Preparation method of hard carbon derived from bagasse and application of hard carbon in sodium battery

Abstract

The invention discloses a preparation method for treating bagasse to obtain hard carbon, application of the hard carbon and a sodium-ion battery negative electrode, and relates to the field of sodium-ion batteries. The preparation method of the bagasse-based hard carbon comprises the following steps: crosslinking lignin and cellulose in the bagasse-based hard carbon by using an acid solution, and partially stripping ash of biomass. And stripping hemicellulose of the bagasse by using a weak base solution to expose cellulose. By regulating and controlling the concentration, the treatment time and the treatment temperature of the alkali solution, reasonable lignin is reserved in the cellulose, so that regulation and control of a plain pore structure in the carbonization process are promoted. After the alkali solution treatment, a hydrochloric acid solution is used for cleaning the solid, and freeze drying is carried out, so that a proper pore structure is reserved. And then carrying out high-temperature heat treatment in a protective atmosphere, wherein the heat treatment is carried out in three stages. The reaction process is a cellulose deoxidation process, the treatment temperature is 300-400 DEG C, and primary carbonization of cellulose is realized; secondly, carbonizing, namely further deoxidizing after primary carbonization, wherein a large number of C = C / C-C bonds are formed at the treatment temperature of 800-1000 DEG C; and finally, forming a hard carbon graphite layer, wherein the treatment temperature is 1300-1500 DEG C. The bagasse-based hard carbon prepared by the preparation method can be efficiently and stably circulated in a sodium ion battery, and shows excellent rate capability.

Description

Technical Field

[0001] This application is aimed at the development of sodium-ion battery negative electrodes, and the content involves a preparation method of hard carbon derived from bagasse waste and its application in sodium-ion batteries. Background Art

[0002] With the rapid development of renewable energy, the development of efficient and low-cost electrochemical energy storage technology has become the key. As a potential energy storage technology to replace lithium-ion batteries, sodium-ion batteries have received unprecedented attention in recent years. Compared with lithium, sodium resources are abundant, widely distributed and low-cost, which makes sodium-ion batteries have significant cost advantages 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 negative electrode materials. Hard carbon materials are considered to be one of the most promising negative electrode materials for sodium-ion batteries due to their unique disordered structure and rich nanopores. Hard carbon can not only provide a large interlayer spacing to accommodate sodium ions, but also has good conductivity and structural stability, and can maintain high capacity and cycle stability during charging and discharging. However, the preparation of hard carbon usually relies on petroleum-based or coal-based precursors, which is not only costly but also contrary to the goal of environmental sustainability. Therefore, finding renewable and low-cost hard carbon precursors for the development of hard carbon for sodium batteries has become a current research hotspot. Sugarcane bagasse, as an abundant agricultural waste in South China, has the characteristics of wide sources, low cost and renewable, and is an ideal precursor for the preparation of hard carbon. Through processes such as pyrolysis and carbonization, sugarcane bagasse can be converted into hard carbon materials with excellent sodium storage properties, which 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] Although in recent years, researchers have extensively explored the application of bagasse-derived hard carbon in sodium-ion batteries and made significant progress. Studies have shown that bagasse-derived hard carbon has rich pore structure, large specific surface area and suitable surface chemical properties, which enable it to show excellent performance in sodium ion storage. However, in the process of developing bagasse-derived hard carbon, there are still many key scientific issues and technical challenges that need to be solved. First, the chemical composition and structure of bagasse vary greatly due to different origins and processing methods, which may lead to inconsistent performance of derived hard carbon. How to further optimize the preparation process of hard carbon to reduce production costs and improve the energy density and cycle life of materials is also a key direction for future research. In addition, since the natural pore structure of biomass-derived hard carbon easily leads to its extremely low first coulombic efficiency in sodium batteries, how to improve the pore structure in hard carbon and improve the reversibility of hard carbon to sodium ions still lacks necessary exploration. In response to the above technical difficulties, we have carried out a comprehensive innovation of bagasse-derived hard carbon to develop a high-performance sodium-ion battery anode. Summary of the invention

[0004] The purpose of the present application is to provide a preparation method of hard carbon derived from bagasse and its application in sodium batteries to solve the above problems.

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

[0006] A method for preparing hard carbon derived from bagasse, comprising:

[0007] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The bagasse shows a slight swelling phenomenon. The bagasse is then rolled to remove most of the water.

[0008] The obtained bagasse is subjected to hemicellulose removal treatment, and firstly, the hemicellulose inside the bagasse is dissolved and stripped by using alkali. By adjusting the type, concentration, treatment temperature and treatment time of the alkali, the hemicellulose is partially retained for the regulation of the microporous structure during the cellulose carbonization process.

