Highly ordered porous sulfur / oxygen co-doped carbon spheres, preparation method thereof and potassium ion battery
By preparing highly ordered porous sulfur/oxygen co-doped carbon spheres, the problem of poor potassium storage performance of hard carbon materials in potassium-ion batteries was solved, achieving high specific capacity and excellent electrochemical performance, making it suitable as a negative electrode material for potassium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGBO UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2023-10-08
- Publication Date
- 2026-08-04
AI Technical Summary
Existing hard carbon materials have poor potassium storage performance in potassium-ion batteries, especially in terms of rate performance and energy density. Current structural designs cannot simultaneously achieve high ion/electron transport speed, high capacity and high energy density.
Highly ordered porous sulfur/oxygen co-doped carbon spheres were prepared by mixing sulfur powder with phenolic resin. By controlling the doping process, the carbon spheres were made to have a uniform atomic distribution and consistent pore size, forming more potassium storage sites and improving electrochemical performance.
The prepared porous sulfur/oxygen co-doped carbon spheres have a large specific surface area and an ordered mesoporous structure, which significantly improves the specific capacity and electrochemical performance of potassium-ion batteries, and exhibits excellent electrochemical reaction kinetics and cycle stability.
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Figure CN117550588B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery materials and relates to a highly ordered porous sulfur / oxygen co-doped carbon sphere, its preparation method, and potassium-ion batteries. Background Technology
[0002] Potassium-ion batteries have advantages such as being environmentally friendly, having abundant potassium reserves, and being inexpensive. Furthermore, potassium metal has an electrode potential that is closer to that of lithium and a lower desolvation energy barrier, making it a promising candidate to replace lithium-ion batteries as a new generation of energy storage devices in specific fields. In recent years, it has become one of the hottest energy systems with active development and has broad application prospects.
[0003] However, the larger radius of potassium ions (0.138 nm) compared to lithium ions (0.076 nm) limits the potassium intercalation capacity and lifetime of traditional graphite anodes. Hard carbon, a carbon-based material composed of graphite microcrystals and amorphous regions, is difficult to graphitize to a high degree. Its large interlayer spacing and abundant porosity give it good potassium storage performance. However, its rate performance and energy density are low. To further improve the electrochemical performance of hard carbon, structural design and heteroatom doping have been shown to increase ion and electron transport speeds and energy density, thereby improving the rate performance of hard carbon materials. Currently reported structural designs, such as hollow structures, disordered porous structures, and spherical structures, have shown some improvement in specific properties, but also at the cost of other performance indicators. For example, hollow structures shorten ion migration paths but significantly reduce energy density; disordered porous structures provide more potassium storage sites but reduce the first coulombic efficiency; and spherical structures have high packing density but low capacity. Therefore, the rational design and synthesis of potassium-ion battery anode materials that simultaneously possess high ion / electron transport speed, high capacity, and high energy density remains a challenge. On the other hand, heteroatom dual doping can more significantly improve the interlayer spacing and electron transport efficiency of carbon materials compared to single-atom doping, thereby more significantly enhancing the potassium storage electrochemical performance of hard carbon materials.
[0004] In summary, existing hard carbon materials still suffer from poor potassium storage performance. Therefore, it is necessary to rationally optimize the design of electrode material structure and its intrinsic atomic characteristics, and develop anode materials with excellent electrochemical performance for use in potassium-ion batteries. Summary of the Invention
[0005] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a method for preparing highly ordered porous sulfur / oxygen co-doped carbon spheres. By mixing sulfur powder with resin materials, the carbon spheres are prepared with uniform distribution of doped atoms and uniform pore size, resulting in a large number of potassium storage sites, which can be applied to potassium-ion batteries.
[0006] The objective of this invention can be achieved through the following technical solutions:
[0007] A method for preparing highly ordered porous sulfur / oxygen co-doped carbon spheres, the method comprising:
[0008] (1) Mix phenol, formaldehyde solution and NaOH solution in a mass-volume ratio of 1g:(3~5)ml:(15~50)ml, then heat and stir to obtain phenolic resin precursor;
[0009] (2) Dissolve the triblock copolymer Pluronic F127 in a solvent and slowly add it dropwise into (1) under heating conditions while stirring continuously;
[0010] (3) Add water to (2) to dilute, continue heating and stirring, the solution changes from colorless and transparent to pink, and then to blood red;
[0011] (4) After diluting the solution in (3) again, perform hydrothermal treatment, cool, centrifuge, and dry to obtain powder;
[0012] (5) The powder in (4) is mixed and ground with sulfur powder at a mass ratio of 1: (1~2), and carbonized in an inert atmosphere to obtain highly ordered porous sulfur / oxygen co-doped carbon spheres.
