Preparation method of porous carbon microspheres, porous carbon microspheres and application thereof

Abstract

The present application relates to a kind of porous carbon microspheres preparation method, porous carbon microspheres and its application, preparation method includes: water glass powder is mixed with water and stirred uniformly to obtain water glass solution, remove metal cation in water glass solution by cation exchange resin bed layer to obtain active silicic acid aqueous solution, using alkaline solution to adjust the pH value of active silicic acid aqueous solution to neutral, then react for a certain time at a certain temperature, obtain silica-containing silica sol, silica sol is mixed with carbon source material and is evenly sprayed dry, carbonization treatment obtains carbon microsphere powder material, then etching, washing, drying are sequentially carried out, remove silica, obtain porous carbon microspheres;The porous carbon microspheres of the present application can be used as carbon matrix to prepare silicon-carbon composite negative material, reduce the volume expansion of silicon, use the silicon-carbon composite negative material to prepare negative electrode sheet and assemble into lithium ion battery, can improve the first coulomb efficiency, rate performance and cycle stability of battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a method for preparing porous carbon microspheres, porous carbon microspheres and their applications. Background Technology

[0002] With the widespread application of lithium-ion batteries in portable electronic devices and electric vehicles, the development of anode materials with high energy density and long cycle life has become particularly important. Silicon has attracted much attention as an anode material for lithium-ion batteries due to its high specific capacity. However, the significant volume expansion of silicon during charge and discharge can easily lead to damage to the electrode structure and degradation of cycle performance. Therefore, using porous carbon as a matrix material for silicon has become a research hotspot.

[0003] Porous carbon not only effectively buffers the volume change of silicon but also possesses excellent conductivity and abundant pore structure, which can improve silicon loading and utilization, thereby enhancing the overall performance of the battery. Hard template methods are widely used in the preparation of porous carbon materials, especially silica as a hard template material due to its wide availability and ease of processing. However, traditional silica templates suffer from poor dispersibility and agglomeration, making it difficult to precisely control the pore structure of porous carbon. In contrast, silica sol, with its nanoscale particles, good dispersibility, and uniform particle size distribution, holds promise as a template agent for obtaining more controllable mesoporous carbon structures.

[0004] Spray drying technology boasts high industrial feasibility, simple operation, and high preparation efficiency. During the preparation process, liquid is rapidly converted into microparticle powder. This rapid drying process significantly improves production efficiency and reduces time and energy consumption compared to traditional drying methods. By controlling the morphology of the prepared particles, spray drying not only ensures a spherical structure but also guarantees particle uniformity and a high specific surface area. The control of parameters such as inlet and outlet temperatures, atomizer frequency, and feed flow rate can effectively influence the size, morphology, and pore structure of the final dried particles. During the carbonization process after spray drying, the template silica sol is gradually removed, forming carbon microspheres with a mesoporous structure. Because the spherical particles generated during spray drying have good dispersibility and uniformity, the pore structure obtained during carbonization is also relatively uniform and controllable. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing porous carbon microspheres, porous carbon microspheres, and their applications.

[0006] To achieve the above objectives, in a first aspect, embodiments of the present invention provide a method for preparing porous carbon microspheres, the method comprising:

[0007] Step S1: Add water glass powder to water and stir until homogeneous to obtain water glass solution;

[0008] Step S2: The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an aqueous solution of active silicic acid.

[0009] Step S3: Adjust the pH of the active silicic acid aqueous solution to neutral using an alkaline solution, and then react at a certain temperature for a certain time to obtain a silica sol containing silica.

[0010] Step S4: Mix the silica sol with the carbon source material evenly, and then obtain the carbon microsphere precursor by spray drying;

[0011] Step S5: The carbon microsphere precursor is placed in a high-temperature device and carbonized under a protective atmosphere to obtain carbon microsphere powder material.

[0012] Step S6: The carbon microsphere powder material is sequentially etched, washed, and dried to remove silicon dioxide, thereby obtaining porous carbon microspheres.

[0013] Preferably, the silica content in the water glass powder is 40wt% to 60wt%; and the solid content of the water glass solution is 10wt% to 25wt%.

[0014] Preferably, the pH value of the active silicic acid aqueous solution is between 2 and 3;

[0015] The alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, or ammonium hydroxide solution;

[0016] The pH value is adjusted to neutral, specifically to a pH value of 8-11.

[0017] The reaction at a certain temperature for a certain time specifically refers to a reaction at 25℃ to 80℃ for 1 to 6 hours.

[0018] Preferably, the carbon source material includes one or more of glucose, sucrose, or phenolic resin;

[0019] The mass ratio of the silica sol to the carbon source material is 1.5:1 to 3:1;

[0020] The spray drying equipment is a spray dryer, with an inlet temperature of 165℃~195℃, an outlet temperature of 65℃~85℃, an atomizer frequency of 150Hz~220Hz, and a feed flow rate of 1.5mL / min~3.5mL / min.

[0021] Preferably, the high-temperature equipment includes any one of the following: tubular furnace, box furnace, fluidized bed, and rotary furnace;

[0022] The protective gas includes any one of nitrogen, helium, or argon.