[0009] After the alkali treatment, the corresponding cellulose is collected and the solid is washed with a hydrochloric acid solution and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water, thereby retaining the pore structure.

[0010] The solid product obtained after freeze drying is subjected to high temperature annealing treatment. The treatment condition is carried out under a protective atmosphere. In the heat treatment, the treatment temperature is divided into three stages. Then, a high temperature heat treatment is carried out under a protective atmosphere. The heat treatment is divided into three stages, namely, a pore opening treatment, a carbonization treatment, and a graphite layer formation treatment.

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

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

[0013] Preferably, the bagasse is subjected to hemicellulose removal treatment, the alkali used includes NaOH, KOH, LiOH, ammonia water, sodium acetate, etc., the pH value is adjusted to 9-14, the heating temperature is 50-80°C, the insulation time is 2-6h, and the stirring speed is 500-2000rmp.

[0014] Preferably, after the alkali treatment, the corresponding cellulose is collected and the solid is washed with a hydrochloric acid solution, the concentration of the hydrochloric acid is 0.5-2 mol / L, and the soaking time is 2 hours. Freeze drying slows down the compression of the carbon material interface by the surface tension of water, and achieves the retention of the pore structure.

[0015] The solid product obtained after freeze drying is subjected to high temperature annealing treatment. The treatment condition is carried out under a protective atmosphere. In the heat treatment, the treatment temperature is divided into three stages. Then, a high temperature heat treatment is carried out under a protective atmosphere. The heat treatment is divided into three stages, namely, a pore opening treatment, a carbonization treatment, and a graphite layer formation treatment.

[0016] Preferably, the protective atmosphere in the high temperature annealing treatment can be nitrogen, argon, nitrogen / hydrogen mixed gas, argon / hydrogen mixed gas, the gas pressure is normal pressure, the gas is flowing gas, and the gas flow rate is 20-100 sccm. The treatment temperature is divided into three stages, wherein the temperature range of the opening stage is 280-320°C, and the holding time is 1-4h; the carbonization treatment temperature is 700-900°C, and the holding time is 1-4h; the graphite layer formation temperature is 1200-1500°C, and the holding time is 1-4h. The heating rate is 1-5°C / min. The cooling is quenching.

[0017] Preferably, after the 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 to 5 mol / L and a soaking time of 2 to 10 hours. After soaking, the soaked hard carbon is then cleaned with deionized water.

[0018] The hard carbon negative electrode is mixed with a binder and coated on a current collector by a doctor blade method. The negative electrode of the sodium battery is obtained by drying, and the electrodes are rolled and assembled into a battery using an ester / ether electrolyte under an argon atmosphere.

[0019] Preferably, the binder includes 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, 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 doctor blade coating method, and the coating thickness is 50 to 300 μm. After drying, the electrode is rolled, and the rolling pressure is 50 to 200 MPa.

[0023] Preferably, ether electrolyte is used for assembling sodium battery, and ether electrolyte includes but is not limited to ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 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, and the concentration of the salt in the electrolyte is 0.5-2 mol / L.

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

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

[0026] The preparation method of hard carbon derived from bagasse provided in the present application uses acid and alkali to cross-link the internal structure of biomass, remove hemicellulose, remove ash and other processes for many times, which can effectively solve the problem of biomass inhomogeneity caused by origin, weather and growth environment. In the preparation process of hard carbon, conventional one-step high-temperature annealing can effectively obtain hard carbon, but because the pore structure of carbon cannot be effectively closed, it often shows extremely low first coulomb efficiency and low platform capacity. In the process of annealing hard carbon, this method adopts three stages, wherein the temperature range of the pore opening stage is 280-320℃, and the insulation time is 1-4h; the carbonization treatment temperature is 700-900℃, and the insulation time is 1-4h; the graphite layer formation temperature is 1200-1500℃, and the insulation time is 1-4h. The heating rate is 1-5℃ / min. The cooling is quenching. The low temperature process is to ensure the effective dehydration and pore opening of biomass, so as to preliminarily regulate the pore structure inside the hard carbon. The medium temperature process is to ensure the deoxidation of the carbon material to form a large number of CC / C=C bonds and further increase the number of micropores. The high temperature process causes partial graphitization of the carbon layer and closes the open pores generated during the dehydration and deoxidation process to further form a closed-pore structure, thereby effectively improving the reversibility of hard carbon during the sodium storage process.

