Biomass derived porous carbon material and preparation method thereof, negative electrode plate and lithium ion battery

Abstract

The invention relates to a biomass derived porous carbon material and a preparation method thereof, a negative electrode plate and a lithium ion battery. The preparation method of the biomass derived porous carbon material comprises the following steps: crushing balsa wood, screening, and collecting powder; carrying out pre-carbonization treatment on the powder to prepare a pre-carbonized material; mixing the pre-carbonized material with potassium hydroxide, and carrying out etching treatment to prepare an etched material; carrying out carbonization treatment on the etched material to prepare a porous carbonized material; and carrying out microwave post-treatment on the porous carbonized material to prepare the biomass derived porous carbon material. According to the preparation method, the prepared biomass derived porous carbon material has relatively high specific surface area, relatively high pore volume, concentrated pore size distribution and relatively high conductivity.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a biomass-derived porous carbon material and a preparation method thereof, a negative electrode sheet, and a lithium-ion battery. Background Art

[0002] At present, lithium-ion batteries have been widely used in the fields of new energy storage power supply, mobile communication power supply and electric energy storage power supply. As the mainstream negative electrode material of lithium-ion batteries, graphite has the advantages of low cost, low operating voltage, high conductivity and good stability. However, graphite has a low theoretical specific capacity and poor Li + The charging anxiety caused by the transmission capacity has greatly limited the application of lithium-ion batteries in electric vehicles and other fields. Silicon has a capacity of about 4200mAh·g -1 Silicon has an ultra-high specific capacity, is abundant in the earth's crust, and has a low working potential, making it the most promising negative electrode candidate material for lithium-ion batteries. However, silicon has low intrinsic conductivity, large volume expansion during lithiation, and small Li + Problems such as diffusion rate have seriously hindered its practical application.

[0003] In order to improve the fast charging capability and stability of silicon-based negative electrodes, the fast Li + Amorphous silicon with high transmission capacity and highly conductive carbon materials are introduced into lithium-ion battery systems to construct silicon-carbon composites. In silicon-carbon composites, the carbon material is usually present in the form of porous carbon. Firstly, it acts as a buffer phase to alleviate the huge volume expansion of silicon and improve the cycling stability of the electrode material; secondly, it acts as a conductive matrix to improve the electronic conductivity of the electrode, thereby enhancing the electrode's rate performance. Therefore, the high specific surface area, high pore volume, specific pore size distribution, and high conductivity of porous carbon are key indicators for improving the overall performance of batteries.

[0004] Biomass is a natural organic material, primarily consisting of crops, crop waste, wood, wood waste, and animal manure. It boasts advantages such as widespread availability, low cost, environmental friendliness, and scalable production. Therefore, biomass' unique natural structure and elemental composition can be exploited to modify and prepare biomass-derived porous carbon materials with superior performance.

[0005] There is a traditional method that uses urea phosphate as a dopant and activator and K2CO3 as a secondary activator to improve the conductivity of biomass carbon materials. However, since two activations are required, it is easy to cause uneven pore size distribution, affecting the rate performance under high current density, and the secondary activation requires a high temperature of 900°C, which has high energy consumption costs. At the same time, too high a temperature will cause the proportion of N atoms in the form of pyridine nitrogen, pyrrole nitrogen, etc. to decrease, and convert them into graphite nitrogen with poor stability, reducing active sites. The P element may form a POC bond, which is easily hydrolyzed in the electrolyte, resulting in increased interfacial impedance; there is also a method that granulates and activates the fine powder produced during the preparation of porous carbon to prepare porous carbon with a three-dimensional conductive network structure to improve electronic conductivity, but the experimental steps require four high-temperature carbonizations under a protective atmosphere. The process is complicated and the steps are cumbersome, which increases the difficulty of operation. It will also cause the micropores of the porous carbon to collapse or the mesopores to shrink, affecting the specific surface area and lithium storage performance of the material.

