Sucrose-based hard carbon nanosheet and preparation method and application thereof

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a sucrose-based hard carbon nanosheet and a preparation method and application thereof. The method comprises the following steps: dissolving sucrose and sodium chloride in water to obtain a mixed solution; performing thickening treatment on the mixed solution to form a colloidal substance, and then performing ball milling treatment to obtain a paste-like mixture; and performing calcination treatment on the paste-like mixture in an inert atmosphere to obtain the sucrose-based hard carbon nanosheet. Compared with the prior art, the preparation method is simpler and safer, the difficulty and danger of experimental operation under high temperature and high pressure are reduced, and a high-pressure hydrothermal reaction link required when hard carbon is prepared by using sucrose in a conventional manner is saved; the template agent is sodium chloride, which can be obtained through distillation again, so that the template agent can be reused and cost is saved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a sucrose-based hard carbon nanosheet and a preparation method and application thereof. BACKGROUND

[0002] In recent years, the demand for renewable energy storage has risen sharply, making the electrochemical storage technology of secondary batteries and supercapacitors develop unprecedentedly. Especially, lithium ion batteries, benefiting from high specific capacity, excellent cycle stability and long service life, occupy the majority of the market share. However, the reserves of lithium resources are not abundant and are extremely unevenly distributed. With the surge in demand for lithium ion batteries, lithium is becoming increasingly rare and expensive like gold, and it is only a matter of time. Sodium and lithium belong to the same group of elements, have similar electrochemical properties, and are abundant in resources, widely distributed and low in price, with reserves about 430 times that of lithium. Therefore, sodium ion batteries have become one of the next-generation energy storage battery technologies with great prospects and suitable for large-scale renewable energy applications.

[0003] Carbon-based materials are considered to be the most promising negative electrode materials for sodium ion batteries due to their low cost, abundant resources, non-toxicity and good electrical conductivity. Due to the large radius of sodium ions and the low binding energy with graphite, it is difficult for sodium ions to be intercalated and deintercalated between the layers of graphite, which makes it almost impossible for graphite to have reversible sodium intercalation capacity in sodium ion batteries. Hard carbon has a unique structure, i.e. microcrystalline, defects and nanopores, and has a unique sodium storage mechanism. In addition, it has the advantages of abundant raw materials, low cost, good electrical conductivity, environmental friendliness and high specific capacity, and is higher than commercial graphite, which is a potential negative electrode material for sodium ion batteries.

[0004] Currently, the core method for preparing hard carbon based on sucrose is hydrothermal-high temperature pyrolysis. This method usually needs to be carried out under high temperature and high pressure conditions, which has strict requirements on experimental environment conditions and significantly increases the risk of experimental operation. In addition, amine-based high-cost and toxic organic reagents need to be added during the reaction process, which further increases the preparation cost and also increases the difficulty of safety control.

[0005] It is worth noting that the hard carbon material prepared based on the existing process with sucrose is mostly in the form of spherical particles. Although such spherical particles have a very high specific surface area, which can improve the capacity of the hard carbon material, the side reactions caused by the spherical particles are also significantly enhanced during the first charge and discharge cycle, which has a significant adverse effect on the first charge and discharge coulombic efficiency. At the same time, the spherical particles have significant disadvantages in terms of ohmic contact characteristics between particles and ion transport efficiency. SUMMARY

[0006] In view of the problems in the prior art, the present application provides a sucrose-based hard carbon nanosheet and a preparation method and application thereof. The present application uses sucrose as a precursor, sodium chloride as a template agent and a peeling promoter, dissolves the sucrose and the sodium chloride in water together, and sequentially performs thickening, ball milling and calcination treatment. With the aid of the sodium chloride as the template agent and the peeling promoter, the sucrose bulk is peeled layer by layer, and finally the sucrose-based hard carbon nanosheet is obtained. Compared with the prior art, the present application realizes the directional conversion of the sucrose bulk to a two-dimensional nanosheet structure by using sodium chloride as the template agent and the peeling promoter, and successfully prepares the sucrose-based hard carbon nanosheet. The preparation method of the present application is simpler and safer in operation, not only reduces the difficulty and danger of experimental operation under high temperature and high pressure, but also eliminates the preparation step of high-pressure hydrothermal reaction required when sucrose is used to prepare hard carbon in the conventional way. In addition, the auxiliary agent used in the present application is sodium chloride, which can be obtained again by distillation, so it can be reused and cost is saved.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0008] The first object of the present application is to provide a preparation method of a sucrose-based hard carbon nanosheet, comprising the following steps:

[0009] S1. Using sucrose as a precursor and sodium chloride as a template agent, dissolving the sucrose and the sodium chloride in water together to obtain a mixed solution.

[0010] S2. Performing thickening treatment on the mixed solution to remove part of the water in the mixed solution and form a gelatinous substance, and then performing ball milling treatment on the gelatinous substance. The cubic crystal structure of the sodium chloride is embedded in the interior and surface of the gelatinous substance to form a composite gelatinous substance in which the sodium chloride crystals are embedded, and the mechanical force generated by the ball milling effectively reduces the thickness of the internal structural units of the gelatinous substance to obtain a paste-like mixture.

[0011] S3. Performing calcination treatment on the paste-like mixture in an inert atmosphere. In the process of increasing the calcination temperature, the sucrose is converted from an organic molecule to hard carbon through dehydration and carbonization, and is shaped under the space template action of the solid sodium chloride to limit the growth dimension of the hard carbon and guide it to form a hard carbon-sodium chloride composite with a cubic pore structure around the sodium chloride template. When the temperature increases and exceeds the melting point of the sodium chloride, the solid sodium chloride melts into a liquid state, and the cubic pore structure of the hard carbon collapses to form a nanosheet. After cooling to room temperature, the liquid sodium chloride completes the reversible phase change process and returns to a solid state. After removing the sodium chloride, the sucrose-based hard carbon nanosheet is obtained.

[0012] Preferably, the mass ratio of the sucrose to the sodium chloride is 0.1-10:1-100, and more preferably, the mass ratio of the sucrose to the sodium chloride is 1:20.

[0013] Preferably, the thickening treatment conditions are: stirring at 45℃~120℃ for 30min~150min to evaporate some of the water until the mixed solution becomes a white gel.

[0014] Preferably, the calcination conditions are: calcination at 900℃~1700℃ for 1h~8h with a heating rate of 1℃ / min~10℃ / min.

[0015] Preferably, the ball milling conditions in step S2 are: ball milling at 200 rpm to 2500 rpm for 30 min to 120 min, so that sodium chloride and sucrose can be fully contacted and the template effect can be fully utilized.

[0016] Preferably, the sodium chloride is ball-milled before dissolution to obtain fine sodium chloride crystals, resulting in faster and more complete dissolution. The ball-milling conditions are: ball milling at 200 rpm to 2500 rpm for 5 to 120 minutes.

[0017] Preferably, the water content in the gel is less than 5%.

[0018] Preferably, the inert atmosphere is selected from at least one of nitrogen or argon.

[0019] Preferably, the sucrose-based hard carbon nanosheets obtained in step S3 are further post-treated. The specific post-treatment operations are as follows:

[0020] Sucrose-based hard carbon nanosheets were subjected to ultrasonic cleaning, filtration, and drying processes to obtain hard carbon nanosheets.

[0021] Preferably, the drying conditions are: drying at 45℃~80℃ for 1h~6h.

[0022] Preferably, the ultrasonic treatment conditions are: ultrasonication at 15W~400W for 5min~120min.

[0023] A second objective of this invention is to provide sucrose-based hard carbon nanosheets prepared by the above-described method.

[0024] Preferably, the sucrose-based hard carbon nanosheets have a two-dimensional nanosheet structure.

