Preparation method and application of high-purity pitch-based hard carbon based on coal pitch polycondensation impurity removal

Abstract

The invention discloses a preparation method and application of high-purity pitch-based hard carbon based on a coal pitch polycondensation impurity removal process, and belongs to the technical field of battery materials. Aiming at the problems of high metal impurity content, high ash content, high magnetic foreign matter content, poor electrochemical performance and the like of the existing coal pitch-based hard carbon, the invention starts from the raw material coal pitch, and performs two-time polycondensation and two-time filtration on the coal pitch through a simple coal pitch polycondensation impurity removal technology and the chemical characteristics of the coal pitch, thereby obtaining the coal pitch-based hard carbon. Metal impurities, ash content and quinoline insolubles in the coal pitch are greatly reduced; then, through a gradient oxidation strategy, a fused ring aromatic structure is gradually scattered, and the disorder degree is improved. And finally, forming of a hard carbon structure is promoted through methods of carbonization, demagnetization and the like. The sodium ion battery prepared by using the material as a negative electrode has the advantages of high specific capacity, high coulombic efficiency, long cycle life and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a preparation method of high-purity asphalt-based hard carbon based on coal tar condensation and impurity removal, and a sodium ion battery. Background Art

[0002] Sodium-ion batteries have attracted much attention in the energy storage industry due to their abundant sodium source reserves, good rate performance, and strong environmental adaptability. Hard carbon is widely used as the optimal solution for sodium-ion battery negative electrodes. Coal tar pitch is considered one of the ideal precursors for hard carbon due to its abundant reserves and low price. However, the high content of impurities and quinoline insolubles in coal tar pitch, large condensed ring molecules and easy graphitization have restricted the development of coal-tar pitch-based hard carbon. The specific capacity of hard carbon prepared from coal tar pitch is only 250 mAh / g, which is much lower than other materials, and the cycle life of the assembled sodium-ion battery is also greatly reduced. Patent CN117550585B authorizes a method for preparing a coal-tar pitch-based hard carbon material and its application. The preparation method includes uniformly mixing an acid anhydride rich in halogen atoms with coal tar pitch, followed by dehydrogenation and cross-linking driven by a high-temperature thermal field, and application in sodium-ion batteries. Although the specific capacity has been improved, the modification cost is too high, and the introduction of new heteroatoms by doping leads to a decrease in the first coulombic efficiency. Therefore, how to efficiently remove impurities, destroy condensed ring molecules and increase disorder, thereby improving sodium storage capacity, first coulombic efficiency and cycle performance is the biggest challenge that needs to be overcome in the development of coal tar-based hard carbon. Summary of the Invention

[0003] In order to solve the problems of high metal impurity content, ash content, magnetic foreign matter content and poor electrochemical performance of coal tar-based hard carbon, the present invention provides a

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A high-purity asphalt-based hard carbon based on coal tar condensation and impurity removal, wherein the high-purity asphalt-based hard carbon is a random block solid powder.

[0006] Furthermore, the Fe 3+ The content is less than 30ppm, the total amount of magnetic foreign matter is less than 0.5ppm, and the ash content is less than 0.5%.

[0007] Furthermore, the content of quinoline insoluble matter in the high-purity pitch-based hard carbon is less than 1%.

[0008] Furthermore, the specific capacity of the high-purity asphalt-based hard carbon is higher than 300 mAh / g, the first efficiency is higher than 90%, and the cycle retention rate of 200 cycles of 1C charge and discharge under 25°C environmental conditions is higher than 95%.

[0009] The above-mentioned method for preparing high-purity asphalt-based hard carbon based on coal tar condensation and impurity removal comprises the following steps:

[0010] Step 1: placing coal tar pitch in a reactor for a first polycondensation reaction, and performing a first hot filtration after the polycondensation is completed to obtain a refined asphalt intermediate;

[0011] Step 2: subjecting the refined asphalt intermediate to a second polycondensation reaction, and performing a second hot filtration after the polycondensation is completed to obtain refined asphalt;

[0012] Step 3: placing the refined asphalt on a setter, and then placing the asphalt together in a muffle furnace for oxidation treatment to obtain oxidized asphalt;

[0013] Step 4: placing the oxidized asphalt in a crucible and placing it in a tube furnace for carbonization treatment to obtain a carbonized material;

[0014] Step 5: Demagnetize the carbonized material at a certain rate through a demagnetizer to obtain high-purity asphalt-based hard carbon.

[0015] Furthermore, the softening point of the coal tar pitch in step 1 is 80-250° C., and the quinoline insoluble matter content is less than 5%.

