A nitrogen-sulfur co-doped petroleum coke porous carbon material, its preparation method and application

Abstract

This invention proposes a nitrogen-sulfur co-doped petroleum coke porous carbon material, its preparation method, and its application. The nitrogen-sulfur co-doped petroleum coke porous carbon material contains 4.53-5.36 wt% nitrogen, 1.05-1.23 wt% sulfur, and 0.1-0.8 wt% phosphorus, and has a specific surface area >2200 m². 2 / g, the proportion of mesopore volume with pore size of 2-50nm is 20%-35%. Among them, sulfur-doped porous carbon material is obtained by pre-treated petroleum coke through acid washing, treatment with ammonium dihydrogen phosphate solution, inert atmosphere activation and secondary acid washing, water washing and drying. Nitrogen-sulfur co-doped petroleum coke porous carbon material is obtained by mixing the above sulfur-doped porous carbon with nitrogen source, doping in an inert atmosphere and then crushing and drying.

Description

Technical Field

[0001] This invention relates to the field of porous carbon materials technology, and more particularly to a nitrogen-sulfur co-doped petroleum coke porous carbon material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles and the large-scale energy storage market, higher demands are being placed on the energy density of lithium-ion batteries. Silicon, due to its high specific capacity, is considered the core material for anodes. However, the significant volume expansion of silicon during charging and discharging leads to electrode pulverization and rapid capacity decay. Combining nano-silicon with porous carbon materials to form silicon-carbon anodes is an effective way to overcome the inherent defects of silicon by utilizing the conductive network and buffer space of carbon materials. Therefore, the performance of the porous carbon substrate is crucial; it needs to possess high specific surface area, excellent conductivity, and good electrolyte wettability.

[0003] Petroleum coke, a byproduct of petroleum refining, is an ideal precursor for preparing porous carbon due to its high carbon content, low cost, and good graphitization potential. However, directly using it as a substrate for silicon-carbon anodes presents several technical challenges: Firstly, the raw material contains numerous impurities, and traditional acid washing is incomplete in removing them. Petroleum coke contains metallic impurities such as Fe, Ni, and V, which are difficult to remove completely with traditional single-acid washing. These residual impurities catalyze the formation of disordered carbon during subsequent high-temperature activation, clogging pores and acting as active sites for electrochemical side reactions, severely impairing the substrate's conductivity, structural stability, and battery cycle life. Secondly, the pore structure generated after traditional acid washing and activation is limited, failing to balance high specific surface area with fast ion transport. Furthermore, current technologies primarily rely on strong alkalis for activation and pore formation, which, while achieving a high specific surface area, results in predominantly micropores with high ion diffusion resistance, failing to meet the rapid ion transport requirements of silicon-carbon anodes during high-rate charge-discharge cycles. This leads to low heteroatom doping efficiency and weak synergistic effects.

[0004] In order to improve the electrochemical activity of carbon materials, nitrogen, sulfur and other heteroatoms are often doped in the existing technology. The doping process is separated from the pore-forming process, which leads to uneven distribution of doped atoms, weak bonding with the carbon skeleton and low doping efficiency. In particular, sulfur is easily volatilized and lost at high temperatures and is difficult to retain effectively. Summary of the Invention

[0005] In view of this, the present invention proposes a nitrogen-sulfur co-doped petroleum coke porous carbon material, its preparation method and application, which solves the technical problems of pore blockage and low nitrogen-sulfur doping efficiency caused by incomplete removal of metal impurities when preparing porous carbon materials using petroleum coke as raw material.

[0006] The technical solution of this invention is implemented as follows: This invention provides a nitrogen-sulfur co-doped petroleum coke porous carbon material. The nitrogen content in this material is 4.53-5.36 wt%, the sulfur content is 1.05-1.23 wt%, and the phosphorus content is 0.1-0.8 wt%, with a specific surface area >2200 m². 2 / g, the mesopore volume ratio of 2-50nm pore size is 20%-35%.

[0007] Secondly, the present invention provides a method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material, comprising the following steps: S1, the pretreated petroleum coke raw material is acid-washed and dispersed evenly, then ammonium dihydrogen phosphate solution is added, and the washing continues until neutral. After drying, the acid-washed petroleum coke powder is obtained. The acidic ammonium phosphate salt is used to react with the metal ions of the petroleum coke raw material to form a soluble complex. S2, the acid-washed petroleum coke powder is mixed with an activator and activated in an inert gas environment. After activation, it is subjected to secondary acid washing, water washing and drying in sequence to obtain sulfur-doped porous carbon material. S3, sulfur-doped porous carbon material is mixed with a nitrogen source, doped in an inert gas environment, pulverized, and dried to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

[0008] Based on this technical solution, and further preferably, step S1 includes: S1.1, dry the petroleum coke raw material at 100-120℃, pulverize it, and pre-oxidize it at 300-450℃ for 0.5-2h. After the treatment, add the first acid solution into the reaction vessel, disperse it evenly, adjust the pH to less than 2.5 and perform acid washing. During the acid washing process, add ammonium dihydrogen phosphate solution dropwise and stir at room temperature for 12-24h. After the acid washing is completed, separate the solid and liquid, wash the solid with deionized water until the washing liquid is neutral, and obtain the solid material. S1.2, the washed solid material is vacuum dried at 120-130℃ for 6-12h to obtain pickled petroleum coke powder.