[0027] The bagasse-derived hard carbon provided in this application has a micron structure, good electrical conductivity, and a closed-cell pore structure. Based on this structure, the obtained bagasse-derived hard carbon can be efficiently and stably circulated in sodium-ion batteries and exhibits excellent rate performance; the bagasse-derived hard carbon has high first coulombic efficiency, high specific capacity, high stability, and has large-scale development prospects.

[0028] The bagasse-derived hard carbon negative electrode for sodium battery provided in this application has excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0030] Figure 1 The scanning electron microscope and transmission electron microscope images of the bagasse-derived hard carbon in Example 1;

[0031] Figure 2 is the X-ray derivative image of the bagasse-derived hard carbon in Example 1;

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

[0033] Figure 4 is the charge and discharge curve of the bagasse-derived hard carbon in Example 1 at a current density of 100 mA / g;

[0034] Figure 5 Long cycle curves of bagasse-derived hard carbon at a current density of 1 A / g-1; DETAILED DESCRIPTION

[0035] A method for preparing bagasse-derived hard carbon, comprising:

[0036] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The bagasse shows a slight swelling phenomenon. The bagasse is then rolled to remove most of the water.

[0037] The obtained bagasse is subjected to hemicellulose removal treatment, and firstly, the hemicellulose inside the bagasse is dissolved and stripped by using alkali. By adjusting the type, concentration, treatment temperature and treatment time of the alkali, the hemicellulose is partially retained for the regulation of the microporous structure during the cellulose carbonization process.

[0038] After the alkali treatment, the corresponding cellulose is collected and the solid is washed with a hydrochloric acid solution and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water, thereby retaining the pore structure.

[0039] The solid product obtained after freeze drying is subjected to high temperature annealing treatment. The treatment condition is carried out under a protective atmosphere. In the heat treatment, the treatment temperature is divided into three stages. Then, a high temperature heat treatment is carried out under a protective atmosphere. The heat treatment is divided into three stages, namely, a pore opening treatment, a carbonization treatment, and a graphite layer formation treatment.

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

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

[0042] In an optional embodiment, bagasse is subjected to hemicellulose removal treatment, the alkali used includes NaOH, KOH, LiOH, ammonia water, sodium acetate, the heating temperature is 50, 60, 70, 80°C, the insulation time is 2, 4, 6h, and the stirring speed is 500, 1000, 1500, 2000rmp.

[0043] In an optional embodiment, after the alkali treatment, the corresponding cellulose is collected and the solid is washed with a hydrochloric acid solution, the concentration of the hydrochloric acid is 0.5, 1, 1.5, 2 mol / L, and the soaking time is 2 hours. Freeze drying is performed to slow down the compression of the carbon material interface by the surface tension of water, thereby retaining the pore structure.

[0044] The solid product obtained after freeze drying is subjected to high temperature annealing treatment. The treatment condition is carried out under a protective atmosphere. In the heat treatment, the treatment temperature is divided into three stages. Then, a high temperature heat treatment is carried out under a protective atmosphere. The heat treatment is divided into three stages, namely, a pore opening treatment, a carbonization treatment, and a graphite layer formation treatment.

[0045] In an optional embodiment, the protective atmosphere in the high temperature annealing treatment can be nitrogen, argon, nitrogen / hydrogen mixed gas, argon / hydrogen mixed gas, the gas pressure is normal pressure, the gas is flowing gas, and the gas flow rate is 20, 50, 80, 100 sccm. The treatment temperature is divided into three stages, wherein the temperature range of the opening stage is 280, 300, 320°C, and the holding time is 1, 2, 4h; the carbonization treatment temperature is 700, 800, 900°C, and the holding time is 1, 2, 4h; the graphite layer formation temperature is 1200, 1300, 1400, 1500°C, and the holding time is 1, 2, 4h. The heating rate is 1, 2, 3, 4, 5°C / min. The cooling is quenching.

[0046] In an optional embodiment, after the high temperature heat treatment, the hard carbon is soaked in an acid solution, the acid solution includes but is not limited to hydrochloric acid, sulfuric acid, and nitric acid solution, the concentration of the acid solution is 0.2, 0.5, 1, 2, 5 mol / L, and the soaking time is 2, 5, 8, 10 hours. After soaking, the soaked hard carbon is washed with deionized water.

[0047] The hard carbon negative electrode is mixed with a binder and coated on a current collector by a doctor blade method. The negative electrode of the sodium battery is obtained by drying, and the electrodes are rolled and assembled into a battery using an ester / ether electrolyte under an argon atmosphere.

