Method for preparing hard carbon material by forming and carbonizing biomass and application of hard carbon material in sodium-ion battery negative electrode material

Abstract

The invention belongs to the technical field of sodium-ion batteries, and provides a method for preparing a hard carbon material through biomass forming carbonization and application of the hard carbon material in a sodium-ion battery negative electrode material. Biomass powder is pressed into blocks under low pressure, high-pressure pressing is performed to obtain a high-compactness hard carbon precursor, and the hard carbon material which is high in tap density, high in carbonization yield, low in defect concentration and increased in graphitization degree is prepared through carbonization. The used raw materials are green and environment-friendly, the process is simple, and the hard carbon material prepared by the method is high in initial coulombic efficiency and good in rate capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and relates to a method for preparing hard carbon materials by biomass molding and carbonization and their application in negative electrode materials of sodium-ion batteries. Background Art

[0002] Sodium-ion batteries are one of the secondary battery technologies that have developed rapidly in recent years, and have the advantages of low price, good stability, and good safety performance. As one of the most commercially promising negative electrode materials for sodium-ion batteries, hard carbon has received extensive attention. The main precursors of hard carbon include coal, resin, biomass, etc. China is a traditional agricultural country with rich biomass resources, and has the conditions to develop biomass-derived hard carbon.

[0003] Biomass is rich in lignin, cellulose, hemicellulose, etc., and is an excellent precursor for preparing hard carbon. At present, the microstructure of hard carbon materials is mainly regulated by changing carbonization conditions, ash removal conditions, etc. A Chinese invention patent (publication number CN111204731B) introduced a method for regulating the microstructure of hard carbon by changing the acid washing and ash removal conditions of biomass precursors. This method can improve the sodium storage performance and increase the initial Coulomb efficiency, but the improvement amplitude is limited, and the upper limit is 77%. Another invention patent (publication number CN118387855A) regulates the structure of biomass-derived hard carbon and improves the electrochemical performance by regulating the carbonization temperature. The above-mentioned inventions all use powdered biomass as the precursor. During the high-temperature carbonization process, a large amount of volatile matter will be released, resulting in a low carbon yield, a low tap density of the obtained hard carbon material, and low utilization rate of biomass raw materials. At the same time, a large number of heteroatoms in biomass will cause the structure of its derived carbon to tend to be disordered, resulting in low electronic conductivity and ionic conductivity of the material, and poor rate performance as an electrode material. The large defect concentration on the surface of biomass-derived hard carbon will also bring more side reactions, resulting in a decrease in the initial Coulomb efficiency.

[0004] At present, there is little research on the influence of material densification on the structure of derived carbon. In view of the above situation, there is an urgent need to develop a preparation method for hard carbon negative electrode materials for sodium-ion batteries that is environmentally friendly, low-cost, and can improve rate performance and initial Coulomb efficiency to meet the requirements of future large-scale energy storage systems for efficient and reliable sodium-ion batteries. Summary of the Invention

[0005] In order to improve the tap density and carbonization yield of biomass-derived hard carbon and enhance the electrochemical performance such as the initial Coulomb efficiency, rate performance, and cycle performance of the material, the present invention provides a method for preparing hard carbon materials by biomass molding and carbonization and their application in negative electrode materials of sodium-ion batteries. This method has a simple process, the prepared hard carbon material has a large tap density and a high carbonization yield, has a certain graphite-like structure, and is applied to the negative electrode of sodium-ion batteries, with a high initial Coulomb efficiency, good rate performance, and good stability.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A method for preparing hard carbon materials by biomass molding and carbonization includes the following steps:

[0008] Step (1): Press the biomass powder into blocks under a relatively low pressure;

[0009] Step (2): Subject the pressed biomass blocks to high-pressure pressing to obtain a highly dense hard carbon precursor;

[0010] Step (3): Place the highly dense hard carbon precursor in a tubular furnace and carbonize it under a protective atmosphere to obtain the hard carbon material.

[0011] The biomass in step (1) is one or more of ginkgo leaves, bagasse, coconut shells, walnut shells, peanut shells, apricot shells, rice husks, coffee shells, coffee grounds, straws, cotton, reeds, algae, moso bamboo, poplar wood, eucalyptus wood, pine wood, fruit wood, rosewood, miscellaneous wood, Chinese fir, and oak.

[0012] The biomass powder in step (1) is obtained by crushing and sieving biomass raw materials.

[0013] Before pressing in step (1), pickling for ash removal, washing with water, and drying of the biomass powder are also included.