[0006] Therefore, it is difficult to achieve higher electrical conductivity while maintaining the high specific surface area and specific pore structure of porous carbon materials using traditional methods. Summary of the Invention

[0007] Based on this, the present application provides a biomass-derived porous carbon material, a preparation method thereof, a negative electrode sheet, and a lithium-ion battery. This preparation method enables the prepared biomass-derived porous carbon material to have a high specific surface area, a high pore volume, a concentrated pore size distribution, and high electrical conductivity.

[0008] In a first aspect of the present application, a method for preparing a biomass-derived porous carbon material is provided, comprising the following steps:

[0009] The balsa wood is crushed and sieved to collect powder, wherein the powder has an aspect ratio of 6 to 10;

[0010] Heating the powder to 350° C. to 450° C. at a rate of 4° C. / min to 6° C. / min for pre-carbonization treatment to prepare a pre-carbonized material;

[0011] Mixing the pre-carbonized material with potassium hydroxide and performing etching treatment to prepare an etching material;

[0012] Heating the etched material to 780° C. to 820° C. at a rate of 3° C. / min to 6° C. / min for carbonization to prepare a porous carbonized material;

[0013] The porous carbonized material is subjected to microwave post-treatment to prepare a biomass-derived porous carbon material.

[0014] In one embodiment, the microwave post-treatment conditions include: microwave temperature of 25° C. to 80° C., microwave power of 140 W to 160 W, and time of 0.5 min to 1.5 min.

[0015] In one embodiment, the microwave post-treatment is performed 1 to 5 times.

[0016] In one embodiment, the aspect ratio of the powder is 6-8.

[0017] In one embodiment, during the carbonization process, the temperature is first increased to 550°C~650°C at a rate of 5°C / min~6°C / min, and then increased to 780°C~820°C at a rate of 3°C / min~4°C / min.

[0018] In one embodiment, the etching process conditions include one or both of the following:

[0019] (1) The mass ratio of the pre-carbonized material to potassium hydroxide is 1:(1-3);

[0020] (2) Mixing by ball milling. The conditions of ball milling include:

[0021] The mass ratio of the total mass of the pre-carbonized material and the potassium hydroxide to the mass of the grinding balls is 1:(2-2.5);

[0022] The grinding balls include, by mass percentage, 20% to 30% of first grinding balls, 30% to 40% of second grinding balls, 20% to 30% of third grinding balls, and 10% to 20% of fourth grinding balls. The diameter of the first grinding balls is 0.15 cm to 0.25 cm, the diameter of the second grinding balls is 0.35 cm to 0.45 cm, the diameter of the third grinding balls is 0.65 cm to 0.75 cm, and the diameter of the fourth grinding balls is 0.95 cm to 1.05 cm.

[0023] The ball milling speed is 300 rpm ~ 400 rpm;

[0024] The ball milling time is 0.5h~1h.

[0025] In a second aspect of the present application, a biomass-derived porous carbon material is provided, which has the following characteristics:

[0026] (1) Specific surface area ≥ 2200m 2 / g;

[0027] (2) In the pore size distribution, the volume proportion of pores with a pore diameter of less than 2.5 nm is ≥90%, and the volume proportion of pores with a pore diameter of more than 20 nm is ≤5%;

[0028] (3) Total pore volume ≥ 1cm 3 / g;

[0029] (4) Micropore volume ≥ 0.9 cm 3 / g;

[0030] (5) Conductivity ≥1.25S / cm.

[0031] In one embodiment, the biomass-derived porous carbon material is prepared by the preparation method described in the first aspect.

[0032] In a third aspect of the present application, a negative electrode plate is provided, comprising the biomass-derived porous carbon material described in the second aspect and a silicon-based material supported on the biomass-derived porous carbon material.

[0033] In a fourth aspect of the present application, a lithium-ion battery is provided, comprising the biomass-derived porous carbon material described in the second aspect or the negative electrode sheet described in the third aspect.

[0034] The above preparation method utilizes the structural characteristics of balsa wood, combines it with its appropriate aspect ratio control, and pre-carbonization, etching, and carbonization under specific conditions to produce a porous carbonized material with structural characteristics of high specific surface area, high pore volume, and concentrated pore size distribution. Furthermore, research has found that further microwave post-treatment of the material can effectively improve the material's electrical conductivity without affecting the aforementioned structural characteristics, resulting in the final biomass-derived porous carbon material having a high specific surface area, high pore volume, concentrated pore size distribution, and high electrical conductivity, meeting its application in lithium-ion battery negative electrodes.