[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 the binder is (2-10):100, preferably 10:100; 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. The electrode is prepared by a doctor blade method with a doctor blade thickness of 50 to 300 μm. After drying, the electrode is rolled with a roller pressure of 50 to 200 MPa.

[0049] In an optional embodiment, an ether electrolyte is preferably used for assembling a sodium battery, and the ether 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, and the concentration of the salt in the electrolyte is 0.5, 1, or 2 mol / L. During the battery assembly process, the oxygen content in the argon atmosphere is less than 1 ppm, and the water content is less than 1 ppm;

[0050] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If specific conditions are not specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0051] Example 1

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

[0053] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The soaking time is 8h, and the mass ratio of bagasse to water is 1:5. After soaking, the bagasse shows a slight swelling phenomenon. Then the bagasse is rolled to remove most of the water, and the roller pressure is 100MPa. The obtained bagasse is subjected to hemicellulose removal treatment, and the hemicellulose inside the bagasse is first dissolved and stripped using alkali. The bagasse is placed in a 0.6mol / L NaOH solution, heated to 80℃, kept warm for 4h, and stirred at a speed of 1500rmp. The obtained sample is then centrifuged and washed and further treated with hydrochloric acid to achieve cross-linking of the biomass and removal of ash. Hydrochloric acid is used in the acid treatment, the concentration of hydrochloric acid is 1mol / L, and the soaking time is 2 hours. The sample is then washed and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water and retain the pore structure. The solid material was frozen at -18°C and then transferred to a freeze dryer with a body temperature of -60°C and an air pressure of 0.1 Pa. The drying time was 24 hours. The obtained solid product was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. During the heat treatment, the treatment temperature was carried out in three stages. First, anneal at 300°C for 2 hours, then heat to 800°C for 2 hours, and then heat to 1300°C for 2 hours. After annealing, the biomass was quenched. The heating rate was 2°C / min, the gas was argon, and the gas flow rate was 50sccm. After heat treatment, the obtained sample was further soaked in a hydrochloric acid solution with an acid solution concentration of 1 mol / L and a soaking time of 4 hours. After soaking, the soaked hard carbon was washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon is as low as 4.8m 2 / g.

[0054] Figure 1 The scanning electron microscope and transmission electron microscope images of the synthesized bagasse-derived hard carbon are shown in Figure 2. Figure 2 is the X-ray diffraction pattern of the synthesized bagasse-derived hard carbon.

[0055] During the battery assembly process, the hard carbon negative electrode is mixed with the sodium carboxymethyl cellulose binder, and the mass ratio of the binder is 10wt%. It is coated on the current collector by a doctor blade method, and the doctor blade thickness is 100μm. The sodium battery negative electrode is dried to obtain the negative electrode, and the electrodes are rolled with a roller pressure of 100MPa, and then the battery is assembled under an argon atmosphere using an ether electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1mol / L sodium hexafluorophosphate for sodium ion battery electrolyte. The battery is assembled in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm in an argon atmosphere.

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

[0057] Example 2

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

[0059] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The soaking time is 4h, and the mass ratio of bagasse to water is 1:10. After soaking, the bagasse shows a slight swelling phenomenon. Then the bagasse is rolled to remove most of the water, and the roller pressure is 100MPa. The obtained bagasse is subjected to hemicellulose removal treatment, and the hemicellulose inside the bagasse is first dissolved and stripped using alkali. The bagasse is placed in a 0.6mol / L NaOH solution, heated to 80℃, kept warm for 4h, and stirred at a speed of 1500rmp. The obtained sample is then centrifuged and washed and further treated with nitric acid to achieve cross-linking of the biomass and removal of ash. Hydrochloric acid is used in the acid treatment, the nitric acid concentration is 1mol / L, and the soaking time is 2h. The sample is then washed and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water and retain the pore structure. The solid material was frozen at -18°C and then transferred to a freeze dryer with a body temperature of -60°C and an air pressure of 0.1Pa. The drying time was 24h. The obtained solid product was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. During the heat treatment, the treatment temperature was carried out in three stages. First, anneal at 320°C for 2h, then heat to 800°C for 2h, and then heat to 1500°C for 2h. After annealing, the biomass was quenched. The heating rate was 2°C / min, the gas was argon, and the gas flow rate was 50sccm. After heat treatment, the obtained sample was further soaked in a hydrochloric acid solution with an acid solution concentration of 1mol / L and a soaking time of 4h. After soaking, the soaked hard carbon was washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon is as low as 7.2m 2 / g.