[0014] The pickling includes pickling successively with hydrochloric acid and hydrofluoric acid; the concentration of hydrochloric acid is 0.1 - 4 mol / L -1 , and the volume fraction of hydrofluoric acid is 1% - 10%.

[0015] The mass of the biomass powder in step (1) is 0.1 - 1 g.

[0016] The pressure for pressing in step (1) is 10 - 30 MPa, and the pressing time is 5 - 10 min.

[0017] The pressure for high-pressure pressing in step (2) is 50 - 600 MPa.

[0018] The high-pressure pressing time in step (2) is 1 - 30 min.

[0019] In step (2), a super high-pressure cold isostatic press is used for high-pressure pressing.

[0020] In step (3), the carbonization temperature is 900 - 1500 °C, and the carbonization time is 1 - 4 h. Further, the heating rate is 0.5 - 5 °C / min -1 , and the protective atmosphere is argon or nitrogen.

[0021] The present invention also provides an application of the hard carbon material obtained by the above method in the hard carbon negative electrode of a sodium-ion battery.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The hard carbon material prepared by the pressing and carbonization process has a large tapped density, a high carbonization yield, and a certain graphite-like structure. When applied to the negative electrode of a sodium-ion battery, it has a high initial Coulombic efficiency, good rate performance, and good stability.

[0024] 1. Good rate performance. By forming the precursor under a certain pressure, the material particles become denser, which hinders the rapid escape of volatile components during the carbonization process. As a result, the volatile components undergo secondary pyrolysis at a certain temperature, and the obtained hard carbon material has a certain graphite-like structure, increasing the reaction kinetics of sodium ions in the hard carbon material and improving the rate performance of the sodium-ion battery.

[0025] 2. High initial Coulombic efficiency. Compared with the prior art, the present invention can effectively reduce the defect concentration on the surface of the hard carbon material, reduce the irreversible decomposition of the electrolyte, and improve the initial Coulombic efficiency of the sodium-ion battery.

[0026] 3. Good economic benefits and environmental friendliness. The process of the present invention is simple, and the tapped density and carbonization yield of the prepared hard carbon material are significantly improved, increasing the utilization rate of biomass raw materials.

[0027] The material carbonized at 1300 °C after being formed at 500 MPa has a reversible specific capacity of 62 mA h g -1 at 2 A g -1 . The initial Coulombic efficiency of the material carbonized at 1300 °C after being formed at 100 MPa is 83.3%. The cycle retention rate of the formed material also increases. Description of the Drawings

[0028] Figure 1 : Scanning electron microscope image of the hard carbon material prepared in Example 3.

[0029] Figure 2 : Transmission electron microscope image of the hard carbon material prepared in Example 3.

[0030] Figure 3 : XRD patterns of the hard carbon materials prepared in Examples 3, 5 and Comparative Example 1.

[0031] Figure 4 : Raman spectra of the hard carbon materials prepared in Examples 3, 5 and Comparative Example 1.

[0032] Figure 5 : Galvanostatic charge-discharge curve of the hard carbon negative electrode of the sodium-ion battery prepared in Example 3 during the first charge-discharge process.

[0033] Figure 6: Constant current charge-discharge curve of the hard carbon anode of the sodium-ion battery prepared in Example 5 during the first charge-discharge process.

[0034] Figure 7 : Constant current charge-discharge curve of the hard carbon anode of the sodium-ion battery prepared in Comparative Example 1 during the first charge-discharge process.

[0035] Figure 8 : Rate performance diagrams of the hard carbon anodes of the sodium-ion batteries prepared in Examples 3 and 5 and Comparative Example 1 at different current densities. Detailed implementation manners

[0036] The technical solutions of the present invention will be further described below in conjunction with specific examples, but the present invention is not limited to these examples.

[0037] During pickling in the examples and comparative examples, the concentration of dilute hydrochloric acid is 0.5 mol / L -1 , and the volume fraction of dilute hydrofluoric acid is 5%.

[0038] Comparative Example 1:

[0039] The biomass was pulverized using a pulverizer and screened through a 150-mesh sieve to obtain biomass powder. The biomass was coffee grounds. After the biomass powder was pickled with hydrochloric acid for 6 h and pickled with hydrofluoric acid for 6 h to remove ash, it was washed with water until neutral and dried at 105 °C for 6 h. 0.4 g of the above-obtained biomass powder was placed in a high-temperature tube furnace and heated to 1300 °C at a heating rate of 2 °C / min -1 , and maintained at this temperature for 2 h, then cooled to 1000 °C at a cooling rate of 2 °C / min -1 , and naturally cooled to room temperature to obtain the hard carbon anode material of the sodium-ion battery. The electrochemical performance is shown in Figure 7 and 8 .