[0035] In addition, the preparation method has low cost, simple process flow and is convenient for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The electrical conductivity of the materials obtained in Examples 1 to 5 and Comparative Example 1 varies with the number of microwave irradiations.

[0037] Figure 2 This is the pore size distribution diagram of the materials obtained in Examples 1 to 5.

[0038] Figure 3 These are the adsorption-desorption isotherms of the materials obtained in Examples 1 to 5. DETAILED DESCRIPTION

[0039] The following describes the biomass-derived porous carbon material and its preparation method, negative electrode plate, and lithium-ion battery of the present application in further detail with reference to specific examples. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to facilitate a more thorough and comprehensive understanding of the disclosure herein.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0041] As used herein, "one or more" refers to any one, any two, or any two or more of the listed items.

[0042] In this application, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, terms such as "first," "second," "third," and "fourth" serve only as non-exhaustive enumeration and description, and should not constitute a closed-ended limitation on quantity.

[0043] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0044] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0045] Unless otherwise specified, the percentage contents mentioned in this application refer to mass percentage for solid-liquid mixture and solid-solid mixture, and refer to volume percentage for liquid-liquid mixture.

[0046] The percentage concentrations mentioned in this application, unless otherwise specified, refer to the final concentration, which refers to the percentage of the added component in the system after the addition of the component.

[0047] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control.

[0048] The room temperature in this application generally refers to 4°C to 30°C, preferably 20±5°C.

[0049] In this application, “micropore” refers to a pore with a pore diameter of less than 2 nm, and “mesopore” refers to a pore with a pore diameter of 2 nm to 50 nm.

[0050] When porous carbon is used as the negative electrode carrier material of lithium-ion batteries: high specific surface area can improve the active material loading and interface reaction efficiency, high specific surface area (≥1750m 2 / g) can provide more active material adsorption sites, making them evenly dispersed in the carbon pores, avoiding volume expansion and rupture caused by agglomeration. At the same time, since lithium ion storage depends on the interfacial reaction between the active material and the electrolyte, the high specific surface area increases the three-phase interface area of ​​"active material-electrolyte-carbon support", thereby improving the lithium ion adsorption / desorption rate; concentrated pore size distribution can optimize ion transport and structural stability. Lithium ions in lithium-ion batteries need to diffuse through the electrolyte in the carbon pores to the surface of the active material. Reasonable pore size distribution (pore size <2.5nm accounts for ≥90%, pore size >20nm accounts for ≤5%) can shorten the ion diffusion path (pore tortuosity <2.0) and reduce mass transfer resistance; the total pore volume determines the active material loading amount and volume expansion buffering capacity, and it is usually necessary to control it to be >0.8cm 3 / g; Micropore volume can regulate lithium ion storage and interface reaction, usually need to be controlled to be >0.7cm 3 / g. At the same time, high conductivity can accelerate electron transfer and reduce polarization. When a lithium battery is working, the negative electrode's main function is to store lithium ions, while electrons need to be quickly conducted to the external circuit through the negative electrode material to form a closed loop. High conductivity can reduce the transmission resistance of electrons in the carbon skeleton, improving electron transfer efficiency, thereby increasing the charge and discharge rate, while reducing internal resistance and energy loss.

[0051] Therefore, the high specific surface area, concentrated pore size distribution, high pore volume and high conductivity of porous carbon are key indicators for improving the overall performance of batteries.

[0052] Based on this, this application optimizes the selection of biomass raw materials and the preparation process. Using low-cost balsa wood as the main raw material, a biomass-derived porous carbon material with a high specific surface area, high pore volume, concentrated pore size distribution and high conductivity is produced under a specific process flow.

