CN110970597B - A flexible sponge-like porous electrode for lithium-sulfur battery and its application - Google Patents
A flexible sponge-like porous electrode for lithium-sulfur battery and its application Download PDFInfo
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- XKTYXVDYIKIYJP-UHFFFAOYSA-N 3h-dioxole Chemical compound C1OOC=C1 XKTYXVDYIKIYJP-UHFFFAOYSA-N 0.000 description 1
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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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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- 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
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- Secondary Cells (AREA)
Abstract
本发明公开一种锂硫电池用柔性海绵状多孔电极，将有机高分子树脂与碳/硫复合物混合，通过蒸汽相转化法制备而成柔性海绵状多孔电极。在制备柔性海绵状多孔电极过程中，靠近集流体侧的高分子树脂彼此交联固化，使电极从集流体脱落形成柔性电极，在穿戴式和便携式电池方面有广泛的应用前景。与应用于锂硫电池的常规电极相比，柔性海绵状多孔电极有较为规整的孔结构，孔径分布集中；将碳/硫复合物紧紧包覆在其中，提高了粘结剂的粘结性能，可用于制备高担量电极，更利于发展高能量密度电池。综上所述，柔性海绵状多孔电极作为锂硫电池正极，在电极制备工艺、提高电极活性物质担量和电池性能等各方面都表现出巨大的优势，具有良好的应用前景。
The invention discloses a flexible sponge-like porous electrode for a lithium-sulfur battery. The flexible sponge-like porous electrode is prepared by mixing an organic polymer resin and a carbon/sulfur composite through a vapor phase transformation method. In the process of preparing flexible sponge-like porous electrodes, the polymer resins close to the current collector are cross-linked and cured, so that the electrodes fall off from the current collectors to form flexible electrodes, which have broad application prospects in wearable and portable batteries. Compared with the conventional electrodes used in lithium-sulfur batteries, the flexible sponge-like porous electrodes have a more regular pore structure and a concentrated pore size distribution; the carbon/sulfur composite is tightly wrapped in it, which improves the bonding performance of the binder. , which can be used to prepare high-load electrodes, which is more conducive to the development of high-energy-density batteries. In summary, flexible sponge-like porous electrodes, as cathodes of lithium-sulfur batteries, show great advantages in electrode preparation process, increase the loading of electrode active materials, and battery performance, and have good application prospects.
Description
Technical Field
The invention relates to a flexible spongy porous electrode for a lithium-sulfur battery.
Background
Among the commercialized secondary batteries, the lithium-sulfur battery, as a new electrochemical energy storage secondary battery, has a high specific discharge capacity (1675mAh g)-1) High theoretical specific energy (2600Wh kg)-1) And the active substance sulfur has the advantages of large natural abundance, low cost, low toxicity, environmental protection and the like, and has good application prospect.
Currently, the Li-S battery mainly focuses on the research of electrode materials, and neglects the optimization of electrode structure design and electrode preparation process design. In the drying process of the traditional Li-S battery anode preparation, firstly, an electrode is unshaped, stacking and drying cannot be carried out, the occupied area is large, and the electrode is easy to collide, so that the loss of an electrode material is caused; secondly, in the traditional drying method, the crystallization degree of the binder is high, the electrode material with high pore volume has poor cohesiveness to a high specific surface, the prepared electrode has serious cracks, and the electrode material gradually falls off from the current collector along with the increase of the sulfur content of the active substance; finally, in the electrode drying process, the solvent is volatilized, the dried electrode is in a compact stacking structure, and the ion transmission in the electrode is blocked; all of the above problems will seriously hinder the further development of Li-S batteries. In addition, the development of flexible lithium sulfur electrodes is crucial in the face of a large market for built-in flexible power supplies for bulky flexible and wearable electronic devices. Currently, most of the common flexible electrodes are made of flexible one-dimensional and two-dimensional materials, such as carbon nanotubes, carbon fibers or graphene, which can be intertwined or stacked. How to use more cost-effective 0D or 3D active materials and conductive agents to avoid the active materials from falling off under bending or high load becomes a new research hotspot.