[0060] During the battery assembly process, the hard carbon negative electrode is mixed with a sodium carboxymethyl cellulose binder, and the mass ratio of the binder is 5wt%. It is coated on the current collector by a scraping method, and the scraping thickness is 100μm. The sodium battery negative electrode is dried, and the electrodes are rolled with a rolling pressure of 100MPa, and then the battery is assembled under an argon atmosphere using an ether electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1mol / L sodium perchlorate for sodium ion battery electrolyte. The battery is assembled in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm in an argon atmosphere.

[0061] Based on the synthesized sugarcane bagasse-derived hard carbon in sodium ion batteries, at a current density of 50mA / g, the first coulombic efficiency is as high as 91%, the first reversible specific capacity is 318mAh / g, the specific capacity after 50 cycles is 305mAh / g, and the capacity retention rate after 50 cycles is greater than 96%. Cycling 5000 times at a high current density of 1A / g, its specific capacity is 163mAh / g.

[0062] Example 3

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

[0064] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The soaking time is 8h, and the mass ratio of bagasse to water is 1:5. After soaking, the bagasse shows a slight swelling phenomenon. Then the bagasse is rolled to remove most of the water, and the roller pressure is 100MPa. The obtained bagasse is subjected to hemicellulose removal treatment, and the hemicellulose inside the bagasse is first dissolved and stripped using alkali. The bagasse is placed in a 1mol / L KOH solution, heated to 60℃, kept warm for 8h, and stirred at a speed of 2000rmp. The obtained sample is then centrifuged and washed and further treated with hydrochloric acid to achieve cross-linking of the biomass and removal of ash. Hydrochloric acid is used in the acid treatment, the concentration of hydrochloric acid is 1mol / L, and the soaking time is 2 hours. The sample is then washed and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water and retain the pore structure. The solid material was frozen at -18°C and then transferred to a freeze dryer with a body temperature of -60°C and an air pressure of 0.1 Pa. The drying time was 24 hours. The obtained solid product was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. During the heat treatment, the treatment temperature was carried out in three stages. First, anneal at 300°C for 2 hours, then heat to 700°C for 2 hours, and then heat to 1500°C for 2 hours. After annealing, the biomass was quenched. The heating rate was 1°C / min, the gas was argon, and the gas flow rate was 100sccm. After heat treatment, the obtained sample was further soaked in a hydrochloric acid solution with an acid solution concentration of 1 mol / L and a soaking time of 4 hours. After soaking, the soaked hard carbon was washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon is as low as 6.3m 2 / g.

[0065] During the battery assembly process, the hard carbon negative electrode is mixed with the sodium carboxymethyl cellulose binder, and the mass ratio of the binder is 10wt%. It is coated on the current collector by a scraping method, and the scraping thickness is 100μm. The sodium battery negative electrode is dried, and the electrodes are rolled with a rolling pressure of 100MPa, and then the battery is assembled under an argon atmosphere using an ether electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1mol / L sodium trifluoromethanesulfonate for sodium ion battery electrolyte. The battery is assembled in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm in an argon atmosphere.

[0066] Based on the synthesized sugarcane bagasse-derived hard carbon in sodium ion batteries, at a current density of 50mA / g, the first coulombic efficiency is as high as 88%, the first reversible specific capacity is 336mAh / g, the specific capacity after 50 cycles is 308mAh / g, and the capacity retention rate after 50 cycles is greater than 96%. Cycling 3000 times at a high current density of 1A / g, its specific capacity is 201mAh / g.

[0067] Example 4

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

[0069] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The soaking time is 8h, and the mass ratio of bagasse to water is 1:5. After soaking, the bagasse shows a slight swelling phenomenon. Then the bagasse is rolled to remove most of the water, and the roller pressure is 100MPa. The obtained bagasse is subjected to hemicellulose removal treatment, and the hemicellulose inside the bagasse is first dissolved and stripped using alkali. The bagasse is placed in a 0.6mol / L NaOH solution, heated to 80℃, kept warm for 4h, and stirred at a speed of 1500rmp. The obtained sample is then centrifuged and washed and further treated with hydrochloric acid to achieve cross-linking of the biomass and removal of ash. Hydrochloric acid is used in the acid treatment, the concentration of hydrochloric acid is 1mol / L, and the soaking time is 2 hours. The sample is then washed and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water and retain the pore structure. The solid material was frozen at -18°C and then transferred to a freeze dryer with a body temperature of -60°C and an air pressure of 0.1Pa. The drying time was 24h. The obtained solid product was subjected to high-temperature annealing. The treatment was carried out under a protective atmosphere. During the heat treatment, the treatment temperature was carried out in three stages. First, anneal at 300°C for 4h, then heat to 700°C for 4h, and then heat to 1300°C for 4h. After annealing, the biomass was quenched. The heating rate was 2°C / min, the gas was argon, and the gas flow rate was 50sccm. After heat treatment, the obtained sample was further soaked in a hydrochloric acid solution with an acid solution concentration of 1mol / L and a soaking time of 4h. After soaking, the soaked hard carbon was washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon is as low as 3.8m 2 / g.

