Hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention provides a preparation method of a hard carbon negative electrode material, which comprises the following steps: carrying out ball milling pretreatment on lignocellulose biomass powder to obtain powder A; mixing the powder A, a phenolic reagent and water, carrying out hydrothermal reaction at 105-185 DEG C, and carrying out cleaning, solid-liquid separation and drying on the obtained product to obtain a precursor B; and carbonizing the precursor B in a protective atmosphere to obtain the hard carbon negative electrode material. According to the preparation method, the derivative hard carbon with a rich closed pore structure, a disordered graphite-like microcrystalline structure and a relatively large carbon layer spacing can be obtained, and the hard carbon has excellent sodium ion storage and deintercalation capabilities and good structural stability, and has excellent cycle performance, initial coulombic efficiency, specific capacity and rate capability when being applied to a battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage battery materials, and in particular relates to a high-performance hard carbon negative electrode material, a preparation method thereof, and applications thereof. Background Art

[0002] Sodium-ion batteries (Na-ion batteries) exhibit significant advantages in resource abundance, cost-effectiveness, safety, and wide temperature adaptability, making them an ideal choice for large-scale energy storage and low-energy-density electronic devices. The commercialization of Na-ion battery cathode materials is relatively high, so the development of high-performance, low-cost anode materials to match them is of great practical significance. Hard carbon, one of the most commercially promising candidates for Na-ion battery anode materials, possesses a low-potential charge-discharge platform, suitable sodium storage capacity, and high safety performance. Its precursors mainly include biomass, resin, and asphalt. Among them, biomass precursors (such as coconut shell, bamboo, and starch) have attracted much attention due to their wide availability, low cost, and compliance with the concept of green and sustainable development. Lignocellulosic biomass, such as bamboo, is a fast-growing plant composed mainly of cellulose, hemicellulose, lignin, and a small amount of lipids and ash. Hard carbon prepared by direct carbonization has a low capacity.

[0003] Wang et al. used NaClO2 and CH3COOH to regulate the component content of bamboo powder. The principle is that the generated ClO2 will attack the β-O-4 bond of lignin and remove part of the lignin. As the lignin is removed, the concentration of free radicals in the bamboo powder precursor increases. The hard carbon obtained by high-temperature carbonization of the precursor with a suitable free radical concentration has a rich closed-pore structure (Adv. Mater. 2024, 36, 2401249).

[0004] Although several methods for manipulating bamboo powder components to produce high-performance hard carbon have been proposed, there are still deficiencies in the process and hard carbon performance. When Wang et al. used NaClO2 and CH3COOH to treat bamboo powder, toxic ClO2 gas was generated, posing a safety hazard in large-scale production. In addition, the energy density of the battery is closely related to the plateau capacity of the hard carbon, which mainly comes from the filling of sodium ions in the closed pores of the hard carbon. Therefore, it is still necessary to find a simple and efficient method to process bamboo powder biomass to prepare high-performance sodium ion hard carbon anodes rich in closed-pore structures. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned problems of the prior art, and its purpose is to provide a high-performance hard carbon negative electrode material, a preparation method thereof, and an application thereof.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In the pure water hydrothermal process, the cellulose and hemicellulose in the lignocellulosic biomass powder, such as bamboo powder, are partially hydrolyzed under the action of heating, pressurization and hydronium ions, and the hydrothermal environment will gradually become acidic; however, the dissolution of lignin in this environment is relatively small. This is because, on the one hand, the temperature required for the lignin reaction is relatively high, and on the other hand, the lignin will undergo self-condensation, that is, in an acidic environment, lignin will generate an electrophilic intermediate carbon cation, which spontaneously combines with the electron-rich aromatic sites on the aromatic ring of lignin, and then a complex intermolecular or intramolecular self-condensation phenomenon will occur, and the self-condensation phenomenon will be aggravated with the increase of temperature. The self-condensation reaction of lignin inside bamboo powder is not conducive to the dissolution of lignin, resulting in the bamboo powder treated with pure water hydrothermal treatment not being effectively regulated in component content, and the electrochemical performance of the derived hard carbon is relatively small. In the present invention, a phenolic reagent is innovatively introduced to promote the removal of lignin in bamboo powder, and the hemicellulose is hydrolyzed under hydrothermal conditions, thereby achieving effective regulation of the bamboo powder-derived hard carbon structure. The mechanism by which phenolic reagents promote the removal of lignin from bamboo powder is as follows: the phenolic reagents in the present invention have higher reactivity and smaller steric hindrance than the benzene ring structure in macromolecular lignin, causing the intermediate carbon cations to preferentially undergo aromatic substitution reactions with the phenolic reagents, thereby inhibiting a large amount of disordered and complex self-condensation between or within lignin molecules; in addition, the phenolic reagents can also act as solvents to dissolve the removed lignin, thereby effectively promoting the removal of lignin. The effective removal of a certain amount of lignin can accelerate the pyrolysis of bamboo powder, causing the precursor to rapidly carbonize, thereby promoting the bending and shrinkage of the carbon layer and forming a rich closed-pore structure; in the process of promoting the dissolution of lignin, the phenolic reagents increase the exposure of cellulose and hemicellulose, promoting the hydrolysis of hemicellulose. After the bamboo powder component content is precisely controlled by phenol hydrothermal treatment, the derived hard carbon has a smaller particle structure, a larger carbon layer interlayer spacing, and a rich closed-pore structure, with high first-cycle coulombic efficiency, high reversible specific capacity, excellent rate performance, and significantly improved cycling performance.

