CN108666533B - Preparation method and application of sulfur electrode of lithium-sulfur battery - Google Patents

Preparation method and application of sulfur electrode of lithium-sulfur battery Download PDF

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CN108666533B
CN108666533B CN201810468684.6A CN201810468684A CN108666533B CN 108666533 B CN108666533 B CN 108666533B CN 201810468684 A CN201810468684 A CN 201810468684A CN 108666533 B CN108666533 B CN 108666533B
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sulfur
graphene
carbon
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electrode
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CN108666533A (en
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吕伟
石会发
牛树章
游从辉
杨全红
康飞宇
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Shenzhen International Graduate School of Tsinghua University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0419—Methods of deposition of the material involving spraying
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a preparation method of a sulfur electrode of a lithium-sulfur battery, and belongs to the technical field of lithium-sulfur batteries. The preparation method comprises the following steps: firstly, preparing a graphene layer/diaphragm substrate, and then spraying a carbon/sulfur composite material layer and the graphene layer on the graphene layer/diaphragm substrate by an electrostatic spraying method to obtain a sulfur electrode with a three-layer structure, wherein compared with the traditional method of coating and drying, the method effectively avoids the problem that electrode active substances are easy to fall off under the conditions of high loading and thick electrode, thereby ensuring the integrity of the electrode, improving the integral energy density of the electrode, and avoiding the use of the traditional metal current collector; the lithium-sulfur battery manufactured by the sulfur electrode prepared by the method has higher surface capacity and excellent cycling stability.

Description

Preparation method and application of sulfur electrode of lithium-sulfur battery
Technical Field
The invention relates to the technical field of lithium-sulfur batteries, in particular to a preparation method and application of a sulfur electrode of a lithium-sulfur battery;
background
Lithium ion batteries are widely used in efficient energy storage systems, such as energy industry and consumer electronics industry, but with the development of society, the traditional lithium ion batteries have difficulty in meeting the increasingly high requirements of the modern society on energy storage systems. The search for new high-capacity electrode materials and the acquisition of high-specific energy storage systems are the key points of energy storage and utilization at present.
The lithium-sulfur battery with sulfur as a positive electrode and metal lithium as a negative electrode shows up to 2600W h kg through electrochemical conversion reaction between the positive electrode and the negative electrode-1The theoretical specific energy of the anode material far exceeds that of the traditional lithium ion battery, and the anode material has rich natural sulfur reserves, wide sources and low priceAnd is environmentally friendly and is considered to be an ideal next-generation secondary battery. Through many years of scientific research and industrial exploration, the improvement of the capacity, efficiency and stability of the lithium-sulfur battery is greatly improved, but still faces many problems. Firstly, sulfur and a discharge product thereof, namely lithium sulfide, have poor lithium ion and electron conductivity, so that in the charging and discharging process, an active substance needs to be uniformly loaded on a conductive substrate, and smooth lithium ion transmission and reaction channels are ensured; secondly, polysulfide generated in the charging and discharging process is easy to cause serious 'shuttle effect', namely long-chain polysulfide generated in the discharging process of active substance sulfur passes through a battery diaphragm to react with lithium of a negative electrode, and short-chain polysulfide Li is generated on the surface of the lithium2S and Li2S2Precipitation, which causes a decrease in the utilization of the active substance and a decrease in the coulombic efficiency; third, the sulfur loading of the current lithium sulfur battery positive electrode is at a relatively low level, i.e., the sulfur content in the positive electrode material is less than 70 wt%, and the area loading is less than 2mg cm-2This results in the surface capacity (2mAh cm) of the lithium-sulfur battery-2) Much lower than the area capacity (4mAh cm) of the current commercial lithium ion battery-2). In order to increase the energy density of the positive electrode of the lithium sulfur battery, the sulfur loading amount needs to be further increased. However, increasing the sulfur loading tends to cause the following problems: (1) with the increase of the thickness of the sulfur-containing active material, the resistance on the ion diffusion and electron transfer process is increased, so that the utilization rate of sulfur is reduced, and the rate performance and the cycle stability of the positive electrode of the lithium-sulfur battery are deteriorated; (2) since the internal sulfur-containing active material cannot be fully utilized, the volumetric specific capacity of the positive electrode of the lithium-sulfur battery is greatly limited. The problem of easy cracking of the lithium-sulfur battery electrode also exists in the process of preparing the high-load lithium-sulfur battery electrode by using the traditional coating and drying method.
