Biomass hard carbon, preparation method thereof and sodium battery

Abstract

The invention discloses biomass hard carbon, a preparation method thereof and a sodium battery, and the preparation method of the biomass hard carbon comprises the following steps: alkali liquor activation: adding a biomass raw material into alkali liquor for activation to obtain activated biomass; carbonization: pre-carbonizing the activated biomass to obtain pre-carbonized biomass, raising the temperature of the pre-carbonized biomass to 1000-1800 DEG C within 1-3 minutes for carbonization, and performing carbonization treatment for 6-10 minutes to obtain initial hard carbon; and hydrophilic treatment: soaking the initial hard carbon in an acid solution to obtain the biomass hard carbon. According to the method, the biomass raw materials are activated through the alkali liquor, the carbonization time is remarkably shortened, energy consumption can be reduced, and the production cost and the labor pressure are greatly reduced; compared with the biomass hard carbon obtained through carbonization for a longer time in the prior art, the biomass hard carbon with relatively good electrochemical performance can be obtained through carbonization for only 6-10 min, and the effect is very remarkable.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a biomass hard carbon and a preparation method thereof, and a sodium battery. Background Art

[0002] In recent years, sodium-ion batteries (SIBs) have shown promise in replacing lithium batteries in large-scale energy storage systems due to their abundant sodium resources and low cost. However, because the diameter of sodium ions (1.02 Å) is larger than that of lithium ions (0.76 Å), the practical application of SIBs often suffers from slow reaction kinetics and electrode volume expansion caused by ion size during charge and discharge. Therefore, the core challenge of SIBs is to design and develop SIBs with reversible sodium ion insertion / extraction properties and high gram capacity.

[0003] Hard carbon, due to its highly disordered structure, abundant defects, and microporous structure, is currently considered the most promising anode material for sodium-ion batteries. However, in practical applications, hard carbon materials still face the problems of low specific capacity and low initial efficiency, especially hard carbon materials prepared from biomass raw materials. Studies have shown that not all biomass hard carbons have good sodium storage behavior. Hard carbon with a graphite interlayer spacing of 0.36-0.40nm is better suited for sodium ion insertion and extraction. Therefore, the development of hard carbon materials with a graphite interlayer spacing of 0.36-0.40nm is very necessary.

[0004] However, the current process of preparing hard carbon materials from biomass raw materials often requires carbonization at a high temperature for a long time, usually more than 30 minutes, resulting in a long preparation time and high energy consumption; and the prepared hard carbon materials do not exhibit excellent electrochemical properties such as reversible capacity and cycle performance. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problems of long preparation time, high energy consumption and no significant improvement in electrical performance of the biomass hard carbon materials disclosed in the prior art, thereby providing a biomass hard carbon and its preparation method and sodium battery that can obtain better electrical performance in a shorter time.

[0006] A method for preparing biomass hard carbon, comprising:

[0007] Alkali activation: adding biomass raw materials into alkali to activate them to obtain activated biomass;

[0008] Carbonization: pre-carbonizing the activated biomass to obtain pre-carbonized biomass, heating the pre-carbonized biomass to 1000-1800°C within 1-3 minutes, and treating for 6-10 minutes to obtain initial hard carbon;

[0009] Hydrophilic treatment: The initial hard carbon is soaked in an acid solution, washed, and dried to obtain biomass hard carbon.

[0010] The heating rate of the pre-carbonized biomass is ≤1500°C / min, preferably 500-1000°C / min.

[0011] The alkali solution used in the alkali solution activation is selected from at least one of KOH solution and NaOH solution;

[0012] The concentration of the alkali solution is 0.5-1.5 mol / L;

[0013] The duration of the alkali solution activation is 5-15 hours.

[0014] In the pre-carbonization step, the heating rate is 1-10°C / min;

[0015] The pre-carbonization treatment temperature is 300-400°C;

[0016] The pre-carbonization treatment time is 1-3 hours.

