Preparation method of sulfur-doped porous sphere carbon material and application of sulfur-doped porous sphere carbon material in preparation of sodium-ion battery

Abstract

The invention provides a preparation method of a sulfur-doped porous carbon sphere material, which comprises the following steps: mixing absolute ethyl alcohol, ammonia water and water, heating and stirring, then adding resorcinol, a formaldehyde solution and thiourea, continuously stirring, carrying out hydrothermal reaction, centrifuging, washing to be neutral, and drying in an inert atmosphere to finally obtain a target product. The material is of a three-dimensional structure assembled by two-dimensional nanosheets, and the structure can enlarge the interlayer spacing of the porous carbon sphere material, introduce defects and active sites, improve the porosity and specific surface area, and enhance the adsorption of the porous carbon sphere material to sodium ions. The sodium-ion battery negative electrode material prepared by taking the material as an active substance has good cycling stability, and the coulombic efficiency at each rate is close to 100%, which shows that sulfur doping optimizes the interfacial compatibility; when the current density is 2.0 C, the battery capacity still reaches 250 mA h / g after 3000 times of circulation, and the electrochemical performance of the sodium ion battery is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy materials, and particularly relates to a preparation method of sulfur-doped porous carbon sphere material and application of the sulfur-doped porous carbon sphere material as a negative electrode material of a sodium ion battery in preparation of a high-performance sodium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in the fields of portable devices, electric vehicles and aerospace, etc. With the large-scale use of lithium ion batteries, the rapid consumption of resources and energy shortage have become increasingly serious. Seeking alternative resources has become the focus of research in recent years. Sodium ion batteries (SIBs) have similar electrochemical performance to lithium ion batteries, and sodium resources are abundant and low in cost, so they have greater application potential in large-scale energy storage. However, due to the larger radius of sodium ions (0.102 nm) than that of lithium ions (0.076 nm), the kinetics of SIBs is slow and the cycle stability is poor. The electrode material is a core component of the battery and plays a crucial role in the performance of the entire battery. Carbon-based materials have good electrical conductivity and relatively stable structure during the charging and discharging process, and are considered to be the key negative electrode material for promoting the practical process of SIBs, but they face the problems of low first-cycle coulombic efficiency, low capacity and poor rate performance, so the structure of the carbon material needs to be reasonably designed.

[0003] Hollow carbon sphere materials are a kind of carbon functional materials with regular spherical morphology, and a large number of different scale pore structures are distributed inside or on the surface of the spheres. They have high specific surface area and porosity, providing abundant active sites and channels for material adsorption, ion transport or catalytic reaction. The flowability and bulkiness of the spherical structure are good, which is convenient for molding and assembly in industrial application, and is widely used in energy storage and catalysis. Through heteroatom doping (such as sulfur, nitrogen, phosphorus, oxygen, boron doping), the porous carbon sphere can be chemically modified. The combination of the structural advantages of the porous carbon sphere and the chemical modification effect of the heteroatom doping can significantly optimize the electronic structure, surface chemistry, and interface effect, thereby improving the core performance of the material in the fields of energy storage, adsorption separation, and catalytic reaction. Chen et al. studied the adsorption of sodium ions on sulfur-doped nanoporous carbon. By optimizing the adsorption site, it was found that the adsorption configuration in the nanopore was the most stable, with a binding energy as high as -2.02 eV (Nano Energy, 2015, 15, 746-754). Zhang et al. increased the interlayer spacing of carbon materials from 0.37 nm to 0.41 nm through sulfur doping, and found that the diffusion barrier was reduced from 203 meV for undoped materials to 158 meV, proving that the expansion of interlayer spacing can reduce the diffusion barrier and promote the diffusion and migration of sodium ions (Adv. Energy Mater., 2016, 6, 1501929). Gao et al. successfully prepared porous carbon nanosheets with a high N / S doping amount of 10.41%, which produced a large number of active sites due to the defect structure, facilitating the storage of sodium ions, and exhibited excellent rate performance and high cycle stability in SIB half-cells (Carbon, 2024, 229, 119481). Liu et al. synthesized N and S co-doped porous carbon microspheres assembled from two-dimensional nanosheets. This strategy improved the structural stability of the negative electrode material, shortened the ion diffusion path, and promoted the reaction kinetics, exhibiting excellent electrochemical performance in both lithium-ion batteries and sodium-ion batteries (Science China Materials, 2024, 67, 3637-3647). Zhang et al. developed sulfur and nitrogen co-doped carbon nanosheet (S&N-CNS) negative electrode materials with porous nanosheet structure and ultra-large specific surface area, effectively promoting charge transfer and ion transport, and enhancing ion storage performance (SusMat, 2025, 5, e70021). Therefore, the application of sulfur-doped porous carbon sphere materials in sodium-ion batteries can achieve high performance and long cycle life, and we need to find a low-cost and scalable preparation method.

