A bio-based hard carbon for an anode material and a preparation method thereof

Abstract

The application relates to the technical field of lithium-based supercapacitors, and discloses a kind of biological hard carbon for negative electrode material and a preparation method thereof, the preparation method of biological hard carbon for negative electrode material includes the following steps: S1, metal salt, waste biomass precursor and carbonate are ball milled to obtain a mixed sample; S2, the mixed sample is pre-fired to obtain an intermediate, washed, dried to obtain an intermediate powder; S3, the intermediate powder is calcined to obtain biological hard carbon; calcination includes first stage calcination and second stage calcination; the first stage calcination is heated to 350-550 DEG C at a heating rate of 4-6 DEG C / min, and the calcination time is 1-6h; the second stage calcination is heated to 650-1050 DEG C at a heating rate of 7-9 DEG C / min, and the calcination time is 1-7h. Through the above technical scheme, the problem of insufficient capacity retention rate of biological hard carbon as the negative electrode of a lithium-based supercapacitor in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium-based supercapacitors, in particular to a bio-based hard carbon for negative electrode material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of global economy, the large consumption of traditional energy not only causes energy shortage, but also brings serious environmental problems, so finding cleaner and more efficient new energy has become an important research topic. Among many energy storage technologies, lithium-based supercapacitors combine lithium ion batteries and supercapacitors, and have the advantages of high energy density and high power density, and are considered to be one of the most promising electric energy storage systems. The positive electrode of lithium-based supercapacitors generally uses capacitive materials such as activated carbon, and the negative electrode uses battery materials such as graphite, hard carbon and soft carbon. Among them, hard carbon is a highly disordered stack of partially graphitized carbon layer structures, and the staggered longitudinal structure is conducive to the insertion and extraction of lithium ions, making hard carbon an optimal negative electrode material for lithium ion capacitors.

[0003] Currently, bio-based hard carbon prepared from waste biomass precursors has become a research focus due to its wide raw material sources, environmental protection, low pollution and low price. However, the application of biomass hard carbon as a negative electrode material in lithium-based supercapacitors faces key challenges in practical application: the capacity retention rate of the material is prone to continuous decay in long-term charge and discharge cycles. Therefore, solving this problem has important promoting significance for the development of energy storage and related fields. SUMMARY

[0004] The present application provides a bio-based hard carbon for negative electrode material and a preparation method thereof, which solves the problem of insufficient capacity retention rate of bio-based hard carbon as a negative electrode of lithium-based supercapacitors in related technologies.

[0005] The technical scheme of the present application is as follows:

[0006] The present application provides a preparation method of a bio-based hard carbon for negative electrode material, comprising the following steps:

[0007] S1, ball milling a metal salt, a waste biomass precursor and a carbonate to obtain a mixed sample;

[0008] S2, pre-burning the mixed sample to obtain an intermediate, washing, drying and obtaining an intermediate powder;

[0009] S3, calcining the intermediate powder to obtain a bio-based hard carbon;

[0010] The calcining comprises first stage calcining and second stage calcining;

[0011] The first stage calcining is heated to 350-550℃ at a heating rate of 4-6℃ / min, and the calcining time is 1-6h.

[0012] The second stage calcination is heated to 650-1050℃ at a heating rate of 7-9℃ / min, and the calcination time is 1-7h.

[0013] As a further technical solution, the mass ratio of the metal salt, the carbonate salt and the waste biomass precursor is 1:0.5:10-20.

[0014] As a further technical solution, the rotation speed of the ball milling is 1000-5000r / min, and the time is 6-10h.

[0015] As a further technical solution, the ball milling uses zirconium oxide beads.

[0016] As a further technical solution, the diameter of the zirconium oxide beads is 0.1-1mm.

[0017] As a further technical solution, the temperature of the pre-burning is 100-250℃, and the holding time is 1-15h.

[0018] As a further technical solution, the atmosphere of the pre-burning is air.

[0019] As a further technical solution, the drying is vacuum drying, the temperature is 80-100℃, and the time is 10-12h.

[0020] As a further technical solution, the atmosphere of the calcination is inert gas.

[0021] As a further technical solution, the inert gas includes helium.

[0022] As a further technical solution, the cleaning agent of the cleaning is a mixed solution of ethanol and water.

[0023] As a further technical solution, in the mixed solution of ethanol and water, the volume ratio of ethanol and water is 1.5:1-15.

[0024] As a further technical solution, the metal salt includes three or more of manganese chloride, sodium nitrate, copper sulfate, potassium nitrate, magnesium nitrate, zinc chloride, aluminum chloride, potassium chloride, calcium chloride and magnesium chloride.