[0013] In the preparation method of the present invention, (4) the phenolic resin precursor powder and sulfur powder are thoroughly mixed and then carbonized and calcined. The sulfur powder can make the sulfur doping uniform. During the calcination process, some sulfur will react with the functional groups of the precursor and be lost with the gas flow. The remaining sulfur forms covalent bonds with carbon. During this process, oxygen atoms are also doped into the carbon structure. During the entire doping process, the highly ordered pore structure of the carbon spheres will not change, but with the introduction of heteroatoms, the carbon interlayer spacing and surface characteristics have changed.
[0014] Preferably, the mass ratio of phenol in (1) to triblock copolymer Pluronic F127 in (2) is 1:(1-3).
[0015] Preferably, the heating and stirring temperature in (1) is 65-85°C and the time is 0.1-2h;
[0016] Preferably, the concentration of the formaldehyde solution in (1) is 32-39 wt%, and the concentration of the NaOH solution is 0.01-0.3 M.
[0017] (1) NaOH is used as a curing agent. If the concentration or amount of NaOH solution exceeds the range, it will affect the morphology of the precursor, resulting in irregular carbon sphere morphology.
[0018] Preferably, the slow dripping time in (2) is 1 to 5 hours; the heating temperature is 65 to 80°C.
[0019] Preferably, the heating and stirring temperature in (3) is 65-85°C and the time is 5-20h.
[0020] Preferably, when diluting with water in (3), the amount of water added is 100-1000% of the mixture in (2).
[0021] Preferably, the hydrothermal temperature in (4) is 110-150°C and the temperature is 12-48h.
[0022] Preferably, the carbonization temperature in step (5) is 650–780°C, the time is 1–5 h, and the heating rate is 3–7°C / min.
[0023] A highly ordered porous sulfur / oxygen co-doped carbon sphere, characterized in that the specific surface area of the highly ordered porous sulfur / oxygen co-doped carbon sphere is 650-800 m². 2 / g, particle size 120–190 nm; pore size 3–4 nm, pore volume 0.45–0.59 cm³. 3 / g.
[0024] Preferably, the highly ordered porous sulfur / oxygen co-doped carbon spheres contain 91-94% C, 3-6% O, and 2-5% S.
[0025] Preferably, the XRD (110) diffraction peak of the highly ordered porous sulfur / oxygen co-doped carbon spheres is around 29.5°, corresponding to a carbon atom interlayer spacing that is larger than that of the undoped hard carbon material.
[0026] The material of this invention has a small interlayer spacing of carbon atoms before sulfidation, which is not conducive to the intercalation-deintercalation reaction of potassium ions; after sulfidation, the interlayer spacing of carbon atoms increases, which is conducive to the intercalation-deintercalation reaction of potassium ions with larger radii, thus improving the electrochemical reaction kinetics.
[0027] Preferably, the ratio of the Raman D peak to the G peak of the highly ordered porous sulfur / oxygen co-doped carbon spheres is 0.85 to 0.90.
[0028] A potassium-ion battery, wherein the active material of the potassium-ion battery comprises highly ordered porous sulfur / oxygen co-doped carbon spheres.
[0029] Preferably, the potassium-ion battery is a half-cell assembled from a negative electrode material containing highly ordered porous sulfur / oxygen co-doped carbon spheres and metallic potassium.
[0030] Preferably, the potassium-ion battery is a full cell assembled from a negative electrode material containing highly ordered porous sulfur / oxygen co-doped carbon spheres and a Prussian blue positive electrode material.
[0031] As a preferred embodiment, the preparation method of the Prussian blue cathode material includes: dissolving ferrous sulfate heptahydrate and potassium citrate in deionized water at a mass ratio of 1:(1-10) under a N2 atmosphere, stirring vigorously, and slowly adding potassium ferrocyanide solution while stirring. After mixing, the mixture is allowed to stand overnight, and then collected by centrifugation and vacuum drying to obtain the final product.
[0032] After adding potassium ferrocyanide solution, a milky white precipitate appeared in the solution, which turned blue after standing overnight, indicating that Fe(II) was partially oxidized to Fe(III).
[0033] Further optimization is that the potassium ferrocyanide is added at a rate of 1–10 ml / min.
[0034] Further optimization involves vigorous stirring for 0.1–10 hours and overnight standing for 10–20 hours.
[0035] Further optimization is to use a vacuum drying temperature of 100–150°C.