[0040] Comparative Example 2:

[0041] The biomass was pulverized using a pulverizer and screened through a 150-mesh sieve to obtain biomass powder. The biomass was coffee grounds. After the biomass powder was pickled with hydrochloric acid for 6 h and pickled with hydrofluoric acid for 6 h to remove ash, it was washed with water until neutral and dried at 105 °C for 6 h. 0.4 g of the above-obtained biomass powder was put into a manual tablet press and pressed into shape at a pressure of 10 MPa for 5 min, and then placed in a high-temperature tube furnace and heated to 1300 °C at a heating rate of 2 °C / min -1 , and maintained at this temperature for 2 h, then cooled to 1000 °C at a cooling rate of 2 °C / min -1 , and naturally cooled to room temperature to obtain the hard carbon anode material of the sodium-ion battery.

[0042] Comparative Example 3:

[0043] The biomass is crushed using a crusher and screened through a 150-mesh sieve to obtain biomass powder. The biomass is algae. After the biomass powder is pickled with hydrochloric acid for 6 h and pickled with hydrofluoric acid for 6 h to remove ash, it is washed with water until neutral and dried at 105 °C for 6 h. Then it is placed in a high-temperature tube furnace and heated to 1300 °C at a heating rate of 2 °C / min -1 and maintained at this temperature for 2 h, and then cooled to 1000 °C at a cooling rate of 2 °C / min -1 , and naturally cooled to room temperature to obtain the hard carbon negative electrode material for sodium-ion batteries.

[0044] Comparative Example 4:

[0045] The biomass is crushed using a crusher and screened through a 150-mesh sieve to obtain biomass powder. The biomass is mahogany. After the biomass powder is pickled with hydrochloric acid for 6 h and pickled with hydrofluoric acid for 6 h to remove ash, it is washed with water until neutral and dried at 105 °C for 6 h. 0.4 g of the obtained biomass powder is placed in a high-temperature tube furnace and heated to 1300 °C at a heating rate of 2 °C / min -1 and maintained at this temperature for 2 h, and then cooled to 1000 °C at a cooling rate of 2 °C / min -1 , and naturally cooled to room temperature to obtain the hard carbon negative electrode material for sodium-ion batteries.

[0046] The sample numbers, some physical properties and electrochemical performances of Comparative Examples 1-4 are shown in Table 1

[0047] Table 1 Physical properties and electrochemical performances of samples of Comparative Examples 1-4

[0048]

[0049] Examples 1-5:

[0050] The biomass is crushed using a crusher and screened through a 150-mesh sieve to obtain biomass powder. The biomass is coffee grounds. After the biomass powder is pickled with hydrochloric acid for 6 h and pickled with hydrofluoric acid for 6 h to remove ash, it is washed with water until neutral and dried at 105 °C for 6 h. 0.4 g of the obtained biomass powder is put into a manual tablet press and pressed for 5 min at a pressure of 10 MPa to form, and then placed in a ultra-high pressure cold isostatic press to further form for 10 min at different pressures. The highly dense hard carbon precursor obtained by further pressing is placed in a high-temperature tube furnace and heated to 1300 °C at a heating rate of 2 °C / min -1 and maintained at this temperature for 2 h, and then cooled to 1000 °C at a cooling rate of 2 °C / min -1 , and naturally cooled to room temperature to obtain the hard carbon negative electrode material for sodium-ion batteries. The electrochemical performance of Example 3 is shown inFigure 8 , the electrochemical performance of Example 5 can be seen in Figure 6 and Figure 8 .

[0051] For the sample numbers, preparation conditions, partial physical properties and electrochemical performance, please refer to Table 2

[0052] Table 2 Details, physical properties and electrochemical performance of samples in Examples 1-5

[0053]

[0054]

[0055] From Comparative Examples 1-2 and Examples 1-5, as the molding pressure increases, both the density and carbonization yield of the material increase. The main reason is that as the pressure increases, the binding between biomass particles becomes tighter, forming a dense structure. This structure will increase the residence time of volatile components during carbonization. Among them, some hydrocarbon volatile components undergo secondary cracking and condensation at a certain temperature, generating more fixed carbon rather than gaseous products, thereby increasing the overall yield of fixed carbon and the density of the material. The graphitization degree of the prepared material first increases and then decreases with the increase of pressure, reaching the maximum value at 100 MPa. The increase in graphitization degree can reduce the surface defects of the material, thereby improving the initial Coulomb efficiency. An appropriate amount of graphite-like structure can improve the ionic conductivity and electronic conductivity, and thus improve the rate performance of the material.

