Process for the preparation of pitch-based hard carbon materials by a secondary oxidation method and the products obtained thereby

Abstract

This invention proposes a method for preparing pitch-based hard carbon materials and the resulting product using a secondary oxidation process, belonging to the field of sodium battery materials technology. The method includes the following steps: 1) heating and melting pitch, then introducing air for liquid-phase oxidation to obtain a liquid-phase oxidation product; 2) subjecting the liquid-phase oxidation product to solid-phase oxidation to obtain a solid-phase oxidation product; 3) carbonizing the solid-phase oxide in an inert gas atmosphere to obtain the pitch-based hard carbon material. The method provided by this invention uses ordinary pitch as raw material, is low-cost, simple and safe to operate, and yields a hard carbon material with good sodium storage performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium battery material preparation technology, and particularly relates to a method for preparing pitch-based hard carbon materials by secondary oxidation and the resulting products. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the demand for lithium batteries has also increased. However, global lithium resources are limited and unevenly distributed, leading to rising lithium prices and highlighting resource bottlenecks. Therefore, the development of high-performance, low-cost alternative energy storage devices has attracted much attention. Since sodium and lithium belong to the same group and have similar physical and chemical properties, and sodium-ion batteries operate on similar principles to lithium-ion batteries, and are abundant in resources, sodium-ion batteries are considered a potential alternative to lithium-ion batteries.

[0003] Traditional lithium-ion batteries use graphite as the negative electrode. However, graphite is not suitable for sodium-ion battery systems, making hard carbon the preferred negative electrode material. Compared to graphite, hard carbon has a larger interlayer spacing and more defects, making it more suitable for sodium storage. Currently, hard carbon precursors are mainly biomass and resin-based. Biomass precursors have lower production difficulty but face challenges such as low carbon yield, suitable precursor selection, and stable batch supply. Resin precursors have easily controllable structures but are expensive. Pitch-based precursors are inexpensive, have a stable supply, and high carbon yield, making them a promising candidate for large-scale sodium-ion battery production.

[0004] In existing technologies, when preparing hard carbon materials from asphalt, high-softening-point asphalt is generally selected to form an effective cross-linked structure during the oxidation stage. For example, patent CN115959647A pre-oxidizes high-softening-point asphalt (≥240℃) under specific temperature and pressure conditions, followed by carbonization to prepare hard carbon. This method is simple, but the high price of high-softening-point asphalt leads to high production costs, and the high-pressure process poses a high risk, making commercialization difficult. Moreover, existing technologies often use acidic reagents to oxidize the asphalt, causing some corrosion to the equipment. Therefore, developing low-cost, safe, and simple hard carbon anode materials with high sodium storage efficiency is a current challenge and a key to the large-scale production of sodium-ion batteries. Summary of the Invention

[0005] This invention provides a method for preparing asphalt-based hard carbon materials by secondary oxidation, as well as the resulting products and applications. The method provided by this invention uses ordinary asphalt as raw material, is low in cost, simple to operate, safe, and produces hard carbon materials with good sodium storage performance.

[0006] To achieve the above objectives, the present invention provides a method for preparing pitch-based hard carbon materials by a secondary oxidation method, comprising the following steps:

[0007] 1) Heat the asphalt to melt it into a liquid, then introduce air to carry out liquid-phase oxidation, and obtain the liquid-phase oxidation product;

[0008] 2) Cool and pulverize the liquid-phase oxidation product into powder, and then perform solid-phase oxidation on the powder to obtain the solid-phase oxidation product;

[0009] 3) Carbonize the solid oxide in an inert gas atmosphere to obtain pitch-based hard carbon material.

[0010] Preferably, the temperature during liquid-phase oxidation in step 1) is 200–380°C, the time is 2–6 h, and the air flow rate is 0.01–2 L / min.

[0011] Preferably, the temperature during solid-phase oxidation in step 2) is 150–450°C, the time is 5–15 h, and the air flow rate is 0.01–1 L / min.

[0012] Preferably, the carbonization temperature in step 3) is 1100–1500°C and the time is 1–10 h.

[0013] Preferably, the asphalt is one or more of coal tar pitch, petroleum pitch, and shale pitch.

