Graded porous carbon sieve negative pressure absorption liquid sulfide composite electrode and preparation method thereof

Abstract

The invention discloses a graded porous carbon sieve negative pressure absorption liquid sulfide composite electrode and a preparation method, and aims to solve the problems of poor conductivity, volume expansion, shuttle effect, uneven active substance distribution and the like of a lithium-sulfur battery positive electrode. The preparation method comprises the following steps: preparing an electrode from a graded porous carbon sieve with a rich pore structure and good conductivity, absorbing a lithium polysulfide solution into pores of the graded porous carbon sieve through negative pressure, and accelerating the drying speed, so that uniform distribution and close contact of active substances in the graded porous carbon sieve are realized; and the prepared positive electrode has relatively large specific capacity, good cycling stability and excellent rate capability.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-sulfur battery positive electrode preparation, and specifically relates to a graded porous carbon sieve negative pressure absorption liquid sulfide composite electrode and a preparation method thereof. Background Art

[0002] The large-scale application of conventional lithium-ion batteries has promoted the development of society, and at the same time, people's demand for batteries with higher energy density has become more urgent. Lithium-sulfur batteries are favored by researchers because of their ultra-high theoretical specific capacity and theoretical specific energy. However, the active substance sulfur and the reaction product lithium sulfide in lithium-sulfur batteries are both insulating materials with extremely poor conductivity and severe battery polarization; at the same time, the two have a large difference in volume, which causes the positive electrode to suffer irreversible damage during the reaction process. The shuttle effect caused by the diffusion of the reaction intermediates to the negative electrode reduces the capacity of the active sulfur, thereby causing the battery performance to decay, which seriously limits the application and development of lithium-sulfur batteries. An effective solution to these problems is to prepare a positive electrode with good conductivity, which can withstand the volume changes of sulfur and lithium sulfide and limit the shuttling of polysulfides.

[0003] To address the problem of poor conductivity, the current main strategy is to use carbon-based materials to composite elemental sulfur. For example, graphene, carbon microtubes, carbon balls, etc. are used to construct a conductive network to improve conductivity, but this cannot solve the problem of volume expansion and limit the polysulfide shuttle effect. The use of core-shell, hollow and other structural materials can provide expansion space for the reaction and physically confine polysulfides, but the preparation process of such composite materials is complicated, and the prepared electrode active substances are unevenly distributed, and the electrochemical performance fluctuates greatly. Summary of the invention

[0004] The purpose of the present invention is to provide a graded porous carbon sieve negative pressure absorption liquid sulfide composite electrode and a preparation method: using medium and low temperature softenable carbon-based materials as raw materials, using pore-forming agents to prepare graded porous carbon sieves with rich pore structures and good conductivity, and preparing them into pole pieces for use as active material carriers, using lithium polysulfide solution as the active material, and realizing uniform distribution and close contact of the active material in the porous carbon through negative pressure absorption rapid drying method, so that the prepared positive electrode has a large specific capacity, good cycle stability and excellent rate performance.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: A method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve comprises the following steps: (1) Preparation of graded porous carbon sieve: The medium-low temperature softened carbon-based material and the pore-forming agent are fully ground in a mortar and then placed in a magnetic boat. The temperature is first increased and maintained in a tubular furnace protected by a nitrogen atmosphere, and then the temperature is increased and maintained again at the same rate. After cooling, the derived carbon product is soaked in 0.5-2M dilute hydrochloric acid, then repeatedly rinsed and filtered with deionized water, and dried to obtain a graded porous carbon sieve; (2) Preparation of lithium polysulfide solution: In a glove box environment, sublimated sulfur and lithium sulfide are added to a solvent and stirred at 40-80°C for more than 72 h to obtain a lithium polysulfide solution with a concentration of 0.05-0.2 M; (3) Preparation of electrode: The graded porous carbon sieve, conductive agent and binder are mixed and stirred in NMP in a mass ratio of 60:30:10 to 85:5:10. After slurry preparation, the slurry is evenly applied to aluminum foil with a scraper and dried. In a glove box, the lithium polysulfide solution is dripped onto the graded porous carbon sieve electrode, and a vacuum negative pressure device is used to maintain negative pressure and dry the electrode at 20 to 80°C to finally obtain a positive electrode.

