Biomass-based doped hard carbon material, preparation method, application and battery

Abstract

The invention provides a biomass-based doped hard carbon material, a preparation method, application and a battery. The preparation method comprises the following steps: sequentially carrying out gradient calcination on a mixture of an algae precursor and a sulfur source to obtain primary hard carbon; and carrying out acid etching on the primary hard carbon to obtain the porous carbon material. The preparation method provided by the invention not only solves the problems of high cost and low heteroatom utilization rate of the traditional hard carbon raw material, but also realizes the balance of high specific capacity, long cycle and high rate performance through modification synergy, promotes the resource utilization of algae wastes, and has significant economic value and environmental protection significance.

Description

Technical Field

[0001] This invention specifically relates to a biomass-based doped hard carbon material, its preparation method, applications, and batteries. Background Technology

[0002] As the global energy structure shifts towards renewable energy, large-scale energy storage technology has become a core pillar supporting the energy revolution. Sodium-ion batteries, due to their abundant sodium resources, low cost, and excellent safety, are considered an ideal choice for large-scale energy storage and low-speed electric vehicles. Hard carbon materials, with their amorphous layered structure, suitable interlayer spacing, and abundant porosity, can effectively adapt to the sodium ion insertion / extraction mechanism, making them one of the best-performing anode materials for sodium-ion batteries. Their performance directly determines the energy density, cycle life, and cost competitiveness of sodium-ion batteries.

[0003] However, the preparation of existing hard carbon materials still faces many core bottlenecks, severely restricting their industrial application. Hard carbon raw materials are expensive and lack environmental friendliness. Currently, hard carbon preparation mostly relies on fossil-based raw materials or food-based biomass. The former faces resource depletion and carbon emission issues, while the latter is controversial regarding its impact on food security. Although some studies have attempted to prepare hard carbon using agricultural and forestry waste, these raw materials have extremely low levels of nitrogen, phosphorus, and other heteroatoms, requiring additional addition of nitrogen and phosphorus sources for doping modification. This not only increases the complexity and cost of the process but may also lead to performance fluctuations due to uneven doping.

[0004] Furthermore, current heteroatom doping efficiency is low and synergy is poor. The sodium ion storage performance of hard carbon is highly dependent on the regulation of surface heteroatoms: nitrogen atoms can enhance the chemisorption of sodium ions through lone pair electrons, phosphorus atoms can lower the ion migration barrier through POC bonds, and sulfur atoms can improve ion diffusion efficiency by increasing interlayer spacing. However, in existing technologies, heteroatom doping often adopts a strategy of introducing external reagents individually, which has many problems: the binding force between doped atoms and the carbon framework is weak, they are easily volatilized during high-temperature carbonization, and the nitrogen and phosphorus residue rates are low; phase separation is easily formed when multiple elements are doped, such as sulfur and nitrogen, which are difficult to bond synergistically and cannot exert a synergistic enhancement effect; the introduction of excessive reagents will lead to the disordering of the carbon framework, which will reduce conductivity.

[0005] To improve the cycling stability of hard carbon, existing technologies often employ coating modification. However, uneven coating thickness can lead to increased charge transfer resistance, and high-density inorganic coating materials can significantly reduce the specific capacity of hard carbon. Therefore, developing novel and efficient heteroatom doping methods for hard carbon is crucial for improving its performance.

[0006] Blue-green algae and other algae are major pollutants in eutrophic waters, with over ten million tons collected globally each year. They naturally contain abundant heteroatoms such as nitrogen, phosphorus, and sulfur, primarily in the form of proteins, phospholipids, and sulfur-containing amino acids. These heteroatoms are tightly bound to the carbon skeleton, making them an ideal "natural heteroatom library." Currently, the preparation of high-performance carbon materials from algae faces significant technical bottlenecks. Existing methods often result in the volatilization of most of the nitrogen and phosphorus in the algae as gases, failing to retain their battery activity. Conventional high-temperature activation processes create pores that disrupt the natural porous structure and heteroatom bonding morphology of blue-green algae. Therefore, there is an urgent need to develop new processes for the high-value preparation of high-performance hard carbon from algal waste to meet environmental and energy demands. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a biomass-based doped hard carbon material, its preparation method, applications, and batteries. The preparation method of this invention solves the problems of high cost and low heteroatom utilization of traditional hard carbon raw materials, and achieves a balance between high specific capacity, long cycle life, and high rate performance through synergistic modification. Simultaneously, it promotes the resource utilization of algal waste, possessing significant economic value and environmental significance.

