Difunctional porous carbon electrode material for sodium-sulfur battery

Abstract

The invention discloses a difunctional porous carbon electrode material for a room-temperature sodium-sulfur battery and a preparation method of the difunctional porous carbon electrode material. The electrode material is composed of a nitrogen-doped porous carbon carrier with a high specific surface area and a series catalytic system composed of anchored nickel single atoms and nickel nanoclusters. The preparation method comprises the following steps: mixing a carbon source, a nitrogen source, a zinc-based micro / mesoporous pore-forming agent and a forming auxiliary agent, carrying out pressure forming, then carrying out one-step high-temperature carbonization and activation in an inert atmosphere, synchronously realizing pore forming and template removal through thermal volatilization, and finally loading the nickel-based catalyst through impregnation-pyrolysis. The electrode material disclosed by the invention can be used as a sulfur positive electrode host and a sodium metal negative electrode substrate at the same time, can efficiently catalyze polysulfide conversion and inhibit a shuttle effect on a positive electrode side, and can guide sodium ions to uniformly deposit and inhibit dendritic crystal growth on a negative electrode side. The sodium-sulfur battery assembled based on the difunctional electrode shows high specific capacity, excellent rate capability and ultra-long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage and battery materials technology, specifically relating to a bifunctional porous carbon electrode material for room temperature sodium-sulfur batteries, its preparation method and application. Background Technology

[0002] Against the backdrop of the accelerated development of renewable energy, grid-connected energy storage systems have created an urgent need for low-cost, large-scale energy storage technologies. Although lithium-ion batteries have been widely used in grid-connected energy storage, their development is limited by global lithium resource reserves and costs. In contrast, room-temperature sodium-sulfur batteries are considered one of the most promising next-generation grid-connected energy storage technologies due to their abundant raw material (sodium and sulfur) reserves, high theoretical energy density, and relatively good safety.

[0003] However, the practical application of room temperature sodium-sulfur batteries still faces severe challenges, and their cycle life and rate performance are still difficult to meet the requirements of grid energy storage. Specifically, the following key problems exist: (1) On the positive electrode side, sulfur and its discharge products have poor conductivity, resulting in sluggish reaction kinetics and low sulfur utilization; soluble polysulfides are easy to dissolve and shuttle, causing continuous loss of active materials and capacity decay; the volume change during charging and discharging is significant, which can easily damage the electrode structure. (2) On the negative electrode side, the uneven deposition of metallic sodium can easily induce dendrite growth, which not only penetrates the separator and causes short circuit risk, but also deteriorates cycle stability.

[0004] To address these challenges, porous carbon-based materials are considered ideal bifunctional electrodes: their high conductivity improves electron transport in sulfur cathodes; their tunable pore structure helps suppress polysulfide shuttle and buffer volume changes; and heteroatom doping or catalyst support provides chemisorption sites and catalyzes polysulfide conversion. However, traditional carbon host materials have limited ability to simultaneously optimize cathode reaction kinetics and anode sodium deposition behavior. Therefore, developing a novel bifunctional electrode material capable of synergistically regulating both cathode and anode reaction processes is crucial for advancing the practical application of room-temperature sodium-sulfur batteries. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings of existing technologies and provide a bifunctional porous carbon electrode material for sodium-sulfur batteries. This material innovatively constructs a tandem catalytic system of nickel single atoms and nickel nanoclusters, which can simultaneously serve as a high-performance sulfur cathode host and a sodium metal anode substrate.

[0006] Another objective of this invention is to provide a method for preparing the aforementioned bifunctional porous carbon electrode material. This method uses micro / mesoporous pore-forming agents and molding aids as its core components, and achieves the loading of single-atom and cluster dual active centers through a one-step carbonization activation followed by a low-temperature impregnation-pyrolysis process. This method features a simple process flow, low cost, and suitability for large-scale production.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a bifunctional porous carbon electrode material includes the following steps:

[0009] (1) Precursor mixing and molding: The carbon source, nitrogen source, micro / mesoporous pore-forming agent and molding aid are weighed according to a predetermined mass ratio, and then thoroughly ground and mixed to obtain a uniform powder. Subsequently, the powder is molded by mechanical pressure to obtain an ingot with a specific geometric shape.