[0004] Based on this, the present application is developed. SUMMARY

[0005] The application aims at solving the problem of insufficient capacity of existing carbon materials, and provides a sulfur-doped porous carbon sphere material, which has the advantages of high reversible capacity, long cycle period and excellent rate performance as a negative electrode material of a sodium ion battery.

[0006] The application further provides a preparation method of the sulfur-doped porous carbon sphere material and application of the sulfur-doped porous carbon sphere material as a negative electrode material of a sodium ion battery in preparation of a high-performance sodium ion battery.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the application is as follows: A preparation method of a sulfur-doped porous carbon sphere material, which comprises the following steps: mixing, heating and stirring anhydrous ethanol, ammonia water and water, then adding resorcinol and formaldehyde solution, and continuously stirring and reacting with thiourea, and finally performing hydrothermal reaction, centrifugation, washing to neutral, and drying in an inert atmosphere to obtain the final target product.

[0008] The preparation method of the sulfur-doped porous carbon sphere material comprises the following steps: firstly, mixing, heating and stirring anhydrous ethanol, ammonia water and water; then, uniformly mixing resorcinol and formaldehyde solution; then, continuously stirring and reacting with formaldehyde solution and thiourea; and finally, performing hydrothermal reaction, centrifugation, washing to neutral, and drying in an inert atmosphere to obtain the final target product.

[0009] Specifically, 70-90ml of anhydrous ethanol and 1-2ml of ammonia water can be uniformly mixed in 150-250ml of deionized water; the concentration of the ammonia water is 5-10%. Further, 1.0-1.3g of resorcinol and 1.3-1.8ml of formaldehyde solution can be added first; then, 0.5-0.7g of thiourea and 1.0-1.3ml of formaldehyde solution can be added; the concentration of the formaldehyde solution is 35-40%.

[0010] As a preferred embodiment, the application provides a preparation method of the sulfur-doped porous carbon sphere material, which comprises the following steps: 1) uniformly mixing 80ml of anhydrous ethanol, 1.0ml of ammonia water and 200ml of deionized water to form a first mixed solution; 2) heating the first mixed solution to 70±10 o C and stirring at a constant temperature for 30±10min to form a second mixed solution; if the stirring time is too short, the anhydrous ethanol and the ammonia water cannot be uniformly dispersed, and if the stirring time is too long, the uniform dispersion degree cannot be further improved; specifically, 80ml of anhydrous ethanol, 1.0ml of ammonia water and 200ml of deionized water can be used; if the volume of the deionized water is too small, the anhydrous ethanol and the ammonia water cannot be fully dissolved; and if the volume of the deionized water is too large, the stirring and drying time is too long; 3) Add 1.1 g of resorcinol and 1.48 ml of formaldehyde solution to the second mixture, stir at 70±10℃ for 30±10 min to form the third mixture; 4) Add 0.63 g of thiourea and 1.1 ml of formaldehyde solution to the third mixture, mix well, and react at 70±10℃ for 24±6 h to form the fourth mixture, so that the sulfur element is uniformly distributed at the atomic level in the carbon material; 5) Transfer the fourth mixture to a stainless steel polytetrafluoroethylene reactor, and perform hydrothermal reaction at 120±20℃ for 24±6 h to form the fifth mixture; if the temperature is too low, the reaction is not complete; if the temperature is too high, there is a safety hazard in the experiment; 6) After the reactor is naturally cooled to room temperature, centrifuge the fifth mixture, and repeatedly wash with deionized water until neutral to obtain the sixth mixture; 7) Under an argon protective atmosphere, heat the sixth mixture to 600-1000 o C for 1-3 h to obtain the final target product. The material is a three-dimensional structure assembled by two-dimensional nanosheets, which can expand the interlayer spacing of the porous carbon sphere material, introduce defects and active sites, increase the porosity and specific surface area, and enhance the adsorption of sodium ions. The sodium ion battery anode material prepared by using the material as the active material has good cycle stability, and the coulombic efficiency at each rate is close to 100%, which indicates that the sulfur doping optimizes the interface compatibility; when the current density is 2.0 C, the battery capacity is still as high as 250 mA h / g after 3000 cycles, which significantly improves the electrochemical performance of the sodium ion battery.

