Preparation method and application of nitrogen and oxygen co-doped three-dimensional hierarchical porous carbon material

Abstract

This invention discloses a method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials. The material is a carbon material with a multi-level three-dimensional porous structure of "aggregates → carbon nanosheets → hierarchical pores," and its main component is a three-dimensional hierarchical porous carbon material with a high content of nitrogen and oxygen atoms doped. This method overcomes the shortcomings of existing carbon-based cathode materials for lithium-sulfur batteries, providing a simple, low-cost method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials. The method is simple, low-cost, and requires no additional template removal step. The resulting material has a multi-level structure of "aggregates → carbon nanosheets → hierarchical pores" and a high content of uniformly distributed N / O heteroatoms, which can effectively suppress polysulfide shuttle, improve electrode reaction kinetics, and alleviate the drawbacks of electrode expansion effects. Simultaneously, this invention provides an application of this material in lithium-sulfur battery cathodes to obtain lithium-sulfur batteries with high capacity and long cycle stability, which is of great significance for improving the performance of lithium-sulfur batteries and promoting their industrial application.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to the preparation method and application of nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials. Background Technology

[0002] Lithium-sulfur batteries, due to sulfur's high theoretical specific capacity (1675 mAh g⁻¹) and energy density (2600 Wh kg⁻¹), as well as its abundant reserves, low cost, and environmental friendliness, have become a highly promising high-energy-density energy storage technology with broad application prospects in electric vehicles, renewable energy storage, and low-altitude drones. However, the practical application of lithium-sulfur batteries faces three major bottlenecks: First, elemental sulfur and its discharge products (Li₂S / Li₂S₂) have extremely poor conductivity (sulfur's electronic conductivity is only 10⁻³⁰ S / cm), resulting in slow electrode reaction kinetics; second, the soluble lithium polysulfides (Li₂Sn, 4≤n≤8) generated during charge and discharge undergo a "shuttle effect" between the positive and negative electrodes, causing loss of active materials, rapid capacity decay, and reduced coulombic efficiency; third, sulfur undergoes approximately 80% volume expansion during charge and discharge cycles, which can easily lead to electrode structure collapse. To address these issues, carbon-based materials, due to their good conductivity, high specific surface area, and tunable pore structure, are widely used to load sulfur and suppress polysulfide shuttle. Hierarchical porous carbon (containing micropores, mesopores, and macropores simultaneously) can mitigate the shuttle effect through "large-pore sulfur storage and mesopore / micropore sulfur limiting," but the weak interaction between non-polarized carbon and polarized lithium polysulfides still leads to the loss of active material and insufficient long-term cycling stability. In existing technologies, doping with heteroatoms (N, O, etc.) or surface functionalization can enhance the chemical interaction between carbon materials and lithium polysulfides, but these methods typically suffer from the following drawbacks:

[0003] (1) The contradiction between heteroatom doping uniformity and cost: Although N / O doping can be achieved by using precursors such as dopamine and pyridine, the unit price of dopamine is as high as 500-3000 yuan / 100g, and multiple separation and purification steps are required to ensure heteroatom uniformity, which makes the cost of large-scale application too high.

[0004] (2) Complexity of template process: Most hierarchical porous carbon requires the use of hard templates such as SiO2 and ZnO. The templates need to be removed with corrosive reagents such as HF and NaOH, which not only increases the number of process steps, but also easily causes the pore structure to collapse and generates environmental pollution.

[0005] (3) Insufficient structure-performance synergy: Existing materials cannot simultaneously satisfy the synergy of "high specific surface area, large pore volume, and high heteroatom content", resulting in the inability to balance polysulfide anchoring and charge transport, and low battery cycle life.

