A method for preparing hard carbon derived from sugarcane bagasse and its application in sodium batteries

Abstract

This application discloses a method for preparing hard carbon from sugarcane bagasse and its application in sodium-ion battery anodes, falling within the field of sodium-ion batteries. The method includes: cross-linking lignin and cellulose in the sugarcane bagasse using an acid solution and partially stripping the ash from the biomass; then stripping the hemicellulose from the bagasse using a weak alkaline solution to expose the cellulose; and finally, by controlling the concentration, treatment time, and temperature of the alkaline solution, retaining appropriate amounts of lignin within the cellulose to promote the regulation of its pore structure during carbonization. After alkaline treatment, the solid is washed with hydrochloric acid and freeze-dried to retain a suitable pore structure. Finally, a high-temperature heat treatment is performed under a protective atmosphere, conducted in three stages. First, pore opening occurs: this reaction process is the deoxidation of cellulose, handled at 300–400℃, achieving initial carbonization of the cellulose. Second, carbonization occurs: this reaction further deoxidizes the cellulose after initial carbonization, handled at 800–1000℃, forming numerous C=C / C-C bonds. Finally, a hard carbon graphite layer is formed, handled at 1300–1500℃. The bagasse-based hard carbon prepared using the above method can achieve efficient and stable cycling in sodium-ion batteries, exhibiting excellent rate performance.

Description

Technical Field

[0001] This application relates to the development of a negative electrode for sodium-ion batteries, specifically a method for preparing hard carbon derived from bagasse waste and its application in sodium-ion batteries. Background Technology

[0002] With the rapid development of renewable energy, the development of efficient and low-cost electrochemical energy storage technologies has become crucial. Sodium-ion batteries, as a potential alternative to lithium-ion batteries, have received unprecedented attention in recent years. Compared to lithium, sodium resources are abundant, widely distributed, and inexpensive, giving sodium-ion batteries a significant cost advantage in large-scale energy storage applications. However, the commercial application of sodium-ion batteries still faces many challenges, the most important of which is the lack of suitable anode materials. Hard carbon materials, due to their unique disordered structure and abundant nanopores, are considered one of the most promising anode materials for sodium-ion batteries. Hard carbon not only provides a large interlayer spacing to accommodate sodium ions but also exhibits good conductivity and structural stability, maintaining high capacity and cycle stability during charge and discharge. However, the preparation of hard carbon typically relies on petroleum-based or coal-based precursors, which are not only costly but also contradict environmental sustainability goals. Therefore, finding renewable and low-cost hard carbon precursors for developing hard carbon for sodium batteries has become a current research hotspot. Sugarcane bagasse, as an abundant agricultural waste in South China, is widely available, inexpensive, and renewable, making it an ideal precursor for hard carbon preparation. Through processes such as pyrolysis and carbonization, sugarcane bagasse can be transformed into hard carbon materials with excellent sodium storage properties. This not only provides a new way for the high-value utilization of agricultural waste, but also provides a new material option for the sustainable development of sodium-ion batteries.

[0003] Despite significant progress in recent years in exploring the application of bagasse-derived hard carbon in sodium-ion batteries, researchers have demonstrated its superior performance in sodium-ion storage due to its abundant pore structure, large specific surface area, and suitable surface chemistry. However, several key scientific and technological challenges remain to be addressed in the development of bagasse-derived hard carbon. Firstly, the chemical composition and structure of bagasse vary considerably depending on its origin and processing method, potentially leading to inconsistent performance of the derived hard carbon. Further optimization of the hard carbon preparation process to reduce production costs and improve energy density and cycle life is a key area for future research. Secondly, the inherent pore structure of biomass-derived hard carbon often results in extremely low initial coulombic efficiency in sodium batteries. Improving the pore structure and enhancing the reversibility of hard carbon for sodium ions remains a challenge. To address these technical challenges, we have comprehensively innovated bagasse-derived hard carbon to develop a high-performance anode for sodium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a method for preparing hard carbon derived from sugarcane bagasse and its application in sodium batteries, so as to solve the above-mentioned problems.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] A method for preparing hard carbon based on sugarcane bagasse, comprising:

[0007] The precursor used was bagasse. The bagasse was first soaked in water to remove the sugar content and some ash. The bagasse exhibited slight swelling. Then, the bagasse was rolled to remove most of the moisture.

[0008] The obtained bagasse undergoes de-hemicellulose treatment, firstly by using alkali to dissolve and peel off the hemicellulose inside the bagasse. By controlling the type and concentration of alkali, the treatment temperature, and the treatment time, some hemicellulose is retained to regulate the microporous structure during the cellulose carbonization process.

[0009] After alkali treatment, the corresponding cellulose is collected and the solid is washed with hydrochloric acid solution, then freeze-dried to reduce the surface tension of water on the carbon material interface and preserve the pore structure.