[0014] Preferably, the asphalt is first distilled before melting to obtain low-run, medium-run, and high-run fractions, and one or two of these fractions are selected as raw materials to prepare hard carbon anode materials; the low-run fraction is the fraction with a temperature of 200-300℃; the medium-run fraction is the fraction with a temperature of 300-400℃; and the high-run fraction is the fraction with a temperature of 400℃-600℃.

[0015] Preferably, when a low-distillate fraction is selected as the raw material, the temperature for liquid-phase oxidation is 200–280°C; the temperature for solid-phase oxidation is 150–320°C; when a medium-distillate fraction is selected as the raw material, the temperature for liquid-phase oxidation is 280–300°C; the temperature for solid-phase oxidation is 320–340°C; when a high-distillate fraction is selected as the raw material, the temperature for liquid-phase oxidation is 300–380°C; the temperature for solid-phase oxidation is 340–450°C.

[0016] Preferably, when two fractions are selected as raw materials, the temperature for liquid-phase oxidation is 320–380°C; and the temperature for solid-phase oxidation is 330–450°C.

[0017] Preferably, low-fraction and high-fraction raw materials are selected to prepare hard carbon anode materials, wherein the mass ratio of low-fraction to high-fraction is 0.8 to 1.2:1.

[0018] The present invention provides a pitch-based hard carbon material prepared by the method described in any one of the above-mentioned methods, wherein the pitch-based hard carbon material has an interlayer spacing of 0.3802 to 0.3911 and an IG / ID of 1.08 to 1.21.

[0019] This invention provides the application of the pitch-based hard carbon material described in any one of the above-mentioned claims in the negative electrode of a sodium battery.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0021] This invention uses air as an oxidant, first performing liquid-phase oxidation and then solid-phase oxidation. The combination of liquid-phase and solid-phase oxidation avoids the melting of asphalt, thereby forming a stable cross-linked structure. This effectively inhibits the graphitization of asphalt during high-temperature carbonization, which is more conducive to obtaining disordered hard carbon materials with large interlayer spacing and improving sodium storage capacity.

[0022] The method provided by this invention operates under normal pressure, making it safer. It uses ordinary asphalt as raw material, which is inexpensive and has a stable supply, thus facilitating industrial production. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a method for preparing pitch-based hard carbon materials via a secondary oxidation process, comprising the following steps:

[0025] 1) Heat the asphalt to melt it into a liquid, then introduce air to carry out liquid-phase oxidation, and obtain the liquid-phase oxidation product;

[0026] 2) Cool and pulverize the liquid-phase oxidation product into powder, and then perform solid-phase oxidation on the powder to obtain the solid-phase oxidation product;

[0027] 3) Carbonize the solid oxide in an inert gas atmosphere to obtain pitch-based hard carbon material.

[0028] This invention involves heating and melting asphalt, then introducing air for liquid-phase oxidation to obtain a liquid-phase oxidation product. In this invention, the asphalt is preferably one or more of coal tar pitch, petroleum pitch, and shale pitch. In this invention, the heating and melting temperature is preferably 110–130°C, and the time is preferably 25–35 min. In this invention, the liquid-phase oxidation temperature is preferably 200–380°C, the time is preferably 2–6 h, and the air flow rate is preferably 0.01–2 L / min.

[0029] After obtaining the liquid-phase oxidation product, the present invention cools and pulverizes the liquid-phase oxidation product into powder, and then performs solid-phase oxidation on the powder to obtain a solid-phase oxidation product. In the present invention, cooling the liquid-phase oxidation product before solid-phase oxidation can solidify the viscous liquid-phase oxidation product into a solid product. In the present invention, the solid-phase oxidation temperature is preferably 150-450℃, the time is preferably 5-15h, and the air flow rate is preferably 0.01-1L / min.

[0030] Asphalt itself has a low softening point. Direct solid-phase oxidation of asphalt will cause melting, and once the asphalt is in a molten state, oxygen cannot diffuse into the interior, resulting in a low degree of oxidation. Using only liquid-phase oxidation, the asphalt easily becomes a highly viscous liquid or a lumpy solid in the later stages of oxidation, thus oxidizing only on the surface and reducing the degree of oxidation. In this invention, air is used as the oxidant, and liquid-phase oxidation is performed first, followed by solid-phase oxidation. This combined liquid-phase and solid-phase oxidation process avoids asphalt melting, thereby forming a stable degree of cross-linking. This effectively inhibits graphitization of asphalt during high-temperature carbonization, and is more conducive to obtaining hard carbon materials with disordered interlayer spacing.