[0006] Therefore, developing a N / O dual-doped three-dimensional hierarchical porous carbon material with a simple preparation process, low cost, uniform heteroatom doping, and the ability to simultaneously achieve synergistic optimization of "sulfur storage-sulfur limitation-charge / ion transport" is of great significance for improving the performance of lithium-sulfur batteries and promoting their industrial application. This invention addresses the aforementioned pain points by combining a self-sacrificing template with a low-cost precursor to achieve synergistic "one-step carbonization-template removal-heteroatom doping," thus overcoming the bottlenecks of existing technologies. Summary of the Invention

[0007] This invention aims to overcome the shortcomings of existing carbon-based cathode materials for lithium-sulfur batteries, and provides a method for preparing and applying nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials. This method is simple, low-cost, and requires no additional template removal step. The resulting material has a multi-level structure of "aggregates → carbon nanosheets → hierarchical pores" and a high content of uniformly distributed N / O heteroatoms, which can effectively suppress polysulfide shuttle, improve electrode reaction kinetics, and alleviate the drawbacks of electrode expansion effect. At the same time, this invention provides the application of this material in the cathode of lithium-sulfur batteries to obtain lithium-sulfur batteries with high capacity and long cycle stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] (I) A method for preparing and applying nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials, characterized by the following steps and their process conditions:

[0010] Step 1: Synthesis of graphitic carbon nitride ( )template

[0011] Urea was placed in a covered alumina crucible and then placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 500-600℃ at a rate of 5℃ / min, held for 2 hours, and then ground after natural cooling to obtain a pale yellow urea solution. powder.

[0012] The optimal conditions are heating to 500-600℃ and holding for 2 hours, and then holding at 550℃ for 2 hours—below 500℃, urea polymerization is incomplete. Poor crystallinity, above 600℃ Excessive decomposition prevents the formation of complete layered structures.

[0013] Step 2: Synthesis precursor

[0014] Take 0.5g of the product obtained in step one. The powder was dispersed in 300 mL of a weakly alkaline buffer solution prepared with deionized water and 5 mL of 1.5 M Tris-HCl (pH = 8.8); under magnetic stirring, 350 μL of diethylenetriamine (DETA) and 0.1375 g of catechol (CAT) were added sequentially, and the pH of the system was adjusted to 8.5-9.0 with dilute hydrochloric acid. The reaction was carried out at room temperature for 12 h; after filtration, the product was washed with deionized water and dried under vacuum at 60 °C for 12 h to obtain... ;

[0015] The aforementioned 0.5g Disperse in 300 mL of weakly alkaline buffer solution. The dosage can be increased or decreased as needed; simply control the amount. The dispersion concentration is 1-2 mg / ml to facilitate sufficient subsequent polymerization modification reaction; the stirring speed is 100-150 rpm under magnetic stirring to avoid violent stirring that could damage the coating; the molar ratio of CAT to DETA is controlled at 1:1-1:3 (preferably 1:2), and the concentration of DETA is 10 mM. This ratio is optimal for polymerization modification and results in the best total amount of heteroatoms after subsequent carbonization; the pH of the system is adjusted to 8.5-9.0 with dilute hydrochloric acid, preferably pH=8.6. When pH<8.5, the polymerization rate of CAT and DETA is too slow and the reaction is incomplete, failing to form a complete coating layer; when pH>9.0, polymerization is too fast, easily leading to severe particle agglomeration.

[0016] Step 3: Preparation of N / O dual-doped three-dimensional hierarchical porous carbon (HNPC)

[0017] The result from step two The material was ground into powder, placed in a tube furnace, and heated to 300℃ for 1 hour at a heating rate of 5℃ / min under an argon atmosphere to remove impurities. The temperature was then further increased to 700-900℃ for 2 hours to carbonize the material. After cooling, N / O dual-doped three-dimensional hierarchical porous carbon material (HNPC) was obtained.

[0018] The calcination at 300℃ for 1 hour is the "pre-carbonization stage," which aims to remove small molecule impurities (such as H2O and NH3) from the polymer. If this step is skipped, the pore structure is easily destroyed due to the violent escape of impurities at high temperatures. The carbonization is carried out by continuing to heat to 700-900℃ for 2 hours. The carbonization temperature is preferably 800℃-750℃. Carbonization is incomplete below 750℃, and the carbon material has poor conductivity (conductivity <10S / m). Above 850℃, a large number of heteroatoms are lost (N content drops to <5%).

