Bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention discloses a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material as well as a preparation method and application thereof, belongs to the technical field of secondary battery negative electrode materials, and relates to a preparation method of a core-shell structure porous hard carbon material. According to the bagasse-based sodium-ion battery hard carbon negative electrode material and the preparation method thereof disclosed by the invention, the optimization of an ion transmission path and the enhancement of interface stability are realized by virtue of a synergistic strategy of constructing pores by virtue of bagasse and asphalt composite core-shell interface engineering and gas activation, and the bagasse-based sodium-ion battery hard carbon negative electrode material with high first efficiency, high capacity and good cycling stability is successfully prepared. According to the preparation method, soft and hard carbon interface reconstruction and gas activation pore channel design are innovatively coupled, and a new way is provided for development of a high-first-efficiency and long-cycle sodium ion battery negative electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material and a preparation method thereof. Background Art

[0002] Growing energy demand is driving a shift from fossil fuels to renewable energy sources such as wind and solar power. However, the intermittent nature of these renewable energy sources makes the development of viable energy storage devices crucial. Electrochemical energy storage is considered a highly effective energy storage technology due to its high energy conversion efficiency, relatively compact size, and fast response time. Among the numerous electrochemical energy storage devices, lithium-ion batteries (LIBs) are currently the dominant energy storage solution. However, the accelerating global energy transition is leading to an increasing shortage of lithium resources, as lithium reserves are limited in the Earth's crust and are highly concentrated geographically. This has driven the development of sodium-ion batteries (SIBs), which offer abundant and low-cost resources. However, the large atomic radius of sodium ions makes conventional graphite anodes in lithium-ion batteries unsuitable for storage needs, necessitating the development of novel anode materials. Hard carbon materials, with their unique disordered carbon layer structure and extended interlayer spacing, can effectively accommodate the insertion and adsorption of sodium ions, making them a key research focus for SIB anodes. Compared to graphite, hard carbon materials exhibit higher specific capacity and improved cycling stability while avoiding the safety risks associated with sodium dendrites.

[0003] Currently, hard carbon materials are mainly divided into three categories based on the source of their precursors: petroleum-based, polymer-based, and biomass-based. Petroleum-based hard carbon uses asphalt or coal tar as raw materials. Although it has certain graphitization properties, its low porosity leads to insufficient cycle performance. Polymer-based hard carbon is prepared by synthesizing high-molecular materials. Its structural design is flexible, but its cost is high and it is difficult to apply on a large scale. Biomass-based hard carbon uses agricultural and forestry waste such as coconut shells and straw as raw materials. It stands out due to its natural porous structure and easy availability of raw materials. Not only is the preparation cost of this type of material significantly lower than that of petroleum-based products, but its rich internal nanopores and defect sites can also optimize the sodium ion transmission path, showing excellent electrochemical performance.

[0004] Despite the broad prospects of biomass hard carbon, its practical application still faces key challenges. The low efficiency in the first cycle is mainly due to the irreversible side reaction between the active groups on the surface of the material and the electrolyte, while the structural collapse during long cycles leads to capacity decay. Recent research has made progress through surface modification and microstructure regulation. For example, passivation treatment is used to reduce side reactions and gradient pores are constructed to optimize ion transport channels, which significantly improves the cycle stability. However, the sodium storage mechanism of biomass hard carbon has not been fully elucidated, and the synergistic effect of intercalation, adsorption and pore filling still needs to be further analyzed. It is necessary to further combine material design and process optimization to develop low-cost, high-efficiency preparation technologies to promote its large-scale application in the field of energy storage. Summary of the Invention

[0005] In response to the problems of insufficient initial efficiency, low capacity and poor cycle stability of sugarcane bagasse-based hard carbon negative electrode materials in the prior art, the present invention provides a sugarcane bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material and its preparation method and application. It is also a core-shell structure porous hard carbon sodium ion battery negative electrode material and its preparation method and application based on the synergistic strategy of core-shell interface engineering and gas activation.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0007] A method for preparing a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material comprises the following steps:

[0008] S1, washing, drying, mechanically crushing, and sieving bagasse to obtain bagasse powder;