[0023] The carbonization process includes: heating to 350℃ to 450℃ at a heating rate of 2℃ / min to 5℃ / min, holding at that temperature for 1 hour to 5 hours, and then heating to 600℃ to 900℃ at a heating rate of 2℃ / min to 5℃ / min, holding at that temperature for 1 hour to 5 hours.

[0024] Preferably, the etching specifically includes: immersing the carbon microsphere powder material in an alkaline solution for etching to remove silicon dioxide, followed by filtration or centrifugation to obtain a precipitate; the alkaline solution includes one or more of sodium hydroxide, potassium hydroxide, or ammonia water;

[0025] The washing process specifically includes: washing the precipitate with acid at least three times, and then washing it with deionized water at least three times; the acid includes dilute hydrochloric acid or dilute nitric acid;

[0026] The drying process specifically includes baking in an oven at 80℃ to 120℃ for 1 to 10 hours.

[0027] In a second aspect, embodiments of the present invention provide a porous carbon microsphere prepared based on the preparation method described in the first aspect, wherein the porosity of the porous carbon microsphere is 50% to 80%, and the number of mesopores accounts for 40% to 70% of the total number of pores in the porous carbon microsphere.

[0028] The porous carbon microspheres have a specific surface area of ​​980 m². 2 / g~1600m 2 / g, pore volume 1.2m 3 / g~3.5m 3 / g.

[0029] Thirdly, embodiments of the present invention provide a silicon-carbon composite anode material, the silicon-carbon composite anode material comprising: the porous carbon microspheres described in the second aspect above, nano-silicon particles deposited in the pores and on the surface of the porous carbon microspheres, and a carbon coating layer covering the surface of the porous carbon microspheres.

[0030] Fourthly, embodiments of the present invention provide a negative electrode sheet, the negative electrode sheet comprising the silicon-carbon composite negative electrode material described in the third aspect above.

[0031] Fifthly, embodiments of the present invention provide a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the fourth aspect above.

[0032] This invention provides a method for preparing porous carbon microspheres, which mainly uses a hard template method with silica sol made of water glass as a template agent and a spray drying method to prepare porous carbon microspheres. Specifically, firstly, water glass powder is mixed and stirred evenly with water to obtain a water glass solution. The metal cations in the water glass solution are removed by passing it through a cation exchange resin bed to obtain an active silicic acid aqueous solution. The pH value of the active silicic acid aqueous solution is adjusted to neutral using an alkaline solution. Then, the solution is reacted at a certain temperature for a certain time to obtain a silica sol containing silica. The silica sol is mixed evenly with a carbon source material and then spray dried and carbonized to obtain carbon microsphere powder material. The carbon microsphere powder material is then etched, washed, and dried in sequence to remove silica, resulting in porous carbon microspheres.

[0033] The preparation method provided in this invention solves the problem of poor dispersibility of traditional silica templates by using relatively inexpensive water glass or recycled water glass as a template agent, effectively controlling the pore structure and improving the preparation efficiency. At the same time, the use of spray drying technology allows for easy control of particle morphology and size. Furthermore, since the use of relatively inexpensive water glass or recycled water glass as a template agent, the preparation method provided in this invention is low in cost, easy to operate, and suitable for large-scale industrial production.

[0034] The porous carbon microspheres prepared by the above-described method in this invention have the characteristics of large specific surface area, large pore volume, spherical structure, and interconnected carbon network. Using these porous carbon microspheres to prepare silicon-carbon composite anode materials can improve the conductivity and volumetric capacity of the silicon-carbon composite anode materials and reduce the volume expansion of silicon. Using these silicon-carbon composite anode materials to prepare anode sheets for assembly into lithium-ion batteries can improve the battery's initial coulombic efficiency, rate performance, and cycle stability. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the preparation method of porous carbon microspheres provided in an embodiment of the present invention.

[0036] Figure 2 This is a scanning electron microscope (SEM) image of the porous carbon microspheres prepared in Example 1 of the present invention.

[0037] Figure 3 This is a SEM image of the porous carbon microspheres prepared in Comparative Example 1 of this invention.

[0038] Figure 4 This is a SEM image of the porous carbon microspheres prepared in Comparative Example 2 of this invention.

[0039] Figure 5 This is a pore size distribution diagram of the porous carbon microspheres prepared in Example 1 of the present invention.

[0040] Figure 6This is a pore size distribution diagram of the porous carbon microspheres prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0043] This invention provides a method for preparing porous carbon microspheres, such as... Figure 1 As shown, the specific steps include:

[0044] Step S1: Add water glass powder to water and stir until homogeneous to obtain water glass solution;

[0045] The silica content in the water glass powder is 40wt% to 60wt%, preferably 55wt%. The silica content can be any value within the range of 40wt% to 60wt%, such as 40%, 45%, 50%, 55%, 60%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The water glass used in this invention is an industrial-grade material that is inexpensive and widely available.

[0046] Ordinary water or deionized water can be used; the solid content of the water glass solution is 10wt% to 25wt%.

[0047] Step S2: The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an aqueous solution of active silicic acid.

