CN112072067B - Carbon-sulfur composite positive electrode for lithium-sulfur battery and preparation method thereof - Google Patents

Carbon-sulfur composite positive electrode for lithium-sulfur battery and preparation method thereof Download PDF

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CN112072067B
CN112072067B CN202010986303.0A CN202010986303A CN112072067B CN 112072067 B CN112072067 B CN 112072067B CN 202010986303 A CN202010986303 A CN 202010986303A CN 112072067 B CN112072067 B CN 112072067B
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黄佳琦
李博权
赵梦
彭彦琪
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Beijing Institute of Technology BIT
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Abstract

The invention discloses a carbon-sulfur composite positive electrode for a lithium-sulfur battery and a preparation method thereof, belonging to the technical field of lithium-sulfur batteries. The carbon-sulfur composite positive electrode is composed of a carbon-sulfur composite layer and a conductive carbon layer which are sequentially coated on a current collector; the carbon-sulfur composite layer is composed of a sulfur material, a carbon material I and an aqueous binder, and the conductive carbon layer is composed of a carbon material II and an organic binder. The double-layer carbon-sulfur composite positive electrode prepared by the method can realize the construction of a high-energy-density lithium-sulfur battery with high sulfur capacity, high sulfur content, high specific capacity and long cycle life. The preparation method of the composite anode is simple and convenient to operate, low in cost and easy to amplify, effectively promotes the design and preparation of the lithium-sulfur battery anode, and provides new possibility for the practicability of the lithium-sulfur battery with high energy density.

Description

Carbon-sulfur composite positive electrode for lithium-sulfur battery and preparation method thereof
Technical Field
The invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a carbon-sulfur composite positive electrode for a lithium-sulfur battery and a preparation method thereof.
Background
High-performance rechargeable batteries play an indispensable role in the fields of electric vehicles, consumer electronics, smart grids, and the like. However, the energy density of the currently commercialized lithium ion batteries tends to its theoretical limit, and it is impossible to achieve more than 400 Whkg −1 High energy density requirements. The lithium-sulfur battery uses elemental sulfur as a positive electrode active material and metal lithium as a negative electrode active material, and the theoretical energy density is as high as 2600 Whkg −1 And is considered to be a promising high energy density secondary battery system and receives a wide attention. However, practical application of lithium sulfur batteries still faces many challenges, including low electron conductivity of charge and discharge products sulfur and lithium sulfide, significant volume deformation during cycling, and dissolution and shuttling of polysulfide intermediates.
In 2009, nazarLF et al proposed a strategy for sulfur/nanocarbon composite positive electrodes, which can effectively solve the basic problem of electronic ion insulation of sulfur and lithium sulfide. Subsequently, carbon-sulfur composite positive electrodes have received extensive research and attention. However, the mass fraction of sulfur in conventional carbon-sulfur composite positive electrodes is typically less than 60%, and the surface loading of sulfur is typically less than 2mgcm −2 The actual specific capacity of sulfur is usually less than 1000 mAhg −1 Therefore, it is impossible to construct a lithium-sulfur battery having a high energy density. Therefore, the development of the carbon-sulfur composite anode with high sulfur content, high sulfur loading capacity and high specific capacity is very important.
Simply increasing the sulfur content and sulfur loading results in a substantial reduction in its specific capacity and cycling performance due to the electronic ionic insulation of sulfur and lithium sulfide. The structural design of the carbon-sulfur composite anode can effectively improve the electrochemical performance of the anode with high sulfur content and high sulfur loading. Among them, a carbon-sulfur double-layer composite structure has received a certain attention. In the prior art, an integrated membrane electrode is formed by overlapping and thermally compounding two layers of materials, and a mechanical thermal compounding method is adopted to process a bottom current collector and a sulfur composite material layer, but the method easily causes sublimation of sulfur materials in a positive electrode, so that unnecessary structural change and loss of active sulfur are caused; meanwhile, the method modifies the carbon material on the diaphragm and then mechanically compounds the carbon-sulfur composite layer, and the solid-solid interface of the mechanical compounding can increase the impedance of the carbon-sulfur anode, reduce the ionic conductivity and the electronic conductivity, and is not beneficial to the capacity exertion and the maintenance of the high-sulfur-content and high-sulfur-carrying capacity sulfur anode. In the prior art, a porous carbon layer is coated on the surface of the carbon-sulfur composite layer by a vacuum low-temperature plasma sputtering method. However, the design of the carbon-sulfur composite positive electrode in this work cannot achieve the goals of high sulfur content and high sulfur loading at the same time, and the preparation process of the composite positive electrode is complex, has high requirements for experimental precision, and is not suitable for a large-scale practical system. On the other hand, the electrochemical performance of the high-sulfur content and high-sulfur loading carbon-sulfur composite positive electrode can be improved by using nano carbon or other organic/inorganic materials with a multi-stage structure to be compounded with sulfur. However, the introduction of the complex nanostructure component increases the complexity of the preparation process and increases the manufacturing cost of the electrode, which is not favorable for the large-scale preparation of the carbon-sulfur composite positive electrode, and thus, is difficult to be practically applied to the construction of a high-energy density lithium-sulfur battery. Therefore, lithium sulfur battery anodes with high sulfur content, high sulfur loading, and high performance still need further rational design and practical development.
