalt is variable, and the design flexibility is greatly improved. At the same time, it also has dual defects of nitrogen atoms and vacancies, which makes it have higher catalytic activity, which helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0101] The electrode prepared by the electrode preparation method provided in the embodiment of the present invention can realize the rapid adsorption, diffusion and conversion of polysulfides, and accelerate the reaction kinetics during the charge and discharge process. It has dual defects of nitrogen atoms and vacancies, has higher catalytic activity, and helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0102] The diaphragm prepared by the diaphragm preparation method provided in the embodiment of the present invention can realize the rapid adsorption, diffusion and conversion of polysulfides and accelerate the reaction kinetics during the charge and discharge process. It has dual defects of nitrogen atoms and vacancies and has higher catalytic activity, which helps to solve the problems of short cycle life and poor cycle stability of lithium-sulfur batteries.

[0103] The battery provided by the embodiment of the present invention can achieve rapid adsorption, diffusion and conversion of polysulfides and accelerate the reaction kinetics during the charge and discharge process, thereby having a longer cycle life and good cycle stability.

[0104] As an option, considering that different electrode materials and diaphragm materials need to be prepared and tested frequently in laboratory work, but the amount of electrodes and diaphragms prepared at a time is not large, in order to facilitate the laboratory preparation of electrode plates and diaphragms, and to minimize material loss and reduce experimental costs, this embodiment also provides a stirring device. The stirring device can be used for stirring and dispersing when preparing positive electrode slurry or diaphragm slurry.

[0105] For details, please combine Figure 3~Figure 10 The stirring device includes: a mounting seat 100, a movable seat 200 and a stirring cup 300.

[0106] The mounting seat 100 is columnar in shape, and a mounting cavity is formed on one end surface of the mounting seat 100 . The mounting cavity extends along the axial direction of the mounting seat 100 , and the mounting cavity and the mounting seat 100 are coaxially arranged.

[0107] Along the depth direction of the installation cavity (the axial direction of the installation seat 100 ), the movable seat 200 is slidably fitted in the installation cavity, and the outer wall of the movable seat 200 is in contact with the inner wall of the installation cavity.

[0108] The bottom of the mixing cup 300 is accommodated and fixedly matched with the mouth of the installation cavity, and the side wall of the bottom of the mixing cup 300 is attached to and fixedly connected to the inner side wall of the mouth of the installation cavity. The mouth of the mixing cup 300 is detachably matched with a cover 310. The mixing cup 300 and the mounting seat 100 are coaxially arranged.

[0109] The baffle plate 320 is disposed inside the blending cup 300, and the baffle plate 320 is disposed perpendicular to the axis of the blending cup 300, and the outer periphery of the baffle plate 320 is in contact with the inner side wall of the blending cup 300. Along the axial direction of the blending cup 300, the baffle plate 320 can be slidably fitted in the blending cup 300, and the baffle plate 320 and the blending cup 300 are slidably sealed.

[0110] The movable seat 200 is fixedly mounted with a reference sleeve 210, which is arranged along the depth direction of the mounting cavity (the axial direction of the mounting seat 100). One end of the reference sleeve 210 is fixedly connected to the side of the movable seat 200 close to the mixing cup 300, and the other end penetrates the bottom of the mixing cup 300 and further penetrates the baffle 320. Along the axial direction of the reference sleeve 210, the bottom of the mixing cup 300 and the baffle 320 are both in a sliding sealing cooperation relationship with the reference sleeve 210. The reference sleeve 210 and the mixing cup 300 are coaxially arranged.

[0111] The movable seat 200 has an inner cavity, and the inner cavity of the movable seat 200 is located at a side of the reference sleeve 210 away from the stirring cup 300 and is spaced apart from the reference sleeve 210 .

[0112] The movable seat 200 is also equipped with a stirring shaft 220, which is rotatably accommodated in the reference sleeve 210, and the stirring shaft 220 is coaxially arranged with the reference sleeve 210. One end of the stirring shaft 220 extends into the inner cavity, and the stirring shaft 220 and the movable seat 200 are in a rotational matching relationship. The other end of the stirring shaft 220 extends along the reference sleeve 210 and extends outside the reference sleeve 210, that is, the stirring shaft 220 extends into the stirring cup 300. Along the axial direction of the stirring shaft 220, the stirring shaft 220 and the movable seat 200 are in a fixed matching relationship.