[0025] As a further technical solution, when the metal salt is manganese chloride, zinc chloride, potassium chloride and magnesium chloride, the mass ratio of manganese chloride, zinc chloride, potassium chloride and magnesium chloride is 1.2:1:0.8:0.9-1.1.

[0026] In the present application, the metal salts are manganese chloride, zinc chloride, potassium chloride and magnesium chloride, and further limited to a mass ratio of 1.2:1:0.8:0.9~1.1, the synergistic effect between the metal salts is fully played, the microstructure and electrochemical performance of the bio-based hard carbon can be precisely controlled, and when the bio-based hard carbon is used as a negative electrode material, the capacity retention rate of the lithium-based supercapacitor at low temperature is improved.

[0027] As a further technical solution, the waste biomass precursor includes one or more of corn stalks, corn silk, wheat straw, walnut shells and almond shells.

[0028] As a further technical solution, the carbonate salt includes one or more of sodium carbonate, magnesium carbonate, lithium carbonate, zinc carbonate, manganese carbonate and sodium aluminum carbonate.

[0029] The present application also provides a bio-based hard carbon for negative electrode material.

[0030] The working principle and beneficial effects of the present application are as follows:

[0031] In the present application, in the preparation process of the bio-based hard carbon, the heating rate of the first stage calcination is controlled to be 4~6℃ / min and the heating rate of the second stage calcination is controlled to be 7~9℃ / min in the final calcination stage, and the bio-based hard carbon prepared has excellent capacity retention rate as a negative electrode material assembled in a lithium-based supercapacitor; controlling the heating rate of the first stage calcination to be 4~6℃ / min helps the macromolecular chains in the organic matter to gradually break and rearrange, forming a relatively stable amorphous carbon structure basis, reducing the structural defects and unevenness caused by rapid heating; increasing the heating rate to 7~9℃ / min in the second stage is to further promote the carbon atoms to have more intense thermal motion and rearrangement on the basis of the amorphous carbon structure formed in the first stage, to provide more active sites and fast channels for the embedding and extraction of lithium ions in the subsequent lithium-based supercapacitor, thereby significantly improving the capacity retention rate of the lithium-based supercapacitor. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are involved in the scope of protection of the present application.

[0033] Embodiment 1

[0034] A preparation method of a bio-based hard carbon for negative electrode material, comprising the following steps:

[0035] S1, ball milling the metal salt, walnut shell and zinc carbonate at a rotating speed of 1000 r / min using zirconium oxide beads with a diameter of 0.1 mm as medium for 10 h (the mass ratio of the zirconium oxide beads to the total mass of the metal salt, walnut shell and zinc carbonate is 2:1), to obtain a mixed sample;

[0036] S2, pre-baking the mixed sample at a low temperature of 100 DEG C in an air atmosphere for 15 h to obtain an intermediate; cleaning the intermediate with a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1.5:15, and then vacuum drying the intermediate at 80 DEG C for 12 h to obtain an intermediate powder;

[0037] S3, performing stage calcination on the intermediate powder in a helium atmosphere, the first stage calcination being performed at a temperature increasing rate of 4 DEG C / min to 350 DEG C and calcining for 6 h; the second stage calcination being performed at a temperature increasing rate of 7 DEG C / min to 650 DEG C and calcining for 7 h, to obtain the bio-based hard carbon;

[0038] The metal salt is manganese chloride, zinc chloride, potassium chloride and calcium chloride in a mass ratio of 1.2:1:0.8:0.7.

[0039] The mass ratio of the metal salt, zinc carbonate and walnut shell is 1:0.5:10.

[0040] Example 2

[0041] A preparation method of a bio-based hard carbon for an anode material, comprising the following steps:

[0042] S1, ball milling the metal salt, wheat straw and magnesium carbonate at a rotating speed of 5000 r / min using zirconium oxide beads with a diameter of 1 mm as medium for 6 h (the mass ratio of the zirconium oxide beads to the total mass of the metal salt, wheat straw and magnesium carbonate is 2:1), to obtain a mixed sample;

[0043] S2, pre-baking the mixed sample at a low temperature of 250 DEG C in an air atmosphere for 1 h to obtain an intermediate; cleaning the intermediate with a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1.5:1, and then vacuum drying the intermediate at 100 DEG C for 10 h to obtain an intermediate powder;

[0044] S3, performing stage calcination on the intermediate powder in a helium atmosphere, the first stage calcination being performed at a temperature increasing rate of 6 DEG C / min to 550 DEG C and calcining for 1 h; the second stage calcination being performed at a temperature increasing rate of 9 DEG C / min to 1050 DEG C and calcining for 1 h, to obtain the bio-based hard carbon;

[0045] The metal salt is manganese chloride, zinc chloride, potassium chloride and calcium chloride in a mass ratio of 1.2:1:0.8:0.7.