Disclosure of Invention
In order to solve the problems, the invention provides a carbon-sulfur composite positive electrode for a lithium-sulfur battery, which is formed by a carbon-sulfur composite layer and a conductive carbon layer which are sequentially coated on a current collector;
the carbon-sulfur composite layer is composed of a sulfur material, a carbon material I and an aqueous binder, and the conductive carbon layer is composed of a carbon material II and an organic binder.
The mass fraction of the water-based binder in the carbon-sulfur composite layer is 5 to 15 percent, and the mass fraction of the sulfur material is 65 to 85 percent; the balance being carbon material I;
the mass fraction of the organic binder in the conductive carbon layer is 1 to 10 percent, and the balance is carbon material II.
The thickness of the conductive carbon layer is 0.1 to 100 mu m; the thickness of the carbon-sulfur composite layer is 20 to 100 mu m.
The water-based binder in the carbon-sulfur composite layer is one or more of polyacrylic acid, carboxymethyl cellulose, LA133 and polyvinyl alcohol; the carbon material I is one or more of carbon nano tube, graphene, carbon black, mesocarbon microbeads, fullerene, porous carbon and activated carbon; the sulfur material is sublimed sulfur; the surface loading capacity of the sulfur material is 2 to 8 mg cm −2 。
The organic binder in the conductive carbon layer is polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, polyvinylpyrrolidone, styrene butadiene rubber, fluorineOne or more of rubber, polyurethane and polyacrylate; the carbon material II is one or more of carbon nano tube, graphene, acetylene black, mesocarbon microbeads, microporous carbon, macroporous carbon, carbon black and Ketjen black; the surface loading amount of the carbon material is 0.1 to 2mg cm −2 。
The current collector is an aluminum foil, and the thickness of the aluminum foil is 15 to 50 mu m.
The preparation method of the carbon-sulfur composite positive electrode for the lithium-sulfur battery comprises the following steps:
1) Mixing the used carbon material I and a sulfur material, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 1 to 5 hours to prepare a carbon-sulfur compound; adding water into the carbon-sulfur composite to obtain a dispersion liquid with the solid content of 20-40%, ball-milling the dispersion liquid for 1-5 hours, adding a water-based binder, and homogenizing for 10-120 minutes to prepare carbon-sulfur composite slurry;
2) Coating the carbon-sulfur composite slurry on a current collector with the thickness of 15 to 50 micrometers in a blade mode, and drying the current collector for 2 to 24 hours in vacuum at the temperature of 50 to 70 ℃ to prepare a carbon-sulfur composite layer;
3) Mixing a carbon material II and an organic binder, wherein the mass fraction of the organic binder is 1-10%, then adding an organic solvent to obtain a dispersion liquid with the solid content of 5-25%, and carrying out ultrasonic treatment for 0.5-12 hours to prepare a conductive carbon slurry;
4) And (3) uniformly coating the conductive carbon slurry on the carbon-sulfur composite layer obtained in the step 2) by using a scraper, and drying in vacuum at 50-90 ℃ for 6-48 hours to obtain the carbon-sulfur composite positive electrode.
The organic solvent is one or a mixture of N-methyl pyrrolidone, dimethyl sulfoxide, butanol, acetonitrile, tetrahydrofuran and N, N-dimethylformamide.