[0113] The stirring shaft 220 has an expanded diameter section 230, the outer diameter of which is the same as that of the reference sleeve 210, and the end surface of the expanded diameter section 230 away from the mouth of the stirring cup 300 is in contact with the end surface of the reference sleeve 210 away from the movable seat 200. The stirring shaft 220 and the reference sleeve 210 are rotationally sealed.

[0114] A driver 410 is disposed in the inner cavity of the movable seat 200 . The driver 410 is in transmission cooperation with the stirring shaft 220 to drive the stirring shaft 220 to rotate relative to the reference sleeve 210 .

[0115] The stirring shaft 220 has an axial through hole, which is coaxially arranged with the stirring shaft 220. A core 260 is disposed in the axial through hole, and the core 260 is slidably matched with the axial through hole along the axial direction of the stirring shaft 220. A first linear driver 420 is installed in the inner cavity of the movable seat 200, and the first linear driver 420 is in transmission cooperation with the core 260, and is used to drive the core 260 to move along the axial direction of the stirring shaft 220.

[0116] The outer wall of the diameter expansion section 230 is provided with a first groove 231 and a second groove 232 which are spaced apart from each other. The first groove 231 and the second groove 232 are both formed by depressions of the outer wall of the diameter expansion section 230 . The first groove 231 and the second groove 232 are both continuously extended in a ring shape along the circumference of the diameter expansion section 230 .

[0117] The first groove 231 is located at one end of the enlarged diameter section 230 away from the reference sleeve 210 and extends to one end of the enlarged diameter section 230 away from the reference sleeve 210. The second groove 232 is located at one end of the enlarged diameter section 230 close to the reference sleeve 210.

[0118] The hole wall of the axial through hole of the stirring shaft 220 is provided with a first cavity 233 and a second cavity 234 , and both the first cavity 233 and the second cavity 234 are formed by depressions in the hole wall of the axial through hole.

[0119] A first notch 235 communicating with the first cavity 233 is defined at one end of the first groove 231 close to the second groove 232 , and a second notch 236 communicating with the second cavity 234 is defined at one end of the second groove 232 close to the first groove 231 .

[0120] The first groove 231 contains a first stirring rod 240, one end of which is hinged to one end of the first groove 231 near the second groove 232, and the hinge axis of the first stirring rod 240 is arranged perpendicular to the axis of the stirring shaft 220. Along the circumference of the expanded diameter section 230, a plurality of first stirring rods 240 are arranged in the first groove 231, and the first stirring rods 240 are arranged evenly spaced. When the first stirring rods 240 are rotated and stored in the first groove 231, the first groove 231 can be filled.

[0121] The hinge shaft of the first stirring rod 240 has a first rack 241 arranged along its circumference, and the first rack 241 extends into the first cavity 233 through the first notch 235 .

[0122] The second groove 232 contains a second stirring rod 250, one end of which is hinged to one end of the second groove 232 near the first groove 231, and the hinge axis of the second stirring rod 250 is arranged perpendicular to the axis of the stirring shaft 220. Along the circumference of the expanded diameter section 230, a plurality of second stirring rods 250 are arranged in the second groove 232, and the second stirring rods 250 are arranged evenly spaced. When the second stirring rod 250 rotates and is received in the second groove 232, the second groove 232 can be filled.

[0123] Optionally, the second groove 232 can also be set to a strip extending axially along the expansion section 230 instead of a ring shape. In this case, only one second stirring rod 250 can be set in the second groove 232. When the second stirring rod 250 is received in the second groove 232, the second groove 232 is just filled.

[0124] Back to the present embodiment, the hinge shaft of the second stirring rod 250 has a second rack 251 arranged along its circumference, and the second rack 251 extends into the second cavity 234 through the second notch 236 .

[0125] The first transmission gear unit 242 is installed in the first cavity 233, and the second transmission gear unit 252 is installed in the second cavity 234. The side wall of the core 260 has a tooth portion (not shown in the figure) arranged along its axial direction, and the tooth portion is in transmission cooperation with the first rack 241 through the first transmission gear unit 242, and the tooth portion is in transmission cooperation with the second rack 251 through the second transmission gear unit 252. When the core 260 slides toward the side where the first linear actuator 420 is located, the core 260 drives the first stirring rod 240 to rotate and extend from the first groove 231 through the first transmission gear unit 242 and the first rack 241, and drives the second stirring rod 250 to rotate and extend from the second groove 232 through the second transmission gear unit 252 and the second rack 251.