[0009] Based on this technical solution, further preferably, the petroleum coke raw material includes low-sulfur petroleum coke with a sulfur content of <1.0wt%, and the particle size of the pulverized petroleum coke raw material is 10-20μm. The first acid solution includes a mixture of hydrochloric acid and sulfuric acid, with the concentration of hydrochloric acid being 0.05-3mol / L and the concentration of sulfuric acid being 0.05-3mol / L. The mass ratio of petroleum coke:hydrochloric acid:sulfuric acid is 1:0.5:0.3. The amount of ammonium dihydrogen phosphate added is 5%-10% of the mass of the petroleum coke raw material.

[0010] Based on this technical solution, and further preferably, step S2 includes: S2.1, the pickled petroleum coke powder is mixed with alkaline solution, dried, then an activator is added and ground, mixed evenly, placed in an inert atmosphere tube furnace, heated to 700-800℃ at a rate of 2-10℃ / min, and kept at the temperature for 2-3 hours to obtain activated petroleum coke powder. S2.2, the activated petroleum coke powder is added to the second acid solution and subjected to a second acid wash at room temperature. It is then washed with deionized water until neutral and dried at 100-150℃ to obtain sulfur-doped porous carbon material.

[0011] Based on this technical solution, further preferably, the alkaline solution includes a sodium hydroxide solution, the solid-liquid ratio of petroleum coke powder to the alkaline solution is 1:3 g / mL, the activator includes at least one of potassium hydroxide, phosphoric acid, potassium carbonate, and zinc chloride, the mass ratio of the acid-washed petroleum coke powder to the activator is 1:1-4, the second acid solution includes a mixture of hydrochloric acid and hydrofluoric acid, wherein the concentration of hydrochloric acid is 1-3 mol / L, the concentration of hydrofluoric acid is 0.1-0.5 mol / L, and the solid-liquid ratio of activated petroleum coke powder to the second acid solution is 0.25-0.5 g / mL.

[0012] Based on this technical solution, and further preferably, step S3 includes: S3.1, the sulfur-doped porous carbon material is ground and mixed evenly with a nitrogen source, and placed in an inert atmosphere tube furnace. The temperature is first raised to 100-300℃ at a rate of 2-5℃ / min, and the reaction is held for 0.5-2h. Then the temperature is raised to 500-800℃ at a rate of 5-10℃ / min, and the reaction is held for 1-5h to obtain the heat-treated material. S3.2, the heat-treated material is crushed to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

[0013] Based on this technical solution, and more preferably, the nitrogen source includes at least one of urea, melamine, polyacrylonitrile, polyaniline, ammonium carbonate, ammonium bicarbonate, ammonium sulfate, and ammonium bisulfate, and the mass ratio of sulfur-doped porous carbon material to nitrogen source is 1:1-5.

[0014] In addition, the present invention also provides an application of nitrogen-sulfur co-doped petroleum coke porous carbon material, such as the application of nitrogen-sulfur co-doped petroleum coke porous carbon material in the preparation of silicon-carbon anode material as described in the first aspect, wherein the silicon-carbon anode material includes nitrogen-sulfur co-doped petroleum coke porous carbon material and silicon active material, and the mass ratio of nitrogen-sulfur co-doped petroleum coke porous carbon material to silicon active material is 1:0.3-1.2.