[0009] S2. mixing bagasse powder and asphalt by ball milling, wherein the amount of asphalt added is 5-30% by mass of the bagasse, to obtain a core-shell precursor;

[0010] S3, pre-carbonizing the obtained core-shell precursor in an inert atmosphere at 300-500° C. for 2-4 hours;

[0011] S4, introducing activation gas into the reaction system and performing activation treatment at 600-800°C for 2-6 hours; the activation gas is carbon dioxide gas;

[0012] S5, carbonizing the activated powder at 900-1300° C. in an inert atmosphere for 2-4 hours to obtain a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material;

[0013] The core-shell structure porous hard carbon negative electrode material is obtained by activating a mixture of sugarcane bagasse and asphalt in a carbon dioxide gas atmosphere and calcining it in an inert gas atmosphere; the core-shell structure porous hard carbon negative electrode material has a first-cycle coulomb efficiency of 77.73-82.40%, a 0.1C gram capacity of 251.28-341.43 mAh / g, and a capacity retention rate of 81.20-92.50%.

[0014] Furthermore, the drying in S1 is carried out at a temperature of 80-120° C. for 8-12 hours; and the screening is carried out through a 100-300 mesh sieve.

[0015] Furthermore, the ball milling described in S2 has a rotation speed of 300-500 r / min and a time of 4-8 h.

[0016] Furthermore, the inert atmosphere described in S3 is nitrogen or argon; and the heating rate of the pre-carbonization treatment is 2-10°C / min.

[0017] Further, in S3, activation treatment is performed at 600-800° C. for 1-4 hours.

[0018] Furthermore, the inert atmosphere described in S5 is nitrogen or argon.

[0019] The present invention also relates to a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material, which is obtained by using the above-mentioned preparation method of the bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material. The core-shell structure porous hard carbon negative electrode material has a first-cycle coulombic efficiency of 77.73-82.40%, a 0.1C gram capacity of 251.28-341.43 mAh / g, and a capacity retention rate of 81.20-92.50%.

[0020] The present invention also relates to the application of the above-mentioned bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material as a negative electrode active material for preparing a sodium ion battery.

[0021] Furthermore, it is used as a negative electrode active material to prepare the negative electrode of a sodium ion battery.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention describes a bagasse-based core-shell porous hard carbon anode material for sodium-ion batteries. Using bagasse as a biomass precursor, the material utilizes a synergistic strategy of core-shell interface engineering and gas activation to create pores. This allows for the targeted construction of a hard carbon composite anode material with both heterogeneous interface enhancement and multi-level pore synergy. This systematically addresses the technical bottlenecks of traditional biomass hard carbon, which suffer from low initial efficiency, limited rate performance, and poor cycling stability. In existing technologies, the traditional single carbonization process results in a disordered pore structure, insufficient surface active sites, and a lack of precise control over the electrode interface, leading to problems such as sluggish sodium ion transport kinetics, low initial Coulombic efficiency, and cyclic stress accumulation. The present invention innovatively combines a bagasse-derived hard carbon core phase with an asphalt-derived carbon shell to form a core-shell heterogeneous structure: the outer continuous carbon shell inhibits electrolyte decomposition and stabilizes SEI film formation through chemical inertness, and the hierarchical porous structure within the core synergistically optimizes sodium ion adsorption, diffusion and volume strain adaptability; the staged gas activation technology simultaneously realizes directional etching of the core-shell interface and pore structure regulation, constructs an ion transmission channel that penetrates the shell layer, and significantly improves the efficiency of interfacial electron conduction and ion migration.