[0048] The pH value of the active silicic acid aqueous solution is between 2 and 3, preferably 2.5;

[0049] The cation exchange resin bed selected in this invention is a sulfonic acid-based ion exchange resin bed, which has advantages such as high efficiency, selectivity, low cost, strong adaptability, and no secondary pollution. It can better remove metal cations from water glass solution and is superior to membrane separation and precipitation methods. The sulfonic acid-based ion exchange resin bed includes, but is not limited to, any one of: polystyrene sulfonic acid ion exchange resin, cross-linked polystyrene-divinylbenzene sulfonic acid cation exchange resin, and fatty sulfonic acid cation exchange resin.

[0050] Step S3: Adjust the pH of the active silicic acid aqueous solution to neutral using an alkaline solution, and then react at a certain temperature for a certain time to obtain a silica sol containing silica.

[0051] The alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, or ammonium hydroxide solution.

[0052] Adjusting the pH value to neutral specifically means adjusting the pH value to 8-11, preferably 9.5;

[0053] The reaction is carried out at a certain temperature for a certain time, specifically 1 to 6 hours at a temperature between 25℃ and 80℃. The temperature range can be any value within the 25℃ to 80℃ range, such as 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc., but is not limited to the listed values; other unlisted temperature values ​​within this range are also applicable. The reaction time can be any time within the 1 to 6 hour range, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, etc., but is not limited to the listed time values; other unlisted time values ​​within this range are also applicable. Within this temperature and reaction time range, silica with optimal particle size can be obtained, which is beneficial for controlling the pore structure of the subsequent porous carbon microspheres within the optimal range.

[0054] Step S4: Mix the silica sol and carbon source material evenly, and then obtain the carbon microsphere precursor by spray drying;

[0055] The carbon source materials include one or more of glucose, sucrose, or phenolic resin.

[0056] The mass ratio of silica sol to carbon source material is 1.5:1 to 3:1;

[0057] The equipment for spray drying is a spray dryer. The inlet temperature of the spray dryer is 165℃~195℃, the outlet temperature is 65℃~85℃, the atomizer frequency is 150Hz~220Hz, and the feed flow rate is 1.5mL / min~3.5mL / min.

[0058] Step S5: The carbon microsphere precursor is placed in a high-temperature device and carbonized under a protective atmosphere to obtain carbon microsphere powder material.

[0059] High-temperature equipment includes any one of the following: tubular furnace, box furnace, fluidized bed, and rotary furnace;

[0060] Protective gases include any one of nitrogen, helium, or argon.

[0061] The carbonization process includes: heating to 350℃ to 450℃ at a heating rate of 2℃ / min to 5℃ / min, holding at that temperature for 1 hour to 5 hours, and then heating to 600℃ to 900℃ at a heating rate of 2℃ / min to 5℃ / min, holding at that temperature for 1 hour to 5 hours.

[0062] Step S6: The carbon microsphere powder material is sequentially etched, washed, and dried to remove silica and obtain porous carbon microspheres.

[0063] The etching process specifically includes: immersing carbon microsphere powder material in an alkaline solution for etching to remove silicon dioxide, followed by filtration or centrifugation to obtain a precipitate; the alkaline solution includes one or more of sodium hydroxide, potassium hydroxide, or ammonia water; the molar concentration of the alkaline solution is 1 mol / L to 2 mol / L; the etching temperature is 50℃ to 80℃, and the etching reaction time is 4 hours to 10 hours;

[0064] The washing process specifically includes: washing the precipitate with acid at least 3 times, and then washing it with deionized water at least 3 times; the acid includes: dilute hydrochloric acid or dilute nitric acid; the molar concentration of the acid is 1 mol / L to 2 mol / L;

[0065] The drying process specifically includes baking in an oven at 80℃ to 120℃ for 1 to 10 hours.

[0066] The porous carbon microspheres prepared by the above preparation method provided in this embodiment of the invention have a porosity of 50% to 80%, which can be any value within the above range, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0067] The mesopores in the porous carbon microspheres constitute 40% to 70% of the total pore size. This can be any value within this range, such as 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., but is not limited to the listed values; other unlisted values ​​within this range also apply. The pore size of the mesopores in the porous carbon microspheres ranges from 3 nm to 15 nm. This can be any value within this range, such as 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, etc., but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0068] The specific surface area of ​​the porous carbon microspheres is 980 m². 2 / g~1600m 2 / g can be any value within the above range, for example: 980m 2 / g, 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0069] The porous carbon microspheres have a pore volume of 1.2 cm³. 3 / g~3.5cm 3 / g can be any value within the above range, for example: 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g, 2.0cm 3 / g, 2.1cm 3 / g, 2.2cm 3 / g, 2.3cm 3 / g, 2.4cm 3 / g, 2.5cm 3 / g, 2.6cm 3 / g, 2.7cm 3 / g, 2.8cm 3 / g, 2.9cm 3 / g, 3.0cm 3 / g, 3.1cm 3 / g, 3.2cm 3 / g, 3.3cm 3 / g, 3.4cm 3 / g, 3.5cm 3 / g, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0070] The porous carbon microspheres provided in this embodiment of the invention are used to prepare silicon-carbon composite anode materials.