[0053] In some embodiments of the present application, a method for preparing a biomass-derived porous carbon material is provided, comprising the following steps:

[0054] S1. Grinding and screening balsa wood to collect powder, wherein the powder has an aspect ratio of 6 to 10;

[0055] S2. Heating the powder to 350° C. to 450° C. at a rate of 4° C. / min to 6° C. / min for pre-carbonization treatment to prepare a pre-carbonized material;

[0056] S3, mixing the pre-carbonized material with potassium hydroxide and performing etching treatment to prepare an etching material;

[0057] S4, heating the etched material to 780° C. to 820° C. at a rate of 3° C. / min to 6° C. / min for carbonization treatment to prepare a porous carbonized material;

[0058] S5. Subjecting the porous carbonized material to microwave post-treatment to prepare a biomass-derived porous carbon material.

[0059] Furthermore, step S1 is a pretreatment step of balsa wood:

[0060] Balsa wood, whose scientific name is Ochroma lagopus Sw., also known as balsa wood and Baise wood, is a plant of the genus Balsa of the Malvaceae family.

[0061] Changes in the morphology of balsa wood powder affect the prepared carbon skeleton structure, thereby affecting the pore formation process and distribution: when the aspect ratio of balsa wood powder is small, the fibers are short and thick, and the balsa wood powder particles obtained after pretreatment are relatively large and regular. During the pre-carbonization process, the short fibers form a dense carbon skeleton, and the pores are mainly small pores inside the fibers and gaps between fibers. When mixed with potassium hydroxide for carbonization, potassium hydroxide mainly acts on the small pores on the fiber surface and inside, and the etching effect is relatively uniform. The resulting pore size distribution is concentrated, but relatively small, mainly micropores and mesopores. When the aspect ratio of balsa wood powder is large, the fibers are slender, and the pretreated balsa wood powder is more diverse in shape and size. After pre-carbonization, the carbon skeleton structure formed by the slender fibers is complex, with more interweaving and entanglement. When mixed with potassium hydroxide for carbonization, potassium hydroxide not only acts on the fiber surface and internal pores, but also easily reacts at the fiber interweaving and gaps caused by fiber shrinkage, etching larger pores, widening the pore size distribution range, increasing the average pore size, and possibly the appearance of some large pores.

[0062] Therefore, the aspect ratio of the balsa wood powder needs to be reasonably controlled to be between 6 and 10. Specifically, the aspect ratio of the powder includes, but is not limited to, 6, 7, 8, 9, 10, or a range between any two of the foregoing. In some embodiments, the aspect ratio of the powder is between 6 and 8.

[0063] In some embodiments, the diameter of the balsa wood powder is 40 μm to 60 μm. Specifically, the diameter of the balsa wood powder includes but is not limited to: 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, or a range between any two of the foregoing.

[0064] In some embodiments, the length of the balsa wood powder is 300 μm to 500 μm. Specifically, the length of the balsa wood powder includes but is not limited to: 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, or a range between any two of the foregoing.

[0065] Furthermore, step S2 is a pre-carbonization step:

[0066] It can be understood that the pre-carbonization treatment is carried out under the protection of a protective gas, and the protective gas can be, for example, nitrogen.

[0067] Specifically, the heating rate of the powder includes but is not limited to: 4°C / min, 5°C / min, 6°C / min or a range between any two of the foregoing.

[0068] Specifically, the temperature of the pre-carbonization treatment includes, but is not limited to, 350° C., 380° C., 400° C., 420° C., 450° C., or a range between any two of the foregoing.

[0069] Without restriction, heat to 350℃~450℃ and keep warm for 0.5min~3min.

[0070] Furthermore, step S3 is an etching process step:

[0071] In some embodiments, the mass ratio of the pre-carbonized material to potassium hydroxide is 1:(1-3). Specifically, the mass ratio of the pre-carbonized material to potassium hydroxide includes but is not limited to: 1:1, 1:2, 1:3, or a range between any two of the foregoing.

[0072] In some embodiments, the mixing is performed by ball milling.

[0073] Without limitation, the mass ratio of the total mass of the pre-carbonized material and the potassium hydroxide to the mass of the grinding balls (ball mass ratio) is 1:(2-2.5). Specifically, the mass ratio of the total mass of the pre-carbonized material and the potassium hydroxide to the mass of the grinding balls includes, but is not limited to, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, or a range between any two of the foregoing.