[0011] Specifically, in step 6), after the reactor is naturally cooled to room temperature, centrifuge the fifth mixture in the centrifuge at a speed of 7000-9000 rpm for 10-20 min. If the reactor is not cooled to room temperature, it is easy to cause burns, and it may also cause the reaction liquid to splash, resulting in loss of raw materials and experimental pollution; after cooling to room temperature, the pressure in the reactor is reduced to normal pressure, which can eliminate the safety hazards in the operation; if the centrifugal speed is too low (such as below 5000 rpm), the centrifugal force is insufficient, resulting in low solid-liquid separation efficiency, and even loss with the supernatant; if the speed is too high (such as above 10000 rpm), the excessive centrifugal force can damage the microporous / mesoporous structure inside.

[0012] Further, in step 7), heat to 600℃, 800℃ or 1000℃ at a heating rate of 3-7℃ / min.

[0013] The application provides a sulfur-doped porous carbon sphere material prepared by the above preparation method.

[0014] The application also provides application of the sulfur-doped porous carbon sphere material as a negative electrode material of a sodium ion battery.

[0015] The application also provides application of the sulfur-doped porous carbon sphere material as a negative electrode material of a sodium ion battery in preparation of a sodium ion battery.

[0016] In the present research, the raw materials (anhydrous ethanol, ammonia, resorcinol, formaldehyde, and thiourea) are all conventional chemical reagents, and no expensive template agent, noble metal catalyst, or special carbon source is needed; the preparation process adopts a template-free method, and the porous structure is spontaneously formed through hydrothermal polymerization and high-temperature carbonization, thereby avoiding the cumbersome steps (such as acid washing and alkali washing) of template removal, greatly simplifying the process flow and reducing the industrial production cost. In addition, thiourea has a dual role of sulfur source and pore-forming agent, and the gas (such as NH3 and CS2) generated by the decomposition of thiourea in the carbonization process can etch the carbon skeleton to form micropores and mesopores, and no additional pore-forming agent is needed, further simplifying the process. As a result, the sulfur-doped porous carbon material can expand the interlayer spacing, introduce defects and active sites, improve the porosity and specific surface area, and thus improve the electrochemical performance of the sodium ion battery.

[0017] Sodium ion batteries (SIBs) have similar electrochemical performance to lithium ion batteries, and sodium resources are abundant and low in cost, so they have greater application potential in the field of large-scale energy storage. However, due to the larger radius of sodium ions (0.102 nm) than that of lithium ions (0.076 nm), the kinetics of SIBs is slow, and the internal stress caused by intercalation is extremely easy to cause the structure of the electrode material to collapse, thereby causing the electrochemical performance to decrease significantly. In order to solve the above problems, some feasible strategies have been proposed by the previous people, that is, introducing heteroatoms into carbon materials to improve the structural stability of the carbon materials, enhance the charge transfer ability, and increase the storage capacity of sodium ions. Based on this, the present application prepares a sulfur-doped porous spherical carbon material which can be used as a negative electrode material of a sodium ion battery by a simple, universal and mild method. The preparation method has the advantages of low cost, easy control and environmental friendliness during the synthesis process, and the prepared sulfur-doped porous carbon material has a clear graphite microcrystalline structure, more defects, and a synergistic structure of high conductivity and high active sites, which can effectively solve the problems of low capacity, poor rate and unstable cycle of carbon-based electrodes of sodium ion batteries, and is an ideal candidate for electrode materials of sodium ion batteries.