[0008] This invention innovatively proposes an integrated strategy of in-situ retention, synergistic doping, and low-temperature interface activation: by pre-carbonizing to lock the nitrogen and phosphorus heteroatoms of algal biomass materials, and then introducing a sulfur source to achieve synergistic doping of sulfur elements, forming a stable CNPS bond structure, and then exposing active sites through acid etching, thereby achieving a balance between high specific capacity, long cycle life, and high rate performance of hard carbon materials.

[0009] This invention provides a method for preparing biomass-based doped hard carbon materials, comprising the following steps:

[0010] The mixture of algal precursor and sulfur source was subjected to gradient calcination to obtain primary hard carbon; the primary hard carbon was then acid etched to obtain the biomass-based doped hard carbon material.

[0011] In this invention, the algal precursor is preferably green algae and / or cyanobacteria. Preferably, the green algae is *Chlorella vulgaris*, and the cyanobacteria is preferably *Chlorococcus globulus*.

[0012] In this invention, the sulfur source preferably includes one or more of thiourea, thioacetamide, carbon disulfide, sodium sulfite, thiophene, sodium sulfide, dimethyl sulfide, ammonium sulfate, sulfur powder, cystine, and methionine.

[0013] In this invention, the mass ratio of the algal precursor to the sulfur source can be 100:(1-10), for example 100:1.3, 100:1.5, 100:2, 100:3, 100:5 or 100:8.

[0014] In this invention, according to conventional practice in the art, the gradient calcination is generally carried out under an inert gas atmosphere. The inert gas is, for example, nitrogen or argon.

[0015] In this invention, gradient calcination refers to calcining where, after the previous calcination stage is completed, no cooling treatment is required, and the temperature is directly increased to the temperature of the next calcination stage based on the previous calcination temperature.

[0016] In this invention, the gradient calcination preferably includes a first stage of calcination and a second stage of calcination.

[0017] The heating rate to the first calcination temperature can be 1-5℃ / min, for example, 2℃ / min or 3℃ / min; the first calcination temperature can be 160-400℃, for example, 200℃, 250℃, 300℃, 350℃ or 380℃; the first calcination time can be 1-8h, for example, 2h, 3h, 4h, 6h or 7h. The heating rate to the second calcination temperature can be 1-5℃ / min, for example, 2℃ / min or 3℃ / min; the second calcination temperature can be 800-1400℃, for example, 900℃, 950℃, 1000℃, 1050℃, 1100℃ or 1200℃; the second calcination time can be 1-12h, for example, 2h, 3h, 4h, 5h or 8h.

[0018] In some preferred embodiments, the gradient calcination includes the following process: first calcining at 160-400℃ for 1-8 hours, and then continuing to calcinate at 800-1400℃ for 1-12 hours.

[0019] In this invention, the acid used for acid etching preferably includes one or more of citric acid, oxalic acid, tartaric acid, phosphoric acid, ethylenediaminetetraacetic acid, and malic acid, for example, citric acid. The mass concentration of the acid used for acid etching can be 3-20 wt%, for example, 5% or 10%. During the acid etching process, the mass ratio of the primary hard carbon to the volume of the acid can be 0.1-5 g / mL, preferably 0.1-2 g / mL, for example, 0.3 g / mL, 0.5 g / mL, 0.8 g / mL, 1 g / mL, or 1.5 g / mL.

[0020] In this invention, the acid etching temperature can be 20-80°C, for example 25°C, 30°C or 50°C, preferably 40-80°C.

[0021] In this invention, the acid etching is generally performed under stirring. After the acid etching is completed, centrifugation, washing, and drying are usually required. The washing operation and conditions can be conventional in the art, and generally require washing until neutral.

[0022] In this invention, the acid etching preferably includes the following process: ultrasonically dispersing, stirring reaction, centrifuging, and drying the mixture of primary hard carbon and acid in sequence.

[0023] The ultrasonic dispersion time can be 10-60 min, for example 20 min, 40 min or 50 min.

[0024] The stirring speed can be 200-600 rpm, for example, 300, 400 or 500 rpm; the stirring time can be 1-4 hours, for example, 1.5 hours, 2 hours or 3 hours. The stirring temperature is the same as the acid etching temperature described above.