[0016] Furthermore, the first polycondensation reaction in step 1 is carried out by heating the temperature to 150-300°C at a rate of 2-5°C / min, maintaining the temperature for 2-8 hours, and maintaining the pressure at 0.5-2 MPa in an inert atmosphere; the inert atmosphere is one of nitrogen and argon, or a mixture of the two;

[0017] Furthermore, the first hot filtration in step 1 is to heat the filter to 150-300° C., and the filter element is one of a ceramic filter element and a stainless steel filter element.

[0018] Furthermore, the second polycondensation in step 2 is carried out by heating the temperature to 250-400°C at a rate of 2-5°C / min, maintaining the temperature for 2-8 hours, and maintaining the pressure at 0.5-2 MPa in an inert atmosphere; the inert atmosphere is one of nitrogen and argon, or a mixture of the two;

[0019] Furthermore, the second hot filtration in step 2 is that the filter is heated to 250-400° C., and the filter element is a ceramic filter element.

[0020] Furthermore, the oxidation treatment in step 3 is carried out at a heating rate of 2-5°C / min, and is maintained at a constant temperature of 100-250°C for 1-5 hours and a constant temperature of 250-350°C for 1-5 hours respectively.

[0021] Furthermore, the carbonization treatment in step 4 is carried out at a heating rate of 2-10°C / min, at 1100-1400°C, and a constant temperature time of 2h.

[0022] Furthermore, the material of the support plate is one of ceramic, corundum high alumina and mullite.

[0023] Furthermore, the crucible is made of one of ceramics, corundum, high-alumina, and graphite.

[0024] Furthermore, in step 5, the excitation current of the demagnetizer is 60-80A; and the carbonized material throughput rate is 1-5kg / h.

[0025] A sodium ion battery, wherein the negative electrode of the sodium ion battery comprises high-purity asphalt-based hard carbon produced by the above preparation method.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The present invention starts with the raw material coal tar, and through a simple coal tar condensation and impurity removal technology, the coal tar is subjected to two condensation and two filtrations by taking advantage of the chemical properties of the coal tar, thereby greatly reducing the metal impurities, ash and quinoline insolubles in the coal tar. 3+ The content is less than 50ppm, the total amount of magnetic foreign matter is less than 1ppm, and the content of quinoline insoluble matter is less than 1%. Subsequently, a gradient oxidation strategy is used to gradually break up the condensed ring aromatic structure and increase the degree of disorder. Finally, carbonization, demagnetization and other methods are used to promote the formation of a hard carbon structure. High-purity asphalt-based hard carbon has high energy density and excellent cycle performance. The sodium ion battery prepared with this material as the negative electrode has the advantages of high specific capacity, high coulombic efficiency and long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0029] Figure 1 This is a 200-cycle diagram of a sodium-ion soft-pack battery at 1C charge and discharge;

[0030] Figure 2 This is the charge and discharge curve of pitch-based hard carbon. DETAILED DESCRIPTION

[0031] To gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description thereof. However, the present invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a comprehensive understanding of the present disclosure.

[0032] Example 1

[0033] This embodiment provides a method for preparing high-purity pitch-based hard carbon based on coal pitch polycondensation and impurity removal, and a sodium ion battery, which specifically includes the following steps:

[0034] Step 1: placing coal tar pitch with a softening point of 80°C and a quinoline insoluble content of 5% in a reactor, heating it to 150°C at a rate of 2°C / min, maintaining the temperature for 2 hours, and performing a nitrogen atmosphere polycondensation reaction at a pressure of 2 MPa. After the polycondensation is completed, hot filtration is performed in a filter at 150°C, using a stainless steel filter element, to obtain a refined asphalt intermediate;

[0035] Step 2: The refined asphalt intermediate was placed in a reactor, heated to 250°C at a rate of 2°C / min, maintained at this temperature for 8 hours, and subjected to a nitrogen atmosphere for secondary polycondensation. After the polycondensation was completed, the product was subjected to secondary hot filtration in a filter at 250°C using a ceramic filter element to obtain refined asphalt. The impurity content of the refined asphalt is shown in Table 1.

[0036] Step 3: Place the refined asphalt on a ceramic support plate, and then place them together in a muffle furnace for oxidation treatment at a heating rate of 2°C / min, and maintain the temperature at 100°C and 250°C for 1 hour to obtain oxidized asphalt;

[0037] Step 4: placing the oxidized asphalt in a crucible made of one of ceramic, corundum, high-alumina, and graphite, and placing them together in a tube furnace for carbonization treatment at a carbonization temperature of 1100° C., a heating rate of 2° C. / min, and a constant temperature time of 2 h to obtain a carbonized material;

[0038] Step 5: The carbonized material is passed through a demagnetizer at a rate of 1 kg / h and an excitation current of 60 A to obtain high-purity asphalt-based hard carbon. The impurity content of the asphalt-based hard carbon is shown in Table 2.