[0007] Specifically, in a first aspect, a method for preparing a hard carbon negative electrode material is provided, comprising: The lignocellulosic biomass powder was pretreated by ball milling to obtain powder A; Powder A, a phenolic reagent, and water are mixed and subjected to a hydrothermal reaction at a temperature of 105 to 185° C. The resulting product is washed, solid-liquid separated, and dried to obtain a precursor B; The precursor B is carbonized under a protective atmosphere to obtain a hard carbon negative electrode material.

[0008] Furthermore, the lignocellulosic biomass powder is one or more of bamboo powder, wood powder, corn straw powder, wheat straw powder, bagasse powder, and coconut shell powder.

[0009] Furthermore, the phenolic reagent is one or more of phenol, 2-naphthol, and p-cresol.

[0010] Furthermore, the mass ratio of the phenolic reagent to powder A is 1:2~5, Furthermore, the mass ratio of the powder A to water is 1:3-10.

[0011] Furthermore, the ball-to-material ratio of the ball mill is 8-30:1.

[0012] Furthermore, the rotation speed of the ball mill is 200-400 rpm.

[0013] Furthermore, the ball milling time is 5 to 10 hours.

[0014] Furthermore, the ball mill is a planetary ball mill.

[0015] Furthermore, the holding time of the hydrothermal reaction is 1 to 4 hours.

[0016] Furthermore, the cleaning is alcohol cleaning, or water washing first and then alcohol cleaning.

[0017] Furthermore, the carbonization temperature is 1200-1400°C; Furthermore, the carbonization holding time is 1 to 3 hours.

[0018] Furthermore, the heating rate during the carbonization is 1-5°C / min.

[0019] Furthermore, after carbonization, the temperature is first lowered to below 500°C at a rate of 1-5°C / min, and then naturally lowered.

[0020] Furthermore, the protective atmosphere is one of argon atmosphere, nitrogen atmosphere, helium atmosphere, or a mixture of two or more.

[0021] In a second aspect, a hard carbon negative electrode material is provided, which is prepared using the aforementioned preparation method.

[0022] The third aspect provides the application of the aforementioned hard carbon negative electrode material in the field of energy storage.

[0023] In a fourth aspect, a sodium ion battery is provided, comprising the aforementioned hard carbon negative electrode material.

[0024] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: The preparation method provided by the present invention uses lignocellulosic biomass as the raw material. After mechanical activation, it is hydrothermally treated with a phenolic reagent and water, and then carbonized at high temperature to obtain a derivative hard carbon with a rich closed-pore structure, a disordered graphite-like microcrystal structure, and a large interlayer spacing between carbon layers. This hard carbon has excellent sodium ion storage and deintercalation capabilities and good structural stability. When used in batteries, it has excellent cycle performance, first coulombic efficiency, specific capacity, and rate performance.

[0025] The preparation method provided by the present invention has a wide range of carbon sources with low cost, a simple process, only requires one step of high-temperature carbonization, has few steps, and does not require additional acid-base treatment. It can achieve cost control of the hard carbon negative electrode and is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 Graph showing the relative percentage contents of cellulose, hemicellulose, lignin and ash in the precursors of Comparative Example 1 and Example 1.

[0028] Figure 2 2 are scanning electron microscope images of the precursors in Comparative Example 1 and Example 1.

[0029] Figure 3 2 are X-ray diffraction patterns of the hard carbon materials obtained in Comparative Example 1 and Example 1.

[0030] Figure 4 These are high-magnification transmission electron microscope images of the hard carbon materials obtained in Comparative Example 1 and Example 1.

[0031] Figure 5 These are the small-angle diffraction patterns of the hard carbon materials obtained in Comparative Example 1 and Example 1.

[0032] Figure 6 This is the first cycle charge and discharge curve of the button battery assembled with the hard carbon material obtained in Example 1.

[0033] Figure 7 This is the first cycle charge and discharge curve of the button battery assembled with the hard carbon material obtained in Comparative Example 1.

