Preparation method for preparing bio-based hard carbon material with assistance of steam explosion method, application of bio-based hard carbon material and product of bio-based hard carbon material

Abstract

The invention relates to the technical field of preparation of hard carbon materials, in particular to a preparation method for preparing a bio-based hard carbon material with the assistance of a steam explosion method, application of the bio-based hard carbon material and a product of the bio-based hard carbon material The preparation method comprises the steps that 1, salix psammophila branches and leaves are coarsely crushed and pretreated to obtain salix psammophila powder; (2) performing steam explosion treatment on the salix psammophila powder, drying and crushing to obtain a steam explosion product; (3) carbonizing the steam explosion product to obtain a carbonized product; and (4) purifying, grinding and screening the carbonized product to obtain the product. The pretreatment in the step (1) comprises the steps of soaking crushed salix psammophila branches and leaves in acid liquor, drying, soaking in alkali liquor, washing and drying; the conditions of the steam explosion treatment in the step (2) are as follows: inert atmosphere is adopted, the pressure is 1-2MPa, the temperature is 140-180 DEG C, and the pressure is maintained for 15-50 minutes. Compared with the prior art, the coulombic efficiency of the salix psammophila hard carbon material is remarkably improved by improving pretreatment and steam explosion treatment of salix psammophila.

Description

Technical Field

[0001] This invention relates to the field of hard carbon material preparation technology, and in particular to a method for preparing bio-based hard carbon materials with the assistance of steam explosion, as well as its applications and products. Background Technology

[0002] Hard carbon materials, due to their excellent properties, have broad application prospects in energy storage, batteries, and other fields. Currently, the preparation of hard carbon materials largely relies on traditional fossil resources or chemical raw materials, which presents problems such as limited resources and environmental unfriendliness. Salix psammophila, a plant widely distributed in desert regions, is characterized by rapid growth and high renewability. Its rich biological components, including cellulose, hemicellulose, and lignin, provide a new raw material option for the preparation of hard carbon materials.

[0003] Chinese patent application CN20231064467.3 discloses a method for preparing carbon-based anode materials for sodium-ion batteries from waste wood. Using waste *Salix psammophila* wood as a biomass carbon source, the method involves ultrasonic washing with deionized water and anhydrous ethanol, followed by drying, pulverizing, and grinding, and then a two-step carbonization process. The resulting product is then acid-washed, dried, and reduced to obtain a high-performance hard carbon anode material for sodium-ion batteries, with a specific capacity reaching 200-300 mAh / g or even higher. This is mainly attributed to its rich pore structure and surface functional groups, which provide more sodium ion adsorption sites. *Salix psammophila* biomass hard carbon materials demonstrate great application potential due to their high specific capacity, excellent cycle stability, good rate performance, and environmental friendliness. However, current research on the application of corresponding hard carbon materials is limited, and the coulombic efficiency of these materials still needs improvement.

[0004] Chinese patent application CN202411640512.4 discloses a method for preparing high-lignosulfonate biomass-based hard carbon materials using a water / alcohol synergistic assisted steam explosion: High-lignosulfonate biomass is soaked, washed, dried, and crushed; then soaked in water and an alcohol reagent; the material is then treated under steam pressure of 1 MPa-3 MPa and temperature of 150℃-280℃ for 1-60 minutes; followed by depressurization and explosion, low-temperature carbonization, impurity removal, high-temperature carbonization, and pulverization and classification to obtain the high-lignosulfonate biomass-based hard carbon material. This invention demonstrates that steam explosion treatment and high-lignosulfonate biomass soaking treatment do not substantially improve the coulombic efficiency of the prepared hard carbon material.

[0005] Therefore, it is essential to find a method to improve the preparation of bio-based hard carbon materials. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing bio-based hard carbon materials using a steam explosion method, along with its applications and products. By rationally utilizing the biological components of *Salix psammophila*, high-performance *Salix psammophila* hard carbon materials are prepared, while simultaneously achieving efficient utilization of *Salix psammophila* resources.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing bio-based hard carbon materials using a steam explosion-assisted method, comprising the following steps: (1) The branches and leaves of the sand willow were coarsely crushed and pretreated to obtain sand willow powder; (2) The sand willow powder is subjected to steam explosion treatment, drying and pulverizing to obtain steam explosion products; (3) The steam explosion products are subjected to carbonization treatment to obtain carbonized products; (4) The carbonization products are purified, ground and sieved to obtain the hard carbon material of sand willow.