[0025] A third objective of this invention is to provide the application of sucrose-based hard carbon nanosheets in the preparation of anode materials for sodium-ion batteries.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. This invention provides a method for preparing sucrose-based hard carbon nanosheets. Sucrose and sodium chloride are dissolved together in water to obtain a mixed solution. The mixed solution is thickened to remove some water and form a gel. The gel is then ball-milled, during which the cubic crystal structure of sodium chloride is embedded in the interior and surface of the gel, forming a composite colloid with embedded sodium chloride crystals. Simultaneously, the mechanical force generated by ball milling compresses the gel, effectively reducing the thickness of its internal structural units, resulting in a paste-like mixture. The paste-like mixture is calcined in an inert atmosphere. During calcination, sucrose undergoes dehydration and carbonization, transforming from organic molecules into hard carbon. Simultaneously, it is shaped by the spatial template effect of sodium chloride, forming a hard carbon-sodium chloride composite with a cubic porous structure. As the temperature further increases and exceeds the melting point of sodium chloride, the sodium chloride melts into a liquid state, causing the cubic porous structure of the hard carbon to collapse and form nanosheets. After cooling to room temperature, the sodium chloride returns to a solid state. After removing the sodium chloride, sucrose-based hard carbon nanosheets are obtained. The preparation method of this invention differs significantly from existing high-temperature hydrothermal processes, eliminating the reliance on high-temperature and high-pressure conditions inherent in traditional methods and effectively reducing safety risks during production. Furthermore, process optimization simplifies the operation steps, demonstrating greater process feasibility and cost advantages while maintaining the performance of sucrose-based hard carbon nanosheets.

[0028] 2. This invention employs a thickening process combined with ball milling technology. The thickening process utilizes a low-temperature thickening method to achieve uniform dispersion of sodium chloride and sucrose in a colloidal system, forming a stable gel. The subsequent ball milling process uses mechanical force to compress the gel, reducing the thickness of the structural units and further enhancing the mixing uniformity of sucrose and sodium chloride. It also provides the necessary energy input for the phase transition of sucrose to two-dimensional nanosheet structures, thereby achieving the effective exfoliation and preparation of sucrose-based hard carbon nanosheets.

[0029] 3. Compared to the spherical particle structure prepared by the traditional hydrothermal method, the sucrose-based hard carbon nanosheets prepared in this invention exhibit a two-dimensional nanosheet structure, fully retaining the typical advantages of two-dimensional materials. Specifically, its two-dimensional nanosheet structure endows the sucrose-based hard carbon nanosheets with excellent ionic conductivity. By shortening the transport path between ions and electrons, it effectively promotes the charge transport kinetics process, thereby improving the electrochemical performance of sodium-ion batteries. Especially in terms of rate performance, compared to the sucrose-based hard carbon nanosphere materials reported in existing literature, the two-dimensional nanosheet structure of this invention enhances the ion diffusion kinetics, enabling sodium-ion batteries to maintain a relatively high specific capacity even under high current density charge and discharge conditions.

[0030] 4. The sodium chloride used in this invention is a template agent, which can be fully separated from the sucrose-based hard carbon nanosheets after the calcination process. After distillation, the sodium chloride can be recovered and reused, significantly reducing the cost of raw materials. Furthermore, the sucrose raw material used in this invention is derived from natural biomass resources such as sugarcane or sugar beets, which are not only inexpensive and widely available but also readily accessible. Simultaneously, sucrose has a high carbon content, exhibiting excellent conversion efficiency during carbonization, effectively reducing side reactions and thus improving the overall efficiency of the carbonization process. Attached Figure Description

[0031] Figure 1 The images shown are scanning electron microscope (SEM) images of the sucrose-based hard carbon nanosheets prepared in Example 1, where a is a low-magnification image and b is a high-magnification image.

[0032] Figure 2 The images shown are scanning electron microscope (SEM) images of the sucrose-based hard carbon nanosheets prepared in Example 2, where a is a low-magnification image and b is a high-magnification image.