[0010] (2) One-step carbonization and activation: The ingot obtained in step (1) is placed in a reaction furnace and heated to 900-1200°C at a heating rate of 3-10°C / min under an inert atmosphere. It is then held at this temperature for 1-5 hours to complete the carbonization, nitrogen doping and pore-forming process. After cooling, porous carbon material NC is obtained.

[0011] (3) Tandem catalyst loading: The porous carbon material NC obtained in step (2) is immersed in an ethanol solution of nickel salt, stirred and dried, and then heat-treated at 150-250℃ for 0.5-4h in a reducing atmosphere to finally obtain a bifunctional porous carbon material Ni-NC loaded with nickel single atoms and nickel nanoclusters.

[0012] In a preferred embodiment, the carbon source in step (1) is selected from biomass-derived organic carbon sources such as glucose, sucrose, and cellulose; the micro / mesoporous pore-forming agent is one or more of zinc chloride, zinc acetate, and zinc nitrate; and the molding aid is one or more of zinc and zinc oxide.

[0013] In a preferred embodiment, the inert atmosphere in step (2) is one or more of nitrogen, argon, and hydrogen, with nitrogen being preferred from a cost perspective. The micro / mesoporous pore-forming agent and molding aid are removed simultaneously through a high-temperature thermal volatilization process, eliminating the need for subsequent acid washing, and the volatilized zinc species can be condensed and recovered.

[0014] In a preferred embodiment, the nickel salt in step (3) is nickel acetate, nickel nitrate, or nickel chloride; the reducing atmosphere is a hydrogen-argon mixture, wherein the volume percentage of hydrogen is 5% to 10%.

[0015] The bifunctional porous carbon electrode material prepared according to the above method is characterized by comprising a nitrogen-doped porous carbon support with high specific surface area and hierarchical pore structure, and a tandem catalytic system consisting of nickel single atoms and nickel nanoclusters anchored thereon.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] 1) A tandem catalytic system of nickel single atoms and nickel nanoclusters was constructed in a porous carbon electrode. On the positive electrode side, the system synergistically catalyzes the continuous conversion of polysulfides through the synergistic effect of different active sites, suppressing the shuttle effect; on the negative electrode side, it provides uniform sodium-loving sites to guide the uniform nucleation and deposition of sodium ions, inhibiting dendrite growth.

[0018] 2) The thermal volatilization method is used to complete carbonization, activation and pore formation in one step, avoiding the traditional cumbersome and polluting pickling steps. The zinc species can be recycled and reused. The process is simple, environmentally friendly and low-cost, and suitable for large-scale production.

[0019] 3) The prepared porous carbon material has both a high specific surface area (>1500 m²) and... 2 The bifunctional electrode, with its hierarchical pore structure and continuous conductive network, forms a continuous electron-ion dual channel, allowing it to be used as a self-supporting electrode without the need for additional binders, conductive agents, or current collectors. Sodium-sulfur batteries assembled based on this bifunctional electrode exhibit excellent overall performance: an initial discharge specific capacity of 1517 mAh / g at 0.1C; a specific capacity of 580 mAh / g at 5C; and a capacity retention of 85.4% after 3000 cycles at 2C. At 5.5 mg / cm³, the specific capacity... 2 After 500 cycles at sulfur surface loading, the specific capacity remained at 850 mAh / g. Attached Figure Description

[0020] Figure 1 The image shows the macroscopic morphology of the bifunctional porous carbon electrode Ni-NC prepared in Example 1 of this invention.

[0021] Figure 2 This is a scanning electron microscope image of the bifunctional porous carbon electrode Ni-NC prepared in Example 1 of the present invention.

[0022] Figure 3 This is a transmission electron microscope image of the bifunctional porous carbon electrode Ni-NC prepared in Example 1 of the present invention.

[0023] Figure 4 Aberration-corrected high-angle annular dark field image of the bifunctional porous carbon electrode Ni-NC prepared in Example 1 of this invention.

[0024] Figure 5 The Fourier transform synchrotron radiation absorption spectrum of the bifunctional porous carbon electrode Ni-NC prepared in Example 1 of this invention is shown.

[0025] Figure 6 The nitrogen adsorption-desorption isotherm of the bifunctional porous carbon electrode Ni-NC prepared in Example 1 of this invention.

[0026] Figure 7This is a symmetrical cell assembled using the bifunctional porous carbon electrode Ni-NC pre-plated with sodium metal prepared in Example 1, at 3 mA / cm². 2 Long-cycle performance curves at current density.