[0006] A further improvement of the present invention is that the medium-low temperature softening carbon-based material is asphalt, heavy oil, cellulose or biomass.

[0007] A further improvement of the present invention is that the pore-forming agent is a mixture of one or more of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

[0008] A further improvement of the present invention is that in step (1), the mass ratio of the medium-low temperature softened carbon-based material to the pore-forming agent is 1:1 to 1:4.

[0009] A further improvement of the present invention is that in step (1), the first heating rate is 2-5°C / min, and after heating to 150-350°C, the temperature is maintained for 0.5-3h.

[0010] A further improvement of the present invention is that in step (1), the temperature is raised again to 600-900° C. and kept at this temperature for 2-4 hours.

[0011] A further improvement of the present invention is that in step (2), the molar ratio of sublimated sulfur to lithium sulfide is 3:1 to 7:1.

[0012] A further improvement of the present invention is that in step (2), the solvent of lithium polysulfide is a mixed solvent of one or more of dioxolane, ethylene glycol dimethyl ether, ethanol, ethylene glycol, methanol and isopropanol.

[0013] A further improvement of the present invention is that in step (3), the drying temperature after the lithium polysulfide is added is 20 to 80° C.; and a vacuum negative pressure device is used to apply and maintain negative pressure during drying after the lithium polysulfide is added.

[0014] A graded porous carbon sieve negative pressure absorption liquid sulfide composite electrode is prepared by adopting the preparation method.

[0015] Compared with the prior art, the present invention has at least the following beneficial technical effects: 1. The raw materials of the graded porous carbon sieve in the present invention are asphalt, heavy oil, cellulose, biomass, etc., and the pore-forming agents are sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate, etc., which have low cost and little pollution. A simple grinding and mixing method is adopted, and a graded porous carbon material with rich pores and good conductivity is obtained after a one-step high-temperature treatment. The equipment is simple and the operation is easy.

[0016] 2 The present invention uses a graded porous carbon sieve as an active material carrier to make an electrode. The prepared electrode has sponge characteristics and a strong solution absorption capacity. It can well accommodate lithium polysulfide solution and increase the electrode active material loading.

[0017] 3. The graded porous carbon sieve used in the present invention has good electrical conductivity, can significantly reduce the impedance of lithium-sulfur batteries, and improve reaction kinetics; at the same time, the rich pore structure of the graded porous carbon sieve can accommodate active substances, has a physical confinement effect, and limits the shuttling of polysulfides.

[0018] 4. The present invention uses lithium polysulfide solution as the active material, simplifies the preparation process of the positive electrode of the lithium-sulfur battery, improves the utilization rate of the active material, and can better fill the pores of the graded porous carbon sieve and increase the loading of the electrode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 is a scanning electron microscope image of the graded porous carbon sieve prepared in Example 1, Example 5, and Example 6 of the present invention, Figure 1 a, b, c are scanning electron microscope images of the materials of Examples 1, 5, and 6, respectively.

[0021] Figure 2 It is the X-ray diffraction pattern of the graded porous carbon sieve prepared in Example 1, Example 5 and Example 6 of the present invention.

[0022] Figure 3 This is a scanning electron microscope image of the cross section of an electrode plate coated with the material prepared in Example 1 of the present invention.

[0023] Figure 4 This is a comparison chart of the cycle performance of a battery assembled with the positive electrode prepared in Example 1 of the present invention and other batteries.

[0024] Figure 5 This is a comparison chart of the rate performance of a battery assembled with the positive electrode prepared in Example 1 of the present invention and other batteries.

[0025] Figure 6 This is an impedance comparison diagram of a battery assembled with the positive electrode prepared in Example 1 of the present invention and other batteries.