[0074] Without limitation, the grinding balls include, by mass percentage, 20% to 30% of first grinding balls, 30% to 40% of second grinding balls, 20% to 30% of third grinding balls, and 10% to 20% of fourth grinding balls. The diameter of the first grinding balls is 0.15 cm to 0.25 cm, the diameter of the second grinding balls is 0.35 cm to 0.45 cm, the diameter of the third grinding balls is 0.65 cm to 0.75 cm, and the diameter of the fourth grinding balls is 0.95 cm to 1.05 cm.

[0075] Without limitation, the grinding balls may be stainless steel balls.

[0076] Without limitation, the ball milling speed is 300-400 rpm, and the ball milling time is 0.5-1 hour. Specifically, the ball milling speed includes, but is not limited to, 300 rpm, 330 rpm, 350 rpm, 370 rpm, 400 rpm, or a range therebetween; the ball milling time includes, but is not limited to, 0.5 hour, 0.8 hour, 1 hour, or a range therebetween. Furthermore, the ball milling conditions include a material-ball mass ratio of 1:(2-2.5).

[0077] Furthermore, step S4 is a carbonization treatment step:

[0078] It can be understood that the carbonization treatment is carried out under the protection of a protective gas, and the protective gas can be, for example, nitrogen.

[0079] Specifically, the heating rate of the etching material includes but is not limited to: 3° C. / min, 4° C. / min, 5° C. / min, 6° C. / min or a range between any two of the foregoing.

[0080] Specifically, the temperature of the carbonization treatment includes, but is not limited to, 780° C., 790° C., 800° C., 810° C., 820° C., or a range between any two of the foregoing.

[0081] In some embodiments, during the carbonization process, the temperature is first raised to 550°C to 650°C at a rate of 5°C / min to 6°C / min, and then raised to 780°C to 820°C at a rate of 3°C / min to 4°C / min. Without limitation, after reaching 780°C to 820°C, the temperature is maintained for 1.5 hours to 3 hours.

[0082] Furthermore, step S5 is a post-processing step:

[0083] It is understood that, prior to microwave post-treatment, a washing step is also included to remove potassium hydroxide from the porous carbon material, i.e., washing to a neutral pH. Without limitation, washing can include at least one acid wash and one water wash. After washing, a drying step is also included to prepare for microwave post-treatment.

[0084] Microwaves are high-frequency electromagnetic waves. When applied to porous carbon materials, polar molecules within the porous carbon rapidly polarize in the microwave field and alternate orientations with the microwave frequency. This rapid molecular orientation change leads to intense intermolecular friction, resulting in a microwave thermal effect. Because organic functional groups are typically less thermally stable than the carbon skeleton, they undergo thermal decomposition reactions at the high microwave temperatures, breaking off from the porous carbon structure and escaping as a gas, thereby removing the organic functional groups. Furthermore, microwave absorption differs between the porous carbon material itself and the organic functional groups within it. Because the organic functional groups are less thermally stable than the carbon skeleton, the regions containing them absorb more microwave energy and are preferentially heated, undergoing thermal decomposition reactions first. These regions break off from the porous carbon structure and escape as a gas. This allows the organic functional groups to decompose and be removed at a relatively low overall temperature without causing significant damage to the porous carbon structure. Therefore, simple microwave post-treatment can improve the electrical conductivity and thermal stability of carbon materials, providing a superior porous carbon support.

[0085] In some embodiments, the microwave post-treatment conditions include: a microwave temperature of 25°C to 80°C, a microwave power of 140W to 160W, and a time of 0.5 min to 1.5 min. Specifically, the microwave temperature includes, but is not limited to, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or a range between any two of the foregoing; the microwave power includes, but is not limited to, 140W, 145W, 150W, 155W, 160W, or a range between any two of the foregoing; and the time includes, but is not limited to, 0.5 min, 1 min, 1.5 min, or a range between any two of the foregoing.

[0086] In some embodiments, the number of microwave post-treatments is 1 to 5 times. Specifically, the number of microwave post-treatments includes, but is not limited to, 1, 2, 3, 4, 5, or a range between any two of the foregoing. It is understood that after the first microwave treatment, the sample is cooled to room temperature before the next microwave treatment.