[0034] Figure 8 This is the first cycle charge and discharge curve of the button battery assembled with the hard carbon material obtained in Comparative Example 2.

[0035] Figure 9This is a comparison chart of rate tests of button-type batteries assembled with the hard carbon negative electrode materials obtained in Example 1, Example 2, and Comparative Example 1.

[0036] Figure 10 This is a comparison chart of the cycle tests of button cells assembled with the hard carbon negative electrode materials obtained in Example 1, Example 2 and Comparative Example 1 at a current density of 1C.

[0037] Figure 11 This is a comparison chart of the cycle tests of button cells assembled with the hard carbon negative electrode materials obtained in Example 1 and Comparative Example 1 at a current density of 2C. DETAILED DESCRIPTION

[0038] Some embodiments provide a method for preparing a hard carbon negative electrode material, comprising: The lignocellulosic biomass powder is pretreated and activated by ball milling to obtain powder A; Powder A, a phenolic reagent, and water are mixed and subjected to a hydrothermal reaction at a temperature of 105 to 185° C. The resulting product is washed, solid-liquid separated, and dried to obtain a precursor B; The precursor B is carbonized under a protective atmosphere to obtain a hard carbon negative electrode material.

[0039] In the above preparation method, lignocellulosic biomass powder refers to biomass powder composed of cellulose, hemicellulose, lignin, etc.; the lignocellulosic biomass powder is one or more of bamboo powder, wood powder, corn straw powder, wheat straw powder, bagasse powder, and coconut shell powder. In some embodiments, the lignocellulosic biomass powder is bamboo powder. Since bamboo powder has a similar chemical composition to the above-mentioned other wood biomass powders, the analysis can also be used for the processing of other lignocellulosic biomass powders.

[0040] In some embodiments, the temperature of the hydrothermal reaction is 105~185°C, for example, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, etc., preferably 105~165°C.

[0041] In some preferred embodiments, the phenolic reagent is one or more of phenol, 2-naphthol, and p-cresol.

[0042] In some preferred embodiments, the mass ratio of the phenolic reagent to powder A is 1:1-5, for example, 1:1, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, etc., preferably 1:2-5.

[0043] In some preferred embodiments, the mass ratio of the powder A to water is 1:3-10, for example, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0044] In some preferred embodiments, the ball-to-material ratio of the ball mill is 8 to 30:1, for example, 8:1, 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, 25:1, 28:1, 30:1, etc.

[0045] In some preferred embodiments, the ball milling speed is 200-400 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, etc.

[0046] In some preferred embodiments, the ball milling time is 5 to 10 h, for example, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, etc.

[0047] In some embodiments, the ball mill is a planetary ball mill.

[0048] In some preferred embodiments, the holding time of the hydrothermal reaction is 1 to 4 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc.

[0049] In some preferred embodiments, the carbonization temperature is 1200-1400°C, for example, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, etc.

[0050] In some preferred embodiments, the carbonization holding time is 1 to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.

[0051] In some preferred embodiments, the heating rate during carbonization is 1-5°C / min.

[0052] In some preferred embodiments, after carbonization, the temperature is first lowered to below 500° C. at a rate of 1-5° C. / min, and then naturally lowered.

[0053] In some preferred embodiments, the protective atmosphere is one of argon atmosphere, nitrogen atmosphere, and helium atmosphere, or a mixture of two or more thereof.

[0054] In some embodiments, the mixing time of the powder A, the phenolic reagent, and water is 10 to 30 minutes, wherein the water can be low in impurities, such as deionized water.

[0055] In the preparation method, the hydrothermal reaction can be carried out in a reactor.

[0056] In the preparation method, the cleaning can be performed by alcohol cleaning, or water (deionized water) cleaning followed by alcohol cleaning, etc. The purpose of cleaning is to elute phenolic reagents and the eluate from the lignocellulosic biomass powder. The purpose of drying is to remove water, which can be performed by conventional drying methods, such as drying, and the drying temperature can be determined conventionally.

[0057] In the preparation method, after carbonization, other operations, such as grinding and sealing, can also be performed.

[0058] Some embodiments provide a hard carbon negative electrode material, which is prepared by the aforementioned preparation method.

[0059] Some embodiments provide the use of a hard carbon negative electrode material in the field of energy storage.

[0060] Some embodiments provide a sodium ion battery comprising the aforementioned hard carbon negative electrode material.

