Carbon sphere negative electrode material with graphite outer layer and preparation method and application thereof

Abstract

The application discloses a carbon sphere negative electrode material with a graphite outer layer and a preparation method and application thereof. A carbon source is subjected to a hydrothermal reaction, is coated with silicon dioxide to prepare silicon dioxide coated carbon spheres, and is subjected to a metal salt solution treatment in an alkaline environment, so that the original silicon dioxide coating layer is changed into a metal silicate coating layer; the prepared metal silicate coated carbon spheres are subjected to high-temperature treatment under inert gas protection to obtain the carbon sphere negative electrode material with a hard carbon inner layer and a graphite outer layer. The preparation method solves the interface problem caused by the mechanical combination of soft and hard carbons, adopts an overall coating idea (surface catalysis) to make the carbon sphere outer layer have a graphite shell as a whole, solves the problem of uneven metal catalytic graphitization (point catalysis), and the obtained carbon sphere negative electrode material with the graphite outer layer has higher charge and discharge capacity and cycle stability, and is suitable for the development requirement of sodium ion battery negative electrode materials.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode materials, and more specifically, to a carbon sphere anode material with a graphite outer layer, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used due to their high energy density, long lifespan, and rechargeability, particularly in portable electronics, new energy vehicles, and smart grids. However, the limited availability and high cost of lithium resources restrict the continued large-scale use of lithium-ion batteries in the future. Therefore, it is necessary to develop new rechargeable batteries to meet the growing demand for energy storage. Sodium-ion batteries share similar working principles and manufacturing processes with lithium-ion batteries. Furthermore, sodium resources are low-cost, abundant, and widely available, making sodium-ion batteries considered the best alternative to lithium-ion batteries. The large radius of sodium ions limits the application of electrode materials; therefore, developing high-performance anode materials suitable for sodium-ion batteries is a research hotspot. Hard carbon, due to its large interlayer spacing, high defect rate, well-developed closed pores, and good sodium storage performance, is often used as the anode material in sodium-ion batteries.

[0003] However, the poor cycling stability and conductivity of hard carbon materials require further improvement and optimization. Existing improvement measures mainly include: 1. Introducing doping elements. Doping elements can alter the interlayer spacing, surface wettability, and electronic conductivity of hard carbon materials, thereby improving their sodium storage performance and cycling stability. However, doping elements may introduce new impurities and defects, affecting the purity and stability of the material. 2. Soft-hard carbon composites. Soft carbon has a high degree of graphitization and good conductivity but low sodium storage capacity. To fully utilize the advantages of high sodium storage capacity of hard carbon and good conductivity of soft carbon, preparing soft-hard carbon composite materials is a feasible strategy. However, existing soft-hard carbon composite technologies mostly employ simple physical bonding between hard and soft carbon, resulting in a weak and uneven interface.

[0004] Patent document CN106910880B discloses a carbon sphere anode material for sodium-ion batteries and its preparation method. The method involves hydrothermal and sintering a carbon source to obtain carbon spheres, followed by liquid-phase impregnation to adsorb cobalt salt onto the surface of the carbon spheres as a template for induction carbonization, resulting in a concentric spherical carbon material with a hard carbon inner layer and an outer layer of carbon with a certain degree of graphitization. However, the metal-catalyzed graphitization carbon growth process in this method involves in-situ growth of the graphitized carbon material on the portion of the carbon sphere surface impregnated with cobalt salt, which is a point catalysis method and suffers from uneven distribution of the graphitized carbon on the carbon sphere surface. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing a carbon sphere anode material with a graphite outer layer.

[0006] Another object of the present invention is to provide a carbon ball anode material having a graphite outer layer prepared by the above-described method for preparing carbon ball anode material having a graphite outer layer.

[0007] Another object of the present invention is to provide a sodium-ion battery negative electrode sheet prepared from the above-mentioned carbon ball negative electrode material having a graphite outer layer.

[0008] Another object of the present invention is to provide an application of the above-mentioned sodium-ion battery negative electrode sheet in sodium-ion batteries.