[0019] (II) The application of the above-mentioned nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials in the cathode of lithium-sulfur batteries includes the following steps:

[0020] Step 1: Preparation of S@HNPC composite material

[0021] The HNPC prepared by the above method was thoroughly ground and mixed with sulfur powder at different mass ratios to obtain S@HNPC composite material.

[0022] Step 2: Preparation of the positive electrode sheet of S@HNPC composite material

[0023] The S@HNPC composite material from step one is mixed evenly with conductive carbon black SuperP and added to an N-methylpyrrolidone (NMP) solution containing dissolved polyvinylidene fluoride (PVDF). The mixture is stirred evenly to form a positive electrode slurry. The positive electrode slurry is then evenly coated onto an aluminum foil, dried at 60°C for 12 hours, and cut into round pieces with a diameter of 12 mm.

[0024] The mass ratio of each component in the positive electrode slurry is "sulfur powder: (HNPC + conductive carbon black SuperP): polyvinylidene fluoride (PVDF) = 60:30:10", wherein the mass ratio of HNPC is 1-10wt%, preferably 5wt%.

[0025] Step 3: Assemble the lithium-sulfur battery

[0026] In an argon-filled glove box, the electrode prepared in step two was used as the cathode, a thin sheet of metallic lithium as the anode, and Celgard 2325 as the diaphragm, containing 1M LiTFSI and The DOL / DME mixture (volume ratio 1:1) is used as the electrolyte to complete the assembly of the lithium-sulfur battery.

[0027] Compared with the prior art, the present invention has the following significant advantages:

[0028] (1) The preparation process is simple, economical and efficient: As a self-sacrificing template and nitrogen source, no additional template removal step is required during the carbonization process. The nitrogen doping and porous structure construction are achieved simultaneously through decomposition and release. The precursors catechol and diethylenetriamine are inexpensive and can be polymerized at room temperature to form a uniform coating layer without the need for complex equipment or strict reaction conditions, which is conducive to large-scale production.

[0029] (2) Excellent material structure and properties: The obtained HNPC has a multi-level structure of "aggregates → carbon nanosheets → hierarchical pores", and the BET specific surface area reaches , total capacity With an average pore size of 35.97 nm, the macropores can store sulfur particles, while the mesopores / micropores inhibit polysulfide diffusion through capillary action and physical confinement. The N and O doping concentrations are 11.7% and 5.1%, respectively, with heteroatoms evenly distributed. These heteroatoms anchor polysulfides through polar action, while simultaneously improving the conductivity and electrolyte wettability of the carbon material.

[0030] (3) Outstanding battery electrochemical performance: When HNPC is used in lithium-sulfur batteries, only a small amount needs to be added to greatly improve the battery's electrochemical performance. The battery with 10% HNPC added has an initial discharge specific capacity of 1554.5 mAh g⁻¹ at 0.1C rate; the reversible specific capacity at 0.2C rate is 1102.1 mAh g⁻¹, and the capacity remains at 426.2 mAh g⁻¹ after 400 cycles; the sample with 5% HNPC added has an initial discharge specific capacity of 1404 mAh g⁻¹ at 0.1C rate, with the best cycle stability, and the average decay rate is as low as 0.018% / cycle after 400 cycles, and the sulfur utilization rate is improved to 85-90% (the initial discharge capacity reaches 92.8% of the theoretical capacity), which solves the key problems of low active sulfur utilization, rapid capacity decay and poor cycle stability of lithium-sulfur batteries. Attached Figure Description

[0031] Figure 1 The image shown is a scanning electron microscope image of the S@HNPC composite material prepared in Example 1.

[0032] Figure 2 Prepared as in Example 1 Scanning electron microscope image of the precursor.

[0033] Figure 3-4 The image shown is a scanning electron microscope image of the HNPC sample prepared in Example 1.

