A high-rate performance porous carbon material and a preparation method thereof

Abstract

The application provides a kind of high rate performance porous carbon material and its preparation method, belongs to supercapacitor electrode material technical field.The application dissolves acrylamide, sodium alginate, crosslinking agent and initiator in low concentration calcium chloride aqueous solution, micron-sized frozen particles are obtained by spray freezing, then through freeze-drying, water is sublimated, the concentration of calcium chloride is gradually increased, in-situ crosslinking of sodium alginate and calcium ions is initiated, precursor particles with interpenetrating double network structure are formed;Subsequently, pre-carbonization, KOH activation and secondary high-temperature carbonization treatment are carried out in turn.The method avoids the damage of mechanical grinding to the pore, and the degree of graphitization of the material is accurately controlled by the secondary carbonization temperature.The obtained porous carbon material has high specific capacitance and excellent rate performance, and has wide application prospect in the field of supercapacitors.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor electrode material technology, and particularly relates to a high-rate performance porous carbon material and its preparation method. Background Technology

[0002] Carbon materials occupy an important position in the field of electrochemical energy storage due to their high specific surface area, excellent conductivity, good chemical stability, and environmental friendliness, especially suitable for high-power output scenarios with stringent rate performance requirements. Porous carbon materials, with their well-developed pore structure, provide abundant ion adsorption sites, which is key to achieving high energy density energy storage. Currently, the main methods for preparing porous carbon materials include template methods, activation methods, and precursor carbonization methods. However, these methods still have the following problems: template methods are complex and costly, and template removal easily introduces impurities; traditional activation methods have limited ability to control the pore structure, resulting in materials with a wide pore size distribution, which is not conducive to rapid ion transport; precursor carbonization methods are prone to structural collapse, leading to performance degradation. More importantly, the materials prepared by existing methods are usually in bulk form, requiring mechanical grinding to obtain powder electrode materials. The grinding process easily damages the fine pore structure inside the material, leading to loss of specific surface area and obstruction of ion diffusion paths, thereby reducing its electrochemical performance, especially its rate performance at high currents. In addition, materials prepared by traditional gelation methods are usually monolithic gel blocks, which are prone to stress concentration due to volume shrinkage during drying and carbonization, affecting the integrity of the structure. Summary of the Invention

[0003] To address the technical challenges of existing porous carbon materials that struggle to simultaneously achieve high specific capacitance and excellent rate performance, and the fact that traditional grinding processes can damage the material's pore structure, this invention provides a high-rate-performance porous carbon material and its preparation method. This method utilizes spray freezing technology combined with a controllable gelation strategy to directly obtain micron-sized porous carbon precursor particles, avoiding subsequent mechanical grinding and fully preserving the material's pore structure. Simultaneously, the pore structure and graphitization degree of the material are precisely controlled through a "pre-carbonization-activation-secondary carbonization" process, enabling it to simultaneously possess high specific capacitance and excellent rate performance.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing high-ratio porous carbon materials, comprising the following steps: (1) Dissolve acrylamide, sodium alginate, crosslinking agent and initiator in a calcium chloride aqueous solution with a concentration of 0.01~0.02wt%, stir evenly to obtain a mixed solution; (2) The mixed solution is atomized and sprayed into a low-temperature medium to obtain frozen particles; (3) Freeze-dry the frozen particles to form dried precursor particles; (4) The dried precursor particles are pre-carbonized under an inert atmosphere to obtain a pre-carbonized product; (5) The pre-carbonized product is impregnated with potassium hydroxide solution, dried, and then activated to obtain the activated product; (6) The activated product is washed and dried, and then carbonized at high temperature at 800~1400℃ to obtain the high-ratio performance porous carbon material.

[0005] This invention employs a spray freezing method combined with in-situ controlled gelation technology to prepare porous carbon precursors, followed by multi-step heat treatment to obtain the target material. Specifically: (1) Acrylamide, sodium alginate, N,N'-methylenebisacrylamide, and initiator were dissolved in a low-concentration calcium chloride aqueous solution and stirred until homogeneous. The initial concentration of calcium chloride (0.01~0.02wt%) was designed to prevent sodium alginate from gelling under these conditions, maintaining good solution flowability for spraying. 0.01~0.02wt% is the critical parameter; below 0.01wt%, even after freeze-drying, the calcium chloride... 2+ If the concentration does not reach the gelation threshold, sodium alginate cannot cross-link, and the particles will collapse. If the concentration is higher than 0.02 wt%, the initial solution viscosity increases, making spraying difficult; and localized gelation may occur before spraying or in the early stages of freezing, resulting in a loss of controllability.