[0036] Compared with the prior art, the present invention has the following beneficial effects:
[0037] 1. This invention controls the ratio of sulfur powder to the phenolic resin precursor of carbon spheres to obtain a hard carbon material with a large specific surface area. This results in highly ordered porous sulfur / oxygen co-doped carbon spheres with a greater number of potassium storage sites, which is beneficial to improving the specific capacity of potassium-ion batteries. If there is too much sulfur powder, too much sulfur will be lost from the highly ordered porous sulfur / oxygen co-doped carbon spheres. At the same time, the specific surface area will decrease due to the blockage of some elemental sulfur. If there is too little sulfur powder, there will be too few sulfur and oxygen doping sites, insufficient porosity, and a low specific surface area.
[0038] 2. In this invention, sulfur powder is used as the sulfur source. During the carbonization and calcination process, a small portion of the sulfur reacts with the functional groups of the phenolic resin precursor and is lost with the airflow. The remaining sulfur forms covalent bonds with carbon. During this process, oxygen atoms are also doped into the carbon structure. In the entire doping process, the highly ordered pore structure of the carbon spheres does not change. However, with the introduction of heteroatoms, the carbon interlayer spacing and surface characteristics change.
[0039] 3. Unlike conventional heteroatom-doped hard carbon materials that use compounds containing target atomic elements, this invention uses sulfur powder as a sulfur source, which can make sulfur doping uniform.
[0040] 4. The highly ordered porous sulfur / oxygen co-doped carbon spheres prepared by this invention have a highly ordered mesoporous structure, a large specific surface area, and uniform size.
[0041] 5. The highly ordered porous sulfur / oxygen co-doped carbon spheres prepared by this invention have sulfur / oxygen co-doping and highly ordered mesoporous structure, which have a synergistic enhancement effect on the potassium storage performance of potassium-ion batteries.
[0042] 6. The highly ordered porous sulfur / oxygen co-doped carbon spheres prepared by this invention, as active materials for potassium-ion batteries, half-cells assembled with metallic potassium, and full cells assembled with Prussian blue cathode materials all exhibit excellent electrochemical performance. Attached Figure Description
[0043] Figure 1 This is a transmission electron microscope (TEM) image of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of the present invention.
[0044] Figure 2 This is a mapping diagram of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of the present invention.
[0045] Figure 3 This is a linear elemental distribution diagram of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of the present invention.
[0046] Figure 4 The images show the XRD patterns of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of this invention and the carbon spheres in Comparative Example 1.
[0047] Figure 5 The images show the Raman diagrams of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of this invention and the carbon spheres in Comparative Example 1.
[0048] Figure 6 This is an electron microscope image of the carbon spheres prepared in Comparative Example 1 of the present invention.
[0049] Figure 7 The cyclic voltammogram shows the results of assembling a button potassium-ion battery using highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of this invention as the active material.
[0050] Figure 8 This diagram shows the cycle life of a button potassium-ion battery assembled using the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of this invention as the active material, at a current density of 100 mA / g.
[0051] Figure 9 The graph shows the rate performance of a button potassium-ion battery assembled using the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of this invention as the active material, under different current densities.
[0052] Figure 10 This diagram illustrates the ultra-long cycle life of a button potassium-ion battery assembled using the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of this invention as the active material, under a high current density of 2 A / g.
[0053] Figure 11This is a transmission electron microscope (TEM) image of a button potassium-ion battery assembled using the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 of this invention as the active material, after cycling.
[0054] Figure 12 This is a charge-discharge curve of a potassium-ion full cell assembled with Prussian blue material using highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 2 of this invention at a current density of 100 mA / g.
[0055] Figure 13 This is a cycle lifetime diagram of a potassium-ion full cell assembled with Prussian blue material using highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Application Example 2 of the present invention at a current density of 100 mA / g. Detailed Implementation
[0056] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.
[0057] Unless otherwise specified, the materials used in this invention are commercially available products, and the methods used are conventional technical means.
[0058] Example 1
[0059] (1) Mix 0.60 g of phenol, 2.1 mL of 37% formaldehyde solution and 15 mL of 0.1 M NaOH solution, and then stir at 70 °C for 0.5 hours to obtain low molecular weight phenolic resin;
[0060] (2) Dissolve 0.96 g of the triblock copolymer Pluronic F127 in 15 mL of water, slowly add it dropwise to (1) at 70 °C and stir for 2 hours;
[0061] (3) Add 50 ml of water to (2) to dilute the solution and continue stirring at 70°C for 12 hours; during this process, the aqueous solution changes from colorless and transparent to pink, and finally to blood red; let the solution stand and store for later use;
[0062] (4) Transfer the solution in (3) to a 50 mL autoclave, then add 25 mL of water to dilute the solution; perform hydrothermal treatment in an oven at 130 °C for 20 hours; collect the yellow powder (spherical phenolic resin-F127 micelles, abbreviated as SPRMs) by centrifugation, wash it several times with distilled water, and dry it in an oven at 60 °C.