The preparation of the flexible spongy porous electrode is not limited by the dimension of the material, has certain flexibility and has wide application prospect in the aspects of wearable and portable batteries. The flexible spongy porous electrode has a more regular pore structure, the pore size and the porosity can be adjusted, and the pore size distribution is concentrated; the electrolyte has higher liquid absorption rate and porosity, and is beneficial to adsorbing more electrolyte, so that polysulfide dissolved in the electrolyte is fixed on one side of the positive electrode, the fly shuttle of the polysulfide is reduced, the synergistic effect of the fly shuttle and a skin layer formed on the surface of the electrode is reduced, the cycle performance of the battery is improved, the lithium ion transmission is facilitated, and the rate capability of the battery is improved; and the binders are crosslinked with each other in the steam phase conversion process, so that the carbon/sulfur compound is tightly coated in the binder, the binding property of the binder is improved, and the binder can be used for preparing high-load electrodes and is more beneficial to developing batteries with high energy density. The flexible spongy porous electrode is used as the anode material of the lithium-sulfur battery, and has the advantages of good cohesiveness, wide material selection range, simple process, low production cost, environment friendliness and the like. The performance of the lithium-sulfur battery is further improved by adjusting the technological parameters of the flexible spongy porous electrode, and the method has important practical significance.
Disclosure of Invention
The invention aims to provide a flexible spongy porous electrode for a lithium-sulfur battery.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a positive electrode for a lithium-sulfur battery is prepared by mixing organic polymer resin with a carbon/sulfur compound, mixing the mixture with the carbon/sulfur compound, and preparing a flexible spongy porous electrode by a steam phase conversion method.
The organic polymer resin is a mixture of PBI and PVDF, the mass of the polymer resin accounts for 20-80 wt% of the total mass of the electrode, and the mixing proportion is m (PBI): m (PVDF) is 0.2-1, and is preferably a mixture of 15% PBI and 15% PVDF;
the carbon/sulfur compound is one or more than two of carbon material and sulfur compound, and the mass of the sulfur in the carbon/sulfur compound accounts for 20-90 wt% of the total mass; the carbon material is one or more of carbon nanotube, graphene, carbon nanofiber, BP2000, KB600, KB300, XC-72, Super P, acetylene black and activated carbon.
The flexible spongy porous electrode is characterized in that: the porous electrode is similar to a sponge and has a high porosity of 60-85%, preferably 75-85%.
The thickness of the flexible spongy porous electrode is 40-2500 mu m, and the pore size is 0.5-5000 nm.
The flexible spongy porous electrode can be prepared by the following steps:
(1) adding organic polymer resin into an organic solvent, and stirring for 0.5-2 hours at the temperature of 20-50 ℃ to form a polymer solution; adding the carbon/sulfur compound, and fully stirring for 2-10 hours at the temperature of 20-50 ℃ to prepare a blending solution; wherein the solid content is 5-30 wt%;
(2) pouring the blended solution prepared in the step (1) on an aluminum foil substrate (current collector), and forming an integral body after blade coating; then putting the whole into a constant temperature and humidity box for 10-60 min (the high polymer resin is completely subjected to vapor phase conversion), wherein the temperature of the constant temperature and humidity box is 50-100 ℃, the humidity is 50-100% (in order to ensure that the vapor phase conversion consumes short time and consumes little energy, the temperature is preferably 50 ℃, and the humidity is preferably 100%), taking out, washing the electrode with water, washing away residual solvent, preparing a porous electrode, and the thickness of the knife-coated electrode is 80-5000 microns;
(3) naturally air-drying or drying the porous electrode prepared in the step (2) at a low temperature to obtain a dried porous electrode; wherein the low-temperature drying is 10-30 ℃, the drying time is 2-24 h, and the drying is carried out by heating, wherein the heating temperature is 50-70 ℃, and the drying time is 2-24 h; the thickness of the dried electrode is 40-2500 μm, the thickness of the electrode is related to the loading amount of sulfur, and the loading amount of sulfur is 0.5-20 mg cm-2To (c) to (d);
the organic solvent is one or more of dimethyl sulfoxide (DMSO), Dimethylacetamide (DMAC), N-methylpyrrolidone (NMP) and N, N-Dimethylformamide (DMF), and is preferably NMP (low in toxicity and cost).