[0017] In the hydrophilic treatment step, the acid solution is selected from at least one of a sulfuric acid solution and a nitric acid solution;

[0018] The concentration of the acid solution is 0.5-1.5 mol / L;

[0019] The initial hard carbon is immersed in the acid solution for 1-6 hours.

[0020] The acid solution is a mixed acid solution of sulfuric acid solution and nitric acid solution, and the molar ratio of sulfuric acid to nitric acid in the mixed acid solution is (2-4):1.

[0021] The biomass raw material is a granular material with a particle size of 20-50 μm, and the above-mentioned granular material is spherical or quasi-spherical and has a rough surface. The pollen of the Rosaceae plant in the present invention is a granular material with granular protrusions distributed on the surface and a certain degree of roughness and is quasi-spherical. At the same time, the pollen of the Impatiens and Tripterygium plants should also meet the above conditions and meet the requirements of the present invention. However, the pollen of the Rosaceae plant is easier to obtain. Therefore, the biomass raw material of the present invention is preferably the pollen of the Rosaceae plant, and more preferably, it is rose pollen and / or rose pollen.

[0022] A biomass hard carbon is prepared by adopting the above preparation method.

[0023] The interlayer spacing of the biomass hard carbon is between 0.36-0.40 nm, preferably between 0.37-0.38 nm.

[0024] A sodium battery comprises a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet comprises the above-mentioned biomass hard carbon.

[0025] The technical solution of the present invention has the following advantages:

[0026] The present invention provides a method for preparing biomass hard carbon, comprising alkali activation: adding a biomass raw material to an alkali solution for activation to obtain activated biomass; carbonization: pre-carbonizing the activated biomass to obtain pre-carbonized biomass, heating the pre-carbonized biomass to 1000-1800°C within 1-3 minutes, and treating for 6-10 minutes to obtain initial hard carbon; and hydrophilic treatment: soaking the initial hard carbon in an acid solution, washing, and drying to obtain the biomass hard carbon. The present invention ensures that the prepared hard carbon material has a higher specific surface area and a rich pore structure through alkali activation, reduces defects in the hard carbon graphite by controlling the heating rate, and makes the hard carbon interlayer spacing more uniform and sufficient by controlling the appropriate holding time. The hydrophilic treatment is performed with an acid solution to remove impurities and optimize the surface structure. The above combination enables the interlayer spacing of the hard carbon material prepared by the present invention to be controlled within a range of 0.36-0.40 nm, thereby enabling a sodium battery prepared using the biomass hard carbon of the present invention to have a high coulombic efficiency of more than 80%, as well as higher charge and discharge specific capacities. In addition, the present invention activates the biomass raw materials through alkaline solution and significantly shortens the carbonization time, which can reduce energy consumption and greatly reduce production costs and labor pressure; compared with the biomass hard carbon obtained by carbonization for a longer time disclosed in the prior art, the present invention only requires a carbonization time of 6-10 minutes to obtain biomass hard carbon with good electrochemical properties, and the effect is very significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 3-6 are the XRD patterns of the biomass hard carbons in Examples 3-6 of the present invention. DETAILED DESCRIPTION

[0029] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0030] In the description of the present invention, it should be noted that the terms "side," "upper," "lower," "top," "bottom," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical connections; direct connections or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0032] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example 1

[0034] A method for preparing biomass hard carbon, comprising:

[0035] Alkali activation: The rose pollen was cleaned with deionized water and then dried. The dried rose pollen was soaked in a 1 mol / L KOH solution for 10 h and then dried. The rose pollen was then ground into powder to obtain activated biomass.

[0036] Carbonization: The activated biomass was placed in a Joule device, heated to a pre-carbonization temperature of 400°C at a heating rate of 5°C / min and kept warm for 2 hours to obtain pre-carbonized biomass. The pre-carbonized biomass was rapidly heated to 1800°C at 1000°C / min, that is, heated to 1800°C in 1.4 minutes, kept at 1800°C for 8 minutes, and then quickly cooled to room temperature within 10 minutes to obtain unacidified initial hard carbon.