[0063] (5) Mix and grind 0.7 g of SPRMs and 1.05 g of sulfur powder, and then carbonize at 700 °C for 2 hours under Ar atmosphere with a heating rate of 5 °C / min to obtain highly ordered porous sulfur / oxygen co-doped carbon spheres (SPC1.5).
[0064] Transmission electron microscopy (TEM) images, mapping diagrams, and linear elemental distribution diagrams of highly ordered porous sulfur / oxygen co-doped carbon spheres are shown below. Figure 1 , 2 As shown in Figure 3, it can be observed that the C, O, and S elements are evenly distributed, with a C content of 91.83%, an O content of 4.93%, and a S content of 3.24%.
[0065] Figure 4 , 5 The XRD and Raman spectra of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in this embodiment and the carbon spheres in Comparative Example 1 are shown; according to Figure 4 It can be seen that the diffraction angle of the (110) peak of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in this embodiment is significantly lower than that of the carbon spheres in Comparative Example 1. According to the Bragg equation, the carbon interlayer spacing of the highly ordered porous sulfur / oxygen co-doped carbon spheres is significantly larger than that of the undoped carbon spheres, which is conducive to the intercalation and deintercalation reaction of potassium ions.
[0066] according to Figure 5 It can be seen that the Raman D peak to G peak ratio of the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in this embodiment is 0.87, which is greater than 0.849 of the carbon spheres in Comparative Example 1. This indicates that the highly ordered porous sulfur / oxygen co-doped carbon spheres in this embodiment have more defect structures, which is beneficial to the electrochemical reaction.
[0067] Example 2
[0068] Compared with Example 1, the difference is that in (5), the mass ratio of SPRMs to sulfur powder is 1:1.
[0069] The highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in this embodiment have a specific surface area of 594.5 m². 2 g -1 Its C content is 93.61%, O content is 4.93%, and S content is 1.46%.
[0070] Example 3
[0071] Compared with Example 1, the difference is that in (5), the mass ratio of SPRMs to sulfur powder is 1:2.
[0072] The highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in this embodiment have a specific surface area of 653.8 m². 2 g -1 Its C content is 87.99%, O content is 5.25%, and S content is 6.76%.
[0073] Comparative Example 1
[0074] Compared with Example 1, the difference is that SPRMs were not mixed with sulfur powder, but the powder obtained in Example 1 (4) was carbonized separately under an Ar atmosphere; that is, there was no sulfur doping in the carbon spheres (PC).
[0075] The electron microscope image of the carbon spheres prepared in this comparative example is shown below. Figure 6 As shown.
[0076] Application Example 1
[0077] The highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 were used as active materials in potassium-ion batteries.
[0078] Preparation of negative electrode materials:
[0079] The mixture was prepared by mixing highly ordered porous sulfur / oxygen co-doped carbon spheres, binder (PVDF), and conductive agent (conductive carbon black) in a mass ratio of 8:1:1.
[0080] The above-mentioned negative electrode material, metallic potassium, binder (PVDF), conductive agent (conductive carbon black), and electrolyte (3M KFSI dissolved in DME solvent) were assembled into a potassium-ion battery, and then performance tests were conducted. The charge-discharge curves of the potassium-ion battery at different current densities are shown in the figure below. Figure 7 As shown, the cycle life diagram at a current density of 100 mA / g is as follows. Figure 8 As shown in the figure, the rate performance at different current densities is as follows: Figure 9 As shown, the cycle life diagram at a high current density of 2 A / g is as follows: Figure 10 As shown;
[0081] As shown in the figure: the initial coulombic efficiency is 52.5%, the discharge specific capacity is 278 mAh / g after 1200 cycles, and the capacity retention rate is 91.1%; at a high current density of 3 A / g, the discharge specific capacity is 220 mAh / g; after 11000 cycles at a current density of 2 A / g, the capacity retention rate is close to 100%.
[0082] Figure 11 The image shows a transmission electron microscope (TEM) image of highly ordered porous sulfur / oxygen co-doped carbon spheres after cyclic testing. The image shows that the material maintained a relatively good spherical porous structure after cyclic testing.