[0015] The nitrogen-sulfur co-doped petroleum coke porous carbon material, its preparation method, and its application described in this invention have the following advantages over existing technologies: By introducing ammonium dihydrogen phosphate into the acid washing step, the phosphate ions released from the ammonium dihydrogen phosphate in the acid solution can react with metallic impurities Fe in the petroleum coke. 3+ Ni 2+ Al 3+ The formation of soluble complexes effectively eliminates the interference of impurities on subsequent processes. During the subsequent activation process, P2O5 generated from the high-temperature thermal decomposition of ammonium dihydrogen phosphate reacts with the alkaline activator, consuming part of the activator and adjusting the etching environment. While etching out micropores with high specific surface area, it also guides the formation of abundant mesopores, thereby optimizing the pore structure. The NH3 released from the decomposition of ammonium dihydrogen phosphate can be pre-adsorbed onto the surface of petroleum coke as a nitrogen source. Simultaneously, the phosphorus-containing active substances generated during the decomposition process can inhibit the volatilization of organic sulfur components in the petroleum coke at high temperatures and promote the binding of sulfur atoms to carbon defect sites. During the nitrogen doping stage, the sulfur atoms effectively stabilized and retained in the previous steps, along with the nitrogen-containing components generated from the decomposition of the added nitrogen source, achieve co-doping within the carbon framework. Ammonium dihydrogen phosphate plays a crucial role in impurity removal, pore formation, and stabilization throughout the process, thereby achieving efficient and stable co-doping of nitrogen and sulfur, enhancing the conductivity and lithium-ion adsorption capacity of carbon materials. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a SEM image of the nitrogen-sulfur co-doped petroleum coke porous carbon material obtained in Example 1 of the present invention after pulverization. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a nitrogen-sulfur co-doped petroleum coke porous carbon material, its preparation method, and its application. It reduces the internal resistance of the porous carbon material and improves its conductivity. In addition, nitrogen and sulfur co-doping will form more defects and active sites, promote ion adsorption, and improve the specific capacity and rate performance of the electrode material. The synergistic effect of nitrogen and sulfur co-doping optimizes the electronic structure and improves the cycle stability of the battery.

[0020] A method for preparing a nitrogen-sulfur co-doped petroleum coke porous carbon material includes the following steps: S1, the pretreated petroleum coke raw material is acid-washed and evenly dispersed, then ammonium dihydrogen phosphate solution is added, and washing continues until neutral. After drying, the acid-washed petroleum coke powder is obtained. The acidic ammonium phosphate salt is used to react with the metal ions of the petroleum coke raw material to form a soluble complex. Specifically, step S1 includes: S1.1, dry the petroleum coke raw material at 100-120℃, pulverize it, and pre-oxidize it at 300-450℃ for 0.5-2h. After the treatment, add the first acid solution into the reaction vessel, disperse it evenly, adjust the pH to less than 2.5 and perform acid washing. During the acid washing process, add ammonium dihydrogen phosphate solution dropwise and stir at room temperature for 12-24h. After the acid washing is completed, separate the solid and liquid, wash the solid with deionized water until the washing liquid is neutral, and obtain the solid material. S1.2, the washed solid material is vacuum dried at 120-130℃ for 6-12 hours to obtain acid-washed petroleum coke powder. The petroleum coke raw material includes low-sulfur petroleum coke with a sulfur content of <1.0wt%. The particle size of the pulverized petroleum coke raw material is 10-20μm. The first acid solution includes a mixture of hydrochloric acid and sulfuric acid, with the concentration of hydrochloric acid being 0.05-3mol / L and the concentration of sulfuric acid being 0.05-3mol / L. The mass ratio of petroleum coke:hydrochloric acid:sulfuric acid is 1:0.5:0.3. The amount of ammonium dihydrogen phosphate added is 5%-10% of the mass of the petroleum coke raw material.

[0021] Pre-oxidation of petroleum coke introduces oxygen-containing functional groups and opens up its dense structure on its surface and inside, significantly improving the permeability and reaction uniformity of subsequent pickling reagents. A mixture of hydrochloric acid and sulfuric acid is chosen as the first acid solution because hydrochloric acid can effectively dissolve most metal oxides, while the strong dehydrating properties of sulfuric acid further destroy organic impurities. The synergy of the two creates a stable strong acid environment, and the pH is controlled below 2.5, which helps to ensure that metal ions are always in a soluble state and prevents them from precipitating near neutrality, thus affecting the impurity removal effect.

[0022] After adding ammonium dihydrogen phosphate solution, the phosphate ions (such as H2PO4) that dissociate are released. - Under strong acid conditions, it can form stable water-soluble complexes with metallic impurity ions such as Fe, Ni, and Al in petroleum coke, thereby achieving deep removal of impurities that are difficult to remove by traditional single acid washing. Simultaneously, this process pre-places phosphorus and nitrogen elements on the surface of the petroleum coke and in newly formed pores through adsorption or weak binding, providing precursors for subsequent elemental doping and structural control. Low-sulfur petroleum coke is used to ensure that the raw material itself contains an appropriate amount of sulfur, which can serve as a partial source for subsequent sulfur doping while avoiding the excessive generation of harmful gases during high-sulfur coke processing.

