Preparation method and application of biomass porous carbon-based sodium-selenium battery cathode material

Abstract

The application provides a biomass porous carbon-based sodium-selenium battery positive electrode material preparation method and application, and belongs to the technical field of new energy electronic materials. The application solves the problem of weak interaction between active selenium and carbon host in a traditional sodium-selenium battery, and the problem of rapid capacity attenuation caused by volume expansion of selenium and "flying shuttle effect" of polyselenides in a cycle process. The method comprises the following steps: mechanically mixing a biomass porous carbon material and selenium powder, and then sequentially performing heat treatment under inert gas protection and tube sealing heat treatment on the mixture to obtain the positive electrode material. The porous carbon material has good physical-chemical binding performance on active selenium, has the characteristics of low cost and simple and easy-to-operate preparation method, can be used for preparing a positive electrode material of a lithium-selenium battery and a sodium-selenium battery, can be used as a good conductive substrate or a skeleton material to load other active materials, and has wide application value.

Description

Technical Field

[0001] This invention relates to the field of new energy electronic materials technology, specifically to a method for preparing and applying a biomass porous carbon-based sodium-selenium battery cathode material. Background Technology

[0002] With the large-scale application of renewable energy, the development of high-energy-density, low-cost energy storage systems has become crucial. Sodium, due to its abundant resources and easy availability, and the similarity between the reaction kinetics and storage mechanisms of sodium-ion batteries and lithium-ion batteries, shows great promise. Among them, room-temperature sodium-selenium batteries have attracted widespread attention from researchers in recent years due to their high energy storage density.

[0003] Currently, the core research focus of sodium-selenium batteries is on improving the conductivity of the positive electrode host material and the loading of selenium in the active material. Previous studies have used various carbon materials such as porous carbon, graphene, and carbon nanotubes as selenium supports, achieving good initial electrochemical performance. However, due to the generally weak physical / chemical interaction between selenium and the carbon host, the active material selenium undergoes significant volume expansion during battery charge-discharge cycles. Its soluble polyselenide intermediates migrate in the electrolyte, triggering a severe "shuttle effect" and causing side reactions with the negative electrode, leading to reduced coulombic efficiency, rapid capacity decay, and shortened cycle life.

[0004] Therefore, to solve the above problems, there is an urgent need to design and develop a porous carbon material with tunable pore structure, specific surface area, and surface chemical properties. This material needs to be able to form effective physical confinement and chemical bonding for active selenium to suppress selenium volume expansion, anchor polyselenides, thereby mitigating the "shuttle effect," improving selenium utilization, and enhancing battery cycle stability. Summary of the Invention

[0005] This invention aims to overcome the problems of weak interaction between selenium and host carbon materials, severe "shuttle effect" of polyselenides during cycling, and rapid capacity decay in existing sodium-selenium battery cathode materials. The technical objective of this invention is to provide a porous carbon material prepared by activation and pyrolysis using biomass nanocellulose as a precursor, and then combining it with selenium. Through an optimized two-step heat treatment process, the active selenium is physically confined and chemically bonded, thereby preparing a sodium-selenium battery cathode material with high loading capacity and high cycle stability, thus improving the overall electrochemical performance of the battery.

[0006] To achieve the above-mentioned technical objectives of this invention, the following technical solution is adopted: A method for preparing a biomass porous carbon-based sodium-selenium battery cathode material includes the following steps: mechanically mixing biomass porous carbon material with selenium powder, followed by sequential heat treatment under inert gas protection and tube sealing heat treatment to obtain the cathode material. In the first step, the selenium powder melts at high temperature and penetrates into the pores of the carbon support, achieving high selenium powder loading. The second step, tube sealing heat treatment, further promotes the interaction between selenium and the carbon host material, forming a more stable selenium-carbon composite structure and improving sulfur dispersibility and conductivity. Furthermore, this step helps remove surface impurities or excess selenium, reducing the shuttle effect and improving battery cycle stability.

[0007] The mechanical mixing refers to the thorough and uniform stirring of the mixture in a ball mill at a speed of 400-800 r / min. -1 Stir for 2 hours.

[0008] Preferably, the heat treatment under inert gas protection is carried out at a temperature of 180-260℃ for 8-12 hours to ensure that selenium melts and diffuses into the pores of the porous carbon. The heat-treated powder is then ground again and subjected to a tube-sealing heat treatment at a temperature of 450-520℃ in a vacuum-sealed quartz tube for 2 hours to ensure that no bound selenium powder volatilizes from the carbon surface, reducing the "shuttle effect" in the electrochemical process and promoting further fusion of selenium powder and carbon materials.

[0009] Preferably, the mass ratio of the biomass porous carbon material to selenium powder is 1:2 to 1:4 to prevent excessive selenium volatilization loss during heat treatment.