[0026] Figure 7 It is a performance comparison chart of batteries assembled with the positive electrodes prepared in Example 1 and Example 4 of the present invention. Figure 7 a is a comparison chart of cycle performance, Figure 7 b is a comparison chart of rate performance. DETAILED DESCRIPTION

[0027] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0028] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0029] It should also be understood that the terms used in the present specification are only for the purpose of describing the set embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0030] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0031] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0032] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0033] The method for preparing a composite electrode for negative pressure absorption of liquid sulfide by a graded porous carbon sieve according to an embodiment of the present invention includes three parts: preparation of a graded porous carbon sieve, preparation of an active material lithium polysulfide solution, and preparation of an electrode. The specific preparation process is as follows: Weigh a certain amount of carbon source and pore-forming agent in a mass ratio of 1:1 to 1:4, grind them evenly with a mortar, put them into a magnetic boat and place them in a tube furnace at 200 ml h -1 Nitrogen was introduced into the tube furnace as a protective atmosphere at a flow rate of 1-5 °C min -1 The temperature was raised to 150-350 °C at a heating rate and kept for two hours, and then raised to 600-900 °C at the same rate and kept for two hours. After cooling, the derived carbon product was soaked in 0.5-2 M dilute hydrochloric acid for 12 h, then repeatedly rinsed and filtered with deionized water to wash away impurity ions, and dried for 24 h to obtain a graded porous carbon sieve.

[0034] In a glove box environment, a certain amount of sublimated sulfur and lithium sulfide are added to a solvent whose molar amount is 5 to 20 times that of the solute in a molar ratio of 3:1 to 7:1, and stirred at 40 to 80°C for more than 72 h to obtain a lithium polysulfide solution with a concentration of 0.05 to 0.2 M.

[0035] The graded porous carbon sieve, conductive agent, binder (PVDF) and NMP were added into a ball mill according to a mass ratio of 60:30:10 to 85:5:10. The slurry was uniformly spread on aluminum foil with a scraper, dried in a vacuum oven for 12 hours, and cut into discs with an electrode cutter. 2 S n The solution was dripped onto the graded porous carbon sieve, and the negative pressure was maintained by using a vacuum negative pressure device on the heating table and dried to obtain HPC / Li 2 S n electrode.

[0036] Embodiment 1: This embodiment provides a method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, which specifically includes the following steps: Step 1: Weigh 8 g of asphalt and 12 g of potassium carbonate, grind them thoroughly in a mortar, put them into a magnetic boat and place them in a tube furnace at 200 ml h -1 Nitrogen was introduced into the tube furnace as a protective atmosphere at a flow rate of 3 °C min -1 The temperature was raised to 300 °C at a heating rate and kept for two hours, and then raised to 800 °C at the same rate and kept for two hours. After cooling, the derived carbon product was soaked in 1 M dilute hydrochloric acid for 12 h, then repeatedly rinsed and filtered with deionized water to wash away impurity ions, and dried for 24 h to obtain a three-dimensional hierarchical porous carbon sieve.

[0037] Step 2: In a glove box, weigh 0.8 g of sublimed sulfur and 0.24 g of lithium sulfide and add them to 10 ml of DOL / DME (volume ratio is 1:1) mixed solvent, stir at 80 °C for more than 72 h to obtain Li 2 S 6 Solution.

[0038] Step 3: Add 65 mg of graded porous carbon, 25 mg of conductive agent, 10 mg of binder (PVDF) and a certain amount of NMP into a ball mill, ball mill for 1 h to obtain a uniform slurry, apply the slurry evenly on aluminum foil with a scraper, dry it in a vacuum oven for 12 h, and cut it into discs with an electrode cutter. In a glove box, 2 S 6 The solution was dripped onto the graded porous carbon sieve electrode sheet, and the negative pressure was maintained by using a vacuum negative pressure device on an 80 °C heating table and dried for 20 min to obtain a positive electrode sheet.

[0039] Embodiment 2: This embodiment provides a method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, which specifically includes the following steps: Step 1: Weigh 8 g of cellulose and 16 g of potassium bicarbonate, grind them thoroughly in a mortar, put them into a magnetic boat and place them in a tube furnace at 200 ml h -1 Nitrogen was introduced into the tube furnace as a protective atmosphere at a flow rate of 3 °C min -1 The temperature was raised to 300 °C at a heating rate and kept for two hours, and then raised to 800 °C at the same rate and kept for two hours. After cooling, the derived carbon product was soaked in 1 M dilute hydrochloric acid for 12 h, then repeatedly rinsed and filtered with deionized water to wash away impurity ions, and dried for 24 h to obtain a three-dimensional hierarchical porous carbon sieve.