[0009] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0010] A method for preparing a carbon ball anode material with a graphite outer layer includes the following steps: preparation of carbon microspheres, silica coating, coating layer modification, and graphitization treatment to obtain a carbon ball anode material with a graphite outer layer; wherein the coating layer modification is to react the silica-coated carbon balls with a metal salt in an alkaline environment to obtain metal silicate-coated carbon balls.

[0011] The carbon ball anode material with a graphite outer layer of the present invention is prepared by first dissolving a carbon source in water and obtaining carbon microspheres through a hydrothermal reaction; then modifying the surface of the carbon microspheres with a cationic surfactant, and then treating them with tetraethyl orthosilicate in an alkaline environment to obtain carbon spheres with a surface coated with silica; then modifying the silica coating layer of the carbon spheres with a metal salt to transform the silica of the coating layer into metal silicate; then carbonizing and graphitizing the carbon spheres coated with metal silicate at high temperature to obtain a carbon ball anode material with a hard carbon inner layer and a graphite outer layer.

[0012] This invention involves first coating the surface of the prepared carbon microspheres with silica, then modifying the coating layer. During subsequent high-temperature carbonization and graphitization, the metal silicate coating layer decomposes into silica and corresponding metal oxides or elemental metals. Under the catalytic action of the metal oxides or elemental metals, the outer carbon layer in contact with it gradually forms a stable graphitized outer layer, while the inner layer remains unaffected, maintaining its disordered hard carbon structure. This results in a carbon microsphere anode material with a hard carbon inner layer and a graphite outer layer. The preparation method of this invention solves the interface problem of existing soft and hard carbon mechanical bonding. By adopting an overall coating approach (surface catalysis), the outer layer of the carbon microsphere has a graphite shell, solving the problem of uneven metal-catalyzed graphitization (point catalysis). Ultimately, a more uniformly coated carbon microsphere anode material is obtained. When used as a sodium-ion battery anode, this material exhibits high charge-discharge capacity and cycle stability.

[0013] Preferably, the metal salt is at least one of metal nitrate, metal sulfate, metal halide, and metal acetate; more preferably, the metal salt is a metal nitrate.

[0014] Preferably, the metal salt is at least one of iron salt, nickel salt, and cobalt salt.

[0015] More preferably, the metal salt is at least one of ferric nitrate, nickel nitrate, and cobalt nitrate.

[0016] Preferably, the reaction temperature for the coating layer modification is 150–200°C, and the reaction time for the coating layer modification is 3–12 h.

[0017] Preferably, the carbon microspheres are prepared by hydrothermal treatment of an aqueous solution of a carbon source to obtain carbon microspheres.

[0018] Preferably, the carbon source is at least one of glucose, sucrose, and fructose.

[0019] Preferably, the reaction temperature of the hydrothermal treatment is 150–240°C, and the reaction time of the hydrothermal treatment is 6–24 h.

[0020] More preferably, the reaction temperature of the hydrothermal treatment is 160–200°C, and the reaction time of the hydrothermal treatment is 6–18 h.

[0021] Preferably, the silica coating is achieved by dispersing the obtained carbon microspheres in a solution containing a cationic surfactant, followed by reaction with tetraethyl orthosilicate in an alkaline environment to obtain silica-coated carbon spheres.

[0022] Preferably, the cationic surfactant is at least one of hexadecyltrimethylammonium bromide, hexadecylpyridine chloride, benzalkonium chloride, benzyl chloride, 5-bromo-5-nitro-1,3-dioxane, dimethyloctadecylammonium chloride, and cerium ammonium bromide octadecyldimethyl.

[0023] Preferably, the dispersion method is at least one of stirring, vortexing, and oscillation. More preferably, the dispersion method is stirring. Even more preferably, the stirring time is 1 to 3 hours, and the stirring speed is 500 to 1000 rpm / min.