[0008] In some implementations, the pretreatment in step (1) involves soaking the crushed willow branches and leaves in acid solution, drying, soaking in alkaline solution, washing, and drying.

[0009] Preferably, the acid is at least one selected from hydrochloric acid, hydrofluoric acid, oxalic acid, and phosphoric acid; more preferably, the concentration of the acid solution is 1-3 mol / L, even more preferably 1.5-2.5 mol / L, and even more preferably 1.8-2.2 mol / L.

[0010] Preferably, the acid soaking conditions are: soaking at 63-77℃ for 4-8 hours; more preferably, soaking at 65-75℃ for 4-8 hours; and even more preferably, soaking at 68-72℃ for 5-7 hours.

[0011] Preferably, the alkali is at least one of potassium hydroxide, ammonium bicarbonate and sodium hydroxide; more preferably, the concentration of the alkali solution is 0.5-2 mol / L, even more preferably 0.5-1.5 mol / L, and even more preferably 0.8-1.2 mol / L.

[0012] Preferably, the alkaline solution soaking conditions are soaking at 40-60℃ for 1-3 hours; more preferably, soaking at 45-55℃ for 1-3 hours; and even more preferably, soaking at 48-52℃ for 1.5-2.5 hours.

[0013] The purpose of washing in this invention is to remove residual alkaline solution and make the washed sample neutral. Therefore, the washing method is not limited, such as centrifugal washing or vacuum filtration washing. Deionized water is preferred for washing.

[0014] In some implementations, the conditions for the steam explosion treatment in step (2) are: inert atmosphere, pressure 1-2 MPa, temperature 140-180℃, pressure holding for 15-50 min; preferably nitrogen atmosphere, pressure 1.2-1.8 MPa, temperature 150-170℃, pressure holding for 20-40 min.

[0015] In some implementations, the crushing in step (2) is to make the material pass through 60-120 mesh; preferably 60-100 mesh; more preferably 70-90 mesh.

[0016] In some implementations, the carbonization process in step (3) is: first low-temperature carbonization, then high-temperature carbonization.

[0017] Preferably, the low-temperature carbonization is performed by heating to 360-440°C at a heating rate of 1.5-2.5°C / min under inert gas protection, holding for 0.5-3 hours, and then cooling to 360-440°C at a cooling rate of 1.5-2.5°C / min.

[0018] A further preferred method is to raise the temperature to 380-420℃ at a heating rate of 1.8-2.2℃ / min under inert gas protection, hold for 1-2 hours, and then cool down to 380-420℃ at a cooling rate of 1.8-2.2℃ / min.

[0019] Preferably, the high-temperature carbonization is performed by heating to 700-1200°C at a heating rate of 4-6°C / min under inert gas protection and holding for 0.5-3 hours.

[0020] A further preferred method is to raise the temperature to 800-1000℃ at a heating rate of 4.5-5.5℃ / min under inert gas protection and hold for 1-2 hours.

[0021] In some implementations, the purification in step (4) is performed by soaking in acid, washing until neutral, and then drying.

[0022] Preferably, the acid in step (4) is at least one of potassium hydroxide, ammonium bicarbonate and sodium hydroxide, and the concentration of the acid solution is 1-3 mol / L, more preferably 1.5-2.5 mol / L, and even more preferably 1.8-2.2 mol / L.

[0023] Preferably, the soaking in step (4) is soaking at 63-77℃ for 6-10 hours; more preferably, soaking at 65-75℃ for 6-10 hours; and even more preferably, soaking at 68-72℃ for 7-9 hours.

[0024] In some implementations, the grinding and sieving in step (4) is to make all the material pass through 200-400 mesh, preferably 250-350 mesh.

[0025] Unless otherwise specified, the drying involved in this invention aims to control the moisture content of the sample to below 10%. Therefore, the specific drying method is not limited to, for example, oven drying, freeze drying, vacuum drying, or spray drying.