[0006] (2) Spray freezing: The above solution is atomized into tiny droplets by a spray device (such as a spray dryer, spray gun, etc.) and sprayed directly into liquid nitrogen (or other low temperature medium) to freeze and solidify the droplets instantly, forming micron-sized frozen particles.

[0007] (3) Freeze-drying: The frozen particles are freeze-dried. During the drying process, as water sublimates, the concentration of calcium chloride in the solution gradually increases. When the concentration reaches the gelation threshold of sodium alginate, sodium alginate cross-links with calcium ions, forming an interpenetrating double gel network inside the polyacrylamide network. This process achieves "in-situ, controllable, and gradual" gelation, enhances the structural stability of the precursor particles, and avoids large-volume shrinkage during the drying of bulk gels.

[0008] (4) Pre-carbonization: Under an inert atmosphere, the freeze-dried precursor particles are pre-carbonized at low temperature, causing thermally initiated polymerization of the acrylamide monomer to form a polyacrylamide (PAM) chemical crosslinking network. At this point, the PAM chemical network and sodium alginate-Ca... 2+ The physical networks interpenetrate to form a dual-network structure. At the same time, low-temperature carbonization initially stabilizes the carbon skeleton, preventing structural collapse during subsequent high-temperature treatment.

[0009] (5) KOH activation: The pre-carbonized product is immersed in KOH solution, utilizing the porous characteristics of the precursor particles to achieve uniform adsorption of the activator. After drying, it undergoes activation treatment to create pores inside the material. KOH is a strong alkaline activator that reacts with carbon at high temperatures to undergo a redox reaction, etching the carbon skeleton and generating a large number of micropores and mesopores, significantly increasing the specific surface area. The advantage of this invention is that the precursor particles themselves are porous, and the KOH solution can be uniformly adsorbed, avoiding the problem of uneven distribution of the activator after traditional bulk grinding.

[0010] (6) Secondary carbonization: After washing and drying the activated product, it is carbonized at high temperature in an inert atmosphere. The carbon atoms rearrange to form a more ordered graphite microcrystalline structure, which further improves the graphitization degree of the material and obtains the final high-rate performance porous carbon material.

[0011] Further, taking the sum of the mass percentages of the acrylamide, sodium alginate, crosslinking agent, and calcium chloride aqueous solution as 100%, the mass fraction of the acrylamide is 7-12%, the mass fraction of the sodium alginate is 0.5-1%, the mass fraction of the crosslinking agent is 0.01-0.05%, and the balance is calcium chloride aqueous solution.

[0012] Further, the crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate or potassium persulfate, and the amount added is 0.01% to 0.05% of the total mass of acrylamide, sodium alginate, crosslinking agent and calcium chloride aqueous solution.

[0013] Furthermore, the cryogenic medium is liquid nitrogen, and the atomization is achieved by a spray device at a pressure of 0.2~0.5MPa, resulting in frozen particles with a particle size of 1~100μm.

[0014] Furthermore, the freeze-drying conditions are as follows: pre-freezing at -50℃ to -10℃ for 2 to 12 hours, and then drying under a vacuum of less than 20 Pa for 24 to 72 hours.

[0015] Furthermore, the pre-carbonization conditions are as follows: heating to 180~230℃ at a heating rate of 0.5~2℃ / min, and then holding at that temperature for 1~3 hours.

[0016] Furthermore, the mass concentration of the potassium hydroxide solution is 5-10%, and the amount added is 300-500% of the mass of the pre-carbonized product.

[0017] Furthermore, the drying conditions are: drying at 80~120℃ for 10~12h.

[0018] Furthermore, the activation treatment conditions are as follows: heating to 700-900℃ at a heating rate of 1-10℃ / min, and then holding at that temperature for 1-3 hours.

[0019] Furthermore, the conditions for high-temperature carbonization are as follows: heating to 800-1400°C at a heating rate of 1-10°C / min, and then holding at that temperature for 1-3 hours.