[0046] The mass ratio of the metal salt, zinc carbonate and wheat straw is 1:0.5:20.

[0047] Example 3

[0048] A preparation method of a bio-based hard carbon for a negative electrode material, comprising the following steps:

[0049] S1, ball milling metal salt, corn straw and sodium carbonate at a rotating speed of 3500 r / min using zirconium oxide beads with a diameter of 1 mm as medium for 8 h (the mass ratio of zirconium oxide beads to the total mass of metal salt, corn straw and sodium carbonate is 2:1) to obtain a mixed sample;

[0050] S2, pre-baking the mixed sample at a low temperature of 160℃ in an air atmosphere for 8 h to obtain an intermediate; then, cyclically cleaning the intermediate with a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1.5:8.5, and then vacuum drying at 90℃ for 9 h to obtain an intermediate powder;

[0051] S3, performing stage calcination on the intermediate powder in a helium atmosphere, the first stage calcination is heated to 400℃ at a heating rate of 5℃ / min and calcined for 3 h; the second stage calcination is heated to 850℃ at a heating rate of 8℃ / min and calcined for 4 h to obtain a bio-based hard carbon;

[0052] The metal salt is manganese chloride, zinc chloride, potassium chloride and calcium chloride with a mass ratio of 1.2:1:0.8:0.7.

[0053] The mass ratio of the metal salt, zinc carbonate and corn straw is 1:0.5:16.

[0054] Example 4

[0055] The difference between this embodiment and Example 3 is only that the heating rate of the first stage calcination is 4℃ / min and the heating rate of the second stage calcination is 7℃ / min during stage calcination.

[0056] Example 5

[0057] The difference between this embodiment and Example 3 is only that the heating rate of the first stage calcination is 6℃ / min and the heating rate of the second stage calcination is 9℃ / min during stage calcination.

[0058] Example 6

[0059] The difference between this embodiment and Example 3 is only that the metal salt is manganese chloride, zinc chloride, potassium chloride and potassium nitrate with a mass ratio of 1.2:1:0.8:0.7.

[0060] Example 7

[0061] The difference between this embodiment and Example 3 is only that the metal salt is manganese chloride, zinc chloride, potassium chloride and sodium nitrate with a mass ratio of 1.2:1:0.8:0.7.

[0062] Example 8

[0063] The difference between this example and Example 3 is only that the metal salt is manganese chloride, zinc chloride, potassium chloride and magnesium chloride with a mass ratio of 1.2:1:0.8:0.7.

[0064] Example 9

[0065] The difference between this example and Example 8 is only that the metal salt is manganese chloride, zinc chloride, potassium chloride and magnesium chloride with a mass ratio of 1.2:1:0.8:0.9.

[0066] Example 10

[0067] The difference between this example and Example 8 is only that the metal salt is manganese chloride, zinc chloride, potassium chloride and magnesium chloride with a mass ratio of 1.2:1:0.8:1.1.

[0068] Example 11

[0069] The difference between this example and Example 8 is only that the metal salt is manganese chloride, zinc chloride, potassium chloride and magnesium chloride with a mass ratio of 1.2:1:0.8:1.3.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 3 is only that in the staged calcination, the temperature rising speed of the first stage calcination is 3℃ / min, and the temperature rising speed of the second stage calcination is 5℃ / min.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 3 is only that in the staged calcination, the temperature rising speed of the first stage calcination is 7℃ / min, and the temperature rising speed of the second stage calcination is 11℃ / min.

[0074] The bio-based hard carbon prepared in Examples 1-11 and Comparative Examples 1-2 is used as the negative electrode of a lithium-based supercapacitor, and the lithium-based supercapacitor is assembled and tested;

[0075] 1. Lithium-based supercapacitor:

[0076] Negative electrode: bio-based hard carbon, carbon black and PVDF are mixed in a mass ratio of 8:1:1, NMP is added to prepare a negative electrode slurry, and then the negative electrode slurry is coated on a stainless steel current collector with a coating thickness of 45μm, and vacuum drying is performed to obtain a negative electrode with a loading of 3.9mg·cm -2 ;