[0034] Figure 5-6 The image shown is a transmission electron microscope (TEM) image of the HNPC sample prepared in Example 1.

[0035] Figure 7 The elemental mapping diagram of the S@HNPC composite material prepared in Example 1.

[0036] Figure 8 The adsorption-desorption curves and pore size distribution of the HNPC sample prepared in Example 1 are shown.

[0037] Figure 9 The images show the XRD patterns of the HNPC sample and the S@HNPC composite material prepared in Example 1.

[0038] Figure 10 The Raman spectrum of the HNPC sample prepared in Example 1.

[0039] Figure 11-14 XPS image of the HNPC sample prepared in Example 1.

[0040] Figure 15-17 The CV curve of the S@HNPC composite battery prepared in Example 1 is shown.

[0041] Figure 18 The image shows the EIS diagram of the S@HNPC composite battery prepared in Example 1.

[0042] Figure 19 The image shows the first charge-discharge curve of the S@HNPC composite battery prepared in Example 1 at 0.1C.

[0043] Figure 20 The rate performance diagram shows the S@HNPC composite material battery prepared in Example 1.

[0044] Figure 21-23 The above is a rate charge-discharge curve of the S@HNPC composite material battery prepared in Example 1.

[0045] Figure 24 The image shows the cycle performance of the S@HNPC composite battery prepared in Example 1.

[0046] Figure 25-26 The cycling performance graphs show different batches of S@HNPC composite batteries prepared in Example 1. Detailed Implementation

[0047] To further illustrate the technical means and effects of the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the technical solution of the present invention. However, the present invention is not limited to the scope of the embodiments.

[0048] Example 1

[0049] Step 1: Preparation of N / O dual-doped three-dimensional hierarchical porous carbon materials (HNPC)

[0050] (1) Take 10g of urea and put it into a covered alumina crucible. Place it in a tube furnace and introduce argon gas as a protective gas. Heat the furnace to 550℃ at a rate of 5℃ / min and hold for 2 hours. After cooling to room temperature naturally, grind the urea to obtain a light yellow color. powder.

[0051] (2) Take 0.5g of the product obtained in step 1 The powder was dispersed in 300 mL of a weakly alkaline buffer solution prepared with deionized water and 5 mL of 1.5 M Tris-HCl (pH = 8.8). Under magnetic stirring, 350 μL of diethylenetriamine (DETA) and 0.1375 g of catechol (CAT) were added sequentially. The pH of the system was adjusted to 8.6 with dilute hydrochloric acid, and the reaction was carried out at room temperature for 12 h. DETA and CAT underwent a condensation reaction under weakly alkaline conditions, forming a three-dimensional cross-linked polymer network. As a hard template to guide the formation of porous structures, a hierarchical porous framework is obtained after carbonization; after filtration, the product is washed with deionized water and dried under vacuum at 60°C for 12 hours to obtain... Precursor. The typical morphology of this precursor is as follows: Figure 2 As shown.

[0052] (3) The result obtained in step 2 The precursor was ground into a fine powder and placed in a tube furnace. Argon gas was introduced, and the temperature was raised to 300℃ for 1 hour at a rate of 5℃ / min. Subsequently, the temperature was further raised to 700℃, 800℃, and 900℃ for 2 hours each. After natural cooling, N / O dual-doped three-dimensional hierarchical porous carbon materials (HNPC) with different carbonization temperatures were obtained. The HNPC sample carbonized at 800℃ exhibited a typical three-dimensional hierarchical porous structure, and its scanning electron microscope (SEM) morphology is shown below. Figure 3 and Figure 4 As shown, the transmission electron microscope (TEM) image is as follows: Figure 5 and Figure 6 As shown, the multi-level structure of "aggregates → carbon nanosheets → hierarchical pores" is clearly demonstrated. The nitrogen adsorption-desorption curves and pore size distribution of this sample are shown in the figure. Figure 8 As shown, it exhibits a high specific surface area and hierarchical pores dominated by mesopores. X-ray diffraction (XRD) pattern ( Figure 9 ) and Raman spectroscopy ( Figure 10 This confirmed its carbon material characteristics and defect structure. X-ray photoelectron spectroscopy (XPS) analysis ( Figure 11-14 The high content of nitrogen and oxygen elements in the material (11.7% and 5.1%, respectively) and their chemical states were further determined.