[0039] The sodium ion battery was prepared using the above-mentioned high-purity pitch-based hard carbon as the negative electrode material. The prepared battery had a specific capacity of 300 mAh / g, an initial efficiency of 91.1%, and a cycle retention rate of 95.2% after 200 cycles of 1C charge and discharge at 25°C, as shown in Table 3.

[0040] Example 2

[0041] This embodiment provides a method for preparing high-purity pitch-based hard carbon based on coal pitch polycondensation and impurity removal, and a sodium ion battery, which specifically includes the following steps:

[0042] Step 1: placing coal tar pitch with a softening point of 200°C and a quinoline insoluble content of 1% in a reactor, heating it to 250°C at a rate of 2°C / min, maintaining the temperature for 4 hours, at a pressure of 1 MPa, in a nitrogen atmosphere, to carry out a polycondensation reaction. After the polycondensation is completed, hot filtration is carried out in a filter at 300°C, using a ceramic filter element, to obtain a refined asphalt intermediate;

[0043] Step 2: The refined asphalt intermediate was placed in a reactor, heated to 350°C at a rate of 2°C / min, maintained at this temperature for 4 hours, and subjected to a nitrogen atmosphere for secondary polycondensation. After the polycondensation was completed, the product was subjected to secondary hot filtration in a filter at 400°C using a ceramic filter element to obtain refined asphalt. The impurity content of the refined asphalt is shown in Table 1.

[0044] Step 3: Place the refined asphalt on a setter made of mullite, and then place them together in a muffle furnace for oxidation treatment at a heating rate of 2°C / min, and maintain the temperature at 250°C and 350°C for 2 hours to obtain oxidized asphalt;

[0045] Step 4: placing the oxidized pitch in a crucible made of graphite and placing them together in a tube furnace for carbonization treatment at a carbonization temperature of 1300° C., a heating rate of 2° C. / min, and a constant temperature time of 2 h to obtain a carbonized material;

[0046] Step 5: The carbonized material is passed through a demagnetizer at a rate of 2 kg / h and the excitation current of the demagnetizer is 80 A to obtain high-purity asphalt-based hard carbon; the impurity content of the asphalt-based hard carbon is shown in Table 2;

[0047] The sodium ion battery was prepared using the above-mentioned high-purity asphalt-based hard carbon as the negative electrode material. The prepared battery had a specific capacity of 330 mAh / g, an initial efficiency of 90.8%, and a cycle retention rate of 97% after 200 cycles of 1C charge and discharge under 25°C ambient conditions, as shown in Table 3.

[0048] Example 3

[0049] This embodiment provides a method for preparing high-purity pitch-based hard carbon based on coal pitch polycondensation and impurity removal, and a sodium ion battery, which specifically includes the following steps:

[0050] Step 1: placing coal tar pitch with a softening point of 250°C and a quinoline insoluble content of 2.8% in a reactor, heating it to 300°C at a rate of 3°C / min, maintaining the temperature for 8 hours, and performing a polycondensation reaction at a pressure of 0.5 MPa in an argon atmosphere. After the polycondensation is completed, hot filtration is performed in a filter at 300°C, using a stainless steel filter element, to obtain a refined asphalt intermediate;

[0051] Step 2: The refined asphalt intermediate was placed in a reactor, heated to 400°C at a rate of 5°C / min, maintained at this temperature for 8 hours, and subjected to secondary polycondensation at a pressure of 0.5 MPa in an argon atmosphere. After the polycondensation was completed, the product was subjected to secondary hot filtration in a filter at 400°C using a ceramic filter element to obtain refined asphalt. The impurity content of the refined asphalt is shown in Table 1.

[0052] Step 3: Place the refined asphalt on a setter made of corundum and high-aluminum, and then place them in a muffle furnace for oxidation treatment at a heating rate of 3°C / min, and maintain the temperature at 200°C and 300°C for 3 hours to obtain oxidized asphalt;

[0053] Step 4: placing the oxidized asphalt in a crucible made of one of ceramic, corundum, high-alumina, and graphite, and placing them together in a tube furnace for carbonization treatment at a carbonization temperature of 1400°C, a heating rate of 10°C / min, and a constant temperature time of 2 hours to obtain a carbonized material;

[0054] Step 5: The carbonized material is passed through a demagnetizer at a rate of 5 kg / h and an excitation current of 70 A to obtain high-purity asphalt-based hard carbon. The impurity content of the asphalt-based hard carbon is shown in Table 2.