[0010] The solid product obtained after freeze-drying was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. The heat treatment was conducted in three stages. Then, high-temperature heat treatment was performed under a protective atmosphere, which was carried out in three stages: pore opening treatment, carbonization treatment, and graphite layer formation treatment.

[0011] After the initial treatment, the hard carbon is soaked again in an acid solution to further remove ash. This yields hard carbon for sodium-ion batteries.

[0012] Preferably, the soaking time is 5–24 hours, and the mass ratio of sugarcane bagasse to water is 1:2–20. Preferably, the soaking time is 8 hours. The pressure of the roller pressing is greater than 50 MPa, preferably 100 MPa.

[0013] Preferably, the sugarcane bagasse is subjected to de-hemicellulose treatment, and the alkali used includes NaOH, KOH, LiOH, ammonia, sodium acetate, etc., the pH value is adjusted to 9-14, the heating temperature is 50-80℃, the holding time is 2-6h, and the stirring speed is 500-2000rpm.

[0014] Preferably, after alkali treatment, the corresponding cellulose is collected and the solid is washed with a hydrochloric acid solution at a concentration of 0.5–2 mol / L for 2 hours. Freeze-drying is then performed to reduce the surface tension of water on the carbon material interface, thus preserving the porous structure.

[0015] The solid product obtained after freeze-drying was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. The heat treatment was conducted in three stages. Then, high-temperature heat treatment was performed under a protective atmosphere, which was carried out in three stages: pore opening treatment, carbonization treatment, and graphite layer formation treatment.

[0016] Preferably, the protective atmosphere in the high-temperature annealing treatment can be nitrogen, argon, a nitrogen / hydrogen mixture, or an argon / hydrogen mixture, with atmospheric pressure, a flowing gas, and a flow rate of 20–100 sccm. The treatment temperature is divided into three stages: the opening stage temperature range is 280–320℃, and the holding time is 1–4 hours; the carbonization treatment temperature is 700–900℃, and the holding time is 1–4 hours; the graphite layer formation temperature is 1200–1500℃, and the holding time is 1–4 hours. The heating rate is 1–5℃ / min. The cooling is quenching.

[0017] Preferably, after high-temperature heat treatment, the hard carbon is soaked in an acid solution, including but not limited to hydrochloric acid, sulfuric acid, and nitric acid solutions, with a concentration of 0.2–5 mol / L and a soaking time of 2–10 hours. After soaking, the hard carbon is then rinsed with deionized water.

[0018] After mixing the hard carbon anode with a binder, it is coated onto the current collector using a blade coating method. After drying, a sodium battery anode is obtained. The electrodes are then rolled together, and the battery is assembled under an argon atmosphere using an ester / ether electrolyte.

[0019] Preferably, the adhesive comprises one or more of sodium carboxymethyl cellulose, sodium alginate, and polystyrene rubber;

[0020] Preferably, the mass ratio of the biomass-derived hard carbon to the binder is (2-10):100, more preferably 10:100;

[0021] Preferably, the current collector for the negative electrode of the sodium battery is any one of copper foil, carbon-coated copper foil, aluminum foil, and carbon-coated aluminum foil.

[0022] Preferably, the electrode is prepared by a blade coating method, with a coating thickness of 50–300 μm. After drying, the electrode is subjected to a roller test with a roller pressure of 50–200 MPa.

[0023] Preferably, ether-based electrolytes are used to assemble sodium batteries. These ether-based electrolytes include, but are not limited to, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The sodium salts used include, but are not limited to, one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium trifluoromethanesulfonate, with a salt concentration in the electrolyte of 0.5-2 mol / L.

[0024] Preferably, during battery assembly, the oxygen content and water content in the argon atmosphere are less than 1 ppm;

[0025] Compared with the prior art, the beneficial effects of this application include:

[0026] The method for preparing hard carbon derived from sugarcane bagasse provided in this application utilizes multiple processes involving acid and alkali to crosslink the internal structure of biomass, remove hemicellulose, and remove ash. This effectively solves the problem of inconsistent biomass composition caused by factors such as origin, weather, and growth environment. In the preparation of hard carbon, conventional one-step high-temperature annealing can effectively obtain hard carbon, but due to the inability of the carbon's pore structure to close effectively, it often exhibits extremely low initial coulombic efficiency and low plateau capacity. This method employs three stages in the hard carbon annealing process: the pore-opening stage has a temperature range of 280–320℃ and a holding time of 1–4 h; the carbonization treatment temperature is 700–900℃ and a holding time of 1–4 h; and the graphite layer formation temperature is 1200–1500℃ and a holding time of 1–4 h. The heating rate is 1–5℃ / min. Cooling is performed by quenching. The low-temperature process ensures effective dehydration and pore opening of the biomass, thus initially regulating the pore structure inside the hard carbon. The intermediate-temperature process ensures the deoxidation of carbon materials, leading to the formation of numerous C / C=C bonds and further increasing the number of micropores. The high-temperature process causes partial graphitization of the carbon layer and closes the open pores generated during dehydration and deoxidation to further form a closed-pore structure, thereby effectively improving the reversibility of hard carbon in the sodium storage process.