[0025] The centrifugation speed can be 6000-10000 r / min, for example 7000 r / min, 8000 r / min or 9000 r / min; the centrifugation washing time can be 5-30 min, for example 8 min, 15 min or 20 min.

[0026] In this invention, the algal precursor is preferably washed, dried, crushed, and sieved in sequence before use.

[0027] The washing operation and conditions can be conventional in the art, and preferably include the following steps: stirring and mixing the mixture containing the algal precursor, and then centrifuging and washing.

[0028] The number of washes is conventional in the art, generally 2-5 times, for example 3 times. The solvent in the mixture containing the algal precursor is conventional in the art, generally deionized water. In the mixture containing the algal precursor, the mass concentration of the algal precursor is 0.1-2 g / mL, preferably 0.2-1 g / mL, for example 0.3 g / mL, 0.5 g / mL or 0.8 g / mL.

[0029] The stirring and mixing are generally carried out in a magnetic stirrer; the stirring speed can be 200-800 r / min, for example 300 r / min, 400 r / min, 500 r / min or 600 r / min; the stirring and mixing time can be 5-60 min, for example 10 min, 20 min or 30 min.

[0030] The centrifugal washing is generally carried out in a high-speed centrifuge; the centrifugal washing speed can be 6000-10000 r / min, for example 7000 r / min, 8000 r / min or 9000 r / min; the centrifugal washing time can be 5-30 min, for example 8 min, 10 min or 15 min.

[0031] The drying process is generally carried out in a vacuum drying oven; the drying temperature can be 50-100℃, for example 60℃ or 80℃; and the drying time can be 6-24h, for example 12h.

[0032] The pulverization operation can be conventional in the art, such as ball milling. The particle size after pulverization is preferably less than 50 μm. The diameter of the grinding balls used in the ball milling can be 5-20 mm, for example, 10 mm or 15 mm; the ball-to-material ratio during the ball milling process can be (5-15):1, for example, 8:1 or 10:1; the rotational speed of the ball mill can be 200-500 r / min, for example, 250 r / min, 300 r / min or 400 r / min; the ball milling time can be 2-8 h, for example, 4 h or 6 h.

[0033] The mesh size of the sieve used for screening is preferably 200-400 mesh, such as 250 mesh, 300 mesh or 350 mesh.

[0034] The present invention also provides a biomass-based doped hard carbon material prepared by the preparation method described above.

[0035] The present invention also provides an application of the biomass-based doped hard carbon material as described above in battery materials.

[0036] The present invention also provides a battery comprising the biomass-based doped hard carbon material as described above.

[0037] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0038] The reagents and raw materials used in this invention are all commercially available.

[0039] The positive and progressive effects of this invention are as follows:

[0040] This invention achieves a multi-dimensional synergistic breakthrough. It not only anchors the inherent nitrogen and phosphorus in algae through low-temperature pre-carbonization and forms a CNPS quaternary bond structure by co-doping with sulfur source, thereby improving the first coulombic sum and efficiency of hard carbon specific capacity and breaking through the bottleneck of unbalanced performance of traditional hard carbon; it also uses algal waste as raw material, which is much cheaper than fossil-based raw materials, does not require additional nitrogen and phosphorus dopants, is suitable for large-scale production, and realizes the high-value utilization of algal waste. Attached Figure Description

[0041] Figure 1 The image shows a SEM image of the hard carbon material prepared in Example 1. Detailed Implementation

[0042] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0043] Example 1

[0044] Step (1): Take 1500g of Chlorella (Jiangsu Caiwei Biotechnology, powder), add 3000mL of deionized water (self-made, Milli-Q), stir at 500r / min for 10min on a magnetic stirrer, then centrifuge at 8000r / min for 10min using a high-speed centrifuge, discard the supernatant and wash twice; transfer the precipitate to a vacuum drying oven and dry at 60℃ and 10Pa for 12h; add the dried algae powder to the agate jar of a planetary ball mill (Nanjing University Instrument Factory, QM-3SP4), the diameter of the grinding balls is 10mm, the ball-to-material ratio is 8:1, and ball mill at 300r / min for 6h, then pass through a 300-mesh sieve.

[0045] Step (2): Take 600g of sieved powder and mix it with 12g of thiourea (Aladdin, analytical grade). Spread it in a graphite boat and purge it with high-purity nitrogen at 50mL / min three times in a tube furnace. Then, heat it to 250℃ at a heating rate of 2℃ / min and hold it for 3h. Then, switch the nitrogen to argon at a flow rate of 50mL / min and continue heating it to 950℃ at a heating rate of 3℃ / min from 250℃ and hold it for 5h. After natural cooling, the primary hard carbon is obtained.