[0056] Examples 6-7:

[0057] The biomass is pulverized using a pulverizer and screened through a 150-mesh sieve to obtain biomass powder. The biomass is coffee grounds. After the biomass powder is pickled with hydrochloric acid for 6 h and hydrofluoric acid for 6 h to remove ash, it is washed with water until neutral and dried at 105 °C for 6 h. Different masses of the obtained biomass powder are put into a manual tablet press and pressed at a pressure of 10 MPa for 5 min to form, and then placed in a ultra-high pressure cold isostatic press and further pressed at a pressure of 100 MPa for 10 min. The highly dense hard carbon precursor obtained by further pressing is placed in a high-temperature tube furnace and heated to 1300 °C at a heating rate of 2 °C / min -1 , and held at this temperature for 2 h, and then cooled to 1000 °C at a cooling rate of 2 °C / min -1 , and naturally cooled to room temperature to obtain the hard carbon negative electrode material for sodium ion batteries.

[0058] For the sample numbers, preparation conditions, partial physical properties and electrochemical performance, please refer to Table 3

[0059] Table 3 Details, physical properties and electrochemical performance of samples in Examples 6-7

[0060]

[0061] As can be seen from Examples 6 - 7 and Example 2, a larger mass will result in a larger volume of the formed material, making it more difficult for volatile components to escape, leading to the formation of more graphite-like structures, further reducing the surface defect concentration, and thus improving the initial Coulombic efficiency.

[0062] Examples 10 - 12:

[0063] The biomass was pulverized using a pulverizer and screened through a 150 - mesh sieve to obtain biomass powder. The biomass was coffee grounds. After the biomass powder was pickled with hydrochloric acid for 6 h and hydrofluoric acid for 6 h to remove ash, it was washed with water until neutral and dried at 105 °C for 6 h. 0.4 g of the obtained biomass powder was put into a manual tablet press and pressed at a pressure of 10 MPa for 5 min, and then placed in a ultra-high pressure cold isostatic press and further pressed at a pressure of 100 MPa for different times. The highly dense hard carbon precursor obtained after further pressing was placed in a high-temperature tube furnace and heated to 1300 °C at a heating rate of 2 °C / min -1 and held at this temperature for 2 h, and then cooled to 1000 °C at a cooling rate of 2 °C / min -1 and naturally cooled to room temperature to obtain the hard carbon negative electrode material for sodium-ion batteries.

[0064] The sample numbers, preparation conditions, some physical properties and electrochemical performances are shown in Table 4 in detail

[0065] Table 4 Detailed information, physical properties and electrochemical performances of the samples in Examples 8 - 10

[0066]

[0067] As can be seen from Examples 8 - 10 and Example 2, when the forming time is less than 20 min, the influence on the structure and performance of the material is relatively small. When the forming time is further increased, the material particles will be more closely packed, forming a more uniform carbon layer stacking structure, which is beneficial to the insertion of sodium ions and the improvement of the initial Coulombic efficiency.

[0068] Example 11

[0069] The biomass was pulverized using a pulverizer and screened through a 150 - mesh sieve to obtain biomass powder. The biomass was algae. After the biomass powder was pickled with hydrochloric acid for 6 h and hydrofluoric acid for 6 h to remove ash, it was washed with water until neutral and dried at 105 °C for 6 h to remove ash and then dried. 0.4 g of the obtained biomass powder was put into a manual tablet press and pressed at a pressure of 10 MPa for 5 min to form, and then placed in a ultra-high pressure cold isostatic press and further pressed at a pressure of 100 MPa for 10 min. The highly dense hard carbon precursor obtained after further pressing was placed in a high-temperature tube furnace and heated at a rate of 2 °C / min-1 Heat it up to 1300 °C at a heating rate of, and hold it at this temperature for 2 h, then at a rate of 2 °C / min -1 Cool it down to 1000 °C at a cooling rate of, and then cool it naturally to room temperature to obtain the hard carbon anode material for sodium-ion batteries.

[0070] Example 12

[0071] Crush the biomass using a crusher and screen it through a 150-mesh sieve to obtain biomass powder. The biomass is mahogany. After pickling the biomass powder with hydrochloric acid for 6 h and hydrofluoric acid for 6 h to remove ash, wash it with water until neutral and dry it at 105 °C for 6 h. Put 0.4 g of the obtained biomass powder into a manual tablet press, press it into shape at a pressure of 10 MPa for 5 min, and then place it in a ultra-high pressure cold isostatic press to further press it at a pressure of 100 MPa for 10 min. Place the highly dense hard carbon precursor obtained by further pressing in a high-temperature tube furnace and heat it up to 1300 °C at a heating rate of 2 °C / min -1 Heat it up to 1300 °C at a heating rate of, and hold it at this temperature for 2 h, then at a rate of 2 °C / min -1 Cool it down to 1000 °C at a cooling rate of, and then cool it naturally to room temperature to obtain the hard carbon anode material for sodium-ion batteries.