Disclosure of Invention
In view of the problems in the background art, an object of the present invention is to provide a method for preparing a sulfur electrode of a lithium-sulfur battery, which is simple to operate and easy for industrial production.
In order to achieve the purpose, the invention adopts the technical scheme that:
in the invention, for writing convenience, the graphene (graphene) is abbreviated as GN, correspondingly, the graphene layer coated on the diaphragm is abbreviated as GN-1, and the graphene layer electrostatically sprayed on the pole piece as a current collector is abbreviated as GN-2; carbon/sulfur composite material layers prepared by using carbon materials as electrode active substance carriers are abbreviated as C @ S; since the separator conventionally used in the art for manufacturing a secondary battery is made of a PP material, the separator according to the present invention is abbreviated as PP.
Sequentially spraying a carbon/sulfur composite material layer and a graphene layer on a graphene/diaphragm substrate by an electrostatic spraying method to obtain a sulfur electrode of a lithium-sulfur battery; in particular, the amount of the solvent to be used,
a preparation method of a sulfur electrode of a lithium-sulfur battery comprises the following steps:
s1, coating the graphene slurry on a diaphragm, and drying to obtain a graphene// diaphragm substrate marked as GN-1// PP;
s2, spraying the carbon/sulfur composite material dispersion liquid on the graphene/diaphragm substrate through an electrostatic spraying method to obtain a carbon @ sulfur composite material layer// graphene layer-1// diaphragm layer, and marking the carbon @ sulfur composite material layer// graphene layer-1// diaphragm layer as a C @ S// GN-1// PP substrate;
s3, spraying the graphene dispersion liquid on the C @ S// GN-1// PP substrate through an electrostatic spraying method to obtain a sulfur electrode with a three-layer structure, namely a graphene layer-2// carbon @ sulfur composite layer// graphene layer-1// diaphragm layer, which is marked as GN-2// C @ S// GN-1// PP; and the graphene layer obtained by electrostatic spraying is used as a current collector.
In the preparation method, step S1 of the invention is to coat the graphene slurry on the graphene layer formed on the diaphragm, which has two functions: (1) to build a polysulfide barrier layer; (2) because the material receiving substrate needs to be conductive during the electrostatic spraying process, a conductive receiving layer can be constructed on the insulated battery diaphragm; the carbon/sulfur composite layer obtained in step S2 is an active material layer, sulfur reversibly reacts during charging and discharging to provide capacity, and the carbon material compounded with the carbon layer is used as a conductive substrate for loading active material sulfur; the graphene layer obtained in the step S3 can be used as a current collector to effectively collect and transmit charges, so that the rate capability of the lithium-sulfur battery is enhanced, the use of heavy metal current collectors such as aluminum and the like is avoided, the weight of inactive components is greatly reduced, and the energy density of the whole battery is improved.
Preferably, the graphene coated on the separator in step S1 may be obtained commercially or by self-manufacturing, and the preparation method is 1 of a redox method, a mechanical exfoliation method, an electrochemical method, or a liquid phase exfoliation method; the graphene obtained by the oxidation-reduction method has a thinner lamellar thickness and a larger specific surface area, the porosity of a barrier layer formed after coating is larger, the transmission of lithium ions between a positive electrode and a negative electrode cannot be hindered, and the graphene obtained by the oxidation-reduction method is further optimized, namely the graphene is obtained by carrying out heat treatment reduction on graphene oxide powder, wherein the heat treatment temperature is 300-1000 ℃;
preferably, the graphene slurry in step S1 further includes a binder, which may be a binder conventionally used in the art, and is further preferably a combination of 1 or more than 2 of polyvinylidene fluoride, polyvinylpyrrolidone, polyacrylic acid, or sodium carboxymethylcellulose; polyvinylidene fluoride is particularly preferable;
preferably, the solvent for graphene slurry in step S1 is deionized water or N-methylpyrrolidone, and more preferably N-methylpyrrolidone;
preferably, the negative voltage range used in the electrostatic spraying method in steps S2 and S3 is-1 to-5 kV, and the positive voltage range is +10 to +20 kV.