[0061] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0062] Unless otherwise defined, all the professional terms used herein have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0063] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0064] Example 1 First, the bamboo powder was ball-milled for pretreatment, with a ball-to-material ratio of 10:1 (i.e. the mass ratio of agate ball milling beads to bamboo powder was 10:1), a rotation speed of 300 rpm, and a ball milling time of 6 h. The ball-milled bamboo powder, phenol and deionized water were mixed and stirred for 30 min at a mass ratio of 2:1:12, then transferred to the inner container of a polytetrafluoroethylene hydrothermal kettle, placed in a reaction kettle and tightened, and placed in an oven at 145°C for 2 h. After the hydrothermal kettle was completely cooled, the inner container was taken out, the reaction product was filtered, washed with deionized water and then washed with washing alcohol, and then placed in an oven at 80°C for drying for 8 h. The obtained bamboo powder residue was sintered into hard carbon in an argon atmosphere in a tube furnace. The sintering temperature was 1300°C, the sintering time was 2 h, and the heating rate was 2°C / min. After the tube furnace was cooled, the hard carbon material was taken out, ground in an agate mortar to uniform particle size, and sealed in a sample tube for storage.

[0065] Button battery assembly: Bamboo powder-derived hard carbon material, acetylene black, and sodium alginate were mixed in a mass ratio of 8:1:1 and ground into a smooth, particle-free slurry in an agate mortar using deionized water as the solvent. The slurry was then evenly coated on a clean, flat copper foil with a scraper. The slurry-coated copper foil was placed in a vacuum oven at 80°C and dried for 8-12 hours. The dried electrode sheets were punched into 13 mm diameter electrode sheets using a cutting machine. The diaphragm used was a glass fiber diaphragm with a diameter of 19 mm, the electrolyte was 1 M NaPF6 (solvent was DIGLYME), the counter electrode was sodium metal, and CR2032 button batteries were assembled.

[0066] Example 2 First, bamboo powder was pre-milled at a ball-to-material ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), a speed of 300 rpm, and a milling time of 6 hours. The milled bamboo powder, phenol, and deionized water were mixed at a mass ratio of 2:1:12 and stirred for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene hydrothermal reactor, placed in the reactor, and tightened. The reactor was then placed in an oven at 125°C for 2 hours. After the hydrothermal reactor completely cooled, the reactor was removed from the reactor. The reaction product was filtered, rinsed with deionized water, and then rinsed with washing alcohol. After filtration, the product was placed in an oven at 80°C and dried for 8 hours. The resulting bamboo powder residue was sintered in a tube furnace under an argon atmosphere to form hard carbon. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed, ground in an agate mortar until the particles were uniform in size, and then sealed in a sample tube for storage.

[0067] Button battery assembly: The assembly method is the same as in Example 1.

[0068] Example 3 First, bamboo powder was pre-milled at a ball-to-material ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), a speed of 300 rpm, and a milling time of 6 hours. The milled bamboo powder, phenol, and deionized water were mixed at a mass ratio of 2:1:12 and stirred for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene hydrothermal reactor, placed in the reactor, and tightened. The reactor was then placed in an oven at 105°C for 2 hours. After the hydrothermal reactor completely cooled, the reactor was removed from the reactor. The reaction product was filtered, rinsed with deionized water, and then rinsed with washing alcohol. After filtration, the product was dried in an 80°C oven for 8 hours. The resulting bamboo powder residue was sintered in a tube furnace under an argon atmosphere to form hard carbon. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed, ground in an agate mortar until the particles were uniform in size, and then sealed in a sample tube for storage.

[0069] Button battery assembly: The assembly method is the same as in Example 1.

[0070] Example 4 First, the bamboo powder was pretreated by ball milling, the ball-to-material ratio was 10:1 (i.e. the mass ratio of agate ball milling beads to bamboo powder was 10:1), the rotation speed was 300 rpm, and the ball milling time was 6 h. The ball-milled bamboo powder, phenol, and deionized water were mixed and stirred for 30 min at a mass ratio of 2:2:12, then transferred to the inner container of a polytetrafluoroethylene hydrothermal kettle, placed in a reaction kettle and tightened, and placed in an oven at 145°C for 2 h. After the hydrothermal kettle was completely cooled, the inner container was removed, the reaction product was filtered, washed with deionized water, and then washed with washing alcohol, and then placed in an oven at 80°C for 8 h. The obtained bamboo powder residue was placed in a tube furnace and sintered into hard carbon under an argon atmosphere. The sintering temperature was 1300°C, the sintering time was 2 h, and the heating rate was 2°C / min. After the tube furnace was cooled, the hard carbon material was removed, ground in an agate mortar to a uniform particle size, and sealed and stored in a sample tube.

[0071] Button cell assembly: the assembly method was the same as in Example 1.