[0037] Hydrophilic treatment: The initial hard carbon was soaked in a mixed acid solution with a volume ratio of H2SO4:HNO3 of 3:1, and the concentrations of H2SO4 and HNO3 were both 1 mol / L. The mixture was stirred for 3 hours. After the soaking was completed, the biomass hard carbon was washed with deionized water until the pH was 7, and the rose pollen-based biomass hard carbon prepared by the present invention was obtained.

[0038] Examples 2-10 and Comparative Examples 1-3

[0039] A method for preparing biomass hard carbon differs from Example 1 in that the type of activator, the temperature and duration of carbonization, and the heating rate in the alkali solution activation and carbonization steps are different. The specific settings are shown in Table 1 below:

[0040] Table 1

[0041]

[0042] Other conditions are exactly the same as in Example 1.

[0043] Examples 11-14

[0044] A method for preparing biomass hard carbon differs from Example 1 in that the treatment concentration and treatment time of the acid solution in the alkali solution activation step and the alkali solution in the hydrophilic treatment step are different, as shown in Table 2 below.

[0045] Table 2

[0046]

[0047] Other conditions are exactly the same as in Example 1.

[0048] Examples 17-20

[0049] A method for preparing biomass hard carbon differs from Example 1 in that the heating rate, pre-carbonization treatment temperature and treatment time in the pre-carbonization step are different, as shown in Table 3 below.

[0050] Table 3

[0051] Heating rate Processing temperature Processing time Example 17 1℃ / min 300℃ 3h Example 18 10℃ / min 400℃ 1h Example 19 1℃ / min 400℃ 1h Example 20 10℃ / min 300℃ 3h

[0052] Other conditions are exactly the same as in Example 1.

[0053] Example 21

[0054] A sodium battery, the specific preparation process is as follows:

[0055] The biomass hard carbon prepared in the above-mentioned embodiments and comparative examples was used as the negative electrode active material, and the negative electrode active material was mixed with the binder PVDF, the thickener CMC, and the conductive agent SP in a mass ratio of 90:5:2.5:2.5. Deionized water was added to prepare the negative electrode slurry, and the negative electrode slurry was evenly coated on the copper foil current collector with a coating thickness of about 50±2um. After vacuum drying, a circular electrode sheet with a diameter of 12 mm was prepared.

[0056] A nanometal sheet was used as the positive electrode, and the electrolyte was an organic mixed solution containing 1.5 mol / L NaFP6. The organic mixed solution was prepared by dissolving NaFP6 in a mixed solution of ethylene carbonate, dimethylcarbonamide, and ethyl methyl carbonate. The volume ratio of ethylene carbonate, dimethylcarbonamide, and ethyl methyl carbonate was 1:2:2.

[0057] The above-mentioned positive electrode sheet, negative electrode sheet and electrolyte were assembled into a sodium ion half-cell in a glove box containing argon gas. A CR2032 specification battery shell was used and a button battery sealing machine was used to seal the assembled battery. After being taken out of the glove box, the button battery was left to stand at room temperature for 10 hours to obtain a sodium ion button half-cell.

[0058] Performance Testing

[0059] 1. XRD test: Cu Kα ray was used to characterize the structure of the biomass hard carbon prepared in Examples 3-6, with a scanning range of 10-80° and a scanning speed of 5° / min. The XRD test data are as follows: Figure 1 and as shown in Table 4 below.

[0060] 2. Electrical Performance Testing: Electrochemical testing was conducted using a Xinwei CT-4008Tn battery testing system at 25°C, an operating voltage of 0-2.5V, and a current density of 0.1C. The charge specific capacity, discharge specific capacity, and first coulombic efficiency of the sodium ion coin-type half-cell prepared in Example 21 were measured at a current density of 0.1C. The performance test results are shown in Tables 5-7.