[0033] Figure 3 The images shown are scanning electron microscope (SEM) images of the sucrose-based hard carbon prepared in Comparative Example 1, where a is a low-magnification image and b is a high-magnification image.

[0034] Figure 4 The graph shows the initial charge-discharge curves of the battery using sucrose-based hard carbon nanosheets from Example 1 at a current density of 250 mA / g. The break in the discharge curve in the graph does not affect the test results.

[0035] Figure 5 The discharge specific capacity diagram of the battery using sucrose-based hard carbon nanosheets from Example 1 at different current densities is shown. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the data in 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.

[0037] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased on the market or prepared by existing methods.

[0038] In existing technologies, although the hydrothermal-high-temperature pyrolysis method has been widely used for the preparation of sucrose-based hard carbon materials, this method typically requires extreme conditions of high temperature and high pressure, which not only imposes stringent requirements on experimental equipment and environment but also significantly increases the safety risks of experimental operations. Furthermore, this method requires the introduction of high-cost and toxic organic reagents such as amines during the reaction process, further increasing the preparation cost and exacerbating the difficulty of safety control. More importantly, sucrose-based hard carbon materials prepared using existing processes often exhibit a spherical particle morphology. While this morphology improves the specific surface area and capacity of the hard carbon material, spherical particles are prone to initiating significant side reactions during the first charge-discharge cycle, adversely affecting the first charge-discharge coulombic efficiency. Simultaneously, spherical particles also exhibit significant disadvantages in terms of interparticle ohmic contact characteristics and ion transport efficiency, limiting their performance in sodium-ion batteries.

[0039] To address the problems existing in the prior art, this invention provides a method for preparing sucrose-based hard carbon nanosheets, comprising the following steps: dissolving sucrose and sodium chloride together in water to obtain a mixed solution; thickening the mixed solution to remove some water and form a gel; then ball milling the gel, embedding the cubic crystal structure of sodium chloride into the interior and surface of the gel to form a composite colloid with embedded sodium chloride crystals, resulting in a paste-like mixture; calcining the paste-like mixture in an inert atmosphere, during which the sucrose undergoes dehydration and carbonization, transforming from organic molecules into hard carbon, and is shaped under the spatial template of solid sodium chloride to form a hard carbon-sodium chloride composite with a cubic pore structure; when the temperature rises and exceeds the melting point of sodium chloride, the solid sodium chloride melts into a liquid state, and the cubic pore structure of the hard carbon collapses to form nanosheets; after cooling to room temperature, the liquid sodium chloride returns to a solid state, and after removing the sodium chloride, sucrose-based hard carbon nanosheets are obtained.

[0040] To address the issue that existing high-pressure hydrothermal-high-temperature pyrolysis methods require extreme high-temperature and high-pressure conditions, this invention overcomes this problem by combining atmospheric pressure low-temperature thickening with ball milling. Specifically, it abandons the high-pressure hydrothermal reactor and uses an oil bath at 45℃~120℃ under atmospheric pressure to colloidalize a mixed solution of sucrose and sodium chloride to obtain a gel-like substance. Ball milling is then used to achieve uniform dispersion and pre-peeling of the gel-like substance, significantly reducing equipment requirements and operational safety risks.

[0041] To address the issue of existing technologies requiring the introduction of high-cost organic reagents, this invention overcomes this problem by using sodium chloride as a template and stripping accelerator. Sodium chloride is non-toxic, inexpensive, and can be recycled and reused after washing with water, which not only reduces raw material costs but also avoids environmental pollution and health hazards to operators caused by organic reagents.

[0042] To address the problems of side reactions, low coulombic efficiency, and high interfacial contact resistance caused by spherical hard carbon particles prepared by existing technologies, the sucrose-based hard carbon nanosheets of the present invention have a two-dimensional nanosheet structure. In sodium-ion battery applications, this structure shortens the sodium ion diffusion path, reduces the interparticle contact resistance, and relatively reduces the specific surface area, thereby suppressing side reactions and improving the first charge-discharge coulombic efficiency to over 92%.