[0077] Positive electrode: mix active carbon, carbon black and PVDF with mass ratio of 8:1:1 to prepare positive electrode slurry, coat the slurry on a stainless steel current collector with the same thickness as the negative electrode, and obtain the positive electrode after drying, with a loading of 2.3 mg·cm -2 ;

[0078] Electrolyte: 1 mol·L -1 LiPF6(EC and DMC with mass ratio of 1:1);

[0079] 2, rate cycle performance: 1C / 3C rate charge-discharge test of the lithium-based supercapacitor prepared above was carried out in the voltage range of 2.2V~3.4V at room temperature;

[0080] 3, low temperature performance: the lithium-based supercapacitor prepared above was charged at 0.5C to 3.4V, then charged at constant voltage until the cutoff current was 0.01C, and then placed at -25℃ for 16h;

[0081] The test results are shown in Table 1:

[0082] Table 1 Performance test results of lithium-based supercapacitors prepared by the bio-based hard carbon prepared in Examples 1~11 and Comparative Examples 1~2

[0083]

[0084] 1, compared with Comparative Examples 1~2, the capacity retention rate of the lithium-based supercapacitors prepared by the bio-based hard carbon prepared in Examples 1~10 after 1000 cycles was significantly higher, indicating that during the preparation of bio-based hard carbon, controlling the heating rate of the first stage of calcination at 4~6℃ / min and the heating rate of the second stage of calcination at 7~9℃ / min can significantly improve the capacity retention rate of the lithium-based supercapacitor.

[0085] 2, compared with Examples 3 and 6~11, the capacity retention rate of the lithium-based supercapacitors prepared by the bio-based hard carbon prepared in Examples 8~11 after low temperature treatment was higher than that of Examples 3 and 6~7, indicating that the use of manganese chloride, zinc chloride, potassium chloride and magnesium chloride as metal salts for the preparation of bio-based hard carbon has significant significance for improving the capacity retention rate of lithium-based supercapacitors at low temperature; among them, the capacity retention rate of the lithium-based supercapacitors prepared by the bio-based hard carbon prepared in Examples 9~10 after low temperature treatment was higher than that of Examples 8 and 11, indicating that further limiting the mass ratio of manganese chloride, zinc chloride, potassium chloride and magnesium chloride to 1.2:1:0.8:0.9~1.1 can further improve the capacity retention rate of lithium-based supercapacitors at low temperature.

[0086] The above merely preferred embodiments of the present application are not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing bio-based hard carbon for anode materials, characterized in that, Includes the following steps: S1. The metal salt, waste biomass precursor and carbonate are ball-milled to obtain a mixed sample; S2. The mixed sample is pre-calcined to obtain an intermediate, which is then washed and dried to obtain an intermediate powder. S3. Calcining the intermediate powder yields bio-based hard carbon; The calcination includes a first-stage calcination and a second-stage calcination; The first stage of calcination involves heating to 350-550°C at a rate of 4-6°C / min for 1-6 hours. The second stage of calcination involves heating to 650-1050℃ at a rate of 7-9℃ / min for 1-7 hours. The metal salt is manganese chloride, zinc chloride, potassium chloride and magnesium chloride, and the mass ratio of manganese chloride, zinc chloride, potassium chloride and magnesium chloride is 1.2:1:0.8:0.9~1.

1.

2. The method for preparing bio-based hard carbon for anode materials according to claim 1, characterized in that, The mass ratio of the metal salt, carbonate, and waste biomass precursor is 1:0.5:10~20.

3. The method for preparing bio-based hard carbon for anode materials according to claim 1, characterized in that, The ball mill operates at a speed of 1000~5000 r / min for 6~10 h.

4. The method for preparing bio-based hard carbon for anode materials according to claim 1, characterized in that, The preheating temperature is 100~250℃, and the holding time is 1~15h.

5. The method for preparing bio-based hard carbon for anode materials according to claim 1, characterized in that, The cleaning agent used for the cleaning is a mixed solution of ethanol and water.

6. The method for preparing bio-based hard carbon for anode materials according to claim 5, characterized in that, In the mixed solution of ethanol and water, the volume ratio of ethanol to water is 1.5:1~15.

7. The method for preparing bio-based hard carbon for anode materials according to claim 1, characterized in that, The waste biomass precursors include one or more of corn stalks, corn silk, wheat straw, walnut shells, and almond shells; The carbonates include one or more of sodium carbonate, magnesium carbonate, lithium carbonate, zinc carbonate, manganese carbonate, and basic sodium aluminum carbonate.

8. A bio-based hard carbon for use as a negative electrode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

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