[0071] By using conventional methods, nano-silicon particles are deposited on the pores and surface of porous carbon microspheres, followed by carbon coating treatment, to prepare silicon-carbon composite anode materials.

[0072] The silicon-carbon composite anode material comprises: nano-silicon particles deposited in the pores and on the surface of porous carbon microspheres, and a carbon coating layer covering the surface of the porous carbon microspheres. This anode material can be used as an active anode material to prepare anode sheets and applied in lithium-ion batteries.

[0073] To better understand the technical solution provided by this invention, the following uses several specific examples to illustrate the preparation process and characteristics of the porous carbon microspheres of this invention.

[0074] Example 1

[0075] This embodiment provides a process for preparing porous carbon microspheres, the specific process of which is as follows.

[0076] (1) Add 0.25 kg of water glass powder (silica content of 55 wt%) to 1 kg of water and stir evenly to obtain water glass solution.

[0077] (2) The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an active silica aqueous solution with a pH of 2.5; wherein the cation exchange resin bed is a polystyrene sulfonic acid type ion exchange resin.

[0078] (3) Using a sodium hydroxide solution with a molar concentration of 1 mol / L, the pH value of the active silicic acid aqueous solution was adjusted to 9.5, and then reacted at 50°C for 1 hour to obtain a silica sol containing silica.

[0079] (4) The silica sol and carbon source material are mixed evenly at a mass ratio of 2:1, and then spray-dried by a spray dryer to obtain carbon microsphere precursor; wherein the inlet temperature is 165℃, the outlet temperature is 85℃, the atomizer frequency is 220Hz, and the feed flow rate is 3.5mL / min.

[0080] (5) The carbon microsphere precursor was placed in a tube furnace and heated to 410°C at a heating rate of 2°C / min under a nitrogen atmosphere. The temperature was held for 1 hour, and then heated to 900°C at a heating rate of 5°C / min. The temperature was held for 2 hours to obtain carbon microsphere powder material.

[0081] (6) The carbon microsphere powder material was mixed with a sodium hydroxide solution with a molar concentration of 2 mol / L and the solid content was controlled at 20 wt%. The silica was removed by etching at 50°C for 4 hours. The precipitate was obtained by centrifugation. The precipitate was then washed three times with dilute hydrochloric acid with a molar concentration of 1 mol / L for 10 minutes each time, and then washed three times with deionized water for 15 minutes each time. Finally, it was placed in an oven and dried at 100°C for 8 hours to obtain porous carbon microspheres.

[0082] SEM image of the porous carbon microspheres prepared in this embodiment, as shown below. Figure 2 As shown in the figure, the porous carbon microspheres in this embodiment have a smooth surface and good uniformity.

[0083] The pore size distribution of the porous carbon microspheres prepared in this embodiment is shown in the figure below. Figure 5 As shown, the porous carbon microspheres in this embodiment have a small pore size range, relatively uniform pore size, and high mesoporosity.

[0084] Example 2

[0085] This embodiment provides a process for preparing porous carbon microspheres, which differs from Example 1 in the reaction time of step (3). The specific process is as follows.

[0086] (1) Add 0.25 kg of water glass powder (silica content of 55 wt%) to 1 kg of water and stir evenly to obtain water glass solution.

[0087] (2) The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an active silica aqueous solution with a pH of 2.5; wherein the cation exchange resin bed is a polystyrene sulfonic acid type ion exchange resin.

[0088] (3) Using a sodium hydroxide solution with a molar concentration of 1 mol / L, the pH value of the active silicic acid aqueous solution was adjusted to 9.5, and then reacted at 50°C for 3 hours to obtain a silica sol containing silica.

[0089] (4) The silica sol and carbon source material are mixed evenly at a mass ratio of 2:1, and then spray-dried by a spray dryer to obtain carbon microsphere precursor; wherein the inlet temperature of the spray dryer is 165℃, the outlet temperature is 85℃, the atomizer frequency is 220Hz, and the feed flow rate is 3.5mL / min.

[0090] (5) The carbon microsphere precursor was placed in a tube furnace and heated to 410°C at a heating rate of 2°C / min under a nitrogen atmosphere. The temperature was held for 1 hour, and then heated to 900°C at a heating rate of 5°C / min. The temperature was held for 2 hours to obtain carbon microsphere powder material.

[0091] (6) The carbon microsphere powder material was mixed with a sodium hydroxide solution with a molar concentration of 2 mol / L and the solid content was controlled at 20 wt%. The silica was removed by etching at 50°C for 4 hours. The precipitate was obtained by centrifugation. The precipitate was then washed three times with dilute hydrochloric acid with a molar concentration of 1 mol / L for 10 minutes each time, and then washed three times with deionized water for 15 minutes each time. Finally, it was placed in an oven and dried at 100°C for 8 hours to obtain porous carbon microspheres.

[0092] Example 3

[0093] This embodiment provides a process for preparing porous carbon microspheres, which differs from Example 1 in the reaction time of step (3). The specific process is as follows.

[0094] (1) Add 0.25 kg of water glass powder (silica content of 55 wt%) to 1 kg of water and stir evenly to obtain water glass solution.