[0027] The bagasse-derived hard carbon provided in this application has a micron-sized structure and exhibits good electrical conductivity and a closed-pore structure. Based on this structure, the obtained bagasse-derived hard carbon achieves efficient and stable cycling in sodium-ion batteries and demonstrates excellent rate performance. This bagasse-derived hard carbon has high initial coulombic efficiency, high specific capacity, high stability, and shows great potential for large-scale development.

[0028] The sodium battery using bagasse-derived hard carbon anode provided in this application exhibits excellent performance. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0030] Figure 1 These are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of sugarcane bagasse-derived hard carbon from Example 1.

[0031] Figure 2 This is an X-ray derivation image of bagasse-derived hard carbon in Example 1;

[0032] Figure 3 The cycling curve of bagasse-derived hard carbon in Example 1 at a current density of 100 mA / g;

[0033] Figure 4 The charge-discharge curves of bagasse-derived hard carbon in Example 1 at a current density of 100 mA / g are shown.

[0034] Figure 5 Long-cycle curve of bagasse-derived hard carbon at a current density of 1 A / g⁻¹; Detailed Implementation

[0035] A method for preparing sugarcane bagasse-derived hard carbon includes:

[0036] The precursor used was bagasse. The bagasse was first soaked in water to remove the sugar content and some ash. The bagasse exhibited slight swelling. Then, the bagasse was rolled to remove most of the moisture.

[0037] The obtained bagasse undergoes de-hemicellulose treatment, firstly by using alkali to dissolve and peel off the hemicellulose inside the bagasse. By controlling the type and concentration of alkali, the treatment temperature, and the treatment time, some hemicellulose is retained to regulate the microporous structure during the cellulose carbonization process.

[0038] After alkali treatment, the corresponding cellulose is collected and the solid is washed with hydrochloric acid solution, then freeze-dried to reduce the surface tension of water on the carbon material interface and preserve the pore structure.

[0039] The solid product obtained after freeze-drying was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. The heat treatment was conducted in three stages. Then, high-temperature heat treatment was performed under a protective atmosphere, which was carried out in three stages: pore opening treatment, carbonization treatment, and graphite layer formation treatment.

[0040] After the initial treatment, the hard carbon is soaked again in an acid solution to further remove ash. This yields hard carbon for sodium-ion batteries.

[0041] In one optional embodiment, the soaking time for bagasse is 5 h, 6 h, 8 h, 10 h, 12 h, 15 h, or 24 h. The mass ratio of bagasse to water is 1:2, 1:3, 1:5, 1:8, 1:10, 1:15, or 1:20, the soaking time is 8 h, and the roller pressing pressure is 50 MPa, 100 MPa, or 200 MPa.

[0042] In an optional embodiment, the bagasse is subjected to de-hemicellulose treatment, using alkalis including NaOH, KOH, LiOH, ammonia, and sodium acetate, with heating temperatures of 50, 60, 70, and 80°C, holding times of 2, 4, and 6 hours, and stirring speeds of 500, 1000, 1500, and 2000 rpm.

[0043] In an optional embodiment, after alkali treatment, the corresponding cellulose is collected and the solid is washed with hydrochloric acid solution at concentrations of 0.5, 1, 1.5, and 2 mol / L for 2 hours. Freeze-drying is then performed to reduce the surface tension of water on the carbon material interface, thereby preserving the porous structure.

[0044] The solid product obtained after freeze-drying was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. The heat treatment was conducted in three stages. Then, high-temperature heat treatment was performed under a protective atmosphere, which was carried out in three stages: pore opening treatment, carbonization treatment, and graphite layer formation treatment.

[0045] In one optional embodiment, the protective atmosphere in the high-temperature annealing treatment can be nitrogen, argon, a nitrogen / hydrogen mixture, or an argon / hydrogen mixture, with atmospheric pressure and a flowing gas velocity of 20, 50, 80, or 100 sccm. The treatment temperature is divided into three stages: the pore-opening stage has a temperature range of 280, 300, and 320°C, with holding times of 1, 2, and 4 hours; the carbonization stage has temperatures of 700, 800, and 900°C, with holding times of 1, 2, and 4 hours; and the graphite layer formation stage has temperatures of 1200, 1300, 1400, and 1500°C, with holding times of 1, 2, and 4 hours. The heating rate is 1, 2, 3, 4, or 5°C / min. Cooling is performed by quenching.

