A method for preparing pitch-based hard carbon materials via triple oxidation

Abstract

This invention provides a method for preparing asphalt-based hard carbon materials using a triple oxidation process, comprising the following steps: (S1) Asphalt, as a carbon precursor, is mixed uniformly with metal oxides, epoxy resin, and glucose to obtain a mixture; (S2) The mixture is pre-oxidized in an oxygen-containing atmosphere to obtain a pre-oxidized precursor; (S3) The pre-oxidized precursor is ground and pre-carbonized by heat treatment in an inert atmosphere; (S4) The pre-carbonized material is washed with an acid solution, filtered, and dried; (S5) The dried material is carbonized at high temperature in an inert atmosphere or a hydrocarbon atmosphere to obtain hard carbon materials. This invention utilizes cost-effective and technologically mature asphalt as the main raw material. By adding metal oxides, epoxy resin, and glucose as oxygen suppliers and supplementary carbon sources during the pre-oxidation process of the asphalt precursor, the oxidation degree of the asphalt precursor is effectively improved, thereby significantly enhancing the sodium storage capacity, initial coulombic efficiency, and cycle stability of the hard carbon materials.

Description

Technical Field

[0001] This invention belongs to the field of battery anode material technology, specifically relating to a method for preparing pitch-based hard carbon materials by a triple oxidation process. Background Technology

[0002] In recent years, various rechargeable battery technologies have developed rapidly, with lithium-ion batteries being one of them, and they have been widely used in portable electronic products and new energy vehicles. However, due to the limited reserves of lithium resources, it is not suitable for large-scale energy storage. In contrast, sodium resources are abundant on Earth, have simple processing technology and low cost, and have similar chemical properties to lithium, making sodium-ion batteries show great potential for large-scale energy storage applications. However, sodium ions cannot be stably embedded in graphite layers like lithium ions, so graphite anodes are not suitable for the ester electrolytes of traditional sodium-ion batteries. Fortunately, hard carbon materials, with their large interlayer spacing (0.37-0.42 nm) and abundant closed-pore structure, provide a suitable anode for sodium-ion batteries. + Reversible storage provides significant benefits, even offering an initial specific capacity of up to approximately 300 mAh / g. However, the precursors for hard carbon are typically resins and fine biomass materials, which keeps the cost of hard carbon materials high, consistently exceeding the price of graphite anodes that can be used for lithium storage, thus hindering the full realization of the cost advantage of sodium-ion batteries (SIBs).

[0003] Asphalt, a mature chemical product composed of aromatic and alkanes, boasts significant advantages in price, yield, and stability, and has been widely used in the production of artificial graphite anode materials, yielding substantial economic benefits. However, when using asphalt as a precursor to prepare secondary battery anodes, it tends to form highly crystalline soft carbon, with a sodium storage capacity typically below 100 mAh / g, limiting its development and utilization in SIB hard carbon anodes. Existing technologies generally utilize direct air oxidation or hydrothermal oxidation to improve the electrochemical properties of hard carbon anode materials. However, these methods fail to ensure complete oxidation of the asphalt, resulting in hard carbon materials with a high degree of graphitization and fewer closed-cell structures, limiting their effectiveness in improving sodium storage performance, and the methods are also inefficient. Unexpectedly, adding a specific proportion of metal oxides as a catalyst during the calcination and carbonization process can significantly optimize the electrochemical performance of asphalt-based hard carbon anode materials. Summary of the Invention

[0004] To address the problems of low sodium storage capacity, low ICE (Induced Electron Efficiency), and low plateau capacity faced by existing pitch-based hard carbon materials used as anodes in sodium-ion batteries, this invention provides a dual oxidation strategy for the preparation of modified pitch-based hard carbon materials, thereby improving their sodium storage performance. By introducing metal oxides, epoxy resins, and glucose into the pitch precursor for triple oxidation, not only is the oxygen content of the precursor increased, but this increased oxidation level also helps to form more micropores and channel structures during subsequent calcination, thus increasing the active sites of the hard carbon and significantly improving its sodium storage capacity and initial coulombic efficiency. This invention provides a triple oxidation method for modifying the sodium storage performance, ICE, and plateau capacity of pitch-based hard carbon materials.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing pitch-based hard carbon materials via a triple oxidation process includes the following steps:

[0007] (S1) Asphalt, as a carbon precursor, is mixed evenly with metal oxides, epoxy resin and glucose to obtain a mixture.