[0024] 2. The present invention describes a method for preparing a porous hard carbon negative electrode material with a core-shell structure based on bagasse for sodium ion batteries. From the perspective of preparation process and sustainability, the present invention breaks through the limitations of the complex multi-step coating process of traditional core-shell materials. Bagasse and asphalt precursors are compounded by ball milling, and pore construction and interface functionalization design are simultaneously completed in combination with staged gas activation, which greatly simplifies the production process and reduces energy consumption. The synergistic effect of the core-shell heterogeneous interface and the multi-level pores not only enhances the structural stability of the material, but also achieves stable ion transmission at high rates by synergistically buffering volume deformation through large pores and elastic interfaces. Compared with petroleum-based or template-based hard carbon materials, this solution uses agricultural waste bagasse and low-cost asphalt as raw materials, avoids the use of highly polluting additives or complex post-processing processes, and achieves the organic unity of resource recycling and green manufacturing while improving electrochemical performance, providing an innovative technical path for the large-scale development of negative electrode materials for sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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.

[0026] Figure 1 This is an SEM image of a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material obtained in Example 4 of the present invention;

[0027] Figure 2 This is an XRD powder diffraction pattern of a bagasse-based sodium ion battery core-shell structure porous hard carbon anode material obtained in Example 4 of the present invention;

[0028] Figure 3 This is a 0.1C first cycle charge-discharge curve of a bagasse-based sodium ion battery core-shell structure porous hard carbon anode material obtained in Example 4 of the present invention;

[0029] Figure 4 This is a 0.1C cycle performance curve of a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material obtained in Example 4 of the present invention. DETAILED DESCRIPTION

[0030] Below in conjunction with embodiment and example, embodiment of the present invention is described in detail, but those skilled in the art will appreciate that the following embodiment and example are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Unspecified conditions are carried out according to the conditions of normal conditions or manufacturer's recommendations. Reagents used or instruments not specified by the manufacturer are conventional products that can be purchased commercially.

[0031] The present invention provides a method for preparing a negative electrode material for a sodium ion battery, comprising the steps of:

[0032] S1, washing, drying, mechanically crushing, and sieving bagasse to obtain bagasse powder;

[0033] S2, mixing bagasse powder and a certain amount of asphalt by ball milling to obtain a core-shell precursor;

[0034] S3, pre-carbonizing the core-shell precursor in an inert atmosphere at 300-500° C. for 2-4 hours;

[0035] S4, introducing activation gas into the reaction system and performing activation treatment at 600-800°C for 1-4 hours;

[0036] S5. Carbonizing the activated powder in an inert atmosphere at 900-1300° C. for 2-4 hours.

[0037] In a specific embodiment of the present invention, in step S1, the sugarcane bagasse is washed with water to remove surface impurities, and after drying, it is mechanically crushed and sifted to obtain raw material powder with uniform particle size, which provides a basis for the uniform reaction of subsequent carbonization activation and improves the consistency of material structure.

[0038] In a specific embodiment of the present invention, in step S2, the pre-treated sugarcane bagasse micron powder and asphalt are uniformly compounded through a ball milling process. Based on the mechanical shear force and interfacial energy regulation, the asphalt component is directed to be coated on the surface of the biomass carbon, forming a core-shell precursor with a dense binding interface, laying the foundation for the stable evolution of the heterogeneous structure during the subsequent carbonization process. The amount of asphalt added is preferably 5-30% of the mass of the sugarcane bagasse. The rotation speed of the ball milling treatment is preferably 300-500r / min, for example, 300, 400, 500r / min; the time of the ball milling treatment is preferably 4-8h, for example, 4, 5, 6, 7, 8h, etc.

[0039] In a specific embodiment of the present invention, in step S3, the pre-carbonization treatment can effectively remove the volatile components in the bagasse and preliminarily form a carbon skeleton structure, providing a stable foundation for the construction of a porous network in the subsequent activation stage, while avoiding the structural collapse caused by high-temperature direct carbonization. The pre-carbonization temperature is preferably 300-500°C, for example, 300, 350, 400, 450, 500°C; the pre-carbonization time is preferably 2-4h, for example, 2, 3, 4h, etc.; during the pre-carbonization process, the temperature is increased to 300-500°C at a heating rate of 2°C / min; as an example, the gas in the inert atmosphere can be nitrogen.

[0040] In a specific embodiment of the present invention, in step S4, the activation gas is carbon dioxide gas.

