Preparation method of biomass waste-based porous carbon material for room-temperature sodium-sulfur battery positive electrode

Abstract

The invention provides a preparation method of a biomass waste-based porous carbon material for a positive electrode of a room-temperature sodium-sulfur battery. The preparation method comprises the following steps: S1, carrying out pre-carbonization treatment on a waste biomass material pine nut shell at a high temperature; s2, putting the pre-carbonized material obtained in the step S1 into a ball milling tank for pulverization; s3, mixing the powder obtained in the step S2 with cobalt potassium cyanide and a KOH solution, stirring for a certain time, centrifuging, and drying; s4, putting the sample obtained in the step S3 into a tubular furnace for high-temperature sintering, and performing alkali washing, acid washing and water washing on the sintered sample until the sample is neutral to obtain a doped modified porous carbon material; and S5, loading sulfur into the porous carbon material obtained in the step S4 through a hot melting method to obtain the sulfur-carbon composite positive electrode material for the sodium-sulfur battery. The cobalt-doped biomass porous material obtained in the invention not only promotes the rapid conversion of polysulfide, but also effectively inhibits the shuttle effect and volume expansion effect of sodium polysulfide, and significantly improves the cycling stability and rate capability of a sodium-sulfur battery.

Description

Technical Field

[0001] This invention relates to the field of preparation of carbon-based cathode materials for room-temperature sodium-sulfur batteries, specifically to the modification of carbon supports. Background Technology

[0002] With the ever-increasing energy demand in modern society, the development of new renewable energy sources (such as wind, solar, and tidal energy) has shown enormous potential. However, these energy sources inherently possess intermittency and volatility, thus necessitating the deployment of energy storage systems to mitigate the instability of power supply. Such systems can store excess energy during peak power generation periods and release it during peak demand periods, thereby ensuring grid reliability and the continuity of energy supply. Over the past few decades, lithium-sulfur (Li-S) batteries have gained popularity due to their high theoretical specific capacity (1675 mAh g⁻¹). -1 The environmental compatibility and low-cost sulfur-based composition of lithium have attracted widespread research interest. However, the limited availability and high cost of lithium resources hinder its large-scale deployment, driving an urgent need for alternative battery technologies. Sodium (Na), comprising 2.36% of the Earth's crust and abundant in seawater, is an economically viable alternative. Room-temperature sodium-sulfur (RT Na-S) batteries, combining low-cost sodium with sulfur, have emerged as a promising energy storage solution. These batteries exhibit theoretical specific capacities comparable to lithium-sulfur systems, while offering greater economic viability. Their ability to meet large-scale market demands and support grid-scale energy storage / conversion applications has made room-temperature sodium-sulfur batteries a focal point of contemporary energy research.

[0003] Currently, room-temperature sodium-sulfur batteries have met the requirements of low cost, excellent energy density, and environmental protection. However, various factors still affect the performance of room-temperature sodium-sulfur batteries, such as the poor conductivity of sulfur, the slow reaction kinetics between long-chain sodium polysulfides and short-chain sodium sulfides, etc. At present, the modification strategies for the above problems mainly include designing carbon-based supports with good conductivity and large specific surface area, introducing transition metal-modified carbon-based supports, and designing novel supports using the reaction of sulfur with organic polymers. Wu et al. used pecan shells as raw materials to finely control the pore structure of biomass-derived carbon frameworks, reducing the pore size to the range of 0.37-0.58 nm, and achieved direct solid-phase conversion of sulfur to Na2S (Energy & Environmental Materials, 2023, 6(4): e12634). However, modifying the pore structure alone will result in a slow kinetic reaction process. This problem will not only lead to low utilization of active materials, but also to large internal polarization of the battery. Therefore, it is necessary to use a highly efficient electrocatalyst to provide power for the conversion. Du et al. conducted a detailed study on how Co catalysts can enable rapid sodium intercalation and rapid reduction of polysulfide molecules. By introducing Co nanoparticles, they found that surface sulfidation can effectively alleviate the polar interactions of polysulfides. Metallic Co plays a catalytic role in the room temperature sodium-sulfur battery system, accelerating the rate of formation of the final product Na2S from long-chain polysulfides (Journal of Colloid and Interface Science, 2020, 565: 63-69.).

[0004] Therefore, it is necessary to study more efficient design methods for the cathode structure of room temperature sodium-sulfur batteries, further improve the structural stability and electrochemical performance of room temperature sodium-sulfur batteries, and promote the early commercial application of room temperature sodium-sulfur batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a biomass waste-based porous carbon material for the cathode of a room-temperature sodium-sulfur battery. This invention uses pine nut shells, a waste biomass material, as the carbon source and potassium hydroxide as the activator. By changing the concentration of the activator, the specific surface area and pore structure distribution of the material are adjusted, resulting in the design and synthesis of a microporous biomass carbon-based material as a cathode support material. Furthermore, by introducing a cobalt-containing catalyst to reduce the influence of the shuttle effect and simultaneously catalyze the rapid conversion of polysulfides, the electrochemical performance of the room-temperature sodium-sulfur battery carbon-based cathode material is significantly improved.