[0055] The sodium ion battery was prepared using the above-mentioned high-purity asphalt-based hard carbon as the negative electrode material. The prepared battery had a specific capacity of 310 mAh / g, an initial efficiency of 91.7%, and a cycle retention rate of 95.9% after 200 cycles of 1C charge and discharge under 25°C ambient conditions, as shown in Table 3.

[0056] Example 4

[0057] This embodiment provides a method for preparing high-purity pitch-based hard carbon based on coal pitch polycondensation and impurity removal, and a sodium ion battery, which specifically includes the following steps:

[0058] Step 1: placing coal tar pitch with a softening point of 160°C and a quinoline insoluble content of 3.5% in a reactor, heating it to 200°C at a rate of 5°C / min, maintaining the temperature for 6 hours, and maintaining the pressure at 1.5 MPa in an atmosphere of a mixture of nitrogen and argon for polycondensation. After the polycondensation is completed, hot filtration is performed in a filter at 250°C, using a ceramic filter element or a stainless steel filter element, to obtain a refined asphalt intermediate;

[0059] Step 2: The refined asphalt intermediate was placed in a reactor, heated to 300°C at a rate of 3°C / min, maintained at this temperature for 2 hours, and subjected to secondary polycondensation at a pressure of 1.5 MPa in an atmosphere of a mixture of nitrogen and argon. After the polycondensation was completed, the product was subjected to secondary hot filtration in a filter at 300°C using a ceramic filter element to obtain refined asphalt. The impurity content of the refined asphalt is shown in Table 1.

[0060] Step 3: Place the refined asphalt on a ceramic support plate, and then place them together in a muffle furnace for oxidation treatment at a heating rate of 5°C / min, and maintain the temperature at 150°C and 300°C for 5 hours to obtain oxidized asphalt;

[0061] Step 4: placing the oxidized asphalt in a crucible made of one of ceramic, corundum, high-alumina, and graphite, and placing them together in a tube furnace for carbonization treatment at a carbonization temperature of 1200° C., a heating rate of 5° C. / min, and a constant temperature time of 2 h to obtain a carbonized material;

[0062] Step 5: The carbonized material is passed through a demagnetizer at a rate of 3 kg / h and an excitation current of 80 A to obtain high-purity asphalt-based hard carbon. The impurity content of the asphalt-based hard carbon is shown in Table 2.

[0063] The sodium ion battery was prepared using the above-mentioned high-purity asphalt-based hard carbon as the negative electrode material. The prepared battery had a specific capacity of 307 mAh / g, an initial efficiency of 91.5%, and a cycle retention rate of 95.8% after 200 cycles of 1C charge and discharge under 25°C ambient conditions, as shown in Table 3.

[0064] Example 5

[0065] This embodiment provides a method for preparing high-purity pitch-based hard carbon based on coal pitch polycondensation and impurity removal, and a sodium ion battery, which specifically includes the following steps:

[0066] Step 1: placing coal tar pitch with a softening point of 170°C and a quinoline insoluble content of 3.7% in a reactor, heating it to 275°C at a rate of 5°C / min, maintaining the temperature for 6 hours, and performing a polycondensation reaction at a pressure of 0.8 MPa in an argon atmosphere. After the polycondensation is completed, hot filtration is performed in a filter at 300°C using a stainless steel filter element to obtain a refined asphalt intermediate;

[0067] Step 2: The refined asphalt intermediate was placed in a reactor, heated to 380°C at a rate of 4°C / min, maintained at this temperature for 6 hours, and subjected to secondary polycondensation at a pressure of 0.8 MPa in an argon atmosphere. After the polycondensation was completed, the product was subjected to secondary hot filtration in a filter at 400°C using a ceramic filter element to obtain refined asphalt. The impurity content of the refined asphalt is shown in Table 1.

[0068] Step 3: Place the refined asphalt on a setter made of mullite, and then place them together in a muffle furnace for oxidation treatment at a heating rate of 2°C / min, and maintain the temperature at 225°C and 350°C for 3 hours to obtain oxidized asphalt;

[0069] Step 4: placing the oxidized asphalt in a crucible made of one of ceramic, corundum, high-alumina, and graphite, and placing them together in a tube furnace for carbonization treatment at a carbonization temperature of 1200° C., a heating rate of 5° C. / min, and a constant temperature time of 2 h to obtain a carbonized material;

[0070] Step 5: The carbonized material is passed through a demagnetizer at a rate of 3 kg / h and an excitation current of 70 A to obtain high-purity asphalt-based hard carbon. The impurity content of the asphalt-based hard carbon is shown in Table 2.