[0018] Compared with the prior art, the present application has the following advantages and beneficial effects: 1) The preparation method of the present application is low in cost, good in repeatability, simple in operation and easy to control; 2) In the preparation process of the present application, thiourea is selected, which has a dual role of sulfur source and pore-forming agent, and the gas (such as NH3 and CS2) generated by the decomposition of thiourea in the carbonization process can etch the carbon skeleton to form micropores and mesopores, and no additional pore-forming agent is needed, further simplifying the process; 3) In the present invention, preferably 800 o C The carbonized material, the graphitization degree is appropriate, the pore structure is reasonable, the conductivity of the material can be effectively improved, more sodium storage sites are provided, and the structure is more stable. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 SEM picture of the sulfur-doped porous spherical carbon material prepared in Example 1 of the present invention; Figure 2 TEM picture of the sulfur-doped porous spherical carbon material prepared in Example 1 of the present invention; Figure 3 XRD picture of the sulfur-doped porous spherical carbon material prepared in Examples 1, 2 and 3 of the present invention; Figure 4 Raman spectrum of the sulfur-doped porous spherical carbon material prepared in Example 1 of the present invention; Figure 5 SEM picture of the sulfur-doped porous spherical carbon material prepared in Example 2 of the present invention; Figure 6 TEM picture of the sulfur-doped porous spherical carbon material prepared in Example 2 of the present invention; Figure 7 Raman spectrum of the sulfur-doped porous spherical carbon material prepared in Example 2 of the present invention; Figure 8 SEM picture of the sulfur-doped porous spherical carbon material prepared in Example 3 of the present invention; Figure 9 TEM picture of the sulfur-doped porous spherical carbon material prepared in Example 3 of the present invention; Figure 10 Raman spectrum of the sulfur-doped porous spherical carbon material prepared in Example 3 of the present invention; Figure 11 Rate performance and long cycle stability of the sodium ion battery using the sulfur-doped porous spherical carbon material prepared in Examples 1, 2 and 3 of the present invention as negative electrode material; wherein: (a) rate performance test of the negative electrode material at 0.1, 0.2, 0.5, 1.0 and 2.0, 5.0 C, and then returning to 0.1 C current density; (b) cycle performance test of the negative electrode material at a current density of 2.0 C. DETAILED DESCRIPTION

[0020] The technical solutions of the present invention are further described in detail below in combination with examples, but the protection scope of the present invention is not limited thereto.

[0021] In the following examples, the raw materials used are all ordinary commercially available products that can be directly purchased, or can be prepared by using conventional techniques in the art. In the examples, the concentration of the ammonia water used is 5-10%; the concentration of the formaldehyde solution used is 35-40%.

[0022] Room temperature refers to 25± 5 o C.

[0023] Example 1 A preparation method of a sulfur-doped porous spherical carbon material, specifically comprising the following steps: 1) uniformly mixing 80 ml of anhydrous ethanol, 1.0 ml of ammonia water, and 200 ml of deionized water to form a first mixed solution; 2) heating the first mixed solution to 70 o C and constant-temperature stirring for 30 min to form a second mixed solution; 3) adding 1.1 g of resorcinol and 1.48 ml of formaldehyde solution to the second mixed solution, and constant-temperature stirring at 70 o C for 30 min to form a third mixed solution; 4) adding 0.63 g of thiourea and 1.1 ml of formaldehyde solution to the third mixed solution, mixing uniformly, and constant-temperature stirring at 70 o C for 24 h to form a fourth mixed solution; 5) transferring the fourth mixed solution to a stainless steel polytetrafluoroethylene reaction kettle, and performing a hydrothermal reaction at 120 o C for 24 h to form a fifth mixed solution; 6) naturally cooling the reaction kettle to room temperature, centrifuging the fifth mixed solution in a centrifuge at a speed of 8000 rpm for 10 min, and washing with deionized water for 3-5 times until neutral to obtain a sixth mixed solution; 7) under an argon protective atmosphere, heating the sixth mixed solution to 600 o C / min to 600 o C and drying for 2 h to finally obtain the target product.

[0024] The SEM, TEM, XRD, and Raman spectra of the obtained sulfur-doped porous spherical carbon material are shown in Figure 1 、 Figure 2 、 Figure 3 and Figure 4 respectively.

[0025] Figure 1 The SEM picture of the sulfur-doped porous spherical carbon material prepared in Example 1 of the present application is given, and it can be obviously seen that the particle dispersibility of the material is poor, the agglomeration phenomenon is serious, the spherical morphology is irregular, and the particle size distribution is uneven.

[0026] Figure 2The TEM picture of the sulfur-doped porous spherical carbon material prepared in Example 1 of the present application is given, and it can be obviously seen that the carbon layer of the material has a high degree of disorder.

[0027] Figure 3 The XRD spectrum of the sulfur-doped porous spherical carbon material prepared in Examples 1, 2 and 3 of the present application is given, and it can be obviously seen that the peak at 23 o nearby is the (002) peak corresponding to the "interlayer stacking structure of carbon layers" in the graphite crystal, and the shape (sharpness, intensity) and position of the peak directly reflect the graphitization degree and interlayer spacing of the carbon material;43 o the peak at nearby is the (100) peak corresponding to the "in-plane six-membered ring structure order" of the carbon material, and it reflects the in-plane crystallinity of the carbon skeleton. The peak at 23 o nearby in Example 1 is wide and diffuse, and has low intensity, indicating that the material is mainly amorphous carbon, and the order of the carbon skeleton is extremely poor, and the graphitization degree is extremely low.