[0010] Preferably, the preparation method of the biomass porous carbon material includes the following steps: mixing an activator solution with a biomass nanocellulose suspension, followed by freeze-drying and pyrolysis treatment to obtain the biomass porous carbon material.

[0011] Preferably, the activator is zinc chloride; the mass ratio of zinc chloride to biomass nanocellulose is 1:1 to 5:1.

[0012] Preferably, the pyrolysis treatment is carried out under an inert atmosphere, with a heating rate of 2-5°C / min. -1 The pyrolysis temperature is 750-1300℃, and the pyrolysis time is 2-4h.

[0013] Preferably, in the step of mixing the activator solution with the biomass nanocellulose suspension, a nitrogen-containing substance and / or a transition metal salt are also added. The nitrogen-containing substance is selected from urea or dopamine, and the transition metal salt is selected from ferric chloride or ammonium molybdate, to regulate the surface properties and catalytic performance of the subsequent carbon materials.

[0014] This invention also provides a biomass porous carbon-based sodium-selenium battery cathode material, and further provides the application of the biomass porous carbon-based sodium-selenium battery cathode material in a sodium-selenium secondary battery, wherein the cathode of the sodium-selenium secondary battery comprises the biomass porous carbon-based sodium-selenium battery cathode material.

[0015] Compared with the prior art, the present invention achieves the following technical effects: This invention provides a method for preparing high-performance sodium-selenium battery cathode materials using inexpensive and abundant waste biomass materials (such as poplar flour, sugarcane bagasse, and pulp) as raw materials. The raw materials are widely available and environmentally friendly, meeting the requirements of sustainable development. The preparation process is simple and easy to implement. Through mechanical mixing combined with two-step heat treatment, efficient loading and strong bonding of selenium in the porous carbon matrix of biomass can be achieved, making it easy to scale up production.

[0016] Secondly, the biomass nanocellulose-based porous carbon material prepared by this invention possesses excellent physicochemical properties. Its precursor nanocellulose surface is rich in hydroxyl groups, allowing for flexible control of the final carbon material's porosity, specific surface area, graphitization degree, and surface polarity / catalytic performance by introducing activators such as zinc chloride and substances like urea and transition metal salts. This provides an ideal carrier for the loading and confinement of selenium. More importantly, a specific two-step heat treatment process—first, melting and diffusion under an inert atmosphere, followed by vacuum sealing and high-temperature treatment—not only promotes selenium melting and full diffusion into the pores of the carbon material but also significantly enhances the chemical bonding between selenium and the carbon framework. This effectively suppresses the volume expansion of active selenium and the dissolution and migration of polyselenides in the electrolyte during charging and discharging, thereby greatly mitigating the "shuttle effect" that leads to capacity decay.

[0017] Finally, the sodium-selenium battery assembled using the aforementioned composite material (PCSe) as the cathode exhibits excellent electrochemical performance. Experiments show that the cathode material can achieve a selenium loading of up to 74.2%, and the selenium exists stably in the cyclic Se8 form. The battery prepared using this material can output up to 595 mAh g⁻¹. - ¹ Maximum reversible specific capacity. After 400 charge-discharge cycles at a high rate of 2C, the specific capacity retention rate still reaches 86%, demonstrating excellent rate performance and long-term cycle stability. This proves the great application potential of the material of this invention in improving the energy density and cycle life of sodium-selenium batteries. Attached Figure Description

[0018] For ease of explanation, the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0019] Figure 1 SEM image of the composite material after one heat treatment; Figure 2Thermogravimetric curve of PCSe; Figure 3 SEM and TEM images of the composite material after two heat treatments; Figure 4 The XRD patterns of the composite material after one heat treatment and two heat treatments are shown. Figure 5 High-resolution XPS image of Se3d; Figure 6 The charge-discharge curves of Na-Se batteries at different rates are shown. Figure 7 This is the rate capability curve for the composite electrode. Detailed Implementation

[0020] The following are specific embodiments of the present invention, described in conjunction with the accompanying drawings, to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments. Specific details, such as particular configurations, are provided in the following description merely to aid in a comprehensive understanding of the embodiments of the present invention. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0022] Example 1 A method for preparing biomass nanocellulose-based porous carbon materials includes the following steps: Step 1: Add 30g of poplar powder to 1500g of distilled water, then add 15g of sodium chlorite and 2ml of glacial acetic acid, and seal with plastic wrap. Heat in an 80℃ constant temperature water bath for 1 hour, then continue to add 15g of sodium chlorite and 2ml of glacial acetic acid. Repeat this process 3 times to wash the sample until neutral. Then, prepare 1000g of a mixed solution containing cellulose and 5% potassium hydroxide from the above wetted material, and heat it directly in a 90℃ constant temperature water bath for 2 hours. Wash until neutral and filter out excess water to obtain purified cellulose in a wetted state. Use ultrasonic mechanical method to prepare a 0.8% (w / w) aqueous suspension to obtain a biomass nanocellulose suspension. Step 2: Add the zinc chloride aqueous solution slowly to the biomass nanocellulose suspension according to the mass ratio of zinc chloride to cellulose of 4:1, and stir vigorously until homogeneous to obtain biomass nanocellulose-based hydrogel. Step 3: Freeze-dry the above biomass nanocellulose-based hydrogel to obtain biomass nanocellulose-based aerogel; Step 4: Place the above-mentioned biomass nanocellulose-based aerogel under an inert gas atmosphere at 3°C ​​for 3 min. -1The temperature was increased to 850℃ and pyrolyzed for 2 hours to obtain biomass nanocellulose-based porous carbon materials.