[0046] In one optional embodiment, after high-temperature heat treatment, the hard carbon is soaked in an acid solution, including but not limited to hydrochloric acid, sulfuric acid, and nitric acid solutions, with concentrations of 0.2, 0.5, 1, 2, and 5 mol / L, and soaking times of 2, 5, 8, and 10 hours. After soaking, the hard carbon is then rinsed with deionized water.

[0047] After mixing the hard carbon anode with a binder, it is coated onto the current collector using a blade coating method. After drying, a sodium battery anode is obtained. The electrodes are then rolled together, and the battery is assembled under an argon atmosphere using an ester / ether electrolyte.

[0048] In an optional embodiment, the binder includes one or more of sodium carboxymethyl cellulose, sodium alginate, and polystyrene rubber; the mass ratio of biomass-derived hard carbon to binder is (2-10):100, preferably 10:100; the current collector for the sodium battery negative electrode is any one of copper foil, carbon-coated copper foil, aluminum foil, and carbon-coated aluminum foil. The electrode is prepared by a blade coating method, with a coating thickness of 50–300 μm. After drying, the electrode is subjected to a roller test with a roller pressure of 50–200 MPa.

[0049] In an optional embodiment, an ether-based electrolyte is preferably used for assembling the sodium battery. The ether-based electrolyte includes, but is not limited to, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The sodium salt used includes, but is not limited to, one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium trifluoromethanesulfonate, with a salt concentration in the electrolyte of 0.5, 1, or 2 mol / L. During battery assembly, the oxygen content and water content in the argon atmosphere are less than 1 ppm.

[0050] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0051] Example 1

[0052] This embodiment provides a method for preparing sugarcane bagasse-derived hard carbon, the preparation method of which is as follows:

[0053] The precursor used was bagasse. The bagasse was first soaked in water to remove sugar components and some ash elements. The soaking time was 8 hours, and the mass ratio of bagasse to water was 1:5. After soaking, the bagasse exhibited slight swelling. Then, the bagasse was roller-pressed to remove most of the water, with a roller pressure of 100 MPa. The resulting bagasse underwent de-hemicellulose treatment, first using alkali to dissolve and peel off the hemicellulose inside the bagasse. The bagasse was placed in a 0.6 mol / L NaOH solution, heated to 80℃, and held at that temperature for 4 hours with a stirring speed of 1500 rpm. The resulting sample was then centrifuged, washed, and further treated with hydrochloric acid to achieve biomass cross-linking and ash removal. Hydrochloric acid was used in the acid treatment at a concentration of 1 mol / L for 2 hours. The sample was then washed and freeze-dried to reduce the surface tension of water on the carbon material interface and preserve the pore structure. The solid material was freeze-dried at -18℃, then transferred to a freeze dryer set at -60℃ and 0.1 Pa for 24 hours. The resulting solid product was then subjected to high-temperature annealing under a protective atmosphere. The heat treatment was carried out in three stages: first, annealing at 300℃ for 2 hours; then at 800℃ for 2 hours; and finally at 1300℃ for 2 hours. After annealing, the biomass was quenched at a rate of 2℃ / min using argon gas at a flow rate of 50 sccm. Following heat treatment, the sample was further soaked in a 1 mol / L hydrochloric acid solution for 4 hours. After soaking, the hard carbon was washed with deionized water and dried. The resulting bagasse-derived hard carbon had a specific surface area as low as 4.8 m². 2 / g.

[0054] Figure 1 The images show scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the synthesized bagasse-derived hard carbon. Figure 2 The image shows the X-ray diffraction pattern of the synthesized bagasse-derived hard carbon.

[0055] During battery assembly, a hard carbon negative electrode is mixed with sodium carboxymethyl cellulose binder at a mass ratio of 10 wt%. This binder is then coated onto a current collector using a blade coating method to a thickness of 100 μm. After drying, the sodium battery negative electrode is obtained. The electrode is then subjected to a roller test at a pressure of 100 MPa. The battery is then assembled under an argon atmosphere using an ether-based electrolyte. The ether electrolyte is 1 mol / L sodium hexafluorophosphate dissolved in ethylene glycol dimethyl ether. The battery assembly is conducted in a glove box under an argon atmosphere with an oxygen content of less than 1 ppm and a water content of less than 1 ppm.

[0056] Based on the synthesized bagasse-derived hard carbon, in sodium-ion batteries, the initial coulombic efficiency reached 90% at a current density of 50 mA / g, with an initial reversible specific capacity of 323 mAh / g and a specific capacity of 299 mAh / g after 50 cycles. Figure 3 After 50 cycles, the capacity retention is greater than 92%. After 3000 cycles at a high current density of 1 A / g, its specific capacity is 180 mAh / g. Figure 4 ).