Preferably, the spraying rate of the electrostatic spraying method in the steps S2 and S3 is 5-20 ml h-1(ii) a More preferably 8 to 12ml h-1。
Preferably, the carbon/sulfur composite dispersion liquid in step S2 is a dispersion liquid in which a carbon-sulfur composite is dispersed in an organic solvent containing a conductive agent and a binder;
preferably, the carbon material in the carbon/sulfur composite material is a combination of 1 or more than 2 of nano carbon material, activated carbon or porous carbon;
preferably, the mass part of the conductive agent is 0-35 wt%, more preferably 5-30 wt%, and particularly preferably 8-15 wt% of the carbon/sulfur composite material;
preferably, the conductive agent may be a conventional conductive agent used in the art, and further preferably 1 or a combination of 2 or more of carbon nanotubes, acetylene black, conductive carbon black, or artificial graphite;
preferably, the mass part of the binder is 5-15% wt of the carbon/sulfur composite material; further preferably 8-12% wt;
preferably, the binder may be a binder conventionally used in the art, and further preferably 1 or a combination of 2 or more of polyvinylidene fluoride, polyvinylpyrrolidone, polyacrylic acid, or sodium carboxymethylcellulose; particularly preferred is polyvinylpyrrolidone; preferably, the average molecular weight of the polyvinylpyrrolidone is 110 to 140 ten thousand, and more preferably 120 to 130 ten thousand;
preferably, the organic solvent is ethanol.
Preferably, the graphene dispersion liquid in step S3 is formed by dispersing graphene into a solvent under the action of a dispersant;
preferably, the solvent of the graphene dispersion liquid is deionized water or 1-methyl-2-pyrrolidone;
preferably, the mass part of the dispersing agent is 10-20% wt of graphene; further preferably 14 to 16% by weight;
preferably, the dispersant is polyvinylpyrrolidone;
preferably, the average molecular weight of the polyvinylpyrrolidone is 3 to 6 ten thousand, and more preferably 4 to 5 ten thousand;
preferably, the graphene in step S3 may be obtained commercially or by self-manufacturing, and the preparation method is 1 of a redox method, a mechanical exfoliation method, an electrochemical method, and a liquid phase exfoliation method; the graphene obtained by the mechanical stripping method has higher conductivity (600S cm)-1) And the lamella is more smooth, and after being sprayed on a substrate, a uniform and compact charge collection layer and a conductive layer can be formed, so that the requirements of a current collector are better met, and the graphene obtained by a mechanical stripping method is further optimized.
The invention also aims to provide a sulfur electrode of a lithium sulfur battery, which is prepared by the method and has a three-layer structure, wherein the sulfur electrode sequentially comprises a polysulfide barrier layer, an active material layer and a current collector from bottom to top;
the polysulfide barrier layer is a graphene layer obtained by coating graphene on a diaphragm by an industrial coating method, and the active substance layer is a carbon/sulfur composite material layer obtained by spraying carbon/sulfur composite material dispersion liquid on a graphene/diaphragm substrate by an electrostatic spraying method; the current collector is the graphene layer obtained by electrostatically spraying the graphene dispersion liquid.
Preferably, the thickness of the polysulfide barrier layer is 2-10 μm; more preferably 2 to 5 μm.
Preferably, the thickness of the active material layer is 20 to 250 μm, which is mainly determined by the surface loading amount of the active material, the higher the surface loading amount, the larger the thickness, and the higher the surface loading amount of the sulfur electrode can be obtained by adjusting the electrostatic spraying time.
Preferably, the thickness of the current collector is 2-10 μm, and more preferably 2-5 μm.
The invention also provides a lithium-sulfur battery, which comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is the sulfur electrode prepared by the method.