The preparation method of the carbon-sulfur composite positive electrode for the lithium-sulfur battery comprises the following steps:
1) Mixing carbon nanotubes and sublimed sulfur according to the following ratio of 6:13, sealing and heating to 155 ℃, and carrying out hot melting for 5 hours at constant temperature to prepare a carbon-sulfur compound; adding water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 20%, ball-milling the dispersion liquid for 1 hour, adding polyacrylic acid with the mass fraction of 5%, and homogenizing for 10 minutes to prepare carbon-sulfur compound slurry;
2) Scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 15 microns by using a scraper, and drying for 24 hours in vacuum at the temperature of 50 ℃ to prepare a carbon-sulfur composite layer; the thickness of the carbon-sulfur composite layer is 20 mu m, the mass fraction of sulfur in the carbon-sulfur composite layer is 65 percent, and the surface loading capacity of sulfur is 2mg cm −2 ；
3) Mixing carbon nano tube and polytetrafluoroethylene according to the weight ratio of 99:1, adding N-methyl pyrrolidone to obtain a dispersion liquid with the solid content of 5%, and performing ultrasonic treatment for 0.5 hour to obtain conductive carbon slurry;
4) Uniformly coating the conductive carbon slurry on a carbon-sulfur composite layer, and drying for 48 hours in vacuum at 50 ℃ to prepare a carbon-sulfur composite anode; wherein the surface loading of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 0.1. Mu.m.
The preparation method of the carbon-sulfur composite positive electrode for the lithium-sulfur battery comprises the following steps:
1) Mixing carbon nanotubes with carbon black and sublimed sulfur according to a ratio of 1:5, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 3 hours to prepare a carbon-sulfur compound; adding water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 3 hours, adding polyvinyl alcohol with the mass fraction of 10%, and homogenizing for 60 minutes to prepare carbon-sulfur compound slurry;
2) Scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 50 microns by using a scraper, and drying the aluminum foil in vacuum at the temperature of 60 ℃ for 10 hours to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 60 microns, the mass fraction of sulfur in the carbon-sulfur composite layer is 75%, and the surface loading capacity of sulfur is 8 mg cm −2 ；
3) Ketjen black and polyacrylate were mixed in a ratio of 9:1, adding N, N-dimethylformamide to obtain a dispersion liquid with the solid content of 20%, and performing ultrasonic treatment for 6 hours to obtain conductive carbon slurry;
4) Uniformly blade-coating conductive carbon slurry on a carbon-sulfur composite layer, and vacuum-drying at 70 ℃ for 24 hours to prepare the carbon-sulfur composite anode, wherein the surface loading of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 10 μm.
The prepared carbon-sulfur composite anode has the first-circle discharge specific capacity higher than 1250 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 200 cycles; the first-circle discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
The invention has the beneficial effects that:
1. the invention overcomes the problems of low sulfur content, low sulfur surface loading capacity, low specific discharge capacity and poor cycle stability of the traditional lithium-sulfur battery anode, designs a double-layer composite carbon-sulfur anode, comprises a carbon-sulfur composite layer based on a water system binder and a conductive carbon layer based on the water system binder, and constructs a lithium-sulfur battery with high sulfur loading capacity, high sulfur content, high specific capacity and long cycle life;
2. the bottleneck that practical high-energy density lithium-sulfur batteries are difficult to effectively prepare in large quantities is overcome, a simple preparation method of the carbon-sulfur composite positive electrode of the lithium-sulfur battery is provided, and a reasonable design and preparation idea of the positive electrode of the lithium-sulfur battery is provided;
3. the lithium-sulfur battery composite positive electrode simultaneously realizes the lithium-sulfur battery with high sulfur capacity and high sulfur content, and the lithium-sulfur battery has higher sulfur utilization rate, more electrochemical active sites, high specific capacity, long cycle life, stable coulombic efficiency and higher energy density;
4. the design promotes the research and preparation of the lithium-sulfur battery anode, and provides new possibility for the research of practical lithium-sulfur batteries with high energy density.