[0070] Figure 1 This is a scanning electron microscope image of the synthesized bagasse-derived hard carbon. Figure 2 Transmission electron micrograph of the synthesized bagasse-derived hard carbon.

[0071] During the battery assembly process, the hard carbon negative electrode is mixed with a sodium carboxymethyl cellulose binder, and the mass ratio of the binder is 10wt%. It is coated on the current collector by a scraping method, and the scraping thickness is 100μm. The sodium battery negative electrode is dried, and the electrodes are rolled with a rolling pressure of 100MPa, and then the battery is assembled under an argon atmosphere using an ether electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1mol / L sodium perchlorate for sodium ion battery electrolyte. The battery is assembled in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm in an argon atmosphere.

[0072] Based on the synthesized sugarcane bagasse-derived hard carbon in sodium ion batteries, at a current density of 50mA / g, the first coulombic efficiency is as high as 89%, the first reversible specific capacity is 315mAh / g, the specific capacity after 50 cycles is 298mAh / g, and the capacity retention rate after 50 cycles is greater than 96%. Cycling 3000 times at a high current density of 1A / g, its specific capacity is 185mAh / g.

[0073] Comparative Example 1

[0074] The sugarcane bagasse is directly subjected to high-temperature annealing treatment. The treatment condition is carried out under a protective atmosphere. During the heat treatment, the treatment temperature is carried out in three stages. First, anneal at 300°C for 4 hours, then heat to 700°C for 4 hours, and then heat to 1300°C for 4 hours. After annealing, the biomass is quenched. The heating rate is 2°C / min, the gas is argon, and the gas flow rate is 50sccm. After heat treatment, the obtained sample is further soaked in hydrochloric acid solution. The concentration of the acid solution is 1mol / L and the soaking time is 4h. After soaking, the soaked hard carbon is washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon is as low as 11.3m 2 / g.

[0075] During the battery assembly process, the hard carbon negative electrode is mixed with a sodium carboxymethyl cellulose binder, and the mass ratio of the binder is 10wt%. It is coated on the current collector by a scraping method, and the scraping thickness is 100μm. The sodium battery negative electrode is dried, and the electrodes are rolled with a rolling pressure of 100MPa, and then the battery is assembled under an argon atmosphere using an ether electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1mol / L sodium perchlorate for sodium ion battery electrolyte. The battery is assembled in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm in an argon atmosphere.

[0076] Based on the synthesized sugarcane bagasse-derived hard carbon in sodium ion batteries, at a current density of 50mA / g, the first coulombic efficiency is as high as 86%, the first reversible specific capacity is 251mAh / g, the specific capacity after 50 cycles is 231mAh / g, and the capacity retention rate after 50 cycles is greater than 96%. Cycling 2000 times at a high current density of 1A / g, its specific capacity is 144mAh / g.

[0077] Comparative Example 2

[0078] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The soaking time is 8h, and the mass ratio of bagasse to water is 1:5. After soaking, the bagasse shows a slight swelling phenomenon. Then the bagasse is rolled to remove most of the water, and the roller pressure is 100MPa. The obtained bagasse is subjected to hemicellulose removal treatment, and the hemicellulose inside the bagasse is first dissolved and stripped using alkali. The bagasse is placed in a 0.6mol / L NaOH solution, heated to 80℃, kept warm for 4h, and stirred at a speed of 1500rmp. The obtained sample is then centrifuged and washed and further treated with hydrochloric acid to achieve cross-linking of the biomass and removal of ash. Hydrochloric acid is used in the acid treatment, the concentration of hydrochloric acid is 1mol / L, and the soaking time is 2 hours. The sample is then washed and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water and retain the pore structure. The solid material was frozen at -18°C and then transferred to a freeze dryer with a body temperature of -60°C and an air pressure of 0.1 Pa. The drying time was 24 hours. The solid product was annealed at 1300°C for 4 hours. The heating rate was 2°C / min, the gas was argon, and the gas flow rate was 50sccm. After annealing, the biomass was cooled at a rate of 10°C / min. After heat treatment, the obtained sample was further soaked in a hydrochloric acid solution with a concentration of 1 mol / L and a soaking time of 4 hours. After soaking, the soaked hard carbon was washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon is as low as 128.0 m 2 / g.