[0008] (S2) The mixture is pre-oxidized in an oxygen-containing atmosphere to obtain a pre-oxidized precursor;

[0009] (S3) Grind the pre-oxidized precursor and heat-treat it under an inert atmosphere to pre-carbonize it.

[0010] (S4) The pre-carbonized material is washed with an acid solution, filtered and then dried;

[0011] (S5) The dried material is carbonized at high temperature in an inert atmosphere or a hydrocarbon gas atmosphere to obtain hard carbon material.

[0012] The inventors discovered that asphalt, as a carbon source, combined with metal oxides, epoxy resins, and glucose as oxygen-supplying agents, and epoxy resins and glucose as auxiliary carbon sources, can not only increase the degree of oxidation of asphalt, but also greatly limit the softening and molecular rearrangement during the carbonization process, inhibit graphitization, and promote the formation of disordered microstructures and closed pores.

[0013] Further, in step (S1), the metal oxide is selected from at least one of ferric oxide, magnesium oxide, copper oxide, zinc oxide, manganese oxide, and titanium dioxide, and the epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol S epoxy resin, and bisphenol F epoxy resin, with an epoxy value of 0.3-0.5.

[0014] Furthermore, the metal oxide is preferably magnesium oxide. The inventors unexpectedly discovered that, compared to other metal oxides, the addition of magnesium oxide resulted in a hard carbon anode material with optimal sodium storage performance. We speculate that this is likely because the addition of magnesium oxide not only provides a certain oxygen source for the oxidation of asphalt but also promotes the spread of heat in the mixture system, ultimately promoting the complete oxidation of the asphalt from the inside out. In addition, magnesium oxide also promotes the reaction of asphalt with molecular oxygen (O2) to generate peroxy radicals (ROO·). These peroxy radicals propagate the oxidation chain reaction, ultimately converting some of the hydrocarbons in the asphalt into ketones, aldehydes, and carboxylic acids. Magnesium oxide stabilizes the relevant transition states and intermediates, thereby improving the overall reaction rate and efficiency. Other metal oxides can also improve the electrochemical performance of hard carbon to varying degrees, but none are as significant as magnesium oxide.

[0015] Further, in step (S1), the mass ratio of asphalt, metal oxide, epoxy resin, and glucose is 100:30-50:20-30:20-30. The combination of the aforementioned metal oxide, epoxy resin, and glucose serves as an oxygen source. When mixed with asphalt in a specific ratio, a hard carbon material with significantly improved electrochemical performance can be prepared. The inventors speculate that this may be because, under high temperature and the action of the metal oxide, the oxygen in the resin / glucose is absorbed by the asphalt during the precipitation process, thereby promoting the oxidation of the asphalt. Moreover, the relatively high degree of graphitization carbon produced by the asphalt facilitates the transport of Na ions into the closed pores generated by the high oxygen characteristics, thus promoting an increase in sodium storage capacity.

[0016] Further, in step (S1), the asphalt materials are coal-based asphalt, petroleum asphalt, and biomass asphalt.

[0017] Furthermore, in step (S1), the method of thorough mixing is not particularly limited, including but not limited to ball milling, grinding, sand milling, etc. Ball milling is preferred, with a ball-to-material ratio of 10-20:1, a rotation speed of 400-700 rpm, and a ball milling time of 3-10 hours.