Drawings
FIG. 1 is a schematic diagram of a composite positive electrode plate of a lithium-sulfur battery;
the device comprises a current collector 1, a carbon-sulfur composite layer 2 and a conductive carbon layer 3.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
the invention provides a preparation method of a composite positive electrode of a lithium-sulfur battery, which comprises the following steps:
1) And mixing the carbon material I used in the carbon-sulfur composite layer with elemental sulfur according to a ratio, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 1 to 5 hours to prepare the carbon-sulfur composite. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 20-40%, ball-milling the dispersion liquid for 1-5 hours, adding a water-based binder, and homogenizing for 10-120 minutes to prepare carbon-sulfur compound slurry; wherein the sulfur in the carbon-sulfur composite slurry is sublimed sulfur; the carbon material selected by the carbon-sulfur composite layer slurry is one or more of carbon nano tube, graphene, carbon black, mesocarbon microbeads, fullerene, porous carbon and activated carbon; the water-based binder in the carbon-sulfur composite slurry is one or more of polyacrylic acid, carboxymethyl cellulose, LA133 and polyvinyl alcohol.
2) Coating carbon-sulfur composite slurry on a current collector with the thickness of 15-50 micrometers by a scraper, and drying the current collector for 2-24 hours at the temperature of 50-70 ℃ in vacuum to prepare a carbon-sulfur composite layer 2, wherein the thickness of the carbon-sulfur composite layer is 20-100 micrometers, the mass fraction of a water-based binder in the carbon-sulfur composite layer is 5-15%, the mass fraction of sulfur in the carbon-sulfur composite layer is 65-85%, the balance is a carbon material I, and the surface loading capacity of the sulfur is 2-8 mg cm −2 。
3) Mixing a carbon material II used in the conductive carbon layer with an organic binder, wherein the mass fraction of the organic binder is 1-10%, adding an organic solvent with a certain volume to obtain a dispersion liquid with the solid content of 5-25%, and performing ultrasonic treatment for 0.5-12 hours to obtain conductive carbon slurry; the carbon material selected by the conductive carbon slurry is one or more of carbon nano tube, graphene, acetylene black, mesocarbon microbeads, microporous carbon, macroporous carbon, carbon black and Ketjen black; the organic solvent is one or a mixture of N-methylpyrrolidone, dimethyl sulfoxide, butanol, acetonitrile, tetrahydrofuran and N, N-dimethylformamide; the organic binder is one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, polyvinylpyrrolidone, styrene butadiene rubber, fluorinated rubber, polyurethane and polyacrylate.
4) Uniformly coating the conductive carbon slurry on the carbon-sulfur composite layer based on the water-based binder in the step 2) by using a scraper with a certain thickness, and drying for 6 to 48 hours in vacuum at the temperature of between 50 and 90 ℃ to prepare the conductive carbon slurryA carbon-sulfur composite positive electrode shown in FIG. 1, which is composed of a carbon-sulfur composite layer 2 and a conductive carbon layer 3 on the carbon-sulfur composite layer, wherein the surface loading of carbon in the conductive carbon layer is 0.1 to 2mg cm −2 . The thickness of the conductive carbon layer in the composite positive electrode is 0.1 to 100 mu m.
The first-circle discharge specific capacity of the lithium-sulfur battery composite positive electrode prepared by the invention is higher than 1250 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 200 cycles; the first-circle discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 1
And (3) preparing the carbon-sulfur composite positive electrode of the lithium-sulfur battery by using polyacrylic acid as a binder of the carbon-sulfur composite layer and polytetrafluoroethylene as a binder of the conductive carbon layer.
Mixing carbon nanotubes and sublimed sulfur according to the following ratio of 6:13, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 5 hours to prepare the carbon-sulfur compound. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 20%, ball-milling the dispersion liquid for 1 hour, adding polyacrylic acid with the mass fraction of 5%, and homogenizing for 10 minutes to prepare carbon-sulfur compound slurry;
scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 15 micrometers by using a scraper, and drying for 24 hours in vacuum at 50 ℃ to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 20 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 65%, and the surface loading capacity of sulfur is 2mg cm −2 ；
Mixing carbon nano tube and polytetrafluoroethylene according to the weight ratio of 99:1, then adding a certain volume of N-methyl pyrrolidone to obtain a dispersion liquid with the solid content of 5%, and performing ultrasonic treatment for 0.5 hour to prepare conductive carbon slurry;
uniformly coating the conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer at 50 ℃ in vacuum for 48 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer arranged on the carbon-sulfur composite layer, wherein the surface loading of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 0.1. Mu.m.
Is prepared byThe first-circle discharge specific capacity of the obtained carbon-sulfur composite positive electrode is higher than 1250 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 200 cycles; the first-coil discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 2
And (3) preparing the carbon-sulfur composite positive electrode of the lithium-sulfur battery by using carboxymethyl cellulose as a binder of the carbon-sulfur composite layer and polyvinylidene fluoride as a binder of the conductive carbon layer.