[0040] Step 2: In a glove box, weigh 0.38 g of sublimed sulfur and 0.18 g of lithium sulfide and add them to 10 ml of DOL / DME (volume ratio of 1:1) mixed solvent, stir at 80 °C for more than 72 h to obtain Li 2 S 4 Solution.

[0041] Step 3: Add 65 mg of graded porous carbon, 25 mg of conductive agent, 10 mg of binder (PVDF) and a certain amount of NMP into a ball mill, ball mill for 1 h to obtain a uniform slurry, apply the slurry evenly on aluminum foil with a scraper, dry it in a vacuum oven for 12 h, and cut it into electrodes of the required size with a cutting machine. In a glove box, place Li 2 S 4 The solution was dripped onto the graded porous carbon sieve electrode sheet, and the negative pressure was maintained by using a vacuum negative pressure device on an 80 °C heating table and dried for 20 min to obtain a positive electrode sheet.

[0042] Embodiment 3: This embodiment provides a method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, which specifically includes the following steps: Step 1: Weigh 8 g of heavy oil and 24 g of sodium bicarbonate, grind them thoroughly in a mortar, put them into a magnetic boat and place them in a tube furnace at 200 ml h -1 Nitrogen was introduced into the tube furnace as a protective atmosphere at a flow rate of 3 °C min -1 The temperature was raised to 300 °C at a heating rate and kept for two hours, and then raised to 800 °C at the same rate and kept for two hours. After cooling, the derived carbon product was soaked in 1 M dilute hydrochloric acid for 12 h, then repeatedly rinsed and filtered with deionized water to wash away impurity ions, and dried for 24 h to obtain a three-dimensional hierarchical porous carbon sieve.

[0043] Step 2: In a glove box, weigh 0.34 g of sublimed sulfur and 0.09 g of lithium sulfide and add them to 10 ml of DOL / DME (volume ratio is 1:1) mixed solvent, stir at 80 °C for more than 72 h to obtain Li 2 S 8 Solution.

[0044] Step 3: Add 65 mg of graded porous carbon, 25 mg of conductive agent, 10 mg of binder (PVDF) and a certain amount of NMP into a ball mill, ball mill for 1 h to obtain a uniform slurry, apply the slurry evenly on aluminum foil with a scraper, dry it in a vacuum oven for 12 h, and cut it into discs with an electrode cutter. In a glove box, 2 S 8The solution was dripped onto the graded porous carbon sieve electrode sheet, and the negative pressure was maintained by using a vacuum negative pressure device on an 80 °C heating table and dried for 20 min to obtain a positive electrode sheet.

[0045] Embodiment 4: This embodiment provides a method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, which specifically includes the following steps: Step 1: Weigh 8 g of asphalt and 12 g of potassium carbonate, grind them thoroughly in a mortar, put them into a magnetic boat and place them in a tube furnace at 200 ml h -1 Nitrogen was introduced into the tube furnace as a protective atmosphere at a flow rate of 3 °C min -1 The temperature was raised to 300 °C at a heating rate and kept for two hours, and then raised to 800 °C at the same rate and kept for two hours. After cooling, the derived carbon product was soaked in 1 M dilute hydrochloric acid for 12 h, then repeatedly rinsed and filtered with deionized water to wash away impurity ions, and dried for 24 h to obtain a three-dimensional hierarchical porous carbon sieve.

[0046] Step 2: In a glove box, weigh 0.8 g of sublimed sulfur and 0.24 g of lithium sulfide and add them to 10 ml of ethanol (volume ratio is 1:1) mixed solvent, stir at 80 °C for more than 72 h to obtain Li 2 S 6 Solution.