[0041] In a specific embodiment of the present invention, in step S4, calcining the bagasse powder under a carbon dioxide atmosphere can directionally etch the carbon skeleton to form a continuous hierarchical porous structure, and simultaneously control the surface chemical state to enhance the sodium ion adsorption capacity. The calcination temperature is preferably 600-800°C, for example, 600, 650, 700, 750, 800°C; the calcination time is preferably 1-4 hours, for example, 1, 2, 3, 4 hours; during the calcination process, the temperature is increased to 600-800°C at a heating rate of 5°C / min.

[0042] In a specific embodiment of the present invention, in step S5, the high-temperature carbonization treatment can promote the orderly arrangement of graphite crystallites in the carbon skeleton of sugarcane bagasse, enhance the electrical conductivity and mechanical strength of the material, while retaining the porous structure constructed in the activation stage, and finally form a hard carbon negative electrode with high sodium ion storage capacity and stable cycle performance. The calcination temperature is preferably 900-1300°C, for example, 900, 1000, 1100, 1200, 1300°C; the calcination time is preferably 2-4h, for example, 2, 3, 4h; during the calcination process, the temperature is increased to 900-1300°C at a heating rate of 5°C / min; as an example, the gas in the inert atmosphere can be nitrogen.

[0043] The present invention also provides a negative electrode plate, comprising the above-mentioned sodium ion battery negative electrode material.

[0044] The sodium ion battery prepared with this negative electrode sheet can effectively improve the energy density of the battery while also taking into account the intrinsic material characteristics of long cycle and high safety.

[0045] The negative electrode sheet can be prepared using a common sheet preparation process in the art. For example, the negative electrode material, conductive agent, and binder are mixed to form a slurry, which is then coated on at least one side of the negative electrode current collector. The slurry is then dried and pressed to obtain the negative electrode sheet.

[0046] In the above-mentioned method for preparing the negative electrode sheet, the type and content of the conductive agent are not specifically limited and can be selected according to actual needs. In some embodiments, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, acetylene black, graphene, carbon nanofibers, etc. It should be understood that other conductive agents that can achieve the functions of the present application can be selected as needed without departing from the spirit of the present application, without being limited by these.

[0047] In the above-mentioned electrode sheet preparation method, the type and content of the binder are not specifically limited and can be selected according to actual needs. In some embodiments, the binder includes at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, sodium polyacrylate, polyacrylamide, and polyamide.

[0048] The type of the negative electrode current collector is not particularly limited and can be selected according to actual needs. For example, the negative electrode current collector can be aluminum foil, copper foil or a polymer conductive film. Preferably, the negative electrode current collector is aluminum foil.

[0049] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0050] Example 1:

[0051] A method for preparing a core-shell structured porous hard carbon material of the present invention comprises the following steps:

[0052] S1. Raw material preparation: Rinse the bagasse with deionized water several times, dry it in a forced air drying oven at 80°C for 12 hours, then mechanically crush it, and pass the mechanically crushed material through a 100-mesh sieve to obtain bagasse powder;

[0053] S2. Preparation of core-shell precursor: Bagasse powder and 10 wt% asphalt were placed in a ball mill and ball milled at 350 rpm for 6 h to obtain core-shell precursor powder;

[0054] S3, pre-carbonization treatment: the core-shell precursor powder was placed in a tube furnace, heated to 300°C at 2°C / min under a nitrogen atmosphere for pre-carbonization for 2 h, and then cooled naturally;

[0055] S4, activation treatment: the pre-carbonized powder is sent into a tube furnace, heated to 600°C at 5°C / min under a carbon dioxide atmosphere for activation for 2 hours, and then cooled naturally;

[0056] S5. Carbonization treatment: The activated powder is sent into a tubular furnace, heated to 1200°C at 5°C / min under a nitrogen atmosphere and carbonized for 2 hours, and then cooled naturally to obtain a porous sugarcane bagasse hard carbon material.

[0057] Example 2:

[0058] The only difference between this embodiment and embodiment 1 is that: step (4) is to heat the mixture powder to 700°C at a heating rate of 5°C / min, calcine for 2 hours and then cool to room temperature. The other steps and specific parameter conditions are the same as those in embodiment 1.