[0057] Example 2

[0058] This embodiment provides a method for preparing sugarcane bagasse-derived hard carbon, the preparation method of which is as follows:

[0059] The precursor used was bagasse. The bagasse was first soaked in water to remove sugar components and some ash elements. The soaking time was 4 hours, and the mass ratio of bagasse to water was 1:10. After soaking, the bagasse exhibited slight swelling. Then, the bagasse was roller-pressed to remove most of the water, with a roller pressure of 100 MPa. The resulting bagasse underwent de-hemicellulose treatment, first using alkali to dissolve and peel off the hemicellulose within the bagasse. The bagasse was placed in a 0.6 mol / L NaOH solution, heated to 80℃, and held at that temperature for 4 hours with a stirring speed of 1500 rpm. The resulting sample was then centrifuged, washed, and further treated with nitric acid to achieve biomass cross-linking and ash removal. Hydrochloric acid was used in the acid treatment, with a nitric acid concentration of 1 mol / L, and the soaking time was 2 hours. The sample was then washed and freeze-dried to reduce the surface tension of water on the carbon material interface, thus preserving the pore structure. The solid material was freeze-dried at -18℃, then transferred to a freeze dryer set at -60℃ and 0.1 Pa for 24 hours. The resulting solid product was then subjected to high-temperature annealing under a protective atmosphere. The heat treatment was carried out in three stages: first, annealing at 320℃ for 2 hours; then, annealing at 800℃ for 2 hours; and finally, annealing at 1500℃ for 2 hours. After annealing, the biomass was quenched at a rate of 2℃ / min using argon gas at a flow rate of 50 sccm. Following heat treatment, the sample was further soaked in a 1 mol / L hydrochloric acid solution for 4 hours. After soaking, the hard carbon was washed with deionized water and dried. The resulting bagasse-derived hard carbon had a specific surface area as low as 7.2 m². 2 / g.

[0060] During battery assembly, a hard carbon negative electrode is mixed with sodium carboxymethyl cellulose binder at a mass ratio of 5 wt%. This binder is then coated onto a current collector using a blade coating method to a thickness of 100 μm. After drying, the sodium battery negative electrode is obtained. The electrode is then subjected to roller pressing at a pressure of 100 MPa, and the battery is assembled under an argon atmosphere using an ether-based electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1 mol / L sodium perchlorate. The battery is assembled in a glove box under an argon atmosphere with an oxygen content of less than 1 ppm and a water content of less than 1 ppm.

[0061] Based on the synthesized bagasse-derived hard carbon, in sodium-ion batteries, the initial coulombic efficiency reached 91% at a current density of 50 mA / g, with an initial reversible specific capacity of 318 mAh / g. After 50 cycles, the specific capacity was 305 mAh / g, and the capacity retention after 50 cycles was greater than 96%. At a high current density of 1 A / g, after 5000 cycles, the specific capacity was 163 mAh / g.

[0062] Example 3

[0063] This embodiment provides a method for preparing sugarcane bagasse-derived hard carbon, the preparation method of which is as follows:

[0064] The precursor used was bagasse. The bagasse was first soaked in water to remove sugar components and some ash elements. The soaking time was 8 hours, and the mass ratio of bagasse to water was 1:5. After soaking, the bagasse exhibited slight swelling. Then, the bagasse was roller-pressed to remove most of the water, with a roller pressure of 100 MPa. The resulting bagasse underwent de-hemicellulose treatment, first using alkali to dissolve and peel off the hemicellulose within the bagasse. The bagasse was placed in a 1 mol / L KOH solution, heated to 60℃, and held at that temperature for 8 hours with a stirring speed of 2000 rpm. The resulting sample was then centrifuged, washed, and further treated with hydrochloric acid to achieve biomass cross-linking and ash removal. Hydrochloric acid was used in the acid treatment at a concentration of 1 mol / L for 2 hours. The sample was then washed and freeze-dried to reduce the surface tension of water on the carbon material interface, thus preserving the pore structure. The solid material was freeze-dried at -18℃, then transferred to a freeze dryer set at -60℃ and 0.1 Pa for 24 hours. The resulting solid product was then subjected to high-temperature annealing under a protective atmosphere. The heat treatment was carried out in three stages: first, annealing at 300℃ for 2 hours, then at 700℃ for 2 hours, and finally at 1500℃ for 2 hours. After annealing, the biomass was quenched at a rate of 1℃ / min using argon gas at a flow rate of 100 sccm. Following heat treatment, the sample was further soaked in a 1 mol / L hydrochloric acid solution for 4 hours. After soaking, the hard carbon was washed with deionized water and dried. The resulting bagasse-derived hard carbon had a specific surface area as low as 6.3 m². 2 / g.