[0043] The technical solution of the present invention will be further explained and illustrated below with examples, as detailed below:

[0044] Example 1

[0045] A method for preparing sucrose-based hard carbon nanosheets includes the following steps:

[0046] S1. Place sodium chloride in a ball mill jar and ball mill at 1500 r / min for 30 min to obtain fine sodium chloride crystals; add 20 g of fine sodium chloride crystals and 1 g of sucrose to 20 mL of deionized water and stir strongly with a magnetic force for 30 min to obtain a mixed solution.

[0047] S2. Place the mixed solution in an oil bath and heat and stir at 98°C for 150 minutes until it thickens to a honey-like colloidal state, i.e., the mixed colloid. Transfer the mixed colloid to a stainless steel ball mill jar for ball milling at 1500 rpm for 90 minutes to obtain a paste-like mixture.

[0048] S3. Transfer the paste mixture to a ceramic boat and place it in a tube furnace for calcination. Under an argon atmosphere, heat it to 1300°C at a heating rate of 5°C / min, hold it at that temperature for 4 hours, and then allow it to cool naturally to obtain a black powder.

[0049] S4. Ultrasonically clean the black powder with deionized water, filter it after cleaning, and then place it in an oven to dry at 60°C for 8 hours to obtain sucrose-based hard carbon nanosheets.

[0050] Example 2

[0051] A method for preparing sucrose-based hard carbon nanosheets is the same as that in Example 1, except that the amount of fine sodium chloride crystals in S1 is replaced from 20g to 10g, and includes the following steps:

[0052] S1. Place sodium chloride in a ball mill jar and ball mill at 1500 r / min for 30 min to obtain fine sodium chloride crystals; add 10 g of fine sodium chloride crystals and 1 g of sucrose to 20 mL of deionized water and stir strongly with a magnetic force for 30 min to obtain a mixed solution.

[0053] S2. Place the mixed solution in an oil bath and heat and stir at 98°C for 150 minutes until it thickens to a honey-like colloidal state, i.e., the mixed colloid. Transfer the mixed colloid to a stainless steel ball mill jar for ball milling at 1500 rpm for 90 minutes to obtain a paste-like mixture.

[0054] S3. Transfer the paste mixture to a ceramic boat and place it in a tube furnace for calcination. Under an argon atmosphere, heat it to 1300°C at a heating rate of 5°C / min, hold it at that temperature for 4 hours, and then allow it to cool naturally to obtain a black powder.

[0055] S4. Ultrasonically clean the black powder with deionized water, filter it after cleaning, and then place it in an oven to dry at 60°C for 8 hours to obtain sucrose-based hard carbon nanosheets.

[0056] Example 3

[0057] A method for preparing sucrose-based hard carbon nanosheets is the same as that in Example 1, except that the amount of fine sodium chloride crystals in S1 is replaced from 20g to 1000g, and includes the following steps:

[0058] S1. Place sodium chloride in a ball mill jar and ball mill at 1500 r / min for 30 min to obtain fine sodium chloride crystals; add 1000 g of fine sodium chloride crystals and 1 g of sucrose to 20 mL of deionized water and stir strongly with a magnetic force for 30 min to obtain a mixed solution.

[0059] S2. Place the mixed solution in an oil bath and heat and stir at 98°C for 150 minutes until it thickens to a honey-like colloidal state, i.e., the mixed colloid. Transfer the mixed colloid to a stainless steel ball mill jar for ball milling at 1500 rpm for 90 minutes to obtain a paste-like mixture.

[0060] S3. Transfer the paste mixture to a ceramic boat and place it in a tube furnace for calcination. Under an argon atmosphere, heat it to 1300°C at a heating rate of 5°C / min, hold it at that temperature for 4 hours, and then allow it to cool naturally to obtain a black powder.

[0061] S4. Ultrasonically clean the black powder with deionized water, filter it after cleaning, and then place it in an oven to dry at 60°C for 8 hours to obtain sucrose-based hard carbon nanosheets.