[0047] Step 3: Add 65 mg of graded porous carbon, 25 mg of conductive agent, 10 mg of binder (PVDF) and a certain amount of NMP into a ball mill, ball mill for 1 h to obtain a uniform slurry, apply the slurry evenly on aluminum foil with a scraper, dry it in a vacuum oven for 12 h, and cut it into discs with an electrode cutter. In a glove box, 2 S 6 The solution was dripped onto the graded porous carbon sieve electrode sheet, and the negative pressure was maintained by using a vacuum negative pressure device on an 80 °C heating table and dried for 20 min to obtain a positive electrode sheet.

[0048] The difference from Example 1 is that the polysulfide solvent type is changed from DOL / DME mixed solvent to ethanol; the rest is exactly the same as Example 1.

[0049] Embodiment 5: This embodiment provides a method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, which specifically includes the following steps: Step 1: Weigh 8 g of asphalt and 12 g of potassium carbonate, grind them thoroughly in a mortar, put them into a magnetic boat and place them in a tube furnace at 200 ml h -1 Nitrogen was introduced into the tube furnace as a protective atmosphere at a flow rate of 3 °C min-1 The temperature was raised to 300 °C at a heating rate and kept for two hours, and then raised to 700 °C at the same rate and kept for two hours. After cooling, the derived carbon product was soaked in 1 M dilute hydrochloric acid for 12 h, then repeatedly rinsed and filtered with deionized water to wash away impurity ions, and dried for 24 h to obtain a three-dimensional hierarchical porous carbon sieve.

[0050] Step 2: In a glove box, weigh 0.8 g of sublimed sulfur and 0.24 g of lithium sulfide and add them to 10 ml of ethanol (volume ratio is 1:1) mixed solvent, stir at 80 °C for more than 72 h to obtain Li 2 S 6 Solution.

[0051] Step 3: Add 65 mg of graded porous carbon, 25 mg of conductive agent, 10 mg of binder (PVDF) and a certain amount of NMP into a ball mill, ball mill for 1 h to obtain a uniform slurry, apply the slurry evenly on aluminum foil with a scraper, dry it in a vacuum oven for 12 h, and cut it into discs with an electrode cutter. In a glove box, 2 S 6 The solution was dripped onto the graded porous carbon sieve electrode sheet, and the negative pressure was maintained by using a vacuum negative pressure device on an 80 °C heating table and dried for 20 min to obtain a positive electrode sheet.

[0052] The difference from Example 1 is that the carbonization temperature during the preparation of hierarchical porous carbon is changed from 800° C. to 700° C.; the rest is exactly the same as Example 1.

[0053] Embodiment 6: This embodiment provides a method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, which specifically includes the following steps: Step 1: Weigh 8 g of asphalt and 12 g of potassium carbonate, grind them thoroughly in a mortar, put them into a magnetic boat and place them in a tube furnace at 200 ml h -1 Nitrogen was introduced into the tube furnace as a protective atmosphere at a flow rate of 3 °C min -1 The temperature was raised to 300 °C at a heating rate and kept for two hours, and then raised to 900 °C at the same rate and kept for two hours. After cooling, the derived carbon product was soaked in 1 M dilute hydrochloric acid for 12 h, then repeatedly rinsed and filtered with deionized water to wash away impurity ions, and dried for 24 h to obtain a three-dimensional hierarchical porous carbon sieve.

[0054] Step 2: In a glove box, weigh 0.8 g of sublimed sulfur and 0.24 g of lithium sulfide and add them to 10 ml of ethanol (volume ratio is 1:1) mixed solvent, stir at 80 °C for more than 72 h to obtain Li 2 S 6 Solution.

[0055] Step 3: Add 65 mg of graded porous carbon, 25 mg of conductive agent, 10 mg of binder (PVDF) and a certain amount of NMP into a ball mill, ball mill for 1 h to obtain a uniform slurry, apply the slurry evenly on aluminum foil with a scraper, dry it in a vacuum oven for 12 h, and cut it into discs with an electrode cutter. In a glove box, 2 S 6 The solution was dripped onto the graded porous carbon sieve electrode sheet, and the negative pressure was maintained by using a vacuum negative pressure device on an 80 °C heating table and dried for 20 min to obtain a positive electrode sheet.