[0024] Preferably, the graphitization process involves heating the obtained metal silicate-coated carbon spheres in an inert atmosphere and then maintaining the temperature for graphitization to obtain a carbon sphere anode material with a graphite outer layer.

[0025] Preferably, the heating rate is 1 to 5 °C / min.

[0026] Preferably, the graphitization treatment temperature is 1000–1800°C, and the graphitization treatment time is 1–3 hours.

[0027] More preferably, the graphitization treatment temperature is 1300–1600°C.

[0028] Preferably, the inert atmosphere is at least one of nitrogen, argon, and helium.

[0029] This invention also protects a carbon sphere anode material with a graphite outer layer prepared by the above preparation method.

[0030] This invention also protects the application of the above-mentioned carbon sphere anode material with a graphite outer layer in the preparation of anode sheets for sodium-ion batteries.

[0031] The present invention also protects a sodium-ion battery comprising the above-mentioned sodium-ion battery negative electrode sheet.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1. The method for preparing carbon sphere anode material with a graphite outer layer provided by the present invention solves the interface problem of existing soft and hard carbon mechanical bonding. Before graphitization, carbon microspheres are coated and the coating layer is modified. The overall coating concept (surface catalysis) is adopted so that the outer layer of the carbon sphere has a graphite shell, which solves the problem of uneven metal catalytic graphitization (point catalysis).

[0034] 2. The sodium-ion battery prepared using the carbon sphere anode material with a graphite outer layer prepared according to the present invention has high charge-discharge capacity and cycle stability. After 1000 charge-discharge cycles at a current density of 0.1 A / g, the cycle performance can still be maintained at 265.1 mAh / g, and the capacity retention rate is 99.3%. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the preparation method of the carbon ball anode material with a graphite outer layer prepared in Example 1 of the present invention.

[0036] Figure 2 The image shows the XRD spectrum of the carbon sphere anode material with a graphite outer layer prepared in Example 1 of this invention.

[0037] Figure 3 This is a SEM image of the carbon sphere anode material with a graphite outer layer prepared in Example 1 of the present invention.

[0038] Figure 4 This is a TEM image of the carbon sphere anode material with a graphite outer layer prepared in Example 1 of the present invention.

[0039] Figure 5The graph shows the constant current cycle charge-discharge performance of a sodium-ion battery made from a carbon sphere anode material with a graphite outer layer prepared in Example 1 of this invention for the first 1000 cycles at a current density of 0.1 A / g.

[0040] Figure 6 The graph shows the first 500 constant current cycle charge-discharge performance curves of the sodium-ion battery made from the carbon sphere negative electrode material with a graphite outer layer prepared in Example 2 of this invention at a current density of 0.1 A / g.

[0041] Figure 7 The graph shows the first 500 constant current cycle charge-discharge performance curves of the sodium-ion battery made from the carbon sphere negative electrode material with a graphite outer layer prepared in Example 3 of this invention at a current density of 0.1 A / g. Detailed Implementation

[0042] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0043] Example 1

[0044] A method for preparing a carbon sphere anode material with a graphite outer layer specifically includes the following steps:

[0045] S1. Dissolve 8g of glucose in 150mL of deionized water and stir thoroughly to obtain a glucose solution. Then place the solution in a stainless steel reactor lined with polytetrafluoroethylene and hydrothermally react at 180℃ for 12h. Wash the spherical glucose polymer suspension after hydrothermal reaction with deionized water and anhydrous ethanol respectively, and dry it in an oven at 70℃ to obtain glucose microspheres.

[0046] S2. Glucose microspheres were dispersed in a mixed solution of anhydrous ethanol and deionized water, sonicated for 30 min, and then transferred to a three-necked flask. 5 g of the cationic surfactant hexadecyltrimethylammonium bromide was added, and the mixture was mechanically stirred at 700 rpm / min for 2 h. Then, 3 mL of ammonia was added, and the reaction continued for 0.5 h to create an alkaline environment. Next, 2 mL of tetraethyl orthosilicate was thoroughly mixed with anhydrous ethanol and slowly added dropwise. After the addition was complete, the reaction continued for 6 h. The resulting solution was allowed to stand, and the lower layer was collected, centrifuged, washed, and dried to obtain SiO2-coated glucose carbon spheres.