[0053] Step 2: Preparation of S@HNPC composite material and assembly of lithium-sulfur battery

[0054] (I) Thoroughly grind and mix the HNPC prepared in step one with sulfur powder at different mass ratios to obtain S@HNPC composite materials. Specifically, weigh the HNPC carrier prepared in step one and elemental sulfur powder at sulfur mass fractions (Swt%) of 60%, 70%, or 80% (corresponding to HNPC to sulfur mass ratios of 2:3, 3:7, and 1:4, respectively). After preliminary grinding and mixing in a mortar for 10-15 minutes, transfer the mixture to a sealed reactor. Under an argon atmosphere, [the mixture is then subjected to...]. The rate of heating up to The mixture was kept at this temperature for 12 hours to ensure that sulfur fully melted, diffused, and penetrated into the hierarchical channels of HNPC. After the reaction, it was naturally cooled to room temperature, and the product was removed and ground again to obtain S@HNPC composite materials with different sulfur loadings. The sulfur loading in the obtained composite materials can be calculated using the above proportions, and its typical morphology and uniform sulfur element distribution are shown in the figure. Figure 1 and Figure 7 As shown.

[0055] (II) The above-mentioned S@HNPC composite material is mixed evenly with conductive carbon black SuperP, and then added to an N-methylpyrrolidone (NMP) solution containing dissolved polyvinylidene fluoride (PVDF). The mixture is stirred evenly to prepare a positive electrode slurry. The mass ratio of each component in the positive electrode slurry is "sulfur powder:(HNPC + conductive carbon black SuperP):polyvinylidene fluoride (PVDF) = 60:30:10", and the mass ratio of HNPC is 2wt%, 5wt%, and 10wt%. The positive electrode slurry is then evenly coated onto aluminum foil. Dry for 12 hours, then punch into round slices with a diameter of 12mm.

[0056] (III) In an argon-filled glove box, using the electrode prepared in step (II) as the cathode, a thin sheet of metallic lithium as the anode, and Celgard 2325 as the diaphragm, containing 1M LiTFSI and The DOL / DME mixture (volume ratio 1:1) is used as the electrolyte to complete the assembly of the lithium-sulfur battery.

[0057] Electrochemical tests were performed on the obtained battery. Its cyclic voltammetry (CV) curve is shown below. Figure 15-17 As shown, typical redox peaks of lithium-sulfur batteries are observed. Electrochemical impedance spectroscopy (EIS) is shown below. Figure 18 As shown. The initial charge-discharge curve of this battery at a 0.1C rate is as follows. Figure 19 As shown, the initial discharge specific capacity reaches The rate performance and corresponding charge / discharge curves are as follows: Figure 20 and Figure 21-23 As shown. The long-cycle stability test results are as follows. Figure 24 As shown, the battery retains a high reversible capacity after 400 cycles at 0.2C. The consistency of cycle performance across different batches is verified as follows: Figure 25 and Figure 26 As shown.

[0058] Example 2

[0059] Step 1: Preparation of N / O dual-doped three-dimensional hierarchical porous carbon materials (HNPC)

[0060] (1) Take 10g of urea and put it into a covered alumina crucible. Place the crucible in a tube furnace and introduce argon gas as a protective gas. The rate of heating up to After keeping it at this temperature for 2 hours and allowing it to cool naturally to room temperature, grind it to obtain a light yellow color. powder.