[0095] (2) The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an active silica aqueous solution with a pH of 2.5; wherein the cation exchange resin bed is a polystyrene sulfonic acid type ion exchange resin.

[0096] (3) Using a sodium hydroxide solution with a molar concentration of 1 mol / L, the pH value of the active silicic acid aqueous solution was adjusted to 9.5, and then reacted at 50°C for 5 hours to obtain a silica sol containing silica.

[0097] (4) The silica sol and carbon source material are mixed evenly at a mass ratio of 2:1, and then spray-dried by a spray dryer to obtain carbon microsphere precursor; wherein the inlet temperature of the spray dryer is 165℃, the outlet temperature is 85℃, the atomizer frequency is 220Hz, and the feed flow rate is 3.5mL / min.

[0098] (5) The carbon microsphere precursor was placed in a tube furnace and heated to 410°C at a heating rate of 2°C / min under a nitrogen atmosphere. The temperature was held for 1 hour, and then heated to 900°C at a heating rate of 5°C / min. The temperature was held for 2 hours to obtain carbon microsphere powder material.

[0099] (6) The carbon microsphere powder material was mixed with a sodium hydroxide solution with a molar concentration of 2 mol / L and the solid content was controlled at 20 wt%. The silica was removed by etching at 50°C for 4 hours. The precipitate was obtained by centrifugation. The precipitate was then washed three times with dilute hydrochloric acid with a molar concentration of 1 mol / L for 10 minutes each time, and then washed three times with deionized water for 15 minutes each time. Finally, it was placed in an oven and dried at 100°C for 8 hours to obtain porous carbon microspheres.

[0100] Example 4

[0101] This embodiment provides a process for preparing porous carbon microspheres. The difference from Example 1 is that the reaction temperature in step (3) is room temperature (25°C). The specific process is as follows.

[0102] (1) Add 0.25 kg of water glass powder (silica content of 55 wt%) to 1 kg of water and stir evenly to obtain water glass solution.

[0103] (2) The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an active silica aqueous solution with a pH of 2.5; wherein the cation exchange resin bed is a polystyrene sulfonic acid type ion exchange resin.

[0104] (3) Using a sodium hydroxide solution with a molar concentration of 1 mol / L, the pH value of the active silicic acid aqueous solution was adjusted to 9.5, and then reacted at 25°C for 1 hour to obtain a silica sol containing silica.

[0105] (4) The silica sol and carbon source material are mixed evenly at a mass ratio of 2:1, and then spray-dried by a spray dryer to obtain carbon microsphere precursor; wherein the inlet temperature is 165℃, the outlet temperature is 85℃, the atomizer frequency is 220Hz, and the feed flow rate is 3.5mL / min.

[0106] (5) The carbon microsphere precursor was placed in a tube furnace and heated to 410°C at a heating rate of 2°C / min under a nitrogen atmosphere. The temperature was held for 1 hour, and then heated to 900°C at a heating rate of 5°C / min. The temperature was held for 2 hours to obtain carbon microsphere powder material.

[0107] (6) The carbon microsphere powder material was mixed with a sodium hydroxide solution with a molar concentration of 2 mol / L and the solid content was controlled at 20 wt%. The silica was removed by etching at 50°C for 4 hours. The precipitate was obtained by centrifugation. The precipitate was then washed three times with dilute hydrochloric acid with a molar concentration of 1 mol / L for 10 minutes each time, and then washed three times with deionized water for 15 minutes each time. Finally, it was placed in an oven and dried at 100°C for 8 hours to obtain porous carbon microspheres.

[0108] Example 5

[0109] This embodiment provides a process for preparing porous carbon microspheres, which differs from Embodiment 1 in the temperature of step (3). The specific process is as follows.

[0110] (1) Add 0.25 kg of water glass powder (silica content of 55 wt%) to 1 kg of water and stir evenly to obtain water glass solution.

[0111] (2) The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an active silica aqueous solution with a pH of 2.5; wherein the cation exchange resin bed is a polystyrene sulfonic acid type ion exchange resin.

[0112] (3) Using a sodium hydroxide solution with a molar concentration of 1 mol / L, the pH value of the active silicic acid aqueous solution was adjusted to 9.5, and then reacted at 80°C for 1 hour to obtain a silica sol containing silica.

[0113] (4) The silica sol and carbon source material are mixed evenly at a mass ratio of 2:1, and then spray-dried by a spray dryer to obtain carbon microsphere precursor; wherein the inlet temperature of the spray dryer is 165℃, the outlet temperature is 85℃, the atomizer frequency is 220Hz, and the feed flow rate is 3.5mL / min.

[0114] (5) The carbon microsphere precursor was placed in a tube furnace and heated to 410°C at a heating rate of 2°C / min under a nitrogen atmosphere. The temperature was held for 1 hour, and then heated to 900°C at a heating rate of 5°C / min. The temperature was held for 2 hours to obtain carbon microsphere powder material.

[0115] (6) The carbon microsphere powder material was mixed with a sodium hydroxide solution with a molar concentration of 2 mol / L and the solid content was controlled at 20 wt%. The silica was removed by etching at 50°C for 4 hours. The precipitate was obtained by centrifugation. The precipitate was then washed three times with dilute hydrochloric acid with a molar concentration of 1 mol / L for 10 minutes each time, and then washed three times with deionized water for 15 minutes each time. Finally, it was placed in an oven and dried at 100°C for 8 hours to obtain porous carbon microspheres.

