Bio-based hard carbon for negative electrode material and preparation method of bio-based hard carbon

Abstract

The invention relates to the technical field of lithium-based supercapacitors, and provides bio-based hard carbon for a negative electrode material and a preparation method of the bio-based hard carbon for the negative electrode material, and the preparation method of the bio-based hard carbon for the negative electrode material comprises the following steps: S1, carrying out ball milling on metal salt, a waste biomass precursor and carbonate to obtain a mixed sample; s2, presintering the mixed sample to obtain an intermediate, cleaning and drying to obtain intermediate powder; s3, calcining the intermediate powder to obtain bio-based hard carbon; calcining comprises first-stage calcining and second-stage calcining; in the first-stage calcination, the temperature is raised to 350-550 DEG C at the temperature raising speed of 4-6 DEG C / min, and the calcination time is 1-6 h; in the second-stage calcination, the temperature is raised to 650-1050 DEG C at the temperature raising speed of 7-9 DEG C / min, and the calcination time is 1-7 h. According to the technical scheme, the problem that the capacity retention ratio is insufficient when bio-based hard carbon serves as the negative electrode of the lithium-based supercapacitor in the prior art is solved.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of the 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 the lithium-based supercapacitor generally uses a capacitive material such as activated carbon, and the negative electrode uses a battery material such as graphite, hard carbon and soft carbon. The hard carbon is highly disordered stacked by locally graphitized carbon layer structure, and the staggered longitudinal and transverse structure is beneficial to the embedding and de-embedding of lithium ions, so that the hard carbon becomes an optimal negative electrode material for lithium ion capacitors.

[0003] At present, the bio-based hard carbon prepared from waste biomass precursors has become a research focus because of its wide raw material sources, environmental protection, low pollution and low price. However, the bio-based hard carbon as a negative electrode material applied to lithium-based supercapacitors faces key challenges in practical application: the capacity retention rate of the material is prone to continuous attenuation 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 application provides a bio-based hard carbon for negative electrode materials and a preparation method thereof, and solves the problem of insufficient capacity retention rate of the bio-based hard carbon as a negative electrode of a lithium-based supercapacitor in the related art.

[0005] The technical scheme of the application is as follows: The application provides a preparation method of a bio-based hard carbon for negative electrode materials, which comprises the following steps: S1, ball milling of a metal salt, a waste biomass precursor and a carbonate to obtain a mixed sample; S2, pre-burning of the mixed sample to obtain an intermediate, washing, drying and obtaining an intermediate powder; S3, calcining of the intermediate powder to obtain a bio-based hard carbon; The calcining comprises first-stage calcining and second-stage calcining; The first-stage calcining is heated to 350-550 DEG C at a heating rate of 4-6 DEG C / min, and the calcining time is 1-6 h; The second-stage calcining is heated to 650-1050 DEG C at a heating rate of 7-9 DEG C / min, and the calcining time is 1-7 h.

[0006] As a further technical solution, the mass ratio of the metal salt, carbonate and waste biomass precursor is 1:0.5:10~20.

[0007] As a further technical solution, the ball mill rotation speed is 1000~5000 r / min, and the time is 6~10 h.

[0008] As a further technical solution, the ball mill uses zirconia beads.

[0009] As a further technical solution, the diameter of the zirconia beads is 0.1~1mm.

[0010] As a further technical solution, the pre-firing temperature is 100~250℃, and the holding time is 1~15h.

[0011] As a further technical solution, the pre-burning atmosphere is air.

[0012] As a further technical solution, the drying is vacuum drying, with a temperature of 80~100℃ and a time of 10~12h.

[0013] As a further technical solution, the calcination atmosphere is an inert gas.

[0014] As a further technical solution, the inert gas includes helium.

[0015] As a further technical solution, the cleaning agent is a mixed solution of ethanol and water.

[0016] As a further technical solution, in the mixed solution of ethanol and water, the volume ratio of ethanol to water is 1.5:1~15.

[0017] As a further technical solution, the metal salt includes three or more of the following: manganese chloride, sodium nitrate, copper sulfate, potassium nitrate, magnesium nitrate, zinc chloride, aluminum chloride, potassium chloride, calcium chloride, and magnesium chloride.

[0018] 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.

[0019] In this invention, the metal salts are manganese chloride, zinc chloride, potassium chloride and magnesium chloride, and the mass ratio is further limited to 1.2:1:0.8:0.9~1.1. The synergistic effect between the metal salts is fully utilized, which can precisely control the microstructure and electrochemical performance of bio-based hard carbon. When used as a negative electrode material, it improves the capacity retention of lithium-based supercapacitors at low temperatures.

[0020] 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.

[0021] As a further technical solution, the carbonate includes one or more of sodium carbonate, magnesium carbonate, lithium carbonate, zinc carbonate, manganese carbonate, and basic sodium aluminum carbonate.

[0022] This invention also proposes a bio-based hard carbon for anode materials, which is prepared by the aforementioned method.