[0006] This invention provides a method for preparing a biomass waste-based porous carbon material for the cathode of a room-temperature sodium-sulfur battery, comprising the following steps: 1) Pre-carbonize the waste biomass pine nut shells at high temperature; 2) Place the pre-carbonized material obtained in step 1) into a ball mill jar for pulverization; 3) Mix the powder obtained in step 2) with potassium cobalt cyanide and KOH solution, stir for a certain period of time, then centrifuge and dry; 4) The sample obtained in step 3) is placed in a tube furnace for high-temperature sintering. After sintering, the sample is washed with alkali, acid and water until neutral to obtain doped modified porous carbon material. 5) The porous carbon material obtained in step 4) is loaded with sulfur by a hot-melt method to obtain a sulfur cathode material.

[0007] Preferably, the pre-carbonization time is 3 hours and the pre-carbonization temperature is 300°C.

[0008] Preferably, the ball milling time is 1-4 hours, and more preferably 2-3 hours.

[0009] Preferably, the mass ratio of potassium cobalt cyanide to pre-carbonized pine nut shell powder is 1:1, and the concentration of KOH solution is 1 mol / L. -1 .

[0010] Preferably, the high-temperature sintering process includes two sintering processes, wherein the first sintering temperature is 0~200℃ and the sintering time is 1.5h; the second sintering temperature is 200~700℃ and the sintering time is 3h, and the sintering atmosphere is high-purity nitrogen.

[0011] This invention provides a microporous biomass carbon-based material supported on a transition metal cobalt, prepared by the above method, as a positive electrode carrier for a room-temperature sodium-sulfur battery.

[0012] The present invention has the following beneficial effects:

[0013] This invention utilizes pine nut shells, a biomass waste, as a carbon source, achieving high-value resource utilization of agricultural waste, reducing environmental pollution, lowering the cost of key battery materials, and leveraging abundant and inexpensive waste resources. It promotes the development of low-cost, sustainable room-temperature sodium-sulfur battery technology, serving large-scale energy storage needs and contributing to energy transition and carbon neutrality goals.

[0014] A porous biomass carbon material with cobalt-loaded transition metal was developed in one step by chemical activation. It has the advantages of rich ultra-microporous structure (pore size < 0.7 nm) and large specific surface area, which effectively alleviates the problems of volume expansion and poor conductivity of sulfur cathode during cycling.

[0015] This invention proposes a one-step method for preparing cobalt-supported microporous biomass carbon materials. The experimental method is simple and convenient to operate.

[0016] The carbon-based support obtained by this invention has a reasonable pore structure distribution and a cobalt loading of transition metal, which promotes the rapid conversion of polysulfides during positive electrode cycling, effectively suppresses the shuttle effect of sodium polysulfides, and has excellent cycle stability and rate performance. Attached Figure Description

[0017] Figure 1 This is a SEM image of the cobalt-supported porous carbon-based support material prepared in Example 4.

[0018] Figure 2 These are comparison diagrams of nitrogen adsorption-desorption isotherms and pore size distribution of the cobalt-supported porous carbon-based carrier materials prepared in Examples 2 and 4.

[0019] Figure 3 This is a comparison chart of the cycle performance of the room temperature sodium-sulfur battery cathode sheets prepared with porous carbon material sulfur carriers in Examples 1, 2, 3, and 4 at 1C.

[0020] Figure 4 This is a comparison chart of the cycle performance of the room temperature sodium-sulfur battery cathode sheets prepared with porous carbon material sulfur carriers in Examples 2 and 4 at -15°C and 0.1C.

[0021] Figure 5 This is a comparison chart of the performance of the room temperature sodium-sulfur battery cathode sheets prepared with porous carbon material sulfur carriers in Examples 1, 2, 3, and 4 at different rates.

[0022] Figure 6 The room-temperature sodium-sulfur battery cathode sheets prepared using porous carbon material sulfur carriers in Examples 1, 2, 3, and 4 are shown at 0.1 mV s. -1 Comparison of the cyclic voltammetry curves for the third cycle.