[0065] During battery assembly, a hard carbon negative electrode is mixed with sodium carboxymethyl cellulose binder at a mass ratio of 10 wt%. This binder is then coated onto a current collector using a blade coating method to a thickness of 100 μm. After drying, the sodium battery negative electrode is obtained. The electrode is then subjected to roller pressing at a pressure of 100 MPa, and the battery is assembled under an argon atmosphere using an ether-based electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1 mol / L sodium trifluoromethanesulfonate. The battery is assembled in a glove box under an argon atmosphere with an oxygen content of less than 1 ppm and a water content of less than 1 ppm.

[0066] Based on the synthesized bagasse-derived hard carbon, in sodium-ion batteries, the initial coulombic efficiency reached 88% at a current density of 50 mA / g, with an initial reversible specific capacity of 336 mAh / g. After 50 cycles, the specific capacity was 308 mAh / g, and the capacity retention after 50 cycles was greater than 96%. At a high current density of 1 A / g for 3000 cycles, the specific capacity was 201 mAh / g.

[0067] Example 4

[0068] This embodiment provides a method for preparing sugarcane bagasse-derived hard carbon, the preparation method of which is as follows:

[0069] The precursor used was bagasse. The bagasse was first soaked in water to remove sugar components and some ash elements. The soaking time was 8 hours, and the mass ratio of bagasse to water was 1:5. After soaking, the bagasse exhibited slight swelling. Then, the bagasse was roller-pressed to remove most of the water, with a roller pressure of 100 MPa. The resulting bagasse underwent de-hemicellulose treatment, first using alkali to dissolve and peel off the hemicellulose inside the bagasse. The bagasse was placed in a 0.6 mol / L NaOH solution, heated to 80℃, and held at that temperature for 4 hours with a stirring speed of 1500 rpm. The resulting sample was then centrifuged, washed, and further treated with hydrochloric acid to achieve biomass cross-linking and ash removal. Hydrochloric acid was used in the acid treatment at a concentration of 1 mol / L for 2 hours. The sample was then washed and freeze-dried to reduce the surface tension of water on the carbon material interface and preserve the pore structure. The solid material was freeze-dried at -18℃, then transferred to a freeze dryer set at -60℃ and 0.1 Pa for 24 hours. The resulting solid product underwent high-temperature annealing under a protective atmosphere. The heat treatment was performed in three stages: first, annealing at 300℃ for 4 hours; then at 700℃ for 4 hours; and finally at 1300℃ for 4 hours. After annealing, the biomass was quenched at a rate of 2℃ / min using argon gas at a flow rate of 50 sccm. Following heat treatment, the sample was further soaked in a 1 mol / L hydrochloric acid solution for 4 hours. After soaking, the hard carbon was washed with deionized water and dried. The resulting bagasse-derived hard carbon had a specific surface area as low as 3.8 m². 2 / g.

[0070] Figure 1 The image shows a scanning electron microscope (SEM) image of the synthesized bagasse-derived hard carbon. Figure 2 Transmission electron microscopy (TEM) image of the synthesized bagasse-derived hard carbon.

[0071] During battery assembly, a hard carbon negative electrode is mixed with sodium carboxymethyl cellulose binder at a mass ratio of 10 wt%. This binder is then coated onto a current collector using a blade coating method to a thickness of 100 μm. After drying, the sodium battery negative electrode is obtained. The electrode is then subjected to roller pressing at a pressure of 100 MPa, and the battery is assembled under an argon atmosphere using an ether-based electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1 mol / L sodium perchlorate. The battery assembly is conducted in a glove box under an argon atmosphere with an oxygen content of less than 1 ppm and a water content of less than 1 ppm.

[0072] Based on the synthesized bagasse-derived hard carbon, in sodium-ion batteries, the initial coulombic efficiency reached 89% at a current density of 50 mA / g, with an initial reversible specific capacity of 315 mAh / g, a specific capacity of 298 mAh / g after 50 cycles, and a capacity retention of over 96% after 50 cycles. At a high current density of 1 A / g for 3000 cycles, the specific capacity reached 185 mAh / g.

[0073] Comparative Example 1

[0074] Sugarcane bagasse was directly subjected to high-temperature annealing under a protective atmosphere. The heat treatment was carried out in three stages: first, annealing at 300℃ for 4 hours; then, annealing at 700℃ for 4 hours; and finally, annealing at 1300℃ for 4 hours. After annealing, the biomass was quenched at a rate of 2℃ / min using argon gas at a flow rate of 50 sccm. Following heat treatment, the resulting sample was further soaked in a 1 mol / L hydrochloric acid solution for 4 hours. After soaking, the hard carbon was washed with deionized water and dried. The resulting bagasse-derived hard carbon had a specific surface area as low as 11.3 m². 2 / g.