Advantageous effects
(1) The sulfur electrode with the three-layer structure prepared by the method has the advantages that the three layers of substances are directly and closely contacted, so that the utilization rate of active substances is greatly improved; the polysulfide barrier layer and the current collector layer are made of graphene materials with good conductivity, the two-dimensional lamellar structure of the polysulfide barrier layer and the current collector layer can be in close contact with the active material layer in the middle layer, and meanwhile, the polysulfide barrier layer and the current collector layer are used as double current collectors in the electrode, so that good electron transmission in the electrode is guaranteed under the condition that the electrode is thickened; moreover, the active material layer obtained by the electrostatic spraying method has a porous structure, so that lithium ions can be rapidly transmitted even under the conditions of high loading capacity and thick electrode of the active material; meanwhile, the design of the three-layer all-carbon layer structure avoids the use of a metal current collector.
(2) In the electrostatic spraying process of the method, the active substances can be naturally and uniformly deposited on the conductive substrate in the process of atomizing and evaporating the solvent in the mixed slurry containing the active substances, the slow evaporation process of the solvent (such as an organic solvent NMP or water) in the traditional coating process is eliminated, the conditions of uneven stress and cracking in the drying process of the interior of the electrode are avoided, the integrity of the electrode is ensured, and the integral energy density of the electrode is improved.
(3) The surface loading capacity of the sulfur electrode prepared by the method can reach 9.4mg cm-2The surface capacity of the nano-silver particles reaches 6.2mAhcm-2The surface capacity (4mAh cm) of the lithium ion battery is obviously higher than that of the current lithium ion battery-2) Discharge specific capacity at 0.1C of 439.9mAhg-1The coulombic efficiency at 200 cycles was 96.9%.
Drawings
FIG. 1 is a picture of a sulfur electrode prepared according to the present invention:
(a) a graphene/separator (GN-1// PP) substrate;
(b) c @ S// GN-1// PP substrate formed by electrostatically spraying a carbon/sulfur composite layer on the graphene/diaphragm;
(c) the sulfur electrode GN-2// C @ S// GN-1// PP;
FIG. 2 is an SEM picture of a cross section of a sulfur electrode prepared according to the present invention;
FIG. 3 is a graph of cycle performance of lithium-sulfur batteries made of sulfur electrodes with different surface loading amounts prepared by the present invention;
Detailed Description
According to the invention, firstly, an industrial coating method is utilized to coat graphene on a battery diaphragm substrate to form a graphene// diaphragm (GN-1// PP) substrate which is used as a conductive substrate; secondly, ultrasonically dispersing the carbon/sulfur composite material in an organic solvent containing a conductive agent and a binder uniformly to obtain a carbon/sulfur composite material dispersion liquid, and spraying the carbon/sulfur composite material dispersion liquid on a graphene// diaphragm substrate by using an electrostatic spraying method to obtain a C @ S// GN-1// PP substrate; finally, carrying out electrostatic spraying on the graphene layer on the obtained C @ S// GN-1// PP substrate to obtain a sulfur electrode GN-2// C @ S// GN-1// PP with a three-layer structure; here, the graphene layer of electrostatic spraying is used as a current collector layer, and all substances in the three-layer structure are in direct close contact, so that the utilization rate of active substances is greatly improved. According to the invention, the carbon/sulfur composite material layer and the graphene layer are sequentially sprayed on the graphene/diaphragm substrate by the electrostatic spraying method, so that the sulfur electrode of the high-load lithium-sulfur battery can be obtained, and the method is simple and easy to operate; meanwhile, in the electrostatic spraying process of the method, the active substances can be naturally and uniformly deposited on the conductive substrate in the solvent atomization and evaporation process of the active substance mixed slurry, so that the situation that the electrode active substances are easy to crack and fall off in the solvent evaporation process under the condition of high-load and thick electrodes is avoided.
The technical solution of the present invention will be described in detail below with reference to specific examples.