[0061] (2) Take 0.5g of the product obtained in step 1 The powder was dispersed in 300 mL of a weakly alkaline buffer solution prepared with deionized water and 5 mL of 1.5 M Tris-HCl (pH = 8.8). DETA and CAT were added sequentially under magnetic stirring, with CAT to DETA molar ratios of 1:1, 1:2, and 1:3, respectively, and the DETA concentration was 10 mM. The pH of the system was adjusted to 8.6 with dilute hydrochloric acid, and the reaction was carried out at room temperature for 12 h. After filtration, the product was washed with deionized water and dried under vacuum at 60 °C for 12 h to obtain polymerized products modified with different CAT / DETA molar ratios. .

[0062] (3) The result obtained in step 2 The precursors were ground into fine powder, placed in a tube furnace, and argon gas was introduced to... The temperature was increased to 300℃ and calcined for 1 hour, then further increased to 800℃ and calcined for 2 hours. After natural cooling, N / O dual-doped three-dimensional hierarchical porous carbon materials (HNPC) with different CAT / DETA molar ratios were obtained. This example is mainly used to explore the influence of precursor ratio on material properties. The main structural and elemental composition characteristics of the obtained materials can be referred to the relevant figures in Example 1. Figure 3-14 The electrochemical performance trend was analyzed and compared with the battery performance of different HNPC addition amounts in Example 1. Figure 15-24 The pattern revealed is consistent with that.

[0063] Step 2: Preparation of S@HNPC composite material and assembly of lithium-sulfur battery

[0064] (a) The HNPC prepared in step one is thoroughly ground and mixed with sulfur powder at different mass ratios to obtain S@HNPC composite material.

[0065] (II) The above-mentioned S@HNPC composite material is mixed evenly with conductive carbon black SuperP, and then added to an N-methylpyrrolidone (NMP) solution containing dissolved polyvinylidene fluoride (PVDF). The mixture is stirred evenly to prepare a positive electrode slurry. The mass ratio of each component in the positive electrode slurry is "sulfur powder:(HNPC + conductive carbon black SuperP):polyvinylidene fluoride (PVDF) = 60:30:10", and the mass ratio of HNPC is 2wt%, 5wt%, and 10wt%. The positive electrode slurry is then evenly coated onto aluminum foil. Dry for 12 hours, then punch into round slices with a diameter of 12mm.

[0066] (III) In an argon-filled glove box, using the electrode prepared in step (II) as the cathode, a thin sheet of metallic lithium as the anode, and Celgard 2325 as the diaphragm, containing 1M LiTFSI and A DOL / DME mixture (volume ratio 1:1) was used as the electrolyte to complete the assembly of the lithium-sulfur battery. The electrochemical performance test results also followed the pattern described in Example 1.

[0067] Example 3

[0068] Step 1: Preparation of N / O dual-doped three-dimensional hierarchical porous carbon materials (HNPC)

[0069] (1) Take 10g of urea and put it into a covered alumina crucible. Place the crucible in a tube furnace and introduce argon gas as a protective gas. The rate of heating up to After keeping it at this temperature for 2 hours and allowing it to cool naturally to room temperature, grind it to obtain a light yellow color. powder.

[0070] (2) Take 0.3g, 0.5g, and 0.6g of the product obtained in step 1 respectively. The powder was dispersed in 300 mL of a weakly alkaline buffer solution prepared with deionized water and 5 mL of 1.5 M Tris-HCl (pH = 8.8); under magnetic stirring, 350 μL of diethylenetriamine (DETA) and 0.1375 g of catechol (CAT) were added sequentially, and the pH of the system was adjusted to 8.6 with dilute hydrochloric acid. The reaction was carried out at room temperature for 12 h; after filtration, the product was washed with deionized water. Vacuum drying for 12 hours yielded different results. Polymerization modification at concentration .

[0071] (3) Take the results from step 2 respectively The precursor is ground into a fine powder, placed in a tube furnace, and argon gas is introduced to... The rate of heating up to Calcination for 1 hour, followed by further heating to After calcination for 2 hours and natural cooling, N / O dual-doped three-dimensional hierarchical porous carbon material (HNPC) was obtained. This example mainly investigates the effect of template concentration on the material structure. The basic structural characteristics of the obtained material are similar to those of the material in Example 1 (see reference). Figure 3-6 , Figure 8-10 Its effect on improving electrochemical performance as a positive electrode additive for batteries is consistent with the conclusions of Examples 1 and 2.