[0023] S2, the acid-washed petroleum coke powder is mixed with an activator and activated in an inert gas environment. After activation, it is subjected to secondary acid washing, water washing and drying in sequence to obtain sulfur-doped porous carbon material. In a preferred embodiment, step S2 includes: S2.1, the acid-washed petroleum coke powder is mixed with an alkaline solution, dried, and then an activator is added and ground until uniformly mixed. The mixture is placed in an inert atmosphere tube furnace and heated to 700-800℃ at a rate of 2-10℃ / min, and kept at this temperature for 2-3 hours to obtain activated petroleum coke powder. The alkaline solution includes sodium hydroxide solution, and the solid-liquid ratio of petroleum coke powder to alkaline solution is 1:3 g / mL. The activator includes at least one of potassium hydroxide, phosphoric acid, potassium carbonate, and zinc chloride, and the mass ratio of acid-washed petroleum coke powder to activator is 1:1-4. S2.2, the activated petroleum coke powder is added to the second acid solution, and subjected to a second acid wash at room temperature. It is then washed with deionized water until neutral, and dried at 100-150°C to obtain sulfur-doped porous carbon material. In a preferred embodiment, the second acid solution comprises a mixture of hydrochloric acid and hydrofluoric acid, wherein the concentration of hydrochloric acid is 1-3 mol / L, the concentration of hydrofluoric acid is 0.1-0.5 mol / L, and the solid-liquid ratio of activated petroleum coke powder to the second acid solution is 0.25-0.5 g / mL.

[0024] The ammonium dihydrogen phosphate added during pickling in step S1, besides complexing and impurity removal, undergoes thermal decomposition and transformation of its residual phosphorus components during the high-temperature activation stage (700-800℃) in step S2. The resulting phosphorus oxides, such as P2O5, react with the KOH activator in the following manner: P2O5 + 6KOH → 2K3PO4 + 3H2O. This reaction consumes the highly corrosive KOH, moderating its etching intensity and making the etching process more controllable. This facilitates the formation of a high specific surface area microporous framework while partially inhibiting the complete etching of the pore walls between adjacent micropores, thereby preserving and developing more mesoporous structures. The final material achieves a mesoporous volume ratio of 20%-35%. The residual phosphorus content is controlled at 0.1-0.8%, which is sufficient for regulation without causing pore blockage due to excessive residue.

[0025] Step S2 first involves wet mixing with a sodium hydroxide solution. The purpose of this is to utilize the fluidity and permeability of the aqueous solution to uniformly load the alkali onto the interior and surface of the petroleum coke particles, achieving initial wetting and pore expansion. After drying, it is then dry-mixed with an activator (such as potassium hydroxide powder). This allows the strong alkali to undergo a localized, deep, and controllable carbonization reaction with the pre-wetting points during the high-temperature activation stage, forming a microporous structure. During the high-temperature activation process, the ammonium dihydrogen phosphate added in step S1 decomposes to produce phosphorus-containing gaseous active species (such as P2O5), which can synergistically act with activators such as potassium hydroxide. This not only forms abundant micropores but also guides the formation of additional mesopores, thereby constructing a pore structure conducive to rapid ion transport.

[0026] Choosing a mixture of hydrochloric acid and hydrofluoric acid for secondary pickling is targeted: hydrochloric acid is mainly used to neutralize and remove residual alkaline activators; while the small amount of added hydrofluoric acid can specifically complex and dissolve impurities such as aluminosilicates that are exposed or generated during the high-temperature activation process and are difficult to remove with conventional acids, thereby thoroughly clearing the pores to prevent pore blockage and ensuring the structural integrity of the porous carbon skeleton.

[0027] S3, sulfur-doped porous carbon material is mixed with a nitrogen source, doped in an inert gas environment, pulverized, and dried to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

[0028] In a preferred embodiment, step S3 includes: S3.1, the sulfur-doped porous carbon material and nitrogen source are ground and mixed evenly, and placed in an inert atmosphere tube furnace. The temperature is first raised to 100-300℃ at a rate of 2-5℃ / min, and the reaction is held for 0.5-2h. Then the temperature is raised to 500-800℃ at a rate of 5-10℃ / min, and the reaction is held for 1-5h to obtain the heat-treated material. The nitrogen source includes at least one of urea, melamine, polyacrylonitrile, polyaniline, ammonium carbonate, ammonium bicarbonate, ammonium sulfate, and ammonium bisulfate. The mass ratio of sulfur-doped porous carbon material to nitrogen source is 1:1-5.

[0029] S3.2, the heat-treated material is crushed to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

[0030] The material is held at 100-300℃ to melt and decompose nitrogen sources such as urea, generating nitrogen-containing active species. These species can then fully adsorb and penetrate into the pores and surface defects of the sulfur-doped porous carbon material obtained in step S2, achieving initial nitrogen fixation. Subsequently, the temperature is raised to 500-800℃ for high-temperature heat treatment, which involves nitrogen atom doping into the carbon lattice, ordering the carbon structure, and synergistic effects among the elements. During this process, the sulfur element already stabilized in the material from the previous steps, as well as the phosphorus component introduced by ammonium dihydrogen phosphate and remaining there, will interact with the newly incorporated nitrogen element. This multi-element synergistic effect can effectively regulate the electronic structure of the carbon material, optimize its local charge distribution, and significantly improve the material's conductivity, electrolyte wettability, and lithium-ion adsorption capacity, ultimately achieving efficient and stable doping of nitrogen and sulfur elements and a synergistic improvement in electrochemical performance.