[0026] Secondly, the present invention provides a hard carbon material of *Salix matsudana* prepared by the above preparation method.

[0027] Thirdly, the present invention provides a hard carbon material electrode sheet, comprising the above-mentioned sand willow hard carbon material, acetylene black and PVDF.

[0028] Preferably, the mass ratio of the sand willow hard carbon material, acetylene black and PVDF is 7.2-8.8:0.5-1.5:0.5-1.5; more preferably it is 7.5-8.5:0.8-1.2:0.8-1.2.

[0029] The hard carbon material electrode sheet of the present invention has no particular limitation on the preparation method and can be prepared by conventional methods. For example, sand willow hard carbon material, acetylene black and PVDF can be mixed, ground and then NMP (N-methyl-2-pyrrolidone) can be used as solvent to adjust the ground powder into a slurry with appropriate viscosity. The slurry is then stirred continuously for more than 6 hours in a magnetic immersion pan, coated onto copper foil and placed in a vacuum drying oven at 120°C for 10 hours. Finally, it is punched on a tablet press with a punch radius of 0.55 cm.

[0030] Fourthly, the present invention provides the application of the above-mentioned sand willow hard carbon material or hard carbon material electrode sheet in the preparation of product groups.

[0031] Preferably, the product group includes at least one of a secondary battery, a battery module, a battery pack, and an electrical device.

[0032] Fifthly, the present invention provides a secondary battery in which the above-mentioned hard carbon material electrode sheet is used as the negative electrode.

[0033] In some embodiments, the secondary battery is at least one of sodium-ion battery, lithium-ion battery, magnesium-ion battery, and potassium-ion battery.

[0034] The secondary battery of the present invention has no particular limitation on shape; it can be cylindrical, square, or any other arbitrary shape.

[0035] The secondary battery of the present invention may include an outer packaging, and there are no particular restrictions on the material of the packaging, such as a hard shell (e.g., hard plastic shell, aluminum shell, steel shell, etc.) or a soft shell (polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.).

[0036] In a sixth aspect, the present invention provides a battery module comprising the aforementioned secondary battery.

[0037] The secondary battery of the present invention can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0038] In some implementations, the battery module includes one or more secondary batteries arranged in any manner.

[0039] Preferably, the secondary battery is secured by fasteners. Preferably, the battery module may further include a housing for accommodating one or more secondary batteries.

[0040] In a seventh aspect, the present invention provides a battery pack comprising the above-described battery module.

[0041] The battery module of the present invention can be assembled into a battery pack, and the battery pack may contain one or more battery modules. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0042] In some implementations, the battery pack may include a battery box and a plurality of battery modules disposed in the battery box, the plurality of battery modules being arranged in any manner within the battery box.

[0043] Eighthly, the present invention provides an electrical device comprising at least one of the above-mentioned secondary battery, battery module and battery pack.

[0044] The secondary battery, battery module, or battery pack described in this invention can be used as a power source for the electrical device, or as an energy storage unit for the electrical device.

[0045] In some implementations, the electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, tablets, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0046] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0047] In some implementations, the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0048] In some implementations, the power-consuming device is a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and can use a rechargeable battery as its power source.

[0049] The beneficial effects of this invention are as follows: (1) Wide range of raw material sources: Sand willow grows rapidly, is highly renewable, and is widely distributed, providing abundant raw materials for the preparation of hard carbon materials.

[0050] (2) High performance: By reasonably controlling the explosion and calcination carbonization process, the prepared hard carbon material has good electrochemical performance. After 500 cycles at a current density of 1.0C (300 mA·g-1), the sand willow hard carbon material can still maintain a high capacity retention rate, which is suitable for energy storage, batteries and other fields.

[0051] (3) Structural advantages of the material itself: The hard carbon material of Salix psammophila has abundant micropores and mesopores, which can provide more active sites and fast ion transport channels. In addition, its surface is rich in oxygen functional groups (such as hydroxyl and carboxyl groups), which can enhance the wettability and ion adsorption capacity of the electrolyte, thereby improving the electrochemical performance.

[0052] (4) Improve the coulombic efficiency of hard carbon materials: Compared with the prior art, the present invention significantly improves the coulombic efficiency of hard carbon materials of sand willow by improving the pretreatment and steam explosion treatment of sand willow.