[0075] During battery assembly, a hard carbon negative electrode is mixed with sodium carboxymethyl cellulose binder at a mass ratio of 10 wt%. This binder is then coated onto a current collector using a blade coating method to a thickness of 100 μm. After drying, the sodium battery negative electrode is obtained. The electrode is then subjected to roller pressing at a pressure of 100 MPa, and the battery is assembled under an argon atmosphere using an ether-based electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1 mol / L sodium perchlorate. The battery assembly is conducted in a glove box under an argon atmosphere with an oxygen content of less than 1 ppm and a water content of less than 1 ppm.

[0076] Based on the synthesized bagasse-derived hard carbon, in sodium-ion batteries, the initial coulombic efficiency reached 86% at a current density of 50 mA / g, with an initial reversible specific capacity of 251 mAh / g, a specific capacity of 231 mAh / g after 50 cycles, and a capacity retention of over 96% after 50 cycles. At a high current density of 1 A / g for 2000 cycles, the specific capacity reached 144 mAh / g.

[0077] Comparative Example 2

[0078] The precursor used was bagasse. The bagasse was first soaked in water to remove sugar components and some ash elements. The soaking time was 8 hours, and the mass ratio of bagasse to water was 1:5. After soaking, the bagasse exhibited slight swelling. Then, the bagasse was roller-pressed to remove most of the water, with a roller pressure of 100 MPa. The resulting bagasse underwent de-hemicellulose treatment, first using alkali to dissolve and peel off the hemicellulose inside the bagasse. The bagasse was placed in a 0.6 mol / L NaOH solution, heated to 80℃, and held at that temperature for 4 hours with a stirring speed of 1500 rpm. The resulting sample was then centrifuged, washed, and further treated with hydrochloric acid to achieve biomass cross-linking and ash removal. Hydrochloric acid was used in the acid treatment at a concentration of 1 mol / L for 2 hours. The sample was then washed and freeze-dried to reduce the surface tension of water on the carbon material interface and preserve the pore structure. The solid material was freeze-dried at -18℃, then transferred to a freeze dryer set at -60℃ and 0.1 Pa for 24 hours. The resulting solid product was annealed at 1300℃ for 4 hours at a heating rate of 2℃ / min using argon gas at a flow rate of 50 sccm. After annealing, the biomass was cooled at a rate of 10℃ / min. The resulting sample was then further soaked in a 1 mol / L hydrochloric acid solution for 4 hours. Following soaking, the hard carbon was washed with deionized water and dried. The resulting bagasse-derived hard carbon had a specific surface area as low as 128.0 m². 2 / g.

[0079] During battery assembly, a hard carbon negative electrode is mixed with sodium carboxymethyl cellulose binder at a mass ratio of 10 wt%. This binder is then coated onto a current collector using a blade coating method to a thickness of 100 μm. After drying, the sodium battery negative electrode is obtained. The electrode is then subjected to roller pressing at a pressure of 100 MPa, and the battery is assembled under an argon atmosphere using an ether-based electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1 mol / L sodium perchlorate. The battery assembly is conducted in a glove box under an argon atmosphere with an oxygen content of less than 1 ppm and a water content of less than 1 ppm.

[0080] Based on the synthesized bagasse-derived hard carbon, in sodium-ion batteries, the initial coulombic efficiency reached 56% at a current density of 50 mA / g, with an initial reversible specific capacity of 268 mAh / g, a specific capacity of 215 mAh / g after 50 cycles, and a capacity retention of over 96% after 50 cycles. At a high current density of 1 A / g for 1000 cycles, its specific capacity was 113 mAh / g.

[0081] Comparative Example 3

[0082] Sugarcane bagasse was used as the precursor. The bagasse was first soaked in water to remove sugar components and some ash elements. The soaking time was 8 hours, and the mass ratio of bagasse to water was 1:5. After soaking, the bagasse exhibited slight swelling. Then, the bagasse was roller-pressed to remove most of the water, with a roller pressure of 100 MPa. The resulting sample was then centrifuged, washed, and further treated with hydrochloric acid to achieve biomass cross-linking and ash removal. Hydrochloric acid (1 mol / L) was used for the acid treatment, and the soaking time was 2 hours. The sample was then washed and freeze-dried to reduce the surface tension of water on the carbon material interface and preserve the pore structure. The solid was freeze-cured at -18°C and then transferred to a freeze dryer set at -60°C and 0.1 Pa for 24 hours. The resulting solid product underwent high-temperature annealing under a protective atmosphere. The heat treatment was carried out in three stages. The biomass was first annealed at 300℃ for 4 hours, then heated to 1300℃ and annealed for another 4 hours. After annealing, the biomass was quenched. The heating rate was 2℃ / min, the gas was argon, and the gas flow rate was 50 sccm. After heat treatment, the obtained sample was further soaked in hydrochloric acid solution with a concentration of 1 mol / L for 4 hours. After soaking, the hard carbon was washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon was as low as 35.4 m². 2 / g.