Mixing graphene and sublimed sulfur according to the weight ratio of 2:7, heating to 155 ℃, and carrying out hot melting for 4 hours at constant temperature to prepare the carbon-sulfur composite. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 30%, ball-milling the dispersion liquid for 2 hours, adding 10% by mass of carboxymethyl cellulose, and homogenizing for 30 minutes to prepare carbon-sulfur compound slurry;
scraping and coating the carbon-sulfur composite slurry on an aluminum foil with the thickness of 20 micrometers by using a scraper, and drying for 10 hours in vacuum at 60 ℃ to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 50 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 70%, and the surface loading of sulfur is 4mg cm −2 ；
Graphene and polyvinylidene fluoride were mixed as 95:5, adding a certain volume of dimethyl sulfoxide to obtain a dispersion liquid with the solid content of 10%, and performing ultrasonic treatment for 1 hour to obtain conductive carbon slurry;
uniformly coating the conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer at 60 ℃ in vacuum for 36 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 10 μm.
The first-circle discharge specific capacity of the prepared carbon-sulfur composite anode is higher than 1150 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 150 cycles; the first-circle discharge specific capacity is higher than 850 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 3
And preparing the carbon-sulfur composite positive electrode of the lithium-sulfur battery by using LA133 as a binder of the carbon-sulfur composite layer and polyethylene oxide as a binder of the conductive carbon layer.
Carbon black and sublimed sulfur were mixed in a ratio of 2:15, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 3 hours to prepare the carbon-sulfur compound. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 3 hours, adding 15% by mass of LA133, and homogenizing for 60 minutes to prepare carbon-sulfur compound slurry;
scraping and coating the carbon-sulfur composite slurry on an aluminum foil with the thickness of 25 micrometers by using a scraper, and drying the aluminum foil for 2 hours in vacuum at 70 ℃ to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 70 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 75%, and the surface loading of sulfur is 6mg cm −2 ；
Acetylene black and polyethylene oxide were mixed according to a 9:1, adding butanol with a certain volume to obtain a dispersion liquid with the solid content of 15%, and performing ultrasonic treatment for 3 hours to prepare conductive carbon slurry;
uniformly coating the conductive carbon slurry on the prepared carbon-sulfur composite layer based on the water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer for 24 hours in vacuum at 70 ℃ to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and the conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 10 μm.
The prepared carbon-sulfur composite anode has the first-circle discharge specific capacity higher than 1100 mAh g under the multiplying power of 0.5C −1 The capacity retention rate after 150 cycles is higher than 80%, and the discharge specific capacity of the first cycle is higher than 800 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 4
And preparing the carbon-sulfur composite positive electrode of the lithium-sulfur battery by using polyvinyl alcohol as a binder of the carbon-sulfur composite layer and polyvinylpyrrolidone as a binder of the conductive carbon layer.
And (3) mixing the mesocarbon microbeads and sublimed sulfur according to the weight ratio of 4:15, sealing and heating to 155 ℃, and carrying out hot melting at constant temperature for 2 hours to prepare the carbon-sulfur composite. Adding a certain amount of water into the carbon-sulfur composite to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 4 hours, adding polyvinyl alcohol with the mass fraction of 10%, and homogenizing for 90 minutes to prepare carbon-sulfur composite slurry;
scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 30 micrometers by using a scraper, and drying for 10 hours in vacuum at 60 ℃ to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 80 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 75%, and the surface loading capacity of sulfur is 6mg cm −2 ；
And (3) mixing mesocarbon microbeads and polyvinylpyrrolidone according to the weight ratio of 9:1, adding a certain volume of acetonitrile to obtain a dispersion liquid with a solid content of 20%, and performing ultrasonic treatment for 6 hours to obtain conductive carbon slurry;
uniformly coating conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer at 80 ℃ in vacuum for 12 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading of carbon in the conductive carbon layer is 1mg cm −2 The thickness of the conductive carbon layer was 50 μm.
The prepared carbon-sulfur composite anode has the first-circle discharge specific capacity higher than 1250 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 200 cycles; the first-circle discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 5
And (3) preparing the carbon-sulfur composite positive electrode of the lithium-sulfur battery by using polyacrylic acid as a binder of the carbon-sulfur composite layer and styrene butadiene rubber as a binder of the conductive carbon layer.