[0053] (6) The synthesis method is universal and simple, which is conducive to its application in industrial production and has potential application value in other energy development and environmental protection fields. Attached Figure Description

[0054] Figure 1 This is a scanning electron microscope image of the *Salix matsudana* hard carbon material prepared in Example 3.

[0055] Figure 2 This is the X-ray diffraction pattern of the *Salix matsudana* hard carbon material prepared in Example 3. Detailed Implementation

[0056] The specific embodiments of the present invention will be described in further detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0057] The “range” disclosed in this document takes the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum ranges are listed as 3, 4, and 5, then the following ranges are all expected: 1-2, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0058] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is simply a shortened representation of these numerical combinations.

[0059] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0060] In this invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0061] The preferred embodiments of the present invention will be described in detail below with reference to specific examples. However, it should be understood that those skilled in the art can make reasonable changes, improvements and combinations to these embodiments without departing from the scope defined by the claims, thereby obtaining new specific implementation methods. These new specific implementation methods obtained through changes, improvements and combinations are also included within the protection scope of the present invention.

[0062] Example 1 A method for preparing bio-based hard carbon materials using a steam explosion assisted process, comprising the following steps: (1) Pretreatment: The branches and leaves of the sand willow were coarsely crushed by a high-speed universal pulverizer and then soaked in 2 mol / L hydrochloric acid at 70°C for 6 hours. After washing and drying in an oven, they were soaked in 1 mol / L ammonium bicarbonate solution at 50°C for 2 hours. Then they were washed with deionized water until neutral and dried to obtain sand willow powder.

[0063] (2) Steam explosion pretreatment: The above-treated sand willow powder is placed in a steam explosion tank, nitrogen is introduced, the pressure is controlled at 1.5MPa and the temperature is 160℃, the pressure is maintained for 30 minutes and then sprayed out. The material is collected and dried in a constant temperature oven at 60℃ for 12 hours. Then it is crushed and ductile iron is added so that all of it passes through 80 mesh to obtain the steam explosion product. (3) Carbonization treatment: The above-mentioned steam explosion product is placed in a low-temperature carbonization furnace and heated to 400°C at a heating rate of 2°C / min under nitrogen protection, held for 1 hour, and then cooled to 400°C at a cooling rate of 2°C / min; then heated to 800°C at a heating rate of 5°C / min under inert gas protection of (2v / v%H2+98v / v%Ar), held for 2 hours to obtain carbonized product.

[0064] (4) Post-treatment: The carbonized product was purified by soaking in 2 mol / L hydrochloric acid at 70°C for 8 hours, washed with deionized water until neutral, and then ground and sieved so that all the powder passed through 300 mesh to obtain the sand willow hard carbon material.

[0065] Example 2 A method for preparing bio-based hard carbon materials using a steam explosion assisted process, comprising the following steps: (1) Pretreatment: The branches and leaves of the sand willow were coarsely crushed by a high-speed universal pulverizer and then soaked in 1 mol / L hydrochloric acid at 63°C for 8 hours. After washing and drying in an oven, they were soaked in 2 mol / L ammonium bicarbonate solution at 40°C for 3 hours. Then they were washed with deionized water until neutral and dried to obtain sand willow powder.

[0066] (2) Steam explosion pretreatment: The above-treated sand willow powder is placed in a steam explosion tank, nitrogen is introduced, the pressure is controlled at 1MPa and the temperature is 140℃, the pressure is maintained for 50 minutes and then sprayed out. The material is collected and dried in a constant temperature oven at 60℃ for 12 h. Then it is crushed and ductile iron is added so that all of it passes through 80 mesh to obtain the steam explosion product. (3) Carbonization treatment: The above-mentioned steam explosion product is placed in a low-temperature carbonization furnace and heated to 360°C at a heating rate of 1.5°C / min under nitrogen protection, and held for 3 hours. Then, it is cooled to 360°C at a cooling rate of 1.5°C / min. Subsequently, it is heated to 700°C at a heating rate of 4°C / min under inert gas protection of (2v / v%H2+ 98v / v%Ar), and held for 3 hours to obtain the carbonized product.