[0072] Step 2: Preparation of S@HNPC composite material and assembly of lithium-sulfur battery

[0073] (a) The HNPC prepared in step one is thoroughly ground and mixed with sulfur powder at different mass ratios to obtain S@HNPC composite material.

[0074] (II) The above-mentioned S@HNPC composite material is mixed evenly with conductive carbon black SuperP, and then added to an N-methylpyrrolidone (NMP) solution containing dissolved polyvinylidene fluoride (PVDF). The mixture is stirred evenly to prepare a positive electrode slurry. The mass ratio of each component in the positive electrode slurry is "sulfur powder:(HNPC + conductive carbon black SuperP):polyvinylidene fluoride (PVDF) = 60:30:10", and the mass ratio of HNPC is 2wt%, 5wt%, and 10wt%. The positive electrode slurry is then evenly coated onto aluminum foil. Dry for 12 hours, then punch into round slices with a diameter of 12mm.

[0075] (III) In an argon-filled glove box, using the electrode prepared in step (II) as the cathode, a thin sheet of metallic lithium as the anode, and Celgard 2325 as the diaphragm, containing 1M LiTFSI and A DOL / DME mixture (volume ratio 1:1) was used as the electrolyte to complete the assembly of the lithium-sulfur battery. The electrochemical performance test results of the assembled battery, together with those of Examples 1 and 2, confirm the positive effect of HNPC material on improving the performance of lithium-sulfur batteries. Figure 15-26 ).

[0076] Cycle performance testing of assembled batteries The tests were conducted within a voltage window of 1.7–2.8 V, with a current density of 335 mA / g corresponding to 0.2C. The initial capacity of the pure sulfur cathode in the control group was 820 mAh / g, which decreased to 35% capacity retention after 100 cycles, while the S@HNPC cathode retained more than 80% capacity.

[0077] The instruments used for material characterization and electrochemical performance testing in the above embodiments are as follows:

[0078] Morphology testing: Images were taken using a field emission scanning electron microscope (GeminiSEM360). Figure 1-4 (e.g., 7) and a high-resolution transmission electron microscope (TalosF200XG2, used for imaging) Figure 5-6 ).

[0079] Material structure and performance testing: The crystal structure of the sample was analyzed using a Bruker D8 Advance X-ray diffractometer (to obtain...). Figure 9 Data), the adsorption-desorption isotherms of the samples were tested using an ASAP2460 analyzer (to obtain Figure 8 Data), using a Horiba Raman spectrometer to analyze the degree of graphitization and defects in the samples (obtained) Figure 10 Data), and characterization of elemental composition and chemical state using X-ray photoelectron spectroscopy (XPS, NexsaG2) (obtained) Figure 11-14 data).

[0080] Electrochemical performance testing: A CHI6600E electrochemical workstation manufactured by Shanghai Chenhua Co., Ltd. was used to specifically test the cyclic voltammetry characteristics of the battery. Figure 15-17 (data) and AC impedance (obtained) Figure 18 The data was used for testing.

[0081] Charge / discharge test: The Wuhan Landian Battery testing system was used. This system has a 20mA current range and a 5V voltage range, and is used to test the battery's charge / discharge curve (to obtain...). Figure 19 , 21 -23 data), scaling performance (obtained) Figure 20 (data) and cycle performance (obtained) Figure 24-26 data).