[0116] To better illustrate the effects of the embodiments of the present invention, Comparative Examples 1-2 are compared with the above embodiments.

[0117] Comparative Example 1

[0118] This comparative example provides a preparation process for porous carbon microspheres, which differs from the steps in Example 1 in that granulation is not performed by spray drying. The specific process is as follows.

[0119] (1) Add 0.25 kg of water glass powder (silica content of 55 wt%) to 1 kg of water and stir evenly to obtain water glass solution.

[0120] (2) The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an active silica aqueous solution with a pH of 2.5; wherein the cation exchange resin bed is a polystyrene sulfonic acid type ion exchange resin.

[0121] (3) Using a sodium hydroxide solution with a molar concentration of 1 mol / L, the pH value of the active silicic acid aqueous solution was adjusted to 9.5, and then reacted at 80°C for 1 hour to obtain a silica sol containing silica.

[0122] (4) Pour the silica sol into a flat plate, ensuring that the liquid layer is of uniform thickness. Then place the plate in an oven and dry it at 80°C until the solution is completely evaporated to obtain a dry powder precursor.

[0123] (5) The dried powder precursor is placed in a nitrogen atmosphere furnace and carbonized according to the following heating program: the temperature is increased to 410°C at a heating rate of 2°C / min and held for 1 hour, and then increased to 900°C at a heating rate of 5°C / min and held for 2 hours to obtain the carbonized product.

[0124] (6) The carbonized product was mixed with a sodium hydroxide solution with a molar concentration of 2 mol / L and the solid content was controlled at 20 wt%. The silicon template was removed by etching at 50 °C for 4 hours. The etched product was thoroughly washed with dilute hydrochloric acid with a molar concentration of 1 mol / L three times for 10 minutes each time, and then washed with deionized water three times for 15 minutes each time to remove NaOH residue. Finally, it was placed in an oven and dried at 100 °C for 8 hours to obtain porous carbon microspheres.

[0125] SEM images of the porous carbon microspheres prepared in this comparative example are shown below. Figure 3 As shown, the porous carbon microspheres prepared in Comparative Example 1 have irregular shapes and poor uniformity.

[0126] The pore size distribution of the porous carbon microspheres prepared in this comparative example is shown in the figure. Figure 6 As shown, the aperture range of Comparative Example 1 is larger than that of Example 1, and the aperture uniformity is inferior to that of Example 1.

[0127] Comparative Example 2

[0128] This comparative example provides a conventional preparation process for porous carbon microspheres, the specific process of which is as follows.

[0129] (1) Nano-silica with a particle size D50 of 7 nm and carbon source glucose are mixed at a mass ratio of 2:1. After being mixed evenly, carbon microsphere powder precursor is obtained by spray drying. The inlet temperature of the spray dryer is 165℃, the outlet temperature is 85℃, the atomizer frequency is 220Hz, and the feed flow rate is 3.5mL / min.

[0130] (2) Under a nitrogen atmosphere, the carbon microsphere powder precursor was placed in an atmosphere furnace and heated from room temperature to 410°C at a heating rate of 2°C / min and held for 1 hour. Then, it was heated to 900°C at a heating rate of 5°C / min and held for 2 hours to obtain carbon microsphere powder material.

[0131] (3) The obtained carbon microsphere powder material was mixed with a sodium hydroxide solution with a molar concentration of 2 mol / L and the solid content was controlled at 20 wt%. The silicon dioxide was removed by etching at 50°C for 4 hours. The precipitate was obtained by centrifugation. The precipitate was then washed three times with dilute hydrochloric acid with a molar concentration of 1 mol / L for 10 minutes each time, and then washed three times with deionized water for 15 minutes each time. Finally, it was placed in an oven and dried at 100°C for 8 hours to obtain porous carbon microspheres.

[0132] SEM images of the porous carbon microspheres prepared in this comparative example are shown below. Figure 4 As shown, although the porous carbon microspheres of Comparative Example 2 are spherical in shape, their surfaces are not smooth, and their uniformity is worse than that of the porous carbon microspheres of Example 1.

[0133] Performance tests were conducted on Examples 1-5 and Comparative Examples 1-2, as detailed below.

[0134] 1. The pore size distribution of the materials prepared in Examples 1-5 and Comparative Examples 1-2 was tested.

[0135] Specifically, the pore size distribution was analyzed by BET testing using a gas adsorption analyzer (Quantachrom-IQ2-XR). The specific surface area, pore size, and pore volume of the final prepared material were tested, as well as the average particle size of the sols (templates) of Examples 1-5 and Comparative Examples 1-2. The test results are shown in Table 1.

[0136] Table 1 shows the specific surface area, pore size, and pore volume of the porous carbon microspheres prepared in Examples 1-5 and Comparative Examples 1-2.