[0061] Table 4

[0062] project <![CDATA[Interlayer spacing of hard carbon graphite layer (d 002 ) / nm]]> Example 3 0.383 Example 4 0.380 Example 5 0.376 Example 6 0.373

[0063] Table 5

[0064] project <![CDATA[Discharge specific capacity (mAh*g -1 )]]> <![CDATA[Charge specific capacity (mAh*g -1 )]]> First coulombic efficiency (%) Example 7 314.29 344.58 91.21％ Comparative Example 1 243.22 311.02 78.20％ Comparative Example 2 235.68 301.45 78.18％ Comparative Example 3 257.11 314.16 81.84％ Example 2 291.02 330.15 88.15％ Comparative Example 4 255.13 325.18 78.46％

[0065] Table 6

[0066] project <![CDATA[Discharge specific capacity (mAh*g -1 )]]> <![CDATA[Charge specific capacity (mAh*g -1 )]]> First coulombic efficiency (%) Example 1 293.52 338.24 86.78％ Example 2 291.02 330.15 88.15％ Example 3 311.42 345.41 90.16％ Example 4 307.04 342.76 89.58％ Example 5 301.95 340.11 88.78％ Example 6 298.56 339.62 87.91％ Example 7 314.29 344.58 91.21％ Example 8 290.15 341.07 85.07％ Example 9 299.41 342.11 87.52％ Example 10 311.83 341.88 91.21％

[0067] Table 7

[0068] project <![CDATA[Discharge specific capacity (mAh*g -1 )]]> <![CDATA[Charge specific capacity (mAh*g -1 )]]> First coulombic efficiency (%) Example 11 301.27 331.12 90.99％ Example 12 297.58 337.45 88.18％ Example 13 289.45 321.43 90.05％ Example 14 288.65 317.57 90.89％ Example 15 294.43 321.45 91.59％ Example 16 291.42 326.78 89.18％ Example 17 290.42 319.44 90.92％ Example 18 294.17 325.43 90.39％ Example 19 288.45 319.78 90.20％ Example 20 285.33 321.31 88.80％

[0069] According to Table 4 and Figure 1The results show that: two obvious diffraction peaks can be observed in the XRD spectrum, located at around 22° and 43° respectively. These two peaks correspond to the (002) and (100) crystal planes of graphite. The peak type of the diffraction peak is relatively wide, indicating that the degree of disorder of the hard carbon prepared by this patent is relatively high. Through Bragg calculation, it is known that the interlayer spacing (d002) of Example 3, Example 4, Example 5, and Example 6 are 0.383nm, 0.380nm, 0.376nm and 0.373nm respectively. The inventors have verified that with the increase of carbonization temperature, the interlayer spacing gradually decreases, but it is larger than the standard interlayer spacing of graphite 0.335nm. The larger interlayer spacing is conducive to the storage and diffusion of sodium ions in the hard carbon microcrystalline structure.

[0070] By comparing the results of Example 7 with Comparative Examples 1-3 in Table 5, and by comparing the results of Example 2 with Comparative Example 4, it can be seen that: by coordinating alkali solution activation with carbonization, the carbonization time can be effectively reduced. When the carbonization treatment time is only 6-10 minutes, biomass hard carbon with an interlayer spacing between 0.36-0.40 nm can still be obtained, which effectively saves energy consumption and reduces costs; and the electrical performance results in Table 5 verify that the alkali solution activation step is coordinated with the shorter carbonization time, and can also significantly improve the charge specific capacity, discharge specific capacity and first coulomb efficiency, and the effect is very significant; the main reason for the above results is that the alkali solution activation uses an excessively long holding time, which will increase the brittleness of the hard carbon material prepared by the present invention, making Na + Deintercalation is difficult, which in turn affects the electrical properties; therefore, in the case of an alkaline solution activation step, the present invention controls the carbonization treatment time to be shortened to only 6-10 minutes, which can significantly improve the charge specific capacity, discharge specific capacity and first coulombic efficiency compared to the carbonization treatment time of more than 30 minutes commonly used in the prior art, and the effect is very significant.