[0020] Furthermore, both the activation treatment and the high-temperature carbonization are carried out under an inert atmosphere, which is at least one of nitrogen, argon, or helium.

[0021] The present invention also provides a high-rate-performance porous carbon material, which is prepared by the above-described preparation method.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects: (1) This invention uses spray freezing technology to directly obtain micron-sized precursor particles, eliminating the traditional bulk gel crushing and grinding steps, thus avoiding mechanical damage to the pore structure from the source. By designing a low initial calcium ion concentration, the calcium ion concentration is naturally increased by the sublimation of water during the freeze-drying process, triggering the gradual gelation of sodium alginate, forming a uniform and stable polyacrylamide / sodium alginate dual network structure.

[0023] (2) The porous carbon material particles prepared by the method of the present invention have complete internal pores and developed specific surface area, and their graphitization degree can be precisely controlled by the secondary carbonization temperature, thereby synergistically optimizing the double layer capacitance and electronic conduction ability of the material.

[0024] (3) The porous carbon material prepared by this invention is in 0.5 A g -1 The specific capacitance at current density can reach 216 F g. -1 , in 15 A g -1 It boasts a capacitance retention rate of up to 92.4% at high rates, combining high specific capacitance with excellent rate performance.

[0025] (4) The present invention uses a spray freezing method to directly obtain micron-sized particles without mechanical grinding, which preserves the fine pore structure formed during the activation and carbonization process of the material to the greatest extent, which is beneficial to electrolyte wetting and rapid ion transport.

[0026] (5) The controllable gelation strategy of the present invention enhances the mechanical stability of the precursor particles, enabling them to maintain good structural integrity during subsequent heat treatment, thereby improving the overall performance and batch consistency of the material. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1SEM image of the high-ratio porous carbon material prepared in Example 2; Figure 2 Here is a SEM image of the carbon material in Comparative Example 1; Figure 3 Transmission electron microscope (TEM) images of porous carbon materials under different secondary high-temperature carbonization conditions in Examples 1-3, where (a) is Example 1 at 800℃, (b) is Example 2 at 1200℃, and (c) is Example 3 at 1400℃. Figure 4 The GCD curves of the porous carbon material in Example 1 at different current densities are shown below. Figure 5 The GCD curves of the porous carbon material in Example 2 at different current densities are shown below. Figure 6 The GCD curves of the porous carbon material in Example 3 at different current densities are shown below. Figure 7 The GCD curves of the carbon material in Comparative Example 1 are shown at different current densities. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] This invention provides a method for preparing high-ratio porous carbon materials, comprising the following steps: (1) Dissolve acrylamide, sodium alginate, crosslinking agent and initiator in a calcium chloride aqueous solution with a concentration of 0.01~0.02wt%, stir evenly to obtain a mixed solution; (2) The mixed solution is atomized and sprayed into a low-temperature medium to obtain frozen particles; (3) Freeze-dry the frozen particles to form dried precursor particles; (4) The dried precursor particles were pre-carbonized under an inert atmosphere to obtain the pre-carbonized product. (5) The pre-carbonized product is impregnated with potassium hydroxide solution, dried, and then activated to obtain the activated product; (6) The activated product is washed and dried, and then carbonized at high temperature at 800~1400℃ to obtain high-ratio porous carbon material.

[0034] In some embodiments of the present invention, based on the sum of the mass percentages of acrylamide, sodium alginate, crosslinking agent and calcium chloride aqueous solution as 100%, the mass fraction of acrylamide is 7-12%, the mass fraction of sodium alginate is 0.5-1%, the mass fraction of crosslinking agent is 0.01-0.05%, and the balance is calcium chloride aqueous solution.

[0035] In some embodiments of the present invention, the crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate or potassium persulfate, and the amount added is 0.01% to 0.05% of the total mass of acrylamide, sodium alginate, crosslinking agent and calcium chloride aqueous solution.

[0036] In some embodiments of the present invention, the cryogenic medium is liquid nitrogen, and atomization is achieved by a spray device at a pressure of 0.2~0.5MPa, resulting in frozen particles with a particle size of 1~100μm.