[0137]

[0138] Table 1

[0139] As can be seen from the test data in Table 1, the main differences between Examples 1-5 and Comparative Examples 1-2 lie in the parameters of specific surface area, pore volume, and pore size. In these examples, silica sols of different sizes were synthesized as templates by controlling the hydrolysis temperature and time of water glass. This allowed for precise control of the pore structure of the porous carbon microspheres. Specifically, by adjusting the hydrolysis time and temperature of the silica sol, the particle size was precisely regulated, resulting in a more stable pore structure and preventing the agglomeration of nano-silica during the template process. This is thanks to the optimization of the hydrolysis temperature and time, which resulted in more uniform silica particle size, thereby improving the uniformity of pore size. Simultaneously, the longer hydrolysis time and appropriate reaction temperature control effectively prevented particle aggregation and gelation, ensuring good dispersibility. In Comparative Example 2, the nano-silica used, without particle size and dispersibility optimization, is prone to agglomeration. This results in excessively large pore sizes and unstable pore structures in the prepared porous carbon microspheres, failing to meet the requirements for uniform pore structure and customized pore structures in silicon-carbon anode materials. These improvements provide an important foundation for the preparation of high-performance lithium-ion battery silicon anode materials and lay a solid foundation for the further application of mesoporous porous carbon materials in catalysis, new energy, and other fields.

[0140] 2. The practical application of the porous carbon microspheres prepared in the embodiments and comparative examples of the present invention in anode materials was tested.

[0141] First, the porous carbon microspheres in Examples 1-5 and Comparative Examples 1-2 were used to prepare silicon-carbon composite anode materials using the following methods: Under a nitrogen atmosphere, 500g of porous carbon microspheres were placed in a deposition furnace, and a mixture of silane and nitrogen with a volume ratio of 3:1 (flow rate of 5L / min) was introduced into the deposition furnace. Vapor phase deposition was performed at a deposition temperature of 600℃ for 5 hours, allowing silicon from the decomposition of silane to be deposited into the porous carbon microspheres. Then, the gas was converted into a mixture of methane and argon with a volume ratio of 2:1 (flow rate of 5L / min), and vapor phase carbon coating was performed at a temperature of 550℃ for 3 hours to obtain the silicon-carbon composite anode material.

[0142] Using the silicon-carbon composite anode materials prepared from the porous carbon microspheres in Examples 1-5 and Comparative Examples 1-2, anode sheets were prepared respectively: silicon-carbon composite anode materials, conductive carbon black (Super P) and binder polyacrylic acid (PAA) were weighed in a mass ratio of 7:1.5:1.5, and an appropriate amount of water was added as a solvent. The mixture was repeatedly and thoroughly ground in an agate mortar to form a viscous slurry with a solid content of about 45 wt%. The slurry was then evenly coated onto commercial battery-grade copper foil using a scraper applicator of a certain thickness. The foil was then placed in a vacuum drying oven for drying at 90°C for 12 hours. After drying, the foil was cut into circular electrode sheets with a diameter of 14 mm using a cutting machine and placed in an argon-filled glove box for later use.

[0143] Half-cell assembly: Assembly was carried out in an argon-filled glove box, with lithium sheets as the counter electrode, and a LiPF6 solution with a molar concentration of 1 mol / L as the electrolyte. The electrolyte solvent consisted of dimethyl carbonate (DMC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, and fluoroethylene carbonate (FEC) at 5% of the total electrolyte mass. A Celgard 2500 membrane was used as the separator. The half-cells were assembled with electrodes prepared from porous carbon microspheres as described in Examples 1-5 and Comparative Examples 1-2.

[0144] Electrochemical performance testing: The above half-cells were tested using a Blue Electric testing system (CT 2001A). The entire testing process was conducted at room temperature. The test results are shown in Table 2.

[0145] The specific test procedure is as follows:

[0146] Cyclic testing was conducted. In the first week, the voltage was first discharged at a rate of 0.5C to 5mV, then discharged at a rate of 0.1C to 5mV, then discharged at a rate of 0.05C to 5mV, and then charged at a rate of 0.1C to 1.5V. In the second week, the stepped discharge steps were repeated, discharging sequentially at rates of 0.5C, 0.1C, and 0.05C to 5mV, and then charging at a rate of 1C to 1.5V. Afterward, charge and discharge were performed at a rate of 1C. The initial discharge specific capacity and initial coulombic efficiency were measured, and the test data are detailed in Table 2.

[0147] For rate testing, the battery was first charged at room temperature at a rate of 0.1C until the battery voltage reached 1.5V. After charging, a rate discharge test was conducted, discharging at current densities of 0.5C, 1C, 2C, and 3C sequentially until the voltage dropped to 5mV. The discharge specific capacity at different current densities was obtained, and the percentage of discharge specific capacity at 3C current density compared to 0.1C current density was calculated. The calculated rate performance data are detailed in Table 2.