[0028] Figure 4 The Raman spectrum of the sulfur-doped porous spherical carbon material prepared in Example 1 of the present application is given, and it can be obviously seen that the D peak (~1450 cm -1 ) corresponds to the defects and disordered structure in the carbon skeleton, and it only appears when the carbon material has disorder / defects; the G peak (~1750 cm -1 ) corresponds to the in-plane vibration of sp 2 hybrid carbon, and it reflects the order of the carbon skeleton (i.e. the graphitization degree), and the sharper and higher the peak, the stronger the graphitization degree. D The I G / I D ratio is used to measure the defect density of the carbon material, and the larger the ratio, the more defects; it can also reflect the size of the graphite crystallite, and the larger the ratio, the smaller the size of the crystallite. The I G / I 2 ratio of Example 1 is the smallest, being 0.87, indicating that the carbonization temperature is low, and the pyrolysis and rearrangement of the carbon precursor are not sufficient, and the carbon skeleton is mainly amorphous sp o carbon (corresponding to the broadened peak in XRD); at the same time, the sulfur atoms are uniformly embedded in the carbon skeleton, and do not occur in large amounts, and the density of defects is not high.

[0029] Example 2 A preparation method of a sulfur-doped porous spherical carbon material, specifically comprising the following steps: 1) uniformly mixing 80 ml of anhydrous ethanol, 1.0 ml of ammonia water and 200 ml of deionized water to form a first mixed solution; 2) heating the first mixed solution to 70 o C and stirring at a constant temperature for 30 min to form a second mixed solution; 3) Add 1.1 g of resorcinol and 1.48 ml of formaldehyde solution to the second mixture, and stir at 70 o C for 30 min to form the third mixture; 4) Add 0.63 g of thiourea and 1.1 ml of formaldehyde solution to the third mixture, mix well, and stir at 70 o C for 24 h to form the fourth mixture; 5) Transfer the fourth mixture to a stainless steel polytetrafluoroethylene reactor, and perform a hydrothermal reaction at 120 o C for 24 h to form the fifth mixture; 6) After the reactor is naturally cooled to room temperature, centrifuge the fifth mixture at 8000 rpm for 10 min, and wash with deionized water for 3-5 times until neutral to obtain the sixth mixture; 7) Under an argon protective atmosphere, heat the sixth mixture to 800 o C at a heating rate of 5 o C / min, and dry for 2 h to obtain the target product.

[0030] The SEM, TEM, XRD, and Raman spectra of the obtained sulfur-doped porous spherical carbon material are shown in Figure 5 、 Figure 6 、 Figure 3 and Figure 7 respectively.

[0031] Figure 5 The SEM picture of the sulfur-doped porous spherical carbon material prepared in Example 2 of the present application is given, and it can be obviously seen that the particle dispersibility of the material is improved, the agglomeration phenomenon still exists, the spherical morphology is relatively regular, and the particle size distribution is relatively uniform.

[0032] Figure 6 The TEM picture of the sulfur-doped porous spherical carbon material prepared in Example 2 of the present application is given, and it can be obviously seen that the carbon layer disorder degree of the material is reduced, local ordered carbon domains appear, and gradually show a graphite crystallite structure.

[0033] Figure 3 The XRD spectra of the sulfur-doped porous spherical carbon materials prepared in Examples 1, 2, and 3 of the present application are given, and it can be obviously seen that the (002) peak near 23 o : corresponds to the "interlayer stacking structure of carbon layers" in graphite crystals, and the shape (sharpness, intensity) and position of the peak directly reflect the graphitization degree and interlayer spacing size of the carbon material; the (100) peak near 43 o : corresponds to the "in-plane six-membered ring structure order" of the carbon material, and reflects the in-plane crystallinity of the carbon skeleton. The broadening degree of the peak of Example 2 is slightly reduced, and the intensity is slightly increased, indicating that local ordered domains begin to appear in the carbon skeleton, and the graphitization degree is preliminarily improved.