[0047] S3. Take 2g of SiO2-coated glucose carbon spheres and dissolve them in 150mL of deionized water. Sonicate for 30min to disperse them evenly and form an emulsion. Take 3g of ferric nitrate, add 50mL of deionized water and stir until fully dissolved. Add 4mL of ammonia water and stir for 60min. Finally, transfer the mixture to a stainless steel autoclave lined with polytetrafluoroethylene and keep it at 180℃ for 6h. After the reaction is complete, centrifuge, wash, and dry to obtain ferric silicate-coated glucose carbon spheres.

[0048] S4. In a tube furnace, glucose carbon spheres coated with iron silicate are heated to 1500℃ at a heating rate of 5℃ / min and held for 2h. Then, they are washed with 20% hydrochloric acid and HF respectively to obtain carbon sphere anode material with a graphite outer layer.

[0049] Example 2

[0050] A method for preparing a carbon sphere anode material with a graphite outer layer specifically includes the following steps:

[0051] S1. Dissolve 5g of glucose in 150mL of deionized water and stir thoroughly to obtain a glucose solution. Then place the solution in a stainless steel reactor lined with polytetrafluoroethylene and hydrothermally react at 150℃ for 24h. Wash the spherical glucose polymer suspension after hydrothermal reaction with deionized water and anhydrous ethanol respectively, and dry it in an oven at 70℃ to obtain glucose microspheres.

[0052] S2. Glucose microspheres were dispersed in a mixed solution of anhydrous ethanol and deionized water, sonicated for 30 min, and then transferred to a three-necked flask. 1 g of the cationic surfactant hexadecylpyridine chloride was added, and the mixture was mechanically stirred at 500 rpm / min for 3 h. Then, 3 mL of ammonia water was added, and the reaction was continued for 0.5 h to create an alkaline environment. Then, 1 mL of tetraethyl orthosilicate was thoroughly mixed with anhydrous ethanol and slowly added dropwise. After the addition was complete, the reaction was continued for 6 h. After the resulting solution was allowed to stand, the lower layer was collected, centrifuged, washed, and dried to obtain SiO2-coated glucose carbon spheres.

[0053] S3. Take 2g of SiO2-coated glucose carbon spheres and dissolve them in 150mL of deionized water. Sonicate for 30min to disperse them evenly and form an emulsion. Take 1.5g of nickel nitrate, add 50mL of deionized water and stir until fully dissolved. Add 4mL of ammonia water and stir for 60min. Finally, transfer the mixture to a stainless steel autoclave lined with polytetrafluoroethylene and keep it at 150℃ for 12h. After the reaction is complete, centrifuge, wash, and dry to obtain nickel silicate-coated glucose carbon spheres.

[0054] S4. In a tube furnace, the glucose carbon spheres coated with nickel silicate are heated to 1000℃ at a heating rate of 1℃ / min and held for 3h. Then, they are washed with 20% hydrochloric acid and HF respectively to obtain carbon sphere anode material with a graphite outer layer.

[0055] Example 3

[0056] A method for preparing a carbon sphere anode material with a graphite outer layer specifically includes the following steps:

[0057] S1. Dissolve 20g of glucose in 150mL of deionized water and stir thoroughly to obtain a glucose solution. Then place the solution in a stainless steel reactor lined with polytetrafluoroethylene and hydrothermally react at 240℃ for 6h. Wash the spherical glucose polymer suspension after hydrothermal reaction with deionized water and anhydrous ethanol respectively, and dry it in an oven at 70℃ to obtain glucose microspheres.