[0027] Figure 8 The discharge specific capacity of sodium-sulfur batteries assembled using the bifunctional porous carbon electrode Ni-NC prepared in Example 1 as the sulfur-loaded positive electrode and the sodium-plated negative electrode at different current rates is measured.

[0028] Figure 9 The image shows the long-cycle performance curve of a sodium-sulfur battery assembled using the bifunctional porous carbon electrode Ni-NC prepared in Example 1 at a 2C rate.

[0029] Figure 10 This is a comparison of the cycling performance of a sodium-sulfur battery assembled with the bifunctional porous carbon electrode Ni-NC prepared in Example 1 at a rate of 0.2C under different sulfur cathode surface loading conditions. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0031] Example 1:

[0032] (1) Grind and mix 4g glucose, 4g urea, 8g zinc chloride and 84g zinc powder thoroughly to obtain a uniform mixed precursor powder. Weigh an appropriate amount of powder and place it in a mold, press it into shape under a pressure of 20MPa to obtain a cylindrical ingot.

[0033] (2) The above ingot is transferred to a tube furnace and heated to 1000°C at a heating rate of 5°C / min under nitrogen atmosphere protection and held for 3 hours. Then it is naturally cooled to room temperature to obtain porous carbon material NC.

[0034] (3) Take 100 mg of the porous carbon material NC prepared above and immerse it in 50 mL of nickel acetate ethanol solution with a concentration of 5 mM. After stirring for 12 h, collect the solid and dry it. Then heat it to 200 °C in a hydrogen-argon mixture and keep it warm for 2 h. After cooling, the bifunctional porous carbon material Ni-NC is obtained.

[0035] The Ni-NC material obtained in Example 1 was characterized as follows: its macroscopic morphology was a complete black block ( Figure 1 ), Scanning electron microscope images ( Figure 2 The image shows that it has a coherent three-dimensional network structure and micron-sized spherical pores; transmission electron microscopy images ( Figure 3 This indicates that the material has abundant nanoscale mesopores; aberration-corrected high-angle annular dark-field image ( Figure 4) and Fourier transform synchrotron radiation spectrum ( Figure 5 This demonstrates that nickel is uniformly distributed in the porous carbon support in the form of single atoms and nanoclusters, successfully constructing a tandem catalytic system; nitrogen adsorption-desorption curves ( Figure 6 This indicates that its specific surface area is as high as 1982 m². 2 / g, which is beneficial for the efficient loading of active sulfur and the physical confinement of polysulfides.

[0036] Electrochemical performance tests showed that the symmetrical battery assembled with Ni-NC pre-plated sodium metal achieved an efficiency of 3 mA / cm². 2 It can be stably cycled for 1000 hours at current density. Figure 7 This demonstrates its ability to effectively promote the stable deposition and stripping of sodium metal; assembling a sodium-sulfur battery using sulfur-loaded Ni-NC as the positive electrode (S / Ni-NC) and sodium-plated Ni-NC as the negative electrode (Na / Ni-NC) exhibits excellent overall performance. Figures 8-10 The initial discharge specific capacity at 0.1C rate reached 1517 mAh / g; the specific capacity at 5C rate reached 580 mAh / g; and the capacity retention after 3000 cycles at 2C rate was 85.4%; at 5.5 mg / cm³... 2 After 500 cycles at sulfur surface loading, the specific capacity remained at 850 mAh / g.

[0037] Example 2:

[0038] The amount of nickel acetate ethanol solution used in step (3) of Example 1 was changed from 50 mL to 25 mL (concentration unchanged), and the rest of the treatment was the same as in Example 1. The nickel in the obtained porous carbon electrode mainly exists in the form of single atoms, and its specific surface area is increased compared with Example 1. However, when used in sodium-sulfur batteries, its rate capability and cycle performance both show a certain degree of decrease.

[0039] Example 3:

[0040] The amount of nickel acetate ethanol solution used in step (3) of Example 1 was changed from 50 mL to 100 mL (concentration unchanged), and the rest of the treatment was the same as in Example 1. The nickel in the obtained porous carbon electrode mainly exists in the form of nanoclusters, and its specific surface area and the overall performance of the sodium-sulfur battery are lower than those in Example 1.