[0023] Step 5: Mix the above porous carbon and selenium powder at 800 rpm. -1 The mixture was stirred evenly in a ball mill and then treated at 260℃ for 12 hours under argon protection to obtain the composite sodium-selenium cathode material. Figure 1 At this point, a large amount of excess selenium adheres to the porous carbon surface, causing a severe shuttle effect in the system.

[0024] Example 2 The difference between this embodiment and Embodiment 1 is that step 5 includes an additional 500°C tube-sealing heat treatment for 2 hours, resulting in a loading capacity of up to 74.2%. Figure 2 This describes a biomass porous carbon-based sodium-selenium battery cathode material. Other preparation steps are the same as in Example 1. Figure 3 The results showed that selenium particles disappeared from the porous carbon surface after different heat treatments for tube sealing. Even under transmission electron microscopy, no obvious selenium particles were found, but weak diffraction peaks were present in the X-ray diffraction pattern. Figure 4 Furthermore, the electron binding energy between selenium and carbon is significantly increased. Figure 5 This indicates that there are chemical bonds and interactions between selenium and carbon.

[0025] Example 3 The composite material PCSe, super P, and polyvinylidene fluoride prepared in Example 2 were mixed evenly in N-methylpyrrolidone at a ratio of 8:1:1. The slurry was then evenly coated onto copper foil using a scraper and dried in a vacuum oven at 80 °C for 12 h. Finally, the coated electrode sheet was cut into suitable shapes for later use, with a loading of 2 mg cm⁻¹. -2 Using PCSe and sodium foil as the positive and negative electrode materials, a 1 M NaClO4 EC:DMC (volume ratio 1:1) solution as the electrolyte, and a 25 μm thick PE film as the separator, a half-cell was assembled in a manual control box for electrochemical testing. Figure 6 , 7 The figures show the charge-discharge curves and rate curves of the composite cathode material, respectively.

[0026] Those skilled in the art to which this application pertains may modify or supplement the specific embodiments described or use similar methods to replace them, but without departing from the inventive concept of this application or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a biomass porous carbon-based sodium-selenium battery cathode material, characterized in that, Includes the following steps: Biomass porous carbon material is mechanically mixed with selenium powder, and then the mixture is subjected to melt heat treatment under inert gas protection and vacuum tube sealing heat treatment in sequence to obtain the cathode material.

2. The preparation method according to claim 1, characterized in that, The heat treatment under inert gas protection is carried out at a temperature of 180-260℃ for 8-12 hours; the heat treatment for sealing the tube is carried out at a temperature of 450-520℃ for 2 hours.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the biomass porous carbon material to selenium powder is 1:2 to 1:

4.

4. The preparation method according to claim 1, characterized in that, The preparation method of the biomass porous carbon material includes the following steps: mixing an activator solution with a biomass nanocellulose suspension, followed by freeze-drying and pyrolysis treatment to obtain the biomass porous carbon material.

5. The preparation method according to claim 4, characterized in that, The activator is zinc chloride; and / or the mass ratio of zinc chloride to biomass nanocellulose is 1:1 to 5:

1.

6. The preparation method according to claim 4, characterized in that, The pyrolysis treatment is carried out under an inert atmosphere, with a heating rate of 2-5℃ / min. -1 The pyrolysis temperature is 750-1300℃, and the pyrolysis time is 2-4h.

7. The preparation method according to claim 4, characterized in that, In the step of mixing the activator solution with the biomass nanocellulose suspension, a nitrogen-containing substance and / or a transition metal salt are also added. The nitrogen-containing substance is selected from urea or dopamine, and the transition metal salt is selected from ferric chloride or ammonium molybdate.

8. A biomass porous carbon-based sodium-selenium battery cathode material, characterized in that, It is prepared by any one of claims 1-7.

9. A sodium-selenium secondary battery, characterized in that, Its positive electrode comprises the biomass porous carbon-based sodium-selenium battery positive electrode material as described in claim 8.

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