The flexible sponge-like porous electrode can be used as a positive electrode in a lithium-sulfur battery.
The beneficial results of the invention are:
(1) the flexible spongy porous electrode prepared by the invention is not limited by the type and physical properties of active materials;
(2) the spongy porous electrode prepared by the method is of a flexible structure and is suitable for application places such as wearable batteries;
(3) the binder in the flexible spongy porous electrode prepared by the invention forms a flexible spongy porous network structure in the process of steam phase conversion, so that the binding property of the binder is improved, and the high-carrying-capacity electrode and the high-energy-density battery can be prepared;
(4) the flexible spongy porous electrode prepared by the invention has centralized pore size distribution;
(5) in the drying process of the flexible spongy porous electrode prepared by the invention, only natural air drying or low-temperature drying is needed, so that the emission of toxic high-boiling-point organic solvent to the atmosphere is reduced, and the flexible spongy porous electrode is energy-saving and environment-friendly;
(6) the flexible spongy porous electrode prepared by the method has high porosity, can adsorb more electrolyte, so that polysulfide dissolved in the electrolyte is fixed on one side of the positive electrode, and the cycle performance of the battery is improved;
(7) the porous structure of the flexible spongy porous electrode prepared by the invention is beneficial to the transmission of lithium ions and improves the rate capability of the battery.
The flexible spongy porous electrode prepared by the invention has the advantages of good ion transmission capability, concentrated pore size distribution, simple process, good cohesiveness, environmental friendliness and the like. The flexible spongy porous electrode is used as a positive electrode material of the lithium-sulfur battery, and the battery shows good comprehensive performance and has good application prospect.
Drawings
FIG. 1: photographs of the example electrode (top) and the comparative example 1 electrode (bottom);
FIG. 2: example 1 surface SEM images (a-d), cross-sectional SEM images (e, f), and comparative example 1 surface SEM image (g) and cross-sectional SEM image (h);
FIG. 3: example 1, comparative example 1 compared to comparative example 9 for porosity;
FIG. 4: example 1, comparative example 1 compared with comparative example 9 for liquid pick-up;
FIG. 5: cycle stability at 0.2C for lithium sulfur batteries assembled with comparative examples 1,5,6,7,8,9 and example 1;
FIG. 6: rate performance test of lithium-sulfur battery assembled with comparative examples 1,5,6,7,8,9 and example 1;
FIG. 7: high supporting capacity (10mg cm) was assembled in accordance with preferred example 2-2) And testing the cycle performance of the lithium-sulfur battery.
Detailed Description
The following examples are further illustrative of the present invention and are not intended to limit the scope of the present invention.
Comparative example 1
10g of commercial KB600 was placed in a tube furnace under Ar protection at 5 ℃ for min-1Heating to 900 deg.C, introducing steam for activation for 1.5h, wherein the flow rate of steam is 600mL min-1The activated carbon material was designated A-KB 600. Mixing 5g A-KB600 and 10g S, heating to 155 deg.C in a tube furnace at a heating rate of 1 deg.C for min-1And keeping the temperature for 20h to obtain the product which is marked as S/A-KB 600.