[0031] Because low-scoring asphalt has a low softening point, it is more prone to melting, preventing oxygen from diffusing into the asphalt and reducing the degree of oxidation. In existing technologies, to improve the degree of oxidation, low-scoring asphalt is generally discarded and high-softening-point asphalt is used. However, high-softening-point asphalt is more expensive, and discarding low-scoring asphalt results in resource waste. The secondary oxidation method combining liquid-phase oxidation and solid-phase oxidation provided by this invention can effectively avoid asphalt melting, thereby enabling low-scoring asphalt to achieve the same effect as high-scoring asphalt in existing technologies, thus avoiding the waste caused by discarding low-scoring asphalt.

[0032] In this invention, the applicant further discovered during experiments that the aromatic rings of low-fractional-content materials have longer alkyl side chains. At low temperatures, this structural feature makes them more susceptible to oxygen attack, leading to the formation of various oxygen-containing functional groups (aldehydes, ketones, carboxyl groups). As the oxidation temperature increases, aldehydes, ketones, and carboxyl groups gradually transform into esters and anhydrides through condensation reactions, forming cross-linked structures. High-fractional-content materials, on the other hand, readily form cross-linked structures at high temperatures, and the addition of high-fractional-content materials increases the softening point of the asphalt, resulting in more stable cross-linked structures. Therefore, combining low-fractional-content and high-fractional-content materials allows for sufficient and effective oxidation, leading to the formation of more and more stable cross-linked structures. This, in turn, inhibits graphitization under high-temperature carbonization, resulting in hard carbon with high disorder and large interlayer spacing, thereby improving capacity and initial cycle efficiency.

[0033] Based on the above findings, in this invention, it is preferable to first distill the asphalt before melting to obtain low-run, medium-run, and high-run fractions; the low-run fraction is preferably a fraction with a temperature of 200–300°C; the medium-run fraction is preferably a fraction with a temperature of 300–400°C; and the high-run fraction is preferably a fraction with a temperature of 400–600°C. Based on these findings, this invention, by dividing the asphalt, can obtain low-run and high-run fractions. Using both low-run and high-run fractions as raw materials, and employing a secondary oxidation method, high-capacity and high-cycle-efficiency hard carbon anode materials can be prepared.

[0034] Meanwhile, to fully utilize the raw materials, the applicant further explored using any one or two of the low, medium, and high fractions as raw materials to prepare hard carbon anode materials. For example, the medium fraction could be selected as the raw material, or both low and medium fractions could be selected as raw materials, employing a secondary oxidation method combining liquid-phase oxidation and solid-phase oxidation to prepare hard carbon anode materials. It was found that while other combination methods were not as effective as using both low and high fractions as raw materials with a secondary oxidation method to prepare hard carbon anode materials, they were still superior to the existing technology of using ordinary asphalt to prepare hard carbon anode materials.

[0035] In this invention, the molecular weight and chemical structure of asphalt can be controlled through distillation. The low-run fraction contains more saturated hydrocarbons and aromatic hydrocarbons with long side chains, exhibiting higher reactivity at low-temperature oxidation. This is mainly due to the greater number of oxygen attack sites (attacking aliphatic hydrogens on aromatic hydrocarbons), leading to the formation of oxygen-containing functional groups such as aldehydes, ketones, or carboxyl groups. As the oxidation temperature increases, aldehydes, ketones, and carboxyl groups gradually transform into esters and anhydrides through condensation reactions, forming cross-linked structures. The high-run fraction contains more gum and asphaltenes, with fewer aromatic hydrocarbons with long side chains and a greater amount of isolated aromatic hydrogens. At the same temperature, aromatic hydrogens are more difficult for oxygen to attack than aliphatic hydrogens, so higher oxidation temperatures are required to form more stable C=O structures. Based on this, in order to obtain a more effective hard carbon anode material, in this invention, when a low-distillation fraction is selected as the raw material, the preferred temperature for liquid-phase oxidation is 200–280°C; the preferred temperature for solid-phase oxidation is 150–320°C. When a medium-distillation fraction is selected as the raw material, the preferred temperature for liquid-phase oxidation is 280–300°C; the preferred temperature for solid-phase oxidation is 320–340°C. When a high-distillation fraction is selected as the raw material, the preferred temperature for liquid-phase oxidation is 300–380°C; the preferred temperature for solid-phase oxidation is 340–450°C. In this invention, when two distillation fractions are selected as the raw material, the preferred temperature for liquid-phase oxidation is 320–380°C; the preferred temperature for solid-phase oxidation is 330–450°C.