[0062] Example 4

[0063] A method for preparing sucrose-based hard carbon nanosheets is the same as that in Example 1, except that the amount of fine sodium chloride crystals in S1 is replaced from 20g to 0.1g, and includes the following steps:

[0064] S1. Place sodium chloride in a ball mill jar and ball mill at 1500 r / min for 30 min to obtain fine sodium chloride crystals; add 0.1 g of fine sodium chloride crystals and 1 g of sucrose together to 20 mL of deionized water, stir strongly with a magnetic force for 30 min to obtain a mixed solution.

[0065] S2. Place the mixed solution in an oil bath and heat and stir at 98°C for 150 minutes until it thickens to a honey-like colloidal state, i.e., the mixed colloid. Transfer the mixed colloid to a stainless steel ball mill jar for ball milling at 1500 rpm for 90 minutes to obtain a paste-like mixture.

[0066] S3. Transfer the paste mixture to a ceramic boat and place it in a tube furnace for calcination. Under an argon atmosphere, heat it to 1300°C at a heating rate of 5°C / min, hold it at that temperature for 4 hours, and then allow it to cool naturally to obtain a black powder.

[0067] S4. Ultrasonically clean the black powder with deionized water, filter it after cleaning, and then place it in an oven to dry at 60°C for 8 hours to obtain sucrose-based hard carbon nanosheets.

[0068] Example 5

[0069] A method for preparing sucrose-based hard carbon nanosheets, which is the same as the preparation method in Example 1, includes the following steps:

[0070] S1. Place sodium chloride in a ball mill jar and ball mill at 1500 r / min for 30 min to obtain fine sodium chloride crystals; add 20 g of fine sodium chloride crystals and 1 g of sucrose to 20 mL of deionized water and stir strongly with a magnetic force for 30 min to obtain a mixed solution.

[0071] S2. Place the mixed solution in an oil bath and heat and stir at 45°C for 90 minutes until it thickens into a honey-like colloidal state, i.e., the mixed colloid. Transfer the mixed colloid to a stainless steel ball mill jar for ball milling at 2500 rpm for 30 minutes to obtain a paste-like mixture.

[0072] S3. Transfer the paste mixture to a ceramic boat and place it in a tube furnace for calcination. Under an argon atmosphere, heat it to 1700°C at a heating rate of 10°C / min, hold it at that temperature for 1 hour, and then allow it to cool naturally to obtain a black powder.

[0073] S4. Ultrasonically clean the black powder with deionized water, filter it after cleaning, and then place it in an oven to dry at 60°C for 8 hours to obtain sucrose-based hard carbon nanosheets.

[0074] Example 6

[0075] A method for preparing sucrose-based hard carbon nanosheets, which is the same as the preparation method in Example 1, includes the following steps:

[0076] S1. Place sodium chloride in a ball mill jar and ball mill at 1500 r / min for 30 min to obtain fine sodium chloride crystals; add 20 g of fine sodium chloride crystals and 1 g of sucrose to 20 mL of deionized water and stir strongly with a magnetic force for 30 min to obtain a mixed solution.

[0077] S2. Place the mixed solution in an oil bath and heat and stir at 120°C for 30 minutes until it thickens into a honey-like colloidal state, i.e., the mixed colloid. Transfer the mixed colloid to a stainless steel ball mill jar for ball milling at 200 rpm for 120 minutes to obtain a paste-like mixture.

[0078] S3. Transfer the paste mixture to a ceramic boat and place it in a tube furnace for calcination. Under an argon atmosphere, heat it to 900°C at a heating rate of 1°C / min, hold it at that temperature for 8 hours, and then allow it to cool naturally to obtain a black powder.

[0079] S4. Ultrasonically clean the black powder with deionized water, filter it after cleaning, and then place it in an oven to dry at 60°C for 8 hours to obtain sucrose-based hard carbon nanosheets.