[0031] In a preferred embodiment, the present invention provides a nitrogen-sulfur co-doped petroleum coke porous carbon material, prepared by the method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material according to any one of the claims. The nitrogen content in the nitrogen-sulfur co-doped petroleum coke porous carbon material is 4.53-5.36 wt%, the sulfur content is 1.05-1.23 wt%, and the phosphorus content is 0.1-0.8 wt%, derived from the residue and conversion of ammonium dihydrogen phosphate. The specific surface area is >2200 m². 2 / g, the mesopore volume ratio of 2-50nm pore size is 20%-35%.

[0032] In a preferred embodiment, the present invention also provides an application of nitrogen-sulfur co-doped petroleum coke porous carbon material, such as the application of nitrogen-sulfur co-doped petroleum coke porous carbon material in the preparation of silicon-carbon anode material as described in the second aspect, wherein the silicon-carbon anode material includes nitrogen-sulfur co-doped petroleum coke porous carbon material and silicon active material, and the mass ratio of nitrogen-sulfur co-doped petroleum coke porous carbon material to silicon active material is 1:0.3-1.2.

[0033] Example 1 100g of low-sulfur petroleum coke raw material with a sulfur content of 0.5wt% was dried at 110℃ for 10h, mechanically pulverized, and sieved to obtain powder with a particle size of 10-20μm. The powder was placed in a muffle furnace and pre-oxidized at 400℃ for 1h under air atmosphere at a rate of 5℃ / min to obtain pre-oxidized petroleum coke powder. 50g of pre-oxidized petroleum coke powder was weighed and mixed with 25g of 2mol / L hydrochloric acid and 15g of 1.5mol / L sulfuric acid. The mixture was stirred and dispersed evenly in a reaction vessel, and the pH of the system was adjusted to 2.0 with concentrated hydrochloric acid. Under continuous stirring, 5g of ammonium dihydrogen phosphate solution dissolved in 20mL of deionized water was slowly added dropwise, and the reaction was stirred at room temperature for 18h. After the reaction was completed, the mixture was filtered, and the solid was repeatedly washed with deionized water until the pH of the washing liquid reached 7. The obtained solid material was vacuum dried at 125℃ for 8h to obtain acid-washed petroleum coke powder.

[0034] Take 30g of the above-mentioned acid-washed petroleum coke powder and mix it with 90mL of 5% sodium hydroxide solution for 2 hours, then dry it at 120℃. Grind the dried intermediate material thoroughly with 60g of potassium hydroxide powder in a mortar until homogeneous. Place the mixture in a tube furnace and heat it to 750℃ at a rate of 5℃ / min under a nitrogen atmosphere, then maintain the temperature at this level for 2.5 hours. After natural cooling, the activated petroleum coke powder is obtained. Add 20g of the activated powder to 80mL of a second acid solution, which is a mixture of 2mol / L hydrochloric acid and 0.3mol / L hydrofluoric acid at a volume ratio of 10:1. Acid wash at room temperature for 18 hours. Then wash with deionized water until neutral and dry at 120℃ for 12 hours to obtain sulfur-doped porous carbon material.

[0035] Take 10g of the above-mentioned sulfur-doped porous carbon material and grind and mix it thoroughly with 30g of urea. Place the mixture in a tube furnace and, under an argon atmosphere, first heat it to 200℃ at a rate of 3℃ / min and hold it for 1 hour, then heat it to 600℃ at a rate of 8℃ / min and hold it for 3 hours, followed by natural cooling. The heat-treated material is then subjected to air jet milling to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material. The SEM image after milling is shown below. Figure 1 As shown.

[0036] Example 2 100g of low-sulfur petroleum coke raw material with a sulfur content of 0.8wt% was dried at 105℃ for 12h, mechanically pulverized, and sieved to obtain powder with a particle size of 10-20μm. The powder was placed in a muffle furnace and pre-oxidized at 450℃ at a rate of 10℃ / min under air atmosphere for 0.5h to obtain pre-oxidized petroleum coke powder. 50g of pre-oxidized petroleum coke powder was weighed and mixed with 27.5g of 1mol / L hydrochloric acid and 16.5g of 0.5mol / L sulfuric acid. The mixture was stirred and dispersed evenly in a reaction vessel, and the pH of the system was adjusted to 2.4 with concentrated sulfuric acid. Under continuous stirring, 3.75g of ammonium dihydrogen phosphate solid powder was added at once, and the reaction was stirred at room temperature for 24h. After the reaction was completed, the mixture was filtered, and the solid was repeatedly washed with deionized water until the pH of the washing liquid reached 7. The obtained solid material was vacuum dried at 125℃ for 8h to obtain acid-washed petroleum coke powder.