[0071] From the results in Table 6 above, it can be seen that: 1) By comparing Example 1 and Example 2, it can be seen that the coulombic efficiency of Example 2 is lower than that of Example 1. The main reason is that the introduction of NaOH leads to a decrease in the graphite interlayer spacing. At the same time, the biomass hard carbon prepared with KOH solution as the activator has better specific capacity and coulombic efficiency. The main reason is that KOH as the activator can ensure that the prepared hard carbon material has a higher specific surface area and a rich pore structure, which is more conducive to the insertion and extraction of sodium ions, thereby ensuring that the prepared hard carbon material has a higher specific capacity and coulombic efficiency. 2) By comparing Example 1 and Example 3-Example 6, it can be seen that when the hard carbon materials prepared at different carbonization temperatures are prepared into half-cells, their first efficiency and specific capacity decrease with the increase of carbonization temperature. The main reason is that the increase of carbonization temperature leads to a decrease in the interlayer spacing of the hard carbon material, which leads to a decrease in electrical performance. 3) By comparing Example 4, Example 7 and Example 8, it can be seen that the heating rate also affects the electrical properties of the hard carbon material. The main reason is that the reduced heating rate can reduce the defects of the hard carbon graphite and improve the coulombic efficiency of the hard carbon material. 4) By comparing Examples 4, 9, and 10, it can be seen that appropriately increasing the holding time also helps the carbonization reaction to be more complete, making the spacing between the hard carbon layers more uniform and sufficient, thereby improving the specific capacity and initial efficiency.

[0072] The results in Table 7 above show that within the range of the alkali activation parameter conditions, pre-carbonization parameter conditions, and hydrophilic treatment parameter conditions of the present invention, the first coulombic efficiency is basically equivalent, and compared with the comparative example with a longer carbonization time and activation without an activator, it has significantly better electrochemical performance.

[0073] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing biomass hard carbon, characterized in that: include: Alkali activation: adding biomass raw materials into alkali to activate them to obtain activated biomass; Carbonization: pre-carbonizing the activated biomass to obtain pre-carbonized biomass, heating the pre-carbonized biomass to 1000-1800°C within 1-3 minutes for carbonization, and obtaining initial hard carbon after carbonization for 6-10 minutes; Hydrophilic treatment: The initial hard carbon is soaked in acid solution to obtain biomass hard carbon.

2. The preparation method according to claim 1, characterized in that The heating rate of the pre-carbonized biomass is ≤1500°C / min, preferably 500-1000°C / min.

3. The preparation method according to claim 1 or 2, characterized in that The alkali solution used in the alkali solution activation is selected from at least one of KOH solution and NaOH solution; The concentration of the alkali solution is 0.5-1.5 mol / L; The duration of the alkali solution activation is 5-15 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the pre-carbonization step, the heating rate is 1-10°C / min; The pre-carbonization treatment temperature is 300-400°C; The pre-carbonization treatment time is 1-3 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that In the hydrophilic treatment step, the acid solution is selected from at least one of a sulfuric acid solution and a nitric acid solution; The concentration of the acid solution is 0.5-1.5 mol / L; The initial hard carbon is immersed in the acid solution for 1-6 hours.

6. The preparation method according to claim 5, characterized in that The acid solution is a mixed acid solution of sulfuric acid solution and nitric acid solution, and the molar ratio of sulfuric acid to nitric acid in the mixed acid solution is (2-4):

1.

7. The preparation method according to any one of claims 1 to 6, characterized in that The biomass raw material is a granular material with a particle size of 20-50 μm, preferably pollen of a plant of the Rosaceae family, more preferably rose pollen and / or Chinese rose pollen.

8. A biomass hard carbon, characterized in that: The preparation method is described in any one of claims 1 to 7.

9. The biomass hard carbon according to claim 8, characterized in that The interlayer spacing of the biomass hard carbon is between 0.36-0.40 nm, preferably between 0.37-0.38 nm.

10. A sodium battery comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The negative electrode sheet includes the biomass hard carbon according to claim 8 or 9.

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