[0037] In some embodiments of the present invention, the freeze-drying conditions are as follows: pre-freezing at -50℃ to -10℃ for 2 to 12 hours, and then drying under a vacuum of less than 20 Pa for 24 to 72 hours.

[0038] In some embodiments of the present invention, the pre-carbonization conditions are as follows: heating to 180-230°C at a heating rate of 0.5-2°C / min, and then holding at that temperature for 1-3 hours.

[0039] In some embodiments of the present invention, the mass concentration of the potassium hydroxide solution is 5-10%, and the amount added is 300-500% of the mass of the precarbonized product.

[0040] In some embodiments of the present invention, the drying conditions are: drying at 80~120℃ for 10~12h.

[0041] In some embodiments of the present invention, the activation treatment conditions are as follows: heating to 700-900°C at a heating rate of 1-10°C / min, and then holding at that temperature for 1-3 hours.

[0042] In some embodiments of the present invention, the conditions for high-temperature carbonization are as follows: heating to 800-1400°C at a heating rate of 1-10°C / min, and then holding at that temperature for 1-3 hours.

[0043] In some embodiments of the present invention, the activation treatment and high-temperature carbonization are both carried out under an inert atmosphere, which is at least one of nitrogen, argon and helium.

[0044] This invention also provides a high-rate-performance porous carbon material, which is prepared by the above-described preparation method.

[0045] For example, the preparation method of high-ratio performance porous carbon material in this embodiment of the invention includes the following steps: (1) Weigh acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in weight ratios of 7-12%, 0.5-1%, and 0.01-0.05%, respectively. Add calcium chloride aqueous solution with a concentration of 0.01-0.02wt% to bring the total to 100%. The amount of calcium chloride aqueous solution can be adjusted according to specific needs to control the relative proportions of other raw materials in the system. Then, mix and dissolve acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in calcium chloride aqueous solution and stir to form a homogeneous solution. Then, add an initiator (ammonium persulfate or potassium persulfate) at 0.01%-0.05% of the total mass of the solution and stir to form a uniformly dispersed mixed solution. (2) The above solution is loaded into a spray gun and atomized under a pressure of 0.2~0.5MPa. It is sprayed into liquid nitrogen and the droplets are instantly frozen. White frozen particles with a particle size of 1~100μm are collected. (3) Freeze-dry the frozen particles. The freeze-drying conditions are: pre-freeze at -50℃ to -10℃ for 2 to 12 hours, and then dry at a vacuum of less than 20 Pa for 24 to 72 hours to fully remove moisture while maintaining the integrity of the three-dimensional network structure of the gel, thus forming dried precursor particles. (4) Under an inert atmosphere, the dried precursor particles are pre-carbonized in a muffle furnace. The pre-carbonization conditions are: heating to 180-230°C at a heating rate of 0.5-2°C / min, and then holding for 1-3 hours to obtain the pre-carbonized product. (5) The pre-carbonized product is impregnated with a 5-10% potassium hydroxide solution (the amount added is 300-500% of the mass of the pre-carbonized product), then dried at 80-120℃ for 10-12h, and then activated. The activation conditions are: under an inert atmosphere, the temperature is raised to 700-900℃ at a heating rate of 1-10℃ / min, and then kept at the temperature for 1-3h to obtain the activated product. (6) The activated product is acid washed (such as by washing with dilute hydrochloric acid or dilute nitric acid to remove residual KOH and inorganic impurities), washed with deionized water until neutral, dried, and then subjected to a second high-temperature carbonization treatment. The conditions for the second high-temperature carbonization treatment are: under an inert atmosphere, the temperature is raised to 800~1400℃ at a heating rate of 1~10℃ / min, and then kept at the temperature for 1~3h to obtain high-ratio porous carbon material.

[0046] The technical solution of the present invention will be further illustrated by the following embodiments.