[0148] Table 2 summarizes the test data of half-cells containing electrodes prepared with porous carbon microspheres from Examples 1-5 and Comparative Examples 1-2:

[0149]

[0150]

[0151] Table 2

[0152] As can be seen from the test data in Table 2, the performance differences between Examples 1-5 and Comparative Examples 1-2 are mainly reflected in three aspects: first-cycle discharge capacity, first-cycle coulombic efficiency, and rate performance. Through comparative analysis, the examples using silica sol as a template provide a more uniform and stable pore structure compared to traditional nano-silica templates. This not only effectively avoids the agglomeration and inhomogeneity problems that easily occur during the preparation process of traditional templates, but also allows the prepared porous carbon microspheres to have a larger specific surface area and pore volume. As a matrix material for silicon deposition, it can effectively alleviate the problem of rapid capacity decay caused by volume and improve the cycle stability of the battery material. The developed mesoporous framework allows silanes to be easily dispersed within its channels and deposited into silicon particles through heating. The large mesoporous structure can maintain its pore structure integrity during high-temperature deposition, providing sufficient space to accommodate the volume expansion of silicon particles during charging and discharging, and further improving the long cycle life of lithium batteries. This improves the electrochemical performance of the battery, especially in terms of first-cycle discharge capacity, first-cycle coulombic efficiency, and rate performance. Precise control of pore structure: By adjusting the hydrolysis time and temperature of the silica sol, the pore structure of porous carbon microspheres can be precisely controlled, thereby customizing different pore size distributions to meet the diverse needs of silicon-carbon anode materials. This precise control not only improves the stability of the material but also significantly enhances battery performance. In contrast, the use of untreated nano-silica templates is prone to aggregation, resulting in excessively large pore sizes and unstable pore structures, which in turn affects the battery's conductivity, cycle stability, and rate performance. This problem is particularly evident in Comparative Example 1, causing its battery performance to be inferior to that of the materials in the examples.

[0153] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing porous carbon microspheres, characterized in that, The preparation method includes: Step S1: Add water glass powder to water and stir until homogeneous to obtain water glass solution; Step S2: The water glass solution is passed through a cation exchange resin bed to remove metal cations, resulting in an aqueous solution of active silicic acid. Step S3: Adjust the pH of the active silicic acid aqueous solution to neutral using an alkaline solution, and then react at a certain temperature for a certain time to obtain a silica sol containing silica. Step S4: Mix the silica sol with the carbon source material evenly, and then obtain the carbon microsphere precursor by spray drying; Step S5: The carbon microsphere precursor is placed in a high-temperature device and carbonized under a protective atmosphere to obtain carbon microsphere powder material. Step S6: The carbon microsphere powder material is sequentially etched, washed, and dried to remove silicon dioxide, thereby obtaining porous carbon microspheres.

2. The preparation method according to claim 1, characterized in that, The silica content in the water glass powder is 40wt% to 60wt%; the solid content in the water glass solution is 10wt% to 25wt%.

3. The preparation method according to claim 1, characterized in that, The pH value of the active silicic acid aqueous solution is between 2 and 3; The alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, or ammonium hydroxide solution; The pH value is adjusted to neutral, specifically to a pH value of 8-11. The reaction at a certain temperature for a certain time specifically refers to a reaction at 25℃ to 80℃ for 1 to 6 hours.

4. The preparation method according to claim 1, characterized in that, The carbon source material includes one or more of glucose, sucrose, or phenolic resin. The mass ratio of the silica sol to the carbon source material is 1.5:1 to 3:1; The spray drying equipment is a spray dryer, with an inlet temperature of 165℃~195℃, an outlet temperature of 65℃~85℃, an atomizer frequency of 150Hz~220Hz, and a feed flow rate of 1.5mL / min~3.5mL / min.

5. The preparation method according to claim 1, characterized in that, The high-temperature equipment includes any one of the following: tubular furnace, box furnace, fluidized bed, and rotary furnace; The protective gas includes any one of nitrogen, helium, or argon; The carbonization process includes: heating to 350℃ to 450℃ at a heating rate of 2℃ / min to 5℃ / min, holding at that temperature for 1 hour to 5 hours, and then heating to 600℃ to 900℃ at a heating rate of 2℃ / min to 5℃ / min, holding at that temperature for 1 hour to 5 hours.

6. The preparation method according to claim 1, characterized in that, The etching process specifically includes: immersing carbon microsphere powder material in an alkaline solution for etching to remove silicon dioxide, followed by filtration or centrifugation to obtain a precipitate; the alkaline solution includes one or more of sodium hydroxide, potassium hydroxide, or ammonia water. The washing process specifically includes: washing the precipitate with acid at least three times, and then washing it with deionized water at least three times; the acid includes dilute hydrochloric acid or dilute nitric acid; The drying process specifically includes baking in an oven at 80℃ to 120℃ for 1 to 10 hours.

7. A porous carbon microsphere prepared by the preparation method according to any one of claims 1-6, characterized in that, The porous carbon microspheres have a porosity of 50% to 80%, and the number of mesopores accounts for 40% to 70% of the total number of pores in the porous carbon microspheres. The porous carbon microspheres have a specific surface area of ​​980 m². 2 / g~1600m 2 / g, pore volume 1.2m 3 / g~3.5m 3 / g.

8. A silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material comprises: the porous carbon microspheres as described in claim 7, nano-silicon particles deposited in the pores and on the surface of the porous carbon microspheres, and a carbon coating layer covering the surface of the porous carbon microspheres.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the silicon-carbon composite negative electrode material as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

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