[0058] S2. Glucose microspheres were dispersed in a mixed solution of anhydrous ethanol and deionized water, sonicated for 30 min, and then transferred to a three-necked flask. 5 g of the cationic surfactant 5-bromo-5-nitro-1,3-dioxane was added, and the mixture was mechanically stirred at 1000 rpm / min for 1 h. Then, 3 mL of ammonia was added, and the reaction continued for 0.5 h to create an alkaline environment. Next, 4 mL of tetraethyl orthosilicate was thoroughly mixed with anhydrous ethanol and slowly added dropwise. After the addition was complete, the reaction continued for 6 h. The resulting solution was allowed to stand, and the lower layer was centrifuged, washed, and dried to obtain SiO2-coated glucose carbon spheres.

[0059] S3. Take 5g of SiO2-coated glucose carbon spheres and dissolve them in 150mL of deionized water. Sonicate for 30min to disperse them evenly into an emulsion. Take 5g of cobalt nitrate, add 50mL of deionized water and stir until fully dissolved. Add 4mL of ammonia water and stir for 60min. Finally, transfer the mixture to a stainless steel autoclave lined with polytetrafluoroethylene and keep it at 200℃ for 3h. After the reaction is complete, centrifuge, wash, and dry to obtain cobalt silicate-coated glucose carbon spheres.

[0060] S4. In a tube furnace, the glucose carbon spheres coated with cobalt silicate are heated to 1800℃ at a heating rate of 5℃ / min and held for 1h. Then, they are washed with 20% hydrochloric acid and HF respectively to obtain carbon sphere anode material with a graphite outer layer.

[0061] Comparative Example 1

[0062] A method for preparing a carbon sphere anode material differs from that in Example 1 in that:

[0063] Steps S2 and S3 are omitted. Take 3g of ferric nitrate, add 50mL of deionized water and stir to dissolve it completely to obtain a homogeneous solution. Then add the glucose microspheres obtained in step S1 and impregnate for 10h. Centrifuge and dry to obtain carbon spheres with iron salt impregnation on the surface.

[0064] Performance testing

[0065] 1. Assemble the battery:

[0066] The obtained carbon sphere anode material with a graphite outer layer was mixed with Ketjen black and polyvinylidene fluoride in a mass ratio of 80:10:10 and placed in a ball mill. N-methylpyrrolidone was added to prepare a slurry. The resulting electrode slurry was coated onto copper foil and dried in an oven at 45°C for 10 hours. The resulting sheet was cut to obtain the anode sheet for a sodium-ion secondary battery. A coin cell was assembled in an argon-filled glove box, using a sodium sheet as the positive electrode, glass fiber as the separator, and 1M NaPF6 in DME as the electrolyte, thus obtaining a sodium-ion battery.

[0067] 2. Morphological analysis:

[0068] like Figure 2 The figure shows the XRD spectrum of the carbon sphere anode material with a graphite outer layer prepared in Example 1. As can be seen from the figure, it exhibits two structures: a disordered hard carbon structure (wide peak, approximately 2θ = 23.6°) and a short-range ordered graphite structure (narrow peak, approximately 2θ = 25.9°), indicating that the prepared carbon material simultaneously possesses both graphitized and disordered structures.

[0069] like Figure 3 The image shown is a SEM image of the carbon sphere anode material with a graphite outer layer prepared in Example 1. As can be seen from the image, the carbon spheres are uniform in size and regular in shape.

[0070] like Figure 4 The image shown is a TEM image of the carbon sphere anode material with a graphite outer layer prepared in Example 1. As can be seen from the image, the hard carbon surface is coated with a graphite outer layer, and the inner layer is a hard carbon sphere.

[0071] 3. Electrochemical performance testing: The prepared sodium-ion battery was subjected to constant current charge-discharge testing with a current density of 0.1 A / g and a charge-discharge voltage range of 0.01–3 V.

[0072] like Figure 5 The figure shows the charge-discharge performance curves of a sodium-ion battery made from a carbon sphere anode material with a graphite outer layer prepared in Example 1 of this invention, under a current density of 0.1 A / g, for the first 1000 constant current cycles. The figure shows that the sodium-ion battery prepared in this example has good electrochemical performance; at a current density of 0.1 A / g, the initial capacity is 267.1 mAg. -1The initial coulomb efficiency was 75.4%, and the capacity after 1000 cycles was 265.1 mAg. -1 The capacity retention rate was 99.3%, indicating that the carbon ball anode material with a graphite outer layer prepared in Example 1 has high charge-discharge capacity and cycle stability.