[0047] Example 1 A method for preparing a high-ratio porous carbon material includes the following steps: (1) Weigh acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in weight ratios of 9%, 1%, and 0.05%, respectively, and add a 0.02wt% calcium chloride aqueous solution to bring the total to 100%. The amount of calcium chloride aqueous solution can be adjusted according to specific needs to control the relative proportions of other raw materials in the system. Then, mix and dissolve acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in the calcium chloride aqueous solution, stir to form a homogeneous solution, and then add 0.05% of the total mass of the solution of initiator (ammonium persulfate), and stir to form a uniformly dispersed mixed solution. (2) The mixed solution was loaded into a spray gun, atomized at a pressure of 0.2 MPa, sprayed into liquid nitrogen, and the droplets were instantly frozen. White frozen particles with a particle size of 1~100 μm were collected. (3) Freeze-dry the frozen particles. The freeze-drying conditions are: pre-freeze at -18℃ for 12h, and then dry at a vacuum of 15Pa for 24h to fully remove moisture while maintaining the integrity of the three-dimensional network structure of the gel, thus forming dried precursor particles. (4) Under an inert atmosphere (argon), the dried precursor particles were pre-carbonized in a muffle furnace. The pre-carbonization conditions were: heating to 200°C at a heating rate of 0.5°C / min, and then holding for 2 hours to obtain the pre-carbonized product. (5) The pre-carbonized product was impregnated with an 8% potassium hydroxide solution (400% of the mass of the pre-carbonized product), then dried at 90°C for 12 hours, and then activated. The activation conditions were: under an inert atmosphere (argon), the temperature was increased to 900°C at a rate of 5°C / min, and then kept at the temperature for 1 hour to obtain the activated product. (6) The activated product is acid-washed (using 10wt.% dilute hydrochloric acid), washed with deionized water until neutral, dried, and then subjected to a second high-temperature carbonization treatment. The conditions for the second high-temperature carbonization treatment are: under an inert atmosphere (argon), the temperature is raised to 800℃ at a heating rate of 5℃ / min, and then kept at the temperature for 2h to obtain a high-ratio porous carbon material.

[0048] Example 2 A method for preparing a high-ratio porous carbon material includes the following steps: (1) Weigh acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in weight ratios of 9%, 1%, and 0.05%, respectively, and add a 0.02wt% calcium chloride aqueous solution to bring the total to 100%. The amount of calcium chloride aqueous solution can be adjusted according to specific needs to control the relative proportions of other raw materials in the system. Then, mix and dissolve acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in the calcium chloride aqueous solution, stir to form a homogeneous solution, and then add 0.05% of the total mass of the solution of initiator (ammonium persulfate), and stir to form a uniformly dispersed mixed solution. (2) The mixed solution was loaded into a spray gun, atomized at a pressure of 0.2 MPa, sprayed into liquid nitrogen, and the droplets were instantly frozen. White frozen particles with a particle size of 1~100 μm were collected. (3) Freeze-dry the frozen particles. The freeze-drying conditions are: pre-freeze at -18℃ for 12h, and then dry at a vacuum of 15Pa for 24h to fully remove moisture while maintaining the integrity of the three-dimensional network structure of the gel, thus forming dried precursor particles. (4) Under an inert atmosphere (argon), the dried precursor particles were pre-carbonized in a muffle furnace. The pre-carbonization conditions were: heating to 200°C at a heating rate of 0.5°C / min, and then holding for 2 hours to obtain the pre-carbonized product. (5) The pre-carbonized product was impregnated with an 8% potassium hydroxide solution (400% of the mass of the pre-carbonized product), then dried at 90°C for 12 hours, and then activated. The activation conditions were: under an inert atmosphere (argon), the temperature was increased to 900°C at a rate of 5°C / min, and then kept at the temperature for 1 hour to obtain the activated product. (6) The activated product is acid-washed (using 10wt.% dilute hydrochloric acid), washed with deionized water until neutral, dried, and then subjected to a second high-temperature carbonization treatment. The conditions for the second high-temperature carbonization treatment are: under an inert atmosphere (argon), the temperature is raised to 1200℃ at a heating rate of 5℃ / min, and then kept at the temperature for 2h to obtain a high-ratio porous carbon material.