[0087] In some other embodiments of the present application, a biomass-derived porous carbon material is provided having one or more of the following characteristics:

[0088] (1) Specific surface area ≥ 2200m 2 / g;

[0089] (2) In the pore size distribution, the volume proportion of pores with a pore diameter of less than 2.5 nm is ≥90%, and the volume proportion of pores with a pore diameter of more than 20 nm is ≤5%;

[0090] (3) Total pore volume ≥ 1cm 3 / g;

[0091] (4) Micropore volume ≥ 0.9 cm 3 / g;

[0092] (5) Conductivity ≥1.25S / cm.

[0093] In some embodiments, the biomass-derived porous carbon material is prepared by the preparation method described above.

[0094] In some other embodiments of the present application, a negative electrode plate is provided, comprising the biomass-derived porous carbon material described above and a silicon-based material supported on the biomass-derived porous carbon material. Without limitation, the silicon-based material is supported in the pores of the biomass-derived porous carbon material by a method such as vapor deposition.

[0095] In some other embodiments of the present application, a lithium-ion battery is provided, comprising the biomass-derived porous carbon material as described above or the negative electrode plate as described above.

[0096] The biomass-derived porous carbon material described above has structural characteristics of large specific surface area, large total pore volume, large micropore volume and narrow pore size distribution. At the same time, it has high electrical conductivity and can meet the pore parameter requirements of porous carbon supports such as silicon-carbon negative electrodes in the field of lithium-ion batteries. It can utilize internal cross-linked through-pores and appropriate pore size to achieve sufficient deposition of silane gas. In addition, the preparation steps are simple, the cost is low, and it has practical application prospects.

[0097] For experimental parameters not specified in the following specific examples, reference is made to the guidance given in this application document, and reference may also be made to experimental manuals in the art or other experimental methods known in the art, or to the experimental conditions recommended by the manufacturer.

[0098] The raw materials and reagents involved in the following specific examples can be obtained commercially, or can be prepared by those skilled in the art according to known methods.

[0099] Example 1

[0100] This embodiment provides a method for preparing a biomass-derived porous carbon material, the steps of which are as follows:

[0101] (1) balsa wood is crushed, ground, sieved, cleaned and dried to obtain balsa wood powder with a diameter of 50 μm and a length of 300 μm, i.e., an aspect ratio of 6;

[0102] (2) Under nitrogen atmosphere, the balsa wood powder prepared in step (1) was placed in a tube furnace, heated to 400°C at a rate of 5°C / min, and kept at this temperature for 1 min for pre-carbonization. The powder was then cooled to room temperature and removed from the furnace;

[0103] (3) The powder of step (2) was mixed with potassium hydroxide in a mass ratio of 1:2 by ball milling for 0.5 h. The mass ratio of the balls was 1:2. In terms of mass percentage, the grinding balls (stainless steel balls) included 25% of first grinding balls, 35% of second grinding balls, 25% of third grinding balls and 15% of fourth grinding balls. The diameter of the first grinding balls was 0.2 cm, the diameter of the second grinding balls was 0.4 cm, the diameter of the third grinding balls was 0.7 cm, and the diameter of the fourth grinding balls was 1 cm. The rotation speed was 350 rpm to obtain a mixed powder.

[0104] (4) Under nitrogen atmosphere, the mixed powder of step (3) was placed in a tube furnace, heated to 600°C at 5°C / min, and then heated to 800°C at 3°C / min, and kept at this temperature for 2 hours for carbonization. After cooling to room temperature in the furnace, the porous carbon was taken out;

[0105] (5) washing the porous carbon obtained in step (4) with acid and water until the pH is neutral and then drying in an oven;

[0106] (6) Under an argon atmosphere, the porous carbon dried in step (5) was microwave-treated at a power of 150 W and a temperature of 60° C. for 1 min, and then cooled to room temperature to obtain a biomass-derived porous carbon material.