Fullerene and sublimed sulfur were mixed according to a ratio of 1:8, sealing and heating to 155 ℃, and carrying out hot melting for 1 hour at constant temperature to prepare the carbon-sulfur composite. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 5 hours, adding polyacrylic acid with the mass fraction of 5%, and homogenizing for 120 minutes to prepare carbon-sulfur compound slurry;
mixing carbonThe sulfur composite slurry is coated on an aluminum foil with the thickness of 35 mu m by a scraper, and is dried for 10 hours in vacuum at the temperature of 60 ℃ to prepare a carbon-sulfur composite layer, the thickness of the carbon-sulfur composite layer is 100 mu m, the mass fraction of sulfur in the carbon-sulfur composite layer is 80 percent, and the surface loading capacity of sulfur is 8 mg cm −2 ；
And (3) mixing microporous carbon and styrene butadiene rubber according to the weight ratio of 9:1, adding a certain volume of tetrahydrofuran to obtain a dispersion liquid with a solid content of 25%, and performing ultrasonic treatment for 12 hours to obtain conductive carbon slurry;
uniformly coating the conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer for 6 hours in vacuum at 90 ℃ to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer arranged on the carbon-sulfur composite layer, wherein the surface loading amount of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 10 μm.
The first-circle discharge specific capacity of the prepared carbon-sulfur composite anode is higher than 1350 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 250 cycles; the first-circle discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 6
And (3) preparing the carbon-sulfur composite positive electrode of the lithium-sulfur battery by using carboxymethyl cellulose as a binder of the carbon-sulfur composite layer and using fluorinated rubber as a binder of the conductive carbon layer.
Porous carbon and sublimed sulfur were mixed according to 1:8, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 5 hours to prepare the carbon-sulfur compound. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 20%, ball-milling the dispersion liquid for 1 hour, adding 10% by mass of carboxymethyl cellulose, and homogenizing for 10 minutes to prepare carbon-sulfur compound slurry;
scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 40 mu m by using a scraper, and drying the aluminum foil in vacuum at 60 ℃ for 10 hours to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 25 mu m, the mass fraction of sulfur in the carbon-sulfur composite layer is 80%, and the surface loading capacity of sulfur is 2mg cm −2 ；
The macroporous carbon and the fluorinated rubber are mixed according to the weight ratio of 9:1, adding a certain volume of N, N-dimethylformamide to obtain a dispersion liquid with a solid content of 10%, and performing ultrasonic treatment for 1 hour to obtain conductive carbon slurry;
uniformly coating the conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer at 70 ℃ in vacuum for 24 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer arranged on the carbon-sulfur composite layer, wherein the surface loading amount of carbon in the conductive carbon layer is 1mg cm −2 The thickness of the conductive carbon layer was 50 μm.
The prepared carbon-sulfur composite positive electrode has the first-circle discharge specific capacity higher than 1250 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 200 cycles; the first-coil discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 7
And LA133 is used as a binder of a carbon-sulfur composite layer, and polyurethane is used as a binder of a conductive carbon layer to prepare the carbon-sulfur composite positive electrode of the lithium-sulfur battery.
Mixing activated carbon and sublimed sulfur according to the weight ratio of 1:17, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 4 hours to prepare the carbon-sulfur compound. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 30%, ball-milling the dispersion liquid for 2 hours, adding 10% by mass of LA133, and homogenizing for 30 minutes to prepare carbon-sulfur compound slurry;
scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 45 micrometers by using a scraper, and drying the aluminum foil in vacuum at 60 ℃ for 10 hours to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 40 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 85%, and the surface loading capacity of sulfur is 4mg cm −2 ；
Carbon black and polyurethane were mixed as follows 9:1, adding a certain volume of tetrahydrofuran to obtain a dispersion liquid with a solid content of 15%, and performing ultrasonic treatment for 3 hours to obtain conductive carbon slurry;
uniformly coating conductive carbon slurry on the prepared carbon-sulfur composite layer based on the water-based binder by using a scraper with a certain thicknessVacuum drying at 70 deg.C for 24 hr to obtain carbon-sulfur composite anode composed of carbon-sulfur composite layer and conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading of carbon in the conductive carbon layer is 2mg cm −2 The thickness of the conductive carbon layer was 100. Mu.m.