[0072] Example 5 First, the bamboo powder was pretreated by ball milling, the ball-to-material ratio was 10:1 (i.e. the mass ratio of agate ball milling beads to bamboo powder was 10:1), the rotation speed was 300 rpm, and the ball milling time was 6 h. The ball-milled bamboo powder, phenol, and deionized water were mixed and stirred for 30 min at a mass ratio of 4:1:12, then transferred to the inner container of a polytetrafluoroethylene hydrothermal kettle, placed in a reaction kettle and tightened, and placed in an oven at 145°C for 2 h. After the hydrothermal kettle was completely cooled, the inner container was removed, the reaction product was filtered, washed with deionized water, and then washed with washing alcohol, and then placed in an oven at 80°C for 8 h. The obtained bamboo powder residue was placed in a tube furnace and sintered into hard carbon under an argon atmosphere. The sintering temperature was 1300°C, the sintering time was 2 h, and the heating rate was 2°C / min. After the tube furnace was cooled, the hard carbon material was removed, ground in an agate mortar to a uniform particle size, and sealed and stored in a sample tube.

[0073] Button cell assembly: the assembly method was the same as in Example 1.

[0074] Example 6 First, bamboo powder was pre-milled at a ball-to-material ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), a speed of 300 rpm, and a milling time of 6 hours. The milled bamboo powder, phenol, and deionized water were mixed at a mass ratio of 2:1:12 and stirred for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene hydrothermal reactor, placed in the reactor, and tightened. The reactor was then placed in an oven at 145°C for 1 hour. After the hydrothermal reactor completely cooled, the reactor was removed. The reaction product was filtered, rinsed with deionized water, and then rinsed with washing alcohol. After filtration, the product was placed in an 80°C oven and dried for 8 hours. The resulting bamboo powder residue was sintered in a tube furnace under an argon atmosphere to form hard carbon. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed and ground in an agate mortar until the particles were uniform in size. The sample tube was then sealed and stored.

[0075] Button battery assembly: The assembly method is the same as in Example 1.

[0076] Example 7 First, bamboo powder was pre-milled at a ball-to-material ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), a speed of 300 rpm, and a milling time of 6 hours. The milled bamboo powder, phenol, and deionized water were mixed at a mass ratio of 2:1:12 and stirred for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene hydrothermal reactor, placed in the reactor, and tightened. The reactor was then placed in an oven at 145°C for 4 hours. After the hydrothermal reactor completely cooled, the reactor was removed from the reactor. The reaction product was filtered, rinsed with deionized water, and then rinsed with washing alcohol. After filtration, the product was placed in an 80°C oven and dried for 8 hours. The resulting bamboo powder residue was sintered in a tube furnace under an argon atmosphere to form hard carbon. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed, ground in an agate mortar until the particles were uniform in size, and then sealed in a sample tube for storage.

[0077] Button battery assembly: The assembly method is the same as in Example 1.

[0078] Example 8 First, bamboo powder was pre-milled at a ball-to-material ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), a speed of 300 rpm, and a milling time of 6 hours. The milled bamboo powder, phenol, and deionized water were mixed at a mass ratio of 2:1:12 and stirred for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene hydrothermal reactor, placed in the reactor, and tightened. The reactor was then placed in an oven at 165°C for 2 hours. After the hydrothermal reactor completely cooled, the reactor was removed from the reactor. The reaction product was filtered, rinsed with deionized water, and then rinsed with washing alcohol. After filtration, the product was placed in an 80°C oven and dried for 8 hours. The resulting bamboo powder residue was sintered in a tube furnace under an argon atmosphere to form hard carbon. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed, ground in an agate mortar until the particles were uniform in size, and then sealed in a sample tube for storage.

[0079] Button battery assembly: The assembly method is the same as in Example 1.

[0080] Example 9 First, bamboo powder was pre-milled at a ball-to-material ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), a speed of 300 rpm, and a milling time of 6 hours. The milled bamboo powder, phenol, and deionized water were mixed at a mass ratio of 2:1:12 and stirred for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene hydrothermal reactor, placed in the reactor, and tightened. The reactor was then placed in an oven at 185°C for 2 hours. After the hydrothermal reactor completely cooled, the reactor was removed from the reactor. The reaction product was filtered, rinsed with deionized water, and then rinsed with washing alcohol. After filtration, the product was placed in an 80°C oven and dried for 8 hours. The resulting bamboo powder residue was sintered in a tube furnace under an argon atmosphere to form hard carbon. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed, ground in an agate mortar until the particles were uniform in size, and then sealed in a sample tube for storage.

[0081] Button battery assembly: The assembly method is the same as in Example 1.

[0082] Comparative Example 1 First, bamboo powder was pre-milled using a ball-to-powder ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), at a speed of 300 rpm, for 6 hours. The milled bamboo powder was then sintered into hard carbon in a tube furnace under an argon atmosphere at a temperature of 1300°C for 2 hours at a heating rate of 2°C / min. After the tube furnace cooled, the hard carbon material was removed and ground in an agate mortar until uniform particle size was achieved. The resulting material was then sealed in a sample tube for storage.