Example 1
Dispersing and stirring 80mg of graphene GN-1 subjected to heat treatment at 900 ℃ and 14.1mg of PVDF binder obtained by a redox method in an NMP solvent for 6 hours to form slurry, coating the slurry on a celgard 2400 battery diaphragm, and drying the battery diaphragm at 60 ℃, wherein the thickness of GN-1 is about 3 mu m;
80mg of commercial carbon sphere BP 2000/sulfur compound, 10mg of multi-walled carbon nanotube and 10mg of polyvinylpyrrolidone (molecular weight of 130,0000) are ultrasonically dispersed and mixed in 10ml of alcohol to obtain a mixed solution, the dispersion is placed in a 10ml medical needle tube and then is sprayed on a GN-1// PP substrate in an electrostatic spraying mode, and the spraying parameters are set as follows: negative pressure of-1 kV, positive pressure of 13kV and spraying speed of 10ml h-1. Repeating the above steps, and continuously spraying on a substrate of 5cm x 5cm for 1h 20min to obtain a surface load of 4.2mg cm-2The thickness of the pole piece is about 105 μm;
commercial mechanically exfoliated graphene dispersion was placed in the above 10ml syringe at a graphene concentration of 5mg ml-1The content of polyvinylpyrrolidone (PVP) dispersant is 1/6 of graphene, and the solvent is NMP. And repeating the spraying process to obtain a layer of highly conductive graphene current collector uniformly covered on the C @ S active matter, wherein the spraying thickness is 2 micrometers.
Example 2
Dispersing and stirring 80mg of graphene GN-1 subjected to heat treatment at 800 ℃ and 20mg of PVDF binder obtained by a redox method in an NMP solvent for 6 hours to form slurry, coating the slurry on a celgard 2400 battery diaphragm, and drying the battery diaphragm at 60 ℃, wherein the GN-1 is about 4 mu m thick;
80mg of commercial carbon sphere BP 2000/sulfur compound, 12mg of multi-walled carbon nanotube and 10mg of polyvinylpyrrolidone (molecular weight of 130,0000) are ultrasonically dispersed and mixed in 10ml of alcohol to obtain a mixed solution, the dispersion is placed in a 10ml medical needle tube and then is sprayed on a GN-1// PP substrate in an electrostatic spraying mode, and the spraying parameters are set as follows: negative pressure of-1 kV, positive pressure of 13kV and spraying speed of 10ml h-1. Repeating the above steps, and continuously spraying on a substrate of 5cm x 5cm for 1h 40min to obtain a surface load of 5.4mg cm-2The thickness of the pole piece is about 135 μm;
the commercial mechanically exfoliated graphene dispersion was loaded into a 10ml syringe in the above procedure, with a graphene concentration of 5mg ml-1, a polyvinylpyrrolidone (PVP) dispersant content of 1/6 for graphene, and a solvent of NMP. And repeating the spraying process to obtain a layer of highly conductive graphene current collector uniformly covered on the C @ S active matter, wherein the spraying thickness is 3 micrometers.
Example 3
Dispersing and stirring 80mg of graphene GN-1 subjected to heat treatment at 700 ℃ and obtained by a redox method and 8.8mg of PVDF binder in an NMP solvent for 6 hours to form slurry, coating the slurry on a celgard 2400 battery diaphragm, and drying the battery diaphragm at 60 ℃, wherein the thickness of GN-1 is about 6 mu m;
80mg of commercial carbon sphere BP 2000/sulfur compound, 10mg of acetylene black and 12mg of polyvinylpyrrolidone (molecular weight of 130,0000) are ultrasonically dispersed and mixed in 10ml of alcohol to obtain a mixed solution, the dispersion is placed in a 10ml medical needle tube and then is sprayed on a GN-1// PP substrate in an electrostatic spraying mode, and the spraying parameters are set as follows: negative pressure of-2 kV, positive pressure of 15kV and spraying speed of 10ml h-1. Repeating the above steps, and continuously spraying on a substrate of 5cm x 5cm for 2h 15min to obtain a surface load of 7.1mg cm-2The thickness of the pole piece is about 192 μm;
the commercial mechanically exfoliated graphene dispersion was loaded into a 10ml syringe in the above procedure, with a graphene concentration of 5mg ml-1Polyethylene (II)The content of the polyvinylpyrrolidone (PVP) dispersant is 1/6 of graphene, and the solvent is NMP. And repeating the spraying process to obtain a layer of highly conductive graphene current collector uniformly covered on the C @ S active matter, wherein the spraying thickness is 4 micrometers.