[0083] During battery assembly, a hard carbon negative electrode is mixed with sodium carboxymethyl cellulose binder at a mass ratio of 10 wt%. This binder is then coated onto a current collector using a blade coating method to a thickness of 100 μm. After drying, the sodium battery negative electrode is obtained. The electrode is then subjected to roller pressing at a pressure of 100 MPa, and the battery is assembled under an argon atmosphere using an ether-based electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1 mol / L sodium perchlorate. The battery assembly is conducted in a glove box under an argon atmosphere with an oxygen content of less than 1 ppm and a water content of less than 1 ppm.

[0084] Based on the synthesized bagasse-derived hard carbon, in sodium-ion batteries, the initial coulombic efficiency reached 83% at a current density of 50 mA / g, with an initial reversible specific capacity of 260 mAh / g, a specific capacity of 233 mAh / g after 50 cycles, and a capacity retention of over 96% after 50 cycles. At a high current density of 1 A / g for 3000 cycles, its specific capacity reached 136 mAh / g.

[0085] It should be noted that the embodiments described herein are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing hard carbon derived from sugarcane bagasse waste, characterized in that, include: The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar content and some ash elements inside the bagasse. The bagasse exhibits a slight swelling phenomenon. Then, the bagasse is rolled to remove most of the moisture. The obtained bagasse is subjected to de-hemicellulose treatment. First, alkali is used to dissolve and peel off the hemicellulose inside the bagasse. By controlling the type, concentration, treatment temperature and treatment time of alkali, some hemicellulose is retained for the purpose of controlling the microporous structure in the cellulose carbonization process. After alkali treatment, the corresponding cellulose is collected and the solid is washed with hydrochloric acid solution, then freeze-dried to reduce the surface tension of water on the carbon material interface and preserve the pore structure. The solid material is subjected to high-temperature annealing; then it is subjected to high-temperature heat treatment under a protective atmosphere. The heat treatment is carried out in three stages: pore opening treatment, carbonization treatment and graphite layer formation treatment. After the treatment, the hard carbon is soaked in an acid solution again to further remove the ash from the hard carbon, thus obtaining hard carbon for sodium-ion batteries. The protective atmosphere consists of nitrogen, argon, a nitrogen / hydrogen mixture, and an argon / hydrogen mixture, at atmospheric pressure. The gas is a flowing gas with a flow rate of 20–100 sccm. The processing temperature is divided into three stages: the opening stage has a temperature range of 280–320℃ and a holding time of 1–4 h; the carbonization stage has a temperature range of 700–900℃ and a holding time of 1–4 h; and the graphite layer formation stage has a temperature range of 1200–1500℃ and a holding time of 1–4 h. The heating rate is 1–5℃ / min, and the cooling is quenching.

2. The preparation method according to claim 1, characterized in that, The soaking time is 5 to 24 hours, the mass ratio of sugarcane bagasse to water is 1:2 to 20, and the pressure of the roller press is greater than 50 MPa.

3. According to the preparation method of claim 1, the alkali used for de-hemicellulose treatment of sugarcane bagasse includes NaOH, KOH, LiOH, ammonia, and sodium acetate, the pH value is adjusted to 9-14, the heating temperature is 50-80℃, the holding time is 2-6h, and the stirring speed is 500-2000rpm.

4. According to the preparation method of claim 1, after alkali treatment, the corresponding cellulose is collected and the solid is washed with hydrochloric acid solution with a concentration of 0.5-2 mol / L for 2 hours, followed by freeze drying to reduce the surface tension of water on the carbon material interface and preserve the pore structure.

5. According to the preparation method of claim 1, after the treatment is completed, the hard carbon is soaked in an acid solution, the acid solution including but not limited to hydrochloric acid, sulfuric acid, and nitric acid solution, the concentration of the acid solution is 0.2-5 mol / L, the soaking time is 2-10 h, and after soaking, the soaked hard carbon is washed with deionized water.

6. A biomass-derived sodium-ion battery negative electrode, characterized in that, The raw materials include hard carbon prepared by the preparation method described in claims 1-5. After the hard carbon negative electrode is mixed with a binder, it is coated onto a current collector by a scraping method and dried to obtain a sodium battery negative electrode. After the electrodes are rolled, the battery is assembled under an argon atmosphere using an ester / ether electrolyte to obtain the battery.

Images