[0046] Step (3): Weigh 250g of primary hard carbon, add 500 mL of 5% citric acid (Aladdin, analytical grade) solution, sonicate for 40 min, transfer to a constant temperature water bath, stir at 50℃ and 400 r / min for 2 h, then centrifuge at 8000 r / min for 15 min, wash until neutral, and then vacuum dry in an oven at 60℃ for 12 h.

[0047] Example 2

[0048] Compared with Example 1, the only difference is that the 12g of thiourea in step (2) is changed to 8g, and the other conditions remain the same.

[0049] Example 3

[0050] Compared with Example 1, except that the heating rate of 2℃ / min to 250℃ and holding for 3h in step (2) is changed to heating rate of 2℃ / min to 350℃ and holding for 3h, all other conditions remain the same.

[0051] Example 4

[0052] Compared with Example 1, except that the heating rate of 2℃ / min to 250℃ and holding for 3h in step (2) is changed to heating rate of 2℃ / min to 250℃ and holding for 6h, all other conditions remain the same.

[0053] Example 5

[0054] Compared with Example 1, except that the heating rate of 3℃ / min to 950℃ and holding for 5h in step (2) is changed to heating rate of 3℃ / min to 1050℃ and holding for 5h, all other conditions remain the same.

[0055] Example 6

[0056] Compared with Example 1, except that the heating rate of 3℃ / min to 950℃ and holding for 5h in step (2) is changed to heating rate of 3℃ / min to 950℃ and holding for 2h, all other conditions remain the same.

[0057] Example 7

[0058] Compared with Example 1, the only difference is that the temperature of the constant temperature water bath in step (3) is adjusted from 50°C to 25°C, while the other conditions remain unchanged.

[0059] Comparative Example 1

[0060] Primary hard carbon prepared in step (2) of Example 1.

[0061] Comparative Example 2

[0062] Compared with Example 1, except that thiourea is not added in step (2), all other conditions remain the same.

[0063] Comparative Example 3

[0064] Step (1): Same as in Example 1.

[0065] Step (2): Take 600g of sieved powder and mix it with 12g of thiourea (Aladdin, analytical grade). Spread it on a graphite boat and replace it three times with high-purity argon gas at 50mL / min in a tube furnace. Heat it to 950℃ at a heating rate of 3℃ / min and hold it for 5h. Then cool it naturally to obtain primary hard carbon.

[0066] Step (3): Same as in Example 1.

[0067] Effect Example

[0068] (1) SEM test

[0069] Figure 1 This is a scanning electron microscope image of the hard carbon material prepared in Example 1.

[0070] (2) Electrochemical performance testing

[0071] Negative electrode preparation: The hard carbon materials prepared in Examples 1 to 7 and Comparative Examples 1-3 were subjected to half-cell tests. The test method was as follows: hard carbon material, superconducting carbon black (Super P), and PVDF were weighed at a mass ratio of 8:1:1, mixed uniformly using a homogenizer, and then coated onto a copper foil current collector. The mixture was then dried overnight in a vacuum oven at 90°C. Subsequently, the obtained electrode was cut into circular battery electrode sheets with a diameter of 12 mm for later use. The average mass loading was approximately... .

[0072] The sodium-ion battery uses a sodium metal sheet as the counter electrode, a single layer of glass fiber as the separator, and a nickel foam disc. The electrolyte is a 1M NaPF6 diethylene glycol dimethyl ether solution. After assembly, the battery was allowed to stand for 8 hours for aging. Constant current charge / discharge tests were performed on a LAND CT2001A battery testing system, with a voltage range of 0.001 to 3.0 V vs. Na / Na. + 1C = 400 mA g -1 The test results are shown in Table 1:

[0073] Table 1

[0074] 0.1C discharge specific capacity mAh / g First Coulomb efficiency % Retention rate % (0.5C) after 500 cycles 5C specific capacity (mAh / g) Example 1 410 88.5 92.0 290 Example 2 395 87.8 90.5 275 Example 3 380 86.2 89.0 260 Example 4 405 90.2 97.9 295 Example 5 390 92.0 98.8 280 Example 6 370 90.7 87.8 250 Example 7 385 86.8 90.0 265 Comparative Example 1 320 82.0 80.5 210 Comparative Example 2 331 85.1 86.5 241 Comparative Example 3 346 83.6 89.5 225