[0072] For the sample numbers, some physical properties and electrochemical performances, see Table 5 for details

[0073] Table 5 Physical properties and electrochemical performances of the samples in Examples 11 - 12

[0074]

[0075] It can be seen from Example 2, Examples 11 - 12 and Comparative Example 1, Comparative Examples 3 - 4 that the method of the present invention has universality for different types of biomass, namely agricultural waste, forestry waste and algal biomass, can effectively increase the carbonization yield, increase the material density and improve the performance of sodium-ion batteries.

[0076] Table 6 Related structure parameters of the samples in each example and comparative example

[0077]

[0078] Characterize the morphology of the hard carbon sample in Example 3 by scanning electron microscopy ( Figure 1 ), and the results show that the carbonized sample after high-pressure forming is generally in the form of larger particles.

[0079] Observe the microstructure of the hard carbon sample in Example 3 by transmission electron microscopy ( Figure 2) The results show that the hard carbon material after high-pressure forming treatment contains a certain amount of graphite-like structure, and the carbon layer spacing is about 0.34 nm. This structure is beneficial to improving the conductivity of the material and then enhancing the rate performance of the material. At the same time, a large number of pseudo-graphite structures provide abundant sodium storage sites for the material, thus obtaining a high capacity.

[0080] The graphitization degree of the hard carbon sample was characterized by X-ray diffractometer and Raman spectroscopy ( Figure 3 、 4 ), and the specific data are listed in Table 6. With the increase of the pretreatment pressure, the carbon layer spacing of the material continuously decreases, and the graphitization degree shows a trend of first increasing and then decreasing. The reason is that forming increases the density of the material, reduces pores and defects, provides a more compact space environment for the orderly arrangement of carbon atoms, and promotes the graphitization process. However, excessive pressure (≥200 MPa) will cause the material to be too dense, and small molecule gases (such as carbon dioxide, water vapor, etc.) generated by the decomposition of biomass during carbonization cannot escape smoothly. The retention of gases causes internal stress concentration, forms defects and destroys the orderliness of the carbon layer, increases the content of sodium storage sites, and improves the capacity.

[0081] The above has made a detailed description of the present invention, aiming to enable those skilled in this field of technology to understand the content of the present invention and implement it. However, it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing hard carbon materials by biomass molding and carbonization, characterized in that: It includes the following steps: Step (1): Press the biomass powder into blocks under a relatively low pressure; Step (2): Perform high-pressure pressing on the pressed biomass blocks to obtain a highly dense hard carbon precursor; Step (3): Place the highly dense hard carbon precursor in a tubular furnace and carbonize it under a protective atmosphere to obtain a hard carbon material.

2. The method for preparing hard carbon materials by biomass molding carbonization according to claim 1, characterized in that: The biomass is one or more of ginkgo leaves, bagasse, coconut shells, walnut shells, peanut shells, apricot shells, rice husks, coffee husks, coffee grounds, straw, cotton, reeds, algae, moso bamboo, poplar wood, eucalyptus wood, pine wood, fruit wood, mahogany, miscellaneous wood, fir wood, and oak wood.

3. The method for preparing hard carbon materials by biomass molding carbonization according to claim 1, wherein: Before pressing in Step (1), it also includes pickling, washing with water, and drying the biomass powder.

4. The method for preparing hard carbon materials by biomass molding carbonization according to claim 1, characterized in that: In Step (1), the mass of the biomass powder is 0.1 - 1 g.

5. The method for preparing hard carbon materials by biomass molding carbonization according to claim 1, characterized in that: In Step (1), the pressing pressure is 10 - 30 MPa, and the pressing time is 5 - 10 min.

6. The method for preparing hard carbon materials by biomass molding carbonization according to claim 1, characterized in that: In Step (2), the high-pressure pressing pressure is 40 - 500 MPa.

7. The method for preparing hard carbon materials by biomass molding carbonization according to claim 1, characterized in that: In Step (2), the high-pressure pressing time is 1 - 30 min.

8. The method for preparing hard carbon materials by biomass molding carbonization according to claim 1, characterized in that: In Step (3), the carbonization temperature is 900 - 1500 °C, and the carbonization time is 1 - 4 h.

9. Application of the hard carbon material obtained by the method according to any one of claims 1 - 8 in the hard carbon negative electrode of a sodium-ion battery.

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