Example 4
Dispersing and stirring 80mg of graphene GN-1 subjected to heat treatment at 500 ℃ and 20mg of PVDF binder obtained by a redox method in an NMP solvent for 6 hours to form slurry, coating the slurry on a diaphragm of a celgard 2400 battery, and drying the battery diaphragm at 60 ℃, wherein the thickness of GN-1 is about 4 mu m;
80mg of commercial carbon sphere BP 2000/sulfur compound, 6mg of oxidized carbon black and 10mg of polyvinylpyrrolidone (molecular weight of 130,0000) are subjected to ultrasonic dispersion mixing in 10ml of alcohol to obtain a mixed solution, the dispersion is placed in a 5ml medical needle tube and then is sprayed on a GN-1// PP substrate in an electrostatic spraying mode, and the spraying parameters are set as follows: negative pressure of-1 kV, positive pressure of 13kV, spraying speed of 20ml h-1. Continuously spraying the mixture on a substrate of 5cm x 5cm for 1h 50min by repeating the above steps to obtain a surface loading of 9.4mg cm-2The thickness of the pole piece is about 250 mu m;
the commercial mechanically exfoliated graphene dispersion was loaded into a 10ml syringe in the above procedure, with a graphene concentration of 5mg ml-1The content of polyvinylpyrrolidone (PVP) dispersant is 1/6 of graphene, and the solvent is NMP. And repeating the spraying process to obtain a layer of highly conductive graphene current collector uniformly covered on the C @ S active matter, wherein the spraying thickness is 2 micrometers.
Example 5
Dispersing and stirring 80mg of graphene GN-1 subjected to heat treatment at 600 ℃ and 14.1mg of PVDF binder obtained by a redox method in an NMP solvent for 6 hours to form slurry, coating the slurry on a celgard 2400 battery diaphragm, and drying the battery diaphragm at 60 ℃, wherein the thickness of GN-1 is about 2 mu m;
80mg of commercial carbon sphere BP 2000/sulfur compound, 8mg of acetylene black and 8mg of polyvinylpyrrolidone (molecular weight of 130,0000) are ultrasonically dispersed and mixed in 10ml of alcohol to obtain a mixed solution, the dispersion is placed in a 5ml medical needle tube and then is sprayed on a GN-1// PP substrate in an electrostatic spraying mode, and the spraying parameters are set as follows: negative pressure of-2 kV, positive pressure of 15kV, spraying speed of 20ml h-1. Repeating the above steps to continuously spray on a substrate of 5cm x 5cm for 40min to obtain a surface loading of 4.3mg cm-2The thickness of the pole piece is about 112 μm;
the commercial mechanically exfoliated graphene dispersion was loaded into a 5ml syringe in the above procedure, with a graphene concentration of 3mg ml-1The content of polyvinylpyrrolidone (PVP) dispersant is 1/5 of graphene, and the solvent is NMP. And repeating the spraying process to obtain a layer of highly conductive graphene current collector uniformly covered on the C @ S active matter, wherein the spraying thickness is 5 micrometers.
Example 6
Dispersing and stirring 80mg of graphene GN-1 subjected to heat treatment at 400 ℃ and 8.8mg of PVDF binder obtained by a redox method in an NMP solvent for 5 hours to form slurry, coating the slurry on a celgard 2400 battery diaphragm, and drying the battery diaphragm at 60 ℃, wherein the thickness of GN-1 is about 5 mu m;
80mg of commercial carbon sphere BP 2000/sulfur compound, 5mg of oxidized carbon black and 12mg of polyvinylpyrrolidone (molecular weight of 130,0000) are ultrasonically dispersed and mixed in 10ml of alcohol to obtain a mixed solution, the dispersion is placed in a 5ml medical needle tube and then is sprayed on a GN-1// PP substrate in an electrostatic spraying mode, and the spraying parameters are set as follows: negative pressure of-2 kV, positive pressure of 15kV and spraying speed of 10ml h-1. Continuously spraying the mixture on a substrate of 5cm x 5cm for 3h 20min by repeating the above steps to obtain a surface loading of 9.1mg cm-2The thickness of the pole piece is about 235 mu m;
filling the mechanically stripped graphene dispersion liquid into a 5ml needle tube in the step, wherein the concentration of graphene is 5mg ml-1The content of polyvinylpyrrolidone (PVP) dispersant is 1/6 of graphene, and the solvent is NMP. And repeating the spraying process to obtain the high-conductivity graphene current collector uniformly covered on the C @ S active material layer, wherein the spraying thickness is 3 micrometers.