[0056] The difference from Example 1 is that the carbonization temperature during the preparation of hierarchical porous carbon is changed from 800° C. to 900° C.; the rest is exactly the same as Example 1.

[0057] The positive electrode of the present invention was assembled into a lithium-sulfur battery for testing. The battery using the positive electrode of the present invention had a first cycle discharge capacity of 1236 mAh g at 0.2C. -1 The battery has good cycle stability and the capacity can still reach 1085 mAh g after 100 cycles. -1 ; The rate performance has also been significantly improved, and its specific capacity can still reach 842.5 mAhg at a high current of 2C -1 , and when the current density returns to 0.2C, its specific capacity also returns to 982.9 mAh g -1 , which is 96.8% of the specific capacity at the initial 0.2C current density, and has good reversibility.

[0058] The application of the composite electrode of graded porous carbon sieve negative pressure absorption of liquid sulfide provided by the present invention is assembled into a lithium-sulfur button battery for testing. The battery using the positive electrode of the present invention has a first cycle discharge specific capacity of 1236 mAhg at 0.2C. -1 The battery has good cycle stability and the capacity can still reach 1085 mAh g after 100 cycles. -1 The rate performance has also been significantly improved. At a high current of 2C, its specific capacity can still reach 842.5 mAh g -1 , and when the current density returns to 0.2C, its specific capacity also returns to 982.9 mAh g -1 , which is 96.8% of the specific capacity at the initial 0.2C current density, and has good reversibility.

[0059] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0060] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, characterized in that: The steps include: (1) Preparation of graded porous carbon sieve: The medium-low temperature softened carbon-based material and the pore-forming agent are fully ground in a mortar and then placed in a magnetic boat. The temperature is first increased and maintained in a tubular furnace protected by a nitrogen atmosphere, and then the temperature is increased and maintained again at the same rate. After cooling, the derived carbon product is soaked in 0.5-2M dilute hydrochloric acid, then repeatedly rinsed and filtered with deionized water, and dried to obtain a graded porous carbon sieve; (2) Preparation of lithium polysulfide solution: In a glove box environment, sublimated sulfur and lithium sulfide are added to a solvent and stirred at 40-80°C for more than 72 h to obtain a lithium polysulfide solution with a concentration of 0.05-0.2 M; (3) Preparation of electrode: The graded porous carbon sieve, conductive agent and binder are mixed and stirred in NMP in a mass ratio of 60:30:10 to 85:5:

10. After slurry preparation, the slurry is evenly applied to aluminum foil with a scraper and dried. In a glove box, the lithium polysulfide solution is dripped onto the graded porous carbon sieve electrode, and a vacuum negative pressure device is used to maintain negative pressure and dry the electrode at 20 to 80°C to finally obtain a positive electrode.

2. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: The medium and low temperature softening carbon-based material is asphalt, heavy oil, cellulose or biomass.

3. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: The pore-forming agent is one or more mixed substances selected from the group consisting of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

4. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: In step (1), the mass ratio of the medium-low temperature softened carbon-based material to the pore-forming agent is 1:1 to 1:

4.

5. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: In step (1), the first heating rate is 2-5°C / min, and the temperature is heated to 150-350°C and then kept at this temperature for 0.5-3h.

6. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: In step (1), the temperature is raised again to 600-900°C and kept at this temperature for 2-4 hours.

7. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: In step (2), the molar ratio of sublimated sulfur to lithium sulfide is 3:1 to 7:

1.

8. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: In step (2), the solvent of lithium polysulfide is one or more mixed solvents selected from the group consisting of dioxolane, ethylene glycol dimethyl ether, ethanol, ethylene glycol, methanol and isopropanol.

9. The method for preparing a composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve according to claim 1, characterized in that: In step (3), the drying temperature after the lithium polysulfide is added is 20 to 80° C.; during the drying process after the lithium polysulfide is added, a vacuum negative pressure device is used to apply and maintain negative pressure.

10. A composite electrode for absorbing liquid sulfide by negative pressure using a graded porous carbon sieve, characterized in that: The preparation method is described in any one of claims 1 to 9.

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