[0059] Example 3:

[0060] The only difference between this embodiment and embodiment 1 is that the temperature program used in step (4) high-temperature smelting is changed to: heating to 800°C at a heating rate of 5°C / min, calcining for 2 hours and then cooling to room temperature. The other steps and specific parameter conditions are the same as those in embodiment 1.

[0061] Example 4:

[0062] The only difference between this embodiment and embodiment 1 is that the temperature program used in step (4) high-temperature smelting is changed to: heating to 800°C at a heating rate of 5°C / min, calcining for 1 hour and then cooling to room temperature. The other steps and specific parameter conditions are the same as those in embodiment 1.

[0063] Figure 1 This is an SEM image of a bagasse-based sodium-ion battery core-shell structure porous hard carbon negative electrode material obtained in Example 4; it can be observed through SEM that after carbon dioxide gas etching treatment, a multi-scale pore structure is formed on the surface of the material particles, providing a structural basis for its excellent electrochemical performance.

[0064] Figure 2 This is the XRD powder diffraction pattern of a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material obtained in Example 4; through XRD characterization, the typical characteristic peaks of amorphous carbon can be clearly observed, namely the crystal plane (002) at about 24° and the (100) at about 43.5°.

[0065] Figure 3 The first cycle charge-discharge curve of a bagasse-based sodium ion battery core-shell porous hard carbon anode material obtained in Example 4 is shown in FIG. 1 . The charge-discharge curve shows that the specific capacity of the bagasse-based core-shell porous hard carbon anode material at a rate of 0.1C is 343.43 mAh·g -1 , the first Coulombic efficiency was 82.29%.

[0066] Figure 4This is a 0.1C cycle performance curve of a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material obtained in Example 4; the cycle performance test results at a rate of 0.1C show that the material still maintains a capacity retention rate of 90.30% after 200 cycles, showing good cycle stability.

[0067] Example 5:

[0068] The only difference between this embodiment and embodiment 1 is that the temperature program used in step (4) high-temperature smelting is changed to: heating to 800°C at a heating rate of 5°C / min, calcining for 4 hours and then cooling to room temperature. The other steps and specific parameter conditions are the same as those in embodiment 1.

[0069] Example 6:

[0070] The only difference between this embodiment and embodiment 4 is that the amount of asphalt added in step (2) core-shell precursor preparation is changed to: sugarcane bagasse powder and 5wt% asphalt are fed into the ball mill, and the other steps and specific parameter conditions are the same as those in embodiment 4.

[0071] Example 7:

[0072] The only difference between this embodiment and embodiment 4 is that the amount of asphalt added in step (2) core-shell precursor preparation is changed to: sugarcane bagasse powder and 15wt% asphalt are fed into the ball mill, and the other steps and specific parameter conditions are the same as those in embodiment 4.

[0073] Comparative Example 1:

[0074] A bagasse-based hard carbon material comprises the following steps:

[0075] S1. Raw material preparation: Rinse the bagasse with deionized water several times, dry it in a forced air drying oven at 80°C for 12 hours, then mechanically crush it, and pass the mechanically crushed material through a 100-mesh sieve to obtain bagasse powder;

[0076] S2, pre-carbonization treatment: the bagasse powder was placed in a tube furnace and heated to 300°C at 2°C / min under a nitrogen atmosphere for pre-carbonization for 2 h, followed by natural cooling;

[0077] S3. Activation treatment: The pre-carbonized powder was placed in a tube furnace and heated to 800°C at 5°C / min under a nitrogen atmosphere for 1 hour, followed by natural cooling.

[0078] S4. Carbonization treatment: The activated powder was placed in a tubular furnace, heated to 1200°C at 5°C / min under a nitrogen atmosphere and carbonized for 2 hours, and then cooled naturally to obtain a bagasse hard carbon material.