Comparative example 1
80mg of commercial carbon sphere BP 2000/sulfur complex, 10mg of multi-walled carbon nanotubes and 10mg of polyvinylpyrrolidone (molecular weight 130,0000) were dispersed and stirred in NMP solvent for 6 hours to form a slurry, coated on a commercial aluminum foil, dried at 60 ℃ and then tested and compared with a 18mm diameter circular disc.
The sulfur electrodes obtained in the above examples and comparative examples were used to fabricate lithium-sulfur batteries, and the specific operation steps were as follows:
(1) preparing a positive pole piece: the sulfur electrode prepared in the embodiment 1 of the invention is used as the positive electrode of the lithium-sulfur button cell, and the substrate is provided with a diaphragm, so that a battery diaphragm does not need to be additionally used;
(2) assembling the lithium-sulfur battery: and drying a dropper, a diaphragm, a positive and negative electrode shell and the like used in the battery assembling process in an oven at 80 ℃, and drying the prepared positive electrode piece in an oven at 60 ℃. The button cell was assembled in an argon atmosphere glove box in the following order: the lithium ion battery comprises a positive electrode shell, a positive electrode plate, electrolyte, a diaphragm, the electrolyte, a lithium plate, a gasket, an elastic sheet and a negative electrode shell, wherein the electrolyte on two sides of the diaphragm is 30 mu L, the electrolyte solvent is a mixed solvent of DME and DOL with the volume ratio of 1:1, the lithium salt is 1M LiTFSI, and the additive is 1% LiNO3. The subsequent positive casing was compacted at the bottom and negative casing at the top using a button cell sealer for testing. Fig. 1 is a picture of each structural layer of the sulfur electrode prepared by the present invention: (a) GN-1// PP substrate; (b) is a C @ S// GN-1// PP substrate; (c) the electrode was a sulfur electrode GN-2// C @ S// GN-1// PP. Fig. 2 is a scanning electron microscope picture of a cross section of the sulfur electrode prepared by the method, and as can be seen from fig. 2, the sulfur electrode prepared by the method has a three-layer structure, wherein the upper layer and the lower layer are graphene layers, the middle layer is a carbon/sulfur composite material layer, and the thickness of the middle layer is about 20 μm.
And (3) electrochemical performance testing: and (3) performing cycle performance test on the half cell at 25 ℃ by using a Land cell test system, wherein the charge-discharge current density is 0.1C, and the charge-discharge voltage range is 1.7-2.8V.
FIG. 3 is a graph showing the cycle stability of lithium-sulfur batteries made of sulfur electrodes with different surface loading amounts prepared by the present invention,
as can be seen from FIG. 3, the surface loading of the sulfur electrode prepared by the present invention is as high as 9.4mg cm-2The surface capacity of the nano-silver particles reaches 6.2mAh cm-2The surface capacity (4mAh cm) of the lithium ion battery is obviously higher than that of the current lithium ion battery-2) After 200 weeks of circulation, the discharge specific capacity at 0.1C rate is 439.9mAh g-1The coulombic efficiency was 96.9%. Therefore, the sulfur electricity obtained by the preparation method of the inventionHas high surface capacity and excellent cycling stability.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims (15)

1. A preparation method of a sulfur electrode of a lithium-sulfur battery is characterized by comprising the following steps:
s1, preparing a graphene/diaphragm substrate: coating the graphene slurry on a diaphragm, and drying to obtain a graphene// diaphragm substrate marked as GN-1// PP;
s2, spraying the carbon/sulfur composite material dispersion liquid on the graphene/diaphragm substrate through an electrostatic spraying method to obtain a carbon @ sulfur composite material layer// graphene layer-1// diaphragm layer, and marking the carbon @ sulfur composite material layer// graphene layer-1// diaphragm layer as a C @ S// GN-1// PP substrate;
s3, spraying the graphene dispersion liquid on the C @ S// GN-1// PP substrate through an electrostatic spraying method to obtain a graphene layer-2// carbon @ sulfur composite material layer// graphene layer-1// membrane layer, and marking the membrane layer as GN-2// C @ S// GN-1// PP.