Dissolving 0.3g polyvinylidene fluoride (PVDF) in 7g N-methylpyrrolidone (NMP), stirring for 1h, adding 0.6g S/A-KB600 and 0.1g Super P, stirring for 5h, adjusting the scraper to 500 μm, blade-coating on an aluminum filmForming film, drying at 70 deg.C overnight, cutting into 14mm diameter small round pieces, weighing, vacuum drying at 60 deg.C for 24 hr, and using S/KB600 coated small round pieces as positive electrode (sulfur loading per piece is about 2mg cm)-2) The lithium sheet is used as a negative electrode, the clegard 2325 is used as a diaphragm, and 1M lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) solution is added with 1 percent LiNO3The electrolyte solution was a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (volume ratio v/v 1:1), the cells were assembled, and the cell cycle performance test was performed at 0.2C rate and the rate performance test was performed at 0.1C to 1C rate.
The first-circle specific discharge capacity under 0.2C multiplying power is 1049mA h g-1The specific capacity is maintained to be 708mA h g after 100 cycles-1The capacity retention rate was 67.4%; when the multiplying power is increased to 2C, the discharge specific capacity is 496mA h g-1。
Comparative example 2
Dissolving 0.3g of polyvinylidene fluoride (PVDF) in 42g N-methylpyrrolidone (NMP), stirring for 1h, adding 5.1g S/A-KB600 and 0.6g of Super P, stirring for 5h, adjusting a scraper to 500 mu m, coating the aluminum film into a film, quickly placing the film in a constant temperature and humidity box (the temperature is 50 ℃ and the humidity is 100%) for 30min, and transferring the film into water. After 1h, the membrane is dispersed in water and flocculent, and cannot be made into an electrode.
Comparative example 3
Dissolving 0.3g of polyvinylidene fluoride (PVDF) in 3g N-methylpyrrolidone (NMP), stirring for 1h, adding 0.033g S/A-KB600, stirring for 5h, adjusting a scraper to 500 mu m, coating an aluminum film to form a film, quickly placing the film in a constant temperature and humidity box (the temperature is 50 ℃ and the humidity is 100%) for 30min, and transferring the film to water. Taking out after 1h, drying at 30 ℃ for 10h, and then drying at 60 ℃ overnight. The electrode is light black in color. The subsequent assembled cell testing procedure was identical to comparative example 1.
The electrode polarization is large, and the charge and discharge test cannot be performed.
Comparative example 4
Dissolving 0.3g of polyvinylidene fluoride (PVDF) in 7g N-methylpyrrolidone (NMP), stirring for 1h, adding 0.6g S/A-KB600 and 0.1g of Super P, stirring for 5h, adjusting a scraper to 500 mu m, blade-coating on an aluminum film to form a film, quickly placing the film in a constant-temperature constant-humidity box (the temperature is 50 ℃ and the humidity is 100%) for 30min, transferring the film into water, taking out the film after 1h, and directly drying the film at 60 ℃ overnight. The electrodes are hard and brittle, without flexibility, and further shearing and assembly of the cell is not possible.
Comparative example 5
Dissolving 0.3g of polyvinylidene fluoride (PVDF) in 7g N-methylpyrrolidone (NMP), stirring for 1h, adding 0.6g S/A-KB600 and 0.1g of Super P, stirring for 5h, adjusting a scraper to 500 mu m, coating on an aluminum film to form a film, quickly placing the film in a constant-temperature constant-humidity box (the temperature is 50 ℃ and the humidity is 100%) for 30min, transferring the film into water, taking out the film after 1h, drying the film for 10h at 30 ℃, and then drying the film at 60 ℃ overnight. Subsequent electrode preparation and cell assembly were the same as in comparative example 1.
The specific discharge capacity of the first coil is 1407mA h g-1Capacity was maintained at 838mA h g after 100 cycles-1The capacity retention rate was 65.5% (calculated based on the fifth round); when the multiplying power is increased to 2C, the specific discharge capacity is 640mA h g-1。
Comparative example 6
0.3g of Polybenzimidazole (PBI) is dissolved in 7g N-methylpyrrolidone (NMP), stirred for 1h, added with 0.6g S/A-KB600 and 0.1g of Super P, stirred for 5h, adjusted to 500 mu m, scraped into a film on an aluminum film, quickly placed in a constant temperature and humidity cabinet (temperature 50 ℃, humidity 100%) for 30min, and transferred into water. Taking out after 1h, drying at 30 ℃ for 10h, and then drying at 60 ℃ overnight. Subsequent electrode preparation and cell assembly were the same as in comparative example 1.