[0067] (4) Post-treatment: The carbonized product was purified by soaking in 1 mol / L hydrochloric acid at 63°C for 10 hours, washed with deionized water until neutral, and then ground and sieved so that all the powder passed through 300 mesh to obtain the sand willow hard carbon material.

[0068] Example 3 A method for preparing bio-based hard carbon materials using a steam explosion assisted process, comprising the following steps: (1) Pretreatment: The branches and leaves of the sand willow were coarsely crushed by a high-speed universal pulverizer and then soaked in 3 mol / L hydrochloric acid at 77°C for 4 hours. After washing and drying in an oven, they were soaked in 0.5 mol / L ammonium bicarbonate solution at 60°C for 1 hour. Then they were washed with deionized water until neutral and dried to obtain sand willow powder.

[0069] (2) Steam explosion pretreatment: The above-treated sand willow powder is placed in a steam explosion tank, nitrogen is introduced, the pressure is controlled at 2MPa, the temperature is 180℃, the pressure is maintained for 15 minutes and then sprayed out, the material is collected and dried in a constant temperature oven at 60℃ for 12 hours, and then crushed and ductile iron is added so that all of it passes through 80 mesh to obtain the steam explosion product. (3) Carbonization treatment: The above-mentioned steam explosion product is placed in a low-temperature carbonization furnace and heated to 440°C at a heating rate of 2.5°C / min under nitrogen protection, held for 0.5 hours, and then cooled to 440°C at a cooling rate of 2.5°C / min; subsequently, it is heated to 1200°C at a heating rate of 6°C / min under inert gas protection of (2v / v%H2+ 98v / v%Ar), held for 0.5 hours, and carbonized product is obtained.

[0070] (4) Post-treatment: The carbonized product was purified by soaking in 3 mol / L hydrochloric acid at 77°C for 6 hours, washed with deionized water until neutral, and then ground and sieved so that all the powder passed through 300 mesh to obtain the sand willow hard carbon material.

[0071] The scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns of the prepared *Salix psammophila* hard carbon material are shown below. Figure 1 and Figure 2 As shown.

[0072] Comparative Example 1 The difference between this comparative example and Example 1 is that the pretreatment method is different.

[0073] Specifically, the preparation steps of bio-based hard carbon materials assisted by the steam explosion method are as follows: (1) Pretreatment: The branches and leaves of the sand willow were coarsely crushed by a high-speed universal pulverizer and then soaked in a mixed solution of water and glycerol with a mass ratio of 7:1 for 12 hours. After drying, sand willow powder was obtained.

[0074] (2) Steam explosion pretreatment: The above-treated sand willow powder is placed in a steam explosion tank, nitrogen is introduced, the pressure is controlled at 1.5MPa and the temperature is 160℃, the pressure is maintained for 30 minutes and then sprayed out. The material is collected and dried in a constant temperature oven at 60℃ for 12 hours. Then it is crushed and ductile iron is added so that all of it passes through 80 mesh to obtain the steam explosion product. (3) Carbonization treatment: The above-mentioned steam explosion product is placed in a low-temperature carbonization furnace and heated to 400°C at a heating rate of 2°C / min under nitrogen protection, held for 1 hour, and then cooled to 400°C at a cooling rate of 2°C / min; then heated to 800°C at a heating rate of 5°C / min under inert gas protection of (2v / v%H2+98v / v%Ar), held for 2 hours to obtain carbonized product.

[0075] (4) Post-processing: The carbonized product is purified by soaking in a mixed solution of water and glycerol with a mass ratio of 7:1, washed with deionized water until neutral, and then ground and sieved so that all the powder passes through 300 mesh, thus obtaining the sand willow hard carbon material.

[0076] Comparative Example 2 The difference between this comparative example and Example 1 is that the pretreatment and steam explosion pretreatment are different.

[0077] Specifically, the preparation method of bio-based hard carbon materials assisted by steam explosion method includes the following steps: (1) Pretreatment: The branches and leaves of the sand willow were coarsely crushed by a high-speed universal pulverizer and then soaked in 0.5 mol / L hydrochloric acid at 80°C for 6 hours. After washing and drying in an oven, they were soaked in 2.5 mol / L ammonium bicarbonate solution at 30°C for 4 hours. Then they were washed with deionized water until neutral and dried to obtain sand willow powder.