[0034] Figure 7 The Raman spectrum of the sulfur-doped porous spherical carbon material prepared in Embodiment 2 of the present application is given, and it can be obviously seen that: the D peak (~1450 cm -1 ) corresponds to defects and disordered structures in the carbon skeleton, and only appears when the carbon material has disorder / defects; the G peak (~1750 cm -1 ) corresponds to the in-plane vibration of sp 2 hybrid carbon, and reflects the order of the carbon skeleton (i.e. the degree of graphitization), and the more sharp and high the peak shape and intensity are, the stronger the degree of graphitization is. The I D / I G ratio is used to measure the defect density of the carbon material, and the larger the ratio is, the more defects there are; and the ratio can also reflect the size of the graphite crystallite, and the larger the ratio is, the smaller the size of the crystallite is. The I D / I G value of Embodiment 2 greatly rises to 1.01, indicating that as the temperature rises, the carbon skeleton begins to be ordered (the degree of graphitization is preliminarily improved, corresponding to the sharpening of the XRD peak), but the sulfur atoms begin to be removed, causing the local order of the carbon skeleton to be destroyed, introducing new edge defects and structural vacancies, and causing the defect density to greatly increase.

[0035] Embodiment 3 A preparation method of a sulfur-doped porous spherical carbon material, specifically comprising the following steps: 1) uniformly mixing 80 ml of anhydrous ethanol, 1.0 ml of ammonia water and 200 ml of deionized water to form a first mixed solution; 2) heating the first mixed solution to 70 o C and constant-temperature stirring for 30 min to form a second mixed solution; 3) adding 1.1 g of resorcinol and 1.48 ml of formaldehyde solution to the second mixed solution, constant-temperature stirring at 70 o C for 30 min to form a third mixed solution; 4) adding 0.63 g of thiourea and 1.1 ml of formaldehyde solution to the third mixed solution, uniformly mixing, and constant-temperature stirring at 70 o C for 24 h to form a fourth mixed solution; 5) transferring the fourth mixed solution to a stainless steel polytetrafluoroethylene reaction kettle, and performing hydrothermal reaction at 120 o C for 24 h to form a fifth mixed solution; 6) naturally cooling the reaction kettle to room temperature, centrifuging the fifth mixed solution in a centrifuge at a speed of 8000 rpm for 10 min, and washing with deionized water for 3-5 times until neutral to obtain a sixth mixed solution; 7) under an argon protective atmosphere, drying the sixth mixed solution at 5 oC / min to 1000 o C dried for 2 h to obtain the target product.

[0036] The SEM, TEM, XRD and Raman spectrum of the obtained sulfur-doped porous spherical carbon material are shown in Figure 8 、 Figure 9 、 Figure 3 and Figure 10 .

[0037] Figure 8 The SEM picture of the sulfur-doped porous spherical carbon material prepared in Example 3 of the present application is given, and it can be obviously seen that the particles of the material are independent and spherical, with a particle size of 200-300 nm and a relatively uniform distribution.

[0038] Figure 9 The TEM picture of the sulfur-doped porous spherical carbon material prepared in Example 3 of the present application is given, and it can be obviously seen that the carbon layers are more regular and form obvious graphite crystallite structures.

[0039] Figure 3 The XRD spectrum of the sulfur-doped porous spherical carbon material prepared in Examples 1, 2 and 3 of the present application is given, and it can be obviously seen that: o the (002) peak near 26°: corresponding to the "interlayer stacking structure of carbon layers" in graphite crystals, the shape (sharpness, intensity) and position of the peak directly reflect the graphitization degree and interlayer distance of the carbon material; o the (100) peak near 43°: corresponding to the "in-plane six-membered ring structure order" of the carbon material, reflecting the in-plane crystallinity of the carbon skeleton. The broadening degree of the peak of Example 3 is further reduced, and the intensity is obviously increased, indicating that the order of the carbon skeleton is significantly improved, and the graphitization degree is greatly enhanced.