[0083] Button battery assembly: The assembly method is the same as in Example 1.

[0084] Comparative Example 2 First, bamboo powder was pre-milled at a ball-to-material ratio of 10:1 (i.e., a mass ratio of agate milling beads to bamboo powder of 10:1), a speed of 300 rpm, and a milling time of 6 hours. The milled bamboo powder was then mixed with deionized water at a mass ratio of 1:6 and stirred for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene hydrothermal reactor, placed in the reactor, and tightened. The reactor was then placed in an oven at 145°C for 2 hours. After the hydrothermal reactor completely cooled, the reactor was removed from the reactor. The reaction product was filtered, rinsed with deionized water, and then rinsed with washing alcohol. After filtration, the product was placed in an 80°C oven and dried for 8 hours. The resulting bamboo powder residue was sintered in a tube furnace under an argon atmosphere to form hard carbon. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed, ground in an agate mortar until the particles were uniform in size, and then sealed in a sample tube for storage.

[0085] Button battery assembly: The assembly method is the same as in Example 1.

[0086] Comparative Example 3 First, bamboo powder was placed in a tube furnace and sintered into hard carbon under an argon atmosphere. The sintering temperature was 1300°C, the sintering time was 2 hours, and the heating rate was 2°C / min. After the tube furnace cooled, the hard carbon material was removed and ground in an agate mortar to a uniform particle size. The sample tube was then sealed and stored.

[0087] Button battery assembly: The assembly method is the same as in Example 1.

[0088] Performance Testing The CR2032 button-type batteries assembled with the bamboo powder-derived hard carbon negative electrode materials prepared in the above examples and comparative examples were subjected to electrochemical testing. The first reversible capacity and first coulomb data are shown in Table 1.

[0089] Result analysis: The component content determination results of the precursor obtained after hydrothermal treatment in Example 1 and the bamboo powder in Comparative Example 1 are as follows: Figure 1 As shown, compared with Comparative Example 1, the content of the precursor components in Example 1 changed significantly. From the relative percentage content of each component, hemicellulose, lignin and ash were obviously partially removed, indicating that phenol hydrothermal treatment of bamboo powder can regulate the component content of bamboo powder.

[0090] The scanning electron microscopy results of the precursors in Example 1 and Comparative Example 1 are as follows: Figure 2As shown, the precursor in Comparative Example 1 (bamboo powder obtained by ball milling pre-activation) exhibits a relatively compact microstructure, and the tubular pore structure found in natural bamboo is difficult to observe. The precursor in Example 1 (bamboo powder obtained by phenol-assisted hydrothermal treatment) has a looser structure than the precursor in Comparative Example 1, and the tubular pore structure of bamboo is clearly observed, indicating that the microstructure of the bamboo powder changes after phenol hydrothermal modification. The loose bamboo powder structure improves the utilization rate of various components during pyrolysis, accelerates pyrolysis efficiency, and promotes the formation of a closed-pore structure. The visible pore structure in the phenol hydrothermal modified bamboo powder facilitates the formation of rapid sodium ion migration channels after carbonization, accelerating the sodium ion transport rate during the charge and discharge processes. Analysis reveals that this is due to the fact that during the pure water hydrothermal process, the cellulose and hemicellulose in the bamboo powder undergo partial hydrolysis under the influence of heat, pressure, and hydronium ions, and the hydrothermal environment gradually becomes acidic. However, lignin dissolution is low in this environment. This is partly due to the high temperature required for the lignin reaction and partly due to the self-condensation of lignin. In an acidic environment, lignin generates electrophilic intermediate carbon cations, which spontaneously bind to electron-rich aromatic sites on the lignin aromatic rings, leading to complex intermolecular and intramolecular self-condensation, which intensifies with increasing temperature. This self-condensation of lignin within the bamboo powder hinders its dissolution, resulting in ineffective control of the component content of the bamboo powder treated with pure water hydrothermal treatment and minimal improvement in the electrochemical performance of the derived hard carbon. Phenolic reagents, however, promote the removal of lignin from the bamboo powder, while simultaneously hydrolyzing the hemicellulose under hydrothermal conditions, effectively controlling the structure of the bamboo powder-derived hard carbon. The mechanism by which phenolic agents promote the removal of lignin from bamboo powder is as follows: compared to the benzene ring structure in macromolecular lignin, phenolic agents have higher reactivity and less steric hindrance, causing the intermediate carbon cation to preferentially undergo aromatic substitution reactions with the phenolic agent, thereby inhibiting the large amount of disordered and complex self-condensation between and within lignin molecules. Furthermore, phenolic agents can act as solvents to dissolve the removed lignin, effectively promoting lignin removal. The effective removal of a certain amount of lignin can accelerate the pyrolysis of bamboo powder, leading to rapid carbonization of the precursor, which in turn promotes the bending and contraction of the carbon layer and the formation of a rich closed-pore structure. In the process of promoting lignin dissolution, phenolic agents increase the exposure of cellulose and hemicellulose, promoting the hydrolysis of hemicellulose.