[0107] Example 2

[0108] This embodiment provides a method for preparing a biomass-derived porous carbon material. The steps are the same as those in Example 1, with the main difference being that the microwave treatment is performed twice. After the first microwave treatment, the material is cooled to room temperature before the second microwave treatment.

[0109] Example 3

[0110] This embodiment provides a method for preparing a biomass-derived porous carbon material. The steps are the same as those in Example 1, with the main difference being that the microwave treatment is performed three times, and after the first microwave treatment, the material is cooled to room temperature before the second microwave treatment.

[0111] Example 4

[0112] This embodiment provides a method for preparing a biomass-derived porous carbon material. The steps are the same as those in Example 1, with the main difference being that the microwave treatment is performed four times, and after the first microwave treatment, the material is cooled to room temperature before the next microwave treatment.

[0113] Example 5

[0114] This embodiment provides a method for preparing a biomass-derived porous carbon material. The steps are the same as those in Example 1, with the main difference being that the microwave treatment is performed five times, and after the first microwave treatment, the material is cooled to room temperature before the next microwave treatment.

[0115] Comparative Example 1

[0116] This comparative example provides a method for preparing a biomass-derived porous carbon material. The steps are the same as those in Example 1, with the main difference being that step (6) is not performed, i.e., microwave treatment is not performed.

[0117] The specific surface area, total pore volume, micropore volume and conductivity of Examples 1 to 5 and Comparative Example 1 were tested, respectively. The specific surface area, total pore volume and micropore volume were obtained by BET test, and the conductivity was tested by a four-probe resistivity tester.

[0118] The results are shown in Table 1 below:

[0119] Table 1

[0120]

[0121] Compared with comparative example 1, the specific surface area, total pore volume and micropore volume of the material remain basically unchanged, indicating that microwave treatment does not affect the specific surface area and pore structure of the material. Figure 1 It can be seen that after one microwave treatment, the electrical conductivity of the material is significantly improved, and then gradually increases with the increase in the number of microwave treatments. It decreases to a certain extent after the third time, but still remains at a high level.

[0122] The pore size distribution test was performed on Examples 1 to 5 (denoted as A1 to A5), and the results were as follows: Figure 2 As shown in the figure, it can be seen that in the pore size distribution, the volume proportion of pores with a pore diameter of less than 2.5 nm is ≥90%, and the volume proportion of pores with a pore diameter of more than 20 nm is ≤5%. The pore size distribution of the obtained porous carbon is relatively concentrated, and with the increase of the number of microwave treatments, the pore size distribution curves basically overlap, indicating that the number of microwave treatments has no obvious effect on the pore size distribution, and the pore size distribution concentration is still relatively high.

[0123] The adsorption-desorption isotherms of Examples 1 to 5 (denoted as A1 to A5) were obtained. Figure 3 As shown in the figure, the obtained porous carbon isotherm is a Type IV isotherm. In the medium-pressure section of the isotherm (relative pressure p / p0 is approximately 0.3-0.8), capillary condensation occurs within the mesopores, causing a sharp increase in adsorption, forming a distinct adsorption platform, indicating a relatively narrow pore size distribution. Furthermore, the figure also shows that the obtained porous carbon isotherm exhibits an H1-type hysteresis loop, indicating that the pores in the material have good symmetry and uniformity.

[0124] Comparative Examples 2 to 5

[0125] Comparative Examples 2 to 5 provide a method for preparing a biomass-derived porous carbon material. The steps are the same as those in Example 1, with the main difference being that the final carbonization temperature in step (4) is different, namely 750°C, 850°C, 900°C, and 1000°C.

[0126] The specific surface area, total pore volume and micropore volume were tested respectively, and the results are shown in Table 2 below:

[0127] Table 2

[0128]

[0129] Compared with Comparative Examples 2 to 5, Example 1 can simultaneously achieve higher specific surface area, total pore volume and micropore volume by adopting a suitable carbonization temperature.

[0130] Comparative Examples 6-7

[0131] Comparative Examples 6 and 7 provide a method for preparing a biomass-derived porous carbon material. The steps are the same as those in Example 1, with the main difference being that the lengths of the balsa wood powder in step (1), i.e., the aspect ratios, are different, namely, 150 μm (aspect ratio of 3) and 650 μm (aspect ratio of 13), respectively.