[0040] Figure 10 The Raman spectrum of the sulfur-doped porous spherical carbon material prepared in Example 3 of the present application is given, and it can be obviously seen that: -1 the D peak (~1500 cm-1) corresponds to defects and disordered structures in the carbon skeleton, and only appears when there are disordered / defects in the carbon material; -1 the G peak (~1750 cm-1) corresponds to the in-plane vibration of sp 2 hybrid carbon, reflecting the order of the carbon skeleton (i.e. the graphitization degree), and the sharper the peak shape and the higher the intensity, the stronger the graphitization degree. D The I G / I D ratio is used to measure the defect density of the carbon material, and the larger the ratio, the more defects; it can also reflect the size of the graphite crystallite, and the larger the ratio, the smaller the crystallite size. The I GThe value slightly increased to 1.02, indicating that the carbonization temperature was further increased, the degree of graphitization was continuously enhanced (the G peak was sharper, corresponding to the formation of graphite crystallites in the electron microscope), but the sulfur atoms were removed more thoroughly, and the defects introduced during the removal process continued to increase; at the same time, the ordering of the carbon skeleton offset the increase in defects to some extent, so the I D / I G The value only slightly increased and remained at a high level as a whole.

[0041] Related tests: The product sulfur-doped porous spherical carbon material prepared in the above Examples 1, 2 and 3 was used as a negative electrode material for sodium ion batteries to produce sodium ion batteries, and the specific operation steps were as follows: 1) Preparation of negative electrode sheet: the product prepared in the above Examples 1, 2, 3 and Comparative Examples 1, 2 was used as a negative electrode material, mixed with conductive carbon black ECP-600JD and binder PVDF at a mass ratio of 7:2:1, a proper amount of solvent N-methyl pyrrolidone was added, stirred for about 48 h to obtain a negative electrode slurry with a solid content of 10-15 wt%, the slurry was coated on a copper foil using a 100 μm doctor blade, and then placed in a 60°C vacuum drying oven for drying for 24 h. The dried copper foil was pressed into a circular sheet with a diameter of 12 mm using a slicing machine, i.e. a negative electrode sheet. The mass of each circular sheet was weighed using an analytical balance, and a number of copper foils without coating under the same conditions were weighed to calculate the average value, and the content of the active substance, i.e. the negative electrode material, was calculated to be 0.4-0.6 mg / cm 2 .

[0042] 2) Preparation of separator: the glass fiber separator was pressed into a circular sheet with a diameter of 18 mm using a slicing machine, and then placed in a 60°C vacuum drying oven for 48 h to obtain a separator for assembling batteries.

[0043] 3) Preparation of sodium sheet: the outer layer of the sodium ingot was cut off using a craft knife, and then rolled to a thickness of 1.0-1.5 mm using a rolling stick, and then a sodium sheet was cut using a 16 mm punch, i.e. a sodium sheet for assembling batteries was obtained.

[0044] 4) Assembly of sodium ion battery: the battery was assembled in an argon-filled glove box using a commercially available CR2032 button cell, and the electrolyte was a commercially available product (purchased from Kelund Dongguan Kelund Experimental Equipment Technology Co., Ltd., 1.0 M NaPF6 in EC:DEC = 1:1 Vol%), and the amount of electrolyte was 150 ul. After assembly, the battery was compacted using a button cell hydraulic sealing machine and then left to stand for 12 h for testing.

[0045] 5) Battery performance test: the battery was placed in a 30°C constant temperature box for cycle performance and rate performance tests.

[0046] Figure 11The rate performance and long cycle stability of the sulfur-doped porous spherical carbon material prepared in the embodiments 1, 2 and 3 of the application as a negative electrode material in a sodium ion battery are given; wherein: (a) the rate performance test of the negative electrode material at 0.1, 0.2, 0.5, 1.0 and 2.0, 5.0 C, and then returning to 0.1 C current density; (b) the cycle performance test of the negative electrode material at a current density of 2.0 C.

[0047] Figure 11 (a) The rate performance of the sulfur-doped porous spherical carbon material prepared in the embodiments 1, 2 and 3 of the application as a negative electrode material in a sodium ion battery is given, and it can be clearly seen from the figure that: in the embodiments 1, 2 and 3, the initial capacity (650 mA h / g) of the embodiment 2 is significantly higher than that of the embodiment 1 (500 mA h / g) and the embodiment 3 (380 mA h / g), which indicates that the sulfur-doped porous spherical carbon material prepared in the embodiment 2 has more abundant sodium storage active sites; as the rate is increased from 0.1 C to 5.0 C, the specific capacity of all samples decreases, but the capacity retention rate of the embodiment 2 is the best (it can still maintain a certain capacity at 5.0 C); the capacity of the embodiment 1 decays most obviously at high rate due to its low graphitization degree and poor conductivity; the capacity of the embodiment 3 is already low at low rate due to its high graphitization degree and insufficient sodium storage sites, and the capacity further decreases sharply at high rate; the coulombic efficiency at each rate is close to 100%, which indicates that the interface side reaction of the sulfur-doped porous spherical carbon material prepared in the embodiments 1, 2 and 3 with the electrolyte is less, and the sulfur doping optimizes the interface compatibility.