[0079] Comparative Example 2:

[0080] A bagasse-based hard carbon material comprises the following steps:

[0081] S1. Raw material preparation: Rinse the bagasse with deionized water several times, dry it in a forced air drying oven at 80°C for 12 hours, then mechanically crush it, and pass the mechanically crushed material through a 100-mesh sieve to obtain bagasse powder;

[0082] S2. Preparation of core-shell precursor: Bagasse powder and 10 wt% asphalt were placed in a ball mill and ball-milled at 350 rpm for 6 h to obtain core-shell precursor powder;

[0083] S3, pre-carbonization treatment: the core-shell precursor powder was placed in a tube furnace, heated to 300°C at 2°C / min under a nitrogen atmosphere for pre-carbonization for 2 h, and then cooled naturally;

[0084] S4, activation treatment: the pre-carbonized powder was placed in a tube furnace, heated to 800°C at 5°C / min under a nitrogen atmosphere for activation for 1 hour, and then cooled naturally;

[0085] S5. Carbonization treatment: The activated powder was placed in a tubular furnace, heated to 1200°C at 5°C / min under a nitrogen atmosphere and carbonized for 2 hours, and then cooled naturally to obtain a sugarcane bagasse hard carbon material.

[0086] Comparative Example 3:

[0087] A bagasse-based hard carbon material comprises the following steps:

[0088] S1. Raw material preparation: Rinse the bagasse with deionized water several times, dry it in a forced air drying oven at 80°C for 12 hours, then mechanically crush it, and pass the mechanically crushed material through a 100-mesh sieve to obtain bagasse powder;

[0089] S2, pre-carbonization treatment: the bagasse powder was placed in a tube furnace and heated to 300°C at 2°C / min under a nitrogen atmosphere for pre-carbonization for 2 h, followed by natural cooling;

[0090] S3. Activation treatment: The pre-carbonized powder is placed in a tube furnace and heated to 800°C at a rate of 5°C / min under a carbon dioxide atmosphere for activation for 1 hour, followed by natural cooling.

[0091] S4. Carbonization treatment: The activated powder was placed in a tubular furnace, heated to 1200°C at 5°C / min under a nitrogen atmosphere and carbonized for 2 hours, and then cooled naturally to obtain a bagasse hard carbon material.

[0092] Button assembly:

[0093] The negative electrode materials prepared in the above embodiments and comparative examples were mixed in a mass ratio of 90:5:5 of negative electrode material: conductive carbon black: binder PVDF, and a negative electrode slurry was prepared using NMP as a solvent. The negative electrode slurry was then coated on an aluminum foil, vacuum dried at 80°C, and rolled to obtain a negative electrode sheet. The negative electrode sheet, the counter electrode sheet (metallic sodium), the electrolyte (1 mol / L DME) and the glass fiber separator were assembled into a button battery (button battery).

[0094] Performance testing:

[0095] (1) First coulombic efficiency: First, place the button battery in a 25±2℃ environment for 8 hours, discharge it at a constant current of 0.1C to 0.1V, and record the resulting capacity as the 0.1C discharge capacity; then let it stand for 5 minutes, and then charge it at a constant current of 0.1C to a voltage of 2.0V, and record the resulting capacity as the 0.1C charge capacity. Finally, stop the operation, and the first coulombic efficiency (first efficiency) = 0.1C charge capacity / 0.1C discharge capacity;

[0096] (2) Capacity retention rate after 200 cycles at 0.1C: First, place the battery in a 25±2℃ environment for 8h, discharge it at 0.1C constant current to 0.1V, then let it stand for 5min, and then charge it at 0.1C constant current to 2.0V. Repeat the above cycle for 200 times. Finally, stop the operation and record the first and 200th charging capacities. Capacity retention rate = 200th charging capacity / first charging capacity.

[0097] Table 1: Performance test results of Examples 1-7 and Comparative Examples 1-3:

[0098]

[0099] Comparative Example 1 presents an undoped bagasse-based hard carbon anode material. Compared to the Examples, this material, which was not treated with pitch doping or CO2 gas etching, exhibits significantly lower initial Coulombic efficiency, specific capacity at a 0.1C rate, and cycling stability than the Examples, demonstrating that pitch doping and CO2 etching significantly enhance the electrochemical performance of bagasse-based hard carbon.