[0091] The X-ray diffraction results of the hard carbon obtained in Example 1 and Comparative Example 1 are as follows: Figure 3 As shown, compared with the hard carbon in Comparative Example 1, the diffraction peak at 2θ≈23° in Example 1 is significantly broadened and shifted to lower angles, indicating that the phenol hydrothermal treatment of bamboo powder can produce a derivative hard carbon with a more disordered graphite microcrystal structure and a larger interlayer spacing between graphite carbon layers. This larger interlayer spacing in the hard carbon facilitates the storage and rapid deintercalation of sodium ions.

[0092] The high magnification transmission electron microscopy results of the hard carbon obtained in Example 1 and Comparative Example 1 are as follows: Figure 4 As shown, the hard carbon prepared in Comparative Example 1 has a relatively flat graphite-like microcrystalline structure, and no obvious closed-pore structure can be observed; while the hard carbon of Example 1 has a more disordered and more curved graphite microcrystalline region, and a rich closed-pore structure can be observed. The rich closed-pore structure is beneficial to improving the platform capacity of the hard carbon.

[0093] The small angle diffraction test results of the hard carbon obtained in Example 1 and Comparative Example 1 are as follows: Figure 5 As shown in the figure, the small angle test curve of the hard carbon prepared in Comparative Example 1 is at Q=0.1 Å −1 There is no obvious platform near the curve of Example 1 at Q = 0.1 Å −1 An obvious platform appeared nearby, confirming that the hard carbon prepared in Example 1 has more closed-pore structures. The rich closed-pore structure is conducive to improving the platform capacity of the hard carbon.

[0094] According to the comparison of the microstructure and property characteristics of the bamboo powder precursor and the derived hard carbon prepared in the above-mentioned embodiment and the comparative example, it is shown that the preparation method provided by the present invention can change the content and microstructure of the bamboo powder components, thereby preparing high-performance bamboo powder-derived hard carbon with increased degree of disorder, enlarged interlayer spacing, and increased number of closed pores.

[0095] The data in Table 1 indicate that the reversible specific capacity of the bamboo powder-derived hard carbons prepared in the Examples of the present invention is higher than that of the hard carbons prepared in Comparative Examples 1 and 2. Specifically, a comparison of the reversible specific capacity of the hard carbons obtained in Comparative Examples 1 and 2 indicates that pure water hydrothermal treatment has a very limited effect on the performance of the bamboo powder-derived hard carbons. A comparison of the reversible specific capacity of the hard carbons obtained in Examples 1 and 2 indicates that the addition of phenol during the hydrothermal treatment effectively modulates the component content and structure of the bamboo powder, increasing the reversible specific capacity of the bamboo powder-derived hard carbon prepared in Example 1 to 345 mAh / g. Comparison of electrochemical performance of hard carbon obtained in Example 1, Example 2 and Comparative Example 1 Figures 6 to 10 As shown, compared with the hard carbon of Comparative Example 1, the reversible specific capacity, rate performance and cycle performance of the hard carbon prepared in Example 1 and Example 2 are significantly improved.

[0096] Specifically, the reversible specific capacity of Example 1 is increased by 45 mAh / g compared with the derived hard carbon prepared in Comparative Example 1, wherein the slope capacity is increased by about 10 mAh / g and the platform capacity is increased by about 35 mAh / g.

[0097] The hard carbon prepared in Example 1 still has a reversible specific capacity of 285 mAh / g at a current density of 3C; the hard carbon prepared in Example 2 still has a reversible specific capacity of 270 mAh / g at a current density of 3C; and the hard carbon prepared in Comparative Example 1 has a reversible specific capacity of only 210 mAh / g at the same current density.

[0098] The hard carbon prepared in Example 1 has a capacity retention rate of 96.2% after 900 cycles at a current density of 1C (1C = 300 mA / g); the hard carbon prepared in Example 2 has a capacity retention rate of 95.9% after 900 cycles at a current density of 1C; and the hard carbon prepared in Comparative Example 1 has a capacity retention rate of only 87.4% after 900 cycles at a current density of 1C, which is much lower than the capacity retention rates of the hard carbons prepared in Example 1 and Example 2.

[0099] Further increasing the density of the test current, the hard carbon prepared in Example 1 can be stably cycled for 1000 cycles at a current density of 2C (1C = 300 mA / g), and has a capacity retention rate of 95.7%. The hard carbon prepared in Comparative Example 1 begins to significantly decay and fluctuate in capacity at about 300 cycles, and fails after 580 cycles, and has capacity retention rates of 94.6% and 87.9% after 100 cycles and 580 cycles, respectively. This result shows that the hard carbon prepared in the present embodiment has superior cycle stability at a higher current density.