The specific discharge capacity of the first loop is 892mA h g-1Capacity was maintained at 767mA hr g after 100 cycles-1The capacity retention rate is 86.0%; when the multiplying power is increased to 2C, the discharge specific capacity is 496mA h g-1。
Comparative example 7
0.15g of Polyacrylonitrile (PAN) and 0.15g of polyvinylidene fluoride (PVDF), dissolved in a solution of 7g of N-methylpyrrolidone (NMP) with stirring, 0.6g S/A-KB600 and 0.1g of Super P are added, stirred for 5 hours, adjusted to 500 mu m, coated on an aluminum film to form a film, quickly placed in a constant temperature and humidity cabinet (temperature 50 ℃ and humidity 100%) for 30min, and transferred to water. Taking out after 1h, drying at 30 ℃ for 10h, and then drying at 60 ℃ overnight. Subsequent electrode preparation and cell assembly were the same as in comparative example 1.
The specific discharge capacity of the first coil is 1308mA h g-1The capacity is maintained at 816mA h g after 100 cycles-1The capacity retention rate was 74.3% (calculated based on the fifth round); when the multiplying power is increased to 2C, the specific discharge capacity is 566mA h g-1。
Comparative example 8
0.15g of Polystyrene (PS) and 0.15g of polyvinylidene fluoride (PVDF) are dissolved in 7g N-methylpyrrolidone (NMP), stirred for 1h, added with 0.6g S/A-KB600 and 0.1g of Super P, stirred for 5h, adjusted to 500 mu m, scraped into a film on an aluminum film, quickly placed in a constant temperature and humidity cabinet (temperature 50 ℃ and humidity 100%) for 30min, and transferred into water. Taking out after 1h, drying at 30 ℃ for 10h, and then drying at 60 ℃ overnight. Subsequent electrode preparation and cell assembly were the same as in comparative example 1.
The specific discharge capacity of the first coil is 1308mA h g-1The capacity is maintained at 816mA h g after 100 cycles-1The capacity retention rate was 71.8% (calculated based on the fifth round); when the multiplying power is increased to 2C, the specific discharge capacity is 515mA h g-1。
Comparative example 9
Weighing 0.15g of Polyacrylonitrile (PAN) and 0.15g of polyvinylidene fluoride (PVDF), stirring and dissolving in a solution of 7g N-methyl pyrrolidone (NMP), adding 0.6g S/A-KB600 and 0.1g of SuperP, stirring for 5h, adjusting a scraper to 500 mu m, scraping and coating on an aluminum film to form a film, quickly immersing in water, taking out after 10min, and drying at 50 ℃ overnight. Subsequent electrode preparation and cell assembly were the same as in comparative example 1.
The specific discharge capacity of the first coil is 1287.3mA h g-1Capacity was maintained at 778mA hg after 100 cycles-1The capacity retention rate was 68.0% (calculated based on the fifth round); when the multiplying power is increased to 2C, the specific discharge capacity is 679mA h g-1。
Example 1
0.15g of Polybenzimidazole (PBI) and 0.15g of polyvinylidene fluoride (PVDF) were weighed, dissolved in a solution of 7g N-methylpyrrolidone (NMP) with stirring, and then added with 0.6g S/A-KB600 and 0.1g of SuperP with stirring for 5 hours to obtain a mixed solution. The subsequent electrode preparation, drying, assembled cell testing procedure was identical to comparative example 1.