[0023] The working principle and beneficial effects of this invention are as follows: In this invention, during the preparation of bio-based hard carbon, the final calcination stage involves controlling the heating rate of the first calcination stage to 4-6°C / min and the second calcination stage to 7-9°C / min. The resulting bio-based hard carbon, used as a negative electrode material, produces lithium-based supercapacitors with excellent capacity retention. Controlling the heating rate of the first calcination stage at 4-6°C / min facilitates the gradual breakage and rearrangement of macromolecular chains in the organic matter, forming a relatively stable amorphous carbon structure and reducing structural defects and inhomogeneities caused by rapid heating. Increasing the heating rate to 7-9°C / min in the second stage further promotes more intense thermal motion and rearrangement of carbon atoms based on the amorphous carbon structure formed in the first stage. This provides more active sites and rapid channels for the insertion and extraction of lithium ions in the subsequent lithium-based supercapacitor, thereby significantly improving the capacity retention of the lithium-based supercapacitor. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 A method for preparing bio-based hard carbon for anode materials includes the following steps: S1. Metal salt, walnut shells and zinc carbonate were ball-milled at 1000 r / min using 0.1 mm diameter zirconia beads as the medium for 10 h (the mass ratio of zirconia beads to the total mass of metal salt, walnut shells and zinc carbonate was 2:1) to obtain a mixed sample. S2. The mixed sample was placed in an air atmosphere and pre-calcined at 100°C for 15 hours to obtain an intermediate. The intermediate was then washed with a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1.5:15 and then vacuum dried at 80°C for 12 hours to obtain an intermediate powder. S3. The intermediate powder was placed in a helium atmosphere and calcined in stages. The first stage of calcination was carried out by heating to 350°C at a heating rate of 4°C / min and calcining for 6 hours. The second stage of calcination was carried out by heating to 650°C at a heating rate of 7°C / min and calcining for 7 hours to obtain bio-based hard carbon. The metal salts are manganese chloride, zinc chloride, potassium chloride, and calcium chloride in a mass ratio of 1.2:1:0.8:0.7. The mass ratio of metal salt, zinc carbonate, and walnut shell is 1:0.5:10.

[0026] Example 2 A method for preparing bio-based hard carbon for anode materials includes the following steps: S1. Metal salt, straw, and magnesium carbonate were ball-milled at 5000 r / min using 1 mm diameter zirconia beads as the medium for 6 h (the mass ratio of zirconia beads to the total mass of metal salt, straw, and magnesium carbonate was 2:1) to obtain a mixed sample. S2. Place the mixed sample in an air atmosphere and pre-calcine at 250°C for 1 hour to obtain an intermediate; wash the intermediate with a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1.5:1, and then vacuum dry at 100°C for 10 hours to obtain intermediate powder. S3. The intermediate powder was placed in a helium atmosphere and calcined in stages. The first stage of calcination was carried out by heating to 550°C at a heating rate of 6°C / min and calcining for 1 hour. The second stage of calcination was carried out by heating to 1050°C at a heating rate of 9°C / min and calcining for 1 hour to obtain bio-based hard carbon. The metal salts are manganese chloride, zinc chloride, potassium chloride, and calcium chloride in a mass ratio of 1.2:1:0.8:0.7. The mass ratio of metal salt, zinc carbonate, and wheat straw is 1:0.5:20.

[0027] Example 3 A method for preparing bio-based hard carbon for anode materials includes the following steps: S1. Metal salt, corn stalks and sodium carbonate were ball-milled at 3500 r / min using 1 mm diameter zirconia beads as the medium for 8 h (the mass ratio of zirconia beads to the total mass of metal salt, corn stalks and sodium carbonate was 2:1) to obtain a mixed sample. S2. The mixed sample was pre-calcined at 160°C for 8 hours in air to obtain an intermediate. The intermediate was then washed with a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1.5:8.5 and dried under vacuum at 90°C for 9 hours to obtain an intermediate powder. S3. The intermediate powder was placed in a helium atmosphere and calcined in stages. The first stage of calcination was carried out by heating to 400°C at a heating rate of 5°C / min and calcining for 3 hours. The second stage of calcination was carried out by heating to 850°C at a heating rate of 8°C / min and calcining for 4 hours to obtain bio-based hard carbon. The metal salts are manganese chloride, zinc chloride, potassium chloride, and calcium chloride in a mass ratio of 1.2:1:0.8:0.7. The mass ratio of metal salt, zinc carbonate, and corn stalks is 1:0.5:16.

[0028] Example 4 The only difference between this embodiment and Embodiment 3 is that during the staged calcination, the heating rate of the first stage calcination is 4℃ / min, and the heating rate of the second stage calcination is 7℃ / min.

[0029] Example 5 The only difference between this embodiment and Embodiment 3 is that during the staged calcination, the heating rate of the first stage calcination is 6℃ / min, and the heating rate of the second stage calcination is 9℃ / min.