[0078] (2) Steam explosion pretreatment: The above-treated sand willow powder is placed in a steam explosion tank, nitrogen is introduced, the pressure is controlled at 1.5MPa and the temperature is 160℃, the pressure is maintained for 10 minutes and then sprayed out. The material is collected and dried in a constant temperature oven at 60℃ for 12 hours. Then it is crushed and ductile iron is added so that all of it passes through 80 mesh to obtain the steam explosion product. (3) Carbonization treatment: The above-mentioned steam explosion product is placed in a low-temperature carbonization furnace and heated to 400°C at a heating rate of 2°C / min under nitrogen protection, held for 1 hour, and then cooled to 400°C at a cooling rate of 2°C / min; then heated to 800°C at a heating rate of 5°C / min under inert gas protection of (2v / v%H2+98v / v%Ar), held for 2 hours to obtain carbonized product.

[0079] (4) Post-treatment: The carbonized product was purified by soaking in 2 mol / L hydrochloric acid at 70°C for 8 hours, washed with deionized water until neutral, and then ground and sieved so that all the powder passed through 300 mesh to obtain the sand willow hard carbon material.

[0080] Comparative Example 3 The difference between this comparative example and Example 1 is that the steam explosion pretreatment and high-temperature carbonization are different.

[0081] Specifically, the preparation method of bio-based hard carbon materials assisted by steam explosion method includes the following steps: (1) Pretreatment: The branches and leaves of the sand willow were coarsely crushed by a high-speed universal pulverizer and then soaked in 2 mol / L hydrochloric acid at 70°C for 6 hours. After washing and drying in an oven, they were soaked in 1 mol / L ammonium bicarbonate solution at 50°C for 2 hours. Then they were washed with deionized water until neutral and dried to obtain sand willow powder.

[0082] (2) Steam explosion pretreatment: The above-treated sand willow powder is placed in a steam explosion tank, nitrogen is introduced, the pressure is controlled at 1.5MPa and the temperature is 160℃, the pressure is maintained for 10 minutes and then sprayed out. The material is collected and dried in a constant temperature oven at 60℃ for 12 hours. Then it is crushed and ductile iron is added so that all of it passes through 80 mesh to obtain the steam explosion product. (3) Carbonization treatment: The above-mentioned steam explosion product is placed in a low-temperature carbonization furnace and heated to 400°C at a heating rate of 2°C / min under nitrogen protection, held for 1 hour, and then cooled to 400°C at a cooling rate of 2°C / min; then heated to 1400°C at a heating rate of 5°C / min under inert gas protection of (2v / v%H2+98v / v%Ar), held for 2 hours to obtain carbonized product.

[0083] (4) Post-treatment: The carbonized product was purified by soaking in 2 mol / L hydrochloric acid at 70°C for 8 hours, washed with deionized water until neutral, and then ground and sieved so that all the powder passed through 300 mesh to obtain the sand willow hard carbon material.

[0084] Electrochemical performance testing The sand willow hard carbon material, acetylene black and PVDF obtained in the above examples or comparative examples were mixed and ground through a 100-mesh sieve at a mass ratio of 8:1:1. Then, using NMP (N-methyl-2-pyrrolidone) as a solvent, a slurry with a solid content of 40wt% was prepared. The slurry was continuously stirred with a magnetic stirrer for 8 hours. The slurry was then coated onto copper foil and placed in a vacuum drying oven at 120℃ for 10 hours. Finally, the slurry was punched on a tablet press (Hefei Kejing MSK-T1) with a punch radius of 0.55cm. The CR2032 button cell casing is encapsulated into a button-type sodium-ion battery (SIB). The electrolyte used is 1 mol / L. −1 The solution is a mixture of NaClO4, ethylene carbonate (EC), and propylene carbonate (PC) in a volume ratio of 1:1:1. The diaphragm used is a glass fiber membrane (Whatman GF / D).

[0085] [Testing Method] Initial capacity: The battery testing system was a Lamborghini battery testing system (model BT-2018AS), and the multi-channel electrochemical workstation was a Shanghai Dumei (model IVIUM-N-Stat). The battery voltage testing range was 0.01-3.0V. 1 The initial capacity and first coulombic efficiency of the battery were tested at a rate of 0.1C (30mA·g-1 current density).