[0079] During the battery assembly process, the hard carbon negative electrode is mixed with a sodium carboxymethyl cellulose binder, and the mass ratio of the binder is 10wt%. It is coated on the current collector by a scraping method, and the scraping thickness is 100μm. The sodium battery negative electrode is dried, and the electrodes are rolled with a rolling pressure of 100MPa, and then the battery is assembled under an argon atmosphere using an ether electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1mol / L sodium perchlorate for sodium ion battery electrolyte. The battery is assembled in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm in an argon atmosphere.

[0080] Based on the synthesized sugarcane bagasse-derived hard carbon in sodium ion batteries, at a current density of 50mA / g, the first coulombic efficiency is as high as 56%, the first reversible specific capacity is 268mAh / g, the specific capacity after 50 cycles is 215mAh / g, and the capacity retention rate after 50 cycles is greater than 96%. Cycling 1000 times at a high current density of 1A / g, its specific capacity is 113mAh / g.

[0081] Comparative Example 3

[0082] The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The soaking time is 8h, and the mass ratio of bagasse to water is 1:5. After soaking, the bagasse shows a slight swelling phenomenon. The bagasse is then rolled to remove most of the water, and the roller pressure is 100MPa. The obtained sample is then centrifuged and washed and further treated with hydrochloric acid to achieve cross-linking of the biomass and removal of ash. Hydrochloric acid is used in the acid treatment, the concentration of hydrochloric acid is 1mol / L, and the soaking time is 2 hours. The sample is then washed and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water and retain the pore structure. The solid solidification temperature is -18°C, and then transferred to a freeze dryer, the body setting temperature is -60°C, and the air pressure is 0.1Pa. The drying time is 24h. The obtained solid product is subjected to high-temperature annealing. The treatment condition is carried out under a protective atmosphere. In the heat treatment, the treatment temperature is carried out in three stages. First anneal at 300℃ for 4h, then heat to 1300℃ and anneal for 4h. After annealing, the biomass is quenched. The heating rate is 2℃ / min, the gas is argon, and the gas flow rate is 50sccm. After heat treatment, the obtained sample is further soaked in hydrochloric acid solution. The concentration of the acid solution is 1mol / L and the soaking time is 4h. After soaking, the soaked hard carbon is washed with deionized water and dried. The specific surface area of ​​the obtained bagasse-derived hard carbon is as low as 35.4m 2 / g.

[0083] During the battery assembly process, the hard carbon negative electrode is mixed with a sodium carboxymethyl cellulose binder, and the mass ratio of the binder is 10wt%. It is coated on the current collector by a scraping method, and the scraping thickness is 100μm. The sodium battery negative electrode is dried, and the electrodes are rolled with a rolling pressure of 100MPa, and then the battery is assembled under an argon atmosphere using an ether electrolyte. The ether electrolyte is ethylene glycol dimethyl ether dissolved in 1mol / L sodium perchlorate for sodium ion battery electrolyte. The battery is assembled in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm in an argon atmosphere.

[0084] Based on the synthesized sugarcane bagasse-derived hard carbon in sodium ion batteries, at a current density of 50mA / g, the first coulombic efficiency is as high as 83%, its first reversible specific capacity is 260mAh / g, the specific capacity after 50 cycles is 233mAh / g, and the capacity retention rate after 50 cycles is greater than 96%. Cycling 3000 times at a high current density of 1A / g, its specific capacity is 136mAh / g.

[0085] It should be noted that the embodiments described herein are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A preparation method based on bagasse waste derivation, characterized in that: include: The precursor used is bagasse. The bagasse is first soaked in water to remove the sugar components and some ash elements inside the bagasse. The bagasse shows a slight swelling phenomenon. The bagasse is then rolled to remove most of the water. The obtained bagasse is subjected to hemicellulose removal treatment, and firstly, the hemicellulose inside the bagasse is dissolved and stripped by using alkali. By adjusting the type, concentration, treatment temperature and treatment time of the alkali, the hemicellulose is partially retained for the regulation of the microporous structure during the cellulose carbonization process. After the alkali treatment, the corresponding cellulose is collected and the solid is washed with a hydrochloric acid solution and freeze-dried to slow down the compression of the carbon material interface by the surface tension of water, thereby retaining the pore structure.

2. The preparation method according to claim 1, characterized in that: The soaking time is 5 to 24 hours, and the mass ratio of bagasse to water is 1:2 to 20. Preferably, the soaking time is 8 hours. The rolling pressure is greater than 50 MPa, preferably 100 MPa.