[0100] In summary, the phenol-assisted hydrothermal method in the present embodiment can successfully remove a certain amount of lignin and hemicellulose and most of the inorganic ash in the bamboo powder, and promote the exposure of cellulose, so as to optimize the component content and microstructure of the bamboo powder, so that the hard carbon derived from the treated bamboo powder has more disordered graphite crystalline regions, larger graphite carbon layer spacing and more closed pores, thereby improving the reversible specific capacity and rate performance of the hard carbon derived from the bamboo powder, and significantly improving the cycle stability.

[0101] Table 1 As can be seen from Table 1, by comparing Examples 1 to 3 and 8 to 9, when the hydrothermal temperature is between 105 and 185°C, the reversible specific capacity of the hard carbon material will also change with the change of the hydrothermal temperature, and will first increase and then decrease with increasing temperature. The reversible specific capacity of the hard carbon material obtained by treatment between 105 and 165°C is higher, which indicates that the precursor can be regulated between 105 and 165°C to obtain the expected components and thus the expected hard carbon material structure and performance. Compared with the hydrothermal treatment at 105 to 165°C, the performance of the corresponding hard carbon material after hydrothermal treatment at 185°C is significantly reduced. It also indicates that temperature has a significant effect on the regulation of the composition of the precursor, and when the temperature is too high, the regulation of the precursor composition cannot achieve the expected effect. , the expected hard carbon structure and performance cannot be obtained. After analysis, this is because when the reaction temperature is too high, the reaction activity of lignin is too high, which will cause more lignin to be released from the bamboo powder, and the excess lignin release is not conducive to the structural optimization and electrochemical performance of the derived hard carbon; By comparing Examples 1, 6~7, it can be seen that the hydrothermal time will also affect the performance of the hard carbon material, indicating that when the hydrothermal time is short or long, the structure and performance of the hard carbon material deteriorate. After analysis, this is because when the treatment time is too short under hydrothermal conditions, less hemicellulose and lignin are dissolved, and when the time is too long, more hemicellulose and lignin are dissolved, both of which are not conducive to the structural optimization and electrochemical performance of the derived hard carbon; in addition, the amount of phenol used will also have a certain impact on the performance of the hard carbon material.

[0102] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon negative electrode material, characterized in that: include: The lignocellulosic biomass powder was pretreated by ball milling to obtain powder A; Powder A, a phenolic reagent, and water are mixed and subjected to a hydrothermal reaction at a temperature of 105 to 185° C. The resulting product is washed, solid-liquid separated, and dried to obtain a precursor B; The precursor B is carbonized under a protective atmosphere to obtain a hard carbon negative electrode material.

2. The method for preparing a hard carbon negative electrode material according to claim 1, wherein: The lignocellulosic biomass powder is one or more of bamboo powder, wood powder, corn straw powder, wheat straw powder, bagasse powder, and coconut shell powder.

3. The method for preparing a hard carbon negative electrode material according to claim 1, wherein: The phenolic reagent is one or more of phenol, 2-naphthol and p-cresol.

4. The method for preparing a hard carbon negative electrode material according to claim 1, wherein: The mass ratio of the phenolic reagent to powder A is 1:2~5; The mass ratio of the powder A to water is 1:3-10.

5. The method for preparing a hard carbon negative electrode material according to claim 1, wherein: The ball-to-material ratio of the ball mill is 8-30:1; Preferably, the ball milling speed is 200-400 rpm; Preferably, the ball milling time is 5 to 10 hours; Preferably, the ball mill is a planetary ball mill.

6. The method for preparing a hard carbon negative electrode material according to claim 1, wherein: The holding time of the hydrothermal reaction is 1 to 4 hours; The cleaning is alcohol cleaning, or water cleaning first and then alcohol cleaning.

7. The method for preparing a hard carbon negative electrode material according to claim 1, wherein: The carbonization temperature is 1200-1400°C; The carbonization holding time is 1 to 3 hours; The heating rate during carbonization is 1-5°C / min; After carbonization, cool down to below 500℃ at a rate of 1~5℃ / min, and then cool down naturally; The protective atmosphere is one of argon atmosphere, nitrogen atmosphere, and helium atmosphere, or a mixture of two or more of the above.

8. A hard carbon negative electrode material, characterized in that: The method is as described in any one of claims 1 to 7.

9. Use of the hard carbon negative electrode material according to claim 8 in the field of energy storage.

10. A sodium ion battery, characterized in that Comprising the hard carbon negative electrode material as claimed in claim 8.

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