[0037] Take 30g of the above-mentioned acid-washed petroleum coke powder and mix it with 90mL of 2.5% sodium hydroxide solution for 2 hours, then dry it at 110℃. Grind the dried intermediate material thoroughly with 45g of potassium hydroxide powder and 15g of potassium carbonate powder in a mortar until homogeneous. Place the mixture in a tube furnace and heat it to 700℃ at a rate of 8℃ / min under a nitrogen atmosphere, then maintain the temperature at this level for 3 hours. After natural cooling, the activated petroleum coke powder is obtained. Add 20g of the activated powder to 80mL of a second acid solution, which is a mixture of 2mol / L hydrochloric acid and 0.1mol / L hydrofluoric acid at a volume ratio of 5:1. Stir and acid wash at room temperature for 12 hours. Then wash with deionized water until neutral and dry at 100℃ for 12 hours to obtain sulfur-doped porous carbon material.

[0038] Take 10g of the above-mentioned sulfur-doped porous carbon material and grind and mix it thoroughly with 25g of melamine. Place the mixture in a tube furnace, heat it to 550℃ at a rate of 10℃ / min under an argon atmosphere, hold it at that temperature for 4 hours, and then allow it to cool naturally. Pulverize the heat-treated material using an air jet mill to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

[0039] Example 3 100g of low-sulfur petroleum coke raw material with a sulfur content of 0.5wt% was dried at 110℃ for 10h, mechanically pulverized, and sieved to obtain powder with a particle size of 10-20μm. The powder was placed in a muffle furnace and pre-oxidized at 400℃ for 1h under air atmosphere at a rate of 5℃ / min to obtain pre-oxidized petroleum coke powder. 50g of pre-oxidized petroleum coke powder was weighed and mixed with 25g of 2mol / L hydrochloric acid and 15g of 1.5mol / L sulfuric acid. The mixture was stirred and dispersed evenly in a reaction vessel, and the pH of the system was adjusted to 2.0 with concentrated hydrochloric acid. Under continuous stirring, 5g of ammonium dihydrogen phosphate solution dissolved in 20mL of deionized water was slowly added dropwise, and the reaction was stirred at room temperature for 18h. Subsequently, to further improve the removal rate of metal impurities, a complexing agent such as EDTA can be added. 0.5g of disodium ethylenediaminetetraacetate was added to the reaction system, and the mixture was stirred at room temperature for another 30 minutes. After the reaction is complete, the solid is filtered and washed repeatedly with deionized water until the pH of the washing liquid is 7. The obtained solid material is then vacuum dried at 125℃ for 8 hours to obtain acid-washed petroleum coke powder.

[0040] Take 30g of the above-mentioned acid-washed petroleum coke powder and mix it with 90mL of 5% sodium hydroxide solution for 2 hours, then dry it at 120℃. Grind the dried intermediate material thoroughly with 60g of potassium hydroxide powder in a mortar until homogeneous. Place the mixture in a tube furnace and heat it to 750℃ at a rate of 5℃ / min under a nitrogen atmosphere, then maintain the temperature at this level for 2.5 hours. After natural cooling, the activated petroleum coke powder is obtained. Add 20g of the activated powder to 80mL of a second acid solution, which is a mixture of 2mol / L hydrochloric acid and 0.3mol / L hydrofluoric acid at a volume ratio of 10:1. Acid wash at room temperature for 18 hours. Then wash with deionized water until neutral and dry at 120℃ for 12 hours to obtain sulfur-doped porous carbon material.

[0041] Take 10g of the above-mentioned sulfur-doped porous carbon material and grind and mix it thoroughly with 30g of urea. Place the mixture in a tube furnace and, under an argon atmosphere, first heat it to 200℃ at a rate of 3℃ / min and hold it for 1 hour, then heat it to 600℃ at a rate of 8℃ / min and hold it for 3 hours, followed by natural cooling. Pulverize the heat-treated material using an air jet mill to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

[0042] Comparative Example 1 The difference from Example 1 is that in step S1, ammonium dihydrogen phosphate is not added; instead, a mixture of hydrochloric acid and sulfuric acid is used for pickling and pre-oxidation treatment using the same process. All other steps and parameters are exactly the same as in Example 1.

[0043] Comparative Example 2 The difference from Example 1 is that in step S1, the pre-oxidation treatment step is omitted, and the petroleum coke raw material is directly subjected to acid washing after drying and pulverizing. Other steps and parameters are the same as in Example 1.