[0075] Based on the above experimental results, the hard carbon material prepared in this invention exhibits superior discharge specific capacity, coulombic efficiency, cycle retention, and high-rate capacity. Comparative Example 1, lacking etching, has no amorphous carbon covering active sites on its surface, resulting in low conductivity and ion transport efficiency. Comparative Example 2, without sulfur doping, lacks CS bond coordination, and its sodium ion adsorption capacity and conductivity are weaker than in Example 1. Comparative Example 3, without gradient calcination and employing only one-step calcination, results in direct high-temperature volatilization of nitrogen and phosphorus, leading to a lack of heteroatom synergistic effects.

[0076] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a biomass-based doped hard carbon material, characterized by, The method comprises the following steps: The mixture of the algal precursor and the sulfur source is sequentially subjected to gradient calcination to obtain a primary hard carbon; and the primary hard carbon is subjected to acid etching to obtain the biomass-based doped hard carbon material.

2. The method for preparing biomass-based doped hard carbon material as described in claim 1, characterized in that, The algal precursor is preferably green algae and / or blue algae; the green algae is preferably Chlorella sp.; and the blue algae is preferably Chroococcus sp. The sulfur source comprises one or more of thiourea, thioacetamide, carbon disulfide, sodium sulfite, thiophene, sodium sulfide, dimethyl sulfide, ammonium sulfate, sulfur powder, cystine, and methionine. The mass ratio of the algal precursor to the sulfur source is 100: (1-10), for example, 100:1.3, 100:1.5, 100:2, 100:3, 100:5, or 100:

8. The gradient calcination comprises a first-stage calcination and a second-stage calcination.

3. The method for preparing biomass-based doped hard carbon material as described in claim 2, characterized in that, The temperature of the first-stage calcination is 160-400°C, for example, 200°C, 250°C, 300°C, 350°C, or 380°C. The time of the first-stage calcination is 1-8h, for example, 2h, 3h, 4h, 6h, or 7h. The temperature of the second-stage calcination is 800-1400°C, for example, 900°C, 950°C, 1000°C, 1050°C, 1100°C, or 1200°C. The time of the second-stage calcination is 1-12h, for example, 2h, 3h, 4h, 5h, or 8h.

4. The method for preparing biomass-based doped hard carbon material as described in claim 1, characterized in that, The acid used in the acid etching comprises one or more of citric acid, oxalic acid, tartaric acid, phosphoric acid, ethylenediaminetetraacetic acid, and malic acid, for example, citric acid. The mass concentration of the acid used in the acid etching is 3-20wt%, for example, 5% or 10%. The mass of the primary hard carbon to the volume of the acid in the acid etching is 0.1-5g / mL, preferably 0.1-2g / mL, for example, 0.3g / mL, 0.5g / mL, 0.8g / mL, 1g / mL, or 1.5g / mL. The temperature of the acid etching is 20-80°C, for example, 25°C, 30°C, or 50°C, preferably 40-80°C.

5. The method for preparing biomass-based doped hard carbon material as described in claim 1, characterized in that, The acid etching comprises the following processes: sequentially performing ultrasonic dispersion, stirring reaction, centrifugation, and drying on the mixture of the primary hard carbon and the acid. The algal precursor is further subjected to washing, drying, crushing, and sieving in sequence before use.

6. The method for preparing biomass-based doped hard carbon material as described in claim 5, characterized in that, The crushing is performed by ball milling. The mesh number of the sieve used in the sieving is 200-400, for example, 250, 300, or 350.

7. The method for preparing biomass-based doped hard carbon material as described in claim 6, characterized in that, The diameter of the grinding ball used in the ball milling is 5-20mm, for example, 10mm or 15mm. The ball-to-material ratio in the ball milling is (5-15):1, for example, 8:1 or 10:

1. The rotation speed of the ball milling is 200-500r / min, for example, 250r / min, 300r / min, or 400r / min. The time of the ball milling is 2-8h, for example, 4h or 6h.

8. A biomass-based doped hard carbon material prepared by the method of any one of claims 1-7.

9. Use of the biomass-based doped hard carbon material of claim 8 in a battery material.

10. A battery, characterized by comprising the biomass-based doped hard carbon material of claim 8.

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