[0126] The length of the first stirring rod 240 is greater than the length of the first groove 231, that is, when the first stirring rod 240 is received in the first groove 231, the end of the first stirring rod 240 away from the hinge axis will extend beyond the end surface of the expanded diameter section 230. The length of the second stirring rod 250 is adapted to the length of the second groove 232. The thickness of the first stirring rod 240 is adapted to the depth of the first groove 231, and the thickness of the second stirring rod 250 is adapted to the depth of the second groove 232.

[0127] A second linear driver 430 is disposed at the bottom of the installation cavity. The second linear driver 430 is in transmission cooperation with the movable seat 200 to drive the movable seat 200 to slide along the depth direction of the installation cavity.

[0128] A control rod 330 is fixedly connected to the side of the baffle 320 away from the cup mouth of the blending cup 300. The control rod 330 passes through the bottom of the blending cup 300, the movable seat 200 and the mounting seat 100. The outer end of the control rod 330 (the end away from the baffle 320) is in transmission cooperation with the third linear actuator 440, so as to control the baffle 320 to move in the blending cup 300 along the axial direction of the blending cup 300. The third linear actuator 440 is installed on an end surface of the mounting seat 100 away from the mouth of the mounting cavity.

[0129] In this embodiment, in the stirring device, the first stirring rod 240 has a protrusion 243 on one side close to the core 260 . When the first stirring rod 240 is received in the first groove 231 , the protrusion 243 is located on the side of the first stirring rod 240 close to the axis of the stirring shaft 220 .

[0130] When the first stirring rod 240 is received in the first groove 231, the end surface of the protrusion 243 close to the hinge axis of the first stirring shaft 220 just fits with the end of the stirring shaft 220 (i.e., the end of the expanded diameter section 230), and the side wall of the protrusion 243 away from the first stirring shaft 220 just fits with the hole wall of the axial through hole of the stirring shaft 220. That is to say, in this state, if the core body 260 extends out of the expanded diameter section 230, the side wall of the protrusion 243 can just fit with the outer side wall of the core body 260.

[0131] The working mode of the stirring device is: after the material to be stirred is put into the stirring cup 300 , the stirring cup 300 is closed by using the cover 310 .

[0132] In the initial state, if Figure 4 As shown, the core 260 is located at the dead point of movement near the mouth of the mixing cup 300. At this time, the end surface of the core 260 is flush with the mouth of the mixing cup 300, the first stirring rod 240 is received in the first groove 231, and the second stirring rod 250 is received in the second groove 232. The surface of the first stirring rod 240 is flush with the outer wall of the expanded diameter section 230, and the surface of the second stirring rod 250 is flush with the outer wall of the expanded diameter section 230. The first stirring rod 240 extends beyond the end surface of the expanded diameter section 230, and the first stirring rod 240 is in contact with the outer wall of the core 260 through the protrusion 243. The end surfaces of the first stirring rod 240 and the protrusion 243 away from the hinge axis are flush and are both flush with the end surface of the core 260. The end surfaces of the first stirring rod 240 and the protrusion 243 away from the hinge axis, as well as the end surface of the core 260, are in contact with the inner side of the cover 310. The baffle 320 is in contact with the bottom of the mixing cup 300 .

[0133] When you start stirring, Figure 5 As shown, the first linear actuator 420 drives the core 260 to slide toward the end where the first linear actuator 420 is located, the core 260 separates from the cover 310 and slides toward the inside of the diameter expansion section 230, and the first stirring rod 240 and the second stirring rod 250 rotate and extend from the first groove 231 and the second groove 232 (optionally, the rotation angles of the first stirring rod 240 and the second stirring rod 250 are both less than 90°). When the first stirring rod 240 and the second stirring rod 250 are smoothly extended, the end surface of the core 260 is just flush with the end surface of the diameter expansion section 230 (which can be achieved by controlling the transmission ratio of the first transmission gear unit 242 and the second transmission gear unit 252), and the ends of the first stirring rod 240 and the second stirring rod 250 are basically in contact with the inner wall of the stirring cup 300 (that is, only a small gap is left, and the size of the gap can be flexibly set). The driver 410 drives the stirring shaft 220 , and the stirring shaft 220 starts to rotate relative to the reference sleeve 210 and the core 260 , and the first stirring rod 240 and the second stirring rod 250 stir the material in the stirring cup 300 .