[0018] Further, in step (S2), the oxygen-containing atmosphere refers to an oxygen content greater than 20%, such as air, oxygen, or a mixture of air and oxygen; the pretreatment is to heat to 250-350°C at a heating rate of 2-10°C / min under an oxygen-containing atmosphere and hold at that temperature for 5-20 hours.

[0019] Further, in step (S3), the pre-carbonization is carried out under an inert atmosphere, with a heating rate of 5-30℃ / min to 500-800℃ and a holding time of 2-5 hours, wherein the inert atmosphere is at least one of argon, helium, and nitrogen.

[0020] Further, in step (S4), the acid solution is hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, phosphoric acid, etc., and the amount used is 1 to 5 times the molar mass of the metal oxide in step (S1). The purpose of acid solution immersion is to remove metallic impurities originally present in the asphalt and those added thereto.

[0021] Furthermore, in step (S5), the hydrocarbon gas is selected from at least one of methane, ethane, propane, butane, ethylene, acetylene, and toluene; preferably, calcination is carried out in a hydrocarbon gas atmosphere, which is beneficial to further improve the first-efficiency and capacity of the hard carbon material.

[0022] Furthermore, in step (S5), the high-temperature carbonization involves heating to 1300-1600℃ at a rate of 5-10℃ / min and holding at that temperature for 2-10 hours. The faster heating rate during pre-carbonization in step (S3) helps prevent asphalt melting and molecular rearrangement into soft carbon with a higher degree of crystallinity, which is detrimental to sodium ion storage and thus unfavorable for increasing material capacity.

[0023] This invention proposes a preparation technology and application of asphalt-based sodium-ion battery anode materials. Utilizing cost-effective and technologically mature asphalt as the main raw material, this invention effectively enhances the oxidation degree of the asphalt precursor by adding metal oxides, epoxy resin, and glucose as oxygen suppliers and carbon sources during the pre-oxidation process of the asphalt precursor. This significantly improves the sodium storage capacity and initial coulombic efficiency of the hard carbon material. Furthermore, under high temperature and the action of metal oxides, especially magnesium oxide, oxygen in the resin / glucose is absorbed by the asphalt during the precipitation process, thus promoting asphalt oxidation. Moreover, the relatively high degree of graphitized carbon generated by the asphalt facilitates the transport of Na ions into the closed pores formed by the high oxygen characteristics, further promoting the increase in sodium storage capacity. This preparation technology is not only low-cost and easy to operate, but also has a high carbon yield, making it very suitable for the mass production of hard carbon materials, which are subsequently used as anode materials for sodium-ion secondary batteries. The metal oxides not only promote uniform heat transfer during the asphalt pre-oxidation process but also provide additional oxygen atoms to the asphalt from the inside, ultimately promoting complete oxidation of the asphalt from the inside out. A higher oxygen content can prevent the melting and molecular rearrangement of the asphalt precursor during carbonization, promoting the disorder of its microstructure. In addition, a higher oxygen content can be removed during carbonization and form a closed-cell structure for sodium storage, thereby providing more sodium storage sites and obtaining a higher sodium storage capacity. Attached Figure Description

[0024] Figure 1 This is a SEM image of the hard carbon material prepared in Example 1.

[0025] Figure 2 This is a TEM image of the hard carbon material prepared in Example 1.

[0026] Figure 3 This is a constant current charge-discharge curve of a sodium-ion battery provided in Example 1.

[0027] Figure 4 This is a cycle curve diagram of a sodium-ion battery provided in Example 1.

[0028] Figure 5 This is a SEM image of the hard carbon material prepared in Comparative Example 1.

[0029] Figure 6 This is a SEM image of the hard carbon material prepared in Comparative Example 2. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. The following embodiments are provided to better understand this invention, but do not limit the invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods.