Claims

1. A method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials, characterized in that, This material is a carbon material with a multi-level three-dimensional porous structure of "aggregates → carbon nanosheets → hierarchical pores". Its main component is a three-dimensional hierarchical porous carbon material with high nitrogen and oxygen atom doping content. The process includes the following steps and their processing conditions: Step 1: Synthesis template Urea was placed in a covered alumina crucible and heated to 500-600℃ at a heating rate of 2-5℃ / min under an inert gas atmosphere. The temperature was maintained for 2 hours, and after natural cooling, the mixture was ground to obtain... powder; Step 2: Synthesis precursor Prepare a buffer solution of deionized water and 1.5 M Tris-HCl, and add the solution obtained in step one. After ultrasonic dispersion of the powder for 10-40 min, diethylenetriamine and catechol were added sequentially under continuous stirring. The pH of the system was adjusted to 8.5-9.0, and the reaction was carried out at room temperature for 10-14 h. After filtration and washing, the powder was dried at 50-70℃ for 8-16 h to obtain the desired product. ; Step 3: Carbonization preparation of nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials Will After grinding, the material is heated to 300℃ for 1 hour at a heating rate of 2-5℃ / min in an inert gas atmosphere, and then heated to 700-900℃ for 1.5-2.5 hours. After cooling, a nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon material is obtained.

2. The method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials according to claim 1, characterized in that, In step one, the inert gas is argon or nitrogen; urea is used as... The precursor; the heating rate is 2-5℃ / min, the calcination temperature is 550℃, and the holding time is 2h.

3. The method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials according to claim 1, characterized in that, In step two, the buffer solution is a weakly alkaline solution composed of deionized water and 1.5 M Tris-HCl. The concentration of the hydroxyl group was 1-2 mg / ml; the molar ratio of catechol to diethylenetriamine was 1:1-1:3, and the concentration of diethylenetriamine was 10 mM; the pH of the mixture solution system was 8.5-9.0; the reaction time at room temperature was 10-14 h, the drying temperature was 60℃, and the drying time was 8-16 h.

4. The method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials according to claim 1, characterized in that, In step three, the inert gas is argon; the heating rate is 2-5℃ / min; it needs to be pre-calcined at 300℃ for 1 hour before high-temperature carbonization; the carbonization temperature is 700-900℃ and the carbonization time is 2 hours.

5. The method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials according to claim 1, characterized in that, This preparation method involves using... To achieve synergistic effects of "one-step carbonization-template removal-heteroatom doping" by combining self-sacrificing templates with low-cost catechol and polyamine precursor polymerization modification.

6. A method for preparing the nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon material as described in claim 5, characterized in that, The material has a multi-level structure of "aggregates → carbon nanosheets → hierarchical pores"; a porous structure with high specific surface area and large pore volume, mainly mesopores with macropores and micropores; and high atomic doping, with nitrogen doping concentration of 8-13% and oxygen doping concentration of 4-7%.

7. The method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials according to claim 6, characterized in that, It also includes the following steps: (1) The nitrogen and oxygen dual-doped three-dimensional hierarchical porous carbon material prepared by the above method is thoroughly ground and mixed with sulfur powder at different mass ratios to obtain S@HNPC composite material; (2) Mix the S@HNPC composite material with conductive carbon black evenly, add it to N-methylpyrrolidone solution in which polyvinylidene fluoride is dissolved, stir evenly to make a positive electrode slurry, coat the positive electrode slurry evenly on the current collector, dry at 60°C for 12 hours, and cut into a positive electrode sheet. (3) Using the positive electrode as the cathode, the lithium metal sheet as the anode, the porous polymer membrane as the separator, and the ether mixture containing lithium salt and additives as the electrolyte, a lithium-sulfur battery is assembled in an inert gas atmosphere.

8. The method for preparing nitrogen- and oxygen-doped three-dimensional hierarchical porous carbon materials according to claim 7, characterized in that, In step (1), the S@HNPC composite material is made by simply grinding and mixing nitrogen and oxygen doped three-dimensional hierarchical porous carbon material with sulfur powder; in step (2), sulfur powder: (nitrogen and oxygen doped three-dimensional hierarchical porous carbon material + conductive carbon black): polyvinylidene fluoride = 60:30:10, wherein the mass ratio of nitrogen and oxygen doped three-dimensional hierarchical porous carbon material is 1-10wt%.

Images