[0132] The specific surface area, total pore volume and micropore volume were tested respectively, and the results are shown in Table 3 below:

[0133] Table 3

[0134]

[0135] Compared with Comparative Examples 6 and 7, Example 1 can simultaneously take into account higher specific surface area, total pore volume and micropore volume by adopting appropriate balsa wood powder size.

[0136] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0137] The embodiments described above only express several implementation methods of the present application, which are convenient for understanding the technical solutions of the present application in a specific and detailed manner, but they cannot be understood as limiting the scope of protection of the patent application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent application of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A method for preparing a biomass-derived porous carbon material, characterized in that: The steps include: The balsa wood is crushed and sieved to collect powder, wherein the powder has an aspect ratio of 6 to 10; Heating the powder to 350° C. to 450° C. at a rate of 4° C. / min to 6° C. / min for pre-carbonization treatment to prepare a pre-carbonized material; Mixing the pre-carbonized material with potassium hydroxide and performing etching treatment to prepare an etching material; Heating the etched material to 780° C. to 820° C. at a rate of 3° C. / min to 6° C. / min for carbonization to prepare a porous carbonized material; The porous carbonized material is subjected to microwave post-treatment to prepare a biomass-derived porous carbon material.

2. The method for preparing a biomass-derived porous carbon material according to claim 1, wherein: The conditions of microwave post-treatment include: microwave temperature of 25° C. to 80° C., microwave power of 140 W to 160 W, and time of 0.5 min to 1.5 min.

3. The method for preparing a biomass-derived porous carbon material according to claim 2, wherein: The number of microwave post-treatments ranged from 1 to 5 times.

4. The method for preparing a biomass-derived porous carbon material according to claim 1, wherein: The aspect ratio of the powder is 6-8.

5. The method for preparing a biomass-derived porous carbon material according to claim 1, wherein: During the carbonization treatment, the temperature is first increased to 550°C~650°C at a rate of 5°C / min~6°C / min, and then increased to 780°C~820°C at a rate of 3°C / min~4°C / min.

6. The method for preparing a biomass-derived porous carbon material according to claim 1, wherein: The conditions for the etching process include one or both of the following: (1) The mass ratio of the pre-carbonized material to potassium hydroxide is 1:(1-3); (2) Mixing by ball milling. The conditions of ball milling include: The mass ratio of the total mass of the pre-carbonized material and the potassium hydroxide to the mass of the grinding balls is 1:(2-2.5); The grinding balls include, by mass percentage, 20% to 30% of first grinding balls, 30% to 40% of second grinding balls, 20% to 30% of third grinding balls, and 10% to 20% of fourth grinding balls. The diameter of the first grinding balls is 0.15 cm to 0.25 cm, the diameter of the second grinding balls is 0.35 cm to 0.45 cm, the diameter of the third grinding balls is 0.65 cm to 0.75 cm, and the diameter of the fourth grinding balls is 0.95 cm to 1.05 cm. The ball milling speed is 300 rpm ~ 400 rpm; The ball milling time is 0.5h~1h.

7. A biomass-derived porous carbon material, characterized in that: It has the following characteristics: (1) Specific surface area ≥ 2200m 2 / g; (2) In the pore size distribution, the volume proportion of pores with a pore diameter of less than 2.5 nm is ≥90%, and the volume proportion of pores with a pore diameter of more than 20 nm is ≤5%; (3) Total pore volume ≥ 1cm 3 / g; (4) Micropore volume ≥ 0.9 cm 3 / g; (5) Conductivity ≥1.25S / cm.

8. The biomass-derived porous carbon material according to claim 7, wherein: It is prepared by the preparation method according to any one of claims 1 to 6.

9. A negative electrode plate, characterized in that: The method comprises the biomass-derived porous carbon material according to claim 7 or 8 and a silicon-based material supported on the biomass-derived porous carbon material.

10. A lithium ion battery, characterized in that: It includes the biomass-derived porous carbon material according to claim 7 or 8 or the negative electrode sheet according to claim 9.

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