[0031] Example 1

[0032] (S1) Coal-based pitch with a softening point of 130℃ is mixed with MgO, epoxy resin E41 and glucose in a mass ratio of 100:50:20:30. The mixture is placed in a ball mill jar, the ball-to-material ratio is controlled at 20:1, the ball mill speed is set at 450 rpm, and the ball mill is in forward and reverse rotation mode for 4 hours to obtain the mixed precursor.

[0033] (S2) The mixed precursor obtained in step (S1) is placed in a muffle furnace and heated in air at a heating rate of 5°C / min, a heating temperature of 300°C, and a holding time of 10 hours. After cooling, a pre-oxidized precursor is obtained.

[0034] (S3) Grind the pre-oxidized precursor from step (S2) into powder, then place it in a tube furnace for calcination at a heating rate of 5℃ / min, raise it to 700℃ and hold it for 3 hours in an Ar atmosphere to obtain a pre-carbonized precursor, which is then ground and refined.

[0035] (S4) Take concentrated hydrochloric acid diluted 5 times according to the molar ratio of MgO:HCl of 1:1, mix it with the pre-carbonized precursor, stir continuously for 24 hours, and then filter and dry to remove metal oxide impurities in the pre-carbonized precursor.

[0036] (S5) The above pre-carbonized drive is placed in a high-temperature tube furnace, argon gas is introduced, and calcination is carried out in an argon gas atmosphere. The heating rate is 5℃ / min. After heating to 1300℃, the temperature is held for 3 hours and then cooled to room temperature to obtain the hard carbon anode material.

[0037] Figure 1 This is a SEM image of the hard carbon material prepared in Example 1; Figure 2 This is a TEM image of the hard carbon material prepared in Example 1. It can be seen that the surface of the hard carbon material particles obtained in Example 1 is dense and smooth, with no pore structure; however, a closed-pore structure composed of complete graphite-like layers can be observed in the TEM image. Figure 2 This study demonstrates that the addition of metal oxides significantly affects the material structure during the preparation of hard carbon materials, resulting in a graphite-like layered structure and the formation of interconnected closed pores. This is primarily because the high oxygen content during the pre-carbonization stage prevents the fusion of aromatic rings and the rearrangement of molecules; simultaneously, during carbonization, oxygen atoms and nearby carbon atoms are removed, leading to the formation of defects and closed pores. This closed-pore structure facilitates the formation of metalloid sodium clusters within the hard carbon, while the increased interlayer spacing promotes the migration of sodium ions between layers. Figure 5 The image shows the SEM image of the hard carbon material prepared in Comparative Example 1. Figure 6 This is a SEM image of the hard carbon material prepared in Comparative Example 2. According to... Figure 5 and Figure 6 Hard carbon materials without added metal oxides or epoxy resins exhibit a relatively regular layered structure, which cannot provide sufficient space to support effective sodium storage.

[0038] Example 2

[0039] The other conditions and operations are the same as in Example 1, except that in step (S1), the mass ratio of coal-based pitch to MgO, epoxy resin E41, and glucose is 100:30:30:30.

[0040] Example 3

[0041] The other conditions and operations are the same as in Example 1, except that in step (S1), the metal oxide is Fe2O3.

[0042] Example 4

[0043] The other conditions and operations are the same as in Example 1, except that in step (S1), the metal oxide is ZnO.

[0044] Example 5

[0045] The other conditions and operations are the same as in Example 1, except that in step (S1), the metal oxide is MnO.

[0046] Example 6

[0047] The other conditions and operations are the same as in Example 1, except that in step (S1), the metal oxide is TiO2.

[0048] Comparative Example 1

[0049] The other conditions and operations are the same as in Example 1, except that magnesium oxide is not added in step (S1).

[0050] Comparative Example 2

[0051] The other conditions and operations are the same as in Example 1, except that epoxy resin E41 is not added in step (S1).

[0052] Comparative Example 3

[0053] The other conditions and operations are the same as in Example 1, except that glucose is not added in step (S1).