[0073] like Figure 6 The figure shows the charge-discharge performance curves of a sodium-ion battery made from a carbon sphere anode material with a graphite outer layer prepared in Example 2 of this invention, under a current density of 0.1 A / g, for the first 500 constant current cycles. The figure shows that the sodium-ion battery prepared in this example has good electrochemical performance; at a current density of 0.1 A / g, the initial capacity is 183.7 mAg. -1 The initial coulomb efficiency was 76.0%, and the capacity after 500 cycles was 181.6 mAg. -1 The capacity retention rate was 98.8%, indicating that the carbon ball anode material with a graphite outer layer prepared in Example 2 has good charge-discharge capacity and cycle stability.

[0074] like Figure 7 The figure shows the charge-discharge performance curves of a sodium-ion battery made from a carbon sphere anode material with a graphite outer layer prepared in Example 3 of this invention, under a current density of 0.1 A / g, for the first 500 constant current cycle. The figure shows that the sodium-ion battery prepared in this example has good electrochemical performance; at a current density of 0.1 A / g, the initial capacity is 209.4 mAg. -1 The initial coulomb efficiency was 70.7%, and the capacity after 500 cycles was 184.0 mAg. -1 The capacity retention rate was 87.9%, indicating that the carbon ball anode material with a graphite outer layer prepared in Example 3 has good charge-discharge capacity and cycle stability.

[0075] A sodium-ion battery made using the carbon sphere anode material prepared in Comparative Example 1 of this invention underwent its first 50 constant-current charge-discharge cycle performance test at a current density of 0.05 A / g. At a current density of 0.05 A / g, the initial capacity was 400.5 mAg. -1 The initial coulomb efficiency was 58%, and the capacity was 290 mAg after only 50 cycles. -1 The capacity retention rate was 72.4%, indicating that the charge-discharge capacity and cycle stability of the carbon ball anode material prepared in Comparative Example 1 were poor.

[0076] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a carbon sphere anode material with a graphite outer layer, characterized in that, Includes the following steps: The preparation of carbon microspheres, silica coating, coating layer modification, and graphitization treatment yielded a carbon microsphere anode material with a graphite outer layer. The carbon microspheres are prepared by hydrothermal treatment of an aqueous solution of a carbon source to obtain carbon microspheres; The silica coating is achieved by dispersing the obtained carbon microspheres in a solution containing a cationic surfactant, followed by reaction with tetraethyl orthosilicate in an alkaline environment to obtain silica-coated carbon spheres. The coating modification involves reacting silica-coated carbon spheres with metal salts in an alkaline environment to obtain metal silicate-coated carbon spheres.

2. The preparation method according to claim 1, characterized in that, The metal salt is at least one of metal nitrate, metal sulfate, metal halide, and metal acetate.

3. The preparation method according to claim 1, characterized in that, The graphitization process involves heating the obtained metal silicate-coated carbon spheres in an inert atmosphere and then maintaining the temperature to perform graphitization, thereby obtaining a carbon sphere anode material with a graphite outer layer.

4. The preparation method according to claim 1, characterized in that, The carbon source is at least one of glucose, sucrose, and fructose.

5. The preparation method according to claim 1, characterized in that, The cationic surfactant is at least one of hexadecyltrimethylammonium bromide, hexadecylpyridine chloride, benzalkonium chloride, benzyl chloride, and dimethyloctadecylammonium chloride.

6. A carbon sphere anode material having a graphite outer layer, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. A sodium-ion battery negative electrode sheet prepared from a carbon sphere negative electrode material having a graphite outer layer as described in claim 6.

8. A sodium-ion battery, comprising the negative electrode sheet as described in claim 7.

Images