[0036] After obtaining the solid-phase oxidation product, the present invention carbonizes the solid-phase oxide in an inert gas atmosphere to obtain a pitch-based hard carbon material. In this invention, the preferred carbonization temperature is 1100–1500°C, and the preferred time is 1–10 hours. In this invention, high-temperature carbonization treatment can further increase its interlayer spacing and disorder, thereby improving capacity and first-cycle efficiency.

[0037] The present invention provides a pitch-based hard carbon material prepared by the method described in any one of the above-mentioned methods, wherein the pitch-based hard carbon material has an interlayer spacing of 0.3802 to 0.3911 and an IG / ID of 1.08 to 1.21.

[0038] This invention provides the application of the pitch-based hard carbon material described in any one of the above-mentioned claims in the negative electrode of a sodium battery.

[0039] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] Coal tar pitch was heated at 120℃ for 30 minutes to melt it, and then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 330℃, oxidation time: 5h, air flow rate: 1L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2 hours to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 340℃, oxidation time: 15h, air flow rate: 1L / min) to obtain a powdered solid-phase oxidation product. This solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1400℃, carbonization time: 5h) to obtain hard carbon material. Test results show: carbonized product yield: 58.5%, interlayer spacing: 0.3795, ID / IG: 1.05, charge specific capacity: 266.5mAh / g, discharge specific capacity: 341.7mAh / g, first efficiency: 78.0%.

[0042] Example 2

[0043] Petroleum asphalt was melted by heating at 130℃ for 25 minutes and then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 300℃, oxidation time: 6 hours, air flow rate: 1.5 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2 hours to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 350℃, oxidation time: 15 hours, air flow rate: 1 L / min) to obtain a powdered solid-phase oxidation product. This solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1100℃, carbonization time: 10 hours) to obtain hard carbon material. Test results show: carbonized product yield: 70%, interlayer spacing: 0.3888, ID / IG: 1.13, charge specific capacity: 265.9mAh / g, discharge specific capacity: 334.4mAh / g, and first-time efficiency: 79.5%.

[0044] Example 3

[0045] Coal tar pitch is distilled and divided into three fractions: low fraction (200–300℃), medium fraction (300–400℃), and high fraction (400–600℃).

[0046] The low-run fraction was heated at 120℃ for 30 min to melt it, and then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 280℃, oxidation time: 5 h, air flow rate: 0.8 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2 h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 320℃, oxidation time: 10 h, air flow rate: 0.5 L / min) to obtain a powdered solid-phase oxidation product. This solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1200℃, carbonization time: 2 h) to obtain hard carbon material. Test results show: carbonized product yield: 62%, interlayer spacing: 0.3802, ID / IG: 1.08, charge specific capacity: 245.1 mAh / g, discharge specific capacity: 335.2 mAh / g, and first-time efficiency: 73.1%.

[0047] Example 4

[0048] The middle fraction obtained in Example 3 was heated at 120°C for 30 min to melt it, and then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 300°C, oxidation time: 2 h, air flow rate: 0.8 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. It was cooled for 2 h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 330°C, oxidation time: 5 h, air flow rate: 0.6 L / min) to obtain a powdered solid-phase oxidation product. The solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1300°C, carbonization time: 8 h) to obtain hard carbon material. Test results show: carbonized product yield: 70%, interlayer spacing: 0.3842, ID / IG: 1.11, charge specific capacity: 263.0 mAh / g, discharge specific capacity: 345.2 mAh / g, first-time efficiency: 76.2%.

[0049] Example 5

[0050] The high-fraction obtained in Example 3 was heated at 120°C for 30 min to melt it, and then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 330°C, oxidation time: 5 h, air flow rate: 1 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. It was cooled for 2 h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The sieve material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 350°C, oxidation time: 15 h, air flow rate: 1 L / min) to obtain a powdered solid-phase oxidation product. The solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1400°C, carbonization time: 5 h) to obtain hard carbon material. Test results show: carbonized product yield: 65%, interlayer spacing: 0.3851, ID / IG: 1.20, charge specific capacity: 274.7mAh / g, discharge specific capacity: 351.9mAh / g, and first-time efficiency: 78.1%.