[0080] Comparative Example 1

[0081] A method for preparing sucrose-based hard carbon is the same as that in Example 1, except that the amount of fine sodium chloride crystals in S1 is replaced with 0g instead of 20g, and includes the following steps:

[0082] S1. Add 1g of sucrose to 20mL of deionized water and stir strongly with a magnetic force for 30min to obtain a sucrose solution.

[0083] S2. Place the sucrose solution in an oil bath and heat and stir at 98°C until it thickens into a honey-like colloidal state, i.e., sucrose colloid. Transfer the sucrose colloid to a stainless steel ball mill jar for ball milling at 1500 rpm for 90 minutes to obtain a paste-like sucrose.

[0084] S3. Transfer the sucrose paste to a ceramic boat and place it in a tube furnace for calcination. Under an argon atmosphere, heat it to 1300°C at a heating rate of 5°C / min, hold it at that temperature for 4 hours, and then allow it to cool naturally to obtain a black powder.

[0085] S4. Ultrasonically clean the black powder with deionized water, filter it after cleaning, and then place it in an oven to dry at 60°C for 8 hours to obtain sucrose-based hard carbon.

[0086] Figure 1The results demonstrate that sucrose-based hard carbon nanosheets were successfully prepared using sucrose as a precursor and sodium chloride as a template. These sucrose-based hard carbon nanosheets exhibit a two-dimensional sheet-like structure with an average thickness of 90 nm and a size ranging from 3 μm to 15 μm. High-magnification SEM images further reveal that the sucrose-based hard carbon nanosheets are assembled from fine particles, indicating that they possess a large specific surface area, which is beneficial for electrolyte storage and provides more active sites.

[0087] Figure 2 The results show that reducing the mass ratio of sodium chloride to sucrose from 20:1 to 10:1 has a significant impact on the two-dimensional nanosheet structure of sucrose-based hard carbon nanosheets. Macroscopically, the two-dimensional nanosheet structure no longer dominates the product; most of the particles are bulk particles. This result indicates that sodium chloride plays an important role as a template in nanosheet formation, and its ratio to sucrose also plays a crucial role in the final formation of sucrose-based hard carbon nanosheets.

[0088] Figure 3 The results show that the sucrose-based hard carbon prepared in Comparative Example 1 without the addition of sodium chloride has a surface composed of bulk particles ranging from 40 to hundreds of micrometers. Figure 2 The results further validated the role of sodium chloride as a template agent in the preparation of two-dimensional sucrose-based hard carbon nanosheets.

[0089] In Examples 1 through 3 of this invention, sucrose-based hard carbon nanosheets were prepared with parallel results. The electrochemical performance of the sucrose-based hard carbon nanosheets prepared in Example 1 will be studied below:

[0090] The preparation method of sodium-ion battery negative electrode and battery assembly method are as follows:

[0091] Sucrose-based hard carbon nanosheets and sodium alginate were mixed at a mass ratio of 95:5 to form a slurry. The slurry was then uniformly coated onto copper foil using a doctor blade method and dried under vacuum at 120°C for 12 hours to obtain the anode for a sodium-ion battery. The loading of sucrose-based hard carbon nanosheets was 2.3 mg / cm³. 2 ;

[0092] The assembly of coin cells in an argon-filled glove box was as follows: Sodium-ion battery negative electrode material was placed in the negative electrode shell of a CR2032 battery, using 1 mol / L NaClO4 as the electrolyte. A Whatman GF / F glass fiber separator was then placed on top, followed by a sodium metal sheet as the counter electrode. Gaskets and springs were added, and finally, the positive electrode shell was covered. Under conditions where humidity and oxygen concentration within the glove box were strictly controlled below 0.1 ppm, the battery was sealed into CR2032 coin cells using a battery sealing machine.

[0093] The testing method is as follows:

[0094] a. Initial coulombic efficiency: The charge / discharge cutoff voltage of the battery was set to 0.01V~3V, and the current density was 50mA / g. Only the first charge / discharge test was performed. Based on the charge specific capacity and discharge specific capacity, the initial coulombic efficiency of the sucrose-based hard carbon nanosheets as the negative electrode of a sodium-ion battery was calculated.