[0030] Example 6 The only difference between this embodiment and Example 3 is that the metal salts are manganese chloride, zinc chloride, potassium chloride and potassium nitrate in a mass ratio of 1.2:1:0.8:0.7.

[0031] Example 7 The only difference between this embodiment and Example 3 is that the metal salts are manganese chloride, zinc chloride, potassium chloride and sodium nitrate in a mass ratio of 1.2:1:0.8:0.7.

[0032] Example 8 The only difference between this embodiment and Example 3 is that the metal salts are manganese chloride, zinc chloride, potassium chloride and magnesium chloride in a mass ratio of 1.2:1:0.8:0.7.

[0033] Example 9 The only difference between this embodiment and Example 8 is that the metal salts are manganese chloride, zinc chloride, potassium chloride and magnesium chloride in a mass ratio of 1.2:1:0.8:0.9.

[0034] Example 10 The only difference between this embodiment and Example 8 is that the metal salts are manganese chloride, zinc chloride, potassium chloride and magnesium chloride in a mass ratio of 1.2:1:0.8:1.1.

[0035] Example 11 The only difference between this embodiment and Example 8 is that the metal salts are manganese chloride, zinc chloride, potassium chloride and magnesium chloride in a mass ratio of 1.2:1:0.8:1.3.

[0036] Comparative Example 1 The only difference between this comparative example and Example 3 is that during the staged calcination, the heating rate of the first stage calcination is 3°C / min, and the heating rate of the second stage calcination is 5°C / min.

[0037] Comparative Example 2 The only difference between this comparative example and Example 3 is that during the staged calcination, the heating rate of the first stage calcination is 7°C / min, and the heating rate of the second stage calcination is 11°C / min.

[0038] The bio-based hard carbon prepared in Examples 1-11 and Comparative Examples 1-2 was used as the negative electrode of a lithium-based supercapacitor to assemble the lithium-based supercapacitor and test the lithium-based supercapacitor. 1. Lithium-based supercapacitors: Negative electrode: Bio-based hard carbon, carbon black, and PVDF were mixed in a mass ratio of 8:1:1, and NMP was added to prepare a negative electrode slurry. The negative electrode slurry was then coated onto a stainless steel current collector with a coating thickness of 45 μm. After vacuum drying, the negative electrode was obtained with a loading of 3.9 mg·cm³. -2 ; Positive electrode: Activated carbon, carbon black, and PVDF are mixed in a mass ratio of 8:1:1 to prepare a positive electrode slurry. The slurry is coated onto a stainless steel current collector with the same thickness as the negative electrode. After drying, the positive electrode is obtained with a loading of 2.3 mg·cm⁻¹. -2 ; The electrolyte is 1 mol·L -1 LiPF6 (EC to DMC mass ratio is 1:1). 2. Rate cycling performance: The lithium-based supercapacitor prepared above was subjected to 1C / 3C rate charge-discharge tests within the voltage range of 2.2V~3.4V at room temperature; 3. Low temperature performance: The lithium-based supercapacitor prepared above was charged to 3.4V by constant current at 0.5C, then charged to the cutoff current at constant voltage at 0.01C, and then placed at -25℃ for 16h. The test results are shown in Table 1: Table 1 Performance test results of lithium-based supercapacitors prepared from bio-based hard carbon obtained in Examples 1-11 and Comparative Examples 1-2

[0039] 1. Compared with Comparative Examples 1 and 2, the lithium-based supercapacitors made of bio-based hard carbon prepared in Examples 1 to 10 showed significantly higher capacity retention after 1000 cycles than those in Comparative Examples 1 and 2. This indicates that when preparing bio-based hard carbon, controlling the heating rate of the first stage calcination at 4 to 6 °C / min and the heating rate of the second stage calcination at 7 to 9 °C / min during the final calcination process can significantly improve the capacity retention of lithium-based supercapacitors.

[0040] 2. Compared with Examples 3 and 6-11, the lithium-based supercapacitors made of bio-based hard carbon prepared in Examples 8-11 have a higher capacity retention rate after low-temperature treatment than those in Examples 3 and 6-7. This indicates that using manganese chloride, zinc chloride, potassium chloride, and magnesium chloride as a metal salt for preparing bio-based hard carbon is significant for improving the capacity retention rate of lithium-based supercapacitors at low temperatures. Among them, the lithium-based supercapacitors made of bio-based hard carbon prepared in Examples 9-10 have a higher capacity retention rate after low-temperature treatment than those in Examples 8 and 11. This indicates 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 temperatures.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

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 the temperature to 650-1050℃ at a rate of 7-9℃ / min for 1-7 hours.

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 metal salt includes three or more of the following: manganese chloride, sodium nitrate, copper sulfate, potassium nitrate, magnesium nitrate, zinc chloride, aluminum chloride, potassium chloride, calcium chloride, and magnesium chloride.

8. The method for preparing bio-based hard carbon for anode materials according to claim 7, characterized in that, 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.

9. 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.

10. 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 9.

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