[0049] Example 3 A method for preparing a high-ratio porous carbon material includes the following steps: (1) Weigh acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in weight ratios of 9%, 1%, and 0.05%, respectively, and add a 0.02wt% calcium chloride aqueous solution to bring the total to 100%. The amount of calcium chloride aqueous solution can be adjusted according to specific needs to control the relative proportions of other raw materials in the system. Then, mix and dissolve acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in the calcium chloride aqueous solution, stir to form a homogeneous solution, and then add 0.05% of the total mass of the solution of initiator (ammonium persulfate), and stir to form a uniformly dispersed mixed solution. (2) The mixed solution was loaded into a spray gun, atomized at a pressure of 0.2 MPa, sprayed into liquid nitrogen, and the droplets were instantly frozen. White frozen particles with a particle size of 1~100 μm were collected. (3) Freeze-dry the frozen particles. The freeze-drying conditions are: pre-freeze at -18℃ for 12h, and then dry at a vacuum of 15Pa for 24h to fully remove moisture while maintaining the integrity of the three-dimensional network structure of the gel, thus forming dried precursor particles. (4) Under an inert atmosphere (argon), the dried precursor particles were pre-carbonized in a muffle furnace. The pre-carbonization conditions were: heating to 200°C at a heating rate of 0.5°C / min, and then holding for 2 hours to obtain the pre-carbonized product. (5) The pre-carbonized product was impregnated with an 8% potassium hydroxide solution (400% of the mass of the pre-carbonized product), then dried at 90°C for 12 hours, and then activated. The activation conditions were: under an inert atmosphere (argon), the temperature was increased to 900°C at a rate of 5°C / min, and then kept at the temperature for 1 hour to obtain the activated product. (6) The activated product is acid-washed (using 10wt.% dilute hydrochloric acid), washed with deionized water until neutral, dried, and then subjected to a second high-temperature carbonization treatment. The conditions for the second high-temperature carbonization treatment are: under an inert atmosphere (argon), the temperature is raised to 1400℃ at a heating rate of 5℃ / min, and then kept at the temperature for 2h to obtain a high-ratio porous carbon material.

[0050] Comparative Example 1 Same as Example 2, except that the spray freezing step in step (2) is replaced with thermal polymerization, specifically: (1) Weigh acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in weight ratios of 9%, 1%, and 0.05%, respectively, and add a 0.02wt% calcium chloride aqueous solution to bring the total to 100%. The amount of calcium chloride aqueous solution can be adjusted according to specific needs to control the relative proportions of other raw materials in the system. Then, mix and dissolve acrylamide, sodium alginate, and N,N'-methylenebisacrylamide in the calcium chloride aqueous solution, stir to form a homogeneous solution, and then add 0.05% of the total mass of the solution of initiator (ammonium persulfate), and stir to form a uniformly dispersed mixed solution. (2) The mixed solution was kept at 70°C for 2 hours to form a gel through thermal polymerization; (3) The gel was freeze-dried under the following conditions: pre-frozen at -18℃ for 12h, and then dried under a vacuum of 15Pa for 24h to remove moisture while maintaining the integrity of the three-dimensional network structure of the gel and forming dried precursor particles. (4) Under an inert atmosphere (argon), the dried precursor particles were pre-carbonized in a muffle furnace. The pre-carbonization conditions were: heating to 200°C at a heating rate of 0.5°C / min, and then holding for 2 hours to obtain the pre-carbonized product. (5) The pre-carbonized product was impregnated with an 8% potassium hydroxide solution (400% of the mass of the pre-carbonized product), then dried at 90°C for 12 hours, and then activated. The activation conditions were: under an inert atmosphere (argon), the temperature was increased to 900°C at a rate of 5°C / min, and then kept at the temperature for 1 hour to obtain the activated product. (6) The activated product is acid-washed (using 10wt.% dilute hydrochloric acid), washed with deionized water until neutral, dried, and then subjected to a second high-temperature carbonization treatment. The conditions for the second high-temperature carbonization treatment are: under an inert atmosphere, the temperature is raised to 1200℃ at a heating rate of 5℃ / min, and then kept at the temperature for 2h to obtain carbon material.

[0051] Comparative Example 2 Same as Example 2, except that the concentration of the calcium chloride aqueous solution is increased to 0.1 wt%. This is because adding a higher concentration of calcium ion solution will cause sodium alginate to gel rapidly, making it impossible to spray.