[0071] In step 6, a sodium ion battery was prepared using high-purity pitch-based hard carbon as the negative electrode material. The prepared battery had a specific capacity of 317 mAh / g, an initial efficiency of 91.2%, and a cycle retention rate of 96% after 200 cycles of 1C charge and discharge at 25°C, as shown in Table 3.

[0072] Table 1 Impurity content of refined asphalt

[0073]

[0074] Table 2 Impurity content of pitch-based hard carbon

[0075]

[0076] Table 3 Electrochemical performance of pitch-based hard carbon

[0077]

[0078] Any matters not described in detail in this specification are prior art known to those skilled in the art. Although the above description of the present invention is based on specific embodiments to facilitate understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the specific embodiments. As long as various modifications are within the spirit and scope of the present invention as defined and determined by the appended claims, such modifications will be obvious to those skilled in the art, and all inventions and creations utilizing the concepts of the present invention are protected.

Claims

1. A high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal, characterized by: The high-purity pitch-based hard carbon is an irregular block solid powder. 3+ The content is less than 30ppm, the total amount of magnetic foreign matter is less than 0.5ppm, and the ash content is less than 0.5%.

2. The high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal according to claim 1, characterized in that: The high-purity pitch-based hard carbon has a specific capacity higher than 300 mAh / g, an initial efficiency higher than 90%, and a cycle retention rate of more than 95% after 200 cycles of 1C charge and discharge under 25°C environmental conditions.

3. A method for preparing high-purity pitch-based hard carbon based on coal tar condensation and impurity removal, characterized by: The following steps are involved: Step 1: placing coal tar pitch in a reactor for a first polycondensation reaction, and performing a first hot filtration after the polycondensation is completed to obtain a refined asphalt intermediate; Step 2: subjecting the refined asphalt intermediate to a second polycondensation reaction, and performing a second hot filtration after the polycondensation is completed to obtain refined asphalt; Step 3: placing the refined asphalt on a setter, and then placing the asphalt together in a muffle furnace for oxidation treatment to obtain oxidized asphalt; Step 4: placing the oxidized asphalt in a crucible and placing it in a tube furnace for carbonization treatment to obtain a carbonized material; Step 5: Demagnetize the carbonized material at a certain rate through a demagnetizer to obtain high-purity asphalt-based hard carbon.

4. The method for preparing high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal according to claim 3, characterized in that: The first polycondensation reaction in step 1 is to heat the temperature to 150-300°C at 2-5°C / min, maintain the temperature for 2-8 hours, and maintain an inert atmosphere at a pressure of 0.5-2 MPa. The first hot filtration in step 1 is to heat the filter to 150-300°C, and the filter element is a ceramic filter element or a stainless steel filter element.

5. The method for preparing high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal according to claim 3, characterized in that: The second polycondensation in step 2 is to increase the temperature to 250-400°C at 2-5°C / min, maintain the temperature for 2-8 hours, and maintain an inert atmosphere at a pressure of 0.5-2 MPa. The second hot filtration in step 2 is to heat the filter to 250-400°C, and the filter element is a ceramic filter element.

6. The method for preparing high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal according to claim 3, characterized in that: The oxidation treatment in step 3 is carried out at a heating rate of 2-5°C / min, and is maintained at a constant temperature of 100-250°C for 1-5 hours and a constant temperature of 250-350°C for 1-5 hours respectively.

7. The method for preparing high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal according to claim 3, characterized in that: The carbonization treatment in step 4 is carried out at a heating rate of 2-10°C / min, at 1100-1400°C, and a constant temperature time of 2h.

8. The method for preparing high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal according to claim 3, characterized in that: The material of the support plate is one of ceramic, corundum high-alumina and mullite; the material of the crucible is one of ceramic, corundum high-alumina and graphite.

9. The method for preparing high-purity pitch-based hard carbon based on coal tar pitch polycondensation and impurity removal according to claim 3, characterized in that: In step 5, the excitation current of the demagnetizer is 60-80A; the carbonized material passing rate is 1-5kg / h.

10. A sodium ion battery, characterized in that: The negative electrode of the sodium ion battery includes high-purity pitch-based hard carbon prepared by the preparation method according to any one of claims 3 to 9.

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