[0134] During the stirring process, the second linear drive 430 can be used to control the movable seat 200 to move closer to or away from the stirring cup 300, so that the reference sleeve 210, the stirring shaft 220 and the core 260 move as a whole along the axial direction of the stirring cup 300 to fully stir the materials at different positions in the stirring cup 300.

[0135] In particular, in order to fully stir the material that may adhere to the cover 310, the second linear actuator 430 can be used to control the movable seat 200 to approach the stirring cup 300, so that the first stirring rod 240 is close to the cover 310. By using the first linear actuator 420 to drive the core 260, the first stirring rod 240 can be at different angles relative to the enlarged diameter section 230. For the first stirring rod 240 at different angles, the distance between its end and the axis of the stirring cup 300 is different, and the distance between its end and the cover 310 is also different. When the first stirring rod 240 is at different angles, the second linear actuator 430 is used to adjust the distance between the movable seat 200 and the stirring cup 300 respectively, so that the end of the first stirring rod 240 at different angles can just fit the inner wall of the cover 310 (that is, only a small gap is left, and the size of the gap can be flexibly set), so that the purpose of cleaning and stirring the surface of the cover 310 by using the first stirring rod 240 at different opening angles can be achieved.

[0136] Similarly, the second stirring rod 250 may be used to clean and stir the surface of the baffle 320 to prevent material from adhering and improve stirring adequacy.

[0137] After stirring, Figure 6 As shown, the control core 260 is reset, and the first stirring rod 240 and the second stirring rod 250 are respectively stored back into the first groove 231 and the second groove 232. After removing the cover 310, the material in the stirring cup 300 can be poured out first, and then the baffle 320 can be driven by the third linear drive 440 to move to be flush with the cup mouth of the stirring cup 300, so that the remaining material in the stirring cup 300 can be fully discharged.

[0138] With this design, the stirring device is very suitable for frequent small-scale experiments in the laboratory and effectively reduces material loss.

[0139] Furthermore, the stirring device further comprises: a base 500 and a bracket 510 . The bracket 510 is mounted on the base 500 .

[0140] The mounting base 100 has rotating shafts on both sides. The mounting base 100 is rotatably matched with the bracket 510 via the rotating shafts, and the rotating shafts are driven by a servo motor (not shown in the figure).