[0041] Example 4:

[0042] In Example 1, step (1) was performed by replacing 4g of glucose with 4g of sucrose, with the remaining treatments being the same as in Example 1. The resulting porous carbon electrode also exhibited a macroscopic bulk structure with a three-dimensional cross-linked network structure, and its specific surface area was comparable to that of Example 1. The performance of the assembled sodium-sulfur battery was similar to that of Example 1.

[0043] Example 5:

[0044] In Example 1, step (1) was performed by replacing 4g of glucose with 8g of glucose, with the remaining treatments being the same as in Example 1. The resulting porous carbon electrode exhibited a similar macroscopic foam morphology and three-dimensional cross-linked network structure to that of Example 1, but its specific surface area and sodium-sulfur battery performance were significantly reduced.

[0045] Example 6:

[0046] In Example 1, step (1) was performed by replacing 8g of zinc chloride with 0g of zinc chloride, with the remaining treatments being the same as in Example 1. The resulting porous carbon electrode also exhibited a macroscopic foam-like structure with a three-dimensional cross-linked network. Due to the lack of a pore-forming agent, its specific surface area and sodium-sulfur battery performance were significantly reduced.

[0047] Example 7:

[0048] In Example 1, step (1) was performed by replacing 4g of urea with 0g of urea, with the remaining treatments being the same as in Example 1. The resulting porous carbon electrode also exhibited a macroscopic foam-like structure with a three-dimensional cross-linked network, and its specific surface area and sodium-sulfur battery performance were significantly reduced.

[0049] It should be noted that the present invention is not limited to the methods and materials described in the specific embodiments above, and those skilled in the art can make appropriate adjustments and modifications according to actual needs. The terminology used herein is only for describing specific embodiments and is not intended to limit the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A bifunctional porous carbon electrode material for sodium-sulfur batteries, characterized in that, The electrode material is composed of a porous carbon carrier and a nickel-based catalyst anchored thereon; the nickel-based catalyst includes nickel monatomic and nickel nanoclusters, both of which constitute a tandem catalytic system; the electrode material can be used as a sulfur positive electrode host and a sodium metal negative electrode substrate at the same time.

2. A method for preparing the bifunctional porous carbon electrode material according to claim 1, characterized in that, It comprises the following steps: (1) precursor mixing and molding: carbon source, nitrogen source, micro / mesopore pore former and molding auxiliary agent are weighed according to the predetermined mass ratio, mixed and ground, and then molded by mechanical pressing to obtain an ingot with a specific geometric shape; (2) one-step carbonization and activation: the ingot obtained in step (1) is placed in a reaction furnace, and under the protection of an inert atmosphere, the temperature is raised from room temperature to 900-1200℃ at a rate of 3-10℃ / min, and then kept at this temperature for 1-5h to complete the carbonization, activation and pore forming process, and then cooled to obtain a porous carbon material NC; (3) tandem catalyst loading: the porous carbon material NC obtained in step (2) is immersed in an ethanol solution of nickel salt, stirred and dried, and then heat treated in a reducing atmosphere at 150-250℃ for 0.5-4h to finally obtain a bifunctional porous carbon material Ni-NC loaded with nickel monatomic and nickel nanoclusters.

3. The method of claim 2, wherein, In step (1), the micro / mesopore pore former is one or more of zinc chloride, zinc acetate and zinc nitrate; the molding auxiliary agent is one or more of zinc powder and zinc oxide.

4. The method of claim 2, wherein, In step (2), the micro / mesopore pore former and the molding auxiliary agent are removed simultaneously by high-temperature thermal volatilization process, without subsequent acid washing treatment.

5. The method of claim 2, wherein, In step (3), the nickel salt is one or more of nickel acetate, nickel nitrate and nickel chloride; the reducing atmosphere is hydrogen-argon mixed gas, in which the volume fraction of hydrogen is 5%-10%.

6. An electrode for sodium-sulfur batteries, characterized by, It is made of the bifunctional porous carbon electrode material of claim 1; when used as a positive electrode, the electrode material is loaded with elemental sulfur or sodium sulfide; when used as a negative electrode, the electrode material is used to carry the deposition of metallic sodium.

7. A sodium-sulfur battery characterized by comprising: It comprises a positive electrode, a negative electrode, a separator and an electrolyte, at least one of the positive electrode and the negative electrode being the electrode for sodium-sulfur battery of claim 6.

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