[0086] Capacity retention: The capacity retention was tested after 500 cycles at a 1 C rate (300 mA·g⁻¹ current density).

[0087] The electrochemical performance test results are shown in Table 1.

[0088] Table 1

[0089] The results show that the *Salix psammophila* hard carbon materials prepared in Examples 1-3 of this invention have good initial capacity and initial coulombic efficiency, and can still maintain a high capacity retention rate after 500 charge-discharge cycles, demonstrating excellent cycle stability.

[0090] The hard carbon materials prepared by Comparative Examples 1-3 showed low initial coulombic efficiency and poor capacity retention.

[0091] The above description, in conjunction with specific embodiments, further illustrates the present invention. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions to the details and form of the technical solutions of the present invention can be made without departing from the spirit and scope of the invention, and all such modifications and substitutions fall within the protection scope of the present invention.

Claims

1. A method for preparing bio-based hard carbon materials using a steam explosion assisted process, characterized in that, Includes the following steps: (1) The branches and leaves of the sand willow were coarsely crushed and pretreated to obtain sand willow powder; (2) The sand willow powder is subjected to steam explosion treatment, drying and pulverizing to obtain steam explosion products; (3) The steam explosion products are subjected to carbonization treatment to obtain carbonized products; (4) The carbonization products are purified, ground and sieved to obtain the sand willow hard carbon material; The pretreatment mentioned in step (1) involves soaking the crushed sand willow branches and leaves in acid solution, drying, soaking in alkaline solution, washing, and drying. The conditions for the steam explosion treatment in step (2) are: inert atmosphere, pressure 1-2 MPa, temperature 140-180℃, and pressure holding time 15-50 min.

2. The preparation method according to claim 1, characterized in that, The concentration of the acid solution in step (1) is 1-3 mol / L, and the soaking conditions of the acid solution are 4-8 h at 63-77℃. The concentration of the alkali solution is 0.5-2 mol / L, and the soaking conditions of the alkali solution are 1-3 h at 40-60℃. Alternatively, the conditions for the steam explosion treatment described in step (2) are: nitrogen atmosphere, pressure 1.2-1.8 MPa, temperature 150-170℃, and pressure holding time 20-40 min.

3. The preparation method according to claim 1, characterized in that, The carbonization process described in step (3) is as follows: first low-temperature carbonization, then high-temperature carbonization; The low-temperature carbonization is as follows: under inert gas protection, the temperature is increased to 360-440℃ at a heating rate of 1.5-2.5℃ / min, held for 0.5-3h, and then cooled to 360-440℃ at a cooling rate of 1.5-2.5℃ / min. The high-temperature carbonization is carried out by heating to 700-1200℃ at a heating rate of 4-6℃ / min under inert gas protection and holding for 0.5-3h.

4. The preparation method according to claim 1, characterized in that, The purification process described in step (4) involves soaking in acid, washing until neutral, and then drying. The concentration of the acid solution is 1-3 mol / L, and the soaking is carried out at 63-77℃ for 6-10 hours.

5. The preparation method according to claim 1, characterized in that, The crushing process described in step (2) involves ensuring that all the material passes through a 60-120 mesh. Or the grinding and sieving process described in step (4) is to make all the material pass through 200-400 mesh.

6. The hard carbon material of *Salix psammophila* prepared by the preparation method according to any one of claims 1-5.

7. A hard carbon material electrode sheet, characterized in that, Includes the hard carbon material of *Salix psammophila* prepared by the preparation method according to any one of claims 1-5.

8. The application of the *Salix psammophila* hard carbon material prepared by the preparation method according to any one of claims 1-5 or the hard carbon material electrode sheet according to claim 7 in the preparation of the product group, characterized in that, The product group includes at least one of secondary batteries, battery modules, battery packs, and electrical devices.

9. A secondary battery, battery module, or battery pack, characterized in that, The hard carbon material electrode sheet described in claim 7 is used as the negative electrode.

10. An electrical device, characterized in that, The secondary battery, battery module, or battery pack described in claim 9 is used as the power source.

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