[0083] Application Example 2
[0084] The highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 1 were used as active materials in potassium-ion batteries.
[0085] Preparation of negative electrode material: It is prepared by mixing highly ordered porous sulfur / oxygen co-doped carbon spheres, binder (PVDF), and conductive agent (conductive carbon black) in a mass ratio of 8:1:1.
[0086] Preparation of Prussian blue cathode material: Under N2 atmosphere, 1.67 g (6 mmol) of ferrous sulfate heptahydrate (FeSO4·7H2O) and 5 g of potassium citrate were dissolved in 100 ml of deionized water; while vigorously stirring the solution, 100 ml of potassium ferrocyanide solution containing 4 mmol was slowly added at a rate of 3 ml / min, and after mixing for 0.5 h, a milky white precipitate was formed; then it was allowed to stand overnight, and the light blue product was collected by centrifugation and then vacuum dried at 120 °C.
[0087] The negative electrode material (SPC), positive electrode material (PBA), and electrolyte (3M KFSI dissolved in DME solvent) were assembled into a potassium-ion full cell (PBC / / SPC) for testing. Figure 12 , 13 The figures show the charge-discharge curves and cycle life of the potassium-ion full cell at a current density of 100 mA / g, respectively.
[0088] As shown in the figure, the initial discharge specific capacity is 96 mAh / g, and the capacity retention rate is >81% after 100 cycles.
[0089] Application Example 3
[0090] Compared with Application Example 1, the difference is that the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 2 are used as active materials in potassium-ion batteries.
[0091] The potassium-ion battery was tested for performance: after 1200 cycles, the discharge specific capacity was 224 mAh / g, and the capacity retention rate was 88.4%; at a high current density of 3 A / g, the discharge specific capacity was 142 mAh / g.
[0092] Application Example 4
[0093] Compared with Application Example 1, the difference is that the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Example 3 are used as active materials in potassium-ion batteries.
[0094] The potassium-ion battery was tested for performance: after 1200 cycles, the discharge specific capacity was 151 mAh / g, and the capacity retention rate was 41.7%; at a high current density of 3 A / g, the discharge specific capacity was 115 mAh / g.
[0095] Application Comparative Example 1
[0096] The difference between Comparative Example 1 and Comparative Example 2 is that the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared in Comparative Example 1 are used as active materials in potassium-ion batteries.
[0097] The potassium-ion battery was tested for performance: the initial coulombic efficiency was 39.8%, the discharge specific capacity after 940 cycles was 159 mAh / g, and the capacity retention rate was 76.2%; after 11,000 cycles at 2 A / g, the capacity retention rate was approximately 53%.
[0098] In summary, the highly ordered porous sulfur / oxygen co-doped carbon spheres prepared by the method of this invention have an ordered porous structure, a large specific surface area, uniform distribution of sulfur / oxygen doping elements, and a large number of active sites, and exhibit excellent electrochemical performance when applied to potassium-ion batteries.
[0099] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.
Claims
1. A potassium-ion battery, characterized in that, The active material of the potassium-ion battery includes highly ordered porous sulfur / oxygen co-doped carbon spheres prepared by the following method. The highly ordered porous sulfur / oxygen co-doped carbon spheres contain 91.83% C, 4.93% O, and 3.24% S; the ratio of their Raman D peak to G peak is 0.
87. The method for preparing the highly ordered porous sulfur / oxygen co-doped carbon spheres includes the following steps: (1) Mix 0.60 g of phenol, 2.1 mL of 37% formaldehyde solution and 15 mL of 0.1 M NaOH solution, and then stir at 70 °C for 0.5 hours to obtain low molecular weight phenolic resin; (2) Dissolve 0.96 g of the triblock copolymer Pluronic F127 in 15 mL of water, slowly add it dropwise to (1) at 70 °C and stir for 2 hours; (3) Add 50 ml of water to (2) to dilute the solution and continue stirring at 70°C for 12 hours; during this process, the aqueous solution changes from colorless and transparent to pink, and finally to blood red; let the solution stand and store for later use; (4) Transfer the solution in (3) to a 50 mL autoclave, then add 25 mL of water to dilute the solution; perform hydrothermal treatment in an oven at 130 °C for 20 hours; collect the yellow powder SPRMs by centrifugation, wash with distilled water several times, and dry in an oven at 60 °C. (5) Mix and grind 0.7 g of SPRMs and 1.05 g of sulfur powder, and then carbonize them at 700 °C for 2 hours under Ar atmosphere with a heating rate of 5 °C / min.