[0023] Figure 7 This is a graph showing the cycle performance of the room-temperature sodium-sulfur battery cathode prepared by the porous carbon material sulfur support in Comparative Example 1 at 1C. Detailed Implementation

[0024] This invention provides a method for preparing a biomass waste-based porous carbon material for the cathode of a room-temperature sodium-sulfur battery, comprising the following steps: 1) Pre-carbonize the waste biomass pine nut shells at high temperature; 2) Place the pre-carbonized material obtained in step 1) into a ball mill jar for pulverization; 3) Mix the powder obtained in step 2) with potassium cobalt cyanide and KOH solution, stir for a certain period of time, then centrifuge and dry; 4) The sample obtained in step 3) is placed in a tube furnace for high-temperature sintering. After sintering, the sample is washed with alkali, acid and water until neutral to obtain doped modified porous carbon material. 5) The porous carbon material obtained in step 4) is loaded with sulfur by a hot-melt method to obtain a sulfur cathode material.

[0025] The present invention does not have any special limitation on the source of the pine nut shells, potassium cobalt cyanide and KOH, and conventional commercially available products in the field can be used.

[0026] In this invention, the water used in the steps is preferably deionized water.

[0027] The present invention does not have any particular limitation on the stirring method or centrifugation method, but it is preferred to use a stirrer or centrifuge for stirring and centrifugation.

[0028] In this invention, the pine nut shells are waste biomass materials.

[0029] In this invention, the pre-carbonization time is 3 hours and the pre-carbonization temperature is 300°C.

[0030] In this invention, the ball milling time is 1 to 4 hours, preferably 2 to 3 hours.

[0031] In this invention, the mass ratio of potassium cobalt cyanide to pre-carbonized pine nut shell powder is 1:1, and the concentration of KOH solution is 1 mol / L. -1 .

[0032] In this invention, the high-temperature sintering process includes two sintering processes. The first sintering process is carried out at a temperature of 0~200℃ for 1.5h. The second sintering process is carried out at a temperature of 200~700℃ for 3h. The sintering atmosphere is high-purity nitrogen.

[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention. Example 1

[0034] 5 g of pine nut shells were weighed and placed in a muffle furnace for sintering at 300 ℃ for 3 h. The sintered material was then placed in a ball mill and ball-milled for 2 h. 1 g of the ball-milled sample was weighed and added to a concentration of 0.5 mol / L. -1 The sample was stirred in a KOH solution for 12 h, centrifuged, and dried in an oven at 80 °C. The dried sample was then sintered in a tube furnace. The first sintering stage was performed at 0–200 °C for 1.5 h; the second sintering stage was performed at 200–700 °C for 3 h. The sintering atmosphere was high-purity nitrogen. A 2 mol / L solution was added to the sintered sample at a time. -1 KOH solution and 2 mol L -1The sample was soaked in a dilute HCl solution for 2 h, then washed until neutral and dried at 80 °C to obtain a porous carbon material sulfur support for room temperature sodium-sulfur batteries. The porous carbon material sulfur support and high-purity elemental sulfur were mixed at a mass ratio of 6:4, transferred to a high-pressure reactor, purged with argon in a glove box, and then heated in an oven at 155 °C for 10 h, followed by heating at 200 °C for 2 h. After cooling to room temperature, a sulfur-carbon composite cathode material was obtained. The cathode material, conductive additive, and binder were stirred at a mass ratio of 7:1.5:1.5, and the resulting slurry was uniformly coated onto carbon-coated aluminum foil and dried in a vacuum drying oven. The electrode was then subjected to performance testing. Example 2

[0035] The difference between this embodiment and Example 1 is that the ball-milled sample was added to a concentration of 1.0 mol / L. -1 The mixture was added to a KOH solution, stirred for 12 h, centrifuged, and then dried in an oven at 80 ℃. Example 3

[0036] The difference between this embodiment and Example 1 is that the ball-milled sample was added to a concentration of 2.0 mol / L. -1 The mixture was added to a KOH solution, stirred for 12 h, centrifuged, and then dried in an oven at 80 ℃. Example 4

[0037] The difference between this embodiment and Example 1 is that the ball-milled sample and potassium cobalt cyanide were mixed at a 1:1 mass ratio and added to a concentration of 1.0 mol / L. -1 The mixture was added to a KOH solution, stirred for 12 h, centrifuged, and then dried in an oven at 80 ℃. Comparative Example 1

[0038] Five g of pine nut shells were weighed and sintered in a muffle furnace at 300 °C for 3 h. The sintered material was then placed in a ball mill and milled for 2 h. One g of the milled sample was weighed and sintered in a tube furnace. The first sintering temperature was 0–200 °C for 1.5 h, and the second sintering temperature was 200–700 °C for 3 h. The sintering atmosphere was high-purity nitrogen. A 2 mol / L solution was added to the sintered sample at a time. -1 KOH solution and 2 mol L -1The sample was soaked in a dilute HCl solution for 2 h, then washed until neutral and dried at 80 °C. A carbon-based sulfur carrier and high-purity elemental sulfur were mixed at a mass ratio of 6:4 and transferred to a high-pressure reactor. After purging with argon in a glove box, the high-pressure reactor was placed in an oven at 155 °C and heated for 10 h, followed by heating at 200 °C for 2 h. After cooling to room temperature, a sulfur-carbon composite cathode material was obtained. The cathode material, conductive additive, and binder were stirred at a mass ratio of 7:1.5:1.5. The resulting slurry was uniformly coated onto carbon-coated aluminum foil and dried in a vacuum drying oven. The electrode was then subjected to performance testing.