[0048] Figure 11 (b) The long cycle stability of the sulfur-doped porous spherical carbon material prepared in the embodiments 1, 2 and 3 of the application as a negative electrode material in a sodium ion battery is given, and it can be clearly seen from the figure that: the long cycle performance of the embodiment 2 is the best, and it can still maintain a high specific capacity of 250 mA h / g after 3000 cycles; the initial capacity of the embodiment 1 fluctuates in the range of 250-300 mA h / g, but it decays rapidly in the later stage (due to the poor structural stability of amorphous carbon, the pores collapse during cycling), and the specific capacity decreases to 125 mA h / g after 3000 cycles; the initial capacity of the embodiment 3 is the lowest, only 240 mA h / g, and the capacity continuously decays in the later stage (due to the insufficient sodium storage sites caused by the high graphitization degree, and the strong structural rigidity and weak resistance to volume expansion), and the specific capacity decreases to 180 mA h / g after 3000 cycles. The coulombic efficiency of the embodiment 2 is stable at a high level throughout the process, while the coulombic efficiency of the embodiments 1 and 3 fluctuates slightly in the later stage, which further confirms that the interface and structural stability of the sulfur-doped porous spherical carbon material prepared in the embodiment 2 is better.

Claims

1. A method for preparing a sulfur-doped porous carbon sphere material, characterized in that, Anhydrous ethanol, ammonia, and water are mixed, heated, and stirred. Then, resorcinol, formaldehyde solution, and thiourea are added and stirring is continued. After hydrothermal reaction, centrifugation, and washing until neutral, the mixture is dried under an inert atmosphere to obtain the final product.

2. The method for preparing sulfur-doped porous carbon spheres according to claim 1, characterized in that, Mix 70-90 ml of anhydrous ethanol and 1-2 ml of ammonia solution evenly in 150-250 ml of deionized water; the concentration of ammonia solution is 5-10%.

3. The method for preparing sulfur-doped porous carbon spheres according to claim 2, characterized in that, First, add 1.0-1.3g of resorcinol and 1.3-1.8ml of formaldehyde solution; then add 0.5-0.7g of thiourea and 1.0-1.3ml of formaldehyde solution; the concentration of the formaldehyde solution is 35-40%.

4. The method for preparing the sulfur-doped porous carbon sphere material according to any one of claims 1 to 3, characterized in that, Includes the following steps: 1) Mix 80ml of anhydrous ethanol, 1.0ml of ammonia and 200ml of deionized water to form mixture No. 1; 2) Heat the No. 1 mixture to 70±10°C. o Stir for 30±10 minutes to form mixture No. 2; 3) Add 1.1g of resorcinol and 1.48ml of formaldehyde solution to mixture No. 2, and stir at a constant temperature of 70±10℃ for 30±10min to form mixture No. 3; 4) Add 0.63g of thiourea and 1.1 ml of formaldehyde solution to mixture No. 3, and stir at a constant temperature of 70±10℃ for 24±6 h to form mixture No. 4; 5) Transfer the No. 4 mixture to a stainless steel polytetrafluoroethylene reactor and carry out a hydrothermal reaction at 120±20℃ for 24±6 h to form the No. 5 mixture; 6) After the reactor has cooled to room temperature, centrifuge the No. 5 mixture and wash it with deionized water until neutral to obtain the No. 6 mixture; 7) Under an argon protective atmosphere, heat mixture No. 6 at a certain heating rate of 600-1000°C. o Dry at C for 1-3 hours to obtain the product.

5. The method for preparing sulfur-doped porous carbon spheres according to claim 4, characterized in that, In step 6), centrifuge at 7000-9000 rpm for 10-20 minutes.

6. The method for preparing sulfur-doped porous carbon spheres according to claim 4, characterized in that, In step 7), the temperature is increased to 600℃, 800℃ or 1000℃ respectively at a heating rate of 3-7℃ / min.

7. Sulfur-doped porous carbon spheres prepared by any one of the preparation methods described in claims 1 to 6.

8. The application of the sulfur-doped porous carbon sphere material of claim 7 as a negative electrode material for sodium-ion batteries.

9. The application of the sulfur-doped porous carbon sphere material of claim 7 as a negative electrode material for sodium-ion batteries in the preparation of sodium-ion batteries.

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