[0051] Example 6

[0052] The low- and medium-distillate fractions obtained in Example 3 were mixed at a 1:1 mass ratio and heated at 120°C for 30 min to melt them. The mixture was then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 320°C, oxidation time: 6 h, air flow rate: 1 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2 h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 350°C, oxidation time: 10 h, air flow rate: 0.6 L / min) to obtain a powdered solid-phase oxidation product. This solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1400°C, carbonization time: 5 h) to obtain hard carbon material. Test results show: carbonized product yield: 60%, interlayer spacing: 0.3802, ID / IG: 1.09, charge specific capacity: 251.3mAh / g, discharge specific capacity: 334.5mAh / g, and first-time efficiency: 75.1%.

[0053] Example 7

[0054] The low- and high-distillate fractions obtained in Example 3 were mixed in a 1:1 mass ratio and heated at 120°C for 30 min to melt them. The mixture was then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 330°C, oxidation time: 5 h, air flow rate: 1 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2 h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 340°C, oxidation time: 10 h, air flow rate: 0.8 L / min) to obtain a powdered solid-phase oxidation product. This solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1300°C, carbonization time: 5 h) to obtain hard carbon material. Test results show: carbonized product yield: 62%, interlayer spacing: 0.3911, ID / IG: 1.21, charge specific capacity: 300.3mAh / g, discharge specific capacity: 333.4mAh / g, and first-time efficiency: 90.1%.

[0055] Example 8

[0056] The middle and high fractions obtained in Example 3 were mixed at a 1:1 mass ratio and heated at 120°C for 30 min to melt them. The mixture was then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 320°C, oxidation time: 6 h, air flow rate: 1.2 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2 h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a tube furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 330°C, oxidation time: 13 h, air flow rate: 0.8 L / min) to obtain a powdered solid-phase oxidation product. This solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1400°C, carbonization time: 4 h) to obtain hard carbon material. Test results show: carbonized product yield: 62%, interlayer spacing: 0.3882, ID / IG: 1.10, charge specific capacity: 277.3 mAh / g, discharge specific capacity: 343.2 mAh / g, first efficiency: 80.8%.

[0057] Comparative Example 1

[0058] Liquid phase oxidation only

[0059] Coal tar pitch was melted by heating at 120℃ for 30 min and then placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 300℃, oxidation time: 6 h, air flow rate: 0.8 L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2 h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1400℃, carbonization time: 2 h) to obtain hard carbon material. The results showed: carbonization product yield: 55%, interlayer spacing: 0.3750, ID / IG: 1.02, charge specific capacity: 213.4 mAh / g, discharge specific capacity: 320.0 mAh / g, and initial efficiency: 66.7%.

[0060] Comparative Example 2

[0061] Solid-phase oxidation only

[0062] Coal tar pitch was subjected to atmospheric pressure solid-phase oxidation in a tubular furnace (oxidation temperature: 320℃, oxidation time: 10h, air flow rate: 0.5L / min) to obtain a powdered solid-phase oxidation product. The solid-phase oxidation product was then transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1200℃, carbonization time: 2h) to obtain hard carbon material. Testing revealed the following: carbonization product yield: 65%; interlayer spacing: 0.3781; ID / IG: 1.05; charge specific capacity: 233.9mAh / g; discharge specific capacity: 330.3mAh / g; initial efficiency: 70.8%.

[0063] Comparative Example 3

[0064] Liquid-phase oxidation using low fractions

[0065] The low-fraction from Example 3 was placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 280℃, oxidation time: 5h, air flow rate: 0.8L / min). After the reaction, a viscous liquid-phase oxidation product was obtained. This product was cooled for 2h to obtain a solid liquid-phase oxidation product. The solid liquid-phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1200℃, carbonization time: 2h) to obtain hard carbon material. The results showed: carbonization product yield: 60%, interlayer spacing: 0.3701, ID / IG: 1.01, charge specific capacity: 180.6mAh / g, discharge specific capacity: 300.8mAh / g, and initial efficiency: 60%.