[0044] Comparative Example 3 The difference from Example 1 is that in step S2, the wet mixing step with sodium hydroxide solution is omitted, and a single dry activation method is used, in which the acid-washed petroleum coke powder is directly mixed with an equal total mass of potassium hydroxide powder and then activated. Other steps and parameters are the same as in Example 1.

[0045] Comparative Example 4 The difference from Example 1 is that no secondary pickling was performed in step S2. All other steps and parameters are the same as in Example 1.

[0046] Comparative Example 5 The difference from Example 1 is that in step S1, sulfur-free petroleum coke is used, while the other steps and parameters are the same as in Example 1.

[0047] The porous carbon materials obtained in the examples and comparative examples were subjected to relevant performance tests. The test content and methods are as follows: Specific surface area and pore size distribution (BET): Tests were conducted at 77 K using a nitrogen adsorption-desorption apparatus. Specific surface area was calculated using the BET model, and pore size distribution and mesopore volume were calculated using the BJH model.

[0048] Metal impurity content (ICP-OES): After dissolving the sample, the content of major metal elements such as Fe, Al, and Ca in the solution was determined using inductively coupled plasma optical emission spectrometry.

[0049] In addition, silicon-carbon anode materials were prepared using the materials obtained from the examples and comparative examples. The silicon-carbon anode material included nitrogen-sulfur co-doped petroleum coke porous carbon material and silicon active material, with a mass ratio of nitrogen-sulfur co-doped petroleum coke porous carbon material to silicon active material of 1:0.8. A lithium metal sheet was used as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 and EC / DEC (volume ratio 1:1) were used as the electrolyte. CR2032 coin cells were assembled in an argon-protected glove box. The initial coulombic efficiency at a voltage window of 1.5V was tested, and long-cycle testing was performed. The discharge specific capacity after different number of cycles was recorded, and the capacity retention rate was calculated.

[0050] Table 1. Performance tests of porous carbon materials obtained from the examples and comparative examples. As shown in Table 1, compared with Example 1, Comparative Example 1, which did not add ammonium dihydrogen phosphate, had the lowest specific surface area and mesopore ratio, and the residual metal Fe was as high as 320 ppm. This indicates that the complexation effect of ammonium dihydrogen phosphate is the key to deep impurity removal. At the same time, the phosphorus-containing gaseous species generated by its high-temperature decomposition help to form mesopores, and the absence of these species directly leads to a comprehensive decline in the electrochemical performance of porous carbon materials.

[0051] Comparative Example 2, which did not undergo pre-oxidation treatment, showed a lower proportion of mesopores compared to Example 1, and its initial efficiency and cycle performance were slightly worse. This indicates that pre-oxidation treatment can effectively open up the dense structure of petroleum coke initially, improving the uniformity and efficiency of subsequent pickling and activation reactions.

[0052] Comparative Example 3, using a single dry activation method, showed a significant decrease in the proportion of mesoporous components and poor electrochemical test results. This may be because wet mixing with sodium hydroxide solution is crucial for achieving uniform loading of the activator, an effect that a single dry method cannot achieve.

[0053] Comparative Example 4, lacking secondary acid washing, resulted in decreased first-efficiency and capacity retention. Comparative Example 5, using sulfur-free petroleum coke, showed high levels of residual metallic impurities (Al, Si, etc.). This indicates that utilizing the intrinsic sulfur in low-sulfur petroleum coke is a pathway to effective sulfur doping; hydrofluoric acid can effectively remove specific impurities such as aluminosilicates generated or exposed during alkali activation. The absence of both factors combined leads to poor interfacial stability and the lowest capacity retention when the material is used as a silicon-carbon substrate.

[0054] In summary, the nitrogen-sulfur co-doped petroleum coke porous carbon material, its preparation method, and its applications obtained by this invention improve the material's capacity. The porous structure and nitrogen and sulfur doping effectively improve the material's conductivity and lithium-ion storage capacity, enhance cycle stability, and optimize the carbon material's structure, reducing capacity decay during long-term battery use. Furthermore, it increases the specific surface area of ​​the petroleum coke-based porous carbon material, which accelerates lithium-ion migration and improves charge / discharge rates. Finally, it increases the material's compressive strength; the nitrogen and sulfur doping provides strength to the porous carbon structure, reducing the high expansion rate of the battery during cycling.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A nitrogen-sulfur co-doped petroleum coke porous carbon material, characterized in that, The nitrogen-sulfur co-doped petroleum coke porous carbon material contains 4.53-5.36 wt% nitrogen, 1.05-1.23 wt% sulfur, and 0.1-0.8 wt% phosphorus, with a specific surface area >2200 m². 2 / g, the proportion of mesopore volume with pore size of 2-50nm is 20%-35%.