The prepared carbon-sulfur composite anode has the first-circle discharge specific capacity higher than 1250 mAh g under the multiplying power of 0.5C −1 The capacity retention rate is higher than 80% after 200 cycles; the first-circle discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 8
And preparing the carbon-sulfur composite positive electrode of the lithium-sulfur battery by using polyvinyl alcohol as a binder of the carbon-sulfur composite layer and polyacrylic ester as a binder of the conductive carbon layer.
Mixing a mixture of carbon nanotubes and carbon black with sublimed sulfur according to a ratio of 1:5, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 3 hours to prepare the carbon-sulfur compound. Adding a certain amount of water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 3 hours, adding 10% by mass of polyvinyl alcohol, and homogenizing for 60 minutes to prepare carbon-sulfur compound slurry;
scraping and coating the carbon-sulfur composite slurry on an aluminum foil with the thickness of 50 micrometers by using a scraper, and drying for 10 hours in vacuum at 60 ℃ to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 60 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 75%, and the surface loading of sulfur is 6mg cm −2 ；
Ketjen black and polyacrylate were mixed in a ratio of 9:1, adding a certain volume of N, N-dimethylformamide to obtain a dispersion liquid with a solid content of 20%, and performing ultrasonic treatment for 6 hours to obtain conductive carbon slurry;
uniformly coating conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer for 24 hours in vacuum at 70 ℃ to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 10 μm.
The prepared carbon-sulfur composite anode has the first-circle discharge specific capacity higher than 1250 mAh g under the multiplying power of 0.5C −1 The capacity retention rate after 200 cycles is higher than 80%, and the first cycle discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.
Example 9
The mixture of polyacrylic acid and carboxymethyl cellulose is used as a binder of a carbon-sulfur composite layer, and the mixture of polytetrafluoroethylene and polyvinylidene fluoride is used as a binder of a conductive carbon layer to prepare the carbon-sulfur composite positive electrode of the lithium-sulfur battery.
Mixing carbon nano tubes, graphene mixture and sublimed sulfur according to the ratio of 1:8, sealing and heating to 155 ℃, and carrying out hot melting at constant temperature for 2 hours to prepare the carbon-sulfur composite. Adding a certain amount of water into the carbon-sulfur composite to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 4 hours, adding a mixture of polyacrylic acid and carboxymethyl cellulose with the mass fraction of 10%, and homogenizing for 90 minutes to prepare carbon-sulfur composite slurry;
scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 20 micrometers by using a scraper, and drying the aluminum foil in vacuum at 60 ℃ for 10 hours to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 50 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 80%, and the surface loading capacity of sulfur is 4mg cm −2 ；
Mixing a mixture of carbon nanotubes and graphene and a mixture of polytetrafluoroethylene and polyvinylidene fluoride in a ratio of 9:1, adding a mixture of N-methyl pyrrolidone and acetonitrile with a certain volume to obtain a dispersion liquid with a solid content of 25%, and performing ultrasonic treatment for 12 hours to obtain conductive carbon slurry;
uniformly coating the conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper with a certain thickness, and drying the carbon-sulfur composite layer at 70 ℃ in vacuum for 24 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer arranged on the carbon-sulfur composite layer, wherein the surface loading amount of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 10 μm.
The prepared carbon-sulfur composite anode has high first-circle discharge specific capacity under the multiplying power of 0.5CAt 1250 mAh g −1 The capacity retention rate after 200 cycles is higher than 80%, and the first-cycle discharge specific capacity is higher than 950 mAh g under the multiplying power of 2.0C −1 And the capacity retention rate is higher than 80% after 100 cycles.

Claims (3)

1. A carbon-sulfur composite positive electrode for a lithium-sulfur battery is characterized in that:
preparing a carbon-sulfur composite positive electrode of the lithium-sulfur battery by using polyvinyl alcohol as a water-based binder of a carbon-sulfur composite layer and polyvinylpyrrolidone as an organic binder of a conductive carbon layer;
1) And (3) mixing the mesocarbon microbeads and sublimed sulfur according to the ratio of 4:15, sealing and heating to 155 ℃, and carrying out hot melting at constant temperature for 2 hours to prepare a carbon-sulfur compound; adding water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 4 hours, adding polyvinyl alcohol with the mass fraction of 10%, and homogenizing for 90 minutes to prepare carbon-sulfur compound slurry;
2) Scraping and coating the carbon-sulfur composite slurry on an aluminum foil with the thickness of 30 micrometers by using a scraper, and drying for 10 hours in vacuum at 60 ℃ to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 80 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 75%, and the surface loading of sulfur is 6mg cm −2 ；
3) And (3) mixing mesocarbon microbeads and polyvinylpyrrolidone according to the weight ratio of 9:1, adding acetonitrile to obtain a dispersion liquid with the solid content of 20%, and performing ultrasonic treatment for 6 hours to obtain conductive carbon slurry;
4) Uniformly coating conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper, and drying the carbon-sulfur composite layer at 80 ℃ in vacuum for 12 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading amount of carbon in the conductive carbon layer is 1mg cm −2 The thickness of the conductive carbon layer was 50 μm.