The first-loop discharge specific capacity is 1395mA h g-1Capacity after 100 cycles was maintained at 994mA hr g-1The capacity retention rate is 79.2%; when the multiplying power is increased to 2C, the specific discharge capacity is 787mA h g-1。
Example 2
0.15g of Polybenzimidazole (PBI) and 0.15g of polyvinylidene fluoride (PVDF) were weighed, dissolved in a solution of 7g N-methylpyrrolidone (NMP) with stirring, and then 0.6g S/A-KB600 and 0.1g of SuperP were added and stirred for 5 hours to obtain a mixed solution, a doctor blade was adjusted to 2500 μm, and the subsequent electrode preparation, drying, battery assembly test procedures were identical to those of comparative example 1.
The sulfur carrying capacity of the electrode is about 10mg cm-2The discharge specific capacity of the assembled battery at the first circle of 0.05C is 1300mA h g-1The specific discharge capacity of 0.1C after activation is maintained at 1011.8mA h g-1The capacity retention after 60 cycles was 90.7%.
In the steam phase conversion process, the high molecular resin is cured to make the whole electrode fall off from the aluminum foil, thereby obtaining the flexible porous electrode. As can be seen from FIG. 1, the electrode prepared according to the comparative example 1 was severely cracked and the material on the electrode gradually fell off as the supporting amount increased, while the electrode prepared according to the example method was flat as a whole and no significant defect was seen, increasing the supporting amount of the active material to 19mg cm-2The electrode structure is still kept complete, which shows that the flexible spongy porous electrode prepared by the steam phase conversion method has stronger cohesiveness to materials than the electrode prepared by the traditional method. In comparison of SEM images of the surfaces of comparative example 1 and example 1, the surface of example 1 is flat and has no cracks, and the pore structure is uniformly distributed, while the comparative example has severe cracks on the surface of the electrode due to thermal shrinkage of the polymer resin during the drying process. From the sectional view of example 1, the interior of the flexible spongy porous electrode is relatively slow in the vapor phase conversion process, the polymer resin is uniformly molded to form a uniform spongy structure, the electrode is fluffy, the porosity is high (as shown in fig. 3), and the electrode is favorable for adsorbing more electrolyte, so that polysulfide dissolved in the electrolyte is fixed on one side of the positive electrode, the flying shuttle of the polysulfide is inhibited, the cycle performance of the battery is improved, and meanwhile, the polysulfide also has the advantages of being capable of absorbing more electrolyteThe reaction provides sufficient lithium ions, and the rate performance of the battery is improved. Based on the above characteristics, as shown in fig. 5 and 6, in the battery using the positive electrode material of example 1, the specific discharge capacity of 1395mA h g in the first turn at 0.2C rate is-1Above, much higher than that of comparative example (1049mA h g-1) The specific discharge capacity is up to 787mA h g at 2C multiplying power-1(ii) a In addition, the PBI and PVDF are better mixed and used in equal proportion than the PVDF (comparative example 5) and the PBI (comparative example 6) which are used as the binding agents independently, and the main reason is that the PBI has higher polarity, so that polysulfide can be chemically adsorbed to improve the cycle performance of the battery, and the polarization of the battery assembled by the prepared electrode is increased, so that the utilization rate of active substances is reduced, and the specific discharge capacity is reduced. Therefore, the PVDF and the PBI are mixed in equal proportion, the advantages of the PVDF and the PBI can be integrated, the polarization of the battery is improved, the utilization rate and the discharge specific capacity of active substances are improved, and the cycle performance of the battery is improved by adsorbing polysulfide through chemical adsorption. Thus, the electrochemical performance of example 1 is superior to that of comparative examples 5 and 6; while the polarity of PAN (comparative example 7) and PS (comparative example 8) with the same polarity is slightly smaller than PBI, so that the chemical adsorption effect is weaker, the cycle performance of the battery is slightly reduced, the adhesion of PAN and PS is weaker than PBI, and the flexibility of the electrode prepared in the same proportion is poorer; the electrode prepared by immersion phase inversion (comparative example 9) also has higher porosity and liquid absorption rate, but the pore structure is a large finger-shaped pore inside and a skin layer with smaller pore diameter on the surface. Only the skin layer has a sulfur resistance effect, and the polarity of PAN is weaker than that of PBI, so that the cycle performance of the comparative example 9 is poorer than that of the example 1, and in addition, the PAN chain has a stronger polar group-CN which has poor compatibility with a lithium electrode and has a serious passivation phenomenon, so the rate performance of the example 1 is slightly better than that of the comparative example 9; in order to further explore the advantages of the flexible spongy porous electrode, the sulfur content of the electrode is increased to 10mg cm by regulating and controlling the thickness of the scraper-2(preferred example 2), the experimental results show that the battery still has higher capacity exertion and better cycle performance (as shown in figure 7), and further illustrate the application prospect of the flexible spongy porous electrode in the field of high-power high-energy-density lithium-sulfur batteries.