2. A method for preparing a nitrogen-sulfur co-doped petroleum coke porous carbon material, characterized in that, Includes the following steps: S1, the pretreated petroleum coke raw material is acid-washed and dispersed evenly, then ammonium dihydrogen phosphate solution is added, and the washing continues until neutral. After drying, the acid-washed petroleum coke powder is obtained. The acidic ammonium phosphate salt is used to react with the metal ions of the petroleum coke raw material to form a soluble complex. S2, the acid-washed petroleum coke powder is mixed with an activator and activated in an inert gas environment. After activation, it is subjected to secondary acid washing, water washing and drying in sequence to obtain sulfur-doped porous carbon material. S3, sulfur-doped porous carbon material is mixed with a nitrogen source, doped in an inert gas environment, pulverized, and dried to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

3. The method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material as described in claim 2, characterized in that, Step S1 includes: S1.1, dry the petroleum coke raw material at 100-120℃, pulverize it, and pre-oxidize it at 300-450℃ for 0.5-2h. After the treatment, add the first acid solution into the reaction vessel, disperse it evenly, adjust the pH to less than 2.5 and perform acid washing. During the acid washing process, add ammonium dihydrogen phosphate solution dropwise and stir at room temperature for 12-24h. After the acid washing is completed, separate the solid and liquid, wash the solid with deionized water until the washing liquid is neutral, and obtain the solid material. S1.2, the washed solid material is vacuum dried at 120-130℃ for 6-12h to obtain pickled petroleum coke powder.

4. The method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material as described in claim 3, characterized in that, The petroleum coke raw material includes low-sulfur petroleum coke with a sulfur content of <1.0wt%. The particle size of the pulverized petroleum coke raw material is 10-20μm. The first acid solution includes a mixture of hydrochloric acid and sulfuric acid, with the concentration of hydrochloric acid being 0.05-3mol / L and the concentration of sulfuric acid being 0.05-3mol / L. The mass ratio of petroleum coke:hydrochloric acid:sulfuric acid is 1:0.5:0.

3. The amount of ammonium dihydrogen phosphate added is 5%-10% of the mass of the petroleum coke raw material.

5. The method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material as described in claim 2, characterized in that, Step S2 includes: S2.1, the pickled petroleum coke powder is mixed with alkaline solution, dried, then an activator is added and ground, mixed evenly, placed in an inert atmosphere tube furnace, heated to 700-800℃ at a rate of 2-10℃ / min, and kept at the temperature for 2-3 hours to obtain activated petroleum coke powder. S2.2, the activated petroleum coke powder is added to the second acid solution and subjected to a second acid wash at room temperature. It is then washed with deionized water until neutral and dried at 100-150℃ to obtain sulfur-doped porous carbon material.

6. The method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material as described in claim 5, characterized in that, The alkaline solution includes sodium hydroxide solution, and the solid-liquid ratio of petroleum coke powder to alkaline solution is 1:3 g / mL. The activator includes at least one of potassium hydroxide, phosphoric acid, potassium carbonate, and zinc chloride. The mass ratio of the acid-washed petroleum coke powder to the activator is 1:1-4. The second acid solution includes a mixture of hydrochloric acid and hydrofluoric acid, wherein the concentration of hydrochloric acid is 1-3 mol / L and the concentration of hydrofluoric acid is 0.1-0.5 mol / L. The solid-liquid ratio of activated petroleum coke powder to the second acid solution is 0.25-0.5 g / mL.

7. The method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material as described in claim 2, characterized in that, Step S3 includes: S3.1, the sulfur-doped porous carbon material is ground and mixed evenly with a nitrogen source, and placed in an inert atmosphere tube furnace. The temperature is first raised to 100-300℃ at a rate of 2-5℃ / min, and the reaction is held for 0.5-2h. Then the temperature is raised to 500-800℃ at a rate of 5-10℃ / min, and the reaction is held for 1-5h to obtain the heat-treated material. S3.2, the heat-treated material is crushed to obtain nitrogen-sulfur co-doped petroleum coke porous carbon material.

8. The method for preparing nitrogen-sulfur co-doped petroleum coke porous carbon material as described in claim 7, characterized in that, The nitrogen source includes at least one of urea, melamine, polyacrylonitrile, polyaniline, ammonium carbonate, ammonium bicarbonate, ammonium sulfate, and ammonium bisulfate, and the mass ratio of sulfur-doped porous carbon material to nitrogen source is 1:1-5.

9. An application of a nitrogen-sulfur co-doped petroleum coke porous carbon material, characterized in that, The application of the nitrogen-sulfur co-doped petroleum coke porous carbon material as described in claim 1 in the preparation of silicon-carbon anode materials, wherein the silicon-carbon anode material includes nitrogen-sulfur co-doped petroleum coke porous carbon material and silicon active material, and the mass ratio of nitrogen-sulfur co-doped petroleum coke porous carbon material to silicon active material is 1:0.3-1.2.

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