[0100] Comparative Example 2 presents a core-shell bagasse-based hard carbon anode material that was not treated with CO2. While this material exhibits improved initial Coulombic efficiency compared to the Examples, its 0.1C specific capacity and cycling stability are lower than those of the Examples, demonstrating that CO2 etching plays a key role in improving the specific capacity and cycling performance of bagasse-based hard carbon.

[0101] Comparative Example 3 presents a porous bagasse-based hard carbon anode material without pitch doping. Compared to the examples, this material exhibits improved 0.1C specific capacity and cycling stability, but its initial coulombic efficiency is lower than that of the examples, indicating that pitch doping improves the initial performance of bagasse-based hard carbon materials.

[0102] The above test results demonstrate that the bagasse-based core-shell porous hard carbon anode material for sodium-ion batteries provided by the embodiments of the present invention not only improves the specific capacity and first-cycle coulombic efficiency of the sodium-ion battery anode material, but also enhances the material's cycling stability. Compared with the comparative example, the specific capacity and first-cycle coulombic efficiency of the bagasse-based sodium-ion material show varying degrees of improvement, demonstrating the excellent performance of the sodium-ion battery anode material provided by the present invention.

[0103] Those skilled in the art will readily appreciate that the above description is provided for clarity of explanation only and is not intended to limit the embodiments. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bagasse-based porous hard carbon negative electrode material with a core-shell structure for sodium ion batteries, characterized by: The steps include: S1, washing, drying, mechanically crushing, and sieving bagasse to obtain bagasse powder; S2. mixing bagasse powder and asphalt by ball milling, wherein the amount of asphalt added is 5-30% by mass of the bagasse, to obtain a core-shell precursor; S3, pre-carbonizing the obtained core-shell precursor in an inert atmosphere at 300-500° C. for 2-4 hours; S4, introducing activation gas into the reaction system and performing activation treatment at 600-800°C for 2-6 hours; the activation gas is carbon dioxide gas; S5. Carbonizing the activated powder at 900-1300°C in an inert atmosphere for 2-4 hours to obtain a bagasse-based core-shell porous hard carbon anode material for sodium ion batteries. The core-shell porous hard carbon anode material has an initial efficiency of 77.73-82.40%, a 0.1C gram capacity of 251.28-341.43 mAh / g, and a capacity retention rate of 81.20-92.50%.

2. The method for preparing a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material according to claim 1, characterized in that: The drying described in S1 is carried out at a temperature of 80-120° C. for 8-12 hours; and the screening is carried out through a 100-300 mesh sieve.

3. The method for preparing a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material according to claim 1, characterized in that: The ball milling described in S2 has a rotation speed of 300-500 r / min and a time of 4-8 h.

4. The method for preparing a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material according to claim 1, characterized in that: The inert atmosphere described in S3 is nitrogen or argon; the heating rate of the pre-carbonization treatment is 2-10°C / min.

5. The method for preparing a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material according to claim 1, characterized in that: In S3, activation treatment is performed at 600-800° C. for 1-4 hours.

6. The method for preparing a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material according to claim 1, characterized in that: The inert atmosphere described in S5 is nitrogen or argon.

7. A bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material, characterized by: The present invention is obtained by using the preparation method of a bagasse-based sodium-ion battery core-shell porous hard carbon anode material according to any one of claims 1 to 6. The core-shell porous hard carbon anode material is obtained by activating a mixture of bagasse and pitch in a carbon dioxide atmosphere and calcining it in an inert gas atmosphere. The core-shell porous hard carbon anode material has an initial efficiency of 77.73-82.40%, a 0.1C gram capacity of 251.28-341.43 mAh / g, and a capacity retention rate of 81.20-92.50%.

8. The use of a bagasse-based porous hard carbon negative electrode material with a core-shell structure for sodium ion batteries according to claim 7, characterized in that: As negative electrode active material, it is used to prepare sodium ion batteries.

9. The use of a bagasse-based sodium ion battery core-shell structure porous hard carbon negative electrode material according to claim 8, characterized in that: As negative electrode active material, it is used to prepare the negative electrode of sodium ion battery.

Images