3. According to claim 1, the sugarcane bagasse is subjected to hemicellulose removal treatment, the alkali used includes NaOH, KOH, LiOH, ammonia water, sodium acetate, etc., the pH value is adjusted to 9-14, the heating temperature is 50-80°C, the insulation time is 2-6h, and the stirring speed is 500-2000rmp. Preferably, the alkali is NaOH or KOH, wherein the concentration of NaOH and KOH is 0.6 mol / L. Preferably, the heating temperature is 80° C., the insulation time is 4 h, and the stirring speed is 100 rpm.

4. According to claim 1, after the alkali treatment, the corresponding cellulose is collected and the solid is washed with a hydrochloric acid solution, the concentration of the hydrochloric acid is 0.5-2 mol / L, and the soaking time is 2 hours. Freeze drying slows down the compression of the carbon material interface by the surface tension of water, and achieves the retention of the pore structure. Preferably, the hydrochloric acid concentration is 1 mol / L, the soaking time is 2 h, and the temperature is room temperature. Preferably, the freeze drying conditions are: the solidification temperature is -18°C, and then the solid is transferred to a freeze dryer, the temperature of the machine body is set to -60°C, the air pressure is 0.1 Pa, and the drying time is 24 hours.

5. The solid product obtained according to claim 1 is subjected to high temperature annealing treatment. The treatment condition is carried out under a protective atmosphere. In the heat treatment, the treatment temperature is carried out in three stages. Then, a high temperature heat treatment is carried out under a protective atmosphere, and the heat treatment is carried out in three stages, namely, a pore opening treatment, a carbonization treatment and a graphite layer formation treatment. After the treatment, the hard carbon is soaked in an acid solution again to further remove the ash in the hard carbon, thereby obtaining hard carbon for sodium ion batteries.

6. According to claim 5, the protective atmosphere can be nitrogen, argon, nitrogen / hydrogen mixed gas, argon / hydrogen mixed gas, the gas pressure is normal pressure, the gas is flowing gas, and the gas flow rate is 20-100 sccm. The treatment temperature is divided into three stages, wherein the temperature range of the hole opening stage is 280-320°C, and the insulation time is 1-4h; the carbonization treatment temperature is 700-900°C, and the insulation time is 1-4h; the graphite layer formation temperature is 1200-1500°C, and the insulation time is 1-4h. The heating rate is 1-5°C / min. The cooling is quenching. Preferably, the protective atmosphere is argon, the gas pressure is normal pressure, and the gas flow rate is 50 sccm. Preferably, the temperature in the pore opening stage is 300°C, and the treatment time is 2 hours; the temperature in the carbonization treatment is 800°C, and the treatment time is 2 hours; and the temperature in the graphite layer formation is 1300°C, and the treatment time is 2 hours. Preferably, the heating rate is 2°C / min, and the cooling process is to quickly cool the material at 1300°C to room temperature.

7. According to claim 5, after the treatment, the hard carbon is soaked in an acid solution, the acid solution includes but is not limited to hydrochloric acid, sulfuric acid, and nitric acid solution, the concentration of the acid solution is 0.2 to 5 mol / L, and the soaking time is 2 to 10 hours. After soaking, the soaked hard carbon is washed with deionized water. Preferably, the acid solution for soaking is a hydrochloric acid solution with a concentration of 1 mol / L and a soaking time of 4 hours.

8. A biomass-derived sodium ion battery negative electrode, characterized in that: The raw materials include those prepared as described in claims 1 to 7. The obtained hard carbon negative electrode is mixed with a binder and then coated on a current collector by a doctor blade method. The sodium battery negative electrode is dried to obtain a negative electrode, and the electrodes are rolled and then assembled in an argon atmosphere using an ester / ether electrolyte to obtain a battery. Preferably, the binder includes one or more of sodium carboxymethyl cellulose, sodium alginate, and polystyrene rubber; Preferably, the mass ratio of the biomass-derived hard carbon to the binder is (2-10):100, preferably 10:100; 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. Preferably, the electrode is prepared by a doctor blade coating method, and the coating thickness is 50 to 300 μm. After drying, the electrode is rolled, and the rolling pressure is 50 to 200 MPa. Preferably, ether electrolyte is used for assembling sodium battery, and ether electrolyte includes but is not limited to ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 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, and the concentration of the salt in the electrolyte is 0.5-2 mol / L. Preferably, during the battery assembly process, the oxygen content in the argon atmosphere is less than 1 ppm, and the water content is less than 1 ppm.

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