[0054] Application examples

[0055] Preparation and testing methods of negative electrode materials: The hard carbon negative electrode material, SuperP, and binder CMC / SBR obtained in the above examples and comparative examples were mixed at a mass ratio of 94:2:4. An appropriate amount of water was added to slurry the mixture, resulting in a uniformly mixed electrode slurry. The prepared electrode slurry was uniformly coated onto copper foil, dried, and then vacuum-dried at 60℃ for 12 hours before being sliced. Using a sodium metal sheet as the counter electrode, glass fiber as the separator, and 1 mol / L NaPF6 (solvent being ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) as the electrolyte, button batteries were assembled in an argon-protected glove box. Constant current charge-discharge tests were performed at a current density of 20 mA / g and a charge-discharge voltage range of 0.001-2.0 V. The test results are shown in Table 1.

[0056] Figure 3 This is a constant current charge-discharge curve of a sodium-ion battery provided in Example 1. Figure 4 This is a cycle curve of a sodium-ion battery provided in Example 1. Regarding electrochemical performance data:

[0057] Table 1 Electrochemical Performance Testing of Pitch-Based Hard Carbon Anode Materials

[0058]

[0059] As can be seen from the half-cell test results of each embodiment in Table 1, the addition of a compound oxygen donor during the preparation process—namely, a compound of metal oxides, epoxy resin, and glucose—significantly improved the capacity, initial coulombic efficiency, and cycle stability of the obtained hard carbon samples. Among the various metal oxides, magnesium oxide exhibited the most superior improvement in electrochemical performance.

Claims

1. A method for preparing pitch-based hard carbon material by a triple oxidation method, characterized by, The method comprises the following steps: (S1) mixing asphalt as a carbon precursor, metal oxide, epoxy resin and glucose uniformly to obtain a mixture; the mass ratio of asphalt, metal oxide, epoxy resin and glucose is 100:30-50:20-30:30; the metal oxide is magnesium oxide; (S2) pre-oxidizing the mixture in an oxygen-containing atmosphere to obtain a pre-oxidized precursor; (S3) grinding the pre-oxidized precursor and performing pre-carbonization by heat treatment under an inert atmosphere; (S4) immersing the pre-carbonized material in an acid solution, filtering and drying; (S5) high-temperature carbonizing the dried material under an inert atmosphere or a hydrocarbon gas atmosphere to obtain a hard carbon material.

2. The production method according to claim 1, characterized by, In step (S1), the epoxy resin is at least one selected from bisphenol A epoxy resin, bisphenol S epoxy resin and bisphenol F epoxy resin, and the epoxy value is 0.3-0.

5.

3. The preparation method according to claim 1, characterized in that, In step (S1), the asphalt substance is selected from coal-based asphalt, petroleum asphalt and biomass asphalt.

4. The method of claim 1, wherein, Further, in step (S2), the oxygen-containing atmosphere refers to an oxygen content of greater than 20%; the pre-oxidation is performed by increasing the temperature to 250-350℃ at a temperature increasing rate of 2-10℃ / min and maintaining the temperature for 5-20 h.

5. The preparation method according to claim 1, characterized in that, In step (S3), the pre-carbonization is performed by increasing the temperature to 500-800℃ at a temperature increasing rate of 5-30℃ / min under an inert atmosphere, and maintaining the temperature for 2-5 h; the inert atmosphere is at least one of argon, helium and nitrogen.

6. The method of claim 1, wherein, In step (S4), the acid solution is hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, phosphoric acid, etc., and the amount is 1-5 times the molar amount of the metal oxide in step (S1).

7. The preparation method according to claim 1, characterized in that, In step (S5), the hydrocarbon gas is at least one selected from methane, ethane, propane, butane, ethylene, acetylene and toluene.

8. The method of claim 1, wherein, In step (S5), the high-temperature carbonization is performed by increasing the temperature to 1300-1600℃ at a temperature increasing rate of 5-10℃ / min and maintaining the temperature for 2-10 h.

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