[0095] b. Rate performance: Seven gradient current densities were set, specifically 20mA / g, 50mA / g, 100mA / g, 150mA / g, 200mA / g, 250mA / g and 300mA / g, and constant current charge-discharge cycle tests were performed. After 10 cycles at each current density, the test was switched to the next density.

[0096] Depend on Figure 4 The results showed that the battery using sucrose-based hard carbon nanosheets from Example 1 had an initial discharge specific capacity of 217.1 mAh / g, a charge specific capacity of 201.5 mAh / g, and an initial charge-discharge coulombic efficiency of 92.9% at a current density of 250 mA / g.

[0097] Cyclic stability test results are as follows Figure 5 As shown, the battery using sucrose-based hard carbon nanosheets from Example 1 achieved an initial discharge specific capacity of 332.5 mAh / g and a coulombic efficiency of 91.8% at an initial current density of 20 mA / g. As the current density gradually increased to 300 mA / g, the sucrose-based hard carbon nanosheet anode maintained a reversible specific capacity of 194.6 mAh / g, demonstrating excellent rate performance. Importantly, when the current density decreased from 300 mA / g back to 20 mA / g, the specific capacity of the sucrose-based hard carbon nanosheet anode rapidly recovered to 98% of its initial value, exhibiting excellent structural stability and cycle reversibility. This sucrose-based hard carbon nanosheet anode demonstrates high specific capacity, excellent rate performance, and cycle stability over a wide current density range, fully validating its feasibility and application potential as a sodium-ion battery anode material. The results of this invention provide new research ideas for the development of high-performance sodium-ion battery electrode materials.

[0098] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A method for preparing sucrose-based hard carbon nanosheets, characterized in that, Includes the following steps: Sucrose and sodium chloride are dissolved together in water to obtain a mixed solution; The mixed solution is thickened to remove some of the water and form a gel. The gel is then ball-milled, and the cubic crystal structure of sodium chloride is embedded in the interior and surface of the gel, forming a composite colloid with embedded sodium chloride crystals, resulting in a paste-like mixture. In an inert atmosphere, a paste-like mixture is calcined. During the calcination process, sucrose undergoes dehydration and carbonization, transforming from organic molecules into hard carbon. Under the spatial template of solid sodium chloride, it is shaped to form a hard carbon-sodium chloride composite with a cubic pore structure. When the temperature rises and exceeds the melting point of sodium chloride, the solid sodium chloride melts into a liquid state, and the cubic pore structure of the hard carbon collapses to form nanosheets. After cooling to room temperature, the liquid sodium chloride returns to a solid state. After removing the sodium chloride, sucrose-based hard carbon nanosheets are obtained. The thickening conditions are: stirring at 45℃~120℃ for 30min~150min.

2. The method for preparing sucrose-based hard carbon nanosheets according to claim 1, characterized in that, The mass ratio of sucrose to sodium chloride is 0.1~10:1~100.

3. The method for preparing sucrose-based hard carbon nanosheets according to claim 1, characterized in that, The calcination conditions are: calcination at 900℃~1700℃ for 1h~8h.

4. The method for preparing sucrose-based hard carbon nanosheets according to claim 1, characterized in that, The ball milling conditions are: ball milling at 200 rpm to 2500 rpm for 30 min to 120 min.

5. The method for preparing sucrose-based hard carbon nanosheets according to claim 1, characterized in that, The water content in the gel is less than 5%.

6. A sucrose-based hard carbon nanosheet, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 5.

7. The sucrose-based hard carbon nanosheets according to claim 6, characterized in that, Sucrose-based hard carbon nanosheets have a two-dimensional nanosheet structure.

8. The application of the sucrose-based hard carbon nanosheets of claim 6 in the preparation of anode materials for sodium-ion batteries.

Images