[0141] With this design, the servo motor can be used to drive the mounting seat 100 to rotate relative to the bracket 510 during the stirring process, or the mounting seat 100 can be periodically flipped to promote stirring and improve the stirring and dispersion effect.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a diaphragm, It is characterized in that The steps include: S1. Place cobalt tetroxide with a particle size of 50-500 nm into a CVD tube furnace and evacuate the furnace until the basic pressure is less than or equal to 1 Pa; S2, purge the system with 100 sccm Ar gas flow, and generate RF plasma at a power of 40-100 W upstream near the furnace mouth; S3, when the reaction temperature reaches 400°C to 800°C, a carbon source gas flow of 10 sccm is introduced into the quartz tube, and after stabilization, a nitrogen gas flow of 5 to 10 sccm is continuously introduced to start growth, and the growth is carried out for 12 to 60 minutes to obtain a graphene-cobalt oxide composite material; The carbon source gas stream includes: at least one of a methane gas stream and a propylene gas stream; F1. Take the graphene-cobalt oxide composite material, conductive carbon black Super P and solid PVDF powder, add N-methylpyrrolidone and disperse for 2 hours to obtain a diaphragm slurry; wherein the mass ratio of the graphene-cobalt oxide composite material, the conductive carbon black Super P, the solid PVDF powder and the N-methylpyrrolidone is 21:6:3:120; F2, coating the diaphragm slurry on the surface of Celgrad-2500 diaphragm, and vacuum drying to obtain a diaphragm; wherein the thickness of the wet film formed by the diaphragm slurry on the surface of Celgrad-2500 diaphragm is 100 μm; The diaphragm slurry is stirred and dispersed by a stirring device; the stirring device comprises: a mounting seat, a movable seat and a stirring cup; A mounting cavity is formed at one end of the mounting seat; the movable seat is slidably fitted in the mounting cavity along the depth direction of the mounting cavity; the bottom of the blending cup is accommodated and fixedly fitted in the mouth of the mounting cavity, and the mouth of the blending cup is detachably fitted with a cover body; A baffle is disposed inside the mixing cup, the baffle is disposed perpendicular to the axis of the mixing cup, the outer periphery of the baffle is in contact with the inner wall of the mixing cup, and a sliding seal is formed between the baffle and the mixing cup; The movable seat is fixedly mounted with a reference sleeve, which is arranged along the depth direction of the mounting cavity and penetrates the bottom of the mixing cup and the baffle; along the axial direction of the reference sleeve, the mixing cup and the baffle are both slidably sealed with the reference sleeve; The movable seat has an inner cavity; the movable seat is also equipped with a stirring shaft, which is rotatably accommodated in the reference sleeve, one end of the stirring shaft extends to the inner cavity, and the other end extends outside the reference sleeve; along the axial direction of the stirring shaft, the stirring shaft is fixedly matched with the movable seat; The stirring shaft has an expanded diameter section, the outer diameter of the expanded diameter section is the same as the outer diameter of the reference sleeve, and the end surface of the expanded diameter section is in contact with the end surface of the reference sleeve away from the movable seat; The stirring shaft and the reference sleeve are rotatably sealed; a driver is arranged in the inner cavity, and the driver is in transmission cooperation with the stirring shaft; The stirring shaft has an axial through hole, which is coaxially arranged with the stirring shaft; a core is placed in the axial through hole, which is slidably matched with the axial through hole, and a first linear drive is installed in the inner cavity, which is in transmission cooperation with the core; The outer side wall of the expanded diameter section is provided with a first groove and a second groove arranged at intervals, and the first groove and the second groove both extend continuously in a ring shape along the circumference of the expanded diameter section; the first groove is located at an end of the expanded diameter section away from the reference sleeve, and the first groove penetrates to the end wall of the expanded diameter section; the second groove is located at an end of the expanded diameter section close to the reference sleeve; The hole wall of the axial through hole is provided with a first cavity and a second cavity; the first groove is provided with a first notch connected to the first cavity at one end close to the second groove, and the second groove is provided with a second notch connected to the second cavity at one end close to the first groove; A first stirring rod is placed in the first groove, one end of the first stirring rod is hinged to one end of the first groove close to the second groove, the hinge shaft of the first stirring rod has a first rack arranged along its circumference, and the first rack extends into the first cavity through the first notch; A second stirring rod is placed in the second groove, one end of the second stirring rod is hinged to one end of the second groove close to the first groove, the hinge shaft of the second stirring rod has a second rack arranged along its circumference, and the second rack extends into the second cavity through the second notch; A first transmission gear unit is installed in the first cavity, and a second transmission gear unit is installed in the second cavity; the side wall of the core body has a tooth portion arranged along its axial direction, and the tooth portion is in transmission cooperation with the first rack through the first transmission gear unit, and the tooth portion is in transmission cooperation with the second rack through the second transmission gear unit; The length of the first stirring rod is greater than the length of the first groove, and the length of the second stirring rod is adapted to the length of the second groove; the thickness of the first stirring rod is adapted to the depth of the first groove, and the thickness of the second stirring rod is adapted to the depth of the second groove; A second linear driver is disposed at the bottom of the installation cavity, and the second linear driver cooperates with the movable seat to drive the movable seat to move along the depth direction of the installation cavity; A control rod is fixedly connected to one side of the baffle away from the cup opening of the mixing cup, the control rod passes through the bottom of the mixing cup, the movable seat and the mounting seat, and the outer end of the control rod is in transmission cooperation with the third linear drive; In the stirring device, the first stirring rod has a protrusion on one side close to the core body, and when the first stirring rod is received in the first groove, the end of the protrusion fits with the end of the stirring shaft, and the protrusion fits with the side wall of the core body; The stirring device further comprises: a base and a bracket; the bracket is mounted on the base; The mounting seat is provided with rotating shafts on both sides, the mounting seat is rotatably matched with the bracket through the rotating shafts, and the rotating shafts are driven by a servo motor.

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