2. The method according to claim 1, wherein the graphene is prepared by 1 of a redox method, a mechanical exfoliation method, an electrochemical method, and a liquid phase exfoliation method in step S1.
3. The method according to claim 1 or 2, wherein the graphene slurry in step S1 further contains a binder, and the binder is a combination of 1 or more than 2 of polyvinylidene fluoride, polyvinylpyrrolidone, polyacrylic acid, or sodium carboxymethylcellulose;
in the step S1, the solvent of the graphene slurry is deionized water or N-methylpyrrolidone.
4. The production method according to claim 1, wherein the carbon/sulfur composite dispersion liquid in step S2 is a dispersion liquid in which a carbon/sulfur composite is dispersed in an organic solvent containing a conductive agent and a binder;
the carbon material of the carbon/sulfur composite material is a combination of 1 or more than 2 of nano carbon material and porous carbon;
the conductive agent accounts for 0-35 wt% of the carbon/sulfur composite material in parts by mass;
the conductive agent is a combination of 1 or more than 2 of carbon nano tubes, conductive carbon black or artificial graphite;
the mass part of the binder is 5-15 wt% of the carbon/sulfur composite material;
the binder is 1 or more than 2 of polyvinylidene fluoride, polyvinylpyrrolidone, polyacrylic acid or sodium carboxymethylcellulose;
the average molecular weight of the polyvinylpyrrolidone is 110-140 ten thousand;
the organic solvent is ethanol.
5. The preparation method according to claim 4, wherein the conductive agent is 5 to 30 wt% of the carbon/sulfur composite material; the mass part of the binder is 8-12 wt% of the carbon/sulfur composite material; the average molecular weight of the polyvinylpyrrolidone is 120-130 ten thousand.
6. The preparation method according to claim 4, wherein the conductive agent accounts for 8-15 wt% of the carbon/sulfur composite material in parts by mass.
7. The method of claim 1, wherein the electrostatic spraying method in steps S2 and S3 uses a negative voltage ranging from-1 kV to-5 kV and a positive voltage ranging from +10kV to +20 kV.
8. The method of claim 1, wherein the electrostatic spraying in the steps S2 and S3 has a spraying rate of 5 to 20 ml-h-1。
9. The method of claim 8, wherein the electrostatic spraying in the steps S2 and S3 has a spraying rate of 8-12 ml-h-1。
10. The method according to claim 1, wherein the graphene dispersion liquid in step S3 is formed by dispersing graphene into a solvent under the action of a dispersant;
the mass part of the dispersing agent is 10-20% wt of graphene;
the dispersing agent is polyvinylpyrrolidone;
the average molecular weight of the polyvinylpyrrolidone is 3-6 ten thousand;
the solvent of the graphene dispersion liquid is deionized water or 1-methyl-2 pyrrolidone.
11. The preparation method according to claim 10, wherein the dispersant is 14 to 16% wt of graphene; the average molecular weight of the polyvinylpyrrolidone is 4-5 ten thousand.
12. The method according to claim 1, wherein the graphene is prepared by 1 of a redox method, a mechanical exfoliation method, an electrochemical method, and a liquid phase exfoliation method in step S3.
13. A sulfur electrode for a lithium sulfur battery, prepared according to the method of any one of claims 1 to 12, consisting of a polysulfide barrier layer, an active material layer, and a current collector;
the thickness of the polysulfide barrier layer is 2-10 mu m;
the thickness of the active material layer is 20-250 μm;
the thickness of the current collector is 2-10 mu m.
14. The lithium sulfur battery sulfur electrode of claim 13, wherein the polysulfide barrier layer has a thickness of 2 to 5 μm; the thickness of the current collector is 2-5 mu m.
15. A lithium-sulfur battery, characterized in that the positive electrode is the sulfur electrode of claim 13 or 14.
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