Claims (7)
1. The application of the flexible spongy porous electrode is characterized in that: the flexible spongy porous electrode is used as a positive electrode in a lithium-sulfur battery;
mixing organic polymer resin with a carbon/sulfur compound, and preparing a flexible spongy porous electrode by a steam phase conversion method;
the organic polymer resin is a mixture of PBI and PVDF, the mass of the polymer resin accounts for 20-80 wt% of the total mass of the electrode, and the mixing proportion is m (PBI): m (PVDF) = 0.2-1;
the preparation method comprises the following steps of preparing the composition,
(1) adding organic polymer resin into an organic solvent, and stirring for 0.5-2 hours at the temperature of 20-50 ℃ to form a polymer solution; adding the carbon/sulfur compound, and fully stirring for 2-10 hours at the temperature of 20-50 ℃ to prepare a blending solution; wherein the solid content is 5-30 wt%;
(2) pouring the blending solution prepared in the step (1) on an aluminum foil substrate, and forming an integral body after blade coating; then putting the whole body into a constant temperature and humidity box for 10-60 min, wherein the temperature of the constant temperature and humidity box is 50-100 ℃, the humidity is 50-100%, in the process of steam phase conversion, the high polymer resin is solidified to enable the whole electrode to fall off from the aluminum foil, taking out the whole electrode, washing the whole electrode with water, washing away residual solvent to prepare a porous electrode, and the thickness of the blade-coated electrode is 80-5000 microns;
(3) naturally air-drying or drying the porous electrode prepared in the step (2) at a low temperature to obtain a dried porous electrode; wherein the low-temperature drying is 10-30 ℃, the drying time is 2-24 h, and the drying is carried out by heating, wherein the heating temperature is 50-70 ℃, and the drying time is 2-24 h; the thickness of the dried electrode is 40-2500 μm, the thickness of the electrode is related to the loading amount of sulfur, and the loading amount of sulfur is 0.5-20 mg cm-2In the meantime.
2. Use according to claim 1, characterized in that: the carbon/sulfur compound is more than two of carbon material and sulfur compound, and the mass of the sulfur in the carbon/sulfur compound accounts for 20-90 wt% of the total mass; the carbon material is one or more of carbon nanotube, graphene, carbon nanofiber, BP2000, KB600, KB300, XC-72, Super P, acetylene black and activated carbon.
3. Use according to claim 1, characterized in that: the blend of PBI and PVDF was a 15wt% blend of PBI and 15wt% PVDF.
4. Use according to claim 1, characterized in that: the electrode has a mesoporous structure similar to a sponge, and has a high porosity of 60-85%.
5. Use according to claim 4, characterized in that: the porosity is 75-85%.
6. Use according to claim 1, characterized in that:
the organic solvent is one or more than two of dimethyl sulfoxide (DMSO), Dimethylacetamide (DMAC), N-methylpyrrolidone (NMP) and N, N-Dimethylformamide (DMF).
7. Use according to claim 6, characterized in that:
the organic solvent is NMP.
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