[0039] Figure 1 This is a SEM image of the cobalt-supported porous carbon-based support material prepared in Example 4. The sample surface after chemical activation treatment exhibits a rich pore structure.

[0040] Figure 2 The figures show a comparison of nitrogen adsorption-desorption isotherms of the cobalt-supported porous carbon-based carrier materials prepared in Examples 2 and 4, indicating the presence of numerous microporous structures (pore size less than 0.7 nm) and a large specific surface area of ​​1269.8 m². 2 g -1 .

[0041] Figure 3 This is a comparison of the cycle performance of the room-temperature sodium-sulfur battery cathode sheets prepared with porous carbon material sulfur support in Examples 1, 2, 3, and 4 at 1C. The experimental results show that the initial capacity of the cobalt-doped cathode material at 1C is 1040.8 mAh g. -1 After 500 cycles, 734.7 mAh g remains. -1 High specific capacity.

[0042] Figure 4 The graph shows a comparison of the cycle performance of the room temperature sodium-sulfur battery cathode sheets prepared by the porous carbon material sulfur support in Examples 2 and 4 at -15 °C and 0.1 C. The experimental results show that the cobalt-doped cathode material has excellent electrochemical performance at low temperatures.

[0043] Figure 5 This is a performance comparison chart of the room-temperature sodium-sulfur battery cathode sheets prepared with porous carbon material sulfur support in Examples 1, 2, 3, and 4 at different rates. The experimental results show that the cobalt-doped cathode material has excellent rate performance, exhibiting 679.6 mAh g⁻¹ at 5C. -1 Specific capacity.

[0044] Figure 6 The room-temperature sodium-sulfur battery cathode sheets prepared using porous carbon material sulfur carriers in Examples 1, 2, 3, and 4 are shown at 0.1 mV s. -1The comparison of the third-cycle voltammetry curves shows that the cobalt-doped cathode material has the highest electrocatalytic activity, accelerating the catalytic conversion of polysulfides.

[0045] Figure 7 The figure shows the cycle performance of the room temperature sodium-sulfur battery cathode prepared by the porous carbon material sulfur support in Comparative Example 1 at 1C. The experimental results show that the cathode material without KOH activation cannot undergo normal charge-discharge cycles.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. This invention provides a method for preparing a biomass waste-based porous carbon material for the cathode of a room-temperature sodium-sulfur battery, characterized in that, Includes the following steps: 1) Pre-carbonize waste biomass materials at high temperatures; 2) Place the pre-carbonized material obtained in step 1) into a ball mill jar for pulverization. 3) Mix the powder obtained in step 2) with a cobalt-containing compound and a KOH solution, stir for a certain period of time, and then centrifuge and dry. 4) The sample obtained in step 3) is placed in a tube furnace for high-temperature sintering. After sintering, the sample is washed with alkali, acid and water until neutral to obtain doped modified porous carbon material. 5) Sulfur is loaded into the porous carbon material obtained in step 4) by hot melting method to obtain a porous carbon-based cathode material for room temperature sodium-sulfur batteries. Among them, the biomass waste material needs to be pine nut shells, and the cobalt-containing compound is potassium cobalt cyanide.

2. As described in claim 1, characterized in that, The pre-carbonization process in step 1) takes 3 hours and the carbonization temperature is 300°C.

3. As described in claim 1, characterized in that, In step 2), the amount of raw material added is controlled to be 10-30% of the volume of the ball mill jar, preferably 15-20%, and the ball milling time is controlled to be 1-4 hours, preferably 2-3 hours.

4. As described in claim 1, characterized in that, In step 3), the optimal ratio of potassium cobalt cyanide to pre-carbonized pine nut shell powder is 1:1, and the optimal concentration of KOH solution is 1 mol / L. -1 .

5. As described in claim 1, characterized in that, The sintering process in step 4) includes a first sintering stage and a second sintering stage performed sequentially. The temperature of the first sintering stage is 0~200℃ and the sintering time is 1.5h. The temperature of the second sintering stage is 200~700℃ and the sintering time is 3h. The sintering atmosphere is high-purity nitrogen.

6. A cobalt-doped porous carbon material prepared from pine nut shells, a biomass waste, by the preparation method according to any one of claims 1 to 5.

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