[0052] Performance testing Figure 1 This is a SEM image of the high-ratio porous carbon material prepared in Example 2. Figure 2The SEM image of the carbon material in Comparative Example 1 shows that the porous carbon material prepared in Example 2 of this invention has a well-developed three-dimensional micron-scale pore structure, with intact particle morphology and interconnected internal channels, which is beneficial for electrolyte wetting and rapid ion transport. This structure originates from a spray-freezing combined with an in-situ controlled gelation strategy, avoiding the damage to the pores caused by traditional grinding. In contrast, the carbon material obtained in Comparative Example 1 (using traditional heating gelation without spray-freezing) exhibits significant structural defects, such as large volume shrinkage, pore collapse, or uneven distribution. This is because the overall gel generates significant internal stress during drying and carbonization, resulting in poor structural integrity and negatively impacting electrochemical performance.

[0053] Figure 3 Transmission electron microscopy (TEM) images of porous carbon materials under different secondary high-temperature carbonization conditions in Examples 1-3 are shown, where (a) is Example 1 at 800℃, (b) is Example 2 at 1200℃, and (c) is Example 3 at 1400℃. It can be seen that as the secondary carbonization temperature increases from 800℃ to 1400℃, the degree of graphitization of the material significantly increases, and graphene sheet structures gradually appear at high temperatures. This indicates that the secondary carbonization temperature is a key parameter for controlling the microscopic order and conductivity of carbon materials.

[0054] Figures 4-6 The GCD curves of the porous carbon materials in Examples 1-3 are shown below under different current densities. Figure 7 The GCD curves of the carbon material in Comparative Example 1 at different current densities show that the porous carbon materials in the embodiments of the present invention all exhibit typical double-layer capacitance characteristics, and the GCD curves are approximately symmetrical triangles. However, compared with the samples carbonized at higher temperatures, the rate performance of the carbon material in Example 1 is limited, which is attributed to insufficient electronic conductivity due to the lower degree of graphitization.

[0055] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a high-ratio porous carbon material, characterized in that, Includes the following steps: (1) Dissolve acrylamide, sodium alginate, crosslinking agent and initiator in a calcium chloride aqueous solution with a concentration of 0.01~0.02wt%, stir evenly to obtain a mixed solution; (2) The mixed solution is atomized and sprayed into a low-temperature medium to obtain frozen particles; (3) Freeze-dry the frozen particles to form dried precursor particles; (4) The dried precursor particles are pre-carbonized under an inert atmosphere to obtain a pre-carbonized product; (5) The pre-carbonized product is impregnated with potassium hydroxide solution, dried, and then activated to obtain the activated product; (6) The activated product is washed and dried, and then carbonized at high temperature at 800~1400℃ to obtain the high-ratio performance porous carbon material.

2. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, With the sum of the mass percentages of the acrylamide, sodium alginate, crosslinking agent, and calcium chloride aqueous solution being 100%, the mass fraction of the acrylamide is 7-12%, the mass fraction of the sodium alginate is 0.5-1%, the mass fraction of the crosslinking agent is 0.01-0.05%, and the remainder is calcium chloride aqueous solution.

3. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, The crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate or potassium persulfate. The amount added is 0.01% to 0.05% of the total mass of acrylamide, sodium alginate, crosslinking agent and calcium chloride aqueous solution.

4. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, The cryogenic medium is liquid nitrogen, and the atomization is achieved by a spray device at a pressure of 0.2~0.5MPa, resulting in frozen particles with a particle size of 1~100μm.

5. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, The freeze-drying conditions are as follows: pre-freezing at -50℃ to -10℃ for 2 to 12 hours, and then drying under a vacuum of less than 20 Pa for 24 to 72 hours.

6. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, The pre-carbonization conditions are as follows: heat to 180-230℃ at a heating rate of 0.5-2℃ / min, and then hold at that temperature for 1-3 hours.

7. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, The potassium hydroxide solution has a mass concentration of 5-10%, and the amount added is 300-500% of the mass of the pre-carbonized product. The drying conditions are: drying at 80~120℃ for 10~12 hours; The activation treatment conditions are as follows: heat to 700-900℃ at a heating rate of 1-10℃ / min, and then keep warm for 1-3 hours.

8. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, The heating rate for high-temperature carbonization is 1~10℃ / min, and the holding time is 1~3h.

9. The method for preparing high-ratio porous carbon material according to claim 1, characterized in that, Both the activation treatment and the high-temperature carbonization are carried out under an inert atmosphere, which is at least one of nitrogen, argon, or helium.

10. A high-ratio porous carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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