[0066] Comparative Example 4

[0067] Solid-phase oxidation followed by liquid-phase oxidation

[0068] Coal tar pitch was transferred to a tubular furnace for atmospheric pressure solid-phase oxidation (oxidation temperature: 340℃, oxidation time: 15h, air flow rate: 1L / min) to obtain a powdered solid-phase oxidation product. The solid-phase oxidation product was then melted at 300℃ for 30min and placed in a stainless steel reactor for atmospheric pressure liquid-phase oxidation (oxidation temperature: 330℃, oxidation time: 5h, air flow rate: 1L / min). After the reaction, it was cooled for 2h, and the solid-liquid phase oxidation product was pulverized and passed through a 100-mesh sieve. The undersize material was transferred to a high-temperature carbonization furnace and carbonized at high temperature in a nitrogen atmosphere (carbonization temperature: 1400℃, carbonization time: 5h) to obtain hard carbon material. Testing showed: carbonization product yield: 66%, interlayer spacing: 0.3785, ID / IG: 1.05, charge specific capacity: 236.5mAh / g, discharge specific capacity: 331.5mAh / g, initial efficiency: 71.3%.

[0069] Among them: D002 interlayer spacing test: The interlayer spacing of the material was detected using an XRD instrument and calculated according to the formula d002=λ / (2sinθ); ID / IG disorder test: The disorder of the material was detected using a Raman spectroscopy instrument and calculated based on the intensity ratio of the D-band and G-band. Battery performance test: The prepared pitch-based hard carbon material was used as the negative electrode, sodium as the positive electrode, and NaPF6 with a concentration of 1mol / L dissolved in EC:DMC:PC=1:1:1, and 1% FEC as the electrolyte additive. The separator was glass fiber (GF / A). The battery was assembled in an argon-filled glove box and charge-discharge tests were performed.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing pitch-based hard carbon materials via a secondary oxidation process, characterized in that, Includes the following steps: 1) Heat asphalt to melt it into a liquid state, then introduce air to carry out liquid-phase oxidation, and obtain liquid-phase oxidation products; 2) Cool and pulverize the liquid-phase oxidation product into powder, and then perform solid-phase oxidation on the powder to obtain the solid-phase oxidation product; 3) Carbonize the solid oxide in an inert gas atmosphere to obtain pitch-based hard carbon material; The asphalt is one or more of coal tar pitch, petroleum pitch and shale pitch; Before melting, the asphalt is first distilled to obtain low-run, medium-run, and high-run fractions, and one or two of these fractions are selected as raw materials to prepare hard carbon anode materials; the low-run fraction is the fraction with a temperature of 200-300℃; the medium-run fraction is the fraction with a temperature of 300-400℃; and the high-run fraction is the fraction with a temperature of 400℃-600℃. When using low-grade distillate as feedstock, the temperature for liquid-phase oxidation is 200–280℃; the temperature for solid-phase oxidation is 150–320℃. When using medium-grade distillate as feedstock, the temperature for liquid-phase oxidation is 280–300℃; the temperature for solid-phase oxidation is 320–340℃. When using high-grade distillate as feedstock, the temperature for liquid-phase oxidation is 300–380℃; the temperature for solid-phase oxidation is 340–450℃. When two fractions are selected as raw materials, the temperature for liquid-phase oxidation is 320~380℃; the temperature for solid-phase oxidation is 330~450℃.

2. The method according to claim 1, characterized in that, The air flow rate during liquid-phase oxidation in step 1) is 0.01~2L / min.

3. The method according to claim 1, characterized in that, The air flow rate during solid-phase oxidation described in step 2) is 0.01~1L / min.

4. The method according to claim 1, characterized in that, The carbonization temperature in step 3) is 1100~1500℃ and the time is 1~10h.

5. The method according to claim 1, characterized in that, Low- and high-scoring fractions are selected as raw materials to prepare hard carbon anode materials, wherein the mass ratio of low- and high-scoring fractions is 0.8 to 1.2:

1.

6. The pitch-based hard carbon material prepared by the method according to any one of claims 1 to 5, characterized in that, The interlayer spacing of the asphalt-based hard carbon material is 0.3802~0.3911, and the IG / ID ratio is 1.08~1.21.