2. A carbon-sulfur composite positive electrode for a lithium-sulfur battery is characterized in that:
preparing a carbon-sulfur composite positive electrode of the lithium-sulfur battery by using LA133 as a water-based binder of a carbon-sulfur composite layer and polyurethane as an organic binder of a conductive carbon layer;
1) Mixing activated carbon and sublimed sulfur according to the weight ratio of 1:17, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 4 hours to prepare a carbon-sulfur compound; adding water into the carbon-sulfur compound to obtain a dispersion liquid with the solid content of 30%, ball-milling the dispersion liquid for 2 hours, adding 10% by mass of LA133, and homogenizing for 30 minutes to prepare carbon-sulfur compound slurry;
2) Scraping the carbon-sulfur composite slurry on an aluminum foil with the thickness of 45 micrometers by using a scraper, and drying the aluminum foil in vacuum at 60 ℃ for 10 hours to prepare a carbon-sulfur composite layer, wherein the thickness of the carbon-sulfur composite layer is 40 micrometers, the mass fraction of sulfur in the carbon-sulfur composite layer is 85%, and the surface loading capacity of sulfur is 4mg cm −2 ；
3) Carbon black and polyurethane were mixed as follows 9:1, adding tetrahydrofuran to obtain a dispersion liquid with the solid content of 15%, and performing ultrasonic treatment for 3 hours to obtain conductive carbon slurry;
4) Uniformly coating conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper, and drying the carbon-sulfur composite layer at 70 ℃ in vacuum for 24 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading amount of carbon in the conductive carbon layer is 2mg cm −2 The thickness of the conductive carbon layer was 100. Mu.m.
3. A carbon-sulfur composite positive electrode for a lithium-sulfur battery is characterized in that:
preparing a carbon-sulfur composite positive electrode of the lithium-sulfur battery by using polyvinyl alcohol as a water-based binder of a carbon-sulfur composite layer and polyacrylic ester as an organic binder of a conductive carbon layer;
1) Mixing a mixture of carbon nanotubes and carbon black with sublimed sulfur according to a ratio of 1:5, sealing and heating to 155 ℃, and carrying out constant-temperature hot melting for 3 hours to prepare a carbon-sulfur compound; adding water into the carbon-sulfur composite to obtain a dispersion liquid with the solid content of 40%, ball-milling the dispersion liquid for 3 hours, adding polyvinyl alcohol with the mass fraction of 10%, and homogenizing for 60 minutes to prepare carbon-sulfur composite slurry;
2) Spreading the carbon-sulfur composite slurry on an aluminum foil with the thickness of 50 mu m by a scraper, and drying the aluminum foil for 10 hours in vacuum at the temperature of 60 ℃ to prepare the carbon-sulfur composite slurryThe thickness of the carbon-sulfur composite layer is 60 mu m, the mass fraction of sulfur in the carbon-sulfur composite layer is 75 percent, and the surface loading capacity of sulfur is 6mg cm −2 ；
3) Ketjen black and polyacrylate were mixed in a ratio of 9:1, then adding N, N-dimethylformamide to obtain a dispersion liquid with the solid content of 20%, and carrying out ultrasonic treatment for 6 hours to prepare conductive carbon slurry;
4) Uniformly coating conductive carbon slurry on a prepared carbon-sulfur composite layer based on a water-based binder by using a scraper, and drying the carbon-sulfur composite layer at 70 ℃ in vacuum for 24 hours to prepare the carbon-sulfur composite anode consisting of the carbon-sulfur composite layer and a conductive carbon layer on the carbon-sulfur composite layer, wherein the surface loading amount of carbon in the conductive carbon layer is 0.1mg cm −2 The thickness of the conductive carbon layer was 10 μm.
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